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11. ALMA 1.33mm images of 10 FU Orionis-type stars
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.
12. ALMA mm observations of VLMS in Taurus
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 .
13. ALMA view of G351.77-0.54
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.
14. 44 and 95GHz observations of class I methanol masers
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.
15. Angular sizes of AGN cores at 2-43GHz
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.
16. A search for new companions with CHARA
ID:
ivo://CDS.VizieR/J/ApJ/745/24
Title:
A search for new companions with CHARA
Short Name:
J/ApJ/745/24
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a comprehensive search for new companions to nearby solar-type stars using the separated fringe packet (SFP) technique at the Center for High Angular Resolution Astronomy (CHARA) Array. Our search included 636 observations of 186 stars, searching for companions with separations of approximately 8-80 mas and moderate brightness ratios ({Delta}K<~1.5). This survey was undertaken to support a comprehensive assessment of companions to solar-type stars within 25 pc. We detected separated fringe companions to two stars (HD 3196 and 79096) and found faint companion signatures to two more stars (HD 98231 and 137763). All of these companions are previously known by spectroscopic methods, and three of them have speckle interferometric observations as well. The faint companion seen to HD 98231 represents the first visual detection of this spectroscopic companion. Our null detection for new companions implies that the presumed gap between spectroscopic and visual techniques has largely been filled for nearby solar-type stars, thanks to systematic radial-velocity observations over multiple decades and a thorough coverage using visual techniques, especially speckle interferometric observations. We also generate simulated fringe packets to derive detection limits for SFP binaries using the CHARA Array.
17. Astrometric classification of 647 VLBI sources
ID:
ivo://CDS.VizieR/J/A+A/618/A80
Title:
Astrometric classification of 647 VLBI sources
Short Name:
J/A+A/618/A80
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the result of our Allan standard deviation based classification according to their astrometric stability. The classification is divided into three categories (stable sources, intermediate sources, unstable sources). Stability of sources is qualified by the astrometric behavior of the source. This determines in which category the source falls into. Then, stability of the source is also quantified by a stability index (two are proposed in the table). Those indexes enable to order sources in each category of the classification.
18. Astrometry and photometry of UCAC4 double stars
ID:
ivo://CDS.VizieR/J/AJ/146/76
Title:
Astrometry and photometry of UCAC4 double stars
Short Name:
J/AJ/146/76
Date:
21 Oct 2021
Publisher:
CDS
Description:
The newly completed Fourth USNO CCD Astrographic Catalog (UCAC4) has proven to be a rich source of double star astrometry and photometry. Following initial comparisons of UCAC4 results against those obtained by speckle interferometry, the UCAC4 catalog was matched against known double stars in the Washington Double Star Catalog in order to provide additional differential astrometry and photometry for these pairs. Matches to 58131 pairs yielded 61895 astrometric and 68935 photometric measurements. Finally, a search for possible new common proper motion (CPM) pairs was made using new UCAC4 proper motion data; this resulted in 4755 new potential CPM doubles (and an additional 27718 astrometric and photometric measures from UCAC and other sources).
19. ATCA observations of 202 compact radio sources
ID:
ivo://CDS.VizieR/J/PASJ/55/351
Title:
ATCA observations of 202 compact radio sources
Short Name:
J/PASJ/55/351
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Australia Telescope Compact Array (ATCA) has been used in support of the VLBI Space Observatory Programme (VSOP) space VLBI mission, to monitor the total and polarised flux densities of 202 objects that make up 83% of the VSOP all-sky Survey of compact extragalactic radio sources south of DE=+10{deg}. The primary goal of the ATCA observations is to provide information on the total and polarised emission from the compact components in these sources, for correlation with parameters obtained from VSOP imaging observations. These data represent the first high resolution, long timescale flux density monitoring observations of a large number of southern compact radio sources. In the future, comparison of the ATCA and VSOP data will be used to investigate relativistic beaming models and identify similarities or differences between the major classes of extragalactic radio sources. As an illustration of the scientific value of the ATCA data we undertake a comparison of the properties of the gamma-ray loud and gamma-ray quiet AGN in the southern component of the VSOP Survey sample, finding that in a flat-spectrum sub-sample the gamma-ray loud AGN are more variable than the gamma-ray quiet AGN.
20. AT20G high-angular-resolution catalogue
ID:
ivo://CDS.VizieR/J/MNRAS/434/956
Title:
AT20G high-angular-resolution catalogue
Short Name:
J/MNRAS/434/956
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the high-angular-resolution catalogue for the Australia Telescope 20GHz (AT20G, Cat. J/MNRAS/402/2403) survey, using the high-angular-resolution 6-km antenna data at the baselines of ~4500m of the Australia Telescope Compact Array. We have used the data to produce the visibility catalogue that separates the compact active galactic nuclei (AGNs) from the extended radio sources at the 0.15arcsec angular scale, corresponding to the linear size scale of 1kpc at redshifts higher than 0.7. We find the radio population at 20GHz to be dominated by compact AGNs constituting 77% of the total sources in the AT20G. We introduce the visibility-spectra diagnostic plot, produced using the AT20G cross-matches with lower frequency radio surveys at 1GHz [the NRAO VLA Sky Survey (NVSS, Cat. VIII/65) and the Sydney University Molonglo Sky Survey (SUMSS, Cat. VIII/81)], that separates the 20GHz population into distinct sub-populations of the compact AGNs, the compact steep-spectrum (CSS) sources, the extended AGN-powered sources and extended flat-spectrum sources. The extended flat-spectrum sources include a local thermal emitting population of high-latitude planetary nebulae and also gravitational lens and binary black hole candidates among the AGNs. We find a smooth transition in properties between the CSS sources and the AGN populations. The visibility catalogue, together with the main AT20G survey, provides an estimate of angular size scales for sources in the AT20G and an estimate of the flux arising from central cores of extended radio sources. The identification of the compact AGNs in the AT20G survey provides high-quality calibrators for high-frequency radio telescope arrays and very large baseline interferometry observations.

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