HAO 2011 Profiles In Science: Dr. Savita Mathur
Contact
303-497-1558
savita@ucar.edu
Dr. Savita Mathur is a Post Doc I in the High Altitude Observatory of NCAR. Her research interests are in helio- and asteroseismology. This includes the study of the dynamics and the structure of the solar core through gravity modes. She is currently working on the data analysis of the Kepler mission to study the oscillations of solar-like stars and red giants, and is involved in the development of the Asteroseismic Modelling Portal. Other interests include effect of flares on acoustic modes, stellar activity, instrumentation, solar modelling, and inversion techniques.
Publications
(1) Mathur, S., Handberg, R., Campante, T. L., García, R. A., Appourchaux, T., Bedding, T. R., Mosser, B., Chaplin, W. J., Ballot, J., Benomar, O., Bonanno, A., Corsaro, E., Gaulme, P., Hekker, S., Régulo, C., Salabert, D., Verner, G., White, T. R., Brandão, I. M., Creevey, O. L., Dogan, G., Elsworth, Y., Huber, D., Hale, S. J., Houdek, G., Karoff, C., Metcalfe, T. S., Molenda-Zakowicz, J., Monteiro, M. J. P. F. G., Thompson, M. J., Christensen-Dalsgaard, J., Gilliland, R. L., Kawaler, S. D., Kjeldsen, H., Quintana, E. V., Sanderfer, D. T., Seader, S. E. Solar-like Oscillations in KIC 11395018 and KIC 11234888 from 8-Months of Kepler Data, The Astrophysical Journal, 733, 95.
Abstract: The Kepler mission is now providing a large amount of photometric data of exquisite quality not only for the search of Earth-like exoplanets but also for asteroseismology. During the survey phase of the mission, a few stars were continuously followed with a short-cadence sampling (58.85s) among which five presented solar-like oscillations (modes that are excited by turbulent motions in the convective zone). We studied eight months of data for two of these stars (KIC 11395018 and KIC 11234888). This is the first time that we have such long continuous data in asteroseismology. We measured the global parameters of the acoustic modes (the mean large separation, which is the difference in frequency between two modes of same degree and consecutive orders, the frequency of maximum power, the maximum amplitude of the modes and the granulation characteristics). By comparing the results of different teams who fitted the individual modes, we could build a minimal list (where more than half of the fitting teams agreed on the frequency of the mode) and maximal list (where at least two teams agreed on the frequency of the modes) of frequencies for both stars. All this information is now being used to model these stars.
Figure 1 caption: Echelle diagrams for eight months of Kepler data for KIC 11395018 (left panel) and KIC 11234888 (right panel). These diagrams are obtained by taking chunks of length the mean large separation of the modes in the power spectrum and staking one chunk on top of the other. We can see the different ridges of the modes l=0 (circles), l=1(triangles), and l=2 (squares). We over-plotted the minimal (solid symbols) and maximal (solid and open symbols) lists of frequencies for each star.
In collaboration with the WG#1 (Solar-like stars) of the Kepler Asteroseismic Scientific Consortium.
(2) Mathur S., Hekker S., Trampedach R., Ballot J., Kallinger T., Buzasi D., García, R. A., Huber D., Jimenez A., Mosser B., Bedding T.R., Elsworth Y., Regulo C., Stello D., Chaplin W.J., De Ridder J., Hale S.J., Kinemuchi K., Kjeldsen H., Mullaly F., and Thompson S.E. Granulation in Red Giants: observations by the Kepler mission and 3D convection simulations, The Astrophysical Journal, in press arXiV 1109.1194.
Abstract: Among the long-cadence data provided by Kepler, we also have access to a large number (~1500) of red giants light curves. We studied the granulation characteristics of these stars by fitting a Harvey-like function to the power spectrum. The granulation pattern that we observe on the surface of the Sun is due to hot plasma from the interior rising to the photosphere where it cools down, and descends back into the interior at the edges of granules. This is the visible manifestation of convection taking place in the outer part of the solar convection zone. To do this analysis, we compared the results of six different methods, which globally are in a good agreement. We showed that the granulation time scale is inversely proportional to the frequency of maximum power while the granulation power is proportional to this frequency, which agrees with the theory. We also compared our observation with 3D simulations of the convection. The results of the granulation time scale and power have similar trends between the observations and the simulations but the absolute values are still quite different suggesting a need to better constrain the simulations.
Figure 2a caption: Power spectrum of a red giant observed by Kepler for 13 months with the background fit of six different methods based on Harvey-like profiles.
Figure 2b caption: Granulation time scale as a function of the frequency of maximum power for ~1200 red giants observed by Kepler. We represent the results obtained six different teams. We noticed that a second branch (in grey) appeared for two of the methods and its origin is still under investigation though it could be of stellar origin.
In collaboration with the WG#8 (Red Giants) of the Kepler Asteroseismic Scientific Consortium.