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

2018 ◽  
Vol 619 ◽  
pp. A152 ◽  
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.

AGN evolution as seen in spectral lines: The case of narrow-line Seyfert 1s

2019 ◽  
Vol 15 (S356) ◽  
pp. 94-94
Author(s):  
Marco Berton
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Spectroscopic Studies ◽  
Spectral Lines ◽  
Narrow Line ◽  
Line Profiles ◽  
Line Shapes ◽  
Fundamental Information ◽  
Line Region ◽  
Gaussian Samples

AbstractLine profiles can provide fundamental information on the physics of active galactic nuclei (AGN). In the case of narrow-line Seyfert 1 galaxies (NLS1s) this is of particular importance since past studies revealed how their permitted line profiles are well reproduced by a Lorentzian function instead of a Gaussian. This has been explained with different properties of the broad-line region (BLR), which may present more pronounced turbulent motions in NLS1s with respect to other AGN. We investigated the line profiles in a recent large NLS1 sample classified using SDSS, and we divided the sources into two subsamples according to their line shapes, Gaussian or Lorentzian. The line profiles seem to separate all the properties of NLS1s. Black hole mass, Eddington ratio, [OIII] luminosity, and Fe II strength are all very different in the Lorentzian and Gaussian samples, as well as their position on the quasar main sequence. We interpret this in terms of evolution within the class of NLS1s. The Lorentzian sources may be the youngest objects, while Gaussian profiles may be typically associated to more evolved objects. Further detailed spectroscopic studies are needed to fully confirm our hypothesis.

A Statistical Study of the Si IV Resonance Line Parameters in 19 Be Stars

2011 ◽  
Vol 20 (4) ◽  
Author(s):  
A. Antoniou ◽  
E. Danezis ◽  
E. Lyratzi ◽  
D. Stathopoulos ◽  
M. S. Dimitrijević
Keyword(s):  
Resonance Line ◽  
Column Density ◽  
Statistical Study ◽  
Radial Velocities ◽  
Spectral Lines ◽  
Physical Parameters ◽  
Be Stars ◽  
Absorbed Energy

AbstractUsing the GR model, we analyze the ultraviolet Si IV resonance lines in the spectra of 19 Be stars of different spectral subtypes, in order to detect the presence of absorption components and to analyze their characteristics. From this analysis we can calculate the values of a group of physical parameters, such as the apparent rotational and radial velocities, the random velocities of the ion thermal motions, as well as the absorbed energy and the logarithm of the column density of the independent regions of matter which produce the main and the satellite components of the studied spectral lines.

scholarly journals Effects of Abundance Changes on the Spectra of Very Cool White Dwarfs

1976 ◽  
Vol 72 ◽  
pp. 25-25
Author(s):  
R. Wehrse
Keyword(s):  
White Dwarfs ◽  
Wavelength Dependence ◽  
Abundance Ratio ◽  
Spectral Lines ◽  
Line Density ◽  
Metal Line ◽  
Metal Contents ◽  
The Difference ◽  
Cool White Dwarfs ◽  
Blue Spectral Region

In order to study the atmospheres of cool white dwarfs of spectral types DA, DF and DG, model atmospheres have been calculated for temperatures 5000 ≤ Teff ≤ 7000 K and gravities 7 ≤ log g ≤ 8.5. The helium to hydrogen abundance ratio ranges from 0.1 to 1000. The abundances of the metals ∈M (relative to hydrogen) vary between the solar value ∈⊙M and ∈⊙M/1000. The models are hydrogen and metal line blanketed and in radiative equilibrium. The models with increased He abundance are characterized by a decreased mean opacity since the absorption cross-section of He is much smaller than that of H–. As a result, the spectral lines become stronger and – due to the much higher pressures – much broader. A reduction of the metal contents also increases the pressures. In this case it is caused by the shortage of electron suppliers. Here the spectral lines also become broader, but in general weaker.These effects strengthen the overlap of the lines due to the high gravity of white dwarfs and more or less lead to a quasi-continuum which may be much below the true continuum. Because of the wavelength dependence of the line density the depression is strongest in the UV and blue spectral region, whereas for wavelengths λ ≥ 4500 Å the difference from the true continuum is only a few per cent. The details will be published elsewhere.

scholarly journals Soft X-Ray Spectroscopy with Exosat

1984 ◽  
Vol 86 ◽  
pp. 59-66
Author(s):  
R. Mewe
Keyword(s):  
Absorption Edge ◽  
White Dwarf ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Atmospheric Model ◽  
Abundance Ratio ◽  
The Other ◽  
X Ray ◽  
Element Abundances ◽  
Medium Resolution

With the 500 and 1000 l/mm transmission gratings aboard the European x-ray Observatory SATellite (EXOSAT) we have measured medium-resolution (Δλ 5 A at 100 A) spectra of some ten objects of various categories such as isolated white dwarfs, cool stars with convective mantles, cataclysmic variables (e.g. AM Her) and a high-luminosity X-ray source (Sco X-1).The Instrument configuration was mostly such that one low-energy telescope was used as a photometer, while the other telescope was used as a spectrometer with the 500 l/mm grating inserted.The white dwarf spectra were measured between about 60 and 300 A. They show a continuum with no clear evidence of aborption and emission lines except for the He II absorption edge at 227 A in the spectrum of Feige 24. For the cooler (28 000 K) white dwarf Sirius B the emission is peaked between about 100 and 160 A and limited to about 200 A. which can be expected from atmospheric model spectra of DA white dwarfs. The soft X-ray emission of the hotter (> 60 000 K) DA white dwarfs (HZ43. Feige 24) is also interpreted in terms of photospheric emission. In the HZ43 spectrum the absorption edge is apparently absent which sets a stringent upper limit to the abundance ratio He/H of about 10−5. On the other hand the spectrum of Feige 24 shows a dominant absorption edge, implying He/H > 10−3. Moreover, here the shape of the continuum may be indicative of a stratification of element abundances in the outer atmosphere.

scholarly journals The Temperatures of White Dwarfs in Accreting Binaries

1989 ◽  
Vol 114 ◽  
pp. 92-96 ◽  
Author(s):  
Paula Szkody ◽  
Edward M. Sion
Keyword(s):  
Mass Transfer ◽  
Energy Distribution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Binary Systems ◽  
Spectral Lines ◽  
Emission Lines ◽  
Minor Amount ◽  
Dwarf Novae ◽  
Optical Flux

Through the use of accreting binary systems, it is possible to study the effects of the deposition of matter and energy on the surface of a white dwarf. The observed atmospheric properties of composition and temperature obtained from direct observation of the spectral lines and the continuum flux can be used to compare with those of single white dwarfs to understand the consequences of mass accretion on binary evolution.Cataclysmic variables provide one of the best targets for this type of study because a) the primaries are all white dwarfs b) the level and the timescale of the accretion cover a large range from the high rate, relatively steady novalike accretors to the dwarf novae systems which are modulated on short timescales in a quasi-periodic manner. Unfortunately, due to the mass transfer process, an accretion disk builds up to the point where its radiation overwhelms the white dwarf light in most cases. Thus, to study the effects on the stellar primary, systems must be found which have low mass transfer rates (generally the short orbital period systems (Patterson 1984)) and/or high inclinations (since most of the disk flux emerges perpendicular to the plane of the disk). The best identification of the white dwarf emerges from IUE spectra which show a broad Lyman α absorption profile (in contrast to the normal emission lines from a disk at quiescence). The shape of this profile provides a sensitive indicator of the temperature and gravity. In some cases, broad absorption lines are also evident in the optical Balmer lines, although the broad emission lines from the disk usually make these difficult to detect. The steeply falling flux distribution of a white dwarf throughout the optical region, combined with a flat disk distribution usually means that the white dwarf contributes a minor amount to the optical flux. However, in the ultraviolet, the rising energy distribution of the white dwarf easily dominates the falling energy distribution of a low accretion rate disk (Mateo and Szkody 1984). White dwarfs are generally acknowledged to be prominent in the dwarf novae U Gem (Panek and Holm 1984), VW Hyi (Mateo and Szkody 1984) and Z Cha (Marsh, Horne and Shipman 1987) and suggested in EK TrA and WZ Sge (Verbunt 1987). In addition, the white dwarf has been seen in some novalike systems which sporadically turn off their mass transfer, (resulting in the disappearance of most of the disk and the resulting appearance of the white dwarf). This has been the case in TT Ari (Shafter et al. 1985) and some limits have been determined for MV Lyr (Szkody and Downes 1982) and V794 Aql (Szkody, Downes and Mateo 1988). Several magnetic white dwarfs have also been seen when the mass transfer ceases in the AM Her systems (summarized in Szkody, Downes and Mateo 1988).

scholarly journals Line Profiles of the Calcium I Resonance Line in Cool Metal-polluted White Dwarfs

2019 ◽  
Vol 875 (2) ◽  
pp. 137 ◽  
Author(s):  
S. Blouin ◽  
N. F. Allard ◽  
T. Leininger ◽  
F. X. Gadéa ◽  
P. Dufour
Keyword(s):  
Resonance Line ◽  
White Dwarfs ◽  
Line Profiles

scholarly journals Diffuse Reflection and Transmission by Uniform Noncoherently Scattering Media

1967 ◽  
Vol 20 (3) ◽  
pp. 271 ◽  
Author(s):  
RBT Black
Keyword(s):  
Spectral Line ◽  
Absorption Line ◽  
Frequency Distribution ◽  
Resonance Line ◽  
Diffuse Reflection ◽  
Incident Light ◽  
Spectral Lines ◽  
Line Profiles ◽  
Scattering Media ◽  
Reflection And Transmission

Diffusely reflected and transmitted spectral line profiles are calculated for uniform noncoherently scattering media onto which radiation of frequency near that of a resonance line of the medium is incident. Profiles are calculated for incident light that is either collimated or unifQrmly diffused and that is either monochromatic, or of uniform frequency distribution, or contains an absorption line centred on the resonance line under discussion. Spectral lines generated by uniformly excited media are also calculated.

scholarly journals Searching for ZZ Ceti white dwarfs in the Gaia survey

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.

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 The nearby magnetic cool DZ white dwarf PM J08186−3110

2020 ◽  
Vol 500 (2) ◽  
pp. 2732-2740
Author(s):  
Adela Kawka ◽  
Stéphane Vennes ◽  
Nicole F Allard ◽  
T Leininger ◽  
F X Gadéa
Keyword(s):  
Magnetic Field ◽  
White Dwarf ◽  
Time Scale ◽  
White Dwarfs ◽  
Spectral Lines ◽  
Heavy Elements ◽  
High Dispersion ◽  
Average Magnetic Field ◽  
Effective Temperatures

ABSTRACT We present an analysis of photometric, spectroscopic, and spectropolarimetric data of the nearby, cool, magnetic DZ white dwarf PM J08186−3110. High-dispersion spectra show the presence of Zeeman splitted spectral lines due to the presence of a surface average magnetic field of 92 kG. The strong magnesium and calcium lines show extended wings shaped by interactions with neutral helium in a dense, cool helium-rich atmosphere. We found that the abundance of heavy elements varied between spectra taken 10 years apart but we could not establish a time-scale for these variations; such variations may be linked to surface abundance variations in the magnetized atmosphere. Finally, we show that volume-limited samples reveal that about 40 per cent of DZ white dwarfs with effective temperatures below 7000 K are magnetic.

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