ALBERT

Description: Data from the Global Oscillation Network Group (GONG) project and other helioseismic experiments provide a test for models of stellar interiors and for the thermodynamic and radiative properties, on which the models depend, of matter under the extreme conditions found in the sun. Current models are in agreement with the helioseismic inferences, which suggests, for example, that the disagreement between the predicted and observed fluxes of neutrinos from the sun is not caused by errors in the models. However, the GONG data reveal subtle errors in the models, such as an excess in sound speed just beneath the convection zone. These discrepancies indicate effects that have so far not been correctly accounted for; for example, it is plausible that the sound-speed differences reflect weak mixing in stellar interiors, of potential importance to the overall evolution of stars and ultimately to estimates of the age of the galaxy based on stellar evolution calculations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Christensen-Dalsgaard -- Dappen -- Ajukov -- Anderson -- Antia -- Basu -- Baturin -- Berthomieu -- Chaboyer -- Chitre -- Cox -- Demarque -- Donatowicz -- Dziembowski -- Gabriel -- Gough -- Guenther -- Guzik -- Harvey -- Hill -- Houdek -- Iglesias -- Kosovichev -- Leibacher -- Morel -- Proffitt -- Provost -- Reiter -- Rhodes Jr -- Rogers -- Roxburgh -- Thompson -- Ulrich -- New York, N.Y. -- Science. 1996 May 31;272(5266):1286-92.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉J. Christensen-Dalsgaard and S. Basu are with Theoretical Astrophysics Center and Institute of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark. W. Dappen and E. J. Rhodes Jr. are with the Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA. S. V. Ajukov is with the Sternberg Astronomical Institute, Moscow, Russia. E. R. Anderson, J. W. Harvey, F. Hill, and J. W. Leibacher are with the National Solar Observatory, National Optical Astronomy Observatories, Tucson, AZ 85726, USA. H. M. Antia and S. M. Chitre are with the Tata Institute of Fundamental Research, Bombay, India. V. A. Baturin, I. W. Roxburgh, and M. J. Thompson are with the Astronomy Unit, Queen Mary and Westfield College, London E1 4NS, UK. G. Berthomieu, P. Morel, and J. Provost are with the Observatoire de la Cote d'Azur, Nice, France. B. Chaboyer is with CITA, University of Toronto, Toronto, Canada. A. N. Cox and J. A. Guzik are with Los Alamos National Laboratory, Los Alamos, NM 87545, USA. P. Demarque is with the Department of Astronomy, Yale University, New Haven, CT 06520, USA. J. Donatowicz and G. Houdek are with the Institut fur Astronomie, Universitat Wien, Vienna, Austria. W. A. Dziembowski is with the Copernicus Center, Warsaw, Poland. M. Gabriel is with the Institut d'Astrophysique, Universite de Liege, Liege, Belgium. D. O. Gough is with the Institute of Astronomy, University of Cambridge, Cambridge, UK. D. B. Guenther is with the Department of Astronomy and Physics, Saint Mary's University, Halifax, Nova Scotia, Canada. C. A. Iglesias and F. J. Rogers are with the Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. A. G. Kosovichev is with Center for Space Science and Astrophysics, Stanford University, Stanford, CA 94305, USA. C. R. Proffitt is with Computer Sciences Corporation, Goddard Space Flight Center, Greenbelt, MD 20771, USA. J. Reiter is with the Mathematisches Institut, Technische Universitat Munchen, Munich, Germany. R. K. Ulrich is with the Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8662456" target="_blank"〉PubMed〈/a〉

Description: Global Oscillation Network Group data reveal that the internal structure of the sun can be well represented by a calibrated standard model. However, immediately beneath the convection zone and at the edge of the energy-generating core, the sound-speed variation is somewhat smoother in the sun than it is in the model. This could be a consequence of chemical inhomogeneity that is too severe in the model, perhaps owing to inaccurate modeling of gravitational settling or to neglected macroscopic motion that may be present in the sun. Accurate knowledge of the sun's structure enables inferences to be made about the physics that controls the sun; for example, through the opacity, the equation of state, or wave motion. Those inferences can then be used elsewhere in astrophysics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gough -- Kosovichev -- Toomre -- Anderson -- Antia -- Basu -- Chaboyer -- Chitre -- Christensen-Dalsgaard -- Dziembowski -- Eff-Darwich -- Elliott -- Giles -- Goode -- Guzik -- Harvey -- Hill -- Leibacher -- Monteiro -- Richard -- Sekii -- Shibahashi -- Takata -- Thompson -- Vauclair -- Vorontsov -- New York, N.Y. -- Science. 1996 May 31;272(5266):1296-300.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉D. O. Gough, J. R. Elliott, and T. Sekii are with the Institute of Astronomy, University of Cambridge, CB3 0HA, UK. A. G. Kosovichev and P. R. Giles are with HEPL, Stanford University, Stanford, CA, USA. J. Toomre is at JILA, University of Colorado, Boulder, CO, USA. E. Anderson, J. W. Harvey, F. Hill, and J. W. Leibacher are at the National Solar Observatory, Tucson, AZ, USA. H. M. Antia and S. M. Chitre are at the Tata Institute for Fundamental Research, Bombay, India. S. Basu and J. Christensen-Dalsgaard are at the Theoretical Astrophysics Centre, Aarhus University, Denmark. B. Chaboyer is at the Canadian Institute for Theoretical Astrophysics, Toronto, Canada. W. A. Dziembowski is at the Copernicus Astronomical Center, Warsaw, Poland. A. Eff-Darwich is at the Instituto Astrofisico de Canarias, Tenerife, Canary Islands. P. R. Goode is at the New Jersey Institute of Technology, Newark, NJ, USA. J. A. Guzik is at the Los Alamos National Laboratory, Los Alamos, NM, USA. M. J. P. F. G. Monteiro is at the University of Oporto, Postugal. O. Richard and S. Vauclair are at the Observatoire Midi-Pyrenees, Toulouse, France. H. Shibahashi and M. Takata are in the Department of Astronomy, University of Tokyo, Tokyo, Japan. M. J. Thompson and S. V. Vorontsov are at Queen Mary and Westfield College, University of London, London, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8662458" target="_blank"〉PubMed〈/a〉

Description: We present results of a search for identification of modes responsible for the six most significant frequency peaks detected in the rapidly rotating slowly pulsating B-type (SPB) star μ Eridani. All published and some unpublished photometric data are used in our new analysis. The mode identification is carried out with the method developed by Daszyłska-Daszkiewicz et al. employing the phases and amplitudes from multiband photometric data and relying on the traditional approximation for the treatment of oscillations in rotating stars. Models consistent with the observed mean parameters are considered. For the five frequency peaks, the candidates for the identifications are searched amongst unstable modes. In the case of the third frequency, which is an exact multiple of the orbital frequency, this condition is relaxed. The systematic search is continued up to a harmonic degree  = 6. Determination of the angular numbers, (, m ), is done simultaneously with the rotation rate, V rot , and the inclination angle, i , constrained by the spectroscopic data on the projected rotational velocity, V rot sin i , which is assumed constant. All the peaks may be accounted for with g-modes of high radial orders and the degrees  ≤ 6. There are differences in some identifications between the models. For the two lowest-amplitude peaks the identifications are not unique. None the less, the equatorial velocity is constrained to a narrow range of (135, 140) km s –1 . Our work presents the first application of the photometric method of mode identification in the framework of the traditional approximation and we believe that it opens a new promising direction in studies of SPB stars.

Description: We report the discovery of a new subclass of double-mode RR Lyrae stars in the Large and Small Magellanic Clouds. The sample of 22 pulsating stars has been extracted from the latest edition of the Optical Gravitational Lensing Experiment collection of RR Lyrae variables in the Magellanic System. The stars pulsating simultaneously in the fundamental (F) and first-overtone (1O) modes have distinctly different properties than regular double-mode RR Lyrae variables (RRd stars). The P 1O / P F period ratios of our anomalous RRd stars are within a range of 0.725–0.738, while ‘classical’ double-mode RR Lyrae variables have period ratios in the range of 0.742–0.748. In contrast to the typical RRd stars, in the majority of the anomalous pulsators, the F-mode amplitudes are higher than the 1O-mode amplitudes. The light curves associated with the F-mode in the anomalous RRd stars show different morphology than the light curves of, both, regular RRd stars and single-mode RRab stars. Most of the anomalous double-mode stars show long-term modulations of the amplitudes (Blazhko-like effect). Translating the period ratios into the abundance parameter, Z , we find for our stars Z (0.002, 0.005) – an order of magnitude higher values than typical for RR Lyrae stars. The mass range of the RRd stars inferred from the W I versus P F diagram is (0.55–0.75) M . These parameters cannot be accounted for with single star evolution assuming a Reimers-like mass-loss. Much greater mass-loss caused by interaction with other stars is postulated. We blame the peculiar pulsation properties of our stars to the parametric resonance instability of the 1O-mode to excitation of the F- and 2O-modes as with the inferred parameters of the stars 2 1O F + 2O .