SW Virginis

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, with a pulsation period of 153.8 days. The star is located at a distance of approximately 590 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −16 km/s. SW Vir is located near the ecliptic and is subject to lunar occultation, which has allowed its angular diameter to be directly measured. The variability of this star was discovered by W. P. Fleming and announced in 1901, when it was known as BD−02°3653. It was given its variable star designation, SW Virginis, in 1912. The star was initially catalogued as an irregular variable but later was classed as a semi-regular variable of type SRb. The stellar classification of M7III: indicates this is an evolved red giant, with the trailing colon indicating some uncertainty about the classification. 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). This is an oxygen-rich non-Mira AGB star that is shedding mass at a rate of 4×10−7 M☉·yr−1. An infrared excess indicates the star has a circumstellar dust envelope consisting of grains of matter that have condensed out of expelled gas. This dust shell displays an asymmetric appearance. Polarization of light from these dust grains indicate a typical size of less than a μm. 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. 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.

Star in the constellation Virgo

SW Virginis

A visual band light curve for SW Virginis, adapted from Percy et al. (2001)[1]
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

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]

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]

References

[edit]

1. ^ Percy, John R.; Wilson, Joseph B.; Henry, Gregory W. (August 2001). "Long-Term VRI Photometry of Small-Amplitude Red Variables. I. Light Curves and Periods". Publications of the Astronomical Society of the Pacific. 113 (786): 983–996. Bibcode:2001PASP..113..983P. doi:10.1086/322153.
2. ^ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
3. ^ ^{a b c d e} 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.
4. ^ ^{a b c} Armour, J. E.; et al. (October 1990), "A Period Analysis of the Semi-Regular Variable SW Vir", Information Bulletin on Variable Stars, 3521: 1, Bibcode:1990IBVS.3521....1A.
5. ^ ^{a b} Lebzelter, T.; Hron, J. (December 2003), "Technetium and the third dredge up in AGB stars. I. Field stars", Astronomy and Astrophysics, 411 (3): 533–542, arXiv:astro-ph/0310018, Bibcode:2003A&A...411..533L, doi:10.1051/0004-6361:20031458.
6. ^ ^{a b} Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
7. ^ ^{a b} Ducati, J. R. (2002), "Catalogue of Stellar Photometry in Johnson's 11-color system.", VizieR Online Data Catalog, CDS/ADC Collection of Electronic Catalogues, 2237, Bibcode:2002yCat.2237....0D.
8. ^ Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
9. ^ ^{a b} Famaey, B.; et al. (May 2009), "Spectroscopic binaries among Hipparcos M giants. I. Data, orbits, and intrinsic variations", Astronomy and Astrophysics, 498 (2): 627–640, arXiv:0901.0934, Bibcode:2009A&A...498..627F, doi:10.1051/0004-6361/200810698, S2CID 18739721.
10. ^ ^{a b c d} Hadjara, M.; Cruzalèbes, P.; Nitschelm, C.; Chen, X.; Michael, E. A.; Moreno, E. (2019-10-01). "A CO-multilayer outer atmosphere for eight evolved stars revealed with VLTI/AMBER". Monthly Notices of the Royal Astronomical Society. 489 (2): 2595–2614. arXiv:1909.03997. Bibcode:2019MNRAS.489.2595H. doi:10.1093/mnras/stz2240. ISSN 0035-8711.
11. ^ ^{a b c} Mondal, Soumen; Chandrasekhar, T. (2005-08-01). "Angular Diameter Measurements of Evolved Variables by Lunar Occultations at 2.2 and 3.8 Microns". The Astronomical Journal. 130 (2): 842–852. arXiv:astro-ph/0504326. Bibcode:2005AJ....130..842M. doi:10.1086/430457. ISSN 0004-6256.
12. ^ "SW Vir". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-10-03.
13. ^ Percy, John R.; et al. (May 2008), "Further Studies of the Photometric Variability of Bright Pulsating Red Giants", Publications of the Astronomical Society of the Pacific, 120 (867): 523, Bibcode:2008PASP..120..523P, doi:10.1086/588612.
14. ^ Schmidtke, P. C.; et al. (April 1986), "Angular diameters by the lunar occultation technique. VII", Astronomical Journal, 91: 961–970, Bibcode:1986AJ.....91..961S, doi:10.1086/114072.
15. ^ Bogdanov, M. B.; Cherepashchuk, A. M. (August 1990), "Estimation of Brightness Distributions Over Stellar Disks from an Analysis of Infrared Observations of Lunar Occultations - the Red Giants SW-Virginis and FY-Librae", Soviet Astronomy, 34 (4): 393, Bibcode:1990SvA....34..393B.
16. ^ Pickering, E. C.; et al. (April 1901), "Sixty-four new variable stars", Astrophysical Journal, 13: 226–230, Bibcode:1901ApJ....13..226P, doi:10.1086/140808.
17. ^ Dunér, Nils Christofer; Hartwig, Ernst; Müller, G. (June 1912). "Benennung von neu entdeckten veränderlichen Sternen". Astronomische Nachrichten. 191 (19): 341–358. Bibcode:1912AN....191..341.. doi:10.1002/asna.19121911902.
18. ^ ^{a b} Guha Niyogi, Suklima; et al. (October 2011), "Investigating spatial distribution of dust around SW Vir", Astronomical Review, 6 (8): 27–38, Bibcode:2011AstRv...6h..27G, doi:10.1080/21672857.2011.11519689.
19. ^ ^{a b c} Khouri, T.; et al. (March 2020), "Inner dusty envelope of the AGB stars W Hydrae, SW Virginis, and R Crateris using SPHERE/ZIMPOL", Astronomy & Astrophysics, 635, id. A200, arXiv:2003.06195, Bibcode:2020A&A...635A.200K, doi:10.1051/0004-6361/201834618.
20. ^ Olofsson, H.; et al. (September 2002), "Mass loss rates of a sample of irregular and semiregular M-type AGB-variables", Astronomy and Astrophysics, 391 (3): 1053–1067, arXiv:astro-ph/0206172, Bibcode:2002A&A...391.1053O, doi:10.1051/0004-6361:20020841.
21. ^ van der Veen, W. E. C. J.; et al. (March 1995), "The distribution of dust around Asymptotic Giant Branch stars", Astronomy and Astrophysics, 295: 445–458, Bibcode:1995A&A...295..445V.
22. ^ Zuckerman, B.; Dyck, H. M. (May 1986). "Carbon Monoxide Emission from Stars in the IRAS and Revised AFGL Catalogs. I. Mass Loss Driven by Radiation Pressure on Dust Grains". Astrophysical Journal. 304: 394–400. Bibcode:1986ApJ...304..394Z. doi:10.1086/164173.
23. ^ Ohnaka, K.; et al. (January 2019), "Spatially resolving the atmosphere of the non-Mira-type AGB star SW Vir in near-infrared molecular and atomic lines with VLTI/AMBER", Astronomy & Astrophysics, 621, id. A6, arXiv:1811.05989, Bibcode:2019A&A...621A...6O, doi:10.1051/0004-6361/201834171.