Astronomy:K2-28

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Short description: Metal-rich red dwarf Star in the constellation Aquarius
K2-28
Observation data
Equinox J2000.0]] (ICRS)
Constellation Aquarius[1]
Right ascension  22h 22m 29.8611s[2]
Declination −07° 57′ 19.853″[2]
Apparent magnitude (V) 16.06[3]
Characteristics
Spectral type M4V[4][5]
Apparent magnitude (J) 11.695±0.030[6]
Apparent magnitude (H) 11.028±0.023[6]
Apparent magnitude (K) 10.746±0.023[6]
Variable type Planetary transit variable[4]
Astrometry
Radial velocity (Rv)11.7[5] km/s
Proper motion (μ) RA: −254.604(41)[2] mas/yr
Dec.: −194.554(30)[2] mas/yr
Parallax (π)15.8734 ± 0.0343[2] mas
Distance205.5 ± 0.4 ly
(63.0 ± 0.1 pc)
Details[4]
Mass0.257±0.048 M☉
Radius0.288±0.028 R☉
Surface gravity (log g)4.93±0.04 cgs
Temperature3214±60 K
Metallicity [Fe/H]0.26±0.10 dex
Other designations
Gaia DR2 2622296783699476864, LP 700-6, NLTT 53655, EPIC 206318379[7]
Database references
SIMBADdata

K2-28 is a metal rich M4-type main sequence star. One confirmed transiting exoplanet is known to orbit this star. There is another star 5.2 arcseconds to the north–east of K2-28 however this star has a different proper motion and is therefore physically unrelated and probably a background star.[4]

Planetary system

Discovery

K2-28b was first noticed as a candidate extrasolar planet by Vanderburg et al. in 2016, who, in a search of 59,174 stars from the Kepler space telescope's first year of K2 observations, found 234 planetary candidates.[8] Shortly thereafter the K2-ESPRINT Project confirmed that the candidate was a super-Earth sized planet in a close orbit around a red dwarf star.[4]

K2-28 transit light curve from the Spitzer Space Telescope.[3]

Characteristics

K2-28b is a sub-Neptune sized planet orbiting its star in only 2.26 days. Despite its short orbital period the equilibrium temperature of the planet is a relatively low 500 Kelvin due to the low luminosity of the parent star.[4] Because of the very small size of the parent star this planet is a particularly favorable target for transmission spectroscopy by the James Webb Space Telescope which should be able to determine if the atmosphere is cloudy or clear by observing roughly 5 transits.[9] Among a group of small and cool planets orbiting relatively bright M-dwarfs its predicted secondary eclipse depth of 230 parts-per-million is second only to Gliese 1214 b.[3]

Secondary eclipse depth vs. temperature of small and cool planets orbiting relatively bright M-dwarfs[3]
The K2-28 planetary system[9]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
K2-28b 7.18+5.92
−3.08 (estimate) M⊕ 		0.0191+0.0037
−0.0029 		2.2604455±0.0000010 0 87.1+0.90
−0.74° 		2.56+0.27
−0.26 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. doi:10.1086/132034. Bibcode: 1987PASP...99..695R.  Vizier query form
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G.  Gaia EDR3 record for this source at VizieR.
  3. ↑ 3.0 3.1 3.2 3.3 Chen, Ge et al. (2018). "An Improved Transit Measurement for a 2.4-R🜨 Planet Orbiting A Bright Mid-M Dwarf K2–28". The Astronomical Journal 155 (5): 223. doi:10.3847/1538-3881/aabd75. Bibcode: 2018AJ....155..223C. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Hirano, Teruyuki et al. (2016). "The K2-ESPRINT Project III: A Close-in Super-Earth around a Metal-rich Mid-M Dwarf". The Astrophysical Journal 820 (1): 41. doi:10.3847/0004-637X/820/1/41. Bibcode: 2016ApJ...820...41H. 
  5. ↑ 5.0 5.1 Dressing, Courtney D. et al. (2017). "Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. I. Classifying Low-mass Host Stars Observed during Campaigns 1–7". The Astrophysical Journal 836 (2): 167. doi:10.3847/1538-4357/836/2/167. Bibcode: 2017ApJ...836..167D. 
  6. ↑ 6.0 6.1 6.2 Skrutskie, Michael F. et al. (1 February 2006). "The Two Micron All Sky Survey (2MASS)". The Astronomical Journal 131 (2): 1163–1183. doi:10.1086/498708. Bibcode: 2006AJ....131.1163S.  Vizier catalog entry
  7. ↑ "K2-28". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=K2-28. 
  8. ↑ Vanderburg, Andrew et al. (2016). "Planetary Candidates from the First Year of the K2 Mission". The Astrophysical Journal Supplement Series 222 (1): 14. doi:10.3847/0067-0049/222/1/14. Bibcode: 2016ApJS..222...14V. 
  9. ↑ 9.0 9.1 Stefansson, Gudmundur et al. (2018). "Diffuser-assisted Photometric Follow-up Observations of the Neptune-sized Planets K2-28b and K2-100b". The Astronomical Journal 156 (6): 266. doi:10.3847/1538-3881/aae6ca. Bibcode: 2018AJ....156..266S. 

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