CD-46 11540 / Gl 674
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This star is located about 14.8 light-years (ly) away from our Sun, Sol, in the northwestern corner (17:28:39.9-46:53:42.7, ICRS 2000.0) of Constellation Ara, the Altar. Much dimmer and smaller than Sol, it is not visible to the unaided Human eye from Earth's surface. On January 9, 2007, a team of astronomers submitted a paper on the discovery of a Neptune-class planet in a tight orbit around this dim star (Bonfils et al, 2007 -- more below).
Due to CD-46 11540's proximity to Sol, the system has been an object of high interest among astronomers. The star has been selected as "Tier 1" target stars 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. (Some summary system information and images of CD-46 11540 may still be available from the SIM Teams), but the SIM project manager announced on November 8, 2010 that the mission was indefinitely postponed due to withdrawal of NASA funding.
Although the star is now commonly referred by some astronomers as GJ 674 or Gliese (or Gl) 674, it was probably first catalogued as CD-46 11540, 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.
|Inner H.Z. Edge?||0.128||27.9||0.0||?||...||...||...||...||...|
|Outer H.Z. Edge?||0.149||75.6||0.0||?||...||...||...||...||...|
CD-46 11540 is a red dwarf star of spectral and luminosity type M2.5-3.0 V, that was once classed as orange as K5 and as dim as a possible subdwarf (VI). This star has been estimated to have around 35 to 36 percent of Sol's mass (Delfosse et al, 2000; and RECONS), 41 to 43 percent of its diameter (Pasinetti-Fracassini et al, 2001; and Johnson and Wright, 1983), and about 1.6 percent of its bolometric luminosity (Bonfils et al, 2007). It may be much younger than Sol at around 550 +/- 450 million years old (Bonfils et al, 2007). The moderatively active star has a rotational period of 34.8 days based on the movement of an observed (and presumably large) starspot (Bonfils et al, 2007) and only around 52 percent of Sol's abundance of iron relative to hydrogen (Bonfils et al, 2005a). Useful star catalogue numbers for CD-46 11540 include: Gl 674, Hip 85523, CP(D)-46 8664, LHS 449, LTT 6942, LFT 1351, and LPM 645.
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 red dwarf star as cool and dim as CD-46 11540, even accounting for infrared heating. According to one type of model calculations performed by the NASA Star and Exoplanet Database, the inner edge of CD-46 11540's habitable zone should be located a quite close to the star, at an orbital distance of around 0.128 AU, while the outer edge is a a little farther out at around 0.249 AU. The distance from this star where a planet like Earth would have liquid water on its surface has been estimated to be around 0.188 AU (NASA Star and Exoplanet Database; and SIM) -- well 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 about 50 days, and it may develop a tidally locked, synchronous orbit around its host star. In addition, such a close is likely to be disrupted by the presence of the recently discovered Neptune-class planet b at an even closer orbital distance of only 0.039 AU from the host star.
On January 9, 2007, a team of astronomers (X. Bonfils, M. Mayor, X. Delfosse, T. Forveille, M. Gillon, C. Perrier, S. Udry, F. Bouchy, C. Lovis, F. Pepe, D. Queloz, N. C. Santos, J.-L. Bertaux) submitted a paper on the discovery of a sub-Neptune- or Uranus-mass planet in a tight orbit around this dim star, using the HARPS spectrograph on the European Southern Observatory's 3.6-meter telescope at La Silla, Chile (Bonfils et al, 2007). The planetary companion has at least 3.49 percent of Jupiter's mass (or 11.1 Earth-masses). Moving around CD-46 11540 at an average distance (semi-major axis) of only 0.039 AUs, planet b's orbit is completed within 4.694 +/- 0.007 days, with an eccentricity (e= 0.2 +/- 0.02) that is similar to that of Mercury's orbit in the Solar System.
The following star systems are located within 10 light-years of CD-46 11540.
|Star System||Spectra &|
|CD-44 11909||M3.5-5 V||1.8|
|L 205-128||M3.5-5 V||5.2|
|L 347-14||M4.5 V||6.7|
|CD-32 13297||M2 V||7.0|
|36 Ophiuchi 3?||K0-1 Ve |
|Ross 154||M3.5 Ve||7.7|
|CD-40 9712||M0-3 V||7.8|
|MLO 4 ABC||K3-4 V |
|BD-12 4523 AB||M3 V |
|CD-25 10553 AB||M3 V |
|Hip 72509||M V||9.5|
|Delta Pavonis||G5-8 V-IV||9.9|
|Epsilon Indi||K3-5 Ve||9.9|
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 Research Consortium on Nearby Stars (RECONS) list of the 100 Nearest Star Systems. Additional information may be available at Roger Wilcox's Internet Stellar Database.
Constellation Ara, the Altar, is located next to the celestial south pole. Ara is another of those constellations created by the Abbé [Abbot] Nicholas Louis de La Caille (1713-1762), who had the great honor of naming 15 of the 88 constellations by becoming the first astronomer to systematically observe the entire night sky by traveling to the Cape of Good Hope at the southern tip of Africa from 1750-54. For more information on stars and other objects in this Constellation and an illustration, go to Christine Kronberg's Ara. For another illustration, see David Haworth's Ara.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
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