HR_2024 Latitude and Longitude:
Sky map 05h 50m 30s, +02° 01′ 28.9″
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HD 39118

Basic layout of the HR 2024 system.
Observation data
Epoch J2000       Equinox J2000
Constellation Orion [a]
Right ascension 05h 50m 30.03s [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]
Distance2300+350
−270  ly
(707.6+107
−83.3  pc) [4]
Absolute magnitude (MV)–2.53
(–2.3 (primary) + –0.75 (secondary)) [3]
Orbit
PrimaryCool primary
CompanionHot secondary
Period (P)2570±13 d
7.04±0.04 year [5]
Semi-major axis (a)4.7×108 km
3.14 AU [5]
Eccentricity (e)0.3±0.007 [5]
Details
K-type giant
Mass3.3+0.3
−0.27 [2]  M☉
Radius23.5+3.7
−1.9 [2]  R☉
Luminosity535 [6]  L☉
Surface gravity (log g)1.52 [7]  cgs
Temperature4,550 [7]  K
Metallicity [Fe/H]-0.34 [7]  dex
Rotational velocity (v sin i)4.19 [8] km/s
Age257 [2]  Myr
B-type star
Temperature11,300 [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 05h 50m 30.03s 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. ^ a b See the color index article

References

  1. ^ 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.
  2. ^ 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.
  3. ^ 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.
  4. ^ 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.
  8. ^ 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.
  9. ^ 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.
  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: 433–460. doi: 10.1051/aas:1999401. ISSN  0365-0138.
  11. ^ "Determining the Limiting Magnitude – Saguaro Astronomy Club". www.saguaroastro.org. Retrieved 2024-05-21.
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