Gl 777 / HR 7670 / BD+29 3872 ABab

Many astronomers now refer to this star by its designation in the famous Gliese Catalogue of Nearby Stars (CNS, now ARICNS database) of Wilhelm Gliese (1915-93), who was a longtime astronomer at the Astronomiches Rechen-Institut at Heidelberg (even when it was at Berlin). The star was included in the third version of the catalogue that was updated with Hartmut Jahreiss (also at (ARI) as "CNS3" in 1991. As a relatively bright star in Earth's night sky, however, Star A is also catalogued as Harvard Revised (HR) 7670, a numbering system derived from the 1908 Revised Harvard Photometry catalogue of stars visible to many Humans with the naked eye. The HR system has been preserved through its successor, the Yale Bright Star Catalogue -- revised and expanded through the hard work of E. Dorrit Hoffleit and others.

Gl 777, however, may have been first designated as BD+29 3872, in a catalogue by Friedrich Wilhelm August Argelander (1799-1875) in 1863 on the position and brightness of 324,198 stars between +90° and -2° declination that were measured over 11 years from Bonn, Germany, made with his assistants Eduard Schönfeld (1828-1891) and Aldalbert Krüger (1832-1896), which became famous as the Bonner Durchmusterung ("Bonn Survey") abbreviated as BD. The BD and the later Cordoba Durchmusterung (CD) that was surveyed from Argentina were greatly expanded and extended into the modern age of photographic surveys with the subsequent creation of the Cape Photographic Durchmusterung from South Africa. (More discussion on star names and catalogue numbers is available from Alan MacRobert at Sky and Telescope and from Professor James B. Kaler's Star Names.)

Gl 777 A

Gl 777 A is a yellow-orange dwarf star of spectral and luminosity type G6-8 V-IV+. The star has about 96 percent of Sol's mass (Santos et al, 2003), around 1.3 to 1.74 times its diameter (Johnson and Wright, 1983, page 695), and 1.13 times of its visual luminosity Geneva data). The star may be 1.78 times as enriched than Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (initial data; Santos et al, 2003; and J.B. Hearnshaw, 1974). With a high velocity and relatively high age (J.B. Hearnshaw, 1974), Gl 777 A appears to be unusually bright and large for its spectral type and may be evolving off the main sequence as a subgiant star. It may have a binary companion (Olin Jeuck Eggen, 1956, pp. 409 and 427), actually a pair of dim binary companions (Stars Bab) located over 2,800 AUs away; however, NASA's NStar Database suggests that the binary pair Star Bab may lie as far as four light-years away (and the pair would not be gravitationally bound to Star A). Useful catalogue numbers and designations for the star include: HR 7670, Gl 777 A, HIP 98767, BD+29 3872, HD 190360, SAO 88133, LHS 3510, LTT 15867, LFT 1515, and Wo or GJ 9683.

Planet "b"

NASA

Cassini-Huygens Mission
to Saturn and Titan


Larger image.


Planetary candidate "b" or "A1" appears to
be a gas giant that is about the same size
as Jupiter (shown here with Europa).

On June 13, 2000, a team of astronomers (Dominique Naef, Francisco Pepe, Michel Mayor, Nuno C. Santos, Didier Queloz, and Stephane Udry) announced the discovery of a Jupiter-class planet around Gl 777 A using highly sensitive radial-velocity methods (press release and initial data). According to the latest radial velocity data, planet "b" (or "A1") has 1.50 +/- 0.13 times Jupiter's mass. It moves around Gl 777 A at an average distance that has been revised to 3.9 +/- 0.2 AUs (a semi-major axis around the outer margins of the Main Asteroid Belt in the Solar System) but with an highly eccentric orbit (e=0.36 +/- 0.03) that takes around 7.9 years (2,891 days +/- 85 days) to complete (Vogt et al, 2005; and Extrasolar Planets Encyclopaedia).

Planet "c"

JPL, NASA



Larger image.



Planetary candidate "c" may be
rocky or gaseous like Neptune,
with a high temperature, given
its inner orbit.

In January 2005, another team of astronomers reported possibly detecting second planet of Neptune size in a highly circular, inner "torch" orbit that is completed in only 17.1 days (e=0.01 +/- 0.1). Planet "c" has around 18.1 +/- 4.8 Earth-masses and orbits Star A at an average distance of only 0.128 +/- 0.002 AUs. While it is possible that this "detection" results from the passage of surface "features across the visible hemispere of the rotating star" which can be verified with new photometry, the discovery team believed that an inner planet with the announced characteristics remained the best explanation for the reduction in residuals of the radial velocity variations detected (Vogt et al, 2005, in pdf; and Extrasolar Planets Encyclopaedia).

The orbit of an Earth-like planet (with liquid water) around GJ 777 A may be centered around 1.1 AU -- between the orbital distances of Earth and Mars in the Solar System -- with an orbital period around 430 days (1.2 years). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.) Astronomers are hoping to use NASA's 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 Gl 777 A. 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.

Gl 777 Ba

NASA -- larger image

Gl 777 Ba and Bb are dim red dwarf stars, like
Gliese 623 A (M2.5 V) and B (M5.8Ve) at lower right.