HR 4523 AB
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This binary system is located about 30.1 light-years (ly) away from our Sun, Sol, in the northernmost portion (11:46:31.07-40:30:01.27, ICRS 2000.0) of Constellation Centaurus, the Centaur -- northwest of Delta Centauri and south of Beta and Zeta Hydrae. According to the Yale Bright Star Catalogue, 1991 5th Revised Edition notes entry for HR 4523, the system is a member of the 61 Cygni and/or the Epsilon Indi group. Although HR 4523 A became one of the top 100 target stars for NASA's proposed Terrestrial Planet Finder (TPF), the project was postponed indefinitely.
As a relatively bright star in Earth's night sky, Star A is catalogued as Harvard Revised (HR) 4523, 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 (1907-2007) and others. (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.)
AB (wide) Binary Star System
HR 4523 A has a very dim companion. Star B has an observed separation from the primary of 235 AUs -- where a= 25.4" with an updated HIPPARCOS parallax of 0.10823 +/- 0.00070" (Poveda et al, 1994, pages 68-69).
This star is probably a yellow-orange main sequence dwarf star of spectral and luminosity type G2 V (Tinney et al, 2011), but it has been classed as orange as a G5. The star has recently been estimated to have as high as 85 percent Sol's mass (Tinney et al, 2011; and Kovacs and Foy, 1978), and it may have around 92 to 96 percent of its diameter (NASA Star and Exoplanet Database, derived using the power law formula of Kenneth R. Lang, 1980) and about 78 percent of its bolometric luminosity (NASA Star and Exoplanet Database, derived using the exponential formula of Kenneth R. Lang, 1980). It appears to be metal deficient compared with Sol, as it is only 20 to 52 percent as enriched with elements heavier than hydrogen ("metallicity") based on its abundance of iron (Tinney et al, 2011; and Cayrel de Strobel et al, 1991, page 292). HR 4523 A may be 9 +/- 3 billion years old (Tinney et al, 2011; and Kovacs and Foy, 1978), as an old disk star (Hearnshaw, 1972). Useful star catalogue numbers for HR 4523 A include: Gl 442 A, Hip 57443, HD 102365, CD-39 7301, CP(D)-39 5265, SAO 223020, LHS 311, LTT 4373, LPM 399, and LFT 848.
|Center of H.Z.?||0.88||0.90||0||...||...||...||...||...||...|
Estimates provided by the NASA Star and Exoplanet Database -- where the inner edge of Star A's habitable zone could be located at around 0.743 AUs from the star and its center around 1.113 AU, while the outer edge lies farther out at around 1.483 AUs -- appear to be unjustified based on the star's significantly sub-Solar luminosity. Based on its estimated bolometric luminosity, the distance from HR 4523 A where an Earth-type planet would be "comfortable" with liquid water is centered around 0.88 AU -- between the orbital distance of Venus and Earth in the Solar System, with an orbital period about 330 days, or about 90 percent of an Earth year.
In October 2010, a team of astronomers revealed the detection of a Neptune-class planet "b" in an inner orbit with a minimum of 16.0 Earth-masses around HR 4523 A. With an orbital semi-major axis of 0.46 +/- 0.04 AU and eccentricity of 0.34 +/- 0.14, the planet has an orbit that takes 122.1 days to complete. The astronomers analysis of the residuals to their Keplerian fit for the planet "indicated that there are no other planets with minimum mass above 0.3" Jupiter-mass orbiting within five AUs and no other "super-Earths" more massive than a 10 Earth-mass object "orbiting at periods shorter than 50 days." For orbital periods of less than 20 days, the astronomers were able to rule out the presence of additional planets larger than 6 Earth-masses (Tinney et al, 2011). Previously, A 2.5-year search analyzing radial velocities failed to find a large Jupiter or brown dwarf within 10 AUs of HR 4523 A (Murdoch et al, 1993, pages 351 and 358).
This star is a very dim, red main sequence dwarf star of spectral and luminosity type M4 V (SIMBAD Astronomical Database). This star may have only seven percent of Sol's mass, 15 percent of its diameter, and about 7/100,000th of its luminosity. Useful star catalogue numbers for the star include: Gl 442 B, LHS 313, VB 5, and 2MASS J11463269-4029476.
NASA -- larger image
HR 4523 B is a dim red dwarf star, like Gliese
623 A (M2.5V) and B (M5.8Ve) at lower right.
Habitable Zone for Star B
As Ross 154 is a main sequence red dwarf of spectral and luminosity type like HR 4523 B, it can be used as a rough proxy for Star B. According to one type of model calculations performed for the NASA Star and Exoplanet Database, the inner edge of Ross 154's habitable zone should be located very close to the star, at around 0.065 AU from the star, while the outer edge lies around 0.126 AUs. Accounting for the great infrared output of M-stars like Ross 154, the equivalent orbital distance for an Earth-type planet be only around 0.096 AUs.
The following star systems are located within 10 light-years, plus more bright stars within 10 to 20 light-years, of HR 4523 AB.
|Star System||Spectra &|
|L 396-7||M3.5 V||4.3|
|CD-31 9113||M2 V||4.4|
|CD-32 8179 AB||K0 V |
|CD-51 5974||K0-M0 V-VI||6.3|
|L 399-68||M3.5 V||7.3|
|CD-26 8883 AB||K4-5 V |
|CD-51 6859||M3 V||7.9|
|L 471-42||M4 V||8.2|
|* plus bright stars *||. . .|
|61 Virginis||G5-6 V||15|
Up-to-date technical summaries on these stars can be found at: Jean Schneider's Extrasolar Planets Encyclopaedia; the Astronomiches Rechen-Institut at Heidelberg's ARICNS for Star A and Star B, the NASA Star and Exoplanet Database, the Research Consortium on Nearby Stars (RECONS); and the SIMBAD Astronomical Database for Stars A and B. Additional information may be available at Roger Wilcox's Internet Stellar Database and from Alcyone.de's entry for HR 4523.
Constellation Centaurus cannot be viewed from middle northern latitudes of around 40 degrees, but should become more easily visible to observers that travel south of the equator. For more information about the stars and objects in this constellation and an illustration, go to Christine Kronberg's Centaurus. For another illustration, see David Haworth's Centaurus.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
Note: Thanks to Daniel Gonsalves for notifying us of a planet detection for Star A.
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