Abstract
We observed the W51 high-mass star-forming complex with the Atacama Large Millimeter/submillimeter Array’s longest-baseline configurations, achieving an angular resolution of ∼20 mas, ...corresponding to a linear resolution of ∼100 au at
D
W51
= 5.4 kpc. The observed region contains three high-mass protostars in which the dust continuum emission at 1.3 mm is optically thick up to a radius ≲1000 au and has brightness temperatures ≳200 K. The high luminosity (≳10
4
L
⊙
) in the absence of free–free emission suggests the presence of massive stars (
M
≳ 20
M
⊙
) at the earliest stages of their formation. Our continuum images reveal remarkably complex and filamentary structures arising from compact cores. Molecular emission shows no clear signs of rotation or infall on scales from 150 to 2000 au; we do not detect disks. The central sources drive young (
t
dyn
∼ 100 yr), fast (
v
∼ 100 km s
−1
), powerful (
M
⊙
yr
−1
), collimated outflows. These outflows provide indirect evidence of accretion disks on scales
r
≲ 100–500 au (depending on the object). The active outflows are connected to fossil flows that have different orientations on larger spatial scales, implying that the orientations of these small disks change over time. These results together support a variant of an accretion model for high-mass star formation in which massive protostars do not form a large, stable Keplerian disk during their early stages but instead accrete material from multiple massive flows with different angular momentum vectors. This scenario therefore contrasts with the simplified classic paradigm of a stable disk+jet system, which is the standard model for low-mass star formation, and provides experimental confirmation of a multidirectional and unsteady accretion model for massive star formation.
Abstract
Using James Webb Space Telescope near-infrared data of the inner Orion Nebula, Pearson & McCaughrean detected 40 Jupiter-mass binary objects (JuMBOs). These systems are not associated with ...stars and their components have masses of giant Jupiter-like planets and separations in the plane of the sky of order ∼100 au. The existence of these wide free-floating planetary-mass binaries was unexpected in our current theories of star and planet formation. Here we report the radio continuum (6.1 and 10.0 GHz) Karl G. Jansky Very Large Array detection of a counterpart to JuMBO 24. The radio emission appears to be steady at a level of ∼50
μ
Jy over timescales of days and years. We set an upper limit of ≃15 km s
−1
to the velocity of the radio source in the plane of the sky. As in the near-infrared, the radio emission seems to be coming from both components of the binary.
For the past few decades, there has been great interest in determining if even the most massive stars in our galaxy (namely the spectral O-type stars) are formed in a similar manner as the low- and ...intermediate-mass stars, that is, through the presence of accreting disks and powerful outflows. Here, using sensitive observations of the Atacama Large Millimeter/Submillimeter Array, we report a resolved Keplerian disk (with 15 synthesized beams across its major axis) surrounding the deeply embedded O-type protostar IRAS 16547−4247. The disk shows some asymmetries that could arise because the disk is unstable and fragmenting or because of different excitation conditions within the disk. The enclosed mass estimated from the disk Keplerian radial velocities is 25 3 M . The molecular disk is at the base of an ionized thermal radio jet and is approximately perpendicular to the jet axis orientation. We additionally find the existence of a binary system of compact dusty objects at the center of the accreting disk, which indicates the possible formation of an O-type star and a companion of lower mass. This is not surprising due to the high binary fraction reported in massive stars. Subtracting the contribution of the dusty disk plus the envelope and the companion, we estimated a mass of 20 M for the central star.
We present sensitive and high angular-resolution (∼0 2-0 3) (sub)millimeter (230 and 345 GHz) continuum and CO(2−1)/CO(3−2) line archive observations of the disk star system in UX Tauri carried out ...with the Atacama Large Millimeter/Submillimeter Array. These observations reveal the gas and dusty disk surrounding the young star UX Tauri A with a large signal-to-noise ratio (>400 in the continuum and >50 in the line), and for the first time we detect the molecular gas emission associated with the disk of UX Tauri C (with a size for the disk of <56 au). No (sub)millimeter continuum emission is detected at the 5 level (0.2 mJy at 0.85 mm) associated with UX Tauri C. For the component UX Tauri C, we estimate a dust disk mass of ≤0.05 M⊕. Additionally, we report a strong tidal disk interaction between both disks, UX Tauri A/C, separated 360 au in projected distance. The CO line observations reveal marked spiral arms in the disk of UX Tauri A and an extended redshifted stream of gas associated with the UX Tauri C disk. No spiral arms are observed in the dust continuum emission of UX Tauri A. Assuming a Keplerian rotation we estimate the enclosed masses (disk+star) from their radial velocities in 1.4 0.6 M for UX Tauri A, and 70 30/sin i Jupiter masses for UX Tauri C (the latter coincides with the mass upper limit value for a brown dwarf). The observational evidence presented here lead us to propose that UX Tauri C has a close approach of a possible wide, evolving, and eccentric orbit around the disk of UX Tauri A, causing the formation of spiral arms and a stream of molecular gas falling toward UX Tauri C.
Abstract
We present a high-angular resolution (∼1″) and wide-field (
2
.′
9
×
1
.′
9
) image of the 1.3 mm continuum, CO(
J
= 2–1) and SiO(
J
= 5–4) line emissions toward an embedded protocluster, ...FIR 3, FIR 4, and FIR 5, in the Orion Molecular Cloud 2 obtained from the Atacama Large Millimeter/submillimeter Array. We identify 51 continuum sources, 36 of which are newly identified in this study. Their dust masses, projected sizes, and H
2
gas number densities are estimated to be 3.8 × 10
−5
–1.1 × 10
−2
M
⊙
, 290–2000 au, and 6.4 × 10
6
–3.3 × 10
8
cm
−3
, respectively. The results of a Jeans analysis show that ∼80% of the protostellar sources and ∼15% of the prestellar sources are gravitationally bound. We identify 12 molecular outflows traced in the CO(
J
= 2–1) emission, six of which are newly detected. We spatially resolve shocked gas structures traced by the SiO(
J
= 5–4) emission in this region for the first time. We identify shocked gas originating from outflows and other shocked regions. These results provide direct evidence of an interaction between dust condensation, FIR 4, and an energetic outflow driven by HOPS-370 located within FIR 3. A comparison of the outflow dynamical timescales, fragmentation timescales, and protostellar ages shows that the previously proposed triggered star formation scenario in FIR 4 is not strongly supported. We also discuss the spatial distribution of filaments identified in our continuum image by comparing it with a previously identified hub-fiber system in the N
2
H
+
line.
We present new Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations including the CO(2−1) line and 1.3 mm continuum emission from the surroundings of the young stellar object DO ...Tauri. The ALMA CO molecular data show three different series of rings at different radial velocities. These rings have radii around 220 and 800 au. We make individual fits to the rings and note that their centers are aligned with DO Tauri and its optical high-velocity jet. In addition, we notice that the velocity of these structures increases with the separation from the young star. We discuss the data under the hypothesis that the rings represent velocity cuts through three outflowing shells that are possibly driven by a wide-angle wind, dragging the environment material along a direction close to the line of sight (i = 19°). We estimate the dynamical ages, the mass, the momentum, and the energy of each individual outflow shell and those of the whole outflow. The results are in agreement with those found in outflows from Class II sources. We make a rough estimate for the size of the jet/wind launching region, which needs to be of 15 au. We report the physical characteristics of DO Tauri's disk continuum emission (almost face-on and with a projected major axis in the north-south direction) and its velocity gradient orientation (north-south), indicative of disk rotation for a 1-2 M central star. Finally, we show a Hubble Space Telescope S ii image of the optical jet and report a measurement of its orientation in the plane of the sky.
Abstract
We report on subarcsecond observations of complex organic molecules (COMs) in the high-mass protostar IRAS 20126+4104 with the Plateau de Bure Interferometer in its most extended ...configurations. In addition to the simple molecules SO, HNCO and H2
13CO, we detect emission from CH3CN, CH3OH, HCOOH, HCOOCH3, CH3OCH3, CH3CH2CN, CH3COCH3, NH2CN and (CH2OH)2. SO and HNCO present a X-shaped morphology consistent with tracing the outflow cavity walls. Most of the COMs have their peak emission at the putative position of the protostar, but also show an extension towards the south(east), coinciding with an H2 knot from the jet at about 800–1000 au from the protostar. This is especially clear in the case of H2
13CO and CH3OCH3. We fitted the spectra at representative positions for the disc and the outflow, and found that the abundances of most COMs are comparable at both positions, suggesting that COMs are enhanced in shocks as a result of the passage of the outflow. By coupling a parametric shock model to a large gas–grain chemical network including COMs, we find that the observed COMs should survive in the gas phase for ∼2000 yr, comparable to the shock lifetime estimated from the water masers at the outflow position. Overall, our data indicate that COMs in IRAS 20126+4104 may arise not only from the disc, but also from dense and hot regions associated with the outflow.
We report on Submillimeter Array observations of the 870 μm continuum and CO (3–2), 13CO (2–1), and C18O (2–1) line emission of a faint object, SMM2E, near the driving source of the HH 797 outflow in ...the IC 348 cluster. The continuum emission shows an unresolved source for which we estimate a mass of gas and dust of 30 M
Jup, and the CO (3–2) line reveals a compact bipolar outflow centred on SMM2E, and barely seen also in 13CO (2–1). In addition, C18O (2–1) emission reveals hints of a possible rotating envelope/disc perpendicular to the outflow, for which we infer a dynamical mass of ∼16 M
Jup. In order to further constrain the accreted mass of the object, we gathered data from Spitzer, Herschel, and new and archive submillimetre observations, and built the spectral energy distribution (SED). The SED can be fitted with one single-modified blackbody from 70 μm down to 2.1 cm, using a dust temperature of ∼24 K, a dust emissivity index of 0.8, and an envelope mass of ∼35 M
Jup. The bolometric luminosity is 0.10 L⊙, and the bolometric temperature is 35 K. Thus, SMM2E is comparable to the known Class 0 objects in the stellar domain. An estimate of the final mass indicates that SMM2E will most likely remain substellar, and the SMM2E outflow force matches the trend with luminosity known for young stellar objects. Thus, SMM2E constitutes an excellent example of a Class 0 proto-brown dwarf candidate which forms as a scaled-down version of low-mass stars. Finally, SMM2E seems to be part of a wide (∼2400 au) multiple system of Class 0 sources.
Abstract
Theoretical and numerical works indicate that a strong magnetic field should suppress fragmentation in dense cores. However, this has never been tested observationally in a relatively large ...sample of fragmenting massive dense cores. Here, we use the polarization data obtained in the Submillimeter Array Legacy Survey of Zhang et al. to build a sample of 18 massive dense cores where both fragmentation and magnetic field properties are studied in a uniform way. We measured the fragmentation level,
N
mm
, within the field of view common to all regions of ∼0.15 pc, with a mass sensitivity of ∼0.5
M
☉
, and a spatial resolution of ∼1000 au. In order to obtain the magnetic field strength using the Davis–Chandrasekhar–Fermi method, we estimated the dispersion of the polarization position angles, the velocity dispersion of the H
13
CO
+
(4–3) gas, and the density of each core, all averaged within 0.15 pc. A strong correlation is found between
N
mm
and the average density of the parental core, although with significant scatter. When large-scale systematic motions are separated from the velocity dispersion and only the small-scale (turbulent) contribution is taken into account, a tentative correlation is found between
N
mm
and the mass-to-flux ratio, as suggested by numerical and theoretical works.
Abstract
We present the
12
CO (
J
= 2–1) sensitive molecular line and 1.3 mm continuum observations from the Submillimeter Array (SMA) of the bipolar outflow associated with the young star located in ...the Bok globule known as CB 26. The SMA observations were carried out in its extended configuration allowing us to study the kinematics and structure of the outflow with about 1″ or 140 au resolution. We find that the dusty and edge-on circumstellar disk related to the outflow has a projected spatial (deconvolved) size of 196 ± 31 × 42 ± 29 au with a total (gas+dust) mass of 0.031 ± 0.015
M
⊙
. We estimated a dynamical mass for the central object of 0.66 ± 0.03
M
⊙
, and the mass of the molecular outflow of 5 ± 1.5 × 10
−5
M
⊙
. All these values are consistent with recent estimations. The observations confirm that the outflow rotation has a similar orientation to that of the edge-on disk. For the outflow, we find that the following quantities: the rotation velocity (∼1–3 km s
−1
), specific angular momentum (∼200–700 au km s
−1
), and launching radius (∼15–35 au) decrease with the height above the midplane, as observed in other molecular rotating outflows. The radius (∼180–280 au) and expansion velocity (∼2–4 km s
−1
) also increase with the height above the disk midplane for
z
< 0 au; however, for
z
> 0 au these quantities do not exhibit this behavior. Estimations of the outflow linear momentum rate, outflow angular momentum rate, and accretion luminosity seem to be well explained by the presence of a disk wind in CB 26.
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