Suchergebnisse

We carry out high-speed photometry on 20 of the shortest-period, detached white dwarf binaries known and discover systems with eclipses, ellipsoidal variations (due to tidal deformations of the visible white dwarf), and Doppler beaming. All of the binaries contain low-mass white dwarfs with orbital periods of less than four hr. Our observations identify the first eight tidally distorted white dwarfs, four of which are reported for the first time here. We use these observations to place empirical constraints on the mass-radius relationship for extremely low-mass (<= 0.30 M-circle dot) white dwarfs. We also detect Doppler beaming in several of these binaries, which confirms their high-amplitude radial-velocity variability. All of these systems are strong sources of gravitational radiation, and long-term monitoring of those that display ellipsoidal variations can be used to detect spin-up of the tidal bulge due to orbital decay. ; NSF AST-0909107, AST-1312678 ; Norman Hackerman Advanced Research Program 003658-0252-2009 ; European Research Council under the European Union's Seventh Framework Programme/ERC 320964 ; NASA NNX12AC96G ; Astronomy

We present a preliminary analysis of the cool pulsating white dwarf (WD) GD 1212, enabled by more than 11.5 days of space-based photometry obtained during an engineering test of the two-reaction-wheel-controlled Kepler spacecraft. We detect at least 19 independent pulsation modes, ranging from 828.2-1220.8 s, and at least 17 nonlinear combination frequencies of those independent pulsations. Our longest uninterrupted light curve, 9.0 days in length, evidences coherent difference frequencies at periods inaccessible from the ground, up to 14.5 hr, the longest-period signals ever detected in a pulsating WD. These results mark some of the first science to come from a two-wheel-controlled Kepler spacecraft, proving the capability for unprecedented discoveries afforded by extending Kepler observations to the ecliptic. ; European Research Council under the European Union 320964 ; NSF AST-0909107, AST-1312678 ; Norman Hackerman Advanced Research Program 003658-0252-2009 ; NASA NNX12AC96G, NNX13AC23G, NNX14AB92G ; Foundation for Fundamental Research on Matter (FOM), Netherlands Organisation for Scientific Research (NWO) ; McDonald Observatory