Phi2 Hydrae

Phi2 Hydrae, Latinized from φ2 Hydrae, is a star in the constellation Hydra. It originally received the Flamsteed designation of 1 Crateris before being placed in the Hydra constellation.[9] Based upon an annual parallax shift of 4.31 mas as seen from Earth, it is located roughly 760 light years from the Sun. The star is faintly visible to the naked with an apparent visual magnitude of 6.09.[2] It forms a triangle with the fainter φ1 Hydrae and the brighter φ3 Hydrae, between μ Hydrae and ν Hydrae.

Pulsations[5]
Period
(days)		 Amplitude
(magnitude)
11.00.008
110.30.012
153.60.015
For other stars with this Bayer designation, see φ Hydrae
Phi2 Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 10h 36m 16.65960s[1]
Declination −16° 20′ 39.5778″[1]
Apparent magnitude (V) 6.0943[2]
Characteristics
Spectral type M1 III[3]
U−B color index +1.95[4]
B−V color index +1.64[4]
Variable type SR[5]
Astrometry
Radial velocity (Rv)+15.7±2.9[2] km/s
Proper motion (μ) RA: −29.14[1] mas/yr
Dec.: +2.31[1] mas/yr
Parallax (π)4.31 ± 0.33 mas[1]
Distance760 ± 60 ly
(230 ± 20 pc)
Absolute magnitude (MV)−0.80[6]
Details
Luminosity703[7] L☉
Temperature3,791[7] K
Other designations
φ2 Hya, BD−15°3087, HD 91880, HIP 51905, HR 4156, SAO 156093[8]
Database references
SIMBADdata

This is an evolved red giant star with a stellar classification of M1 III.[10] It is currently on the asymptotic giant branch,[10] and is a semiregular variable that undergoes changes in luminosity according to three pulsation periods.[5] The star is radiating an estimated 703[7] times the Sun's luminosity from its photosphere at an effective temperature of 3,791 K.[7]

Phi2 Hydrae has a faint visual companion: a magnitude 12.20 star at an angular separation of 3.50 arc seconds along a position angle of 280°, as of 1959.[11]


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. 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.
  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. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  5. Tabur, V.; et al. (2009), "Long-term photometry and periods for 261 nearby pulsating M giants", Monthly Notices of the Royal Astronomical Society, 400 (4): 1945–61, arXiv:0908.3228, Bibcode:2009MNRAS.400.1945T, doi:10.1111/j.1365-2966.2009.15588.x, S2CID 15358380.
  6. 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.
  7. 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.
  8. "* phi02 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-03-17.{{cite web}}: CS1 maint: postscript (link)
  9. Wagman, M. (August 1987), "Flamsteed's Missing Stars", Journal for the History of Astronomy, 18 (3): 216, Bibcode:1987JHA....18..209W, doi:10.1177/002182868701800305, S2CID 118445625.
  10. Eggen, Olin J. (July 1992), "Asymptotic giant branch stars near the sun", Astronomical Journal, 104 (1): 275–313, Bibcode:1992AJ....104..275E, doi:10.1086/116239.
  11. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
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