HR 4523 AB

JPL, NASA



Larger image.



Planetary candidate "b" is
probably an "ice-giant"
like Neptune.

JPL, CalTech, NASA


Larger illustration


Astronomers have identified
HR 4523 A as a prime target
for the Terrestrial Planet Finder
(TPF), now 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).

HR 4523 A

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.

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	Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass (Earths)	Diameter (Earths)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
HR 4523	0.0	...	...	...	280,000	0.92-0.96	...	...	0.20-0.52
Planet "b"	0.46	0.0.334	0.34	?	=>16.0	3-4?	...	...	...
Center of H.Z.?	0.88	0.90	0	...	...	...	...	...	...

Habitable Zone for Star A

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.

Planet "b"

JPL, NASA



Larger image.



Planetary candidate "b" is
probably an "ice-giant"
like Neptune.

HR 4523 B

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.

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