Astronomy:Theta Hydrae
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 14m 21.866s[1] |
| Declination | +02° 18′ 51.64″[1] |
| Apparent magnitude (V) | 3.888[2] |
| Characteristics | |
| Spectral type | B9.5 V + DA 1.6[3] |
| U−B color index | −0.118[2] |
| B−V color index | −0.065[2] |
| Astrometry | |
| Radial velocity (Rv) | −10.7±0.3[4] km/s |
| Proper motion (μ) | RA: +128.152[1] mas/yr Dec.: −327.709[1] mas/yr |
| Parallax (π) | 28.4019 ± 0.3682[1] mas |
| Distance | 115 ± 1 ly (35.2 ± 0.5 pc) |
| Absolute magnitude (MV) | +0.92[5] |
| Details | |
| θ Hya A | |
| Mass | 2.52[3] M☉ |
| Luminosity | 52[5] L☉ |
| Surface gravity (log g) | 3.80±0.08[6] cgs |
| Temperature | 10,099±145[6] K |
| Metallicity [Fe/H] | −0.42±0.09[6] dex |
| Rotational velocity (v sin i) | 95[7] km/s |
| θ Hya B | |
| Mass | 0.68[8] or 1.21[3] M☉ |
| Temperature | 30,700[3] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
Theta Hydrae, Latinized from θ Hydrae, is a binary star[8] system in the constellation Hydra. It is visible to the naked eye with an apparent visual magnitude of 3.9.[2] The star system has a high proper motion[8] with an annual parallax shift of 28.4 mas,[1] indicating a distance of about 115 light years. Theta Hydrae forms a double with a magnitude 9.9 star located at an angular separation of 29 arcseconds.[10]
The primary component of this system is a B-type main sequence star with a stellar classification of B9.5 V.[3] It is a candidate Lambda Boötis star, indicating it displays an underabundance of iron peak elements.[11] However, it is also underabundant in oxygen, a characteristic not shared by other Lambda Boötis stars. Instead, it may be a peculiar B star.[12]
An orbiting white dwarf companion was discovered in 1998 from its X-ray emission. This degenerate star must have evolved from a progenitor that was once more massive than the current primary.[8] Burleigh and Barstow (1999) gave a mass estimate of 0.68[8] times the mass of the Sun, whereas Holberg et al. (2013) put it as high as 1.21[3] times the Sun's mass. The latter would put it beyond the theoretical upper limit for white dwarf remnants of typical single stars that did not undergo a merger or mass loss.[13]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. Gaia DR2 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 2.3 Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars 8: 59, Bibcode: 1984SAAOC...8...59C.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Holberg, J. B. et al. (November 2013), "Where are all the Sirius-like binary systems?", Monthly Notices of the Royal Astronomical Society 435 (3): 2077–2091, doi:10.1093/mnras/stt1433, Bibcode: 2013MNRAS.435.2077H.
- ↑ Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35,495 Hipparcos stars in a common system", Astronomy Letters 32 (11): 759–771, doi:10.1134/S1063773706110065, Bibcode: 2006AstL...32..759G.
- ↑ 5.0 5.1 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A.
- ↑ 6.0 6.1 6.2 Wu, Yue et al. (January 2011), "Coudé-feed stellar spectral library – atmospheric parameters", Astronomy and Astrophysics 525: A71, doi:10.1051/0004-6361/201015014, Bibcode: 2011A&A...525A..71W.
- ↑ Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics 537: A120, doi:10.1051/0004-6361/201117691, Bibcode: 2012A&A...537A.120Z.
- ↑ 8.0 8.1 8.2 8.3 8.4 Burleigh, M. R.; Barstow, M. A. (January 1999), "Theta Hya: spectroscopic identification of a second B star+white dwarf binary", Astronomy and Astrophysics 341: 795–798, Bibcode: 1999A&A...341..795B.
- ↑ "tet Hya". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=tet+Hya.
- ↑ Privett, Grant; Jones, Kevin (2013), The Constellation Observing Atlas, The Patrick Moore Practical Astronomy Series, Springer Science & Business Media, p. 104, ISBN 978-1461476481, Bibcode: 2013coa..book.....P, https://books.google.com/books?id=uN69BAAAQBAJ&pg=PA104.
- ↑ King, J. R. (July 1994), "Accretion from Circumstellar Discs and the Lambda-Bootis Phenomenon", Monthly Notices of the Royal Astronomical Society 269 (1): 209–217, doi:10.1093/mnras/269.1.209, Bibcode: 1994MNRAS.269..209K, http://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1236&context=physastro_pubs.
- ↑ Baschek, Bodo; Searle, Leonard (February 1969), "The Chemical Composition of the Lambda Bootis Stars", Astrophysical Journal 155: 537, doi:10.1086/149890, Bibcode: 1969ApJ...155..537B.
- ↑ Vennes, S.; Kawka, A. (September 2008), "On the empirical evidence for the existence of ultramassive white dwarfs", Monthly Notices of the Royal Astronomical Society 389 (3): 1367–1374, doi:10.1111/j.1365-2966.2008.13652.x, Bibcode: 2008MNRAS.389.1367V.
External links
- Kaler, James B. (May 8, 2015), "Theta Hydrae", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/thetahya.html, retrieved 2016-01-04.
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