61 Virginis

Steven Vogt,
UCSC,




Larger map.




61 Virginis
is located
southwest of
the bright
type-B binary
Spica, Alpha
Virginis, in
Constellation
Virgo (more).

On December 14, 2009, a team of astronomers announced the discovery of one super-Earth and two Neptune-class planets (with at least 5, 18, and 24 Earth-masses, respectively) in moderately circular, inner orbits around 61 Virginis with periods of 4.2, 38.0, and 124.0 days (U.C. Santa Cruz news release; AAO press release; Keck press release; the Lick-Carnegie Exoplanet Survey Team's "Systemic Console;" and Vogt et al, 2009 -- more below). The super-Earths is one of the first two found around a spectral type G star, like our Sun, Sol. According to astronomers working with the Spitzer Space Telescope, a thick belt of dust (that is probably being generated by collisions between Edgeworth-Kuiper-Belt-type, icy objects) lies some 96 to 195 AUs out from the star (Bryden et al, 2009; Tanner et al, 2009, see HD 115617; and Vogt et al, 2009 -- more below).

U. New South Wales,
Carnegie Institution/DTM,



Larger and jumbo
illustrations.




Two super-Earths and a
Neptune-class planet
were discovered
around 61 Virginis
in 2009 (more).

The Star

61 Virginis is a yellow-orange main sequence dwarf of spectral and luminosity type G5-6 V, with about 92 to 96 percent of Sol's mass (95 percent using the isochrone mass estimate of Valenti and Fischer, 2005; and NASA Star and Exoplanet Database, based on David F. Gray, 1992), 94 to 98 percent of its diameter (96 percent for Valenti and Fischer, 2005; Johnson and Wright, 1983, page 677; and NASA Star and Exoplanet Database, based on Kenneth R. Lang, 1980), and around 78 percent of its visual luminosity and nearly 81 percent of its theoretical bolometric luminosity, with infrared radiation (Sousa et al, 2008; Valenti and Fischer, 2005; NASA Star and Exoplanet Database, based on Kenneth R. Lang, 1980). The star may be as much as 1.1 times as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (NASA Star and Exoplanet Database from Valenti and Fischer, 2005; and Cayrel de Strobel et al, 1991, page 295). It appears to be "an old, inactive star" of 6.3 to 9.0 billion years in age (Vogt et al, 2009; Takeda et al, 2007; and Valenti and Fischer, 2005). Over 16 years of photometric observations indicate that 61 Virginis is photometically stable (Vogt et al, 2009). Useful star catalogue numbers for the star include: 61 Vir, HR 5019, Gl 506, Hip 64924, HD 115617, BD-17 3813, SAO 157844, FK5 1345, LHS 349, LTT 5111, LPM 467, LFT 990, and GC 18007.

Sky View, NASA



Larger false-color image.



61 Virginis is a little
smaller, less massive,
and dimmer than our
Sun, Sol.

Debris Disk

Planetary System

Prior to 2009, small but significant variations in radial velocity had been detected which may have been caused by a substellar companion of one to nine Jupiter-masses with an orbital period of 50 years of less (Campbell et al, 1988, pages 904, 906, and 919). A subsequent radial velocity study also failed to detect a brown dwarf sized companion (with 20 to 80 times the mass of Jupiter) within 10 AUs of 61 Virginis (Murdoch et al, 1993). A few years later, even a brown dwarf or Jupiter- or Saturn-class planet in a inner orbit was discounted with further observations (Cumming et al, 1999).

The orbit of an Earth-like planet (with liquid water) around this star would be centered around 0.9 AU -- inside the orbital distance of Earth in the Solar System -- with an orbital period of around 317 days, or about 87 percent of an Earth year. Astronomers are hoping to use NASA's planned Terrestrial Planet Finder (TPF) and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around 61 Virginis. As currently planned, the TPF will include two complementary observatory groups: a visible-light coronagraph to launch around 2014; and a "formation-flying" infrared interferometer to launch before 2020, while Darwin will launch a flotilla of three mid-infrared telescopes and a fourth communications hub beginning in 2015. (See an animation of the planetary orbits, dust disk, and potentially habitable zone around 61 Virginis, with a table of basic orbital and physical characteristics.)