CD-46 11540 / Gl 674

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.

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 are available from the SIM Teams).

JPL, CalTech, NASA



Larger illustration of NASA's
Space Interferometry Mission.



Astronomers have identified
CD-46 11540 as a prime target
for NASA's optical SIM mission.

The Star

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.

Planet "b"

JPL, NASA



Larger image.



It is not yet known whether
planetary candidate "b" is
rocky or gaseous -- like
Neptune.

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) similar to Mercury's orbit in the Solar System.

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 CD-46 11540, at around 0.13 AU) -- accounting for infrared heating. Hence, the orbit is likely to be disrupted by the presence of the recently discovered Neptune-class planet b at an inner even closer orbital distance of only 0.039 AUs. (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)