SIMBAD references

The presence of a small amount of hydrogen is expected in most single-degenerate scenarios for producing a Type Ia supernova (SN Ia). While hydrogen may be detected in very early high-resolution optical spectra, in early radio spectra, and in X-ray spectra, here we examine the possibility of detecting hydrogen in early low-resolution spectra such as those that will be obtained by proposed large-scale searches for nearby SNe Ia. We find that definitive detections will require both very early spectra (less than 5 days after explosion) and perhaps slightly higher amounts of hydrogen than are currently predicted to be mixed into the outer layers of SNe Ia. Thus, the nondetection of hydrogen so far does not in and of itself rule out any current progenitor models. Nevertheless, very early spectra of SNe Ia will provide significant clues to the amount of hydrogen present and hence to the nature of the SN Ia progenitor system. Spectral coverage in both the optical and IR will be required to definitively identify hydrogen in low-resolution spectra.