Publications (2)6.02 Total impact
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Article: Evidence for Type Ia Supernova Diversity from Ultraviolet Observations with the Hubble Space Telescope
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ABSTRACT: We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This dataset provides unique spectral time series down to 2000 Angstrom. Significant diversity is seen in the near maximum-light spectra (~ 2000--3500 Angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminosities measured in uvw1/F250W are found to correlate with the B-band light-curve shape parameter dm15(B), but with much larger scatter relative to the correlation in the broad-band B band (e.g., ~0.4 mag versus ~0.2 mag for those with 0.8 < dm15 < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by ~0.9 mag and ~2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.10/2011; -
Article: On interacting helium star-white dwarf pairs as supernova precursors
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ABSTRACT: The authors explore the possibility that some Type Ib and some Type Ia supernovae might be the consequence of mass transfer from a helium star to a carbon-oxygen degenerate dwarf. Such mass-transferring systems are formed by close binaries of intermediate mass if the orbital separation is appropriately reduced by common envelope action. If the helium star is kept in contact with its Roche lobe by angular momentum loss due to gravitational wave radiation alone, mass-transfer rates on the order of a few times 10-8M_sun;yr-1 arise, and helium is ignited when the mass of the accreted helium shell reaches 0.1 - 0.3 M_sun;. The nature of the outburst depends on the angular momentum of the accreting dwarf and on the abundance of 14N in the accreted material.The Astrophysical Journal 05/1987; 317:717-723. · 6.02 Impact Factor
