MEASURING THE EVOLUTIONARY RATE OF COOLING OF ZZ Ceti

Journal Article · Mon Jul 01 00:00:00 EDT 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/771/1/17· OSTI ID:22140231

Mukadam, Anjum S.; Fraser, Oliver; Riecken, T. S.; Kronberg, M. E. ^[1]; Bischoff-Kim, Agnes ^[2]; Corsico, A. H. ^[3]; Montgomery, M. H.; Winget, D. E.; Hermes, J. J.; Winget, K. I.; Falcon, Ross E.; Reaves, D. ^[4]; Kepler, S. O.; Romero, A. D. ^[5]; Chandler, D. W. ^[6]; Kuehne, J. W. ^[7]; Sullivan, D. J. ^[8]; Von Hippel, T. ^[9]; Mullally, F. ^[10]; Shipman, H. ^[11] ; others, and

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1. Department of Astronomy, University of Washington, Seattle, WA 98195 (United States)
2. Georgia College and State University, Milledgeville, GA 31061 (United States)
3. Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata (Argentina)
4. Department of Astronomy, University of Texas at Austin, Austin, TX 78759 (United States)
5. Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, RS (Brazil)
6. Meyer Observatory, Central Texas Astronomical Society, 3409 Whispering Oaks, Temple, TX 76504 (United States)
7. McDonald Observatory, Fort Davis, TX 79734 (United States)
8. Victoria University of Wellington, P.O. Box 600, Wellington (New Zealand)
9. Embry-Riddle Aeronautical University, 600 South Clyde Morris Boulevard, Daytona Beach, FL 32114 (United States)
10. SETI Institute, NASA Ames Research Center, MS 244-30, Moffet Field, CA 94035 (United States)
11. Delaware Asteroseismic Research Center, Mt. Cuba Observatory, Greenville, DE 19807 (United States)

We have finally measured the evolutionary rate of cooling of the pulsating hydrogen atmosphere (DA) white dwarf ZZ Ceti (Ross 548), as reflected by the drift rate of the 213.13260694 s period. Using 41 yr of time-series photometry from 1970 November to 2012 January, we determine the rate of change of this period with time to be dP/dt = (5.2 {+-} 1.4) Multiplication-Sign 10{sup -15} s s{sup -1} employing the O - C method and (5.45 {+-} 0.79) Multiplication-Sign 10{sup -15} s s{sup -1} using a direct nonlinear least squares fit to the entire lightcurve. We adopt the dP/dt obtained from the nonlinear least squares program as our final determination, but augment the corresponding uncertainty to a more realistic value, ultimately arriving at the measurement of dP/dt = (5.5 {+-} 1.0) Multiplication-Sign 10{sup -15} s s{sup -1}. After correcting for proper motion, the evolutionary rate of cooling of ZZ Ceti is computed to be (3.3 {+-} 1.1) Multiplication-Sign 10{sup -15} s s{sup -1}. This value is consistent within uncertainties with the measurement of (4.19 {+-} 0.73) Multiplication-Sign 10{sup -15} s s{sup -1} for another similar pulsating DA white dwarf, G 117-B15A. Measuring the cooling rate of ZZ Ceti helps us refine our stellar structure and evolutionary models, as cooling depends mainly on the core composition and stellar mass. Calibrating white dwarf cooling curves with this measurement will reduce the theoretical uncertainties involved in white dwarf cosmochronometry. Should the 213.13 s period be trapped in the hydrogen envelope, then our determination of its drift rate compared to the expected evolutionary rate suggests an additional source of stellar cooling. Attributing the excess cooling to the emission of axions imposes a constraint on the mass of the hypothetical axion particle.

• OSTI ID: 22140231
• Journal Information: Astrophysical Journal, Vol. 771, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ATMOSPHERES
AXIONS
COOLING
EMISSION
HYDROGEN
LEAST SQUARE FIT
LIMITING VALUES
MASS
NONLINEAR PROBLEMS
OSCILLATIONS
PHOTOMETRY
PROPER MOTION
STAR EVOLUTION
TRAPPING
WHITE DWARF STARS