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)	−16.74±0.56[2] km/s
Proper motion (μ)	RA: −28.610(19) mas/yr[2] Dec.: −2.774(19) mas/yr[2]
Parallax (π)	4.9528±0.0169 mas[2]
Distance	659 ± 2 ly (201.9 ± 0.7 pc)
Orbit[5]
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[6] km/s
Age	4.4+3.8 −2.6 Gyr
Other designations
HAT-P-27, TOI-5672, TIC 461239485, WASP-40, GSC 00333-00351, 2MASS J14510418+0556505[7]
Database references
SIMBAD	data
Exoplanet Archive	data

A very dim stellar companion was detected in 2015 at a projected separation of 0.656″^[5] 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] A 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.^[6] No orbital decay was detected as of 2018, despite the close proximity of the planet to the star.^[8]

The presence of an additional planet in the system has been suspected since 2015.^[9]

In 2024, a detection of a possible Neptune-like planet was reported. It is expected to be an analog of Neptune in terms of radius, although much hotter due to the low orbital separation; one year on this planet lasts 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.^[10]

The HAT-P-27 planetary system^[3][10]

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[6]°	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🜨