HD 39118 (HD 39119, HR 2024) is a spectroscopic binary star in the constellation Orion, close to the celestial equator. It is made up from three stars: a cool primary (a K-type giant star) and a hot secondary, which is a binary star formed from a B-type main-sequence star and an A-type main-sequence star. A 2021 estimate derive a distance of 708 parsecs (2,310 ly) to HD 39118, and it is moving away from Earth at a speed of 4.24 km/s. The apparent magnitude is 5.976, making it visible to the naked eye only from dark skies.
Characteristics edit
HR 2024 is a spectroscopic binary (more precisely a single-lined spectroscopic binary)[10] made up of a cool primary and a hot secondary, which is also a binary star.[3] The designations “cold” and “hot” refer to the effective temperature of the components. They are separated by 4.7×108 kilometres (3.1 AU), and complete an orbit around each other every 2,570 days (7 years).[5] The orbital eccentricity is equivalent to 0.3.[5]
HD 39118 can be seen in the northern celestial hemisphere, close to the celestial equator, at a distance of 708 parsecs (2,310 light-years) in the constellation Orion.[1][4][b] It has an apparent magnitude of 5.976.[1] At this magnitude, it is visible to the naked eye only in dark skies, being close to the limiting magnitude to naked-eye vision of 6.5.[11] The absolute magnitude, i.e. its brightness if it was seen at a distance or 10 parsecs (32.6 ly), is –2.53.[3] It is moving away from Earth at a velocity of 4.24 km/s.[1]
It was double cataloged in the Henry Draper Catalogue, receiving the designations HD 39118 and HD 39119.[1]
Primary star edit
The primary has an spectral classification of K0II,[3] meaning that it is a K-type star that has left the main sequence, being now a bright giant star. Currently, it is in the red giant branch of evolution.[2] It is 3.28 times more massive has expanded to 25 times the Sun's size.[2] It emitts a luminosity 535[6] times the solar luminosity from its photosphere at an effective temperature of 4,550 K, which is around 1,200 K cooler than the Sun.[7][c] It has a subsolar metallicity, having an abundance of iron on its surface equivalent to 46% that of the Sun.[7][d] The age of the primary is estimated at 263 million years,[2] much younger than the Sun (4.6 billion years) despite its advanced evolutionary stage. It rotates under its own axis at a velocity of 4.19 km/s.[8] The B-V index is of 1.12,[3] giving it the typical orange hue of a K-type star.[e]
Hot companion edit
The hot companion is made up of two other stars, one is a late B-type main-sequence star (spectral type B7V/B8V) and the other is an early A-type main-sequence star (spectral type A0V).[3] It has an absolute magnitude about 1.55 magnitudes fainter than the primary companion.[3] The B-type star has an effective temperature of 11,300 K.[9] The B-V index of the hot companion is of –0.09,[3] meaning that it has a typical hue of a B-type star.[e]
Notes edit
References edit
- ^ a b c d e f g h i j k l m "BD+01 1148". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved May 6, 2024.
- ^ a b c d e f g Stock, Stephan; Reffert, Sabine; Quirrenbach, Andreas (2018-08-01). "Precise radial velocities of giant stars. X. Bayesian stellar parameters and evolutionary stages for 372 giant stars from the Lick planet search". Astronomy and Astrophysics. 616: A33. arXiv:1805.04094. doi:10.1051/0004-6361/201833111. ISSN 0004-6361. HD 39118's database entry at VizieR.
- ^ a b c d e f g h i j k l m Ginestet, N.; Carquillat, J. M. (2002-12-01). "Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components". The Astrophysical Journal Supplement Series. 143: 513–537. doi:10.1086/342942. ISSN 0067-0049.
- ^ a b c Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Demleitner, M.; Andrae, R. (2021-03-01). "Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3". The Astronomical Journal. 161 (3): 147. arXiv:2012.05220. Bibcode:2021AJ....161..147B. doi:10.3847/1538-3881/abd806. ISSN 0004-6256. Data about this star can be seen here.
- ^ a b c d e Griffin, R. F. (1990-12-01). "Composite Spectra - Part 5 - Orbital Elements for 30 Systems". Journal of Astrophysics and Astronomy. 11: 491–505. doi:10.1007/BF02709763. ISSN 0250-6335.
- ^ a b McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (2012-11-01). "Fundamental parameters and infrared excesses of Hipparcos stars". Monthly Notices of the Royal Astronomical Society. 427: 343–357. arXiv:1208.2037. doi:10.1111/j.1365-2966.2012.21873.x. ISSN 0035-8711. HD 39118's database entry at VizieR.
- ^ a b c d e Soubiran, Caroline; Le Campion, Jean-François; Brouillet, Nathalie; Chemin, Laurent (2016-06-01). "The PASTEL catalogue: 2016 version". Astronomy and Astrophysics. 591: A118. arXiv:1605.07384. doi:10.1051/0004-6361/201628497. ISSN 0004-6361. HD 39118's database entry at VizieR.
- ^ a b Hekker, S.; Meléndez, J. (2007-12-01). "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters". Astronomy and Astrophysics. 475: 1003–1009. arXiv:0709.1145. doi:10.1051/0004-6361:20078233. ISSN 0004-6361. HD 39118's database entry at VizieR.
- ^ a b Hunsch, M.; Reimers, D. (1993-09-01). "Circumstellar MG II absorption in UV spectra of hot companions of red giants and the meaning of the MG II asymmetry dividing line". Astronomy and Astrophysics. 276: 161–170. ISSN 0004-6361. HD 39118's database entry at VizieR.
- ^ de Medeiros, J. R.; Mayor, M. (1999-11-01). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement Series. 139: 433–460. doi:10.1051/aas:1999401. ISSN 0365-0138.
- ^ "Determining the Limiting Magnitude – Saguaro Astronomy Club". www.saguaroastro.org. Retrieved 2024-05-21.