HAT-P-23

HAT-P-23 is a G-type main-sequence star 1192 light-years away. It has a rapid rotation (rotation period equal to 7 days) for its advanced age of 4 billion years, and exhibits a strong starspot activity.^[7] The star may be in the process of being spun up by the giant planet on close orbit.^[8] The star is enriched in heavy elements, having about 140% amount of metals compared to solar abundance.

HAT-P-23 / Moriah

Observation data Epoch J2000      Equinox J2000
Constellation	Delphinus[1]
Right ascension	20h 24m 29.7235s[2]
Declination	+16° 45′ 43.812″[2]
Apparent magnitude (V)	11.94[3]
Characteristics
Evolutionary stage	main sequence[4]
Spectral type	G0[4]
Apparent magnitude (J)	11.103±0.022[5]
Apparent magnitude (H)	10.846±0.022[5]
Apparent magnitude (K)	10.791±0.020[5]
Variable type	Planetary transit[4]
Astrometry
Radial velocity (Rv)	−16.67±0.88[2] km/s
Proper motion (μ)	RA: 13.325(11) mas/yr[2] Dec.: −5.505(11) mas/yr[2]
Parallax (π)	2.7358±0.0108 mas[2]
Distance	1,192 ± 5 ly (366 ± 1 pc)
Details[4]
Mass	1.13±0.035 M☉
Radius	1.203±0.074 R☉
Luminosity	1.58±0.23 L☉
Surface gravity (log g)	4.33±0.05 cgs
Temperature	5905±80 K
Metallicity	0.15±0.04
Rotation	7.015 d[6]
Rotational velocity (v sin i)	8.1±0.5 km/s
Age	4.0±1.0 Gyr
Other designations
Moriah, TYC 1632-1396-1, GSC 01632-01396, 2MASS J20242972+1645437[3]
Database references
SIMBAD	data
Exoplanet Archive	data

Naming

In 2019, the HAT-P-23 star has received a proper name Moriah and planet HAT-P-23b - Jebus at an international NameExoWorlds contest.^[9] These names mean the ancient name of the mount at the center of Jerusalem city, and ancient (pre-Roman) name of Jerusalem itself, respectively.

Planetary system

In 2010 a transiting hot Jupiter like planet was detected.^[4] It has a measured dayside temperature of 2154±90 K.^[10] The planet is believed to be on an unstable orbit, and expected to be engulfed by its parent star about 7.5^+2.9
_−1.8 million years from now,^[4] although timing measurements of multiple transits since the discovery have been unable to detect any reduction in the orbital period.^[6][11] The planetary orbit is probably aligned with the equatorial plane of the star, misalignment equal to 15±22°.^[12] The color of planetary atmosphere is grey.^[13] The atmosphere is mostly devoid of clouds, and shows tentatively a presence of Titanium(II) oxide.^[14]

Size comparison of HAT-P-23 b and Jupiter

The HAT-P-23 planetary system^{[4][15][10][13]}

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b (Jebus)	2.09±0.111 MJ	0.0232±0.0002	1.2128868±0.0000004	0.096	85.1±1.5°	1.224±0.037 RJ