Astrophysicists at UC Santa Barbara are the first scientists to identify two white dwarf stars in an eclipsing binary system, allowing for the first direct radius measurement of a rare white dwarf composed of pure helium. The results will be published in the Astrophysical Journal Letters. These observations are the first to confirm a theory about a certain type of white dwarf star
Brief eclipses were discovered during observations of the star NLTT 11748 with the Faulkes Telescope North of the Las Cumbres Observatory Global Telescope (LCOGT), a UC Santa Barbara -affiliated institution. NLTT 11748 is one of the few very low-mass, helium-core white dwarfs that are under careful study for their brightness variations.
Scientists were able to measure the changing Doppler shift of the star NLTT 11748 as it orbited its faint, but more massive, white dwarf companion with the use of the 10-meter Keck Telescope, located on Mauna Kea in Hawaii, just five weeks after the first observation.
One of the stars in the newly discovered binary is a relatively rare helium-core white dwarf with a mass only 10 to 20 percent of that of the sun. Until now, their size had never been measured. The observations of the star NLTT 11748 by this research group have yielded the first direct radius measurement of an unusual white dwarf.
The new findings, from two separate studies published in the Proceedings of the National Academy of Sciences (PNAS), suggest that infection intensity –– the severity of the disease among individuals –– determines whether frog populations will survive or succumb to chytridiomycosis. The research identifies a critical tipping point in infection intensity, beyond which chytridiomycosis causes mass mortalities and extinctions.