HD 17925

HD 17925 is a variable star in the equatorial constellation of Eridanus. It has the Gould designation 32 G. Eridani and the variable star designation EP Eri. The star has a yellow-orange hue and is dimly visible to the naked eye in good seeing conditions with an apparent visual magnitude that varies from 6.03 down to 6.08.[15] It is located nearby at a distance of 34 light years from the Sun based on parallax,[1] and is drifting further away with a radial velocity of +18 km/s.[6] It is a likely member of the Local Association of nearby, co-moving stars.[11] The spectrum shows a strong abundance of lithium, indicating that it is young star.[16] This likely makes its point of origin the nearby Scorpio–Centaurus Complex.[17]

HD 17925
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
Right ascension 02h 52m 32.12819s[1]
Declination –12° 46′ 10.9706″[1]
Apparent magnitude (V) 6.04[2]
Characteristics
Evolutionary stage Main sequence
Spectral type K1V[3]
U−B color index +1.41[4]
B−V color index +0.86[4]
Variable type RS CVn[5]
Astrometry
Radial velocity (Rv)+17.77±0.08[6] km/s
Proper motion (μ) RA: 397.346[1] mas/yr
Dec.: −189.114[1] mas/yr
Parallax (π)96.5400 ± 0.0435[1] mas
Distance33.78 ± 0.02 ly
(10.358 ± 0.005 pc)
Absolute magnitude (MV)5.97[7]
Details
Mass0.88[8] M☉
Radius0.85±0.05[9] R☉
Luminosity0.409±0.001[1] L☉
Surface gravity (log g)4.58[8] cgs
Temperature5,225±5[10] K
Metallicity [Fe/H]+0.10[11] dex
Rotation6.6 days[11]
Rotational velocity (v sin i)4.80[12] km/s
Age100[13] Myr
Other designations
32 G. Eridani, EP Eri, GJ 117, HD 17925, HIP 13402, HR 857, SAO 148647,[14] YPC 599
Database references
SIMBADdata

The stellar classification of HD 17925 is K1V,[3] which indicates this is a K-type main-sequence star that is engaged in core hydrogen fusion. It is an active star[16] that is classified as a RS Canum Venaticorum variable,[15] showing a rotational modulation with a period of 6.9 days, and has been observed to flare.[5] The star has an estimated age of 100[13] million years and is spinning with a projected rotational velocity of 4.8 km/s.[12] The rotation period of 6.6 days days can be determined from its activity cycle.[11] The star has 88%[8] of the mass of the Sun and 85%[9] of the Sun's radius. It is radiating 41%[1] of the luminosity of the Sun from its photosphere at an effective temperature of 5,225 K.[10]

The presence of an unseen companion has been suggested based on variations in the widths of absorption lines in the star's photosphere.[16] It displays low-amplitude radial velocity variation, which may indicate it is a spectroscopic binary.[9] However, the binary hypothesis doesn't appear to be consistent with Hipparcos satellite data.[11] An infrared excess has been detected around this star, most likely indicating the presence of a circumstellar disk at a radius of 17.9 AU. The temperature of this dust is 52 K.[18]

References
  1. 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. Gaia DR2 record for this source at VizieR.
  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. Montes, D.; et al. (2001), "Late-type members of young stellar kinematic groups - I. Single stars", Monthly Notices of the Royal Astronomical Society, 328 (1): 45–63, arXiv:astro-ph/0106537, Bibcode:2001MNRAS.328...45M, doi:10.1046/j.1365-8711.2001.04781.x.
  4. Vieytes, M.; et al. (May 2007), Heinzel, P.; Dorotovič, I.; Rutten, R. J. (eds.), "Chromospheric Activity in K Stars", The Physics of Chromospheric Plasmas. Proceedings of the conference held 9-13 October, 2006 at the University of Coimbra in Coimbra, Portugal, ASP Conference Series, San Francisco: Astronomical Society of the Pacific, 368, p. 265, Bibcode:2007ASPC..368..265V.
  5. Abbott, B. P.; Pomerance, B. H.; Ambruster, C. W. (March 1995), "UBVRI Photometry of the Solar Neighborhood Pleiades-Age K Dwarfs HD 17925 and HD 1405", Bulletin of the American Astronomical Society, 27: 842, Bibcode:1995AAS...186.2210A.
  6. Karataş, Y.; et al. (April 2004), "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution", Monthly Notices of the Royal Astronomical Society, 349 (3): 1069–1092, arXiv:astro-ph/0404219, Bibcode:2004MNRAS.349.1069K, doi:10.1111/j.1365-2966.2004.07588.x.
  7. Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191.
  8. Luck, R. Earle (March 2018), "Abundances in the Local Region. III. Southern F, G, and K Dwarfs", The Astronomical Journal, 155 (3): 31, Bibcode:2018AJ....155..111L, doi:10.3847/1538-3881/aaa9b5, 111.
  9. Ambruster, C. W.; et al. (October 2003), Brown, A.; Harper, G. M.; Ayres, T. R. (eds.), "The Radii of Solar Neighborhood ZAMS Stars", The Future of Cool-Star Astrophysics: 12th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (2001 July 30 - August 3), pp. 912–915, Bibcode:2003csss...12..912A.
  10. Kovtyukh, V. V.; et al. (2003), "High precision effective temperatures for 181 F-K dwarfs from line-depth ratios", Astronomy and Astrophysics, 411 (3): 559–564, arXiv:astro-ph/0308429, Bibcode:2003A&A...411..559K, doi:10.1051/0004-6361:20031378.
  11. Maldonado, J.; et al. (October 2010), "A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups", Astronomy and Astrophysics, 521: A12, arXiv:1007.1132, Bibcode:2010A&A...521A..12M, doi:10.1051/0004-6361/201014948.
  12. Mishenina, T. V.; et al. (November 2012), "Activity and the Li abundances in the FGK dwarfs", Astronomy & Astrophysics, 547: 8, arXiv:1210.6843, Bibcode:2012A&A...547A.106M, doi:10.1051/0004-6361/201118412, A106.
  13. Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008), "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics", The Astrophysical Journal, 687 (2): 1264–1293, arXiv:0807.1686, Bibcode:2008ApJ...687.1264M, doi:10.1086/591785.
  14. "HD 17925". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-11.
  15. Samus', N. N; et al. (2017), "General catalogue of variable stars", Astronomy Reports, GCVS 5.1, 61 (1): 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  16. Pandey, J. C.; Singh, K. P. (July 2008), "A study of X-ray flares - I. Active late-type dwarfs", Monthly Notices of the Royal Astronomical Society, 387 (4): 1627−1648, arXiv:0805.3882, Bibcode:2008MNRAS.387.1627P, doi:10.1111/j.1365-2966.2008.13342.x.
  17. Cayrel de Strobel, G.; Cayrel, R. (July 1989), "Strong lithium in the very nearby K-dwarf HD 17925", Astronomy and Astrophysics, 218 (1–2): L9–L12, Bibcode:1989A&A...218L...9C
  18. Eiroa, C.; et al. (July 2013), "DUst around NEarby Stars. The survey observational results", Astronomy & Astrophysics, 555: A11, arXiv:1305.0155, Bibcode:2013A&A...555A..11E, doi:10.1051/0004-6361/201321050.

Further reading
  • Christian, D. J.; Mathioudakis, M.; Jevremović, D. (October 2008), "6Li in the Atmosphere of GJ 117 Revisited", The Astrophysical Journal, 686 (1): 542–547, arXiv:0807.3693, Bibcode:2008ApJ...686..542C, doi:10.1086/591727CS1 maint: multiple names: authors list (link)
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