HAT-P-21

HAT-P-21 is a G-type main-sequence star about 910 light-years away. The star has amount of metals similar to solar abundance. The survey in 2015 has failed to detect any stellar companions.[4] The star is rotating rapidly, being spun up by the tides of giant planet on close orbit.[3]

HAT-P-21
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension  11h 25m 05.9858s[1]
Declination +41° 01′ 40.6692″[1]
Apparent magnitude (V) 11.46[1]
Characteristics
Spectral type G3V
Astrometry
Radial velocity (Rv)-51.98 km/s
Proper motion (μ) RA: -1.088 mas/yr
Dec.: 13.243 mas/yr
Parallax (π)3.5781 ± 0.0410[1] mas
Distance910 ± 10 ly
(279 ± 3 pc)
Details[2][3]
Mass0.947±0.042 M☉
Radius1.105±0.083 R☉
Luminosity1.06+0.20
−0.16 L☉
Surface gravity (log g)4.33±0.06 cgs
Temperature5634±67 K
Metallicity0.04±0.08
Rotation15.9±0.8 d
Rotational velocity (v sin i)3.5±0.5 km/s
Age10.2±2.5 Gyr
Other designations
Mazalaai, Gaia DR2 770622651659107712, TYC 3013-1229-1, GSC 03013-01229, 2MASS J11250598+4101406[1]
Database references
SIMBADdata

Naming

In 2019, the HAT-P-21 star havs received a proper name Mazalaai and planet HAT-P-21b - Bambaruush at an international NameExoWorlds contest.[5]. These names mean the Mongolian name for the endangered Gobi bear subspecies, and Mongolian term for 'bear cub', respectively.

Planetary system

In 2010 a transiting hot super-Jovian planet on moderately eccentric orbit was detected.[6] Its equilibrium temperature is 1283±50 K. The transit-timing variation survey in 2011 have failed to rule out or confirm the existence of additional planets in the system, until the orbital parameters of HAT-P-21b are known with better precision.[7]

Size comparison of HAT-P-21 b and Jupiter
The HAT-P-21 planetary system[6][8]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b (Bambaruush) 4.063±0.161 MJ 0.0494±0.0007 4.124481±0.000007 0.228±0.016 88.6° 1.08±0.18 RJ
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gollark: They've already stopped working.
gollark: I guess so... why?
gollark: Right, so just sign in with your license key or whatever on the remote endpoint.
gollark: I think you would need to set up the license key or something, but yes.

References
  1. HAT-P-21 -- Star
  2. ACCURATE, EMPIRICAL RADII AND MASSES OF PLANETS AND THEIR HOST STARS WITH GAIA PARALLAXES, 2016, arXiv:1609.04389
  3. A comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars, 2015, arXiv:1503.09111
  4. A Lucky Imaging search for stellar companions to transiting planet host stars, 2015, arXiv:1507.01938
  5. IAU 100 NameExoWorlds Approved Names
  6. HAT-P-20b–HAT-P-23b: FOUR MASSIVE TRANSITING EXTRASOLAR PLANETS, 2010, arXiv:1008.3388
  7. Prospecting transit duration variations in extrasolar planetary systems, 2011, arXiv:1109.0936
  8. Light Curve Analysis of Ground‐Based Data from Exoplanets Transit Database, 2019, arXiv:1910.11438

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