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{{short description|Brightest star in the constellation Orion}}
{{other uses}} {{other uses}}
{{Use dmy dates|date=August 2020}}
{{Starbox begin {{Starbox begin
| name = Rigel | name = Rigel
Line 6: Line 8:
| image = | image =
{{Location mark {{Location mark
| image = Orion constellation map.svg | width = 280 | image = Orion constellation map.svg | width = 280

| alt = Map of the constellation Orion | float = center

| mark = Red circle.svg | mark_width = 15
| float = center
| mark = Red circle.svg | mark_width = 15 | mark_link = β Ori
| x = 730 | y = 742 | x = 730 | y = 742
}} }}
| caption = Rigel in the constellation Orion (circled) | caption = Location of Rigel (circled)
}} }}
{{Starbox observe 2s {{Starbox observe 2s
| epoch = J2000.0 | epoch = J2000.0
| constell = ] | constell = ]
| pronounce = {{IPAc-en|ˈ|r|aɪ|dʒ|əl}} or {{IPAc-en|-|g|əl}}<ref name=ddc/> | pronounce = {{IPAc-en|ˈ|r|aɪ|dʒ|əl}}<ref name=Kunitzsch/> or {{IPAc-en|-|g|əl}}<ref name=ddc/>
| component1 = A | component1 = A
| ra1 = {{RA|05|14|32.27210}}<ref name=aaa474_2_653/> | ra1 = {{RA|05|14|32.27210}}<ref name=aaa474_2_653/>
| dec1 = {{DEC|−08|12|05.8981}}<ref name=aaa474_2_653/> | dec1 = {{DEC|−08|12|05.8981}}<ref name=aaa474_2_653/>
| appmag_v1 = 0.13<ref name=ducati/> {{nowrap|(0.05 - 0.18<ref name=guinan/>)}} | appmag_v1 = 0.13<ref name=ducati/> {{nowrap|(0.05–0.18<ref name=guinan/>)}}
| component2 = BC | component2 = BC
| ra2 = {{RA|05|14|32.049}}<ref name=DENIS/> | ra2 = {{RA|05|14|32.049}}<ref name=DENIS/>
| dec2 = {{DEC|−08|12|14.78}}<ref name=DENIS/> | dec2 = {{DEC|−08|12|14.78}}<ref name=DENIS/>
| appmag_v2 = 6.67<ref name=sanford/> {{nowrap|(7.6/7.6<ref name=msc/>)}} | appmag_v2 = 6.67<ref name=sanford/> {{nowrap|(7.5/7.6<ref name=WDS/>)}}
}} }}
{{Starbox character {{Starbox character
| component1 = A | component1 = A
| type=] | type=]
| class = B8&nbsp;Ia<ref name=aaa445_3_1099/> | class = B8 Ia<ref name=aaa445_3_1099/>
| b-v = −0.03<ref name=aass34_1/> | b-v = −0.03<ref name=aass34_1/>
| u-b = −0.66<ref name=aass34_1/> | u-b = −0.66<ref name=aass34_1/>
Line 36: Line 40:
| type2=] | type2=]
| class2 = B9V + B9V<ref name=msc/> | class2 = B9V + B9V<ref name=msc/>
| b-v2 =
| u-b2 =
| variable2 =
}} }}
{{Starbox astrometry {{Starbox astrometry
Line 44: Line 45:
| prop_mo_ra = +1.31<ref name=aaa474_2_653/> | prop_mo_ra = +1.31<ref name=aaa474_2_653/>
| prop_mo_dec = +0.50<ref name=aaa474_2_653/> | prop_mo_dec = +0.50<ref name=aaa474_2_653/>
| parallax = 3.78 | parallax = 3.78
| p_error = 0.34 | p_error = 0.34
| parallax_footnote = <ref name=aaa474_2_653/> | parallax_footnote =<ref name=aaa474_2_653/>
| dist_pc = {{Val|260|20}}
| absmag_v = –7.84<ref name=schultz2011/>
| dist_ly = {{val|848|65}}
| dist_footnote = <ref name=deAlmeida>{{cite journal|doi=10.1093/mnras/stac1617|title=Combined spectroscopy and intensity interferometry to determine the distances of the blue supergiants P Cygni and Rigel |year=2022 |last1=De Almeida |first1=E S G. |last2=Hugbart |first2=M. |last3=Domiciano De Souza |first3=A. |last4=Rivet |first4=J-P |last5=Vakili |first5=F. |last6=Siciak |first6=A. |last7=Labeyrie |first7=G. |last8=Garde |first8=O. |last9=Matthews |first9=N. |last10=Lai |first10=O. |last11=Vernet |first11=D. |last12=Kaiser |first12=R. |last13=Guerin |first13=W. |journal=Monthly Notices of the Royal Astronomical Society |volume=515 |issue=1 |pages=1–12 |doi-access=free |arxiv=2204.00372 |bibcode=2022MNRAS.515....1D}}</ref>
| absmag_v = −7.84<ref name=aaa445_3_1099/>
}} }}
{{Starbox orbit {{Starbox orbit
| reference = <ref name=sanford/> | reference =<ref name=msc/>
| name=BC
| primary=A
| period=24,000
}}
{{Starbox orbit
| reference =<ref name=sanford/>
| primary = Ba | primary = Ba
| name = Bb | name = Bb
| period =
| period_unitless = 9.860 days | period_unitless = 9.860 days
| axis =
| axis_unitless =
| eccentricity = 0.1 | eccentricity = 0.1
| inclination =
| node = <!--Longitude of node (in degrees)-->
| periastron = <!--Periastron epoch-->
| periarg = <!--Argument of periastron (in degrees), secondary -->
| periarg_primary = <!--Argument of periastron (in degrees), primary -->
| k1 = 25.0 | k1 = 25.0
| k2 = 32.6 | k2 = 32.6
}} }}
{{Starbox orbit|reference = <ref name=msc/>|primary=B|name=C|period=63}} {{Starbox orbit
|reference =<ref name=msc/>
|primary=B
|name=C
|period=63
}}
{{Starbox detail {{Starbox detail
| component1 = A | component1 = A
Line 72: Line 79:
| metal_fe = {{val|-0.06|0.10}}<ref name=aaa445_3_1099/> | metal_fe = {{val|-0.06|0.10}}<ref name=aaa445_3_1099/>
| mass = {{val|21|3}}<ref name=schultz/> | mass = {{val|21|3}}<ref name=schultz/>
| radius = {{val|78.9|7.4}}<ref name=apj2012_747_108/> | radius = {{val|74.1|6.1|7.3}}<ref name=baines/>
| rotational_velocity = {{val|25|3}}<ref name=przybilla/> | rotational_velocity = {{val|25|3}}<ref name=przybilla/>
| luminosity_bolometric = {{val|1.20|+0.25|-0.21}}×10<sup>5</sup><ref name=apj2012_747_108/> | luminosity_bolometric = {{val|120000|25000|21000|fmt=commas}}<ref name=apj2012_747_108/>
| temperature = {{val|12100|150}}<ref name=przybilla/> | temperature = {{val|12100|150|fmt=commas}}<ref name=przybilla/>
| gravity = {{val|1.75|0.10}}<ref name=przybilla/> | gravity = {{val|1.75|0.10}}<ref name=przybilla/>
}} }}
{{Starbox detail|no_heading=y {{Starbox detail
|no_heading=y
| component1 = Ba | component1 = Ba
| age_myr =
| metal_fe =
| mass = 3.84<ref name=msc/> | mass = 3.84<ref name=msc/>
| radius =
| rotational_velocity =
| luminosity_bolometric =
| temperature =
| gravity =
| component2 = Bb | component2 = Bb
| mass2 = 2.94<ref name=msc/> | mass2 = 2.94<ref name=msc/>
}} }}
{{Starbox detail|no_heading=y {{Starbox detail
|no_heading=y
| component1 = C | component1 = C
| age_myr =
| metal_fe =
| mass = 3.84<ref name=msc/> | mass = 3.84<ref name=msc/>
}} }}
{{Starbox catalog {{Starbox catalog
| names = ]&nbsp;Orionis, ]&nbsp;3823, ]&nbsp;668, ]&nbsp;33, ]&nbsp;J05145-0812, ]&nbsp;J05145-0812<ref name="simbad"/> | names = ], ]{{nbs}}3823, ]{{nbs}}668, ]{{nbs}}555,<ref name=WDS/> ]{{nbs}}33,<ref name="Herschel1782"/> ]{{nbs}}J05145-0812, ]{{nbs}}J05145-0812<ref name="simbad"/>
| component1 = A | component1 = A
| names1 = Rigel, Algebar, Elgebar, ]&nbsp;Orionis, ]&nbsp;34085, ]&nbsp;1713, ]&nbsp;24436, ]&nbsp;131907, ]-08°1063, ]&nbsp;194 | names1 = Rigel, Algebar, Elgebar, ], ]{{nbs}}34085, ]{{nbs}}1713, ]{{nbs}}24436, ]{{nbs}}131907, ]−08°1063, ]{{nbs}}194
| component2 = B | component2 = B
| names2 = Rigel B, ]&nbsp;3111, STF 688B, BU 555B | names2 = Rigel B, ]{{nbs}}3111
}} }}
{{Starbox reference {{Starbox reference
| Simbad = RIGEL | Simbad = RIGEL|sn=Rigel
| Simbad2 = bet+Ori+B|sn2=Rigel B
}} }}
{{Starbox end}} {{Starbox end}}


'''Rigel''' ({{IPAc-en|ˈ|r|aɪ|dʒ|əl|,_|-|g|əl}}), also designated '''β Orionis''' (] to '''Beta Orionis''', abbreviated '''Beta Ori''', '''β Ori'''), is a ]. It is, on average, the ] in the ] and the brightest star in the ] of ]—though occasionally it is outshone within the constellation by ], another variable star. The ] of Rigel varies irregularly between +0.05 and +0.18. '''Rigel''' is a ] star in the ] of ]. It has the ] '''β Orionis''', which is ] to '''Beta Orionis''' and abbreviated '''Beta Ori''' or '''β Ori'''. Rigel is the brightest and most ] component{{snd}}and the ]{{snd}}of a ] of at least four ]s that appear as a single blue-white point of light to the ]. This system is located at a distance of approximately {{convert|860|ly|pc|sigfig=2|lk=on}} from the Sun.


A star of ] B8Ia, Rigel is 120,000 times ] as the Sun, and is 18 to 24 times ], depending on the method and assumptions used. Its radius is more than seventy times ], and its ] is {{val|12,100|ul=K|fmt=commas}}. Due to its ], Rigel's ] is estimated to be ten million times that of the Sun. With an estimated age of seven to nine million years, Rigel has exhausted its core hydrogen fuel, expanded, and cooled to become a supergiant. It is expected to end its life as a ] ], leaving a ] or a ] as a final remnant, depending on the initial mass of the star.
Although appearing as a single star to the naked eye, Rigel is actually a multiple ]. The name ''Rigel'' strictly refers to the brightest component of this system. It is a ] ] estimated to be anywhere from 61,500 to 363,000 times ], depending on the method used to calculate its properties and assumptions about its distance, thought to be about {{convert|860|ly|pc|sigfig=2}}. Rigel has exhausted the ] in its core, causing the star to expand; its radius is over 70 times that of the ]. Pulsations cause Rigel's small intrinsic brightness variation; it is classified as an ].


Rigel varies slightly in brightness, its ] ranging from 0.05 to 0.18. It is classified as an ] due to the amplitude and periodicity of its brightness variation, as well as its spectral type. Its ] is caused by pulsations in its unstable atmosphere. Rigel is generally the ] in the ] and the brightest star in Orion, though it is occasionally outshone by ], which varies over a larger range.
Rigel's brightest companion is itself a likely ], separated from Rigel by {{val|9.5|ul="}}. Often referred to as Rigel B, it has a combined apparent magnitude of 6.7 but is still over 400 times fainter than the primary star and visible only with a telescope. Rigel B is a ] composed of the components Ba and Bb. It also has a very close visual companion, component C, of almost equal brightness to B.

A triple-star system is separated from Rigel by an angle of {{val|9.5|ul=arc seconds}}. It has an apparent magnitude of 6.7, making it 1/400th as bright as Rigel. Two stars in the system can be seen by large telescopes, and the brighter of the two is a ]. These three stars are all ], each three to four times as massive as the Sun. Rigel and the triple system orbit a common center of gravity with a period estimated to be 24,000 years. The inner stars of the triple system orbit each other every 10 days, and the outer star orbits the inner pair every 63 years. A much fainter star, separated from Rigel and the others by nearly an ], may be part of the same star system.


== Nomenclature == == Nomenclature ==
], with Rigel at bottom right, at optical wavelengths plus the H{{mvar|α}} (]) spectral line to emphasize gas clouds]]
The modern name ''Rigel'' was likely first recorded in the ] of 1521. It is derived from the Arabic name ''{{transl|ar|Rijl Jauzah al Yusrā}}'', "the left leg (foot) of Jauzah" (i.e. ''rijl'' meaning "leg, foot"),<ref name=allen/> which can be traced to the 10th century.<ref name="KUNITZSCH1959"/> "Jauzah" was a proper name of the Orion figure, an alternative Arabic name was {{lang|ar|رجل الجبار}} ''{{transl|ar|riǧl al-ǧabbār}}'', "the foot of the great one", which is the source of the rarely used variant names ''Algebar'' or ''Elgebar''. The ''Alphonsine Tables'' saw its name split into "Rigel" and "Algebar", with the note, ''et dicitur Algebar. Nominatur etiam Rigel.''<ref name=Kunitzsch86/> Alternate spellings from the 17th century include ''Regel'' by Italian astronomer ], ''Riglon'' by German astronomer ], and ''Rigel Algeuze'' or ''Algibbar'' by English scholar ].<ref name="allen"/> In 2016, the ] officially recognized Rigel for β Orionis A, the blue supergiant component visible to the ].<ref name="IAU-CSN"/>


In 2016, the ] (IAU) included the name "Rigel" in the IAU Catalog of Star Names.<ref name="IAU-CSN"/><ref name="WGSN2018"/> According to the IAU, this proper name applies only to the primary component A of the Rigel system. The system is listed variously in historical ] as {{nobr|] 33,}} {{nobr|] 668,}} {{nobr|] 555,}} or {{nobr|] 3823.}} For simplicity, Rigel's companions are referred to as Rigel&nbsp;B,<ref name=WGSN2018/> C, and D;<ref name=kalerrigel/><ref name=garfinkle1997/> the IAU describes such names as "useful nicknames" that are "unofficial".<ref name=WGSN2018/> In modern comprehensive catalogs, the whole multiple star system is known as {{nobr|] 05145-0812}} or {{nobr|] 05145–0812.<ref name=WDS/><ref name=CCDM/>}}<!--SIMBAD adds J; i.e. WDS J05145-0812 or CCDM J05145-0812-->
''β Orionis'' (] to ''Beta Orionis'') is the star's ], although it is usually the brightest star in Orion. Astronomer ] has speculated that perhaps Rigel was designated by Bayer during a rare period where it was outshone by the variable star Betelgeuse, resulting in the latter star being designated ''alpha'' and Rigel designated ''beta''.<ref name="kalerrigel"/> Rigel is included in the ], but since it already has a Bayer designation, β Orionis, it has no separate ].<ref name=baa/>


The designation of Rigel as {{nobr|{{mvar|β}} Orionis}} (] to ''beta Orionis'') was made by ] in 1603. The "beta" designation is usually given to the second-brightest star in each constellation, but Rigel is almost always brighter than {{nobr|{{mvar|α}} Orionis}} (]).<ref name=schaaf/> Astronomer ] speculated that Bayer assigned letters during a rare period when variable star Betelgeuse temporarily outshone Rigel, resulting in Betelgeuse being designated "alpha" and Rigel designated "beta".<ref name=kalerrigel/> However, closer examination of Bayer's method shows that he did not strictly order the stars by brightness, but instead grouped them first by magnitude, then by ].<ref name=ridpath/> Rigel and Betelgeuse were both classed as ], and in Orion the stars of each class appear to have been ordered north to south.<ref name=moore1996/>
==Observation==
Rigel is the seventh-brightest star in the ] excluding the Sun. It is usually fainter than ],<ref name="schaaf"/> although both are slightly variable in brightness. Rigel is an irregular ] with a range in ] from 0.05 to 0.18.<ref name=guinan/> Although Rigel has the ] "beta", it is almost always brighter than Alpha Orionis (]).<ref name="schaaf"/> Since 1943, the ] of this star has served as a spectral reference for class B8Ia, for use as a comparison when ] the spectra of other stars.<ref name=mkk/><ref name=baas25_1319/> Rigel appears slightly blue-white, almost white, and has a (B–V) ] of −0.06.<ref name="csiro"/>


Rigel has many other ] taken from various catalogs, including the {{nobr|] 19 Orionis}} (19&nbsp;Ori), the ] entry HR&nbsp;1713, and the ] number HD&nbsp;34085. These designations frequently appear in the scientific literature,<ref name=msc/><ref name=schultz/><ref name=markova/> but rarely in popular writing.<ref name=garfinkle1997/><ref name=burnham/>
Culminating at midnight on 12 December, and at 9 pm on 24 January, Rigel is visible in winter evenings in the ] and summer in the southern.<ref name="schaaf"/> In the ], Rigel is the first bright star of Orion visible as the constellation rises.<ref name=ellyard/> The star forms a vertex of the "]", an ] that includes ], Capella, ], ], and ]. This formation is visible from most locations on Earth and is prominent in the night sky from December through March.<ref name=Penprase2010/> Rigel is one of the most important ], since it is bright, easily located and equatorial, which means it is visible all around the world's oceans (the exception is the area within 8° of the ]).<ref name=kerigan/>
Rigel is listed in the ], but since its familiar ] is used instead of creating a separate ].<ref name=baa/>

== Observation ==
]
Rigel is an ] star with an ] ranging from 0.05 to 0.18.<ref name=guinan/> It is typically the seventh-brightest star in the ], excluding the Sun, although occasionally fainter than Betelgeuse.<ref name=burnham/> Rigel appears slightly blue-white and has a ] index of −0.06.<ref name="csiro"/> It contrasts strongly with reddish Betelgeuse.<ref name=DK/>

] every year at midnight on 12 December, and at 9:00{{nbs}}pm on 24 January, Rigel is visible on winter evenings in the ] and on summer evenings in the ].<ref name="schaaf"/> In the Southern Hemisphere, Rigel is the first bright star of Orion visible as the constellation rises.<ref name=ellyard/> Correspondingly, it is also the first star of Orion to set in most of the Northern Hemisphere. The star is a vertex of the "]", an ] that includes ], ], ], ], and ]. Rigel is a prominent ], being easily located and readily visible in all the world's oceans (the exception is the area north of the ]).<ref name=kerigan/>


=== Spectroscopy === === Spectroscopy ===
] with Rigel at bottom right, at optical wavelengths plus ] to emphasize gas clouds]]
The general ] of Rigel as B8 is well-established and it has been used as a defining point of the spectral classification sequence for supergiants.<ref name=morgan1978/><ref name=morgan1950/> The overall spectrum is typical for a ] B class star, with strong ]s of the hydrogen ] together with neutral helium lines and some of heavier elements such as oxygen, calcium, and magnesium.<ref name=zeus/> The luminosity class for B8 stars is determined from the strength and narrowness of the hydrogen spectral lines, and Rigel is assigned to the ] class Ia.<ref name=mkk/>


Rigel's ] is a defining point of the classification sequence for supergiants.<ref name=morgan1978/><ref name=morgan1950/> The overall spectrum is typical for a ] B class star, with strong ]s of the hydrogen ] as well as neutral helium lines and some of heavier elements such as oxygen, calcium, and magnesium.<ref name=abetti/> The ] for B8 stars is estimated from the strength and narrowness of the hydrogen spectral lines, and Rigel is assigned to the ] class Ia.<ref name=mkk/> Variations in the spectrum have resulted in the assignment of different classes to Rigel, such as B8 Ia, B8 Iab, and B8 Iae.<ref name=schultz/><ref name=bally/>
As early as 1888, the ] of Rigel, as determined from the ]s of its spectral lines, was seen to vary. This was confirmed and interpreted as a spectroscopic companion with a period of about 22 days.<ref name=plaskett/> The radial velocity has since been measured to vary by about {{val|10|ul=km/s}} around a mean of {{val|21.5|u=km/s}}.<ref name=morrison/>


As early as 1888, the heliocentric ] of Rigel, as estimated from the ]s of its spectral lines, was seen to vary. This was confirmed and interpreted at the time as being due to a spectroscopic companion with a period of about 22 days.<ref name=plaskett/> The radial velocity has since been measured to vary by about {{val|10|ul=km/s}} around a mean of {{val|21.5|u=km/s}}.<ref name=morrison/>
In 1933, the ] spectral line was seen to be unusually weak and shifted {{val|0.1|ul=nm}} towards shorter wavelengths, while there was a narrow ] about {{val|1.5|u=nm}} to the long wavelength side of the main absorption line.<ref name=struve/> This is now known as a ] after a star that shows this feature strongly in its spectrum. It is associated with strong mass loss where there is simultaneously emission from dense wind close to the star and absorption from circumstellar material expanding away from the star.<ref name=struve/>


In 1933, the ] line in Rigel's spectrum was seen to be unusually weak and shifted {{val|0.1|ul=nm}} towards shorter wavelengths, while there was a narrow ] about {{val|1.5|u=nm}} to the long wavelength side of the main absorption line.<ref name=struve/> This is now known as a ] after a star that shows this feature strongly in its spectrum. It is associated with ] where there is simultaneously emission from a dense wind close to the star and absorption from circumstellar material expanding away from the star.<ref name=struve/>
The unusual Hα line profile has since been observed to vary unpredictably: around a third of the time it is a normal absorption line; about a quarter of the time it is a double-peaked line, that is an absorption line with an emission core or an emission line with an absorption core; about a quarter of the time it has a P Cygni profile; most of the rest of the time the line has an inverse P Cygni profile, where the emission component is on the short wavelength side of the line; rarely there is a pure emission Hα line.<ref name=morrison/> The line profile changes are interpreted as variations in the quantity and velocity of material being expelled from the star. Occasional very high velocity outflows are inferred, and, more rarely, infalling material. The overall picture is one of large ] arising from the ] and driven by magnetic fields.<ref name=israelian/>


The unusual Hα line profile is observed to vary unpredictably. It is a normal absorption line around a third of the time. About a quarter of the time, it is a double-peaked line, that is, an absorption line with an emission core or an emission line with an absorption core. About a quarter of the time it has a P Cygni profile; most of the rest of the time, the line has an inverse P Cygni profile, where the emission component is on the short wavelength side of the line. Rarely, there is a pure emission Hα line.<ref name=morrison/><!--cites five previous sentences--> The line profile changes are interpreted as variations in the quantity and velocity of material being expelled from the star. Occasional very high-velocity outflows have been inferred, and, more rarely, infalling material. The overall picture is one of large ] arising from the ] and driven by magnetic fields.<ref name=israelian/>
The variations in the spectrum have been reflected in published spectral classes, such as B8 Ia, B8 Iab, and B8 Iae.<ref name=schultz/><ref name=bally/>


=== Variability === === Variability ===
] for Rigel, adapted from Moravveji ''et al.'' (2012)<ref name=apj2012_747_108/>]]
Rigel has been known to vary in brightness since at least 1930, although the exact range and type of variability was unclear. Published results showed variations of less than 0.1 magnitudes with no obvious period. Observations over 18 nights in 1984 showed variations at red, blue, and yellow wavelengths of up to 0.13 magnitudes on timescales of a few hours to several days, but again no clear period. The ] also varied but in general was not strongly correlated with the brightness variations.<ref name=guinan1985/>
Rigel has been known to vary in brightness since at least 1930. The small amplitude of Rigel's brightness variation requires ] or ] to be reliably detected. This brightness variation has no obvious period. Observations over 18 nights in 1984 showed variations at red, blue, and yellow wavelengths of up to 0.13 magnitudes on timescales of a few hours to several days, but again no clear period. Rigel's ] varies slightly, but this is not significantly correlated with its brightness variations.<ref name=guinan1985/>

From an analysis of ] satellite photometry, Rigel was identified as belonging to the ] class of variable star in 1998,<ref name="waelkens 1998"/> which are defined as "non-radially pulsating supergiants of the Bep–AepIa spectral types".<ref name=Samus2017/> (The 'e' indicates it displays ]s in the spectrum, while the 'p' means it has an unspecified spectral peculiarity.) It was added to the ] in the following year in the 74th namelist of variable stars.<ref name=IBVS/> The Hipparcos photometry showed variations with a photographic amplitude of 0.039 magnitudes and a possible period of 2.075 days.<ref name=lefevre/>


Rigel was observed with the Canadian ] satellite for nearly 28 days in 2009. The light variations in this supergiant star were at the milli-magnitude level. The gradual changes in the flux highlights the presence of long-period pulsation modes in the star.<ref name=apj2012_747_108/> From analysis of '']'' satellite photometry, Rigel is identified as belonging to the ] class of variable stars,<ref name="waelkens 1998"/> defined as "non-radially pulsating supergiants of the Bep–AepIa spectral types".<ref name=Samus2017/> In those spectral types, the 'e' indicates that it displays emission lines in its spectrum, while the 'p' means it has an unspecified spectral peculiarity. Alpha Cygni type variables are generally considered to be irregular<ref name=AAVSOvartyps/> or have ]s.<ref name=vangenderen/> Rigel was added to the General Catalogue of Variable Stars in the 74th name-list of variable stars on the basis of the Hipparcos photometry,<ref name=IBVS/> which showed variations with a photographic amplitude of 0.039 magnitudes and a possible period of 2.075 days.<ref name=lefevre/> Rigel was observed with the Canadian ] satellite for nearly 28 days in 2009. Milli-magnitude variations were observed, and gradual changes in flux suggest the presence of long-period pulsation modes.<ref name=apj2012_747_108/>
{{clear left}}


=== Mass loss === === Mass loss ===
From observations of the Hα spectral line, the mass loss from Rigel is estimated to be {{val|1.5|0.4|e=−7}} solar masses per year ({{solar mass}}/yr), around ten million times more than the mass loss from the ].<ref name=chesneau2010/> More detailed optical and ] infrared spectroscopic observations, together with ] interferometry, were taken from 2006 to 2010. Analysis of the Hα and ] spectral line profiles, and measurement of the regions producing the lines, show that the ] varies greatly in structure and strength. Loop and arm structures were also detected within the wind. Calculations of mass loss from the Hγ line give {{val|9.4|0.9|e=−7}} {{solar mass}}/yr in 2006-7 and {{val|7.6|1.1|e=−7}} {{solar mass}}/yr in 2009-10. Calculations using the Hα line give lower results, around {{val|1.5|e=−7}} {{solar mass}}/yr. The terminal wind velocity is 300&nbsp;km·s<sup>−1</sup>.<ref name=chesneau2014/>


From observations of the variable Hα spectral line, Rigel's mass-loss rate due to stellar wind is estimated be {{val|1.5|0.4|e=−7}} solar masses per year ({{solar mass|link=n}}/yr)—about ten million times more than the mass-loss rate from the ].<ref name=chesneau2010/> More detailed optical and ] infrared spectroscopic observations, together with ] interferometry, were taken from 2006 to 2010. Analysis of the Hα and ] line profiles, and measurement of the regions producing the lines, show that Rigel's stellar wind varies greatly in structure and strength. Loop and arm structures were also detected within the wind. Calculations of mass loss from the Hγ line give {{val|9.4|0.9|e=−7|u={{solar mass}}/yr}} in 2006-7 and {{val|7.6|1.1|e=−7|u={{solar mass}}/yr}} in 2009–10. Calculations using the Hα line give lower results, around {{val|1.5|e=−7|u={{solar mass}}/yr}}. The terminal wind velocity is {{val|300|u=km/s}}.<ref name=chesneau2014/> It is estimated that Rigel has lost about three solar masses ({{solar mass}}) since beginning life as a star of {{val|24|3|u={{solar mass}}}} seven to nine million years ago.<ref name=aaa445_3_1099/>
==Distance==
] ] in ]. Rigel B is not visible in the glare of the main star.]]
The distance to Rigel has been difficult to estimate with accuracy, as its brightness is not easy to determine independently, and it is too distant for accurate ] measurements. As it is both bright and moving through a region of nebulosity, Rigel lights up several dust clouds in its vicinity, most notably the 5°<ref name=Guieu2010/>–long ] (the Witch Head Nebula),<ref name="Jedicke1992"/> located at an ] of 2.5° from the star.<ref name=Guieu2010/> These are thought to be about {{convert|40|ly|pc|abbr=off}} distant from the star itself.<ref name="kalerrigel"/> For stars associated with this nebulosity, a distance of {{convert|291|±|2|pc|ly|0|abbr=off|order=flip}} is estimated.<ref name=Kounkel2018/>


== Distance ==
Rigel has been classified as an outlying member of the ], which is located at a distance of up to {{convert|500|pc|ly|abbr=off|order=flip}} from Earth. It has also been listed as a member of the poorly-defined ], somewhat closer at {{convert|360|pc|ly|abbr=off|order=flip}}.<ref name=markova/><ref name=racine/> Rigel is thought to be considerably closer than most of the members of Orion OB1 and the ]. ] and ] lie at a similar distance as Rigel, although Betelgeuse is a ] with a complex history and might have originally formed in the main body of the association.<ref name=bally/>
] ] in ]. Rigel B is not visible in the glare of the main star.]]


The revised 2007 ] reduction of Rigel's parallax gives a distance of {{convert|863|ly|pc|abbr=off}}, with a ] of about 9%.<ref name=aaa474_2_653/> A companion star to Rigel, usually considered to be physically associated and at the same distance, has a ] parallax of {{val|2.9186|0.0761|ul=mas}}, implying a distance around {{convert|340|pc|ly|abbr=off|order=flip}}. However, the measurements for this object show a number of features, suggesting they may be unreliable, possibly because it is a close double star.<ref name=dr2b/> Rigel's distance from the Sun is somewhat uncertain, different estimates being obtained by different methods. Old estimates placed it 166 parsecs (or 541 light years) away from the Sun.<ref>{{Cite book |url=http://archive.org/details/Galaxy_v23n06_1965-08 |title=Galaxy v23n06 (1965 08)}}</ref> The 2007 ] of Rigel's ] is {{val|3.78|0.34|ul=mas}}, giving a distance of {{convert|863|ly|pc|abbr=off}} with a ] of about 9%.<ref name=aaa474_2_653/> Rigel B, usually considered to be physically associated with Rigel and at the same distance, has a ] parallax of {{val|3.2352|0.0553|u=mas}}, suggesting a distance around {{convert|310|pc|ly|abbr=off|order=flip}}. However, the measurements for this object may be unreliable.<ref name=Gaia3/>

Indirect distance estimation methods have also been employed. For example, Rigel is believed to be in a region of ], its radiation illuminating several nearby clouds. Most notable of these is the 5°-long ] (Witch Head Nebula),<ref name=Guieu2010/><ref name="Jedicke1992"/> located at an ] of 2.5° from the star,<ref name=Guieu2010/> or a projected distance of {{convert|12|pc|ly|abbr=off|order=flip}} away.<ref name="kalerrigel"/> From measures of other nebula-embedded stars, IC{{nbs}}2118's distance is estimated to be {{convert|291|±|2|pc|ly|0|abbr=off|order=flip}}.<ref name=Kounkel2018/>

Rigel is an outlying member of the ], which is located at a distance of up to {{convert|500|pc|ly|abbr=off|order=flip}} from Earth. It is a member of the loosely defined ], somewhat closer at {{convert|360|pc|ly|abbr=off|order=flip}}.<ref name=markova/><ref name=racine/> Rigel is thought to be considerably closer than most of the members of Orion OB1 and the ]. Betelgeuse and ] lie at a similar distance to Rigel, although Betelgeuse is a ] with a complex history and might have originally formed in the main body of the association.<ref name=bally/>


== Stellar system == == Stellar system ==

<div style="float:left; width:240px; border:solid black 1px; text-align: center; margin: 8px; padding: 4px; font-size: 90%;">
<div style="float:right; width:240px; border:solid black 1px; text-align: center; margin: 8px; padding: 4px; font-size: 90%;">
{{chart/start}} {{chart/start}}
{{chart|border=1| |, |S1| |S1='''Rigel''' }} {{chart|border=1| |, |S1| |S1='''Rigel''' }}
{{chart|border=0| |! |PA|PA=Separation=9.5″<br/>Period=24,000&nbsp;y }} {{chart|border=0| |! |PA|PA=Separation = 9.5″{{break}}Period = 24,000{{nbs}}y }}
{{chart|border=1| |( | |, |- |S2|S2='''Ba''' }} {{chart|border=1|-|( | |, |- |S2|S2='''Ba''' }}
{{chart|border=0| |! |, |( |PB|PB=Separation=0.58&nbsp;mas<br/>Period={{Val|9.860|u=days}} }} {{chart|border=0| |! |, |( |PB|PB=Separation = {{val|0.58|u=mas}}{{break}}Period = {{Val|9.860|u=days}} }}
{{chart|border=1| |! |! |` |- |S3|S3='''Bb''' }} {{chart|border=1| |! |! |` |- |S3|S3='''Bb''' }}
{{chart|border=0| |` |( |PC|PC=Separation={{Val|0.1|u=arcsecond}}<br/>Period=63&nbsp;y }} {{chart|border=0| |` |( |PC|PC=Separation = {{Val|0.1|u=arcsecond}}{{break}}Period = 63{{nbs}}y }}
{{chart|border=1| | |` |S4| |S4='''C''' }} {{chart|border=1| | |` |S4| |S4='''C''' }}
{{chart/end}} {{chart/end}}
] for Rigel's components<ref name=msc/> ] for Rigel's components<ref name=msc/>
<!--The hierarchy structure divides multiple stars into sub-systems which are assumed to be gravitational attached. As some stars in Rigel have little evidence of orbital motion, which is questioned by some astronomers, we cannot say it is a 'Hierarchy of orbits'. --> <!--This hierarchy structure separates stars into subsystems which are assumed to be gravitationally attached. As some stars in the Rigel system have little evidence of orbital motion, which is questioned by some astronomers, we cannot say it is a "hierarchy of orbits".-->
</div> </div>


Rigel forms a ] with up to five or six components.<!--This number of components depends if A star (Rigel A) is a spectroscopic binary (Aa) as stated in the last line of this section. Stars here are A, Ba, Bb, C, D (5 stars) & Aa (6th star). --> The blue supergiant primary has a ] which is itself a likely a close triple star, plus a more distant visual companion that may also form part of the multiple star system. The ] of which Rigel is a part has at least four components. Rigel (sometimes called Rigel A to distinguish from the other components) has a ], which is likely a close triple-star system. A fainter star at a wider separation might be a fifth component of the Rigel system.


] discovered Rigel to be a visual double star on 1 October 1781, and it was catalogued as ] 33 (or H 2 33<ref name="WDS"/>).<ref name="Herschel1782"/> ] first measured the relative position of the companion in 1822, cataloging the visual pair as Σ 668.<ref name="Webb1917"/> The secondary star can be referred to as Rigel B or β Ori B. The ] of β Ori B from the primary star is 9.5 arc seconds to its south along ] 204°.<ref name="WDS"/><ref name=bakich/> Although not particularly faint at ] 6.7, the overall difference in brightness from the primary (about 6.6 magnitudes or 440 times fainter) makes it a challenging target for telescope apertures smaller than {{convert|15|cm|in|abbr=on|sigfig=1}}.<ref name=sanford/> ] discovered Rigel to be a visual double star on 1 October 1781, cataloguing it as star 33 in the "second class of double stars" in his Catalogue of Double Stars,<ref name="Herschel1782"/> usually abbreviated to H{{nbs}}II{{nbs}}33, or as H{{nbs}}2{{nbs}}33 in the Washington Double Star Catalogue.<ref name="WDS"/> ] first measured the relative position of the companion in 1822, cataloguing the visual pair as Σ 668.<ref name=FGWStruve/><ref name="Webb1917"/> The secondary star is often referred to as Rigel B or β Orionis B. The angular separation of Rigel B from Rigel A is 9.5 arc seconds to its south along ] 204°.<ref name="WDS"/><ref name=bakich/> Although not particularly faint at ] 6.7, the overall difference in brightness from Rigel A (about 6.6 magnitudes or 440 times fainter) makes it a challenging target for telescope apertures smaller than {{convert|15|cm|in|abbr=on|sigfig=1}}.<ref name=sanford/>


At Rigel's estimated distance, β Ori B's ] from its primary is over 2,200&nbsp;]. Since its discovery, there has been no sign of orbital motion, although both stars share similar ].<ref name=sb9/><ref name="Jedicke1992"/> The pair would have a minimum orbital period of around 18,000&nbsp;years.<ref name=msc/> ] (DR2) contains a somewhat unreliable parallax for β Ori B, placing it at about {{convert|340|pc|ly|abbr=off|order=flip}}, further away than the Hipparcos distance for Rigel, but similar to the Taurus-Orion R1 association. There is no parallax for Rigel in Gaia DR2. The Gaia DR2 proper motions for β Ori B and the Hipparcos proper motions for Rigel are both small, although not quite the same.<ref name=dr2b/> At Rigel's estimated distance, Rigel B's ] from Rigel A is over 2,200{{nbs}}]s (AU). Since its discovery, there has been no sign of orbital motion, although both stars share a similar ].<ref name="Jedicke1992" /><ref name=sb9/> The pair would have an estimated orbital period of 24,000{{nbs}}years.<ref name=msc/> Gaia Data Release 2{{nbsp}}(DR2) contains a somewhat unreliable parallax for Rigel B, placing it at about {{convert|340|pc|ly|abbr=off|order=flip}}, further away than the Hipparcos distance for Rigel, but similar to the Taurus-Orion R1 association. There is no parallax for Rigel in Gaia DR2. The Gaia DR2 proper motions for Rigel B and the Hipparcos proper motions for Rigel are both small, although not quite the same.<ref name=dr2b/>


in 1871, ] suspected β Ori B to be double, and in 1878, he resolved it into two nearly equal components.<ref name=aitken/> Their measured separation varies from less than 0.1" to nearly 0.2". In 2009, ] showed two almost identical components separated by 0.124".<ref name=mason/> The companion is designated as component C (β Ori C). Both stars have apparent visual magnitudes of 7.6. Their derived orbital period is 63&nbsp;years.<ref name=msc/> In 1871, ] suspected Rigel B to be a binary system, and in 1878, he resolved it into two components.<ref name="burnham1900"/> This visual companion is designated as component C (Rigel C), with a measured separation from component B that varies from less than {{val|0.1|u="}} to around {{val|0.3|u="}}.<ref name=WDS/><ref name="burnham1900"/> In 2009, ] showed the two almost identical components separated by {{val|0.124|u="}},<ref name=mason/> with visual magnitudes of 7.5 and 7.6, respectively.<ref name=WDS/> Their estimated orbital period is 63{{nbs}}years.<ref name=msc/> Burnham listed the Rigel multiple system as β{{nbs}}555 in his ]<ref name="burnham1900"/> or BU{{nbs}}555 in modern use.<ref name=WDS/>


β Ori B appears to be a double-lined ] system, which indicates that the individual ]s of both components is visible in the ]. It consists of two ] stars that orbit each other every 9.86&nbsp;days. These two stars do not seem to correspond to the visual binary components B and C, so the BC sub-system might be a triple, although the actual arrangement is unclear.<ref name=sb9/><ref name=sanford/> Component B is a double-lined ] system, which shows two sets of ]s combined within its single ]. Periodic changes observed in relative positions of these lines indicate an orbital period of 9.86{{nbs}}days. The two spectroscopic components Rigel Ba and Rigel Bb cannot be resolved in optical telescopes but are known to both be hot stars of spectral type around B9. This spectroscopic binary, together with the close visual component Rigel C, is likely a physical triple-star system,<ref name=sb9/> although Rigel C cannot be detected in the spectrum, which is inconsistent with its observed brightness.<ref name=sanford/>


In 1878, Burnham found a nearby 15th magnitude star, catalogued as component D (β Ori D), whose 2017 separation from Rigel was {{val|44.5|ul="}} almost due north at position angle of 1°,<ref name=WDS/> although it is unclear whether it is physically related or a coincidental alignment. Gaia DR2 finds it to be a 12th magnitude sunlike star at approximately the same distance as Rigel.<ref name=dr2d/> Most likely to be an orange dwarf, this star would have an orbital period of around 250,000 years, if it is part of the stellar system.<ref name="kalerrigel"/> In 1878, Burnham found another possibly associated star of approximately 13th magnitude. He listed it as component D of β{{nbs}}555,<ref name="burnham1900"/> although it is unclear whether it is physically related or a coincidental alignment. Its 2017 separation from Rigel was {{val|44.5|ul="}}, almost due north at a position angle of 1°.<ref name=WDS/> Gaia DR2 finds it to be a 12th magnitude sunlike star<!--Does "orange dwarf" count as "sunlike"?--> at approximately the same distance as Rigel.<ref name=dr2d/> Likely a ], this star would have an orbital period of around 250,000 years, if it is part of the Rigel system.<ref name="kalerrigel"/>


Another spectroscopic companion to Rigel has been reported on the basis of ] variations, and even an orbit calculated, but it is thought that the star does not exist and the pulsations are intrinsic to Rigel itself.<ref name=sb9/> A spectroscopic companion to Rigel was reported on the basis of radial velocity variations, and its orbit was even calculated, but subsequent work suggests the star does not exist and that observed pulsations are intrinsic to Rigel itself.<ref name=sb9/>


== Physical characteristics == == Physical characteristics ==
]]] ]]]
Rigel is an intrinsically highly luminous star.<ref name=burnham/><ref name="schaaf"/> Using the Hipparcos distance of {{val|264|u=pc}}, the luminosity of Rigel is estimated to be 120,000 times that of the Sun.<ref name=apj2012_747_108/> Its surface temperature is determined from the spectrum and colour and is around 12,100&nbsp;K. The ]-measured ] of this star, after correction for ], is {{val|2.75|0.01|u=]}}.<ref name=auf/> At its estimated distance, this yields a size of about 78.9 times the ] ({{solar radius}}).<ref name=apj2012_747_108/>


Rigel is a ] that has exhausted the hydrogen fuel in its core, expanded and cooled as it moved away from the ] across the upper part of the ].<ref name=guinan/><ref name=seeds/> When it was on the main sequence, its ] would have been around {{val|30,000|fmt=commas|ul=K}}.<ref name=saio/> Rigel's complex variability at ] is caused by ] similar to those of ]. Further observations of radial velocity variations indicate that it simultaneously oscillates in at least 19 non-radial modes with periods ranging from about 1.2 to 74 days.<ref name=apj2012_747_108/>
Assuming a distance of {{convert|360|±|40|pc|ly|abbr=off|order=flip}}, Rigel is estimated to be around 218,000 times as luminous as the Sun and to have a radius of {{solar radius|{{val|109|12}}}}. Comparison to evolutionary tracks gives a mass of {{solar mass|{{val|21|3}}}}, while modelling to match the spectrum gives a mass of {{solar mass|{{val|24|8}}}}.<ref name=aaa445_3_1099/>


Estimation of many physical characteristics of blue supergiant stars, including Rigel, is challenging due to their rarity and uncertainty about how far they are from the Sun. As such, their characteristics are mainly estimated from theoretical ].<ref name=demarque2008/> Its effective temperature can be estimated from the spectral type and color to be around {{val|12,100|fmt=commas|ul=K}}.<ref name=przybilla/> A mass of {{val|21|3|u=solar mass}} at an age of {{val|8|1}}{{nbsp}}million years has been estimated by comparing evolutionary tracks, while atmospheric modeling from the spectrum gives a mass of {{solar mass|{{val|24|8}}}}.<ref name=aaa445_3_1099/>
A 2018 study using the ] measured the angular diameter of {{val|2.606|0.009|ul=mas}}, yielding the radius as {{solar radius|{{val|74.1|+6.1|-7.3}}}}. Fitting to the ] (SED) of Rigel, using historical photometry and assuming a distance of {{val|264|u=pc}}, gives a luminosity {{val|61515|11486|fmt=commas}} times that of the Sun.<ref name=baines/>


Although Rigel is often considered the most luminous star within 1,000 light-years of the Sun,<ref name="schaaf" /><ref name=burnham/> its energy output is poorly known. Using the Hipparcos distance of {{convert|264|pc|ly|abbr=off|order=flip}}, the estimated relative luminosity for Rigel is about 120,000 times that of the Sun ({{solar luminosity|link=y}}),<ref name=apj2012_747_108/> but another recently published distance of {{convert|360|±|40|pc|ly|abbr=off|order=flip}} suggests an even higher luminosity of {{solar luminosity|219,000}}.<ref name=aaa445_3_1099/> Other calculations based on theoretical stellar evolutionary models of Rigel's atmosphere give luminosities anywhere between {{solar luminosity|83,000}} and {{solar luminosity|363,000}},<ref name=markova/> while summing the ] from historical photometry with the Hipparcos distance suggests a luminosity as low as {{val|61515|11486|u={{solar luminosity}}|fmt=commas}}.<ref name=baines/> A 2018 study using the ] measured the ] as {{val|2.526|u=mas}}. After correcting for ], the angular diameter is found to be {{val|2.606|0.009|u=mas}}, yielding a radius of {{solar radius|{{val|74.1|+6.1|-7.3}}|link=y}}.<ref name=baines/> An older measurement of the angular diameter gives {{val|2.75|0.01|u=mas}},<ref name=auf/> equivalent to a radius of {{solar radius|78.9}} at {{val|264|u=pc}}.<ref name=apj2012_747_108/> These radii are calculated assuming the Hipparcos distance of {{val|264|u=pc}}; adopting a distance of {{val|360|u=pc}} leads to a significantly larger size.<ref name=chesneau2014/> Older distance estimates were mostly far lower than modern estimates, leading to lower radius estimates; a 1922 estimate by ] gave Rigel a diameter of 25 million miles, or approximately {{Solar radius|28.9}}, smaller than its neighbor ].<ref>{{Cite journal |last=Plaskett |first=J. S. |date=1922 |title=The Dimensions of the Stars |url=https://www.jstor.org/stable/40668597 |journal=Publications of the Astronomical Society of the Pacific |volume=34 |issue=198 |pages=79–93 |doi=10.1086/123157 |jstor=40668597 |bibcode=1922PASP...34...79P |issn=0004-6280}}</ref>
Models of Rigel's atmosphere based on its spectrum give a luminosity is somewhere between {{solar luminosity|83,000}} and {{solar luminosity|363,000}}, respectively based on the Hipparcos distance of {{convert|240|pc|ly|abbr=off|order=flip}} and an Orion OB1 association distance of {{convert|500|pc|ly|abbr=off|order=flip}}.<ref name=markova/>


Due to their closeness to each other and ambiguity of the spectrum, little is known about the intrinsic properties of the members of the Rigel BC triple system. All three stars seem to be near equally hot ]s that are three to four times as massive as the Sun.<ref name=msc/>
Rigel is a ] that has exhausted burning the hydrogen fuel in its core and left the main sequence, expanded, and brightened as it progresses across the ]. Puzzlingly, the pulsation properties of this star suggest it passed through the ] phase, whereas the surface abundances indicate it evolved directly to a blue supergiant.<ref name=saio/> Przybilla estimated that it has lost around 3 solar masses since beginning life as a star of {{val|24|3}} solar masses 7 to 9 million years ago.<ref name=aaa445_3_1099/> It is expected to eventually end its stellar life by exploding as a ] from a red supergiant, in the process flinging out material that will serve to seed future generations of stars.<ref name=apj2012_749_74/> It is one of the closest known potential supernova progenitors to Earth,<ref name=apj2012_747_108/> and would be expected to have an apparent magnitude of around {{val|-11}} at its peak.<ref name=guinan/>


== Evolution ==
Rigel's variability is complex and is caused by ] similar to those of ], the prototype of the class of Alpha Cygni pulsating stars. The radial velocity variations of Rigel prove that it simultaneously oscillates in at least 19 non-radial modes with periods ranging from about 1.2 to 74 days.<ref name=apj2012_747_108/> While its pulsations are powered by the nuclear reactions in a hydrogen-burning shell that is at least partially non-convective, the star also ] in its core.<ref name=apj2012_749_74 />


] models suggest the pulsations of Rigel are powered by nuclear reactions in a hydrogen-burning shell that is at least partially non-convective. These pulsations are stronger and more numerous in stars that have evolved through a ] phase and then increased in temperature to again become a blue supergiant. This is due to the decreased mass and increased levels of fusion products at the surface of the star.<ref name=saio/>
Visual double star β Ori B appears to be a close triple star system (Rigel Ba, Bb, and C), but due to their proximity, little is known about their individual intrinsic properties. All seem to be near equally hot ]s that are 3 to 4 times as massive as the Sun.<ref name=msc/>


Rigel is likely to be ] in its core.<ref name=apj2012_749_74 /> Due to strong convection of helium produced in the core while Rigel was on the main sequence and in the hydrogen-burning shell since it became a supergiant, the fraction of helium at the surface has increased from 26.6% when the star formed to 32% now. The surface abundances of carbon, nitrogen, and oxygen seen in the spectrum are compatible with a post-red supergiant star only if its internal convection zones are modeled using non-homogeneous chemical conditions known as the ].<ref name=saio/>
==Etymology and cultural significance==
In the constellation of Orion, Rigel represents Orion's knee or (as its name suggests) his foot; with the nearby star ] marking Orion's footstool.<ref name="schaaf"/> Rigel is presumably the star known as "]'s toe" in ].<ref name=cleasby/> In the Caribbean, Rigel represented the severed leg of the folkloric figure ''Trois Rois'', himself represented by the three stars of Orion's Belt. The leg had been severed with a cutlass by the maiden ''Bįhi'' (]).<ref name=taylor/> The ] people of southern ] knew it as ''tunsel'' ("little woodpecker").<ref name=milbraith/>


Rigel is expected to eventually end its stellar life as a ].<ref name=apj2012_749_74/> It is one of the closest known potential ] progenitors to Earth,<ref name=apj2012_747_108/> and would be expected to have a maximum apparent magnitude of around {{val|-11}} (about the same brightness as a quarter Moon or around 300 times brighter than Venus ever gets).<ref name=guinan/> The supernova would leave behind either a black hole or a neutron star.<ref name=apj2012_749_74/>
Rigel was known as ''Yerrerdet-kurrk'' to the ] ] of southeastern ], and held to be the mother-in-law of ''Totyerguil'' (]). The distance between them signified the taboo preventing a man from approaching his mother-in-law.<ref name=mudrooroo/> The indigenous ] people of northwestern Victoria named Rigel as ''Collowgullouric Warepil''.<ref name=hamacher/> The ] of northern Australia know Rigel as the Red ] Leader ''Unumburrgu'' and chief conductor of ceremonies in a songline when Orion is high in the sky. ], the river, marks a line of stars in the sky leading to it, and the other stars of Orion are his ceremonial tools and entourage. Betelgeuse is ''Ya-jungin'' "Owl Eyes Flicking", watching the ceremonies.<ref name=harney/> The ] of New Zealand named Rigel as '']''; this was said to be a daughter of ''Rehua'' (]), the chief of all stars.<ref name=parker/> Its ] also presaged the appearance of '']'' (the ]) in the dawn sky which marked the Māori New Year in late May or early June. The ] of the ], as well as some Maori groups in New Zealand, marked the start of their New Year with Rigel rather than the Pleiades.<ref name="kelley"/> ''Puaka'' was a local variant used in the South Island.<ref name="Best22"/> In ], the Minamoto or ] chose Rigel and its white color as its symbol, calling the star ''Genji-boshi'' ({{lang|ja|源氏星}}), while the Taira or ] adopted Betelgeuse and its red color. The two powerful families fought the ]; the stars were seen as facing each other off and only kept apart by ].<ref name="RENSHAW1"/><ref name=daijirin/><ref name=hojiri/> Rigel was also known as ''Gin-waki'', ({{lang|ja|銀脇}}), "the Silver (Star) beside ('']'')".


== Etymology and cultural significance ==
==In modern culture==
]'s '']''. The foot on the left is annotated ''rijl al-jauza al-yusra'', the Arabic name from which ''Rigel'' is derived.{{efn|1=Al-Sufi's book was translated into Latin and other European languages. Al-Sufi himself planned the figures, two for each constellation: one shows how they appear to an observer looking up toward the heavens; the other how they appear to the observer looking down upon a celestial globe.<ref name=ck2018/>}} ]]
]
The ] was originally a Norwegian ship, built in Copenhagen in 1924. It was requisitioned by the Germans during the ] and sunk in 1944 while being used to transport prisoners of war.<ref name=minnehallen/> Two US Navy ships have borne the name ].


The earliest known recording of the name ''Rigel'' is in the '']'' of 1521. It is derived from the Arabic name ''{{transl|ar|Rijl Jauzah al Yusrā}}'', "the left leg (foot) of Jauzah" (i.e. ''rijl'' meaning "leg, foot"),<ref name=allen/> which can be traced to the 10th century.<ref name="KUNITZSCH1959"/> "Jauzah" was a proper name for Orion; an alternative Arabic name was {{lang|ar|رجل الجبار}} ''{{transl|ar|rijl al-jabbār}}'', "the foot of the great one", from which stems the rarely used variant names ''Algebar'' or ''Elgebar''. The ''Alphonsine tables'' saw its name split into "Rigel" and "Algebar", with the note, ''et dicitur Algebar. Nominatur etiam Rigel.''{{efn|1=lit."... and it is called Algebar. It is also named Rigel."}}<ref name=Kunitzsch86/> Alternate spellings from the 17th century include ''Regel'' by Italian astronomer ], ''Riglon'' by German astronomer ], and ''Rigel Algeuze'' or ''Algibbar'' by English scholar ].<ref name="allen"/>
The ] was a ] program for the ] that was cancelled in 1953 before reaching deployment.<ref>{{cite book | last=Yenne | first= Bill | year= 2018 | title=A Complete History of U.S. Cruise Missiles | location= Forest Lake, MN | publisher= Specialty Press| isbn=978-1-58007-256-4 | pages=61, 70}}</ref>


With the constellation representing the mythological Greek huntsman ], Rigel is his knee or (as its name suggests) foot; with the nearby star ] marking Orion's footstool.<ref name="schaaf"/> Rigel is presumably the star known as "]'s toe" in ].<ref name=cleasby/> In the Caribbean, Rigel represented the severed leg of the folkloric figure ''Trois Rois'', himself represented by the three stars of Orion's Belt. The leg had been severed with a cutlass by the maiden ''Bįhi'' (Sirius).<ref name=taylor/> The ] of southern Mexico knew it as ''tunsel'' ("little woodpecker").<ref name=milbraith/>
The ] are a chain of small islands in ], renamed after originally being called Utskjera. They were given their current name as Rigel was used as an ].<ref name=skerries/> ], also in Antarctica, is also named after the star.<ref name=mountrigel/>


Rigel was known as ''Yerrerdet-kurrk'' to the ] ] of southeastern Australia, and held to be the mother-in-law of ''Totyerguil'' (]). The distance between them signified the taboo preventing a man from approaching his mother-in-law.<ref name=mudrooroo/> The indigenous ] people of northwestern Victoria named Rigel as ''Collowgullouric Warepil''.<ref name=hamacher/> The ] of northern Australia know Rigel as the Red ] Leader ''Unumburrgu'' and chief conductor of ceremonies in a songline when Orion is high in the sky. ], the river, marks a line of stars in the sky leading to it, and the other stars of Orion are his ceremonial tools and entourage. Betelgeuse is ''Ya-jungin'' "Owl Eyes Flicking", watching the ceremonies.<ref name=harney/>
The name Rigel, or reference to the star itself, occurs frequently in ].

The ] of New Zealand named Rigel as '']'', said to be a daughter of ''Rehua'' (]), the chief of all-stars.<ref name=parker/> Its ] presages the appearance of '']'' (the ]) in the dawn sky, marking the Māori New Year in late May or early June. The ] of the ], as well as some Māori groups in New Zealand, mark the start of their New Year with Rigel rather than the Pleiades.<ref name="kelley"/> ''Puaka'' is a ] used in the South Island.<ref name="Best22"/>

In Japan, the Minamoto or ] chose Rigel and its white color as its symbol, calling the star ''Genji-boshi'' ({{lang|ja|源氏星}}), while the Taira or ] adopted Betelgeuse and its red color. The two powerful families fought the ]; the stars were seen as facing off against each other and kept apart only by the three stars of ].<ref name="RENSHAW1"/><ref name=daijirin/><ref name=hojiri/>

== In modern culture ==

The ] was originally a Norwegian ship, built in Copenhagen in 1924. It was requisitioned by the Germans during ] and sunk in 1944 while being used to transport prisoners of war.<ref name=minnehallen/> Two US Navy ships have borne the name ].<ref name=silverstone1968/><ref name=history/><ref name=navymil/> The ] was a ] program for the ] that was cancelled in 1953 before reaching deployment.<ref name=yenne/>

The ] are a chain of small islands in ], renamed after originally being called Utskjera. They were given their current name as Rigel was used as an ].<ref name=skerries/> ], elevation {{convert|1910|m|ft|abbr=on}}, is also in Antarctica.<ref name=mountrigel/>{{clear}}

== See also ==
* ]

== Notes ==

{{notelist}}


== References == == References ==

{{Reflist|30em|refs= {{Reflist|30em|refs=


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<ref name=skerries>{{cite web |title=Antarctica Detail: ID 12640 |url=https://geonames.usgs.gov/apex/f?p=gnispq:5:0::NO::P5_ANTAR_ID:12640 |website=U.S. Geological Survey |publisher=U.S. Department of the Interior |accessdate=2 February 2019}}</ref> <ref name=mountrigel>{{cite web |title=Antarctica Detail: ID 12639 |url=https://geonames.usgs.gov/apex/f?p=gnispq:5:0::NO::P5_ANTAR_ID:12639 |website=U.S. Geological Survey |publisher=] |access-date=2 February 2019 |archive-date=5 November 2020 |archive-url=https://web.archive.org/web/20201105125200/https://geonames.usgs.gov/apex/f?p=gnispq:5:0::NO::P5_ANTAR_ID:12639 |url-status=dead }}</ref>


<ref name=skerries>{{cite web|title=Antarctica Detail: ID 12640|url=https://geonames.usgs.gov/apex/f?p=gnispq:5:0::NO::P5_ANTAR_ID:12640|website=U.S. Geological Survey|publisher=]|access-date=2 February 2019|archive-url=https://web.archive.org/web/20190202042601/https://geonames.usgs.gov/apex/f?p=gnispq:5:0::NO::P5_ANTAR_ID:12640|archive-date=2 February 2019|url-status=live}}</ref>
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<ref name=milbraith>{{cite book|last=Milbrath|first=Susan |title=Star Gods of the Maya: Astronomy in Art, Folklore, and Calendars|publisher=University of Texas Press|location=Austin, Texas|date=1999|page=39|isbn=978-0292752269|url=https://books.google.com/?id=DgqLplWtGPgC&pg=PA39&dq=betelgeuse+folklore#v=onepage&q=betelgeuse%20folklore&f=false}}</ref> <ref name=milbraith>{{cite book|last=Milbrath|first=Susan|title=Star Gods of the Maya: Astronomy in Art, Folklore, and Calendars|publisher=]|location=Austin, Texas|date=1999|page=39|isbn=978-0-292-75226-9|url=https://books.google.com/books?id=JD5qAAAAMAAJ&pg=PA39 }}</ref>


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<ref name=morrison>{{cite journal|bibcode=2008cihw.conf..155M|title=Hα line profile variability in the B8Ia-type supergiant Rigel (β Ori)|journal=Clumping in Hot-Star Winds|pages=155|last1=Morrison|first1=N. D.|last2=Rother|first2=R.|last3=Kurschat|first3=N.|year=2008}}</ref> <ref name=morrison>{{cite conference|bibcode=2008cihw.conf..155M|title=Hα line profile variability in the B8Ia-type supergiant Rigel (β Ori)|conference=Clumping in Hot-Star Winds|pages=155|last1=Morrison|first1=N. D.|last2=Rother|first2=R.|last3=Kurschat|first3=N.|year=2008}}</ref>


<ref name=israelian>{{cite journal|doi=10.1093/mnras/290.3.521|title=The inhomogeneous circumstellar envelope of Rigel (β Orionis A)|journal=Monthly Notices of the Royal Astronomical Society|volume=290|issue=3|pages=521–532|year=1997|last1=Israelian|first1=G.|last2=Chentsov|first2=E.|last3=Musaev|first3=F.}}</ref> <ref name=israelian>{{cite journal|doi=10.1093/mnras/290.3.521|title=The inhomogeneous circumstellar envelope of Rigel (β Orionis A)|journal=]|volume=290|issue=3|pages=521–532|year=1997|last1=Israelian|first1=G.|last2=Chentsov|first2=E.|last3=Musaev|first3=F.|bibcode=1997MNRAS.290..521I|doi-access=free}}</ref>


<ref name="kalerrigel">{{cite web |last1=Kaler |first1=James B. |title=Rigel |url=http://stars.astro.illinois.edu/sow/rigel.html |website=Stars |accessdate=1 February 2019| date=26 September 2009}}</ref> <ref name="kalerrigel">{{cite web |last1=Kaler |first1=James B. |title=Rigel |url=http://stars.astro.illinois.edu/sow/rigel.html |website=Stars |access-date=1 February 2019 |date=26 September 2009 |archive-url=https://web.archive.org/web/20190422025056/http://stars.astro.illinois.edu/sow/rigel.html |archive-date=22 April 2019 |url-status=live }}</ref>


<ref name=bakich>{{cite book|url=https://books.google.co.uk/books?id=qEhpS7d5ZdAC&pg=PA434|page=434|publisher=Springer|author=Michael E. Bakich|title=1,001 Celestial Wonders to See Before You Die|date=2010|isbn=9781441917775}}</ref> <ref name=bakich>{{cite book|url=https://books.google.com/books?id=qEhpS7d5ZdAC&pg=PA434|page=434|publisher=]|location=New York|first=Michael E.|last=Bakich|title=1,001 Celestial Wonders to See Before You Die|date=2010|isbn=978-1441917775|bibcode=2010ocws.book.....B|access-date=1 February 2019|archive-url=https://web.archive.org/web/20190201171936/https://books.google.co.uk/books?id=qEhpS7d5ZdAC&pg=PA434|archive-date=1 February 2019|url-status=live}}</ref>


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<ref name=saio>{{cite journal|doi=10.1093/mnras/stt796|title=Evolution of blue supergiants and α Cygni variables: Puzzling CNO surface abundances|journal=Monthly Notices of the Royal Astronomical Society|volume=433|issue=2|pages=1246–1257|year=2013|last1=Saio|first1=Hideyuki|last2=Georgy|first2=Cyril|last3=Meynet|first3=Georges|bibcode=2013MNRAS.433.1246S|arxiv=1305.2474}}</ref> <ref name=saio>{{cite journal|doi=10.1093/mnrasl/slt165|arxiv=1311.4744|title=The puzzle of the CNO abundances of α Cygni variables resolved by the Ledoux criterion|journal=Monthly Notices of the Royal Astronomical Society: Letters|volume=439|pages=L6–L10|year=2014|last1=Georgy|first1=Cyril|last2=Saio|first2=Hideyuki|last3=Meynet|first3=Georges|doi-access=free |bibcode=2014MNRAS.439L...6G|s2cid=118557550}}</ref>


<ref name=minnehallen>{{cite web | url=http://minnehallen.no/skip_2/rigel-ms | title=MS. Rigel | work=Minnehallen (The Memorial Hall) |accessdate=5 January 2019}}</ref> <ref name=minnehallen>{{cite web|url=http://minnehallen.no/skip_2/rigel-ms|title=MS. Rigel|website=Minnehallen (The Memorial Hall)|lang=no|access-date=5 January 2019|archive-url=https://web.archive.org/web/20190204174537/http://minnehallen.no/skip_2/rigel-ms|archive-date=4 February 2019|url-status=live}}</ref>


<ref name=chesneau2010>{{cite journal|bibcode=2010A&A...521A...5C|title=Time, spatial, and spectral resolution of the Hα line-formation region of Deneb and Rigel with the VEGA/CHARA interferometer|journal=Astronomy and Astrophysics|volume=521|pages=A5|author1=Chesneau|first1=O.|last2=Dessart|first2=L.|last3=Mourard|first3=D.|last4=Bério|first4=Ph.|last5=Buil|first5=Ch.|last6=Bonneau|first6=D.|last7=Borges Fernandes|first7=M.|last8=Clausse|first8=J. M.|last9=Delaa|first9=O.|last10=Marcotto|first10=A.|last11=Meilland|first11=A.|last12=Millour|first12=F.|last13=Nardetto|first13=N.|last14=Perraut|first14=K.|last15=Roussel|first15=A.|last16=Spang|first16=A.|last17=Stee|first17=P.|last18=Tallon-Bosc|first18=I.|last19=McAlister|first19=H.|last20=Ten Brummelaar|first20=T.|last21=Sturmann|first21=J.|last22=Sturmann|first22=L.|last23=Turner|first23=N.|last24=Farrington|first24=C.|last25=Goldfinger|first25=P. J.|year=2010|doi=10.1051/0004-6361/201014509|arxiv = 1007.2095}}</ref> <ref name=chesneau2010>{{cite journal|bibcode=2010A&A...521A...5C|title=Time, spatial, and spectral resolution of the Hα line-formation region of Deneb and Rigel with the VEGA/CHARA interferometer|journal=Astronomy and Astrophysics|volume=521|pages=A5|last1=Chesneau|first1=O.|last2=Dessart|first2=L.|last3=Mourard|first3=D.|last4=Bério|first4=Ph.|last5=Buil|first5=Ch.|last6=Bonneau|first6=D.|last7=Borges Fernandes|first7=M.|last8=Clausse|first8=J. M.|last9=Delaa|first9=O.|last10=Marcotto|first10=A.|last11=Meilland|first11=A.|last12=Millour|first12=F.|last13=Nardetto|first13=N.|last14=Perraut|first14=K.|last15=Roussel|first15=A.|last16=Spang|first16=A.|last17=Stee|first17=P.|last18=Tallon-Bosc|first18=I.|last19=McAlister|first19=H.|last20=Ten Brummelaar|first20=T.|last21=Sturmann|first21=J.|last22=Sturmann|first22=L.|last23=Turner|first23=N.|last24=Farrington|first24=C.|last25=Goldfinger|first25=P. J.|year=2010|doi=10.1051/0004-6361/201014509|arxiv=1007.2095|s2cid=10340205}}</ref>


<ref name=chesneau2014>{{cite journal|bibcode=2014A&A...566A.125C|title=The variable stellar wind of Rigel probed at high spatial and spectral resolution|journal=Astronomy and Astrophysics|volume=566|pages=A125|last1=Chesneau|first1=O.|last2=Kaufer|first2=A.|last3=Stahl|first3=O.|last4=Colvinter|first4=C.|last5=Spang|first5=A.|last6=Dessart|first6=L.|last7=Prinja|first7=R.|last8=Chini|first8=R.|year=2014|arxiv=1405.0907|doi=10.1051/0004-6361/201322894}}</ref> <ref name=chesneau2014>{{cite journal|bibcode=2014A&A...566A.125C|title=The variable stellar wind of Rigel probed at high spatial and spectral resolution|journal=Astronomy and Astrophysics|volume=566|pages=A125|last1=Chesneau|first1=O.|last2=Kaufer|first2=A.|last3=Stahl|first3=O.|last4=Colvinter|first4=C.|last5=Spang|first5=A.|last6=Dessart|first6=L.|last7=Prinja|first7=R.|last8=Chini|first8=R.|year=2014|arxiv=1405.0907|doi=10.1051/0004-6361/201322894|s2cid=118404460}}</ref>


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<ref name=Samus2017>{{cite journal <ref name=Samus2017>{{cite journal
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}} }}


== External links == == External links ==

{{Commonscat|Rigel}}
* {{APOD |date=2018 January 15 |title=Rigel and the Witch Head Nebula}} {{Commons category|Rigel}}
* {{APOD|date=15 January 2018|title=Rigel and the Witch Head Nebula}}
* {{APOD |date=2015 November 16 |title=A Blazing Fireball between the Orion Nebula and Rigel }} * {{APOD|date=16 November 2015|title=A Blazing Fireball between the Orion Nebula and Rigel}}
* Astronomical Society of Southern Africa * Astronomical Society of Southern Africa
* AAVSO * AAVSO


{{Stars of Orion}} {{Stars of Orion}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Sky|05|14|32.272|-|08|12|05.91|800}} {{Sky|05|14|32.272|-|08|12|05.91|800}}


{{featured article}}
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Latest revision as of 22:14, 28 December 2024

Brightest star in the constellation Orion For other uses, see Rigel (disambiguation).

Rigel
Location of Rigel (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Orion
Pronunciation /ˈraɪdʒəl/ or /-ɡəl/
A
Right ascension 05 14 32.27210
Declination −08° 12′ 05.8981″
Apparent magnitude (V) 0.13 (0.05–0.18)
BC
Right ascension 05 14 32.049
Declination −08° 12′ 14.78″
Apparent magnitude (V) 6.67 (7.5/7.6)
Characteristics
A
Evolutionary stage Blue supergiant
Spectral type B8 Ia
U−B color index −0.66
B−V color index −0.03
Variable type Alpha Cygni
BC
Evolutionary stage Main sequence
Spectral type B9V + B9V
Astrometry
Radial velocity (Rv)17.8±0.4 km/s
Proper motion (μ) RA: +1.31 mas/yr
Dec.: +0.50 mas/yr
Parallax (π)3.78 ± 0.34 mas
Distance848±65 ly
(260±20 pc)
Absolute magnitude (MV)−7.84
Orbit
PrimaryA
CompanionBC
Period (P)24,000 yr
Orbit
PrimaryBa
CompanionBb
Period (P)9.860 days
Eccentricity (e)0.1
Semi-amplitude (K1)
(primary)		25.0 km/s
Semi-amplitude (K2)
(secondary)		32.6 km/s
Orbit
PrimaryB
CompanionC
Period (P)63 yr
Details
A
Mass21±3 M☉
Radius74.1+6.1
−7.3 R☉
Luminosity (bolometric)120,000+25,000
−21,000 L☉
Surface gravity (log g)1.75±0.10 cgs
Temperature12,100±150 K
Metallicity −0.06±0.10 dex
Rotational velocity (v sin i)25±3 km/s
Age8±1 Myr
Ba
Mass3.84 M☉
Bb
Mass2.94 M☉
C
Mass3.84 M☉
Other designations
β Orionis, ADS 3823, STF 668, BU 555, H II 33, CCDM J05145-0812, WDS J05145-0812
A: Rigel, Algebar, Elgebar, 19 Orionis, HD 34085, HR 1713, HIP 24436, SAO 131907, BD−08°1063, FK5 194
B: Rigel B, GCRV 3111
Database references
SIMBADRigel
Rigel B

Rigel is a blue supergiant star in the constellation of Orion. It has the Bayer designation β Orionis, which is Latinized to Beta Orionis and abbreviated Beta Ori or β Ori. Rigel is the brightest and most massive component – and the eponym – of a star system of at least four stars that appear as a single blue-white point of light to the naked eye. This system is located at a distance of approximately 860 light-years (260 pc) from the Sun.

A star of spectral type B8Ia, Rigel is 120,000 times as luminous as the Sun, and is 18 to 24 times as massive, depending on the method and assumptions used. Its radius is more than seventy times that of the Sun, and its surface temperature is 12,100 K. Due to its stellar wind, Rigel's mass-loss is estimated to be ten million times that of the Sun. With an estimated age of seven to nine million years, Rigel has exhausted its core hydrogen fuel, expanded, and cooled to become a supergiant. It is expected to end its life as a type II supernova, leaving a neutron star or a black hole as a final remnant, depending on the initial mass of the star.

Rigel varies slightly in brightness, its apparent magnitude ranging from 0.05 to 0.18. It is classified as an Alpha Cygni variable due to the amplitude and periodicity of its brightness variation, as well as its spectral type. Its intrinsic variability is caused by pulsations in its unstable atmosphere. Rigel is generally the seventh-brightest star in the night sky and the brightest star in Orion, though it is occasionally outshone by Betelgeuse, which varies over a larger range.

A triple-star system is separated from Rigel by an angle of 9.5 arc seconds. It has an apparent magnitude of 6.7, making it 1/400th as bright as Rigel. Two stars in the system can be seen by large telescopes, and the brighter of the two is a spectroscopic binary. These three stars are all blue-white main-sequence stars, each three to four times as massive as the Sun. Rigel and the triple system orbit a common center of gravity with a period estimated to be 24,000 years. The inner stars of the triple system orbit each other every 10 days, and the outer star orbits the inner pair every 63 years. A much fainter star, separated from Rigel and the others by nearly an arc minute, may be part of the same star system.

Nomenclature

Bright points of light against a dark background with wisps of colored nebulosity
Orion, with Rigel at bottom right, at optical wavelengths plus the Hα (hydrogen-alpha) spectral line to emphasize gas clouds

In 2016, the International Astronomical Union (IAU) included the name "Rigel" in the IAU Catalog of Star Names. According to the IAU, this proper name applies only to the primary component A of the Rigel system. The system is listed variously in historical astronomical catalogs as H II 33, Σ 668, β 555, or ADS 3823. For simplicity, Rigel's companions are referred to as Rigel B, C, and D; the IAU describes such names as "useful nicknames" that are "unofficial". In modern comprehensive catalogs, the whole multiple star system is known as WDS 05145-0812 or CCDM 05145–0812.

The designation of Rigel as β Orionis (Latinized to beta Orionis) was made by Johann Bayer in 1603. The "beta" designation is usually given to the second-brightest star in each constellation, but Rigel is almost always brighter than α Orionis (Betelgeuse). Astronomer J.B. Kaler speculated that Bayer assigned letters during a rare period when variable star Betelgeuse temporarily outshone Rigel, resulting in Betelgeuse being designated "alpha" and Rigel designated "beta". However, closer examination of Bayer's method shows that he did not strictly order the stars by brightness, but instead grouped them first by magnitude, then by declination. Rigel and Betelgeuse were both classed as first magnitude, and in Orion the stars of each class appear to have been ordered north to south.

Rigel has many other stellar designations taken from various catalogs, including the Flamsteed 19 Orionis (19 Ori), the Bright Star Catalogue entry HR 1713, and the Henry Draper Catalogue number HD 34085. These designations frequently appear in the scientific literature, but rarely in popular writing. Rigel is listed in the General Catalogue of Variable Stars, but since its familiar Bayer designation is used instead of creating a separate variable star designation.

Observation

Rigel A and Rigel B as they appear in a small telescope

Rigel is an intrinsic variable star with an apparent magnitude ranging from 0.05 to 0.18. It is typically the seventh-brightest star in the celestial sphere, excluding the Sun, although occasionally fainter than Betelgeuse. Rigel appears slightly blue-white and has a B-V color index of −0.06. It contrasts strongly with reddish Betelgeuse.

Culminating every year at midnight on 12 December, and at 9:00 pm on 24 January, Rigel is visible on winter evenings in the Northern Hemisphere and on summer evenings in the Southern Hemisphere. In the Southern Hemisphere, Rigel is the first bright star of Orion visible as the constellation rises. Correspondingly, it is also the first star of Orion to set in most of the Northern Hemisphere. The star is a vertex of the "Winter Hexagon", an asterism that includes Aldebaran, Capella, Pollux, Procyon, and Sirius. Rigel is a prominent equatorial navigation star, being easily located and readily visible in all the world's oceans (the exception is the area north of the 82nd parallel north).

Spectroscopy

Rigel's spectral type is a defining point of the classification sequence for supergiants. The overall spectrum is typical for a late B class star, with strong absorption lines of the hydrogen Balmer series as well as neutral helium lines and some of heavier elements such as oxygen, calcium, and magnesium. The luminosity class for B8 stars is estimated from the strength and narrowness of the hydrogen spectral lines, and Rigel is assigned to the bright supergiant class Ia. Variations in the spectrum have resulted in the assignment of different classes to Rigel, such as B8 Ia, B8 Iab, and B8 Iae.

As early as 1888, the heliocentric radial velocity of Rigel, as estimated from the Doppler shifts of its spectral lines, was seen to vary. This was confirmed and interpreted at the time as being due to a spectroscopic companion with a period of about 22 days. The radial velocity has since been measured to vary by about 10 km/s around a mean of 21.5 km/s.

In 1933, the Hα line in Rigel's spectrum was seen to be unusually weak and shifted 0.1 nm towards shorter wavelengths, while there was a narrow emission spike about 1.5 nm to the long wavelength side of the main absorption line. This is now known as a P Cygni profile after a star that shows this feature strongly in its spectrum. It is associated with mass loss where there is simultaneously emission from a dense wind close to the star and absorption from circumstellar material expanding away from the star.

The unusual Hα line profile is observed to vary unpredictably. It is a normal absorption line around a third of the time. About a quarter of the time, it is a double-peaked line, that is, an absorption line with an emission core or an emission line with an absorption core. About a quarter of the time it has a P Cygni profile; most of the rest of the time, the line has an inverse P Cygni profile, where the emission component is on the short wavelength side of the line. Rarely, there is a pure emission Hα line. The line profile changes are interpreted as variations in the quantity and velocity of material being expelled from the star. Occasional very high-velocity outflows have been inferred, and, more rarely, infalling material. The overall picture is one of large looping structures arising from the photosphere and driven by magnetic fields.

Variability

A light curve for Rigel, adapted from Moravveji et al. (2012)

Rigel has been known to vary in brightness since at least 1930. The small amplitude of Rigel's brightness variation requires photoelectric or CCD photometry to be reliably detected. This brightness variation has no obvious period. Observations over 18 nights in 1984 showed variations at red, blue, and yellow wavelengths of up to 0.13 magnitudes on timescales of a few hours to several days, but again no clear period. Rigel's color index varies slightly, but this is not significantly correlated with its brightness variations.

From analysis of Hipparcos satellite photometry, Rigel is identified as belonging to the Alpha Cygni class of variable stars, defined as "non-radially pulsating supergiants of the Bep–AepIa spectral types". In those spectral types, the 'e' indicates that it displays emission lines in its spectrum, while the 'p' means it has an unspecified spectral peculiarity. Alpha Cygni type variables are generally considered to be irregular or have quasi-periods. Rigel was added to the General Catalogue of Variable Stars in the 74th name-list of variable stars on the basis of the Hipparcos photometry, which showed variations with a photographic amplitude of 0.039 magnitudes and a possible period of 2.075 days. Rigel was observed with the Canadian MOST satellite for nearly 28 days in 2009. Milli-magnitude variations were observed, and gradual changes in flux suggest the presence of long-period pulsation modes.

Mass loss

From observations of the variable Hα spectral line, Rigel's mass-loss rate due to stellar wind is estimated be (1.5±0.4)×10 solar masses per year (M☉/yr)—about ten million times more than the mass-loss rate from the Sun. More detailed optical and K band infrared spectroscopic observations, together with VLTI interferometry, were taken from 2006 to 2010. Analysis of the Hα and Hγ line profiles, and measurement of the regions producing the lines, show that Rigel's stellar wind varies greatly in structure and strength. Loop and arm structures were also detected within the wind. Calculations of mass loss from the Hγ line give (9.4±0.9)×10 M☉/yr in 2006-7 and (7.6±1.1)×10 M☉/yr in 2009–10. Calculations using the Hα line give lower results, around 1.5×10 M☉/yr. The terminal wind velocity is 300 km/s. It is estimated that Rigel has lost about three solar masses (M☉) since beginning life as a star of 24±3 M☉ seven to nine million years ago.

Distance

A very bright blue-white star with fainter stars near a sharply defined strip of nebulosity
Rigel and reflection nebula IC 2118 in Eridanus. Rigel B is not visible in the glare of the main star.

Rigel's distance from the Sun is somewhat uncertain, different estimates being obtained by different methods. Old estimates placed it 166 parsecs (or 541 light years) away from the Sun. The 2007 Hipparcos new reduction of Rigel's parallax is 3.78±0.34 mas, giving a distance of 863 light-years (265 parsecs) with a margin of error of about 9%. Rigel B, usually considered to be physically associated with Rigel and at the same distance, has a Gaia Data Release 3 parallax of 3.2352±0.0553 mas, suggesting a distance around 1,000 light-years (310 parsecs). However, the measurements for this object may be unreliable.

Indirect distance estimation methods have also been employed. For example, Rigel is believed to be in a region of nebulosity, its radiation illuminating several nearby clouds. Most notable of these is the 5°-long IC 2118 (Witch Head Nebula), located at an angular separation of 2.5° from the star, or a projected distance of 39 light-years (12 parsecs) away. From measures of other nebula-embedded stars, IC 2118's distance is estimated to be 949 ± 7 light-years (291 ± 2 parsecs).

Rigel is an outlying member of the Orion OB1 association, which is located at a distance of up to 1,600 light-years (500 parsecs) from Earth. It is a member of the loosely defined Taurus-Orion R1 Association, somewhat closer at 1,200 light-years (360 parsecs). Rigel is thought to be considerably closer than most of the members of Orion OB1 and the Orion Nebula. Betelgeuse and Saiph lie at a similar distance to Rigel, although Betelgeuse is a runaway star with a complex history and might have originally formed in the main body of the association.

Stellar system

Rigel
Separation = 9.5″
Period = 24,000 y
Ba
Separation = 0.58 mas
Period = 9.860 d
Bb
Separation = 0.1″
Period = 63 y
C

Hierarchical scheme for Rigel's components

The star system of which Rigel is a part has at least four components. Rigel (sometimes called Rigel A to distinguish from the other components) has a visual companion, which is likely a close triple-star system. A fainter star at a wider separation might be a fifth component of the Rigel system.

William Herschel discovered Rigel to be a visual double star on 1 October 1781, cataloguing it as star 33 in the "second class of double stars" in his Catalogue of Double Stars, usually abbreviated to H II 33, or as H 2 33 in the Washington Double Star Catalogue. Friedrich Georg Wilhelm von Struve first measured the relative position of the companion in 1822, cataloguing the visual pair as Σ 668. The secondary star is often referred to as Rigel B or β Orionis B. The angular separation of Rigel B from Rigel A is 9.5 arc seconds to its south along position angle 204°. Although not particularly faint at visual magnitude 6.7, the overall difference in brightness from Rigel A (about 6.6 magnitudes or 440 times fainter) makes it a challenging target for telescope apertures smaller than 15 cm (6 in).

At Rigel's estimated distance, Rigel B's projected separation from Rigel A is over 2,200 astronomical units (AU). Since its discovery, there has been no sign of orbital motion, although both stars share a similar common proper motion. The pair would have an estimated orbital period of 24,000 years. Gaia Data Release 2 (DR2) contains a somewhat unreliable parallax for Rigel B, placing it at about 1,100 light-years (340 parsecs), further away than the Hipparcos distance for Rigel, but similar to the Taurus-Orion R1 association. There is no parallax for Rigel in Gaia DR2. The Gaia DR2 proper motions for Rigel B and the Hipparcos proper motions for Rigel are both small, although not quite the same.

In 1871, Sherburne Wesley Burnham suspected Rigel B to be a binary system, and in 1878, he resolved it into two components. This visual companion is designated as component C (Rigel C), with a measured separation from component B that varies from less than 0.1″ to around 0.3″. In 2009, speckle interferometry showed the two almost identical components separated by 0.124″, with visual magnitudes of 7.5 and 7.6, respectively. Their estimated orbital period is 63 years. Burnham listed the Rigel multiple system as β 555 in his double star catalog or BU 555 in modern use.

Component B is a double-lined spectroscopic binary system, which shows two sets of spectral lines combined within its single stellar spectrum. Periodic changes observed in relative positions of these lines indicate an orbital period of 9.86 days. The two spectroscopic components Rigel Ba and Rigel Bb cannot be resolved in optical telescopes but are known to both be hot stars of spectral type around B9. This spectroscopic binary, together with the close visual component Rigel C, is likely a physical triple-star system, although Rigel C cannot be detected in the spectrum, which is inconsistent with its observed brightness.

In 1878, Burnham found another possibly associated star of approximately 13th magnitude. He listed it as component D of β 555, although it is unclear whether it is physically related or a coincidental alignment. Its 2017 separation from Rigel was 44.5″, almost due north at a position angle of 1°. Gaia DR2 finds it to be a 12th magnitude sunlike star at approximately the same distance as Rigel. Likely a K-type main-sequence star, this star would have an orbital period of around 250,000 years, if it is part of the Rigel system.

A spectroscopic companion to Rigel was reported on the basis of radial velocity variations, and its orbit was even calculated, but subsequent work suggests the star does not exist and that observed pulsations are intrinsic to Rigel itself.

Physical characteristics

A chart showing several labelled stars against shaded colored areas with axes of spectral type and absolute magnitude, and Rigel labelled near the top
Rigel's place at top-center on the Hertzsprung–Russell diagram

Rigel is a blue supergiant that has exhausted the hydrogen fuel in its core, expanded and cooled as it moved away from the main sequence across the upper part of the Hertzsprung–Russell diagram. When it was on the main sequence, its effective temperature would have been around 30,000 K. Rigel's complex variability at visual wavelengths is caused by stellar pulsations similar to those of Deneb. Further observations of radial velocity variations indicate that it simultaneously oscillates in at least 19 non-radial modes with periods ranging from about 1.2 to 74 days.

Estimation of many physical characteristics of blue supergiant stars, including Rigel, is challenging due to their rarity and uncertainty about how far they are from the Sun. As such, their characteristics are mainly estimated from theoretical stellar evolution models. Its effective temperature can be estimated from the spectral type and color to be around 12,100 K. A mass of 21±3 M☉ at an age of 8±1 million years has been estimated by comparing evolutionary tracks, while atmospheric modeling from the spectrum gives a mass of 24±8 M☉.

Although Rigel is often considered the most luminous star within 1,000 light-years of the Sun, its energy output is poorly known. Using the Hipparcos distance of 860 light-years (264 parsecs), the estimated relative luminosity for Rigel is about 120,000 times that of the Sun (L☉), but another recently published distance of 1,170 ± 130 light-years (360 ± 40 parsecs) suggests an even higher luminosity of 219,000 L☉. Other calculations based on theoretical stellar evolutionary models of Rigel's atmosphere give luminosities anywhere between 83,000 L☉ and 363,000 L☉, while summing the spectral energy distribution from historical photometry with the Hipparcos distance suggests a luminosity as low as 61,515±11,486 L☉. A 2018 study using the Navy Precision Optical Interferometer measured the angular diameter as 2.526 mas. After correcting for limb darkening, the angular diameter is found to be 2.606±0.009 mas, yielding a radius of 74.1+6.1
−7.3 R☉. An older measurement of the angular diameter gives 2.75±0.01 mas, equivalent to a radius of 78.9 R☉ at 264 pc. These radii are calculated assuming the Hipparcos distance of 264 pc; adopting a distance of 360 pc leads to a significantly larger size. Older distance estimates were mostly far lower than modern estimates, leading to lower radius estimates; a 1922 estimate by John Stanley Plaskett gave Rigel a diameter of 25 million miles, or approximately 28.9 R☉, smaller than its neighbor Aldebaran.

Due to their closeness to each other and ambiguity of the spectrum, little is known about the intrinsic properties of the members of the Rigel BC triple system. All three stars seem to be near equally hot B-type main-sequence stars that are three to four times as massive as the Sun.

Evolution

Stellar evolution models suggest the pulsations of Rigel are powered by nuclear reactions in a hydrogen-burning shell that is at least partially non-convective. These pulsations are stronger and more numerous in stars that have evolved through a red supergiant phase and then increased in temperature to again become a blue supergiant. This is due to the decreased mass and increased levels of fusion products at the surface of the star.

Rigel is likely to be fusing helium in its core. Due to strong convection of helium produced in the core while Rigel was on the main sequence and in the hydrogen-burning shell since it became a supergiant, the fraction of helium at the surface has increased from 26.6% when the star formed to 32% now. The surface abundances of carbon, nitrogen, and oxygen seen in the spectrum are compatible with a post-red supergiant star only if its internal convection zones are modeled using non-homogeneous chemical conditions known as the Ledoux Criteria.

Rigel is expected to eventually end its stellar life as a type II supernova. It is one of the closest known potential supernova progenitors to Earth, and would be expected to have a maximum apparent magnitude of around −11 (about the same brightness as a quarter Moon or around 300 times brighter than Venus ever gets). The supernova would leave behind either a black hole or a neutron star.

Etymology and cultural significance

Medieval illustration showing the stars of Orion overlaid with an image of a warrior
Orion illustrated in a copy of Abd al-Rahman al-Sufi's Book of Fixed Stars. The foot on the left is annotated rijl al-jauza al-yusra, the Arabic name from which Rigel is derived.

The earliest known recording of the name Rigel is in the Alfonsine tables of 1521. It is derived from the Arabic name Rijl Jauzah al Yusrā, "the left leg (foot) of Jauzah" (i.e. rijl meaning "leg, foot"), which can be traced to the 10th century. "Jauzah" was a proper name for Orion; an alternative Arabic name was رجل الجبار rijl al-jabbār, "the foot of the great one", from which stems the rarely used variant names Algebar or Elgebar. The Alphonsine tables saw its name split into "Rigel" and "Algebar", with the note, et dicitur Algebar. Nominatur etiam Rigel. Alternate spellings from the 17th century include Regel by Italian astronomer Giovanni Battista Riccioli, Riglon by German astronomer Wilhelm Schickard, and Rigel Algeuze or Algibbar by English scholar Edmund Chilmead.

With the constellation representing the mythological Greek huntsman Orion, Rigel is his knee or (as its name suggests) foot; with the nearby star Beta Eridani marking Orion's footstool. Rigel is presumably the star known as "Aurvandil's toe" in Norse mythology. In the Caribbean, Rigel represented the severed leg of the folkloric figure Trois Rois, himself represented by the three stars of Orion's Belt. The leg had been severed with a cutlass by the maiden Bįhi (Sirius). The Lacandon people of southern Mexico knew it as tunsel ("little woodpecker").

Rigel was known as Yerrerdet-kurrk to the Wotjobaluk koori of southeastern Australia, and held to be the mother-in-law of Totyerguil (Altair). The distance between them signified the taboo preventing a man from approaching his mother-in-law. The indigenous Boorong people of northwestern Victoria named Rigel as Collowgullouric Warepil. The Wardaman people of northern Australia know Rigel as the Red Kangaroo Leader Unumburrgu and chief conductor of ceremonies in a songline when Orion is high in the sky. Eridanus, the river, marks a line of stars in the sky leading to it, and the other stars of Orion are his ceremonial tools and entourage. Betelgeuse is Ya-jungin "Owl Eyes Flicking", watching the ceremonies.

The Māori people of New Zealand named Rigel as Puanga, said to be a daughter of Rehua (Antares), the chief of all-stars. Its heliacal rising presages the appearance of Matariki (the Pleiades) in the dawn sky, marking the Māori New Year in late May or early June. The Moriori people of the Chatham Islands, as well as some Māori groups in New Zealand, mark the start of their New Year with Rigel rather than the Pleiades. Puaka is a southern name variant used in the South Island.

In Japan, the Minamoto or Genji clan chose Rigel and its white color as its symbol, calling the star Genji-boshi (源氏星), while the Taira or Heike clan adopted Betelgeuse and its red color. The two powerful families fought the Genpei War; the stars were seen as facing off against each other and kept apart only by the three stars of Orion's Belt.

In modern culture

The MS Rigel was originally a Norwegian ship, built in Copenhagen in 1924. It was requisitioned by the Germans during World War II and sunk in 1944 while being used to transport prisoners of war. Two US Navy ships have borne the name USS Rigel. The SSM-N-6 Rigel was a cruise missile program for the US Navy that was cancelled in 1953 before reaching deployment.

The Rigel Skerries are a chain of small islands in Antarctica, renamed after originally being called Utskjera. They were given their current name as Rigel was used as an astrofix. Mount Rigel, elevation 1,910 m (6,270 ft), is also in Antarctica.

See also

Notes

  1. Al-Sufi's book was translated into Latin and other European languages. Al-Sufi himself planned the figures, two for each constellation: one shows how they appear to an observer looking up toward the heavens; the other how they appear to the observer looking down upon a celestial globe.
  2. lit."... and it is called Algebar. It is also named Rigel."

References

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