BD-05 5715 / Gl 849

Although the star is now commonly referred by some astronomers as GJ 849 or Gliese (or Gl) 849, it was probably first designated as BD-05 5715, in a catalogue that was originally published in 1863 by Friedrich Wilhelm August Argelander (1799-1875) on the position and brightness of 324,198 stars between +90° and -2° declination that were measured over 11 years from Bonn, Germany with his assistants Eduard Schönfeld (1828-1891) and Aldalbert Krüger (1832-1896). The catalogue became famous as the Bonner Durchmusterung ("Bonn Survey") and is typically abbreviated as BD. It was later expanded and extended during the early 20th Century with the Cordoba (observed from Argentina) then the Cape Photographic Durchmusterung (observed from South Africa).

Due to BD-05 5715's relative proximity to Sol and the discovery of a planetary companion, the system has been suggested for selection as a target star for NASA's optical Space Interferometry Mission (SIM). The mission will attempt to detect planets as small as three Earth-masses within two AUs of each star.

JPL, CalTech, NASA



Larger illustration of NASA's
Space Interferometry Mission.



The discoverers of planet "b"
have suggested that BD-05 5715
become a prime target for NASA's
optical SIM mission.

The Star

BD-05 5715 is a red dwarf star of spectral and luminosity type M3.5 V. This star has been estimated to have around 49 +/- 5 percent of Sol's mass (Butler et al, 2006; Delfosse et al, 2000; and Henry and McCarthy, 1993), 45 percent of its diameter (Pasinetti-Fracassini et al, 2001; and Johnson and Wright, 1983), and about 0.43 percent of its visual luminosity. It may be more enriched than Sol, with 1.4 +0.8/-0.5 times Sol's abundance of iron relative to hydrogen (Butler et al, 2006; Bonfils et al, 2005a; and Sandy K. Leggett, 1992). The star's low chromospheric activity and slow rotation are consistent with a middle–age dwarf that is older than three billions (Butler et al, 2006; and Andrew West, private communication with Bulter et al). Useful star catalogue numbers for BD-05 5715 include: Gl 849, Hip 109388, G 27-16, LHS 517, LTT 8889, LFT 1689, LPM 814, Vys/MCC 73, and Wolf 1329.

Planet "b"

NASA

Cassini-Huygens Mission
to Saturn and Titan


Larger image.


Planetary candidate "b" appears to
be a gas giant with at least 82 percent of
Jupiter's mass (shown here with Europa).

Between October 6 and 26, 2006, a team of astronomers submitted a paper on the discovery of a Jupiter-class planet in a 5.2-year orbit around this dim star, with indications of a second planetary companion (Butler et al, 2006 -- more below). The planetary companion has at least 82 percent of Jupiter's mass. Moving around BD-05 5715 at an average distance (semi-major axis) of 2.35 AUs, planet b's highly circular orbit (e= 0.06 +/- 0.09) takes 5.16 +/- 0.36 years to complete.

In order to be warmed sufficiently have liquid water at the surface, an Earth-type rocky planet would have to be located very close to such a cool and dim red dwarf star like BD-05 5715, at around 0.066 AU) -- not accounting for infrared heating. At such a close distance, such a planet can easily become tidally locked -- with one side in perpetual day -- and race around the star in less than 8.8 days. (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)