HD 39118

HD 39118

Basic layout of the HR 2024 system.
Observation data Epoch J2000      Equinox J2000
Constellation	Orion[a]
Right ascension	05^h 50^m 30.03^s[1]
Declination	02° 01′ 28.93″[1]
Apparent magnitude (V)	5.976[1]
Characteristics
Cool primary
Evolutionary stage	Red giant branch[2]
Spectral type	K0II[3]
Apparent magnitude (B)	6.83±0.015[1]
Apparent magnitude (G)	5.64[1]
Apparent magnitude (J)	4.193±0.238[1]
Apparent magnitude (H)	3.502±0.194[1]
Apparent magnitude (K)	3.337±0.19[1]
B−V color index	1.12[3]
Hot secondary
Evolutionary stage	B-type main-sequence star + A-type main-sequence star
Spectral type	B7V/B8V + A0V[3]
B−V color index	-0.09[3]
Astrometry
Radial velocity (Rv)	4.24[3] km/s
Proper motion (μ)	RA: 1.097 mas/yr[1] Dec.: -5.161 mas/yr[1]
Parallax (π)	1.47 ± 0.23 mas[4]
Distance	2300+350 −270 ly (707.6+107 −83.3 pc)[4]
Absolute magnitude (MV)	–2.53 (–2.3 (primary) + –0.75 (secondary))[3]
Orbit
Primary	Cool primary
Companion	Hot secondary
Period (P)	2570±13 d 7.04±0.04 year[5]
Semi-major axis (a)	4.7×10^8 km 3.14 AU[5]
Eccentricity (e)	0.3±0.007[5]
Details
K-type giant
Mass	3.3+0.3 −0.27[2] M☉
Radius	23.5+3.7 −1.9[2] R☉
Luminosity	535[6] L☉
Surface gravity (log g)	1.52[7] cgs
Temperature	4,550[7] K
Metallicity [Fe/H]	-0.34[7] dex
Rotational velocity (v sin i)	4.19[8] km/s
Age	257[2] Myr
B-type star
Temperature	11,300[9] K
Other designations
BD+01 1148, Gaia DR2 3316078695157768448, Gaia DR3 3316078695157768448, HD 39118/39119, HIP 27588, HR 2024, SAO 113198, PPM 149543, TIC 158867386, TYC 120-877-1, GSC 00120-00877, IRAS 05478+0200, 2MASS J05503003+0201290
Database references
SIMBAD	data

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

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

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

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

1. Obtained with a right ascension of 05^h 50^m 30.03^s and a declination of +02° 01′ 28.9″ on this website.
2. Constellation obtained with SIMBAD's celestial coordinates placed on this website
3. The Sun's effective temperature is 5772 K.
4. From a logarithm of -0.34
5. See the color index article

References

1. "BD+01 1148". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved May 6, 2024.
2. 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. Bibcode:2018A&A...616A..33S. doi:10.1051/0004-6361/201833111. ISSN 0004-6361. HD 39118's database entry at VizieR.
3. 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 (2): 513–537. Bibcode:2002ApJS..143..513G. doi:10.1086/342942. ISSN 0067-0049.
4. 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.
5. Griffin, R. F. (1990-12-01). "Composite Spectra - Part 5 - Orbital Elements for 30 Systems". Journal of Astrophysics and Astronomy. 11: 491–505. Bibcode:1990JApA...11..491G. doi:10.1007/BF02709763. ISSN 0250-6335.
6. 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. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x. ISSN 0035-8711. HD 39118's database entry at VizieR.
7. 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. Bibcode:2016A&A...591A.118S. doi:10.1051/0004-6361/201628497. ISSN 0004-6361. HD 39118's database entry at VizieR.
8. Hekker, S.; Meléndez, J. (2007-12-01). "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters". Astronomy and Astrophysics. 475 (3): 1003–1009. arXiv:0709.1145. Bibcode:2007A&A...475.1003H. doi:10.1051/0004-6361:20078233. ISSN 0004-6361. HD 39118's database entry at VizieR.
9. 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. Bibcode:1993A&A...276..161H. ISSN 0004-6361. HD 39118's database entry at VizieR.
10. 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 (3): 433–460. Bibcode:1999A&AS..139..433D. doi:10.1051/aas:1999401. ISSN 0365-0138.
11. "Determining the Limiting Magnitude – Saguaro Astronomy Club". www.saguaroastro.org. Retrieved 2024-05-21.