WASP-84

WASP-84, also known as BD+02 2056, is a G-type main-sequence star 327 light-years (100 parsecs) away in the constellation Hydra. Its surface temperature is 5350±31 K and is slightly enriched in heavy elements compared to the Sun, with a metallicity Fe/H index of 0.05±0.02. It is rich in carbon and depleted of oxygen.^[4] WASP-84's age is probably older than the Sun at 8.5^+4.1
_−5.5 billion years.^[3] The star appears to have an anomalously small radius, which can be explained by the unusually high helium fraction or by it being very young.^[6]

WASP-84

Observation data Epoch J2000      Equinox J2000
Constellation	Hydra
Right ascension	08h 44m 25.70315s[1]
Declination	+01° 51′ 36.1055″[1]
Apparent magnitude (V)	10.83
Characteristics
Evolutionary stage	main-sequence star
Spectral type	G9V[2]
Astrometry
Radial velocity (Rv)	−11.63±0.21[1] km/s
Proper motion (μ)	RA: −23.344 mas/yr[1] Dec.: −31.570 mas/yr[1]
Parallax (π)	9.9636 ± 0.0149 mas[1]
Distance	327.3 ± 0.5 ly (100.4 ± 0.2 pc)
Details[3]
Mass	0.842+0.037 −0.036 M☉
Radius	0.748±0.015 R☉
Surface gravity (log g)	4.63±0.06[4] cgs
Temperature	5350±31[4] K
Metallicity [Fe/H]	0.05±0.02[4] dex
Rotation	14.36±0.35 d
Rotational velocity (v sin i)	4.10±0.30 km/s
Age	8.5+4.1 −5.5 Gyr
Other designations
BD+02 2056, Gaia DR2 3078836109158636928, WASP-84, TYC 211-706-1, GSC 00211-00706, 2MASS J08442570+0151361[5]
Database references
SIMBAD	data

A multiplicity survey did not detect any stellar companions to WASP-84 as of 2015.^[7]

Planetary system

In 2013, one exoplanet, named WASP-84b, was discovered on a tight, circular orbit.^[8] The planet is a hot Jupiter that cannot have formed in its current location and likely migrated from elsewhere. The planetary orbit is well aligned with the equatorial plane of the star, misalignment being equal to 0.3±1.7°. Planetary equilibrium temperature is 832±13 K.^[2]

In 2023, a second planet was discovered around WASP-84. This appears to be a dense rocky planet despite its high mass, comparable to Uranus.^[9]

The WASP-84 planetary system^[9]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
c	15.2+4.5 −4.2 M🜨	0.02359±0.00100	1.4468849+0.0000022 −0.0000016	—	83.20+0.51 −0.49°	1.95±0.12 R🜨
b	0.692±0.058 MJ	0.0778±0.0021	8.52349648(60)	<0.077[3]	88.292+0.045 −0.042°	0.956±0.024 RJ

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. Anderson, D. R.; Triaud, A. H. M. J.; Turner, O. D.; Brown, D. J. A.; Clark, B. J. M.; Smalley, B.; Cameron, A. Collier; Doyle, A. P.; Gillon, M.; Hellier, C.; Lovis, C.; Maxted, P. F. L.; Pollacco, D.; Queloz, D.; Smith, A. M. S. (2015), "THE WELL-ALIGNED ORBIT OF WASP-84b: EVIDENCE FOR DISK MIGRATION OF a HOT JUPITER", The Astrophysical Journal, 800 (1): L9, arXiv:1409.6335, Bibcode:2015ApJ...800L...9A, doi:10.1088/2041-8205/800/1/L9, S2CID 13606807
3. Bonomo, A. S.; Desidera, S.; Benatti, S.; Borsa, F.; Crespi, S.; Damasso, M.; Lanza, A. F.; Sozzetti, A.; Lodato, G.; Marzari, F.; Boccato, C.; Claudi, R. U.; Cosentino, R.; Covino, E.; Gratton, R.; Maggio, A.; Micela, G.; Molinari, E.; Pagano, I.; Piotto, G.; Poretti, E.; Smareglia, R.; Affer, L.; Biazzo, K.; Bignamini, A.; Esposito, M.; Giacobbe, P.; Hébrard, G.; Malavolta, L.; et al. (2017), "The GAPS Programme with HARPS-N@TNG XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets", Astronomy & Astrophysics, A107: 602, arXiv:1704.00373, Bibcode:2017A&A...602A.107B, doi:10.1051/0004-6361/201629882, S2CID 118923163
4. Teske, Johanna K.; Thorngren, Daniel; Fortney, Jonathan J.; Hinkel, Natalie; Brewer, John M. (2019), "Do Metal-rich Stars Make Metal-rich Planets? New Insights on Giant Planet Formation from Host Star Abundances", The Astronomical Journal, 158 (6): 239, arXiv:1912.00255, Bibcode:2019AJ....158..239T, doi:10.3847/1538-3881/ab4f79, S2CID 208527082
5. "BD+02 2056". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-25.
6. Maxted, P. F. L.; Serenelli, A. M.; Southworth, J. (2015), "Comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars", Astronomy & Astrophysics, 577: A90, arXiv:1503.09111, Bibcode:2015A&A...577A..90M, doi:10.1051/0004-6361/201525774, S2CID 53324330
7. Wöllert, Maria; Brandner, Wolfgang (2015), "A Lucky Imaging search for stellar sources near 74 transit hosts", Astronomy & Astrophysics, 579: A129, arXiv:1506.05456, Bibcode:2015A&A...579A.129W, doi:10.1051/0004-6361/201526525, S2CID 118903879
8. Anderson, D. R.; Collier Cameron, A.; Delrez, L.; Doyle, A. P.; Faedi, F.; Fumel, A.; Gillon, M.; Gómez Maqueo Chew, Y.; Hellier, C.; Jehin, E.; Lendl, M.; Maxted, P. F. L.; Pepe, F.; Pollacco, D.; Queloz, D.; Ségransan, D.; Skillen, I.; Smalley, B.; Smith, A. M. S.; Southworth, J.; Triaud, A. H. M. J.; Turner, O. D.; Udry, S.; West, R. G. (2014), "Three newly discovered sub-Jupiter-mass planets: WASP-69b and WASP-84b transit active K dwarfs and WASP-70Ab transits the evolved primary of a G4+K3 binary", Monthly Notices of the Royal Astronomical Society, 445 (2): 1114–1129, arXiv:1310.5654, Bibcode:2014MNRAS.445.1114A, doi:10.1093/mnras/stu1737, S2CID 54750890
9. Maciejewski, G.; Golonka, J.; et al. (May 2023). "A hot super-Earth planet in the WASP-84 planetary system". Monthly Notices of the Royal Astronomical Society. 525 (1): L43–L49. arXiv:2305.09177. Bibcode:2023MNRAS.525L..43M. doi:10.1093/mnrasl/slad078.