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Asteroseismic Signatures of Small Convective Cores  

Travis S. Metcalfe   Submitted: 2007-05-21 10:23

We present an analytical study of the effect of small convective cores on the oscillations of solar-like pulsators. Based on an asymptotic analysis of the wave equation near the center of the star, we derive an expression for the perturbations to the frequencies of radial modes generated by a convective core and discuss how these perturbations depend on the properties of the core. Moreover, we propose a diagnostic tool to isolate the predicted signature of the core, constructed from a particular combination of the oscillation frequencies, and we validate this tool with simulated data. We also show that the proposed tool can be applied to the pulsation data soon expected from satellite missions such as CoRoT and Kepler to constrain the amplitude of the discontinuity in the sound speed at the edge of the convective core, the ratio between the sound speed and the radius at this same location, and the stellar age.

Authors: M.S. Cunha and T.S. Metcalfe
Projects: None

Publication Status: ApJ (accepted)
Last Modified: 2007-05-21 10:48
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Asteroseismic Signatures of Stellar Magnetic Activity Cycles  

Travis S. Metcalfe   Submitted: 2007-04-12 10:12

Observations of stellar activity cycles provide an opportunity to study magnetic dynamos under many different physical conditions. Space-based asteroseismology missions will soon yield useful constraints on the interior conditions that nurture such magnetic cycles, and will be sensitive enough to detect shifts in the oscillation frequencies due to the magnetic variations. We derive a method for predicting these shifts from changes in the Mg II activity index by scaling from solar data. We demonstrate this technique on the solar-type subgiant beta Hyi, using archival International Ultraviolet Explorer spectra and two epochs of ground-based asteroseismic observations. We find qualitative evidence of the expected frequency shifts and predict the optimal timing for future asteroseismic observations of this star.

Authors: T.S. Metcalfe, W.A. Dziembowski, P.G. Judge, M. Snow
Projects: None

Publication Status: MNRAS Letters (accepted)
Last Modified: 2007-04-12 16:33
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The Citation Impact of Digital Preprint Archives for Solar Physics Papers  

Travis S. Metcalfe   Submitted: 2006-07-05 11:16

Papers that are posted to a digital preprint archive are typically cited twice as often as papers that are not posted. This has been demonstrated for papers published in a wide variety of journals, and in many different subfields of astronomy. Most astronomers now use the arXiv.org server (astro-ph) to distribute preprints, but the solar physics community has an independent archive hosted at Montana State University. For several samples of solar physics papers published in 2003, I quantify the boost in citation rates for preprints posted to each of these servers. I show that papers on the MSU archive typically have citation rates 1.7 times higher than the average of similar papers that are not posted as preprints, while those posted to astro-ph get 2.6 times the average. A comparable boost is found for papers published in conference proceedings, suggesting that the higher citation rates are not the result of self-selection of above-average papers.

Authors: Travis S. Metcalfe
Projects:

Publication Status: Solar Physics (accepted)
Last Modified: 2006-10-18 15:05
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Asteroseismic Signatures of Small Convective Cores
Asteroseismic Signatures of Stellar Magnetic Activity Cycles
The Citation Impact of Digital Preprint Archives for Solar Physics Papers

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