Theta2 Sagittarii, Latinized from θ2 Sagittarii, is a solitary[10] star in the zodiac constellation of Sagittarius. It is faintly visible to the naked eye with an apparent visual magnitude of +5.30.[2] The star is progressing in the general direction of the Sun with a radial velocity of −17.60 km/s.[4] Based upon an annual parallax shift of 20.62 mas as seen from Earth,[1] it is located around 158 light years from the Sun. The star is drifting closer with a radial velocity of −17.6 km/s.[4]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 59m 51.35684s[1] |
| Declination | −34° 41′ 52.0797″[1] |
| Apparent magnitude (V) | +5.30[2] |
| Characteristics | |
| Spectral type | A4/A5 IV[3] |
| U−B color index | +0.06[2] |
| B−V color index | +0.17[2] |
| Astrometry | |
| Radial velocity (Rv) | −17.60[4] km/s |
| Proper motion (μ) | RA: +108.23[1] mas/yr Dec.: −69.51[1] mas/yr |
| Parallax (π) | 20.62 ± 0.28 mas[1] |
| Distance | 158 ± 2 ly (48.5 ± 0.7 pc) |
| Absolute magnitude (MV) | +1.87[5] |
| Details | |
| Mass | 1.93[6] M☉ |
| Luminosity | 14[7] L☉ |
| Surface gravity (log g) | 4.07±0.14[6] cgs |
| Temperature | 8,113±276[6] K |
| Rotational velocity (v sin i) | 45.2±0.5[8] km/s |
| Age | 809[6] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The spectrum of Theta2 Sagittarii matches a stellar classification of A4/A5 IV,[3] indicating that, at the estimated age of 809 million years,[6] this is an evolving A-type subgiant star. It is a suspected Am star and may display photometric variability, at least during a 1992 observation period.[11] The star has an estimated 1.93[6] times the mass of the Sun and is radiating 14[7] times the Sun's luminosity from its photosphere at an effective temperature of 8,113 K.[6] It is spinning with a projected rotational velocity of 45.2 km/s.[8]
Theta2 Sagittarii has a pair of visual companions. Component B is a magnitude 11.3 star at an angular separation of 32.8 arc seconds along a position angle of 165°, as of 2000. Component C lies at an angular separation of 1.5 arc seconds along a position angle of 104° from component B, as of 1965.[12] Neither is physically associated with Theta2 Sagittarii itself.[10]
References edit
- ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
- ^ a b c d Mendoza, E. E.; et al. (June 1978), "UBVRI photometry of 225 AM stars", Astronomical Journal, 83: 606–614, Bibcode:1978AJ.....83..606M, doi:10.1086/112242.
- ^ a b Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1982mcts.book.....H.
- ^ a b c Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169.
- ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
- ^ a b c d e f g David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
- ^ a b McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
- ^ a b Díaz, C. G.; et al. (July 2011), "Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum", Astronomy & Astrophysics, 531: A143, arXiv:1012.4858, Bibcode:2011A&A...531A.143D, doi:10.1051/0004-6361/201016386, S2CID 119286673.
- ^ "tet02 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-07.
{{cite web}}: CS1 maint: postscript (link) - ^ a b Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
- ^ Anders, G. J. (September 1992), "Theta2 Sgr: Serendipitous Discovery of Variability in an Am Star?", Information Bulletin on Variable Stars, 3768: 1, Bibcode:1992IBVS.3768....1A.
- ^ Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466, Bibcode:2001AJ....122.3466M, doi:10.1086/323920, retrieved 2015-07-22.