Astronomy:HD 39118
Coordinates: 
05h 50m 30s, +02° 01′ 28.9″
230px Basic layout of the HR 2024 system. | |
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Orion[1] |
| Right ascension | 05h 50m 30.03s[2] |
| Declination | +02° 01′ 28.9″[2] |
| Apparent magnitude (V) | 5.976[2] |
| Characteristics | |
| Cool primary | |
| Evolutionary stage | Horizontal branch[3] |
| Spectral type | K0II[4] |
| Apparent magnitude (B) | 6.83±0.015[2] |
| Apparent magnitude (G) | 5.64[2] |
| Apparent magnitude (J) | 4.193±0.238[2] |
| Apparent magnitude (H) | 3.502±0.194[2] |
| Apparent magnitude (K) | 3.337±0.19[2] |
| B−V color index | 1.12[4] |
| Hot secondary | |
| Evolutionary stage | B-type main-sequence star + A-type main-sequence star |
| Spectral type | B7V/B8V + A0V[4] |
| B−V color index | -0.09[4] |
| Astrometry | |
| Radial velocity (Rv) | 4.24[4] km/s |
| Proper motion (μ) | RA: 1.097[2] mas/yr Dec.: -5.161[2] mas/yr |
| Parallax (π) | 1.47 ± 0.23[5] mas |
| Distance | 2300+350 −270 ly (707.6+107 −83.3 pc) |
| Absolute magnitude (MV) | –2.53 (–2.3 (primary) + –0.75 (secondary))[4] |
| Orbit | |
| Primary | Cool primary |
| Companion | Hot secondary |
| Period (P) | 2570±13 d 7.04±0.04 year[6] |
| Semi-major axis (a) | 4.7×108 km 3.14 AU[6] |
| Eccentricity (e) | 0.3±0.007[6] |
| Details | |
| K-type giant | |
| Mass | 3.3+0.3 −0.27[3] M☉ |
| Radius | 23.5+3.7 −1.9[3] R☉ |
| Luminosity | 535[7] L☉ |
| Surface gravity (log g) | 1.52[8] cgs |
| Temperature | 4,550[8] K |
| Metallicity [Fe/H] | -0.34[8] dex |
| Rotational velocity (v sin i) | 4.19[9] km/s |
| Age | 257[3] Myr |
| B-type star | |
| Temperature | 11,300[10] K |
| Other designations | |
| 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)[11] made up of a cool primary and a hot secondary, which is also a binary star.[4] The designations “cold” and “hot” refer to the effective temperature of the components. They are separated by 4.7×108 kilometres (3.1 astronomical unit|AU), and complete an orbit around each other every 2,570 days (7 years).[6] The orbital eccentricity is equivalent to 0.3.[6]
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.[2][5][1] It has an apparent magnitude of 5.976.[2] 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.[12] The absolute magnitude, i.e. its brightness if it was seen at a distance or 10 parsecs (32.6 ly), is –2.53.[4] It is moving away from Earth at a velocity of 4.24 km/s.[2]
It was double cataloged in the Henry Draper Catalogue, receiving the designations HD 39118 and HD 39119.[2]
Primary star
The primary has an spectral classification of K0II,[4] 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 horizontal branch of evolution.[3] It is 3.28 times more massive has expanded to 25 times the Sun's size.[3] It emitts a luminosity 535[7] 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.[8][lower-alpha 1] It has a subsolar metallicity, having an abundance of iron on its surface equivalent to 46% that of the Sun.[8][lower-alpha 2] The age of the primary is estimated at 263 million years,[3] 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.[9] The B-V index is of 1.12,[4] giving it the typical orange hue of a K-type star.[lower-alpha 3]
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).[4] It has an absolute magnitude about 1.55 magnitudes fainter than the primary companion.[4] The B-type star has an effective temperature of 11,300 K.[10] The B-V index of the hot companion is of –0.09,[4] meaning that it has a typical hue of a B-type star.[lower-alpha 3]
Notes
- ↑ The Sun's effective temperature is 5772 K.
- ↑ From a logarithm of -0.34
- ↑ 3.0 3.1 See the color index article
References
- ↑ 1.0 1.1 Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific 99 (617): 695. doi:10.1086/132034. Bibcode: 1987PASP...99..695R Constellation record for this object at VizieR.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 "BD+01 1148". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=BD%2B01+1148.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 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. doi:10.1051/0004-6361/201833111. ISSN 0004-6361. Bibcode: 2018A&A...616A..33S. https://ui.adsabs.harvard.edu/abs/2018A&A...616A..33S. HD 39118's database entry at VizieR.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 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. doi:10.1086/342942. ISSN 0067-0049. Bibcode: 2002ApJS..143..513G. https://ui.adsabs.harvard.edu/abs/2002ApJS..143..513G.
- ↑ 5.0 5.1 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. doi:10.3847/1538-3881/abd806. ISSN 0004-6256. Bibcode: 2021AJ....161..147B. Data about this star can be seen here.
- ↑ 6.0 6.1 6.2 6.3 6.4 Griffin, R. F. (1990-12-01). "Composite Spectra - Part 5 - Orbital Elements for 30 Systems". Journal of Astrophysics and Astronomy 11 (4): 491–505. doi:10.1007/BF02709763. ISSN 0250-6335. Bibcode: 1990JApA...11..491G. https://ui.adsabs.harvard.edu/abs/1990JApA...11..491G.
- ↑ 7.0 7.1 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 (1): 343–357. doi:10.1111/j.1365-2966.2012.21873.x. ISSN 0035-8711. Bibcode: 2012MNRAS.427..343M. HD 39118's database entry at VizieR.
- ↑ 8.0 8.1 8.2 8.3 8.4 Soubiran, Caroline; Le Campion, Jean-François; Brouillet, Nathalie; Chemin, Laurent (2016-06-01). "The PASTEL catalogue: 2016 version". Astronomy and Astrophysics 591: A118. doi:10.1051/0004-6361/201628497. ISSN 0004-6361. Bibcode: 2016A&A...591A.118S. https://ui.adsabs.harvard.edu/abs/2016A&A...591A.118S. HD 39118's database entry at VizieR.
- ↑ 9.0 9.1 Hekker, S.; Meléndez, J. (2007-12-01). "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters". Astronomy and Astrophysics 475 (3): 1003–1009. doi:10.1051/0004-6361:20078233. ISSN 0004-6361. Bibcode: 2007A&A...475.1003H. https://ui.adsabs.harvard.edu/abs/2007A&A...475.1003H. HD 39118's database entry at VizieR.
- ↑ 10.0 10.1 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. Bibcode: 1993A&A...276..161H. https://ui.adsabs.harvard.edu/abs/1993A&A...276..161H. 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 (3): 433–460. doi:10.1051/aas:1999401. ISSN 0365-0138. Bibcode: 1999A&AS..139..433D. https://ui.adsabs.harvard.edu/abs/1999A&AS..139..433D.
- ↑ "Determining the Limiting Magnitude – Saguaro Astronomy Club". https://www.saguaroastro.org/determining-the-limiting-magnitude/.
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