In the context of the ESPaDOnS and Narval spectropolarimetric surveys of Herbig Ae/Be stars, we discovered and then monitored the magnetic field of HD 190073 over more than four years, from 2004 to ...2009. Our observations all displayed similar Zeeman signatures in the Stokes V spectra, indicating that HD 190073 hosted an aligned dipole, stable over many years, consistent with a fossil origin. We obtained new observations of the star in 2011 and 2012 and detected clear variations of the Zeeman signature on timescales of days to weeks, indicating that the configuration of its field has changed between 2009 and 2011. Such a sudden change of external structure of a fossil field has never previously been observed in any intermediate or high-mass star. HD 190073 is an almost entirely radiative pre-main sequence star, probably hosting a growing convective core. We propose that this dramatic change is the result of the interaction between the fossil field and the ignition of a dynamo field generated in the newly-born convective core.
Context. Many aspects of the design trade-off of a space-based instrument and its performance can best be tackled through simulations of the expected observations. The complex interplay of various ...noise sources in the course of the observations make such simulations an indispensable part of the assessment and design study of any space-based mission. Aims. We present a formalism to model and simulate photometric time series of CCD images by including models of the CCD and its electronics, the telescope optics, the stellar field, the jitter movements of the spacecraft, and all of the important natural noise sources. Methods. This formalism has been implemented in a versatile end-to-end simulation software tool, specifically designed for the PLATO (Planetary Transists and Oscillations of Stars) space mission to be operated from L2, but easily adaptable to similar types of missions. We call this tool Plato Simulator. Results. We provide a detailed description of several noise sources and discuss their properties in connection with the optical design, the allowable level of jitter, the quantum efficiency of the detectors, etc. The expected overall noise budget of generated light curves is computed, as a function of the stellar magnitude, for different sets of input parameters describing the instrument properties. The simulator is offered to the scientific community for future use.
Aim
To evaluate the biological effects in vitro of MTA‐Angelus (MTA‐Ang; Angelus, Londrina, PR, Brazil), MTA Repair HP (MTA‐HP; Angelus) and NeoMTA Plus (NeoMTA‐P; Avalon Biomed Inc, Bradenton, FL, ...USA) on human dental pulp stem cells (hDPSCs).
Methodology
Cell viability and cell migration assays were performed using eluates of each material. To evaluate cell morphology and cell attachment to the different materials, hDPSCs were directly seeded onto the material surfaces and analysed by immunocytofluorescence and scanning electron microscopy, respectively. The chemical composition of the materials was determined by energy‐dispersive X‐ray (EDX), and eluates were analysed by inductively coupled plasma–mass spectrometry (ICP‐MS). Statistical analysis was performed with the analysis of variance and Bonferroni or Tukey post‐test (α < 0.05).
Results
Undiluted MTA‐Ang, MTA‐HP and NeoMTA‐P displayed a significant increase in cell viability greater than that obtained using complete medium alone (control) (*P < 0.05; **P < 0.01; ***P < 0.001). Moreover, a cell migration assay revealed cell migration rates after incubation with extracts of MTA‐Ang, MTA‐HP and NeoMTA‐P that were similar to levels obtained in the control group. In addition, stretched cytoskeletal F‐actin fibres were detected in the cells treated with the three material extracts. SEM studies revealed a high degree of cell proliferation and attachment on all three materials. EDX analysis demonstrated similar weight percentages of C, O and Ca in all three materials, whilst other elements such as Al, Si and S were also found.
Conclusions
MTA‐Ang, MTA‐HP and NeoMTA‐P were associated with biological effects on hDPSCs in terms of cell proliferation, morphology, migration and attachment.
Aims. Using the CoRoT space based photometry of the O-type binary HD 46149, stellar atmospheric effects related to rotation can be separated from pulsations, because they leave distinct signatures in ...the light curve. This offers the possibility of characterising and exploiting any pulsations seismologically. Methods. Combining high-quality space based photometry, multi-wavelength photometry, spectroscopy and constraints imposed by binarity and cluster membership, the detected pulsations in HD 46149 are analyzed and compared with those for a grid of stellar evolutionary models in a proof-of-concept approach. Results. We present evidence of solar-like oscillations in a massive O-type star, and show that the observed frequency range and spacings are compatible with theoretical predictions. Thus, we unlock and confirm the strong potential of this seismically unexplored region in the HR diagram.
In this paper we report the results of high-resolution circular spectropolarimetric monitoring of the Herbig Ae star V380 Ori, in which we discovered a magnetic field in 2005. A careful study of the ...intensity spectrum reveals the presence of a cool spectroscopic companion. By modelling the binary spectrum, we infer the effective temperature of both stars: 10 500 ± 500 K for the primary and 5500 ± 500 K for the secondary, and we argue that the high metallicity (M/H= 0.5), required to fit the lines, may imply that the primary is a chemically peculiar star. We observe that the radial velocity of the secondary's lines varies with time, while that of the primary does not. By fitting these variations, we derive the orbital parameters of the system. We find an orbital period of 104 ± 5 d and a mass ratio (MP/MS) larger than 2.9. The intensity spectrum is heavily contaminated with strong, broad and variable emission. A simple analysis of these lines reveals that a disc might surround the binary and that a wind occurs in the environment of the system. Finally, we performed a magnetic analysis using the least-squares deconvolved profiles of the Stokes V spectra of both stars and adopting the oblique rotator model. From rotational modulation of the primary's Stokes V signatures, we infer its rotation period P= 4.312 76 ± 0.000 42 d and find that it hosts a centred dipole magnetic field of polar strength 2.12 ± 0.15 kG, with a magnetic obliquity β= 66°± 5° and a rotation axis inclination i= 32°± 5°. However, no magnetic field is detected in the secondary, and if it hosts a dipolar magnetic field, its strength must be below about 500 G, to be consistent with our observations.
Context. Stellar activity cycles are the manifestation of dynamo process running in the stellar interiors. They have been observed from years to decades thanks to the measurement of stellar magnetic ...proxies on the surface of the stars, such as the chromospheric and X-ray emissions, and to the measurement of the magnetic field with spectropolarimetry. However, all of these measurements rely on external features that cannot be visible during, for example, a Maunder-type minimum. With the advent of long observations provided by space asteroseismic missions, it has been possible to penetrate the stars and study their properties. Moreover, the acoustic-mode properties are also perturbed by the presence of these dynamos. Aims. We track the temporal variations of the amplitudes and frequencies of acoustic modes allowing us to search for signature of magnetic activity cycles, as has already been done in the Sun and in the CoRoT target HD 49933. Methods. We used asteroseimic tools and more classical spectroscopic measurements performed with the NARVAL spectropolarimeter to check that there are hints of any activity cycle in three solar-like stars observed continuously for more than 117 days by the CoRoT satellite: HD 49385, HD 181420, and HD 52265. To consider that we have found a hint of magnetic activity in a star we require finding a change in the amplitude of the p modes that should be anti-correlated with a change in their frequency shifts, as well as a change in the spectroscopic observations in the same direction as the asteroseismic data. Results. Our analysis gives very small variation in the seismic parameters preventing us from detecting any magnetic modulation. However, we are able to provide a lower limit of any magnetic-activity change in the three stars that should be longer than 120 days, which is the length of the time series. Moreover we computed the upper limit for the line-of-sight magnetic field component being 1, 3, and 0.6 G for HD 49385, HD 181420, and HD 52265, respectively. More seismic and spectroscopic data would be required to have a firm detection in these stars.
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 ${\rm \mu Hz}$. The p-mode amplitudes are slightly less than 4 ppm with a line width of about 8 ${\rm \mu Hz}$ at the maximum of the p modes. The inclination angle is estimated to be around $45 \degr$. The large mode line-width combined with the observed mode spacing make it difficult to identify the $\ell=2$ modes and to estimate the rotational splitting. We explore two scenarios for the identification of the modes.
Context. B-type stars are promising targets for asteroseismic modelling, since their frequency spectrum is relatively simple. Aims. We deduce and summarise observational constraints for the hybrid ...pulsator, HD 50230, earlier reported to have deviations from a uniform period spacing of its gravity modes. The combination of spectra and a high-quality light curve measured by the CoRoT satellite allow a combined approach to fix the position of HD 50230 in the HR diagram. Methods. To describe the observed pulsations, classical Fourier analysis was combined with short-time Fourier transformations and frequency spacing analysis techniques. Visual spectra were used to constrain the projected rotation rate of the star and the fundamental parameters of the target. In a first approximation, the combined information was used to interpret multiplets and spacings to infer the true surface rotation rate and a rough estimate of the inclination angle. Results. We identify HD 50230 as a spectroscopic binary and characterise the two components. We detect the simultaneous presence of high-order g modes and low-order p and g-modes in the CoRoT light curve, but were unable to link them to line profile variations in the spectroscopic time series. We extract the relevant information from the frequency spectrum, which can be used for seismic modelling, and explore possible interpretations of the pressure mode spectrum.
We have obtained high-resolution spectropolarimetric data for the planet-hosting star τ Bootis, using the ESPaDOnS spectropolarimeter at the Canada–France–Hawaii Telescope (CFHT). A weak but clear ...Stokes V signature is detected on three of the four nights of 2006 June during which we have recorded data. This polarimetric signature indicates with no ambiguity the presence of a magnetic field at the star's surface, with intensity of just a few gauss. The analysis of the photospheric lines of τ Boo at ultra-high signal-to-noise ratio reveals the presence of an 18 per cent relative differential rotation. Tentative Zeeman–Doppler imaging, using our spectropolarimetric observations covering only a fraction of the star's rotational phase, indicates a magnetic field with a dominant potential field component. The data are best fitted when a 3.1-d period of modulation and an intermediate inclination are assumed. Considering the level of differential rotation of τ Boo, this implies a rotation period of 3.0 d at the equator and of 3.7 d at the pole, and a topology of the magnetic field where its main non-axisymmetric part is located at low latitudes. The planet is probably synchronized with the star's rotation at intermediate latitudes, while the non-axisymmetric part of the magnetic field seems located at lower latitudes. Our limited data do not provide sufficient constraints on the magnetic field to study a possible interaction of the planet with the star's magnetosphere. Investigating this issue will require data with much better phase coverage. Similar studies should also be performed for other stars hosting close-in giant planets.
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 $M_\odot$, the radius, R = 1.96 ± 0.046 $R_\odot$, and the age ~2.4 Gyr.
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