Title: Limits on Mode Coherence in Pulsating DA White Dwarfs Due to a Nonstatic Convection Zone

Abstract

The standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. Modes which are calculated to be linearly driven should increase their amplitudes exponentially with time; the fact that nearly constant amplitudes are usually observed is evidence that nonlinear mechanisms inhibit the growth of finite amplitude pulsations. Models predict that the mass of convection zones in pulsating hydrogen-atmosphere (DAV) white dwarfs is very sensitive to temperature (i.e., M_CZ α T^–90_eff), leading to the possibility that even low-amplitude pulsators may experience significant nonlinear effects. In particular, the outer turning point of finite-amplitude g-mode pulsations can vary with the local surface temperature, producing a reflected wave that is out of phase with what is required for a standing wave. This can lead to a lack of coherence of the mode and a reduction in its global amplitude. In this paper we show that: (1) whether a mode is calculated to propagate to the base of the convection zone is an accurate predictor of its width in the Fourier spectrum, (2) the phase shifts produced by reflection from the outer turning point are large enough to produce significant damping, and (3) amplitudes and periods aremore » predicted to increase from the blue edge to the middle of the instability strip, and subsequently decrease as the red edge is approached. Furthermore, this amplitude decrease is in agreement with the observational data while the period decrease has not yet been systematically studied.« less

Authors:

Montgomery, Michael H  ^[1];

• Search DOE PAGES for author "Montgomery, Michael H"
• Search DOE PAGES for ORCID "0000-0002-6748-1748"

Hermes, J. J. ^[2]; Winget, Donald E.  ^[1];

• Search DOE PAGES for author "Winget, Donald E."
• Search DOE PAGES for ORCID "0000-0003-0181-2521"

Dunlap, Bart H.  ^[1];

• Search DOE PAGES for author "Dunlap, Bart H."
• Search DOE PAGES for ORCID "0000-0002-1086-8685"

Bell, Keaton J.  ^[3]

• Search DOE PAGES for author "Bell, Keaton J."
• Search DOE PAGES for ORCID "0000-0002-0656-032X"

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+ Show Author Affiliations

1. Univ. of Texas and McDonald Observatory, Austin, TX (United States)
2. Boston Univ., MA (United States)
3. Univ. of Washington, Seattle, WA (United States)

Publication Date:

Fri Feb 07 00:00:00 EST 2020

Research Org.:

Univ. of Texas, Austin, TX (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1729870

Grant/Contract Number:  

NA0003843

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal (Online); Journal Volume: 890; Journal Issue: 1; Journal ID: ISSN 1538-4357

Publisher:

Institute of Physics (IOP)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; White dwarf stars; DA stars; Computational methods; Stellar oscillations; Analytical mathematics; Stellar interiors