October 24, 2014

Astro-Challenge: Hunting for Van Maanen’s Star.

A Earth-sized star. (Credit: NASA/RXTE).

It’s sobering to ponder the ultimate fate of our Sun. We orbit a middle-aged main sequence star, one that will continue to happily fuse hydrogen into helium for our energy consuming convenience for the next few billion years. We see the ultimate fate of our Sun, however, when we look out at planetary nebulae and burned out cinders known as white dwarfs.

This week’s astro-challenge is one such object. Gliese 35, also known as Van Maanen’s star, is one of the best telescopic examples of a white dwarf within the grasp of backyard telescopes. Shining at magnitude +12.4, Van Maanen’s star is only 14.1 light years distant, making it the 32nd nearest star to our solar system and the 3rd nearest white dwarf. The second “a” is silent, and Van Maanen is pronounced Van MUN (rhymes with “fun”) –nens star.

A wide field view of Pisces and Van Maanen’s Star.

Keen readers of this column will recall that Omicron Eridani & Sirius B are closer, but Omicron Eridani is in a trinary star system and Sirius B is extremely difficult to discern due to its nearby dazzling primary. Van Maanen’s star is thus the nearest solitary white dwarf to our solar system. One can’t help but wonder if it might just harbor a detectable exoplanet or two?

A narrow one degree field of view showing Van Maanen’s star.

The star was first noticed by Dutch astronomer Adriaan van Maanen as having a large proper motion during a 1917 sky survey. In fact, Van Maanen’s star has an annual proper motion of 3 arc seconds a year. One of the stars with the highest annual proper motions is 61 Cygni at 5.22” per year. This means that Van Maanen’s star will move about 4’ arc minutes across our sky in 80 years, a little over 10% the diameter of the Full Moon.

Keep in mind, the term white dwarf was coined years later 1922 by William Luyten; 18 white dwarfs had been identified by 1939, and thanks to the modern Sloan Digital Sky Survey, over 9,000 have now been identified. Van Maanen’s star packs 63% the mass of our Sun into a sphere about the size of the Earth; such a strange high density body squeezes matter into a degenerate state. White dwarfs can be thought of as cooling cinders, slowly and miserly releasing remnant heat back out into the universe. Eventually, these stars will cool down to black dwarf status in about 1015 years (that’s a 1 with 15 zeroes after it, or 1,000,000,000,000,000=a quadrillion years, give or take an odd eon). The universe, of course, is only 0.0013% of this age, and thus, no black dwarfs have had time to cool down yet! The very fact that there are no black dwarfs detected (and the current age of white dwarfs seen) speaks to the relative “youth” of the universe and is one of the pillars of modern cosmological theory.

But back to our Earthly vantage point. Van Maanen’s star is within three arc minutes north east of the +5.7 magnitude double star 96 Piscium. Van Maanen’s star is well placed high to the southeast just after local sunset in December for northern hemisphere observers. Its position in 2000.0 epoch coordinates is;

RA 00H 49′ 10″

Dec +05 23′ 19″

Van Maanen’s Star also makes an appearance in Larry Niven’s Rip Van Winkle tale of A World Out of Time.

Much like sighting a 14th magnitude quasar, part of the fun of spying a white dwarf is knowing what you are seeing. As the December 28th Full Moon slides out of the evening sky, Van Maanen’s star makes for a fine holiday treat to check off of your cosmic life list!

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