HAT-P-27

HAT-P-27, also known as WASP-40, is the primary of a binary star system about 659 light-years away. It is a G-type main-sequence star. The star's age is similar to the Sun's at 4.4 billion years.^[3] HAT-P-27 is enriched in heavy elements, having a 195% concentration of iron compared to the Sun.

HAT-P-27

Observation data Epoch J2000      Equinox J2000
Constellation	Virgo[1]
Right ascension	14h 51m 04.1870s[2]
Declination	+05° 56′ 50.549″[2]
Apparent magnitude (V)	12.214[3]
Characteristics
Evolutionary stage	main-sequence star[4]
Spectral type	G8[4]
Astrometry
Radial velocity (Rv)	-15.901[5] km/s
Proper motion (μ)	RA: −28.610(19) mas/yr[2] Dec.: −2.774(19) mas/yr[2]
Parallax (π)	4.952±0.0169 mas[2]
Distance	659 ± 2 ly (201.9 ± 0.7 pc)
Orbit[6]
Primary	HAT-P-27
Companion	HAT-P-27 B
Semi-major axis (a)	0.656±0.021" (131 AU)
Details[3]
Mass	0.945±0.035 M☉
Radius	0.898+0.054 −0.039 R☉
Luminosity	0.57+0.09 −0.07 L☉
Surface gravity (log g)	4.51±0.04 cgs
Temperature	5300±90 K
Metallicity [Fe/H]	0.29±0.10 dex
Rotation	0.4±0.4
Rotational velocity (v sin i)	0.6+0.7 −0.4[7] km/s
Age	4.4+3.8 −2.6 Gyr
Other designations
HAT-P-27, Gaia DR2 1159336403336463872, WASP-40, GSC 00333-00351, 2MASS J14510418+0556505[8]
Database references
SIMBAD	data

The very dim stellar companion was detected in 2015 at a projected separation of 0.656″^[6] and proven to be physically bound to the system in 2016.^[4]

Planetary system

In 2011 a transiting hot Jupiter type planet b was detected in a mildly eccentric orbit. The planetary equilibrium temperature is 1207±41 K.^[3] The survey in 2013 failed to find any Rossiter-McLaughlin effect and therefore was unable to constrain the inclination of planetary orbit to the equatorial plane of the parent star.^[7] No orbital decay was detected as in 2018, despite the close proximity of the planet to the star.^[9]

The presence of an additional planet in the system has been suspected since 2015.^[10]

In 2024, a detection of a possible Neptune-like planet was reported. It is expected to be analog with Neptune in terms of radius, although is much hotter due to the low orbital separation, one year in this planet last one day and five hours, causing the planetary equilibrium temperature to be 1,426 K (1,153 °C). More observations are needed to validate its existence.^[11]

The HAT-P-27 planetary system^[3][11]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	0.660±0.033 MJ	0.0403±0.0005	3.039586±0.000012	0.078±0.047	85.0±0.2[7]°	1.038+0.077 −0.058 RJ
c (unconfirmed)	17.8+13.8 −0.81 M🜨	—	1.1994(2)	<0.19	—	4.33±0.44 R🜨