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Abstract We present a detailed model atmosphere analysis of massive white dwarfs withM> 0.9M⊙andTeff≥ 11,000 K in the Montreal White Dwarf Database 100 pc sample and the Pan-STARRS footprint. We obtained follow-up optical spectroscopy of 109 objects with no previous spectral classification in the literature. Our spectroscopic follow-up is now complete for all 204 objects in the sample. We find 118 normal DA white dwarfs, including 45 massive DAs near the ZZ Ceti instability strip. There are no normal massive DBs: the six DBs in the sample are strongly magnetic and/or rapidly rotating. There are 20 massive DQ white dwarfs in our sample, and all are found in the crystallization sequence. In addition, 66 targets are magnetic (32% of the sample). We use magnetic white dwarf atmosphere models to constrain the field strength and geometry using offset dipole models. We also use magnetism, kinematics, and rotation measurements to constrain the fraction of merger remnant candidates among this population. The merger fraction of this sample increases from 25% for 0.9–1M⊙white dwarfs to 49% for 1.2–1.3M⊙. However, this fraction is as high as % for 1.1–1.2M⊙white dwarfs. Previous works have demonstrated that 5%–9% of high-mass white dwarfs stop cooling for ∼8 Gyr due to the22Ne distillation process, which leads to an overdensity of Q-branch stars in the solar neighborhood. We demonstrate that the overabundance of the merger remnant candidates in our sample is likely due to the same process.
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An Isolated White Dwarf with a 70 s Spin Period
Abstract We report the discovery of an isolated white dwarf with a spin period of 70 s. We obtained high-speed photometry of three ultramassive white dwarfs within 100 pc and discovered significant variability in one. SDSS J221141.80+113604.4 is a 1.27M⊙(assuming a CO core) magnetic white dwarf that shows 2.9% brightness variations in the BG40 filter with a 70.32 ± 0.04 s period, becoming the fastest spinning isolated white dwarf currently known. A detailed model atmosphere analysis shows that it has a mixed hydrogen and helium atmosphere with a dipole field strength ofBd= 15 MG. Given its large mass, fast rotation, strong magnetic field, unusual atmospheric composition, and relatively large tangential velocity for its cooling age, J2211+1136 displays all of the signatures of a double white dwarf merger remnant. Long-term monitoring of the spin evolution of J2211+1136 and other fast-spinning isolated white dwarfs opens a new discovery space for substellar and planetary mass companions around white dwarfs. In addition, the discovery of such fast rotators outside of the ZZ Ceti instability strip suggests that some should also exist within the strip. Hence, some of the monoperiodic variables found within the instability strip may be fast-spinning white dwarfs impersonating ZZ Ceti pulsators.
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- Award ID(s):
- 1906379
- PAR ID:
- 10484950
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 923
- Issue:
- 1
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L6
- Size(s):
- Article No. L6
- Sponsoring Org:
- National Science Foundation
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