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101. The core/envelope symmetry in pulsating stars

Author

Montgomery, M. H., Metcalfe, T. S., and Winget, D. E.

Subjects
Astrophysics
Abstract

We demonstrate that there is an inherent symmetry in the way high-overtone stellar pulsations sample the core and the envelope, which can potentially lead to an ambiguity in the asteroseismologically derived locations of internal structures. We provide an intuitive example of the source of this symmetry by analogy with a vibrating string. For the stellar case, we focus on the white dwarf stars, establishing the practical consequences for high-order white dwarf pulsations both analytically and numerically. In addition, we verify the effect empirically by cross-fitting two different structural models, and we discuss the consequences that this approximate symmetry may have for past and present asteroseismological fits of the pulsating DBV, GD 358. Finally, we show how the signatures of composition transition zones that are brought about by physically distinct processes may be used to help alleviate this potential ambiguity in our asteroseismological interpretation of the pulsation frequencies observed in white dwarf stars., Comment: Accepted for publication in MNRAS; 8 pages, 8 figures

Published
2003
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102. Stellar Structure Modeling using a Parallel Genetic Algorithm for Objective Global Optimization

Author

Metcalfe, T. S. and Charbonneau, P.

Subjects
Astrophysics
Abstract

Genetic algorithms are a class of heuristic search techniques that apply basic evolutionary operators in a computational setting. We have designed a fully parallel and distributed hardware/software implementation of the generalized optimization subroutine PIKAIA, which utilizes a genetic algorithm to provide an objective determination of the globally optimal parameters for a given model against an observational data set. We have used this modeling tool in the context of white dwarf asteroseismology, i.e., the art and science of extracting physical and structural information about these stars from observations of their oscillation frequencies. The efficient, parallel exploration of parameter-space made possible by genetic-algorithm-based numerical optimization led us to a number of interesting physical results: (1) resolution of a hitherto puzzling discrepancy between stellar evolution models and prior asteroseismic inferences of the surface helium layer mass for a DBV white dwarf; (2) precise determination of the central oxygen mass fraction in a white dwarf star; and (3) a preliminary estimate of the astrophysically important but experimentally uncertain rate for the ^12C(alpha,gamma)^16O nuclear reaction. These successes suggest that a broad class of computationally-intensive modeling applications could also benefit from this approach., Comment: 22 pages, minor changes, to appear in Journal of Computational Physics (JCPH2002-0129), software available at http://whitedwarf.org/parallel/

Published
2002
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103. The ^12C(alpha,gamma)^16O Nuclear Reaction Rate from Asteroseismology of the DBV White Dwarf CBS 114

Author

Metcalfe, T. S. and Handler, G.

Subjects
Astrophysics
Abstract

We have identified seven independent pulsation modes in the helium-atmosphere variable (DBV) white dwarf star CBS 114, based on 65 hours of time-resolved CCD photometry from the 0.75-m telescope at SAAO. We interpret these pulsations as non-radial g-modes with the same spherical degree l=1, as suggested by the mean period spacing of 37.1+/-0.7 seconds. We use a genetic-algorithm-based fitting method to find the globally optimal model parameters, including the stellar mass (M_* = 0.73 M_sun), the effective temperature (T_eff = 21,000 K), the mass of the atmospheric helium layer (log[M_He/M_*] = -6.66), and the central oxygen mass fraction (X_O = 0.61). The latter value implies a rate for the ^12C(alpha,gamma)^16O reaction near S_300 = 180 keV b, consistent with laboratory measurements., Comment: 4 pages, 1 figure, to appear in proceedings of ``Asteroseismology Across the HR Diagram''

Published
2002

104. The asteroseismological potential of the pulsating DB white dwarf stars CBS 114 and PG 1456+103

Author

Handler, G., Metcalfe, T. S., and Wood, M. A.

Subjects
Astrophysics
Abstract

We have acquired 65 h of single-site time-resolved CCD photometry of the pulsating DB white dwarf star CBS 114 and 62 h of two-site high-speed CCD photometry of another DBV, PG 1456+103. The pulsation spectrum of PG 1456+103 is complicated and variable on time scales of about one week and could only partly be deciphered with our measurements. The modes of CBS 114 are more stable in time and we were able to arrive at a frequency solution somewhat affected by aliasing, but still satisfactory, involving seven independent modes and two combination frequencies. These frequencies also explain the discovery data of the star, taken 13 years earlier. We find a mean period spacing of 37.1 +/- 0.7 s significant at the 98% level between the independent modes of CBS 114 and argue that they are due to nonradial g-mode pulsations of spherical degree l=1. We performed a global search for asteroseismological models of CBS 114 using a genetic algorithm, and we examined the susceptibility of the results to the uncertainties of the observational frequency determinations and mode identifications (we could not provide m values). The families of possible solutions are identified correctly even without knowledge of m. Our optimal model suggests Teff = 21,000 K and M_* = 0.730 M_sun as well as log(M_He/M_*) = -6.66, X_O = 0.61. This measurement of the central oxygen mass fraction implies a rate for the ^12C(alpha,gamma)^16O nuclear reaction near S_300=180 keV b, consistent with laboratory measurements., Comment: 10 pages, 10 embedded figures, 3 embedded tables. Accepted for publication in MNRAS

Published
2002
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105. Measuring ^{12}C(&alpha,&gamma)^{16}O from White Dwarf Asteroseismology

Author

Metcalfe, T. S., Salaris, M., and Winget, D. E.

Subjects
Astrophysics
Abstract

During helium burning in the core of a red giant, the relative rates of the 3&alpha and ^{12}C(&alpha,&gamma)^{16}O reactions largely determine the final ratio of carbon to oxygen in the resulting white dwarf star. The uncertainty in the 3&alpha reaction at stellar energies due to the extrapolation from high-energy laboratory measurements is relatively small, but this is not the case for the ^{12}C(&alpha,&gamma)^{16}O reaction. Recent advances in the analysis of asteroseismological data on pulsating white dwarf stars now make it possible to obtain precise measurements of the central ratio of carbon to oxygen, providing a more direct way to measure the ^{12}C(&alpha,&gamma)^{16}O reaction rate at stellar energies. We assess the systematic uncertainties of this approach and quantify small shifts in the measured central oxygen abundance originating from the observations and from model settings that are kept fixed during the optimization. Using new calculations of white dwarf internal chemical profiles, we find a rate for the ^{12}C(&alpha,&gamma)^{16}O reaction that is significantly higher than most published values. The accuracy of this method may improve as we modify some of the details of our description of white dwarf interiors that were not accessible through previous model-fitting methods., Comment: 8 pages, 4 figures, 3 tables, uses emulateapj5.sty, Accepted for publication in the Astrophysical Journal

Published
2002
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106. Constraints on 12C(alpha,gamma)16O from White Dwarf Seismology

Author

Metcalfe, T. S., Salaris, M., and Winget, D. E.

Subjects
Astrophysics
Abstract

For many years, astronomers have promised that the study of pulsating white dwarfs would ultimately lead to useful information about the physics of matter under extreme conditions of temperature and pressure. We can now make good on that promise. Using observational data from the Whole Earth Telescope and a new analysis method employing a genetic algorithm, we empirically determine the central oxygen abundance of the helium-atmosphere variable white dwarf GD 358. We use this value, combined with detailed evolutionary calculations of the internal chemical profiles to place constraints on the 12C(alpha,gamma)16O nuclear reaction cross-section., Comment: 4 pages, 1 figure, to appear in proceedings of IAU Colloquium 185

Published
2001

107. Preliminary Constraints on 12C(alpha,gamma)16O from White Dwarf Seismology

Author

Metcalfe, T. S., Winget, D. E., and Charbonneau, P.

Subjects
Astrophysics
Abstract

For many years, astronomers have promised that the study of pulsating white dwarfs would ultimately lead to useful information about the physics of matter under extreme conditions of temperature and pressure. In this paper we finally make good on that promise. Using observational data from the Whole Earth Telescope and a new analysis method employing a genetic algorithm, we empirically determine that the central oxygen abundance in the helium-atmosphere variable white dwarf GD 358 is 84+/-3 percent. We use this value to place preliminary constraints on the 12C(alpha,gamma)16O nuclear reaction cross-section. More precise constraints will be possible with additional detailed simulations. We also show that the pulsation modes of our best-fit model probe down to the inner few percent of the stellar mass. We demonstrate the feasibility of reconstructing the internal chemical profiles of white dwarfs from asteroseismological data, and find an oxygen profile for GD 358 that is qualitatively similar to recent theoretical calculations., Comment: Accepted for publication in the Astrophysical Journal, 7 pages, 6 figures, 2 tables, uses emulateapj5.sty

Published
2001
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108. The effect of 3-He diffusion on the pulsational spectra of DBV models

Author

Montgomery, M. H., Metcalfe, T. S., and Winget, D. E.

Subjects
Astrophysics
Abstract

We consider envelopes of DB white dwarfs which are not composed of pure 4-He, but rather a mixture of 3-He and 4-He. Given this assumption, the same diffusive processes which produce a relatively pure H layer overlying a He layer in the DA's should work to produce a 3-He layer overlying a 4-He layer in the DB's. We examine the relevant timescales for diffusion in these objects, and compare them to the relevant evolutionary timescales in the context of the DBV white dwarfs. We then explore the consequences which 3-He separation has on the pulsational spectra of DBV models. Since GD 358 is the best-studied member of this class of variables, we examine fits to its observed pulsation spectrum. We find that the inclusion of a 3-He layer results in a modest improvement in a direct fit to the periods, while a fit to the period spacings is significantly improved., Comment: 4 pages, 4 figures

Published
2000

109. Genetic-Algorithm-based Asteroseismological Analysis of the DBV White Dwarf GD 358

Author

Metcalfe, T. S., Nather, R. E., and Winget, D. E.

Subjects
Astrophysics
Abstract

White dwarf asteroseismology offers the opportunity to probe the structure and composition of stellar objects governed by relatively simple physical principles. The observational requirements of asteroseismology have been addressed by the development of the Whole Earth Telescope (WET), but the analytical procedures still need to be refined before this technique can yield the complete physical insight that the data can provide. Toward this end, we have utilized a genetic-algorithm-based optimization method to fit our models to the observed pulsation frequencies of the DBV white dwarf GD 358 obtained with the WET in 1990. This new approach has finally exploited the sensitivity of our models to the core composition, and will soon yield some interesting constraints on nuclear reaction cross-sections., Comment: 8 pages using emulateapj.sty, 4 figures (1 color), 2 tables. Accepted for publication in ApJ

Published
2000
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110. Evolutionary Timescale of the DAV G117-B15A: The Most Stable Optical Clock Known

Author

Kepler, S. O., Mukadam, Anjum, Winget, D. E., Nather, R. E., Metcalfe, T. S., Reed, M. D., Kawaler, S. D., and Bradley, Paul A.

Subjects
Astrophysics
Abstract

We observe G117-B15A, the most precise optical clock known, to measure the rate of change of the main pulsation period of this blue-edge DAV white dwarf. Even though the obtained value is only within 1 sigma, Pdot = (2.3 +/- 1.4) x 10^{-15} s/s, it is already constraining the evolutionary timescale of this cooling white dwarf star., Comment: Accepted for publication in ApJL

Published
2000
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111. The Asteroseismology Metacomputer

Author

Metcalfe, T. S. and Nather, R. E.

Subjects
Astrophysics
Abstract

We have developed a specialized computational instrument for fitting models of pulsating white dwarfs to observations made with the Whole Earth Telescope. This metacomputer makes use of inexpensive PC hardware and free software, including a parallel genetic algorithm which performs a global search for the best-fit set of parameters., Comment: Submitted to Baltic Astronomy, 5 pages, plain TeX, uses balticw.tex

Published
1999
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112. The Orbital and Absolute Magnitude Distributions of Main Belt Asteroids

Author

Jedicke, R. and Metcalfe, T. S.

Subjects
Astrophysics
Abstract

We have developed a model-independent analytical method for debiasing the four-dimensional (a,e,i,H) distribution obtained in any asteroid observation program and have applied the technique to results obtained with the 0.9m Spacewatch Telescope. From 1992 to 1995 Spacewatch observed ~3740 deg^2 near the ecliptic and made observations of more than 60,000 asteroids to a limiting magnitude of V~21. The debiased semi-major axis and inclination distributions of Main Belt asteroids in this sample with 11.5<= H <16 match the distributions of the known asteroids with H <11.5. The absolute magnitude distribution was studied in the range 8< H <17.5. We have found that the set of known asteroids is complete to about absolute magnitudes 12.75, 12.25 and 11.25 in the inner, middle and outer regions of the belt respectively. The number distribution as a function of absolute magnitude cannot be represented by a single power-law (10^{alpha H}) in any region. We were able to define broad ranges in H in each part of the belt where alpha was nearly constant. Within these ranges of H the slope does not correspond to the value of 0.5 expected for an equilibrium cascade in self-similar collisions (Dohnanyi, 1971). The value of alpha varies with absolute magnitude and shows a `kink' in all regions of the belt for H~13. This absolute magnitude corresponds to a diameter ranging from about 8.5 to 12.5 km depending on the albedo or region of the belt., Comment: 33 pages, 6 figures, 6 tables. published in Icarus

Published
1998
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117. LBT/PEPSI Spectropolarimetry of a Magnetic Morphology Shift in Old Solar-type Stars

Author

Metcalfe, T. S., Kochukhov, Oleg, Ilyin, I. V., Strassmeier, K. G., Godoy-Rivera, D., Pinsonneault, M. H., Metcalfe, T. S., Kochukhov, Oleg, Ilyin, I. V., Strassmeier, K. G., Godoy-Rivera, D., and Pinsonneault, M. H.

Abstract

Solar-type stars are born with relatively rapid rotation and strong magnetic fields. Through a process known as magnetic braking, the rotation slows over time as stellar winds gradually remove angular momentum from the system. The rate of angular momentum loss depends sensitively on the magnetic morphology, with the dipole field exerting the largest torque on the star. Recent observations suggest that the efficiency of magnetic braking may decrease dramatically in stars near the middle of their main-sequence lifetimes. One hypothesis to explain this reduction in efficiency is a shift in magnetic morphology from predominantly larger to smaller spatial scales. We aim to test this hypothesis with spectropolarimetric measurements of two stars that sample chromospheric activity levels on opposite sides of the proposed magnetic transition. As predicted, the more active star (HD 100180) exhibits a significant circular polarization signature due to a nonaxisymmetric large-scale magnetic field, while the less active star (HD 143761) shows no significant signal. We identify analogs of the two stars among a sample of well-characterized Kepler targets, and we predict that the asteroseismic age of HD 143761 from future Transiting Exoplanet Survey Satellite observations will substantially exceed the age expected from gyrochronology. We conclude that a shift in magnetic morphology likely contributes to the loss of magnetic braking in middle-aged stars, which appears to coincide with the shutdown of their global dynamos.

Published
2019
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118. Signatures of Magnetic Activity: On the Relation between Stellar Properties and p-mode Frequency Variations

Author

Santos, A. R. G., primary, Campante, T. L., additional, Chaplin, W. J., additional, Cunha, M. S., additional, van Saders, J. L., additional, Karoff, C., additional, Metcalfe, T. S., additional, Mathur, S., additional, García, R. A., additional, Lund, M. N., additional, Kiefer, R., additional, Aguirre, V. Silva, additional, Davies, G. R., additional, Howe, R., additional, and Elsworth, Y., additional

Published
2019
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122. Keplerobservations of the asteroseismic binary HD 176465

Author

White, T. R., primary, Benomar, O., additional, Silva Aguirre, V., additional, Ball, W. H., additional, Bedding, T. R., additional, Chaplin, W. J., additional, Christensen-Dalsgaard, J., additional, Garcia, R. A., additional, Gizon, L., additional, Stello, D., additional, Aigrain, S., additional, Antia, H. M., additional, Appourchaux, T., additional, Bazot, M., additional, Campante, T. L., additional, Creevey, O. L., additional, Davies, G. R., additional, Elsworth, Y. P., additional, Gaulme, P., additional, Handberg, R., additional, Hekker, S., additional, Houdek, G., additional, Howe, R., additional, Huber, D., additional, Karoff, C., additional, Marques, J. P., additional, Mathur, S., additional, McQuillan, A., additional, Metcalfe, T. S., additional, Mosser, B., additional, Nielsen, M. B., additional, Régulo, C., additional, Salabert, D., additional, and Stahn, T., additional

Published
2017
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124. DETECTION OF SOLAR-LIKE OSCILLATIONS, OBSERVATIONAL CONSTRAINTS, AND STELLAR MODELS FOR θ CYG, THE BRIGHTEST STAR OBSERVED BY THE KEPLER MISSION

Author

Guzik, J. A., Houdek, G., Chaplin, W. J., Smalley, B., Kurtz, Donald Wayne, Gilliland, R. L., Mullally, F., Rowe, J. F., Bryson, S. T., Still, M. D., Antoci, V., Appourchaux, T., Basu, S., Bedding, T. R., Benomar, O., Garcia, R. A., Huber, D., Kjeldsen, H., Latham, D. W., Metcalfe, T. S., Pápics, P. I., White, T. R., Aerts, C., Ballot, J., Boyajian, T. S., Briquet, M., Bruntt, H., Buchhave, L. A., Campante, T. L., Catanzaro, G., Christensen-Dalsgaard, J., Davies, G. R., Doğan, G., Dragomir, D., Doyle, A. P., Elsworth, Y., Frasca, A., Gaulme, P., Gruberbauer, M., Handberg, R., Hekker, S., Karoff, C., Lehmann, H., Mathias, P., Mathur, S., Miglio, A., Molenda-Żakowicz, J., Mosser, B., Murphy, S. J., Régulo, C., Ripepi, V., Salabert, D., Sousa, S. G., Stello, D., Uytterhoeven, K., Guzik, J. A., Houdek, G., Chaplin, W. J., Smalley, B., Kurtz, Donald Wayne, Gilliland, R. L., Mullally, F., Rowe, J. F., Bryson, S. T., Still, M. D., Antoci, V., Appourchaux, T., Basu, S., Bedding, T. R., Benomar, O., Garcia, R. A., Huber, D., Kjeldsen, H., Latham, D. W., Metcalfe, T. S., Pápics, P. I., White, T. R., Aerts, C., Ballot, J., Boyajian, T. S., Briquet, M., Bruntt, H., Buchhave, L. A., Campante, T. L., Catanzaro, G., Christensen-Dalsgaard, J., Davies, G. R., Doğan, G., Dragomir, D., Doyle, A. P., Elsworth, Y., Frasca, A., Gaulme, P., Gruberbauer, M., Handberg, R., Hekker, S., Karoff, C., Lehmann, H., Mathias, P., Mathur, S., Miglio, A., Molenda-Żakowicz, J., Mosser, B., Murphy, S. J., Régulo, C., Ripepi, V., Salabert, D., Sousa, S. G., Stello, D., and Uytterhoeven, K.

Abstract

θ Cygni is an F3 spectral type magnitude V = 4.48 main-sequence star that was the brightest star observed by the original Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a custom aperture were first obtained during Quarter 6 (2010 June–September) and subsequently in Quarters 8 and 12–17. We present analyses of solar-like oscillations based on Q6 and Q8 data, identifying angular degree l = 0, 1, and 2 modes with frequencies of 1000–2700 μHz, a large frequency separation of 83.9 ± 0.4 μHz, and maximum oscillation amplitude at frequency νmax = 1829 ± 54 μHz. We also present analyses of new ground-based spectroscopic observations, which, combined with interferometric angular diameter measurements, give Teff = 6697 ± 78 K, radius 1.49 ± 0.03 Re, [Fe/H] = −0.02 ± 0.06 dex, and log g = 4.23 ± 0.03. We calculate stellar models matching these constraints using the Yale Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit models have masses of 1.35–1.39 Me and ages of 1.0–1.6 Gyr. θ Cyg’s Teff and log g place it cooler than the red edge of the γ Doradus instability region established from pre-Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show γ Dor gravity modes driven by the 1 convective blocking mechanism, with frequencies of 1–3 cycles per day (11 to 33 μHz). However, gravity modes were not seen in Kepler data; one signal at 1.776 cycles per day (20.56 μHz) may be attributable to a faint, possibly background, binary.

Published
2016

125. Erratum:Sounding stellar cycles with Kepler - II. Ground-based observations [Mon. Not. R. Astron. Soc, 433, (2013), (3227-3238)] DOI: 10.1093/mnras/stt964

Author

Karoff, C., Metcalfe, T. S., Chaplin, W. J., Frandsen, S., Grundahl, F., Kjeldsen, H., Christensen-Dalsgaard, J., Nielsen, M. B., Frimann, S., Thygesen, A. O., Arentoft, T., Amby, T. M., Sousa, S. G., and Buzasi, D. L.

Subjects
oscillations [Stars], activity [Sun], helioseismology [Sun], activity [Stars]
Abstract

The paper 'Sounding stellar cycles with Kepler - II. Ground-based observations' was published in Mon. Not. R. Astron. Soc. 433, 3227-3238 (2013). Here we correct equation 15, which should read: log Prot = (0.59 ± 0.29) log Age + 0.45 ± 0.19 (1) and equation 16, which should read: log Prot = (0.47 ± 0.22) log Age + log f (B - V ) + 0.81 ± 0.10. (2) The error arose from erroneously swapping the y-intercept and the slope. The solid lines in Figs. 14 & 15 are still correct and none of the conclusions in the paper have changed.

Published
2014

127. DETECTION OF SOLAR-LIKE OSCILLATIONS, OBSERVATIONAL CONSTRAINTS, AND STELLAR MODELS FORθCYG, THE BRIGHTEST STAR OBSERVED BY THEKEPLERMISSION

Author

Guzik, J. A., primary, Houdek, G., additional, Chaplin, W. J., additional, Smalley, B., additional, Kurtz, D. W., additional, Gilliland, R. L., additional, Mullally, F., additional, Rowe, J. F., additional, Bryson, S. T., additional, Still, M. D., additional, Antoci, V., additional, Appourchaux, T., additional, Basu, S., additional, Bedding, T. R., additional, Benomar, O., additional, Garcia, R. A., additional, Huber, D., additional, Kjeldsen, H., additional, Latham, D. W., additional, Metcalfe, T. S., additional, Pápics, P. I., additional, White, T. R., additional, Aerts, C., additional, Ballot, J., additional, Boyajian, T. S., additional, Briquet, M., additional, Bruntt, H., additional, Buchhave, L. A., additional, Campante, T. L., additional, Catanzaro, G., additional, Christensen-Dalsgaard, J., additional, Davies, G. R., additional, Doğan, G., additional, Dragomir, D., additional, Doyle, A. P., additional, Elsworth, Y., additional, Frasca, A., additional, Gaulme, P., additional, Gruberbauer, M., additional, Handberg, R., additional, Hekker, S., additional, Karoff, C., additional, Lehmann, H., additional, Mathias, P., additional, Mathur, S., additional, Miglio, A., additional, Molenda-Żakowicz, J., additional, Mosser, B., additional, Murphy, S. J., additional, Régulo, C., additional, Ripepi, V., additional, Salabert, D., additional, Sousa, S. G., additional, Stello, D., additional, and Uytterhoeven, K., additional

Published
2016
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128. SpaceInn hare-and-hounds exercise: Estimation of stellar properties using space-based asteroseismic data

Author

Reese, D. R., primary, Chaplin, W. J., additional, Davies, G. R., additional, Miglio, A., additional, Antia, H. M., additional, Ball, W. H., additional, Basu, S., additional, Buldgen, G., additional, Christensen-Dalsgaard, J., additional, Coelho, H. R., additional, Hekker, S., additional, Houdek, G., additional, Lebreton, Y., additional, Mazumdar, A., additional, Metcalfe, T. S., additional, Silva Aguirre, V., additional, Stello, D., additional, and Verma, K., additional

Published
2016
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129. Magnetic variability in the young solar analog KIC 10644253

Author

Salabert, D., primary, Régulo, C., additional, García, R. A., additional, Beck, P. G., additional, Ballot, J., additional, Creevey, O. L., additional, Pérez Hernández, F., additional, do Nascimento Jr., J.-D., additional, Corsaro, E., additional, Egeland, R., additional, Mathur, S., additional, Metcalfe, T. S., additional, Bigot, L., additional, Ceillier, T., additional, and Pallé, P. L., additional

Published
2016
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130. Hot super-Earths stripped by their host stars

Author

Lundkvist, M. S., primary, Kjeldsen, H., additional, Albrecht, S., additional, Davies, G. R., additional, Basu, S., additional, Huber, D., additional, Justesen, A. B., additional, Karoff, C., additional, Silva Aguirre, V., additional, Van Eylen, V., additional, Vang, C., additional, Arentoft, T., additional, Barclay, T., additional, Bedding, T. R., additional, Campante, T. L., additional, Chaplin, W. J., additional, Christensen-Dalsgaard, J., additional, Elsworth, Y. P., additional, Gilliland, R. L., additional, Handberg, R., additional, Hekker, S., additional, Kawaler, S. D., additional, Lund, M. N., additional, Metcalfe, T. S., additional, Miglio, A., additional, Rowe, J. F., additional, Stello, D., additional, Tingley, B., additional, and White, T. R., additional

Published
2016
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131. KOI-3158: The oldest known system of terrestrial-size planets

Author

Campante, T. L., Barclay, T., Swift, J. J., Huber, D., Adibekyan, V. Zh., Cochran, W., Burke, C. J., Isaacson, H., Quintana, E. V., Davies, G. R., Aguirre, V. Silva, Ragozzine, D., Riddle, R., Baranec, C., Basu, S., Chaplin, W. J., Christensen-Dalsgaard, J., Metcalfe, T. S., Bedding, T. R., Handberg, R., Stello, D., Brewer, J. M., Hekker, S., Karoff, C., Kolbl, R., Law, N. M., Lundkvist, M., Miglio, A., Rowe, J. F., Santos, N. C., Van Laerhoven, C., Arentoft, T., Elsworth, Y. P., Fischer, D. A., Kawaler, S. D., Kjeldsen, H., Lund, M. N., Marcy, G. W., Sousa, S. G., Sozzetti, A., White, T. R., Campante, T. L., Barclay, T., Swift, J. J., Huber, D., Adibekyan, V. Zh., Cochran, W., Burke, C. J., Isaacson, H., Quintana, E. V., Davies, G. R., Aguirre, V. Silva, Ragozzine, D., Riddle, R., Baranec, C., Basu, S., Chaplin, W. J., Christensen-Dalsgaard, J., Metcalfe, T. S., Bedding, T. R., Handberg, R., Stello, D., Brewer, J. M., Hekker, S., Karoff, C., Kolbl, R., Law, N. M., Lundkvist, M., Miglio, A., Rowe, J. F., Santos, N. C., Van Laerhoven, C., Arentoft, T., Elsworth, Y. P., Fischer, D. A., Kawaler, S. D., Kjeldsen, H., Lund, M. N., Marcy, G. W., Sousa, S. G., Sozzetti, A., and White, T. R.

Abstract

The first discoveries of exoplanets around Sun-like stars have fueled efforts to find ever smaller worlds evocative of Earth and other terrestrial planets in the Solar System. While gas-giant planets appear to form preferentially around metal-rich stars, small planets (with radii less than four Earth radii) can form under a wide range of metallicities. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were far less abundant. We report Kepler spacecraft observations of KOI-3158, a metal-poor Sun-like star from the old population of the Galactic thick disk, which hosts five planets with sizes between Mercury and Venus. We used asteroseismology to directly measure a precise age of 11.2+/-1.0 Gyr for the host star, indicating that KOI-3158 formed when the Universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, providing scope for the existence of ancient life in the Galaxy., Comment: Submitted to EPJ Web of Conferences, to appear in the Proceedings of the 3rd CoRoT Symposium, Kepler KASC7 joint meeting; 4 pages, 1 figure

Published
2015
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132. Oscillation frequencies for 35Keplersolar-type planet-hosting stars using Bayesian techniques and machine learning

Author

Davies, G. R., primary, Aguirre, V. Silva, additional, Bedding, T. R., additional, Handberg, R., additional, Lund, M. N., additional, Chaplin, W. J., additional, Huber, D., additional, White, T. R., additional, Benomar, O., additional, Hekker, S., additional, Basu, S., additional, Campante, T. L., additional, Christensen-Dalsgaard, J., additional, Elsworth, Y., additional, Karoff, C., additional, Kjeldsen, H., additional, Lundkvist, M. S., additional, Metcalfe, T. S., additional, and Stello, D., additional

Published
2015
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134. Magnetic Activity Cycles in the Exoplanet Host Star ǫ Eridani

Author

Metcalfe, T. S., Buccino, Andrea Paola, Brown, B. P., Mathur, S., Soderblom, D. R., Henry, T. J., Mauas, Pablo Jacobo David, Petrucci, Romina Paola, Hall, J. C., and Basu, S.

Subjects
Astronomía, Ciencias Físicas, chromospheres [Stars], Surveys, individual(HD 22049) [Stars], activity [Stars], CIENCIAS NATURALES Y EXACTAS
Abstract

The active K2 dwarf ǫ Eri has been extensively characterized, both as a young solar analog and more recently as an exoplanet host star. As one of the nearest and brightest stars in the sky, it provides an unparalleled opportunity to constrain stellar dynamo theory beyond the Sun. We confirm and document the 3 year magnetic activity cycle in ǫ Eri originally reported by Hatzes and coworkers, and we examine the archival data from previous observations spanning 45 years. The data show coexisting 3 year and 13 year periods leading into a broad activity minimum that resembles a Maunder minimum-like state, followed by the resurgence of a coherent 3 year cycle. The nearly continuous activity record suggests the imultaneous operation of two stellar dynamos with cycle periods of 2.95 ± 0.03 years and 12.7 ± 0.3 years, which by analogy with the solar case suggests a revised identification of the dynamo mechanisms that are responsible for the so-called “active” and “inactive” sequences as proposed by Böhm-Vitense. Finally, based on the observed properties of ǫ Eri we argue that the rotational history of the Sun is what makes it an outlier in the context of magnetic cycles observed in other stars (as also suggested by its Li depletion), and that a Jovian-mass companion cannot be the universal explanation for the solar peculiarities. Fil: Metcalfe, T. S.. Space Science Institute; Estados Unidos Fil: Buccino, Andrea Paola. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Brown, B. P.. University Of Wisconsin; Estados Unidos Fil: Mathur, S.. Space Science Institute; Estados Unidos. High Altitude Observatory, NCAR; Estados Unidos Fil: Soderblom, D. R.. Space Telescope Science Institute; Estados Unidos Fil: Henry, T. J.. Georgia State University; Estados Unidos Fil: Mauas, Pablo Jacobo David. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Petrucci, Romina Paola. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "el Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico ; Argentina Fil: Hall, J. C.. Lowell Observatory; Estados Unidos Fil: Basu, S.. University Of Yale; Estados Unidos

Published
2013

135. Accurate fundamental parameters and detailed abundance patterns from spectroscopy of 93 solar-type Kepler targets

Author

Bruntt, H., Basu, S., Smalley, B., Chaplin, W. J., Verner, G. A., Bedding, T. R., Catala, C., Gazzano, J. -C., Molenda-Zakowicz, J., Thygesen, A. O., Uytterhoeven, K., Hekker, S., Huber, D., Karoff, C., Mathur, S., Mosser, B., Appourchaux, T., Campante, T. L., Elsworth, Y., Garcia, R. A., Handberg, R., Metcalfe, T. S., Quirion, P. -O., Regulo, C., Roxburgh, I. W., Stello, D., Christensen-Dalsgaard, J., Kawaler, S. D., Kjeldsen, H., Morris, R. L., Quintana, E. V., Sanderfer, D. T., Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), and Low Energy Astrophysics (API, FNWI)

Subjects
[SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph]
Abstract

International audience; We present a detailed spectroscopic study of 93 solar-type stars that are targets of the NASA/Kepler mission and provide detailed chemical composition of each target. We find that the overall metallicity is well represented by Fe lines. Relative abundances of light elements (CNO) and a elements are generally higher for low-metallicity stars. Our spectroscopic analysis benefits from the accurately measured surface gravity from the asteroseismic analysis of the Kepler light curves. The accuracy on the log g parameter is better than 0.03 dex and is held fixed in the analysis. We compare our Teff determination with a recent colour calibration of VT-KS [TYCHO V magnitude minus Two Micron All Sky Survey (2MASS) KS magnitude] and find very good agreement and a scatter of only 80 K, showing that for other nearby Kepler targets, this index can be used. The asteroseismic log g values agree very well with the classical determination using Fe iFe ii balance, although we find a small systematic offset of 0.08 dex (asteroseismic log g values are lower). The abundance patterns of metals, a elements and the light elements (CNO) show that a simple scaling by [Fe/H] is adequate to represent the metallicity of the stars, except for the stars with metallicity below -0.3, where a-enhancement becomes important. However, this is only important for a very small fraction of the Kepler sample. We therefore recommend that a simple scaling with [Fe/H] be employed in the asteroseismic analyses of large ensembles of solar-type stars.

Published
2012

136. Acoustic glitches in solar-type stars from Kepler

Author

Mazumdar, A., Monteiro, M. J. P. F. G., Ballot, J, Antia, H. M., Basu, S, Houdek, Günter, Mathur, S, Cunha, M. S., Silva Aguirre, Victor, García, R. A., Salabert, D, Verner, G. A., Christensen-Dalsgaard, Jørgen, Metcalfe, T. S., and Chaplin, W. J.

Subjects
Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics
Abstract

We report the measurement of the acoustic locations of layers of sharp variation in sound speed in the interiors of 19 solar-type stars observed by the Kepler mission. The oscillatory signal in the frequencies arising due to the acoustic glitches at the base of the convection zone and the second helium ionisation zone was utilised to determine their location by four independent methods. Despite the significantly different methods of analysis, remarkable agreement was found between the results of these four methods. Further, the extracted locations of these layers were found to be consistent with representative models of the stars.

Published
2012

137. Ages and fundamental properties ofKeplerexoplanet host stars from asteroseismology

Author

Silva Aguirre, V., primary, Davies, G. R., additional, Basu, S., additional, Christensen-Dalsgaard, J., additional, Creevey, O., additional, Metcalfe, T. S., additional, Bedding, T. R., additional, Casagrande, L., additional, Handberg, R., additional, Lund, M. N., additional, Nissen, P. E., additional, Chaplin, W. J., additional, Huber, D., additional, Serenelli, A. M., additional, Stello, D., additional, Van Eylen, V., additional, Campante, T. L., additional, Elsworth, Y., additional, Gilliland, R. L., additional, Hekker, S., additional, Karoff, C., additional, Kawaler, S. D., additional, Kjeldsen, H., additional, and Lundkvist, M. S., additional

Published
2015
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138. AN ANCIENT EXTRASOLAR SYSTEM WITH FIVE SUB-EARTH-SIZE PLANETS

Author

Campante, T. L., primary, Barclay, T., additional, Swift, J. J., additional, Huber, D., additional, Adibekyan, V. Zh., additional, Cochran, W., additional, Burke, C. J., additional, Isaacson, H., additional, Quintana, E. V., additional, Davies, G. R., additional, Silva Aguirre, V., additional, Ragozzine, D., additional, Riddle, R., additional, Baranec, C., additional, Basu, S., additional, Chaplin, W. J., additional, Christensen-Dalsgaard, J., additional, Metcalfe, T. S., additional, Bedding, T. R., additional, Handberg, R., additional, Stello, D., additional, Brewer, J. M., additional, Hekker, S., additional, Karoff, C., additional, Kolbl, R., additional, Law, N. M., additional, Lundkvist, M., additional, Miglio, A., additional, Rowe, J. F., additional, Santos, N. C., additional, Van Laerhoven, C., additional, Arentoft, T., additional, Elsworth, Y. P., additional, Fischer, D. A., additional, Kawaler, S. D., additional, Kjeldsen, H., additional, Lund, M. N., additional, Marcy, G. W., additional, Sousa, S. G., additional, Sozzetti, A., additional, and White, T. R., additional

Published
2015
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139. Asteroseismic modelling of the solar-type subgiant star $��$ Hydri

Author

Brand��o, I. M., Dogan, G., Christensen-Dalsgaard, J., Cunha, M. S., Bedding, T. R., Metcalfe, T. S., Kjeldsen, H., Bruntt, H., and Arentoft, T.

Subjects
Astrophysics::Solar and Stellar Astrophysics, FOS: Physical sciences, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

Comparing models and data of pulsating stars is a powerful way to understand the stellar structure better.��Hyi is an evolved solar-type pulsator with mixed modes in its frequency spectrum, making it very interesting for asteroseismic studies.The goal of this work is to search for the best model of the solar-type star ��Hyi, based on up-to-date non-seismic and seismic data.We present a revised list of frequencies for 33 modes, which we produced by analysing the power spectrum of the published observations again using a new weighting scheme that minimises the daily sidelobes.We ran several grids of evolutionary models with different input parameters and different physics, using the stellar evolutionary code ASTEC.For the models that are inside the observed error box of ��Hyi, we computed their frequencies with the pulsation code ADIPLS.We used two approaches to find the model that oscillates with the frequencies that are closest to the observed frequencies of ��Hyi:(i)we assume that the best model is the one that reproduces the star's interior based on the radial oscillation frequencies alone, to which we have applied the correction for the near-surface effects;(ii)we assume that the best model is the one that produces the lowest value of the chi-square (\chi2), i.e. that minimises the difference between the observed frequencies of all available modes and the model predictions, after all model frequencies are corrected for near-surface effects.We show that after applying this correction to the frequencies of the best models, we can reproduce the observed modes well, including the mixed modes.The model that gives the lowest value of the \chi2 is a post-main-sequence model with a mass of 1.04 MSun and a metallicity slightly lower than that of the Sun.Our results underscore the importance of having individual frequencies to constrain the properties of the stellar model.

Published
2010
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140. Masses, radii, and orbits of small Kepler planets:the transition from gaseous to rocky planets

Author

Marcy, Geoffrey W., Isaacson, Howard, Howard, Andrew W., Rowe, Jason F., Jenkins, Jon M., Bryson, Stephen T., Latham, David W., Howell, Steve B., Gautier III, Thomas N., Batalha, Natalie M., Rogers, Leslie, Ciardi, David, Fischer, Debra A., Gilliland, Ronald L., Kjeldsen, Hans, Christensen-Dalsgaard, Jorgen, Huber, Daniel, Chaplin, William J., Basu, Sarbani, Buchhave, Lars A., Quinn, Samuel N., Borucki, William J., Koch, David G., Hunter, Roger, Caldwell, Douglas A., Van Cleve, Jeffrey, Kolbl, Rea, Weiss, Lauren M., Petigura, Erik, Seager, Sara, Morton, Timothy, Johnson, John Asher, Ballard, Sarah, Burke, Chris, Cochran, William D., Endl, Michael, MacQueen, Phillip, Everett, Mark E., Lissauer, Jack J., Ford, Eric B., Torres, Guillermo, Fressin, Francois, Brown, Timothy M., Steffen, Jason H., Charbonneau, David, Basri, Gibor S., Sasselov, Dimitar D., Winn, Joshua, Sanchis-Ojeda, Roberto, Christiansen, Jessie, Adams, Elisabeth, Henze, Christopher, Dupree, Andrea, Fabrycky, Daniel C., Fortney, Jonathan J., Tarter, Jill, Holman, Matthew J., Tenenbaum, Peter, Shporer, Avi, Lucas, Philip W., Welsh, William F., Orosz, Jerome A., Bedding, T. R., Campante, T. L., Davies, G. R., Elsworth, Y., Handberg, R., Hekker, S., Karoff, C., Kawaler, S. D., Lund, M. N., Lundkvist, M., Metcalfe, T. S., Miglio, A., Aguirre, V. Silva, Stello, D., White, T. R., Boss, Alan, Devore, Edna, Gould, Alan, Prsa, Andrej, Agol, Eric, Barclay, Thomas, Coughlin, Jeff, Brugamyer, Erik, Mullally, Fergal, Quintana, Elisa V., Still, Martin, Thompson, Susan E., Morrison, David, Twicken, Joseph D., Desert, Jean-Michel, Carter, Josh, Crepp, Justin R., Hebrard, Guillaume, Santerne, Alexandre, Moutou, Claire, Sobeck, Charlie, Hudgins, Douglas, Haas, Michael R., Robertson, Paul, Lillo-Box, Jorge, Barrado, David, Marcy, Geoffrey W., Isaacson, Howard, Howard, Andrew W., Rowe, Jason F., Jenkins, Jon M., Bryson, Stephen T., Latham, David W., Howell, Steve B., Gautier III, Thomas N., Batalha, Natalie M., Rogers, Leslie, Ciardi, David, Fischer, Debra A., Gilliland, Ronald L., Kjeldsen, Hans, Christensen-Dalsgaard, Jorgen, Huber, Daniel, Chaplin, William J., Basu, Sarbani, Buchhave, Lars A., Quinn, Samuel N., Borucki, William J., Koch, David G., Hunter, Roger, Caldwell, Douglas A., Van Cleve, Jeffrey, Kolbl, Rea, Weiss, Lauren M., Petigura, Erik, Seager, Sara, Morton, Timothy, Johnson, John Asher, Ballard, Sarah, Burke, Chris, Cochran, William D., Endl, Michael, MacQueen, Phillip, Everett, Mark E., Lissauer, Jack J., Ford, Eric B., Torres, Guillermo, Fressin, Francois, Brown, Timothy M., Steffen, Jason H., Charbonneau, David, Basri, Gibor S., Sasselov, Dimitar D., Winn, Joshua, Sanchis-Ojeda, Roberto, Christiansen, Jessie, Adams, Elisabeth, Henze, Christopher, Dupree, Andrea, Fabrycky, Daniel C., Fortney, Jonathan J., Tarter, Jill, Holman, Matthew J., Tenenbaum, Peter, Shporer, Avi, Lucas, Philip W., Welsh, William F., Orosz, Jerome A., Bedding, T. R., Campante, T. L., Davies, G. R., Elsworth, Y., Handberg, R., Hekker, S., Karoff, C., Kawaler, S. D., Lund, M. N., Lundkvist, M., Metcalfe, T. S., Miglio, A., Aguirre, V. Silva, Stello, D., White, T. R., Boss, Alan, Devore, Edna, Gould, Alan, Prsa, Andrej, Agol, Eric, Barclay, Thomas, Coughlin, Jeff, Brugamyer, Erik, Mullally, Fergal, Quintana, Elisa V., Still, Martin, Thompson, Susan E., Morrison, David, Twicken, Joseph D., Desert, Jean-Michel, Carter, Josh, Crepp, Justin R., Hebrard, Guillaume, Santerne, Alexandre, Moutou, Claire, Sobeck, Charlie, Hudgins, Douglas, Haas, Michael R., Robertson, Paul, Lillo-Box, Jorge, and Barrado, David

Abstract

We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm–3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than ~2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).

Published
2014

141. Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC20058-5234

Author

WET Collaboration, Sullivan, D. J., Metcalfe, T. S., O'Donoghue, D., Winget, D. E., Kilkenny, D., van Wyk, F., Kanaan, A., Kepler, S. O., Nitta, A., Kawaler, S. D., Montgomery, M. H., Nather, R. E., O'Brien, M. S., Bischoff-Kim, A., Wood, M., Jiang, X. J., Leibowitz, E. M., Ibbetson, P., Zola, S., Krzesinski, J., Pajdosz, G., Vauclair, G., Dolez, N., Chevreton, M., Brain imaging (LIAMA), Laboratoire Franco-Chinois d'Informatique, d'Automatique et de Mathématiques Appliquées (LIAMA), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Chinese Academy of Sciences [Changchun Branch] (CAS)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institute of Automation - Chinese Academy of Sciences-Centre National de la Recherche Scientifique (CNRS)-Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Chinese Academy of Sciences [Changchun Branch] (CAS)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institute of Automation - Chinese Academy of Sciences-Centre National de la Recherche Scientifique (CNRS), Laboratoire Astrophysique de Toulouse-Tarbes (LATT), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), and Université Fédérale Toulouse Midi-Pyrénées

Subjects
oscillations [stars], Stellar mass, FOS: Physical sciences, Astrophysics, Compact star, stars: interiors, 01 natural sciences, law.invention, Photometry (optics), Telescope, photometric [techniques], [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Análise asterosismológica, techniques: photometric, Observatory, law, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, white dwarfs, Physics, interiors [stars], 010308 nuclear & particles physics, Estrelas ZZ Ceti, Astrophysics (astro-ph), White dwarf, Astronomy and Astrophysics, Effective temperature, stars: individual: EC 20058-5234, individual: EC 20058-5234 [stars], Fotometria astronômica, Anãs brancas, Pulsacoes estelares, 13. Climate action, Space and Planetary Science, stars: oscillations, Instability strip
Abstract

We present the analysis of a total of 177h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058-5234. The bulk of the observations (135h) were obtained during a WET campaign (XCOV15) in July 1997 that featured coordinated observing from 4 southern observatory sites over an 8-day period. The remaining data (42h) were obtained in June 2004 at Mt John Observatory in NZ over a one-week observing period. This work significantly extends the discovery observations of this low-amplitude (few percent) pulsator by increasing the number of detected frequencies from 8 to 18, and employs a simulation procedure to confirm the reality of these frequencies to a high level of significance (1 in 1000). The nature of the observed pulsation spectrum precludes identification of unique pulsation mode properties using any clearly discernable trends. However, we have used a global modelling procedure employing genetic algorithm techniques to identify the n, l values of 8 pulsation modes, and thereby obtain asteroseismic measurements of several model parameters, including the stellar mass (0.55 M_sun) and T_eff (~28200 K). These values are consistent with those derived from published spectral fitting: T_eff ~ 28400 K and log g ~ 7.86. We also present persuasive evidence from apparent rotational mode splitting for two of the modes that indicates this compact object is a relatively rapid rotator with a period of 2h. In direct analogy with the corresponding properties of the hydrogen (DAV) atmosphere pulsators, the stable low-amplitude pulsation behaviour of EC 20058 is entirely consistent with its inferred effective temperature, which indicates it is close to the blue edge of the DBV instability strip. (abridged), 19 pages, 8 figures, 5 tables, MNRAS accepted

Published
2008

143. Asteroseismic inference on rotation, gyrochronology and planetary system dynamics of 16 Cygni

Author

Davies, G. R., primary, Chaplin, W. J., additional, Farr, W. M., additional, García, R. A., additional, Lund, M. N., additional, Mathis, S., additional, Metcalfe, T. S., additional, Appourchaux, T., additional, Basu, S., additional, Benomar, O., additional, Campante, T. L., additional, Ceillier, T., additional, Elsworth, Y., additional, Handberg, R., additional, Salabert, D., additional, and Stello, D., additional

Published
2014
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144. Rotation and magnetism ofKeplerpulsating solar-like stars

Author

García, R. A., primary, Ceillier, T., additional, Salabert, D., additional, Mathur, S., additional, van Saders, J. L., additional, Pinsonneault, M., additional, Ballot, J., additional, Beck, P. G., additional, Bloemen, S., additional, Campante, T. L., additional, Davies, G. R., additional, do Nascimento Jr., J.-D., additional, Mathis, S., additional, Metcalfe, T. S., additional, Nielsen, M. B., additional, Suárez, J. C., additional, Chaplin, W. J., additional, Jiménez, A., additional, and Karoff, C., additional

Published
2014
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145. Erratum: Sounding stellar cycles with Kepler – II. Ground-based observations

Author

Karoff, C., primary, Metcalfe, T. S., additional, Chaplin, W. J., additional, Frandsen, S., additional, Grundahl, F., additional, Kjeldsen, H., additional, Christensen-Dalsgaard, J., additional, Nielsen, M.B., additional, Frimann, S., additional, Thygesen, A. O., additional, Arentoft, T., additional, Amby, T. M., additional, Sousa, S. G., additional, and Buzasi, D. L., additional

Published
2014
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146. PROPERTIES OF 42 SOLAR-TYPE KEPLER TARGETS FROM THE ASTEROSEISMIC MODELING PORTAL

Author

Metcalfe, T. S., primary, Creevey, O. L., additional, Doğan, G., additional, Mathur, S., additional, Xu, H., additional, Bedding, T. R., additional, Chaplin, W. J., additional, Christensen-Dalsgaard, J., additional, Karoff, C., additional, Trampedach, R., additional, Benomar, O., additional, Brown, B. P., additional, Buzasi, D. L., additional, Campante, T. L., additional, Çelik, Z., additional, Cunha, M. S., additional, Davies, G. R., additional, Deheuvels, S., additional, Derekas, A., additional, Mauro, M. P. Di, additional, García, R. A., additional, Guzik, J. A., additional, Howe, R., additional, MacGregor, K. B., additional, Mazumdar, A., additional, Montalbán, J., additional, Monteiro, M. J. P. F. G., additional, Salabert, D., additional, Serenelli, A., additional, Stello, D., additional, Ste¸ślicki, M., additional, Suran, M. D., additional, Yıldız, M., additional, Aksoy, C., additional, Elsworth, Y., additional, Gruberbauer, M., additional, Guenther, D. B., additional, Lebreton, Y., additional, Molaverdikhani, K., additional, Pricopi, D., additional, Simoniello, R., additional, and White, T. R., additional

Published
2014
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147. LIMITS ON SURFACE GRAVITIES OFKEPLERPLANET-CANDIDATE HOST STARS FROM NON-DETECTION OF SOLAR-LIKE OSCILLATIONS

Author

Campante, T. L., primary, Chaplin, W. J., additional, Lund, M. N., additional, Huber, D., additional, Hekker, S., additional, García, R. A., additional, Corsaro, E., additional, Handberg, R., additional, Miglio, A., additional, Arentoft, T., additional, Basu, S., additional, Bedding, T. R., additional, Christensen-Dalsgaard, J., additional, Davies, G. R., additional, Elsworth, Y. P., additional, Gilliland, R. L., additional, Karoff, C., additional, Kawaler, S. D., additional, Kjeldsen, H., additional, Lundkvist, M., additional, Metcalfe, T. S., additional, Silva Aguirre, V., additional, and Stello, D., additional

Published
2014
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148. Magnetic activity of F stars observed byKepler

Author

Mathur, S., primary, García, R. A., additional, Ballot, J., additional, Ceillier, T., additional, Salabert, D., additional, Metcalfe, T. S., additional, Régulo, C., additional, Jiménez, A., additional, and Bloemen, S., additional

Published
2014
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149. MEASUREMENT OF ACOUSTIC GLITCHES IN SOLAR-TYPE STARS FROM OSCILLATION FREQUENCIES OBSERVED BYKEPLER

Author

Mazumdar, A., primary, Monteiro, M. J. P. F. G., additional, Ballot, J., additional, Antia, H. M., additional, Basu, S., additional, Houdek, G., additional, Mathur, S., additional, Cunha, M. S., additional, Silva Aguirre, V., additional, García, R. A., additional, Salabert, D., additional, Verner, G. A., additional, Christensen-Dalsgaard, J., additional, Metcalfe, T. S., additional, Sanderfer, D. T., additional, Seader, S. E., additional, Smith, J. C., additional, and Chaplin, W. J., additional

Published
2014
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150. MASSES, RADII, AND ORBITS OF SMALL KEPLER PLANETS: THE TRANSITION FROM GASEOUS TO ROCKY PLANETS

Author

Marcy, Geoffrey W., primary, Isaacson, Howard, additional, Howard, Andrew W., additional, Rowe, Jason F., additional, Jenkins, Jon M., additional, Bryson, Stephen T., additional, Latham, David W., additional, Howell, Steve B., additional, Gautier, Thomas N., additional, Batalha, Natalie M., additional, Rogers, Leslie, additional, Ciardi, David, additional, Fischer, Debra A., additional, Gilliland, Ronald L., additional, Kjeldsen, Hans, additional, Christensen-Dalsgaard, Jørgen, additional, Huber, Daniel, additional, Chaplin, William J., additional, Basu, Sarbani, additional, Buchhave, Lars A., additional, Quinn, Samuel N., additional, Borucki, William J., additional, Koch, David G., additional, Hunter, Roger, additional, Caldwell, Douglas A., additional, Van Cleve, Jeffrey, additional, Kolbl, Rea, additional, Weiss, Lauren M., additional, Petigura, Erik, additional, Seager, Sara, additional, Morton, Timothy, additional, Johnson, John Asher, additional, Ballard, Sarah, additional, Burke, Chris, additional, Cochran, William D., additional, Endl, Michael, additional, MacQueen, Phillip, additional, Everett, Mark E., additional, Lissauer, Jack J., additional, Ford, Eric B., additional, Torres, Guillermo, additional, Fressin, Francois, additional, Brown, Timothy M., additional, Steffen, Jason H., additional, Charbonneau, David, additional, Basri, Gibor S., additional, Sasselov, Dimitar D., additional, Winn, Joshua, additional, Sanchis-Ojeda, Roberto, additional, Christiansen, Jessie, additional, Adams, Elisabeth, additional, Henze, Christopher, additional, Dupree, Andrea, additional, Fabrycky, Daniel C., additional, Fortney, Jonathan J., additional, Tarter, Jill, additional, Holman, Matthew J., additional, Tenenbaum, Peter, additional, Shporer, Avi, additional, Lucas, Philip W., additional, Welsh, William F., additional, Orosz, Jerome A., additional, Bedding, T. R., additional, Campante, T. L., additional, Davies, G. R., additional, Elsworth, Y., additional, Handberg, R., additional, Hekker, S., additional, Karoff, C., additional, Kawaler, S. D., additional, Lund, M. N., additional, Lundkvist, M., additional, Metcalfe, T. S., additional, Miglio, A., additional, Aguirre, V. Silva, additional, Stello, D., additional, White, T. R., additional, Boss, Alan, additional, Devore, Edna, additional, Gould, Alan, additional, Prsa, Andrej, additional, Agol, Eric, additional, Barclay, Thomas, additional, Coughlin, Jeff, additional, Brugamyer, Erik, additional, Mullally, Fergal, additional, Quintana, Elisa V., additional, Still, Martin, additional, Thompson, Susan E., additional, Morrison, David, additional, Twicken, Joseph D., additional, Désert, Jean-Michel, additional, Carter, Josh, additional, Crepp, Justin R., additional, Hébrard, Guillaume, additional, Santerne, Alexandre, additional, Moutou, Claire, additional, Sobeck, Charlie, additional, Hudgins, Douglas, additional, Haas, Michael R., additional, Robertson, Paul, additional, Lillo-Box, Jorge, additional, and Barrado, David, additional

Published
2014
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