HD 189245

HD 189245 is the Henry Draper catalogue designation for a solitary[10] star in the southern constellation of Sagittarius. It has an apparent visual magnitude of 5.66,[2] which means it is faintly visible to the naked eye. Parallax measurements from the Hipparcos satellite indicate a distance of around 69 light years from the Sun.[1]

HD 189245
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension  20h 00m 20.24779s[1]
Declination −33° 42′ 12.4315″[1]
Apparent magnitude (V) 5.66[2]
Characteristics
Spectral type F8.5 V Fe−0.6 CH−0.5[3]
U−B color index −0.04[2]
B−V color index +0.498[4]
Astrometry
Radial velocity (Rv)−13.2[5] km/s
Proper motion (μ) RA: +126.61[1] mas/yr
Dec.: −290.04[1] mas/yr
Parallax (π)47.06 ± 0.41[1] mas
Distance69.3 ± 0.6 ly
(21.2 ± 0.2 pc)
Absolute magnitude (MV)4.06[6]
Details
Surface gravity (log g)4.31[3] cgs
Temperature6,333[3] K
Metallicity [Fe/H]−0.09[3] dex
Rotational velocity (v sin i)72.6[7] km/s
Age100 or 500[4] Myr
Other designations
262 G. Sgr,[8] CD−34° 14082, GJ 773.4, GJ 9679, HD 189245, HIP 98470, HR 7631, SAO 211724.[9]
Database references
SIMBADdata

The stellar classification of this star is F8.5 V Fe−0.6 CH−0.5,[3] indicating that it is an F-type main sequence star with a spectrum that shows deficiencies in iron (Fe) and methylidyne (CH) in its outer atmosphere. It is a variable star with an active chromosphere and is a source of X-ray emission.[3][11] HD 189245 is spinning rapidly with a projected rotational velocity of 72.6[7] km/s. Gyrochronology indicates this is a young star with an estimated age of 500 million years. However, the amount of X-ray emission suggests an even younger star that is roughly 100 million years old.[4]

The velocity components of HD 189245 indicate that it is a likely member of the AB Doradus moving group of stars, which share a common motion through space. This group has an age of around 50 million years and is centered at a point 98 ly (30 pc) from the Sun.[12]

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.
  2. Corben, P. M.; et al. (1972), "U, B, V photometry of 500 southern stars", Monthly Notes of the Astronomical Society of South Africa, 31: 7–22, Bibcode:1972MNSSA..31....8C.
  3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637.
  4. Vican, Laura (June 2012), "Age Determination for 346 Nearby Stars in the Herschel DEBRIS Survey", The Astronomical Journal, 143 (6): 135, arXiv:1203.1966, Bibcode:2012AJ....143..135V, doi:10.1088/0004-6256/143/6/135.
  5. Nordström, B.; et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14,000 F and G dwarfs", Astronomy and Astrophysics, 418: 989–1019, arXiv:astro-ph/0405198, Bibcode:2004A&A...418..989N, doi:10.1051/0004-6361:20035959.
  6. Reiners, A. (January 2006), "Rotation- and temperature-dependence of stellar latitudinal differential rotation", Astronomy and Astrophysics, 446 (1): 267–277, arXiv:astro-ph/0509399, Bibcode:2006A&A...446..267R, doi:10.1051/0004-6361:20053911.
  7. Schröder, C.; et al. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo" (PDF), Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377.
  8. Gould, Benjamin Apthorp (1879), Uranometria Argentina: brightness and position of every fixed star, down to the seventh magnitude, within one hundred degrees of the South Pole, Resultados, Universidad Nacional de Córdoba Observatorio Astronómico, 1, Observatorio Nacional Argentino, p. 181". Coordinates are for the 1875 equinox."
  9. "HD 189245". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-07-19.
  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.
  11. Jeffries, R. D.; Jewell, S. J. (September 1993), "The Kinematics of Active Late Type Stars Observed by the ROSAT Wide-Field Camera", Monthly Notices of the Royal Astronomical Society, 264 (1): 106, Bibcode:1993MNRAS.264..106J, doi:10.1093/mnras/264.1.106.
  12. Nakajima, Tadashi; Morino, Jun-Ichi (January 2012), "Potential Members of Stellar Kinematic Groups within 30 pc of the Sun", The Astronomical Journal, 143 (1): 2, Bibcode:2012AJ....143....2N, doi:10.1088/0004-6256/143/1/2.
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