- ID:
- ivo://CDS.VizieR/J/A+A/643/A61
- Title:
- Prestellar cores H2D+ and N2H+ maps
- Short Name:
- J/A+A/643/A61
- Date:
- 07 Mar 2022 07:18:04
- Publisher:
- CDS
- Description:
- The study of prestellar cores is critical as they set the initial conditions in star formation and determine the final mass of the stellar object. To date, several hypotheses are describing their gravitational collapse. Deriving the dynamical model that fits both the observed dust and the gas emission from such cores is therefore of great importance. We perform detailed line analysis and modelling of H_2_D^+^ 1_10_-1_11_ and N_2_H^+^ 4-3 emission at 372GHz, using 2'x2' maps (JCMT).Our goal is to test the most prominent dynamical models by comparing the modelled gas kinematics and spatial distribution (H_2_D^+^ and N_2_H^+^) with observations towards four prestellar (L1544, L183, L694-2, L1517B) and one protostellar core (L1521f). We fit the line profiles at all offsets showing emission using single Gaussian distributions. We investigate how the line parameters (V_LSR_, FWHM and T_A_*) change with offset, to examine the velocity field, the degree of non-thermal contributions to the line broadening, and the distribution of the material in these cores. To assess the thermal broadening, we derive the average gas kinetic temperature towards all cores using the non-LTE radiative transfer code RADEX. We perform a more detailed non-LTEradiative transfer modelling using RATRAN, where we compare the predicted spatial distribution and line profiles of H_2_D^+^ and N_2_H^+^ with observations towards all cores. To do so, we adopt the physical structure for each core predicted by three different dynamical models taken from literature: Quasi-Equilibrium Bonnor-Ebert Sphere (QE-BES), Singular Isothermal Sphere (SIS), and Larson-Penston (LP) flow. In addition, we compare these results to those of a static sphere, whose density and temperature profiles are based on the observed dust continuum. Lastly, we constrain the abundance profiles of H_2_D^+^ and N_2_H^+^ towards each core. We find that variable non-thermal contributions (variations by a factor of 2.5) are required to explain the observed line width of both H_2_D^+^ and N_2_H^+^, while the non-thermal contributions are found to be 50% higher for N_2_H^+^. The RADEX modelling results in average core column densities of ~9x10^12^cm^-2^ for H_2_D+and N_2_H^+^. The LP flow seems to be the dynamical model that can reproduce the observed spatial distribution and line profiles of H_2_D^+^ on a global scale of prestellar cores, while the SIS model systematically and significantly overestimates the width of the line profiles and underestimates the line peak intensity. We find similar abundance profiles for the prestellar cores and the protostellar core. The typical abundances of H_2_D^+^ vary between 10^-9^-10^-10^ for the inner 5000au, and drop by about an order of magnitude for the outer regions of the core (2x10^-10^-6x10^-11^). In addition, a higher N_2_H^+^ abundance by about a factor of 4 compared to H_2_D^+^ is found towards the two cores with detected emission. The presence ofN_2_H^+^ 4-3 towards the protostellar core and towards one of the prestellar cores reflects the increasing densities as the core evolves. Our analysis provides an updated picture of the physical structure of prestellar cores. Although the dynamical models account for mass differences by up to a factor of 7, the velocity structure drives the shape of the line profiles, allowing for a robust comparison between the models. We find that the SIS model can be cleary excluded in explaining the gas emission towards the cores,but a larger sample is required to differentiate clearly between the LP flow, the QE-BES and the static models. All models of collapse underestimate the intensity of the gas emission by up to several factors towards the only protostellar core in our sample, indicating that different dynamics take place in different evolutionary core stages. If the LP model is confirmed towards a larger sample of prestellarcores, it would indicate that they may form by compression or accretion of gas from larger scales. If the QE-BES model is confirmed, it means that quasi hydrostatic cores can exist within turbulent ISM.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/684/1240
- Title:
- Prestellar cores in Perseus, Serpens and Ophiuchus
- Short Name:
- J/ApJ/684/1240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an unbiased census of starless cores in Perseus, Serpens, and Ophiuchus, assembled by comparing large-scale Bolocam 1.1mm continuum emission maps with Spitzer c2d surveys. We use the c2d catalogs to separate 108 starless from 92 protostellar cores in the 1.1mm core samples from Enoch and Young and their coworkers. A comparison of these populations reveals the initial conditions of the starless cores.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A36
- Title:
- Probing the ISF in Orion A with ArTeMiS
- Short Name:
- J/A+A/651/A36
- Date:
- 17 Jan 2022 11:38:53
- Publisher:
- CDS
- Description:
- The Orion molecular cloud is the closest region of high-mass star formation. It is an ideal target for investigating the detailed structure of massive star-forming filaments at high resolution and the relevance of the filament paradigm for the earliest stages of intermediate- to high-mass star formation. Within the Orion A molecular cloud, the integral-shaped filament (ISF) is a prominent, degree-long structure of dense gas and dust with clear signs of recent and ongoing high-mass star formation. Our aim is to characterise the structure of this massive filament at moderately high angular resolution (8" or ~0.016pc) in order to measure the intrinsic width of the main filament, down to scales well below 0.1pc, which has been identified as the characteristic width of filaments. We used the ArTeMiS bolometer camera at APEX to map a ~0.6x0.2deg^2^ region covering OMC-1, OMC-2, and OMC-3 at 350 and 450um. We combined these data with Herschel- SPIRE maps to recover extended emission. The combined Herschel-ArTeMiS maps provide details on the distribution of dense cold material, with a high spatial dynamic range, from our 8" resolution up to the transverse angular size of the map, ~10-15'. By combining Herschel and ArTeMiS data at 160, 250, 350, and 450um, we constructed high-resolution temperature and H_2_ column density maps. We extracted radial intensity profiles from the column density map in several representative portions of the ISF, which we fitted with Gaussian and Plummer models to derive their intrinsic widths. We also compared the distribution of material traced by ArTeMiS with that seen in the higher-density tracer N_2_H^+^(1-0) that was recently observed with the ALMA interferometer. All the radial profiles that we extracted show a clear deviation from a Gaussian, with evidence for an inner plateau that had not previously been seen clearly using Herschel-only data. We measure intrinsic half-power widths in the range 0.06 to 0.11pc. This is significantly larger than the Gaussian widths measured for fibres seen in N_2_H^+^, which probably only traces the dense innermost regions of the large-scale filament. These half-power widths are within a factor of two of the value of ~0.1 pc found for a large sample of nearby filaments in various low-mass star-forming regions, which tends to indicate that the physical conditions governing the fragmentation of pre-stellar cores within transcritical or supercritical filaments are the same over a large range of masses per unit length.
- ID:
- ivo://CDS.VizieR/J/ApJS/216/33
- Title:
- Probing the Local Bubble with DIBs. III.
- Short Name:
- J/ApJS/216/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new high signal-to-noise ratio (S/N) observations of the diffuse interstellar bands (DIBs) in the Local Bubble and its surroundings. We observed 432 sightlines and obtain the equivalent widths of the {lambda}5780 and {lambda}5797{AA} DIBs up to a distance of ~200pc. All of the observations were carried out using the Intermediate Dispersion Spectrograph on the 2.5m Isaac Newton Telescope, during three years, to reach a minimum S/N of ~2000. All of the {lambda}5780 and {lambda}5797 absorptions are presented in this paper and we tabulate the observed values of the interstellar parameters, {lambda}5780, {lambda}5797, Na ID_1_, and Na ID_2_, including the uncertainties.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A30
- Title:
- Properties of cores in OMC 2/3
- Short Name:
- J/A+A/588/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new measurements of the dust emissivity index, {beta}, for the high-mass, star-forming OMC 2/3 filament. We combined 160-500um data from Herschel with long-wavelength observations at 2mm and fit the spectral energy distributions across a=~2pc long, continuous section of OMC 2/3 at 15000AU (0.08pc) resolution. With these data, we measured {beta} and reconstructed simultaneously the filtered-out large-scale emission at 2mm. We implemented both variable and fixed values of {beta}, finding that {beta}=1.7-1.8 provides the best fit across most of OMC 2/3. These {beta} values are consistent with a similar analysis carried out with filtered Herschel data. Thus, we show that {beta} values derived from spatial filtered emission maps agree well with those values from unfiltered data at the same resolution. Our results contradict the very low {beta} values (~0.9) previously measured in OMC 2/3 between 1.2mm and 3.3mm data, which we attribute to elevated fluxes in the 3.3mm observations. Therefore, we find no evidence of rapid, extensive dust grain growth in OMC 2/3. Future studies with Herschel data and complementary ground-based long-wavelength data can apply our technique to obtain reliable determinations of {beta} in nearby cold molecular clouds.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A206
- Title:
- Propynethial (HCCCHS) submm spectroscopy
- Short Name:
- J/A+A/642/A206
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The majority of sulfur-containing molecules detected in the interstellar medium (ISM) are analogs of oxygen-containing compounds. Propynal was detected in the ISM in 1988, hence propynethial, its sulfur derivative, is a good target for an ISM search. Our aim is to measure the rotational spectrum of propynethial and use those measurements to search for this species in the ISM. To date, measurements of the rotational spectra of propynethial have been limited to a small number or transitions below 52GHz. The extrapolation of the prediction to lines in the milimeter-wave domain is inaccurate and does not provide data to permit an unambiguous detection. The rotational spectrum was re-investigated up to 630GHz. Using the new prediction lines of propynethial, as well as the related propynal, a variety of astronomical sources were searched, including star-forming regions and dark clouds. A total of 3288 transitions were newly assigned and fit together with those from previous studies, reaching quantum numbers up to J=107 and K_a_=24. Watson's symmetric top Hamiltonian in the I^r^ representation was used for the analysis, because the molecule is very close to the prolate limit. The search for propynethial resulted in a non-detection; upper limits to the column density were derived in each source.
- ID:
- ivo://CDS.VizieR/J/A+A/588/L8
- Title:
- Protonated formaldehyde in L1689B
- Short Name:
- J/A+A/588/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Complex organic molecules (COMs) are detected in many regions of the interstellar medium, including prestellar cores. However, their formation mechanisms in cold (~10K) cores remain to this date poorly understood. The formyl radical HCO is an important candidate precursor for several O-bearing terrestrial COMs in cores, as an abundant building block of many of these molecules. Several chemical routes have been proposed to account for its formation, both on grain surfaces, as an incompletely hydrogenated product of H addition to frozen-out CO molecules, or in the gas phase, either the product of the reaction between H_2_CO and a radical, or as a product of dissociative recombination of protonated formaldehyde H_2_COH^+^. The detection and abundance determination of H_2_COH^+^, if present, could provide clues as to whether this latter scenario might apply. We searched for protonated formaldehyde H_2_COH^+^ in the prestellar core L1689B using the IRAM 30m telescope. The H_2_COH^+^ ion is unambiguously detected, for the first time in a cold (~10K) source. The derived abundance agrees with a scenario in which the formation of H_2_COH^+^ results from the protonation of formaldehyde. We use this abundance value to constrain the branching ratio of the dissociative recombination of H2COH+ towards the HCO channel to ~10-30%. This value could however be smaller if HCO can be efficiently formed from gas-phase neutral- neutral reactions, and we stress the need for laboratory measurements of the rate constants of these reactions at 10K. Given the experimental difficulties in measuring branching ratios experimentally, observations can bring valuable constraints on these values, and provide a useful input for chemical networks.
718. Protostellar cores
- ID:
- ivo://CDS.VizieR/J/A+A/291/943
- Title:
- Protostellar cores
- Short Name:
- J/A+A/291/943
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Basing on the coagulation model of Ossenkopf (1993A&A...280..617O), we systematically computed and tabulated the opacity of dust in dense protostellar cores between 1 micrometers and 1.3 mm. The possible physical conditions were varied especially considering the influence of different gas densities and molecular depletion ratios. In comparison to the dust opacity in the diffuse interstellar medium, we found nowhere changes by more than the factor 5 for ice-covered dust grains. Possible uncertainties and deviations in environments with different physical conditions are discussed. Although one may imagine very special situations in which the dust opacity is changed by more than a factor 10, for physically reasonable conditions in dense protostellar cores, all possible deviations from the tabulated values may not sum up to more than a factor of 2. Using these tables of dust opacities, the submm continuum radiation of cold dust in protostellar cores is a good tracer of their total mass.
- ID:
- ivo://CDS.VizieR/J/other/Sci/345.791
- Title:
- Pseudo-3D maps of DIB at 862nm
- Short Name:
- J/other/Sci/345.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo-three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB research.
- ID:
- ivo://CDS.VizieR/J/ApJ/701/1965
- Title:
- Radial dust properties of SINGS galaxies
- Short Name:
- J/ApJ/701/1965
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed analysis of the radial distribution of dust properties in the SINGS sample, performed on a set of ultraviolet (UV), infrared (IR), and HI surface brightness profiles, combined with published molecular gas profiles and metallicity gradients. By applying physical dust models to our radial spectral energy distributions, we have derived radial profiles of the total dust mass surface density, the fraction of the total dust mass contributed by polycyclic aromatic hydrocarbons (PAHs), and the intensity of the radiation field heating the grains.
