Muphrid (Eta Boötis) 2?

Muphrid A?

Star A is probably a yellow-orange subgiant of spectral and luminosity type G0 IV (NASA Stars and Exoplanet Database; and Garrison and Beattie, 1998). Sensitive to estimate's of the star's abundance of "metals" (elements heavier than hydrogen), Star A appears to have 1.6 to 1.7 times Sol's mass (van Belle et al, 2007; Guenther et al, 2005; D.B. Guenther, 2004; and Carrier et al, 2004), about 2.7 times Sol's diameter (van Belle et al, 2007; Fracassini et al, 1994; and Johnson and Wright, 1983, page 679), and around 8.9 times Sol's bolometric luminosity (van Belle et al, 2007; and Thévenin et al, 2005). It appears to be "super metal-rich," with around 1.4 to 2.0 times as enriched as Sol with elements heavier than hydrogen ("metallicity") based on its abundance of iron (NASA Stars and Exoplanet Database; Feltzing and Gonzales, 2001; and Cayrel de Strobel et al, 2001). The star may only be around 2.4 to 2.7 billion years old, much younger than Sol's 4.6 billion years (Guenther et al, 2005; and Thévenin et al, 2005). As a subgiant, the star has entered the post-main-sequence phase of evolution having exhausted core hydrogen and transitioned to the hydrogen-shell-burning phase around a helium-rich core, evolving toward the red giant branch (di Mauro et al, 2003). Useful catalogue numbers and designations for the star include: Eta Boo A, 8 Boo A, Gl 534 A, HR 5235, Hip 67927, HD 121370, BD+19 2725, SAO 100766, FK5 513, LTT 14060, and USNO 849.

Muphrid has been suspected of having a binary companion for more than a century. Variations in Muphrid's radial velocity were first published by Joseph Haines Moore (1878-1949) in 1905 and an orbit was calculated by William Edmund Harper (1878-1940) in 1910, with improvements in orbital elements by Emilo Bianchi (1875-1941) in 1920 (F.C. Bertiau, 1957). According to van Belle et al (2007), a 1938 astrometric detection by Zaccheus Daniel and Keivin Burns (Pub. American Astronomical Society, 9, 46) seems unlikely as both the expected separation and the brightness ratio. Although speckle interferometery observations have failed to provide supporting evidence, Father Florian C. Bertiau, S.J.'s 1957 paper on the star's binary nature (F.C. Bertiau, 1957) suggested a late K- or M-type dwarf companion for the G-type subgiant and a brightness difference that is large enough to be consistent with the speckle non-detections (van Belle et al, 2007). According to van Belle et al (2007), moreover, the spectroscopy of Brown et al (1997) indicates that the star's barycentric velocity is being influenced by a binary companion, which Christensen-Dalsgaard et al (1995) suggested is more likely to be a red dwarf than a white dwarf, subsequently further limited by van Belle et al's 2007 analysis to type M7 or later (van Belle et al, 2007). Finally, the possibility that the star may have a a white dwarf companion has been raised by Emeritus Professor Jim Kaler in this web page on Muphrid).

According to the Sixth Catalog of Orbits of Visual Binaries, Stars A and B move around each other at an average distance of 0.041 AUs (semi-major axis a= 0.03602") in a moderately eccentric (e= 0.26) orbit that takes 494.2 (1.355 years) to complete. The two stars get as close as 0.030 AUs and as far away from each other as 0.52 AUs, and their orbits around each other is inclined by 115.7° with respect to an observer on Earth (Jancar et al, 2005; Vansina and de Greve, 1982, pp. 392 and 393; Abt and Levy, 1976; and F.C. Bertiau, 1957). No confirmations thus far from from speckle interferometry (Hartkopf and McAlister, 1984; and Bonneau et al, 1980, page 188).

An Earth-type planet could have liquid water in a stable orbit centered around 3.0 AU from Star A -- between the orbital distances of Earth and Mars in the Solar System. Such a planet would have an orbital period around 4.0 years (1,456 days). It would, however, be difficult to detect using present astronomical methods and equipment.

NASA -- larger image

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

Muphrid B?

Star B may be a main sequence red dwarf star of spectral and luminosity type M7 or later (van Belle et al, 2007). Although some astronomers have speculated on the possibility of the spectroscopic companion being a white dwarf stellar remnant, Christensen-Dalsgaard et al (1995) reported that a ultraviolet spectrum of Star A taken by the International Ultraviolet Explorer (IUE) failed to provide supporting evidence for the companion object as a white dwarf (Cappelli et al, 1989). .