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Upsilon Andromedae

From Biocrawler, the free encyclopedia.

**Upsilon Andromedae**
Epoch 2000
Constellation	Andromeda
Right Ascension	01^h 36^m 48.527^s
Declination	+41° 24' 38.71"
Distance	43.93 ly (13.47 pc)
Spectral Type	f8V
Apparent Magnitude	4.09
Other Designations	HR 458, HIP 7513 HD 9826

Upsilon Andromedae (υ And ) is a star, approximately 44 light-years from Earth, and approximately 3 billion years old, two thirds the age of our Sun. Viewed from Earth, υ Andromedae is in the Andromeda Constellation, and is about 10 degrees east of the Andromeda Galaxy.

υ Andromedae was the first main sequence star determined to have more than one extrasolar planet. So far, three planets have been discovered within the system; all three are believed to be gas giants.

Contents

1 Extrasolar planets

1.1 υ Andromedae b
1.2 υ Andromedae c
1.3 υ Andromedae d

2 History of discovery

3 See also

4 External links

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Extrasolar planets

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υ Andromedae b

**υ Andromedae b**
Orbital elements
Semi-major axis (a)	0.059 AU
Eccentricity (e)	0.012 ± 0.15
Orbital period (P)	4.617 ± 0.0003 d
Inclination (i)	?°
Longitude of periastron (ϖ)	73°
Time of periastron (τ)	2,450,002.093 JD
Physical characteristics
Mass	>0.69 M_J
Radius	? R_J
Density	? kg/m³
Temperature	? K
Discovery
Discoverers	Butler, Marcy
Discovery date	1997

υ Andromedae b is a gas giant that orbits extremely close to the star.

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υ Andromedae c

**υ Andromedae c**
Orbital elements
Semi-major axis (a)	0.829 AU
Eccentricity (e)	0.28 ± 0.11
Orbital period (P)	241.5 ± 1.1 d
Inclination (i)	?°
Longitude of periastron (ϖ)	250°
Time of periastron (τ)	2,450,160.5 JD
Physical characteristics
Mass	>1.89 M_J
Radius	? R_J
Density	? kg/m³
Temperature	? K
Discovery
Discoverers	Butler, Marcy Fischer, Brown
Discovery date	1999

υ Andromedae c is a gas giant with twice the mass of Jupiter that orbits closer to the star than Earth is to the Sun.

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υ Andromedae d

**υ Andromedae d**
Orbital elements
Semi-major axis (a)	2.53 AU
Eccentricity (e)	0.27 ± 0.11
Orbital period (P)	1284 ± 30 d
Inclination (i)	?°
Longitude of periastron (ϖ)	260°
Time of periastron (τ)	2,450,064 JD
Physical characteristics
Mass	>3.75 M_J
Radius	? R_J
Density	? kg/m³
Temperature	? K
Discovery
Discoverers	Butler, Marcy Fischer, Brown
Discovery date	1999

υ Andromedae d is a large gas giant 4 times the mass of Jupiter. It has an eccentric orbit within the star's habitability zone.

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History of discovery

The innermost planet (b) was discovered in 1996 and announced in January of 1997 by Geoffrey Marcy and R. Paul Butler, both astronomers at San Francisco State University (SFSU). Because of its closeness to the parent star, it induced a large wobble which was detected relatively easily. However, some additional wobble in the star remained unexplained, and it was suggested there might be a second planet in orbit. In the end, astronomers at both SFSU and the Harvard-Smithsonian Center for Astrophysics independently concluded that, in fact, a three-planet model best fit the data. These results were announced on April 15, 1999.

The existence of further planets too small to detect has not been ruled out.

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External links

"SIMBAD query result for Upsilon Andromedae (http://simbad.u-strasbg.fr/sim-id.pl?Ident=Upsilon%20Andromedae)." SIMBAD. Accessed on April 4, 2005.
SFSU page on Upsilon Andromedae (http://www.physics.sfsu.edu/~gmarcy/planetsearch/upsand/upsand.html)
Harvard-Smithsonian CfA page on Upsilon Andromedae (http://cfa-www.harvard.edu/afoe/upsAnd.html)
Upsilon Andromedae (http://www.extrasolar.net/star.asp?StarID=3) from extrasolar.net (http://www.extrasolar.net) and:
- Upsilon Andromedae b (http://www.extrasolar.net/planet.asp?PlanetID=3)
- Upsilon Andromedae c (http://www.extrasolar.net/planet.asp?PlanetID=72)
- Upsilon Andromedae d (http://www.extrasolar.net/planet.asp?PlanetID=73)
Mystery Solved: How The Orbits Of Extrasolar Planets Became So Eccentric (http://www.spacedaily.com/news/extrasolar-05t.html) (SpaceDaily)it:Upsilon Andromedae