Upsilon2 Hydrae

Upsilon² Hydrae, Latinised from υ² Hydrae, is a solitary^[10] star in the equatorial constellation of Hydra. Visible to the naked eye, it is photometrically stable^[11] with an apparent visual magnitude of 4.59.^[2] Based upon an annual parallax shift of 10.40 mas as seen from Earth,^[1] it is located about 314 light-years from the Sun.

For other stars with this Bayer designation, see υ Hydrae.

Upsilon² Hydrae

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Hydra
Right ascension	10h 05m 07.46888s[1]
Declination	−13° 03′ 52.6561″[1]
Apparent magnitude (V)	4.59[2]
Characteristics
Spectral type	B9 III-IV[3]
U−B color index	−0.27[2]
B−V color index	−0.08[2]
Astrometry
Radial velocity (Rv)	+24.3±2.6[4] km/s
Proper motion (μ)	RA: −39.39[1] mas/yr Dec.: +19.65[1] mas/yr
Parallax (π)	10.40 ± 0.23 mas[1]
Distance	314 ± 7 ly (96 ± 2 pc)
Absolute magnitude (MV)	−0.31[5]
Details
Mass	3.29±0.03[6] M☉
Radius	3.2[7] R☉
Luminosity	182[6] L☉
Surface gravity (log g)	3.87[8] cgs
Temperature	11758±400[8] K
Rotational velocity (v sin i)	58[8] km/s
Age	97[8] Myr
Other designations
υ2 Hya, 40 Hydrae, BD−12°3073, FK5 1261, HD 87504, HIP 49402, HR 3970, SAO 155713[9]
Database references
SIMBAD	data

This is a B-type star with a stellar classification of B9 III-IV,^[3] showing partial traits of a subgiant and giant star in its spectrum. However, Zorec and Royer (2012) estimate the star still only 79% of the way through its life span on the main sequence.^[6] With an age of around 97 million years,^[8] it is spinning with a projected rotational velocity of 58 km/s.^[8] The star has an estimated 3.29^[6] times the mass of the Sun and around 3.2^[7] times the Sun's radius. It is radiating 182^[6] times the solar luminosity from its photosphere at an effective temperature of about 11,758 K.^[8]

References

1. 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.
2. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
3. Houk, Nancy; Smith-Moore, M. (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H.
4. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
5. 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.
6. Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
7. Pasinetti Fracassini, L. E.; Pastori, L.; Covino, S.; Pozzi, A. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics, 367 (3rd ed.): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
8. 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.
9. "* ups02 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-03-21.{{cite web}}: CS1 maint: postscript (link)
10. 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.
11. Adelman, S. J.; et al. (October 2000), "On the Variability of Late B III-V Stars", Information Bulletin on Variable Stars, 4968 (4968): 1, Bibcode:2000IBVS.4968....1A.