Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Improved Stark Broadened Profiles for Neutral Helium Lines Using Computer Simulations

Patrick Tremblay, Alain Beauchamp, Pierre Bergeron, Antoine Bédard

TL;DR

A new grid of line profiles for 13 neutral helium lines in the optical range is created and the impact of these new profiles on the determination of physical parameters for a range of astrophysical objects, including DB white dwarfs and other helium-rich stars is examined.

Abstract

The study of Stark broadening of neutral helium lines, despite significant advances over recent decades, has not led to updated large grids of helium line profiles relevant to the spectroscopic study of helium-rich stars. While the semi-analytical approach based on the standard Stark broadening theory is efficient for generating such grids, it presents challenges in incorporating additional physical effects into the model. Motivated by recent studies that highlight potential issues with line profiles in the context of white dwarf stars, this paper leverages advances in computer simulations to create a new grid of line profiles for 13 neutral helium lines in the optical range. These profiles cover densities ranging from 10^14 to 6 x 10^17 cm^-3 and temperatures from 10,000 K to 40,000 K, with the exception of the narrower He I 4713 line, for which the profile grid begins at 10^15.5 cm^-3. The primary goal of this research is to present the new grid and compare it with both the semi-analytical approach and other simulation results. By doing so, corrections to the previous grid will be explored, providing a foundation for future studies that utilize this updated grid. We also examine the impact of these new profiles on the determination of physical parameters for a range of astrophysical objects, including DB white dwarfs and other helium-rich stars.

Improved Stark Broadened Profiles for Neutral Helium Lines Using Computer Simulations

TL;DR

A new grid of line profiles for 13 neutral helium lines in the optical range is created and the impact of these new profiles on the determination of physical parameters for a range of astrophysical objects, including DB white dwarfs and other helium-rich stars is examined.

Abstract

The study of Stark broadening of neutral helium lines, despite significant advances over recent decades, has not led to updated large grids of helium line profiles relevant to the spectroscopic study of helium-rich stars. While the semi-analytical approach based on the standard Stark broadening theory is efficient for generating such grids, it presents challenges in incorporating additional physical effects into the model. Motivated by recent studies that highlight potential issues with line profiles in the context of white dwarf stars, this paper leverages advances in computer simulations to create a new grid of line profiles for 13 neutral helium lines in the optical range. These profiles cover densities ranging from 10^14 to 6 x 10^17 cm^-3 and temperatures from 10,000 K to 40,000 K, with the exception of the narrower He I 4713 line, for which the profile grid begins at 10^15.5 cm^-3. The primary goal of this research is to present the new grid and compare it with both the semi-analytical approach and other simulation results. By doing so, corrections to the previous grid will be explored, providing a foundation for future studies that utilize this updated grid. We also examine the impact of these new profiles on the determination of physical parameters for a range of astrophysical objects, including DB white dwarfs and other helium-rich stars.
Paper Structure (19 sections, 31 equations, 21 figures)

This paper contains 19 sections, 31 equations, 21 figures.

Table of Contents

  1. Introduction
  2. Theoretical Background
  3. Standard Stark Broadening Theory
  4. Computer Simulations
  5. The Power Spectrum Method
  6. Generation and Reinjection of Particles
  7. Time Evolution Operator
  8. Implementation Details
  9. Results
  10. Statistical Distribution of the Electric Field Intensity
  11. Autocorrelation vs. Power Spectrum Methods
  12. Normalization of the Profiles from the Standard Theory
  13. Comparison of He i $\lambda\lambda$4471 and 4922
  14. Comparison Between Computer Simulations and Standard Theory for All Spectral Lines
  15. Applications
  16. ...and 4 more sections

Figures (21)

  • Figure 1: Autocorrelation function of He i$\lambda$4471 for $T = 20,000$ K and electron densities $10^{14}$, $10^{15}$, and $10^{16}$ cm$^{-3}$ over the simulation time-step index $k=t_k/\Delta_t$.
  • Figure 2: Same as Figure \ref{['fig:Ct4471']} but for He i$\lambda$4713 for $T = 20,000$ K and electron densities $10^{15}$ and $10^{16}$ cm$^{-3}$.
  • Figure 3: Microfield distribution for a temperature of 20,000 K and an electronic density of $10^{15}$ cm$^{-3}$ at three time-step indices $k=t_k/\Delta_t$ of 0, $N_t/2$ and $N_t-1$. $\beta$ is the intensity of the electric field normalized by the Holtzmark field. The distribution from Hooper68 is shown in black, while the generated distribution is represented by the orange histogram.
  • Figure 4: Same as Figure \ref{['fig:hooper10_15']} but for an electronic density of $10^{17}$ cm$^{-3}$.
  • Figure 5: Microfield distribution for a temperature of 20,000 K and an electronic density of $10^{15}$ cm$^{-3}$ over all time indices.
  • ...and 16 more figures