AF Andromedae

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AF Andromedae
AFAndLightCurve.png
A red band light curve for AF Andromedae, adapted from Joshi et al. (2019) [1]
Observation data
Epoch J2000        Equinox J2000
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
Mass 50–120 [7]   M☉
Radius 63 [4]   R☉
Luminosity 1,500,000 [6]   L☉
Temperature 33,000±3,000 K (normal)
7,000 (outburst) [8]   K
Other designations
AF  Andromedae, AF And, HV 4013, 2MASS  00433308+4112103, Var 19
Database references
SIMBAD data

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.

Contents

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. arXiv: 1908.01893 . Bibcode:2019AJ....158..175J. doi: 10.3847/1538-3881/ab39e9 . S2CID   199452971.
  2. 1 2 3 4 Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics . 649: A1. arXiv: 2012.01533 . Bibcode:2021A&A...649A...1G. doi: 10.1051/0004-6361/202039657 . S2CID   227254300. (Erratum:  doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  3. 1 2 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. Bibcode:1984ApJ...278..124H. doi: 10.1086/161774 .
  4. 1 2 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. 1 2 3 4 Humphreys, R. M. (1975). "The spectra of AE Andromedae and the Hubble-Sandage variables in M31 and M33". Astrophysical Journal. 200: 426. Bibcode:1975ApJ...200..426H. doi:10.1086/153806.
  6. 1 2 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. arXiv: 1707.01916 . Bibcode:2017ApJ...844...40H. doi: 10.3847/1538-4357/aa7cef . S2CID   119357524.
  7. 1 2 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. 1 2 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. arXiv: 1908.01893 . Bibcode:2019AJ....158..175J. doi: 10.3847/1538-3881/ab39e9 . S2CID   199452971.
  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. Bibcode:1929AN....234..377G. doi:10.1002/asna.19282342002.
  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. 1 2 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. Bibcode:1978ApJ...219..445H. doi: 10.1086/155797 .
  15. ↑ Hubble, Edwin; Sandage, Allan (1953). "The Brightest Variable Stars in Extragalactic Nebulae. I. M31 and M33". Astrophysical Journal. 118: 353. Bibcode:1953ApJ...118..353H. doi:10.1086/145764.
  16. 1 2 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. arXiv: 1407.2259 . Bibcode:2014ApJ...790...48H. doi:10.1088/0004-637X/790/1/48. S2CID   119177378.
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