Kepler-68

Kepler-68 is a Sun-like main sequence star. It is known to have at least three planets orbiting around it. The outermost planet has a mass similar to Jupiter but orbits within the habitable zone.[5]

Kepler-68

Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	19^h 24^m 07.7660^s[1]
Declination	+49° 02′ 24.9282″[1]
Apparent magnitude (V)	10.08[2]
Astrometry
Proper motion (μ)	RA: −7.334 ± 0.039[1] mas/yr Dec.: −10.430 ± 0.048[1] mas/yr
Parallax (π)	6.9076 ± 0.0208[1] mas
Distance	472 ± 1 ly (144.8 ± 0.4 pc)
Details[3]
Mass	1.079±0.051 M☉
Radius	1.243±0.019 R☉
Temperature	5793±74 K
Metallicity [Fe/H]	0.12 (± 0.074) dex
Rotational velocity (v sin i)	2.4±0.5[4] km/s
Age	6.3±1.7 Gyr
Other designations
KOI-246, KIC 11295426, TYC 3551-189-1, GSC 03551-00189, 2MASS J19240775+4902249[4]
Database references
SIMBAD	data
KIC	data

High resolution imaging observations of Kepler-68 carried out with the lucky imaging instrument AstraLux on the 2.2m telescope at Calar Alto Observatory detected a wide companion candidate approximately 11 arcseconds away. Comparing these observations to the 2MASS positions shows that the companions proper motion is consistent with it being bound to the Kepler-68 system, but further observations are needed to confirm this conclusion.[6] Eleven arcseconds at the distance of Kepler-68 leads to a sky projected separation of approximately 1600 Astronomical units. A circular orbit at that distance would have a period of roughly 50,000 years.[7]

Planetary system

Currently, three planets have been discovered to orbit around Kepler-68. Two of the innermost planets were discovered by the planetary transit method. Follow-up Doppler measurements helped to determine the mass of Kepler-68b and helped to discover Kepler-68d.[8] There is an additional signal present in the radial velocity measurements indicating another body in the system at a period of greater than 10 years. The mass of this object is unknown and it could be either another planet or a stellar companion.[7]

The Kepler-68 planetary system[7][5]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	7.65+1.37 −1.32 M⊕	0.06170±0.00056	5.398763	—	87.60±0.90°	2.31+0.06 −0.09 R⊕
c	2.02+1.72 −1.78 M⊕	0.09059±0.00082	9.605065	—	86.93±0.41°	0.953+0.037 −0.042 R⊕
d	≥0.77±0.03 MJ	1.40±0.03	634.6+4.1 −3.7	0.112+0.035 −0.034	—	—

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
2. Høg, E. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
3. "Notes on Kepler-68 b". Retrieved 17 January 2016.
4. "Kepler-68". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-10-16.
5. Gilliland, Ronald L.; et al. (2013). "Kepler-68: Three Planets, One with a Density Between That of Earth and Ice Giants". The Astrophysical Journal. 766 (1). 40. arXiv:1302.2596. Bibcode:2013ApJ...766...40G. doi:10.1088/0004-637X/766/1/40.
6. Ginski, C.; et al. (2016). "A lucky imaging multiplicity study of exoplanet host stars – II". Monthly Notices of the Royal Astronomical Society. 457 (2): 2173–2191. arXiv:1601.01524. Bibcode:2016MNRAS.457.2173G. doi:10.1093/mnras/stw049.
7. Mills, Sean M.; et al. (2019). "Long-period Giant Companions to Three Compact, Multiplanet Systems". The Astronomical Journal. 157 (4). 145. arXiv:1903.07186. Bibcode:2019AJ....157..145M. doi:10.3847/1538-3881/ab0899. S2CID 119197547.
8. Marcy, Geoffrey W.; et al. (2014). "Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets". The Astrophysical Journal Supplement Series. 210 (2). 20. arXiv:1401.4195. Bibcode:2014ApJS..210...20M. doi:10.1088/0067-0049/210/2/20.