Comparative seismology of pre- and main sequence stars in the instability strip

Pulsational properties of 1.8 M$_{\odot}$ stellar models covering the latest stages of contraction toward the main sequence up to early hydrogen burning phases are investigated by means of linear nonadiabatic analyses. Results confirm that pre-main sequence stars (pms) which cross the classical instability strip on their way toward the main sequence are pulsationally unstable with respect to the classical opacity mechanisms. For both pms and main sequence types of models in the lower part of the instability strip, the unstable frequency range is found to be roughly the same. Some non-radial unstable modes are very sensitive to the deep internal structure of the star. It is shown that discrimination between pms and main sequence stages is possible using differences in their oscillation frequency distributions in the low frequency range.Comment: 8 pages, 9 figures, accepted for publication in A&

Discovery of fossil magnetic fields in the intermediate-mass pre-main sequence stars

It is now well-known that the surface magnetic fields observed in cool, lower-mass stars on the main sequence (MS) are generated by dynamos operating in their convective envelopes. However, higher-mass stars (above 1.5 Msun) pass their MS lives with a small convective core and a largely radiative envelope. Remarkably, notwithstanding the absence of energetically-important envelope convection, we observe very strong (from 300 G to 30 kG) and organised (mainly dipolar) magnetic fields in a few percent of the A and B-type stars on the MS, the origin of which is not well understood. In this poster we propose that these magnetic fields could be of fossil origin, and we present very strong observational results in favour of this proposal.Comment: To appear in Proceedings IAU Symposium No. 259, 2009. Cosmic Magnetic Fields: From Planets, to Stars and Galaxie

A small survey of the magnetic fields of planet-host stars

Using spectropolarimetry, we investigate the large-scale magnetic topologies of stars hosting close-in exoplanets. A small survey of ten stars has been done with the twin instruments TBL/NARVAL and CFHT/ESPaDOnS between 2006 and 2011. Each target consists of circular-polarization observations covering 7 to 22 days. For each of the 7 targets in which a magnetic field was detected, we reconstructed the magnetic field topology using Zeeman-Doppler imaging. Otherwise, a detection limit has been estimated. Three new epochs of observations of Tau Boo are presented, which confirm magnetic polarity reversal. We estimate that the cycle period is 2 years, but recall that a shorter period of 240 days can not still be ruled out. The result of our survey is compared to the global picture of stellar magnetic field properties in the mass-rotation diagram. The comparison shows that these giant planet-host stars tend to have similar magnetic field topologies to stars without detected hot-Jupiters. This needs to be confirmed with a larger sample of stars.Comment: Accepted for publication in Monthly Notices of The Royal Astronomical Societ

Seismology and activity of the F type star HD 49933

A 10-night asteroseismic observation programme has been conducted in January 2004 with the spectrometer Harps at the ES0 3.6-m telescope. The selected target, the 6th magnitude F5V star HD 49933, was chosen among the prime candidates of Corot, the European space mission dedicated to characterize stellar oscillations mode with high precision photometry measurements. This star shows important line profiles variations, indicating a surprisingly high activity with respect to its low rotation rate. However, with the help of tools developed for disentangling the signatures of activity and oscillations, we are able to observe its oscillation spectrum in the frequency range [1.2, 2.2 mHz]. We measure the large separation (88.7+-0.4 microHz) and the maximum amplitude (around 0.4+-0.1 m/s rms), respectively in agreement and marginal agreement with the predicted values.Comment: accepted in A&A Letter

Seismic constraints on rotation of Sun-like star and mass of exoplanet

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.Comment: Published in Proceedings of the National Academy of Sciences (5 pages, 5 figures, 3 tables). Available at http://www.pnas.org/cgi/doi/10.1073/pnas.130329111

Asteroseismology of solar-type stars with Kepler: III. Ground-based data

peer reviewedWe report on the ground-based follow-up program of spectroscopic and photometric observations of solar-like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more than a thousand objects which are the subject of an intensive study by the Kepler Asteroseismic Science Consortium Working Group 1 (KASC WG-1). In the current work we will discuss the methods we use to determine the fundamental stellar atmospheric parameters using high-quality stellar spectra. These provide essential constraints for the asteroseismic modelling and make it possible to verify the parameters in the Kepler Input Catalogue (KIC)

Deviations from a uniform period spacing of gravity modes in a massive star

The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core, preventing precise predictions of stellar evolution. The unknown nature of the mixing processes as well as the extent of the central mixed region is particularly problematic for massive stars. Oscillations in stars with masses a few times that of the Sun offer a unique opportunity to disentangle the nature of various mixing processes, through the distinct signature they leave on period spacings in the gravity mode spectrum. Here we report the detection of numerous gravity modes in a young star with a mass of about seven solar masses. The mean period spacing allows us to estimate the extent of the convective core, and the clear periodic deviation from the mean constrains the location of the chemical transition zone to be at about 10 per cent of the radius and rules out a clear-cut profile.Peer reviewe

The global retinoblastoma outcome study : a prospective, cluster-based analysis of 4064 patients from 149 countries

DATA SHARING : The study data will become available online once all analyses are complete.BACKGROUND : Retinoblastoma is the most common intraocular cancer worldwide. There is some evidence to suggest that major differences exist in treatment outcomes for children with retinoblastoma from different regions, but these differences have not been assessed on a global scale. We aimed to report 3-year outcomes for children with retinoblastoma globally and to investigate factors associated with survival. METHODS : We did a prospective cluster-based analysis of treatment-naive patients with retinoblastoma who were diagnosed between Jan 1, 2017, and Dec 31, 2017, then treated and followed up for 3 years. Patients were recruited from 260 specialised treatment centres worldwide. Data were obtained from participating centres on primary and additional treatments, duration of follow-up, metastasis, eye globe salvage, and survival outcome. We analysed time to death and time to enucleation with Cox regression models. FINDINGS : The cohort included 4064 children from 149 countries. The median age at diagnosis was 23·2 months (IQR 11·0–36·5). Extraocular tumour spread (cT4 of the cTNMH classification) at diagnosis was reported in five (0·8%) of 636 children from high-income countries, 55 (5·4%) of 1027 children from upper-middle-income countries, 342 (19·7%) of 1738 children from lower-middle-income countries, and 196 (42·9%) of 457 children from low-income countries. Enucleation surgery was available for all children and intravenous chemotherapy was available for 4014 (98·8%) of 4064 children. The 3-year survival rate was 99·5% (95% CI 98·8–100·0) for children from high-income countries, 91·2% (89·5–93·0) for children from upper-middle-income countries, 80·3% (78·3–82·3) for children from lower-middle-income countries, and 57·3% (52·1-63·0) for children from low-income countries. On analysis, independent factors for worse survival were residence in low-income countries compared to high-income countries (hazard ratio 16·67; 95% CI 4·76–50·00), cT4 advanced tumour compared to cT1 (8·98; 4·44–18·18), and older age at diagnosis in children up to 3 years (1·38 per year; 1·23–1·56). For children aged 3–7 years, the mortality risk decreased slightly (p=0·0104 for the change in slope). INTERPRETATION : This study, estimated to include approximately half of all new retinoblastoma cases worldwide in 2017, shows profound inequity in survival of children depending on the national income level of their country of residence. In high-income countries, death from retinoblastoma is rare, whereas in low-income countries estimated 3-year survival is just over 50%. Although essential treatments are available in nearly all countries, early diagnosis and treatment in low-income countries are key to improving survival outcomes.The Queen Elizabeth Diamond Jubilee Trust and the Wellcome Trust.https://www.thelancet.com/journals/langlo/homeam2023Paediatrics and Child Healt

Stellar Physics at Dome C

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