SW Virginis
Star in the constellation Virgo
From Wikipedia, the free encyclopedia
SW Virginis is a variable star in the equatorial constellation of Virgo, abbreviated SW Vir. It ranges in brightness from an apparent visual magnitude of 6.65 down to 7.95,[4] with a pulsation period of 153.8 days.[13] The star is located at a distance of approximately 590 light years from the Sun based on parallax measurements,[3] but is drifting closer with a radial velocity of −16 km/s.[9] SW Vir is located near the ecliptic and is subject to lunar occultation, which has allowed its angular diameter to be directly measured.[14][15][11]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Virgo[2] |
| Right ascension | 13h 14m 04.383s[3] |
| Declination | −02° 48′ 25.13″[3] |
| Apparent magnitude (V) | 6.65 to 7.95[4] |
| Characteristics | |
| Evolutionary stage | AGB[5] |
| Spectral type | M7III:[6] |
| U−B color index | 0.72[7] |
| B−V color index | 1.67[7] |
| Variable type | SRb[8] |
| Astrometry | |
| Radial velocity (Rv) | −15.78±3.51[9] km/s |
| Proper motion (μ) | RA: −35.131 mas/yr[3] Dec.: −2.769 mas/yr[3] |
| Parallax (π) | 5.5526±0.4437 mas[3] |
| Distance | 590 ± 50 ly (180 ± 10 pc) |
| Details | |
| Mass | 1–1.25[10] M☉ |
| Radius | 244±42[11] R☉ |
| Luminosity | 4,500±1,100[10] L☉ |
| Surface gravity (log g) | −0.3±0.1[10] cgs |
| Temperature | 3,060±130[11] K |
| Metallicity [Fe/H] | ~0.0[10] dex |
| Other designations | |
| SW Vir, BD−02°3653, HD 114961, HIP 64569, SAO 139236, PPM 179000[12] | |
| Database references | |
| SIMBAD | data |
The variability of this star was discovered by W. P. Fleming and announced in 1901, when it was known as BD−02°3653.[16] It was given its variable star designation, SW Virginis, in 1912.[17] The star was initially catalogued as an irregular variable but later was classed as a semi-regular variable of type SRb.[4] The stellar classification of M7III: indicates this is an evolved red giant, with the trailing colon indicating some uncertainty about the classification.[6] In 2003, the isotope 99Tc was detected in the atmosphere of SW Vir. The short lifespan of this element is an indicator that the star is undergoing the third dredge-up during the thermally pulsating phase of the asymptotic giant branch (AGB).[5]
This is an oxygen-rich non-Mira AGB star[18][19] that is shedding mass at a rate of 4×10−7 M☉·yr−1.[20] An infrared excess indicates the star has a circumstellar dust envelope consisting of grains of matter that have condensed out of expelled gas.[21] This dust shell displays an asymmetric appearance.[18][19] Polarization of light from these dust grains indicate a typical size of less than a μm.[19] The shell's thermal (non-maser) mm-wave spectral line emission from carbon monoxide was detected in 1986, and showed that the circumstellar envelope is expanding at 8.6 km/sec.[22] The spectrum of molecular water has been detected in the star's extended outer atmosphere – out to twice the stellar radius – with a column density of 1019–1020 cm–2.[23]