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Research paper thumbnail of Hydrogen Line Shape Uncertainties in White Dwarf Model Atmospheres

Frontiers in Astronomy and Space Sciences, 2022

For isolated white dwarf (WD) stars, fits to their observed spectra provide the most precise esti... more For isolated white dwarf (WD) stars, fits to their observed spectra provide the most precise estimates of their effective temperatures and surface gravities. Even so, recent studies have shown that systematic offsets exist between such spectroscopic parameter determinations and those based on broadband photometry. These large discrepancies (10% inTeff, 0.1 M⊙in mass) provide scientific motivation for reconsidering the atomic physics employed in the model atmospheres of these stars. Recent simulation work of ours suggests that the most important remaining uncertainties in simulation-based calculations of line shapes are the treatment of 1) the electric field distribution and 2) the occupation probability (OP) prescription. We review the work that has been done in these areas and outline possible avenues for progress.

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Research paper thumbnail of Modeling the Spectra of Dense Hydrogen Plasmas: Beyond Occupation Probability

arXiv: Solar and Stellar Astrophysics, 2016

Accurately measuring the masses of white dwarf stars is crucial in many astrophysical contexts (e... more Accurately measuring the masses of white dwarf stars is crucial in many astrophysical contexts (e.g., asteroseismology and cosmochronology). These masses are most commonly determined by fitting a model atmosphere to an observed spectrum; this is known as the spectroscopic method. However, for cases in which more than one method may be employed, there are well known discrepancies between masses determined by the spectroscopic method and those determined by astrometric, dynamical, and/or gravitational-redshift methods. In an effort to resolve these discrepancies, we are developing a new model of hydrogen in a dense plasma that is a significant departure from previous models. Experiments at Sandia National Laboratories are currently underway to validate these new models, and we have begun modifications to incorporate these models into stellar-atmosphere codes.

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Research paper thumbnail of Reaching Higher Densities for Laboratory White Dwarf Photospheres to Measure Spectroscopic Line Profiles

arXiv: Solar and Stellar Astrophysics, 2016

As part of our laboratory investigation of the theoretical line profiles used in white dwarf atmo... more As part of our laboratory investigation of the theoretical line profiles used in white dwarf atmosphere models, we extend the electron-density ($n_{\rm e}$) range measured by our experiments to higher densities (up to nesim80times1016n_{e}\sim80\times10^{16}nesim80times1016 cm$^{-3}$). Whereas inferred parameters using the hydrogen-$\beta$ spectral line agree among different line-shape models for nrmelesssim30times1016n_{\rm e}\lesssim30\times10^{16}nrmelesssim30times1016 cm$^{-3}$, we now see divergence between models. These are densities beyond the range previously benchmarked in the laboratory, meaning theoretical profiles in this regime have not been fully validated. Experimentally exploring these higher densities enables us to test and constrain different line-profile models, as the differences in their relative H-Balmer line shapes are more pronounced at such conditions. These experiments also aid in our study of occupation probabilities because we can measure these from relative line strengths.

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Research paper thumbnail of Dark Stars: Evolution and First Pulsation Results

Bulletin of the American Physical Society, 2015

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Research paper thumbnail of Dark Stars: Improved Models and First Pulsation Results

The Astrophysical Journal, 2015

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Research paper thumbnail of An experimental platform for creating white dwarf photospheres in the laboratory

High Energy Density Physics, 2013

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Research paper thumbnail of White dwarf variability with gPhoton: pulsators

Monthly Notices of the Royal Astronomical Society, 2017

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Research paper thumbnail of Recent Progress Characterizing Convection Using White Dwarf Light Curves from the Whole Earth Telescope

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Research paper thumbnail of BPM 37093: The Way to the Interior of Crystallized Stars

Open Astronomy, 1998

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Research paper thumbnail of White Dwarf and Pre-White Dwarf Pulsations

AIP Conference Proceedings, 2009

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Research paper thumbnail of Convection: A Seismological Perspective

AIP Conference Proceedings, 2007

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Research paper thumbnail of KIC 4552982: OUTBURSTS AND ASTEROSEISMOLOGY FROM THE LONGEST PSEUDO-CONTINUOUS LIGHT CURVE OF A ZZ Ceti

The Astrophysical Journal, 2015

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Research paper thumbnail of The Evolution and Pulsation of Crystallizing White Dwarf Stars

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Research paper thumbnail of 1. Star Formation History and Physics from the White Dwarf Stars

We explore the physics of crystallization in the deep interiors of white dwarf stars using the co... more We explore the physics of crystallization in the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of white dwarf stars and provide the first empirical evidence that the phase transition is first order: latent heat is released in the process of crystallization as predicted by van Horn (1968). We outline how this data can be used to observationally constrain the value of Γ ≡ ECoulomb/Ethermal near the onset of crystallization, the central carbon/oxygen abundance, and the importance of phase separation. Subject headings: white dwarfs — dense matter — equation of state

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Research paper thumbnail of Discovery of an Ultramassive Pulsating White Dwarf

The Astrophysical Journal, 2013

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Research paper thumbnail of Empirical Determination of Convection Parameters in White Dwarfs. I. Whole Earth Telescope Observations of EC14012-1446

The Astrophysical Journal, 2012

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Research paper thumbnail of Redefining the Empirical ZZ Ceti Instability Strip

The Astrophysical Journal, 2004

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Research paper thumbnail of Pulsational Mapping of Calcium Across the Surface of a White Dwarf

The Astrophysical Journal, 2010

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Research paper thumbnail of Evidence for Temperature Change and Oblique Pulsation from Light Curve Fits of the Pulsating White Dwarf GD 358

The Astrophysical Journal, 2010

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Research paper thumbnail of Ensemble Characteristics of the ZZ Ceti Stars

The Astrophysical Journal, 2006

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Research paper thumbnail of Hydrogen Line Shape Uncertainties in White Dwarf Model Atmospheres

Frontiers in Astronomy and Space Sciences, 2022

For isolated white dwarf (WD) stars, fits to their observed spectra provide the most precise esti... more For isolated white dwarf (WD) stars, fits to their observed spectra provide the most precise estimates of their effective temperatures and surface gravities. Even so, recent studies have shown that systematic offsets exist between such spectroscopic parameter determinations and those based on broadband photometry. These large discrepancies (10% inTeff, 0.1 M⊙in mass) provide scientific motivation for reconsidering the atomic physics employed in the model atmospheres of these stars. Recent simulation work of ours suggests that the most important remaining uncertainties in simulation-based calculations of line shapes are the treatment of 1) the electric field distribution and 2) the occupation probability (OP) prescription. We review the work that has been done in these areas and outline possible avenues for progress.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modeling the Spectra of Dense Hydrogen Plasmas: Beyond Occupation Probability

arXiv: Solar and Stellar Astrophysics, 2016

Accurately measuring the masses of white dwarf stars is crucial in many astrophysical contexts (e... more Accurately measuring the masses of white dwarf stars is crucial in many astrophysical contexts (e.g., asteroseismology and cosmochronology). These masses are most commonly determined by fitting a model atmosphere to an observed spectrum; this is known as the spectroscopic method. However, for cases in which more than one method may be employed, there are well known discrepancies between masses determined by the spectroscopic method and those determined by astrometric, dynamical, and/or gravitational-redshift methods. In an effort to resolve these discrepancies, we are developing a new model of hydrogen in a dense plasma that is a significant departure from previous models. Experiments at Sandia National Laboratories are currently underway to validate these new models, and we have begun modifications to incorporate these models into stellar-atmosphere codes.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Reaching Higher Densities for Laboratory White Dwarf Photospheres to Measure Spectroscopic Line Profiles

arXiv: Solar and Stellar Astrophysics, 2016

As part of our laboratory investigation of the theoretical line profiles used in white dwarf atmo... more As part of our laboratory investigation of the theoretical line profiles used in white dwarf atmosphere models, we extend the electron-density ($n_{\rm e}$) range measured by our experiments to higher densities (up to nesim80times1016n_{e}\sim80\times10^{16}nesim80times1016 cm$^{-3}$). Whereas inferred parameters using the hydrogen-$\beta$ spectral line agree among different line-shape models for nrmelesssim30times1016n_{\rm e}\lesssim30\times10^{16}nrmelesssim30times1016 cm$^{-3}$, we now see divergence between models. These are densities beyond the range previously benchmarked in the laboratory, meaning theoretical profiles in this regime have not been fully validated. Experimentally exploring these higher densities enables us to test and constrain different line-profile models, as the differences in their relative H-Balmer line shapes are more pronounced at such conditions. These experiments also aid in our study of occupation probabilities because we can measure these from relative line strengths.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Dark Stars: Evolution and First Pulsation Results

Bulletin of the American Physical Society, 2015

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Dark Stars: Improved Models and First Pulsation Results

The Astrophysical Journal, 2015

Bookmarks Related papers MentionsView impact

Research paper thumbnail of An experimental platform for creating white dwarf photospheres in the laboratory

High Energy Density Physics, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of White dwarf variability with gPhoton: pulsators

Monthly Notices of the Royal Astronomical Society, 2017

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Recent Progress Characterizing Convection Using White Dwarf Light Curves from the Whole Earth Telescope

Bookmarks Related papers MentionsView impact

Research paper thumbnail of BPM 37093: The Way to the Interior of Crystallized Stars

Open Astronomy, 1998

Bookmarks Related papers MentionsView impact

Research paper thumbnail of White Dwarf and Pre-White Dwarf Pulsations

AIP Conference Proceedings, 2009

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Convection: A Seismological Perspective

AIP Conference Proceedings, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of KIC 4552982: OUTBURSTS AND ASTEROSEISMOLOGY FROM THE LONGEST PSEUDO-CONTINUOUS LIGHT CURVE OF A ZZ Ceti

The Astrophysical Journal, 2015

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Evolution and Pulsation of Crystallizing White Dwarf Stars

Bookmarks Related papers MentionsView impact

Research paper thumbnail of 1. Star Formation History and Physics from the White Dwarf Stars

We explore the physics of crystallization in the deep interiors of white dwarf stars using the co... more We explore the physics of crystallization in the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of white dwarf stars and provide the first empirical evidence that the phase transition is first order: latent heat is released in the process of crystallization as predicted by van Horn (1968). We outline how this data can be used to observationally constrain the value of Γ ≡ ECoulomb/Ethermal near the onset of crystallization, the central carbon/oxygen abundance, and the importance of phase separation. Subject headings: white dwarfs — dense matter — equation of state

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Discovery of an Ultramassive Pulsating White Dwarf

The Astrophysical Journal, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Empirical Determination of Convection Parameters in White Dwarfs. I. Whole Earth Telescope Observations of EC14012-1446

The Astrophysical Journal, 2012

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Redefining the Empirical ZZ Ceti Instability Strip

The Astrophysical Journal, 2004

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Pulsational Mapping of Calcium Across the Surface of a White Dwarf

The Astrophysical Journal, 2010

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Evidence for Temperature Change and Oblique Pulsation from Light Curve Fits of the Pulsating White Dwarf GD 358

The Astrophysical Journal, 2010

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Ensemble Characteristics of the ZZ Ceti Stars

The Astrophysical Journal, 2006

Bookmarks Related papers MentionsView impact