HD 179070

HD 179070, also known as Kepler-21, is a F-type subgiant star 354 light-years (109 parsecs) away in the constellation Lyra. A transiting exoplanet was discovered orbiting this star by the Kepler spacecraft.[4] At a magnitude of 8.25 this was the brightest star observed by Kepler to host a validated planet until the discovery of an exoplanet orbiting HD 212657 in 2018.[3][8]

HD 179070
HD 179070
Observation data
Epoch J2000      Equinox J2000
Constellation Lyra[1]
Right ascension 19h 09m 26.8350s[2]
Declination +38° 42′ 50.456″[2]
Apparent magnitude (V) 8.25[3]
Characteristics
Spectral type F6IV[4]
Apparent magnitude (J) 7.229±0.032[5]
Apparent magnitude (H) 7.031±0.023[5]
Apparent magnitude (K) 6.945±0.018[5]
Variable type Planetary transit variable[4]
Astrometry
Radial velocity (Rv)−19.19±0.14[2] km/s
Proper motion (μ) RA: 28.093(18) mas/yr[2]
Dec.: 28.546(20) mas/yr[2]
Parallax (π)9.2181 ± 0.0173 mas[2]
Distance353.8 ± 0.7 ly
(108.5 ± 0.2 pc)
Details[6]
Mass1.408+0.021
−0.030 M☉
Radius1.902+0.018
−0.012 R☉
Luminosity5.188+0.142
−0.128 L☉
Surface gravity (log g)4.026±0.004 cgs
Temperature6305±50 K
Metallicity [Fe/H]−0.03±0.10 dex
Rotation12.62±0.03 d[3]
Rotational velocity (v sin i)8.4±0.5[3] km/s
Age2.60±0.16 Gyr
Other designations
HIP 94112, Kepler-21, KOI-975, KIC 3632418, TYC 3120-963-1, 2MASS J19092683+3842505[7]
Database references
SIMBADdata

Planetary system

The single known planet orbiting this star was identified as a candidate based on photometry from the first four months of data from the Kepler spacecraft.[9] Confirmation was obtained in 2012 after extensive follow-up observations and analysis of the Kepler light curves.[4]

The calculated density of the planet is approximately 6.4 g cm−3, similar to Earth's 5.5 g cm−3, which suggests a rocky composition. With an equilibrium temperature of 2025 Kelvin, the top few-hundred kilometers of the planet is probably molten.[3]

Calculations of the rate of orbital decay from tidal effects results in a decrease in the orbital period of 3.88 milliseconds per year, since this would be a change of only 4 seconds every thousand years it would be undetectable in any reasonable length of time.[10]

The HD 179070 planetary system[3][11]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 7.5±1.3 M🜨 0.0427172±0.0000003 2.7858212±0.0000032 0.02±0.1 83.20+0.28
−0.26°		 1.639+0.019
−0.015 R🜨

References
  1. Roman, Nancy G. (1987). "Identification of a Constellation From a Position". Publications of the Astronomical Society of the Pacific. 99 (617): 695–699. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Vizier query form
  2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. López-Morales, Mercedes; et al. (2016). "Kepler-21b: A Rocky Planet Around a V = 8.25 Magnitude Star". The Astronomical Journal. 152 (6). 204. arXiv:1609.07617. Bibcode:2016AJ....152..204L. doi:10.3847/0004-6256/152/6/204.
  4. Howell, Steve B.; et al. (2012). "Kepler-21b: A 1.6 REarth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070". The Astrophysical Journal. 746 (2). 123. arXiv:1112.2165. Bibcode:2012ApJ...746..123H. doi:10.1088/0004-637X/746/2/123.
  5. Skrutskie, Michael F.; et al. (1 February 2006). "The Two Micron All Sky Survey (2MASS)". The Astronomical Journal. 131 (2): 1163–1183. Bibcode:2006AJ....131.1163S. doi:10.1086/498708. Vizier catalog entry
  6. Silva Aguirre, V.; et al. (2015). "Ages and fundamental properties of Kepler exoplanet host stars from asteroseismology". Monthly Notices of the Royal Astronomical Society. 452 (2): 2127–2148. arXiv:1504.07992. Bibcode:2015MNRAS.452.2127S. doi:10.1093/mnras/stv1388.
  7. "HD 179070". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-06-10.
  8. Mayo, Andrew W.; et al. (2018). "275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0–10". The Astronomical Journal. 155 (3). 136. arXiv:1802.05277. Bibcode:2018AJ....155..136M. doi:10.3847/1538-3881/aaadff.
  9. Borucki, William J.; et al. (2011). "Characteristics of Planetary Candidates Observed by Kepler. II. Analysis of the First Four Months of Data". The Astrophysical Journal. 736 (1). 19. arXiv:1102.0541. Bibcode:2011ApJ...736...19B. doi:10.1088/0004-637X/736/1/19.
  10. Luna, S. H.; Navone, H. D.; Melita, M. D. (September 2020). "The dynamical evolution of close-in binary systems formed by a super-Earth and its host star". Astronomy & Astrophysics. 641. A109. arXiv:1907.10575. Bibcode:2020A&A...641A.109L. doi:10.1051/0004-6361/201936551.
  11. Bonomo, A. S.; Dumusque, X.; et al. (April 2023). "Cold Jupiters and improved masses in 38 Kepler and K2 small-planet systems from 3661 high-precision HARPS-N radial velocities. No excess of cold Jupiters in small-planet systems". Astronomy & Astrophysics. arXiv:2304.05773. doi:10.1051/0004-6361/202346211. S2CID 258078829.
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