Laboratory Hydrogen-Beta Emission Spectroscopy for Analysis of Astrophysical White Dwarf Spectra

Abstract

This work communicates a review on Balmer series hydrogen beta line measurements and applications for analysis of white dwarf stars. Laser-induced plasma investigations explore electron density and temperature ranges comparable to white dwarf star signatures such as Sirius B, the companion to the brightest star observable from the earth. Spectral line shape characteristics of the hydrogen beta line include width, peak separation, and central dip-shift, thereby providing three indicators for electron density measurements. The hydrogen alpha line shows two primary line-profile parameters for electron density determination, namely, width and shift. Both Boltzmann plot and line-to-continuum ratios yield temperature. The line-shifts recorded with temporally- and spatially- resolved optical emission spectroscopy of hydrogen plasma in laboratory settings can be larger than gravitational redshifts that occur in absorption spectra from radiating white dwarfs. Published astrophysical spectra display significantly diminished Stark or pressure broadening contributions to red-shifted atomic lines. Gravitational redshifts allow one to assess the ratio of mass and radius of these stars, and subsequently, the mass from cooling models.

Laser-Plasma and Self-Absorption Measurements with Applications to Analysis of Atomic and Molecular Stellar Astrophysics Spectra

“…Results for the H β and H α and analysis were presented previously [5,6]. Electron densities from H β agree with those from H α [5,6]. Averages of the spatially resolved data along the slit yield spectra that appear similar to those recorded with a linear diode array [7].…”

“…The displayed image values represent spectral radiance in arbitrary units. Results for the H β and H α and analysis were presented previously [5,6]. Electron densities from H β agree with those from H α [5,6].…”

“…The experimental arrangement for laboratory measurements of laser-induced plasma [6] includes a Q-switched Nd:YAG laser device typically generating 6 ns laser pulses with an energy of 150 mJ per pulse at the fundamental wavelength of 1064 nm. Radiation is tightly focused to a spot size of the order of 10 µm to achieve a peak irradiance above 1 TW/cm 2 , or well above optical breakdown of SATP laboratory air and gaseous hydrogen of the order of one atmosphere.…”

“…This work presents characterization of gaseous hydrogen micro-plasma from the first four Balmer series members, H α , H β , H γ , and H δ lines. Previously communicated work primarily were results from H α and H β lines [5,6]. The electron density, N e , of interest ranges from 10 16 cm −3 to 10 19 cm −3 for laser-plasma emission experiments.…”

“…Selected white dwarf spectral data display absorption profiles from atmospheres with electron densities of ∼ 1 − 5 × 10 17 cm −3 , or η = 0.004 -0.02 amg, consequently, the H β line appears most suited for diagnosis of such electron density. The H β line allows one to determine electron density from full-width at half-maximum, peak-separation, and central dip-shifts [5,6] for N e in the range 2 -20 ×10 17 cm −3 .…”