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ABSTRACT We study a suite of extremely high-resolution cosmological Feedback in Realistic Environments simulations of dwarf galaxies ($$M_{\rm halo} \lesssim 10^{10}\rm \, M_{\odot }$$), run to z = 0 with $$30\, \mathrm{M}_{\odot }$$ resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with $$M_{\rm halo} \gtrsim 10^{8.6}\, \mathrm{M}_{\odot }$$ is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. Our ultra-faint dwarfs (UFDs; $$M_{\ast }\lt 10^{5}\, \mathrm{M}_{\odot }$$) have their star formation (SF) truncated early (z ≳ 2), likely by reionization, while classical dwarfs ($$M_{\ast }\gt 10^{5}\, \mathrm{M}_{\odot }$$) continue forming stars to z < 0.5. The systems have bursty star formation histories, forming most of their stars in periods of elevated SF strongly clustered in both space and time. This allows our dwarf with M*/Mhalo > 10−4 to form a dark matter core $${\gt}200\rm \, pc$$, while lower mass UFDs exhibit cusps down to $${\lesssim}100\rm \, pc$$, as expected from energetic arguments. Our dwarfs with $$M_{\ast }\gt 10^{4}\, \mathrm{M}_{\odot }$$ have half-mass radii (R1/2) in agreement with Local Group (LG) dwarfs (dynamical mass versus R1/2 and stellar rotation also resemble observations). The lowest mass UFDs are below surface brightness limits of current surveys but are potentially visible in next-generation surveys (e.g. LSST). The stellar metallicities are lower than in LG dwarfs; this may reflect pre-enrichment of the LG by the massive hosts or Pop-III stars. Consistency with lower resolution studies implies that our simulations are numerically robust (for a given physical model).
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General relativistic pulsations of ultra-massive ZZ Ceti stars
ABSTRACT Ultra-massive white dwarf stars are currently being discovered at a considerable rate, thanks to surveys such as the Gaia space mission. These dense and compact stellar remnants likely play a major role in Type Ia supernova explosions. It is possible to probe the interiors of ultra-massive white dwarfs through asteroseismology. In the case of the most massive white dwarfs, general relativity could affect their structure and pulsations substantially. In this work, we present results of relativistic pulsation calculations employing relativistic ultra-massive ONe-core white dwarf models with hydrogen-rich atmospheres and masses ranging from 1.29 to $$1.369 \ \mathrm{M}_{\odot }$$ with the aim of assessing the impact of general relativity on the adiabatic gravity (g)-mode period spectrum of very high mass ZZ Ceti stars. Employing the relativistic Cowling approximation for the pulsation analysis, we find that the critical buoyancy (Brunt–Väisälä) and acoustic (Lamb) frequencies are larger for the relativistic case, compared to the Newtonian case, due to the relativistic white dwarf models having smaller radii and higher gravities for a fixed stellar mass. In addition, the g-mode periods are shorter in the relativistic case than those in the Newtonian computations, with relative differences of up to ∼$50$ per cent for the highest mass models ($$1.369 \ \mathrm{M}_{\odot }$$) and for effective temperatures typical of the ZZ Ceti instability strip. Hence, the effects of general relativity on the structure, evolution, and pulsations of white dwarfs with masses larger than ∼$$1.29 \ \mathrm{M}_{\odot }$$ cannot be ignored in the asteroseismological analysis of ultra-massive ZZ Ceti stars.
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- PAR ID:
- 10439350
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 524
- Issue:
- 4
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 5929-5943
- Size(s):
- p. 5929-5943
- Sponsoring Org:
- National Science Foundation
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