ROTANEV (Beta Delphini). The two brighter stars of the exquisite
constellation Delphinus (the Dolphin) fall
well outside the traditional systems of naming stars after their
characters or constellation placements (however confused these have
become). Instead, they honor the astronomer Nicolaus Venator, who
was assistant to the famed astronomer Giuseppe Piazzi, the latter
the discoverer (in 1801) of the first-known (and largest) asteroid,
Ceres. Both stars are at the bright end of fourth magnitude. The
Alpha star, which is slightly the fainter of the two (magnitude
3.77), is called Sualocin, the Beta
star (at magnitude 3.63 the constellation's luminary) Rotanev,
which represent the honoree's names spelled backwards. While
nearby on the sky and tied by name, the pair have nothing to do
with each other, Sualocin 2.5 times farther away than Rotanev,
which lies at a distance of 97 light years. Like Sualocin, Rotanev
is double. Unlike its hotter constellation-mate, however,
Rotanev's components are very similar, both the same class (F5
subgiants) and temperature (6500 Kelvin). But don't try to seem
them individually through the average telescope, as they are very
close together, averaging only 0.65 seconds of arc apart (the
angular size of a US penny seen at a distance of 10 kilometers, 6
miles). The brighter is mid-fourth magnitude (4.0), the fainter
almost a magnitude dimmer (4.9), which from their distances yield
luminosities of 18 and 8 times that of the Sun. The rotation speed of one or both is
modest, around 40 kilometers per second (20 times that of the
slowly rotating Sun), and like so many stars of the mid-temperature
classes, Rotanev shows peculiar abundances (particularly for
strontium) as a result of settling and lofting of various kinds of
atoms. The standard iron abundance, however, is quite normal.
Averaging just over 13 astronomical units (AU) apart, their
elliptical orbits take them from 18 AU (about the distance between
Uranus and the Sun) to 8 AU (just under Saturn's distance from the
Sun) over a 26.7 year period. They will be at their greatest
separation as viewed from the Earth in the year 2002. Solutions of
the orbit, as well as their luminosities, give masses somewhat
under twice that of the Sun, the brighter somewhat the more
massive. Neither of these could have an individual planet, as its
orbit would be unstable. A distant planet could have a stable
orbit around the pair, but it would have to be so far away that no
Earth-life as we know it could survive. No matter, really, since
both -- as subgiants -- are shutting down their internal hydrogen
fusion and are preparing to become giant stars, the brighter one a
bit farther along in its evolution, their fate to produce a pair of
orbiting white dwarfs.