Probing the Gravitational Dependence of the Fine-Structure Constant from Observations of White Dwarf Stars

Matthew Bainbridge,Martin Barstow,Thomas Ayres,John Webb,John Barrow,Nicole Reindl,Vladimir Dzuba,Vincent Dumont,Simon Preval,Wim Ubachs,Julian Berengut,Jay Holberg,Victor Flambaum,Jiting Hu,W.-Ü Tchang-Brillet

doi:10.3390/universe3020032

Abstract

Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling, and fundamental physics in the search for variation in the fine structure constant. This variation manifests as shifts in the observed wavelengths of absorption lines, such as quadruply ionized iron (FeV) and quadruply ionized nickel (NiV), when compared to laboratory wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801) demonstrated the validity of such an analysis using high-resolution Space Telescope Imaging Spectrograph (STIS) spectra of G191-B2B. We have made three important improvements by: (a) using three new independent sets of laboratory wavelengths; (b) analysing a sample of objects; and (c) improving the methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method). A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. Here we describe our approach and present preliminary results from nine objects using both FeV and NiV.

Highlights

Within the absorption spectra of white dwarfs, variation in α is manifested as shifts in the observed wavelengths of absorption lines when compared to laboratory wavelengths [13], providing us with an opportunity for a direct observational test
We have extended this work by: (a) using new laboratory wavelengths; (b) analysing a sample of objects rather than a single object; and (c) refining the analysis methodology by incorporating robust techniques from previous studies towards quasars
The apparent systematic effect in the Raassen NiV laboratory wavelengths noted by Berengut et al (2013) [14] does not appear to be present in the new Nave NiV wavelengths from NIST

Summary

Introduction

Within the absorption spectra of white dwarfs, variation in α is manifested as shifts in the observed wavelengths of absorption lines when compared to laboratory wavelengths [13], providing us with an opportunity for a direct observational test. Spectrograph (STIS) spectra of the hot white dwarf star G191-B2B to constrain ∆α/α, by observing the wavelength shifts in 96 quadruply ionized iron (FeV) and 32 quadruply ionized nickel (NiV) We have extended this work by: (a) using new laboratory wavelengths; (b) analysing a sample of objects rather than a single object; and (c) refining the analysis methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method [15,16,17]).

Results

Conclusion