VV CRV (VV Corvi). Modestly glowing in northeastern Corvus (the Crow), fifth magnitude (5.08) VV Corvi's name is as much a tangle as its physical nature. Through the telescope, we see a visual binary made of similar mid-F (probably F5) sixth magnitude dwarfs (magnitudes 5.84, 5.82) separated by 5.1 seconds of arc. The magnitudes are uncertain, but the leader is clearly somewhat the fainter of the two. They have no singular common name, neither Greek letter nor Flamsteed number. But they are distinctive enough for each to carry its own number from the Bright Star Catalogue, HR 4821 and HR 4822. They have in fact been called the "A-B pair." There are insufficient data on motion to compute an orbit, but at a distance of 278 (give or take around 9) light years, they are estimated to go around each other every 4500 years, which (from the masses below) implies a separation of some 800 Astronomical Units. Each of these stars is a spectroscopic binary, with respective periods of 1.46 days (for "A") and 44.1 days. The first was later found by photometry to be an "alias" for the true period of 3.1445 days: a false period that fit the then-available data. Photometry also revealed the fainter western star "A" to be a totally-eclipsing binary with a maximum variation of 0.15 magnitudes. Since the star is variable it was assigned the variable-star name VV Corvi, which has confusingly at times been applied to the whole system.
VV Crv The light curve of the eclipsing binary VV Corvi (HR 4821) is scaled in magnitudes in yellow light on the left and in blue light on the right. The "phase" on the lower axis is the fraction of time covered over the full orbital period of 3.144536 days. Each star eclipses the other once over the full period, yielding two minima of a couple tenths of a magnitude. With velocity data we can determine a wide range of stellar properties. (Light curve from a paper by F.C.Fekel, G.W.Henry, and J.R.Sowell in the Astrophysical Journal, vol. 146, December 2013.)
With brightness and velocity variation known we can calculate most all of the parameters of the western eclipsing star's (HR 4821's) parameters, including masses (1.978 and 1.513 Suns) and radii (3.375 and 1.650 solar times solar). They are separated by only 0.064 AU(with an 8.5 percent eccentricity) or about 14 solar radii, values not much bigger than the stars themselves but still "detached," one not feeding mass on to the other. with projected equatorial rotation velocities of 81 and 24 kilometers per second, the primary components spins in 2.1 days (less than orbital synchronicity) the other in 3.5 days (more than synchronicity). Given the period of 44.1 days the companion to the eastern star should orbit at a distance of roughly 0.35 AU. So we have a double-double of nearly identical stars, a bit like Castor, Mizar, or Epsilon Lyrae except that one pair eclipses. But wait, there's more. Nearly a minute of arc (59.5") away is a 10th magnitude (10.3) neighbor that was long thought to be "optical," that is, just in the line of sight. Apparently, though, it isn't. It's now believed to belong to the system. If so, it is roughly a solar-type star at least 5000 AU away from the inner quartet and would take around 150,000 years to make a full orbit. Moreover, there is just the barest suggestion in the data of yet another star with a period of 9 years, making poor mis-named VV Corvi (which seemingly can be applied to either the actual eclipsing binary or to the whole system) sextuple star. And who knows what red dwarfs may lurk within. Probably not many, as gravitational interactions would have thrown them out. It's rather hard to figure even where a 9-year-period member would fit in. Ignoring the small companions, the temperatures of the two bright F stars are very similar at 6570 Kelvin, while the luminosities are 18.2 and 147 times that of the Sun. The brighter component is an evolving subgiant, while the lesser star is still on the hydrogen-fusing main sequence. The VV Crv system is speeding along at 48 kilometers per second relative to the Sun, about three times normal. Its motion may be related to the metal content (relative to hydrogen), which appears to be almost double that of the Sun, that is, the star is something of an interloper into our part of the Galaxy. (Much of this discussion was taken from a paper by F.C.Fekel, G.W.Henry, and J.R.Sowell in the Astrophysical Journal, vol. 146, December 2013, with thanks.)

Written byJim Kaler 05/19/17. Return to STARS.