27 research outputs found
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
Testing kinematic distances under a realistic Galactic potential
Obtaining reliable distance estimates to gas clouds within the Milky Way is
challenging in the absence of certain tracers. The kinematic distance approach
has been used as an alternative, derived from the assumption of circular
trajectories around the Galactic centre. Consequently, significant errors are
expected in regions where gas flow deviates from purely circular motions. We
aim to quantify the systematic errors that arise from the kinematic distance
method in the presence of a Galactic potential that is non-axisymmetric. We
investigate how these errors differ in certain regions of the Galaxy and how
they relate to the underlying dynamics. We perform 2D isothermal hydrodynamical
simulation of the gas disk with the moving-mesh code Arepo, adding the
capability of using an external potential provided by the Agama library for
galactic dynamics. We introduce a new analytic potential of the Milky Way,
taking elements from existing models and adjusting parameters to match recent
observational constraints. We find significant errors in the kinematic distance
estimate for gas close to the Sun, along sight lines towards the Galactic
centre and anti-centre, and significant deviations associated with the Galactic
bar. Kinematic distance errors are low within the spiral arms as gas resides
close to local potential minima and the resulting line-of-sight velocity is
close to what is expected for an axisymmetric potential. Interarm regions
exhibit large deviations at any given Galactic radius. This is caused by the
gas being sped up or slowed down as it travels into or out of the spiral arm.
We are able to define 'zones of avoidance' in the lv-diagram, where the
kinematic distance method is particularly unreliable and should only be used
with caution. We report a power law relation between the kinematic distance
error and the deviation of the project line-of-sight velocity from circular
motion.Comment: 23 pages, 22 figures, 6 tables, submitted to A&
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