HD 187420/187421

HD 187420/187421

Location of HD 187420 and 187421 (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Telescopium
HD 187420
Right ascension	19^h 52^m 37.72117^s[1]
Declination	−54° 58′ 15.6700″[1]
Apparent magnitude (V)	5.71±0.01[2]
HD 187421
Right ascension	19^h 52^m 39.13201^s[3]
Declination	−54° 58′ 35.1997″[3]
Apparent magnitude (V)	6.37±0.01[2]
Characteristics
HD 187420
Spectral type	G8/K0 III[4]
U−B color index	+0.67[5]
B−V color index	+0.92[5]
HD 187421
Spectral type	A1/3 V[4]
U−B color index	+0.13[5]
B−V color index	+0.10[5]
Astrometry
HD 187420
Radial velocity (Rv)	−17.9±1.2[6] km/s
Proper motion (μ)	RA: +18.630 mas/yr[1] Dec.: +3.076 mas/yr[1]
Parallax (π)	8.0046 ± 0.0705 mas[1]
Distance	407 ± 4 ly (125 ± 1 pc)
Absolute magnitude (MV)	−0.33[7]
HD 187421
Radial velocity (Rv)	−21.5±1.9[8] km/s
Proper motion (μ)	RA: +19.549 mas/yr[3] Dec.: +2.252 mas/yr[3]
Parallax (π)	7.8714 ± 0.037 mas[3]
Distance	414 ± 2 ly (127.0 ± 0.6 pc)
Absolute magnitude (MV)	+2.69[7]
Details
HD 187420
Mass	3.00±0.04[1] M☉
Radius	11.6±0.6[9] R☉
Luminosity	88.3^+1.4 −1.5[1] L☉
Surface gravity (log g)	2.59[10] cgs
Temperature	5,140±122[11] K
Metallicity [Fe/H]	−0.17[12] dex
Rotational velocity (v sin i)	2.4±1.2[13] km/s
Age	377±37[1] Myr
HD 187421
Mass	2.31[14] M☉
Radius	2.72±0.14[9] R☉
Luminosity	37.1^+2.4 −2.0[11] L☉
Surface gravity (log g)	3.92[14] cgs
Temperature	9,099±309[14] K
Metallicity [Fe/H]	+0.20[15] dex
Rotational velocity (v sin i)	170±2[16] km/s
Age	560[14] Myr
Other designations
HD 187420: 71 G. Telescopii[17], CD−55°8312, CPD−55°9221, GC 27482, HD 187420, HIP 97816, HR 7548, SAO 246311, CCDM J19526-5458A, WDS J19526-5458A[18]
HD 187421: 72 G. Telescopii[17], CD−55°8313, CPD−55°9222, GC 27483, HD 187421, HIP 97819, HR 7549, SAO 246312, CCDM J19526-5458B, WDS J19526-5458B[19]
Database references
SIMBAD	HD 187420
	HD 187421

HD 187420 (HR 7548; 71 G. Telescopii) and HD 187421 (HR 7549; 72 G. Telescopii), are the components of a binary star located in the southern constellation Telescopium. Gaia DR3 parallax measurements place the stars at a distance of 407 and 414 light years respectively.^[1][3] The two are separated by 23″, and they are approaching the Solar System with heliocentric radial velocities of −17.9 km/s and −21.5 km/s respectively.^[6][8]

The system

HD 187420 is the primary of the system. It has an apparent magnitude of 5.71,^[2] making it faintly visible to the naked eye as a yellowish-orange-hued star. However, its brightness is diminished by 0.17 magnitudes due to interstellar dust.^[20] Meanwhile, the secondary HD 187421 has an apparent magnitude of 6.37,^[2] placing it near the limit for naked eye visibility. It too suffers from extinction, which makes it 0.25 magnitudes dimmer.^[20] The stars have absolute magnitudes of −0.33 and +2.69 respectively.^[7] HD 187421 is located 23.5" away from HD 187420 along a position angle of 148° as of 2016.^[21] They were first observed as a double star in 1826 by astronomer James Dunlap.^[22]

HD 187420

HD 187420 has a stellar classification of G8/K0 III,^[4] indicating that it is an evolved star with the characteristics of a G8 and K0 giant star. It has 3 times the mass of the Sun but at the age of 377 million years,^[1] it has expanded to 11.6 times the radius of the Sun. It radiates 88.3 times the luminosity of the Sun^[1] from its photosphere at an effective temperature of 5,140 K.^[11] HD 187420 is metal deficient at [Fe/H] = −0.17^[12] and spins modestly with a projected rotational velocity of 2.4 km/s.

HD 187421

HD 187421 is an A-type star with the characteristics of an A1 and A3 main sequence star, which corresponds to a classification of A1/3 V.^[4] It has 2.31 times the mass of the Sun^[14] and 2.72 times the Sun's radius.^[9] It radiates 37.1 times the luminosity of the Sun^[11] from its photosphere at an effective temperature of 9,099 K,^[14] giving it a white hue. HD 187421 is particularly metal enriched at [Fe/H] = +0.2^[15] and is estimated to be 560 million years old.^[14] Like many hot stars it spins rapidly, having a projected rotational velocity of 170 km/s.^[16]

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. S2CID 17128864.
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. Houk, N.; Cowley, A. P. (1975). University of Michigan Catalogue of two-dimensional spectral types for the HD stars: Declinations −90° to −53°. Vol. 1. Bibcode:1975mcts.book.....H.
5. Wayman, P. A. (1962). "Photoelectric magnitudes and colours of Southern double stars". Royal Greenwich Observatory Bulletins. 50: 61. Bibcode:1962RGOB...50...61W.
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. Kharchenko, N.V.; Scholz, R.-D.; Piskunov, A.E.; Röser, S.; Schilbach, E. (November 2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889–896. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. eISSN 1521-3994. ISSN 0004-6337. S2CID 119323941.
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. Perdigon, J.; de Laverny, P.; Recio-Blanco, A.; Fernandez-Alvar, E.; Santos-Peral, P.; Kordopatis, G.; Álvarez, M. A. (March 2021). "The AMBRE Project: Origin and evolution of sulfur in the Milky Way". Astronomy & Astrophysics. 647: A162. arXiv:2102.01961. Bibcode:2021A&A...647A.162P. doi:10.1051/0004-6361/202040147. eISSN 1432-0746. ISSN 0004-6361. S2CID 231786605.
11. 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.
12. Anders, F.; et al. (August 2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy & Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. eISSN 1432-0746. ISSN 0004-6361. S2CID 131780028.
13. De Medeiros, J. R.; Alves, S.; Udry, S.; Andersen, J.; Nordström, B.; Mayor, M. (January 2014). "A catalog of rotational and radial velocities for evolved stars V: Southern stars *". Astronomy & Astrophysics. 561: A126. arXiv:1312.3474. Bibcode:2014A&A...561A.126D. doi:10.1051/0004-6361/201220762. eISSN 1432-0746. ISSN 0004-6361. S2CID 54046583.
14. David, Trevor J.; Hillenbrand, Lynne A. (12 May 2015). "The Ages of Early-type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. eISSN 1538-4357. S2CID 33401607.
15. 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.
16. Díaz, C. G.; González, J. F.; Levato, H.; Grosso, M. (July 2011). "Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum". Astronomy & Astrophysics. 531: A143. arXiv:1012.4858. Bibcode:2011A&A...531A.143D. doi:10.1051/0004-6361/201016386. eISSN 1432-0746. ISSN 0004-6361. S2CID 119286673.
17. 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.
18. "HD 187420". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved March 3, 2023.
19. "HD 187421". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved March 3, 2023.
20. 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.
21. 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. S2CID 119533755.
22. Dunlop, James (1829). "Approximate Places of Double Stars in the Southern Hemisphere, observed at Paramatta in New South Wales". Memoirs of the Royal Astronomical Society. 3: 257–276. Bibcode:1829MmRAS...3..257D. ISSN 0369-1829. S2CID 210251896.