HD 202951 is a probable binary star system located in the northern constellation of Equuleus. It is near the lower limit of visibility to the naked eye, having an apparent visual magnitude of 5.97.[2] The distance to this system can be estimated from the annual parallax shift of 2.74 mas,[1] yielding a value of roughly 1,190 light years. It is moving closer with a heliocentric radial velocity of −37 km/s.[4]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Equuleus |
| Right ascension | 21h 18m 52.02476s[1] |
| Declination | +11° 12′ 12.1752″[1] |
| Apparent magnitude (V) | 5.97[2] |
| Characteristics | |
| Spectral type | K5 III[2] |
| B−V color index | 1.648[3] |
| Astrometry | |
| Radial velocity (Rv) | −37.3±2.5[4] km/s |
| Proper motion (μ) | RA: +23.728 mas/yr Dec.: +15.448 mas/yr |
| Parallax (π) | 2.7415 ± 0.1321 mas[1] |
| Distance | 1,190 ± 60 ly (360 ± 20 pc) |
| Absolute magnitude (MV) | −1.97[3] |
| Orbit[5] | |
| Period (P) | 999.8±2.4 d |
| Eccentricity (e) | 0.229±0.018 |
| Periastron epoch (T) | 53771 ± 12 MJD |
| Argument of periastron (ω) (secondary) | 3±5° |
| Semi-amplitude (K1) (primary) | 4.09±0.08 km/s |
| Details | |
| Luminosity | 5.15[2] L☉ |
| Rotational velocity (v sin i) | 4.4[6] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Griffin (2012) found this to be a single-lined spectroscopic binary system with an orbital period of 2.7373 ± 0.0066 yr and an eccentricity of 0.23. The a sin i value for the primary component is 54.8 ± 1.1 Gm (0.366 ± 0.007 AU), where a is the semimajor axis and i is the (unknown) orbital inclination. This value provides a lower bound for the actual semimajor axis.[5]
The visible component is an evolved K-type giant star with a stellar classification of K5 III.[2] It is a candidate variable star of unknown type, showing an amplitude variation of 0.0115 magnitude with a frequency of 0.47645 times per day, or one cycle per 2.1 days.[8] X-ray emission has been detected from this system.[9]
References
edit- ^ a b c d Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051.
- ^ a b c d e 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 Ryon, Jenna; et al. (August 2009), "Comparing the Ca ii H and K Emission Lines in Red Giant Stars", Publications of the Astronomical Society of the Pacific, 121 (882): 842, arXiv:0907.3346, Bibcode:2009PASP..121..842R, doi:10.1086/605456, S2CID 17821279.
- ^ a b Gontcharov, G. A. (2006), "Pulkovo Compilation of Radial Velocities for 35 495 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.
- ^ a b Griffin, R. F. (February 2012), "Spectroscopic binary orbits from photoelectric radial velocities - Paper 222: HR 4241, HR 7208, HR 8026, and HR 8149", The Observatory, 132 (1): 16–33, Bibcode:2012Obs...132...16G.
- ^ De Medeiros, J. R.; et al. (October 2002), "The Rotation of Binary Systems with Evolved Components", The Astrophysical Journal, 578 (2): 943–950, arXiv:astro-ph/0207288, Bibcode:2002ApJ...578..943D, doi:10.1086/342613, S2CID 16196039.
- ^ "HD 202951". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-07-20.
- ^ Koen, Chris; Eyer, Laurent (2002), "New periodic variables from the Hipparcos epoch photometry", Monthly Notices of the Royal Astronomical Society, 331 (1): 45–59, arXiv:astro-ph/0112194, Bibcode:2002MNRAS.331...45K, doi:10.1046/j.1365-8711.2002.05150.x, S2CID 10505995.
- ^ Smith, Graeme H.; Shetrone, Matthew D. (2000), "CaII K Emission-Line Asymmetry among Red Giants Detected by the ROSAT Satellite", The Publications of the Astronomical Society of the Pacific, 112 (776): 1320, Bibcode:2000PASP..112.1320S, doi:10.1086/316634.