- ID:
- ivo://CDS.VizieR/J/A+A/636/A116
- Title:
- VLTI/PIONIER images of 15 Herbig Ae/Be stars
- Short Name:
- J/A+A/636/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The innermost astronomical unit (au) in protoplanetary disks is a key region for stellar and planet formation, as exoplanet searches have shown a large occurrence of close-in planets, located within the first au around their host star. We aim to reveal the morphology of the disk inner rim using near-infrared interferometric observations with milli-arcsecond resolution provided by near-infrared multi-telescope interferometry. Methods: We provide model-independent reconstructed images of 15 objects selected from the Herbig AeBe survey carried out with VLTI/PIONIER, using the semi-parametric approach for image reconstruction of chromatic objects (SPARCO). We propose a set of methods to reconstruct and analyze the images in a consistent way. 40% of the systems (6/15) are found to be centro-symmetric at the angular resolution of the observations. For the rest of the objects, we find evidence for asymmetric emission due to moderate-to-strong inclination of a disk-like structure for ~30% of the objects (5/15), and non-centro-symmetric morphology due to an non-axisymmetric and possible variable environment (4/15, ~27%). Among the systems with disk-like structure, 20% (3/15) show a resolved dust-free cavity. Finally, we do not detect extended emission beyond the inner rim. The image reconstruction process is a powerful tool to reveal complex disk inner rim morphologies which is complementary to the fit of geometrical models. At the angular resolution reached by near-infrared interferometric observations most of the images are compatible with a centrally peaked emission (no cavity). For the most resolved targets, image reconstruction reveals morphologies that cannot be reproduced by generic parametric models (e.g., perturbed inner rims, complex brightness distributions). Moreover, the non-axisymmetric disks show that the spatial resolution probed by optical interferometers makes the observations of the near-infrared emission (inside a few au) sensitive to temporal evolution with a time-scale down to few weeks. The evidence of non-axisymmetric emission that cannot be explained by simple inclination and radiative transfer effects requires for alternative explanations such as a warping of the inner disks. Interferometric observations can therefore be used to follow the evolution of the asymmetry of those disks at an au or sub-au scale.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/898/L38
- Title:
- VLT/SPHERE Y-band images of MWC 758 at two epochs
- Short Name:
- J/ApJ/898/L38
- Date:
- 21 Mar 2022 09:24:26
- Publisher:
- CDS
- Description:
- More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses-companion-disk interaction and gravitational instability (GI)-predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ~5yr using the SPHERE instrument on the Very Large Telescope (VLT), we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint "missing planet" driving the disk arms. The average spiral pattern speed is 0.22+/-0.03/yr, pointing to a driver at 172_-14_^+18^ au around a 1.9M_{sun}_ central star if it is on a circular orbit. In addition, we witness time-varying shadowing effects on a global scale that are likely originating from an inner disk.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/31
- Title:
- VMC survey. XXIX. Star formation in the SMC
- Short Name:
- J/ApJ/858/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we report a clustering analysis of upper main-sequence stars in the Small Magellanic Cloud, using data from the VMC survey (the VISTA near-infrared YJKs survey of the Magellanic system). Young stellar structures are identified as surface overdensities on a range of significance levels. They are found to be organized in a hierarchical pattern, such that larger structures at lower significance levels contain smaller ones at higher significance levels. They have very irregular morphologies, with a perimeter-area dimension of 1.44+/-0.02 for their projected boundaries. They have a power-law mass-size relation, power-law size/mass distributions, and a log-normal surface density distribution. We derive a projected fractal dimension of 1.48+/-0.03 from the mass-size relation, or of 1.4+/-0.1 from the size distribution, reflecting significant lumpiness of the young stellar structures. These properties are remarkably similar to those of a turbulent interstellar medium, supporting a scenario of hierarchical star formation regulated by supersonic turbulence.
- ID:
- ivo://CDS.VizieR/J/ApJ/778/116
- Title:
- V1647 Ori long-term optical & NIR observations
- Short Name:
- J/ApJ/778/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed study of McNeil's nebula (V1647 Ori) in its ongoing outburst phase starting from 2008 September to 2013 March. Our 124 nights of photometric observations were carried out in optical V, R, I, and near-infrared J, H, K bands, and 59 nights of medium-resolution spectroscopic observations were done in the 5200-9000{AA} wavelength range. All observations were carried out with the 2m Himalayan Chandra Telescope and 2m IUCAA Girawali Telescope. Our observations show that over the past four and a half years, V1647 Ori and region C near the Herbig-Haro object HH 22A have been undergoing a slow dimming at a rate of ~0.04mag/yr and ~0.05mag/yr, respectively, in R band, which is six times slower than the rate during a similar stage of V1647 Ori in the 2003 outburst. We detected change in flux distribution over the reflection nebula, implying changes in circumstellar matter distribution between the 2003 and 2008 outbursts. Apart from steady wind of velocity ~350km/s, we detected two episodic magnetic reconnection driven winds. Forbidden [OI]{lambda}6300 and [FeII]{lambda}7155 lines were also detected, implying shock regions probably from jets. We tried to explain the outburst timescales of V1647 Ori using the standard models of the FUors kind of outburst and found that pure thermal instability models like Bell and Lin cannot explain the variations in timescales. In the framework of various instability models we conclude that one possible reason for the sudden ending of the 2003 outburst in 2005 November was a low-density region or gap in the inner region (~1AU) of the disk.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/138
- Title:
- VRIJHK photometry of IRAS 09149-4743 region
- Short Name:
- J/ApJ/751/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The RCW41 star-forming region is embedded within the Vela Molecular Ridge, hosting a massive stellar cluster surrounded by a conspicuous HII region. Understanding the role of interstellar magnetic fields and studying the newborn stellar population is crucial to building a consistent picture of the physical processes acting on this kind of environment. We carried out a detailed study of the interstellar polarization toward RCW41 with data from an optical and near-infrared polarimetric survey. Additionally, deep near-infrared images from the 3.5 meter New Technology Telescope were used to study the photometric properties of the embedded young stellar cluster, revealing several YSO candidates. By using a set of pre-main-sequence isochrones, a mean cluster age in the range 2.5-5.0 million years was determined, and evidence of sequential star formation was revealed. An abrupt decrease in R-band polarization degree was noticed toward the central ionized area, probably due to low grain alignment efficiency caused by the turbulent environment and/or the weak intensity of magnetic fields. The distortion of magnetic field lines exhibits dual behavior, with the mean orientation outside the area approximately following the borders of the star-forming region and directed radially toward the cluster inside the ionized area, in agreement with simulations of expanding H II regions. The spectral dependence of polarization allowed a meaningful determination of the total-to-selective extinction ratio by fittings of the Serkowski relation. Furthermore, a large rotation of polarization angle as a function of wavelength was detected toward several embedded stars.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A139
- Title:
- Water lines spectra of 4 protostellar objects
- Short Name:
- J/A+A/587/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Herschel/HIFI observations of 14 water lines in a small sample of galactic massive protostellar objects: NGC6334I(N), DR21(OH), IRAS16272-4837, and IRAS05358+3543. Using water as a tracer of the structure and kinematics, we aim to individually study each of these objects, to estimate the amount of water around them, but to also shed light on the high-mass star formation process. We analyze the gas dynamics from the line profiles using Herschel-HIFI observations acquired as part of the WISH key-project of 14 far-IR water lines (water, H_2_^17^O, H_2_^18^O), and several other species. Then through modeling of the observations using the RATRAN radiative transfer code, we estimate outflow, infall, turbulent velocities, molecular abundances, and investigate any correlation with the evolutionary status of each source. The four sources (plus previously studied W43-MM1) have been ordered in terms of evolution based on their SED: NGC64334I(N)-W43-MM1-DR21(OH)-IRAS16272-4837-IRAS05358+3543. The molecular line profiles exhibit a broad component coming from the shocks along the cavity walls associated with the protostars, and an infalling (or expansion for IRAS05358+3543) and passively heated envelope component, with highly supersonic turbulence likely increasing with the distance from the center. Accretion rates between 6.3x10^-5^ and 5.6x10^-4^M_{sun}_/yr are derived from the infall observed in three of our sources. The outer water abundance is estimated to be at the typical value of a few 10^-8^ while the inner abundance varies from 1.7x10^-6^ to 1.4x10^-4^ with respect to H_2_ depending on the source. We confirm that regions of massive star formation are highly turbulent and that the turbulence likely increases in the envelope with the distance to the star. The inner abundances are lower than the expected 10^-4^ perhaps because our observed lines do not probe deep enough into the inner envelope, or because photodissociation through protostellar UV photons is more efficient than expected. We show that the higher the infall/expansion velocity in the protostellar envelope, the higher is the inner abundance, maybe indicating that larger infall/expansion velocities generate shocks that will sputter water from the ice mantles of dust grains in the inner region. High-velocity water must be formed in the gas-phase from shocked material.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/61
- Title:
- Water maser and NH_3_ survey of GLIMPSE EGOs
- Short Name:
- J/ApJ/764/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a Nobeyama 45m H_2_O maser and NH_3_ survey of all 94 northern GLIMPSE extended green objects (EGOs), a sample of massive young stellar objects (MYSOs) identified based on their extended 4.5{mu}m emission. We observed the NH_3_(1,1), (2,2), and (3,3) inversion lines, and detected emission toward 97%, 63%, and 46% of our sample, respectively (median rms~50mK). The H_2_O maser detection rate is 68% (median rms~0.11Jy). The derived H_2_O maser and clump-scale gas properties are consistent with the identification of EGOs as young MYSOs. To explore the degree of variation among EGOs, we analyze subsamples defined based on mid-infrared (MIR) properties or maser associations. H_2_O masers and warm dense gas, as indicated by emission in the higher-excitation NH_3_ transitions, are most frequently detected toward EGOs also associated with both Class I and II CH_3_OH masers. Ninety-five percent (81%) of such EGOs are detected in H_2_O (NH_3_(3,3)), compared to only 33% (7%) of EGOs without either CH_3_OH maser type. As populations, EGOs associated with Class I and/or II CH_3_OH masers have significantly higher NH_3_ line widths, column densities, and kinetic temperatures than EGOs undetected in CH_3_OH maser surveys. However, we find no evidence for statistically significant differences in H_2_O maser properties (such as maser luminosity) among any EGO subsamples. Combining our data with the 1.1mm continuum Bolocam Galactic Plane Survey, we find no correlation between isotropic H_2_O maser luminosity and clump number density. H_2_O maser luminosity is weakly correlated with clump (gas) temperature and clump mass.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A46
- Title:
- W3(H2O/OH) continuum & line data cubes at 1.3mm
- Short Name:
- J/A+A/618/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The fragmentation mode of high-mass molecular clumps and the properties of the central rotating structures surrounding the most luminous objects have yet to be comprehensively characterised. We study the fragmentation and kinematics of the high-mass star-forming region W3(H_2_O), as part of the IRAM NOrthern Extended Millimeter Array (NOEMA) large programme CORE. Using the IRAM NOEMA and the IRAM 30m telescope, the CORE survey has obtained high-resolution observations of 20 well-known highly luminous star-forming regions in the 1.37 mm wavelength regime in both line and dust continuum emission. We present the spectral line set-up of the CORE survey and a case study for W3(H_2_O). At ~0.35" (700AU at 2.0kpc) resolution, the W3(H_2_O) clump fragments into two cores (west and east), separated by ~2300AU. Velocity shifts of a few km/s are observed in the dense-gas tracer, CH_3_CN, across both cores, consistent with rotation and perpendicular to the directions of two bipolar outflows, one emanating from each core. The kinematics of the rotating structure about W3(H_2_O) W shows signs of differential rotation of material, possibly in a disk-like object. The observed rotational signature around W3(H_2_O) E may be due to a disk-like object, an unresolved binary (or multiple) system, or a combination of both. We fit the emission of CH_3_CN (12K-11K) K=4-6 and derive a gas temperature map with a median temperature of ~165K across W3(H_2_O). We create a Toomre Q map to study the stability of the rotating structures against gravitational instability. The rotating structures appear to be Toomre unstable close to their outer boundaries, with a possibility of further fragmentation in the differentially rotating core, W3(H_2_O) W. Rapid cooling in the Toomre unstable regions supports the fragmentation scenario. Combining millimetre dust continuum and spectral line data toward the famous high-mass star-forming region W3(H_2_O), we identify core fragmentation on large scales, and indications for possible disk fragmentation on smaller spatial scales.
- ID:
- ivo://CDS.VizieR/J/ApJ/827/96
- Title:
- WISE census of YSOs in Canis Major
- Short Name:
- J/ApJ/827/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the Wide-field Infrared Survey Explorer (WISE), we searched for young stellar objects (YSOs) in a 100deg^2^ region centered on the lightly studied Canis Major star-forming region. Applying stringent magnitude cuts to exclude the majority of extragalactic contaminants, we find 144 Class I candidates and 335 Class II candidates. The sensitivity to Class II candidates is limited by their faintness at the distance to Canis Major (assumed as 1000pc). More than half the candidates (53%) are found in 16 groups of more than four members, including four groups with more than 25 members each. The ratio of Class II to Class I objects, N_II_/N_I_, varies from 0.4 to 8.3 in just the largest four groups. We compare our results to those obtainable with combined Two Micron All Sky Survey and post-cryogenic Spitzer Space Telescope data; the latter approach recovers missing Class II sources. Via a comparison to protostars characterized with the Herschel Space Observatory, we propose new WISE color criteria for flat-spectrum and Class 0 protostars, finding 80 and 7 of these, respectively. The distribution of YSOs in CMa OB1 is consistent with supernova-induced star formation, although the diverse N_II_/N_I_ ratios are unexpected if this parameter traces age and the YSOs are due to the same supernova. Less massive clouds feature larger N_II_/N_I_ ratios, suggesting that initial conditions play a role in determining this quantity.
- ID:
- ivo://CDS.VizieR/J/AJ/150/100
- Title:
- WISE YSO candidates near {sigma} and {lambda} Ori
- Short Name:
- J/AJ/150/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a sensitive search down to the hydrogen burning limit for unextincted stars over ~200 square degrees around Lambda Orionis and 20 square degrees around Sigma Orionis using the methodology of Koenig & Leisawitz (2014ApJ...791..131K; K14). From WISE and 2MASS data we identify 544 and 418 candidate young stellar objects (YSOs) in the vicinity of {lambda} and {sigma} respectively. Based on our followup spectroscopy for some candidates and the existing literature for others, we found that ~80% of the K14-selected candidates are probable or likely members of the Orion star-forming region. The yield from the photometric selection criteria shows that WISE sources with K_S_-w3>1.5mag and K_S_ between 10 and 12mag are most likely to show spectroscopic signs of youth, while WISE sources with K_S_-w3>4mag and K_s_>12 were often active galactic nuclei when followed up spectroscopically. The population of candidate YSOs traces known areas of active star formation, with a few new "hot spots" of activity near Lynds 1588 and 1589 and a more dispersed population of YSOs in the northern half of the HII region bubble around {sigma} and {epsilon} Ori. A minimal spanning tree analysis of the two regions to identify stellar groupings finds that roughly two-thirds of the YSO candidates in each region belong to groups of 5 or more members. The population of stars selected by WISE outside the MST groupings also contains spectroscopically verified YSOs, with a local stellar density as low as 0.5 stars per square degree.
