Outflow Structure and Velocity Field of Orion Source I: ALMA Imaging of SiO Isotopologue Maser and Thermal Emission

Using Science Verification data from the Atacama Large Millimeter/Submillimeter Array (ALMA), we have identified and imaged five rotational transitions (J=5-4 and J=6-5) of the three silicon monoxide isotopologues 28SiO v=0, 1, 2 and 29SiO v=0 and 28Si18O v=0 in the frequency range from 214 to 246 GHz towards the Orion BN/KL region. The emission of the ground-state 28SiO, 29SiO and 28Si18O shows an extended bipolar shape in the northeast-southwest direction at the position of Radio Source I, indicating that these isotopologues trace an outflow (~18 km/s, P.A. ~50deg, ~5000 AU in diameter) that is driven by this embedded high-mass young stellar object (YSO). Whereas on small scales (10-1000 AU) the outflow from Source I has a well-ordered spatial and velocity structure, as probed by Very Long Baseline Interferometry (VLBI) imaging of SiO masers, the large scales (500-5000 AU) probed by thermal SiO with ALMA reveal a complex structure and velocity field, most likely related to the effects of the environment of the BN/KL region on the outflow emanating from Source I. The emission of the vibrationally-excited species peaks at the position of Source I. This emission is compact and not resolved at an angular resolution of ~1.5" (~600 AU at a distance of 420 pc). 2-D Gaussian fitting to individual velocity channels locates emission peaks within radii of 100 AU, i.e. they trace the innermost part of the outflow. A narrow spectral profile and spatial distribution of the v=1 J=5-4 line similar to the masing v=1 J=1-0 transition, provide evidence for the most highly rotationally excited (frequency > 200 GHz) SiO maser emission associated with Source I known to date. The maser emission will enable studies of the Source I disk-outflow interface with future ALMA longest baselines.Comment: Accepted to A&A, 11 pages, 13 figure

No Evidence for Significant Age Spreads in Young Massive LMC Clusters

Recent discoveries have put the picture of stellar clusters being simple stellar populations into question. In particular, the color-magnitude diagrams of intermediate age (1-2 Gyr) massive clusters in the Large Magellanic Cloud (LMC) show features that could be interpreted as age spreads of 100-500 Myr. If multiple generations of stars are present in these clusters then, as a consequence, young (<1 Gyr) clusters with similar properties should have age spreads of the same order. In this paper we use archival Hubble Space Telescope (HST) data of eight young massive LMC clusters (NGC 1831, NGC 1847, NGC 1850, NGC 2004, NGC 2100, NGC 2136, NGC 2157 and NGC 2249) to test this hypothesis. We analyzed the color-magnitude diagrams of these clusters and fitted their star formation history to derive upper limits of potential age spreads. We find that none of the clusters analyzed in this work shows evidence for an extended star formation history that would be consistent with the age spreads proposed for intermediate age LMC clusters. Tests with artificial single age clusters show that the fitted age dispersion of the youngest clusters is consistent with spreads that are purely induced by photometric errors. As an additional result we determined a new age of NGC 1850 of ~100 Myr, significantly higher than the commonly used value of about 30 Myr, although consistent with early HST estimates.Comment: 19 pages, 33 figures, accepted for publication in A&

Apparent age spreads in clusters and the role of stellar rotation

We use the Geneva syclist isochrone models that include the effects of stellar rotation to investigate the role that rotation has on the resulting colour-magnitude diagram of young and intermediate age clusters. We find that if a distribution of rotation velocities exists within the clusters, rotating stars will remain on the main sequence for longer, appearing to be younger than non-rotating stars within the same cluster. This results in an extended main sequence turn-off (eMSTO) that appears at young ages (∼30Myr) and lasts beyond 1Gyr. If this eMSTO is interpreted as an age spread, the resulting age spread is proportional to the age of the cluster, i.e. young clusters (<100Myr) appear to have small age spreads (tens of Myr) whereas older clusters (∼1Gyr) appear to have much large spreads, up to a few hundred Myr. We compare the predicted spreads for a sample of rotation rates to observations of young and intermediate age clusters, and find a strong correlation between the measured ‘age spread' and the age of the cluster, in good agreement with models of stellar rotation. This suggests that the ‘age spreads' reported in the literature may simply be the result of a distribution of stellar rotation velocities within cluster

Ethnische Minderheiten in der Geschichte der Tschechoslowakei / Tschechiens

Am 28. Oktober 1918 entstand die erste unabhängige Tschechoslowakische Republik als ein multinationaler Staat mit starken Minderheiten. Diese Minderheiten beeinflussten wesentlich das gesellschaftliche und politische Leben des neuen Staates und führten zu seinem Niedergang. Nach dem 2.Weltkrieg wurde eine neue national einheitliche Tschechoslowakei gegründet, Minderheiten wurden in diesem neuen sozialistisch geführten Staate nur als eine Randerscheinung wahrgenommen. Nach der Samtenen Revolution, den Beitritten zu wichtigen internationalen und regionalen Organisationen und dem Beitritt zur Europäischen Union verbesserte sich die Lage für zahlreiche Minderheitengruppierungen. Einige Minderheitengruppen können jetzt nicht nur ihr kulturelles Leben frei entfalten, sondern auch auf politische Prozesse Einfluss nehmen