Astronomy:AF Andromedae

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Short description: Luminous blue variable star in the constellation Andromeda
AF Andromedae
AFAndLightCurve.png
A red band light curve for AF Andromedae, adapted from Joshi et al. (2019)[1]
Observation data
Equinox J2000.0]] (ICRS)
Constellation Andromeda
Right ascension  00h 43m 33.086s[2]
Declination +41° 49′ 10.31″[2]
Characteristics
Spectral type LBV
U−B color index ~ −0.9[3]
B−V color index ~ +0.1[3]
Variable type LBV[4]
Astrometry
Radial velocity (Rv)−152±9[5] km/s
Proper motion (μ) RA: 0.088[2] mas/yr
Dec.: −0.076[2] mas/yr
Parallax (π)−0.0026 ± 0.0674 mas
Distance~2.5Mly ly
(~780kpc pc)
Absolute magnitude (MV)−8.2[6]
Details
Mass50-120[7] M☉
Radius63[4] R☉
Luminosity1,500,000[6] L☉
Temperature33,000±3,000 K (normal)
7,000 (outburst)[8] K
Other designations
AF Andromedae, AF And, HV 4013, 2MASS 00433308+4112103, Var 19
Database references
SIMBADdata

AF Andromedae (AF And) is a luminous blue variable (LBV), a type of variable star. The star is one of the most luminous variables in M31, the Andromeda Galaxy.

Discovery

The star was discovered to be variable in 1927, with a photographic magnitude range of 15.3 to 16.5, at the Harvard College Observatory and designated HV 4013. It was considered to be the brightest variable star in M31[9][10] Two years later it was given the variable star designation AF Andromedae.[11] Between 1917 and 1953, five or six major eruptions were detected and two or three minor ones. More eruptions were observed in 1970-74, 1987-92, 1998-2001, [8] and 2017.[12]

AF And was often referred to as var 19, after its number in a Hubble list of variable stars in M31 and M33. It was identified as one of the five Hubble–Sandage variables: Var A, Var B, Var C, and Var 2 in M33, and Var 19 in M31.[13][14][15] On the basis of color–color comparisons, it was assigned as spectral type B and described as related to the P Cygni variables. Observations from 1960 to 1970 showed irregular variations in the B (blue) magnitude between 15.5 and 17.6, with visual magnitudes somewhat brighter.[13] The first detailed spectrum was published in 1975.[5]

Spectrum

AF And in outbursts has a peculiar emission line spectrum described as very much like Eta Carinae, likely due to a dense stellar wind.[5] When quiescent, the spectrum is similar to late Of or WN stars.[16]

AF And has prominent allowed and forbidden FeII and hydrogen lines in its emission spectrum, as well as weaker HeI lines. The variability and lack of absorption lines defy a normal spectral classification, but it was suggested that it may be close to class A.[5]

The 250.7 nm FeII line is unusually strong in emission. The same feature in Eta Carinae's spectrum has been attributed to a UV laser.[16]

Properties

AF And was the brightest star in M31 when it was first noticed during an outburst, at an apparent magnitude around 15, over a million times more luminous than the Sun. Newer calculations give a luminosity slightly less than a million times that of the Sun.

The star's mass has not been calculated explicitly, but this type of star is massive, typically 50–120 M☉.[7]

See also

References

  1. ↑ Joshi, Yogesh C.; Sharma, Kaushal; Gangopadhyay, Anjasha; Gokhale, Rishikesh; Misra, Kuntal (November 2019). "A Long-term Photometric Variability and Spectroscopic Study of Luminous Blue Variable AF And in M31". The Astronomical Journal 158 (5): 175. doi:10.3847/1538-3881/ab39e9. Bibcode: 2019AJ....158..175J. 
  2. ↑ 2.0 2.1 2.2 2.3 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G.  Gaia EDR3 record for this source at VizieR.
  3. ↑ 3.0 3.1 Humphreys, R. M.; Blaha, C.; d'Odorico, S.; Gull, T. R.; Benvenuti, P. (1984). "IUE and ground-based observations of the Hubble-Sandage variables in M31 and M33". The Astrophysical Journal 278: 124. doi:10.1086/161774. Bibcode: 1984ApJ...278..124H. 
  4. ↑ 4.0 4.1 Szeifert, T.; Humphreys, R. M.; Davidson, K.; Jones, T. J.; Stahl, O.; Wolf, B.; Zickgraf, F.-J. (1996). "HST and groundbased observations of the 'Hubble-Sandage' variables in M 31 and M 33". Astronomy and Astrophysics 314: 131. Bibcode: 1996A&A...314..131S. 
  5. ↑ 5.0 5.1 5.2 5.3 Humphreys, R. M. (1975). "The spectra of AE Andromedae and the Hubble-Sandage variables in M31 and M33". Astrophysical Journal 200: 426. doi:10.1086/153806. Bibcode: 1975ApJ...200..426H. 
  6. ↑ 6.0 6.1 Humphreys, Roberta M.; Davidson, Kris; Hahn, David; Martin, John C.; Weis, Kerstin (2017). "Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram". The Astrophysical Journal 844 (1): 40. doi:10.3847/1538-4357/aa7cef. Bibcode: 2017ApJ...844...40H. 
  7. ↑ 7.0 7.1 Burggraf, B.; Weis, K.; Bomans, D. J. (2006). "LBVs in M33: Their Environments and Ages". Stellar Evolution at Low Metallicity: Mass Loss 353: 245. Bibcode: 2006ASPC..353..245B. 
  8. ↑ 8.0 8.1 Joshi, Yogesh C.; Sharma, Kaushal; Gangopadhyay, Anjasha; Gokhale, Rishikesh; Misra, Kuntal (2019). "A Long-term Photometric Variability and Spectroscopic Study of Luminous Blue Variable AF and in M31". The Astronomical Journal 158 (5): 175. doi:10.3847/1538-3881/ab39e9. Bibcode: 2019AJ....158..175J. 
  9. ↑ Luyten, W. J. (1927). "Two New Variables in the Region of the Andromeda Nebula". Harvard College Observatory Bulletin 851: 4. Bibcode: 1927BHarO.851R...4L. 
  10. ↑ Luyten, W. J. (1928). "A New Variable in the Andromeda Nebula, H.V. 4476". Harvard College Observatory Bulletin 859 (859): 1. Bibcode: 1928BHarO.859....1L. 
  11. ↑ Guthnick, P.; Prager, R. (1929). "Benennung von veränderlichen Sternen". Astronomische Nachrichten 234 (20): 377. doi:10.1002/asna.19282342002. Bibcode: 1929AN....234..377G. 
  12. ↑ Martin, John C.; Humphreys, Roberta M.; Hornoch, Kamil (2017). "AF and - an LBV/S Dor Variable in Outburst". The Astronomer's Telegram 10383: 1. Bibcode: 2017ATel10383....1M. 
  13. ↑ 13.0 13.1 Sharov, A. S. (1973). "Bright variable stars in the Andromeda M31 and Triangulum M33 nebulae". Perem. Zvezdy 19: 3. Bibcode: 1973PZ.....19....3S. 
  14. ↑ Humphreys, R. M. (1978). "Luminous variable stars in M31 and M33". The Astrophysical Journal 219: 445. doi:10.1086/155797. Bibcode: 1978ApJ...219..445H. 
  15. ↑ Hubble, Edwin; Sandage, Allan (1953). "The Brightest Variable Stars in Extragalactic Nebulae. I. M31 and M33". Astrophysical Journal 118: 353. doi:10.1086/145764. Bibcode: 1953ApJ...118..353H. 
  16. ↑ 16.0 16.1 Humphreys, Roberta M.; Weis, Kerstin; Davidson, Kris; Bomans, D. J.; Burggraf, Birgitta (2014). "Luminous and Variable Stars in M31 and M33. II. Luminous Blue Variables, Candidate LBVs, Fe II Emission Line Stars, and Other Supergiants". The Astrophysical Journal 790 (1): 48. doi:10.1088/0004-637X/790/1/48. Bibcode: 2014ApJ...790...48H. 

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