Mu Herculis 4?
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This star system is located about 27.4 light-years from Sol. It lies in the south central part (17:46:27.53+27:43:14.43, ICRS 2000.0) of Constellation Hercules, northeast of Lamda Herculis and Sarin (Delta Herculis) and southwest of Nu, Omicron, and Xi or Ksi Herculis. Mu Herculis was first discovered to have a dimmer companion in 1781 with a relatively wide orbit by Sir William Friedrich Wilhelm Herschel (1738-1822, portrait), who was born Friedrich Wilhelm Herschel and who discovered the planet Uranus -- which led to his appointment in 1782 as private astronomer to the King of England. Subsequently, the dimmer companion was itself found to be a close double in 1856. Today, many astronomers also believe that the primary itself may have another close orbiting, stellar or large substellar companion. The system is part of the Wolf 630 group.
Mu Herculis A is a yellow-orange star of spectral and luminosity type G5 IV. It has the same mass as Sol (Bedding et al, 1996, page 1157) -- possibly 1.1 Solar-mass according to Professor Kaler's Mu Herculis page, about 1.77 to 1.86 times Sol's diameter, and about 2.2 to 2.7 (with infrared) times its luminosity. The star may be 1.3 to three times as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Cayrel de Strobel et al, 1991, page 30). Useful star catalogue numbers for Star A include: Mu Her, 86 Her, HR 6623, Gl 695 A, Hip 86974, HD 161797, BD+27 2888, SAO 85397, FK5 667, LHS 3326, LDS 1002, LTT 15266, LFT 1374, GC 24138, ADS 10786, and AC 7.
Mu Herculis A (or Aa) appears to have an unseen, close companion (Mu Herculis D or Ab) with as much as a fifth of Sol's mass. In turn, this close binary pair (Aab) has another companion binary of stars (BC). According to the Astronomisches Rechen-Institut's Catalogue of Nearby Stars (ARICNS) notes on Star B, the BC companion binary pair has an observed separation of about 286 AUs (34.0" at a HIPPARCOS parallax of 0.11905+/-0.00062") from primary pair Aab at an orbital inclination of 247° (1955) from the perspective of an observer on Earth. (See an animation of the orbits of Stars Aa, Ab/D, B, C, and their potentially habitable zones, with a table of basic orbital and physical characteristics.)
The orbit of an Earth-like planet (with liquid water) around this star would be centered around 1.6 AU -- somewhat farther than the orbital distance of Mars in the Solar System -- with an orbital period of about 2.0 Earth years. However, Mu Herculis A is unusually bright for its spectral type. It appears to be a subgiant star that is evolving off the main sequence, as it begins to fuse the increasing amounts of helium "ash" mixed with hydrogen at its core. This implies that any Earth-like planet that time to develop life in at an orbital distance when Mu Herculis A was less luminous would probably has been "roasted" dry by this time.
NASA -- larger image
Mu Herculis BC are dim red dwarf stars, like the binary pair
Gliese 623 A (M2.5V) and B (M5.8Ve) -- at lower right.
Mu Herculis B
This is a red main sequence dwarf star of spectral and luminosity type M3.5 V. It has a mass of about 31 (+/- 10) percent of Sol's (James F. Wanner, 1967), about 48 percent of its diameter, and less than 5/1,000th of its luminosity. Star B and its stellar companion C are separated by an "average" semi-major axis) of 11.4 AUs. They have an elliptical orbit (e= 0.18) that swings them between 9.4 and 13.5 AUs apart in an orbit that lasts about 43.2 years (Paul Couteau, 1960). Useful star catalogue numbers for the star include Gl 695 B and LHS 3325.
This is a red main sequence dwarf star of spectral and luminosity type M4 V. It has about 31 (+/- 10) percent of Sol's mass (Wanner, 1967), about four tenths of its diameter, and less than 3/1,000th of its luminosity. Useful star catalogue numbers for the star include HR 6623 C and Gl 695 C.
Astrometric analysis suggests that Star D is in an elliptical orbit (e= 0.34) around Star Aa and has roughly a fifth of Sol's mass (Wulff Dieter Heintz, 1994, pages 2341 and 2346; and Heintz, 1987, page 1080 -- which Heintz referred to as Stars A and Aa versus the more typical designations Aa and Ab). According to the Astronomisches Rechen-Institut's Catalogue of Nearby Stars (ARICNS), Heintz's 1994 analysis of Mu Herculis Aa also derived an updated period of 65 years which would imply a semi-major axis of just under 17.2 AUs, assuming that the combined mass of Mu Herculis Aab is 1.2 times that of Sol's (which is consistent with Wanner's 1967 estimate of the mass ratio of 0.50 (+/- 0.04) for the binary pair BC -- combined -- to the primary).
In 1994, Cochran and Hatzes also reported possible evidence of a brown dwarf or large Jupiter-class companion around Mu Herculis A based on a steady downward drift of its radial velocities over five years (Mazeh et al, 1996, page 423). More recent application of the highly sensitive radial-velocity techniques of Geoffrey W. Marcy and R. Paul Butler, however, have not as yet confirmed the existence of such a companion object (Cumming et al, 1999).
The following star systems are located within 10 light-years of Mu Herculis.
|Star System||Spectra &|
|BD+18 3421||M0 V||4.5|
|G 184-19 AB||M4.5 V |
|BD+25 3173||M2 V||8.5|
|BD+33 2777||K7 V||8.6|
|G 203-47||M3.5 V||8.6|
|BD+43 2796||M3.5 V||8.7|
|G 169-29||M V||8.9|
|AC+20 1463-148 A||M2 V-VI||9.6|
|AC+20 1463-148 B||M2 V-VI||9.8|
Up-to-date technical summaries on these stars can be found at: the Astronomiches Rechen-Institut at Heidelberg's ARICNS, the Nearby Stars Database, and the Research Consortium on Nearby Stars (RECONS). Additional information may be available at Roger Wilcox's Internet Stellar Database.
In Greek mythology, Hercules was the son of the God Zeus and the Alkmene, the wife of Amphitryon who was fooled by Zeus into believing that he was Amphitryon. Hera, the wife of Zeus, somehow arranged that the first born son of Alkmene became Eurystheus, who under Hera's influence eventually gave his half brother twelve tasks to complete or perish. For more information about the stars and objects in this constellation and an illustration, go to Christine Kronberg's Hercules. For another illustration, see David Haworth's Hercules.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
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