MARFAK-EAST (Theta Cassiopeiae). While proper names are commonly used for stars of first magnitude, and for a few other special cases, and while charming and illustrative of cultural history, they sure can be confusing. "Denebs" (from the Arabic word for "tail"), for example, abound, appearing in Deneb proper, Deneb Algedi, Deneb Kaitos, Denebola, and others. At least in this case there are notable variations on the theme. "Marfak" (again, Arabic, referring to the "elbow" of a constellation figure) is much worse, discrimination coming down to deliberate spelling variations and appended descriptions. Alpha Persei is in these pages given as "Mirfak," Lambda Ophiuchi as "Marfik," and the elbow of Cassiopeia, the celestial Queen, as "Marfak" (each of these also spelled like the other, with additional variations). The latter is a bit of an extreme, as Marfak refers not to just one, but to TWO stars, Mu Cassiopeiae (which we here call Marfak-West) and Theta Cas (Marfak-East). Beyond that, Marfak-E (best to call it Theta) has few distinctive marks, in part because it is underserved by astronomers, showing that we are a long way from understanding all the naked-eye -- even the brighter naked-eye -- stars. Though lying close together in the sky, the two Marfaks have nothing to do with each other. Mu Cas is a fifth magnitude G5 dwarf only 25 light years away, while
The two Marfaks shine in the center of the picture, Marfak-East (Theta Cas, the brighter) to the right, Marfak-West (Mu Cas) to the left, both surrounded by the glory of Cassiopeia's Milky Way. North is roughly down. The bright stars at lower left are Shedar (Alpha Cas, the brighter) and Achird (Eta Cas). Up and to the right of them (in a rough equilateral triangle) is the faint glow of the diffuse nebula NGC 281.
Theta, a fourth magnitude (4.33) class A (A7) dwarf, lies at a distance of 137 light years, 5.5 times farther. With a well defined surface temperature of 7940 Kelvin, Theta shines with a luminosity 25 times that of the Sun, from which we derive a radius of 2.6 solar, a mass just over 2.0 solar, and an age of about 800 million years, placing the star about three-quarters of the way through its hydrogen-fusing lifetime. (There is a slim chance that the star could have a lower mass of 1.85 solar and be done with hydrogen fusion, but that would make the star a subgiant, and it is clearly classified as a dwarf.) Theta Cas is distinguished by a fairly fast equatorial spin speed of at least 103 kilometers per second, which gives a rotation period under 1.3 days (an upper limit since the star's axial tilt is not known). It is also a "Vega" candidate, as it may have a surrounding infrared-radiating disk of dust (which for some stars implies the possibility of planets). The metal abundance is also up a bit from the Sun's, up to 40 percent higher (relative to hydrogen), though that is arguable. And that is about it. Theta's suspected spectroscopic companion has never been confirmed, nor have suspected variations as a Delta Scuti star. A "companion" just over two minutes of arc away is clearly just a line of sight coincidence. Enjoy the Marfaks now, as Mu is a high-velocity mover, and the two will over (astronomical) time separate, the "elbow" straightening out.
Written by Jim Kaler. Return to STARS.