- ID:
- ivo://CDS.VizieR/J/ApJ/836/199
- Title:
- IRDC G028.23-00.19 NIR polarimetry analysis
- Short Name:
- J/ApJ/836/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The importance of the magnetic (B) field in the formation of infrared dark clouds (IRDCs) and massive stars is an ongoing topic of investigation. We studied the plane-of-sky B field for one IRDC, G028.23-00.19, to understand the interaction between the field and the cloud. We used near-IR background starlight polarimetry to probe the B field and performed several observational tests to assess the field importance. The polarimetric data, taken with the Mimir instrument, consisted of H-band and K-band observations, totaling 17160 stellar measurements. We traced the plane-of-sky B-field morphology with respect to the sky-projected cloud elongation. We also found the relationship between the estimated B-field strength and gas volume density, and we computed estimates of the normalized mass-to-magnetic flux ratio. The B-field orientation with respect to the cloud did not show a preferred alignment, but it did exhibit a large-scale pattern. The plane-of-sky B-field strengths ranged from 10 to 165{mu}G, and the B-field strength dependence on density followed a power law with an index consistent with 2/3. The mass-to-magnetic flux ratio also increased as a function of density. The relative orientations and relationship between the B field and density imply that the B field was not dynamically important in the formation of the IRDC. The increase in mass-to-flux ratio as a function of density, though, indicates a dynamically important B field. Therefore, it is unclear whether the B field influenced the formation of G28.23. However, it is likely that the presence of the IRDC changed the local B-field morphology.
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292. IRDC18223 images
- ID:
- ivo://CDS.VizieR/J/A+A/584/A67
- Title:
- IRDC18223 images
- Short Name:
- J/A+A/584/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Filamentary structures in the interstellar medium are crucial ingredients of the star formation process. They fragment to form individual star-forming cores, and at the same time they may also funnel gas toward the central gas cores, providing an additional gas reservoir. We want to resolve the length scales for filament formation and fragmentation (resolution <=0.1pc), in particular the Jeans length and cylinder fragmentation scale. We have observed the prototypical high-mass star-forming filament IRDC 18223 with the Plateau de Bure Interferometer (PdBI) in the 3.2mm continuum and N_2_H^+^(1-0) line emission in a ten-field mosaic at a spatial resolution of ~4{deg} (~14000au).
- ID:
- ivo://CDS.VizieR/J/A+A/603/A22
- Title:
- IRDCs cores spectra of HCN and HNC isotopologue
- Short Name:
- J/A+A/603/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the measurement of nitrogen fractionation in a sample of infrared-dark clouds (IRDCs) cores which are believed to be the precursors of high-mass stars and star clusters. We observed the J=1-0 transitions of HCN, H^13/^CN, HC^15/^N, HN^13/^C, and H^15/^NC towards a sample of 22 cores in four IRDCs using the IRAM 30m telescope.Assuming LTE and a temperature of 15K, the 14N/^15/^N ratios measured are consistent with the terrestrial atmosphere(TA) and protosolar nebula(PSN) values, and with the ratios measured in low-mass prestellar cores. However, the 14N/^15/^N ratios measured in cores C1, C3, F1, F2, and G2 do not agree with the results from similar studies towards the same cores using nitrogen bearing molecules with nitrile functional group(-CN) and nitrogen hydrides (-NH) although the ratio spread covers a similar range. Relatively low 14N/^15/^N ratios amongst the four-IRDCs were measured in IRDC G which are comparable to those measured in small cosmomaterials and protoplanetary disks. The low average gas density of this cloud suggests that the gas density, rather than the gas temperature, may be the dominant parameter influencing the initial nitrogen isotopic composition in young PSN.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/112
- Title:
- IR polarization data in the BN region
- Short Name:
- J/ApJ/741/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New visible and K-band polarization measurements of stars surrounding molecular clouds in Orion A and stars in the Becklin-Neugebauer (BN) vicinity are presented. Our results confirm that magnetic fields located inside the Orion A molecular clouds and in their close neighborhood are spatially connected. On and around the BN object, we measured the angular offsets between the K-band polarization data and available submillimeter (submm) data. We find high values of the polarization degree, P_K_, and of the optical depth, {tau}_K_, close to an angular offset position of 90{deg} whereas lower values of P_K_ and {tau}_K_ are observed for smaller angular offsets. We interpret these results as evidence for the presence of various magnetic field components toward lines of sight in the vicinity of BN. On a larger scale, we measured the distribution of angular offsets between available H-band polarization data and the same submm data set. Here we find an increase of <P_H_> with angular offset, which we interpret as a rotation of the magnetic field by <~60{deg}. This trend generalizes previous results on small scales toward and around lines of sight to BN and is consistent with a twist of the magnetic field on a larger scale toward OMC-1. A comparison of our results with several other studies suggests that a two-component magnetic field, perhaps helical, could be wrapping the OMC-1 filament.
- ID:
- ivo://CDS.VizieR/J/A+A/392/239
- Title:
- IR survey of outflows in Orion A
- Short Name:
- J/A+A/392/239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have made an unbiased imaging survey of a 1.2 square degree area in the Orion A giant molecular cloud searching for molecular hydrogen emission line features seen in the v=1-0 S(1) line at a wavelength of 2.12{mu}m originating in shocks in outflows from young stellar objects. This survey provides for the first time an unbiased census of outflows over a significant portion of a giant molecular cloud, and yields a sample of outflows free from selection effects and with all objects located at roughly the same, well-known distance. In this paper, we present the data gathered in the course of the survey, provide a comprehensive list of all molecular hydrogen emission features found, and give a list of the 76 candidate outflows identified in the data set.
- ID:
- ivo://CDS.VizieR/J/A+A/357/219
- Title:
- ISOCAM observations in Cha I.
- Short Name:
- J/A+A/357/219
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an ISOCAM survey of the Chamaeleon I dark cloud conducted in two broad-band filters at 6.7 and 14.3{mu}m. In an area of 0.59deg^2^. we have detected a total of 282 mid-IR sources with 103 sources observed in both filters. Combining the ISOCAM observations with the I, J, and K_s_ data obtained with DENIS, we have found 108 pre-main-sequence (PMS) stars in the region, of which 34 were previously unidentified. Several of these newly discovered young stellar objects are relatively faint suggesting a population in Cha I of very low mass objects that probably includes brown dwarfs in their early contraction phases. Finally, most of the PMS stars show the spectral index computed between 2.2 and 14.3{mu}m typical of Class II sources. The luminosity function (LF) derived for our detected PMS stars is discussed.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/167
- Title:
- JCMT Gould Belt Survey: dense cores in Orion B
- Short Name:
- J/ApJ/817/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a first look at the SCUBA-2 observations of three sub-regions of the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850{mu}m map, and present their basic properties, including their peak fluxes, total fluxes, and sizes, and an estimate of the corresponding 450{mu}m peak fluxes and total fluxes, using the FellWalker source extraction algorithm. Assuming a constant temperature of 20K, the starless dense cores have a mass function similar to that found in previous dense core analyses, with a Salpeter-like slope at the high-mass end. The majority of cores appear stable to gravitational collapse when considering only thermal pressure; indeed, most of the cores which have masses above the thermal Jeans mass are already associated with at least one protostar. At higher cloud column densities, above 1-2x10^23^/cm2, most of the mass is found within dense cores, while at lower cloud column densities, below 1x10^23^/cm2, this fraction drops to 10% or lower. Overall, the fraction of dense cores associated with a protostar is quite small (<8%), but becomes larger for the densest and most centrally concentrated cores. NGC 2023/2024 and NGC 2068/2071 appear to be on the path to forming a significant number of stars in the future, while L1622 has little additional mass in dense cores to form many new stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/461/4022
- Title:
- JCMT Gould Belt Survey: Southern Orion A
- Short Name:
- J/MNRAS/461/4022
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the JCMT Gould Belt Survey's first look results of the southern extent of the Orion A Molecular Cloud ({delta}<=-5:31:27.5). Employing a two-step structure identification process, we construct individual catalogues for large-scale regions of significant emission labelled as islands and smaller-scale subregions called fragments using the 850{mu}m continuum maps obtained using SCUBA-2. We calculate object masses, sizes, column densities, and concentrations. We discuss fragmentation in terms of a Jeans instability analysis and highlight interesting structures as candidates for follow-up studies. Furthermore, we associate the detected emission with young stellar objects (YSOs) identified by Spitzer and Herschel. We find that although the population of active star-forming regions contains a wide variety of sizes and morphologies, there is a strong positive correlation between the concentration of an emission region and its calculated Jeans instability. There are, however, a number of highly unstable subregions in dense areas of the map that show no evidence of star formation. We find that only ~72 per cent of the YSOs defined as Class 0+I and flat-spectrum protostars coincide with dense 850{mu}m emission structures (column densities >3.7x10^21^cm^-2^). The remaining 28 per cent of these objects, which are expected to be embedded in dust and gas, may be misclassified. Finally, we suggest that there is an evolution in the velocity dispersion of YSOs such that sources which are more evolved are associated with higher velocities.
- ID:
- ivo://CDS.VizieR/J/AJ/121/974
- Title:
- JHK photometry in Cha I
- Short Name:
- J/AJ/121/974
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a near-infrared imaging survey covering ~1deg^2^ of the Chamaeleon I dark cloud. The survey is complete for K<15.0, H<16.0, and J<16.5, roughly 2 magnitudes more sensitive than previous large-scale surveys. We use the large number of background stars detected to derive an accurate near-infrared extinction law for the cloud and select new candidate members with near-infrared color excesses. We list ~100 candidates of the cloud with K>=2.0, based on their positions in the J-H, H-K color-color diagram. These new stars have low luminosities (K~12-16, H-K>~0.5-1.5) and may have masses close to or even below the hydrogen-burning limit.
- ID:
- ivo://CDS.VizieR/J/A+A/464/909
- Title:
- JHK photometry near IRAS 06145+1455
- Short Name:
- J/A+A/464/909
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our goal in this paper is to study stars and molecular gas in the direction of IRAS 06145+1455 (WB89-789). The kinematic distance of the associated molecular cloud is 11.9kpc. With a galactocentric distance of ~20.2kpc, this object is at the edge of the (molecular) disk of the Galaxy. We use near-IR (J, H, K), molecular line-, and dust continuum observations.
