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ALPHA FOR (Alpha Fornacis). Many are the quiet areas of the sky,those that have myriad faint stars but lack the luster of theOrions and the Bears and the Argos. To the ancients, these regionswere the "unformed." With the explosion of astronomical knowledgethat began with Copernicus, however, there was a distinct need to"fill in the blanks" with new constellation patterns. Rather thanfrom myth, many were chosen from the culture of the times. Thus wesee a microscope (Microscopium), a telescope (Telescopium), and among many others,Fornax, the Furnace. While not an easy pattern to see,at least its luminary, known but as Alpha Fornacis, or Alpha For,reaches toward the brighter end of fourth magnitude (3.87). Rathernearby, only 46 light years away, it is a pity that the star is solittle known, as it harbors a delight. Most stars that make theconstellation patterns are far more luminous than theSun. In Alpha For, however, we see a doublestar that consists of a pair that spans the solar qualities. Thebrighter, fourth magnitude (3.9) Alpha For A, is a coolish (6240Kelvin) class F (F8) subgiant with a luminosity four times that ofthe Sun. The fainter (Alpha For B), is a near-seventh-magnitude(6.5) cooler (5500 Kelvin) class G (G7) dwarf with a luminosityonly half that of the Sun. The difference between the two iscaused by mass. The "A" component has a mass somewhat over 1 1/4that of the Sun, while the "B" member has only 3/4 of the solarmass. This difference in itself will make "A" more luminous than"B" since the core temperature is higher as a result of increasedgravitational compression. Higher mass stars also die first. Asa subgiant, higher-mass "A" is coming close to ceasing hydrogenfusion in its core if it has not done so already. Lower-mass "B,"however, still has a long way to go, a few billion years or so,before it follows "A"s lead. The pair is close enough for us towatch the orbital motion. They loop around each other with a 269year period at an average distance of 56 Astronomical Units (the AUthe distance between the Earth and Sun), or about 4 seconds of arcas seen from Earth. The elliptical orbit takes them from a maximumof 97 AU apart to a minimum of 15; they made their most recentclose pass in 1947 and will be at their maximum separation in 2082. In 2004, we will finally have seen a full orbit since discovery ofbinarity in 1835. The orbital characteristics give higher massesthan does evolutionary theory, probably as a result of simple andalways-present observational error.
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