PRESS RELEASE, January 2002
A DOZEN NEW STARS FOUND IN THE SUN'S NEIGHBORHOOD
Dr. Todd J. Henry
Dr. Philip A. Ianna
Dr. Rene A. Mendez
A dozen new nearby stars have been discovered lurking near the Sun, underscoring how little astronomers know even about stellar neighbors living just down the block. Using relatively small telescopes located in the foothills of the Chilean Andes, Todd Henry, Wei-Chun Jao, and John Subasavage of Georgia State University in Atlanta, and Phil Ianna of the University of Virginia have discovered one white dwarf and 11 red dwarf stars that are among the Sun's nearest few hundred neighbors. Their results are being presented at the American Astronomical Society meeting in Washington, DC.
The international team, which also includes Rene Mendez of the European Southern Observatory and Edgardo Costa of the Universidad de Chile, both in Santiago, Chile, is observing more than 200 stellar systems with the 0.9m (36in) and 1.5m (60in) telescopes at the Cerro Tololo Interamerican Observatory located near La Serena, Chile. Although these telescopes are dwarfed by many of today's behemoth 8m and 10m aperture telescopes, these smaller ``Mighty Mouse'' telescopes are helping Henry's RECONS (Research Consortium on Nearby Stars) team develop a three-dimensional map of nearby space. The search for new nearby stars is carried out under the auspices of the National Science Foundation's NOAO Surveys Program, which awards large blocks of telescope observing time to carry out comprehensive surveys.
The southern skies have proven to be happy hunting grounds for discoveries because historically, research on nearby stars has been far less extensive in the south than in the north. Since discovering the 20th nearest star in 1997 (GJ 1061 at a distance of 3.7 pc, or 11.9 light years), Henry and Ianna have been searching the southern skies for more of our elusive neighbors. The new dozen stars are found in 9 stellar systems, made up of 7 single stars, one double star system, and one triple. These new neighbors are all additions to the elite RECONS sample of stars --- all stars known within 10 parsecs (33 light years) of the Sun (current count 316 objects in 228 systems). Twenty-four more new systems containing 29 stars have been found within 25 parsecs (82 light years).
Henry, a professor of astronomy at Georgia State University in Atlanta (a sort of ``nearby space cartographer''), likens the search for new nearby stars to a treasure hunt, where each new find is a gem. ``Each of the new stars provides a fresh target where we can look for planets, and ultimately, for life on those planets. And you never know, a few hundred years from now, we may even want to live on a planet circling one of these stars.''
A nearby star is identified by making a series of positional measurements relative to background stars over a few years. These astrometric measurements are used to trace out the wiggly snake-like paths of nearby stars caused by the superposition of a star's linear proper motion across the sky and its elliptical parallactic motion.
The proper motion is the result of a star's random motion through our Milky Way Galaxy relative to our Sun, much like how fireflies slide across our view as we walk through a meadow. The parallactic motion is caused by our changing perspective of the heavens as the Earth orbits the Sun each year --- nearby stars wobble back and forth once each year relative to more distant stars. The same effect can be seen if you simply blink one eye, then the other, and carefully note the changing position of a nearby firefly relative to more distant fireflies on the other side of the meadow. Even the nearest star, Proxima Centauri, at 1.3 pc (4.2 light years) has a parallax less than one arcsecond, corresponding to a wobble of only about 1/2000th the width of the full moon.
The new neighbors have been overlooked because they are thousands of times fainter than stars seen with the naked eye. The nearest of the new discoveries is LHS 1723, a small ember of a star only one-third the mass and diameter of the Sun, emitting less than 1% of the Sun's light. With a parallax of 0.1834 arcseconds, it is only 20 light years away, and ranks as the 55th nearest system. Although it is relatively easy to sketch a two-dimensional map of the stars in the sky (right ascension and declination), providing the third dimension --- the stars' distances --- is much more difficult. Nonetheless, with perseverance, the RECONS team has managed to measure most of the new stellar distances to an accuracy of 2% or better.
This work has been supported by the National Science Foundation (observing time at CTIO) and financially by NASA via the Nearby Stars Project at NASA-Ames and the Space Interferometry Mission at the Jet Propulsion Laboratory.