HD 204018

HD 204018, also designated as HR 8202, is a visual binary located in the southern constellation Microscopium. The primary has an apparent magnitude of 5.58,^[2] making it faintly visible to the naked eye under ideal conditions. The companion has an apparent magnitude of 8.09.^[2] The system is located relatively close at a distance of 176 light years based on Gaia DR3 parallax measurements^[1][3] but is receding with a heliocentric radial velocity of 18.3 km/s.^[8] At its current distance, HD 204018's combined brightness is diminished by 0.13 magnitudes due to interstellar dust.^[22]

HD 204018

location of HD 204018 (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Microscopium
A
Right ascension	21h 27m 01.62303s[1]
Declination	−42° 32′ 52.5560″[1]
Apparent magnitude (V)	5.58±0.01[2]
B
Right ascension	21h 27m 01.75500s[3]
Declination	−42° 32′ 55.0458″[3]
Apparent magnitude (V)	8.09±0.01[2]
Characteristics
A
Evolutionary stage	subgiant[4]
Spectral type	kA4 hF0 V mF6[5]
U−B color index	+0.15[6]
B−V color index	+0.39[6]
B
Spectral type	F8 V[7]
U−B color index	+0.06[7]
B−V color index	+0.55[7]
Astrometry
Radial velocity (Rv)	18.3±2.8[8] km/s
A
Proper motion (μ)	RA: −48.257 mas/yr[1] Dec.: +13.160 mas/yr[1]
Parallax (π)	18.489 ± 0.0498 mas[1]
Distance	176.4 ± 0.5 ly (54.1 ± 0.1 pc)
Absolute magnitude (MV)	+1.74[9]
B
Proper motion (μ)	RA: −53.002 mas/yr[3] Dec.: +15.410 mas/yr[3]
Parallax (π)	18.5325 ± 0.0349 mas[3]
Distance	176.0 ± 0.3 ly (54.0 ± 0.1 pc)
Absolute magnitude (MV)	+4.00[7]
Details
A
Mass	1.65±0.11[10] M☉
Radius	2.55±0.13[11] R☉
Luminosity	15±1.2[12] L☉
Surface gravity (log g)	3.86±0.08[13] cgs
Temperature	6,778[14] K
Rotational velocity (v sin i)	85[15] km/s
Age	1.36±0.19[1] Gyr
B
Mass	1.02[16] M☉
Radius	1.09±0.21[17] R☉
Surface gravity (log g)	4.29[16] cgs
Temperature	6,235±115[18] K
Metallicity [Fe/H]	−0.11[19] dex
Age	3.46[19] Gyr
Other designations
69 G. Microscopii[20], CD−43°14539, CPD−43°9451, GC 30021, HD 204018, HIP 105913, HR 8202, SAO 230692, WDS J21270-4233AB[21]
Database references
SIMBAD	The system
	A
	B

HD 204018A is an Am star with a stellar classification of kA4hF0 VmF6,^[5] indicating that it has the calcium K-line of an A4 star, the hydrogen lines of a F0 main-sequence star and the metallic lines of a F6 star. It has 1.65 times the mass of the Sun^[10] and 2.55 times the Sun's radius.^[11] It radiates 15 times the luminosity of the Sun^[12] from its photosphere at an effective temperature of 6,778 K,^[14] giving it a yellowish-white hue. At an age of 1.5 billion years, HD 2014018A is estimated to be on the subgiant branch.^[4] An alternate model places it on the main sequence at an age of 1,35 billion years.^[1] The object spins at a moderate speed with a projected rotational velocity of 85 km/s.^[15]

The companion is an F8 main sequence star^[7] located 2+1⁄2" away along a position angle of 151°.^[23] It has an angular diameter of 0.186±0.035 arcseconds,^[18] which yields a radius of 1.09 R_☉ at its estimated distance.^[17] It has 102% times the mass of the Sun^[16] and an effective temperature of 6,235 K.^[18] HD 204018B is estimated to be 3.46 billion years old and is slightly metal deficient.^[19]

There is a magnitude 12 co-moving companion located 295.3" away from the system along a position angle of 75°.^[23] It is a red dwarf with an estimated spectral class of K6 and any orbit would take over a million years.^[24]

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. Fabricius, C.; Høg, E.; Makarov, V. V.; Mason, B. D.; Wycoff, G. L.; Urban, S. E. (March 2002). "The Tycho double star catalogue". Astronomy & Astrophysics. 384 (1): 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822. eISSN 1432-0746. ISSN 0004-6361.
3. 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.
4. Corbally, C. J. (December 1984). "Close visual binaries. III - Parameters and evolutionary status". The Astronomical Journal. 89: 1887. Bibcode:1984AJ.....89.1887C. doi:10.1086/113700. ISSN 0004-6256.
5. Abt, Helmut A.; Morrell, Nidia I. (July 1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". The Astrophysical Journal Supplement Series. 99: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182. ISSN 0067-0049.
6. Feinstein, A. (April 1967). "Multicolor UBVRI observations of metallic-line stars". Publications of the Astronomical Society of the Pacific. 79: 184. Bibcode:1967PASP...79..184F. doi:10.1086/128464. eISSN 1538-3873. ISSN 0004-6280.
7. Corbally, C. J. (August 1984). "Close visual binaries. I - MK classifications". The Astrophysical Journal Supplement Series. 55: 657. Bibcode:1984ApJS...55..657C. doi:10.1086/190973. eISSN 1538-4365. ISSN 0067-0049.
8. 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.
9. 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.
10. Allende Prieto, C.; Lambert, D. L. (December 1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555–562. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. ISSN 0004-6361.
11. Kervella, P.; Thévenin, F.; Di Folco, E.; Ségransan, D. (October 2004). "The angular sizes of dwarf stars and subgiants". 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.
12. Chandler, Colin Orion; McDonald, Iain; Kane, Stephen R. (17 February 2016). "The Catalog of Earth-Like Exoplanet Survey Targets (CELESTA): A Database of Habitable Zones Around Nearby Stars". The Astronomical Journal. 151 (3): 59. arXiv:1510.05666. Bibcode:2016AJ....151...59C. doi:10.3847/0004-6256/151/3/59. eISSN 1538-3881.
13. Stassun, Keivan G.; et al. (9 September 2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467. eISSN 1538-3881. hdl:1721.1/124721. S2CID 166227927.
14. Schofield, Mathew; et al. (14 March 2019). "The Asteroseismic Target List for Solar-like Oscillators Observed in 2 minute Cadence with the Transiting Exoplanet Survey Satellite". The Astrophysical Journal Supplement Series. 241 (1): 12. arXiv:1901.10148. Bibcode:2019ApJS..241...12S. doi:10.3847/1538-4365/ab04f5. eISSN 1538-4365.
15. Huang, Su-Shu (September 1953). "A Statistical Study of the Rotation of the Stars". The Astrophysical Journal. 118: 285. Bibcode:1953ApJ...118..285H. doi:10.1086/145751. eISSN 1538-4357. ISSN 0004-637X.
16. Anders, F.; et al. (February 2022). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G = 18.5". Astronomy & Astrophysics. 658: A91. arXiv:2111.01860. Bibcode:2022A&A...658A..91A. doi:10.1051/0004-6361/202142369. eISSN 1432-0746. ISSN 0004-6361.
17. Lang, Kenneth R. (2006). Astrophysical formulae. Astronomy and astrophysics library. Vol. 1 (3 ed.). Birkhäuser. ISBN 3-540-29692-1.. The radius (R_*) is given by:

    ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(54\cdot 0.187\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 2.17\cdot R_{\bigodot }\end{aligned}}}$

18. Stevens, Daniel J.; Stassun, Keivan G.; Gaudi, B. Scott (29 November 2017). "Empirical Bolometric Fluxes and Angular Diameters of 1.6 Million Tycho-2 Stars and Radii of 350,000 Stars with Gaia DR1 Parallaxes". The Astronomical Journal. 154 (6): 259. arXiv:1708.05025. Bibcode:2017AJ....154..259S. doi:10.3847/1538-3881/aa957b. eISSN 1538-3881. S2CID 119191064.
19. Gontcharov, G. A. (December 2012). "Dependence of kinematics on the age of stars in the solar neighborhood". Astronomy Letters. 38 (12): 771–782. arXiv:1606.08814. Bibcode:2012AstL...38..771G. doi:10.1134/S1063773712120031. eISSN 1562-6873. ISSN 1063-7737.
20. 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.
21. "HR 8202". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 21 December 2022.
22. 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.
23. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (December 2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920. ISSN 0004-6256.
24. Tokovinin, Andrei (23 February 2018). "The Updated Multiple Star Catalog". The Astrophysical Journal Supplement Series. 235 (1): 6. arXiv:1712.04750. Bibcode:2018ApJS..235....6T. doi:10.3847/1538-4365/aaa1a5. eISSN 1538-4365.