HD 984 is a F-type main-sequence star located in the equatorial constellation Cetus. It is a young star, estimated 30 to 200 million years old, and is orbited by a brown dwarf companion. Parallax measurements by the Gaia spacecraft imply a distance of 150 light-years (46 pc) to HD 984. At an apparent magnitude of 7.32, the star is too dim to be visible to the naked eye.
 HD 984 is the brightest star in this Sloan Digital Sky Survey image. The spiral galaxy NGC 47 can be seen at upper left. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cetus[note 1] |
| Right ascension | 00h 14m 10.25283s[1] |
| Declination | −07° 11′ 56.8127″[1] |
| Apparent magnitude (V) | 7.32[2] |
| Characteristics | |
| A | |
| Evolutionary stage | Main sequence[3] |
| Spectral type | F7V[3] |
| B−V color index | 0.522±0.01[4] |
| B | |
| Evolutionary stage | Brown dwarf[4][5] |
| Spectral type | M6.5±1.5[6] |
| Apparent magnitude (J) | 13.28±0.06[6] |
| Apparent magnitude (H) | 12.6±0.05[6] |
| Astrometry | |
| Radial velocity (Rv) | 1.04±0.25[1] km/s |
| Proper motion (μ) | RA: 104.775 mas/yr[1] Dec.: −68.016 mas/yr[1] |
| Parallax (π) | 21.877 ± 0.0249 mas[1] |
| Distance | 149.1 ± 0.2 ly (45.71 ± 0.05 pc)[1] |
| Absolute magnitude (MV) | 3.95±0.07[4] |
| Orbit[5] | |
| Primary | A |
| Companion | B |
| Period (P) | 140+50 −30 yr |
| Semi-major axis (a) | 28+7 −4 AU |
| Eccentricity (e) | 0.76±0.05 |
| Inclination (i) | 120.8+1.8 −1.6° |
| Details | |
| A | |
| Mass | 1.2±0.06[4] M☉ |
| Radius | 1.247±0.053[4] R☉ |
| Luminosity | 2.218+0.142 −0.134[6] L☉ |
| Surface gravity (log g) | 4.38±0.06[3] cgs |
| Temperature | 6326±80[3] K |
| Metallicity [Fe/H] | −0.01±0.12[3] dex |
| Rotation | 1.39±0.05[7] d |
| Rotational velocity (v sin i) | 42.13±1.65[4] km/s |
| Age | 30–200[4] Myr |
| B | |
| Mass | 61±4[5] MJup |
| Radius | 0.162[5][a] R☉ |
| Luminosity | 1.318+0.094 −0.088×10−3[5] L☉ |
| Temperature | 2730+120 −180[6] K |
| Metallicity [Fe/H] | −0.62±0.02[3][note 2] dex |
| Rotational velocity (v sin i) | 12.72+0.03 −0.02[3] km/s |
| Position (relative to A)[4] | |
| Component | B |
| Epoch of observation | 2015 |
| Angular distance | 201.6±0.4 mas |
| Position angle | 92.2±0.5° |
| Other designations | |
| Database references | |
| SIMBAD | data |
Characteristics
editThe apparent magnitude of HD 984, i.e. its brightness relative to Earth, is 7.32.[2] Such brightness is lower than the limit for naked-eye visibility, generally defined as 6.5m, meaning that HD 984 can't be seen with the naked eye. It may be visible by a small telescope[8] or binoculars instead.[9] The absolute magnitude, i.e. the magnitude of HD 984 if it was seen at 10 parsecs (32.6 ly), is 3.95.[4] Kinematically, the system it is part of the Columba group.[4][10] It has a relatively high proper motion.[4]
The star is visually close (57") to BD-08 25,[11] which is a star of apparent magnitude 9.14 unrelated to the system, being 1,800 light-years (550 pc) away from Earth based on its parallax.[12] The galaxy NGC 47 lies just 320" from HD 984.[11]
Age estimates
editBased on the assumption that HD 984 is part of the Columba group, the stellar age would be of 30 Myr. However, there is still a possibility that HD 984 is a kinematic interloper or the Columba group is not sufficiently characterized to reliably assign an age. Previous isochronal ages of <0.48, 1.2+0.7
−0.9 and 3.1+1
−1.6 Gyr have been given by earlier studies. Since HD 984 A is a main sequence star, all isochronal ages will have high uncertainty.[4]
An analysis by HD 984 B's discovery team say that the system is likely to be less than 200 million years, based on HD 984 A's rotation and stellar activity. The same research also says that ages less than 30 million years can be ruled out, based on isochronal age constraints for HD 984 B. Therefore, the age is very likely between 30 and 200 million years.[4]
HD 984 A
editHD 984 A has a spectral classification F7V, with the luminosity class V classifying it as a main sequence star.[2][4] This star is 20% more massive than the Sun and 25% larger.[4] It is more energetic than the Sun as well, emitting 2.2 times more luminosity.[6] Its surface has an effective temperature of 6,326 K (6,053 °C),[3] giving it a yello-white hue typical of F-type stars.[13] HD 984 A rotates faster than 99% of all stars, with a rotation period estimated to be less than 1.6 days (38 hours).[3] The Sun's rotational period is 27 days for comparison.
Its rotation, coronal activity and cromospheric activity indicates that it is a young and active main-sequence star, likely less than 200 million years old. It is expected to live 5 billion years on the main sequence.[4] After that, it will cease its hydrogen at its core and evolve into a red giant star, increasing in size and luminosity, while decreasing in temperature.
HD 984 B
editHD 984 B is a brown dwarf, a class of astronomical objects that are intermediate between planets and stars, having masses between 13 and 75 MJ, and, unlike stars, can't produce thermonuclear fusion of hydrogen.[14] It was discovered in 2015 by Meshkat et al., using direct imaging from the Apodizing Phase Plate coronagraph at the Very Large Telescope with NaCo.[4]
Orbit
editHD 984 B takes 140 years to complete an orbit around HD 984 A, about the same as Neptune. The orbit's semi-major axis is of 28 astronomical units (4.2×109 km), also similar to Neptune. New observations have shown that its orbit is highly-eccentric (e = 0.76±0.05), meaning that its orbital distance vary from 6.72 to 49.3 AU.[b] Previous studies found a lower eccentricity (e = 0.23+0.11
−0.23), as well as a lower semi-major axis of 17.6+4.3
−8.1 AU. This difference is explained due to the increased orbit coverage and astrometric acceleration used in the new value.[5]
HD 984 B is expected to be in periastron in 2028.[5]
Physical parameters
editIts mass was firstly estimated using the age of the system by Meshkat et al. (2015) and Jonson-Groh et al. (2017).[6][4] Using this method, masses ranging from 34 MJ to 94 MJ are obtained, assuming ages of 30 and 200 million years respectively.[6] Assuming the largest mass and age, HD 984 B would be in the stellar mass regime. A 2022 study found a dynamical mass of 61±4 MJ, which places HD 984 B in the brown dwarf regime at 99.7% confidence. This mass was obtained using astrometric acceleration, new direct imaging of the object and radial velocity measurements, and is consistent with evolutionary models.[5]
HD 984 B is a hot brown dwarf[3] and has a spectral class of M6.5, with an uncertainty of 1.5. Having this spectral type, HD 984 B has an effective temperature of 2730 K.[6] At a luminosity of about 1.318×10−3 L☉,[5] this corresponds to a radius of 0.162 R☉ (1.576 RJ) based on the Stefan–Boltzmann law.[a] Its metallicity, i.e. its abundance of elements other than hydrogen and helium, is −0.62±0.02 dex, just one-fourth of the solar metalicity (0 dex), although this value might be biased. This brown dwarf more likely formed via gravitational collapse or disk instability rather than core accretion.[3]
See also
edit- Epsilon Indi, 54 Piscium and Eta Telescopii, another stars orbited by brown dwarfs
- List of brown dwarfs
- List of stars in Cetus
Notes
edit- ^ a b Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
- .
- ^ Calculated using the semi-major axis and the orbital eccentricity.
28×(1-0.76) = 6.72 AU.
28×(1+0.76) = 49.28 AU.
References
edit- ^ a b c d e f g Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
- ^ a b c "HD 984". SIMBAD. Centre de données astronomiques de Strasbourg.
- ^ a b c d e f g h i j k Costes, J. C.; Xuan, J. W.; Vigan, A.; Wang, J.; D’Orazi, V.; Mollière, P.; Baker, A.; Bartos, R.; Blake, G. A.; Calvin, B.; Cetre, S.; Delorme, J.; Doppmann, G.; Echeveri, D.; Finnerty, L. (2024-06-01). "Fresh view of the hot brown dwarf HD 984 B through high-resolution spectroscopy". Astronomy & Astrophysics. 686: A294. arXiv:2404.11523. Bibcode:2024A&A...686A.294C. doi:10.1051/0004-6361/202348370. ISSN 0004-6361.
- ^ a b c d e f g h i j k l m n o p q r Meshkat, T.; Bonnefoy, M.; Mamajek, E. E.; Quanz, S. P.; Chauvin, G.; Kenworthy, M. A.; Rameau, J.; Meyer, M. R.; Lagrange, A.-M.; Lannier, J.; Delorme, P. (2015-11-01). "Discovery of a Low-Mass Companion to the F7V star HD 984". Monthly Notices of the Royal Astronomical Society. 453 (3): 2379–2387. arXiv:1507.08291. doi:10.1093/mnras/stv1732. ISSN 0035-8711.
- ^ a b c d e f g h i Franson, Kyle; Bowler, Brendan P.; Brandt, Timothy D.; Dupuy, Trent J.; Tran, Quang H.; Brandt, G. Mirek; Li, Yiting; Kraus, Adam L. (2022-02-01). "Dynamical Mass of the Young Substellar Companion HD 984 B". The Astronomical Journal. 163 (2): 50. arXiv:2111.01803. Bibcode:2022AJ....163...50F. doi:10.3847/1538-3881/ac35e8. ISSN 0004-6256.
- ^ a b c d e f g h i Johnson-Groh, Mara; Marois, Christian; De Rosa, Robert J.; Nielsen, Eric L.; Rameau, Julien; Blunt, Sarah; Vargas, Jeffrey; Ammons, S. Mark; Bailey, Vanessa P.; Barman, Travis S.; Bulger, Joanna; Chilcote, Jeffrey K.; Cotten, Tara; Doyon, René; Duchêne, Gaspard (2017-04-01). "Integral Field Spectroscopy of the Low-mass Companion HD 984 B with the Gemini Planet Imager". The Astronomical Journal. 153 (4): 190. arXiv:1703.02607. Bibcode:2017AJ....153..190J. doi:10.3847/1538-3881/aa6480. ISSN 0004-6256.
- ^ Bowler, Brendan P.; Tran, Quang H.; Zhang, Zhoujian; Morgan, Marvin; Ashok, Katelyn B.; Blunt, Sarah; Bryan, Marta L.; Evans, Analis E.; Franson, Kyle; Huber, Daniel; Nagpal, Vighnesh; Wu, Ya-Lin; Zhou, Yifan (2023-04-01). "Rotation Periods, Inclinations, and Obliquities of Cool Stars Hosting Directly Imaged Substellar Companions: Spin–Orbit Misalignments Are Common". The Astronomical Journal. 165 (4): 164. arXiv:2301.04692. Bibcode:2023AJ....165..164B. doi:10.3847/1538-3881/acbd34. ISSN 0004-6256.
- ^ "★ HD 984". Stellar Catalog. Retrieved 2024-06-16.
- ^ Macrobert, Alan. "Binoculars: Halfway to a Telescope". Sky & Telescope. American Astronomical Society. Retrieved June 16, 2024.
- ^ Nielsen, E. L.; De Rosa, R.; Macintosh, B.; Wang, J.; Ruffio, J.; Chiang, E.; Marley, M.; Saumon, D.; Savransky, D.; Gemini Planet Imager Exoplanet Survey Team (2020-01-01). "The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10-100 AU". American Astronomical Society Meeting Abstracts #235. 235: 280.02. Bibcode:2020AAS...23528002N.
- ^ a b "coord 00 14 10.2528328224-07 11 56.812684848 (ICRS, J2000, 2000.0), radius: 7 arcmin". simbad.cds.unistra.fr. Retrieved 2024-06-15.
- ^ "BD-08 25". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved June 15, 2024.
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16
- ^ "Brown dwarf | Astronomy, Formation & Characteristics | Britannica". www.britannica.com. 2024-04-22. Retrieved 2024-04-24.