HD 70642 / CD-39 4247

© PPARC, David A. Hardy



Larger image.




Planetary candidate "b" seen
with its host star through
wispy rings and two moons
from a third rocky moon, as
imagined by Hardy (more).

The star was first designated as CD-39 4247 (as in ChView data files) 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. Today, however, many astronomers refer to this star as HD 70642, as designated in the Henry Draper (1837-82) Catalogue with 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.

The Star

John Rowe, AAO





Larger animation still.





Planet b seen with its
host star and four moons,
as imagined by Rowe
(more animation images).

Some astronomers have recently classed HD 70642 as a yellow-orange dwarf star of spectral and luminosity type G5 V, but others once thought that it was a more evolved subgiant (Carter et al, 2003, in pdf). The star appears to a mass (1.00 +/- 0.05) similar to Sol, probably a similar diameter, and about 93 percent of Sol's luminosity. On the other hand, HD 70642 appears to be 1.4 times as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron. The star appears to be photometrically stable, with a chromospherically inferred age of around four billion years (Carter et al, 2003, in pdf). Useful catalogue numbers and designations for this star include: Gl 304, HIP 40952, HD 70642, CD-39 4247, CP(D)-39 2308, SAO 199126, and LTT 3116.

Planet "b"

NASA

Cassini-Huygens Mission
to Saturn and Titan


Larger image.


Planet b is probably a gas giant
at least twice as massive as
Jupiter (shown here with Europa).

On July 3, 2003, a team of astronomers (including Hugh R. A. Jones, R. Paul Butler, Chris G. Tinney, Geoffrey W. Marcy, Alan J. Penny, Chris McCarthy, Brad Carter, and Debra A. Fischer) announced the discovery of a giant planet around this Sun-like star (press release, exoplanets.org, Anglo-Australian Observatory, and Carter et al, 2003, in pdf. Radial velocity measurements suggest that HD 70642 has a companion "b" with at least 2.0 times Jupiter's mass. It moves around HD 70642 at an average distance of 3.32 AUs (a semi-major axis around the orbital distance of the Main Asteroid Belt in the Solar System) in a highly circular orbit (e=0.05) that takes about 2,199 +/- 400 days (or around 6.02 years) to complete (exoplanets.org). The orbit of an Earth-like planet (with liquid water) around HD 70642 may be centered around 0.97 AUs -- just within the orbital distance of Earth in the Solar System -- with an orbital period of around 350 days. Astronomers would find it very difficult to detect an Earth-type planet in the water zone of this star using present methods. (See an animation of the planetary and potentially habitable zone orbits of the HD 70642 system, with a table of basic orbital and physical characteristics.)

© PPARC




Another illustration.





Planet b has a
highly circular
orbit similar to
those found in
the Solar System
(more from
PPARC).