V476 Cygni

V476 Cygni or Nova Cygni 1920 was a nova which occurred in the constellation Cygnus in 1920. It was discovered by William Frederick Denning, an English amateur astronomer, at 09:30 GMT on 20 August 1920, at which time it had a magnitude of 3.7.[4] It reached a peak brightness of magnitude 1.7 on 23 August 1920.[5][6][7] Its quiescent brightness is magnitude 17.09.

The light curve of V476 Cygni, plotted from AAVSO data
V476 Cygni

RGB composite color image of the shell surrounding the nova V476 Cygni, made from three narrow band images: Blue = 4800Å, green = Hα at 6563 Å and red = [NII] at 6583 Å. From Santamaria et al. 2020[1]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
Right ascension 19h 58m 24.46s[2]
Declination +53° 37′ 07.5″[2]
Apparent magnitude (V) 1.7Max.
17.09Min.
Astrometry
Distance665+107
−53[3] pc
Characteristics
Variable type Nova
Other designations
V476 Cyg, Nova Cygni 1920, GCRV 12334, AAVSO 1955+53B
Database references
SIMBADdata
The location of V476 Cygni (circled in red)

V476 Cygni's light curve is quite unusual, showing a rapid decline from maximum brightness, followed by a slow nearly linear fading. It is classified as a very fast nova,[8] with a very long tail. The light curve shows a "dust dip", a fast decline to a local brightness minimum, then a small increase in brightness, and finally a long, slow decline. This dust dip is believed to is believed to coincide with the formation of dust in the material ejected from the nova as it moves away from the star and cools.[9]

All novae consist of a close binary star pair, with a white dwarf star and a "donor" star orbiting each other. The stars are so close together that the less dense donor star transfers matter to the white dwarf. In the case of V476 Cygni, modeling indicates that the white dwarf has a mass of 1.18M⊙, and it is receiving 6×10−10 M⊙ of material from the donor star, per year.[10]

Two images of the shell surrounding V476 Cygni taken 25 years apart, showing the nebula's expansion. Both were taken with Hα filters, left at the William Herschel Telescope, and right with the Nordic Optical Telescope.[1]

A small emission nebula (shell) is visible around the star, which resembles a planetary nebula. Santamaria et al. examined images of the nebula taken in 1944, 1993 and 2018 and found that the shell is clearly expanding. It is slightly elliptical, with major and minor axes of 14.6×13.4 arc seconds (as of 2018) expanding at a rate of 0.073×0.067 arc seconds per year, implying a physical expansion rate of 230×200 km/sec.[1] Surprisingly, a 1997 attempt to image the shell using the Hubble Space Telescope, was unsuccessful.[11]

References
  1. Santamaria, E.; Guerrero, M.A.; Ramos-Larios, G.; Toala, J.A.; Sabin, L.; Rubio, G.; Quino-Mendoza, J.A. (March 2020). "Angular Expansion of Nova Shells". The Astrophysical Journal. 892 (1). arXiv:2002.06749. doi:10.3847/1538-4357/ab76c5. Retrieved 6 December 2020.
  2. "V476 Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 4 December 2020.
  3. Schaefer, Bradley E. (20 September 2018). "The distances to Novae as seen by Gaia" (PDF). Monthly Notices of the Royal Astronomical Society. 481 (3): 3033–3051. doi:10.1093/mnras/sty2388. Retrieved 4 December 2020.
  4. Denning, W.F. (September 1920). "Estimated magnitudes of Nova Cygni (1920)". Astronomische Nachrichten. 211: 419. doi:10.1002/asna.19202112205. Retrieved 4 December 2020.
  5. "Download Data". AAVSO. Retrieved 4 December 2020.
  6. Warner, B. (February 2006). "Where have all the novae gone?". Astronomy & Geophysics. 47 (1): 29–32. Retrieved 30 November 2020.
  7. {Beech, M. (1998). "The Makings of Meteor Astronomy: Part XVII. W.F. Denning and Comets, Nebulae, and Novae". WGN, Journal of the International Meteor Organization. 26 (6): 268–272. Retrieved 30 November 2020.
  8. Slavin, A.J.; O'Brien, T.J.; Dunlop, J.S. (September 1995). "A deep optical imaging study of the nebular remnants of classical novae". 276. 276 (2): 353–371. doi:10.1093/mnras/276.2.353. Retrieved 4 December 2020.
  9. Strope, Richard J.; Schaefer, Bradley E.; Henden, Arne A. (July 2010). "Catalog of 93 Nova Light Curves: Classification and Properties" (PDF). The Astronomical Journal. 140 (1): 34–62. doi:10.1088/0004-6256/140/1/34. Retrieved 5 December 2020.
  10. Shara, Michael M.; Prialnik, Dina; Hillman, Yael; Kovetz, Attay (June 2018). "The Masses and Accretion Rates of White Dwarfs in Classical and Recurrent Novae". The Astrophysical Journal. 860 (2): 110. arXiv:1804.06880. doi:10.3847/1538-4357/aabfbd. Retrieved 4 December 2020.
  11. Gill, C.D.; O'Brien, T.J. (May 2000). "Hubble Space Telescope imaging and ground-based spectroscopy of old nova shells - I. FH Ser, V533 Her, BT Mon, DK Lac and V476 Cyg" (PDF). Monthly Notices of the Royal Astronomical Society. 314 (1): 175–182. doi:10.1046/j.1365-8711.2000.03342.x. Retrieved 4 December 2020.
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