HD 233731

HD 233731, or HAT-P-22, is a suspected multiple star system in the northern circumpolar constellation of Ursa Major. It is invisible to the naked eye, having an apparent visual magnitude of 9.732.^[2] This system is located at a distance of 267 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +13 km/s.^[1]

HD 233731

Observation data Epoch J2000      Equinox J2000
Constellation	Ursa Major
Right ascension	10h 22m 43.5923s[1]
Declination	+50° 07′ 42.062″[1]
Apparent magnitude (V)	9.732[2]
Characteristics
Spectral type	G5V[3]
B−V color index	0.86[3]
Astrometry
Radial velocity (Rv)	12.86(15)[1] km/s
Proper motion (μ)	RA: −26.110(14) mas/yr[1] Dec.: 83.806(16) mas/yr[1]
Parallax (π)	12.2731 ± 0.0155 mas[1]
Distance	265.7 ± 0.3 ly (81.5 ± 0.1 pc)
Absolute magnitude (MV)	5.22±0.14[2]
Details[3]
Mass	0.936+0.028 −0.033 M☉
Radius	1.062+0.046 −0.013 R☉
Luminosity	0.77±0.09[2] L☉
Surface gravity (log g)	4.357+0.039 −0.005 cgs
Temperature	5,314±50 K
Metallicity [Fe/H]	0.30±0.09 dex
Rotation	28.7±0.4 d
Rotational velocity (v sin i)	1.65±0.26 km/s
Age	9.0+1.4 −2.2 Gyr[3] 12.4±2.6[2] Gyr
Other designations
HAT-P-22, Gaia DR2 846946629987527168, HD 233731, TYC 3441-925-1, GSC 03441-00925, 2MASS J10224361+5007420[4]
Database references
SIMBAD	data

The stellar classification of the primary is G5V,^[3] matching an ordinary G-type main-sequence star. The star has a low level of stellar activity with an estimated age of 9 to 12 billion years old. Its metallicity is twice that of the Sun, unusual for its advanced age.^[3] HD 233731 has a similar mass and radius as the Sun, and is spinning with a rotation period of 28.7 days.^[3] It is radiating 77%^[2] of the luminosity of the Sun from its photosphere at an effective temperature of 5314 K.^[3]

A faint stellar companion (2MASS J10224397+5007504) with a red hue is located at an angular separation of 9 arcseconds from the primary.^[2] In 2015, a spectroscopic stellar companion was reported with a semimajor axis of less than 33 AU. This star has an effective temperature of 4,000+250
−400 K with a mass of 0.63+0.07
−0.17 M_☉.^[5]

Planetary system

In 2010 a transiting hot Jupiter like planet was detected, designated HAT-P-22b.^[2] It has an equilibrium temperature of 1,463±19 K, and planetary atmosphere is cloudy.^[6] The measurement of Rossiter-McLaughlin effect in 2018 has allowed to detect what the planetary orbit is well aligned with the equatorial plane of the star, with a misalignment angle equal to 25°±18°.^[3]

In 2017, analysis of additional HARPS data showed a long-term trend that suggested the presence of an additional orbiting companion, HAT-P-22c.^[7]

Size comparison of HAT-P-22 b and Jupiter

The HAT-P-22 planetary system^[2][3][7]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	2.192+0.073 −0.013 MJ	0.04171+0.00042 −0.00050	3.21223328	0.016±0.009	86.46±0.41°	1.060±0.048 RJ
c (unconfirmed)	≥3.0 MJ	—	≥20.8 years	—	—	—

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. Bakos, G. Á.; et al. (2010), "HAT-P-20b – HAT-P-23b: Four Massive Transiting Extrasolar Planets", The Astrophysical Journal, 742 (2): 116, arXiv:1008.3388, Bibcode:2011ApJ...742..116B, doi:10.1088/0004-637X/742/2/116, S2CID 119182075.
3. Mancini, L.; et al. (2018), "The GAPS programme with HARPS-N at TNG XVI. Measurement of the Rossiter-McLaughlin effect of transiting planetary systems HAT-P-3, HAT-P-12, HAT-P-22, WASP-39, and WASP-60", Astronomy & Astrophysics, A41: 613, arXiv:1802.03859, Bibcode:2018A&A...613A..41M, doi:10.1051/0004-6361/201732234, S2CID 73565379.
4. "HD 233731". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2015-12-10.{{cite web}}: CS1 maint: postscript (link)
5. Piskorz, Danielle; et al. (2015), "Friends of Hot Jupiters. III. An Infrared Spectroscopic Search for Low-Mass Stellar Companions", The Astrophysical Journal, 814 (2): 148, arXiv:1510.08062, Bibcode:2015ApJ...814..148P, doi:10.1088/0004-637X/814/2/148, S2CID 11525988.
6. Turner, Jake D.; et al. (2016), "Ground-based near-UV observations of 15 transiting exoplanets: Constraints on their atmospheres and no evidence for asymmetrical transits", Monthly Notices of the Royal Astronomical Society, 459 (1): 789–819, arXiv:1603.02587, Bibcode:2016MNRAS.459..789T, doi:10.1093/mnras/stw574, S2CID 8769245.
7. Bonomo, A. S.; et al. (2017), "The GAPS Programme with HARPS-N at TNG. XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets", Astronomy and Astrophysics, 602, A107, arXiv:1704.00373, Bibcode:2017A&A...602A.107B, doi:10.1051/0004-6361/201629882.