Context. The second short run (SRa02) of the CoRoT space mission for asteroseismology was partly devoted to stars belonging to the Mon OB2 association. An intense monitoring has been performed on ...Plaskett’s star (HD 47129) and the unprecedented quality of the light curve allows us to shed new light on this very massive, non-eclipsing binary system. Aims. We particularly aimed at detecting periodic variability that might be associated with pulsations or interactions between both components. We also searched for variations related to the orbital cycle that could help to constrain the inclination and the morphology of the binary system. Methods. We applied an iterative Fourier-based prewhitening and a multiperiodic fitting procedure to analyse the time series and extract the frequencies of variations from the CoRoT light curve. We describe the noise properties to tentatively define an appropriate significance criterion and, in consequence, to only point out the peaks at a certain significance level. We also detect the variations related to the orbital motion and study them with the NIGHTFALL programme. Results. The periodogram computed from Plaskett’s star CoRoT light curve mainly exhibits a majority of peaks at low frequencies. Among these peaks, we highlight a list of 43 values, notably including two different sets of harmonic frequencies whose fundamental peaks are located at about 0.07 and 0.82 d-1. The former represents the orbital frequency of the binary system, whilst the latter could probably be associated with non-radial pulsations. The study of the 0.07 d-1 variations reveals a hot spot most probably situated on the primary star and facing the secondary. Conclusions. The investigation of this unique dataset constitutes a further step in the understanding of Plaskett’s star. These results provide a first basis for future seismic modelling and put forward the probable existence of non-radial pulsations in Plaskett’s star. Moreover, the fit of the orbital variations confirms the problem of the distance of this system which was already mentioned in previous works. A hot region between both components renders the determination of the inclination ambiguous.
Aim
To evaluate in a laboratory setting the effects of Endosequence BC Sealer HiFlow (Brasseler USA, Savannah, GA, USA), a novel calcium silicate‐based sealer developed for use in warm canal filling ...techniques, on human periodontal ligament stem cells (hPDLSCs).
Methodology
Eluates of EndoSequence BC Sealer HiFlow (BCHiF) (Brasseler USA), EndoSequence BC Sealer (BCS) (Brasseler USA) and AH Plus (AHP) (Dentsply DeTrey GmbH, Konstanz, Germany) were placed in contact with hPDLSCs. The characterization of the chemical elements of the root canal sealers was assessed using scanning electron microscopy and energy‐dispersive X‐ray analysis (SEM‐EDX). Inductively coupled plasma‐mass spectrometry (ICP‐MS) was used to determine the ion release of the sealers. MTT assay and wound healing techniques were used to determine cell viability and migration, respectively. Cell morphology and cell attachment were assessed using a direct contact technique of hPDLSCs onto the surface of the sealers and analysed by SEM. The bioactivity potential was carried out with the Alizarin Red and qPCR testing methods. The statistical differences were evaluated using one‐way anova and Tukey’s test (P < 0.05).
Results
ICP‐MS and EDX revealed significantly more zirconium in BCHiF than BCS (P < 0.05), whereas BCS had slightly higher levels of Ca2+ than BCHiF (P < 0.05). The cell viability assay revealed no relevant differences between BCS and BCHiF when compared with the control group (P > 0.05). Both BCS and BCHiF had similar rates of cell migration to the control group at 24 and 48 h. Cell morphology and adhesion capacity were also similar for BCS and BCHiF groups, whilst the AHP group was associated with reduced adhesion capacity. The Alizarin Red assay revealed a significant difference between the BCS and the control group (P < 0.001), as well as for the BCHiF group (P < 0.001). Finally, BCS and BCHiF promoted overexpression of osteo/cementogenic genes.
Conclusions
In general, EndoSequence BC Sealer HiFlow possesses suitable biological properties to be safely used as a root canal filling material and promote increased expression of oste/cementogenic genes by hPDLSCs.
We present the analysis of the time series observations of CoRoT 102699796 obtained by the Convection, Rotation and planetary Transits (CoRoT) satellite that show the presence of five independent ...oscillation frequencies in the range 3.6-5 c d−1. Using spectra acquired with FLAMES@VLT, we derive the following stellar parameters: spectral type F1V, T
eff= 7000 ± 200 K, log (g) = 3.8 ± 0.4, M/H=−1.1 ± 0.2, v sin i= 50 ± 5 km s−1, L/L⊙= 21+21
− 11. Thus, for the first time we report the existence of a metal-poor, intermediate-mass pre-main-sequence (PMS) pulsating star. Ground-based and satellite data are used to derive the spectral energy distribution (SED) of CoRoT 102699796 extending from the optical to mid-infrared wavelengths. The SED shows a significant IR excess at wavelengths greater than ∼5 μm. We conclude that CoRoT 102699796 is a young Herbig Ae (F1Ve) star with a transitional disc likely associated with the H ii region FT96213.1-2.2.
The pulsation frequencies have been interpreted in the light of the non-radial pulsation theory, using the losc code in conjunction with static and rotational evolutionary tracks. A minimization algorithm was used to find the best-fitting model with M= 1.84 M⊙, T
eff= 6900 K which imply an isochronal age of t∼ 2.5 Myr. This result is based on the interpretation of the detected frequencies as g modes of low-moderate n-value. To our knowledge, this is the first time that such modes are identified in a intermediate-mass PMS pulsating star. Since CoRoT 102699796 lies in the region of the Hertzsprung-Russell (HR) diagram where the δ Sct and γ Dor instability strips intersect, we argue that the observed pulsation characteristics are intermediate between these classes of variables, i.e. CoRoT 102699796 is likely the first PMS hybrid γ Dor-δ Sct pulsator ever studied.
Asteroseismology and interferometry Cunha, M. S.; Aerts, C.; Christensen-Dalsgaard, J. ...
The Astronomy and astrophysics review,
11/2007, Volume:
14, Issue:
3-4
Journal Article
Peer reviewed
Open access
Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like ...pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research. PUBLICATION ABSTRACT
Context. HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from its host star. Stellar light reflected by the planet was tentatively identified in the 34-day CoRoT run acquired in ...October − November 2008. Aims. We constrain the properties of the magnetic field of HD 46375 based on spectropolarimetric observations with the NARVAL spectrograph at the Pic du Midi observatory. In addition, we use a high-resolution NARVAL flux spectrum to contrain the atmospheric parameters. With these constraints, we perform an asteroseismic analysis and modelling of HD 46375 using the frequencies extracted from the CoRoT light curve. Methods. We used Zeeman Doppler imaging to reconstruct the magnetic map of the stellar surface. In the spectroscopic analysis we fitted isolated lines using 1D LTE atmosphere models. This analysis was used to constrain the effective temperature, surface gravity, and chemical composition of the star. To extract information about the p-mode oscillations, we used a technique based on the envelope autocorrelation function (EACF). Results. From the Zeeman Doppler imaging observations, we observe a magnetic field of ≈5 Gauss. From the spectral analysis, HD 46375 is inferred to be an unevolved K0 type star with high metallicity Fe/H = +0.39. Owing to the relative faintness of the star (mhip = 8.05), the signal-to-noise ratio is too low to identify individual modes. However, we measure the p-mode excess power and large separation Δν0 = 153.0 ± 0.7μHz. Conclusions. We are able do constrain the fundamental parameters of the star thanks to spectrometric and seismic analyses. We conclude that HD 46375 is similar to a young version of α Cen B. This work is of special interest because of its combination of exoplanetary science and asteroseismology, which are the subjects of the current Kepler mission and the proposed Plato mission.
Context. The general context of this paper is the study of magnetic fields in the pre-main sequence intermediate mass Herbig Ae/Be stars. Magnetic fields are likely to play an important role in ...pre-main sequence evolution at these masses, in particular in controlling the gains and losses of stellar angular momentum. Aims. The particular aim of this paper is to announce the detection of a structured magnetic field in the Herbig Ae star HD 190073, and to discuss various scenarii for the geometry of the star, its environment and its magnetic field. Methods. We have used the ESPaDOnS spectropolarimeter at CFHT in 2005 and 2006 to obtain high-resolution, high signal-to-noise circular polarization spectra which demonstrate unambiguously the presence of a magnetic field in the photosphere of this star. Results. Nine circular polarization spectra were obtained, each one showing a clear Zeeman signature. This signature is suggestive of a magnetic field structured on large scales. The signature, which corresponds to a longitudinal magnetic field of 74\pm 10 G, does not vary detectably on a one- year timeframe, indicating either an azimuthally symmetric field, a zero inclination angle between the rotation axis and the line of sight, or a very long rotation period. The optical spectrum of HD 190073 exhibits a large number of emission lines. We discuss the formation of these emission lines in the framework of a model involving a turbulent heated region at the base of the stellar wind, possibly powered by magnetic accretion. Conclusions. This magnetic detection contributes an important new observational discovery which will aid our understanding of stellar magnetism at intermediate masses.
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 recently discovered magnetic Herbig Ae and Be stars may provide qualitatively new information about the formation and evolution of magnetic Ap and Bp stars. We have performed a detailed ...investigation of one particularly interesting binary system with a Herbig Ae secondary and a late B-type primary possessing a strong, globally ordered magnetic field. 20 high-resolution Stokes V spectra of the system were obtained with the ESPaDOnS instrument mounted on the Canada–France–Hawaii Telescope. In these observations we see clear evidence for a magnetic field in the primary, but no evidence for a magnetic field in the secondary. A detailed abundance analysis was performed for both stars, revealing strong chemical peculiarities in the primary and normal chemical abundances in the secondary. The primary is strongly overabundant in Si, Cr and other iron-peak elements, as well as Nd, and underabundant in He. The primary therefore appears to be a very young Bp star. In this context, line profile variations of the primary suggest non-uniform lateral distributions of surface abundances. Interpreting the 0.639 95 ± 0.000 09 d variation period of the Stokes I and V profiles as the rotational period of the star, we have modelled the magnetic field geometry and the surface abundance distributions of Si, Ti, Cr and Fe using magnetic Doppler imaging. We derive a dipolar geometry of the surface magnetic field, with a polar strength Bd= 1230 G and an obliquity β= 57°. The distributions Ti, Cr and Fe are all qualitatively similar, with an elongated patch of enhanced abundance situated near the positive magnetic pole. The Si distribution is somewhat different, and its relationship to the magnetic field geometry less clear.
We present the analysis of the time series observations of CoRoT102699796 obtained by the Convection, Rotation and planetary Transits (CoRoT) satellite that show the presence of five independent ...oscillation frequencies in the range 3.6-5 c d-1. Using spectra acquired with FLAMESatVLT, we derive the following stellar parameters: spectral type F1V, Teff= 7000 +/- 200K, log(g) = 3.8 +/- 0.4, M/H=-1.1 +/- 0.2, vsini= 50 +/- 5 kms-1, L/Lodot= 21+21- 11. Thus, for the first time we report the existence of a metal-poor, intermediate-mass pre-main-sequence (PMS) pulsating star. Ground-based and satellite data are used to derive the spectral energy distribution (SED) of CoRoT102699796 extending from the optical to mid-infrared wavelengths. The SED shows a significant IR excess at wavelengths greater than similar to 5 mu m. We conclude that CoRoT102699796 is a young Herbig Ae (F1Ve) star with a transitional disc likely associated with the Hii region FT96213.1-2.2. The pulsation frequencies have been interpreted in the light of the non-radial pulsation theory, using the losc code in conjunction with static and rotational evolutionary tracks. A minimization algorithm was used to find the best-fitting model with M= 1.84 Modot, Teff= 6900K which imply an isochronal age of t similar to 2.5Myr. This result is based on the interpretation of the detected frequencies as g modes of low-moderate n-value. To our knowledge, this is the first time that such modes are identified in a intermediate-mass PMS pulsating star. Since CoRoT102699796 lies in the region of the Hertzsprung-Russell (HR) diagram where the delta Sct and gamma Dor instability strips intersect, we argue that the observed pulsation characteristics are intermediate between these classes of variables, i.e. CoRoT102699796 is likely the first PMS hybrid gamma Dor- delta Sct pulsator ever studied.
We present the results of multisite observations spanning two years of the pre-main-sequence Herbig Ae star HD 104237. The star was observed in high resolution spectroscopy (R greater than or equal ...to 35 000) for a total of 157.3 h of effective exposure time, over 42 nights, corresponding to a data base of 1888 individual echelle spectra. We confirm that the HD 104237 system includes a spectroscopic binary, whose primary component HD 104237 A is pulsating. The resulting high quality radial velocity curve allows us to detect for the first time by spectroscopic means multiperiodic oscillations in a pre-main sequence star. Five different modes are detected with very high confidence, with frequencies ranging between 28.5 and 35.6 d super(-1), typical of delta Scuti pulsations; an additional 3 frequencies have been extracted from the data, but with a lower level of confidence. The pattern of frequencies indicates that at least some of the detected modes are non-radial. The precise orbit determination and the measurement of the double line spectroscopic binary observed around periastron enabled us to determine a mass ratio of 1.29 plus or minus 0.02 between the primary and the secondary; based on the primary mass of 2.2 plus or minus 0.1 M sub( )we conclude that the spectroscopic secondary HD 104237 b should have a mass of 1.7 plus or minus 0.1 M sub( )and lie outside the pre-main sequence instability strip towards later spectral types. A search for pulsations in the radial velocity curve of the much weaker secondary component was not conclusive at this stage. The location of the primary in the HR diagram and its position with respect to recent pre-main sequence evolutionary tracks and isochrones implies a location of the secondary indicative of spectral type K3.
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