Upsilon Andromedae c

Upsilon Andromedae c (υ Andromedae c, abbreviated Upsilon And c, υ And c), formally named Samh /ˈsɑːm/ (a homophone with the star Salm), is an extrasolar planet orbiting the Sun-like star Upsilon Andromedae A every 241.3 days. Its discovery in April 1999 by Geoffrey Marcy and R. Paul Butler made this the first multiple-planet system to be discovered around a main-sequence star, and the first multiple-planet system known in a multiple star system. Upsilon Andromedae c is the second known planet in order of distance from its star.

Upsilon Andromedae c

An artist's impression of Upsilon Andromedae c.
Discovery
Discovered by	Marcy et al.
Discovery site	California and Carnegie Planet Search  USA
Discovery date	April 15, 1999
Detection method	Radial velocity
Orbital characteristics
Apastron	~9.11 Gm
Periastron	~91.6 Gm
Semi-major axis	~124.1 Gm
Eccentricity	0.260±0.079[1]
Orbital period	241.26±0.64[1] d ~0.66228[1] y
Inclination	7.868 ± 1.003[2]
Longitude of ascending node	236.853 ± 7.528[2]
Time of periastron	2,499,922.53 ± 1.17[2]
Argument of periastron	247.66 ± 1.76[2]
Semi-amplitude	56.26 ± 0.52[1]
Star	Upsilon Andromedae A
Physical characteristics
Mass	13.98+2.3 −5.3[2] MJ

Name

In July 2014 the International Astronomical Union launched a process for giving proper names to certain exoplanets and their host stars.[3] The process involved public nomination and voting for the new names.[4] In December 2015, the IAU announced the winning name was Samh for this planet.[5] The winning name was submitted by the Vega Astronomy Club of Morocco and honours the 11th Century astronomer Ibn al-Samh of Muslim Spain.[6]

Discovery

Upsilon Andromedae c was detected by measuring variations in its star's radial velocity as a result of the planet's gravity. This was done by making precise measurements of the Doppler shift of the spectrum of Upsilon Andromedae A. At the time of discovery, Upsilon Andromedae A was already known to host one extrasolar planet, the hot Jupiter Upsilon Andromedae b, however by 1999 it was clear that the inner planet could not explain the velocity curve.

In 1999, astronomers at both San Francisco State University and the Harvard-Smithsonian Center for Astrophysics independently concluded that a three-planet model best fit the data.[7] The two new planets were designated Upsilon Andromedae c and Upsilon Andromedae d.

Orbit and mass

Like the majority of long-period extrasolar planets, the orbit of Upsilon Andromedae c is eccentric, more so than any of the major planets in the Solar System (including Pluto).[8] If placed in the Solar System, Upsilon Andromedae c would lie between the orbits of Earth and Venus.

The high orbital eccentricity may be the result of gravitational perturbations from the planet Upsilon Andromedae d. Simulations suggest that the orbit of Upsilon Andromedae c returns to its original circular state roughly once every 9,000 years.[9]

One proposal is that interactions between Upsilon Andromedae d and a (now lost) outer planet moved Upsilon Andromedae d into an orbit closer to the star, where it gradually caused the orbit of Upsilon Andromedae c to become eccentric. If so, the rogue planet would have had to eject immediately.[10]

A limitation of the radial velocity method used to detect Upsilon Andromedae c is that the orbital inclination is unknown, and only a lower limit on the planet's mass can be obtained. However, by combining radial velocity measurements from ground-based telescopes with astrometric data from the Hubble Space Telescope, astronomers have determined the orbital inclination as well as the actual mass of Upsilon Andromedae c, which is about 13.98 times the mass of Jupiter.[2] The mutual inclination between c and d is 29.9 degrees.[2]

Characteristics

Given the planet's high mass, it is likely that Upsilon Andromedae c is a gas giant with no solid surface. Since the planet has only been detected indirectly through observations of its star, properties such as its radius, composition, and temperature are unknown.

Since its actual mass is approximately 14 times that of Jupiter, and its star's metallicity is similar to that of the Sun, Upsilon Andromedae c may actually be a small brown dwarf.

Trivia

• The planet was given the moniker "Stampy" in the Xkcd strip "Exoplanet names" in August, 2013.[11]

See also

• Eccentric Jupiter

References

1. Ligi, R.; et al. (2012). "A new interferometric study of four exoplanet host stars : θ Cygni, 14 Andromedae, υ Andromedae and 42 Draconis". Astronomy & Astrophysics. 545: A5. arXiv:1208.3895. Bibcode:2012A&A...545A...5L. doi:10.1051/0004-6361/201219467.
2. McArthur, Barbara E.; et al. (2010). "New Observational Constraints on the υ Andromedae System with Data from the Hubble Space Telescope and Hobby Eberly Telescope" (PDF). The Astrophysical Journal. 715 (2): 1203. Bibcode:2010ApJ...715.1203M. doi:10.1088/0004-637X/715/2/1203.
3. NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
4. NameExoWorlds The Process
5. Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
6. NameExoWorlds The Approved Names
7. Butler, R. Paul; et al. (1999). "Evidence for Multiple Companions to υ Andromedae". The Astrophysical Journal. 526 (2): 916–927. Bibcode:1999ApJ...526..916B. doi:10.1086/308035.
8. Butler, R. P.; et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal. 646 (1): 505–522. arXiv:astro-ph/0607493. Bibcode:2006ApJ...646..505B. doi:10.1086/504701. (web version)
9. Ford, Eric B.; et al. (2005). "Planet-planet scattering in the upsilon Andromedae system". Nature. 434 (7035): 873–876. arXiv:astro-ph/0502441. Bibcode:2005Natur.434..873F. doi:10.1038/nature03427. PMID 15829958.
10. Rory Barnes; Richard Greenberg (2008). "Extrasolar Planet Interactions". arXiv:0801.3226v1 [astro-ph].
11. "Exoplanet Names".