Resolution-Corrected White Dwarf Gravitational Redshifts Validate SDSS-V Wavelength Calibration and Enable Accurate Mass-Radius Tests

TL;DR

This paper identifies biases in low-resolution spectroscopic measurements of white dwarf gravitational redshifts, provides correction methods, and demonstrates improved agreement with theoretical models, thereby enhancing the accuracy of white dwarf mass-radius tests.

Contribution

It introduces resolution-dependent corrections for white dwarf gravitational redshift measurements, improving the accuracy of mass-radius relation tests from low-resolution spectroscopic data.

Findings

Biases of 5-15 km/s in low-resolution radial velocities identified

Resolution corrections improve agreement with theoretical mass-radius relations

Best practices established for white dwarf velocity measurements from large surveys

Abstract

Leveraging the large sample size of low-resolution spectroscopic surveys to constrain white dwarf stellar structure requires an accurate understanding of the shapes of hydrogen absorption lines, which are pressure broadened by the Stark effect. Using data from both the Sloan Digital Sky Survey and the Type Ia Supernova Progenitor Survey, we show that substantial biases (5-15 km/s) exist in radial velocity measurements made from observations at low spectral resolution relative to similar measurements from high-resolution spectra. Our results indicate that the physics of line formation in high-density plasmas, especially in the wings of the lines, are not fully accounted for in state-of-the-art white dwarf model atmospheres. We provide corrections to account for these resolution-induced redshifts in a way that is independent of an assumed mass-radius relation, and we demonstrate that statistical measurements of gravitational redshift with these corrections yield improved agreement with theoretical mass-radius relations. Our results provide a set of best practices for white dwarf radial velocity measurements from low-resolution spectroscopy, including those from the Sloan Digital Sky Survey, the Dark Energy Spectroscopic Instrument, the 4-meter Multi-Object Spectroscopic Telescope, and the Wide-Field Multiplexed Spectroscopic Facility.