White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14

Kepler, S. O.; Pelisoli, Ingrid; Koester, D.; Reindl, N.; Geier, S.; Romero, A. D.; Ourique, Gustavo; Oliveira, Cristiane de Paula; Amaral, Larissa Antunes

doi:10.1093/mnras/stz960

Cited by 117 publications

(145 citation statements)

References 86 publications

(84 reference statements)

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“…We note the misidentification is skewed toward DA-type objects with 5.2% (22/423) of these objects on the He-rich side of the cut, compared to 2.2% (4/183) for the non-DA types. An inspection of the spectra for the DA-type objects in the He-rich region finds the majority (16/22) are either He-rich DAs or DA+DC binaries (Rolland et al 2018;Kepler et al 2019), suggesting those objects may sit correctly in the photometric analysis. A further 5 objects on both sides show evidence of metal pollution or strong magnetic fields.…”

Section: Resultsmentioning

confidence: 99%

From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing

Cunningham

Tremblay

Fusillo

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present a study of the hypothesis that white dwarfs undergo a spectral change from hydrogen-to helium-dominated atmospheres using a volume-limited photometric sample drawn from the Gaia DR2 catalogue, the Sloan Digital Sky Survey (SDSS) and the Galaxy Evolution Explorer (GALEX). We exploit the strength of the Balmer jump in hydrogen-atmosphere DA white dwarfs to separate them from helium-dominated objects in SDSS colour space. Across the effective temperature range from 20 000 K to 9000 K we find that 22% of white dwarfs will undergo a spectral change, with no spectral evolution being ruled out at 5σ. The most likely explanation is that the increase in He-rich objects is caused by the convective mixing of DA stars with thin hydrogen layers, in which helium is dredged up from deeper layers by a surface hydrogen convection zone. The rate of change in the fraction of He-rich objects as a function of temperature, coupled with a recent grid of 3D radiation-hydrodynamic simulations of convective DA white dwarfs -which include the full overshoot region -lead to a discussion on the distribution of total hydrogen mass in white dwarfs. We find that 60% of white dwarfs must have a hydrogen mass larger than M H /M WD = 10 −10 , another 25% have masses in the range M H /M WD = 10 −14 − 10 −10 , and 15% have less hydrogen than M H /M WD = 10 −14 . These results have implications for white dwarf asteroseismology, stellar evolution through the asymptotic giant branch (AGB) and accretion of planetesimals onto white dwarfs.

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Section: Resultsmentioning

confidence: 99%

From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing

Cunningham

Tremblay

Fusillo

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…The dependence of the spectral evolution on the effective temperature is expected since it is directly related to convection episodes during the white dwarf evolution. Kepler et al (2019) show that the mass distribution for DBs has a mean of 0.618±0.004 M , assuming pure Helium atmospheres, with a very small number of DBs at higher masses, in agreement with Genest-Beaulieu & Bergeron (2019) and Ourique et al (2019). This is an indication that the process that results in extremely thin -or non-existent -hydrogen layer white dwarfs (probably Late Thermal Pulse, Very Late Thermal Pulse, or merger) is not effective for the progenitors of white dwarfs with masses higher than 0.75 M .…”

Section: Discussionmentioning

confidence: 99%

Evidence of spectral evolution on the white dwarf sample from the Gaia mission

Ourique

Romero

Klippel

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Since the Gaia data release 2, several works were published describing a bifurcation in the observed white dwarf colour−magnitude diagram for G BP − G RP > 0. Some possible explanations in the literature include the existence of a double population with different initial mass function or two distinct populations, one formed by hydrogen− and one formed by helium−envelope white dwarfs. We propose instead spectral evolution to explain the bifurcation. From a population synthesis approach, we find that the spectral evolution occurs for effective temperature below 11 000 K and masses mainly between 0.64 M and 0.74 M , which correspond to around 16 per cent of all DA white dwarfs. We also find the Gaia white dwarf colour-magnitude diagram indicates a star formation history that decreases abruptly for objects younger than 1.4 Gyr and a top-heavy initial mass function for the white dwarf progenitors.

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“…The type Ia SN rate is in z < 0.5 [49]. The WD masses in the Milky Way from the SDSS data show nearly a Gaussian distribution, peaked at 0.6 [50]. Assuming that the mass distribution of WD in NS-WD binaries is similar to the SDSS result and that the massive WD ( 0.6 )-NS (1.4 ) binaries (total mass 2.0 ) will mostly form magnetars, the magnetar formation rate will be roughly < 50% of the NS-WD merger rate.…”

Section: Discussion On Emission and Formation Rate Of Remnantsmentioning

confidence: 94%

The Remnant of Neutron Star-White Dwarf Merger and the Repeating Fast Radio Bursts

Ling¹

2020

IJAA

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Fast radio bursts (FRBs) at cosmological distances still hold concealed physical origins. Previously Liu (2018) proposes a scenario that the collision between a neutron star (NS) and a white dwarf (WD) can be one of the progenitors of non-repeating FRBs and notices that the repeating FRBs can also be explained if a magnetar formed after such NS-WD merger. In this paper, we investigate this channel of magnetar formation in more detail. We propose that the NS-WD post-merger, after cooling and angular momentum redistribution, may collapse to either a black hole or a new NS or even remains as a hybrid WDNS, depending on the total mass of the NS and WD. In particular, the newly formed NS can be a magnetar if the core of the WD collapsed into the NS while large quantities of degenerate electrons of the WD compressed to the outer layers of the new NS. A strong magnetic field can be formed by the electrons and positive charges with different angular velocities induced by the differential rotation of the newborn magnetar. Such a magnetar can power the repeating FRBs by the magnetic reconnections due to the crustal movements or starquakes.

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White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14

Cited by 117 publications

References 86 publications

From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing

From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing

Evidence of spectral evolution on the white dwarf sample from the Gaia mission

The Remnant of Neutron Star-White Dwarf Merger and the Repeating Fast Radio Bursts

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