ALPHA VOL (Alpha Volantis). We immediately assume that the "alpha" of anything is the one on top. Stars usually follow the rule, the brightest indeed often being "Alpha." But the rule is also often broken, as witness such constellations as Gemini, Sagittarius, and several others that include a modern figure of the southern hemisphere, Volans (the Flying Fish), in which Gamma Vol tops the list. (A couple -- Leo Minor and Norma -- do not even HAVE Alpha stars, a quirk of boundaries and naming.) While Alpha Volantis is not at the top of its domain, it does have some style in that it is the very definition of a fourth magnitude star (coming in right at 4.00) and that it also illustrates some severe difficulties in classification. Nominally, it's a white class A (A2.5) subgiant that lies 124 light years away. That and a rather ill-defined temperature of 8430 Kelvin lead to a luminosity 29 times that of the Sun, a radius of 2.5 solar, a mass of 2.2 solar, and a realization that the star is hardly a subgiant (which implies cessation of core hydrogen fusion), but a dwarf about half-way through its 890-million-year H-burning lifetime. The problem is that it is another one of these slowly rotating (for its class) metallic-line stars in which chemical elements are separated by diffusion in a quiet atmosphere, some lofted upward via radiation, others settling downward under the force of gravity. The measured equatorial rotation speed of 34 kilometers per second (and a rotation period of under 3.7 days) is apparently not sufficient to keep things stirred up. The phenomenon then makes a mess out of spectral classification, which is based on a chemistry of "normal" solar proportions. Depending on what chemical elements are used, we can get anything from the nominal class A2.5 to much cooler A7. Wait, there's more confusion. Many class A stars (Vega, Fomalhaut) are surrounded by dusty disks that imply some kind of real (or failed) planetary systems. Some sources say Alpha Vol is one of their number, others say no. The star is also referred to as a double, one that is observed only via the spectrum. But the reference goes back to 1905 and is probably the result of not-surprisingly poor observations. Such confusion, however, should delight, as it provides new opportunities for study and research.
Written by Jim Kaler 5/18/07. Return to STARS.