Star formation in cluster environments at Mm and Submm wavelenghts

[spa] En este trabajo se han observado 4 regiones de formación estelar en modo de cúmulo a longitudes de onda milimétricas y submilimétricas con alta resolución angular (2''-4'') y alta sensibilidad. Para llevar a cabo el proceso de selección de las regiones, se han observado 8 regiones con el radiointerferómetro Very Large Array y el radiotelescopio IRAM 30m. Para cada una de las 4 regiones seleccionadas, se ha estudiado la naturaleza de los objetos estelares jóvenes y la interacción entre ellos, con el objetivo de comprender mejor la formación estelar en cúmulos. En la región HH211 no se ha encontrado evidencia de interacción entre las diferentes fuentes. Se ha estudiado con el interferómetro Submillimeter Array la formación de uno de los miembros más jóvenes, HH211mm, en el continuo submilimétrico y en CO(3-2) y SiO(8-7). La emisión de CO y SiO muestra un chorro de gas molecular de alta velocidad muy colimado, mientras que la emisión de continuo submilimétrico revela una fuente compacta en el centro de simetría del chorro y ligeramente alargada en la dirección perpendicular al chorro, que traza el disco protoestelar. Además, se ha encontrado que un viento de ángulo ancho parece ser el mecanismo que impulsa el chorro altamente colimado de esta fuente. Por tanto, HH211mm constituye un claro ejemplo de una estrella formándose de modo aislado, aun dentro de un cumulo. Para el caso de IRAS 00117+6412, observada con el interferómetro Plateau de Bure a 1 y 3 mm, en N2H+(1-0), CS(5-4) y CH3OH(5-4), se han detectado dos fuentes compactas en el milimétrico, sumergidas en una nube de gas denso trazada por N2H+, y que parecen estar asociadas a objetos estelares jóvenes en diferentes estados evolutivos. Justo en el borde este de la nube de gas denso se ha detectado una región de gas ionizado ultracompacta, por lo que IRAS 00117+6412 es un excelente candidato para estudiar la interacción entre un frente de ionización y una nube molecular con formación estelar activa. La región IRAS 20343+4129 se ha observado con el Submillimeter Array a 1 mm y en CO(2-1), y se ha descubierto un flujo molecular bipolar alargado en la dirección este-oeste que está impulsado por una fuente infrarroja clasificada como Clase I de masa intermedia. Se propone que otra de las fuentes infrarrojas está creando una cavidad y acumulando material ambiente en sus paredes, trazado por las fuentes milimétricas que se han detectado, que parecen estar asociadas a condensación es en un estado previo a la formación estelar. Finalmente, en la región IRAS 20293+3952, observada con el interferómetro Berkeley-Illinois-Maryland Array, se ha encontrado dos nubes de gas denso trazado por N2H+(1-0) y NH3(1,1) y NH3(2,2), y una gran variedad de objetos estelares jóvenes, la mayoría asociados a la zona norte de la nube principal. Los diferentes objetos estelares abarcan como mínimo un orden de magnitud en masa y se encuentran en estados evolutivos diferentes, indicando formación estelar continuada. Se ha derivado mapas de temperatura rotación al y densidad columnar de NH3 en las dos nubes, y se ha encontrado que la diferenciación química en la nube principal es importante, así como la interacción entre las diferentes fuentes. Con estos nuevos datos y otros recogidos de la literatura, se ha compilado una tabla de 5 regiones que albergan protoestrellas de masa intermedia/alta observadas con sensibilidades mejores que 1 masa solar, y se ha encontrado que el número de fuentes milimétricas alrededor de la protoestrella de alta masa es menor que el número de fuentes infrarrojas. Dado que nuestras observaciones sugieren que la formación estelar en cúmulos es continuada, el menor número de fuentes milimétricas parece indicar que la escala de tiempo en que un objeto estelar joven es brillante en el milimétrico es menor que la escala de tiempo en que un objeto estelar joven es brillante en el infrarrojo. Además, se ha encontrado una escala espacial típica de 0.1-0.3 pc asociada a un estado evolutivo particular. Para acabar, la distribución espacial de los objetos estelares jóvenes en las regiones estudiadas no se puede explicar únicamente por la interacción entre los diferentes objetos, sino que además es necesario suponer diferentes condiciones iniciales en la nube molecular original. Aun así, las interacciones pueden inducir la formación estelar en algunos casos concretos

Unveiling the nature and interaction of the intermediate/high-mass YSOs in IRAS 20343+4129

In order to elucidate the nature of the brightest infrared sources associated with IRAS 20343+4129, IRS1 and IRS3, we observed with the Submillimeter Array (SMA) the 1.3 mm continuum and CO(2-1) emission of the region. Faint millimeter dust continuum emission was detected toward IRS1, and we derived an associated gas mass of ~0.8 Msun. The IRS1 spectral energy distribution agrees with IRS1 being an intermediate-mass Class I source of about 1000 Lsun, whose circumstellar material is producing the observed large infrared excess. We have discovered a high-velocity CO bipolar outflow in the east-west direction, which is clearly associated with IRS1, and the outflow parameters are similar to those of intermediate-mass young stellar objects. Associated with the blue large scale CO outflow lobe, detected with single-dish observations, we only found two elongated low-velocity structures on either side of IRS3. The large-scale outflow lobe is almost completely resolved out by the SMA. Our detected low-velocity CO structures are coincident with elongated H2 emission features. The strongest millimeter continuum condensations in the region are found on either side of IRS3, where the infrared emission is extremely weak, and the CO and H2 elongated structures follow the border of the millimeter continuum emission that is facing IRS3. All these results suggest that the dust is associated with the walls of an expanding cavity driven by IRS3, estimated to be a B2 star. Within and beyond the expanding cavity, the millimeter continuum sources can be sites of future low-mass star formation.Comment: 12 pages, 7 figures, accepted for publication in A&

Resolving the chemical substructure of Orion-KL

The Kleinmann-Low nebula in Orion (Orion-KL) is the nearest example of a high-mass star-forming environment. For the first time, we complemented 1.3 mm Submillimeter Array (SMA) interferometric line survey with IRAM 30 m single-dish observations of the Orion-KL region. Covering a 4 GHz bandwidth in total, this survey contains over 160 emission lines from 20 species (25 isotopologues), including 11 complex organic molecules (COMs). At a spatial resolution of 1200 AU, the continuum substructures are resolved. Extracting the spectra from individual substructures and providing the intensity-integrated distribution map for each species, we studied the small-scale chemical variations in this region. Our main results are: (1) We identify lines from the low-abundance COMs CH3COCH3 and CH3CH2OH, as well as tentatively detect CH3CHO and long carbon-chains C6H and HC7N. (2) We find that while most COMs are segregated by type, peaking either towards the hot core (e.g., N-bearing species) or the compact ridge (e.g., O-bearing species like HCOOCH3 and CH3OCH3), while the distributions of others do not follow this segregated structure (e.g., CH3CH2OH, CH3OH, CH3COCH3). (3) We find a second velocity component of HNCO, SO2, 34SO2, and SO lines, which may be associated with a strong shock event in the low-velocity outflow. (4) Temperatures and molecular abundances show large gradients between central condensations and the outflow regions, illustrating a transition between hot molecular core and shock-chemistry dominated regimes. Our observations of spatially resolved chemical variations in Orion-KL provide the nearest reference source for hot molecular core and outflow chemistry, which will be an important example for interpreting the chemistry of more distant HMSFRs.Comment: 51 pages, 17 figures, accepted on 12 March 2015 Dashed lines in Figure 10 of the published paper was missin

A line confusion-limited millimeter survey of Orion KL. III. Sulfur oxide species

We present a study of the sulfur-bearing species detected in a line confusion-limited survey towards Orion KL performed with the IRAM 30m telescope in the range 80-281 GHz. The study is part of an analysis of the line survey divided into families of molecules. Our aim is to derive accurate physical conditions and molecular abundances in the different components of Orion KL from observed SO and SO2 lines. First we assumed LTE conditions obtain rotational temperatures. We then used a radiative transfer model, assuming either LVG or LTE excitation to derive column densities of these molecules in the different components of Orion KL. We have detected 68 lines of SO, 34SO, 33SO, and S18O and 653 lines of SO2, 34SO2, 33SO2, SO18O and SO2 v2=1. We provide column densities for all of them and also upper limits for the column densities of S17O, 36SO, 34S18O, SO17O and 34SO2 v2=1 and for several undetected sulfur-bearing species. In addition, we present 2'x2' maps around Orion IRc2 of SO2 transitions with energies from 19 to 131 K and also maps with four transitions of SO, 34SO and 34SO2. We observe an elongation of the gas along the NE-SW direction. An unexpected emission peak appears at 20.5 km/s in most lines of SO and SO2. A study of the spatial distribution of this emission feature shows that it is a new component ~5" in diameter, which lies ~4" west of IRc2. We suggest the emission from this feature is related to shocks associated to the BN object. The highest column densities for SO and SO2 are found in the high-velocity plateau (a region dominated by shocks) and in the hot core. These values are up to three orders of magnitude higher than the results for the ridge components. We also find high column densities for their isotopologues in both components. Therefore, we conclude that SO and SO2 are good tracers, not only of regions affected by shocks, but also of regions with warm dense gas.Comment: Paper (ref AA/2013/21285) accepted for publication by A&A. 52 Pages, 26 figures, 13 table

Extended warm gas in Orion KL as probed by methyl cyanide

In order to study the temperature distribution of the extended gas within the Orion Kleinmann-Low nebula, we have mapped the emission by methyl cyanide (CH3CN) in its J=6_K-5_K, J=12_K-11_K, J=13_K-12_K, and J=14_K-13_K transitions at an average angular resolution of ~10 arcsec (22 arcsec for the 6_K-5_K lines), as part of a new 2D line survey of this region using the IRAM 30m telescope. These fully sampled maps show extended emission from warm gas to the northeast of IRc2 and the distinct kinematic signatures of the hot core and compact ridge source components. We have constructed population diagrams for the four sets of K-ladder emission lines at each position in the maps and have derived rotational excitation temperatures and total beam-averaged column densities from the fitted slopes. In addition, we have fitted LVG model spectra to the observations to determine best-fit physical parameters at each map position, yielding the distribution of kinetic temperatures across the region. The resulting temperature maps reveal a region of hot (T > 350 K) material surrounding the northeastern edge of the hot core, whereas the column density distribution is more uniform and peaks near the position of IRc2. We attribute this region of hot gas to shock heating caused by the impact of outflowing material from active star formation in the region, as indicated by the presence of broad CH3CN lines. This scenario is consistent with predictions from C-shock chemical models that suggest that gas-phase methyl cyanide survives in the post-shock gas and can be somewhat enhanced due to sputtering of grain mantles in the passing shock front.Comment: 24 pages, 20 figures, accepted for publication in A&