Difference between revisions of "Gliese 570"

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Gliese 570 is a triple star system and is located 19.3 (ly) away from Sol. It lies in the southwestern part of the constellation Libra, the Scales. According to the new Sixth Catalog of Orbits of Visual Binaries, Star A and the close binary pair BC have a wide average separation of about 190 AUs (semi-major axis of 32.34"), moving in an eccentric orbit (e= 0.20) that lasts some 2,130 years and is inclined from the perspective of an observer on Earth at 72.53°^[1]. The triple star system is said to exhibit moderate chromospheric activity^[2]. It has a galactic motion (eccentricity of 0.195 and inclination of sin i = 0.553) that is consistent with an assignation to the old disk population^[3].

Gliese 570 A

This main sequence, orange-red dwarf (K4-5 Ve) may have just over three fourths (76 percent) of Sol's mass ^[4], about 77 percent of its diameter,^[5], only 15.6 percent of its luminosity, and a rotational period of 48.3 days. The star appears to be as enriched (102 percent) as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron ^[6].

Star A's late spectral type and dim luminosity puts it possibly close to the lower limit of habitability for (multicellular) Earth-type plant and animal life, given the redness of its light and the increased risk of tidal locking from the closeness of the orbit necessary for liquid water on a planetary surface. The distance from Star A where an Earth-type planet would be "comfortable" with liquid water is centered around 0.40 AU -- within the orbital distance of Mercury in the Solar System. At that distance from the star, such a planet would have an orbital period of 104 days, or less than a third of an Earth year.

Gliese 570 B

This is a red dwarf of spectral and luminosity type M1 V. It has about 55 percent of Sol's mass ^[4], perhaps less than 65 percent of its diameter, and 1.9 percent of its brightness. The star is a double-lined spectroscopic binary. Speckle interferometry resolved that Star B has a stellar companion "C" (with a possible mass ratio of 0.71 +/- 0.02)^[2].

According to the new Sixth Catalog of Orbits of Visual Binaries, the B and C pair of stars have an average separation around 0.79 AUs (semi-major axis of 0.133" at a distance of 19.26 ly) in a highly eccentric orbit (e= 0.765) lasting about 309 days with an inclination from the perspective of an observer on Earth of about 110° ^[7][2]. For Star B, the water zone orbit lies near 0.14 AU. Assuming that Star C does not perturb its orbital stability, a planet in Star B's water zone would have a period of about 25 days. However, tidal locking of such a closely orbiting planet would resulting in perpetual day on one side and perpetual night on the other.

Gliese 570 C

A rather dim red dwarf, Star C is of spectral and luminosity type M3 V, with only about 35 percent of Sol's mass ^[4] and slightly over 0.3 percent of its visual luminosity. It appears to have a high rotational velocity^[2].

For Star C, the water zone orbit lies near 0.056 AU. Assuming that Star B does not perturb its orbital stability, a planet in Star C's water zone would have a period of about 8.2 days. However, tidal locking of such a closely orbiting planet would resulting in perpetual day on one side and perpetual night on the other.

Gliese 570 d

On January 15, 2000, astronomers at the Infrared Processing and Analysis Center^[8] on the Caltech campus in Pasadena, California announced that they had found one of the coolest brown dwarfs then known around Gliese 570 ABC. The object was observed at a wide separation of more than 1,500 AUs (258.3"+/-0.4" at 19.26 ly) from the triple star system. It has an estimated mass of 50 +/- 20 Jupiters^[9].

The status of object "d" as a methane brown dwarf was confirmed by taking its spectral fingerprint with the 4-meter telescope at the Cerro Tololo Interamerican Observatory in Chile. Found as one of 12 objects discovered since 1995 in the 2-Micron All Sky Survey^[10], the surface temperature of this substellar object was found to be a relatively cool 900° F (500° C), compared with Sol's 10,000° F (5,500°C). Gliese 570 d is significantly cooler (by 160° K) and less luminous than any other known brown dwarf, including the prototype "T" dwarf, Gliese 229 b. Classed as T7-8 V, it is estimated to be between two and five billion years old^[11].

Notes

1. ↑ (Alan Hale, 1994, pp. 312, 314, and 317; and Duquennoy and Mayor, 1988)
2. ↑ ^{2.0 2.1 2.2 2.3} (Duquennoy and Mayor, 1988)
3. ↑ (Augensen and Buscombe, 1978; and Glenn J. Veeder, 1974)
4. ↑ ^{4.0 4.1 4.2} (RECONS)
5. ↑ (Alan Hale, 1994, page 320; and Soderblom et al, 1991)
6. ↑ (Cayrel de Strobel et al, 1991, page 297)
7. ↑ (Dmitri Pourbaix, 2000)
8. ↑ (IPAC)
9. ↑ (see Burgasser et al, 2000)
10. ↑ (a collaborative project between IPAC and the University of Massachusetts known as 2MASS)
11. ↑ (Geballe et al, 2001)