ALFECCA MERIDIANA (Alpha Coronae Australis).
South of Sagittarius
lies one of the sky's more charming figures, Corona Australis, the Southern Crown. The counterpart
of Ariadne's Corona Borealis (the Northern
Crown), the Southern version may represent the crown of Sagittarius
itself. While the Northern Crown's "lucida," its brightest star,
is at second magnitude quite prominent, the Southern Crown's
lucidae (of which there are two) are not, the Alpha and Beta stars
tied at mid-fourth magnitude (4.11). Alpha at least boasts a name,
one not so much its own but one that reflects the Northern Crown's
prominence. The brightest star in Corona Borealis is named "Alphecca," from Arabic for "break," the
name coming from the half or broken circlet of stars that makes the
Crown's figure. Probably in response, the Alpha star of Corona
Australis is known as Alfecca (note the curious spelling change)
Meridiana. The name at first makes no sense, as "Meridiana," from
Latin, refers to noon, when the star would hardly be visible.
However, when a resident of the northern hemisphere looks to the
Sun at noon, he or she looks to the south, leading to an
alternative definition of "meridiana" as "southern," Alfecca
Meridiana thus referring directly to Corona Australis. Other than
the problem of the name, the star is rather ordinary, one of vast
numbers of warm class A hydrogen-fusing dwarfs that dot the sky and
make so much of our familiar constellations. At a distance of 130
light years, the star shines 31 times more brightly than does the
Sun, from a surface with a temperature of
9100 Kelvin. There is some argument as to the spectral class, some
authorities moving it to hotter class A1 or even A0 (though that is
out of line with temperature). A decidedly single star (so far as
anyone knows), Alfecca Meridiana is a fast rotator, spinning at
least at 180 kilometers per second at its equator, 90 times faster
than the Sun. With a radius 2.3 times solar, it makes a full
rotation in under 18 hours (the Sun taking 25 days). More
interesting, Alfecca Meridiana is a "Vega" candidate, a star that
like Vega radiates excess infrared
radiation that seems to come from a surrounding disk of cool dust,
suggestive of some kind of surrounding planetary system (for which
there is no other evidence). With a mass around 2.3 times solar,
Alfecca Meridiana is about half-way through its hydrogen-fusing
main-sequence lifetime, and will eventually turn into a relatively
heavy white dwarf, just like all the stars of its class. Thanks to
David Bright for advice on the star's name.