CD-27 14659 / HR 7722 / Gl 785

JPL, CalTech, NASA


Larger illustration


Astronomers have identified
CD-27 14659 as a prime target
for the Terrestrial Planet Finder
(TPF), now postponed indefinitely.

Although the star is now commonly referred by some astronomers as GJ 875 or Gliese (or Gl) 875, the star was originally designated as CD-27 14659 in a visual survey of southern stars begun in 1892 at the Astronomical Observatory of Cordoba in Argentina under the direction of its second director John M. Thome (1843-1908). Thome died before the completion of this southern sky atlas in 1914, when 578,802 stars from declination -22° to -90° were published as the Cordoba Durchmusterung ("Survey"). The "CD" is an extension of an older 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 CD were greatly expanded and extended into the modern age of photographic surveys with the subsequent creation of the Cape Photographic Durchmusterung from South Africa.

As a relatively bright star in Earth's night sky, the star is catalogued as Harvard Revised (HR) 7722, 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 (1907-2007) and others. CD-27 14659 is also listed as HD 192310 in the Henry Draper (1837-82) Catalogue with extension (HDE), a massive photographic stellar spectrum survey carried out by Annie Jump Cannon (1863-1941) and Edward Charles Pickering (1846-1919) from 1911 to 1915 under the sponsorship of a memorial fund created by Henry's wife, Anna Mary Palmer. (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.)

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	Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass (Earths)	Diameter (Earths)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
HR 7722	0.0	...	...	...	266,000	81-100	...	...	0.78-1.2
Planet "b"	0.32	0.20	0.13	90?	=>21.6	3-4?	...	...	...
Inner H.Z. Edge?	0.439	0.325	0	90?	...	...	...	...	...
Outer H.Z. Edge?	0.878	0.920	0	90?	...	...	...	...	...
Planet "c"	1.18	1.44	0.32	90?	~24	3-4?	...	...	...

The Star

CD-27 14659 is a main-sequence orange-red dwarf star of spectral and luminosity type K3 V, that has been class as orange as K0. It may have around 78 to 80 percent of Sol's mass (Pepe et al, 2011, Table 3; and Howard et al, 2010, for Gl 785 on Table 1, page 3), 68 to 84 percent of its diameter (Howard et al, 2010, for Gl 785 on Table 1, page 3; and Johnson and Wright, 1983, page 695), and 30 to 39 percent of its bolometric luminosity (Pepe et al, 2011, Table 3; Howard et al, 2010, for Gl 785 on Table 1, page 3; and the NASA Star and Exoplanet Database, derived from the exponential formula of Kenneth R. Lang, 1980). It appears to be 78 to 120 percent as enriched as Sol in elements heavier than hydrogen ("metals") based on its abundance of iron (Pepe et al, 2011, Table 3; Howard et al, 2010, for Gl 785 on Table 1, page 3; and Cayrel de Strobel et al, 1991, page 307). CD-27 14659 appears to be a chromospherically inactive star (Howard et al, 2010), with a rotational period of 47.67 +/- 4.88 days (Pepe et al, 2011, Table 3). It may be 7.5 to 8.9 billion years old based on chromospheric activity and rotational period alone (Mamajek et al, 2008, see HD 192310 in Table 13, page 1289), similar to other estimates of 7.8 to 8.7 billion years (Pepe et al, 2011, Table 3; and Lachaume et al, 1999; in Beichman et al, 2006, see HD 192310 in Table 1) but less than estimates of 9.3 to 10.2 summarized in Lawler et al, 2009 (of Valenti and Fischer in 2005 and Ibukiyama and Arimoto in 2002). No strong evident of a warm inner or cold outer, dust disk has been detected (Lawler et al, 2009; Kóspál et al, 2009; Beichman et al, 2006, see HD 192310 in Table 2; and Laureiji et al, 2002). CD-27 14659 is a Catalogue of Suspected Variable Star designated as CSV 101960 and a New Suspected Variable star designated as NSV 12933. Useful star catalogue numbers for CD-27 14659 include: HR 7722, Gl 785, Hip 99825, HD 192310, CP(D)-27 6972, SAO 189065, LHS 488, LTT 8009, LFT 1535, and LPM 731.

Habitable Zone

Revised calculations performed using a particular climate model for the NASA Star and Exoplanet Database indicate that the inner edge of Star A's habitable zone could be located at around 0.439 AUs from the star, while the outer edge lies farther out at around 0.878 AU. The calculations suggest that the of the habitable zone is centered around 0.621 AU, between the orbital distances of Mercury and Venus in the Solar System. An Earth-type in such a water-zone orbit would probably would have a period of around 200 days or just over half an Earth year.

Planetary System

CD-27 14659 B?

According to the Astronomiches Rechen-Institut at Heidelberg's ARICNS entry for Gl 785, CD-27 14659 is suspected of having a spectroscopic companion star.

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