J. Herschel 5173 AB

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© Torben Krogh & Mogens Winther,

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

J. Herschel 5173 A is an orange-red
dwarf star, like Epsilon Eridani
at left center of meteor. (See a
Digitized Sky Survey field image
of J. Herschel 1573 from the
Nearby Stars Database.)

System Summary

This system is located about 19.7 light-years (ly) away from our Sun, Sol, at the southeast corner (20:11:11.9-36:6:4.4 for Star A and 20:11:12.2-36:6:6 C~ for Star B, ICRS 2000.0) of Constellation Sagittarius, the Archer -- southeast of Theta1 and Theta2 Sagittarii. The binary pair was first discovered by Sir John Frederick William Herschel (1792-1871), portrait), the son of Sir William Friedrich Wilhelm Herschel (1738-1822, portrait). An early pioneer in photography with interests in chemistry, mathematics, and law, Sir John Herschel's first major publication in astronomy was a 1824 catalogue of double stars presented to the Royal Society for which he received honours, the Lalande Prize in 1825, and the Astronomical Society's Gold Medal in 1826. Later travelling to the Cape of Good Hope in South Africa, he observed the return of Halley's Comet in 1835 and discovered that gas was evaporating from it and that a repulsive force was acting on it -- when eventually led to the discovery of the Solar wind.

As a nearby and so relatively bright star in Earth's night sky, Star A is also catalogued as Harvard Revised (HR) 7703, 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 -- revised and expanded through the hard work of E. Dorrit Hoffleit and others. HR 7703 is also listed as HD 191408 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.)

J. Herschel (HJ) 5173 A

The star is a orange-red main sequence dwarf star of spectral and luminosity type K3 V, that has been classified as orange as K2. This star has about 82 percent of Sol's mass (RECONS estimate), 71 to 80 percent of its diameter (Pasinetti-Fracassini et al, 2001), and less than 23 percent of its visual luminosity. HJ 5173 A appears to be 85 percent as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Cayrel de Strobel et al, 1991, page 35). It may be an old disk star (Olin Jeuck Eggen (1919-1998), 1979, page 3), which implies an age up to 10 billion years.

HJ 5173 A has a binary stellar companion at an observed separation of about 43 AUs (based on a separation 7.1" and a HIPPARCOS distance estimate of 19.74 ly) -- just beyond the "average" orbital distance (semi-major axis) of Pluto in the Solar System --in 1949, in approach from a wider separation of 9.8" in 1880 (ARICNS of Astronomisches Rechen-Institut at Heidelberg; and Poveda et al, 1994, pages 36 and 38). The stars has two optical companions that are not gravitationally bound, which are themselves binary systems (Gl 783.1 A and B; and Gl 738.2 A and B). Useful star catalogue numbers for this star include: HR 7703, Gl 783 A, Hip 99461, HD 191408, CD-36 13940, CP(D)-36 9037, SAO 211885, LHS 486, LTT 7988, LFT 1529, and HJ 5173.

HJ 5173 B

NASA -- larger image

HJ 5173 B is a dim red dwarf star, like Gliese
623 A (M2.5V) and B (M5.8Ve) at lower right.

HR 7703 B is a red main sequence dwarf of spectral and luminosity type M3.5-4.0 V, that also has been classified as a subdwarf star (VI/sd) and even a giant star (III) by the SIMBAD Astronomical Database (which may be using an older reference). This star has about 20 percent of Sol's mass (RECONS estimate), 28 percent of its diameter (Pasinetti-Fracassini et al, 2001), and less than 77/100,000th of its visual luminosity. HJ 5173 B appears to be only 26 percent as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Fe/H = -0.58, Cayrel de Strobel et al, 1991, page 35). Useful star catalogue numbers for this star include Gl 783 B, CD-36 13940 B, LHS 487, LTT 7989, and LFT 1530.

Hunt for Substellar Companions

The distance from HJ 5173 A where an Earth-type planet would be "comfortable" with liquid water is centered around only 0.48 AU -- between the orbital distances of Mercury and Venus in the Solar System. At that distance from the star, such a planet would have an orbital period of about 134 days -- less than half of an Earth year. Similarly, the distance from HJ 5173 B where an Earth-type planet would be located is centered around only 0.028 AU, where such a planet would complete an orbital period within 3.8 Earth days. Astronomers would find both stars very difficult to detect using present methods.

Closest Neighbors

The following star systems are located within 10 light-years of HJ 5173 AB.

Star System	Spectra & Luminosity	Distance (light-years)
CD-49 13515 / Gl 832	M1.5 V	3.2
L 347-14	M4.5 V	4.5
CD-49 13515 / Gl 832	M1.5 V	7.1
Hip 103039	?	7.2
Lacaille 8760	K7-M2 Ve	7.8
CD-27 14659	K0-3 V	9.8
CD-44 11909	M3.5-5 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, the Nearby Stars Database, and the Research Consortium on Nearby Stars (RECONS) list of the 100 Nearest Star Systems. Additional information may be available at Roger Wilcox's Internet Stellar Database.

Sagittarius is Latin for "archer," often represented as a centaur wielding a bow and arrow since ancient times. The constellation also contains the Great Sagittarius Star Cloud, where a vast milky swarm of millions of stars mark the way to the center of the galaxy. For more information about the stars and objects in this constellation and an illustration, go to Christine Kronberg's Sagittarius. For another illustration, see David Haworth's Sagittarius.

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