Pierre Dufour

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White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is(More)
We present extensive early photometric (ultraviolet through near-infrared) and spectroscopic (optical and near-infrared) data on supernova (SN) 2008D as well as X-ray data analysis on the associated Swift X-ray transient (XRT) 080109. Our data span a time range of 5 hr before the detection of the X-ray transient to 150 days after its detection, and a(More)
We present accurate trigonometric parallaxes for 20 new members of the 25 pc white dwarf (WD) sample as part of the Discovery and Evalution of Nearby Stellar Embers (DENSE) project. 7 Previously, there were a total of 112 WD systems with trigonometric parallaxes placing them within 25 pc and of these, 99 have trigonometric parallaxes known to better than(More)
We present medium resolution spectroscopy and multi-epoch V RI photometry for 21 new nearby (< 50 pc) white dwarf systems brighter than V ∼ 17. Of the new systems, ten are DA (including a wide double degenerate system with two DA components), eight are DC, two are DZ, and one is DB. In addition, we include multi-epoch V RI photometry for eleven known white(More)
We report the discovery of a new class of hydrogen-deficient stars: white dwarfs with an atmosphere primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch (AGB)(More)
We present extensive early photometric (U BV Rr ′ Ii ′ JHK s) and spectroscopic (optical and near-infrared) data on supernova (SN) 2008D as well as X-ray data on the associated X-ray transient (XRT) 080109 which was serendipitously discovered in Swift data during follow-up observations of SN Ib 2007uy in the same galaxy, NGC 2770. Our data span a time range(More)
We present a detailed analysis of a large spectroscopic and photometric sample of DZ white dwarfs based on our latest model atmosphere calculations. We revise the atmospheric parameters of the trigonometric parallax sample of Bergeron, Leggett, & Ruiz (12 stars) and analyze 147 new DZ white dwarfs discovered in the Sloan Digital Sky Survey. The inclusion of(More)
A reanalysis of the strongly metal-blanketed DZ white dwarf G165-7 is presented. An improved grid of model atmospheres and synthetic spectra is used to analyze BV RI, JHK, and ugriz photometric observations as well as a high quality Sloan Digital Sky Survey spectrum covering the energy distribution from 3600 to 9000Å. The detection of splitting in several(More)
We present an analysis of spectroscopic and photometric data for cool DQ white dwarfs based on improved model atmosphere calculations. In particular, we revise the atmospheric parameters of the trigonometric parallax sample of Bergeron et al. (2001), and discuss the astrophysical implications on the temperature scale and mean mass, as well as the chemical(More)
Measurements of differential cross sections for quasielastic electron-deuteron scattering e + d-e + p + n have been made in which recoil protons were detected in coincidence with the scattered electrons. The ratios of the elastic electron-neutron to the electron-proton scattering cross sections are derived from the proton coincidence data. For comparison,(More)