Measurements of Physical Parameters of White Dwarfs: A Test of the Mass–Radius Relation

ABSTRACT Several white dwarfs (WDs) with atmospheric metal pollution have been found to host small planetary bodies (planetesimals) orbiting near the tidal disruption radius. We study the physical properties and dynamical origin of these bodies under the hypothesis that they underwent high-eccentricity migration from initial distances of several astronomical units. We examine two plausible mechanisms for orbital migration and circularization: tidal friction and ram-pressure drag in a compact disc. For each mechanism, we derive general analytical expressions for the evolution of the orbit that can be rescaled for various situations. We identify the physical parameters that determine whether a planetesimal’s orbit can circularize within the appropriate time-scale and constrain these parameters based on the properties of the observed systems. For tidal migration to work, an internal viscosity similar to that of molten rock is required, and this may be naturally produced by tidal heating. For disc migration to operate, a minimal column density of the disc is implied; the inferred total disc mass is consistent with estimates of the total mass of metals accreted by polluted WDs.

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Searching for ZZ Ceti white dwarfs in the Gaia survey

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320000265 ◽

2019 ◽

Vol 15 (S357) ◽

pp. 123-126

Author(s):

Olivier Vincent ◽

Pierre Bergeron ◽

David Lafrenière

Keyword(s):

White Dwarf ◽

White Dwarfs ◽

Physical Parameters ◽

Hydrogen Line ◽

Instability Strip ◽

Dwarf Stars ◽

White Dwarf Stars ◽

Effective Temperatures

AbstractThe Gaia satellite recently released parallax measurements for nearly 400,000 white dwarf stars, allowing for precise measurements of their physical parameters. By combining these parallaxes with Pan-STARRS and CFIS-u photometry, we measured the effective temperatures and surface gravities for all white dwarfs within 100 pc and identified a sample of ZZ Ceti white dwarf candidates within the instability strip. We report the results of a photometric follow-up, currently under way, aimed at identifying new ZZ Ceti stars among this sample using the PESTO camera attached to the 1.6-m telescope at the Mont Mégantic Observatory. Our goal is to verify that ZZ Ceti stars occupy a region in the logg-Teff plane where no nonvariable stars are found, supporting the idea that ZZ Ceti pulsators represent a phase through which all hydrogen-line (DA) white dwarfs must evolve.

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Line shapes of the magnesium resonance lines in cool DZ white dwarf atmospheres

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834067 ◽

2018 ◽

Vol 619 ◽

pp. A152 ◽

Cited By ~ 6

Author(s):

N. F. Allard ◽

J. F. Kielkopf ◽

S. Blouin ◽

P. Dufour ◽

F. X. Gadéa ◽

...

Keyword(s):

White Dwarf ◽

Resonance Line ◽

White Dwarfs ◽

Ad Hoc ◽

Full Range ◽

Abundance Ratio ◽

Spectral Lines ◽

Physical Parameters ◽

Line Profiles ◽

Line Shapes

Context. Line shapes of the magnesium resonance lines in white dwarf spectra are determined by the properties of magnesium atoms and the structure of the white dwarf atmosphere. Through their blanketing effect, these lines have a dominant influence on the model structure and thus on the determination from the spectra of other physical parameters that describe the stellar atmosphere and elemental abundances. Aims. In continuation of previous work on Mg+He lines in the UV, we present theoretical profiles of the resonance line of neutral Mg perturbed by He at the extreme density conditions found in the cool largely transparent atmosphere of DZ white dwarfs. Methods. We accurately determined the broadening of Mg by He in a unified theory of collisional line profiles using ab initio calculations of MgHe potential energies and transition matrix elements among the singlet electronic states that are involved for the observable spectral lines. Results. We computed the shapes and line parameters of the Mg lines and studied their dependence on helium densities and temperatures. We present results over the full range of temperatures from 4000 to 12 000 K needed for input to stellar spectra models. Atmosphere models were constructed for a range of effective temperatures and surface gravities typical for cool DZ white dwarfs. We present synthetic spectra tracing the behavior of the Mg resonance line profiles under the low temperatures and high gas pressures prevalent in these atmospheres. Conclusions. The determination of accurate opacity data of magnesium resonance lines together with an improved atmosphere model code lead to a good fit of cool DZ white dwarf stars. The broadening of spectral lines by helium needs to be understood to accurately determine the H/He and Mg/He abundance ratio in DZ white dwarf atmospheres. We emphasize that no free potential parameters or ad hoc adjustments were used to calculate the line profiles.

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Population synthesis of accreting white dwarfs: Rates and evolutionary pathways of H and He novae

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab1160 ◽

2021 ◽

Author(s):

Alex J Kemp ◽

Amanda I Karakas ◽

Andrew R Casey ◽

Robert G Izzard ◽

Ashley J Ruiter ◽

...

Keyword(s):

White Dwarfs ◽

Binary Systems ◽

Physical Parameters ◽

Population Synthesis ◽

Common Envelope ◽

Evolutionary Pathways ◽

Binary Evolution ◽

Observational Estimate ◽

Almost All ◽

Event Rates

Abstract Novae are some of the most commonly detected optical transients and have the potential to provide valuable information about binary evolution. Binary population synthesis codes have emerged as the most effective tool for modelling populations of binary systems, but such codes have traditionally employed greatly simplified nova physics, precluding detailed study. In this work, we implement a model treating H and He novae as individual events into the binary population synthesis code binary_c. This treatment of novae represents a significant improvement on the ‘averaging’ treatment currently employed in modern population synthesis codes. We discuss the evolutionary pathways leading to these phenomena and present nova event rates and distributions of several important physical parameters. Most novae are produced on massive white dwarfs, with approximately 70 and 55 per cent of nova events occurring on O/Ne white dwarfs for H and He novae respectively. Only 15 per cent of H-nova systems undergo a common-envelope phase, but these systems are responsible for the majority of H nova events. All He-accreting He-nova systems are considered post-common-envelope systems, and almost all will merge with their donor star in a gravitational-wave driven inspiral. We estimate the current annual rate of novae in M31 (Andromeda) to be approximately 41 ± 4 for H novae, underpredicting the current observational estimate of $65^{+15}_{-16}$, and 0.14 ± 0.015 for He novae. When varying common-envelope parameters, the H nova rate varies between 20 and 80 events per year.

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Physical parameters of the DA white dwarfs from ESO SN Ia Progenitor Survey data

10.1063/1.3527861 ◽

2010 ◽

Author(s):

M. Nalezyty ◽

A. Majczyna ◽

J. Madej ◽

Klaus Werner ◽

T. Rauch

Keyword(s):

Survey Data ◽

White Dwarfs ◽

Physical Parameters

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Semi-analytical formulas for the Hertzsprung-Russell diagram

Serbian Astronomical Journal ◽

10.2298/saj0877073z ◽

2008 ◽

pp. 73-85 ◽

Cited By ~ 8

Author(s):

L. Zaninetti

Keyword(s):

Theoretical Basis ◽

Taylor Expansion ◽

White Dwarfs ◽

New Technique ◽

Physical Parameters ◽

Planck Distribution ◽

Visual Magnitude ◽

Analytical Formulas ◽

Bolometric Correction

The absolute visual magnitude as function of the observed color (B-V), also named Hertzsprung-Russell diagram, can be described through five equations; that when calibrated stars are available means eight constants. The developed framework allows to deduce the remaining physical parameters, mass, radius and luminosity. This new technique is applied to the first 10 pc, the first 50 pc, the Hyades and to the determination of the distance of a cluster. The case of the white dwarfs is analyzed assuming the absence of calibrated data: our equation produces a smaller ?2 with respect to the standard color-magnitude calibration when applied to the Villanova Catalog of Spectroscopically Identified White Dwarfs. The theoretical basis of the formulas for the colors and the bolometric correction of the stars is clarified by a Taylor expansion in the temperature of the Planck distribution.

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Some Results of the Spectroscopic Study of Four Close Binary Systems of Early Spectral Types

International Astronomical Union Colloquium ◽

10.1017/s025292110002755x ◽

1965 ◽

Vol 5 ◽

pp. 120-130

Author(s):

T. S. Galkina

Keyword(s):

Spectroscopic Study ◽

Spectral Type ◽

Spectroscopic Investigation ◽

Binary Systems ◽

Quantitative Information ◽

Close Binary ◽

Physical Parameters ◽

Absorption And Emission ◽

Close Binary Systems ◽

Quantitative Estimates

It is necessary to have quantitative estimates of the intensity of lines (both absorption and emission) to obtain the physical parameters of the atmosphere of components.Some years ago at the Crimean observatory we began the spectroscopic investigation of close binary systems of the early spectral type with components WR, Of, O, B to try and obtain more quantitative information from the study of the spectra of the components.

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A theory of contamination in electron microscopes by surface diffusion

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100107721 ◽

1978 ◽

Vol 36 (1) ◽

pp. 116-117

Author(s):

J.T. Fourie

Keyword(s):

Electron Beam ◽

Surface Diffusion ◽

High Vacuum ◽

Ultra High Vacuum ◽

Physical Parameters ◽

Carbon Compounds ◽

Hydrocarbon Molecules ◽

Electron Microscopes ◽

Primary Electrons ◽

Long Chain

Contamination in electron microscopes can be a serious problem in STEM or in situations where a number of high resolution micrographs are required of the same area in TEM. In modern instruments the environment around the specimen can be made free of the hydrocarbon molecules, which are responsible for contamination, by means of either ultra-high vacuum or cryo-pumping techniques. However, these techniques are not effective against hydrocarbon molecules adsorbed on the specimen surface before or during its introduction into the microscope. The present paper is concerned with a theory of how certain physical parameters can influence the surface diffusion of these adsorbed molecules into the electron beam where they are deposited in the form of long chain carbon compounds by interaction with the primary electrons.

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Electron Microscopy in the Study of Natural Phytoplankton Assemblages

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100119831 ◽

1985 ◽

Vol 43 ◽

pp. 620-623

Author(s):

Linda Sicko-Goad

Keyword(s):

Electron Microscopy ◽

Aquatic Environment ◽

Size Range ◽

Physical Parameters ◽

Specific Information ◽

Phytoplankton Assemblages ◽

Phytoplankton Productivity ◽

Ecosystem Effects ◽

Time Of Year ◽

Species Specific

Although the use of electron microscopy and its varied methodologies is not usually associated with ecological studies, the types of species specific information that can be generated by these techniques are often quite useful in predicting long-term ecosystem effects. The utility of these techniques is especially apparent when one considers both the size range of particles found in the aquatic environment and the complexity of the phytoplankton assemblages.The size range and character of organisms found in the aquatic environment are dependent upon a variety of physical parameters that include sampling depth, location, and time of year. In the winter months, all the Laurentian Great Lakes are uniformly mixed and homothermous in the range of 1.1 to 1.7°C. During this time phytoplankton productivity is quite low.

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