SU Andromedae
Star in the constellation Andromeda
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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]
SU Andromedae in optical light | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 00h 04m 36.4076s[1] |
| Declination | +43° 33′ 04.726″[1] |
| Apparent magnitude (V) | 8.0 to 8.5[2] |
| Characteristics | |
| Evolutionary stage | AGB[3] |
| Spectral type | C6,4(C5II)[2] |
| U−B color index | +4.13[4] |
| B−V color index | +2.58[4] |
| Variable type | LC[2] |
| Astrometry | |
| Proper motion (μ) | RA: −3.362±0.058 [1] mas/yr Dec.: −2.097±0.040 [1] mas/yr |
| Parallax (π) | 0.6979±0.0439 mas[1] |
| Distance | 4,700 ± 300 ly (1,430 ± 90 pc) |
| Absolute magnitude (MV) | −2.2[5] |
| Details | |
| SU And | |
| Luminosity | 2,535[6] L☉ |
| Temperature | 2,905[6] K |
| co-moving companion | |
| Radius | 1.95[7] R☉ |
| Luminosity | 9.833[7] L☉ |
| Temperature | 7,311[7] K |
| Other designations | |
| SU Andromedae, SU And, HD 225217, HIP 363, BD+42 4827 | |
| Database references | |
| SIMBAD | data |
Variability
Thomas Espin noted the possible variability of this star in 1895.[9] 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.[10]
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,[11] indicating a fairly cool carbon star and the subscript 4 showing modest Swan band intensity.[12]
Under the modern revised Morgan-Keenan system, SU Andromedae is classified as C-N5 C26-.[13] 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.[4]
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[7] 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.[5]