VISION - Vienna survey in Orion. III. Young stellar objects in Orion A

38 pages, 25 figures, Accepted for publication by A&A. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESOWe extend and refine the existing young stellar object (YSO) catalogs for the Orion A molecular cloud, the closest massive star-forming region to Earth. This updated catalog is driven by the large spatial coverage (18.3 deg^2, ~950 pc^2), seeing limited resolution (~0.7''), and sensitivity (Ks<19 mag) of the ESO-VISTA near-infrared survey of the Orion A cloud (VISION). Combined with archival mid- to far-infrared data, the VISTA data allow for a refined and more robust source selection. We estimate that among previously known protostars and pre-main-sequence stars with disks, source contamination levels (false positives) are at least ∼7% and ∼2.5%, respectively, mostly due to background galaxies and nebulosities. We identify 274 new YSO candidates using VISTA/Spitzer based selections within previously analyzed regions, and VISTA/WISE based selections to add sources in the surroundings, beyond previously analyzed regions. The WISE selection method recovers about 59% of the known YSOs in Orion A's low-mass star-forming part L1641, which shows what can be achieved by the all-sky WISE survey in combination with deep near-infrared data in regions without the influence of massive stars. The new catalog contains 2978 YSOs, which were classified based on the de-reddened mid-infrared spectral index into 188 protostars, 184 flat-spectrum sources, and 2606 pre-main-sequence stars with circumstellar disks. We find a statistically significant difference in the spatial distribution of the three evolutionary classes with respect to regions of high dust column-density, confirming that flat-spectrum sources are at a younger evolutionary phase compared to Class IIs, and are not a sub-sample seen at particular viewing angles.Peer reviewedFinal Accepted Versio

Formación de núcleos densos en las nubes moleculares de Tauro y Perseo

La formación de núcleos densos en las nubes moleculares es el paso más crítico en el proceso de formación estelar. La transformación del gas difuso en núcleos densos determina tanto la tasa de formación estelar como la distribución de masas de las estrellas en las nubes moleculares. Sin embargo, y tras décadas de estudio, la comprensión de los mecanismos físicos que gobiernan la formación de núcleos densos sigue siendo materia de un amplio debate en la comunidad científica. Con el objetivo de caracterizar observacionalmente el proceso de formación de núcleos densos en las nubes moleculares, en esta Tesis hemos investigado 3 regiones prototípicas de formación de estrellas: L1517, Barnard 213 y NGC 1333. Estas regiones, pertenecientes a las nubes moleculares de Tauro y Perseo, han sido seleccionadas por presentar distintos grados de actividad y complejidad y por cubrir los diferentes modos de formación estelar, desde las regiones con formación aislada hasta aquellas con formación en cúmulos. En todos los casos hemos estudiado cada una de estas regiones mediante observaciones radioastronómicas a gran escala en el rango de ondas milimétricas y submilimétricas tanto en el continuo como, y muy especialmente, a partir de su emisión en líneas moleculares. Nuestro trabajo ha estado principalmente enfocado a la caracterización de la cinemática del gas mediante el estudio simultaneo de diferentes trazadores moleculares sensibles a los distintos rangos de densidad presentes en las nubes moleculares. Para llevar a cabo este estudio, en esta Tesis hemos desarrollado una nueva metodología de análisis de datos moleculares a gran escala a la que hemos denominado Friends-In-Velocity (FIVe). Basado en una aproximación de Friends-of-Friends, FIVe está específicamente diseñado para identificar automáticamente las diferentes componentes del gas presentes en los espectros mediante el estudio de la distribución y la continuidad de los centroides de línea en el espacio Posición-Posición-Velocidad (PPV)

Multi-line characterization of whole molecular clouds using stratified random sampling

We have developed a new technique to characterize the multi-line emission from molecular clouds using statistical sampling. Our method uses available extinction maps to select a relatively small sample of cloud positions that cover the full range of column densities in the cloud, and that can be observed with only a modest investment of telescope time. Here we present the first results of applying this technique to the Perseus molecular cloud, a nearby star-forming region that contains a population of both isolated and clustered protostars. We have used the IRAM 30m telescope to observe a sample of 100 random positions that cover two orders of magnitude in H2 column density. These positions have been observed over the full 3mm wavelength band together with selected portions of the 2 and 1mm bands. We find that the emission properties of most species are strongly correlated with the column density over the whole cloud, and that they can be reproduced using a relative simple radiative transfer model

Three ages for the Martian lithosphere

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

The spatial evolution of young massive clusters

International audienceContext. Better understanding of star formation in clusters with high-mass stars requires rigorous dynamical and spatial analyses of star-forming regions.Aims. We seek to demonstrate that “INDICATE” is a powerful spatial analysis tool which when combined with kinematic data from Gaia DR2 can be used to probe star formation history in a robust way.Methods. We compared the dynamic and spatial distributions of young stellar objects (YSOs) at various evolutionary stages in NGC 2264 using Gaia DR2 proper motion data and INDICATE.Results. The dynamic and spatial behaviours of YSOs at different evolutionary stages are distinct. Dynamically, Class II YSOs predominately have non-random trajectories that are consistent with known substructures, whereas Class III YSOs have random trajectories with no clear expansion or contraction patterns. Spatially, there is a correlation between the evolutionary stage and source concentration: 69.4% of Class 0/I, 27.9% of Class II, and 7.7% of Class III objects are found to be clustered. The proportion of YSOs clustered with objects of the same class also follows this trend. Class 0/I objects are both found to be more tightly clustered with the general populous/objects of the same class than Class IIs and IIIs by a factor of 1.2/4.1 and 1.9/6.6, respectively. An exception to these findings is within 0.05° of S Mon where Class III objects mimic the behaviours of Class II sources across the wider cluster region. Our results suggest (i) current YSOs distributions are a result of dynamical evolution, (ii) prolonged star formation has been occurring sequentially, and (iii) stellar feedback from S Mon is causing YSOs to appear as more evolved sources.Conclusions. Designed to provide a quantitative measure of clustering behaviours, INDICATE is a powerful tool with which to perform rigorous spatial analyses. Our findings are consistent with what is known about NGC 2264, effectively demonstrating that when combined with kinematic data from Gaia DR2 INDICATE can be used to study the star formation history of a cluster in a robust way