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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]
| 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 | |
| Database references | |
| SIMBAD | data |
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]
| 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🜨 |
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