HD 240237 b

HD 240237 b is a super-Jupiter exoplanet orbiting the K-type giant star HD 240237 about 4,900 light-years (1,500 parsecs, or nearly 4.6×10¹⁶ km) away from Earth in the constellation Cassiopeia. It orbits outside of the habitable zone of its star at a distance of 1.9 AU. The exoplanet was found by using the radial velocity method, from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star. The planet has a mildly eccentric orbit.

HD 240237 b

Artistic simulation of HD 240237 b orbiting its host star. The stellar corona can be seen emitting from the surface.
Discovery
Discovery date	9 October 2011
Detection method	Doppler spectroscopy
Orbital characteristics
Semi-major axis	1.9 AU (280,000,000 km)
Eccentricity	0.4 (± 0.1)
Orbital period	745.7 (± 13.8) d
Time of periastron	54,292 ± 28.3
Argument of periastron	108.1 ± 21.8
Semi-amplitude	91.5 ± 12.8
Star	HD 240237 (BD+57° 2714)
Physical characteristics
Mean radius	~1.11 RJ
Mass	5.3[1] MJ
Temperature	781 K (508 °C; 946 °F)

Characteristics

Mass, radius and temperature

HD 240237 b is a "super-Jupiter", an exoplanet that has a radius and mass larger than that of the gas giants Jupiter and Saturn. It has a temperature of 781 K (508 °C; 946 °F), around that of the surface temperature of Venus.[2] It has an estimated mass of around 5.3 M_J and a potential radius of around 9% larger than Jupiter (1.11 R_J, or 12.2 R_⊕) based on its mass, since it is more massive than the jovian planet.

Host star

The planet orbits a (K-type) giant star named HD 240237. It has exhausted the hydrogen supply in its core and is currently fusing helium. The star has a mass of 1.69 M_☉ and a radius of around 32 R_☉. It has a surface temperature of 4361K and is likely 2 billion years old based on its mass and evolution. In comparison, the Sun is about 4.6 billion years old[3] and has a surface temperature of 5778 K.[4]

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 8.19. Therefore, HD 240237 is too dim to be seen with the naked eye.

Orbit

HD 240237 b orbits its star with nearly 331 times the Sun's luminosity (331 L_☉) every 746 days at a distance of 1.9 AU (compared to Mars' orbital distance from the Sun, which is 1.52 AU). It has a mildly eccentric orbit, with an eccentricity of 0.4.

Discovery

The planet was detected through Doppler spectroscopy, the method of observing exoplanets through the measurement of radial velocities of a star. If there is a wobble, it could mean that there is a possible planetary companion orbiting it.

Observations were taken with the Hobby-Eberly Telescope equipped with the High-Resolution Spectrograph in a queue-scheduled mode.[1] From July 2004 to October 2009, 40 epochs were measured, with SNR values ranging from 161–450. These observations eventually led the team to conclude that there was in fact a planetary companion orbiting around HD 240237, and they estimated its parameters to be a mass of 5.3 times that of Jupiter, an orbital period of 746 days, an eccentricity of 0.4, and a semi-major axis of 1.9 AU. The discovery, along with 2 other exoplanets, were announced on October 9, 2011.[1]

See also

• Epsilon Tauri b

References

1. Gettel, S.; Wolszczan, A.; Niedzielski, A.; Nowak, G.; Adamów, M.; Zieliński, P.; Maciejewski, G. (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.
2. http://www.hpcf.upr.edu/~abel/phl/hec_plots/hec_orbit/hec_orbit_HD_240237_b.png
3. Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 2011-02-19.
4. Fraser Cain (September 15, 2008). "Temperature of the Sun". Universe Today. Retrieved 2011-02-19.

External links

• "Notes for planet HD 240237 b". The Extrasolar Planets Encyclopaedia. Retrieved 2016-07-29.