Machine learning based data mining for Milky Way filamentary structures reconstruction

We present an innovative method called FilExSeC (Filaments Extraction, Selection and Classification), a data mining tool developed to investigate the possibility to refine and optimize the shape reconstruction of filamentary structures detected with a consolidated method based on the flux derivative analysis, through the column-density maps computed from Herschel infrared Galactic Plane Survey (Hi-GAL) observations of the Galactic plane. The present methodology is based on a feature extraction module followed by a machine learning model (Random Forest) dedicated to select features and to classify the pixels of the input images. From tests on both simulations and real observations the method appears reliable and robust with respect to the variability of shape and distribution of filaments. In the cases of highly defined filament structures, the presented method is able to bridge the gaps among the detected fragments, thus improving their shape reconstruction. From a preliminary "a posteriori" analysis of derived filament physical parameters, the method appears potentially able to add a sufficient contribution to complete and refine the filament reconstruction.Comment: Proceeding of WIRN 2015 Conference, May 20-22, Vietri sul Mare, Salerno, Italy. Published in Smart Innovation, Systems and Technology, Springer, ISSN 2190-3018, 9 pages, 4 figure

VizieR Online Data Catalog: L1157-B1 DCN (2-1) and H13CN (2-1) datacubes (Busquet+, 2017)

IRAM NOEMA observations of DCN(2-1) and H13CN(2-1) towa brightest bow-shock B1 of the L1157 molecular outflow. All data cubes are provided in fits format smoothed to a velocity resolution of 0.5km/s. (2 data files)

Astrochemistry at work in the L1157-B1 shock: acetaldehyde formation

The formation of complex organic molecules (COMs) in protostellar environments is a hotly debated topic. In particular, the relative importance of the gas phase processes as compared to a direct formation of COMs on the dust grain surfaces is so far unknown. We report here the first high-resolution images of acetaldehyde (CH3CHO) emission towards the chemically rich protostellar shock L1157-B1, obtained at 2 mm with the IRAM Plateau de Bure interferometer. Six blueshifted CH3CHO lines with Eu = 26-35 K have been detected. The acetaldehyde spatial distribution follows the young (̃ 2000 yr) outflow cavity produced by the impact of the jet with the ambient medium, indicating that this COM is closely associated with the region enriched by iced species evaporated from dust mantles and released into the gas phase. A high CH3CHO relative abundance, 2-3 × 10-8, is inferred, similarly to what found in hot corinos. Astrochemical modelling indicates that gas phase reactions can produce the observed quantity of acetaldehyde only if a large fraction of carbon, of the order of 0.1 per cent, is locked into iced hydrocarbons

The origin and structure of clumps along molecular outflows: the test case of CB3

We investigate the origin of the small, chemically rich molecular clumps observed along the main axis of chemically rich outflows such as CB3 and L1157. We develop a chemical model where we explore the chemical evolution of these clumps, assuming they are partially pre-existing to the outflow, or alternatively newly formed by the impact of the outflow on the surrounding medium. The effects of the impact of the outflow are reproduced by density and temperature changes in the clump. We find that the observed abundances of CH3OH, SO and SO2 are best reproduced by assuming a scenario where the dense molecular gas observed is probably pre-existing in the interstellar medium before the formation of their exciting (proto)stars and that the clumpiness and the rich chemistry of the clumps are a consequence of a pre-existing density enhancement and of its interaction with the outflow.Comment: 11 pages, 5 figures, accepted by MNRAS; corrected label in figure

A study of the cold cores population in the Serpens star-forming region

As part of the Herschel Gould Belt survey, the Serpens star-forming region was observed with the Herschel PACS and SPIRE instruments. Data analysis is ongoing and a first version of the source catalog is ready; here we show some preliminary results

Distance biases in the estimation of the physical properties of Hi-GAL compact sources - I. Clump properties and the identification of high-mass star-forming candidates

The degradation of spatial resolution in star-forming regions, observed at large distances (d ≳ 1 kpc) with Herschel, can lead to estimates of the physical parameters of the detected compact sources (clumps), which do not necessarily mirror the properties of the original population of cores. This paper aims at quantifying the bias introduced in the estimation of these parameters by the distance effect. To do so, we consider Herschel maps of nearby star-forming regions taken from the Herschel Gould Belt survey, and simulate the effect of increased distance to understand what amount of information is lost when a distant star-forming region is observed with Herschel resolution. In the maps displaced to different distances we extract compact sources, and we derive their physical parameters as if they were original Herschel infrared Galactic Plane Survey maps of the extracted source samples. In this way, we are able to discuss how the main physical properties change with distance. In particular, we discuss the ability of clumps to form massive stars: we estimate the fraction of distant sources that are classified as high-mass stars-forming objects due to their position in the mass versus radius diagram, that are only 'false positives'. We also give a threshold for high-mass star formation M>1282 (r/ [pc])^{1.42} M_{☉}. In conclusion, this paper provides the astronomer dealing with Herschel maps of distant star-forming regions with a set of prescriptions to partially recover the character of the core population in unresolved clumps

A study of the cold cores population in the Perseus star-forming regions

As part of the Herschel Gould Belt survey, the Perseus star-forming cloud was observed with the Herschel PACS and SPIRE instruments. Source catalogs are preliminary, as well as the here presented core mass function

ISO -LWS two-colour diagram of young stellar objects

We present a [60-100] versus [100-170]μm two-colour diagram for a sample of 61 young stellar objects (YSOs) observed with the Long Wavelength Spectrometer (LWS) on-board the Infrared Space Observatory (ISO). The sample consists of 17 Class 0 sources, 15 Class I, nine Bright Class I (Lbol>104Lsolar) and 20 Class II (14 Herbig Ae/Be stars and six T Tauri stars). We find that each class occupies a well-defined region in our diagram with colour temperatures increasing from Class 0 to Class II. Therefore the [60-100] versus [100-170] two-colour diagram is a powerful and simple tool to derive from future (e.g. with the Herschel Space Observatory) photometric surveys the evolutionary status of YSOs. The advantage over other tools already developed is that photometry at other wavelengths is not required: three flux measurements are enough to derive the evolutionary status of a source. As an example we use the colours of the YSO IRAS 18148-0440 to classify it as Class I. The main limitation of this work is the low spatial resolution of the LWS which, for some objects, causes a high uncertainty in the measured fluxes due to background emission or to source confusion inside the LWS beam

Strong H_2O and high-J CO emission towards the Class 0 protostar L1448-mm

The spectrum of the Class 0 source L1448-mm has been measured over the wavelength range extending from 6 to 190 mu m with the Long Wavelength Spectrometer (LWS) and the Short Wavelength Spectrometer (SWS) on the Infrared Space Observatory (ISO). The far infrared spectrum is dominated by strong emission from gaseous H_2O and from CO transitions with rotational quantum numbers J >= 14; in addition, the H_2 pure rotational lines S(3), S(4) and S(5), the OH fundamental line at 119 mu m, as well as emission from [O I] 63 mu m and [C Ii] 158 mu m are also observed. The strong CO and water emission can be consistently explained as originating in a warm gas component at T ~ 700-1400 K and n_H_2 ~ (3-50) 10(4 ) cm(-3) , which fills about 0.2-2% of the ~ 75\arcsec LWS field of view (corresponding, assuming a single emitting region, to a physical size of about (3-12)\arcsec or (0.5-2) 10(-2) pc at d = 300 pc). We derive an H_2O/CO abundance ratio ~ 5, which, assuming a standard CO/H_2 abundance of 10(-4) , corresponds to H_2O/H_2 ~ 5 10(-4) . This value implies that water is enhanced by about a factor ~ 10(3) with respect to its expected abundance in the ambient gas. This is consistent with models of warm shocked regions which predict that most of the free atomic oxygen will be rapidly converted into water once the temperature of the post-shocked gas exceeds ~ 300 K. The relatively high density and compact size inferred for this emission may suggest an origin in the shocked region along the molecular jet traced by SiO and EHV CO millimeter line emission. Further support is given by the fact that the observed enhancement in H_2O can be explained by shock conditions similar to those expected to produce the abundant SiO observed in the region. L1448-mm shows the largest water abundance so far observed by ISO amongst young sources displaying outflow activity; we argue that the occurrence of multiple shocks over a relatively short interval of time, like that evidenced in the surroundings of L1448-mm, could have contributed to enrich the molecular jet with a high H_2O column density. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NAS