Upsilon2 Hydrae

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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]
Spectral type B9 III-IV[3]
U−B color index −0.27[2]
B−V color index −0.08[2]
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[1] mas
Distance 314 ± 7 ly
(96 ± 2 pc)
Mass 3.29±0.03[5] M
Radius 3.2[6] R
Luminosity 182[5] L
Surface gravity (log g) 3.87[7] cgs
Temperature 11758±400[7] K
Rotational velocity (v sin i) 58[7] km/s
Age 97[7] Myr
Other designations
υ2 Hya, 40 Hya, BD−12° 3073, FK5 1261, HD 87504, HIP 49402, HR 3970, SAO 155713.[8]
Database references

Upsilon2 Hydrae (υ2 Hya) is a solitary[9] star in the equatorial constellation of Hydra. Visible to the naked eye, it is photometrically stable[10] 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.

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.[5] With an age of around 97 million years,[7] it is spinning with a projected rotational velocity of 58 km/s.[7] The star has an estimated 3.29[5] times the mass of the Sun and around 3.2[6] times the Sun's radius. It is radiating 182[5] times the solar luminosity from its photosphere at an effective temperature of about 11,758 K.[7]


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M. 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. ^ a b Houk, Nancy; Smith-Moore, M. (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988MSS...C04....0H. 
  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, Bibcode:2012A&A...546A..61D, arXiv:1208.3048Freely accessible, doi:10.1051/0004-6361/201219219, A61. 
  5. ^ a b c d e Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, Bibcode:2012A&A...537A.120Z, arXiv:1201.2052Freely accessible, doi:10.1051/0004-6361/201117691. 
  6. ^ a b 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 (3rd ed.), 367: 521–524, Bibcode:2001A&A...367..521P, arXiv:astro-ph/0012289Freely accessible, doi:10.1051/0004-6361:20000451. 
  7. ^ 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, Bibcode:2015ApJ...804..146D, arXiv:1501.03154Freely accessible, doi:10.1088/0004-637X/804/2/146. 
  8. ^ "ups02 Hya -- Variable Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-03-21. 
  9. ^ 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, Bibcode:2008MNRAS.389..869E, arXiv:0806.2878Freely accessible, doi:10.1111/j.1365-2966.2008.13596.x. 
  10. ^ Adelman, S. J.; et al. (October 2000), "On the Variability of Late B III-V Stars", Information Bulletin on Variable Stars (4968): 1, Bibcode:2000IBVS.4968....1A.