CD-32 8179 / HR 4458 AB

© Torben Krogh & Mogens Winther,

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

CD-32 8179 is an orange-red
dwarf star, like Epsilon Eridani
at left center of meteor. (See
a Digitized Sky Survey image
of CD-32 8179 from the
Nearby Stars Database.)

System Summary

The CD-32 8179 binary system is located about 31.1 light-years (ly) away from our Sol, in the south central edge (11:34:29.5-32:49:52.8, ICRS 2000.0) of Constellation Hydra, the Water Serpent -- southwest of Xi Hydrae, west of Beta Hydrae, and southeast of Chi1 Hydrae. The system may be visible to many Humans without a telescope. (See an animation of the orbits of Stars A and B and their potentially habitable zones, with a table of basic orbital and physical characteristics.)

Its designation as CD-32 8179 came from 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.

As a relatively bright star in Earth's night sky, Star A is catalogued as Harvard Revised (HR) 4458, a numbering system derived from the 1908 Revised Harvard Photometry catalogue of stars visible to many Humans with the naked eye. The HR system has been preserved through its successor, the Yale Bright Star Catalogue -- updated and expanded through the hard work of E. Dorrit Hoffleit and others. HR 4458 is also listed as HD 100623 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. (More discussion on star names and catalogue numbers is available from Alan MacRobert at Sky and Telescope and from Professor James B. Kaler's Star Names.)

CD-32 8179 A

CD-32 8179 is a main-sequence orange-red dwarf star of spectral and luminosity type K0 V. It may have around 87 percent of Sol's mass, 84 percent of its diameter (Johnson and Wright, 1983, page 673), and 31 percent of its luminosity. Useful star catalogue numbers for CD-32 8179 A include: HR 4458, Gl 432 A, Hip 56452, HD 100623, CP(D)-32 3122, SAO 202583, LHS 308, LTT 4280, LFT 823, LPM 389, and E 439-246.

Star A has an average separation of about 80.5 AUs from its binary companion "B" -- a semi-major axis of 16.2" at a HIPPARCOS distance estimate of 31.1 ly (Poveda et al, 1994, pp. 68-69). Given estimated masses of 0.87 Solar for Star A and 0.08 Solar for Star B, their orbital period may last some 741 years. (See an animation of the orbits of Stars A and B and their potentially habitable zones, with a table of basic orbital and physical characteristics.)

NASA -- larger image

CD-32 8179 B is a very dim red dwarf star, dimmer than
even Gliese 623 A (M2.5V) and B (M5.8Ve) at lower right.

CD-32 8179 B

Star B is a main-sequence orange-red dwarf of spectral and luminosity type M V. It may only have around 8 percent of Sol's mass, 15 percent of its diameter (Johnson and Wright, 1983, page 673), and only 76 millionths of its luminosity. Useful catalogue numbers for Star B include: HR 4459 B, Gl 432 B, LHS 309, and VB 4.

Hunt for Substellar Companions

The distance from Star A where an Earth-type planet would be "comfortable" with liquid water is centered around only 0.56 AU -- between the orbital distances of Mercury and Venus in the Solar System. An Earth-type in such a water-zone orbit would probably would have a period of around 164 days or roughly half of an Earth year. For Star B, an Earth-type planet would have to orbit at around 0.0087 AUs away with a period of about 18.4 hours. As relatively small planets at close distances to their host stars, astronomers would have great difficulty in detecting such planets around either star using present methods.

Closest Neighbors

The following star systems are located within 10 light-years of CD-32 8179.

Star System	Spectra & Luminosity	Distance (light-years)
CD-31 9113	M2 V	1.7
HR 4523 AB	G3-5 V M V	4.4
CD-26 8883 AB	K4.5 V ?	4.5
L 396-7	M3.5 V	5.5
CD-23 9765	M3 V	6.8
Ross 695	M4 V	9.9
L 471-42	M4 V	10.0

Other Information

Up-to-date technical summaries on these stars can be found at: the Astronomiches Rechen-Institut at Heidelberg's ARICNS for Star A and Star B, and the Nearby Stars Database. Additional information may be available at Roger Wilcox's Internet Stellar Database.

There are two ancient Greek myths involving Constellation Hydra. One involved an enormous water snake with nine heads that was killed by Hercules with the help of the Goddess Athena. Another referred to a water serpent brought by a pet Raven sent by the God Apollo for water, which the hungry Raven falsely claimed to have been attacked when it actually was delayed in waiting for a meal of ripening figs; both were flung into the Heavens by the angry God. For more information on this constellation, go to Christine Kronberg's Hydra. For another illustration, see Richard Dibon-Smith's Hydra.

For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.