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Dragonfly Telephoto Array

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Astronomical telescope built from multiple camera lenses

The Dragonfly Telephoto Array is a ground-based optical telescope array developed at the Dunlap Institute for Astronomy & Astrophysics of the University of Toronto in Canada. The array uses a combination of telephoto lenses to observe extragalactic objects. Its main purpose is to take images of ultra-low surface brightness galaxies at visible wavelengths of light. It is well suited for this purpose because its lenses have specially-coated optical glass that reduces scattered light.

Design

A Canon EF 400mm f/2.8L IS II USM lens, the model used in the array

The telescope was designed by Roberto Abraham of the University of Toronto and Pieter van Dokkum of Yale University. It was commissioned in 2013 and initially had eight commercially available Canon EF 400mm f/2.8L IS II USM camera lenses. This was first increased to ten lenses, and then extended to two clusters of 24 lenses each in 2016. The array is designed to accommodate the addition of lenses to increase its effective aperture with each additional lens.

With 48 lenses, the instrument has a light gathering power equivalent to a 400 mm f/0.4 lens, or a refracting telescope with an objective lens diameter of 990 mm (39 in). In March 2021 plans were announced to add 120 more lenses.

By using a lens based refactor design rather than a mirror based reflector design the telescope suffers less from issues introduced by diffraction and light scattering. Reflector designs have more light scattering due to interactions with dust and any slight roughness on the mirror. Issues with diffraction occur due to the need to place obstructions in the optical path of reflecting telescopes.

Research

Astronomers used the Dragonfly Telephoto Array to discover Dragonfly 44, a galaxy that is roughly as massive as the Milky Way, with 99.9% of its mass composed of dark matter. At the other end of the scale it was also used to discover NGC 1052-DF2, which measurements with other instruments initially suggested was a galaxy with very little dark matter. Further work indicated that NGC 1052-DF2 was closer to the earth than previous thought. If this is the case then the galaxy would appear to contain a typical amount of dark matter. Though this distance debate was continued and rebutted by a follow up observation which measured the tip of the red-giant branch distance to NGC 1052-DF2 using Hubble Space Telescope, confirming the earlier surface brightness fluctuation measurements and resolving the ambiguous distance.

References

  1. ^ "Dragonfly - Dunlap Institute". Dunlap Institute for Astronomy and Astrophysics. Retrieved 5 March 2018.
  2. "A New Kind of Telescope". University of Toronto Magazine. April 2015. Retrieved 29 May 2020.
  3. ^ Abraham, Roberto G.; van Dokkum, Pieter (January 2014). "Ultra – Low Surface Brightness Imaging with the Dragonfly Telephoto Array". Publications of the Astronomical Society of the Pacific. 126 (935): 55. arXiv:1401.5473. Bibcode:2014PASP..126...55A. doi:10.1086/674875. S2CID 119197160.
  4. "How Do You Make A Galaxy Without Dark Matter?". Dunlap Institute for Astronomy and Astrophysics. Retrieved 15 Apr 2019.
  5. Estes, Adam C. (14 July 2014). "Astronomers Invent New Telescope by Tying Telephoto Lenses Together". Gizmodo. Retrieved 5 March 2018.
  6. "Dragonfly - Yale University". Retrieved 5 March 2018.
  7. Lens array captures dim objects missed by giant telescopes, Science, Vol 371 p1301 26 March 2021
  8. ^ Jielai Zhang (2018). The Development and Scientific Application of the Dragonfly Telephoto Array (PDF) (PhD). University of Toronto. p. 10.
  9. "Meet Dragonfly 44, the galaxy made of 99.9% dark matter". Wired UK. Wired. Retrieved 5 March 2018.
  10. Van Dokkum, Pieter; Danieli, Shany; Cohen, Yotam; Merritt, Allison; Romanowsky, Aaron J; Abraham, Roberto; Brodie, Jean; Conroy, Charlie; Lokhorst, Deborah; Mowla, Lamiya; o'Sullivan, Ewan; Zhang, Jielai (2018). "A galaxy lacking dark matter". Nature. 555 (7698): 629–632. arXiv:1803.10237. Bibcode:2018Natur.555..629V. doi:10.1038/nature25767. PMID 29595770. S2CID 4460376.
  11. Trujillo, Ignacio (14 March 2019). "A distance of 13 Mpc resolves the claimed anomalies of the galaxy lacking dark matter". Monthly Notices of the Royal Astronomical Society. 486 (1): 1192–1219. arXiv:1806.10141. Bibcode:2019MNRAS.486.1192T. doi:10.1093/mnras/stz771. S2CID 118889598. Retrieved 5 June 2019.
  12. Shen, Zili; Danieli, Shany; van Dokkum, Pieter; Abraham, Roberto; Brodie, Jean P.; Conroy, Charlie; Dolphin, Andrew E.; Romanowsky, Aaron J.; Diederik Kruijssen, J. M.; Dutta Chowdhury, Dhruba (2021-06-01). "A Tip of the Red Giant Branch Distance of 22.1 ± 1.2 Mpc to the Dark Matter Deficient Galaxy NGC 1052–DF2 from 40 Orbits of Hubble Space Telescope Imaging". The Astrophysical Journal Letters. 914 (1): L12. arXiv:2104.03319. Bibcode:2021ApJ...914L..12S. doi:10.3847/2041-8213/ac0335. ISSN 2041-8205.

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