CD-27 14659 / HR 7722 / Gl 785
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© Torben Krogh & Mogens Winther,
(Amtsgymnasiet and EUC Syd Gallery,
student photo used with permission)
CD-27 14659 is an orange-red
dwarf star, like Epsilon Eridani
at left center of meteor. (See a
2MASS Survey image of
CD-27 14659 from the NASA
Star and Exoplanet Database.)
On August 17, 2011, astronomers associated with the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the European Southern Observatory (ESO) uploaded a pre-print that revealed the discovery of a second planet of around 24 +/- 5 Earth-masses in an outer orbit, while downsizing the minimum size of the previously discovered inner planet to 16.9 +/- 0.9 Earth-masses (Pepe et al, 2011, Table 6).
On November 1, 2010, a team of astronomers revealed the detection of a Neptune-class planet in an inner orbit with a minimum of 21.6 Earth-masses around CD-27 14659 (Howard et al, 2010 -- more below).
CD-27 14659 is located about 28.8 light-years (ly) away from our Sun, Sol, in the southwest corner (20:15:17.4:-27:1:58.7, ICRS 2000.0) of Constellation Capricornus, the She-Goat -- west of Omega and Phi Capricorni, northeast of Ascella (Zeta Sagittarii) and southeast of M75 (NGC 6864). The star may be visible to many Humans without a telescope, but it may have a spectroscopic companion star, that is currently not even visible with a telescope. Although CD-27 14659 became one of the top 100 target stars for NASA's proposed Terrestrial Planet Finder (TPF), the project was 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.)
|Inner H.Z. Edge?||0.439||0.325||0||90?||...||...||...||...||...|
|Outer H.Z. Edge?||0.878||0.920||0||90?||...||...||...||...||...|
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.
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.
Planet "b" - On November 1, 2010, a team of astronomers working with the NASA-UC Eta-Earth Survey revealed the detection of a Neptune-class planet in an inner orbit. In 2011, the planet was estimated to have a revised minimum of 16.9 +/- 0.9 Earth-masses around CD-27 14659, using radial-velocity measures from the Keck Observatory's High Resolution Echelle Spectrometer (HIRES). Planet "b" completes an inner orbit around CD-27 14659 in 74.72 +/- 0.10 days (just over one fifth of an Earth-year) at an average orbital distance of 0.32 +/- 0.005 AU. Its orbit is mildly eccentric, where e = 0.13 ± 0.04 (Pepe et al, 2011, Table 6; and Howard et al, 2010, Table 3, page 4).
Planet "c" - On August 17, 2011, astronomers associated with the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the European Southern Observatory (ESO) uploaded a pre-print that revealed the discovery of a second Neptune-class planet of around 24 +/- 5 Earth-masses in an outer orbit, with a minimum of 24 +/- 5 Earth-masses around CD-27 14659. Planet "c" completes an inner orbit around CD-27 14659 in 525.8 +/- 9.2 days (more than 1.4 Earth-years) at an average orbital distance of 1.18 +/- 0.025 AU. Its orbit is moderatesly eccentric, where e = 0.32 ± 0.11, and the astronomers' models fixed the orbital inclination at 90 degrees (Pepe et al, 2011, Table 6; and Howard et al, 2010, Table 3, page 4).
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.
The following star systems are located within 10 light-years, plus more bright stars within 10 to 20 light-years, of CD-27 14659.
|Star System||Spectra &|
|AU Microscopii||M0-1 Ve||5.5|
|AC+20 76187||DA /VII||6.0|
|AT Microscopii AB||M4.5 Vpe |
|HJ 5173 AB||K3 V |
|* plus bright stars *||. . .|
|Deneb Algedi AB||A5-7 IVm |
|Delta Pavonis||G5-8 V-IV||18|
|HD 172051 / HR 6998||G4-5 V||19|
|HR 7898||G8-K0 V||19|
|L 489-58 AB||G0 IV|
|41 Arae AB / HR 6416 AB||G8-K0 V |
|Psi Capricorni||F4-5 V||20|
Up-to-date technical summaries on these stars can be found at: Jean Schneider's Extrasolar Planets Encyclopaedia; the Astronomiches Rechen-Institut at Heidelberg's ARICNS, the NASA Star and Exoplanet Database, and the SIMBAD Astronomical Database. Additional information may be available at Roger Wilcox's Internet Stellar Database.
There appear to be many possible origins for Constellation Capricornus. According to some, it may represent the Shepherd-god Pan of the Ancient Greeks. Others say that he was quite a different god, Aegipan. For more information on the constellation and an illustration, go to Christine Kronberg's Capricornus. For another illustration, see David Haworth's Capricornus.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
Note: Thanks to Spike Valance for notifying us of a planet detection around this star.
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