HD 177830

From Wikipedia, the free encyclopedia

**HD 177830**
Observation data Equinox 2000
Constellation	Lyra
Right ascension	19^h 5^m 20.77^s
Declination	+25° 55' 14.38"
Apparent magnitude (V)	7.18
Distance	192.54 ly (59.06 pc)
Spectral type	K0
Other designations
BD+25°3719, HIP 93746

HD 177830 is a 7th magnitude star in the constellation Lyra. It is slightly more massive than our Sun, but cooler being a type K star. Therefore it is a subgiant clearly more evolved than the Sun. In visual light it is four times brighter than the Sun, but because of its distance, about 190 light years, it is not visible to the unaided eye. With binoculars it should be easily visible.

The star is known to have an extrasolar planet orbiting it.

[edit] HD 177830 b

**HD 177830 b**
Orbital elements
Extrasolar planet		Lists of extrasolar planets
Semimajor axis	(a)	1.227±0.071 AU
Eccentricity	(e)	0.096±0.048
Orbital period	(P)	410.1±2.2 d
Inclination	(i)	?°
Longitude of periastron	(ω)	189°
Time of periastron	(τ)	2,450,254±42 JD
Physical characteristics
Mass	(m)	>1.53±0.13 M_J
Radius	(r)	? R_J
Density	(ρ)	? kg/m³
Temperature	(T)	? K
Discovery information
Discovery date		1999
Discoverer(s)		Vogt, Marcy Butler, Apps
Detection method		Radial velocity
Discovery status		Published

HD 117830 b is a planet orbiting star HD 117830. It was discovered in 1999 by the California and Carnegie Planet Search team using the very successful radial velocity method. The planet has a minimum mass 1.28 times that of Jupiter. Since the inclination of the planet's orbit is not known, actual mass is likely to be somewhat more. Although not detected directly, the planet is certainly a gas giant.

Mean distance from the star is exactly same as Earth's distance from the Sun. However, the orbit is very eccentric. At the periastron distance from the star is almost halved, and at apoastron it is as distant as Mars is from the Sun. No doubt the seasons on the planet would be extreme. Because the star is more luminous than the Sun, the planet must be hotter than Earth.

In 2000 a group of scientists proposed, based on preliminary Hipparcos astrometrical satellite data, that the orbital inclination is as little as 1.3°. If that was the case, the planet would have a mass of 55 times that of Jupiter making it a brown dwarf instead of a planet. However, it is very unlikely that the planet would have such orbit. Furthermore, brown dwarfs with short orbits around solar-mass stars are exceedingly rare (the so-called "brown dwarf desert") making the claim even more unlikely.