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Communications in Asteroseismology Communications in Asteroseismology Volume 148 December, 2006 Austrian Academy of Sciences Press Vienna 2006 Editor: Michel Breger,T¨urkenschanzstraße 17, A - 1180 Wien, Austria [email protected] Layout and Production: Paul Beck [email protected] Editorial Board: Gerald Handler, Don Kurtz, Jaymie Matthews, Ennio Poretti http://www.univie.ac.at/tops/ COVER ILLUSTRATION Color-Magnitude Diagram for NGC 2660 with a special focus on variable stars. British Library Cataloguing in Publication data. A Catalogue record for this book is available from the British Library. All rights reserved ISBN 13: 978-3-7001-3805-1 ISBN 10: 3-7001-3805-9 ISSN 1021-2043 Copyright c 2006 by Austrian Academy of Sciences Vienna Austrian Academy of Sciences Press A-1011 Wien, Postfach 471, Postgasse 7/4 Tel. +43-1-515 81/DW 3402-3406, +43-1-512 9050 Fax +43-1-515 81/DW 3400 http://verlag.oeaw.ac.at, e-mail: [email protected] Contents Introductory Remarks by Michel Breger, Editor 4 The Potential of Non-standard Pulsation Models for Asteroseismology by T. Collins, J. Guzik 5 NGC 2660 revisited by T.E. Mølholt, S. Frandsen, F. Grundahl, L. Glowienka 12 The moving bump in the light curves of SS For and RR Lyr by E. Guggenberger, K. Kolenberg 21 HD 114839 - An Am star showing both δ Scuti and γ Dor pulsations discovered through MOST photometry byH.King,J.M.Matthews,J.F.Row,etal. 28 Discovery of hybrid γ Dor and δ Sct pulsations in BD+18 4914 through MOST spacebased photometry by J.F. Rowe, J.M. Matthews, C. Cameron, et al. 34 1 Mon: The ’lost’ 1979 - 1985 data by M. Breger, Yu. Fedotov 44 Amplitude variability of the cepheid V473 Lyr by M. Breger 52 MOST Photometry of the roAp star HD 134214 by C. C. Cameron, J.M. Matthews, J.F. Rowe, et al 57 Towards accurate component properties of the Hyades binary θ2 Tau by P. Lampens, Y. Fr´emat,P.DeCat,H.Hensberge 65 New frequency analyses of the multiperiodic δ Scuti variables CR Lyn and GG UMa by C.W. Robertson, P. Van Cauteren, P. Lampens, et al. 70 Spectroscopy of HIP 113790 at the 5th OHP NEON summer school by Y. Fr´emat, A. Antonova, Y. Damerdji, et al. 77 Comm. in Asteroseismology Vol. 148, 2006 Introductory Remarks We hope that you will find vol. 148 interesting and scientifically stimulating. CoAst is evolving: the number of satellite astronomy papers has been increas- ing. This probably reflects a general trend. (Nevertheless, us earthbound as- tronomers are still in the majority.) The papers published by CoAst are not only listed in ADS (Astrophysics Data System at NASA), but will now also be included in the SIMBAD database. All papers are refereed - my thanks to all the hardworking referees and the fast responses to these referees’ reports by the authors. The Workshop on the ’Future of Asteroseismology’, which was held in Vi- enna, has just finished. On a personal note, I would like to take the opportunity to thank everybody for their good wishes during the workshop on the occasion of a round birthday. Probably the best gift was the high quality of all the talks: the meeting was a packed powerhouse of information and discussion. Not in the sense of a crowded schedule of talks - in fact, the schedule was quite good allowing for many discussions. ’Packed’ in the sense of scientific information that one ’wanted’ to listen to. You will be able to read about it in a next issue of CoAst, which will incorporate the proceedings of the workshop. For many years, Wolfgang Zima has done a wonderful job in helping with the publication of CoAst in Vienna. He has now finished his studies and is a postdoc at Leuven: our loss is their gain. Paul Beck has taken over Wolfi’s job. Michel Breger Editor New Link to download Period04 for Windows, Linux, Mac OSX (Intel or Power-PC): http://www.univie.ac.at/tops/Period04/ Comm. in Asteroseismology Vol. 148, 2006 The Potential of Non-standard Pulsation Models for Asteroseismology T. Collins1,J.Guzik1 1 Los Alamos National Laboratory Abstract The process of building seismic models of observed stars that match the ob- served pulsation frequencies often proves to be a difficult one. The outputs of computational codes used to perform these calculations match observational data fairly well for the sun, but fail to do so as well for larger-mass stars. This suggests that the codes are neglecting potentially significant processes that occur more strongly in larger stars. We examine some hydrodynamically mo- tivated modifications to the standard stellar models that might help to bring theoretical calculations into agreement with observational data. The analysis of Press (1981) and Press & Rybicki (1981) is applied to the case of the δ Scuti star FG Vir, and presented. Introduction Current stellar evolution and pulsation models rely on a number of simplifying assumptions in order to make the problem of stellar modeling more tractable, especially when dealing with the hydrodynamics of stellar interiors. Stars exhibit a wide variety of hydrodynamic processes that affect the evolution and structure of a star to some extent, while most stellar evolution and pulsation models neglect the majority of these effects in favor of computational efficiency and simplicity. For example, the mixing-length treatment of B¨ohm-Vitense (1958) still seems to be the standard in general convection treatments. Non-convective instabilities are often ignored altogether in stellar evolution modeling. This set of hydrodynamic approximations has worked quite well for the solar case. Despite the recently increased discrepancy between solar models and helioseismology with the new solar abundances these assumptions still yield far better results for the sun than they do for δ Scuti stars. Previous attempts 6 The Potential of Non-standard Pulsation Models for Asteroseismology at modeling the δ Scuti star FG Vir by Breger et al. (1999), Templeton et al. (2001), and Guzik et al. (2004) have met with difficulty and have yet to produce a model that can match all the frequencies observed. Templeton et al. (2001) and Guzik et al. (2004) however both had some success in improving the agreement between the predicted and observed frequencies via increased mixing between the convective core and the stable envelope. In the case of Guzik et al. (2004) core mixing was introduced into the model, not through the use of a convective overshooting parameter, as was done by Templeton et al. (2001), but instead by applying a large opacity multiplier from the core out into the radiative transport region. This multiplier caused approximately 0.8 − 0.9 Hp overshooting. However Deupree (2000) found in 2-D hydrodynamic simulations that for stars with under 3 M overshooting was only found to extend to 0.3 Hp. Even for more massive stars Deupree (2000) found that mixing extended only to a height of 0.45 Hp. The amount of overshooting induced by Guzik et al. (2004) was probably too high; however the level of mixing might be justified as there are other processes that could mix hydrogen-rich envelope material into the core. In the solar case, agreement between theoretical and observed pulsation frequencies and sound speed profiles was worsened by a downward revision of the solar metallicities. This has prompted a large number of papers examining a range of possible modifications to the solar models that could restore the previous agreement. Bahcall et al. (2005) found that a small opacity increase of roughly 10% between 2 × 106K and 5 × 106K (the temperature regime in the region below the convective zone) very nearly restored the agreement that had been lost in the sound speed profiles, predicted surface helium abundance, and the depth of the convective zone. In the two separate cases of both the Sun and FG Vir opacity modifications near the boundaries of convective regions inserted into otherwise standard evo- lution and pulsation codes have resulted in improved agreement between predic- tions and observations. This suggests the possibility of a potentially significant hydrodynamic effect in the stable layers near the boundaries of the convective regions. This possibility was brought to our attention by Arnett, Meakin, and Young (private communication, in preparation). With this possibility in mind we have undertaken a large survey of possible models of FG Vir examining mod- ifications near the surface convective zone and the core convective zone, both separately and in combination to see if this possibility could improve the agree- ment between frequency predictions and observation for this object. The results of that computational study are to be presented in Collins & Guzik (in prepa- ration). Our focus here is to consider the theoretical justification for that study. T. Collins, J. Guzik 7 Opacity Modification by g modes Excited by Convective Over- shooting We consider now the work of Press (1981) and Press & Rybicki (1981) (from here on P81 and PR81 respectively), who carefully examined exactly this pos- sibility in detail. We begin with considering the characterization of the internal wave. P81 chose to represent the fluid flow of an internal wave in Cartesian coordinates to be vx = −ucosαsin(kV z + kH x + ωt)(1) vy =0 (2) vz = u sin α sin (kV z + kH x + ωt)(3) We wish to show that the results of their analysis are invariant under ro- 2 2 2 tations of k with the constraint that k = kV + kH . The motivation for this being that in higher mass stars there are multiple convective regions to excite propagating g modes that would propagate both inward and outward. If the effective opacity increase predicted by PR81 is independent of the direction of wave propagation, then it should be more broadly applicable than the limited solar case considered in P81.
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