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Star in the constellation Andromeda From Wikipedia, the free encyclopedia
R Andromedae (R And) is a Mira-type variable star in the constellation Andromeda. Its spectral class is type S because it shows absorption bands of zirconium monoxide (ZrO) in its spectrum. It was among the stars found by Paul Merrill to show absorption lines of the unstable element technetium,[10] establishing that nucleosynthesis must be occurring in stars. The SH molecule was found for the first time outside earth in the atmosphere of this star.[11] The star is losing mass due to stellar winds at a rate of 1.09×10−6 M☉/yr.[5]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 00h 24m 01.946s[1] |
| Declination | +38° 34′ 37.37″[1] |
| Apparent magnitude (V) | 5.8 - 15.2[2] |
| Characteristics | |
| Spectral type | S3,5e-S8,8e(M7e)[2] |
| B−V color index | 1.97[3] |
| Variable type | Mira[2] |
| Astrometry | |
| Radial velocity (Rv) | −6.40 [4] km/s |
| Proper motion (μ) | RA: −16.021±0.148[1] mas/yr Dec.: −32.794±0.141[1] mas/yr |
| Parallax (π) | 2.6444 ± 0.1600 mas[1] |
| Distance | 1,230 ± 70 ly (380 ± 20 pc) |
| Absolute magnitude (MV) | −5.19[5] |
| Details | |
| Radius | 476±120 - 493±129[6] R☉ |
| Luminosity | 6,300[7] L☉ |
| Surface gravity (log g) | −1.02[8] cgs |
| Temperature | 2,500[8] K |
| Metallicity [Fe/H] | −1.01[9] dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
R Andromedae shows periodic variations in its brightness approximately every 409 days. The maximum brightness is not the same every cycle and can reach a peak magnitude of mv = 5.8, with the lowest known minima nearly 10 magnitudes fainter. The rise to maximum brightness is approximately twice as fast as the fall to minimum brightness. It is classified as a Mira variable. Those stars contract and expand regularly, changing size and temperature, and this causes the brightness variations.[2]
R Andromedae has a spectral type that varies as its brightness changes. At a typical maximum it is assigned a spectral type of S5/4.5e. This makes it an S-type star, a red giant similar to class M stars but with unusually strong molecular bands of ZrO in its spectrum compared to the titanium oxide (TiO) bands seen in other cool giants. S stars are intermediate between carbon stars and the more typical oxygen-rich giants. The S5 indicates its relative temperature, while the number after the slash is a measure of the relative C:O ratio, 4.5 meaning carbon is about 97% as abundant as oxygen. ZrO bands in R Andromedae are about twenty times stronger than those of TiO.[12] When it is fainter, the spectral type has been classified as late as S8,8e. On this older classification system for S stars, the number after the comma is an indication of the relative strength of ZrO and TiO bands which used to be considered to show the C:O ratio.[13]
R Andromedae, like all Mira variables, is an asymptotic giant branch star, one that has exhausted its core helium and is burning it in a shell outside the core and hydrogen in a shell closer to the surface. These stars undergo dredge-up events which cause convection of fusion products to the surface and anomalies such as enhanced carbon and zirconium. Asymptotic giant branch stars are very cool and luminous red giants; R Andromedae varies in temperature and luminosity but is typically about 2,500 K and 6,300 L☉. The angular diameter of R Andromedae has been measured at 8.63±1.42 mas and 8.32±1.27 mas on different dates, corresponding to radii of 493±129 R☉ and 476±120 R☉ respectively, assuming a distance of 532 pc.[6]
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