SU Andromedae is a carbon star in the constellation of Andromeda. It is a variable star classified as a slow irregular pulsating supergiant, and varies from an apparent visual magnitude of 8.5 at minimum brightness to a magnitude of 8.0 at maximum brightness with no clear period.[2]
visual band light curve of SU Andromedae, adapted from Miles (2010)[7]
Thomas Espin noted the possible variability of this star in 1895.[8]Williamina Fleming, in 1906, was examining photographic plates taken for the purpose of creating the Henry Draper Catalogue when she independently discovered and confirmed it as a variable star.[9]
Spectrum
The spectrum of SU Andromedae is dominated by Swan bands from the molecule C2. These stars were classified as type N under the Harvard scheme, stars with the blue continuum completely obscured by molecular absorption bands. Carbon star spectral types were later refined in the Morgan-Keenan system and SU Andromedae was typically classified as C64,[10] indicating a fairly cool carbon star and the subscript 4 showing modest Swan band intensity.[11]
Under the modern revised Morgan-Keenan system, SU Andromedae is classified as C-N5 C26-.[12] The C-N spectral type is to distinguish those stars from the C-R type where the blue continuum is not entirely hidden by absorption bands. A classification based on the infrared spectrum is C5 II, again a moderately cool carbon star with a luminosity class of II for a bright giant.[3]
Companion
SU Andromedae is 22" from a magnitude 12.77 star, probably an F0 main sequence star. This star has a Gaia Data Release 2 parallax of 0.7479±0.0905[6] and an absolute magnitude of about +2.4. It has an almost identical space motion as SU Andromedae and is assumed to be a distant co-moving companion. Based on that assumption, the absolute magnitude of SU Andromedae is calculated to be about −2.2.[4]
N. N. Samus; O. V. Durlevich; etal. "SU And database entry". Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.). CDS. Retrieved 2018-10-14.
Richer, Harvey B. (1971). "Some Intrinsic Properties of Carbon Stars". Astrophysical Journal. 167: 521–535. Bibcode:1971ApJ...167..521R. doi:10.1086/151049.
Olson, B. I.; Richer, H. B. (1975). "The absolute magnitudes of carbon stars - Carbon stars in binary systems". Astrophysical Journal. 200: 88–94. Bibcode:1975ApJ...200...88O. doi:10.1086/153763.
Miles, Richard (June 2010). "SU Andromedae Light curve". British Astronomical Association Variable Star Section Circular. 144: 27. Bibcode:2010BAAVC.144...27M. Retrieved 11 October 2021.
Pickering, E. C.; Fleming, W. P. (1906). "Stars having peculiar spectra. Thirteen new variable stars". Astrophysical Journal. 23: 257–261. Bibcode:1906ApJ....23..257P. doi:10.1086/141337.
Keenan, Philip C.; Morgan, W. W. (1941). "The Classification of the Red Carbon Stars". Astrophysical Journal. 94: 501–510. Bibcode:1941ApJ....94..501K. doi:10.1086/144356.
Barnbaum, Cecilia; Stone, Remington P. S.; Keenan, Philip C. (1996). "A Moderate-Resolution Spectral Atlas of Carbon Stars: R, J, N, CH, and Barium Stars". Astrophysical Journal Supplement. 105: 419–473. Bibcode:1996ApJS..105..419B. doi:10.1086/192323.
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