KOI-5

KOI-5 is a triple star system composed of three stars: KOI-5 A, KOI-5 B and KOI-5 C, orbiting 1,870±70 light-years away.

KOI-5

Observation data Epoch J2000      Equinox
Constellation	Cygnus[1]
Right ascension	19h 18m 57.5306s[2]
Declination	+44° 38′ 50.619″[2]
Apparent magnitude (V)	11.78[3]
Characteristics
Spectral type	G2V[4]
Astrometry
Radial velocity (Rv)	−35.16[2] km/s
Proper motion (μ)	RA: +3.216[2] mas/yr Dec.: −10.925[2] mas/yr
Parallax (π)	1.7436±0.0666 mas[2]
Distance	1,870 ± 70 ly (570 ± 20 pc)
Position (relative to KOI-5A)[3]
Component	KOI-5B
Epoch of observation	2016
Angular distance	0.029±0.050″
Position angle	142.1±1.0°
Projected separation	16[citation needed] AU
Position (relative to KOI-5A)[3]
Component	KOI-5C
Epoch of observation	2016
Angular distance	0.141±0.050″
Position angle	304.3±2.2°
Projected separation	78[citation needed] AU
Details[5]
KOI-5A
Mass	1.13[6] M☉
Radius	1.840±0.017 R☉
Luminosity	3.86±0.17 L☉
Surface gravity (log g)	4.19[7] cgs
Temperature	5861[7] K
Age	3.49±0.41 Gyr
KOI-5B
Mass	1.09[6] M☉
Other designations
TOI-1241, 2MASS J19185753+4438507, KIC 8554498, Gaia EDR3 2126945668448657664
KOI-5A:
KOI-5B:
Database references
SIMBAD	data

The two dim stellar companions to KOI-5A were discovered in 2016.^[3] KOI-5 A and B orbit each other every 29 years, and KOI-5 C orbits stars A and B every 400 years.^[6] KOI-5C is physically associated with the core stellar pair with probability 99.98%.^[8]

Planetary system

Two planets orbiting one of KOI-5's stars were suspected since 2009 based on Kepler data, but KOI-5Ab was confirmed only in January 2021 after TESS determined the planet is orbiting KOI-5A. The exoplanet has caused interest in the scientific community because its orbital plane is misaligned with the closer star, suggesting it gave KOI-5Ab a gravitational kick during its development, resulting in the misalignment and inward migration to the current orbit.^[6][9] However, the confirmation of this planet has yet to be published in any peer-reviewed journal.

A second candidate planet was initially suspected, but was later found to be a false positive.^[10]

The KOI-5A planetary system^[8][6][10]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	0.179 MJ	0.0596060	5	—	—	7.07 R🜨