Reaching Higher Densities for Laboratory White Dwarf Photospheres to Measure Spectroscopic Line Profiles (original) (raw)

Which Hydrogen Balmer Lines Are Most Reliable for Determining White Dwarf Atmospheric Parameters?

Our preliminary results from laboratory experiments studying white dwarf (WD) photospheres show a systematic difference between experimental plasma conditions inferred from measured H$\beta$ absorption line profiles versus those from H$\gamma$. One hypothesis for this discrepancy is an inaccuracy in the relative theoretical line profiles of these two transitions. This is intriguing because atmospheric parameters inferred from H Balmer lines in observed WD spectra show systematic trends such that inferred surface gravities decrease with increasing principal quantum number, nnn. If conditions inferred from lower-$n$ Balmer lines are indeed more accurate, this suggests that spectroscopically determined DA WD masses may be greater than previously thought and in better agreement with the mean mass determined from gravitational redshifts.

Hydrogen Line Shape Uncertainties in White Dwarf Model Atmospheres

Frontiers in Astronomy and Space Sciences, 2022

For isolated white dwarf (WD) stars, fits to their observed spectra provide the most precise estimates of their effective temperatures and surface gravities. Even so, recent studies have shown that systematic offsets exist between such spectroscopic parameter determinations and those based on broadband photometry. These large discrepancies (10% inTeff, 0.1 M⊙in mass) provide scientific motivation for reconsidering the atomic physics employed in the model atmospheres of these stars. Recent simulation work of ours suggests that the most important remaining uncertainties in simulation-based calculations of line shapes are the treatment of 1) the electric field distribution and 2) the occupation probability (OP) prescription. We review the work that has been done in these areas and outline possible avenues for progress.

Simulation of Stark-broadened Hydrogen Balmer-line Shapes for DA White Dwarf Synthetic Spectra

The Astrophysical Journal, 2022

White dwarfs (WDs) are useful across a wide range of astrophysical contexts. The appropriate interpretation of their spectra relies on the accuracy of WD atmosphere models. One essential ingredient of atmosphere models is the theory used for the broadening of spectral lines. To date, the models have relied on Vidal et al., known as the unified theory of line broadening (VCS). There have since been advancements in the theory; however, the calculations used in model atmosphere codes have only received minor updates. Meanwhile, advances in instrumentation and data have uncovered indications of inaccuracies: spectroscopic temperatures are roughly 10% higher and spectroscopic masses are roughly 0.1 M ⊙ higher than their photometric counterparts. The evidence suggests that VCS-based treatments of line profiles may be at least partly responsible. Gomez et al. developed a simulation-based line-profile code Xenomorph using an improved theoretical treatment that can be used to inform question...

Helium line profile variations in the DAB white dwarf HS 0209+0832

Astronomy and Astrophysics

HS 0209+0832, the only white dwarf known to show helium lines in the DB gap region, is reported to display profile variations of helium lines. A quantitative spectroscopic analysis using NLTE model atmospheres reveals that the line profile variations are consistent with a constant T_eff_=36100K and log g=7.91 but with a varying helium abundance. It decreased from a high abundance state (He/H=0.012, by number) by a factor of 2 to 3 in 1995 and recovered back to the high abundance state in 1996. The previously suggested possibility that HS0209+0832 is a composite spectrum (DA+DB) object is ruled out by the spectral analysis. Hence HS0209+0832 is the first DAB star to be unambigously near the middle of the DB gap and appears to be explainable by a homogeneous He/H atmosphere with the helium abundance lower by a factor of 2-3 in one observation.

Stark Broadening Parameters For White Dwarf Atmospheres Research

2010

Stark broadening parameters of C II lines were determined within 3d-nf series using semiclassical perturbation method. The atomic energy levels needed for calculations were taken from TOPBASE as well as the oscillator strengths, which were additionally calculated using the method of Bates and Damgaard. The both results were compared and only insignificant differences were found. Calculations were performed for plasma conditions relevant for atmospheres of DQ white dwarfs and for a new type of white dwarfs, with surface composed mostly of carbon, discovered in 2007 by Dufour et al. The aim of this work is to provide accurate C II Stark broadening data, which are crucial for this type of white dwarf atmosphere modellisation. Obtained results will be included in STARK-B database (http://stark-b.obspm.fr/), entering in the FP7 project of European Virtual Atomic and Molecular Data Center VAMDC aiming at building an interoperable e- Infrastructure for the exchange of atomic and molecular ...

Sr V -VI line widths in hot white dwarf atmospheres

Monthly Notices of the Royal Astronomical Society, 2022

Missing Stark widths for 37 spectral lines of strontium ions (17 Sr V lines and 20 Sr VI lines) have been calculated using a quantum-mechanical method. Twenty-three spectral lines of Sr V have been recently disco v ered, for the first time, in the ultraviolet spectrum of the hot white dwarf RE 0503 −289. This recent disco v ery prompts us to calculate the Stark widths of the new lines. These calculations can fill the lack of the data base STARK-B and can be used to investigate the observed spectra in such stars. To perform the line broadening calculations, preliminary structure and collision calculations have been carried out using the sequence of the Univ ersity Colle ge London codes (SUPERSTRUCTURE , DISTORTED WAVE , and JAJOM). Results for the 37 lines are provided for different electron temperatures and at density N e = 10 17 cm −3. These results will enter the STARK-B data base, which is a node of the Virtual Atomic and Molecular Data Center. We hope that the obtained results will be useful for the non-local thermodynamic equilibrium modelling of stellar atmospheres.