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]
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]
^ abLissauer, Jack J.; Marcy, Geoffrey W.; Rowe, Jason F.; Bryson, Stephen T.; Adams, Elisabeth; Buchhave, Lars A.; Ciardi, David R.; Cochran, William D.; Fabrycky, Daniel C.; Ford, Eric B.; Fressin, Francois; Geary, John; Gilliland, Ronald L.; Holman, Matthew J.; Howell, Steve B.; Jenkins, Jon M.; Kinemuchi, Karen; Koch, David G.; Morehead, Robert C.; Ragozzine, Darin; Seader, Shawn E.; Tanenbaum, Peter G.; Torres, Guillermo; Twicken, Joseph D. (10 May 2012). "Almost All of Kepler's Multiple Planet Candidates are Planets". The Astrophysical Journal. 750 (2): 112. arXiv:1201.5424. Bibcode:2012ApJ...750..112L. doi:10.1088/0004-637X/750/2/112. S2CID30549908.
^Berger, Travis A.; Huber, Daniel; van Saders, Jennifer L.; Gaidos, Eric; Tayar, Jamie; Kraus, Adam L. (2020), "The Gaia-Kepler Stellar Properties Catalog. I. Homogeneous Fundamental Properties for 186,301 Kepler Stars", The Astronomical Journal, 159 (6): 280, arXiv:2001.07737, Bibcode:2020AJ....159..280B, doi:10.3847/1538-3881/159/6/280, S2CID210859307
^Ford, Eric B.; Rowe, Jason F.; Fabrycky, Daniel C.; Carter, Joshua A.; Holman, Matthew J.; Lissauer, Jack J.; Ragozzine, Darin; Steffen, Jason H.; Batalha, Natalie M.; Borucki, William J.; Bryson, Steve; Caldwell, Douglas A.; Dunham, Edward W.; Gautier, Thomas N.; Jenkins, Jon M.; Koch, David G.; Li, Jie; Lucas, Philip; Marcy, Geoffrey W.; McCauliff, Sean; Mullally, Fergal R.; Quintana, Elisa; Still, Martin; Tenenbaum, Peter; Thompson, Susan E.; Twicken, Joseph D. (2011), "Transit Timing Observations from Kepler : I. Statistical Analysis of the First Four Months", The Astrophysical Journal Supplement Series, 197 (1): 2, arXiv:1102.0544, Bibcode:2011ApJS..197....2F, doi:10.1088/0067-0049/197/1/2, S2CID118472942