HD 240237

HD 240237 is a star in the northern constellation of Cassiopeia.[5] It is an orange star that can be viewed with binoculars or a small telescope, but is too faint to be seen with the naked eye at an apparent visual magnitude of 8.19.[2] This object is located at a distance of approximately 3,100 light years away from the Sun based on parallax, but is drifting closer with a radial velocity of −25 km/s.[1]

HD 240237
Observation data
Epoch J2000      Equinox J2000
Constellation Cassiopeia
Right ascension  23h 15m 42.22441s[1]
Declination +58° 02′ 35.6705″[1]
Apparent magnitude (V) 8.19[2]
Characteristics
Spectral type K2III[3]
B−V color index 1.682±0.029[2]
Astrometry
Radial velocity (Rv)−24.82±0.04[1] km/s
Proper motion (μ) RA: −0.203[1] mas/yr
Dec.: −4.290[1] mas/yr
Parallax (π)1.0437 ± 0.0364[1] mas
Distance3,100 ± 100 ly
(960 ± 30 pc)
Details
Mass1.69±0.42[3] or 0.61[4] M☉
Radius78.13+7.31
−5.66[1] R☉
Luminosity1,244±65[1] L☉
Temperature3,878+148
−170[1] K
Metallicity [Fe/H]−0.26±0.07[3] dex
Rotation≥ 1010 d[3]
Age270[3] Myr
Other designations
BD+57°2714, HD 240237, HIP 114840, SAO 35269[5]
Database references
SIMBADdata

This is an aging giant star with a stellar classification of K2III;[3] a star that has exhausted the supply of hydrogen at its core and expanded to 78 times the radius of the Sun.[1] S. Gettel and associates (2011) estimate the star is around 270 million years old with 1.7 times the mass of the Sun.[3] However, S. G. Sousa and associates found a much lower mass of 0.61 times the mass of the Sun.[4] It is radiating 1,244 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,878 K.[1]

In 2011, Gettel et al. announced the discovery of a planet orbiting this star. They estimated a mass around 5 times that of Jupiter, with an orbital period of 2.042 years and a moderate eccentricity. Sousa et al. (2015) gave a much lower estimate of 1.53 MJ.[4] The designation b for this object, derives from the order of discovery. The designation of b is given to the first planet orbiting a given star, followed by the other lowercase letters of the alphabet.[6] In the case of HD 240237, there was only one planet, so only the letter b is used.

The HD 240237 planetary system[3]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 5.3 MJ 1.9 745.7±13.8 0.4±0.1 — —

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. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015.
  3. Gettel, S.; et al. (2011). "Substellar-Mass Companions to the K-Giants HD 240237, BD +48 738 and HD 96127". The Astrophysical Journal. 745: 28. arXiv:1110.1641. Bibcode:2012ApJ...745...28G. doi:10.1088/0004-637X/745/1/28.
  4. Sousa, S. G.; et al. (April 2015). "Homogeneous spectroscopic parameters for bright planet host stars from the northern hemisphere . The impact on stellar and planetary mass". Astronomy & Astrophysics. 576: 8. arXiv:1503.02443. Bibcode:2015A&A...576A..94S. doi:10.1051/0004-6361/201425227. A94.
  5. "HD 240237". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 7 June 2014.
  6. Hessman, F. V.; et al. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
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