Context. IC 348 is a nearby (≈310 pc), young (∼2-3 Myr) open cluster with >300 members identified from optical and infrared observations. It comprises young stellar objects in various evolutionary phases from protostars over disk-bearing to diskless premain sequence stars. This gives us the opportunity to study evolutionary effects in the high-energy emissions in a homogeneous environment. Aims. We study the properties of the coronae of the young low-mass stars in IC 348 combining X-ray and optical/infrared data. In particular, we intend to shed light on the dependence of X-ray luminosity and spectral hardness on evolutionary stage and on stellar parameters such as mass, effective temperature, and bolometric luminosity. Methods. The four existing Chandra observations of IC 348 were merged, thus providing a deeper and spatially more complete X-ray view than previous X-ray studies of the cluster. We have compiled a comprehensive catalog of IC 348 members taking into account recent updates to the cluster census. Our data collection comprises fundamental stellar parameters, infrared excess indicating the presence of disks, Hα emission as a tracer of chromospheric emission or accretion, and mass accretion rates. Results. We have detected 290 X-ray sources in four merged Chandra exposures, of which 187 are associated with known cluster members, which corresponds to a detection rate of ∼60% for the cluster members of IC 348 that are identified in optical/infrared studies. According to the most recent spectral classification of IC 348 members, only four of the X-ray sources are brown dwarfs (spectral type M6 and later). The detection rate is highest for diskless Class III stars and increases with stellar mass. This may be explained with higher X-ray luminosities for higher mass and later evolutionary stage that is evident in the X-ray luminosity functions. In particular, we find that for the lowest examined masses (0.1−0.25 M ) there is a difference between the X-ray luminosity functions of accreting and non-accreting stars (classified on the basis of their Hα emission strength) as well as those of disk-bearing and diskless stars (classified on the basis of the slope of the spectral energy distribution). These differences disappear for higher masses. This is related to our finding that the L x /L bol ratio is non-constant across the mass/luminosity sequence of IC 348 with a decrease toward lower luminosity stars. Our analysis of an analogous stellar sample in the Orion Nebula Cluster suggests that the decline of L x /L bol for young stars at the low-mass end of the stellar sequence is likely universal.

Context. The physical origin of the strong magnetic activity in T Tauri stars and its relation to stellar rotation is not yet wellunderstood. Aims. We investigate the relation between the X-ray activity, rotation, and Rossby number for a sample of young stars in the ≈3 Myr old cluster IC 348. Methods. We use the data of four Chandra observations of IC 348 to derive the X-ray luminosities of the young stars. Basic stellar parameters and rotation rates are collected from the literature. This results in a sample of 82 X-ray detected stars with known rotation periods. We determine the Rossby numbers (i.e. the ratio of rotation period to convective turnover time) of 76 of these stars from stellar structure-and evolution-models for pre-main sequence stars.Results. The young stars in IC 348 show no correlation between X-ray activity and rotation period. For the Rossby numbers, nearly all IC 348 stars are in the saturated regime of the activity-rotation relation defined by main-sequence stars. Searching for possible super-saturation effects, we find a marginal (but statistically in-significant) trend that the stars with the smallest Rossby numbers have slightly lower X-ray activity levels. There are no significant differences in the X-ray activity level for stars of different spectral types and no relation between spectral type and Rossby number is seen. In addition, for stars belonging to different IR-classes, no significant differences are present for the X-ray activity level as well as for their Rossby numbers. We compare the dispersion in the fractional X-ray luminosities of the stars in the saturated rotation regime in IC 348 to that seen in younger and older stellar populations. The scatter seen in the ≈3 Myr old IC 348 [σ log (L X /L bol ) = 0.43] is considerably smaller than for the ≈1 Myr old Orion nebula cluster [σ log(L X /L bol ) = 0.63], but, at the same time, considerably larger than the dispersion seen in the ≈30 Myr old cluster NGC 2547 [σ log(L X /L bol ) = 0.24] and in main-sequence stars. Conclusions. The results of our X-ray analysis of IC 348 show that neither the rotation rates nor the presence/absence of circumstellar disks are of fundamental importance for determining the level of X-ray activity in TTS. Our results suggest that the scatter in the X-ray activity levels for the rapidly rotating members of young clusters decreases with the age of the stellar population. We interpret this as a signature of the changing interior structure of pre-main sequence stars and the consequent changes in the dynamo mechanisms that are responsible for the magnetic field generation.

Studies based on the gamma-ray lines from radioactive decay of unstable isotopes produced in massive-star and supernova nucleosynthesis have been among INTEGRAL's prominent science achievements. 26 Al has become a tool to study specific source regions, such as massive-star groups and associations in nearby regions which can be discriminated from the galactic-plane background, and the inner Galaxy where Doppler shifted lines add to the astronomical information. 60 Fe is co-produced by the sources of 26 Al, and the isotopic ratio from their nucleosynthesis encodes stellar-structure information. Here we summarize latest results using the accumulated multi-year database of observations, point to the relevant publications, and discuss their astrophysical implications."An INTEGRAL view of the high-energy sky (the first 10 years)" 9th INTEGRAL Workshop and celebration of the 10th anniversary of the launch,