Astronomy:HD 81817
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Draco |
| Right ascension | 09h 37m 05.28778s[1] |
| Declination | +81° 19′ 34.9711″[1] |
| Apparent magnitude (V) | 4.28[2] |
| Characteristics | |
| Spectral type | K3III + ? + DA2.8[3] |
| B−V color index | +1.488±0.001[2] |
| Astrometry | |
| Radial velocity (Rv) | −6.98±0.10[2] km/s |
| Proper motion (μ) | RA: −16.62[1] mas/yr Dec.: −16.41[1] mas/yr |
| Parallax (π) | 3.28 ± 0.15[1] mas |
| Distance | 990 ± 50 ly (300 ± 10 pc) |
| Absolute magnitude (MV) | −3.14[2] |
| Details[4] | |
| A | |
| Mass | 4.3±0.5 M☉ |
| Radius | 83.8±7.8 R☉ |
| Luminosity | 1,822.9 L☉ |
| Temperature | 4,140±55 K |
| Metallicity [Fe/H] | −0.17±0.1 dex |
| Rotation | 801 d |
| Rotational velocity (v sin i) | 4.7±0.1 km/s |
| Age | 150±40 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
HD 81817 is a possible binary star system[6] with two brown dwarf companions[4][7] in the northern circumpolar constellation of Draco. It has an orange hue and is visible to the naked eye with an apparent visual magnitude of 4.28.[2] The system is located at a distance of approximately 990 light years from the Sun based on parallax,[1] and is drifting closer with a radial velocity of −7 km/s.[2] It is a member of the IC 2391 moving group.[8]
The primary component of this system is an aging giant star with a stellar classification of K3III.[3] The star's chromosphere is of the type called "hybrid", displaying a cool stellar wind in combination with hot emission lines.[9] It appears to be the source for the X-ray emission coming from this system.[10] The star is 150 million years old with 4.3 times the mass of the Sun.[4] With the supply of hydrogen at its core exhausted, the star has expanded to 83.8 times the Sun's radius.[4] It is radiating 1,823 times the luminosity of the Sun from its photosphere at an effective temperature of 4,140 K.[4]
A possible companion star was discovered in 1984 based upon its ultraviolet spectrum. The distribution of the far ultraviolet flux matches that of a white dwarf star of class DA.[6] A 2020 study finds it unlikely that there is a white dwarf companion; instead claiming the radial velocity variations are caused by a substellar object HD 80817 b, probably a brown dwarf, and possibly another substellar object. HD 80817 b would have a minimum mass of 27.1 |♃|J}}}}}} and orbit at 3.3 AU with a period of 1047.1 days and an eccentricity of 0.17. Gaia DR2 astrometry also suggested a companion with a mass of about 124 |♃|J}}}}}} (with a high margin of error) orbiting at 2.67 AU, consistent with the radial velocity detection. If the latter mass estimate is correct, this object would be a low-mass star, probably a red dwarf.[4] Further observations through 2022 have confirmed that the companion is indeed a brown dwarf, in addition to the detection of a second brown dwarf on a closer orbit.[7] By some definitions, these objects could be considered supermassive planets, similar to those around Nu Ophiuchi.[citation needed]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (years) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| c | ≥22.609+1.859 −1.876 MJ |
2.325+0.087 −0.095 |
1.706±0.006 | 0.095+0.058 −0.044 |
— | — |
| b | 24.128+9.747 −0.691 MJ |
3.233+0.125 −0.131 |
2.796+0.037 −0.027 |
0.097+0.090 −0.057 |
95.594+29.637 −35.307° |
— |
See also
- List of exoplanets discovered in 2020 - HD 81817 b
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A.
- ↑ 3.0 3.1 Holberg, J. B. et al. (2013). "Where are all the Sirius-like binary systems?". Monthly Notices of the Royal Astronomical Society 435 (3): 2077. doi:10.1093/mnras/stt1433. Bibcode: 2013MNRAS.435.2077H.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Bang, Tae-Yang et al. (June 2020). "Hybrid star HD 81817 accompanied by brown dwarf or substellar companion". Astronomy & Astrophysics 638: A148. doi:10.1051/0004-6361/201936613. Bibcode: 2020A&A...638A.148B.
- ↑ "HD 81817". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+81817.
- ↑ 6.0 6.1 Reimers, D. (July 1984). "Discovery of a white dwarf companion of the "hybrid" K giant HD 81817". Astronomy and Astrophysics 136: L5–L6. Bibcode: 1984A&A...136L...5R.
- ↑ 7.0 7.1 7.2 Feng, Fabo et al. (August 2022). "3D Selection of 167 Substellar Companions to Nearby Stars". The Astrophysical Journal Supplement Series 262 (21): 21. doi:10.3847/1538-4365/ac7e57. Bibcode: 2022ApJS..262...21F.
- ↑ Montes, D. et al. (November 2001). "Late-type members of young stellar kinematic groups - I. Single stars". Monthly Notices of the Royal Astronomical Society 328 (1): 45–63. doi:10.1046/j.1365-8711.2001.04781.x. Bibcode: 2001MNRAS.328...45M.
- ↑ Ayres, Thomas R. (January 2005). "X-Rays from Hybrid Stars". The Astrophysical Journal 618 (1): 493–501. doi:10.1086/425891. Bibcode: 2005ApJ...618..493A.
- ↑ Bilíková, Jana et al. (November 2010). "Hard X-ray Emission Associated with White Dwarfs. III.". The Astronomical Journal 140 (5): 1433–1443. doi:10.1088/0004-6256/140/5/1433. Bibcode: 2010AJ....140.1433B.
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