ABSTRACT We study the dynamics of the stellar interior of the early red-giant star KIC 4448777 by asteroseismic inversion of 14 splittings of the dipole mixed modes obtained from Kepler observations. ...In order to overcome the complexity of the oscillation pattern typical of red-giant stars, we present a procedure to extract the rotational splittings from the power spectrum. We find not only that the core rotates from a minimum of 8 to a maximum of 17 times faster than the surface, confirming previous inversion results generated for other red giants (Deheuvels et al.), but we also estimate the variation of the angular velocity within the helium core with a spatial resolution of 0.001R and verify the hypothesis of a sharp discontinuity in the inner stellar rotation. The results show that the entire core rotates rigidly and provide evidence for an angular velocity gradient around the base of the hydrogen-burning shell; however, we do not succeed in characterizing the rotational slope, due to the intrinsic limits of the applied techniques. The angular velocity, from the edge of the core, appears to decrease with increasing distance from the center, reaching an average value in the convective envelope of 68 22 nHz. We conclude that a set of data that includes only dipolar modes is sufficient to infer quite accurately the rotation of a red giant not only in the dense core but also, with a lower level of confidence, in part of the radiative region and in the convective envelope.
The $\ion{Mg}{ii}$ k emission line is a good indicator of the level of chromospheric activity in late-type stars. We investigate the dependence of this activity indicator on fundamental stellar ...parameters. To this purpose we use IUE observations of the $\ion{Mg}{ii}$ k line in 225 late-type stars of luminosity classes I–V, with different levels of chromospheric activity. We first re-analyse the relation between $\ion{Mg}{ii}$ k line luminosity and stellar absolute magnitude, performing linear fits to the points. The ratio of $\ion{Mg}{ii}$ surface flux to total surface flux is found to be independent of stellar luminosity for evolved stars and to increase with decreasing luminosity for dwarfs. We also analyse the $\ion{Mg}{ii}$ k line surface flux-metallicity connection. The $\ion{Mg}{ii}$ k emission level turns out to be not dependent on metallicity. Finally, the $\ion{Mg}{ii}$ k line surface flux-temperature relation is investigated by treating separately, for the first time, a large sample of very active and normal stars. The stellar surface fluxes in the k line of normal stars are found to be strongly dependent on the temperature and slightly dependent on the gravity, thus confirming the validity of recently proposed models. In contrast, data relative to RS CVn binaries and BY Dra stars, which show very strong chromospheric activity, are not justified in the framework of a description based only on acoustic waves and uniformly distributed magnetic flux tubes so that they require more detailed models.
We present the results of the asteroseismic analysis of the red-giant star KIC 4351319 (TYC 3124-914-1), observed for 30 d in short-cadence mode with the Kepler satellite. The analysis has allowed us ...to determine the large and small frequency separations,
Hz and
Hz, respectively, and the frequency of maximum oscillation power,
Hz.
The high signal-to-noise ratio of the observations allowed us to identify 25 independent pulsation modes whose frequencies range approximately from 300 to
Hz.
The observed oscillation frequencies together with the accurate determination of the atmospheric parameters (effective temperature, gravity and metallicity), provided by additional ground-based spectroscopic observations, enabled us to theoretically interpret the observed oscillation spectrum.
KIC 4351319 appears to oscillate with a well-defined solar-type p-mode pattern due to radial acoustic modes and non-radial nearly pure p modes. In addition, several non-radial mixed modes have been identified.
Theoretical models well reproduce the observed oscillation frequencies and indicate that this star, located at the base of the ascending red-giant branch, is in the hydrogen-shell-burning phase, with a mass of ∼1.3 M⊙, a radius of
and an age of ∼5.6 Gyr. The main parameters of this star have been determined with an unprecedented level of precision for a red-giant star, with uncertainties of 2 per cent for mass, 7 per cent for age, 1 per cent for radius and 4 per cent for luminosity.
We present an asteroseismic approach to study the dynamics of the stellar interior in red giant stars by asteroseismic inversion of the splittings induced by the stellar rotation on the oscillation ...frequencies. We show preliminary results obtained for the red giant KIC4448777 observed by the space mission Kepler.
A study of the rotation-activity-age relationships in a large sample of single late-type main-sequence stars is carried out, based on rotation period data from the literature, on our measurements of ...the Mg II k line chromospheric flux in IUE high-resolution spectra, and on Hipparcos parallaxes. The analysis of the rotation period data of open clusters and field stars indicates that the rotational period decreases linearly with increasing mass in stars of the same age and evolves as a power of age as unk. This information has enabled us to disentangle the role of age in the chromospheric activity-rotation relationship, as well as to analyze the behavior of the Mg II emission flux in terms of "activity evolutionary paths" and of "activity isochrones." It is shown that the Mg II emission maintains a saturated level in very young stars until a certain age that depends on stellar mass, while at later stages it decays at a faster rate for more massive stars. We have also determined the convection turnover time from observational data and analyzed the relationship between the Mg II emission flux and the Rossby number. We reach the conclusion that there is no clear advantage in using the Rossby number instead of stellar age in describing the chromospheric Mg II losses, at least with the convective turnover time values currently in use.
We explore the possible evolutionary status of the primary component of the binary 85 Pegasi, listed as a target for asteroseismic observations by the MOST satellite. In spite of the assessed ...‘subdwarf’ status, and of the accurate distance determination from the Hipparcos data, the uncertainties in the metallicity and age, coupled with the uncertainty in the theoretical models, lead to a range of predictions on the oscillation frequency spectrum. Nevertheless, the determination of the ratio between the small separation in frequency modes, and the large separation as suggested by Roxburgh, provides a very good measure of the star age, quite independent of the metallicity in the assumed uncertainty range. In this range, the constraint on the dynamical mass and the further constraint provided by the assumption that the maximum age is 14 Gyr limits the mass of 85 Peg A to the range from 0.75 to 0.82 M⊙. This difference of a few hundredths of a solar mass leads to well detectable differences both in the evolutionary stage (age) and in the asteroseismic properties. We show that the age determination which will be possible through the asteroseismic measurements for this star is independent either of the convection model adopted or the microscopic metal diffusion. The latter conclusion is strengthened by the fact that, although metal diffusion is still described in an approximate way, recent observations suggest that real stars suffer a smaller metal sedimentation compared with the models.
An investigation is carried out on the Wilson-Bappu effect in the Mgii k line at 2796.34 Å. The work is based on a selection of 230 stars observed by both the IUE and HIPPARCOS satellites, covering a ...wide range of spectral types (F to M) and absolute visual magnitudes (- $5.4\le M_{V} \le9.0$). A semi-automatic procedure is used to measure the line widths, which applies also in the presence of strong central absorption reversal. The Wilson-Bappu relationship here provided is considered to represent an improvement over previous recent results for the considerably larger data sample used, as well as for a proper consideration of the measurement errors. No evidence has been found for a possible dependence of the WB effect on stellar metallicity and effective temperature.
The purpose of the study was to investigate in detail the esophageal, gastric and duodenal passage of non-disintegrating capsules in a fasted, healthy volunteer using Magnetic Marker Monitoring ...(MMM). Five independent experiments were performed. In each case the same healthy male volunteer ingested one magnetically marked capsule after fasting for at least 8 h. The magnetic dipole fields of the capsules were recorded by biomagnetic multichannel measuring equipment. The positions of the capsules were calculated from the recorded data by methods established in magnetic source imaging. The esophageal, gastric and duodenal passages of the capsules were successfully reconstructed from all recorded data sets. The spatial resolution of the capsules' three-dimensional positions in the organs of the gastrointestinal tract was within a range of several millimeters, with a chosen temporal resolution of up to four milliseconds. The esophageal transit times were between 3-13 s, the gastric residence times were between 14-133 min and the duodenal transit times were between 7-245 s. The data demonstrate that Magnetic Marker Monitoring permits the detailed investigation of the gastrointestinal transit of solids.
We present an on-going study of CoRoT 102931335. Our preliminary results indicate that the target is an eclipsing binary system with an orbital period of
and a primary component pulsating in the ...frequency range 0.6–0.8 c/d. The results of a ground-based follow-up program provided four-colour Strömgren photometry and allowed us to infer the spectral class and the primary effective temperature. We devised and applied an iterative procedure to disentangle the effects of binarity from those of pulsations and could test that a detailed binary modelling is essential for the purpose. Our results suggest that the pulsating component of CoRoT 102931335 could be a
γ
Dor variable, a rare occurrence in an eclipsing system.
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