CD-60 1303 / HD 40307

Today, many astronomers refer to this star as HD 40307, as designated in the Henry Draper (1837-82) Catalogue with subsequent 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. However, it was probably first designated as CD-60 1303 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.

The Star

© Torben Krogh & Mogens Winther,


(Amtsgymnasiet and EUC Syd Gallery,
student photo used with permission)


HD 40307 is an orange-red
dwarf star, similar to Epsilon
Eridani at left center of meteor.
(See a 2MASS Survey image
of HD 40307 from the NASA
Star and Exoplanet Database.)

HD 40307 is an orange-red main-sequence dwarf star of spectral and luminosity type K2.5 V (Mayor et al, 2008). Taking into account HD 40307's sub-Solar metallicity (see below), the star is estimated to have around 77 percent of Sol's mass (Sousa et al, 2004; and Santos et al, 2001), around 68 percent of its diameter (NASA Star and Exoplanet Database, derived from Kenneth R. Lang, 1980), and 18.5 percent of its visual and around 24 percent of its bolometric luminosity (NASA Star and Exoplanet Database, derived from Kenneth R. Lang, 1980). It appears to be only 49 to 56 percent as enriched as Sol in iron relative to the abundance of hydrogen and only 37 percent as enriched as Sol in elements other than hydrogen, helium, and iron (Mayor et al, 2008; Gray et al, 2006; and Santos et al, 2001). HD 40307 appears to be around 6.1 +/- 1.6 billion years old (Barnes et al, 2009). It is a relatively inactive star with a rotational period of around 48 days (Mayor et al, 2008). Useful catalogue numbers and designations for the star include: HD 40307, Hip 27887, CD-60 1303, CP-60 508, and SAO 249388.

Planetary System

Unknown artist,
© ESO




Larger illustration
(with scale in AUs).




Three inner super-Earths
move in very tight orbits
around HD 40307 (more).

On June 16, 2008, a team of astronomers announced at the 2008 Extra Solar Super-Earths Workshop in France their discovery of three "super-Earth" class planets in tight orbits around this star (ESO press release; Barnes et al, 2009; and Mayor et al, 2009). Based on five years of radial-velocity observations as of June 2008, the innermost planetary candidate "b" has 4.2 times Earth's mass and completes its orbit around HD 40307 in only 4.3 days (Barnes et al, 2009; and Mayor et al, 2008 and 2009). Based on the drift of residual radial velocities, moreover, there may be a fourth sub-stellar object in the system (Mayor et al, 2008). Moving outwards, planet "c" has 6.7 Earth-masses and an orbital period of 9.6 days. Finally, planet "d" has 9.4 Earth-masses and an orbital period of 20.4 days. All three planets are assumed to have highly circular orbits at an orbital distance from HD 40307 that would be well within the orbit of Mercury in the Solar System.

Trent Schindler, NSF


Larger and jumbo illustrations
(more images and videos).


Planetary candidates "b," "c,"
and "d" may be rocky and have
atmospheres with clouds, like
Gliese 876 d, as imagined by
Schindler (more).

If you include infrared radiation, the orbit of an Earth-like planet with surface water would be centered beyond 0.4 AU -- outside the orbital distance of Mercury in the Solar System. Despite possible orbital eccentricity, planetary candidate "g" average orbit distance of around 0.6 AU should keep it wholly within HD 40307's habitable-zone between 0.4 and 1.0 AU, even if the object is relatively cloudless. Astronomers would find it very difficult to detect an Earth-sized planet around this star using present methods. (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)