CD-49 13515 / Gl 832

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-49 13515's proximity to Sol and the discovery of at least on planet around this otherwise dim red dwarf, the system has been an object of high interest among astronomers. CD-49 13515 has been selected as a target star by 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 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 832 or Gliese (or Gl) 832, it was probably first catalogued as CD-49 13515 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-49 13515	0.0	...	...	...	149,000	47-52	...	...	0.49
Inner H.Z. Edge?	0.130	25.5	0.0	?	...	...	...	...	...
Planet "c"	~0.163	35.7	0.18	?	=>5.4	>1	...	...	...
Outer H.Z. Edge?	0.237	62.8	0.0	?	...	...	...	...	...
Planet "b"	3.4	9.4	0.12	?	203	~10	...	...	...

The Star

CD-49 13515 is a red dwarf star of spectral and luminosity type M1.5-3.0 V. This star has been estimated to have around 45 +/- 0.05 percent of Sol's mass (Bailey et al, 2008), 43 to 48 percent of its diameter (NASA Star and Exoplanet Database, as derived from the power law formula of Kenneth R. Lang, 1980; and Pasinetti-Fracassini et al, 2001; and Johnson and Wright, 1983, page 699), and about 0.7 percent of its visual luminosity and 2.8 percent of its bolometric luminosity (NASA Star and Exoplanet Database, as derived from the exponential formula of Kenneth R. Lang, 1980). It is chromospherically quiescent and appears to have only around 49 percent of Sol's abundance of iron relative to hydrogen (Bonfils et al, 2005a). Useful star catalogue numbers for CD-49 13515 include: Gl 832, Hip 106440, HD 204961, CP(D)-49 11439, LHS 3685, LTT 8573, LFT 1640, LPM 787, L 354-89, Sm 83, and 2MASS J21333397-4900323.

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-49 13515 , even accounting for infrared heating. According to the discoverers of planet c, the conservative habitable zone for a planet of five Earth-masses lies between 0.130 and 0.237 AU (Wittenmyer et al, 2014; and Kopparapu et al, 2014). This would be well within the orbital distance of Mercury in the Solar System. At planet c's 0.16-AU distance from its host star, it may develop a tidally locked, synchronous orbit around its host star.

Planet "c"

On June 21, 2014, a team of astronomers submitted a preprint which revealed their detection of a super-Earth around CD-49 13515 (or Gl 832). Designated "c" after a previously discovered Jupiter-class planet b in a cold outer orbit, planet c has about 5.4 +/- 1.0 Earth-masses, an orbital period of 35.68 +/- 0.03 days at a semi-major axis of 0.163 +/- 0.006 AU, an orbital eccentricity of e= 0.18 +/- 0.13, and an orbital distance near the inner edge of its host star's habitable zone. If it has an Earth-like terrestrial atmosphere, planet c may have Earth-like temperatures with possibly with large seasonal shifts, given a similar terrestrial atmosphere, but a denser atmosphere as would be expected for massive super-Earths could easily make the planet too hot for life and more akin to a super-Venus instead (Sci-News.com, June 29, 2014; Astronomy Picture of the Day; and Wittenmyer et al, 2014).

Efrain Morales Rivera,
ASC, PHL, UPR Arecibo


Larger and jumbo composite image.


Planet "c" appears to be a super-Earth
with sufficient mass to attract a dense
atmosphere and so may resemble a hot
super-Venus (more).

Planet "b"

NASA, Cassini-Huygens Mission
to Saturn and Titan


Larger image.


Planetary candidate "b"
ia massive enough to be
a gas giant like Jupiter
(shown here with Europa).

On September 8, 2008, a team of astronomers (Jeremy Bailey, R. Paul Butler, G.C. Tinney, Hugh R.A. Jones, Simon O'Toole, Brad D. Carter, and Geoffrey W. Marcy) submitted a paper for publication on the discovery of a Jupiter-class planet in orbit around this dim star (Bailey et al, 2008). The planetary companion has at least 64 percent (+/- 0.06) of Jupiter's mass (or 203 Earth-masses). Moving around CD-49 13515 at an average distance (semi-major axis) of 3.4 +/- 0.4 AUs, planet b's orbit is completed within 9.4 years (3,416 +/- 131 days), with an eccentricity (e= 0.12 +/- 0.11) within the Main Asteroid Belt in the Solar System.

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