Kepler-33

Kepler-33 is a star about 4,000 light-years (1,200 parsecs) in the constellation of Cygnus, with a system of five known planets. Having just begun to evolve off from the main sequence,^[4] its radius and mass are difficult to ascertain, although data available in 2020 shows its best-fit mass of 1.3M_☉ and radius of 1.6R_☉ are compatible with a model of a subgiant star.^[5]

Kepler-33

Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	19h 16m 18.6100s[1]
Declination	+46° 00′ 18.814″[1]
Apparent magnitude (V)	13.988
Characteristics
Spectral type	G1IV
Astrometry
Radial velocity (Rv)	12.18±3.65[1] km/s
Proper motion (μ)	RA: −1.107(15) mas/yr[1] Dec.: −13.099(14) mas/yr[1]
Parallax (π)	0.8136±0.0118 mas[1]
Distance	4,010 ± 60 ly (1,230 ± 20 pc)
Details[2]
Mass	1.26+0.03 −0.06 M☉
Radius	1.66±0.03 R☉
Luminosity	3.1+0.2 −0.1 L☉
Temperature	5947±60 K
Metallicity [Fe/H]	0.14±0.04 dex
Age	4.2+1.3 −0.3 Gyr
Other designations
KOI-707, KIC 9458613, 2MASS J19161861+4600187, Gaia DR2 2127355923723254272[3]
Database references
SIMBAD	data

Planetary system

The first detections of the candidate four-body planetary system were reported in February 2011.^[6] On January 26, 2012, the planetary system around the star was confirmed, including a fifth planet.^[4] However, unlike some other planets confirmed via Kepler, their masses were initially not known, as Doppler spectroscopy measurements were not done before the announcement. Judging by their radii, b may be a large super-Earth or small hot Neptune while the other four are all likely to be the latter. As of 2022^[update], the masses of planets e & f have been measured, with upper limits on the masses of planets c & d. These mass measurements confirm Kepler-33 d, e & f to be low-density, gaseous planets.^[2]

Planets b and c may actually be in a 7:3 resonance, as there is a 0.05 day discrepancy; there is also a small 0.18 day discrepancy between a 5:3 resonance between planets c and d. The other planets do not seem to be in any resonances, though near resonances are 3d:2e and 4e:3f.

The planetary system in its current configuration is highly susceptible to perturbations, therefore assuming stability, no additional giant planets can be located within 30 AU from the parent star.^[7]

The Kepler-33 planetary system^[2]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	—	0.0673+0.0004 −0.0012	5.66816±0.00005	<0.2	>87.0°	1.54+0.06 −0.05 R🜨
c	<19 M🜨	0.1181+0.0008 −0.0020	13.17552±0.00005	<0.05	>88.6°	2.73±0.06 R🜨
d	<8.2 M🜨	0.165+0.001 −0.003	21.77574+0.00006 −0.00004	<0.03	>89.02°	4.67±0.09 R🜨
e	6.6+1.1 −1.0 M🜨	0.212+0.001 −0.004	31.7852±0.0002	<0.02	89.4±0.1°	3.54+0.09 −0.07 R🜨
f	8.2+1.6 −1.2 M🜨	0.252+0.002 −0.004	41.0274±0.0002	<0.02	89.7+0.2 −0.1°	3.96+0.09 −0.07 R🜨

See also

• 55 Cancri
• Kepler-11
• Kepler-20