Kepler-46

Kepler-46, previously designated KOI-872, is a star located in the constellation Lyra. Observed since 2009 by the Kepler space observatory, it has since been found to possess a planetary system consisting of at least two planets and while it has a similar mass to the Sun (90%) it is significantly older at ten billion years.[3]

Kepler-46

Artist's conception of the Kepler-46 system showing the two planets. Planet b transits its star, the same method by which it was detected.
Observation data Epoch J2000      Equinox J2000
Constellation	Lyra
Right ascension	19^h 17^m 04.4929^s[1]
Declination	42° 36′ 15.041″[1]
Characteristics
Apparent magnitude (J)	13.814[2]
Apparent magnitude (H)	13.436[2]
Apparent magnitude (K)	13.347[2]
Astrometry
Proper motion (μ)	RA: 3.156±0.046[1] mas/yr Dec.: 0.894±0.053[1] mas/yr
Parallax (π)	1.2586 ± 0.0277[1] mas
Distance	2,590 ± 60 ly (790 ± 20 pc)
Absolute bolometric magnitude (Mbol)	5.18 (predicted)[note 1]
Details
Mass	0.902+0.040 −0.038[3] M☉
Radius	0.938+0.038 −0.039[3] R☉
Temperature	5155±150[3] K
Metallicity [Fe/H]	0.41±0.10[3][note 2] dex
Rotation	27.859±0.075 days[4]
Age	9.7+3.7 −3.5[3] Gyr
Other designations
Gaia DR2 2102700131386216576, KOI-872, KIC 7109675, 2MASS J19170449+4236150[2]
Database references
SIMBAD	data
KIC	data

Kepler-46 b (previously KOI-872.01), was the first planet discovered in the system. It was found through detailed analysis of Kepler space observatory data. An additional planet, Kepler-46 c, was discovered by an outside group using Kepler public data through analysis of transit timing variations. While only one additional planet was confirmed by the analysis, the study revealed the potential existence of either an unconfirmed planet KOI-872.03 (KOI-872 d).[5] Validation by multiplicity method allowed to confirm the existence of this planet which was then renamed Kepler-46d.

Planetary system

Planet b is a gas giant planet with a mass slightly less than that of Jupiter.[3] The second planet in the system was among the first to be discovered through the method of transit timing variations, and through its confirmation of KOI-872 c with a 99% confidence level has shown that the method of detection may be used to detect future extrasolar planets and, possibly, extrasolar moons.[6] This second planet exerted a gravitational force on the first planet, orbiting its host star in just 34 days. While this usually occurs on an extremely regular schedule, additional planets within the system can disrupt the time of the transit, and these disruptions can indicate the presence of a planet, even if the disrupting planet does not pass in front of the host star itself.[6]

The data show that Kepler-46 c is an approximately Saturn-mass object with an orbital period of 57 days.[6] As the planet does not itself transit its host star, there is no way of knowing its size (probably a similar size to its sibling). The measurements also suggest the existence of another planet orbiting with a period of about 6.8 days,[5] this planet was confirmed in 2016.[7]

The method in which the planet was detected is similar to the way that the planet Neptune was discovered, in which the newly discovered planet is known by its pull on another which is already known to exist.[8]

The Kepler-46 planetary system[5][3]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	0.885+0.374 −0.343 MJ	0.1971±0.0001	33.648+0.004 −0.005	0.0321+0.0069 −0.0078	89.04±0.14°	0.810+0.035 −0.36 RJ
c	0.362±0.016 MJ	0.2811±0.0003	57.325+0.116 −0.098	0.0354+0.0057 −0.0059	88.66+0.26 −0.27°	—
d	—	0.0679±0.0035	6.76671+0.00013 −0.00012	0(assumed)	88.55+0.49 −0.69°	0.1510+0.0094 −0.0098 RJ

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. "Kepler-46". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved May 16, 2012.
3. Saad-Olivera, Ximena; et al. (2017). "Masses of Kepler-46b, c from Transit Timing Variations". The Astronomical Journal. 153 (4). 198. arXiv:1704.01541. Bibcode:2017AJ....153..198S. doi:10.3847/1538-3881/aa64e0. S2CID 119513521.
4. McQuillan, A.; Mazeh, T.; Aigrain, S. (2013). "Stellar Rotation Periods of The Kepler objects of Interest: A Dearth of Close-In Planets Around Fast Rotators". The Astrophysical Journal Letters. 775 (1). L11. arXiv:1308.1845. Bibcode:2013ApJ...775L..11M. doi:10.1088/2041-8205/775/1/L11. S2CID 118557681.
5. Nesvorny, D.; et al. (2012). "The Detection and Characterization of a Nontransiting Planet by Transit Timing Variations". Science. 336 (6085): 1133–6. arXiv:1208.0942. Bibcode:2012Sci...336.1133N. doi:10.1126/science.1221141. PMID 22582018. S2CID 41455466.
6. Moskowitz, Clara (May 10, 2012). "Hidden Alien Planet Revealed by Its Own Gravity". Space.com. Space.com. Retrieved May 10, 2012.
7. WARM JUPITERS ARE LESS LONELY THAN HOT JUPITERS: CLOSE NEIGHBOURS, 2016, arXiv:1601.05095
8. Crockett, Christopher (May 12, 2012). "New planet found in distant solar system by its tug on another world". EarthSky. Earthsky Communications. Retrieved May 19, 2012.

Notes

1. Figure based on the following equations, which calculated bolometric (total) luminosity across all spectra based on effective temperature: ${\displaystyle m_{\rm {star}}=m_{\rm {sun}}-2.5\log _{10}\left({L_{\rm {star}} \over L_{\odot }}\cdot \left({\frac {d_{\rm {sun}}}{d_{\rm {star}}}}\right)^{2}\right)}$ (cf. Luminosity) and ${\displaystyle M=m_{\rm {star}}-5((\log _{10}{D_{L}})-1)\!\,}$ (cf. Absolute magnitude)
2. This measurement indicates the log₁₀ of the relative abundance of iron in the measured star to that of the Sun.