Author name code: roxburgh ADS astronomy entries on 2022-09-14 author:"Roxburgh, Ian" ------------------------------------------------------------------------ Title: Inversions of Stellar Structure From Asteroseismic Data Authors: Buldgen, Gaël; Bétrisey, Jérôme; Roxburgh, Ian W.; Vorontsov, Sergei V.; Reese, Daniel R. Bibcode: 2022FrASS...9.2373B Altcode: 2022arXiv220611507B The advent of space-based photometry missions in the early 21st century enabled the application to asteroseismic data of advanced inference techniques until then restricted to the field of helioseismology. The high quality of the observations, the discovery of mixed modes in evolved solar-like oscillators and the need for an improvement in the determination of stellar fundamental parameters such as mass, radius and age led to the development of sophisticated modelling tools, amongst which seismic inversions play a key role. In this review, we will discuss the existing inversion techniques for the internal structure of distant stars adapted from helio-to asteroseismology. We will present results obtained for various Kepler targets, their coupling to other existing modelling techniques as well as the limitations of seismic analyses and the perspectives for future developments of these approaches in the context of the current TESS and the future PLATO mission, as well as the exploitation of the mixed modes observed in post-main sequence solar-like oscillators, for which variational formulations might not provide sufficient accuracy. Title: PLATO hare-and-hounds exercise: asteroseismic model fitting of main-sequence solar-like pulsators Authors: Cunha, M. S.; Roxburgh, I. W.; Aguirre Børsen-Koch, V.; Ball, W. H.; Basu, S.; Chaplin, W. J.; Goupil, M. -J.; Nsamba, B.; Ong, J.; Reese, D. R.; Verma, K.; Belkacem, K.; Campante, T.; Christensen-Dalsgaard, J.; Clara, M. T.; Deheuvels, S.; Monteiro, M. J. P. F. G.; Noll, A.; Ouazzani, R. M.; Rørsted, J. L.; Stokholm, A.; Winther, M. L. Bibcode: 2021MNRAS.508.5864C Altcode: 2021MNRAS.tmp.2643C; 2021arXiv211003332C Asteroseismology is a powerful tool to infer fundamental stellar properties. The use of these asteroseismic-inferred properties in a growing number of astrophysical contexts makes it vital to understand their accuracy. Consequently, we performed a hare-and-hounds exercise where the hares simulated data for six artificial main-sequence stars and the hounds inferred their properties based on different inference procedures. To mimic a pipeline such as that planned for the PLATO mission, all hounds used the same model grid. Some stars were simulated using the physics adopted in the grid, others a different one. The maximum relative differences found (in absolute value) between the inferred and true values of the mass, radius, and age were 4.32, 1.33, and 11.25 per cent, respectively. The largest systematic differences in radius and age were found for a star simulated assuming gravitational settling, not accounted for in the model grid, with biases of -0.88 per cent (radius) and 8.66 per cent (age). For the mass, the most significant bias (-3.16 per cent) was found for a star with a helium enrichment ratio outside the grid range. Moreover, an ~7 per cent dispersion in age was found when adopting different prescriptions for the surface corrections or shifting the classical observations by ±1σ. The choice of the relative weight given to the classical and seismic constraints also impacted significantly the accuracy and precision of the results. Interestingly, only a few frequencies were required to achieve accurate results on the mass and radius. For the age the same was true when at least one l = 2 mode was considered. Title: Mixed Modes and the Asteroseismic Surface Term Authors: Ong, Joel J. M.; Basu, Sarbani; McKeever, Jean; Roxburgh, Ian; Lund, Mikkel N.; Bieryla, Allyson; Viani, Lucas S.; Latham, David W. Bibcode: 2021plat.confE..43O Altcode: We present new methodological developments regarding the treatment of the asteroseismic surface term in stars with mixed modes. Models of solar-like oscillators yield acoustic modes at different frequencies than would be seen in actual stars possessing identical interior structure, due to modelling error near the surface. This asteroseismic ``surface term'' must be corrected when mode frequencies are used to infer stellar structure. This is typically done by way of likelihood functions intended to diagnose whether or not differences between two sets of mode frequencies are consistent with a structural perturbation localised to the stellar surface. Different choices of these prescriptions modify the posterior distributions of fundamental stellar properties — such as the mass, radius, and age — inferred from individual stars using asteroseismology. These in turn induce population-level systematic biases. Existing prescriptions developed for p-modes are also not immediately applicable to the mixed modes seen in more evolved solar-like oscillators. We examine some outstanding issues in how the surface term is currently treated in stellar modelling with asteroseismology, and how these new methods may address these shortcomings, with a particular focus on the interaction between mode mixing and these systematic effects. Title: Mixed Modes and Asteroseismic Surface Effects. I. Analytic Treatment Authors: Ong, J. M. Joel; Basu, Sarbani; Roxburgh, Ian W. Bibcode: 2021ApJ...920....8O Altcode: 2021ApJ...920....8J; 2021arXiv210703405O Normal-mode oscillation frequencies computed from stellar models differ from those that would be measured from stars with identical interior structures because of modeling errors in the near-surface layers. These frequency differences are referred to as the asteroseismic "surface term." The vast majority of solar-like oscillators that have been observed, and that are expected to be observed in the near future, are evolved stars that exhibit mixed modes. For these evolved stars, the inference of stellar properties from these mode frequencies has been shown to depend on how this surface term is corrected for. We show that existing parameterizations of the surface term account for mode mixing only to first order in perturbation theory, if at all, and therefore may not be adequate for evolved stars. Moreover, existing nonparametric treatments of the surface term do not account for mode mixing. We derive both a first-order construction and a more general approach for one particular class of nonparametric methods. We illustrate the limits of first-order approximations from both analytic considerations and using numerical injection-recovery tests on stellar models. First-order corrections for the surface term are strictly only applicable where the size of the surface term is much smaller than both the coupling strength between the mixed p and g modes, as well as the local g-mode spacing. Our more general matrix construction may be applied to evolved stars, where perturbation theory cannot be relied upon. Title: PBjam: A Python Package for Automating Asteroseismology of Solar-like Oscillators Authors: Nielsen, M. B.; Davies, G. R.; Ball, W. H.; Lyttle, A. J.; Li, T.; Hall, O. J.; Chaplin, W. J.; Gaulme, P.; Carboneau, L.; Ong, J. M. J.; García, R. A.; Mosser, B.; Roxburgh, I. W.; Corsaro, E.; Benomar, O.; Moya, A.; Lund, M. N. Bibcode: 2021AJ....161...62N Altcode: 2020arXiv201200580N Asteroseismology is an exceptional tool for studying stars using the properties of observed modes of oscillation. So far the process of performing an asteroseismic analysis of a star has remained somewhat esoteric and inaccessible to nonexperts. In this software paper we describe PBjam, an open-source Python package for analyzing the frequency spectra of solar-like oscillators in a simple but principled and automated way. The aim of PBjam is to provide a set of easy-to-use tools to extract information about the radial and quadropole oscillations in stars that oscillate like the Sun, which may then be used to infer bulk properties such as stellar mass, radius, age, or even structure. Asteroseismology and its data analysis methods are becoming increasingly important as space-based photometric observatories are producing a wealth of new data, allowing asteroseismology to be applied in a wide range of contexts such as exoplanet, stellar structure and evolution, and Galactic population studies. * Release 1.0.0 Zenodo, doi:10.5281/zenodo.4300079. Title: TESS asteroseismology of the known planet host star λ2 Fornacis Authors: Nielsen, M. B.; Ball, W. H.; Standing, M. R.; Triaud, A. H. M. J.; Buzasi, D.; Carboneau, L.; Stassun, K. G.; Kane, S. R.; Chaplin, W. J.; Bellinger, E. P.; Mosser, B.; Roxburgh, I. W.; Çelik Orhan, Z.; Yıldız, M.; Örtel, S.; Vrard, M.; Mazumdar, A.; Ranadive, P.; Deal, M.; Davies, G. R.; Campante, T. L.; García, R. A.; Mathur, S.; González-Cuesta, L.; Serenelli, A. Bibcode: 2020A&A...641A..25N Altcode: 2020arXiv200700497N Context. The Transiting Exoplanet Survey Satellite (TESS) is observing bright known planet-host stars across almost the entire sky. These stars have been subject to extensive ground-based observations, providing a large number of radial velocity measurements.
Aims: The objective of this work is to use the new TESS photometric observations to characterize the star λ2 Fornacis, and following this to update the parameters of the orbiting planet λ2 For b.
Methods: We measured the frequencies of the p-mode oscillations in λ2 For, and in combination with non-seismic parameters estimated the stellar fundamental properties using stellar models. Using the revised stellar properties and a time series of archival radial velocities from the UCLES, HIRES and HARPS instruments spanning almost 20 years, we refit the orbit of λ2 For b and searched the residual radial velocities for remaining variability.
Results: We find that λ2 For has a mass of 1.16 ± 0.03 M and a radius of 1.63 ± 0.04 R, with an age of 6.3 ± 0.9 Gyr. This and the updated radial velocity measurements suggest a mass of λ2 For b of 16.8-1.3+1.2 M, which is ∼5M less than literature estimates. We also detect an additional periodicity at 33 days in the radial velocity measurements, which is likely due to the rotation of the host star.
Conclusions: While previous literature estimates of the properties of λ2 For are ambiguous, the asteroseismic measurements place the star firmly at the early stage of its subgiant evolutionary phase. Typically only short time series of photometric data are available from TESS, but by using asteroseismology it is still possible to provide tight constraints on the properties of bright stars that until now have only been observed from the ground. This prompts a reexamination of archival radial velocity data that have been accumulated in the past few decades in order to update the characteristics of the planet hosting systems observed by TESS for which asteroseismology is possible. Title: Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi Authors: Chaplin, William J.; Serenelli, Aldo M.; Miglio, Andrea; Morel, Thierry; Mackereth, J. Ted; Vincenzo, Fiorenzo; Kjeldsen, Hans; Basu, Sarbani; Ball, Warrick H.; Stokholm, Amalie; Verma, Kuldeep; Mosumgaard, Jakob Rørsted; Silva Aguirre, Victor; Mazumdar, Anwesh; Ranadive, Pritesh; Antia, H. M.; Lebreton, Yveline; Ong, Joel; Appourchaux, Thierry; Bedding, Timothy R.; Christensen-Dalsgaard, Jørgen; Creevey, Orlagh; García, Rafael A.; Handberg, Rasmus; Huber, Daniel; Kawaler, Steven D.; Lund, Mikkel N.; Metcalfe, Travis S.; Stassun, Keivan G.; Bazot, Michäel; Beck, Paul G.; Bell, Keaton J.; Bergemann, Maria; Buzasi, Derek L.; Benomar, Othman; Bossini, Diego; Bugnet, Lisa; Campante, Tiago L.; Orhan, Zeynep çelik; Corsaro, Enrico; González-Cuesta, Lucía; Davies, Guy R.; Di Mauro, Maria Pia; Egeland, Ricky; Elsworth, Yvonne P.; Gaulme, Patrick; Ghasemi, Hamed; Guo, Zhao; Hall, Oliver J.; Hasanzadeh, Amir; Hekker, Saskia; Howe, Rachel; Jenkins, Jon M.; Jiménez, Antonio; Kiefer, René; Kuszlewicz, James S.; Kallinger, Thomas; Latham, David W.; Lundkvist, Mia S.; Mathur, Savita; Montalbán, Josefina; Mosser, Benoit; Bedón, Andres Moya; Nielsen, Martin Bo; Örtel, Sibel; Rendle, Ben M.; Ricker, George R.; Rodrigues, Thaíse S.; Roxburgh, Ian W.; Safari, Hossein; Schofield, Mathew; Seager, Sara; Smalley, Barry; Stello, Dennis; Szabó, Róbert; Tayar, Jamie; Themeßl, Nathalie; Thomas, Alexandra E. L.; Vanderspek, Roland K.; van Rossem, Walter E.; Vrard, Mathieu; Weiss, Achim; White, Timothy R.; Winn, Joshua N.; Yıldız, Mutlu Bibcode: 2020NatAs...4..382C Altcode: 2020NatAs.tmp....7C; 2020arXiv200104653C Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies1. Although these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to date precisely the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called Gaia-Enceladus1, leading to substantial pollution of the chemical and dynamical properties of the Milky Way. Here we identify the very bright, naked-eye star ν Indi as an indicator of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be 11.0 ±0.7 ? (stat) ±0.8 ? (sys) billion years. The star bears hallmarks consistent with having been kinematically heated by the Gaia-Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 billion years ago, at 68% and 95% confidence, respectively. Computations based on hierarchical cosmological models slightly reduce the above limits. Title: VizieR Online Data Catalog: High-precision radial velocities for HD 221416 (Huber+, 2019) Authors: Huber, D.; Chaplin, W. J.; Chontos, A.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Bedding, T. R.; Ball, W.; Brahm, R.; Espinoza, N.; Henning, T.; Jordan, A.; Sarkis, P.; Knudstrup, E.; Albrecht, S.; Grundahl, F.; Andersen, M. F.; Palle, P. L.; Crossfield, I.; Fulton, B.; Howard, A. W.; Isaacson, H. T.; Weiss, L. M.; Handberg, R.; Lund, M. N.; Serenelli, A. M.; Rorsted Mosumgaard, J.; Stokholm, A.; Bieryla, A.; Buchhave, L. A.; Latham, D. W.; Quinn, S. N.; Gaidos, E.; Hirano, T.; Ricker, G. R.; Vanderspek, R. K.; Seager, S.; Jenkins, J. M.; Winn, J. N.; Antia, H. M.; Appourchaux, T.; Basu, S.; Bell, K. J.; Benomar, O.; Bonanno, A.; Buzasi, D. L.; Campante, T. L.; Celik Orhan, Z.; Corsaro, E.; Cunha, M. S.; Davies, G. R.; Deheuvels, S.; Grunblatt, S. K.; Hasanzadeh, A.; di Mauro, M. P.; Garcia, R. A.; Gaulme, P.; Girardi, L.; Guzik, J. A.; Hon, M.; Jiang, C.; Kallinger, T.; Kawaler, S. D.; Kuszlewicz, J. S.; Lebreton, Y.; Li, T.; Lucas, M.; Lundkvist, M. S.; Mann, A. W.; Mathis, S.; Mathur, S.; Mazumdar, A.; Metcalfe, T. S.; Miglio, A.; Monteiro, M. J. P. F. G.; Mosser, B.; Noll, A.; Nsamba, B.; Ong, J. M. J.; Ortel, S.; Pereira, F.; Ranadive, P.; Regulo, C.; Rodrigues, T. S.; Roxburgh, I. W.; Aguirre, V. S.; Smalley, B.; Schofield, M.; Sousa, S. G.; Stassun, K. G.; Stello, D.; Tayar, J.; White, T. R.; Verma, K.; Vrard, M.; Yildiz, M.; Baker, D.; Bazot, M.; Beichmann, C.; Bergmann, C.; Bugnet, L.; Cale, B.; Carlino, R.; Cartwright, S. M.; Christiansen, J. L.; Ciardi, D. R.; Creevey, O.; Dittmann, J. A.; Do Nascimento, J. -D., Jr.; van Eylen, V.; Furesz, G.; Gagne, J.; Gao, P.; Gazeas, K.; Giddens, F.; Hall, O. J.; Hekker, S.; Ireland, M. J.; Latouf, N.; Lebrun, D.; Levine, A. M.; Matzko, W.; Natinsky, E.; Page, E.; Plavchan, P.; Mansouri-Samani, M.; McCauliff, S.; Mullally, S. E.; Orenstein, B.; Soto, A. G.; Paegert, M.; van Saders, J. L.; Schnaible, C.; Soderblom, D. R.; Szabo, R.; Tanner, A.; Tinney, C. G.; Teske, J.; Thomas, A.; Trampedach, R.; Wright, D.; Yuan, T. T.; Zohrabi, F. Bibcode: 2019yCat..51570245H Altcode: We obtained high-resolution spectra of HD 221416 using several facilities within the TESS Follow-up Observation Program (TFOP), including HIRES (Vogt et al. 1994SPIE.2198..362V) on the 10 m telescope at Keck Observatory (Maunakea, Hawai'i); the Hertzsprung SONG Telescope at Teide Observatory (Tenerife; Grundahl et al. 2017ApJ...836..142G); HARPS (Mayor et al. 2003Msngr.114...20M), FEROS (Kaufer et al. 1999Msngr..95....8K), Coralie (Queloz et al. 2001Msngr.105....1Q), and FIDEOS (Vanzi et al. 2018MNRAS.477.5041V) on the MPG/ESO 3.6 m, 2.2 m, 1.2 m, and 1 m telescopes at La Silla Observatory (Chile); Veloce (Gilbert et al. 2018SPIE10702E..0YG) on the 3.9 m Anglo-Australian Telescope at Siding Spring Observatory (Australia); TRES (Furesz 2008, PhD thesis Univ. Szeged) on the 1.5 m Tillinghast reflector at the F. L. Whipple Observatory (Mt. Hopkins, Arizona); and iSHELL (Rayner et al. 2012SPIE.8446E..2CR) on the NASA IRTF Telescope (Maunakea, Hawai'i). All spectra used in this paper were obtained between 2018 November 11 and December 30 and have a minimum spectral resolution of R~44000.

(1 data file). Title: A Hot Saturn Orbiting an Oscillating Late Subgiant Discovered by TESS Authors: Huber, Daniel; Chaplin, William J.; Chontos, Ashley; Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen; Bedding, Timothy R.; Ball, Warrick; Brahm, Rafael; Espinoza, Nestor; Henning, Thomas; Jordán, Andrés; Sarkis, Paula; Knudstrup, Emil; Albrecht, Simon; Grundahl, Frank; Fredslund Andersen, Mads; Pallé, Pere L.; Crossfield, Ian; Fulton, Benjamin; Howard, Andrew W.; Isaacson, Howard T.; Weiss, Lauren M.; Handberg, Rasmus; Lund, Mikkel N.; Serenelli, Aldo M.; Rørsted Mosumgaard, Jakob; Stokholm, Amalie; Bieryla, Allyson; Buchhave, Lars A.; Latham, David W.; Quinn, Samuel N.; Gaidos, Eric; Hirano, Teruyuki; Ricker, George R.; Vanderspek, Roland K.; Seager, Sara; Jenkins, Jon M.; Winn, Joshua N.; Antia, H. M.; Appourchaux, Thierry; Basu, Sarbani; Bell, Keaton J.; Benomar, Othman; Bonanno, Alfio; Buzasi, Derek L.; Campante, Tiago L.; Çelik Orhan, Z.; Corsaro, Enrico; Cunha, Margarida S.; Davies, Guy R.; Deheuvels, Sebastien; Grunblatt, Samuel K.; Hasanzadeh, Amir; Di Mauro, Maria Pia; García, Rafael A.; Gaulme, Patrick; Girardi, Léo; Guzik, Joyce A.; Hon, Marc; Jiang, Chen; Kallinger, Thomas; Kawaler, Steven D.; Kuszlewicz, James S.; Lebreton, Yveline; Li, Tanda; Lucas, Miles; Lundkvist, Mia S.; Mann, Andrew W.; Mathis, Stéphane; Mathur, Savita; Mazumdar, Anwesh; Metcalfe, Travis S.; Miglio, Andrea; Monteiro, Mário J. P. F. G.; Mosser, Benoit; Noll, Anthony; Nsamba, Benard; Ong, Jia Mian Joel; Örtel, S.; Pereira, Filipe; Ranadive, Pritesh; Régulo, Clara; Rodrigues, Thaíse S.; Roxburgh, Ian W.; Silva Aguirre, Victor; Smalley, Barry; Schofield, Mathew; Sousa, Sérgio G.; Stassun, Keivan G.; Stello, Dennis; Tayar, Jamie; White, Timothy R.; Verma, Kuldeep; Vrard, Mathieu; Yıldız, M.; Baker, David; Bazot, Michaël; Beichmann, Charles; Bergmann, Christoph; Bugnet, Lisa; Cale, Bryson; Carlino, Roberto; Cartwright, Scott M.; Christiansen, Jessie L.; Ciardi, David R.; Creevey, Orlagh; Dittmann, Jason A.; Do Nascimento, Jose-Dias, Jr.; Van Eylen, Vincent; Fürész, Gabor; Gagné, Jonathan; Gao, Peter; Gazeas, Kosmas; Giddens, Frank; Hall, Oliver J.; Hekker, Saskia; Ireland, Michael J.; Latouf, Natasha; LeBrun, Danny; Levine, Alan M.; Matzko, William; Natinsky, Eva; Page, Emma; Plavchan, Peter; Mansouri-Samani, Masoud; McCauliff, Sean; Mullally, Susan E.; Orenstein, Brendan; Garcia Soto, Aylin; Paegert, Martin; van Saders, Jennifer L.; Schnaible, Chloe; Soderblom, David R.; Szabó, Róbert; Tanner, Angelle; Tinney, C. G.; Teske, Johanna; Thomas, Alexandra; Trampedach, Regner; Wright, Duncan; Yuan, Thomas T.; Zohrabi, Farzaneh Bibcode: 2019AJ....157..245H Altcode: 2019arXiv190101643H We present the discovery of HD 221416 b, the first transiting planet identified by the Transiting Exoplanet Survey Satellite (TESS) for which asteroseismology of the host star is possible. HD 221416 b (HIP 116158, TOI-197) is a bright (V = 8.2 mag), spectroscopically classified subgiant that oscillates with an average frequency of about 430 μHz and displays a clear signature of mixed modes. The oscillation amplitude confirms that the redder TESS bandpass compared to Kepler has a small effect on the oscillations, supporting the expected yield of thousands of solar-like oscillators with TESS 2 minute cadence observations. Asteroseismic modeling yields a robust determination of the host star radius (R = 2.943 ± 0.064 R ), mass (M = 1.212 ± 0.074 M ), and age (4.9 ± 1.1 Gyr), and demonstrates that it has just started ascending the red-giant branch. Combining asteroseismology with transit modeling and radial-velocity observations, we show that the planet is a “hot Saturn” (R p = 9.17 ± 0.33 R ) with an orbital period of ∼14.3 days, irradiance of F = 343 ± 24 F , and moderate mass (M p = 60.5 ± 5.7 M ) and density (ρ p = 0.431 ± 0.062 g cm-3). The properties of HD 221416 b show that the host-star metallicity-planet mass correlation found in sub-Saturns (4-8 R ) does not extend to larger radii, indicating that planets in the transition between sub-Saturns and Jupiters follow a relatively narrow range of densities. With a density measured to ∼15%, HD 221416 b is one of the best characterized Saturn-size planets to date, augmenting the small number of known transiting planets around evolved stars and demonstrating the power of TESS to characterize exoplanets and their host stars using asteroseismology. Title: Overfitting and correlations in model fitting with separation ratios Authors: Roxburgh, Ian W Bibcode: 2018arXiv180807556R Altcode: The $r_{01}$ and $r_{10}$ separation ratios are not independent so combing them into a single series $r_{010}$ is overfitting the data, this can lead to almost singular covariance matrices with very large condition numbers, and hence to spurious results when comparing models and observations. Since the $r_{02}$ ratios are strongly correlated with $r_{10}$ and $r_{01}$ ratios, they should be combined into a single series $r_{102}$ (or $r_{012}$), which are not overfitted, and models and observation compared using the covariance matrix $cov_{102}$ (or $cov_{012}$) of the combined set. I illustrate these points by comparing the revised Legacy Project data with my results on the 10 Kepler stars in common. Title: Anomalies in the Kepler Asteroseismic Legacy Project Data A re-analysis of 16 Cyg A & B, KIC 8379927 and 6 solar-like stars Authors: Roxburgh, Ian W. Bibcode: 2017A&A...604A..42R Altcode: 2017arXiv170604408R I compare values of the frequencies, separation ratios, errors and covariance matrices from a new analysis of 9 solar-like stars with the Legacy project values reported by Lund et al and, for 16Cyg A&B and KIC 8379927, with values derived by Davies et al. There is good agreement between my results and Davies's for these 3 stars, but no such agreement with the Legacy project results. My frequencies differ from the Legacy values, there are inconsistencies in the Legacy frequency covariance matrices which are not positive definite, and the Legacy errors on separation ratios are up to 40 times larger than mine and the values and upper limits derived from the Legacy frequency covariances. There are similar anomalies for 6 other solar-like stars: frequencies and separation ratio errors disagree and 2 have non positive definite covariance matrices. There are inconsistencies in the covariance matrices of 27 the 66 stars in the full Legacy set and problems with the ratio errors for the vast majority of these stars. Title: PLATO as it is : A legacy mission for Galactic archaeology Authors: Miglio, A.; Chiappini, C.; Mosser, B.; Davies, G. R.; Freeman, K.; Girardi, L.; Jofré, P.; Kawata, D.; Rendle, B. M.; Valentini, M.; Casagrande, L.; Chaplin, W. J.; Gilmore, G.; Hawkins, K.; Holl, B.; Appourchaux, T.; Belkacem, K.; Bossini, D.; Brogaard, K.; Goupil, M. -J.; Montalbán, J.; Noels, A.; Anders, F.; Rodrigues, T.; Piotto, G.; Pollacco, D.; Rauer, H.; Prieto, C. Allende; Avelino, P. P.; Babusiaux, C.; Barban, C.; Barbuy, B.; Basu, S.; Baudin, F.; Benomar, O.; Bienaymé, O.; Binney, J.; Bland-Hawthorn, J.; Bressan, A.; Cacciari, C.; Campante, T. L.; Cassisi, S.; Christensen-Dalsgaard, J.; Combes, F.; Creevey, O.; Cunha, M. S.; Jong, R. S.; Laverny, P.; Degl'Innocenti, S.; Deheuvels, S.; Depagne, É.; Ridder, J.; Matteo, P. Di; Mauro, M. P. Di; Dupret, M. -A.; Eggenberger, P.; Elsworth, Y.; Famaey, B.; Feltzing, S.; García, R. A.; Gerhard, O.; Gibson, B. K.; Gizon, L.; Haywood, M.; Handberg, R.; Heiter, U.; Hekker, S.; Huber, D.; Ibata, R.; Katz, D.; Kawaler, S. D.; Kjeldsen, H.; Kurtz, D. W.; Lagarde, N.; Lebreton, Y.; Lund, M. N.; Majewski, S. R.; Marigo, P.; Martig, M.; Mathur, S.; Minchev, I.; Morel, T.; Ortolani, S.; Pinsonneault, M. H.; Plez, B.; Moroni, P. G. Prada; Pricopi, D.; Recio-Blanco, A.; Reylé, C.; Robin, A.; Roxburgh, I. W.; Salaris, M.; Santiago, B. X.; Schiavon, R.; Serenelli, A.; Sharma, S.; Aguirre, V. Silva; Soubiran, C.; Steinmetz, M.; Stello, D.; Strassmeier, K. G.; Ventura, P.; Ventura, R.; Walton, N. A.; Worley, C. C. Bibcode: 2017AN....338..644M Altcode: 2017arXiv170603778M Deciphering the assembly history of the Milky Way is a formidable task, which becomes possible only if one can produce high-resolution chrono-chemo-kinematical maps of the Galaxy. Data from large-scale astrometric and spectroscopic surveys will soon provide us with a well-defined view of the current chemo-kinematical structure of the Milky Way, but will only enable a blurred view on the temporal sequence that led to the present-day Galaxy. As demonstrated by the (ongoing) exploitation of data from the pioneering photometric missions CoRoT, Kepler, and K2, asteroseismology provides the way forward: solar-like oscillating giants are excellent evolutionary clocks thanks to the availability of seismic constraints on their mass and to the tight age-initial-mass relation they adhere to. In this paper we identify five key outstanding questions relating to the formation and evolution of the Milky Way that will need precise and accurate ages for large samples of stars to be addressed, and we identify the requirements in terms of number of targets and the precision on the stellar properties that are needed to tackle such questions. By quantifying the asteroseismic yields expected from PLATO for red-giant stars, we demonstrate that these requirements are within the capabilities of the current instrument design, provided that observations are sufficiently long to identify the evolutionary state and allow robust and precise determination of acoustic-mode frequencies. This will allow us to harvest data of sufficient quality to reach a 10% precision in age. This is a fundamental pre-requisite to then reach the more ambitious goal of a similar level of accuracy, which will only be possible if we have to hand a careful appraisal of systematic uncertainties on age deriving from our limited understanding of stellar physics, a goal which conveniently falls within the main aims of PLATO's core science. Title: Using red clump stars to correct the Gaia DR1 parallaxes Authors: Davies, Guy R.; Lund, Mikkel N.; Miglio, Andrea; Elsworth, Yvonne; Kuszlewicz, James S.; North, Thomas S. H.; Rendle, Ben; Chaplin, William J.; Rodrigues, Thaíse S.; Campante, Tiago L.; Girardi, Léo; Hale, Steven J.; Hall, Oliver; Jones, Caitlin D.; Kawaler, Steven D.; Roxburgh, Ian; Schofield, Mathew Bibcode: 2017A&A...598L...4D Altcode: 2017arXiv170102506D Recent results have suggested that there is tension between the Gaia DR1 TGAS distances and the distances obtained using luminosities determined by eclipsing binaries or asteroseismology on red giant stars. We use the Ks-band luminosities of red clump stars, identified and characterized by asteroseismology, to make independent distance estimates. Our results suggest that Gaia TGAS distances contain a systematic error that decreases with increasing distance. We propose a correction to mitigate this offset as a function of parallax that is valid for the Kepler field and values of parallax that are less than 1.6 mas. For parallaxes greater than this, we find agreement with previously published values. We note that the TGAS distances to the red clump stars of the open cluster M67 show a high level of disagreement that is difficult to correct for. Title: A new asteroseismic diagnostic for internal rotation in γ Doradus stars Authors: Ouazzani, Rhita-Maria; Salmon, S. J. A. J.; Antoci, V.; Bedding, T. R.; Murphy, S. J.; Roxburgh, I. W. Bibcode: 2017MNRAS.465.2294O Altcode: 2016arXiv161006184O With four years of nearly continuous photometry from Kepler, we are finally in a good position to apply asteroseismology to γ Doradus stars. In particular, several analyses have demonstrated the possibility to detect non-uniform period spacings, which have been predicted to be directly related to rotation. In this paper, we define a new seismic diagnostic for rotation in γ Doradus stars which are too rapidly rotating to present rotational splittings. Based on the non-uniformity of their period spacings, we define the observable Σ as the slope of the period spacing when plotted as a function of period. We provide a one-to-one relation between this observable Σ and the internal rotation, which applies widely in the instability strip of γ Doradus stars. We apply the diagnostic to a handful of stars observed by Kepler. Thanks to g modes in γ Doradus stars, we are now able to determine the internal rotation of stars on the lower main sequence, which is still not possible for Sun-like stars. Title: 16CygA&B and Kepler Legacy values : Differences between the values of frequencies by different fitters Authors: Roxburgh, Ian W Bibcode: 2016arXiv160900568R Altcode: The differences between the oscillation frequencies and uncertainty estimates of a star derived by different fitters can be large, sufficiently large so that, were one to find a stellar model that fitted one frequency set ($\chi^2\sim 1$), it does not fit an alternative set. I give 21 examples, comparing frequency sets in common between the Kepler Legacy project and frequency sets from Appourchaux et al (2014) and Davies et al (2015). For 16CygA&B the differences are large; the $\chi^2$ of the fit of Legacy to Davies's values ranging from 1.64 to 11.47 for 16CygA and 1.62 to 1.79 for 16CygB, depending on which error estimates are used. I analyse both stars in some detail applying my own mode fitting code to both the Legacy and Davies's power spectra and find reasonable agreement with Davies's full frequency sets and very good agreement between values for modes with signal/noise > 1 ($\chi^2 = 0.06, \chi^2_B=0.03$). But the difference with the Legacy values remains large even for modes with S/N>1. I also examine the effects of different power spectra (weighted and unweighted) using the kasoc light curves for Q6-17.2 and Q7-Q16, the effect of different mode height ratios and different rotational splitting and inclination. Title: Asteroseismic model fitting by comparing ɛnℓ values (Corrigendum) Authors: Roxburgh, Ian W. Bibcode: 2016A&A...586C...2R Altcode: No abstract at ADS Title: I.2 Seeds take root in Europe Authors: Fridlund, M.; Roxburgh, I.; CoRot Team Bibcode: 2016cole.book....7F Altcode: No abstract at ADS Title: Asteroseismic model fitting by comparing ɛnℓ values Authors: Roxburgh, Ian W. Bibcode: 2016A&A...585A..63R Altcode: We present an asteroseismic model fitting algorithm based on comparing model and observed ɛ(ν) values defined in terms of frequencies by νnℓ = Δ [ n + ℓ/ 2 + ɛnℓ) ] where Δ is an average large separation. We show that if two stellar models have the same interior structure but different outer layers then the difference between their ɛ(ν) values, interpolated to the same frequencies, collapses to a function only of frequency, independent of angular degree ℓ. The algorithm tests the goodness fit by comparing the difference in model and observed ɛ values after having subtracted off a best fit ℓ independent function of frequency ℱ(ν), and only requires interpolation in model values and not in observed values so the errors on the observed values are uncorrelated; it is independent of the n values assigned to the radial ordering of the frequencies and does not require the calculation of inner phase shifts of the model. We contrast this to a proposed direct frequency matching technique which minimises the difference between observed and model frequencies after having subtracted off an ℓ independent fit to these differences. We show this technique is flawed in principle, that all models with the same dimensionless structure but any mass and radius have the same quality of fit to an observed data set, and that it can give erroneous best fit models. We illustrate the epsilon matching technique by comparing stellar models and then apply it to data on HD 177153 (aka Perky). On comparing observations with a set of main sequence evolutionary models we find that models which satisfy constraints on the luminosity, radius, Δ, and on ɛ matching, have masses in the range 1.155 ± 0.035 M and ages in the range 4.486 ± 0.250 × 109 yr. Since the large separation and the radius are surface layer dependent we examine "pure surface layer independent" model fitting where the only constraints on the model fitting are on the luminosity and epsilon matching, and show that the best fit models have M/M = 1.13 ± 0.06 and age = 4.62 ± 0.39 × 109 yr. Title: Scaled models, scaled frequencies, and model fitting Authors: Roxburgh, Ian W. Bibcode: 2015A&A...584A..71R Altcode: I show that given a model star of mass M, radius R, and density profile ρ(x) [x = r/R], there exists a two parameter family of models with masses Mk, radii Rk, density profile ρk(x) = λρ(x) and frequencies νknℓ = λ1/2νnℓ, where λ,Rk/RA are scaling factors. These models have different internal structures, but all have the same value of separation ratios calculated at given radial orders n, and all exactly satisfy a frequency matching algorithm with an offset function determined as part of the fitting procedure. But they do not satisfy ratio matching at given frequencies nor phase shift matching. This illustrates that erroneous results may be obtained when model fitting with ratios at given n values or frequency matching. I give examples from scaled models and from non scaled evolutionary models. Title: Asteroseismology of Solar-Type Stars with K2: Detection of Oscillations in C1 Data Authors: Chaplin, W. J.; Lund, M. N.; Handberg, R.; Basu, S.; Buchhave, L. A.; Campante, T. L.; Davies, G. R.; Huber, D.; Latham, D. W.; Latham, C. A.; Serenelli, A.; Antia, H. M.; Appourchaux, T.; Ball, W. H.; Benomar, O.; Casagrande, L.; Christensen-Dalsgaard, J.; Coelho, H. R.; Creevey, O. L.; Elsworth, Y.; García, R. A.; Gaulme, P.; Hekker, S.; Kallinger, T.; Karoff, C.; Kawaler, S. D.; Kjeldsen, H.; Lundkvist, M. S.; Marcadon, F.; Mathur, S.; Miglio, A.; Mosser, B.; Régulo, C.; Roxburgh, I. W.; Silva Aguirre, V.; Stello, D.; Verma, K.; White, T. R.; Bedding, T. R.; Barclay, T.; Buzasi, D. L.; Dehuevels, S.; Gizon, L.; Houdek, G.; Howell, S. B.; Salabert, D.; Soderblom, D. R. Bibcode: 2015PASP..127.1038C Altcode: 2015arXiv150701827C We present the first detections by the NASA K2 Mission of oscillations in solar-type stars, using short-cadence data collected during K2 Campaign\,1 (C1). We understand the asteroseismic detection thresholds for C1-like levels of photometric performance, and we can detect oscillations in subgiants having dominant oscillation frequencies around $1000\,\rm \mu Hz$. Changes to the operation of the fine-guidance sensors are expected to give significant improvements in the high-frequency performance from C3 onwards. A reduction in the excess high-frequency noise by a factor of two-and-a-half in amplitude would bring main-sequence stars with dominant oscillation frequencies as high as ${\simeq 2500}\,\rm \mu Hz$ into play as potential asteroseismic targets for K2. Title: A note on the use of surface offset corrections in asteroseismic model fitting Authors: Roxburgh, Ian W. Bibcode: 2015A&A...581A..58R Altcode: We critically investigate the practice of adding a power-law surface offset correction f(ν) to the frequencies of stellar models prior to seeking best fit models to an observed star. We show that surface layer independent indicators of the internal structure, phase shifts and separation ratios, are displaced in frequency by f(ν) and are therefore not the same as those of the model. Consequently such best fit models do not have exactly the same interior structure as the observed star. Using results on the star HD 177153 we show that the difference between observed and model frequencies for best fit models obtained using surface layer independent procedures have a wide range of different offsets which do not in general follow a Kjeldsen-like power law, and further that best fit models obtained using the offset correction procedure do not necessarily satisfy surface layer independent constraints on the internal structure. Title: Pulsations of rapidly rotating stars. II. Realistic modelling for intermediate-mass stars Authors: Ouazzani, R. -M.; Roxburgh, I. W.; Dupret, M. -A. Bibcode: 2015A&A...579A.116O Altcode: 2015arXiv150501088O Context. Very high precision seismic space missions such as CoRoT and Kepler provide the means for testing the modelling of transport processes in stellar interiors. For some stars, such as δ Scuti, γ Doradus, and Be stars, the observed pulsation spectra are modified by rotation to such an extent that it prevents any fruitful interpretation.
Aims: Our aim is to characterise acoustic pulsation spectra of realistic stellar models in order to be able to interpret asteroseismic data from such stars.
Methods: The 2D oscillation code ACOR, which treats rotation in a non-perturbative manner, is used to study pulsation spectra of highly distorted evolved models of stars. Two-dimensional models of stars are obtained by a self-consistent method that distorts spherically averaged stellar models a posteriori, at any stage of evolution, and for any type of rotation law.
Results: Four types of modes are calculated in a very dense frequency spectrum, among which are island modes. The regularity of the island modes spectrum is confirmed and yields a new set of quantum numbers, with which an échelle diagram can be built. Mixed gravito-acoustic modes are calculated in rapidly rotating models for the first time. Title: Surface layer independent model fitting by phase matching: theory and application to HD 49933 and HD 177153 (aka Perky) Authors: Roxburgh, Ian W. Bibcode: 2015A&A...574A..45R Altcode: 2014arXiv1406.6491R
Aims: Our aim is to describe the theory of surface layer independent model fitting by phase matching and to apply this to the stars HD 49933 observed by CoRoT, and HD 177153 (aka Perky) observed by Kepler.
Methods: We use theoretical analysis, phase shifts, and model fitting.
Results: We define the inner and outer phase shifts of a frequency set of a model star and show that the outer phase shifts are (almost) independent of degree ℓ, and that a function of the inner phase shifts (the phase function) collapses to an ℓ independent function of frequency in the outer layers. We then show how to use this result in a model fitting technique to find a best fit model to an observed frequency set by calculating the inner phase shifts of a model using the observed frequencies and determining the extent to which the phase function collapses to a single function of frequency in the outer layers. This technique does not depend on the radial order n assigned to the observed frequencies. We give two examples applying this technique to the frequency sets of HD 49933 observed by CoRoT and HD 177153 (aka Perky) observed by Kepler, for which measurements of angular diameters and bolometric fluxes are available. For HD 49933 we find a very wide range of models to be consistent with the data (all with convective core overshooting) - and conclude that the data is not precise enough to make any useful restrictions on the structure of this star. For HD 177153 our best fit models have no convective cores, masses in the range 1.15-1.17 M, ages of 4.45-4.70 × 109 yr, Z in the range 0.021-0.024, XH = 0.71-0.72, Y = 0.256 - 0.266 and mixing length parameter α = 1.8. We compare our results to those of previous studies. We contrast the phase matching technique to that using the ratios of small to large separations, showing that it avoids the problem of correlated errors in separation ratio fitting and of assigning radial order n to the modes. Title: On the use of the average large separation in surface layer independent model fitting and mass estimation Authors: Roxburgh, Ian W. Bibcode: 2014A&A...571A..88R Altcode: 2014arXiv1406.1997R The physics of the outer layers of a star are not well understood but these layers make a major contribution to the large separation. We quantify this using stellar models and show that the contribution ranges from 6% from the outer 0.1% of the radius to 30% from the outer 5%; it would therefore be inconsistent to impose the large separation as a constraint on surface layer independent model fitting. The mass and luminosity are independent of the outer layers and can be used as constraints, the mass being determined from binarity or from surface gravity and radius. The radius can be used as a constraint but with enhanced error estimates. Using stellar models we show that the errors in estimating mass from the scaling relation between mass, radius and large separation can be up to 30%, and that the errors are not reduced on using the asymptotic value of the large separation estimated by extrapolation to high frequencies. Title: The PLATO 2.0 mission Authors: Rauer, H.; Catala, C.; Aerts, C.; Appourchaux, T.; Benz, W.; Brandeker, A.; Christensen-Dalsgaard, J.; Deleuil, M.; Gizon, L.; Goupil, M. -J.; Güdel, M.; Janot-Pacheco, E.; Mas-Hesse, M.; Pagano, I.; Piotto, G.; Pollacco, D.; Santos, Ċ.; Smith, A.; Suárez, J. -C.; Szabó, R.; Udry, S.; Adibekyan, V.; Alibert, Y.; Almenara, J. -M.; Amaro-Seoane, P.; Eiff, M. Ammler-von; Asplund, M.; Antonello, E.; Barnes, S.; Baudin, F.; Belkacem, K.; Bergemann, M.; Bihain, G.; Birch, A. C.; Bonfils, X.; Boisse, I.; Bonomo, A. S.; Borsa, F.; Brandão, I. M.; Brocato, E.; Brun, S.; Burleigh, M.; Burston, R.; Cabrera, J.; Cassisi, S.; Chaplin, W.; Charpinet, S.; Chiappini, C.; Church, R. P.; Csizmadia, Sz.; Cunha, M.; Damasso, M.; Davies, M. B.; Deeg, H. J.; Díaz, R. F.; Dreizler, S.; Dreyer, C.; Eggenberger, P.; Ehrenreich, D.; Eigmüller, P.; Erikson, A.; Farmer, R.; Feltzing, S.; de Oliveira Fialho, F.; Figueira, P.; Forveille, T.; Fridlund, M.; García, R. A.; Giommi, P.; Giuffrida, G.; Godolt, M.; Gomes da Silva, J.; Granzer, T.; Grenfell, J. L.; Grotsch-Noels, A.; Günther, E.; Haswell, C. A.; Hatzes, A. P.; Hébrard, G.; Hekker, S.; Helled, R.; Heng, K.; Jenkins, J. M.; Johansen, A.; Khodachenko, M. L.; Kislyakova, K. G.; Kley, W.; Kolb, U.; Krivova, N.; Kupka, F.; Lammer, H.; Lanza, A. F.; Lebreton, Y.; Magrin, D.; Marcos-Arenal, P.; Marrese, P. M.; Marques, J. P.; Martins, J.; Mathis, S.; Mathur, S.; Messina, S.; Miglio, A.; Montalban, J.; Montalto, M.; Monteiro, M. J. P. F. G.; Moradi, H.; Moravveji, E.; Mordasini, C.; Morel, T.; Mortier, A.; Nascimbeni, V.; Nelson, R. P.; Nielsen, M. B.; Noack, L.; Norton, A. J.; Ofir, A.; Oshagh, M.; Ouazzani, R. -M.; Pápics, P.; Parro, V. C.; Petit, P.; Plez, B.; Poretti, E.; Quirrenbach, A.; Ragazzoni, R.; Raimondo, G.; Rainer, M.; Reese, D. R.; Redmer, R.; Reffert, S.; Rojas-Ayala, B.; Roxburgh, I. W.; Salmon, S.; Santerne, A.; Schneider, J.; Schou, J.; Schuh, S.; Schunker, H.; Silva-Valio, A.; Silvotti, R.; Skillen, I.; Snellen, I.; Sohl, F.; Sousa, S. G.; Sozzetti, A.; Stello, D.; Strassmeier, K. G.; Švanda, M.; Szabó, Gy. M.; Tkachenko, A.; Valencia, D.; Van Grootel, V.; Vauclair, S. D.; Ventura, P.; Wagner, F. W.; Walton, N. A.; Weingrill, J.; Werner, S. C.; Wheatley, P. J.; Zwintz, K. Bibcode: 2014ExA....38..249R Altcode: 2014ExA...tmp...41R; 2013arXiv1310.0696R PLATO 2.0 has recently been selected for ESA's M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence) providing a wide field-of-view (2232 deg 2) and a large photometric magnitude range (4-16 mag). It focusses on bright (4-11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50 % of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete our knowledge of planet diversity for low-mass objects, - correlate the planet mean density-orbital distance distribution with predictions from planet formation theories,- constrain the influence of planet migration and scattering on the architecture of multiple systems, and - specify how planet and system parameters change with host star characteristics, such as type, metallicity and age. The catalogue will allow us to study planets and planetary systems at different evolutionary phases. It will further provide a census for small, low-mass planets. This will serve to identify objects which retained their primordial hydrogen atmosphere and in general the typical characteristics of planets in such low-mass, low-density range. Planets detected by PLATO 2.0 will orbit bright stars and many of them will be targets for future atmosphere spectroscopy exploring their atmosphere. Furthermore, the mission has the potential to detect exomoons, planetary rings, binary and Trojan planets. The planetary science possible with PLATO 2.0 is complemented by its impact on stellar and galactic science via asteroseismology as well as light curves of all kinds of variable stars, together with observations of stellar clusters of different ages. This will allow us to improve stellar models and study stellar activity. A large number of well-known ages from red giant stars will probe the structure and evolution of our Galaxy. Asteroseismic ages of bright stars for different phases of stellar evolution allow calibrating stellar age-rotation relationships. Together with the results of ESA's Gaia mission, the results of PLATO 2.0 will provide a huge legacy to planetary, stellar and galactic science. Title: Seismic analysis of HD 43587Aa, a solar-like oscillator in a multiple system Authors: Boumier, P.; Benomar, O.; Baudin, F.; Verner, G.; Appourchaux, T.; Lebreton, Y.; Gaulme, P.; Chaplin, W.; García, R. A.; Hekker, S.; Regulo, C.; Salabert, D.; Stahn, T.; Elsworth, Y.; Gizon, L.; Hall, M.; Mathur, S.; Michel, E.; Morel, T.; Mosser, B.; Poretti, E.; Rainer, M.; Roxburgh, I.; do Nascimento, J. -D., Jr.; Samadi, R.; Auvergne, M.; Chaintreuil, S.; Baglin, A.; Catala, C. Bibcode: 2014A&A...564A..34B Altcode: 2014arXiv1402.5053B Context. The object HD 43587Aa is a G0V star observed during the 145-day LRa03 run of the COnvection, ROtation and planetary Transits space mission (CoRoT), for which complementary High Accuracy Radial velocity Planet Searcher (HARPS) spectra with S/N > 300 were also obtained. Its visual magnitude is 5.71, and its effective temperature is close to 5950 K. It has a known companion in a highly eccentric orbit and is also coupled with two more distant companions.
Aims: We undertake a preliminary investigation of the internal structure of HD 43587Aa.
Methods: We carried out a seismic analysis of the star, using maximum likelihood estimators and Markov chain Monte Carlo methods.
Results: We established the first table of the eigenmode frequencies, widths, and heights for HD 43587Aa. The star appears to have a mass and a radius slightly larger than the Sun, and is slightly older (5.6 Gyr). Two scenarios are suggested for the geometry of the star: either its inclination angle is very low, or the rotation velocity of the star is very low.
Conclusions: A more detailed study of the rotation and of the magnetic and chromospheric activity for this star is needed, and will be the subject of a further study. New high resolution spectrometric observations should be performed for at least several months in duration. Title: Seismological Diagnostics for Solar-like Stars Authors: Roxburgh, Ian W Bibcode: 2014arXiv1402.1391R Altcode: The oscillations in solar like stars are described in terms of the phase shifts of the eigenmodes from simple sine-waves. We discuss model fitting and inversion techniques based on this representation. We analyse the periodic signatures from the HeII ionisation zone and base of the convective envelope of the CoRoT star HD49933. Title: Asteroseismic Analysis of the CoRoT Target HD 169392 Authors: Mathur, S.; Bruntt, H.; Catala, C.; Benomar, O.; Davies, G. R.; García, R. A.; Salabert, D.; Ballot, J.; Mosser, B.; Régulo, C.; Chaplin, W. J.; Elsworth, Y.; Handberg, R.; Hekker, S.; Mantegazza, L.; Michel, E.; Poretti, E.; Rainer, M.; Roxburgh, I. W.; Samadi, R.; Steslicki, M.; Uytterhoeven, K.; Verner, G. A.; Auvergne, M.; Baglin, A.; Barceló Forteza, S.; Baudin, F.; Roca Cortés, T. Bibcode: 2013ASPC..479..155M Altcode: 2013arXiv1308.0647M The satellite CoRoT (Convection, Rotation, and planetary Transits) has provided high-quality data for almost six years. We show here the asteroseismic analysis and modeling of HD 169392A, which belongs to a weakly-bound binary system as the distance between the two components is ∼4250 au. The main component, HD 169392A, is a G0 IV star with a magnitude of 7.50 while the second component is a G0 V - G2 IV star with a magnitude of 8.98. This analysis focuses on the main component, as the secondary is too faint for the measurement of seismic parameters. A complete modeling has been possible thanks to complementary spectroscopic observations from HARPS (High Accuracy Radial Velocity Planet Searcher), providing Teff = 5985 ± 60 K, log g = 3.96 ± 0.07, and [Fe/H] = -0.04 ± 0.10. Title: On the use of the ratio of small to large separations in asteroseismic model fitting Authors: Roxburgh, Ian W.; Vorontsov, Sergei V. Bibcode: 2013A&A...560A...2R Altcode: 2013arXiv1307.5069R
Aims: We aim to show that model fitting by searching for a best fit of observed and model separation ratios at the same radial orders n is in principle incorrect, and to show that a correct procedure is to compare the model ratios interpolated to the observed frequencies.
Methods: We compare models with different interior structures and outer layers, relate the separation ratios to phase shift differences, conduct model fitting experiments using separation ratios, and relate phase shift differences to internal phase shifts.
Results: We show that the separation ratios of stellar models with the same interior structure, but different outer layers, are not the same when compared at the same radial order n, but are the same when evaluated at the same frequencies by interpolation. The separation ratios trace the phase shift differences as a function of frequency, not of n, and it is the phase shift differences which are determined by the interior structure. We give examples from model fitting where the ratios at the same n values agree but the models have different interior structure, and where the ratios agree when interpolated to the same frequencies and the models have the same interior structure. The correct procedure is to compare observed ratios with model values interpolated to the observed frequencies. Title: Seismic constraints on rotation of Sun-like star and mass of exoplanet Authors: Gizon, L.; Ballot, J.; Michel, E.; Stahn, T.; Vauclair, G.; Bruntt, H.; Quirion, P. -O.; Benomar, O.; Vauclair, S.; Appourchaux, T.; Auvergne, M.; Baglin, A.; Barban, C.; Baudin, F.; Bazot, M.; Campante, T.; Catala, C.; Chaplin, W.; Creevey, O.; Deheuvels, S.; Dolez, N.; Elsworth, Y.; Garcia, R.; Gaulme, P.; Mathis, S.; Mathur, S.; Mosser, B.; Regulo, C.; Roxburgh, I.; Salabert, D.; Samadi, R.; Sato, K.; Verner, G.; Hanasoge, S.; Sreenivasan, K. R. Bibcode: 2013PNAS..11013267G Altcode: 2013arXiv1308.4352G Rotation is thought to drive cyclic magnetic activity in the Sun and Sun-like stars. Stellar dynamos, however, are poorly understood owing to the scarcity of observations of rotation and magnetic fields in stars. Here, inferences are drawn on the internal rotation of a distant Sun-like star by studying its global modes of oscillation. We report asteroseismic constraints imposed on the rotation rate and the inclination of the spin axis of the Sun-like star HD 52265, a principal target observed by the CoRoT satellite that is known to host a planetary companion. These seismic inferences are remarkably consistent with an independent spectroscopic observation (rotational line broadening) and with the observed rotation period of star spots. Furthermore, asteroseismology constrains the mass of exoplanet HD 52265b. Under the standard assumption that the stellar spin axis and the axis of the planetary orbit coincide, the minimum spectroscopic mass of the planet can be converted into a true mass of 1.85 (+0.52,-0.42) M_Jupiter, which implies that it is a planet, not a brown dwarf. Title: Solar-like oscillations in distant stars as seen by CoRoT : the special case of HD 42618, a solar sister Authors: Barban, C.; Deheuvels, S.; Goupil, M. J.; Lebreton, Y.; Mathur, S.; Michel, E.; Morel, Th; Ballot, J.; Baudin, F.; Belkacem, K.; Benomar, O.; Boumier, P.; Davies, G. R.; García, R. A.; Hall, M. P.; Mosser, B.; Poretti, E.; Régulo, C.; Roxburgh, I.; Samadi, R.; Verner, G.; CoRoT Team Bibcode: 2013JPhCS.440a2030B Altcode: We report the observations of a main-sequence star, HD 42618 (Teff = 5765 K, G3V) by the space telescope CoRoT. This is the closest star to the Sun ever observed by CoRoT in term of its fundamental parameters. Using a preliminary version of CoRoT light curves of HD 42618, p modes are detected around 3.2 mHz associated to l = 0, 1 and 2 modes with a large spacing of 142 μHz. Various methods are then used to derive the mass and radius of this star (scaling relations from solar values as well as comparison between theoretical and observationnal frequencies) giving values in the range of (0.80 - 1.02)Msolar and (0.91 - 1.01)Rsolar. A preliminary analysis of l = 0 and 1 modes allows us also to study the amount of penetrative convection at the base of the convective envelope. Title: VizieR Online Data Catalog: Abundances of 93 solar-type Kepler targets (Bruntt+, 2012) Authors: 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. Bibcode: 2013yCat..74230122B Altcode: The spectra were obtained with the ESPaDOnS spectrograph at the 3.6-m Canada-France-Hawaii Telescope (CFHT) in USA and with the NARVAL spectrograph mounted on the 2-m Bernard Lyot Telescope at the Pic du Midi Observatory in France. In both the facilities, the observations were carried out as service observations from May to September in 2010.

(3 data files). Title: Pulsations of rapidly rotating evolved stars Authors: Ouazzani, R-M.; Roxburgh, I. W.; Dupret, M-A Bibcode: 2013arXiv1301.2496O Altcode: A new two dimensional non-perturbative code to compute accurate oscillation modes of rapidly rotating stars is presented. The 2D calculations fully take into account the centrifugal distorsion of the star while the non perturbative method includes the full influence of the Coriolis acceleration. This 2D non-perturbative code is used to study pulsational spectra of highly distorted evolved models of stars. 2D models of stars are obtained by a self consistent method which distorts spherically averaged stellar models a posteriori. We are also able to compute gravito-acoustic modes for the first time in rapidly rotating stars. We present the dynamics of pulsation modes in such models, and show regularities in their frequency spectra. Title: Study of HD 169392A observed by CoRoT and HARPS Authors: Mathur, S.; Bruntt, H.; Catala, C.; Benomar, O.; Davies, G. R.; García, R. A.; Salabert, D.; Ballot, J.; Mosser, B.; Régulo, C.; Chaplin, W. J.; Elsworth, Y.; Handberg, R.; Hekker, S.; Mantegazza, L.; Michel, E.; Poretti, E.; Rainer, M.; Roxburgh, I. W.; Samadi, R.; Stȩślicki, M.; Uytterhoeven, K.; Verner, G. A.; Auvergne, M.; Baglin, A.; Barceló Forteza, S.; Baudin, F.; Roca Cortés, T. Bibcode: 2013A&A...549A..12M Altcode: 2012arXiv1209.5696M Context. The results obtained by asteroseismology with data from space missions such as CoRoT and Kepler are providing new insights into stellar evolution. After five years of observations, CoRoT is continuing to provide high-quality data and we here present an analysis of the CoRoT observations of the double star HD 169392, complemented by ground-based spectroscopic observations.
Aims: This work aims at characterising the fundamental parameters of the two stars, their chemical composition, the acoustic-mode global parameters including their individual frequencies, and their dynamics.
Methods: We analysed HARPS observations of the two stars to derive their chemical compositions. Several methods were used and compared to determine the global properties of stars' acoustic modes and their individual frequencies from the photometric data of CoRoT.
Results: The new spectroscopic observations and archival astrometric values suggest that HD 169392 is a weakly bound wide binary system. We obtained spectroscopic parameters for both components which suggest that they originate from the same interstellar cloud. However, only the signature of oscillation modes of HD 169392 A was measured; the signal-to-noise ratio of the modes in HD 169392B is too low to allow any confident detection. For HD 169392 A we were able to extract parameters of modes for ℓ = 0, 1, 2, and 3. The analysis of splittings and inclination angle gives two possible solutions: one with with splittings and inclination angles of 0.4-1.0 μHz and 20 - 40°, the other with 0.2-0.5 μHz and 55-86°. Modelling this star using the Asteroseismic Modeling Portal (AMP) gives a mass of 1.15 ± 0.01 M, a radius of 1.88 ± 0.02 R, and an age of 4.33 ± 0.12 Gyr. The uncertainties come from estimated errors on the observables but do not include uncertainties on the surface layer correction or the physics of stellar models.

The CoRoT space mission, launched on December 27 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain.This work is based on ground-based observations made with the ESO 3.6 m-telescope at La Silla Observatory under the ESO Large Programme LP185-D.0056.Tables 5 and 7 are available in electronic form at http://www.aanda.org Title: Pulsations of an Evolved Self-consistently Distorted Star Authors: Ouazzani, R. -M.; Dupret, M. -A.; Roxburgh, I. W.; Goupil, M. -J. Bibcode: 2012ASPC..462..402O Altcode: A new two-dimensional (2D) non-perturbative method to compute accurate oscillation modes of rapidly rotating stars is presented. The 2D calculations fully take into account the centrifugal distortion of the star while the non-perturbative method includes the full influence of the Coriolis acceleration, and are used to compute oscillation modes of rapid rotators — high-order p-modes in δ Scuti stars, as well as low-order p- and g-modes in β Cephei stars. We compare the oscillation spectra obtained for centrifugally distorted polytropes with those of Reese et al. (2006), and give the first results for a realistic 2D model of a rapidly rotating 2 M evolved star computed with the method developed by Roxburgh (2006). Title: Calibrating Convective Properties of Solar-like Stars in the Kepler Field of View Authors: Bonaca, Ana; Tanner, Joel D.; Basu, Sarbani; Chaplin, William J.; Metcalfe, Travis S.; Monteiro, Mário J. P. F. G.; Ballot, Jérôme; Bedding, Timothy R.; Bonanno, Alfio; Broomhall, Anne-Marie; Bruntt, Hans; Campante, Tiago L.; Christensen-Dalsgaard, Jørgen; Corsaro, Enrico; Elsworth, Yvonne; García, Rafael A.; Hekker, Saskia; Karoff, Christoffer; Kjeldsen, Hans; Mathur, Savita; Régulo, Clara; Roxburgh, Ian; Stello, Dennis; Trampedach, Regner; Barclay, Thomas; Burke, Christopher J.; Caldwell, Douglas A. Bibcode: 2012ApJ...755L..12B Altcode: 2012arXiv1207.2765B Stellar models generally use simple parameterizations to treat convection. The most widely used parameterization is the so-called mixing-length theory where the convective eddy sizes are described using a single number, α, the mixing-length parameter. This is a free parameter, and the general practice is to calibrate α using the known properties of the Sun and apply that to all stars. Using data from NASA's Kepler mission we show that using the solar-calibrated α is not always appropriate, and that in many cases it would lead to estimates of initial helium abundances that are lower than the primordial helium abundance. Kepler data allow us to calibrate α for many other stars and we show that for the sample of stars we have studied, the mixing-length parameter is generally lower than the solar value. We studied the correlation between α and stellar properties, and we find that α increases with metallicity. We therefore conclude that results obtained by fitting stellar models or by using population-synthesis models constructed with solar values of α are likely to have large systematic errors. Our results also confirm theoretical expectations that the mixing-length parameter should vary with stellar properties. Title: Accurate fundamental parameters and detailed abundance patterns from spectroscopy of 93 solar-type Kepler targets Authors: Bruntt, H.; Basu, S.; Smalley, B.; Chaplin, W. J.; Verner, G. A.; Bedding, T. R.; Catala, C.; Gazzano, J. -C.; Molenda-Żakowicz, J.; Thygesen, A. O.; Uytterhoeven, K.; Hekker, S.; Huber, D.; Karoff, C.; Mathur, S.; Mosser, B.; Appourchaux, T.; Campante, T. L.; Elsworth, Y.; García, R. A.; Handberg, R.; Metcalfe, T. S.; Quirion, P. -O.; Régulo, C.; Roxburgh, I. W.; Stello, D.; Christensen-Dalsgaard, J.; Kawaler, S. D.; Kjeldsen, H.; Morris, R. L.; Quintana, E. V.; Sanderfer, D. T. Bibcode: 2012MNRAS.423..122B Altcode: 2012arXiv1203.0611B; 2012MNRAS.tmp.3037B 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 α 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 I-Fe II balance, although we find a small systematic offset of 0.08 dex (asteroseismic log g values are lower). The abundance patterns of metals, α 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 α-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. Title: Verification of the Kepler Input Catalog from Asteroseismology of Solar-type Stars Authors: Verner, G. A.; Chaplin, W. J.; Basu, S.; Brown, T. M.; Hekker, S.; Huber, D.; Karoff, C.; Mathur, S.; Metcalfe, T. S.; Mosser, B.; Quirion, P. -O.; Appourchaux, T.; Bedding, T. R.; Bruntt, H.; Campante, T. L.; Elsworth, Y.; García, R. A.; Handberg, R.; Régulo, C.; Roxburgh, I. W.; Stello, D.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen, H.; Allen, C.; Clarke, B. D.; Girouard, F. R. Bibcode: 2011ApJ...738L..28V Altcode: 2011arXiv1109.0869V We calculate precise stellar radii and surface gravities from the asteroseismic analysis of over 500 solar-type pulsating stars observed by the Kepler space telescope. These physical stellar properties are compared with those given in the Kepler Input Catalog (KIC), determined from ground-based multi-color photometry. For the stars in our sample, we find general agreement but we detect an average overestimation bias of 0.23 dex in the KIC determination of log (g) for stars with log (g)KIC > 4.0 dex, and a resultant underestimation bias of up to 50% in the KIC radii estimates for stars with R KIC < 2 R sun. Part of the difference may arise from selection bias in the asteroseismic sample; nevertheless, this result implies there may be fewer stars characterized in the KIC with R ~ 1 R sun than is suggested by the physical properties in the KIC. Furthermore, if the radius estimates are taken from the KIC for these affected stars and then used to calculate the size of transiting planets, a similar underestimation bias may be applied to the planetary radii. Title: Global asteroseismic properties of solar-like oscillations observed by Kepler: a comparison of complementary analysis methods Authors: Verner, G. A.; Elsworth, Y.; Chaplin, W. J.; Campante, T. L.; Corsaro, E.; Gaulme, P.; Hekker, S.; Huber, D.; Karoff, C.; Mathur, S.; Mosser, B.; Appourchaux, T.; Ballot, J.; Bedding, T. R.; Bonanno, A.; Broomhall, A. -M.; García, R. A.; Handberg, R.; New, R.; Stello, D.; Régulo, C.; Roxburgh, I. W.; Salabert, D.; White, T. R.; Caldwell, D. A.; Christiansen, J. L.; Fanelli, M. N. Bibcode: 2011MNRAS.415.3539V Altcode: 2011MNRAS.tmp..892V; 2011arXiv1105.0571V We present the asteroseismic analysis of 1948 F-, G- and K-type main-sequence and subgiant stars observed by the National Aeronautics and Space Administration Kepler mission. We detect and characterize solar-like oscillations in 642 of these stars. This represents the largest cohort of main-sequence and subgiant solar-like oscillators observed to date. The photometric observations are analysed using the methods developed by nine independent research teams. The results are combined to validate the determined global asteroseismic parameters and calculate the relative precision by which the parameters can be obtained. We correlate the relative number of detected solar-like oscillators with stellar parameters from the Kepler Input Catalogue and find a deficiency for stars with effective temperatures in the range 5300 ≲Teff≲ 5700 K and a drop-off in detected oscillations in stars approaching the red edge of the classical instability strip. We compare the power-law relationships between the frequency of peak power, νmax, the mean large frequency separation, Δν, and the maximum mode amplitude, Amax, and show that there are significant method-dependent differences in the results obtained. This illustrates the need for multiple complementary analysis methods to be used to assess the robustness and reproducibility of results derived from global asteroseismic parameters. Title: Kepler observations of the variability in B-type stars Authors: Balona, L. A.; Pigulski, A.; De Cat, P.; Handler, G.; Gutiérrez-Soto, J.; Engelbrecht, C. A.; Frescura, F.; Briquet, M.; Cuypers, J.; Daszyńska-Daszkiewicz, J.; Degroote, P.; Dukes, R. J.; Garcia, R. A.; Green, E. M.; Heber, U.; Kawaler, S. D.; Lehmann, H.; Leroy, B.; Molenda-Żaaowicz, J.; Neiner, C.; Noels, A.; Nuspl, J.; Østensen, R.; Pricopi, D.; Roxburgh, I.; Salmon, S.; Smith, M. A.; Suárez, J. C.; Suran, M.; Szabó, R.; Uytterhoeven, K.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Caldwell, D. A.; Girouard, F. R.; Sanderfer, D. T. Bibcode: 2011MNRAS.413.2403B Altcode: 2011MNRAS.tmp..298B; 2011arXiv1103.0644B The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies, characteristic of slowly pulsating B (SPB) stars. Seven of these stars also show a few weak, isolated high frequencies and they could be considered as SPB/β Cephei (β Cep) hybrids. In all cases, the frequency spectra are quite different from what is seen from ground-based observations. We suggest that this is because most of the low frequencies are modes of high degree which are predicted to be unstable in models of mid-B stars. We find that there are non-pulsating stars within the β Cep and SPB instability strips. Apart from the pulsating stars, we can identify stars with frequency groupings similar to what is seen in Be stars but which are not Be stars. The origin of the groupings is not clear, but may be related to rotation. We find periodic variations in other stars which we attribute to proximity effects in binary systems or possibly rotational modulation. We find no evidence for pulsating stars between the cool edge of the SPB and the hot edge of the δ Sct instability strips. None of the stars shows the broad features which can be attributed to stochastically excited modes as recently proposed. Among our sample of B stars are two chemically peculiar stars, one of which is a HgMn star showing rotational modulation in the light curve. Title: Accurate p-mode measurements of the G0V metal-rich CoRoT target HD 52265 Authors: Ballot, J.; Gizon, L.; Samadi, R.; Vauclair, G.; Benomar, O.; Bruntt, H.; Mosser, B.; Stahn, T.; Verner, G. A.; Campante, T. L.; García, R. A.; Mathur, S.; Salabert, D.; Gaulme, P.; Régulo, C.; Roxburgh, I. W.; Appourchaux, T.; Baudin, F.; Catala, C.; Chaplin, W. J.; Deheuvels, S.; Michel, E.; Bazot, M.; Creevey, O.; Dolez, N.; Elsworth, Y.; Sato, K. H.; Vauclair, S.; Auvergne, M.; Baglin, A. Bibcode: 2011A&A...530A..97B Altcode: 2011arXiv1105.3551B Context. The star HD 52265 is a G0V metal-rich exoplanet-host star observed in the seismology field of the CoRoT space telescope from November 2008 to March 2009. The satellite collected 117 days of high-precision photometric data on this star, showing that it presents solar-like oscillations. HD 52265 was also observed in spectroscopy with the Narval spectrograph at the same epoch.
Aims: We characterise HD 52265 using both spectroscopic and seismic data.
Methods: The fundamental stellar parameters of HD 52265 were derived with the semi-automatic software VWA, and the projected rotational velocity was estimated by fitting synthetic profiles to isolated lines in the observed spectrum. The parameters of the observed p modes were determined with a maximum-likelihood estimation. We performed a global fit of the oscillation spectrum, over about ten radial orders, for degrees l = 0 to 2. We also derived the properties of the granulation, and analysed a signature of the rotation induced by the photospheric magnetic activity.
Results: Precise determinations of fundamental parameters have been obtained: Teff = 6100 ± 60 K, log g = 4.35 ± 0.09, [M/H] = 0.19 ± 0.05, as well as vsini=3.6+0.3-1.0kms. We have measured a mean rotation period Prot = 12.3 ± 0.15 days, and find a signature of differential rotation. The frequencies of 31 modes are reported in the range 1500-2550 μHz. The large separation exhibits a clear modulation around the mean value Dnu=98.3 ± 0.1 μHz. Mode widths vary with frequency along an S-shape with a clear local maximum around 1800 μHz. We deduce lifetimes ranging between 0.5 and 3 days for these modes. Finally, we find a maximal bolometric amplitude of about 3.96 ± 0.24 ppm for radial modes.

The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain. Title: Predicting the Detectability of Oscillations in Solar-type Stars Observed by Kepler Authors: Chaplin, W. J.; Kjeldsen, H.; Bedding, T. R.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Appourchaux, T.; Elsworth, Y.; García, R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Verner, G. A.; Batalha, N.; Borucki, W. J.; Brown, T. M.; Bryson, S. T.; Christiansen, J. L.; Clarke, B. D.; Jenkins, J. M.; Klaus, T. C.; Koch, D.; An, D.; Ballot, J.; Basu, S.; Benomar, O.; Bonanno, A.; Broomhall, A. -M.; Campante, T. L.; Corsaro, E.; Creevey, O. L.; Esch, L.; Gai, N.; Gaulme, P.; Hale, S. J.; Handberg, R.; Hekker, S.; Huber, D.; Mathur, S.; Mosser, B.; New, R.; Pinsonneault, M. H.; Pricopi, D.; Quirion, P. -O.; Régulo, C.; Roxburgh, I. W.; Salabert, D.; Stello, D.; Suran, M. D. Bibcode: 2011ApJ...732...54C Altcode: 2011arXiv1103.0702C Asteroseismology of solar-type stars has an important part to play in the exoplanet program of the NASA Kepler Mission. Precise and accurate inferences on the stellar properties that are made possible by the seismic data allow very tight constraints to be placed on the exoplanetary systems. Here, we outline how to make an estimate of the detectability of solar-like oscillations in any given Kepler target, using rough estimates of the temperature and radius, and the Kepler apparent magnitude. Title: Evidence for the Impact of Stellar Activity on the Detectability of Solar-like Oscillations Observed by Kepler Authors: Chaplin, W. J.; Bedding, T. R.; Bonanno, A.; Broomhall, A. -M.; García, R. A.; Hekker, S.; Huber, D.; Verner, G. A.; Basu, S.; Elsworth, Y.; Houdek, G.; Mathur, S.; Mosser, B.; New, R.; Stevens, I. R.; Appourchaux, T.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen, H.; Ballot, J.; Benomar, O.; Corsaro, E.; Campante, T. L.; Gaulme, P.; Hale, S. J.; Handberg, R.; Jarvis, E.; Régulo, C.; Roxburgh, I. W.; Salabert, D.; Stello, D.; Mullally, F.; Li, J.; Wohler, W. Bibcode: 2011ApJ...732L...5C Altcode: 2011arXiv1103.5570C We use photometric observations of solar-type stars, made by the NASA Kepler Mission, to conduct a statistical study of the impact of stellar surface activity on the detectability of solar-like oscillations. We find that the number of stars with detected oscillations falls significantly with increasing levels of activity. The results present strong evidence for the impact of magnetic activity on the properties of near-surface convection in the stars, which appears to inhibit the amplitudes of the stochastically excited, intrinsically damped solar-like oscillations. Title: A power-spectrum autocorrelation technique to detect global asteroseismic parameters Authors: Verner, G. A.; Roxburgh, I. W. Bibcode: 2011arXiv1104.0631V Altcode: This article describes a moving-windowed autocorrelation technique which, when applied to an asteroseismic Fourier power spectrum, can be used to automatically detect the frequency of maximum p-mode power, large and small separations, mean p-mode linewidth, and constrain the stellar inclination angle and rotational splitting. The technique is illustrated using data from the CoRoT and Kepler space telescopes and tested using artificial data. Title: Asteroseismology of solar-type stars with Kepler I: Data analysis Authors: Karoff, C.; Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; Garcia, R. A.; Houdek, G.; Metcalfe, T. S.; Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Basu, S.; Bedding, T. R.; Campante, T. L.; Eggenberger, P.; Fletcher, S. T.; Gaulme, P.; Handberg, R.; Hekker, S.; Martic, M.; Mathur, S.; Mosser, B.; Regulo, C.; Roxburgh, I. W.; Salabert, D.; Stello, D.; Verner, G. A.; Belkacem, K.; Biazzo, K.; Cunha, M. S.; Gruberbauer, M.; Guzik, J. A.; Kupka, F.; Leroy, B.; Ludwig, H. -G.; Mathis, S.; Noels, A.; Noyes, R. W.; Roca Cortes, T.; Roth, M.; Sato, K. H.; Schmitt, J.; Suran, M. D.; Trampedach, R.; Uytterhoeven, K.; Ventura, R. Bibcode: 2010AN....331..972K Altcode: 2010arXiv1005.0507K We report on the first asteroseismic analysis of solar-type stars observed by Kepler. Observations of three G-type stars, made at one-minute cadence during the first 33.5 days of science operations, reveal high signal-to-noise solar-like oscillation spectra in all three stars: About 20 modes of oscillation can clearly be distinguished in each star. We discuss the appearance of the oscillation spectra, including the presence of a possible signature of faculae, and the presence of mixed modes in one of the three stars. Title: Solar-like oscillations in cluster stars Authors: Stello, D.; Basu, S.; Bedding, T. R.; Brogaard, K.; Bruntt, H.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Demarque, P.; Elsworth, Y. P.; García, R. A.; Gilliland, R. L.; Hekker, S.; Huber, D.; Karoff, C.; Kjeldsen, H.; Lebreton, Y.; Mathur, S.; Meibom, S.; Molenda-Żakowicz, J.; Noels, A.; Roxburgh, I. W.; Silva Aguirre, V.; Sterken, C.; Szabó, R. Bibcode: 2010AN....331..985S Altcode: 2010arXiv1007.0009S This article summaries a talk given at the HELAS IV international meeting We present a brief overview of the history of attempts to obtain a clear detection of solar-like oscillations in cluster stars, and discuss the results on the first clear detection, which was made by the Kepler Asteroseismic Science Consortium (KASC) Working Group 2.

Data from Kepler. Title: A Precise Asteroseismic Age and Radius for the Evolved Sun-like Star KIC 11026764 Authors: Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Molenda-Żakowicz, J.; Appourchaux, T.; Chaplin, W. J.; Doǧan, G.; Eggenberger, P.; Bedding, T. R.; Bruntt, H.; Creevey, O. L.; Quirion, P. -O.; Stello, D.; Bonanno, A.; Silva Aguirre, V.; Basu, S.; Esch, L.; Gai, N.; Di Mauro, M. P.; Kosovichev, A. G.; Kitiashvili, I. N.; Suárez, J. C.; Moya, A.; Piau, L.; García, R. A.; Marques, J. P.; Frasca, A.; Biazzo, K.; Sousa, S. G.; Dreizler, S.; Bazot, M.; Karoff, C.; Frandsen, S.; Wilson, P. A.; Brown, T. M.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Campante, T. L.; Fletcher, S. T.; Handberg, R.; Régulo, C.; Salabert, D.; Schou, J.; Verner, G. A.; Ballot, J.; Broomhall, A. -M.; Elsworth, Y.; Hekker, S.; Huber, D.; Mathur, S.; New, R.; Roxburgh, I. W.; Sato, K. H.; White, T. R.; Borucki, W. J.; Koch, D. G.; Jenkins, J. M. Bibcode: 2010ApJ...723.1583M Altcode: 2010arXiv1010.4329M The primary science goal of the Kepler Mission is to provide a census of exoplanets in the solar neighborhood, including the identification and characterization of habitable Earth-like planets. The asteroseismic capabilities of the mission are being used to determine precise radii and ages for the target stars from their solar-like oscillations. Chaplin et al. published observations of three bright G-type stars, which were monitored during the first 33.5 days of science operations. One of these stars, the subgiant KIC 11026764, exhibits a characteristic pattern of oscillation frequencies suggesting that it has evolved significantly. We have derived asteroseismic estimates of the properties of KIC 11026764 from Kepler photometry combined with ground-based spectroscopic data. We present the results of detailed modeling for this star, employing a variety of independent codes and analyses that attempt to match the asteroseismic and spectroscopic constraints simultaneously. We determine both the radius and the age of KIC 11026764 with a precision near 1%, and an accuracy near 2% for the radius and 15% for the age. Continued observations of this star promise to reveal additional oscillation frequencies that will further improve the determination of its fundamental properties. Title: PLATO : PLAnetary Transits and Oscillations of Stars - The Exoplanetary System Explorer Authors: Catala, C.; Arentoft, T.; Fridlund, M.; Lindberg, R.; Mas-Hesse, J. M.; Micela, G.; Pollacco, D.; Poretti, E.; Rauer, H.; Roxburgh, I.; Stankov, A.; Udry, S. Bibcode: 2010ASPC..430..260C Altcode: PLATO’s objective is to characterize exoplanets and their host stars in the solar neighbourhood. While it builds on the heritage from CoRoT and Kepler, the major breakthrough will come from its strong focus on bright targets (mV ≤ 11). The PLATO targets will also include a large number of very bright (mV ≤ 8) and nearby stars. The prime science goals of PLATO are: (i) the detection and characterization of exoplanetary systems of all kinds, including both the planets and their host stars, reaching down to small, terrestrial planets in the habitable zone; (ii) the identification of suitable targets for future, more detailed characterization, including a spectroscopic search for bio-markers in nearby habitable exoplanets. These ambitious goals will be reached by ultra-high precision, long (few years), uninterrupted photometric monitoring in the visible of very large samples of bright stars, which can only be done from space. The resulting high quality light curves will be used on the one hand to detect planetary transits, as well as to measure their characteristics, and on the other hand to provide a seismic analysis of the host stars of the detected planets, from which precise measurements of their radii, masses, and ages will be derived. The PLATO space-based data will be complemented by ground-based follow-up observations, in particular very precise radial velocity monitoring, which will be used to confirm the planetary nature of the detected events and to measure the planet masses. The full set of parameters of exoplanetary systems will thus be measured, including all characteristics of the host stars and the orbits, radii, masses, and ages of the planets, allowing us to derive planet mean densities, and estimate their temperature and radiation environment. Finally, the knowledge of the age of the exoplanetary systems will allow us to put them in an evolutionary perspective. Title: The solar-like CoRoT target HD 170987: spectroscopic and seismic observations Authors: Mathur, S.; García, R. A.; Catala, C.; Bruntt, H.; Mosser, B.; Appourchaux, T.; Ballot, J.; Creevey, O. L.; Gaulme, P.; Hekker, S.; Huber, D.; Karoff, C.; Piau, L.; Régulo, C.; Roxburgh, I. W.; Salabert, D.; Verner, G. A.; Auvergne, M.; Baglin, A.; Chaplin, W. J.; Elsworth, Y.; Michel, E.; Samadi, R.; Sato, K.; Stello, D. Bibcode: 2010A&A...518A..53M Altcode: 2010arXiv1004.4891M Context. The CoRoT mission is in its third year of observation and the data from the second long run in the galactic centre direction are being analysed. The solar-like oscillating stars that have been observed up to now have given some interesting results, specially concerning the amplitudes that are lower than predicted. We present here the results from the analysis of the star HD 170987.
Aims: The goal of this research work is to characterise the global parameters of HD 170987. We look for global seismic parameters such as the mean large separation, maximum amplitude of the modes, and surface rotation because the signal-to-noise ratio in the observations does not allow us to measure individual modes. We also aim to retrieve the parameters of the star and its chemical composition.
Methods: We studied the chemical composition of the star through ground-based observations performed with the NARVAL spectrograph. We used several methods to calculate the global parameters from the acoustic oscillations based on CoRoT data. The light curve of the star has been interpolated with inpainting algorithms to reduce the effect of data gaps.
Results: We found the power excess related to p modes in the range [400-1200] μHz with a mean large separation of 55.2 ± 0.8 μHz with a probability above 95 % that increases to 55.9 ± 0.2 μHz in a higher frequency range [500-1250] μHz and a rejection level of 1%. A hint of the variation of this quantity with frequency was also found. The rotation period of the star is estimated to be around 4.3 days with an inclination axis of i = 50° +20-13. We measured a bolometric amplitude per radial mode in a range [2.4-2.9] ppm around 1000 μHz. Finally we estimate the stellar mass with a grid of models, M = 1.43 ± 0.05 M_⊙, the radius, R = 1.96 ± 0.046 R_⊙, and the age ~2.4 Gyr.

The CoRoT space mission, launched on 2006 December 27, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain. Title: Asteroseismology of solar and stellar models Authors: Roxburgh, Ian W. Bibcode: 2010Ap&SS.328....3R Altcode: 2009Ap&SS.tmp..245R I discuss several asteroseismology diagnostic techniques that can be applied to the high quality data on stellar oscillations obtained, and to be obtained in the future, from ground based and space based experiments. In particular I discuss techniques using the representation of oscillation frequencies in terms of inner and outer phase shifts which can be used both for model fitting and inversion procedures to probe the inner structure of stars, and hence to test and improve our modelling. Title: Seismic and spectroscopic characterization of the solar-like pulsating CoRoT target HD 49385 Authors: Deheuvels, S.; Bruntt, H.; Michel, E.; Barban, C.; Verner, G.; Régulo, C.; Mosser, B.; Mathur, S.; Gaulme, P.; Garcia, R. A.; Boumier, P.; Appourchaux, T.; Samadi, R.; Catala, C.; Baudin, F.; Baglin, A.; Auvergne, M.; Roxburgh, I. W.; Pérez Hernández, F. Bibcode: 2010A&A...515A..87D Altcode: 2010arXiv1003.4368D Context. The star HD 49385 is the first G-type solar-like pulsator observed in the seismology field of the space telescope CoRoT. The satellite collected 137 days of high-precision photometric data on this star, confirming that it presents solar-like oscillations. HD 49385 was also observed in spectroscopy with the NARVAL spectrograph in January 2009.
Aims: Our goal is to characterize HD 49385 using both spectroscopic and seismic data.
Methods: The fundamental stellar parameters of HD 49385 are derived with the semi-automatic software VWA, and the projected rotational velocity is estimated by fitting synthetic profiles to isolated lines in the observed spectrum. A maximum likelihood estimation is used to determine the parameters of the observed p modes. We perform a global fit, in which modes are fitted simultaneously over nine radial orders, with degrees ranging from ℓ = 0 to ℓ = 3 (36 individual modes).
Results: Precise estimates of the atmospheric parameters (Teff, [M/H], log g) and of the ν sin i of HD 49385 are obtained. The seismic analysis of the star leads to a clear identification of the modes for degrees ℓ = 0,1,2. Around the maximum of the signal (ν ≃ 1013 μHz), some peaks are found significant and compatible with the expected characteristics of ℓ = 3 modes. Our fit yields robust estimates of the frequencies, linewidths and amplitudes of the modes. We find amplitudes of ~5.6 ± 0.8 ppm for radial modes at the maximum of the signal. The lifetimes of the modes range from one day (at high frequency) to a bit more than two days (at low frequency). Significant peaks are found outside the identified ridges and are fitted. They are attributed to mixed modes.

Based on data obtained from the CoRoT (Convection, Rotation and planetary Transits) space mission, developed by the French Space agency CNES in collaboration with the Science Programs of ESA, Austria, Belgium, Brazil, Germany and Spain.Based on data obtained using the Télescope Bernard Lyot at Observatoire du Pic du Midi, CNRS and Université Paul Sabatier, France. Title: Detection of Solar-like Oscillations from Kepler Photometry of the Open Cluster NGC 6819 Authors: Stello, Dennis; Basu, Sarbani; Bruntt, Hans; Mosser, Benoît; Stevens, Ian R.; Brown, Timothy M.; Christensen-Dalsgaard, Jørgen; Gilliland, Ronald L.; Kjeldsen, Hans; Arentoft, Torben; Ballot, Jérôme; Barban, Caroline; Bedding, Timothy R.; Chaplin, William J.; Elsworth, Yvonne P.; García, Rafael A.; Goupil, Marie-Jo; Hekker, Saskia; Huber, Daniel; Mathur, Savita; Meibom, Søren; Sangaralingam, Vinothini; Baldner, Charles S.; Belkacem, Kevin; Biazzo, Katia; Brogaard, Karsten; Suárez, Juan Carlos; D'Antona, Francesca; Demarque, Pierre; Esch, Lisa; Gai, Ning; Grundahl, Frank; Lebreton, Yveline; Jiang, Biwei; Jevtic, Nada; Karoff, Christoffer; Miglio, Andrea; Molenda-Żakowicz, Joanna; Montalbán, Josefina; Noels, Arlette; Roca Cortés, Teodoro; Roxburgh, Ian W.; Serenelli, Aldo M.; Silva Aguirre, Victor; Sterken, Christiaan; Stine, Peter; Szabó, Robert; Weiss, Achim; Borucki, William J.; Koch, David; Jenkins, Jon M. Bibcode: 2010ApJ...713L.182S Altcode: 2010arXiv1001.0026S Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance, and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819—one of the four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation, Δν, and the frequency of maximum oscillation power, νmax. We find that the asteroseismic parameters allow us to test cluster membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about 2 orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler. Title: Solar-like Oscillations in Low-luminosity Red Giants: First Results from Kepler Authors: Bedding, T. R.; Huber, D.; Stello, D.; Elsworth, Y. P.; Hekker, S.; Kallinger, T.; Mathur, S.; Mosser, B.; Preston, H. L.; Ballot, J.; Barban, C.; Broomhall, A. M.; Buzasi, D. L.; Chaplin, W. J.; García, R. A.; Gruberbauer, M.; Hale, S. J.; De Ridder, J.; Frandsen, S.; Borucki, W. J.; Brown, T.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Jenkins, J. M.; Kjeldsen, H.; Koch, D.; Belkacem, K.; Bildsten, L.; Bruntt, H.; Campante, T. L.; Deheuvels, S.; Derekas, A.; Dupret, M. -A.; Goupil, M. -J.; Hatzes, A.; Houdek, G.; Ireland, M. J.; Jiang, C.; Karoff, C.; Kiss, L. L.; Lebreton, Y.; Miglio, A.; Montalbán, J.; Noels, A.; Roxburgh, I. W.; Sangaralingam, V.; Stevens, I. R.; Suran, M. D.; Tarrant, N. J.; Weiss, A. Bibcode: 2010ApJ...713L.176B Altcode: 2010arXiv1001.0229B We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30 minute sampling, reveal clear oscillations in a large sample of G and K giants, extending in luminosity from the red clump down to the bottom of the giant branch. We confirm a strong correlation between the large separation of the oscillations (Δν) and the frequency of maximum power (νmax). We focus on a sample of 50 low-luminosity stars (νmax > 100 μHz, L <~ 30 L sun) having high signal-to-noise ratios and showing the unambiguous signature of solar-like oscillations. These are H-shell-burning stars, whose oscillations should be valuable for testing models of stellar evolution and for constraining the star formation rate in the local disk. We use a new technique to compare stars on a single échelle diagram by scaling their frequencies and find well-defined ridges corresponding to radial and non-radial oscillations, including clear evidence for modes with angular degree l = 3. Measuring the small separation between l = 0 and l = 2 allows us to plot the so-called C-D diagram of δν02 versus Δν. The small separation δν01 of l = 1 from the midpoint of adjacent l = 0 modes is negative, contrary to the Sun and solar-type stars. The ridge for l = 1 is notably broadened, which we attribute to mixed modes, confirming theoretical predictions for low-luminosity giants. Overall, the results demonstrate the tremendous potential of Kepler data for asteroseismology of red giants. Title: The Asteroseismic Potential of Kepler: First Results for Solar-Type Stars Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; García, R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Brown, T. M.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Borucki, W. J.; Koch, D.; Jenkins, J. M.; Ballot, J.; Basu, S.; Bazot, M.; Bedding, T. R.; Benomar, O.; Bonanno, A.; Brandão, I. M.; Bruntt, H.; Campante, T. L.; Creevey, O. L.; Di Mauro, M. P.; Doǧan, G.; Dreizler, S.; Eggenberger, P.; Esch, L.; Fletcher, S. T.; Frandsen, S.; Gai, N.; Gaulme, P.; Handberg, R.; Hekker, S.; Howe, R.; Huber, D.; Korzennik, S. G.; Lebrun, J. C.; Leccia, S.; Martic, M.; Mathur, S.; Mosser, B.; New, R.; Quirion, P. -O.; Régulo, C.; Roxburgh, I. W.; Salabert, D.; Schou, J.; Sousa, S. G.; Stello, D.; Verner, G. A.; Arentoft, T.; Barban, C.; Belkacem, K.; Benatti, S.; Biazzo, K.; Boumier, P.; Bradley, P. A.; Broomhall, A. -M.; Buzasi, D. L.; Claudi, R. U.; Cunha, M. S.; D'Antona, F.; Deheuvels, S.; Derekas, A.; García Hernández, A.; Giampapa, M. S.; Goupil, M. J.; Gruberbauer, M.; Guzik, J. A.; Hale, S. J.; Ireland, M. J.; Kiss, L. L.; Kitiashvili, I. N.; Kolenberg, K.; Korhonen, H.; Kosovichev, A. G.; Kupka, F.; Lebreton, Y.; Leroy, B.; Ludwig, H. -G.; Mathis, S.; Michel, E.; Miglio, A.; Montalbán, J.; Moya, A.; Noels, A.; Noyes, R. W.; Pallé, P. L.; Piau, L.; Preston, H. L.; Roca Cortés, T.; Roth, M.; Sato, K. H.; Schmitt, J.; Serenelli, A. M.; Silva Aguirre, V.; Stevens, I. R.; Suárez, J. C.; Suran, M. D.; Trampedach, R.; Turck-Chièze, S.; Uytterhoeven, K.; Ventura, R.; Wilson, P. A. Bibcode: 2010ApJ...713L.169C Altcode: 2010arXiv1001.0506C We present preliminary asteroseismic results from Kepler on three G-type stars. The observations, made at one-minute cadence during the first 33.5 days of science operations, reveal high signal-to-noise solar-like oscillation spectra in all three stars: about 20 modes of oscillation may be clearly distinguished in each star. We discuss the appearance of the oscillation spectra, use the frequencies and frequency separations to provide first results on the radii, masses, and ages of the stars, and comment in the light of these results on prospects for inference on other solar-type stars that Kepler will observe. Title: A fresh look at the seismic spectrum of HD49933: analysis of 180 days of CoRoT photometry Authors: Benomar, O.; Baudin, F.; Campante, T. L.; Chaplin, W. J.; García, R. A.; Gaulme, P.; Toutain, T.; Verner, G. A.; Appourchaux, T.; Ballot, J.; Barban, C.; Elsworth, Y.; Mathur, S.; Mosser, B.; Régulo, C.; Roxburgh, I. W.; Auvergne, M.; Baglin, A.; Catala, C.; Michel, E.; Samadi, R. Bibcode: 2009A&A...507L..13B Altcode: 2009arXiv0910.3060B Context: Solar-like oscillations have now been observed in several stars, thanks to ground-based spectroscopic observations and space-borne photometry. CoRoT, which has been in orbit since December 2006, has observed the star HD49933 twice. The oscillation spectrum of this star has proven difficult to interpret.
Aims: Thanks to a new timeseries provided by CoRoT, we aim to provide a robust description of the oscillations in HD49933, i.e., to identify the degrees of the observed modes, and to measure mode frequencies, widths, amplitudes and the average rotational splitting.
Methods: Several methods were used to model the Fourier spectrum: Maximum Likelihood Estimators and Bayesian analysis using Markov Chain Monte-Carlo techniques.
Results: The different methods yield consistent result, and allow us to make a robust identification of the modes and to extract precise mode parameters. Only the rotational splitting remains difficult to estimate precisely, but is clearly relatively large (several μHz in size).

The CoRoT space mission, launched on 2006 December 27, was developed and is operated by the CNES, with participation of the Science Programs of ESA, ESA's RSSD, Austria, Belgium, Brazil, Germany and Spain.

Figures 5-9 and Table 2 are only available in electronic form at http://www.aanda.org Title: The CoRoT target HD 175726: an active star with weak solar-like oscillations Authors: Mosser, B.; Michel, E.; Appourchaux, T.; Barban, C.; Baudin, F.; Boumier, P.; Bruntt, H.; Catala, C.; Deheuvels, S.; García, R. A.; Gaulme, P.; Regulo, C.; Roxburgh, I.; Samadi, R.; Verner, G.; Auvergne, M.; Baglin, A.; Ballot, J.; Benomar, O.; Mathur, S. Bibcode: 2009A&A...506...33M Altcode: 2009arXiv0908.2244M Context: The CoRoT short runs give us the opportunity to observe a large variety of late-type stars through their solar-like oscillations. We report observations of the star HD 175726 that lasted for 27 days during the first short run of the mission. The time series reveals a high-activity signal and the power spectrum presents an excess due to solar-like oscillations with a low signal-to-noise ratio.
Aims: Our aim is to identify the most efficient tools to extract as much information as possible from the power density spectrum.
Methods: The most productive method appears to be the autocorrelation of the time series, calculated as the spectrum of the filtered spectrum. This method is efficient, very rapid computationally, and will be useful for the analysis of other targets, observed with CoRoT or with forthcoming missions such as Kepler and Plato.
Results: The mean large separation has been measured to be 97.2±0.5 μHz, slightly below the expected value determined from solar scaling laws. We also show strong evidence for variation of the large separation with frequency. The bolometric mode amplitude is only 1.7±0.25 ppm for radial modes, which is 1.7 times less than expected. Due to the low signal-to-noise ratio, mode identification is not possible for the available data set of HD 175726.

The CoRoT space mission, launched on 2006 December 27, was developed and is operated by the CNES, with participation of the Science Programs of ESA, ESAs RSSD, Austria, Belgium, Brazil, Germany and Spain. Title: Solar-like oscillations in HD 181420: data analysis of 156 days of CoRoT data Authors: Barban, C.; Deheuvels, S.; Baudin, F.; Appourchaux, T.; Auvergne, M.; Ballot, J.; Boumier, P.; Chaplin, W. J.; García, R. A.; Gaulme, P.; Michel, E.; Mosser, B.; Régulo, C.; Roxburgh, I. W.; Verner, G.; Baglin, A.; Catala, C.; Samadi, R.; Bruntt, H.; Elsworth, Y.; Mathur, S. Bibcode: 2009A&A...506...51B Altcode: Context: The estimate of solar-like oscillation properties, such as their frequencies, amplitudes and lifetimes, is challenging because of their low amplitudes and will benefit from long and uninterrupted observing runs. The space telescope CoRoT allows us to obtain high-performance photometric data over a long and quasi continuous period. Among its main targets are stars for which we expect solar-like oscillations.
Aims: HD 181420, an F2 main sequence star, has been observed by CoRoT during its first long run covering about 156 days. With this unprecedently high-quality set of data, our aim is to derive the p-mode parameters that can be used to probe the stellar interior.
Methods: The CoRoT data obtained on HD 181420 is analysed using a classical Fourier approach for the search for the p mode signature. The p-mode parameters are then derived using global fitting of the power spectrum by a Lorentzian model, as used widely in the solar case.
Results: From the p-mode frequencies, the mean value of the large spacing is estimated to be 75 {μ Hz}. The p-mode amplitudes are slightly less than 4 ppm with a line width of about 8 {μ Hz} at the maximum of the p modes. The inclination angle is estimated to be around 45 °. The large mode line-width combined with the observed mode spacing make it difficult to identify the ℓ=2 modes and to estimate the rotational splitting. We explore two scenarios for the identification of the modes.

The CoRoT space mission, launched on 2006 December 27, was delopped and is operated by the CNES with participation of the Science Programs of ESA; ESA's RSSD, Austria, Belgium, Brazil, Germany and Spain. Title: Solar-like oscillations with low amplitude in the CoRoT target HD 181906 Authors: García, R. A.; Régulo, C.; Samadi, R.; Ballot, J.; Barban, C.; Benomar, O.; Chaplin, W. J.; Gaulme, P.; Appourchaux, T.; Mathur, S.; Mosser, B.; Toutain, T.; Verner, G. A.; Auvergne, M.; Baglin, A.; Baudin, F.; Boumier, P.; Bruntt, H.; Catala, C.; Deheuvels, S.; Elsworth, Y.; Jiménez-Reyes, S. J.; Michel, E.; Pérez Hernández, F.; Roxburgh, I. W.; Salabert, D. Bibcode: 2009A&A...506...41G Altcode: 2009arXiv0907.0608G Context: The F8 star HD 181906 (effective temperature ∼6300 K) was observed for 156 days by the CoRoT satellite during the first long run in the direction of the galactic centre. Analysis of the data reveals a spectrum of solar-like acoustic oscillations. However, the faintness of the target (mv = 7.65) means the signal-to-noise (S/N) in the acoustic modes is quite low, and this low S/N leads to complications in the analysis.
Aims: We extract global variables of the star, as well as key parameters of the p modes observed in the power spectrum of the lightcurve.
Methods: The power spectrum of the lightcurve, a wavelet transform and spot fitting were used to obtain the average rotation rate of the star and its inclination angle. Then, the autocorrelation of the power spectrum and the power spectrum of the power spectrum were used to properly determine the large separation. Finally, estimations of the mode parameters were done by maximizing the likelihood of a global fit, where several modes were fit simultaneously.
Results: We have been able to infer the mean surface rotation rate of the star (~4 μHz) with indications of the presence of surface differential rotation, the large separation of the p modes (~87 μHz), hence also the “ridges” corresponding to overtones of the acoustic modes.

CoRoT (Convection, Rotation and planetary Transits) is a minisatellite developed by the French Space agency CNES in collaboration with the Science Programmes of ESA, Austria, Belgium, Brazil, Germany and Spain. Title: Narrow frequency-windowed autocorrelations as a diagnostic of solar-like stars Authors: Roxburgh, I. W. Bibcode: 2009A&A...506..435R Altcode: Aims: This paper investigates the diagnostic potential of narrow, frequency-windowed autocorrelation as a tool for probing the properties of solar-like oscillating stars when the determination of individual frequencies is impossible or is subject to large uncertainties, and when mode identification is difficult.
Methods: I use theoretical analysis including phase-shifts, modelling, and data analysis.
Results: Narrow-windowed autocorrelation of a time series can reveal the variation with frequency of the large separations Δ(ν) and the half large separations Δ01, Δ10, thus helping with mode identification. This technique is applied to the CoRoT p-mode oscillators HD 49933, HD 175726, HD 181420, and HD 181906. Theoretical analysis and modelling are presented to illustrate the technique. Title: Response of a spaceborne gravitational wave antenna to solar oscillations Authors: Polnarev, A. G.; Roxburgh, I. W.; Baskaran, D. Bibcode: 2009PhRvD..79h2001P Altcode: 2009arXiv0904.1943P We investigate the possibility of observing very small amplitude low frequency solar oscillations with the proposed laser interferometer space antenna (LISA). For frequencies ν below 3×10-4Hz the dominant contribution is from the near zone time-dependent gravitational quadrupole moments associated with the normal modes of oscillation. For frequencies ν above 3×10-4Hz the dominant contribution is from gravitational radiation generated by the quadrupole oscillations which is larger than the Newtonian signal by a factor of the order (2πrν/c)4, where r is the distance to the Sun, and c is the velocity of light. The low order solar quadrupole pressure and gravity oscillation modes have not yet been detected above the solar background by helioseismic velocity and intensity measurements. We show that for frequencies ν≲2×10-4Hz, the signal due to solar oscillations will have a higher signal to noise ratio in a LISA type space interferometer than in helioseismology measurements. Our estimates of the amplitudes needed to give a detectable signal on a LISA type space laser interferometer imply surface velocity amplitudes on the sun of the order of 1-10mm/sec in the frequency range 1×10-4-5×10-4Hz. If such modes exist with frequencies and amplitudes in this range they could be detected with a LISA type laser interferometer. Title: ``Galileo Galilei'' (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein Authors: Nobili, Anna M.; Comandi, Gian Luca; Doravari, Suresh; Bramanti, Donato; Kumar, Rajeev; Maccarrone, Francesco; Polacco, Erseo; Turyshev, Slava G.; Shao, Michael; Lipa, John; Dittus, Hansjoerg; Laemmerzhal, Claus; Peters, Achim; Mueller, Jurgen; Unnikrishnan, C. S.; Roxburgh, Ian W.; Brillet, Alain; Marchal, Christian; Luo, Jun; van der Ha, Jozef; Milyukov, Vadim; Iafolla, Valerio; Lucchesi, David; Tortora, Paolo; de Bernardis, Paolo; Palmonari, Federico; Focardi, Sergio; Zanello, Dino; Monaco, Salvatore; Mengali, Giovanni; Anselmo, Luciano; Iorio, Lorenzo; Knezevic, Zoran Bibcode: 2009ExA....23..689N Altcode: 2009ExA...tmp....2N “Galileo Galilei” (GG) is a small satellite designed to fly in low Earth orbit with the goal of testing the Equivalence Principle—which is at the basis of the General Theory of Relativity—to 1 part in 1017. If successful, it would improve current laboratory results by 4 orders of magnitude. A confirmation would strongly constrain theories; proof of violation is believed to lead to a scientific revolution. The experiment design allows it to be carried out at ambient temperature inside a small 1-axis stabilized satellite (250 kg total mass). GG is under investigation at Phase A-2 level by ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino, while a laboratory prototype (known as GGG) is operational at INFN laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica Nucleare) and ASI. A final study report will be published in 2009. Title: Small separations and phase shift differences of ℓ = 0, 1 p-modes Authors: Roxburgh, I. W. Bibcode: 2009A&A...493..185R Altcode: Aims: We investigate the diagnostic potential of ℓ = 0,1 p-modes and the origin of the periodicity in their small separations.
Methods: We used theoretical analysis, phase-shifts, modelling. and data analysis.
Results: The periodicity in the small separations between modes of ℓ = 0, 1 is determined by the acoustic radius of the base of the outer convective envelope. The mean variation is determined primarily by the structure of the inner core. The separations are related to the inner phase shifts differences δ_1-δ0 which we show can be determined directly from the frequencies. The modulation period is shifted slightly by the frequency dependence of the phase shifts and the amplitudes. We present results using data from the BiSON, IRIS, and GOLF experiments, and a solar model, all of which give a modulation period of ~359±5 μHz corresponding to an acoustic radius ~1422±20 s. Title: First asteroseismic results from CoRoT Authors: Michel, E.; Baglin, A.; Weiss, W. W.; Auvergne, M.; Catala, C.; Aerts, C.; Appourchaux, T.; Barban, C.; Baudin, F.; Briquet, M.; Carrier, F.; Degroote, P.; De Ridder, J.; Garcia, R. A.; Garrido, R.; Gutiérrez-Soto, J.; Kallinger, T.; Lefevre, L.; Neiner, C.; Poretti, E.; Samadi, R.; Sarro, L.; Alecian, G.; Andrade, L.; Ballot, J.; Benomar, O.; Berthomieu, G.; Boumier, P.; Charpinet, S.; de Batz, B.; Deheuvels, S.; Dupret, M. -A.; Emilio, M.; Fabregat, J.; Facanha, W.; Floquet, M.; Frémat, Y.; Fridlund, M.; Goupil, M. -J.; Grotsch-Noels, A.; Handler, G.; Huat, A. -L.; Hubert, A. -M.; Janot-Pacheco, E.; Kjeldsen, H.; Lebreton, Y.; Leroy, B.; Martayan, C.; Mathias, P.; Miglio, A.; Montalban, J.; Monteiro, M. J. P. F. G.; Mosser, B.; Provost, J; Regulo, C.; Renan de Medeiros, J.; Ribas, I.; Roca Cortés, T.; Roxburgh, I.; Suso, J.; Thoul, A.; Toutain, T.; Tiphene, D.; Turck-Chieze, S.; Vauclair, S.; Vauclair, G.; Zwintz, K. Bibcode: 2008CoAst.156...73M Altcode: About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first results to illustrate how these data of unprecedented quality shed a new light on the field of stellar seismology. Title: CoRoT Measures Solar-Like Oscillations and Granulation in Stars Hotter Than the Sun Authors: Michel, Eric; Baglin, Annie; Auvergne, Michel; Catala, Claude; Samadi, Reza; Baudin, Frédéric; Appourchaux, Thierry; Barban, Caroline; Weiss, Werner W.; Berthomieu, Gabrielle; Boumier, Patrick; Dupret, Marc-Antoine; Garcia, Rafael A.; Fridlund, Malcolm; Garrido, Rafael; Goupil, Marie-Jo; Kjeldsen, Hans; Lebreton, Yveline; Mosser, Benoît; Grotsch-Noels, Arlette; Janot-Pacheco, Eduardo; Provost, Janine; Roxburgh, Ian W.; Thoul, Anne; Toutain, Thierry; Tiphène, Didier; Turck-Chieze, Sylvaine; Vauclair, Sylvie D.; Vauclair, Gérard P.; Aerts, Conny; Alecian, Georges; Ballot, Jérôme; Charpinet, Stéphane; Hubert, Anne-Marie; Lignières, François; Mathias, Philippe; Monteiro, Mario J. P. F. G.; Neiner, Coralie; Poretti, Ennio; Renan de Medeiros, José; Ribas, Ignasi; Rieutord, Michel L.; Roca Cortés, Teodoro; Zwintz, Konstanze Bibcode: 2008Sci...322..558M Altcode: 2008arXiv0812.1267M Oscillations of the Sun have been used to understand its interior structure. The extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. The CoRoT (Convection Rotation and Planetary Transits) satellite, launched in December 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. The oscillation amplitudes are about 1.5 times as large as those in the Sun; the stellar granulation is up to three times as high. The stellar amplitudes are about 25% below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars. Title: CoRoT sounds the stars: p-mode parameters of Sun-like oscillations on HD 49933 Authors: Appourchaux, T.; Michel, E.; Auvergne, M.; Baglin, A.; Toutain, T.; Baudin, F.; Benomar, O.; Chaplin, W. J.; Deheuvels, S.; Samadi, R.; Verner, G. A.; Boumier, P.; García, R. A.; Mosser, B.; Hulot, J. -C.; Ballot, J.; Barban, C.; Elsworth, Y.; Jiménez-Reyes, S. J.; Kjeldsen, H.; Régulo, C.; Roxburgh, I. W. Bibcode: 2008A&A...488..705A Altcode: Context: The first asteroseismology results from CoRoT are presented, on a star showing Sun-like oscillations. We have analyzed a 60 day lightcurve of high-quality photometric data collected by CoRoT on the F5 V star HD 49933. The data reveal a rich spectrum of overtones of low-degree p modes.
Aims: Our aim was to extract robust estimates of the key parameters of the p modes observed in the power spectrum of the lightcurve.
Methods: Estimation of the mode parameters was performed using maximum likelihood estimation of the power spectrum. A global fitting strategy was adopted whereby 15 mode orders of the mode spectrum (45 modes) were fitted simultaneously.
Results: The parameter estimates that we list include mode frequencies, peak linewidths, mode amplitudes, and a mean rotational frequency splitting. We find that the average large frequency (overtone) spacing derived from the fitted mode frequencies is 85.9 ± 0.15 μHz. The frequency of maximum amplitude of the radial modes is at 1760 μHz, where the observed rms mode amplitude is 3.75 ± 0.23 ppm. The mean rotational splitting of the non-radial modes appears to be in the range ≈2.7 μHz to ≈3.4 μHz. The angle of inclination offered by the star, as determined by fits to the amplitude ratios of the modes, appears to be in the range ≈50 degrees to ≈62 degrees.

The CoRoT space mission, launched on

2006 December 27, was developed and is operated by the CNES, with

participation of the Science Programs of ESA, ESA's RSSD, Austria,

Belgium, Brazil, Germany and Spain. Title: The STAROX stellar evolution code Authors: Roxburgh, Ian W. Bibcode: 2008Ap&SS.316...75R Altcode: 2007Ap&SS.tmp..434R This paper describes the STAROX stellar evolution code for the calculation of the evolution of a model of a spherical star. The code calculates a model at time t k , that is the run of pressure, density, temperature, radius, energy flux and related variables on a mesh in mass M i , given the distribution of chemical elements X j ( i) at t k and the model at the previous time step t k-1. It then advances the chemical composition to the next time step t k+1 and calculates a new model at time t k+1. This process is iterated to convergence. The model equations are solved by Newton Raphson relaxation; the chemical equations are solved by an iterative procedure, each element being advanced in turn, and the process repeated to convergence. Convection is modelled by a mixing length model and convective mixing is treated as a diffusive process; chemical overshooting can be incorporated in parametric form. The equation of state is taken from OPAL tables and the opacity from a blend of OPAL and Alexander tables. Nuclear reaction rates are from NACRE but only cover the p p chain and CNO cycle. The atmospheric layers are incorporated in the model by applying the surface boundary condition at small optical depth ( τ≈0.001). The mesh in mass M i is usually taken as fixed except that there is a moveable mesh point at the boundary of a convective core. Results are given for models of mass 0.9 and 5.0 M with initial composition X=0.7, Z=0.02 evolved to a state where the central hydrogen abundance is X c =0.35, and for a model of mass 2.0 M with initial X=0.72, Z=0.02, evolved to X c =0.01 and with core overshooting. In this latter case we compute two models one with and one without a moveable mesh point at the boundary of the convective core to illustrate the importance of having such a moveable mesh point for the determination of the Brunt Väisälä frequency in the layers outside the core. Title: The OSCROX stellar oscillaton code Authors: Roxburgh, Ian W. Bibcode: 2008Ap&SS.316..141R Altcode: 2007Ap&SS.tmp..342R This paper describes the OSCROX stellar oscillation code for the calculation of the adiabatic oscillations of low degree ℓ of a spherical star. There are two principal versions: one in Lagrangian variables (oscroxL), the second in Eulerian variables (oscroxE). The Lagrangian code does not require values of the Brunt Väisälä frequency or equivalently the density gradient. For ℓ=1 the oscillation equations have both an exact integral and an exact partial wave solution, and codes oscroxL1 and oscroxE1 incorporate these exact solutions. The difference in the frequencies obtained with the various codes gives some estimate of the uncertainty in the results due both to limited accuracy of hydrostatic support of the stellar model, and the limited accuracy of the integration of the oscillation equations. We compare the results of the different methods by calculating the frequencies in the range 20 2500 μHz of a model of a 1.5 M main-sequence star (ModelJC) kindly provided by J. Christensen-Dalsgaard for the purposes of cross comparison of codes, a modified version of this model (ModelJCA) with improved hydrostatic support, and of a highly accurate n=3 polytropic model of a star with the same mass and radius. For the polytropic model the frequencies as calculated by all codes agree to within 0.001 μHz, whereas for the 1.5 M main sequence model the frequency differences reach a maximum of 0.04 μHz, due primarily to the limited accuracy of hydrostatic support in the model; this is reduced to 0.01 μHz for ModelJCA. Title: CoRoT/ESTA TASK 1 and TASK 3 comparison of the internal structure and seismic properties of representative stellar models. Comparisons between the ASTEC, CESAM, CLES, GARSTEC and STAROX codes Authors: Lebreton, Yveline; Montalbán, Josefina; Christensen-Dalsgaard, Jørgen; Roxburgh, Ian W.; Weiss, Achim Bibcode: 2008Ap&SS.316..187L Altcode: 2008arXiv0801.0928L; 2008Ap&SS.tmp...39L We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT. Title: The CoRoT evolution and seismic tools activity. Goals and tasks Authors: Lebreton, Y.; Monteiro, M. J. P. F. G.; Montalbán, J.; Moya, A.; Baglin, A.; Christensen-Dalsgaard, J.; Goupil, M. -J.; Michel, E.; Provost, J.; Roxburgh, I. W.; Scuflaire, R.; ESTA Team Bibcode: 2008Ap&SS.316....1L Altcode: 2008arXiv0805.0977L; 2008Ap&SS.tmp..157L The forthcoming data expected from space missions such as CoRoT require the capacity of the available tools to provide accurate models whose numerical precision is well above the expected observational errors. In order to secure that these tools meet the specifications, a team has been established to test and, when necessary, to improve the codes available in the community. The CoRoT Evolution and Seismic Tool Activity (ESTA) has been set up with this mission. Several groups have been involved. The present paper describes the motivation and the organisation of this activity, providing the context and the basis for the presentation of the results that have been achieved so far. This is not a finished task as future even better data will continue to demand more precise and complete tools for asteroseismology. Title: Inter-comparison of the g-, f- and p-modes calculated using different oscillation codes for a given stellar model Authors: Moya, A.; Christensen-Dalsgaard, J.; Charpinet, S.; Lebreton, Y.; Miglio, A.; Montalbán, J.; Monteiro, M. J. P. F. G.; Provost, J.; Roxburgh, I. W.; Scuflaire, R.; Suárez, J. C.; Suran, M. Bibcode: 2008Ap&SS.316..231M Altcode: 2007arXiv0711.2587M; 2008Ap&SS.tmp...49M In order to make asteroseismology a powerful tool to explore stellar interiors, different numerical codes should give the same oscillation frequencies for the same input physics. Any differences found when comparing the numerical values of the eigenfrequencies will be an important piece of information regarding the numerical structure of the code. The ESTA group was created to analyze the non-physical sources of these differences. The work presented in this report is a part of Task 2 of the ESTA group. Basically the work is devoted to test, compare and, if needed, optimize the seismic codes used to calculate the eigenfrequencies to be finally compared with observations. The first step in this comparison is presented here. The oscillation codes of nine research groups in the field have been used in this study. The same physics has been imposed for all the codes in order to isolate the non-physical dependence of any possible difference. Two equilibrium models with different grids, 2172 and 4042 mesh points, have been used, and the latter model includes an explicit modelling of semiconvection just outside the convective core. Comparing the results for these two models illustrates the effect of the number of mesh points and their distribution in particularly critical parts of the model, such as the steep composition gradient outside the convective core. A comprehensive study of the frequency differences found for the different codes is given as well. These differences are mainly due to the use of different numerical integration schemes. The number of mesh points and their distribution are crucial for interpreting the results. The use of a second-order integration scheme plus a Richardson extrapolation provides similar results to a fourth-order integration scheme. The proper numerical description of the Brunt-Väisälä frequency in the equilibrium model is also critical for some modes. This influence depends on the set of the eigenfunctions used for the solution of the differential equations. An unexpected result of this study is the high sensitivity of the frequency differences to the inconsistent use of values of the gravitational constant ( G) in the oscillation codes, within the range of the experimentally determined ones, which differ from the value used to compute the equilibrium model. This effect can provide differences for a given equilibrium model substantially larger than those resulting from the use of different codes or numerical techniques; the actual differences between the values of G used by the different codes account for much of the frequency differences found here. Title: Sir Hermann Bondi KCB Authors: Roxburgh, Ian W. Bibcode: 2007BMFRS..53...45R Altcode: Hermann Bondi was an Applied Mathematician of distinction who will be remembered by fellow scientists for his outstanding contributions to astronomy, cosmology and General Relativity, and particularly for his pioneering contributions to our understanding of gravitational waves, his foundational work on accretion, and as co-creator with Tommy Gold and Fred Hoyle of the steady state theory of cosmology. But Hermann had an equally important second career in scientific administration: advising the UK Government on the Thames Barrier, as Director General of the European Space Research Organisation (ESRO; now the European Space Agency (ESA)), as Chief Scientific Advisor to the UK Government on Defence and then on Energy, as Chairman of the Natural Environmental Research Council (NERC), and finally as Master of Churchill College, Cambridge. He was knighted in 1973. He continued his research on gravitational radiation throughout his administrative career and published his 16th paper in the series on gravitational waves in 2004. Hermann will be remembered not only for his contributions to science and administration, but for his outstanding communication skills and as a charismatic, warm, and stimulating person. Title: Joint Discussion 17 Highlights of recent progress in the seismology of the Sun and Sun-like stars Authors: Bedding, Timothy R.; Brun, Allan S.; Christensen-Dalsgaard, Jørgen; Crouch, Ashley; De Cat, Peter; García, Raphael A.; Gizon, Laurent; Hill, Frank; Kjeldsen, Hans; Leibacher, John W.; Maillard, Jean-Pierre; Mathis, S.; Rabello-Soares, M. Cristina; Rozelot, Jean-Pierre; Rempel, Matthias; Roxburgh, Ian W.; Samadi, Réza; Talon, Suzanne; Thompson, Michael J. Bibcode: 2007HiA....14..491B Altcode: The seismology and physics of localized structures beneath the surface of the Sun takes on a special significance with the completion in 2006 of a solar cycle of observations by the ground-based Global Oscillation Network Group (GONG) and by the instruments on board the Solar and Heliospheric Observatory (SOHO). Of course, the spatially unresolved Birmingham Solar Oscillation Network (BiSON) has been observing for even longer. At the same time, the testing of models of stellar structure moves into high gear with the extension of deep probes from the Sun to other solar-like stars and other multi-mode pulsators, with ever-improving observations made from the ground, the success of the MOST satellite, and the recently launched CoRoT satellite. Here we report the current state of the two closely related and rapidly developing fields of helio- and asteroseimology. Title: Acoustic wave reflection by stellar cores: can it be seen in the autocorrelation function of p-mode measurements? Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2007MNRAS.379..801R Altcode: 2007MNRAS.tmp..557R The rapid variation of density with depth in a stellar core can distort acoustic wave propagation in stellar interiors, producing a reflected wave. The reflectivity can come from a rapid density change at the boundary of a convective core, or from the steep gradients established in a radiative core during chemical evolution. We analyse this wave reflection within the framework of wave scattering theory, and address the question of the detectability of the reflected wave in the autocorrelation function of stellar p-mode measurements. Title: The PLATO mission concept Authors: Roxburgh, Ian; Catala, Claude; PLATO Consortium Bibcode: 2007CoAst.150..357R Altcode: PLATO is a project for a future space mission that is intended to be submitted in response to the upcoming ESA "Cosmic Vision" announcement of opportunity. The science goal of PLATO is to provide a solid observational basis to understand the formation and evolution of stars and their planetary systems. This goal will be achieved by determining statistically the distribution of sizes and orbits of exoplanets, down to sub-earth sized planets and up to orbits at several AU, and the properties of their parent stars through asteroseismology. The observational concept of PLATO is based on ultra-high precision photometry from space. The strategy is to identify a sample of more than 100 000 bright stars, and to perform on all of them a long-term high precision monitoring in white-light visible photometry. This monitoring will be used on one hand to search for and characterize planetary transits in front of these stars, and on the other hand to detect and analyse oscillations of the same stars and thus probe their internal structure and dynamics. The requirements for such a mission are challenging: a very wide field-of-view, near 900 square degrees, as well as a large effective collecting area, of the order of 1 m^2, are necessary to monitor simultaneously a sufficiently large sample of bright stars, with a sufficient photometric precision. The duration of the monitoring must be of at least 5 years. We present an example of instrumental concept compliant with these requirements. It involves a large number of small pupil optics, each one illuminating its own large format focal plane. Although challenging, this concept builds on heritage from previous missions and previous studies, and presents a low technological risk. Detailed industrial studies of the proposed mission are currently being undertaken by Astrium and by Alcatel/Alenia, and the final form of the mission concept to be submitted to ESA will doubtless draw heavily on these studies. Due to secrecy agreements with these companies we are not permitted, at this time, to discuss the current stage of their studies. Title: Convection in Astrophysics (IAU S239) Authors: Kupka, Friedrich; Roxburgh, Ian; Chan, Kwing Lam Bibcode: 2007IAUS..239.....K Altcode: Preface; Session A. Modelling convection and radiative transfer; Session B. Observational probes of convection; Session C. Convection in planets and brown dwarfs; Session D. Stellar evolution, nucleosynthesis and convective mixing; Session E. Oscillations, mass loss and convection; Session F. Convection and rotation; Session G. MHD convection and dynamos. Title: Reynolds stress models of convection in convective cores Authors: Roxburgh, Ian W.; Kupka, Friedrich Bibcode: 2007IAUS..239...77R Altcode: No abstract at ADS Title: Mixing length model of convection in stellar cores Authors: Roxburgh, Ian W.; Kupka, Friedrich Bibcode: 2007IAUS..239...98R Altcode: No abstract at ADS Title: Round table discussion of session F: convection and rotation Authors: Roxburgh, Ian W. Bibcode: 2007IAUS..239..443R Altcode: No abstract at ADS Title: Evaluation of the Scientific Performances for the Seismology Programme Authors: Appourchaux, T.; Berthomieu, G.; Michel, E.; Ballot, J.; Barban, C.; Baudin, F.; Boumier, P.; De Ridder, J.; Floquet, M.; Garcia, R. A.; Garrido, R.; Goupil, M. -J.; Lambert, P.; Lochard, J.; Mazumdar, A.; Neiner, C.; Poretti, E.; Provost, J.; Roxburgh, I.; Samadi, R.; Toutain, T. Bibcode: 2006ESASP1306..429A Altcode: The Data Analysis Team of the Seismology Working Group of COROT performed several hare-and-hound exercises. These exercises aimed at putting the team in a situation as if they would analyze data coming out of the COROT spacecraft. In total the team performed five different exercises simulating solar-like stars (HH#1, HH#2, HH#3), classical pulsators (HH#5), validating seismic calibration of stellar model (HH#2, HH#3) and pushing the limit of detection (HH#4). This paper tries both to serve as a summary and as a portal to other publications of the DAT. Title: Data Analysis Tools for the Seismology Programme Authors: Appourchaux, T.; Berthomieu, G.; Michel, E.; Aerts, C.; Ballot, J.; Barban, C.; Baudin, F.; Boumier, P.; De Ridder, J.; Floquet, M.; Garcia, R. A.; Garrido, R.; Goupil, M. -J.; Lambert, P.; Lochard, J.; Neiner, C.; Poretti, E.; Provost, J.; Roxburgh, I.; Samadi, R.; Toutain, T. Bibcode: 2006ESASP1306..377A Altcode: Tools developed by helioseismologists and by classical-pulsator astronomers have been used in the hare-and-hound exercises for having a several different ways of deriving the oscillation mode parameters such as frequency or amplitude. These tools are used for deriving what we call recipes that will allow us to obtain the mode parameters from light curves either for solar-like stars or for classical pulsators. The recipes are used for tagging the mode parameters as being those of COROT. They will be used as reference or yardstick for other fitting strategies. We will also address the issue of mode detection. Additional tools such as time-frequency analysis will be presented. Title: The Quest for a European Space Mission in Stellar Seismology and Planet Finding Authors: Roxburgh, Ian W. Bibcode: 2006ESASP1306..521R Altcode: The idea of a space mission for stellar activity and seismology was conceived in France 1981-2 and underwent a series of developments leading to the EVRIS experiment as a passenger experiment on Mars96. Modified versions of EVRIS were proposed for other missions including SOHO, and it was eventually launched on Mars96 and immediately lost when Mars96 failed. In parallel more ambitious and larger missions were proposed to ESA including PRISMA, STARS and Eddington. CoRoT was originally conceived as a follow up mission to EVRIS but has matured into the present CNES/International project that is the subject of this volume. Initially these missions were devoted to stellar seismology and activity, but were expanded to incorporate searching for planets. The Eddington mission was initially selected by ESA in 2000 with reserve status, then fully approved in 2002, but withdrawn from the ESA programme in 2004, as part of the programme reduction needed to solve the financial problems of ESA's Science Programme. The small Danish seismology mission MONS was approved in 2002 but also subsequently cancelled, whereas the Canadian microsatellite mission MOST was proposed in 1997, successfully launched in 2003 and is currently collecting data. Title: Report on the CoRoT Evolution and Seismic Tools Activity Authors: Monteiro, M. J. P. F. G.; Lebreton, Y.; Montalban, J.; Christensen-Dalsgaard, J.; Castro, M.; Degl'Innocenti, S.; Moya, A.; Roxburgh, I. W.; Scuflaire, R.; Baglin, A.; Cunha, M. S.; Eggenberger, P.; Fernandes, J.; Goupil, M. J.; Hui-Bon-Hoa, A.; Marconi, M.; Marques, J. P.; Michel, E.; Miglio, A.; Morel, P.; Pichon, B.; Prada Moroni, P. G.; Provost, J.; Ruoppo, A.; Suarez, J. -C.; Suran, M.; Teixeira, T. C. Bibcode: 2006ESASP1306..363M Altcode: 2006astro.ph..5685M We present the work undertaken by the Evolution and Seismic Tools Activity (ESTA) team of the CoRoT Seismology Working Group. We have focused on two main tasks: Task 1 now finished has aimed at testing, comparing and optimising seven stellar evolution codes which will be used to model the internal structure and evolution of the CoRoT target stars. Task 2, still underway, aims at testing, comparing and optimising different seismic codes used to calculate the oscillations of models for different types of stars. The results already obtained are quite satisfactory, showing minor differences between the different numerical tools provided the same assumptions on the physical parameters are made. This work gives us confidence on the numerical tools that will be available to interpret the future CoRoT seismic data. Title: The Seismology Programme of CoRoT Authors: Michel, E.; Baglin, A.; Auvergne, M.; Catala, C.; Aerts, C.; Alecian, G.; Amado, P.; Appourchaux, T.; Ausseloos, M.; Ballot, J.; Barban, C.; Baudin, F.; Berthomieu, G.; Boumier, P.; Bohm, T.; Briquet, M.; Charpinet, S.; Cunha, M. S.; De Cat, P.; Dupret, M. A.; Fabregat, J.; Floquet, M.; Fremat, Y.; Garrido, R.; Garcia, R. A.; Goupil, M. -J.; Handler, G.; Hubert, A. -M.; Janot-Pacheco, E.; Lambert, P.; Lebreton, Y.; Lignieres, F.; Lochard, J.; Martin-Ruiz, S.; Mathias, P.; Mazumdar, A.; Mittermayer, P.; Montalban, J.; Monteiro, M. J. P. F. G.; Morel, P.; Mosser, B.; Moya, A.; Neiner, C.; Nghiem, P.; Noels, A.; Oehlinger, J.; Poretti, E.; Provost, J.; Renan de Medeiros, J.; De Ridder, J.; Rieutord, M.; Roca-Cortes, T.; Roxburgh, I.; Samadi, R.; Scuflaire, R.; Suarez, J. C.; Theado, S.; Thoul, A.; Toutain, T.; Turck-Chieze, S.; Uytterhoeven, K.; Vauclair, G.; Vauclair, S.; Weiss, W. W.; Zwintz, K. Bibcode: 2006ESASP1306...39M Altcode: 2008arXiv0811.1080M We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution. Title: The European Space Agency's Science Program and CoRoT Authors: Fridlund, M.; Roxburgh, I.; Favata, F.; Volonté, S. Bibcode: 2006ESASP1306..135F Altcode: No abstract at ADS Title: Seismic Determination of Stellar Parameters Authors: Provost, J.; Berthomieu, G.; Gonczi, G.; Morel, P.; Toutain, T.; Barban, C.; Goupil, M. -J.; Lebreton, Y.; Michel, E.; Roxburgh, I. Bibcode: 2006ESASP1306..443P Altcode: In the context of the preparation for CoRoT, we have studied some theoretical properties of the frequencies of solar-like stars. In order to prepare for the interpretation of future data, we have defined between Meudon (LESIA) and Nice (Cassini) an hare and hounds exercise as follows: from a set of frequencies provided by each group and given to the other group, find the characteristics of the corresponding stellar model. Here are reported preliminary results obtained by the Nice group. A discussion on the numerical accuracy of theoretical frequencies is also given. Title: The DynaMICS perspective Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies, S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.; Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.; Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat, E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.; Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes, I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.; Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.; Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.; Thompson, M.; Vauclair, S.; Zahn, J. P. Bibcode: 2006ESASP.624E..24T Altcode: 2006soho...18E..24T No abstract at ADS Title: 2-dimensional models of rapidly rotating stars. II. Hydrostatic and acoustic models with Ω=Ω(r,θ) Authors: Roxburgh, I. W. Bibcode: 2006A&A...454..883R Altcode: Aims.We show how to construct 2-dimensional models of rapidly rotating stars in hydrostatic equilibrium for any Ω(r,θ), given the density ρ_m(r) along any one angle θ_m. If the hydrogen abundance X_m(r) is given on θm then the adiabatic exponent Γ_1(r,θ) can by determined, yielding a self consistent acoustic model that can be used to investigate the oscillation properties of rapidly rotating stars.
Methods: .The system of equations governing the hydrostatic structure is solved by iteration using the method of characteristics and spectral expansion, subject to the condition that ρ(r,θ)=ρ_m(r) on θ=θ_m. Γ_1(r,θ) is calculated from the equation of state under the assumption that X(r,θ_m)=X_m(r) and is constant on surfaces of constant entropy. Alternatively Γ1 can be approximated by taking X constant in the equation of state and equal to the surface value.
Results: .Results are presented for an evolved main sequence star of 2~M_⊙ with the angular velocity a function only of radius Ω=Ω(r), evolved to a central hydrogen abundance of X_c=0.35. The model is first calculated using a spherically averaged stellar evolution code, where the averaged centrifugal force 2Ω2 r/3 is added to gravity. The resulting ρ_m(r), X_m(r) are then used as input to determine the 2-dimensional model.
Conclusions: .The procedure described here gives self consistent hydrostatic and acoustic models of rapidly rotating stars for any Ω(r,θ). Title: PLATO: PLAnetary Transits and Oscillations of stars Authors: Roxburgh, I. W.; Catala, C. Bibcode: 2006IAUJD..17E..32R Altcode: PLATO is a project for a future space mission that is intended to be presented in response to the upcoming ESA "Cosmic Vision" announcement of opportunity. The science goal of PLATO is to provide a solid observational basis to understand the formation and evolution of stars and their planetary systems. This goal will be achieved by determining statistically the distribution of sizes and orbits of exoplanets, down to sub-earth sized planets and up to orbits at several AU. The observational concept of PLATO is based on ultra-high precision photometry from space. The strategy is to identify a sample of more than 100,000 bright stars, and to perform on all of them a long-term high precision monitoring in white-light visible photometry. This monitoring will be used on one hand to search for and characterize planetary transits in front of these stars, and on the other hand to detect and analyse oscillations of the same stars and thus probe their internal structure and dynamics. The requirements for such a mission are challenging: a very wide field-of-view, near 900 square degrees, as well as a large effective collecting area, of the order of one square metre, are necessary to monitor simultaneously a sufficiently large sample of bright stars, with a sufficient photometric precision. The duration of the monitoring must be of at least five years. We present an example instrumental concept compliant with these requirements. It involves a large number of small pupil optics, each one illuminating its own large format focal plane. Although challenging, this concept builds on heritage from previous missions and previous studies, and presents a low technological risk. Title: The CoRoT mission: Asteroseismology and Planet Finding Authors: Roxburgh, I. W.; Baglin, A. Bibcode: 2006IAUJD..17E..31R Altcode: The CoRoT mission, scheduled for launch in October 2006, has two core science goals: the detection and characterisation of planets, both earth like and gaseous giants, around other stars; and the detection of oscillations of selected target stars and the use of such oscillations to probe the interior structure and dynamics of stars, and so to test and develop our understanding of stellar structure and evolution. CoRoT has been developed within the framework of the French CNES small- satellite programme, with contributions from Austria, Belgium, Brazil, ESA, ESTEC, Germany, and Spain. It will perform relatively broad- band photometry in visible light with a 28 cm off- axis telescope and four CCDs, two of which are devoted to the planet search programme and two to the seismology programme. It will have several ( five or six ) long observing runs (150 days) on several target fields; in the seismology programme it will simultaneously observe ten target stars per field (with m[v][ ] < 9), chosen to give wide coverage of the H-R diagram. In addition to the long runs there will be two initial runs of 60 and 30 days duration, and five or six short runs of 20 days. There is a Guest Investigator programme in which the data from the planet search fields (about 4000 stars) can be used for seismology on fainter stars, and for other science goals than planet finding, and a few short runs which can be for other science than the core planet finding and seismology. Title: Scientific Objectives of the Novel Formation Flying Mission Aspiics Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies, S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.; Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.; Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat, E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.; Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes, I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.; Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.; Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.; Thompson, M.; Vauclair, S.; Zahn, J. P. Bibcode: 2006ESASP.617E.164L Altcode: 2006soho...17E.164L No abstract at ADS Title: The EUV Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO): Science Plan and Instrument Overview Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies, S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.; Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.; Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat, E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.; Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes, I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.; Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.; Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.; Thompson, M.; Vauclair, S.; Zahn, J. P. Bibcode: 2006ESASP.617E.165W Altcode: 2006soho...17E.165W No abstract at ADS Title: The autocorrelation function of stellar p-mode measurements and its diagnostic properties Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2006MNRAS.369.1491R Altcode: 2006MNRAS.tmp..549R The basic properties of acoustic wave propagation in stellar interiors can be analysed from the autocorrelation function (ACF) of intensity (or velocity) observations without measuring the resonant p-mode frequencies. We show how the strength of acoustic wave refraction in the stellar core, or forward acoustic amplitude, can be measured from a modulation in the ACF. This is the basic physical quantity which governs the so-called `small frequency separations', and its measurement from the ACF can be used for determining the small frequency separations when the data is of insufficient quality for a reliable identification of the stellar p-mode frequencies. Title: The Dynamics Project Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies, S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.; Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.; Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat, E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.; Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes, I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.; Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.; Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.; Thompson, M.; Vauclair, S.; Zahn, J. P. Bibcode: 2006ESASP.617E.162T Altcode: 2006soho...17E.162T No abstract at ADS Title: The life of stars and their planets Authors: Catala, C.; Aerts, C.; Aigrain, S.; Antonello, E.; Appourchaux, T.; Auvergne, M.; Baglin, A.; Barge, P.; Barstow, M. A.; Baudin, F.; Boumier, P.; Collier Cameron, A.; Christensen-Dalsgaard, J.; Cutispoto, G.; Deeg, H.; Deleuil, M.; Desidera, S.; Donati, J. -F.; Favata, F.; Foing, B. H.; Gameiro, J. F.; Garcia, R.; Garrido, F.; Horne, K.; Lanza, A. F.; Lanzafame, A. C.; Lecavelier Des Etangs, A.; Léger, A.; Mas-Hesse, M.; Messina, S.; Micela, G.; Michel, E.; Monteiro, M. J. P. F. G.; Mosser, B.; Noels, A.; Pagano, I.; Piotto, G.; Poretti, E.; Rauer, H.; Roca-Cortes, T.; Rodono, M.; Rouan, D.; Roxburgh, I.; Schneider, J.; Strassmeier, K.; Turck-Chièze, S.; Vauclair, S.; Vidal-Madjar, A.; Weiss, W. W.; Wheatley, P. Bibcode: 2005ESASP.588...99C Altcode: 2005tssc.conf...99C We lack a reliable scenario for the formation and evolution of stars and their planetary systems, involving key factors such as magnetic fields and turbulence. We present the case for a mission concept that will clarify these problems and give us a global view of the evolution of combined star and planetary systems. This will be achieved by simultaneously addressing the search for planetary transits in front of a large number of stars, including many nearby stars, the study of their internal structure and evolution via asteroseismology, and that of their magnetic activity, via UV monitoring. Title: The ratio of small to large separations of stellar p-modes Authors: Roxburgh, I. W. Bibcode: 2005A&A...434..665R Altcode: In previous papers we showed that the ratios of the small to large separations of acoustic oscillations in solar-like stars are approximately independent of the structure of the outer layers, and are therefore diagnostics of the interior structure alone. Here we present similar results for a range stellar models of mass 0.8, 1.0, 1.2, 1.5, 2, 10~ M_⊙, all of which show this same property. Title: 2-dimensional models of rapidly rotating stars I. Uniformly rotating zero age main sequence stars Authors: Roxburgh, I. W. Bibcode: 2004A&A...428..171R Altcode: We present results for 2-dimensional models of rapidly rotating main sequence stars for the case where the angular velocity Ω is constant throughout the star. The algorithm used solves for the structure on equipotential surfaces and iteratively updates the total potential, solving Poisson's equation by Legendre polynomial decomposition; the algorithm can readily be extended to include rotation constant on cylinders. We show that this only requires a small number of Legendre polynomials to accurately represent the solution. We present results for models of homogeneous zero age main sequence stars of mass 1, 2, 5, 10 M with a range of angular velocities up to break up. The models have a composition X=0.70, Z=0.02 and were computed using the OPAL equation of state and OPAL/Alexander opacities, and a mixing length model of convection modified to include the effect of rotation. The models all show a decrease in luminosity L and polar radius Rp with increasing angular velocity, the magnitude of the decrease varying with mass but of the order of a few percent for rapid rotation, and an increase in equatorial radius Re. Due to the contribution of the gravitational multipole moments the parameter Ω2 Re3/GM can exceed unity in very rapidly rotating stars and Re/Rp can exceed 1.5. Title: The Eddington Mission Authors: Roxburgh, I.; Favata, F. Bibcode: 2004IAUS..215..323R Altcode: No abstract at ADS Title: Planet Detection Capabilities of the Eddington Mission Authors: Deeg, Hans J.; Horne, Keith; Favata, Fabio; Eddington Science Team; Aerts, C.; Antonello, E.; Badiali, M.; Catala, C.; Christensen-Dalsgaard, J.; Gimenez, A.; Grenon, M.; Penny, A.; Rauer, H.; Roxburgh, I. W.; Schneider, J.; Waltham, N. R. Bibcode: 2004IAUS..202..448D Altcode: No abstract at ADS Title: Small frequency separations as seen in the autocorrelation function of the whole-disk measurements Authors: Kholikov, Sh. S.; Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2004ESASP.538..331K Altcode: 2004sshp.conf..331K We address the origin of the apparent modulation in the amplitudes of the even and odd peaks in the autocorrelation function of whole-disk measurements, and show that this modulation is directly related to the small frequency separations of the low-degree p-modes. This modulation can be used for estimating the small separations when the data quality is insufficient for reliable identification of oscillation frequencies in noisy power spectra. Title: Eddington and the internal constitution of the stars Authors: Roxburgh, I. W. Bibcode: 2004ESASP.538...23R Altcode: 2004sshp.conf...23R Eddington will provide sets of frequencies of multimode oscillations for a very large number of stars of different masses, ages, compositions and angular velocities. This will enable us to infer their interior structure and dynamics, and hence to test our current understanding of stellar structure and to develop an empirically based theory of stellar evolution. Here I discuss some of the techniques available for inferring the structure of stars from a given set of frequencies. In particular, I demonstrate that, at least in solar type stars, the ratio of small to large separations subtracts off the contribution of the surface layers yielding a diagnostic of the stellar interior alone. Title: Science requirements and their translation into instrumental design Authors: Catala, C.; Aricha, A.; Boulade, O.; Diaz, E.; Epstein, G.; Favata, F.; Horne, K.; Kjeldsen, H.; Lumb, D.; Mas-Hesse, M.; Roxburgh, I. W. Bibcode: 2004ESASP.538...39C Altcode: 2004sshp.conf...39C The detailed science requirement of Eddington are reviewed, as derived from the major scientific objectives of the mission. An analysis of these requirements in terms of basic mission specifications is then given, in particular concerning the focal plane assembly and the CCD operation mode. Title: The scattering of acoustic waves by a stellar core as seen in the small frequency separations Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2004ESASP.538..403R Altcode: 2004sshp.conf..403R The propagation of acoustic waves in the interior of relatively young stars is nearly classical and can be accurately described by ray-tracing techniques. At later stages of evolution, the development of a steep density gradient in the central core leads to wave diffraction and partial wave scattering. Scattering is also produced by a small convective core with a rapid density variation at the boundary. We discuss the signatures of this scattering in the small frequency separations of low-degree p-modes. Title: The ratio of small to large separations of acoustic oscillations as a diagnostic of the interior of solar-like stars Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2003A&A...411..215R Altcode: By considering stellar models with the same interior structure but different outer layers we demonstrate that the ratio of the small to large separations of acoustic oscillations in solar-like stars is essentially independent of the structure of the outer layers, and is determined solely by the interior structure. Defining the scaled Eulerian pressure perturbation psil (omega ,t) = r p' /(rho c)1/2 we define the internal phase shift deltal (omega ,t) through the relation omega psi /(dpsi /dt)=tan (omega t -pil /2 + deltal ). The deltal are almost independent of acoustic radius t=int dr/c outside the stellar core and can be determined as a continuous functions of omega from partial wave solutions for the interior - that is solutions of the oscillation equations for any omega that satisfy the Laplace boundary condition at a sufficiently large acoustic radius tf outside the stellar core. If the omega are eigenfrequencies then they satisfy the Eigenfrequency Equation omega T=(n+l/2) pi +alpha (omega )-deltal (omega ) where alpha (omega ) is the l independent surface phase shift (Roxburgh & Vorontsov 2000). Using this result we show that the ratio of small to large separations is determined to high accuracy solely by the internal phase shifts deltal (omega ) and hence by the interior structure alone. The error in this result is estimated and shown to be smaller than that associated with the errors in the determination of the frequencies (~0.1-0.3 mu Hz) from the upcoming space missions MOST, COROT and Eddington. Title: The cronos hydrogen maser clock redshift experiment on Radioastron Authors: Busca, G.; Bernier, L. G.; Schweda, H.; Kardashev, N.; Andreianov, V.; Roxburgh, I. W.; Polnarev, S. Bibcode: 2003AdSpR..32.1421B Altcode: The Radioastron satellite, having a highly elliptical orbit with a period of 28 hours and a mission duration of more than 3 years, offers the interesting possibility of a redshift experiment. The Space Hydrogen Maser, recently introduced as a new instrument on the satellite in order to be used as local oscillator for the Space VLBI, can in fact be tracked in frequency from the ground stations, implementing only minor modifications in the originally planned frequency transfer system. The modified system allows also the measurements of the geometric and ionospheric Doppler shifts. An analysis of the best strategy for achieving the highest measurement precision is presented. The analysis takes into account the maser frequency stability, its environmental sensitivities, and the other known sources of noise. The error budget of the experiment is established. Title: The Eddington Mission Authors: Roxburgh, I. Bibcode: 2003Ap&SS.285..363R Altcode: The Eddington mission was given full approval by the European Space Agency on the 23rd May 2002, with launch scheduled for 2007/8. Its science objectives are stellar evolution and asteroseismology, and planet finding. In its current design it consists of 4 × 60 cm folded Schmidt telescopes, each with 6o × 6o field of view and its own CCD array camera. Eddington will spend 2 years primarily devoted to asteroseismology with 1 3 months on different target fields monitoring up to 50,000 stars per field, and 3 years continuously on a single field monitoring upwards of 100,000 stars for planet searching. The asteroseismic goal is to be able to detect oscillations frequencies of stars with a precision 0.1 0.3 μHz, to probe their interior structure and the study the physical processes that govern their evolution. Title: Numerical 3D constraints on convective eddy time-correlations: Consequences for stochastic excitation of solar p modes Authors: Samadi, R.; Nordlund, Å.; Stein, R. F.; Goupil, M. J.; Roxburgh, I. Bibcode: 2003A&A...404.1129S Altcode: 2003astro.ph..4457S A 3D simulation of the upper part of the solar convective zone is used to obtain information on the frequency component, chik , of the correlation product of the turbulent velocity field. This component plays an important role in the stochastic excitation of acoustic oscillations. A time analysis of the solar simulation shows that a Gaussian function does not correctly reproduce the nu -dependency of chik inferred from the 3D simuation in the frequency range where the acoustic energy injected into the solar p modes is important (nu =~ 2 - 4 mHz). The nu -dependency of chik is fitted with different analytical functions which can then conveniently be used to compute the acoustic energy supply rate P injected into the solar radial oscillations. With constraints from a 3D simulation, adjustment of free parameters to solar data is no longer necessary and is not performed here. The result is compared with solar seismic data. Computed values of P obtained with the analytical function which fits best chik are found ~ 2.7 times larger than those obtained with the Gaussian model and reproduce better the solar seismic observations. This non-Gaussian description also leads to a Reynolds stress contribution of the same order as the one arising from the advection of the turbulent fluctuations of entropy by the turbulent motions. Some discrepancy between observed and computed P values still exist at high frequency and possible causes for this discrepancy are discussed. Title: Numerical constraints on the model of stochastic excitation of solar-type oscillations Authors: Samadi, R.; Nordlund, Å.; Stein, R. F.; Goupil, M. J.; Roxburgh, I. Bibcode: 2003A&A...403..303S Altcode: 2003astro.ph..3198S Analyses of a 3D simulation of the upper layers of a solar convective envelope provide constraints on the physical quantities which enter the theoretical formulation of a stochastic excitation model of solar p modes, for instance the convective velocities and the turbulent kinetic energy spectrum. These constraints are then used to compute the acoustic excitation rate for solar p modes, P. The resulting values are found ~ 5 times larger than the values resulting from a computation in which convective velocities and entropy fluctuations are obtained with a 1D solar envelope model built with the time-dependent, nonlocal Gough (\cite{Gough77}) extension of the mixing length formulation for convection (GMLT). This difference is mainly due to the assumed mean anisotropy properties of the velocity field in the excitation region. The 3D simulation suggests much larger horizontal velocities compared to vertical ones than in the 1D GMLT solar model. The values of P obtained with the 3D simulation constraints however are still too small compared with the values inferred from solar observations. Improvements in the description of the turbulent kinetic energy spectrum and its depth dependence yield further increased theoretical values of P which bring them closer to the observations. It is also found that the source of excitation arising from the advection of the turbulent fluctuations of entropy by the turbulent movements contributes ~ 65-75 % to the excitation and therefore remains dominant over the Reynolds stress contribution. The derived theoretical values of P obtained with the 3D simulation constraints remain smaller by a factor ~ 3 compared with the solar observations. This shows that the stochastic excitation model still needs to be improved. Title: The Eddington Mission Authors: Roxburgh, Ian; Favata, Fabio Bibcode: 2003Ap&SS.284...17R Altcode: The Eddington mission was given full approval by the European Space Agency on the 23rd May 2002, as part of the new `Cosmic Vision' Science programme, with launch scheduled for 2007/8. Its twin science objectives are asteroseismology and planet finding. In its current design it consists of 4 × 60 cm folded Schmidt telescopes, each with 6° × 6° field of view and its own CCD array camera. The current observing plan is to spend 2 years primarily devoted to asteroseismology with 1-3 months on different target fields monitoring up to 50,000 stars per field, and 3 years continuously on a single target field monitoring upwards of 100,000 stars as required for planet searching. The asteroseismic goal is to be able to detect oscillations frequencies with a precision 0.1-0.3 μHz. Title: The European Ultra-High Precision Stellar Photometry Road Map for Asteroseismology and Planet Finding Authors: Roxburgh, Ian; Favata, Fabio; Baglin, Annie; Christensen-Dalsgaard, Jørgen Bibcode: 2003acfp.conf..479R Altcode: We give a brief description of the 3 European space missions COROT, MONS and Eddington, devoted to asteroseismology and planet finding. Title: Characterizing the Dynamic Properties of the Solar Turbulence with 3-D Simulations: Consequences in Term of p-mode Excitation Authors: Samadi, R.; Nordlund, Å.; Stein, R. F.; Goupil, M. -J.; Roxburgh, I. Bibcode: 2003IAUS..210P..C2S Altcode: 2002astro.ph..8577S A 3D simulation of the upper part of the solar convective zone is used to derive constraints about the averaged and dynamic properties of solar turbulent convection. Theses constraints are then used to compute the acoustic energy supply rate P(nu) injected into the solar radial oscillations according to the theoretical expression in Samadi & Goupil (2001). The result is compared with solar seismic data. Assuming, as it is usually done, a gaussian model for the frequency (nu) component chi_k(nu) of the model of turbulence, it is found that the computed P(nu) is underestimated compared with the solar seismic data by a factor ~ 2.5. A frequency analysis of the solar simulation shows that the gaussian model indeed does not correctly model chi_k(nu) in the frequency range where the acoustic energy injected into the solar p-modes is important (nu ~ 2 - 4 mHz). One must consider an additional non-gaussian component for chi_k(nu) to reproduce its behavior. Computed values of P obtained with this non-gaussian component reproduce better the solar seismic observations. This non-gaussian component leads to a Reynolds stress contribution of the same order than the one arising from the advection of the turbulent fluctuations of entropy by the turbulent motions. Title: The Asteroseismic Diagram for =0,1 p-modes Authors: Mazumdar, A.; Roxburgh, I. Bibcode: 2003aahd.conf..477M Altcode: No abstract at ADS Title: Diagnostics of the Internal Structure of Stars using the Differential Response Technique Authors: Roxburgh, Ian; Vorontsov, Sergei Bibcode: 2003Ap&SS.284..187R Altcode: We address the problem of the diagnosing the deep interior structure of stars using acoustic p-modes, and investigate the diagnostic capabilities of two complementary approaches both based on the differential response technique (Vorontsov, 1998): (a) direct calibration using a grid of evolutionary stellar models, and (b) linear and non-linear (with consecutive linearisations) inversion of low-degree frequencies. We apply this analysis to the frequencies of a model of an old 0.8Msolar star, and to the solar frequencies obtained from BiSON measurements, using a 2-D grid of reference models of different mass and age. We explore the convergence and stability of the asteroseismic inversion, performed with the adaptive regularisation technique of Strakhov and Vorontsov (2001). Title: Consequences of the non gaussian character of the stochastic excitation for solar-type oscillations Authors: Samadi, R.; Nordlund, A.; Stein, R. F.; Goupil, M. -J.; Roxburgh, I. Bibcode: 2002sf2a.conf..489S Altcode: 2002astro.ph.10028S Stochastic excitation of stellar p-modes of low massive stars (M < 2Mo) are attribued to regular turbulent cells moving in the upper convective zone. The current calculation of the acoustic energy supply rate P - which ensures the p-modes excitation - is mainly based on this simplifying picture and thus assume a crude description of the static and dynamic properties of the turbulent medium. With the help of a 3D simulation of the solar convective zone, we show that the gaussian model does not sastisfactory model the dynamical behavior of the turbulent medium in the frequency range where the acoustic energy injected into the solar p-modes is important (frequency : 2 - 4 mHz). Instead, one has to consider an additionnal component - which slowly decreases with frequency - to reproduce better the dynamic of the turbulence. This non-gaussian component is suggested arising from presence of plumes in the solar convection region. Inclusion of it leads to a Reynolds stress contribution of the same order than the one arising from the advection of the turbulent fluctuations of entropy by the turbulent movements. In the present work we investigate some consequences of this non-gaussian component for the p-modes excitation in low massive stars (M < 2Mo) and compare our computations of P with previous estimates. Title: Semiclassical analysis of stellar p modes Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2002ESASP.485..345R Altcode: 2002sshp.conf..345R We present a brief overview of our first studies in developing classical and semiclassical approximations for low-degree stellar p modes, as an alternative to the formal high-frequency asymptotic expansions used earlier. The complete account of this work can be found in Roxburgh and Vorontsov (2000, 2001). Title: Preface (Stellar structure and habitable planet finding) Authors: Favata, Fabio; Roxburgh, Ian W.; Giménez, Alvaro Bibcode: 2002ESASP.485D...3F Altcode: 2002sshp.confD...3F No abstract at ADS Title: The tools of asteroseismology Authors: Roxburgh, I. W. Bibcode: 2002ESASP.485...75R Altcode: 2002sshp.conf...75R One of the twin goals of the Eddington mission is to measure stellar oscillations and to use the measured frequencies and line profiles to further our understanding of the structure and evolution of stars. We here cover some of the techniques that can be used to achieve this aim. Title: Inversion for the structure of a star of 1.45 Msolar using the internal phase shift Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2002ESASP.485..341R Altcode: 2002sshp.conf..341R We describe the results of an inversion for the internal structure of a star of 1.45 Msolar using the internal phase shifts. We derive the internal phase shifts from frequencies of p-modes with l = 0,1,2,3 in the range 500 - 2000 μHz, with random errors of the order of 0.3 μHz. To deduce the interior structure of the star we model the star by a set of values Di = Γ1dlogρ/dlogP at fractional mass points qi and search for the values of Di that give the best fit to the internal phase shifts. The internal density profile and the mass of the convective core are satisfactorily reproduced. Title: Stellar structure and habitable planet finding Authors: Battrick, B.; Favata, F.; Roxburgh, I. W.; Galadi, D. Bibcode: 2002ESASP.485.....B Altcode: 2002sshp.conf.....B No abstract at ADS Title: Inversion for a 0.8 Msolar star using differential-response technique Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2002ESASP.485..337R Altcode: 2002sshp.conf..337R We describe the results of an artificial asteroseismic inversion for an old 0.8 Msolar star using a limited set of low-degree p-mode frequencies. Two separate inversions were performed with artificial p-mode data in the degree range l = 0-3, frequency range ν = 1-5 mHz, and l = 0-2, ν = 2-4 mHz. The p-mode eigenfrequencies have been added with 0.3 μHz Gaussian noise. The stellar mass and radius were not supposed to be known. A recent solar model was used as an initial reference model in the iterative nonlinear inversion. Title: Probing the solar core with low-degree p modes Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2002ESASP.485..349R Altcode: 2002sshp.conf..349R We address the question of what could be learned about the solar core structure if the seismic data were limited to low-degree modes only. The results of three different experiments are described. The first is the linearized structural inversion of the p-mode frequencies of a solar model modified slightly in the energy-generating core, using the original (unmodified) model as an initial guess. In the second experiment, we invert the solar p-mode frequencies measured in the 32-month subset of BiSON data (Chaplin et al. 1998), degraded with additional 0.1 μHz random errors, using a model of 2.6 Gyr age from the solar evolutionary sequence as an initial approximation. This second inversion is non-linear. In the third experiment, we compare the same set of BiSON frequencies with current reference solar model. Title: Background to the Eddington mission Authors: Roxburgh, I. W. Bibcode: 2002ESASP.485...11R Altcode: 2002sshp.conf...11R The Eddington mission to measure stellar oscillations and search for other planets builds on a solid history of earlier proposals and studies for space missions to study stellar seismology and stellar activity and to search for planets. The idea of such a mission for stellar activity and seismology was conceived in France 1981 and underwent a series of developments leading to the EVRIS mission which was a passenger experiment on Mars96 and was lost when Mars96 failed. Subsequent proposals PRISMA and STARS underwent Phase A studies in ESA but were not selected for launch. The small French mission COROT, originally conceived as a successor to EVRIS was selected by CNES and is now scheduled for launch in 2004. The much more ambitious Eddington mission, devoted to stellar seismology and planet searching was selected as a mission (albeit with a "reserve" status) in the 2000 F2/F3 selection round in ESA. The mission is proceeding with detailed industrial and working group studies with the aim of being ready for launch in 2007/8 should the mission be fully approved as part of the ESA programme. Title: Gravitational multipole moments of the Sun determined from helioseismic estimates of the internal structure and rotation Authors: Roxburgh, I. W. Bibcode: 2001A&A...377..688R Altcode: We determine the gravitational multipole moments J2n, n=1,5, of the sun using a model of the interior structure and of solar rotation obtained from helioseismic inversions. The differential rotation of the convective zone and the underlying transition zone make only a small (~0.5%) contribution to the quadrupole moment J_2 which is found to have a value ~2.21x 10-7. Title: Solar Neutrino Emission Deduced from a Seismic Model Authors: Turck-Chièze, S.; Couvidat, S.; Kosovichev, A. G.; Gabriel, A. H.; Berthomieu, G.; Brun, A. S.; Christensen-Dalsgaard, J.; García, R. A.; Gough, D. O.; Provost, J.; Roca-Cortes, T.; Roxburgh, I. W.; Ulrich, R. K. Bibcode: 2001ApJ...555L..69T Altcode: Three helioseismic instruments on the Solar and Heliospheric Observatory have observed the Sun almost continuously since early 1996. This has led to detailed study of the biases induced by the instruments that measure intensity or Doppler velocity variation. Photospheric turbulence hardly influences the tiny signature of conditions in the energy-generating core in the low-order modes, which are therefore very informative. We use sound-speed and density profiles inferred from GOLF and MDI data including these modes, together with recent improvements to stellar model computations, to build a spherically symmetric seismically adjusted model in agreement with the observations. The model is in hydrostatic and thermal balance and produces the present observed luminosity. In constructing the model, we adopt the best physics available, although we adjust some fundamental ingredients, well within the commonly estimated errors, such as the p-p reaction rate (+1%) and the heavy-element abundance (+3.5%); we also examine the sensitivity of the density profile to the nuclear reaction rates. Then, we deduce the corresponding emitted neutrino fluxes and consequently demonstrate that it is unlikely that the deficit of the neutrino fluxes measured on Earth can be explained by a spherically symmetric classical model without neutrino flavor transitions. Finally, we discuss the limitations of our results and future developments. Title: Semiclassical approximation for low-degree stellar p modes - III. Acoustic resonances and diagnostic properties of the oscillation frequencies Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2001MNRAS.322...85R Altcode: We extend the classical approximation for low-degree acoustic oscillations to take account of the effects of wave resonances associated with the partial reflection of waves at internal boundaries in the stellar interior. We consider explicitly the effect of a rapid density variation at the boundary of the convective core on the small frequency separations, and the reflection of waves at the base of the outer convective envelope, observable in the `surface phase-shift' function. We describe a technique that allows us to infer the `surface phase-shift' function, known to be a valuable diagnostic tool in solar seismology, from frequency measurements limited to p modes of low degree only. Title: Response of a Spaceborn Gravitational Wave Antenna to Solar Oscillations Authors: Roxburgh, I. W.; Polnarev, A. G.; Giampieri, G.; Vorontsov, S. V. Bibcode: 2001astro.ph..3472R Altcode: We investigate the possibility of observing very small amplitude low frequency solar oscillations with the proposed laser interferometer space antenna LISA. For frequencies below $\sim 2\times 10^{-4}$ Hz the dominant contribution is from the near zone time dependent gravitational quadrupole moments associated with the normal modes of oscillation. For frequencies $\nu$ above $\sim 3\times 10^{-4}$ Hz the dominant contribution is from gravitational radiation generated by the quadrupole oscillations which is larger than the Newtonian signal by a factor $\sim (2 \pi r \nu/ c)^4$, where $r$ is the distance to the Sun, and $c$ is the velocity of light. The low order solar quadrupole pressure and gravity oscillation modes have not yet been detected above the solar background by helioseismic velocity and intensity measurements. Our estimates of the amplitudes needed to give a detectable signal on a LISA type space laser interferometer imply surface velocity amplitudes on the sun of the order of 1-10 mm/sec in the frequency range $1 - 5~10^{-4}$Hz. Such surface velocities are below the current sensitivity limits on helioseismic measurements. If modes exist with frequencies and amplitudes in this range they could be detected with a LISA type laser interferometer. Title: Non linear inversion for the sound speed in the solar interior using BiSON and SOI/MDI p-mode frequencies Authors: Marchenkov, K. I.; Roxburgh, I. W.; Vorontsov, S. V.; Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; New, R. Bibcode: 2001ESASP.464..531M Altcode: 2001soho...10..531M The results of the global sound-speed inversion obtained with solar p-mode frequencies provided by the recent high-quality observational data (BiSON, SOI/MDI) are presented and discussed. The iterative nonlinear inversion technique used here is a generalization (for the case of exact solution of the adiabatic oscillation equations) of the Born quasiasymptotic approximate inversion developed by Marchenkov et al. (2000). Title: Numerical Simulation of Penetrative Convection above a Stellar Convection Zone (CD-ROM Directory: contribs/singh) Authors: Singh, H. P.; Saikia, E.; Roxburgh, I. W.; Chan, K. L.; Srivastava, M. P. Bibcode: 2001ASPC..223..874S Altcode: 2001csss...11..874S No abstract at ADS Title: Semiclassical approximation for low-degree stellar p modes - I. The classical eigenfrequency equation Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2000MNRAS.317..141R Altcode: A new eigenfrequency equation for low-degree solar-like oscillations in stars is developed, based on the assumption of purely classical propagation in the stellar interior of acoustic waves modified by buoyancy and gravity. Compared with high-frequency asymptotic analysis, the eigenfrequency equation has a new functional form, with expansion in powers of l(l+1) instead of 1/ω. Basic observable quantities, the `large' and `small' frequency separations, are interpreted as the dependence on frequency and refraction angle of a classical action integral for waves propagating close to the stellar diameter. The new eigenfrequency equation gives a significant improvement in accuracy over previous analyses when tested with solar p modes, suggesting this as an alternative and more powerful tool for applications in stellar seismology. Title: Semiclassical approximation for low-degree stellar p modes - II. Classical ray tracing Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 2000MNRAS.317..151R Altcode: Using ray-tracing techniques, we consider nearly forward refraction in the stellar interior of acoustic waves modified by buoyancy and gravity. Our analysis is based on a local dispersion relation developed to second order in the high-frequency asymptotic approximation. The phase shifts δlδ0(ω)+l(l+1)Dδ (ω) of the partial waves of stellar p modes, which govern the eigenfrequency equation in its classical limit, are developed in terms of explicit integrals containing the radial profiles of seismic parameters in the stellar interior. The accuracy of the resulting description of low-degree stellar p modes is tested using an evolutionary sequence of solar models. Title: `Galileo Galilei' (GG) small-satellite project: an alternative to the torsion balance for testing the equivalence principle on Earth and in space Authors: Nobili, A. M.; Bramanti, D.; Polacco, E.; Roxburgh, I. W.; Comandi, G.; Catastini, G. Bibcode: 2000CQGra..17.2347N Altcode: `Galileo Galilei' (GG) is a proposal for a small, low-orbit satellite devoted to testing the equivalence principle (EP) of Galileo, Newton and Einstein. The GG report on the phase A study recently carried out with funding from ASI (Agenzia Spaziale Italiana) concluded that GG can test the equivalence principle to 1 part in 1017 at room temperature. The main novelty is to modulate the expected differential signal of an EP violation at the spin rate of the spacecraft (2 Hz). Compared with other experiments, the modulation frequency is increased by more than a factor of 104, thus reducing 1/f (low-frequency) electronic and mechanical noise. The challenge for an EP test in space is to improve over the sensitivity of ground-based experiments (about 1 part in 1012) by many orders of magnitude, so as to deeply probe a so far totally unexplored field; doing that with more than one pair of bodies is an unnecessary complication. For this reason GG is now proposed with a single pair of test masses. At present the best and most reliable laboratory-controlled tests of the equivalence principle have been achieved by the `Eöt-Wash' group with small test cylinders arranged on a torsion balance placed on a turntable which provides the modulation of the signal (a 1-2 h rotation period). The torsion balance is not a suitable instrument in space. We have designed and built the GGG (`GG on the Ground') prototype. It is made of coaxial test cylinders weakly coupled (via mechanical suspensions) and quickly rotating (6 Hz achieved so far); in addition, it is well suited to be flown in space - where the driving signal is about three orders of magnitude stronger and the absence of weight is very helpful - inside the coaxial, co-rotating GG cylindrical spacecraft. The GGG apparatus is now operational. Preliminary measurement data indicate that weakly coupled, fast-spinning macroscopic rotors can be a suitable instrument to detect small differential effects. Rotation (up to 6 Hz so far) is stabilized by a small passive oil damper. A finer active damper, using small capacitance sensors and actuators as in the design of the space experiment, is in preparation. The current sensitivity of the GGG system is of 10-9 m s-2/√Hz at about 300 s, which can be improved because horizontal seismic noise is rejected very well; perturbing effects of terrain tilts (due to microseismicity and tides) will be reduced by adding a passive cardanic suspension. As for the capacitance read-out, the current sensitivity (5 pm displacements in 1 s integration time at room temperature) is adequate to make GGG competitive with the torsion balance. Because of the stronger signal and weaker coupling of the test rotors in space, this sensitivity is also adequate for GG to reach its target accuracy (10-17). Information, references, research papers and photographs of the apparatus are available on the Web (http://tycho.dm.unipi.it/nobili). Title: Fundamental parameters of COROT seismology targets Authors: Catala, C.; Bouret, J. -C.; Butler, J.; Garrido, R.; Lignieres, F.; Roxburgh, I.; Lueftinger, T.; Soubiran, C.; Katz, D.; van't Veer, C.; Ballereau, D.; Hua, T. Bibcode: 2000mons.proc...37C Altcode: We have started a ground-based effort to determine the fundamental parameters (Teff, log g, Fe/H, vsini, etc...) of 1,100 potential targets of the COROT central and exploratory asteroseismology programmes. We are setting up a database of high (35,000 - 40,000) resolution echelle spectra and Stromgren photometric data for all of these stars. We use echelle spectrographs at OHP (France), Sutherland (South Africa) and La Palma (Canary Islands), as well as a semi-automatic photometric telescope near Granada (Spain). We intend to gather all of these data, as well as the determined parameters and characteristics, in a single database accessible by the community. Title: Eddington: a proposal to ESA for asteroseismology and planet-finding Authors: Favata, F.; Roxburgh, I.; Christensen-Dalsgaard, J. Bibcode: 2000mons.proc...49F Altcode: Eddington is a proposal to the European Space Agency (ESA) for a moderate-size (d~= 1.2 m), wide-field (Ω >= 6 sq. deg) optical telescope, which will be used for asteroseismic investigations as well as for extra-solar planet finding. The mission has been proposed to ESA in the framework of the F2/F3 mission opportunity and has recently been selected for a study, with a final selection due in September 2000. This paper briefly describes the proposed mission, as well as the current study baseline and organization. Title: Convective overshooting in stellar interiors Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L. Bibcode: 2000BASI...28...81S Altcode: The region of turbulent convective motions in stellar envelopes provides for both energy transport and the redistribution of chemical elements by mixing processes. Penetration or overshooting of these convective motions into the surrounding stable layers extends the unstable region thereby influencing the mixing and hence the structure and evolution of stars. We review here different approaches to the study of convective overshooting with special emphasis on numerical simulations. Overshooting from convective cores is also discussed. Title: Non-linear inversion for the hydrostatic structure of the solar interior Authors: Marchenkov, Konstantin; Roxburgh, Ian; Vorontsov, Sergei Bibcode: 2000MNRAS.312...39M Altcode: We present the results of a non-linear inverse analysis for the hydrostatic, spherically symmetric component of the solar internal structure using the observed p-mode frequencies. The iterative non-linear inversion technique used here is based on the succesive Born approximation description of solar p-modes developed by Roxburgh & Vorontsov. This description can give a high resolution of regions of rapid variation of seismic parameters with depth (e.g., the base of the convection zone), and accounts accurately for the strong influence of gravity perturbations on low-degree modes which penetrate deep into the solar core. The inversion procedure is non-linear; the eigenfrequency equation obtained from the Born approximation is solved by iteration. The particular target of our inverse analysis is to achieve the highest possible resolution of the region near the base of the solar convection zone, searching for possible signatures of penetrative convection, element diffusion and/or strong magnetic fields. The results of the global inversion obtained with solar p-mode frequencies provided by the recent high-quality observational data (GONG, SOI/MDI, GOLF) are presented and discussed. Title: Examination of Scaling Relationships Involving Penetration Distance at the Bottom of a Stellar Convective Envelope Authors: Saikia, E.; Singh, Harinder P.; Chan, K. L.; Roxburgh, I. W.; Srivastava, M. P. Bibcode: 2000ApJ...529..402S Altcode: A number of studies in the recent past have proposed a variety of scaling relationships among the penetration depth (Δd) at the bottom of a convective region, the vertical velocity of the fluid (Vz), and the input flux (Fb). While a relationship of the form Δd~V3/2z has been proposed by Schmitt and coworkers on the basis of the equations of motion for buoyant plumes, Zahn proposed a similar relationship based on scaling arguments. The relationships involving Δd, Vz, and the input flux are based on recent two-dimensional numerical simulations by Hurlburt and coworkers. All these scalings were recently looked into by Singh, Roxburgh, & Chan, who performed full three-dimensional simulations of turbulent compressible convection for a stable-unstable-stable sandwich configuration. In the present study, we numerically solve the full set of Navier-Stokes equations in three dimensions in order to study the behavior of convective motions penetrating into the bottom stable layer. We take up a series of models differing in resolution or mesh size and aspect ratio with a view to examine, in greater detail, the scaling relationships between the penetration distance and other flow parameters. Title: Power series solutions of the polytrope equations Authors: Roxburgh, Ian W.; Stockman, Lynne M. Bibcode: 1999MNRAS.303..466R Altcode: We derive recurrence relations for the coefficients a_k in the power series expansion theta(xi)=∑ a_kxi^2k of the solution of the Lane-Emden equation, and examine the convergence of these series. For values of the polytropic index n<n_1~1.9 the series appear to converge everywhere inside the star. For n>n_1 the series converge in the inner part of the star but then diverge. We also derive the series expansions for theta, xi in powers of m=q^2/3, where q=-xi^2dtheta/dxi is the polytropic mass. These series appear to converge everywhere within the star for all n <= 5. Finally we show that theta(xi) can be satisfactorily approximated (~ 1 per cent) by (1-cxi^2)/(1+exi^2)^m, and give the values of the constants determined by a Pade approximation to the series, and by a two-parameter fit to the numerical solutions. Title: Asteroseismological Constraints on Stellar Convective Cores Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1999ASPC..173..257R Altcode: 1999sstt.conf..257R No abstract at ADS Title: Convective Penetration in Main Sequence Stars Authors: Roxburgh, I. W. Bibcode: 1999ASPC..173..103R Altcode: 1999sstt.conf..103R No abstract at ADS Title: Response of a Spaceborn Gravitational Wave Antenna to Solar Oscillations Authors: Polnarev, A. G.; Giampieri, G.; Roxburgh, I. W.; Vorontsov, S.; Martchenkov, K. Bibcode: 1999magr.meet.1118P Altcode: No abstract at ADS Title: COROT: Seismology of Stars Authors: Roxburgh, I. W.; COROT Team Bibcode: 1999ASPC..173..357R Altcode: 1999sstt.conf..357R No abstract at ADS Title: A study of penetration at the bottom of a stellar convective envelope and its scaling relationships Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L. Bibcode: 1998A&A...340..178S Altcode: {A number of scaling relationships have been proposed by several authors relating the penetration depth (Delta_ {d}) at the bottom of a convective region to the velocity of the penetrating motions and the input flux (F_b). These may be expressed as Delta_ {d} ~ Vzo(3/2) for the case where the radiative conductivity varies smoothly from the unstable to the stable zone; Vzo being the vertical velocity at the bottom of the convection zone. When the conductivity varies stepwise from one zone to another, it has been suggested that Delta_ {d} ~ (Vzo(3) /F_b) for adiabatic penetration and Delta_ {d} ~ Fb(1/2) for non-adiabatic penetration. In this paper, we study the general behaviour of motions penetrating into the stable region at the bottom of a convective envelope by numerically solving the full set of Navier-Stokes equations in three dimensions. We compute a series of models which allow us to examine the scaling relationships between the penetration distance, the input flux and the vertical velocity.} Title: Proposed noncryogenic, nondrag-free test of the equivalence principle in space Authors: Nobili, A. M.; Bramanti, D.; Catastini, G.; Polacco, E.; Genta, G.; Brusa, E.; Mitrofanov, V. P.; Bernard, A.; Touboul, P.; Cook, A. J.; Hough, J.; Roxburgh, I. W.; Polnarev, A.; Flury, W.; Barlier, F.; Marchal, C. Bibcode: 1998NewA....3..175N Altcode: Ever since Galileo scientists have known that all bodies fall with the same acceleration regardless of their mass and composition. Known as the Universality of Free Fall, this is the most direct experimental evidence of the Weak Equivalence Principle, a founding pillar of General Relativity according to which the gravitational (passive) mass mg and the inertial mass mi are always in the same positive ratio in all test bodies. A space experiment offers two main advantages: a signal about a factor of a thousand bigger than on Earth and the absence of weight. A new space mission named GALILEO GALILEI (GG) has been proposed (Nobili et al., 1995 [J. Astronautical Sciences, 43, 219]; GALILEO GALILEI (GG), PRE PHASE A REPORT, ASI (Agenzia Spaziale Italiana), September 1996) aimed at testing the weak Equivalence Principle (EP) to 1 part in 10 17 in a rapidly spinning (5 Hz) drag-free spacecraft at room temperature, the most recent ground experiments having reached the level of 10 -12 (Adelberger et al., 1990 [PhRvD, 42, 3267]; Su et al., 1994 [PhRvD, 50, 3614]). Here we present a nondrag-free version of GG which could reach a sensitivity of 1 part in 10 16. The main feature of GG is that, similarly to the most recent ground experiments, the expected (low frequency) signal is modulated at higher frequency by spinning the system, in this case by rotating the test bodies (in the shape of hollow cylinders) around their symmetry axes, the signal being in the perpendicular plane. They are mechanically suspended inside the spacecraft and have very low frequencies of natural oscillation (due to the weakness of the springs that can be used because of weightlessness) so as to allow self-centering of the axes; vibrational noise around the spin/signal frequency is attenuated by means of mechanical suspensions. The signal of an EP violation would appear at the spin frequency as a relative ( differential) displacement of the test masses perpendicularly to the spin axis, and be detected by capacitance sensors; thermal stability across the test masses and for the required integration time is obtained passively thanks to both the fast spin and the cylindrical symmetry. In the nondrag-free version the entire effect of atmospheric drag is retained, but a very accurate balancing of the test bodies must be ensured (through a coupled suspension) so as to reach a high level of Common Mode Rejection and reduce the differential effects of drag below the target sensitivity. In so doing the complexities of a drag-free spacecraft are avoided by putting more stringent requirements on the experiment. The spacecraft must have a high area-to-mass ratio in order to reduce the effects of nongravitational forces; it is therefore a natural choice to have three pairs of test masses (in three experimental chambers) rather than one as by Nobili et al. (1995) [J. Astronautical Sciences, 43, 219] and the mission called GALILEO GALILEI [PRE PHASE A REPORT, ASI (Agenzia Spaziale Italiana), September 1996]. The GG setup is specifically designed for space; however, a significant EP test on the ground is possible — because the signal is in the transverse plane — by exploiting the horizontal component of the gravitational and the centrifugal field of the Earth. This ground test is underway. Title: Helioseismic Constraints on Solar Structure and the Solar Neutrino Problem Authors: Roxburgh, Ian W. Bibcode: 1998Ap&SS.261...57R Altcode: 1999Ap&SS.261...57R No abstract at ADS Title: After Dinner Poster Paper Authors: Roxburgh, Ian W. Bibcode: 1998Ap&SS.261..213R Altcode: 1999Ap&SS.261..213R No abstract at ADS Title: Numerical simulation of penetrative convection - verifying the scaling relation between penetration distance and the vertical velocity Authors: Singh, H. P.; Roxburgh, I. W.; Chan, K. L. Bibcode: 1998ASPC..138..313S Altcode: 1998stas.conf..313S No abstract at ADS Title: COROT: Seismology of Stars Authors: Roxburgh, Ian W. Bibcode: 1998Ap&SS.261...19R Altcode: 1999Ap&SS.261...19R No abstract at ADS Title: On the Diagnostic Properties of Low Degree Acoustic Modes Authors: Roxburgh, Ian W.; Vorontsov, Sergei V. Bibcode: 1998Ap&SS.261...21R Altcode: 1999Ap&SS.261...21R No abstract at ADS Title: Convective Overshooting and Mixing in Stellar Evolution Authors: Roxburgh, Ian W. Bibcode: 1998Ap&SS.261...43R Altcode: 1999Ap&SS.261...43R No abstract at ADS Title: Stellar Convective Cores Authors: Roxburgh, I. W. Bibcode: 1998IAUS..185...73R Altcode: No abstract at ADS Title: On the formation of line profiles of solar p-modes Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1998IAUS..185..229R Altcode: No abstract at ADS Title: Convective overshooting and stellar evolution Authors: Roxburgh, I. W. Bibcode: 1998ASPC..138..411R Altcode: 1998stas.conf..411R No abstract at ADS Title: Helioseismic Constraints on the Solar Core Authors: Roxburgh, Ian W. Bibcode: 1998Ap&SS.261...37R Altcode: 1999Ap&SS.261...37R No abstract at ADS Title: Space Asteroseismology on Later-type Stars Authors: Roxburgh, Ian W.; Thompson, Michael J. Bibcode: 1998Ap&SS.261...13R Altcode: 1999Ap&SS.261...13R No abstract at ADS Title: Semiclassical Approximation of Low-Degree Stellar p Modes Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1998ESASP.418..527R Altcode: 1998soho....6..527R Semiclassical description of the adiabatic acoustic oscillations is developed and its accuracy is addressed in different approximations. For modes of low degree ell, the semiclassical analysis suggests an expansion in powers of ell+1/2 in the eigenfrequency equation, as an alternative to the standard expansion in powers of 1/ω given by the high-frequency asymptotic analysis. New eigenfrequency equation demonstrates far superior accuracy in matching the oscillation frequencies, even when the applicability of the semiclassical analysis is significantly violated locally in the core of a centrally-condenced star. We discuss the diagnostic capabilities of this approximate description by applying it to solar p-mode data. Title: The Effect of Solar Oscillations on Space Gravitational Wave Experiments Authors: Giampieri, G.; Polnarev, A.; Roxburgh, I.; Vorontsov, S. Bibcode: 1998Ap&SS.261...35G Altcode: 1999Ap&SS.261...35G No abstract at ADS Title: A Parametric Study of 3-D Simulation of Penetrative Convection Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L. Bibcode: 1998Ap&SS.261...53S Altcode: 1999Ap&SS.261...53S No abstract at ADS Title: Line Profiles of Solar P-Modes Authors: Roxburgh, Ian W.; Vorontsov, Sergei V. Bibcode: 1998Ap&SS.261...39R Altcode: 1999Ap&SS.261...39R No abstract at ADS Title: Asymptotic description and the diagnostic properties of low-degree stellar p-modes Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1998IAUS..185..391R Altcode: We describe a new development of the asymptotic theory of high-frequency stellar acoustic oscillations, which focuses on low-degree modes and which is motivated by its application in stellar seismology, when the ammount of the observational data and the accuracy of frequency measurements are rather limited. When developing the asymptotic expansion of the solutions of the wave equations, we use new small parameter (ell + 1/2) omega, with degree ell and frequency omega, instead of a standard small parameter 1 omega. Such an alternative choise of the small parameter leads to a simple second-order asymptotic eigenfrequency equation which fits the exact frequencies with much better accuracy. Fitting with observational data thus provides an efficient separation of the diagnostic information contained in the stellar frequencies, filtering the contribution of the stellar core and the near-surface effects. Title: Non Linear Inversion for the Hydrostatic Structure of the Solar Interior Authors: Marchenkov, K. I.; Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1998Ap&SS.261...51M Altcode: 1999Ap&SS.261...51M No abstract at ADS Title: Nonlinear inversion for the hydrostatic structure of the solar interior Authors: Marchenkov, Konstantin; Roxburgh, Ian; Vorontsov, Sergei Bibcode: 1998IAUS..185..117M Altcode: We present the results of a nonlinear inverse analysis of the hydrostatic spherically-symmetric component of the solar internal structure using p-mode frequencies from the observational data sets now available. The technique which we use is an iterative nonlinear inversion technique, based on the "quasi-asymptotic" description of solar p-modes developed by Roxburgh and Vorontsov (1996, MNRAS 278, 940). As a significant improvement of the standard asymptotic analysis, this description incorporates Born approximation to allow a detailed treatment of regions of rapid variation of seismic parameters with depth (base of the convection zone) and strong influence of gravity perturbations (low-degree modes which penetrate deep into the solar core). The primary target of our current analysis is to achive the highest possible resolution of the region around the base of the solar convection zone, for searching possible signatures of penetrative convection, element diffusion and/or strong magnetic fields. Title: Numerical simulation of penetrative convection - a parametric study Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L. Bibcode: 1998IAUS..185..123S Altcode: In an earlier study (Singh, Roxburgh, & Chan, 1995, A & A 295, 703), we presented results of a series of 3D numerical experiments on convective penetration into stable layers below some deep stellar - type convective envelopes. A number of models were computed by systematically varying the stability of the lower stable layer and it was observed that the penetration distance decreased as the stability of the lower stable layer was increased. In this paper we present the results of some further studies wherein we have varied a number of input parameters like the input flux and the aspect ratio. The effect of the changes on the penetration distance below a convection zone has been analyzed. Title: Nonlinear Iterative Inversion for the Hydrostatic Structure of the Solar Interior Authors: Marchenkov, K. I.; Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1998ESASP.418..491M Altcode: 1998soho....6..491M We present the results of a nonlinear inverse analysis of the hydrostatic spherically-symmetric component of the solar internal structure using the observational p-mode frequencies (GONG, SOI/MDI, GOLF). The technique which we use is an iterative nonlinear inversion technique, based on the asymptotic description of solar p modes developed by Roxburgh and Vorontsov (1996). As a significant improvement of the standard asymptotic analysis, this description incorporates a Born approximation to allow for an accurate treatment of regions of rapid variation of seismic parameters with depth (e.g. base of the convection zone), and for better treatment of the influence of gravity perturbations on low-degree modes which penetrate deep into the solar core. The main target of our inverse analysis is to achive the highest possible resolution in the solar interior, including the region near the base of the solar convection zone, for searching possible signatures of penetrative convection, element diffusion and/or strong magnetic fields. Title: Steady Convection in Deep Compressible Layers Authors: Roxburgh, Ian W. Bibcode: 1998Ap&SS.261...55R Altcode: 1999Ap&SS.261...55R No abstract at ADS Title: Convective Overshooting and Mixing Authors: Roxburgh, I. Bibcode: 1997ASSL..225...23R Altcode: 1997scor.proc...23R Convection is of major importance in both energy transport and mixing in stars. Convective penetration, or overshooting, from unstable into the surrounding stable layers, extends the zone of effective mixing influencing both the thermal structure and evolution of stars. We here consider a range of approaches that can advance our understanding of this phenomenon: the fitting of stellar models to clusters and binary systems, theoretical studies, numerical simulation, and the new tools of helio- and asteroseismology. Other mixing processes that may affect the evolution of the sun and stars are also discussed, as is the possible effect of mixing on the solar neutrino problem. Title: Experiments on fundamental physics on the space station Authors: Spallicci, A.; Brillet, A.; Busca, G.; Catastini, G.; Pinto, I.; Roxburgh, I.; Salomon, C.; Soffel, M.; Veillet, C. Bibcode: 1997CQGra..14.2971S Altcode: Original proposals and experiments on gravitation and fundamental metrology on the space station are described. These experiments were formulated in the Metrology and Gravitation Science Team, in two ESA industrial study contracts, on microsatellites and on time and frequency science, within the space station scenario. Although limited by the design constraints of the space station, the experiments range from clock-based tests on special and general relativity to, with additional infrastructure, the equivalence principle and the detection of gravitational waves. Supporting technology, such as damping systems and microgravity cooled atom clocks, is also described. Finally, the major scientific goals, the experiments, hardware and the status are summarized. This work represents the first coordinated attempt, at least within the European space programmes, to consider experiments on relativity and fundamental physics without resorting to experiment dedicated space missions. For details on specific issues a large bibliography is referred to. Title: On the formation of spectral line profiles of solar P modes Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1997MNRAS.292L..33R Altcode: We address the problem of the opposite asymmetry of low-frequency p-mode line profiles observed in intensity and velocity measurements. We use a simple model to illustrate that this feature can be explained by including a contribution from the stochastic excitation velocity field to the non-resonant background in the Doppler measurements. Title: Numerical simulation of penetrative convection Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L. Bibcode: 1996BASI...24..281S Altcode: No abstract at ADS Title: Solar astrophysics: an overview Authors: Roxburgh, Ian W. Bibcode: 1996BASI...24...89R Altcode: No abstract at ADS Title: The Current State of Solar Modeling Authors: Christensen-Dalsgaard, J.; Dappen, W.; Ajukov, S. V.; Anderson, E. R.; Antia, H. M.; Basu, S.; Baturin, V. A.; Berthomieu, G.; Chaboyer, B.; Chitre, S. M.; Cox, A. N.; Demarque, P.; Donatowicz, J.; Dziembowski, W. A.; Gabriel, M.; Gough, D. O.; Guenther, D. B.; Guzik, J. A.; Harvey, J. W.; Hill, F.; Houdek, G.; Iglesias, C. A.; Kosovichev, A. G.; Leibacher, J. W.; Morel, P.; Proffitt, C. R.; Provost, J.; Reiter, J.; Rhodes, E. J., Jr.; Rogers, F. J.; Roxburgh, I. W.; Thompson, M. J.; Ulrich, R. K. Bibcode: 1996Sci...272.1286C Altcode: 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. Title: An asymptotic description of solar acoustic oscillation of low and intermediate degree Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1996MNRAS.278..940R Altcode: We present an asymptotic description of high-frequency solar p modes which permits an accurate treatment of regions where the seismic parameters vary rapidly with depth, and incorporates the strong effect of gravity perturbations on low-degree modes. The description is based on an asymptotic reduction of the governing fourth-order system of linear differential equations to second order. Approximate solutions of the second-order equation are then developed using a Born-type asymptotic expansion. The accuracy of the resulting description is tested numerically on a standard solar model. Higher order Born approximations give fractional accuracies of at least 10^-3. This is approximately an order of magnitude better than results from an earlier, more straightforward second-order analysis by Vorontsov. Title: STARS - Seismic Telescope for Astrophysical Research from Space. Report on the phase A study. Authors: Badiali, M.; Catala, C.; Favata, F.; Fridlund, M.; Frandsen, S.; Gough, D. O.; Hoyng, P.; Pace, O.; Roca-Cortés, T.; Roxburgh, I. W.; Sterken, C.; Volonté, S. Bibcode: 1996star.book.....B Altcode: STARS is an asteroseismology mission, which, through the acquisition of very accurate light curves, will detect oscillations in a wide variety of stars. This will allow, for the first time, the internal structure of stars of different age, composition and spectral type, to be studied directly, bringing the spectacular successes of helioseismology within reach for a large number of other stars spreading over most of the Hertzsprung-Russell diagram, including solar-type stars in open clusters. The results of the phase A study are presented in this report. Title: (Erratum) Limits on convective penetration from stellar cores. Authors: Roxburgh, I. W. Bibcode: 1996A&A...306..336R Altcode: Erratum to Astron. Astrophys. 226, 291-293 (1992). Title: On the Transport of Angular Momentum in Magnetic Stellar Interiors Authors: Ocaña, G.; Roxburgh, I. W. Bibcode: 1996ApL&C..34...29O Altcode: No abstract at ADS Title: STARS: Seismic Telescope for Astrophysical Research from Space Authors: Badiali, M.; Catala, C.; Favata, F.; Fridlund, M.; Frandsen, S.; Gough, D. O.; Hoyng, P.; Pace, O.; Roca-Cortes, T.; Roxburgh, I. W.; Sterken, C.; Volonte, A. Bibcode: 1996ESADS...4....1B Altcode: No abstract at ADS Title: Gravitation experiment payloads for non dedicated space missions. Report of the Columbus Metrology and Gravitation Science Team Authors: Spallicci, A.; Brillet, A.; Busca, G.; Fuligni, F.; Nobili, A.; Roxburgh, I. Bibcode: 1996step.symp..382S Altcode: No abstract at ADS Title: Upper limits on the cosmological gravitational wave background and maser clocks in space Authors: Polnarev, A. G.; Roxburgh, I. W. Bibcode: 1995GReGr..27..379P Altcode: We consider the possibility of detecting gravitational waves through the measurement of a time varying phase shift using a hydrogen maser clock on a satellite. Such measurements enable us to put interesting upper limits on the contribution of the gravitational-wave background to the dimensionless density of the Universe. The requirements on residual accelerations and the sensitivity of an accelerometer on the spacecraft are shown to be realistic and could be achieved using the accelerometer technology developed by ONERA for the ARISTOTELES mission. Such an experiment placing upper limits on the cosmological gravitational wave background could be conducted using the proposed Russian satellite “Millimetron”. Title: Three-dimensional simulation of penetrative convection: penetration below a convection zone. Authors: Singh, H. P.; Roxburgh, I. W.; Chan, K. L. Bibcode: 1995A&A...295..703S Altcode: We perform full three-dimensional numerical simulations to study the behaviour of penetrative compressible convection below a deep stratified stellar-type convective envelope. The domain of computations is divided into three distinct regions; the upper 2% and the lower 40% is kept convectivly stable while the middle 58% is made unstable to convection. Four series of solutions have been computed by varying the polytropic index and thus the stability of the lower stable layer. The penetration distance is found to decrease as the stability of the region beneath the convection zone is increased. Title: An asymptotic description of solar acoustic oscillations with an elementary excitation source Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1995MNRAS.272..850R Altcode: We extend the asymptotic description of solar p-modes to include an excitation source. The linear dynamic response of a star is considered within the general framework of a Fourier transform of the source function in time, and a vector spherical harmonic decomposition in space. Quantitative analysis is developed for the linear response to an `elementary' harmonic excitation source described by a delta-function in the radial direction, using a simplified description of the energy leakage from the acoustic cavity. The synthetic p-mode power spectra are computed numerically for different depths of the excitation source, and their simple properties are discussed. The asymptotic eigenfrequency equation is generalized to describe the frequencies of maximum amplitudes in the theoretical response function. The resulting frequency equation with modified `surface phase shift' degenerates into the standard eigenfrequency equation at low frequencies, and describes the high-frequency `pseudo-modes' in the high-frequency limit, joining both these well-known theoretical descriptions in the intermediate frequency range. Title: Synthetic p-Mode Power Spectra with an Elementary Excitation Source Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1995ASPC...76..362R Altcode: 1995gong.conf..362R No abstract at ADS Title: Convective Penetration in Stars (Abstract) Authors: Roxburgh, I. W.; Simmons, J.; Singh, H. P.; Vorontsov, S. V. Bibcode: 1995LIACo..32..231R Altcode: 1995sews.book..231R No abstract at ADS Title: Simulated Power Spectra of Solar-Type Oscillations Driven by an Elementary Excitation Source Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1995ASPC...83..111R Altcode: 1995IAUCo.155..111R; 1995aasp.conf..111R No abstract at ADS Title: Physical Processes in Astrophysics Authors: Roxburgh, Ian W.; Masnou, Jean-Louis Bibcode: 1995LNP...458.....R Altcode: 1995QB460.P48...... This volume, in honour of Evry Schatzman, contains in-depth reviews on central topics of modern astrophysics, such as stellar physics, covering stellar evolution, solar neutrinos, stellar rotation and spin down, convection transport processes, neutron stars, white dwarfs, and novae. All the talks were given by leading experts who had time both to develop the basics of their subject and to cover recent work. The volume is meant for both graduate students and researchers. Title: Quasi-Asymptotic Description of Adiabatic Acoustic Oscillations Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1995ASPC...76..370R Altcode: 1995gong.conf..370R No abstract at ADS Title: Overshooting from convective cores Authors: Roxburgh, Ian W. Bibcode: 1995LNP...458..239R Altcode: Convective overshooting increases the fraction of the star which is effectively mixed, thus altering models of stellar evolution. If the feed back of overshooting on the structure of the star is neglected the estimated extent of overshooting is very small. If the feed back is included in these estimates then the adiabatic core is extended by a substantial fraction (of order 25%) of the radius of the unstable region. An upper limit on convective overshooting is given by the integral constraint (Roxburgh 1978, 1989) with viscous dissipation neglected. For small cores this gives an increase in core mass of 50 85%. Numerical simulations of two-dimensional compressible convection in a fluid where the central regions are naturally convectively unstable, and the surrounding layers are stable, have been undertaken for different values of the Prandtl number. The results indicate that for low Prandtl numbers viscous dissipation is of decreasing importance and the simple integral condition gives a reasonable estimate of the extent of overshooting. Title: Seismology of the Solar Envelope - the Base of the Convective Zone as Seen in the Phase Shift of Acoustic Waves Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1994MNRAS.268..880R Altcode: At the base of the convective zone, discontinuities in the derivatives of the sound speed produce a phase shift in acoustic waves. This phase shift, α0(ν), is inferred by matching the measured solar p-modes to a second-order asymptotic description, the contribution from the surface layers and the second helium ionization zone being subtracted using modes with turning points well inside the convective zone. The resulting phase shift varies quasi-periodically with frequency with a period ≍220 μHz, and has an amplitude ≍8(±4) × 10-4 at a frequency of 3000 μHz. The phase shift α0(ν) is also calculated using the same technique for two solar models, one with no convective penetration and one with penetration extending for 1 per cent of the solar mass.

We estimate the predicted phase shift for models of the convective zone, including possible convective penetration modelled by extending the zone a distance ɛHp below the classical boundary; α(ν) has a quasi-periodic contribution with period ≍1/(2τβ), where τβ = ∫ dr/c is the acoustic depth of the base of the zone, and with amplitude where f(ɛ) and h(ɛ) are functions of ɛ which also depend on the variation of opacity with temperature and density. For ν = 3000 μHz, and typical values at the base of the convective zone, AV = 5& × 10-4 for ɛ = 0, decreases slightly for small ɛ and then increases to 1 × 10-3 for ɛ = 0.25, and to 1.7 × 10-3 for ɛ = 0.5.

The currently available data are consistent with an overshooting parameter 0≤ɛ≤0.25. Title: The Asymptotic Theory of Stellar Acoustic Oscillations - a Fourth-Order Approximation for Low-Degree Modes Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1994MNRAS.268..143R Altcode: The asymptotic description of low-degree stellar acoustic modes is extended to fourth order in inverse powers of the cyclical frequency. The accuracy of the asymptotic approximation is tested by comparing the predicted values of the eigenfrequencies and the `small frequency separations' with those calculated by solving the full equations governing the adiabatic oscillations of a standard solar model. Title: The seismology of stellar cores: a simple theoretical description of the small frequency separations. Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1994MNRAS.267..297R Altcode: We present a new theoretical description of the 'small frequency separations' delta omegal, n = omegal, n - omegal + 2, n - 1 for high-frequency stellar p-modes of low degree, these separations being the observable quantities that are primarily sensitive to the structure of the deep stellar interior. The description is based on an integral representation of the phase shift of acoustic waves due to scattering off the stellar core, taking into account the effects of buoyancy and gravitational perturbations. The accuracy of the theoretical description is tested by comparing the predicted frequency separations with values determined by numerically solving the full set of eigenfrequency equations for a standard solar model and for simple zero-age and evolved models of a 3-solar mass main-sequence star with a convective core. Title: Three-dimensional simulation of penetrative convection-penetration above a convection zone Authors: Singh, Harinder P.; Roxburgh, Ian W.; Chan, Kwing L. Bibcode: 1994A&A...281L..73S Altcode: We study the general behavior of three-dimensional penetrative convection of deep stellar-type envelopes. The convectively unstable region may be bounded from above and below by stable layers. We confine our attention at present to the penetration into the upper stable layer. To achieve this the unstable layer is made appreciably thick and sufficient room is provided for penetration above this layer. We perform the numerical experiment for five different cases covering a range of control parameters including stratification and the total flux flowing through the region. Although we find a noticable penetration region above the convective layer in all the cases, the penetration distance is found to increase with the factor (flux / density at the top of the convective layer). Title: IRIS VI Authors: Gough, D. O.; Roxburgh, I. W. Bibcode: 1994iris.conf.....G Altcode: No abstract at ADS Title: Overshooting from convective cores: theory and numerical simulation. Authors: Roxburgh, I. W. Bibcode: 1994ems..conf..299R Altcode: Convective overshooting increases the fraction of the star which is effectively mixed, thus altering models of stellar evolution. If the feed back of overshooting on the structure of the star is neglected the estimated extent of overshooting is very small. If the feed back is included in these estimates then the adiabatic core is extended by a distance comparable to a substantial fraction of the radius of the unstable region. An upper limit on convective overshooting is given by the integral constraint (Roxburgh 1978, 1989) with viscous dissipation neglected. If this constraint is applied to small convective cores then the maximum extent of the penetration region is shown to be at most about 0.18 times the radius of the core independent of the details of energy generation and opacity. The ratio of the maximum penetration distance to the scale height at the edge of the "classical boundary" varies very strongly with core size, and modelling overshooting by taking the penetration distance as a multiple of the scale height is likely to give misleading results. Numerical simulations of two-dimensional compressible convection in a fluid where the central regions are naturally convectively unstable, and the surrounding layers are stable, have been undertaken for different values of the Prandtl number. The results indicate that for low Prandtl numbers viscous dissipation is of decreasing importance and the simple integral condition gives a reasonable estimate of the extent of overshooting. Stellar seismology offers the possibility of detecting the location of the core-envelope interface through a periodic variation of the small frequency separation with frequency. Title: Equivalence principle, constant of gravitation, special and general relativity experiments in the COLUMBUS space programme Authors: Spallicci, A.; Brillet, A.; Busca, G.; Fuligni, F.; Nobili, A.; Roxburgh, I. Bibcode: 1993CQGra..10S.259S Altcode: No abstract at ADS Title: On the Structure and Secular Stability of Plane-Parallel Stellar Objects Authors: Roxburgh, I. W. Bibcode: 1993MNRAS.264..636R Altcode: The structure of self-gravitating, plane-parallel, vertically stratified stellar objects, with the energy generation and opacity given by the power laws ɛ = ɛ0ρTη, κ = κ0ραT, is studied. It is shown that the condition for secular stability in such objects is 5 + α + β - η > 0, whereas for spherical stars the corresponding condition is η + β -3 -3α > 0. Exact solutions (in closed form) are presented both for fully radiative models and for models with a convective central region. Approximate analytic solutions are given for models with a convective central region and radiative outer layers. Numerical models are readily calculated. Title: On the Generation of the Largescale and Turbulent Magnetic Fields in the Solar Type Stars Authors: Durney, Bernard R.; De Young, David S.; Roxburgh, Ian W. Bibcode: 1993SoPh..145..207D Altcode: It is thought that the large-scale solar-cycle magnetic field is generated in a thin region at the interface of the radiative core (RC) and solar convection zone (SCZ). We show that the bulk of the SCZ virogoursly generates a small-scale turbulent magnetic field. Rotation, while not essential, increases the generation rate of this field. Title: Overshooting from convective cores: Theory and numerical simulation Authors: Roxburgh, Ian W. Bibcode: 1993SSRv...66..299R Altcode: Convective overshooting increases the fraction of the star which is effectively mixed, thus altering models of stellar evolution. If the feed back of overshooting on the structure of the star is neglected the estimated extent of overshooting is very small. If the feed back is included in these estimates then the adiabatic core is extended by a distance comparable to a substantial fraction of the radius of the unstable region. An upper limit on convective overshooting is given by the integral constraint (Roxburgh 1978, 1989) with viscous dissipation neglected. If this constraint is applied to small convective cores then the maximum extent of the penetration region is shown to be at most about 0.18 times the radius of the core independent of the details of energy generation and opacity. The ratio of the maximum penetration distance to the scale height at the edge of the “classical boundary” varies very strongly with core size, and modelling overshooting by taking the penetration distance as a multiple of the scale height is likely to give misleading results. Numerical simulations of two-dimensional compressible convection in a fluid where the central regions are naturally convectively unstable, and the surrounding layers are stable, have been undertaken for different values of the Prandtl number. The results indicate that for low Prandtl numbers viscous dissipation is of decreasing importance and the simple integral condition gives a reasonable estimate of the extent of overshooting. Stellar seismology offers the possibility of detecting the location of the core — envelope interface through a periodic variation of the small frequency separation with frequency. Title: Seismology of the Solar Envelope - the Base of the Convective Zone as Seen in the Phase Shift of Acoustic Waves Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1993ASPC...42..169R Altcode: 1993gong.conf..169R No abstract at ADS Title: Integral Constraints On Convective Overshooting - Two-Dimensional Numerical Studies Authors: Roxburgh, Ian W.; Simmons, John Bibcode: 1993ASPC...40..290R Altcode: 1993ist..proc..290R; 1993ASPC...40..290M No abstract at ADS Title: Convective Overshooting in Stars Authors: Narasimha, D.; Roxburgh, I. W. Bibcode: 1993ASPC...42...73N Altcode: 1993gong.conf...73N No abstract at ADS Title: Asymptotic theory of low-degree stellar acoustic oscillations Authors: Roxburgh, I. W.; Vorontsov, S. V. Bibcode: 1993ASPC...40..535R Altcode: 1993ist..proc..535R; 1993IAUCo.137..535R No abstract at ADS Title: Key issues - A round table discussion Authors: Brown, T. M.; Demarque, P.; Noyes, R.; Praderie, F.; Roxburgh, I. W.; Schatzman, E. Bibcode: 1993ASPC...40..776B Altcode: 1993ist..proc..776B; 1993IAUCo.137..776B An overview of a round table discussion on the internal dynamics of stars, some problems in stellar structure and evolution, a study of stellar activity mechanisms using PRISMA, the seismology of sunlike stars, and directions of future research is presented. It is concluded that models that take into account just one physical process generally do not agree with the observations. This provides evidence for the presence of other physical processes. In each phenomenon which is considered, a variety of physical processes are involved. All physical processes should be taken into account simultaneously. Stars need to be considered globally. It is recommended that attention be given to such unsolved problems as the helium content of the sun, the abundance of lithium in fast rotating stars, and the origin and evolution of stellar magnetic fields. Title: Post Newtonian limit of Finsler space theories of gravity and solar system tests. Authors: Roxburgh, I. W. Bibcode: 1993rges.conf..500R Altcode: 1993rges.rept..500R The properties of generalised Finsler spaces are discussed. The post Newtonian limit for the strongly spherically symmetric one-body problem is considered by expanding the Finsler space about the Minkowski space of Special Relativity. In a Finsler space the second order gravitational red-shift experiment need not give the same values of PPN parameters as are obtained from time delay and perihelion advance. Thus a second order red-shift experiment would help test the Riemannian metric hypothesis of General Relativity. Title: The Phase Shift of Low L-Modes due to the Helium Ionisation Zone and the Base of the Convective Envelope Authors: Roxburgh, I. W. Bibcode: 1993ASPC...42..173R Altcode: 1993gong.conf..173R No abstract at ADS Title: Limits on convective penetration from stellar cores Authors: Roxburgh, I. W. Bibcode: 1992A&A...266..291R Altcode: The Integral Constraint on convective penetration gives an upper limit on the extent of convective penetration. If this is applied to small convective cores then the maximum extent of the penetration region is shown to be at most about 0.18 times the radius of the core independent of the details of energy generation and opacity. For larger cores the penetration distance depends on the particular properties of the nuclear reactions and opacity. Using simple power law approximations for the energy generation and opacity, the upper bound to the penetration distance is found to be approximately 0.2 of the core radius, and the core mass to be about 1.8 times the value without penetration, for a range of conditions and core sizes. The ratio of the maximum penetration distance to the scale height at the edge of the 'classical boundary' varies very strongly with core size, and modelling penetration by taking the penetration distance as a multiple of the scale height is likely to give misleading results. This is especially true for small cores such as exist in the early stages of the evolution of solar type stars. Title: Post-Newtonian limit of Finsler space theories of gravity and solar system tests Authors: Roxburgh, Ian W. Bibcode: 1992GReGr..24..419R Altcode: Finsler geometry is considered as a wider framework for analysing solar system tests of theories of gravity than is afforded by Riemannian geometry. The post-Newtonian limit for the spherically symmetric one-body problem is examined by expanding the Finsler metric about the Minkowski space of Special Relativity for those Finsler spaces whose null surface is Riemannian. In such a framework there are five PPN parameters instead of the three in Riemannian geometry. The classical solar system tests can readily be satisfied leaving two arbitrary parameters. These parameters could be determined from measurements of the second order gravitational red-shift and periodic perturbations in particle orbits, thus providing a consistency check on the Riemannian metric hypothesis of General Relativity. Such an experiment is possible on a satellite on an orbit with perihelion of a few solar radii. Title: Proceedings of Columbus Metrology Science Team Authors: Brillet, A.; Busca, G.; Fuligni, F.; Nobili, A.; Roxburgh, I.; Spallicci, A. Bibcode: 1991cms2.meet....1B Altcode: No abstract at ADS Title: Proceedings of Columbus Metrology Science Team Authors: Brillet, A.; Busca, G.; Fuligni, F.; Nobili, A.; Roxburgh, I.; Spallicci, A. Bibcode: 1991cms1.meet....1B Altcode: No abstract at ADS Title: Finsler spaces with Riemannian geodesics Authors: Roxburgh, Ian W. Bibcode: 1991GReGr..23.1071R Altcode: In Finsler spaces the intervalds=F(x i ,dx i ) is an arbitrary function of the coordinatesx i and coordinate incrementsdx i withF homogeneous of degree one in thedx i . It is shown that for Riemannian spacesds R 2=g ij dx i dx i which admit a non trivial covariantly constant tensorH i .(x k ) there is an associated Finsler space with the same geodesic structure. The subset of such Finsler spaces withH i .(x k ) a vector or second rank decomposable tensor is determined. Title: Differential Rotation of Fully Convective Pre-Main Sequence Stars Authors: Roxburgh, I. W. Bibcode: 1991ASIC..340...83R Altcode: 1991amey.conf...83R No abstract at ADS Title: Angular Momentum Transport Rotational Instabilities Magnetic Fields and Mixing Authors: Roxburgh, I. W. Bibcode: 1991ASIC..340..365R Altcode: 1991amey.conf..365R No abstract at ADS Title: Convective Cores in Stellar Models Authors: Roxburgh, I. W.; Monteiro, M. Bibcode: 1991LNP...380...95R Altcode: 1991IAUCo.130...95R; 1991sacs.coll...95R The condition for homogeneous radiative stellar models to be marginally stable to convection at the centre is investigated for the family of models where the opacity and energy generation are given by power laws in temperature and density = K0 T-, = 0 Tη. The Naur-Osterbrock (1953) condition 6η > 6 + 10β - 15α is a necessary but not sufficient condition. A better estimate is obtained by taking the effective polytropic index n = dlogP/dlogT - 1 to be a linear function of temperature T throughout the model. This gives the condition <tbody> &

$6eta = 10beta - 15alpha + frac{{12 + 4beta }}{{1 + alpha }}$

; Title: Challenges to Theories of the Structure of Moderate-Mass Stars Authors: Roxburgh, Ian W. Bibcode: 1991LNP...388..411R Altcode: 1991ctsm.conf..411R No abstract at ADS Title: Comparison of Solar Models with Los Alamos and Livermore Opacities Authors: Roxburgh, Ian W. Bibcode: 1991LNP...388...57R Altcode: 1991ctsm.conf...57R Models of the present sun were computed using the Los Alamos and the new Livermore opacities. The relative abundance abundance of heavy elements was the Grevesse mixture and the ratio Z/X was taken as 0.02765. The models were iterated to have R = Rsun and L = Lsun at an age of to = 4.6 109 years. The differences between the two models are presented. Title: Variability in the Solar Output Authors: Roxburgh, I. W. Bibcode: 1990RSPTA.330..641R Altcode: Evidence for variability in the solar output is briefly discussed. If the solar neutrino flux and the solar oscillation frequencies vary over a solar cycle this could indicate that the solar cycle has its origin in the solar core rather than be due to dynamo action in the solar convective zone. Title: The Newton mission - a proposed manmade planetary system in space to measure the gravitational constant. Authors: Nobili, A. M.; Milani, A.; Polacco, E.; Roxburgh, I. W.; Barlier, F.; Aksnes, K.; Everitt, C. W. F.; Farinella, P.; Anselmo, L.; Boudon, Y. Bibcode: 1990ESAJ...14..389N Altcode: A space mission is described which consists of a rigid spin-axis-stabilised spacecraft with two small, high-density masses free-falling inside. The gravitational attraction of the masses dominates all perturbations, providing a miniature "planet-satellite" system that can only be realised in space. Unlike any celestial two-body system, the masses can be weighed on Earth before launch. Thus, monitoring their motion by means of an inward-looking tracking camera allows the value of the universal constant of gravity, G, to be determined. A careful analysis of all perturbing forces shows that G can be measured at least to 1 part in 105, and perhaps even somewhat better. Title: Variability in the solar output. Authors: Roxburgh, I. W. Bibcode: 1990ecvs.conf..641R Altcode: Evidence for variability in the solar output is briefly discussed. If the solar neutrino flux and the solar oscillation frequencies vary over a solar cycle this could indicate that the solar cycle has its origin in the solar core rather than be due to dynamo action in the solar convective zone. Title: Integral constraints on convective overshooting Authors: Roxburgh, I. W. Bibcode: 1989A&A...211..361R Altcode: The integral constraint used to estimate the uncertainty in present knowledge of convection and convective overshooting is rederived for the general compressible case and shown to reduce to the previous result for almost adiabatically stratified convective zones when viscous dissipation is neglected. It is further shown that the objections by Baker and Kuhfuss (1987) require the stratification to be strongly nonadiabatic and that this then renders invalid standard models of stellar structure. Evidence from solar oscillations does not indicate such a large departure from adiabaticity. Title: Future research on close binaries. Authors: Roxburgh, I. W. Bibcode: 1988covp.conf..469R Altcode: Short conference summary. Title: Problems of the Solar Interior Authors: Roxburgh, Ian W. Bibcode: 1987ASSL..137....1R Altcode: 1987isav.symp....1R The 'standard model' of the sun is discussed and it is noted that the initial burning of He-3 and C-12 may produce a central convective core which may be sustained for some time by convective overshooting. In effect, g modes of oscillation may be excited by the He-3 and C-12 profiles which may also influence evolution. The solar neutrino problem is studied in detail together with the He-3 instability, convective overshooting, and internal rotation. Title: The internal rotation of the Sun. Authors: Roxburgh, Ian W. Bibcode: 1986ASIC..169..249R Altcode: 1986ssds.proc..249R Recent results on the internal rotation of the Sun are difficult to explain. These problems are reviewed and it is conjectured that a 3He driven mixed shell near 0.3 R_sun; magnetically separates the inner core from the outer regions. Such a shell may rotate differentially and may separate a more rapidly spinning core from the rest of the Sun. Title: Simulation of General Relativistic Corrections in Longterm Numerical Integrations of Planetary Orbits Authors: Nobili, Anna; Roxburgh, Ian W. Bibcode: 1986IAUS..114..105N Altcode: 1986rcma.conf..105N Long term numerical integrations of planetary orbits designed to study the stability of the Solar System over timescales comparable to its age have become very promising thanks to the availability of very powerful computers and to a substantial improvement in methods of investigating the stability of hierarchical dynamical systems. The stability of such numerical integrations relies on the ability to control all possible sources of error. Among the errors caused by the inadequacy of the physical model are those due to the fact that Newton's theory of gravitation is used instead of general relativity. It is shown that the secular advance of perihelia predicted by general relativity can be simulated exactly by a 1/r-squared perturbing potential with almost negligible additional cost in computer time. Title: Finite amplitude limit of the 3He instability. Authors: Roxburgh, I. W. Bibcode: 1986ASIC..169..265R Altcode: 1986ssds.proc..265R The models of solar type stars are unstable to non-radial oscillations driven by burning 3He. These oscillations modify the distribution of 3He leading to finite amplitude oscillations with typical temperature perturbations δT/T≡0.1. Title: Sound speed in the interior of solar models Authors: Roxburgh, I. W. Bibcode: 1986ASIC..169..121R Altcode: 1986ssds.proc..121R No abstract at ADS Title: Present Problems of the Solar Interior Authors: Roxburgh, I. W. Bibcode: 1985SoPh..100...21R Altcode: The standard model of solar evolution is reviewed and a number of problems highlighted. A fundamental question is whether there is any mixing of matter in the central regions, since such mixing could radically alter the model of the present Sun and modify our understanding of the evolution of other stars. Standard models of solar evolution become unstable to 3He driven global oscillations at an age of 3 × 108 years and this may drive some mixing, even if this is not the case the finite amptitude limit of these oscillations is likely to produce modifications in the standard model. Convective overshooting at the bottom of the outer convective zone leads to an increased depth of this zone and small changes in the interior. It is pointed out that the young Sun had a 12C driven convective core whose extent and duration depends on the extent of overshooting. Such a core is likely to produce a magnetic field which will affect the internal dynamics. The internal rotation of the Sun remains an enigma and absence of knowledge of any internal magnetic field makes it difficult to study the problem. Rotationally driven instabilities are ineffective in the central chemically inhomogenous regions but may contribute to the inward diffusion of lithium from the convective zone. These and other problems are considered, but few solutions are proposed. Title: Instabilities, mixing and solar neutrinos Authors: Roxburgh, I. W. Bibcode: 1985AIPC..126...88R Altcode: 1985snna.proc...88R Instabilities driven by differential rotation during spin down of a rotating solar model are analysed and it is shown that with a very small composition gradient, the first unstable mode is the Axisymmetric Baroclynic Diffusive (ABCD) instability. It is argued that if this instability occurs, it leads to an almost horizontal re-adjustment of chemical composition and only very slight mixing.

Mixing due to the 3He instability is energetically possible but it is argued that finite amplitude oscillations lead to a quasi-steady state without mixing with 3He being burnt to 4He during such oscillations. Title: Report of IAU Commission 49: The interplanetary plasma and the heliosphere (Plasma interplanétaire et l'héliosphère). Authors: Roxburgh, I. W. Bibcode: 1985IAUTA..19..697R Altcode: No abstract at ADS Title: Rotational instabilities in the solar interior turbulent diffusion and the solar neutrino problem Authors: Roxburgh, I. W. Bibcode: 1984MmSAI..55..273R Altcode: The sun is losing angular momentum through the mass loss in the solar wind and must therefore have spun down from higher velocities during its lifetime. This angular momentum loss will produce differential rotation in the solar interior unless magnetic fields are retained in the interior and are able to transport angular momentum by magnetic stresses. In this paper the author assumes magnetic fields are not effective in the bulk of the interior and shows that when the radial angular velocity reaches a critical value, baroclynic overstability sets in. This instability drives the inward diffusion of 1H. The increase of the central 1H abundance will lead to a reduction of the detectable neutrino flux. Title: On the Tassoul Approximation Scheme for Determining the Structure of Rotating Stars Authors: Roxburgh, I. W. Bibcode: 1984IAUS..105..517R Altcode: The method used by Tassoul and Tassoul assumes a "turbulent viscosity" which is important in determining the dynamics, but is unimportant in heat transport. This approximation is shown to be inconsistent. Title: On Turbulent Mixing Authors: Roxburgh, I. W. Bibcode: 1984IAUS..105..519R Altcode: Several authors have suggested that turbulent mixing takes place in some, if not all, stars, and in particular that such mixing can explain the low solar neutrino flux. This turbulence is thought to be caused by differential rotation produced by braking due to angular momentum loss in a stellar wind, and/or to the effect of meridional circulation currents in redistributing angular momentum. Whilst such instabilities may exist even in the presence of a stabilizing distribution of chemical composition, they do not necessarily cause mixing. To be effective in mixing, the energy available to the instability be it differential rotation or any other mechanism, has to be sufficient to lift the helium rich matter in the interior of the star to the outer regions. Title: Magnetic Fields and Angular Momentum Loss Authors: Gill, R. S.; Roxburgh, I. W. Bibcode: 1984srps.conf..335G Altcode: Angular momentum loss rates are calculated for stars with dipole and quadrupole magnetic fields, and isothermal coronae. The angular momentum loss rate for dipole fields is found to be considerably higher than that for quadrupole fields. If the dynamo produced magnetic field changes from quadrupole to dipole as the angular velocity decreases, there should be a sudden increase in the rate of angular momentum loss. The resulting decrease in the angular velocity with time is calculated assuming that the stars rotate uniformly throughout and used to determine the predicted distribution of angular velocity amongst stars of the same mass. This distribution has two peaks in qualitative agreement with the observations of Vaughan. Title: Space experiments in relativity and gravitation. Authors: Roxburgh, I. W. Bibcode: 1984ESASP1070...84R Altcode: No abstract at ADS Title: Internal rotation of the Sun Authors: Spruit, H. C.; Knobloch, E.; Roxburgh, I. W. Bibcode: 1983Natur.304..520S Altcode: The low surface rotation rate of the Sun and other main-sequence stars is believed to be the result of angular momentum loss due to a stellar wind1. This loss also leads to a differential rotation, the interior spinning more rapidly than the surface. The rate of increase with depth of the rotation speed is limited by hydrodynamic instabilities, which cause an outward diffusion of angular momentum2. The conditions for the occurrence of hydrodynamic instabilities in a radiative stellar interior are reviewed here assuming that the rotation is constant on spheres. The instability with the lowest threshold is a double diffusive one, the axisymmetric baroclinic diffusive (ABCD) instability. A minimum rotation curve for the present Sun is calculated using the assumption that the efficiency of this instability is sufficiently high that the rotation of the Sun is close to marginal stability. This lower limit to the internal rotation rate is roughly consistent with present observations of the rotational splitting of solar oscillations. Title: Stellar winds and spindown in solar type stars Authors: Roxburgh, I. W. Bibcode: 1983IAUS..102..449R Altcode: A simple model of stellar wind-induced angular momentum loss is presented in which the field is potential when the flow speed is lower than the Alfven speed, and radial when greater. The consequence, an increasing angular momentum loss rate with increasing simplicity of the magnetic geometry, is used to explain the rotational discontinuity across the Vaughan-Preston gap as due to a sudden angular momentum loss when the dynamo field switches from quadrupole to dipole geometry. Attention is given to the evolution of the internal rotation of stars as a result of surface angular momentum loss, and to recent results on solar oscillation rotational splitting which suggest that the inside of the sun is spinning faster than the surface. Title: Microinstabilities and Models of the Solar Wind Authors: Rowse, D. P.; Roxburgh, I. W.; Schwartz, S. J. Bibcode: 1981SoPh...74..179R Altcode: The collision-dominated two-fluid plasma models of the solar wind are shown to become collisionless and subject to microinstabilities at a few solar radii. Assuming that once the plasma is unstable it stays close to marginal stability models of the solar wind are constructed including waves and proton heating. The resulting models have higher velocities and proton temperatures than the collision dominated two fluid models. Title: Modelling Coronal Magnetic Fields Authors: Rowse, D. P.; Roxburgh, I. W. Bibcode: 1981SoPh...74..165R Altcode: The `hairy ball' model of coronal magnetic fields has a spherical source surface separating potential and radial magnetic fields. In the present model the source surface is chosen such that the wind speed equals the Alfvénic speed at selected points on the source surface. Results have been obtained for a dipole base field and an isothermal corona. Title: Solutions of the Two-Fluid Solar Wind Equations - Adiabatic and Conduction Dominated Solutions Authors: Rowse, D. P.; Roxburgh, I. W. Bibcode: 1981SoPh...74..169R Altcode: The equations governing the two-fluid spherically symmetric models of the solar wind have been solved numerically for a wide range of base conditions. As predicted from an asymptotic analysis we find a whole domain of solutions which are asymptotically adiabatic with the proton and electron temperatures tending to equality and varying like r- 4/3. In these 4/3 solutions the electron and proton heat conduction is asymptotically negligible and if it is neglected the resulting equations can be integrated analytically and shown to have the 4/3, 4/3 behaviour. Title: Solar Neutrinos Authors: Roxburgh, I. W. Bibcode: 1981IrAJ...15..106R Altcode: No abstract at ADS Title: Solar physics at Oxford Authors: Roxburgh, I. W.; Jordan, C. Bibcode: 1981Natur.292..194R Altcode: No abstract at ADS Title: The solar neutrino problem. Authors: Roxburgh, I. W. Bibcode: 1981ASIC...68..399R Altcode: 1981spss.conf..399R No abstract at ADS Title: Long Term Variations of the Solar Constant Authors: Roxburgh, I. W. Bibcode: 1981sucl.conf..261R Altcode: No abstract at ADS Title: Internal structure of the sun and stars. Authors: Roxburgh, I. W. Bibcode: 1981ASIC...68...59R Altcode: 1981spss.conf...59R The current theory of the internal structures of the sun and other main-sequence stars is reviewed in light of the importance of structural factors to the calculation of stellar luminosities and effective temperatures. The basic physics of stellar interiors is discussed based on a picture of stellar equilibrium supported by the balancing of self-gravitation against the internal pressure generated by fusion reactions, which act as a source of energy radiated or convected to the surface. Simple stellar models are examined, and the importance of convective effects, which are usually modelled by mixing length theory, is emphasized. The evolution of stellar structure in its pre-main sequence, main sequence and post-main sequence stages is then surveyed and problems in the understanding of the details of stellar structure are pointed out. Title: The Solar Neutrino Problem Authors: Roxburgh, I. W. Bibcode: 1981sucl.conf..269R Altcode: No abstract at ADS Title: A 'fast' model of the solar convection zone Authors: Belvedere, G.; Paterno, L.; Roxburgh, I. W. Bibcode: 1980A&A....91..356B Altcode: A model of solar convection zone incorporates the mixing-length theory in the method developed by Faulkner (1965) which accurately represents the superadiabatic layers. Interpolation formulas which save computer time, and are sufficiently accurate to limit discrepancies in pressure distribution and density through the convection zone, are used; the computer programs are 20 times faster than the programs of Baker and Temesvary (1966). Title: Instabilities in the Solar Wind Authors: Schwartz, S. J.; Roxburgh, I. W. Bibcode: 1980RSPTA.297..555S Altcode: 1980RSLPT.297..555S We review recent progress in the possible role of microturbulence in the solar wind. The solar wind is expected to excite plasma microinstabilities owing to its transition from a collision-dominated to a collisionless plasma, with potentially drastic consequences for thermal transport and other physical processes. We discuss both the extensive linear theory of this subject and also our present understanding of nonlinear plasma turbulence. The solar wind is an excellent laboratory for studying many aspects of solar and plasma physics, and may soon provide some answers to several fundamental questions. Title: The origin of supergranulation and giant cells in the solar convective zone. Authors: Roxburgh, I. W.; Tavakol, R. K. Bibcode: 1979SoPh...61..247R Altcode: In the standard model of the solar convective zone, turbulent eddies transport entropy rather than temperature. We consider the turbulent mean field equations for the convective zone, including entropy transport, and show that the zone can be unstable to larger scale motion which we identify with the supergranulation and giant cells. Title: Non-Riemann geometrizable effects in the gravitational one-body problem. Authors: Roxburgh, I. W.; Tavakol, R. K. Bibcode: 1979GReGr..10..307R Altcode: We consider the question of whether the “correct” theory of gravity is a metric theory. The metric hypothesis is shown to place severe restrictions on the form of the equation of motion for the one-body problem. By relaxing these restrictions we include nonmetric contributions to the equation of motion, and the solution in the post-Newtonian approximation is given. The solution given here contains five arbitrary parameters in place of the usual two (β, γ) of metric theories. One of them produces a secular change in the eccentricity; the others contribute to the perihelion advance and to periodic terms. Only certain combinations of these parameters can be determined even from orbits with different eccentricities. Title: The internal structure of the sun and solar type stars. Authors: Roxburgh, I. W. Bibcode: 1979psa..conf..243R Altcode: No abstract at ADS Title: European Space Agency studies of the solar probe Authors: Roxburgh, I. W. Bibcode: 1978clus.nasa..556R Altcode: The feasibility and scientific objectives of a solar probe were studied by a Mission Definition Group in 1975 and 1976. The orbit analysis program was developed and an extended study of the orbit analysis was done in 1977. The results of these studies are in the Report of the Mission Definition Study (1976) and an E.S.O.C. report (1978), and the reader is referred to these sources for greater details. In this report, only brief discussion on mission concept and objectives, satellite design, orbit, orbit analysis, are presented. Title: The importance of determining the solar quadrupole moment Authors: Roxburgh, I. W. Bibcode: 1978clus.nasa...11R Altcode: Current theoretical modelling of the sun is in difficulty. Additional observations must be made to place constraints on the plethora of conjectures that have been advanced to explain the low neutrino flux and to guide solar model builders in their search to understand the deep interior of the sun. A determination of the magnitude of the solar quadrupole moment, is one such constraint; it places limits on the density, angular velocity and magnetic field distributions inside the sun. Title: Convection and stellar structure. Authors: Roxburgh, I. W. Bibcode: 1978A&A....65..281R Altcode: The 'theory' of convection used to model stellar convective zones neglects the flux of turbulent kinetic energy and is therefore only applicable to zones that are small compared to a scale height, yet the resulting models have convective zones that are several scale heights thick. In this paper we attempt to quantify the error involved by retaining the kinetic energy flux and assuming that the viscous dissipation is small. This 'theory' leads to a new criterion to determine the extent of convective zones which requires the convection to penetrate into the surrounding stable layers. This new criterion is used in constructing models of main sequence stars, the convective cores in these stars are found to have 50-70% more mass than the old models and slightly lower luminosities so extending the main sequence phase of stellar evolution by up to 70% over previous estimates. Title: The Structure of Close Binaries Authors: Roxburgh, I. W.; Williams, P. S. Bibcode: 1978Ap&SS..54..199R Altcode: A method for calculating the structure of a close binary component is presented. It is seen that the effect of binary distortion is to shift the zero age main sequence to the right. Attempts to construct contact systems with these models confirm the results of earlier workers that this is not possible. Title: Origin of planetary nebulae Authors: Roxburgh, I. W. Bibcode: 1978IAUS...76..295R Altcode: The origin of planetary nebulae is discussed from the viewpoint of healthy scepticism about theoretical models used in stellar physics. The hypothesis that luminous red giants are the progenitors of planetary nebulae is adopted, and predictions of stellar evolution theory concerning the internal structure and evolution of stars from the main sequence to the giant phase are summarized. Uncertainties in these calculations are examined, particularly with regard to turbulent convection, coronal-driven mass loss, rotation, magnetic fields, the opacity of stellar material, neutrino energy losses, and dynamical phases. Various proposed theories of nebula ejection are reviewed, and the possibility of binary-star remnants of planetary nebulae is considered. Title: The Solar Interior Authors: Roxburgh, I. W. Bibcode: 1978pfsl.conf...21R Altcode: 1978ESPM....2...21R No abstract at ADS Title: Solar Neutrinos and the Solar Interior Authors: Roxburgh, I. W. Bibcode: 1978sfsn.conf..207R Altcode: No abstract at ADS Title: Microturbulence and the Solar Wind Authors: Schwartz, S. J.; Roxburgh, I. W. Bibcode: 1978pfsl.conf..317S Altcode: 1978ESPM....2..317S No abstract at ADS Title: Multicell Convection in the Solar Envelope Authors: Tavakol, R. K.; Roxburgh, I. W. Bibcode: 1978pfsl.conf...63T Altcode: 1978ESPM....2...63T No abstract at ADS Title: Meridional circulation in the surface layers of rotating stars. Authors: Smith, B. L.; Roxburgh, I. W. Bibcode: 1977A&A....61..747S Altcode: The influence of self-inertia on the meridional circulation in the radiative envelopes of rotating early-type stars is examined. It is found that the inertia of the circulation becomes important in a shallow subsurface boundary layer having a relative depth determined by the approximate ratio of centrifugal to gravitational force, and by the ratio of the free-fall time to the Kelvin-Helmholtz contraction time. The structure equations appropriate to the boundary layer are derived using stretched variable techniques, and qualitative features of the flow discussed. There is found to be minimal deviation from the Von Zeipel gravity darkening law through the boundary layer for all rotation speeds. Title: Cosmological solutions of the mass integral formulation of general relativity. Authors: Roxburgh, I. W. Bibcode: 1977MNRAS.181..637R Altcode: The cosmological solutions of general relativity give three isotropic homogeneous cosmological models determined by the curvature of three-space (k = 0, +1, -1). In the mass integral formulation of Hoyle and Narlikar (1964), the differential form of the theory is identical to general relativity but because of the integral form of the mass field, these solutions must satisfy a self-consistency condition. By mapping the k = -1 model into the uniformly expanding Milne model, the mass integral is evaluated and shown to be self-consistent. Thus this formulation of general relativity does not uniquely determine the cosmological solution. Title: Large number hypothesis and continuous creation cosmologies Authors: Roxburgh, I. W. Bibcode: 1977Natur.268..504R Altcode: The large number hypothesis and the condition that general relativity is satisfied in Einstein units, allows a family of cosmological models, two of which are the Dirac model without creation and the more recent Dirac model with multiplicative creation. The new models have multiplicative creation, a cosmological scale factor S(t) ~ tm, and are spatially flat; a multiplicative steady state model also satisfies the hypotheses. How these models affect the temperature of the Earth and the cosmological deceleration parameter is important. Title: The onset of microinstability and its consequences in the solar wind Authors: Singer, C. E.; Roxburgh, I. W. Bibcode: 1977JGR....82.2677S Altcode: A simple and general method for applying the results of a microinstability analysis to models of the solar wind is described. Existing two-fluid models are found to become unstable at heliocentric distances varying from 3 to 11 RS. The development of these ‘heat conduction’ microinstabilities affects the energy and momentum transport, observable wave spectrum, cosmic ray diffusion, and properties of minor ions in the solar wind. A proposal which would rationally modify the energy transport is developed. It is suggested that the plasma fluctuations observed near the earth could largely be a result of these instabilities. The observed temperatures and velocities of helium ions can be explained qualitatively in terms of resonant interaction with the different waves which are expected to be generated under different solar wind conditions. Title: Christmas Lecture: Is the Universe Unique? Authors: Roxburgh, I. W. Bibcode: 1977JBAA...87..341R Altcode: No abstract at ADS Title: Testing Relativity and Gravitational Theories by Radar Ranging to a Heliocentric Satellite Authors: Roxburgh, I. W. Bibcode: 1977RSPTA.284..589R Altcode: 1977RSLPT.284..589R Laser ranging to the Moon and radar ranging to the planets and space probes are providing increasingly more accurate estimates of post-Newtonian gravitational effects. This paper summarizes the results obtained so far and outlines future possibilities of more accurate tests of relativity by laser and X and K band ranging to space probes, particularly to a highly eccentric or direct impact solar probe. Title: Testing Relativity and Gravitational Theories by Radar Ranging to a Heliocentric Satellite: Discussion Authors: Weightman, J. A.; Roxburgh, I. W. Bibcode: 1977RSPTA.284..593W Altcode: No abstract at ADS Title: Nonlinear Lagrangian theories of gravity. Authors: Roxburgh, Ian W. Bibcode: 1977GReGr...8..219R Altcode: Gravitational theories derived from an action principle where the Lagrange density is a power of the curvature scalerR n are investigated. For all values ofn the theories have the correct Newtonian limit and forn = 1 the same weak field solution, which predicts a bending of light of three-quarters of the value predicted by general relativity (n=1). Title: Dirac's continuous creation cosmology and the temperature of the Earth (reply) Authors: Roxburgh Bibcode: 1977Natur.265..763R Altcode: No abstract at ADS Title: Theories of Gravitation and the Solar System Authors: Roxburgh, I. W. Bibcode: 1977grep.conf..171R Altcode: No abstract at ADS Title: Solar Interior Authors: Durrant, C. J.; Roxburgh, I. W. Bibcode: 1977ASSL...69....1D Altcode: 1977igss.conf....1D Solar Standard Model Internal Rotation Energy Generation Solar Neutrinos Convection Zone Convective Theory Boussinesq Assumption Title: The stability of low mass contact binaries. Authors: Williams, P. S.; Roxburgh, I. W. Bibcode: 1976MNRAS.176...81W Altcode: The equilibrium of a low-mass contact binary system is investigated by considering the stability of main-sequence components of 0.6 solar mass to both mass loss and mass gain. A contact system of equal masses is shown to be unstable to mass exchange on a dynamical time scale and to evolve rapidly into a detached system with a mass ratio of 0.8. As the system readjusts on a thermal time scale, it will either evolve into a nearly-contact stable system with this mass ratio or oscillate between two unstable nearly-contact states, spending most of the time as a nearly-contact unequal-mass system. Title: Dirac's continuous creation cosmology and the temperature of the Earth Authors: Roxburgh, Ian W. Bibcode: 1976Natur.261..301R Altcode: DIRAC1,2 has modified his earlier cosmological model based on the large number hypothesis3,4, that the observed approximate equalities are not accidental but causal-even though we are as yet unaware of the nature of the relationship between cosmology and local physics (e is the electronic charge, G the gravitational constant, c the velocity of light, ρ the mean density of the Universe, H Hubble's constant and m an atomic mass). In the earlier version, Dirac assumed mass conservation and that equalities (1) held for all time, thus where R(t) is the cosmological scale factor, H = R/R. In the modified version, Dirac argues (unconvincingly in my view) that R(t) ~ t, in which case that is, matter is continuously created such that ρ0 ~ t 2 where t is the age of the Universe. This newly created matter could be produced uniformly throughout space, or locally in proportion to the amount and composition of matter already present. Dirac prefers the second alternative, but we shall show that this leads to an unacceptable past temperature for the Earth. Title: The Internal Structure of the Sun and Solar Type Stars Authors: Roxburgh, I. W. Bibcode: 1976IAUS...71..453R Altcode: No abstract at ADS Title: The Dogon tribe and Sirius Authors: Roxburgh, I. W.; Williams, I. P. Bibcode: 1975Obs....95..215R Altcode: No abstract at ADS Title: The gravitational theories of Poincaré and Milne and the non-Riemannian kinematic models of the universe. Authors: Roxburgh, I. W.; Tavakol, R. Bibcode: 1975MNRAS.170..599R Altcode: Milne's general kinematic discussion on cosmological models is reviewed, revised and extended and it is shown that Riemannian geometry is insufficient for describing the general class of Milne's theories and that these theories if they are to be geometrized need the more general framework of Finsler spaces. Poincare's early relativistic gravitational theory is then reviewed and applied to the one-body and cosmological problems. It is shown that this theory is not Riemannian geometrizable but is Finsler geometrizable. The cosmological solution is explicitly evaluated and shown to be an example of Milne's general kinematic models. Title: On the Effect of Latitude Dependent Base Conditions on the Structure of the Solar Wind Authors: Roxburgh, I. W.; Singer, C. Bibcode: 1975SoPh...41..241R Altcode: The isothermal solar wind equations are solved for the case where the coronal conditions vary with latitude. It is found that the solutions are not uniquely determined by the base density but require knowledge of the injection angle of the fluid. Even for the case of spherically symmetric density at the corona, the solutions are not unique and form a one parameter set, but the latitude variation decreases rapidly with increasing heliocentric distance. Title: Solar neutrinos and solar rotation. Authors: Roxburgh, I. W. Bibcode: 1975MNRAS.170P..35R Altcode: Recent criticisms by Monaghan (1974) of suggestions that rapid rotation lowers the neutrino flux from the sun are replied to and shown to be invalid. Rapid differential rotation is capable of lowering the neutrino flux provided the ratio of centrifugal force to gravity decreases outwards in the sun. Title: The effect of rotation in stellar structure and evolution Authors: Roxburgh, I. W. Bibcode: 1975MSRSL...8...15R Altcode: 1975phs..conf...15R The development of our understanding of rotation in stellar structure and evolution is briefly reviewed. More recent work on rotation and convection, solar oblateness, the stability of differential rotation and the effect of rapid rotation on the solar neutrino flux is discussed. Title: Splitting the stars. Authors: Roxburgh, I. W. Bibcode: 1974JBAA...85....8R Altcode: No abstract at ADS Title: On the Nature of the Asymptotically Adiabatic Solution of the Two-Fluid Solar Wind Authors: Roxburgh, Ian W. Bibcode: 1974ApJ...191..557R Altcode: It is shown that there are the four degrees of freedom in the asymptotically adiabatic solutions of the solarwind models. The electron and proton temperatures tend to equality at large distances like T0r -413, T0 being the same for both the electron and proton gases. For a given T0 there exists another branch of solutions that converge on to this in an asymptotically irregular manner like S0r1 '2 - 413) exp (- r), where is a constant, known in terms of T0, and 5o represents the extra degree of freedom required to specify arbitrarily the density and electron and proton temperature at the Sun. Subject heading: solar wind Title: The masses of stable gas clouds Authors: Roxburgh, I. W.; van der Reijden, W. Bibcode: 1974MmSAI..45..485R Altcode: No abstract at ADS Title: The pre main sequence contraction of rapidly rotating stars and equatorial mass loss Authors: Roxburgh, I. W.; Williams, P. S. Bibcode: 1974MmSAI..45..477R Altcode: No abstract at ADS Title: A Note on Anisotropic Convection and the Rotation of Stellar Convective Zones Authors: Roxburgh, Ian W. Bibcode: 1974Ap&SS..27..419R Altcode: The interaction of rotation and convection produces a latitude dependent anisotropic turbulent viscosity. When this friction is dominant, equilibrium of a convective outer layer of a star is achieved by an equatorial acceleration and a two-zone circulation, towards the equator at low surface latitudes. Title: A Note on the Solution of the Saturation Flux Limited Solar Wind Equations Authors: Roxburgh, Ian W. Bibcode: 1974SoPh...35..481R Altcode: The solution curves of the differential equations determining the behavior of the solar wind are calculated for the case where the heat flux has its maximum value 3/2 nkTvth. All the supersonic solutions are asymptotically adiabatic, T ∼r-4/3. Title: Non-Uniformly Rotating, Self-Gravitating, Compressible Masses with Internal Meridian Circulation Authors: Roxburgh, Ian W. Bibcode: 1974Ap&SS..27..425R Altcode: The structure of self-gravitating, inviscid, compressible fluids is investigated assuming a polytropic relation between pressure and density. A class of solutions with non-uniform rotation and internal meridian circulation are presented and the stream lines of the flow calculated using a perturbation technique. Title: Internal rotation of the Sun and the solar neutrino flux Authors: Roxburgh, Ian W. Bibcode: 1974Natur.248..209R Altcode: THE low upper limit of 1 SNU (10-36 captures per 37Cl atom s-1) on the observed neutrino flux from the Sun obtained by Davis1 has proved an embarrassment to stellar physicists, and in spite of considerable intellectual gymnastics the standard solar models predict at least 6 SNU (ref. 2). The essential difficulty has been to produce a model with a low enough central temperature that can still produce the observed luminosity of the Sun with an age of 4.7 × 109 yr. Title: Solar oblateness and the solar quadrupole moment Authors: Roxburgh, I. W. Bibcode: 1974exgr.conf..525R Altcode: No abstract at ADS Title: Neutron stars. Authors: Roxburgh, I. W. Bibcode: 1973PhB....24..664R Altcode: No abstract at ADS Title: The Asymptotic Behavior of the Supersonic Solutions of the Two-Fluid Solar Wind Equations Authors: Roxburgh, I. W. Bibcode: 1972SoPh...27..478R Altcode: Three different asymptotic branches of the two-fluid equations are found with τeαλm, τpαλn, where, λ is the inverse distance from the Sun, with (m, n) = (2/7, 2/7), (2/7, 6/7), (4/3, 4/3); other special solutions are also found but they correspond to special choices of density and temperature at the corona. In all the (4/3, 4/3) solutions, the electron and proton temperatures tend to equality at large distances. Title: Late supergiant evolution. Authors: Roxburgh, I. W.; Williams, I. P. Bibcode: 1972css..conf..279R Altcode: 1971css..conf..279R No abstract at ADS Title: Inhomogeneous convection and the equatorial acceleration of the sun. Authors: Durney, B. R.; Roxburgh, I. W. Bibcode: 1971BAAS....3S.260D Altcode: No abstract at ADS Title: Inhomogeneous Convection and the Equatorial Acceleration of the Sun Authors: Durney, B. R.; Roxburgh, I. W. Bibcode: 1971SoPh...16....3D Altcode: The interaction of rotation and turbulent convection is assumed to give rise to an inhomogeneous, but isotropic, latitude dependent turbulent energy transport, which is described by a `convective conduction coefficient κc' which varies with latitude. Energy balance in the convective zone is then possible only with a slow meridian circulation in the outer convective zone of the sun. The angular momentum transported by this circulation is balanced in a steady state by turbulent viscous transport down an angular velocity gradient. A detailed model is constructed allowing for the transition from convective transport to radiative transport at the boundaries of the convective zone, by using a perturbation analysis in which the latitude variation of κc is small. The solution for a thin compressible shell gives equatorial acceleration and a hotter equator than pole, assuming that the convection is preferentially stabilised at the equator. For agreement with the sun's equatorial acceleration the model predicts an equatorial temperature excess of 70 K and a surface meridional velocity of 350 cm/sec from pole to equator. Title: On the Equatorial Acceleration of the Sun Authors: Roxburgh, I. W. Bibcode: 1970stro.coll..318R Altcode: 1970IAUCo...4..318R No abstract at ADS Title: Models of close and contact binary stars 1.Polytropic models Authors: Durney, B. R.; Roxburgh, I. W. Bibcode: 1970MNRAS.148..239D Altcode: Polytropic models of close and contact binary stars are constructed using a combination of perturbation techniques and a Laplace approximation previously applied to uniformly rotating stars. Synchronism between orbital and intrinsic angular velocity is assumed. Models are constructed including the effects of distortion for polytropes with indices fl = 1, , 2, 3 and 4. The conditions for the two stars to be just in contact are determined and contact models with a mass ratio of unity are constructed, right up to the limiting case when the stars fill all the available space inside the critical Roche surface surrounding the two stars. When the two stars are built on the same polytropic model contact stars with mass ratios different from unity are not possible. Title: Plasma physics in an astrophysical environment. Authors: Roxburgh, I. W. Bibcode: 1969ppaa.book.....R Altcode: No abstract at ADS Title: The oblateness of the Sun. Authors: Roxburgh, I. W. Bibcode: 1969ampe.conf...29R Altcode: No abstract at ADS Title: Pulsation Periods of Rotating White Dwarfs Authors: Durney, B. R.; Faulkner, J.; Gribbin, J. R.; Roxburgh, I. W. Bibcode: 1968Natur.219...20D Altcode: When uniform rotation is included, the periods of pulsation for white dwarfs can become as small as 0.9 s. With non-uniform rotation, periods as short as 0.1 s may be possible. Title: Uniformly Rotating Main-Sequence Stars Authors: Faulkner, J.; Roxburgh, I. W.; Strittmatter, P. A. Bibcode: 1968ApJ...151..203F Altcode: Models of homogeneous, uniformly rotating main-sequence stars have been constructed by an ex- tension of the method described by Roxburgh, Griffith, and Sweet and results for three stellar masses are presented here Detailed opacity and nuclear energy generation data were included and the prescription due to Faulkner, Griffiths, and Hoyle was adopted to determine the surface boundary conditions. By subsequently fitting appropriate "gray" atmospheres at each latitude the changes in visual magnitude V and color index B - V were evaluated for a range of rotational velocities and aspect angles At maxi- mum rotational speed there are found to be differences of up to 1.3 mag in V and 0.25 mag in B - V for stars of the same mass seen at different orientation. The maximum spread in the main sequence ranges between 0.4 and 1.2 mag depending on color Title: The Origin and Early Evolution of Close Binary Stars Authors: Roxburgh, I. W. Bibcode: 1968HiA.....1..451R Altcode: No abstract at ADS Title: Solar Oblateness Authors: Roxburgh, I. W. Bibcode: 1967Natur.216.1286R Altcode: In this article the author answers criticism, by Dicke and Goldenberg, on his theory of why the Sun is oblate. Title: On the densities of middle-aged stars Authors: Faulkner, J.; Roxburgh, I. W. Bibcode: 1967Obs....87..171F Altcode: No abstract at ADS Title: Origin of Planetary Nebulae Authors: Roxburgh, Ian W. Bibcode: 1967Natur.215..838R Altcode: STATISTICAL arguments have been advanced to demonstrate that all or a large fraction of stars with masses comparable with that of the Sun become planetary nebulae during the course of their evolution1,2. It has further been argued that these stars are the evolutionary products of horizontal branch stars, although the mechanism for the ejection of the expanding shell has remained a mystery. Title: Implications of the Oblateness of the Sun Authors: Roxburgh, Ian W. Bibcode: 1967Natur.213.1077R Altcode: Recent measurements of the oblateness of the Sun have been used to determine its quadrupole moment and thus its effect on the perihelion of Mercury. It is shown that these calculations could well be incorrect and that the measured oblateness is that expected if the Sun is slowly rotating throughout, since the surface is not one of constant potential. Title: The Structure and Stability of Rotating Massive Stars in General Relativity Authors: Roxburgh, I. W. Bibcode: 1967LIACo..14..131R Altcode: 1967MSRSL..15..131R; 1967LIACo...6..131R No abstract at ADS Title: Effect of Rotation and Magnetic Fields on the Formation of Single and Multiple Stars Authors: Roxburgh, I. W. Bibcode: 1967LIACo..14..343R Altcode: 1967LIACo...6..343R; 1967MSRSL..15..343R No abstract at ADS Title: Genesis of binaries (capture, accretion, scission, novae, etc.): Effect of rotation and magnetic fields on the formation of single and multiple stars Authors: Roxburgh, I. W. Bibcode: 1967oeds.conf...60R Altcode: No abstract at ADS Title: Rotation and Magnetism in Stellar Structure and Evolution Authors: Roxburgh, Ian W. Bibcode: 1967mrs..conf...45R Altcode: No abstract at ADS Title: Rotating Massive Stars in General Relativity Authors: Durney, B. R.; Roxburgh, I. W. Bibcode: 1967RSPSA.296..189D Altcode: Equilibrium models of uniformly rotating massive stars are investigated, using a weak field, slow rotation approximation, which is shown to be adequate for all cases of interest. The fate of radial perturbations about these equilibrium configurations is investigated using a linearized stability analysis to determine the oscillation frequency σ in a peturbation propto e1σ t. An eigenvalue equation for σ^2 is obtained which can be made self adjoint with respect to the spatial metric, and a variational principle to determine σ^2 is derived. Numerical determinations of σ^2 have been carried out for a variety of masses, radii and rotational velocities, and these results are incorporated in a simple formula that gives the dependence of σ^2 on these quantities. The condition for instability, σ^2 negative, is determined, and it is found that for large masses and maximum rotation velocity, so that when centrifugal force balances gravity at the surface, a massive star becomes unstable when its radius is 208 times the Schwarzschild radius 2GM/c^2. Title: The effect of a toroidal magnetic field on the radial oscillations of stars Authors: Roxburgh, I. W.; Durney, B. R. Bibcode: 1967MNRAS.135..329R Altcode: The internal structure of a polytrope n =3 containing a toroidal magnetic field is investigated. For static equilibrium configurations the general solution for the structure of the field is given and a particular solution Ht rp sin 0 is investigated in detail. The linearized equations for small radial motion about the equilibrium configuration are presented and with a time dependence ei these equations reduce to an eigenvalue equation for 2 A variational principle for determiing is derived and 2 is estimated using this principle as well as by direct numerical iteration, for values of the ratio of specific heats of the gas F = 4/3,413+ , and 5/3. Results are given for different field strengths. For F =4/3 the star is neutrally stable whether or not there is a magnetic field, whereas for the other values of F the magnetic field decreases the value of a as compared to the non-magnetic values. Title: Decay of Stellar Magnetic Fields Authors: Roxburgh, I. W.; Suffolk, G. C. J. Bibcode: 1967ZA.....66....1R Altcode: No abstract at ADS Title: Determination of rotational velocity and aspect for stars in clusters Authors: Roxburgh, I. W.; Sargent, W. L. W.; Strittmatter, P. A. Bibcode: 1966Obs....86..118R Altcode: No abstract at ADS Title: KO Aquilae as an example of systems with undersize subgiant secondaries in pre-main sequence contraction. Authors: Roxburgh, I. W. Bibcode: 1966AJ.....71..133R Altcode: No abstract at ADS Title: On stellar rotation, III. Thermally generated magnetic fields Authors: Roxburgh, I. W. Bibcode: 1966MNRAS.132..201R Altcode: The battery effect of the electron partial pressure must generate a toroidal magnetic field in an initially non-magnetic rotating star, since there is no steady state solution that gives the centrifugal force curl free, whether or not there is maintained meridian circulation. The magnitude of the thermally generated field is discussed and a detailed calculation of the case with zero circulation is presented when the limit on the growth of the field comes from Ohmic dissipation. Results are presented for both the steady state, and the build up to the steady state solution. The work presented here differs from previous work of Biermaun and Schluter in that the solution is fully self-consistent, both with the electro-dynamics and the conditions of dynamical and thermal equilibrium. Title: Magnetostatic equilibrium of polytropes Authors: Roxburgh, I. W. Bibcode: 1966MNRAS.132..347R Altcode: The equilibrium structure of magnetic fields in stars is investigated assuming the star to be a polytrope and the structure of the field is determined for values of the polytropic index fl=0, I, , 2 and 3, using a first order perturbation theory. As the magnetic body force becomes vanishingly small in the surface layers this method is satisfactory. The first three eigen solutions are determined and it is shown that whereas for n I the number of nodes of the field increases with an increasing ratio of toroidal to poloidal field strength, for n> I the field has no nodes between centre and surface, for all values of this ratio. Title: On the Fission Theory of the Origin of Binary Stars Authors: Roxburgh, Ian W. Bibcode: 1966ApJ...143..111R Altcode: The pre-main-sequence evolution of a rotating non-magnetic star is investigated. Stars forming out of interstellar gas clouds are shown to have sufficient angular momentum to cause centrifugal force to balance gravity before reaching the stable Hayashi phase, so that during subsequent evolution matter must be left behind from the equatorial regions. During contraction through the fully convective Hayasbi phase the coupling of central and surface regions by convection determines a definite rotation law which we take to be uniform rotation. YVith continued contraction the star develops a radiative core and the "viscosity" effect of the turbulence is no longer operative; each element of the growing core therefore conserves its angular momentum causing an inward increase in angular velocity. It is shown that the ratio of centrifugal force to gravity increases in the central regions and that for stars with mass > 0.8 Mo rotational instability is likely to occur. This is imagined to cause the splitting of the original star into two components and so form a binary system. Assuming conservation of angular momentum on fission it is shown that stars with mass 4 Mo can form a contact binary system whereas more massive stars will produce separated binaries. The theoretical limits of Mo and 4 Mo for the total mass of contact binanes are in good agreement with observations of V Ursae ajoris systems, as is the distribution of total angular momentum with mass. Title: Structure, Oscillations and Stability of Rotating White Dwarfs Authors: Roxburgh, I. W.; Durney, B. R. Bibcode: 1966ZA.....64..504R Altcode: No abstract at ADS Title: On steller rotation, V. The Structure of rotating stars Authors: Roxburgh, I. W.; Strittmatter, P. A. Bibcode: 1966MNRAS.133..345R Altcode: In previous papers in this series the structure of rotating, upper main sequence stars was examined, and the distributions of angular momentum and magnetic field strength were derived under the assumption that there was no large scale meridional circulation. In this paper we obtain the changes in the remaining physical quantities due to the effect of rotation. Results are given for models with Schwarzschild, Kramers and electron scattering opacity laws and, in the latter case, for a series of values of magnetic field strength. The change in the position of a star in a plot of Mbol v. log Te is given in terms of the parameter A - c2R u3/GM both for stars viewed pole on and perpendicular to the rotation axis. ( c' the angular velocity of the convective core, Ru the radius of a non-rotating star of mass M.) It is shown that the total luminosity of a star is reduced by rotation but that at a given value of Te rotating stars appear brighter than their non-rotating counterparts. Title: On stellar rotation. IV, Thermally generated magnetic fields limited by the Hall field Authors: Roxburgh, I. W.; Strittmatter, P. A. Bibcode: 1966MNRAS.133....1R Altcode: The analysis of previous papers is extended to consider the structure of the rotation and magnetic fields inside non-uniformly rotating early main sequence stars, where the limit on the growth of the thermally generated toroidal magnetic field comes from the Hall effect than rather the olimic field. Assuming a steady state with vanishing circulation currents the structure and electrodynamic equations are solved simultaneously using a first order perturbation analysis. The solutions obtained depend on the assumpt&.on regarding the structure of magnetic fields in convective zones, but all give an outward increase in angular velocity, in contrast to the solutions derived in Papers I and II of this series. If, as is usual, we assume that there is no large scale component of magnetic field in the convective core, then the angular velocity at the surface is I o86 times the value in the central convective core. The magnetic field has a maximum at of the radius of x 107A1I2MR-2 Gauss where A is the ratio of centrifugal force to gravity at the surface of the star. This gives a field of 3 X 100 Gauss in a typical rapidly rotating 0 or B star. Title: Stability of Rotating Massive Stars in General Relativity Authors: Durney, B.; Roxburgh, I. W. Bibcode: 1965Natur.208.1304D Altcode: THE suggestion by Hoyle and Fowler1 that stars with masses of 106-1010 Msolar may provide the energy for radio sources, and the subsequent discovery of quasars, has stimulated considerable interest in the structure of very massive stars2. Iben3, using a binding-energy argument, showed that within the framework of general relativity a spherical massive star becomes unstable long before it has contracted to the stage at which nuclear reactions become important. A similar conclusion was obtained by Chandrasekhar4, using a detailed stability analysis on the spherically symmetric relativistic equations and calculating the relaxation oscillations from a variational principle. Similar results have been obtained by Fowler5 using a virial theorem approach. Title: KO Aquilae as an Example of Close Binary Systems with Undersize Subgiant Secondaries in Pre-Main Sequence Contraction. Authors: Roxburgh, Ian W. Bibcode: 1965AJ.....70..690R Altcode: The hypothesis is advanced that close binary systems with an undersize subgiant secondary are in the pre-main sequence evolutionary phase, and applied to the system KO Aquilae. Since KO Aquilae is a single spectrum binary a complete description of the system can be obtained by supposing that the primary is contracting towards the main sequence, and the age of the system is found to be 3.5 x 1013 sec, the mass of the primary 2.9M0. and the secondary 0.58Mo.. The radius of the primary is found to be 2.6R0. and that of the secondary 2.lR0., while the distance between the mass centers is 13R0.. To confirm our hypothesis we compute the radius of a star of 0.58M0 after 3.5 x 1013 sec and this is found to lie between 1.9Ro. and 2.3Ra., in good agreement with the previous determination. The angular momentum of the system is computed and is found to be in satisfactory agreement with the predictions of the fission theory as advanced by Roxburgh (1965). Title: Effect of Rotation on the Stability of Very Massive Stars Authors: Roxburgh, Ian W. Bibcode: 1965Natur.207..363R Altcode: No abstract at ADS Title: On the Fission Theory of the Origin of Binary Stars. Authors: Roxburgh, Ian W. Bibcode: 1965AJ.....70..330R Altcode: The pre-main sequence evolution of a rotating nonmagnetic star is investigated and it is found that rotational instability will occur in the central regions of the star during the development of a radiative core, provided that the total mass exceeds 0.8M0.. This is imagined to give rise to the splitting of the central regions and the formation of a binary system. A discussion of the angular momentum of the objects predicts that for a total mass between 0.8M0 and 4.0M0. the end product should be a contact configuration of the W Ursae Majoris type. For larger masses the star must form a separated binary system. The predicted distribution of angular momentum with mass is in good agreement with observations of W Ursae Majoris systems. Title: Solar rotation and the perihelion advance of the planets a reply to comments by G.M. Clemence on the paper by I.W. Roxburgh Authors: Roxburgh, Ian W. Bibcode: 1965Icar....4..220R Altcode: No abstract at ADS Title: Rotational Spread of the Main Sequence Authors: Roxburgh, I. W.; Strittmatter, P. A. Bibcode: 1965ZA.....63...15R Altcode: No abstract at ADS Title: A note on the boundary of convective zones in stars Authors: Roxburgh, Ian W. Bibcode: 1965MNRAS.130..223R Altcode: Convective motions overshoot the boundary of convective zones in stellar models, producing an extended convective zone. This overshooting is considered and the radius of the extended zone is evaluated. The importance of this overshooting for the theory of stellar rotation is discussed. Title: The growth of condensations in a Newtonian model of the steady state universe Authors: Roxburgh, I. W.; Saffman, P. G. Bibcode: 1965MNRAS.129..181R Altcode: A Newtonian model of the cold steady-state universe is proposed in which new material is created with the same velocity as its surroundings, and the stability of such a universe is examined. If K= 47T/3 Gp0 H- 2is greater than 2 the universe is unstable against small disturbances; if K is less than 2 the universe is stable against regular small disturbances, but it is shown that there still exist non-regular disturbances for which the universe is unstable. An exact similarity solution of the equations governing the growth of a spherically symmetric condensation is given for the case K< 2, and the condensation is found to grow like e3aHt, where 2oL = (I +4K) - I. The ondition that the universe be self-propagating gives the relation - 1+'1 for the number density N of condensations with mass M. Title: The structure of rapidly rotating polytropes Authors: Monaghan, J. J.; Roxburgh, I. W. Bibcode: 1965MNRAS.131...13M Altcode: The structure of rapidiy rotating polytropes is investigated using an approximation technique of integrating outwards from the centre and inwards from the surface, matching the two solutions at an interface. Results are presented for values of the polytropic index fl= I, , 2, , 3, , 4. The method used is an extension of Jeans' generalized Roche model. Title: On Models of Non Spherical Stars I. The Theory of Rapildy Rotating Main Sequence Stars. With 3 Figures in the Text Authors: Roxburgh, I. W.; Griffith, J. S.; Sweet, P. A. Bibcode: 1965ZA.....61..203R Altcode: No abstract at ADS Title: On Models of Non Spherical Stars. II. Rotating White Dwarfs. With 2 Figures in the Text Authors: Roxburgh, I. W. Bibcode: 1965ZA.....62..134R Altcode: No abstract at ADS Title: Some steady, self-consistent solutions for rotating magnetic stars Authors: Roxburgh, I. W. Bibcode: 1965IAUS...22..103R Altcode: No abstract at ADS Title: Solar Rotation and the Perihelion Advance of the Planets Authors: Roxburgh, Ian W. Bibcode: 1964Icar....3...92R Altcode: The hypothesis that the inside of the Sun is rotating much more rapidly than the surface layers is examined and found to be consistent with present ideas on the formation of the solar system and the internal constitution of the Sun. The angular velocity of the inner region is estimated and it is shown that the rotational distortion of the Sun produces a perihelion advance of the planets. If the angular velocity inside the Sun has the same magnitude as in a typical rapidly rotating star, then the anomalous advance of the perihelion of Mercury, usually counted as one of the crucial tests of general relativity, can be explained by the gravitational effect of the rotating Sun. Title: On stellar rotation, I. The rotation of upper main-sequence stars Authors: Roxburgh, I. W. Bibcode: 1964MNRAS.128..157R Altcode: The centrifugal perturbation to the thermal field drives meridional circulation in radiative zones of rotating stars. Transport of angnlar momentum by the circulation changes the angnlar velocity field and hence the circulation itself. We here assume that the system approaches a steady state in which there is no meridional circulation, and calculate that distribution of angnlar velocity that does not upset radiative equllibrium, assuming that the star has no internal magnetic field. Results are obtained for two upper main-sequence stellar models: one with the opacity given by a modified Kramer's law, the other with electron scattering. The angnlar velocity is found to be a monotonically decreasing function of distance from the centre of the star and to be independent of latitude, so that the star rotates in spherical shells. The solution is shown to be dynamically stable. Title: On stellar rotation, II. The rotation of lower main-sequence stars Authors: Roxburgh, I. W. Bibcode: 1964MNRAS.128..237R Altcode: The first-order perturbation analysis developed in Paper I is extended to stars with a radiative core and convective envelope and with the proton-proton chain as the source of energy. The variation of angnlar velocity with distance from the centre of the star is calculated for a model of the Sun in its initial main-sequence state. The inward increase in angnlar velocity is too small to alter significantly the value of the star's angnlar momentum computed under the assumption of uniform rotation. Title: Stellar hydromagnetics Authors: Roxburgh, I. W. Bibcode: 1963stev.conf..446R Altcode: No abstract at ADS Title: Steady meridian circulation in rotating magnetic stars Authors: Roxburgh, I. W. Bibcode: 1963MNRAS.126...67R Altcode: It is well-known that non-spherical perturbations such as centrifugal and magnetic forces lead, in general, to a thermally-driven meridian circulation in stellar radiative zones. A circulation fast enough to be of interest tends to distort the perturbation field that drives it. In this paper we suppose that a steady state has been reached, and study those rotation and magnetic fields that are unaffected by the circulation field they generate. Only two cases are easy to treat: one with the centrifugal force the dominant perturbation, and nearly uniform rotation maintained by a weak poloidal magnetic field; the other with the toroidal component of the magnetic field dominant. Title: On the Thermal Generation of Toroidal Magnetic Fields in Rotating Stars. Authors: Mestel, L.; Roxburgh, I. W. Bibcode: 1962ApJ...136..615M Altcode: Biermann (1950) has shown that in a rotating star without any initial magnetic field the electron partial pressure slowly generates a toroidal magnetic field of considerable strength. The problem is here reconsidered, assuming the star to have a primeval magnetic field, with its poloidal component very much weaker than the toroidal field predicted by Biermann. It is shown that the interaction of the magnetic torque and the rotation field is sufficient to insure that the electron pressure has negligible effect, whether or not there is meridian circulation of matter inside the star.