What type of supernova starts as a white dwarf, does not show a lot of hydrogen in their spectrum,  and leaves only a confused companion?

The type of supernova that starts as a white dwarf, does not show a lot of hydrogen in their spectrum, and leaves only a confused companion is known as a Type Ia supernova.

Here are the steps that lead to this conclusion:

1. Supernovae are classified into two broad types based on their light curves and spectra: Type I and Type II.

2. Type I supernovae are further classified into Type Ia, Ib, and Ic. Among these, Type Ia supernovae are characterized by the absence of hydrogen lines in their spectra.

3. Type Ia supernovae are thought to originate from white dwarf stars in a close binary system. As the white dwarf accretes matter from its companion star, it approaches a critical mass (the Chandrasekhar limit) and undergoes a thermonuclear explosion.

4. After the explosion, the white dwarf is completely destroyed, leaving no remnant behind, only a "confused" companion star.

Therefore, the type of supernova that starts as a white dwarf, does not show a lot of hydrogen in their spectrum, and leaves only a confused companion is a Type Ia supernova.