S. Catalano

Rotational periods of solar-mass young stars in Orion

Context. The evolution of the angular momentum in young low-mass stars is still a debated issue. The stars presented here were discovered as X-ray sources in the ROSAT All-Sky Survey (RASS) of the Orion complex and subsequently optically identified thanks to both low and high resolution spectroscopy. Aims. The determination of the rotational periods in young low-mass stars of different age is fundamental for the understanding of the angular momentum evolution. Methods. We performed a photometric monitoring program on a sample of 40 solar-mass young stars in the Orion star-forming region, almost all previously identified as weak T Tauri stars (WTTS) candidates. Photometric B and V data were collected from 1999 to 2006 at Catania Astrophysical Observatory (OAC). Data were also acquired in December 1998 at Calar Alto Observatory (CA) and in 1999, 2000, and 2003 at San Pedro Martir (SPM). From the observed rotational modulation, induced by starspots, we derived the rotation periods, using both the Lomb-Scargle periodogram and the CLEAN deconvolution algorithms. Results. In total, we were able to determine the rotation periods for 39 stars, spanning from about 0.5 to 13 days, showing a rather flat distribution with a peak around 1-2 days. Though some of these stars were found to be spectroscopic binaries, only the systems with shorter orbital periods and circular orbits turned out to be synchronized. In the other cases, the rotational period is shorter than the period of pseudo-synchronization at periastron. Conclusions. The new data provide further evidence for the spin up of solar-mass stars predicted by models of angular momentum evolution of pre-main sequence (PMS) stars.

Photospheric and chromospheric active regions on three single-lined RS CVn binaries

A monitoring of three active RSxa0CVn binaries has been performed with medium resolution spectroscopy with the aim of investigating the behavior of chromospheric and photospheric inhomogeneities. Surface temperature, as recovered from line-depth ratios (LDRs), allowed us to map the photospheric spots, while the H α xa0emission has been used as an indicator of chromospheric inhomogeneities. We have found that the rotational modulation of the H α emission is always in anti-phase with the temperature wave, i.e. at the time of our observations active regions at chromospheric and photospheric levels are closely spatially associated in these active stars. The residual H α profiles, obtained as the difference between the observed spectra and non-active templates, are well reproduced by a two Gaussian fitting. The broad emission component, responsible for the wide emission wings in near all the spectra, is often blue-shifted with respect to the center of the stellar disk. The narrow H α emission displays a phase-dependent variation in all stars and is anti-correlated with the photospheric diagnostics, while the broad one displays no or little rotational modulation. We suggest that the broad emission component is mainly related to physical phenomena, like micro-flaring or strong chromospheric velocity fields, occurring all over the star disk, while the central narrow emission is more affected by chromospheric plages. We have also detected a modulation of the intensity of the

Deriving temperature, mass, and age of evolved stars from high-resolution spectra - Application to field stars and the open cluster IC 4651

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Measuring starspot temperature from line-depth ratios - II. Simultaneous modeling of light and temperature curves

xa0D 3 xa0line with the star rotation, suggesting surface features also in the upper chromosphere of these stars.

Magnetic activity in HD 111456, a young F5-6 main-sequence star

Aims. We test our capability of deriving stellar physical parameters of giant stars by analysing a sample of field stars and the well studied open cluster IC 4651 with different spectroscopic methods. Methods. The use of a technique based on line-depth ratios (LDRs) allows us to determine with high precision the effective temperature of the stars and to compare the results with those obtained with a classical LTE abundance analysis. Results. (i) For the field stars we find that the temperatures derived by means of the LDR method are in excellent agreement with those found by the spectral synthesis. This result is extremely encouraging because it shows that spectra can be used to firmly derive population characteristics (e.g., mass and age) of the observed stars. (ii) For the IC 4651 stars we use the determined effective temperature to derive the following results. a) The reddening E(B − V) of the cluster is 0.12 ± 0.02, largely independent of the color-temperature calibration used. b) The age of the cluster is 1.2 ± 0.2 Gyr. c) The typical mass of the analysed giant stars is 2.0 ± 0.2 M� . Moreover, we find a systematic difference of about 0.2 dex in log g between spectroscopic and evolutionary values. Conclusions. We conclude that, in spite of known limitations, a classical spectroscopic analysis of giant stars may indeed result in very reliable stellar parameters. We caution that the quality of the agreement, on the other hand, depends on the details of the adopted spectroscopic analysis.

Temperature and size of starspots from line depth ratios

We present and apply to VYxa0Ari, IMxa0Peg and HKxa0Lac a new method to determine spot temperaturesxa0( T sp ) and areasxa0( A rel ) from the analysis of simultaneous light curves and temperature modulations deduced from line-depth ratios. A spot model, developed by us, has been applied to light and temperature curves. Grids of solutions with comparable χ -square have been found for a wide range of spot temperatures. The behavior of the solution grids for temperature and light curves in the T sp – A rel xa0plane is very different and a rather small and unique intersection area can be found. In our spot-model we used spectral energy distributions (SEDs) based on the Planck law and on model atmospheres to evaluate the flux ratio between spots and unspotted photosphere and we found higher spot temperatures with SEDs based on model atmospheres than on the Planck law.

Physical Parameters of Evolved Stars in Clusters and in the Field from Line-depth Ratios

We present spectroscopic and photometric observations of the young F5–6 V field star HD 111456 which exhibits emission cores in the

Effective temperature vs. line‐depth ratio for ELODIE spectra: Gravity and rotational velocity effects

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The chromospheric Lymanα emission of Altair (A7IV-V) observed with the IUE

H and K lines and a filling in the H α line. Absorption lines of

Absolute fluxes of K chromospheric emission in main-sequence stars

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