Van Maanen's Star

The observed number of white dwarfs in the Solar neighborhood comprises only about one percent of its dynamical mass density (Liebert et al, 1988), but most white dwarfs companions in binary systems with bright, main sequence stars probably have not been detected because of their relative faintness and because of the glare from the primary star (James Liebert, 1980). A recent survey of 146 DZ white dwarfs and their "externatlly polluted atmospheres" suggests that at least 3.5 percent of white dwarfs may harbor the remnants of terrestrial planetary systems, while another study of 129 white dwarfs within 20 parsecs (65.2 light-years) of the Solar System suggests that at least one fifth (20 percent) have "photospheric metals" that may have come from accretion of circumstallar debris disks which may have eventually produced planets or asteroid-like bodies (Farihi et al, 2010; and Sion et al, 2009). All the known white dwarfs within 20 parsecs (65.2 light-years) of the Solar System appear to be members of the thin disk, as none exhibit kinematic properties of the halo or extended thick disk Sion et al, 2009).

The Star

Van Maanen's Star (also known as Van Maanen 2) is a stellar remnant of spectral and luminosity type DZ8.1 (Holberg et al, 2008), previously typed as DF-G. As a DZ white dwarf, it is relatively cool with metallic but no hydrogen or helium lines in its spectrum (Weidemann and Koester, 1989). It is the closest white dwarf to Sol without a stellar companion (i.e., as a stand-alone object), and its relative coolness suggests that it is a very old star, perhaps near or older than 10 billion years, but recent studies have presumed an age of 3.7 to 5 billion years based on cooling age, particularly in searches for a detectable brown dwarf companion (Burleigh et al, 2008; and Farihi et al, 2004; Bergeron et al, 2001).

Van Maanen's Star has about 0.57 to 0.63 (up to a modelled 0.83) of Sol's mass (Burleigh et al, 2008; Farihi et al, 2004; Bergeron et al, 2001; and Volker Weidemann, 1960), but with only about 1.3 percent of its diameter (Gatewood and Russell, 1974), and less than 2/10,000th of its brightness. White dwarfs are incredibly dense objects because they squeeze a stellar mass into a planetary volume. According to Robert Burnham, Jr., Van Maanen's Star has a computed diameter of about 7,800 miles (just under the Earth's diameter of 7,930 miles), which results in a density of about 20 tons to the cubic inch, or about 10 times the computed density of Sirius B, the closest known white dwarf. While tiny compared to main sequence stars, white dwarf stars are actually intensely hot, but without the internal heat of fusion to keep them burning, they gradually cool and fade away. Some alternative names and useful star catalogue numbers are: Gl 35, Hip 3829, G 1-27, G 70-16, LHS 7, LTT 10292, LFT 76, Wolf 28, WD 0046+05, WD 0046+051, and W 5.

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