Aims. We aim at constraining the angular momentum evolution of low-mass stars by measuring their rotation rates when they begin to evolve freely towards the zero-age main sequence (ZAMS), i.e., after the disk accretion phase has stopped. Methods. We conducted a multisite photometric monitoring of the young open cluster h Persei, which has an age of ∼13 Myr. The observations were done in the I-band using four different telescopes, and the variability study is sensitive to periods from less than 0.2 day to 20 days. Results. Rotation periods are derived for 586 candidate cluster members over the mass range 0.4 ≤ M/M ≤ 1.4. The rotation period distribution indicates a slightly higher fraction of fast rotators for the lower mass objects, although the lower and upper envelopes of the rotation period distribution, located respectively at ∼0.2-0.3 d and ∼10 d, are remarkably flat over the whole mass range. We combine this period distribution with previous results obtained in younger and older clusters to model the angular momentum evolution of low mass stars during the pre-main sequence (PMS) phase. Conclusions. The h Per cluster provides the first statistically robust estimate of the rotational period distribution of solar-type and lower mass stars at the end of the PMS accretion phase (≥10 Myr). The results are consistent with models that assume significant core-envelope decoupling during the angular momentum evolution to the ZAMS.

Context. The CoRoT -Convection Rotation and planetary Transits -space mission is a great opportunity for monitoring stars with excellent time-sampling and unprecedented photometric precision for up to 150 days. As an important benefit, high-quality RR Lyrae light curves are obtained with a quasi-uninterrupted coverage over several pulsation and Blazhko cycles. Aims. The Blazhko effect in RR Lyrae stars is an unsolved problem of astrophysics. We used the high-precision space data to contribute more precise knowledge to explain the possible physical processes behind the phenomenon. Methods. We applied different period-finding techniques including Period04, MuFrAn, PDM and SigSpec. Amplitude and phase modulation were investigated by an analytical function method as well as with the traditional O-C diagrams. Results. The Blazhko modulation frequency is directly detected in the spectrum, as well as its first and second harmonics. It shows the non-linear nature of the Blazhko modulation. Besides the triplets, further higher-order modulation side peaks appear around the pulsation frequency as quintuplet, septuplet, nonuplet, undecaplet, tredecaplet, quindecaplet and sepdecaplet structures. Additional frequencies, not belonging to the classical multiplet structures, are detected, as well as their linear combinations with the fundamental radial mode. We interpret these additional terms as non-radial modes. During the five consecutive Blazhko cycles, there is a shift of the maximum phase around 0.011 pulsation phase which is likely the consequence of a long term modulation.

Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich emission line spectrum. In 2014 the star faded by ∼3 mag in the V band and went into a long-lasting minimum. In 2010 the star underwent a similar fading, although less pronounced. These events in RW Aur A are very unusual among the CTTS, and have been attributed to occultations by passing dust clouds. Aims. We want to find out if any spectral changes took place after the last fading of RW Aur A with the intention of gathering more information on the occulting body and the cause of the phenomenon. Methods. We collected spectra of the two components of RW Aur. The photometry was performed before and during the minimum. Results. The overall spectral signatures reflecting emission from accretion flows from disk to star did not change after the fading. However, blue-shifted absorption components related to the stellar wind increased in strength in certain resonance lines, and the profiles and strengths but not the fluxes of forbidden lines became drastically different. Conclusions. The extinction through the obscuring cloud is grey indicating the presence of large dust grains. At the same time, there are no traces of related absorbing gas. The cloud occults the star and the interior part of the stellar wind, but not the wind or jet further out. The dimming in 2014 was not accompanied by changes in the accretion flows at the stellar surface. There is evidence that the structure and velocity pattern of the stellar wind did change significantly. The dimmings could be related to passing condensations in a tidally disrupted disk, as proposed earlier, but we also speculate that large dust grains have been stirred up from the inclined disk into the line of sight through the interaction with an enhanced wind.

We present new brightness and magnetic images of the weak‐line T Tauri star V410 Tau, made by using data from the Narval spectropolarimeter at Télescope Bernard Lyot (TBL). The brightness image shows a large polar spot and significant spot coverage at lower latitudes. The magnetic maps show a field that is predominantly dipolar and non‐axisymmetric with a strong azimuthal component. The field is 50 per cent poloidal and 50 per cent toroidal, and very little differential rotation is apparent from the magnetic images. A photometric monitoring campaign on this star has previously revealed V‐band variability of up to 0.6 mag, but in 2009 the light curve is much flatter. The Doppler image presented here is consistent with this low variability. Calculating the flux predicted by the mapped spot distribution gives a peak‐to‐peak variability of 0.04 mag. The reduction in the amplitude of the light curve, compared with previous observations, appears to be related to a change in the distribution of the spots rather than the number or area. This paper is the first from a Zeeman–Doppler imaging campaign being carried out on V410 Tau between 2009 and 2012 at the TBL. During this time, it is expected that the light curve will return to a high‐amplitude state, allowing us to ascertain whether the photometric changes are accompanied by a change in the magnetic field topology.

Context. Optical spectra of classical T Tauri stars (cTTS) are rich in emission lines of low-excitation species that are composed of narrow and broad components, which indicates the existence of two emitting regions with different kinematics, densities, and temperatures. The photospheric spectrum is often veiled by an excess continuous emission. This veiling is usually attributed to radiation from a heated region beneath the accretion shock. The broad emission lines of H i, He ii, Ca ii, Fe ii, and other species are thought to form in a larger volume of gas. Aims. The aim of this research is to clarify the nature of the veiling, and whether the narrow chromospheric lines of Fe i and other metals represent a standard chromosphere of a late-type star, or are induced by mass accretion. Methods. We carried out high-resolution spectroscopy of selected cTTS with a special focus on DR Tauri and followed variations of chromospheric features, such as narrow Fe i emission lines, and accretion signatures such as the veiling continuum and the He ii line emission. Results. We found that the amount of veiling in DR Tau varies from practically nothing to factors more than 10 times the stellar continuum intensity, and that the veiling is caused by both a non-photospheric continuum and chromospheric line emission filling in the photospheric absorption lines. The latter causes differential veiling because stronger lines are more veiled. We developed methods to separate the two sources of veiling. Several veiled T Tauri stars show a common effect: the radial velocities of photospheric and chromospheric lines vary in anti-phase. This is caused by an area with enhanced chromospheric emission, which is offset from the pole of rotation and is associated with the hot spot formed at the footprint of the magnetic funnel of mass accretion. Conclusions. The enhanced chromospheric emission in cTTS is linked not only to solar-like magnetic activity, but is powered to a greater extent by the accreting gas. We suggest that the area of enhanced chromospheric emission is induced by mass accretion, which modifies the local structure of stellar atmosphere in an area that is more extended than the hot accretion spot. The narrow emission lines from this extended area are responsible for the extra component in the veiling through line-filling of photospheric absorption lines.