An observational correlation between stellar brightness variations and surface gravity

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Abstract

Surface gravity is a basic stellar property, but it is difficult to measure accurately, with typical uncertainties of 25 to 50 per cent if measured spectroscopically1,2 and 90 to 150 per cent if measured photometrically3. Asteroseismology measures gravity with an uncertainty of about 2 per cent but is restricted to relatively small samples of bright stars, most of which are giants4,5,6. The availability of high-precision measurements of brightness variations for more than 150,000 stars7,8 provides an opportunity to investigate whether the variations can be used to determine surface gravities. The Fourier power of granulation on a star’s surface correlates physically with surface gravity9,10: if brightness variations on timescales of hours arise from granulation11, then such variations should correlate with surface gravity. Here we report an analysis of archival data that reveals an observational correlation between surface gravity and root mean squared brightness variations on timescales of less than eight hours for stars with temperatures of 4,500 to 6,750 kelvin, log surface gravities of 2.5 to 4.5 (cgs units) and overall brightness variations of less than three parts per thousand. A straightforward observation of optical brightness variations therefore allows a determination of the surface gravity with a precision of better than 25 per cent for inactive Sun-like stars at main-sequence to giant stages of evolution.

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Figure 1: Simple measures of brightness variations reveal a fundamental ‘flicker sequence’ of stellar evolution.
Figure 2: Stellar surface gravity manifests in a simple measure of brightness variations.
Figure 3: An integrative view of stellar evolution in a new diagram of brightness variations.

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Acknowledgements

The research described in this paper makes use of Filtergraph (http://filtergraph.vanderbilt.edu), an online data visualization tool developed at Vanderbilt University through the Vanderbilt Initiative in Data-intensive Astrophysics. We acknowledge discussions with P. Cargile, K. Carpenter, W. Chaplin, D. Huber, M. Paegert, M. Sinha and D. Weintraub. We thank D. Huber and T. Metcalfe for sharing the average asteroseismic parameters of Kepler stars with us. F.A.B. acknowledges support from a NASA Harriet Jenkins Fellowship and a Vanderbilt Provost Graduate Fellowship. F.A.B. and K.G.S. acknowledge NSF PAARE grant AST-0849736.

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F.A.B. and K.G.S. contributed equally to the identification and analysis of the major correlations. F.A.B. principally wrote the first version of the manuscript. K.G.S. prepared the figures. G.B. calculated the variability statistics of the Kepler light curves and performed an independent check of the analysis. J.P. checked against biases in the datasets. All authors contributed to the interpretation of the results and to the final manuscript.

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Correspondence to Fabienne A. Bastien.

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The authors declare no competing financial interests.

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Bastien, F., Stassun, K., Basri, G. et al. An observational correlation between stellar brightness variations and surface gravity. Nature 500, 427–430 (2013). https://doi.org/10.1038/nature12419

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