- ID:
- ivo://CDS.VizieR/J/A+A/533/A121
- Title:
- Missing low-mass stars in S254-S258
- Short Name:
- J/A+A/533/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this study was to find an explanation for the remarkable morphology of the central part of the S254-S258 star forming complex. We performed a deep Chandra X-ray observation of the S254-S258 region in order to efficiently discriminate young stars (with and without circumstellar matter) from the numerous older field stars in the area. We detected 364 X-ray point sources in a 17'x17' field. This X-ray catalog provides, for the first time, a complete sample of all young stars in the region down to about 0.5M_{sun}_.
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- ID:
- ivo://CDS.VizieR/J/A+A/607/A22
- Title:
- Monoceros R2 filament hub FIR observations
- Short Name:
- J/A+A/607/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830pc distance, containing several sites of active star formation), as observed at 70um, 160um, 250um, 350um, and 500um by the PACS and SPIRE instruments on the Herschel Space Observatory as part of the HOBYS Key programme. The Herschel data are complemented by SCUBA-2 data in the submillimetre range, and WISE and Spitzer data in the mid-infrared. In addition, C^18^O data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with getsources, and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of 177 Herschel sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A58
- Title:
- Oph A mosaic image
- Short Name:
- J/A+A/631/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity, which are intimately connected to the evolution of protoplanetary disks and the formation of planets. We have carried out sensitive continuum observations toward the Ophiuchus A star-forming region using the Karl G. Jansky Very Large Array (VLA) at 10GHz over a field-of-view of 6' with a spatial resolution of {theta}_maj_x{theta}_min_~0.4"x0.2". We achieved a 5{mu}Jy/beam root-mean-square noise level at the center of our mosaic field of view. Among the eighteen sources we detected, sixteen are YSOs (three Class 0, five Class I, six Class II, and two Class III) and two are extragalactic candidates.We find that thermal dust emission generally contributes less that 30% of the emission at 10GHz. The radio emission is dominated by other types of emission such as gyro-synchrotron radiation from active magnetospheres, free-free emission from thermal jets, free-free emission from the outflowing photo-evaporated disk material, and/or synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections towards Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain the disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve with time. The sensitivity of our data cannot exclude photoevaporation due to X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys with the Square Kilometre Array will be able to provide strong constraints on disk photoevaporation.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A106
- Title:
- Probing midplane structure with DCO+ in HD169142
- Short Name:
- J/A+A/614/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the radial distribution of DCO^+^ in the protoplanetary disk around HD 169142, a Herbig Ae type star, with the aim of determining possible formation scenarios of DCO^+^. Using a simple chemical model, we investigate the effect of gas-phase CO abundance and gas temperature on the production of DCO^+^ near the disk midplane. Model fits to the DCO^+^ radial profile suggest a much colder disk midplane than the disk physical structure obtained from the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A72
- Title:
- Resolved molecular line observations
- Short Name:
- J/A+A/646/A72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Physical processes that govern the star and planet formation sequence influence the chemical composition and evolution of protoplanetary disks. Recent studies allude to an early start to planet formation already ongoing during the formation of a disk. To understand the chemical composition of protoplanets, we need to constrain the composition and structure of the disks from whence they are formed. We aim to determine the molecular abundance structure of the young disk around the TMC1A protostar on au scales in order to understand its chemical structure and any possible implications for disk formation. We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of CO, HCO^+^, HCN, DCN, and SO line emission, as well as dust continuum emission, in the vicinity of TMC1A. Molecular column densities are estimated both under the assumption of optically thin emission from molecules in local thermodynamical equilibrium (LTE) as well as through more detailed non-LTE radiative transfer calculations. From the derived HCO^+^ abundance, we estimate the ionization fraction of the disk surface and find values that imply that the accretion process is not driven by the magneto-rotational instability. The molecular abundances averaged over the TMC1A disk are similar to its protostellar envelope and other, older Class II disks. We meanwhile find a discrepancy between the young disk's molecular abundances relative to Solar System objects. Abundance comparisons between the disk and its surrounding envelope for several molecular species reveal that the bulk of planet-forming material enters the disk unaltered. Differences in HCN and H_2_O molecular abundances between the disk around TMC1A, Class II disks, and Solar System objects trace the chemical evolution during disk and planet formation.
- ID:
- ivo://CDS.VizieR/J/A+A/577/A30
- Title:
- SDC335.579-0.292 6, 8, 23 and 25GHz images
- Short Name:
- J/A+A/577/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent ALMA observations identified one of the most massive star-forming cores yet observed in the Milky Way: SDC335-MM1, within the infrared dark cloud SDC335.579-0.292. Along with an accompanying core MM2, SDC335 appears to be in the early stages of its star formation process. We aim to constrain the properties of the stars forming within these two massive millimetre sources. Observations of SDC335 at 6, 8, 23 and 25GHz were made with the Australia Telescope Compact Array.We report the results of these continuum measurements, which combined with archival data, allow us to build and analyse the spectral energy distributions (SEDs) of the compact sources in SDC335.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A142
- Title:
- SDC G335.579-0.292 ALMA images and datacubes
- Short Name:
- J/A+A/645/A142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The infrared dark cloud (IRDC) SDC335.579-0.292 (hereafter, SDC335) is a massive (~5000 solar masses) star-forming cloud which has been found to be globally collapsing towards one of the most massive star forming cores in the Galaxy, which is located at its centre. SDC335 is known to host three high-mass protostellar objects at early stages of their evolution and archival ALMA Cycle 0 data (at ~5 arcsecond resolution) indicate the presence of at least one molecular outflow in the region detected in HNC. Observations of molecular outflows from massive protostellar objects allow us to estimate the accretion rates of the protostars as well as to assess the disruptive impact that stars have on their natal clouds during their formation. The aim of this work is to identify and analyse the properties of the protostellar-driven molecular outflows within SDC335 and use these outflows to help refine the properties of the young massive protostars in this cloud. We imaged the molecular outflows in SDC335 using new data from the Australia Telescope Compact Array (ATCA) of SiO and Class I CH_3_OH maser emission (at a resolution of ~3 arcsecond) alongside} observations of four CO transitions made with the Atacama Pathfinder EXperiment (APEX) and archival Atacama Large Millimeter/submillimeter Array (ALMA) CO, 13CO (~1 arcsecond), and HNC data. We introduced a generalised argument to constrain outflow inclination angles based on observed outflow properties. We then used the properties of each outflow to infer the accretion rates on the protostellar sources driving them. These accretion properties allowed us to deduce the evolutionary characteristics of the sources. Shock-tracing SiO emission and CH_3_OH Class I maser emission allowed us to locate regions of interaction between the outflows and material infalling to the central region via the filamentary arms of SDC335.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A32
- Title:
- Sub-mm images of SSTB213 J041757.75+274105.5
- Short Name:
- J/A+A/564/A32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed the proto brown dwarf candidate SSTB213 J041757 with the Submillimeter Array to search for CO molecular outflow emission from the source. Our CO maps do not show any outflow emission from the proto brown dwarf candidate. The non-detection implies that the molecular outflows from the source are weak; deeper observations are therefore needed to probe the outflows from the source.
- ID:
- ivo://CDS.VizieR/J/MNRAS/458/3479
- Title:
- SVM selection of WISE YSO Candidates
- Short Name:
- J/MNRAS/458/3479
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explored the AllWISE catalogue of the Wide-field Infrared Survey Explorer mission and identified Young Stellar Object candidates. Reliable 2MASS and WISE photometric data combined with Planck dust opacity values were used to build our dataset and to find the best classification scheme. A sophisticated statistical method, the Support Vector Machine (SVM) is used to analyse the multi-dimensional data space and to remove source types identified as contaminants (extragalactic sources, main sequence stars, evolved stars and sources related to the interstellar medium). Objects listed in the SIMBAD database are used to identify the already known sources and to train our method. A new all-sky selection of 133,980 Class I/II YSO candidates is presented. The estimated contamination was found to be well below 1% based on comparison with our SIMBAD training set. We also compare our results to that of existing methods and catalogues. The SVM selection process successfully identified >90% of the Class I/II YSOs based on comparison with photometric and spectroscopic YSO catalogues. Our conclusion is that by using the SVM, our classification is able to identify more known YSOs of the training sample than other methods based on colour-colour and magnitude-colour selection. The distribution of the YSO candidates well correlates with that of the Planck Galactic Cold Clumps in the Taurus-Auriga-Perseus-California region.
- ID:
- ivo://CDS.VizieR/J/AN/333/634
- Title:
- Torun methanol source catalogue
- Short Name:
- J/AN/333/634
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the observations of 289 methanol maser sources at 6.7GHz obtained over a two month period with the Torun 32m telescope. The data form a catalogue of all objects north of {delta}=22{deg} brighter than 7.5Jy in the peak emission. The positions of sub-arcsecond accuracy are updated for 76% of the objects. We find that about one third of the sources show changes in the peak fluxes by a factor of two or more on time scales of 8.5-9.5 years.
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