scholarly journals Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

2020 ◽  
Vol 636 ◽  
pp. A108 ◽  
Author(s):  
J. Bouvier ◽  
K. Perraut ◽  
J.-B. Le Bouquin ◽  
G. Duvert ◽  
C. Dougados ◽  
...  
Keyword(s):  
Geometric Model ◽  
Stellar System ◽  
Line Emission ◽  
Position Angle ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Disk System ◽  
Compact Region ◽  
Magnetospheric Accretion ◽  
The Continuum

Context. Young stellar objects are thought to accrete material from their circumstellar disks through their strong stellar magnetospheres. Aims. We aim to directly probe the magnetospheric accretion region on a scale of a few 0.01 au in a young stellar system using long-baseline optical interferometry. Methods. We observed the pre-transitional disk system DoAr 44 with VLTI/GRAVITY on two consecutive nights in the K-band. We computed interferometric visibilities and phases in the continuum and in the Brγ line in order to constrain the extent and geometry of the emitting regions. Results. We resolve the continuum emission of the inner dusty disk and measure a half-flux radius of 0.14 au. We derive the inclination and position angle of the inner disk, which provides direct evidence that the inner and outer disks are misaligned in this pre-transitional system. This may account for the shadows previously detected in the outer disk. We show that Brγ emission arises from an even more compact region than the inner disk, with an upper limit of 0.047 au (~5 R⋆). Differential phase measurements between the Brγ line and the continuum allow us to measure the astrometric displacement of the Brγ line-emitting region relative to the continuum on a scale of a few tens of microarcsec, corresponding to a fraction of the stellar radius. Conclusions. Our results can be accounted for by a simple geometric model where the Brγ line emission arises from a compact region interior to the inner disk edge, on a scale of a few stellar radii, fully consistent with the concept of magnetospheric accretion process in low-mass young stellar systems.

scholarly journals The GRAVITY young stellar object survey

2021 ◽  
Vol 645 ◽  
pp. A50
Author(s):  
◽  
M. Koutoulaki ◽  
R. Garcia Lopez ◽  
A. Natta ◽  
R. Fedriani ◽  
...  
Keyword(s):  
Near Infrared ◽  
Ad Hoc ◽  
Line Emission ◽  
Position Angle ◽  
Local Thermal Equilibrium ◽  
Continuum Emission ◽  
Geometrical Properties ◽  
Ring Model ◽  
Free Region ◽  
The Continuum

Context. 51 Oph is a Herbig Ae/Be star that exhibits strong near-infrared CO ro-vibrational emission at 2.3 μm, most likely originating in the innermost regions of a circumstellar disc. Aims. We aim to obtain the physical and geometrical properties of the system by spatially resolving the circumstellar environment of the inner gaseous disc. Methods. We used the second-generation Very Large Telescope Interferometer instrument GRAVITY to spatially resolve the continuum and the CO overtone emission. We obtained data over 12 baselines with the auxiliary telescopes and derive visibilities, and the differential and closure phases as a function of wavelength. We used a simple local thermal equilibrium ring model of the CO emission to reproduce the spectrum and CO line displacements. Results. Our interferometric data show that the star is marginally resolved at our spatial resolution, with a radius of ~10.58 ± 2.65R⊙. The K-band continuum emission from the disc is inclined by 63° ± 1°, with a position angle of 116° ± 1°, and 4 ± 0.8 mas (0.5 ± 0.1 au) across. The visibilities increase within the CO line emission, indicating that the CO is emitted within the dust-sublimation radius. By modelling the CO bandhead spectrum, we derive that the CO is emitted from a hot (T = 1900–2800 K) and dense (NCO = (0.9–9) × 1021 cm−2) gas. The analysis of the CO line displacement with respect to the continuum allows us to infer that the CO is emitted from a region 0.10 ± 0.02 au across, well within the dust-sublimation radius. The inclination and position angle of the CO line emitting region is consistent with that of the dusty disc. Conclusions. Our spatially resolved interferometric observations confirm the CO ro-vibrational emission within the dust-free region of the inner disc. Conventional disc models exclude the presence of CO in the dust-depleted regions of Herbig AeBe stars. Ad hoc models of the innermost disc regions, that can compute the properties of the dust-free inner disc, are therefore required.

scholarly journals The GRAVITY young stellar object survey

2020 ◽  
Vol 635 ◽  
pp. L12 ◽  
Author(s):  
◽  
A. Caratti o Garatti ◽  
R. Fedriani ◽  
R. Garcia Lopez ◽  
M. Koutoulaki ◽  
...  
Keyword(s):  
Near Infrared ◽  
Major Axis ◽  
Position Angle ◽  
Young Stellar Objects ◽  
High Mass ◽  
Continuum Emission ◽  
Stellar Objects ◽  
Axis Position ◽  
The Continuum ◽  
Gaseous Disc

Context. The inner regions of the discs of high-mass young stellar objects (HMYSOs) are still poorly known due to the small angular scales and the high visual extinction involved. Aims. We deploy near-infrared spectro-interferometry to probe the inner gaseous disc in HMYSOs and investigate the origin and physical characteristics of the CO bandhead emission (2.3–2.4 μm). Methods. We present the first GRAVITY/VLTI observations at high spectral (ℛ = 4000) and spatial (mas) resolution of the CO overtone transitions in NGC 2024 IRS 2. Results. The continuum emission is resolved in all baselines and is slightly asymmetric, displaying small closure phases (≤8°). Our best ellipsoid model provides a disc inclination of 34° ±1°, a disc major axis position angle (PA) of 166° ± 1°, and a disc diameter of 3.99 ± 0.09 mas (or 1.69  ±  0.04 au, at a distance of 423 pc). The small closure phase signals in the continuum are modelled with a skewed rim, originating from a pure inclination effect. For the first time, our observations spatially and spectrally resolve the first four CO bandheads. Changes in visibility, as well as differential and closure phases across the bandheads are detected. Both the size and geometry of the CO-emitting region are determined by fitting a bidimensional Gaussian to the continuum-compensated CO bandhead visibilities. The CO-emitting region has a diameter of 2.74±0.070.08 mas (1.16  ±  0.03 au), and is located in the inner gaseous disc, well within the dusty rim, with inclination and PA matching the dusty disc geometry, which indicates that both dusty and gaseous discs are coplanar. Physical and dynamical gas conditions are inferred by modelling the CO spectrum. Finally, we derive a direct measurement of the stellar mass of M* ∼ 14.7−3.6+2 M⊙ by combining our interferometric and spectral modelling results.

scholarly journals Water maser and radio continuum emission towards IRAS 23139+5939

2007 ◽  
Vol 3 (S242) ◽  
pp. 180-181
Author(s):  
M. A. Trinidad ◽  
S. Curiel ◽  
J. M. Torrelles ◽  
L. F. Rodríguez ◽  
V. Migenes ◽  
...  
Keyword(s):  
Flux Density ◽  
Line Emission ◽  
The Other ◽  
Radio Continuum ◽  
High Mass ◽  
Continuum Emission ◽  
Maser Line ◽  
Water Masers ◽  
Water Maser ◽  
The Continuum

AbstractWe present simultaneous observations of continuum (3.5 and 1.3cm) and water maser line emission (1.3cm) carried out with the VLA-A toward the high-mass object IRAS 23139+5939. We detected two radio continuum sources at 3.5cm separated by 0”5 (~2400 AU), I23139 and I23139S. Based on the observed continuum flux density and the spectral index, we suggest that I23139 is a thermal radio jet associated with a high-mass YSO. On the other hand, based on the spatio-kinematical distribution of the water masers, together with the continuum emission information, we speculate that I23139S is also a jet source powering some of the masers detected in the region.

scholarly journals Constraints on high-J CO emission lines in z ∼ 6 quasars

2019 ◽  
Author(s):  
S Carniani ◽  
S Gallerani ◽  
L Vallini ◽  
A Pallottini ◽  
M Tazzari ◽  
...  
Keyword(s):  
Black Body ◽  
Continuum Emission ◽  
Molecular Gas ◽  
X Ray ◽  
Compact Region ◽  
Upper Limits ◽  
Gas Heating ◽  
Co Emission ◽  
Co Observations ◽  
The Continuum

Abstract We present Atacama Large Millimiter/submillimiter Array (ALMA) observations of eight highly excited CO (${\rm J_{\rm up}}$ >8) lines and continuum emission in two z ∼ 6 quasars: SDSS J231038.88+185519.7 (hereafter J2310), for which CO(8-7), CO(9-8), and CO(17-16) lines have been observed, and ULAS J131911.29+095951.4 (J1319), observed in the CO(14-13), CO(17-16) and CO(19-18) lines. The continuum emission of both quasars arises from a compact region (<0.9 kpc). By assuming a modified black-body law, we estimate dust masses of Log(Mdust/M⊙) = 8.75 ± 0.07 and Log(Mdust/M⊙) = 8.8 ± 0.2 and dust temperatures of Tdust = 76 ± 3 K and $T_{\rm dust}=66^{+15}_{-10}~{\rm K}$, respectively for J2310 and J1319. Only CO(8-7) and CO(9-8) in J2310 are detected, while 3σ upper limits on luminosities are reported for the other lines of both quasars. The CO line luminosities and upper limits measured in J2310 and J1319 are consistent with those observed in local AGN and starburst galaxies, and other z ∼ 6 quasars, except for SDSS J1148+5251 (J1148), the only quasar at z = 6.4 with a previous CO(17-16) line detection. By computing the CO SLEDs normalised to the CO(6-5) line and FIR luminosities for J2310, J1319, and J1149, we conclude that different gas heating mechanisms (X-ray radiation and/or shocks) may explain the different CO luminosities observed in these z ∼ 6 quasar. Future ${\rm J_{\rm up}}$ >8 CO observations will be crucial to understand the processes responsible for molecular gas excitation in luminous high-z quasars.

scholarly journals A Search for Disks around Massive Young Stellar Objects

2004 ◽  
Vol 221 ◽  
pp. 425-430 ◽  
Author(s):  
A. G. Gibb ◽  
M. G. Hoare ◽  
L. G. Mundy ◽  
F. Wyrowski
Keyword(s):  
Near Infrared ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Circumstellar Disk ◽  
Mass Yield ◽  
Stellar Objects ◽  
Strong Emission ◽  
Yield Values ◽  
Infrared Data ◽  
The Continuum

We present subarcsecond observations at 2.7 and 1.4 mm of a sample of massive young stellar objects made with the BIMA millimetre array. For most sources the continuum emission on the smallest scales at 2.7 mm is dominated by free-free emission from the stellar wind or jet. Strong emission at 1.4 mm shows the presence of significant dust associated with Cep A and GL 490 but our resolution is not sufficient to resolve any structure. The 2.7-mm emission from GL 490 is resolved but it is not clear whether we are seeing a single circumstellar disk or a secondary companion, although near-infrared data support the disk hypothesis. Estimates of the dust mass yield values of ∼1–4 M⊙ within radii of 150 to 1000 AU.

scholarly journals Kinematics around the B335 protostar down to au scales

2019 ◽  
Vol 631 ◽  
pp. A64 ◽  
Author(s):  
Per Bjerkeli ◽  
Jon P. Ramsey ◽  
Daniel Harsono ◽  
Hannah Calcutt ◽  
Lars E. Kristensen ◽  
...  
Keyword(s):  
Morphological Properties ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Small Scale ◽  
Short Baseline ◽  
Stellar Objects ◽  
Spatially Resolved ◽  
Long Baseline ◽  
The Relationship ◽  
The Continuum

Context. The relationship between outflow launching and the formation of accretion disks around young stellar objects is still not entirely understood, which is why spectrally and spatially resolved observations are needed. Recently, the Atacama Large Millimetre/sub-millimetre Array (ALMA) carried out long-baseline observations towards a handful of young sources, revealing connections between outflows and the inner regions of disks. Aims. Here we aim to determine the small-scale kinematical and morphological properties of the outflow from the isolated protostar B335 for which no Keplerian disk has, so far, been observed on scales down to 10 au. Methods. We used ALMA in its longest-baseline configuration to observe emission from CO isotopologues, SiO, SO2, and CH3OH. The proximity of B335 provides a resolution of ~3 au (0.03′′). We also combined our long-baseline data with archival observations to produce a high-fidelity image covering scales up to 700 au (7′′). Results. 12CO has an X-shaped morphology with arms ~50 au in width that we associate with the walls of an outflow cavity, similar to what is observed on larger scales. Long-baseline continuum emission is confined to <7 au from the protostar, while short-baseline continuum emission follows the 12CO outflow and cavity walls. Methanol is detected within ~30 au of the protostar. SiO is also detected in the vicinity of the protostar, but extended along the outflow. Conclusions. The 12CO outflow does not show any clear signs of rotation at distances ≳30 au from the protostar. SiO traces the protostellar jet on small scales, but without obvious rotation. CH3OH and SO2 trace a region <16 au in diameter, centred on the continuum peak, which is clearly rotating. Using episodic, high-velocity, 12CO features, we estimate the launching radius of the outflow to be <0.1 au and dynamical timescales of the order of a few years.

scholarly journals STATCONT: A statistical continuum level determination method for line-rich sources

2018 ◽  
Vol 609 ◽  
pp. A101 ◽  
Author(s):  
Á. Sánchez-Monge ◽  
P. Schilke ◽  
A. Ginsburg ◽  
R. Cesaroni ◽  
A. Schmiedeke
Keyword(s):  
Synthetic Data ◽  
Line Emission ◽  
Continuum Emission ◽  
Determination Method ◽  
Emission Level ◽  
Synthetic Spectra ◽  
Statistical Continuum ◽  
Statistical Approaches ◽  
Rich Spectrum ◽  
The Continuum

STATCONT is a python-based tool designed to determine the continuum emission level in spectral data, in particular for sources with a line-rich spectrum. The tool inspects the intensity distribution of a given spectrum and automatically determines the continuum level by using different statistical approaches. The different methods included in STATCONT are tested against synthetic data. We conclude that the sigma-clipping algorithm provides the most accurate continuum level determination, together with information on the uncertainty in its determination. This uncertainty can be used to correct the final continuum emission level, resulting in the here called ‘corrected sigma-clipping method’ or c-SCM. The c-SCM has been tested against more than 750 different synthetic spectra reproducing typical conditions found towards astronomical sources. The continuum level is determined with a discrepancy of less than 1% in 50% of the cases, and less than 5% in 90% of the cases, provided at least 10% of the channels are line free. The main products of STATCONT are the continuum emission level, together with a conservative value of its uncertainty, and datacubes containing only spectral line emission, i.e., continuum-subtracted datacubes. STATCONT also includes the option to estimate the spectral index, when different files covering different frequency ranges are provided.

scholarly journals Compact gaseous accretion disk in Keplerian rotation around MWC 147

2019 ◽  
Vol 623 ◽  
pp. A38
Author(s):  
Edward Hone ◽  
Stefan Kraus ◽  
Claire L. Davies ◽  
Alexander Kreplin ◽  
John D. Monnier ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Accretion Disk ◽  
Near Infrared ◽  
Geometric Model ◽  
Rotational Velocity ◽  
Kinematic Model ◽  
Position Angle ◽  
Central Star ◽  
Be Stars ◽  
The Continuum

Context. The disks around some Herbig Be stars have been observed to be more compact than the expected dust sublimation radius for such objects. Highly refractory dust grains and optically thick gas emission have been proposed as possible explanations for this phenomenon. Aims. Previously, the “undersized” Herbig Be star MWC 147 was observed with interferometry, and the results indicated a presence of a compact gaseous disk based on the measured wavelength-dependence of near-infrared or mid-infrared visibilities. Our aim is to search for direct evidence for the presence of hot gas inside of the expected dust sublimation radius of MWC 147. Methods. By combining VLTI/AMBER spectro-interferometry (R = 12 000) with CRIRES spectroscopy (R = 100 000) we can both spectrally and spatially resolve the Brγ line-emitting gas around MWC 147. Additionally, using CHARA/CLIMB enables us to achieve baseline lengths up to 330 m, offering ~2 times higher angular resolution (and a better position angle coverage) than has previously been achieved with interferometry for MWC 147. To model the continuum we fit our AMBER and CLIMB measurements with a geometric model of an inclined Gaussian distribution as well as a ring model. We fit our high-resolution spectra and spectro-interferometric data with a kinematic model of a disk in Keplerian rotation. Results. Our interferometric visibility modelling of MWC 147 indicates the presence of a compact continuum disk with a close to face-on orientation. We model the continuum with an inclined Gaussian and a ring with a radius of 0.60 mas (0.39 au), which is well within the expected dust sublimation radius of 1.52 au. We detect no significant change in the measured visibilities across the Brγ line, indicating that the line-emitting gas is located in the same region as the continuum-emitting disk. Using our differential phase data we construct photocentre displacement vectors across the Brγ line, revealing a velocity profile consistent with a rotating disk. We fit our AMBER spectro-interferometry data with a kinematic model of a disk in Keplerian rotation, where both the line-emitting and continuum-emitting components of the disk originate from the same compact region close to the central star. The presence of line-emitting gas in the same region as the K-band continuum supports the interpretation that the K-band continuum traces an optically thick gas disk. Conclusions. Our spatially and spectrally resolved observations of MWC 147 reveal that the K-band continuum and Brγ emission both originate from a similar region which is 3.9 times more compact than the expected dust sublimation radius for the star; Brγ is emitted from the accretion disk or disk wind region and exhibits a rotational velocity profile. We conclude that we detect the presence of a compact, gaseous accretion disk in Keplerian rotation around MWC 147.

scholarly journals Discovery of Molecular-line Polarization in the Disk of TW Hya

2021 ◽  
Vol 922 (2) ◽  
pp. 139
Author(s):  
Richard Teague ◽  
Charles L. H. Hull ◽  
Stéphane Guilloteau ◽  
Edwin A. Bergin ◽  
Anne Dutrey ◽  
...  
Keyword(s):  
Linear Polarization ◽  
Line Emission ◽  
Emission Lines ◽  
Continuum Emission ◽  
Azimuthal Dependence ◽  
Molecular Line ◽  
Polarization Fraction ◽  
Co Emission ◽  
Higher Sensitivity ◽  
The Continuum

Abstract We report observations of polarized line and continuum emission from the disk of TW Hya using the Atacama Large Millimeter/submillimeter Array. We target three emission lines, 12CO (3–2), 13CO (3–2), and CS (7–6), to search for linear polarization due to the Goldreich–Kylafis effect, while simultaneously tracing the continuum polarization morphology at 332 GHz (900 μm), achieving a spatial resolution of 0.″5 (30 au). We detect linear polarization in the dust continuum emission; the polarization position angles show an azimuthal morphology, and the median polarization fraction is ∼0.2%, comparable to previous, lower frequency observations. Adopting a “shift-and-stack” technique to boost the sensitivity of the data, combined with a linear combination of the Q and U components to account for their azimuthal dependence, we detect weak linear polarization of 12CO and 13CO line emission at a ∼10σ and ∼5σ significance, respectively. The polarization was detected in the line wings, reaching a peak polarization fraction of ∼5% and ∼3% for the two molecules between disk radii of 0.″5 and 1″. The sign of the polarization was found to flip from the blueshifted side of the emission to the redshifted side, suggesting a complex, asymmetric polarization morphology. Polarization is not robustly detected for the CS emission; however, a tentative signal, comparable in morphology to that found for the 12CO and 13CO emission, is found at a ≲3σ significance. We are able to reconstruct a polarization morphology, consistent with the azimuthally averaged profiles, under the assumption that this is also azimuthally symmetric, which can be compared with future higher-sensitivity observations.

scholarly journals Observations and modeling of the ultraviolet emission of solar flares

2015 ◽  
Vol 11 (S320) ◽  
pp. 57-59
Author(s):  
Katarzyna Mikuła ◽  
Arkadiusz Berlicki ◽  
Petr Heinzel
Keyword(s):  
Uv Radiation ◽  
Solar Flares ◽  
Line Emission ◽  
Uv Spectra ◽  
Interface Region ◽  
Continuum Emission ◽  
Ultraviolet Emission ◽  
Imaging Spectrograph ◽  
The Continuum

AbstractIn this paper we present the method of using far UV spectra of the flare observed by Interface Region Imaging Spectrograph (IRIS) for determination of the contribution of the continuum emission to the total UV radiation observed e.g. by SDO in 1600 Å channel. In our method the Si IV (1402.77 Å) line observed by IRIS is used as a proxy of C IV line emission contained in SDO/AIA UV images. Determined intensity of the flare continuum emission can be used to study the physics of the flare heated chromosphere and for better understanding of the emission mechanisms.

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