» Finding White Dwarfs: UV-Bright Objects Confirmed as Stellar Conclusions
Finding White Dwarfs: UV-Bright Objects Confirmed as Stellar Conclusions
Submitted by Nola Redd on Mon, 3/14/2011, 2:10 PM
Searching the sky for objects bright in the ultraviolet but visually dim led to confirmation of several white dwarfs.
The spectra of some of the DA white dwarfs located within the galactic plane.
White dwarfs make fantastic astrochronometers. Because of their predictable cooling rate, astronomers can use them to gauge the age of the regions they lay within. By analyzing a catalog of high-velocity ultraviolet-bright sources, AMNH researcher Sebastien Lepine was able to determine the age, mass, and temperature for several white dwarfs within the plane of the Milky Way.
Although the plane of the galaxy is home to a host of objects, there are very few UV surveys taken. The brightness of the region overpowers more modern telescopes and can damage sensitive electronic components. Lepine, along with Pierre Bergeron (Université de Montréal) and Howard Lanning (National Optical Observatories), turned to photographic images from the 1960s. They identified objects that were bright in the UV—and thus have high temperatures—but were not visually bright. They had also previously obtained the proper motion of the stars and realized they were relatively nearby.
DB, DZ, and DC white dwarfs spectra. The DB white dwarfs reveal neutral helium lines. Lines of calcium dominates the DZ white dwarf. The DC white dwarfs appear featureless. Also shown are the stars the team classified as hot subdwarfs (sdO and sdB).
"When you have a star that is very hot but not very bright, it's usually a white dwarf," Lepine explained. "We followed up with spectroscopy to see if we could indeed confirm they were white dwarfs, and it worked!"
Four objects originally thought to be white dwarfs due to their UV brightness and relative velocities. Their spectra proved them to be field F stars.
Of the 46 objects studied, 39 were white dwarfs, 3 were hot subdwarfs—objects with gravities that are lower than main-sequence stars but not as high as white dwarfs'—and 4 were F star interlopers. Most of the white dwarfs were hydrogen white dwarfs, one with a low-mass main sequence companion. Five were helium white dwarfs, three had featureless spectra, and the last had calcium lines present. Most of the targets studied had spent less than a billion years as a white dwarf.
By spectroscopically confirming the status of these UV-bright objects as white dwarfs, Lepine and his team determined that the youngest of their targets were not associated with recent star formation in the area surrounding them. The study also contributed to forming a complete census necessary for learning about white dwarfs, the last stages of evolution for most stars in the universe.
