- ID:
- ivo://CDS.VizieR/J/A+A/587/A47
- Title:
- SMA 1.3mm image of OMC 1 North
- Short Name:
- J/A+A/587/A47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The filamentary structure of molecular clouds may set important constraints on the mass distribution of stars forming within them. It is therefore important to understand which physical mechanism dominates filamentary cloud fragmentation and core formation. Orion A is the nearest giant molecular cloud, and its so-called S-shaped filament is a very active star-forming region that is a good target for such a study. We have recently reported on the collapse and fragmentation properties of the northernmost part of this structure, located ~2.4pc north of Orion KL - Orion Molecular Cloud (OMC) 3. As part of our project to study the S-shaped filament, we analyze the fragmentation properties of the northern OMC 1 filament (located <~0.3pc north of Orion KL). This filament is a dense structure previously identified by JCMT/SCUBA submillimeter continuum and VLA NH_3_ observations and was shown to have fragmented into clumps. Our aim is to search for cores and young protostars embedded within OMC 1n and to study how the filament is fragmenting to form them. We observed OMC 1North (hereafter OMC 1n) with the Submillimeter Array (SMA) at 1.3mm and report on our analysis of the continuum data.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/821/125
- Title:
- SMA obs. of giant molecular clouds in NGC 300
- Short Name:
- J/ApJ/821/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first high angular resolution study of giant molecular clouds (GMCs) in the nearby spiral galaxy NGC 300, based on observations from the Submillimeter Array (SMA). We target eleven 500pc sized regions of active star formation within the galaxy in the ^12^CO(J=2-1) line at 40pc spatial and 1km/s spectral resolution and identify 45 individual GMCs. We characterize the physical properties of these GMCs, and find that they are similar to GMCs in the disks of the Milky Way and other nearby spiral galaxies. For example, the GMC mass spectrum in our sample has a slope of 1.80+/-0.07. Twelve clouds are spatially resolved by our observations, of which ten have virial mass estimates that agree to within a factor of two with mass estimates derived directly from ^12^CO integrated intensity, suggesting that the majority of these GMCs are bound. The resolved clouds show consistency with Larson's fundamental relations between size, linewidth, and mass observed in the Milky Way. We find that the linewidth scales with the size as {Delta}V{propto}R^0.52+/-0.20^, and the median surface density in the subsample is 54M_{sun}_/pc^2^. We detect ^13^CO in four GMCs and find a mean ^12^CO/^13^CO flux ratio of 6.2. Our interferometric observations recover between 30% and 100% of the integrated intensity from the APEX single dish ^12^CO observations of Faesi et al. (2014, J/ApJ/789/81), suggesting the presence of low-mass GMCs and/or diffuse gas below our sensitivity limit. The fraction of APEX emission recovered increases with the SMA total intensity, as well as with the star formation rate.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A34
- Title:
- SOFIA Horsehead nebula region datacube
- Short Name:
- J/A+A/595/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new multi-pixel high resolution (R>~10^7^) spectrometer for the Stratospheric Observatory for far-infrared astronomy (SOFIA). The receiver uses 2x7-pixel subarrays in orthogonal polarization, each in an hexagonal array around a central pixel. We present the first results for this new instrument after commissioning campaigns in May and December 2015 and after science observations performed in May 2016. The receiver is designed to ultimately cover the full 1.8-2.5THz frequency range but in its first implementation, the observing range was limited to observations of the [CII] line at 1.9THz in 2015 and extended to 1.83-2.07THz in 2016. The instrument sensitivities are state-of-the-art and the first scientific observations performed shortly after the commissioning confirm that the time electronic efficiency for large scale imaging is improved by more than an order of magnitude as compared to single pixel receivers. An example of large scale mapping around the Horsehead Nebula is presented here illustrating this improvement. The array has been added to SOFIA's instrument suite already for ongoing observing cycle 4.
- ID:
- ivo://CDS.VizieR/J/A+A/399/995
- Title:
- SOFI and ISOCAM observations of Cha II
- Short Name:
- J/A+A/399/995
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An infrared study including ISOCAM images at 6.75 and 14.3{mu}m of a large portion (28'x26') of the Chamaeleon II dark cloud and sub-arcsec resolution JHKs images of the central (4.9'x4.9') area is presented. Combining the ISOCAM observations with J and Ks photometry obtained with DENIS, we have found 12 young stars, of which 8 are previously identified sources.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A113
- Title:
- Southern outer Galaxy star forming regions
- Short Name:
- J/A+A/645/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star formation in the outer Galaxy is thought to be different from that in the inner Galaxy, as it is subject to different environmental parameters such as metallicity, interstellar radiation field, or mass surface density, which all change with galactocentric radius. Extending our star formation knowledge, from the inner to the outer Galaxy, helps us to understand the influences of the change of the environment on star formation throughout the Milky Way. We aim to obtain a more detailed view on the structure of the outer Galaxy, determining physical properties for a large number of star forming clumps and understanding star formation outside the solar circle. As one of the largest expanding Galactic super-shellsis present in the observed region, a unique opportunity is taken here to investigate the influence of such an expanding structure on star formation as well. We used pointed ^12^CO(2-1) observations conducted with the APEX telescope to determine the velocity components towards 830 dust clumps identified from 250um Herschel/Hi-GAL SPIRE emission maps in the outer Galaxy between 225<l<260. We determined kinematic distances from the velocity components, in order to analyze the structure of the outer Galaxy and to estimate physical properties such as dust temperatures, bolometric luminosities, clump masses, and H2 column densities for 611 clumps. Forthis, we determined the dust spectral energy density distributions from archival mid-infrared to sub- millimeter (submm) emission maps. We find the identified CO clouds to be strongly correlated with the highest column density parts of the Hiemission distribution, spanning a web of bridges, spurs, and blobs of star forming regions between the larger complexes, unveiling the complex three-dimensional structure of the outer Galaxy in unprecedented detail. Using the physical properties of the clumps, we find an upper limit of 6% (40 sources) capable of forming high-mass stars. This is supported by the fact that only two methanol Class II masers,or 34 known or candidate HII regions, are found in the whole survey area, indicating an even lower fraction that are able to form high-mass stars in the outer Galaxy. We fail to find any correlation of the physical parameters of the identified (potential) star forming regions with the expanding supershell, indicating that although the shell organizes the interstellar material into clumps, the properties of the latter are unaffected. Using the APEX telescope in combination with publicly available Hi-GAL, MSX, and Wise continuum emission maps, we were able to investigate the structure and properties of a region of the Milky Way in unprecedented detail.
- ID:
- ivo://CDS.VizieR/J/ApJ/787/107
- Title:
- Spatial structure of young stellar clusters. I.
- Short Name:
- J/ApJ/787/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The clusters of young stars in massive star-forming regions show a wide range of sizes, morphologies, and numbers of stars. Their highly subclustered structures are revealed by the MYStIX project's sample of 31754 young stars in nearby sites of star formation (regions at distances <3.6kpc that contain at least one O-type star.) In 17 of the regions surveyed by MYStIX, we identify subclusters of young stars using finite mixture models --collections of isothermal ellipsoids that model individual subclusters. Maximum likelihood estimation is used to estimate the model parameters, and the Akaike Information Criterion is used to determine the number of subclusters. This procedure often successfully finds famous subclusters, such as the BN/KL complex behind the Orion Nebula Cluster and the KW-object complex in M17. A catalog of 142 subclusters is presented, with 1-20 subclusters per region. The subcluster core radius distribution for this sample is peaked at 0.17pc with a standard deviation of 0.43dex, and subcluster core radius is negatively correlated with gas/dust absorption of the stars --a possible age effect. Based on the morphological arrangements of subclusters, we identify four classes of spatial structure: long chains of subclusters, clumpy structures, isolated clusters with a core-halo structure, and isolated clusters well fit by a single isothermal ellipsoid.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A37
- Title:
- Spectral cube toward NGC 6334 I and I(N)
- Short Name:
- J/A+A/593/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HF molecule has been proposed as a sensitive tracer of diffuse interstellar gas, while at higher densities its abundance could be influenced heavily by freeze-out onto dust grains. We investigate the spatial distribution of a collection of absorbing gas clouds, some associated with the dense, massive star-forming core NGC 6334 I, and others with diffuse foreground clouds elsewhere along the line of sight. For the former category, we aim to study the dynamical properties of the clouds in order to assess their potential to feed the accreting protostellar cores. We use far-infrared spectral imaging from the Herschel SPIRE iFTS to construct a map of HF absorption at 243um in a 6'x3.5' region surrounding NGC 6334 I and I(N).
- ID:
- ivo://CDS.VizieR/J/ApJS/232/3
- Title:
- Spectral line surveys of 30 regions
- Short Name:
- J/ApJS/232/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral line surveys are an indispensable tool for exploring the physical and chemical evolution of astrophysical environments due to the vast amount of data that can be obtained in a relatively short amount of time. We present deep, broadband spectral line surveys of 30 interstellar clouds using two broadband {lambda}=1.3mm receivers at the Caltech Submillimeter Observatory. This information can be used to probe the influence of physical environment on molecular complexity. We observed a wide variety of sources to examine the relative abundances of organic molecules as they relate to the physical properties of the source (i.e., temperature, density, dynamics, etc.). The spectra are highly sensitive, with noise levels <=25mK at a velocity resolution of ~0.35km/s. In the initial analysis presented here, column densities and rotational temperatures have been determined for the molecular species that contribute significantly to the spectral line density in this wavelength regime. We present these results and discuss their implications for complex molecule formation in the interstellar medium.
- ID:
- ivo://CDS.VizieR/J/A+A/547/A85
- Title:
- Spectra of 7 H{alpha} emission line stars in MBM 18
- Short Name:
- J/A+A/547/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate star formation in translucent, high-latitude clouds. Our aim is to understand the star-formation history and rate in the solar neighbourhood. We used spectroscopic observations of newly found candidate H{alpha} emission-line stars to establish their pre-main-sequence nature. The environment was studied through molecular line observations of the cloud (MBM 18/LDN 1569) in which the stars are presumably embedded.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/1964
- Title:
- Spectra of three nearby star-forming regions
- Short Name:
- J/ApJ/703/1964
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze samples of Spitzer Infrared Spectrograph spectra of T Tauri stars in the Ophiuchus, Taurus, and Chamaeleon I star-forming regions, whose median ages lie in the <1-2Myr range. The median mid-infrared spectra of objects in these three regions are similar in shape, suggesting, on average, similar disk structures. When normalized to the same stellar luminosity, the medians follow each other closely, implying comparable mid-infrared excess emission from the circumstellar disks. We use the spectral index between 13 and 31um and the equivalent width of the 10um silicate emission feature to identify objects whose disk configuration departs from that of a continuous, optically thick accretion disk. Based on their medians and fraction of evolved disks, T Tauri stars in Taurus and Chamaeleon I are very alike.
