White Dwarf Merger Remnants: The DAQ Subclass
The Astrophysical Journal(2024)
摘要
Four years after the discovery of a unique DAQ white dwarf with a
hydrogen-dominated and carbon-rich atmosphere, we report the discovery of four
new DAQ white dwarfs, including two that were not recognized properly in the
literature. We find all five DAQs in a relatively narrow mass and temperature
range of M=1.14-1.19 M_⊙ and T_ eff=13,000-17,000 K. In
addition, at least two show photometric variations due to rapid rotation with
≈10 min periods. All five are also kinematically old, but appear
photometrically young with estimated cooling ages of about 1 Gyr based on
standard cooling tracks, and their masses are roughly twice the mass of the
most common white dwarfs in the solar neighborhood. These characteristics are
smoking gun signatures of white dwarf merger remnants. Comparing the DAQ sample
with warm DQ white dwarfs, we demonstrate that there is a range of hydrogen
abundances among the warm DQ population, and the distinction between DAQ and
warm DQ white dwarfs is superficial. We discuss the potential evolutionary
channels for the emergence of the DAQ subclass, and suggest that DAQ white
dwarfs are trapped on the crystallization sequence, and may remain there for a
significant fraction of the Hubble time.
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关键词
White dwarf stars,Atmospheric composition,Stellar evolutionary types,Stellar mergers,DQ stars
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