In this paper 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 which involves a combination of different methods to extract the rotational splittings from the power spectrum.We find not only that the core rotates faster than the surface, confirming previous inversion results generated for other red giants (Deheuvels et al. 2012(Deheuvels et al. , 2014), but we also estimate the variation of the angular velocity within the helium core with a spatial resolution of ∆r = 0.001R and verify the hypothesis of a sharp discontinuity in the inner stellar rotation (Deheuvels et al. 2014). The results show that the entire core rotates rigidly with an angular velocity of about Ω c /2π = 748 ± 18 nHz and provide evidence for an angular velocity decrease through a region between the helium core and part of the hydrogen burning shell; however we do not succeed to characterize the rotational slope, due to the intrinsic limits of the applied techniques. The angular velocity, from the edge of the core and through the hydrogen burning shell, appears to decrease with increasing distance from the center, reaching an average value in the convective envelope of Ω s /2π = 68 ± 22 nHz. Hence, the core in KIC 4448777 is rotating from a minimum of 8 to a maximum of 17 times faster than the envelope.We conclude that a set of data which 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.

Oscillating stars in binary systems are among the most interesting stellar laboratories, as these can provide information on the stellar parameters and stellar internal structures. Here we present a red giant with solar-like oscillations in an eclipsing binary observed with the NASA Kepler satellite. We compute stellar parameters of the red giant from spectra and the asteroseismic mass and radius from the oscillations. Although only one eclipse has been observed so far, we can already determine that the secondary is a main-sequence F star in an eccentric orbit with a semi-major axis larger than 0.5 AU and orbital period longer than 75 days.

We present accurate optical and radio astrometry for the unresolved contact binary system Cyg OB2 No. 5 and its weaker component to the northeast. While the radio and optical positions of the primary component (taken to be the unresolved contact binary) agree within observational error (∼70 mas), we find that the weaker radio component does not agree in position with the second optical component of the system, but falls in between the two optical components. We conclude that the weaker radio component of this system is not associated with the secondary star but appears to be synchrotron emission produced at the shock interaction zone between the winds of the stars. Differential B-and V-band CCD and Hipparcos photometry was used to derive the approximate spectral type (B0 V-B2 V) of the secondary. Ram pressure arguments in the colliding-wind model give a massloss rate for the secondary star consistent with the expected one, considering the earliest spectral type.

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.

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 t 0:45 . This information has enabled us to disentangle the role of age in the chromospheric activityYrotation 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.