Systematic uncertainties in the characterisation of helium-dominated metal-polluted white dwarf atmospheres

Abstract

White dwarf photospheric parameters are usually obtained by means of spectroscopic or photometric analysis. These results are not always consistent with each other, with the published values often including just the statistical uncertainties. The differences are more dramatic for white dwarfs with helium-dominated photospheres, so to obtain realistic uncertainties we have analysed a sample of 13 of these white dwarfs, applying both techniques to up to three different spectroscopic and photometric data sets for each star. We found mean standard deviations of < $\sigma T_{\mathrm{eff}}$ > = 524 K, < $\sigma \log g$ > = 0.27 dex and < $\sigma \log (H/He)$ > = 0.31 dex for the effective temperature, surface gravity and relative hydrogen abundance, respectively, when modelling diverse spectroscopic data. The photometric fits provided mean standard deviations up to < $\sigma T_{\mathrm{eff}}$ > = 1210 K and < $\sigma \log g$ > = 0.13 dex. We suggest these values to be adopted as realistic lower limits to the published uncertainties in parameters derived from spectroscopic and photometric fits for white dwarfs with similar characteristics. In addition, we investigate the effect of fitting the observational data adopting three different photospheric chemical compositions. In general, pure helium model spectra result in larger $T_{\mathrm{eff}}$ compared to those derived from models with traces of hydrogen. The $\log g$ shows opposite trends: smaller spectroscopic values and larger photometric ones when compared to models with hydrogen. The addition of metals to the models also affects the derived atmospheric parameters, but a clear trend is not found.

arXiv comment25 pages, 16 figures, submitted to MNRAS

References in corpus (53)

• emcee: The MCMC Hammer
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope
• The Multi-Object, Fiber-Fed Spectrographs for SDSS and the Baryon Oscillation Spectroscopic Survey
• The Pan-STARRS1 Photometric System
• Gaia Early Data Release 3: Photometric content and validation
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• Automated data reduction workflows for astronomy
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• An Improved Spectroscopic Analysis of DA White Dwarfs from the Sloan Digital Sky Survey Data Release 4
• A $Gaia$ Data Release 2 catalogue of white dwarfs and a comparison with SDSS
• A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4
• SDSS DR7 White Dwarf Catalog
• Photometric and Spectroscopic Analysis of Cool White Dwarfs with Trigonometric Parallax Measurements
• Spectroscopic Analysis of DA White Dwarfs: Stark Broadening of Hydrogen Lines Including Non-Ideal Effects
• A Comprehensive Spectroscopic Analysis of DB White Dwarfs
• The Chemical Composition of an Extrasolar Minor Planet
• A catalogue of white dwarfs in Gaia EDR3
• On the Spectral Evolution of Hot White Dwarf Stars. I. A Detailed Model-Atmosphere Analysis of Hot White Dwarfs from SDSS DR12
• The Element Abundances in Bare Planetary Nebula Central Stars and the Shell Burning in AGB Stars
• Accretion and diffusion in white dwarfs. New diffusion timescales and applications to GD362 and G29-38
• New white dwarf stars in the Sloan Digital Sky Survey Data Release 10
• The formation and evolution of hydrogen-deficient post-AGB white dwarfs: the emerging chemical profile and the expectations for the PG1159-DB-DQ evolutionary connection
• A Catalog of Spectroscopically Identified White Dwarf Stars in the First Data Release of the Sloan Digital Sky Survey
• Know Your Neighborhood: A Detailed Model Atmosphere Analysis of Nearby White Dwarfs
• Spectroscopic analysis of DA white dwarfs with 3D model atmospheres
• The White Dwarf Luminosity Function from SDSS Imaging Data
• Chemical Abundances in the Externally Polluted White Dwarf GD 40: Evidence of a Rocky Extrasolar Minor Planet
• On the Spectral Evolution of Cool, Helium-Atmosphere White Dwarfs: Detailed Spectroscopic and Photometric Analysis of DZ Stars
• Analysis of Helium-Rich White Dwarfs Polluted by Heavy Elements in the Gaia Era
• $Gaia$ white dwarfs within 40 pc II: the volume-limited northern hemisphere sample
• Rocky Extrasolar Planetary Compositions Derived from Externally-Polluted White Dwarfs
• DB white dwarfs in the Sloan Digital Sky Survey Data Release 10 and 12
• Fundamental parameter accuracy of DA and DB white dwarfs in Gaia Data Release 2
• White Dwarf Cosmochronology in the Solar Neighborhood
• On the Spectral Evolution of Helium-Atmosphere White Dwarfs Showing Traces of Hydrogen
• Spectroscopic Identification of Cool White Dwarfs in the Solar Neighbourhood
• Element abundances in cool white dwarfs. II. Ultraviolet observations of DZ white dwarfs
• Trace hydrogen in helium atmosphere white dwarfs as a possible signature of water accretion
• Discovery of a Cool, Massive, and Metal-Rich DAZ White Dwarf
• A Photometric and Spectroscopic Investigation of the DB White Dwarf Population using SDSS and Gaia Data
• The Solar Neighborhood. XIX. Discovery and Characterization of 33 New Nearby White Dwarf Systems
• From Hydrogen to Helium: The Spectral Evolution of White Dwarfs as Evidence for Convective Mixing
• 3D spectroscopic analysis of helium-line white dwarfs
• Toward a Spectroscopic Census of White Dwarfs Within 40 parsecs of the Sun
• Calibration of the mixing length theory for structures of helium-dominated atmosphere white dwarfs
• New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey
• Analysis of IUE spectra of helium-rich white dwarf stars
• GD424 -- a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal
• Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample
• On the formation of hydrogen-deficient post-AGB stars
• The Pulsating Helium-Atmosphere White Dwarfs I: New DBVs from the Sloan Digital Sky Survey

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• The 40 pc sample of white dwarfs from Gaia
• New chondritic bodies identified in eight oxygen-bearing white dwarfs
• PEWDD: A database of white dwarfs enriched by exo-planetary material
• Do White Dwarfs Sample Water-Rich Planetary Material?
• I Can Do It With A Broken Planetesimal: Characterising the planetary debris in heavily polluted cool white dwarfs