- ID:
- ivo://CDS.VizieR/J/A+A/636/A67
- Title:
- ALMA maps of 6 sources of star forming regions
- Short Name:
- J/A+A/636/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As a building block for amino acids, formamide (NH_2_CHO) is an important molecule in astrobiology and astrochemistry, but its formation path in the interstellar medium is not understood well. We aim to find empirical evidence to support the chemical relationships of formamide to HNCO and H_2_CO. We examine high angular resolution (~0.2") Atacama Large Millimeter/submillimeter Array (ALMA) maps of six sources in three high-mass star-forming regions and compare the spatial extent, integrated emission peak position, and velocity structure of HNCO and H_2_CO line emission with that of NH_2_CHO by using moment maps. Through spectral modeling, we compare the abundances of these three species. In these sources, the emission peak separation and velocity dispersion of formamide emission is most often similar to HNCO emission, while the velocity structure is generally just as similar to H_2_CO and HNCO (within errors). From the spectral modeling, we see that the abundances between all three of our focus species are correlated, and the relationship between NH_2_CHO and HNCO reproduces the previously demonstrated abundance relationship. In this first interferometric study, which compares two potential parent species to NH_2_CHO, we find that all moment maps for HNCO are more similar to NH_2_CHO than H_2_CO in one of our six sources (G24 A1). For the other five sources, the relationship between NH_2_CHO, HNCO, and H_2_CO is unclear as the different moment maps for each source are not consistently more similar to one species as opposed to the other.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/256/30
- Title:
- ALMA 1.33mm images of 10 FU Orionis-type stars
- Short Name:
- J/ApJS/256/30
- Date:
- 03 Mar 2022
- Publisher:
- CDS
- Description:
- The FU Orionis-type objects (FUors) are low-mass pre-main-sequence stars undergoing a temporary but significant increase of mass accretion rate from the circumstellar disk onto the protostar. It is not yet clear what triggers the accretion bursts and whether the disks of FUors are in any way different from the disks of nonbursting young stellar objects. Motivated by this, we conducted a 1.3mm continuum survey of 10 FUors and FUor-like objects with ALMA, using both the 7m array and the 12m array in two different configurations to recover emission at the widest possible range of spatial scales. We detected all targeted sources and several nearby objects as well. To constrain the disk structure, we fit the data with models of increasing complexity from 2D Gaussian to radiative transfer, enabling comparison with other samples modeled in a similar way. The radiative transfer modeling gives disk masses that are significantly larger than what is obtained from the measured millimeter fluxes assuming optically thin emission, suggesting that the FUor disks are optically thick at this wavelength. In comparison with samples of regular class II and class I objects, the disks of FUors are typically a factor of 2.9-4.4 more massive and a factor of 1.5-4.7 smaller in size. A significant fraction of them (65%-70%) may be gravitationally unstable.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A139
- Title:
- ALMA mm observations of VLMS in Taurus
- Short Name:
- J/A+A/645/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of giant planets orbiting very low mass stars (VLMS) and the recent observed substructures in disks around VLMS is challenging planet formation models. Specifically, radial drift of dust particles is a catastrophic barrier in these disks, which prevents the formation of planetesimals and therefore planets. We aim to estimate if structures, such as cavities, rings, and gaps, are common in disks around VLMS and to test models of structure formation in these disks. We also aim to compare the radial extent of the gas and dust emission in disks around VLMS, which can give us insight about radial drift. We studied six disks around VLMS in the Taurus star-forming region using ALMA Band 7 (~340GHz) at a resolution of ~0.1". The targets were selected because of their high disk dust content in their stellar mass regime. Our observations resolve the disk dust continuum in all disks. In addition, we detect the ^12^CO (J=3-2) emission line in all targets and ^13^CO (J=3-2) in five of the six sources. The angular resolution allows the detection of dust substructures in three out of the six disks, which we studied by using UV-modeling. Central cavities are observed in the disks around stars MHO6 (M5.0) and CIDA1 (M4.5), while we have a tentative detection of a multi-ringed disk around J0433. We estimate that a planet mass of 0.1M_Jup_ or 0.4M_Saturn_ is required for a single planet to create the first gap in J0433. For the cavities of MHO6 and CIDA1, a Saturn-mass planet (0.3M_Jup_) is required. The other three disks with no observed structures are the most compact and faintest in our sample, with the radius enclosing 90% of the continuum emission varying between 13-21au. The emission of ^12^CO and ^13^CO is more extended than the dust continuum emission in all disks of our sample. When using the ^12^CO emission to determine the gas disk extension Rgas, the ratio of Rgas/Rdust in our sample varies from 2.3 to 6.0. One of the disks in our sample, CIDA7, has the largest Rgas/Rdust ratio observed so far, which is consistent with models of radial drift being very efficient around VLMS in the absence of substructures. Given our limited angular resolution, substructures were only directly detected in the most extended disks, which represent 50% of our sample, and there are hints of unresolved structured emission in one of the bright smooth sources. Our observations do not exclude giant planet formation on the substructures observed. A comparison of the size and luminosity of VLMS disks with their counterparts around higher mass stars shows that they follow a similar relation .
- ID:
- ivo://CDS.VizieR/J/A+A/603/A10
- Title:
- ALMA view of G351.77-0.54
- Short Name:
- J/A+A/603/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The fragmentation of high-mass gas clumps and the formation of the accompanying accretion disks lie at the heart of high-mass star formation research. We resolve the small-scale structure around the high-mass hot core G351.77-0.54 to investigate its disk and fragmentation properties. Using the Atacama Large Millimeter Array at 690GHz with baselines exceeding 1.5km, we study the dense gas, dust, and outflow emission at an unprecedented spatial resolution of 0.06" (130AU at 2.2kpc). Within the inner few 1000AU, G351.77 is fragmenting into at least four cores (brightness temperatures between 58 and 201K). The central structure around the main submm source #1 with a diameter of ~0.5" does not show additional fragmentation. While the CO(6-5) line wing emission shows an outflow lobe in the northwestern direction emanating from source #1, the dense gas tracer CH_3_CN shows a velocity gradient perpendicular to the outflow that is indicative of rotational motions. Absorption profile measurements against the submm source #2 indicate infall rates on the order of 10^-4^ to 10^-3^M_{sun}_/yr, which can be considered as an upper limit of the mean accretion rates. The position-velocity diagrams are consistent with a central rotating disk-like structure embedded in an infalling envelope, but they may also be influenced by the outflow. Using the CH_3_CN(37k-36k) k-ladder with excitation temperatures up to 1300K, we derive a gas temperature map for source #1 exhibiting temperatures often in excess of 1000K. Brightness temperatures of the submm continuum barely exceed 200K. This discrepancy between gas temperatures and submm dust brightness temperatures (in the optically thick limit) indicates that the dust may trace the disk mid-plane, whereas the gas could trace a hotter gaseous disk surface layer. We conduct a pixel-by-pixel Toomre gravitational stability analysis of the central rotating structure. The derived high Q values throughout the structure confirm that this central region appears stable against gravitational instability. Resolving for the first time a high-mass hot core at 0.06 resolution at submm wavelengths in the dense gas and dust emission allowed us to trace the fragmenting core and the gravitationally stable inner rotating disk-like structure. A temperature analysis reveals hot gas and comparably colder dust that may be attributed to different disk locations traced by dust emission and gas lines. The kinematics of the central structure #1 reveal contributions from a rotating disk, an infalling envelope, and potentially an outflow as well, whereas the spectral profile toward source #2 can be attributed to infall.
- ID:
- ivo://CDS.VizieR/J/MNRAS/511/4724
- Title:
- alpha Leo spectro-interferometric observation
- Short Name:
- J/MNRAS/511/4724
- Date:
- 15 Mar 2022 08:32:16
- Publisher:
- CDS
- Description:
- Differential Interferometry allows to obtain the differential visibility and phase, in addition to the spectrum. The differential phase contains important information about the structure and motion of stellar photosphere such as stellar spots and non-radial pulsations, and particularly the rotation. Thus, this interferometric observable strongly helps to constrain the stellar fundamental parameters of fast rotators. The spectroastrometry mainly uses the photocentre displacements, which is a first approximation of the differential phase, and is applicable only for unresolved or marginally objects. We study here the sensitivity of relevant stellar parameters to the simulated photocentres using the scirocco code: a semi-analytical algorithm dedicated to fast rotators, applied to two theoretical modelling stars based on Achernar and Regulus, in order to classify the importance of these parameters and their impact on the modelling. We compare our simulations with published VLTI/AMBER data. This work sets the limits of application of photocentre displacements to fast rotators, and under which conditions we can use the photocentres and/or the differential phase, through a pre-established physical criterion. To validate our theoretical study, we apply our method of analysis on observed data of the edge-on fast rotator Regulus. For unresolved targets, with a visibility V~1, the photocentre can constrain the main stellar fundamental parameters of fast rotators, whereas from marginally resolved objects (0.8<=V<1), mainly the rotation axis position angle (PA_rot_) can be directly deduced from the vectorial photocentre displacement, which is very important for young cluster studies.
- ID:
- ivo://CDS.VizieR/J/ApJS/248/18
- Title:
- 44 and 95GHz observations of class I methanol masers
- Short Name:
- J/ApJS/248/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a simultaneous 44 and 95GHz class I methanol maser survey toward 144 sources from the 95GHz class I methanol maser catalog. The observations were made with the three telescopes of the Korean very long baseline interferometry network operating in single-dish mode. The detection rates are 89% at 44GHz and 77% at 95GHz. There are 106 new discoveries at 44GHz. Comparing the previous 95GHz detections with new observations of the same transitions made using the Purple Mountain Observatory 13.7m radio telescope shows no clear evidence of variability on a timescale of six years. Emission from the 44 and 95GHz transitions shows strong correlations in peak velocity, peak flux density, and integrated flux density, indicating that they are likely cospatial. We found that the peak flux density ratio S_pk,95_/S_pk,44_ decreases as the 44GHz peak flux density increases. We found that some class I methanol masers in our sample might be associated with infrared dark clouds, while others are associated with HII regions, indicating that some sources occur at an early stage of high-mass star formation, while others are located toward more evolved sources.
- ID:
- ivo://CDS.VizieR/J/A+A/476/L17
- Title:
- 86 and 43GHz observations of NRAO 150
- Short Name:
- J/A+A/476/L17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NRAO 150, a compact and bright radio to mm source showing core/jet structure, has been recently identified as a quasar at redshift z=1.52 through a near-IR spectral observation. The aim is to study the jet kinematics on the smallest accessible scales and to compute the first estimates of its basic physical properties. We have analysed the ultra-high-resolution images from a new monitoring program at 86GHz and 43GHz with the Global mm VLBI Array and the VLBA, respectively. An additional archival calibration VLBA data set, covering the period from 1997 to 2007, has been used. Our data show an extreme projected counter-clockwise jet position angle swing at an angular rate of up to ~11{deg}/yr within the inner ~3pc of the jet, which is associated with a non-ballistic superluminal motion of the jet within this region.
- ID:
- ivo://CDS.VizieR/J/A+A/490/213
- Title:
- 1.4 and 3.4mm interferometry of W3 IRS5
- Short Name:
- J/A+A/490/213
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of PdBI 1.4 and 3.4mm interferometric observations of the high-mass star-forming region W3 IRS5 in the AB configurations. From the continuum maps we identified five individual sources with counterparts in the NIR, MIR or radio (Q-band), except for one source that is a new identification. Three of the sources are within the inner 2100AU, where the protostellar number density exceeds 10^6^ protostars pc^-3^ assuming spherical symmetry. Lower limits for the circumstellar masses of the sources range from ~0.3 to ~40M_{sun}_ although they were strongly affected by the spatial filtering of the interferometer. We mapped the SiO(2-1), SiO(5-4), SO2(22-22), and SO2(8-9) molecular transitions. We identify five molecular outflows in SiO, two of them nearly in the line of sight direction. The SO2 velocity structure indicates a rotating, bound system, and we find tentative signatures of converging flows as predicted by the gravoturbulent star formation and converging flow theories. The obtained data strongly indicate that the clustered environment has a major influence on the formation of high-mass stars; however, our data do not clearly allow us to distinguish whether the ongoing star-forming process follows a monolithic collapse or a competitive accretion mechanism.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/4274
- Title:
- Angular sizes of AGN cores at 2-43GHz
- Short Name:
- J/MNRAS/452/4274
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured the angular sizes of radio cores of active galactic nuclei (AGN) and analyzed their sky distributions and frequency dependencies to study synchrotron opacity in AGN jets and the strength of angular broadening in the interstellar medium. We have used archival very long baseline interferometry (VLBI) data of more than 3000 compact extragalactic radio sources observed at frequencies, {nu}, from 2 to 43GHz to measure the observed angular size of VLBI cores. We have found a significant increase in the angular sizes of the extragalactic sources seen through the Galactic plane (|b|<10{deg}) at 2, 5 and 8GHz, about 1/3 of which show significant scattering. These sources are mainly detected in directions to the Galactic bar, the Cygnus region, and a region with galactic longitudes 220{deg}<l<260{deg} (the Fitzgerald window). The strength of interstellar scattering of the AGNs is found to correlate with the Galactic H{alpha} intensity, free-electron density, and Galactic rotation measure. The dependence of scattering strengths on source redshift is insignificant, suggesting that the dominant scattering screens are located in our Galaxy. The observed angular size of Sgr-A* is found to be the largest among thousands of AGN observed over the sky; we discuss possible reasons of this strange result. Excluding extragalactic radio sources with significant scattering, we find that angular size of opaque cores in AGN scales typically as {nu}^-1^ confirming predictions of a conical synchrotron jet model with equipartition.
- ID:
- ivo://CDS.VizieR/J/A+A/555/A24
- Title:
- Aperture-synthesis imaging of Antares
- Short Name:
- J/A+A/555/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present aperture-synthesis imaging of the red supergiant Antares (alpha Sco) in the CO first overtone lines. Our goal is to probe the structure and dynamics of the outer atmosphere.
