Difference between revisions of "85 Pegasi"

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This multiple star system is located about 40.5 light-years from Sol. It lies near the northeastern edge of the constellation Pegasus, the Winged Horse. It is believed to consist of three stars A, Ba and Bb.

85 Pegasi A

The primary is now believed to be a yellow-orange main sequence dwarf star of spectral and luminosity type G5 Vb, although it was once classed as yellow as G2^[1]. This star may have as much as 88 percent of Sol's mass^[2], 91 percent of its diameter^[3], and about 61 percent of its luminosity. Based on measurements of the star's abundance of iron, 85 Pegasi A may be 58 to 75 percent as enriched as Sol with elements heavier than hydrogen ("metallicity") ^[2][4][5].

According to relatively recent measurements^[6] found in the Sixth Catalog of Orbits of Visual Binaries, Star A and the close binary pair Bab are separated by an "average" distance of about 10.3 AUs -- just beyond the orbit of Saturn in the Solar System -- in an elliptical orbit (e= 0.38) of 26.28 years. Hence, Star A and the Bab pair get as close as 6.4 AUs and as far away as 14.2 AUs. When observed from Earth, the inclination of their orbit is about 49 degrees.

The orbit of an Earth-like planet with surface water around this ancient star's liquid water zone would have to be centered around 0.78 AU -- between the orbits of Venus and Earth in the Solar System. At that distance from Star A, it would have an orbital period around 270 days or roughly three-fourths of an Earth year.

85 Pegasi Ba

This star is now believed to be a orange-red main sequence dwarf of spectral and luminosity type K7 V^[1]. It may have about 55 percent of Sol's mass^[2], 67 percent of its diameter^[3], and around 0.5 percent of its luminosity. Astronomers are now reasonably certain that Star Ba has a very dim, low-mass, red dwarf companion Bb in a tight orbit -- possibly within two AUs^[2].

The orbit of an Earth-like planet around Star Ba in the liquid water zone would have to be centered around 0.2 AU -- around half of Mercury's orbital distance around Sol -- with an orbital period around 52 days. However, if the existence of a relatively close, stellar companion (see Star Bb below) around Ba is confirmed, then a planetary orbit in Star Ba's water zone may not be stable if Star Bb lies substantially less than one AU of Star Ba.

85 Pegasi Bb

This close companion of Star Ba is probably a main sequence, red dwarf star of spectral and luminosity type M V. It may have about 11 percent of Sol's mass^[2]. A stable orbit for this dim companion star may exist within two AUs of Ba.

(Data from SolStation.com)

Notes

1. ↑ ^{1.0 1.1} (ten Brummelaar et al, 2000)
2. ↑ ^{2.0 2.1 2.2 2.3 2.4} (Fernandes et al, 2002)
3. ↑ ^{3.0 3.1} (Johnson and Wright, 1983, page 705)
4. ↑ (Cayrel de Strobel et al, 1991, page 312)
5. ↑ (Wallerstein and Helper, 1958)
6. ↑ (Staffan Soderhjelm, 1999)