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.
Written by Jim Kaler. Return to STARS.