HAT-P-17

HAT-P-17 is a K-type main-sequence star about 92.4 parsecs (301 ly) away. It has a mass of about 0.857 ± 0.039 M_☉. It is the host of two planets, HAT-P-17b and HAT-P-17c, both discovered in 2010.^[4][8] A search for a binary companion star using adaptive optics at the MMT Observatory was negative.^[9] A candidate companion was detected by a spectroscopic search of high-resolution K band infrared spectra taken at the Keck observatory.^[10]

HAT-P-17

Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus[1]
Right ascension	21h 38m 08.7310s[2]
Declination	+30° 29′ 19.446″[2]
Apparent magnitude (V)	10.38[3]
Characteristics
Spectral type	early K[4]
Astrometry
Proper motion (μ)	RA: −80.280(16) mas/yr[2] Dec.: −127.037(15) mas/yr[2]
Parallax (π)	10.8195±0.0182 mas[2]
Distance	301.5 ± 0.5 ly (92.4 ± 0.2 pc)
Details
Mass	0.857±0.039 M☉
Radius	0.837 R☉
Luminosity	0.48±0.04 L☉
Surface gravity (log g)	4.53±0.02[5] cgs
Temperature	5345±70[5] K
Metallicity	0.06±0.08[5]
Rotational velocity (v sin i)	0.56+0.12 −0.14[6] km/s
Age	7.8±3.3 Gyr
Other designations
TYC 2717-417-1, GSC 02717-00417, 2MASS J21380873+3029193[7]
Database references
SIMBAD	data

Comparison of the exoplanet HAT-P-17 b with the planet Jupiter

Planetary system

In 2010 a multi-planet system consisting of a transiting hot Saturn in an eccentric orbit and a Jupiter like planet in an outer orbit was detected. The transiting planet HAT-P-17b was detected by the HATNet Project using telescopes located in Hawaii, Arizona and at Wise Observatory in Israel. It was confirmed with radial velocity measurements taken at the Keck telescope which also led to the discovery of the second planet on a much wider orbit.^[4] In 2013 radial velocity measurements of the Rossiter-McLaughlin effect showed that the sky-projected angle between the stellar spin axis and the orbit of planet b was approximately 19°.^[6] The measurement in 2022 have resulted in slightly larger misalignment of 26.3±6.7°^[11]

The HAT-P-17 planetary system^[4][12]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	0.537±0.017 MJ	0.0882+0.0013 −0.0014	10.338523+0.000088 −0.000089	0.3417±0.0036	89.20+0.20 −0.10°	1.010±0.029 RJ
c	> 2.88±0.10 MJ	4.67±0.14	3972+185 −146	0.295±0.021	—	—