CD-66 2307 / HD 181433

Today, many astronomers refer to this star as HD 181433, 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-66 2307 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

HD 181433 may be a subgiant rather than a main-sequence, orange-red dwarf star (Sousa et al, 2008; and ARICNS), but is probably not an giant, star (SIMBAD) of spectral and luminosity type K3-5 V-III. The star probably has a mass somewhat smaller (around 78 percent) than Sol's (Sousa et al, 2008; and NASA Star and Exoplanet Database, derived from Kenneth R. Lang, 1980), and it appears to have only around 78.7 percent of its diameter (Masana et al, 2006). Most revealing, HD 181433 only has around 25 percent of Sol's visual and around 31 to 34 percent of its bolometric luminosity (Sousa et al, 2008; and Nordström et al, 2004; NASA Star and Exoplanet Database, derived from Kenneth R. Lang, 1980; and ARICNS). It appears to be around 1.8 to 2.1 times as enriched as Sol in iron relative to the abundance of hydrogen and nearly 3.2 times as enriched as Sol in elements other than hydrogen, helium, and iron (Sousa et al, 2008; Gray et al, 2006; and Kotoneva et al, 2002). If HD 181433 has a mass less than Sol's but is more evolved (i.e., where it may have already shut down hydrogen fusion in its helium-rich core), then it may be significantly older than Sol's 4.6 billion years. Useful catalogue numbers and designations for the star include: Gl/GJ 756.1, Hip 95467, HD 181433, CD-66 2307, CPD-66 3431, SAO 254563, LTT 7669, and 2MASS J19250951-6628075.

Trent Schindler, NSF


Larger and jumbo illustrations
(more images and videos).


Planetary candidate "b" is a "super-Earth"
class planet with 7.5 Earth-masses in a
tight orbit. It may be rocky and have
atmospheres with clouds, like Gliese 876 d,
as imagined by Schindler (more).

On June 16, 2008, a team of astronomers announced at the 2008 Extra Solar Super-Earths Workshop in France their discovery of one "super-Earth" type planet in a tight orbit around this star with two other gas giant planets in outer orbits (ESO press release and Bouchy et al, 2009). Planet "b" has 7.5 Earth-masses at an average orbital distance of 0.08 with a period of only 9.5 days and an orbital eccentricity near 0.40. Moving outwards from host star, planet "c" has 72 percent of Jupiter's mass and an orbital period of 2.8 years (1,024 days) with an average orbital distance of 1.76 AUs and eccentricity around 0.28. Lastly, there may be an additional third planet "d," which may have around 54 percent of Jupiter's mass and an average orbital distance of around 3 AUs with a period of around 6 years (2,172 +/- 158 and an eccentricity near 0.48. (Bouchy et al, 2009).

NASA
Cassini-Huygens Mission
to Saturn and Titan


Larger image.


Planetary candidate "c" appears
to be a gas giant with 72 percent
of Jupiter's mass (shown here with
Europa) in an outer orbit.

If you include infrared radiation, the orbit of an Earth-like planet with surface water would be centered around 0.57 AU -- between the orbital distances of Mercury and Venus in the Solar System. Such an orbit would take around six months to complete. It is possible, however, that the presence of massive planetary candidate c at an orbital distance around two AUs could disrupt the orbital stability of an Earth-mass planet in the habitable zone. 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.)