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- ID:
- ivo://CDS.VizieR/J/A+A/565/A127
- Title:
- SiO masers v=1,2,3 for 4 AGB
- Short Name:
- J/A+A/565/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The v=1 and 2 J=1-0 (43GHz), and v=1 J=2-1 (86GHz) SiO masers are intense in AGB stars and have been mapped using VLBI showing ring-like distributions. Those of the v=1, 2 J=1-0 masers are similar, but the spots are rarely coincident, while the v=1 J=2-1 maser arises from a well separated region farther out. These relative locations can be explained by models including the overlap of two IR lines of SiO and H_2_O. The v=3 J=1-0 line is not directly affected by any line overlap and its spot structure and position, relative to the other lines, will be a good test to the standard pumping models The aims is to gain insight into the properties of the different SiO masers and the general theoretical considerations that can help to understand them. We present single-dish and VLBI simultaneous observations of the v=1, 2, 3 J=1-0 maser transitions of ^28^SiO in several AGB stars. The results are compared with the predictions of radiative models of SiO masers both including and not including the effect of IR line overlap. The spatial distribution of the SiO maser emission in the v=3 J=1-0 transition from AGB stars is systematically composed of a series of spots occupying a ring-like structure (as often found in SiO masers). The overall ring structure is extremely similar to that found in the other 43 GHz transitions, and very different from the structure of the v=1 J=2-1 maser. The positions of the individual spots of the different 43 GHz lines are however very rarely coincident, being in general separated by about 0.3AU (between 1 and 5mas). These results are very difficult to reconcile with standard pumping models, which predict the masers of rotational transitions within a given vibrational state to require very similar excitation conditions (since the levels are placed practically at the same energy from the ground), while the transitions of different vibrational states (which are separated by an energy of 1800K) should appear in different positions. However, models including line overlap tend to predict v=1, 2, 3 J=1-0 population inversion to occur under very similar conditions, while the requirements for v=1 J=2-1 appears clearly different, and are compatible with the observational results.
1373. SIRTF First-Look Survey
- ID:
- ivo://CDS.VizieR/J/AJ/125/2411
- Title:
- SIRTF First-Look Survey
- Short Name:
- J/AJ/125/2411
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The First-Look Survey (FLS) of the Space Infrared Telescope Facility (SIRTF) will cover about 5deg^2^ centered on J2000.0 (17:18+59:30) in order to characterize the extragalactic infrared sky 2 orders of magnitude deeper than the IRAS survey. We expect that most of the FLS far-infrared ({lambda} = 160, 70, and 24 {mu}m) sources will be star-forming galaxies obeying the very tight far-infrared/radio correlation and will be continuum radio sources with flux densities S>~100{mu}Jy at {nu}=1.4GHz. Conversely, radio sources stronger than 100{mu}Jy are usually powered by star-forming galaxies, plus some active galactic nuclei, and most should be detectable by the SIRTF FLS. Thus, a sensitive radio survey can be used to select and identify most of the SIRTF FLS source population before launch. We used the B configuration of the VLA to make an image of the FLS area at {nu}=1.4GHz with {sigma}=~23{mu}Jy/beam rms fluctuations, {theta}=5'' resolution, and {sigma}_{alpha}_=~{sigma}_{delta}_=~0.5'' rms uncertainties in right ascension and declination. The resulting radio image and catalog of 3565 radio components with peak flux densities Sp>=5{sigma}=115{mu}Jy/beam have been released via the Web to expedite follow-up optical identification and spectroscopy.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A76
- Title:
- Six infrared dark clouds multi-wavelength obs.
- Short Name:
- J/A+A/598/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet they play a crucial role in breeding newly-formed stars. In order to further understand the dynamics, chemistry, and evolution of IRDCs, we carried out multi-wavelength observations towards a small sample. We performed new observations with the IRAM 30m and CSO 10.4m telescopes, with tracers HCO^+^, HCN, N_2_H^+^, C^18^O, DCO^+^, SiO, and DCN towards six IRDCs G031.97+00.07, G033.69-00.01, G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05.
- ID:
- ivo://CDS.VizieR/J/AJ/136/580
- Title:
- Sixth VLBA calibrator survey: VCS6
- Short Name:
- J/AJ/136/580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the sixth part of the Very Long Baseline Array (VLBA) Calibrator Survey. It contains the positions and maps of 264 sources of which 169 were not previously observed with very long baseline interferometry. This survey, based on two 24h VLBA observing sessions, was focused on (1) improving positions of 95 sources from previous VLBA Calibrator Surveys that were observed either with very large a priori position errors or were observed not long enough to get reliable positions and (2) observing remaining new flat-spectrum sources with predicted correlated flux density in the range 100-200mJy that were not observed in previous surveys. Source positions were derived from astrometric analysis of group delays determined at the 2.3 and 8.6GHz frequency bands using the Calc/Solve software package. The VCS6 catalog of source positions, plots of correlated flux density versus projected baseline length, contour plots and fits files of naturally weighted CLEAN images, as well as calibrated visibility function files, are available on the Web at http://vlbi.gsfc.nasa.gov/vcs6.
- ID:
- ivo://CDS.VizieR/J/ApJ/766/37
- Title:
- Sizes of MRC radio galaxies and QSOs
- Short Name:
- J/ApJ/766/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the currently popular orientation-based unified scheme, a radio galaxy appears as a quasar when its principal radio-axis happens to be oriented within a certain cone opening angle around the observer's line of sight. Due to geometrical projection, the observed sizes of quasars should therefore appear smaller than those of radio galaxies. We show that this simple, unambiguous prediction of the unified scheme is not borne out by the actually observed angular sizes of radio galaxies and quasars. Except in the original 3CR sample, based on which the unified scheme was proposed, in other much larger samples no statistically significant difference is apparent in the size distributions of radio galaxies and quasars. The population of low-excitation radio galaxies with apparently no hidden quasars inside, which might explain the observed excess number of radio galaxies at low redshifts, cannot account for the absence of any foreshortening of the sizes of quasars at large redshifts. On the other hand, from infrared and X-ray studies, there is evidence of a hidden quasar within a dusty torus in many radio galaxies, at z>0.5. It is difficult to reconcile this with the absence of foreshortening of quasar sizes at even these redshifts, and perhaps one has to allow that the major radio axis may not have anything to do with the optical axis of the torus. Otherwise, to resolve the dichotomy of radio galaxies and quasars, a scheme quite different from the present might be required.
- ID:
- ivo://CDS.VizieR/J/ApJS/74/181
- Title:
- Small-diameter radiosources catalogue
- Short Name:
- J/ApJS/74/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A survey of the Galactic plane in the longitude range -20deg=<l<=120deg for Galactic latitudes |b|=<0.8deg has been carried out at 1400MHz using the VLA in the B configuration. We present here a catalog of the 1992 discrete sources detected in this survey which is ~75% complete to a limiting peak flux density of 25mJy for sources smaller than ~20" in diameter, although sources as faint as 8mJy and as large as 90" are also included. The catalog includes for each entry a position accurate to ~<3", peak and integrated flux densities, source extent, and information on counterparts both from earlier radio surveys of the plane (for which a comprehensive bibliography is included) and from the IRAS point source catalog. An extensive analysis of the integrity and completeness of the survey is presented here: in separate publications, we discuss the source content of the survey as derived from statistical analysis of the spatial distribution of the sources and from radio, optical and infrared follow up observations .
- ID:
- ivo://CDS.VizieR/J/A+A/561/A55
- Title:
- Small-diameter sources in Sino-German 6cm survey
- Short Name:
- J/A+A/561/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out the Sino-German 6cm polarisation survey of the Galactic plane at 6cm in total and polarised intensity using the Urumqi 25-m telescope of Xinjiang (formerly Urumqi) Astronomical Observatory, Chinese Academy of Sciences. The angular resolution is 9.5-arcmin. The surveyed area covers 10{deg} to 230{deg} in Galactic longitude and absolute Galactic latitudes of up to 5{deg}. The measured rms-noise is about 6.1 mJy/beam area for total intensities and 3.05mJy/beam area for polarised intensities. The survey maps are accessible from http://zmtt.bao.ac.cn/6cm/ .
- 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.
- 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.