HD 203842

HD 203842, also known as HR 8191 or rarely 30 G. Equueli, is a solitary, yellowish-white hued star located in the constellation Equuleus. It has an apparent magnitude of 6.32, placing it near the limit for naked eye visibility, even under ideal conditions. Gaia DR3 parallax measurements imply a distance of 374 light years,[1] and it is currently drifting closer with a somewhat constrained heliocentric radial velocity of −21.8 km/s.[6] At its current distance HD 203842's brightness is diminished by 0.15 magnitudes due to interstellar dust[16] and it has an absolute magnitude of +1.06.[7]

HD 203842
Location of HD 203842 (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Equuleus
Right ascension 21h 24m 24.56372s[1]
Declination +10° 10′ 27.1976″[1]
Apparent magnitude (V) 6.32±0.01[2]
Characteristics
Evolutionary stage Hertzsprung gap[3]
Spectral type F5 III[4]
U−B color index +0.13[5]
B−V color index +0.47[5]
Astrometry
Radial velocity (Rv)−21.8±3.6[6] km/s
Proper motion (μ) RA: +75.072 mas/yr[1]
Dec.: +20.436 mas/yr[1]
Parallax (π)8.7242 ± 0.1771 mas[1]
Distance374 ± 8 ly
(115 ± 2 pc)
Absolute magnitude (MV)+1.06[7]
Details
Mass2.00[8] M☉
Radius4.54±0.23[9] R☉
Luminosity31.1±1.2[1] L☉
Surface gravity (log g)3.47[10] cgs
Temperature6,271±42[11] K
Metallicity [Fe/H]+0.19+0.04
−0.05[12] dex
Rotational velocity (v sin i)80.6[13] km/s
Age1.24[8] Gyr
Other designations
30 G. Equulei[14], AG+09°2981, BD+09°4800, GC 29969, HD 203842, HIP 105695, HR 8191, SAO 126774[15]
Database references
SIMBADdata

A 2005 Hipparcos survey noticed variations in its proper motion, which would indicate that it is an astrometric binary.[17] However, a subsequent survey revealed that HD 203842 is not an astrometric binary (32% chance) and is more likely to be solitary.[18] This object is part of the Hyades Stream.[19]

HD 203842 has a stellar classification of F5 III,[4] indicating that it is an evolved F-type giant star. It is currently in the Hertzsprung gap, meaning that it exhausting its supply of hydrogen and evolving towards the red giant branch. It has double times the Sun's mass but at the age of 1.24 billion years,[8] it has expanded to 4.54 times the Sun's radius.[9] It radiates 31.1 times the Sun's luminosity[1] from its enlarged photosphere at an effective temperature of 6,271 K.[11] HD 203842 is metal enriched with 155% the Sun's iron abundance[12] and spins quickly with a projected rotational velocity of 80.6 km/s.[13]

References
  1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (March 2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H. ISSN 0004-6361.
  3. Wallerstein, George; Bohm-Vitense, Erika; Vanture, Andrew D.; Gonzalez, Guillermo (June 1994). "The lithium content and other properties of F2-G5 giants in the Hertzsprung Gap". The Astronomical Journal. 107: 2211. Bibcode:1994AJ....107.2211W. doi:10.1086/117031. ISSN 0004-6256. S2CID 122349333.
  4. Roman, Nancy G. (December 1955). "A Catalogue of High-Velocity Stars". The Astrophysical Journal Supplement Series. 2: 195. Bibcode:1955ApJS....2..195R. doi:10.1086/190021. eISSN 1538-4365. ISSN 0067-0049.
  5. Johnson, H. L.; Mitchell, R. I.; Iriarte, B.; Wisniewski, W. Z. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4: 99–110. Bibcode:1966CoLPL...4...99J.
  6. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35,495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. eISSN 1562-6873. ISSN 1063-7737. S2CID 119231169.
  7. Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. eISSN 1562-6873. ISSN 1063-7737. S2CID 119257644.
  8. Demarque, Pierre; Woo, Jong‐Hak; Kim, Yong‐Cheol; Yi, Sukyoung K. (December 2004). "Y2 Isochrones with an Improved Core Overshoot Treatment". The Astrophysical Journal Supplement Series. 155 (2): 667–674. Bibcode:2004ApJS..155..667D. doi:10.1086/424966. eISSN 1538-4365. ISSN 0067-0049.
  9. Kervella, P.; Thévenin, F.; Di Folco, E.; Ségransan, D. (October 2004). "The angular sizes of dwarf stars and subgiants. Surface brightness relations calibrated by interferometry". Astronomy & Astrophysics. 426 (1): 297–307. arXiv:astro-ph/0404180. Bibcode:2004A&A...426..297K. doi:10.1051/0004-6361:20035930. eISSN 1432-0746. ISSN 0004-6361. S2CID 6077801.
  10. Casagrande, L.; Schönrich, R.; Asplund, M.; Cassisi, S.; Ramírez, I.; Meléndez, J.; Bensby, T.; Feltzing, S. (26 May 2011). "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s): Improved astrophysical parameters for the Geneva-Copenhagen Survey⋆". Astronomy & Astrophysics. 530: A138. arXiv:1103.4651. Bibcode:2011A&A...530A.138C. doi:10.1051/0004-6361/201016276. eISSN 1432-0746. ISSN 0004-6361. S2CID 56118016.
  11. Luck, R. Earle (25 August 2015). "Abundances in the Local Region. I. G and K Giants". The Astronomical Journal. 150 (3): 88. arXiv:1507.01466. Bibcode:2015AJ....150...88L. doi:10.1088/0004-6256/150/3/88. eISSN 1538-3881. ISSN 0004-6256. S2CID 118505114.
  12. Bochanski, John J.; Faherty, Jacqueline K.; Gagné, Jonathan; Nelson, Olivia; Coker, Kristina; Smithka, Iliya; Desir, Deion; Vasquez, Chelsea (12 March 2018). "Fundamental Properties of Co-moving Stars Observed byGaia". The Astronomical Journal. 155 (4): 149. arXiv:1801.00537. Bibcode:2018AJ....155..149B. doi:10.3847/1538-3881/aaaebe. eISSN 1538-3881. S2CID 119256051.
  13. Solano, E.; Fernley, J. (April 1997). "Spectroscopic survey of δ Scuti stars". Astronomy and Astrophysics Supplement Series. 122 (1): 131–147. Bibcode:1997A&AS..122..131S. doi:10.1051/aas:1997329. eISSN 1286-4846. ISSN 0365-0138.
  14. Gould, Benjamin Apthorp (1878). "Uranometria Argentina : brillantez y posicion de las estrellas fijas, hasta la septima magnitud, comprendidas dentro de cien grados del polo austral : con atlas". Resultados del Observatorio Nacional Argentino. 1. Bibcode:1879RNAO....1.....G.
  15. "HD 203842". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved July 2, 2021.
  16. Gontcharov, George A.; Mosenkov, Aleksandr V. (28 September 2017). "Verifying reddening and extinction for Gaia DR1 TGAS main sequence stars". Monthly Notices of the Royal Astronomical Society. 472 (4): 3805–3820. arXiv:1709.01160. Bibcode:2017MNRAS.472.3805G. doi:10.1093/mnras/stx2219. eISSN 1365-2966. ISSN 0035-8711. S2CID 118879856.
  17. Makarov, V. V.; Kaplan, G. H. (May 2005). "Statistical Constraints for Astrometric Binaries with Nonlinear Motion". The Astronomical Journal. 129 (5): 2420–2427. Bibcode:2005AJ....129.2420M. doi:10.1086/429590. eISSN 1538-3881. ISSN 0004-6256. S2CID 55186471.
  18. Frankowski, A.; Jancart, S.; Jorissen, A. (19 December 2006). "Proper-motion binaries in the Hipparcos catalogue: Comparison with radial velocity data". Astronomy & Astrophysics. 464 (1): 377–392. arXiv:astro-ph/0612449. Bibcode:2007A&A...464..377F. doi:10.1051/0004-6361:20065526. eISSN 1432-0746. ISSN 0004-6361. S2CID 14010423.
  19. Montes, D.; López-Santiago, J.; Gálvez, M. C.; Fernández-Figueroa, M. J.; De Castro, E.; Cornide, M. (1 November 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. ISSN 0035-8711. S2CID 55727428.
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