CD-46 11540 / Gl 674

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,
now indefinitely postponed.

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.

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	Orbital Distance (a=AUs)	Orbital Period (P=days)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass (Earths)	Diameter (Earths)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
CD-46 11540	0.0	...	...	...	119,000	41-43	...	...	0.52
Planet "b"	0.039	4.7	0.2	?	>11.1	...	...	...	...
Inner H.Z. Edge?	0.128	27.9	0.0	?	...	...	...	...	...
Outer H.Z. Edge?	0.149	75.6	0.0	?	...	...	...	...	...

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.

Habitable Zone

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.

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

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