K2-315

K2-315 is a star in the southern zodiac constellation Libra.[5] It has an apparent magnitude of 17.67,[3] requiring a powerful telescope to be seen. The star is relatively close at a distance of 185 light years[2] but is receding with a radial velocity of 6.25 km/s.[4]

K2-315
The location of K2-315 (circled in red)
The location of K2-315 (circled in red)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Libra[1]
Right ascension 15h 12m 05.1944s[2]
Declination −20° 06′ 30.5428″[2]
Apparent magnitude (V) 17.67[3]
Characteristics
Evolutionary stage Red dwarf
Spectral type M3.5±0.5 V[4]
Astrometry
Radial velocity (Rv)6.25±0.17[4] km/s
Proper motion (μ) RA: −120.013 mas/yr[2]
Dec.: +74.471 mas/yr[2]
Parallax (π)17.6353 ± 0.0492 mas[2]
Distance184.9 ± 0.5 ly
(56.7 ± 0.2 pc)
Details[4]
Mass0.174±0.004 M☉
Radius0.2±0.01 R☉
Luminosity0.398% L☉
Surface gravity (log g)5.094±0.006 cgs
Temperature3,300±30 K
Metallicity [Fe/H]−0.24±0.09 dex
Rotational velocity (v sin i)<5 km/s
Age>1 Gyr
Other designations
K2-315, EPIC 249631677
Database references
SIMBADdata

K2-315 has a stellar classification of M3.5±0.5 V, indicating that it is a M-type main-sequence star (with 14% uncertainty).[4] It has 17.4% the mass of the Sun and 20% its radius.[4] Typical for red dwarves, it has a luminosity less than 1% of the Sun, which yields an effective temperature of 3,300 K.[4] Unlike most planetary hosts, K2-315 is metal-deficient, with an iron abundance only 57% that of the Sun.[4] It is estimated to be over a billion years old, and has a projected rotational velocity less than 5 km/s.[4]

Planetary system

In 2020, an exoplanet was discovered orbiting the star via transit. Astronomers have nicknamed it the "Pi Planet" due to its orbit of 3.14 d.[6][7][4]

The K2-315 planetary system[4]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 1? M🜨 0.023±0.006 3.1443189±0.0000049 — 88.74+0.21
−0.16°		 0.95±0.06 R🜨

See also
  • K2-315b, an exoplanet rotating around K2-315.

References
  1. "Find the constellation which contains given sky coordinates". djm.cc.
  2. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  3. Muirhead, Philip S.; Dressing, Courtney D.; Mann, Andrew W.; Rojas-Ayala, Bárbara; Lépine, Sébastien; Paegert, Martin; De Lee, Nathan; Oelkers, Ryan (4 April 2018). "A Catalog of Cool Dwarf Targets for the <i>Transiting Exoplanet Survey Satellite</i>". The Astronomical Journal. 155 (4): 180. arXiv:1710.00193. Bibcode:2018AJ....155..180M. doi:10.3847/1538-3881/aab710. eISSN 1538-3881.
  4. Niraula, Prajwal; et al. (21 September 2020). "π Earth: A 3.14 day Earth-sized Planet from K2's Kitchen Served Warm by the SPECULOOS Team". The Astronomical Journal. 160 (4): 172. arXiv:2006.07308. Bibcode:2020AJ....160..172N. doi:10.3847/1538-3881/aba95f. eISSN 1538-3881. ISSN 0004-6256.
  5. "Odkryto "Ziemię Pi". Okrąża swoją gwiazdę raz na 3,14 dnia". www.national-geographic.pl.
  6. "Astronomers discover an Earth-sized "pi planet" with a 3.14-day orbit". MIT News | Massachusetts Institute of Technology. 21 September 2020. Retrieved 2020-10-15.
  7. Starr, Michelle (22 September 2020). "Astronomers Discover 'Pi Earth' Exoplanet Orbits Its Star Once Every 3.14 Days". ScienceAlert.
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