scholarly journals Modelling the distributions of white dwarf atmospheric pollution: a low Mg abundance for accreted planetesimals?

2019 ◽  
Author(s):  
Samuel G D Turner ◽  
Mark C Wyatt
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Formation Processes ◽  
Normal Distributions ◽  
Average Mass ◽  
Pollution Levels ◽  
Single Body ◽  
Incorrect Assumption ◽  
Mass Fractions

Abstract The accretion of planetesimals onto white dwarf atmospheres allows determination of the composition of this polluting material. This composition is usually inferred from observed pollution levels by assuming it originated from a single body. This paper instead uses a stochastic model wherein polluting planetesimals are chosen randomly from a mass distribution, finding that the single body assumption is invalid in ${>20\%}$ of cases. Planetesimal compositions are modelled assuming parent bodies that differentiated into core, mantle and crust components. Atmospheric levels of Ca, Mg and Fe in the model are compared to a sample of 230 DZ white dwarfs for which such pollution is measured. A good fit is obtained when each planetesimal has its core, mantle and crust fractions chosen independently from logit-normal distributions which lead to average mass fractions of fCru = 0.15, fMan = 0.49 and fCor = 0.36. However, achieving this fit requires a factor 4 depletion of Mg relative to stellar material. This depletion is unlikely to originate in planetesimal formation processes, but might occur from heating while the star is on the giant branch. Alternatively the accreted material has stellar abundance, and either the inferred low Mg abundance was caused by an incorrect assumption that Mg sinks slower than Ca and Fe, or there are unmodelled biases in the observed sample. Finally, the model makes predictions for the timescale on which the observed pollutant composition varies, which should be the longer of the sinking and disc timescales, implying variability on decadal timescales for DA white dwarfs.

scholarly journals Hot Subluminous Stars

1980 ◽  
Vol 5 ◽  
pp. 255-262
Author(s):  
Jesse L. Greenstein
Keyword(s):  
Mass Loss ◽  
Accretion Disk ◽  
Excellent Agreement ◽  
White Dwarf ◽  
White Dwarfs ◽  
Close Binary ◽  
Maximum Temperature ◽  
Effective Temperatures ◽  
Line Strengths

Extensive mass loss is observed for hot subluminous stars, through P Cygni lines in the ultraviolet. This persists in some sub-dwarf 0 stars, but is generally not observed in white dwarfs. The ultraviolet provides determination of effective temperatures. Among nine sdO’s, the maximum temperature reported is definitely below 60, 000 K; an object at 100, 000 K would be distinguishable. The sdO’s show a wide variety of line strengths, notably in N V, C IV and Si TV, as well as He II. One halo sdB is reported as rich in peculiar elements; it shows anomalous N V for its temperature. The comparison of effective temperatures of white dwarfs observed from space and from the ground gives excellent agreement. The hottest white dwarfs are near 60, 000 K, although one (helium-rich) reaches 80, 000 K. Another helium-rich close binary probably has an accretion disk; it is the only white dwarf to show the expanding shell of N V, C IV, Si IV characteristic of some subdwarfs. Two magnetic white dwarfs have been observed; one has strong unidentifiable features and the smallest known radius.

scholarly journals Extending the White Dwarf Sequence: Plans and Prospects

1978 ◽  
Vol 80 ◽  
pp. 437-440
Author(s):  
James Liebert
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Selection Effects ◽  
Number Density ◽  
Low Velocity ◽  
Luminosity Functions ◽  
Current Sample ◽  
The Many

The recent discovery that the parallax star LP701-29 is a white dwarf has firmly extended the degenerate sequence below MV= +16m(Dahnet al. 1978). As the search for white dwarfs extends to cooler and fainter stars, however, it becomes particularly important to develop a plan for selecting candidates among the many thousands of red proper motion stars. We begin by assessing the completeness of the known sample within 10 parsecs in the northern two thirds of the sky. Some color-dependent selection effects must be evaluated, however, since these may preferentially inhibit the discovery of cooler stars. A correction factor for the missing low velocity white dwarfs is estimated. Then, Green's(1977) recent determination of the number density of blue degenerates is used to normalize various theoretical luminosity functions, the benchmarks against which the current sample out to 10 pc can be compared. It is concluded that the sample may be approaching completeness in the northern sky for white dwarfs with tangential velocities (vT) ≥ 40 km/sec (μ ≥ 1″.0/yr.) and Mbol< +15m. The implied luminosity function is thus consistent with that found by Sion and Liebert (1977). Below Mbol= +15mthe different theoretical functions predict substantially different numbers.

scholarly journals BC Cassiopeiae: First detection of IW Andromedae-type phenomenon among post-eruption novae

2020 ◽  
Vol 72 (6) ◽  
Author(s):  
Taichi Kato ◽  
Naoto Kojiguchi
Keyword(s):  
Mass Transfer ◽  
White Dwarf ◽  
Transfer Rate ◽  
White Dwarfs ◽  
Mass Transfer Rate ◽  
Cataclysmic Variables ◽  
High Mass ◽  
Average Mass ◽  
Classical Nova ◽  
Decline Rate

Abstract IW And-type dwarf novae are a recently recognized group of cataclysmic variables which are characterized by a sequence of brightening from a standstill-like phase with damping oscillations often followed by a deep dip. We found that the supposed classical nova BC Cas which erupted in 1929 experienced a state of an IW And-type dwarf nova in 2018, 89 yr after the eruption. This finding suggests that a high mass-transfer rate following the nova eruption is associated with the IW And-type phenomenon. The mass of the white dwarf inferred from the decline rate of the nova is considerably higher than the average mass of the white dwarfs in cataclysmic variables, and these massive white dwarfs may be responsible for the manifestation of the IW And-type phenomenon.

scholarly journals Size distribution of EC and OC in the aerosol of Alpine valleys during summer and winter

2005 ◽  
Vol 5 (3) ◽  
pp. 3773-3809 ◽  
Author(s):  
J.-L. Jaffrezo ◽  
G. Aymoz ◽  
J. Cozic
Keyword(s):  
Chemical Species ◽  
Rural Site ◽  
Size Spectrum ◽  
Size Distributions ◽  
Formation Processes ◽  
Secondary Formation ◽  
Mass Fractions ◽  
Intensive Sampling ◽  
Alpine Valleys

Abstract. Collections of samples were conducted for the determination of the size distributions of EC and OC during the intensive sampling campaigns of the POVA program, in two Alpine valleys of the French Alps, in summer and in winter. The comparison of concentrations obtained for samples collected in parallel with impactor- and filter-based methods indicates that the correction of pyrolysis seems to work for the impactor samples despite non even deposits. The size distributions of the concentrations of EC and OC present large evolutions between winter and summer, and between a suburban and a rural site. In winter, an overwhelming proportion of the mass fraction of both species is found in the droplet and accumulation modes, often (but not always) in association with sulfate and other chemical species resulting from secondary formation processes. Some indications of gas/particles exchanges can be found for the other parts of the size spectrum (the Aitken and super micron modes) in the case of the rural site. In summer, the changes are more drastic with, according to the case, a dominant droplet or accumulation mode. Particularly at the rural site, the large extent of processing of the aerosol due to gas/particles exchanges is evident for the Aitken and super micron modes, with increasing of the OC mass fractions in these size ranges. All of these observations give indications on the degree of internal vs. external mixing of the species investigated in the different modes.

scholarly journals Size distribution of EC and OC in the aerosol of Alpine valleys during summer and winter

2005 ◽  
Vol 5 (11) ◽  
pp. 2915-2925 ◽  
Author(s):  
J.-L. Jaffrezo ◽  
G. Aymoz ◽  
J. Cozic
Keyword(s):  
Chemical Species ◽  
Rural Site ◽  
Size Spectrum ◽  
Size Distributions ◽  
Formation Processes ◽  
Secondary Formation ◽  
Mass Fractions ◽  
Intensive Sampling ◽  
Alpine Valleys

Abstract. Collections of samples were conducted for the determination of the size distributions of EC and OC during the intensive sampling campaigns of the POVA program, in two Alpine valleys of the French Alps, in summer and in winter. The comparison of concentrations obtained for samples collected in parallel with impactor- and filter-based methods is rather positive with slopes of 0.95 and 0.76 for OC and EC, respectively and correlations close to 1 (0.92 and 0.90 for OC and EC, respectively, n=26). This is an indication that the correction of pyrolysis seems to work for the impactor samples despite non even deposits. The size distributions of the concentrations of EC and OC present large evolutions between winter and summer, and between a suburban and a rural site. In winter, an overwhelming proportion of the mass fraction of both species is found in the droplet and accumulation modes, often (but not always) in association with sulfate and other chemical species resulting from secondary formation processes. Some indications of gas/particles exchanges can be found for the other parts of the size spectrum (the Aitken and super micron modes) in the case of the rural site. In summer, the changes are more drastic with, according to the case, a dominant droplet or accumulation mode. Particularly at the rural site, the large extent of processing of the aerosol due to gas/particles exchanges is evident for the Aitken and super micron modes, with increasing of the OC mass fractions in these size ranges. All of these observations give indications on the degree of internal vs. external mixing of the species investigated in the different modes.

scholarly journals White Dwarf Candidates for Trigonometrical Parallax Determinations

1985 ◽  
Vol 111 ◽  
pp. 365-368
Author(s):  
T. J. Moffett ◽  
Thomas G. Barnes ◽  
David S. Evans
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Surface Brightness ◽  
Small Range

The visual surface brightness relation is applied to the determination of parallaxes of white dwarfs on the assumption, borne out by previous studies of white dwarfs of known parallax, that these show only a small range of linear diameters.

scholarly journals Magnetic White Dwarfs with Strong Fields and the Origin of Magnetism in White Dwarfs and Neutron Stars

1979 ◽  
Vol 53 ◽  
pp. 313-316 ◽  
Author(s):  
J. R. P. Angel
Keyword(s):  
Neutron Star ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
White Dwarf ◽  
White Dwarfs ◽  
Strong Fields ◽  
Work In Progress ◽  
Field Strengths

Work in progress at Steward Observatory covering three aspects of magnetism in degenerate dwarfs is reviewed. First, the identification of the Minkowski bands in Grw + 70° 8247 with Zeeman transitions in hydrogen. Second, a determination of field strengths in the more strongly magnetic white dwarfs. Third, some observations and speculations concerning the origin of white dwarf and neutron star magnetic fields.

scholarly journals A white dwarf bound to the transiting planetary system WASP-98

2020 ◽  
Vol 497 (4) ◽  
pp. 4416-4422
Author(s):  
John Southworth ◽  
Pier-Emmanuel Tremblay ◽  
Boris T Gänsicke ◽  
Daniel Evans ◽  
Teo Močnik
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Planetary System ◽  
Planetary Systems ◽  
Precise Determination ◽  
Spectral Lines ◽  
Low Metallicity ◽  
Gaia Dr2 ◽  
Rule Out

ABSTRACT WASP-98 is a planetary system containing a hot Jupiter transiting a late-G dwarf. A fainter star, 12 arcsec away, has previously been identified as a white dwarf, with a distance and proper motion consistent with a physical association with the planetary system. We present spectroscopy of the white dwarf, with the aim of determining its mass, radius, and temperature and hence the age of the system. However, the spectra show the featureless continuum and lack of spectral lines characteristic of the DC class of white dwarfs. We therefore fitted theoretical white dwarf spectra to the ugriz apparent magnitudes and Gaia DR2 parallax of this object in order to determine its physical properties and the age of the system. We find that the system is old, with a lower limit of 3.6 Gyr, but theoretical uncertainties preclude a precise determination of its age. Its kinematics are consistent with membership of the thick disc, but do not allow us to rule out the thin-disc alternative. The old age and low metallicity of the system suggest that it is subject to an age–metallicity relation, but analysis of the most metal-rich and metal-poor transiting planetary systems yields only insubstantial evidence of this. We conclude that the study of bound white dwarfs can yield independent ages to planetary systems, but such analysis may be better suited to DA and DB rather than DC white dwarfs.

scholarly journals White Dwarf Probes of Interstellar Deuterium

2000 ◽  
Vol 198 ◽  
pp. 485-486
Author(s):  
Wayne Landsman
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
White Dwarf ◽  
White Dwarfs ◽  
Accurate Determination ◽  
The Sun ◽  
Local Interstellar Medium ◽  
Space Telescope ◽  
Imaging Spectrograph

We review the advantages of using hot white dwarfs (WDs) as probes of the deuterium abundance in the local interstellar medium. We then discuss advantages of the Space Telescope Imaging Spectrograph (STIS) for such observations, as compared with earlier observations with the Goddard High Resolution Spectrograph (GHRS). The GHRS Ly α profile of the white dwarf HZ 43 is probably modified by the hot ‘hydrogen wall’ surrounding the Sun; but despite this complication, the sightline remains a promising one for an accurate determination of the deuterium abundance in the local interstellar medium.

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