Context. Fast jets are thought to be a crucial ingredient of star formation because they might extract angular momentum from the disk and thus allow mass accretion onto the star. However, it is ...unclear whether jets are ubiquitous, and likewise, their contribution to mass and angular momentum extraction during protostar formation remains an open question. Aims. Our aim is to investigate the ejection process in the low-mass Class 0 protostar L1157. This source is associated with a spectacular bipolar outflow, and the recent detection of high-velocity SiO suggests the occurrence of a jet. Methods. Observations of CO 2 −1 and SiO 5 − 4 at ~ \hbox{$0\farcs8$} 0 .̋ 8 resolution were obtained with the IRAM Plateau de Bure Interferometer (PdBI) as part of the CALYPSO large program. The jet and outflow structure were fit with a precession model. We derived the column density of CO and SiO, as well as the jet mass-loss rate and mechanical luminosity. Results. High-velocity CO and SiO emission resolve for the first time the first 200 au of the outflow-driving molecular jet. The jet is strongly asymmetric, with the blue lobe ~0.65 times slower than the red lobe. This suggests that the large-scale asymmetry of the outflow is directly linked to the jet velocity and that the asymmetry in the launching mechanism has been at work for the past 1800 yr. Velocity asymmetries are common in T Tauri stars, which suggests that the jet formation mechanism from Class 0 to Class II stages might be similar. Our model simultaneously fits the properties of the inner jet and of the clumpy 0.2 pc scale outflow by assuming that the jet precesses counter-clockwise on a cone inclined by 73° to the line of sight with an opening angle of 8° on a period of ~1640 yr. The estimated jet mass flux and mechanical luminosity are Ṁjet ~ 7.7 × 10-7M⊙ yr-1 and Ljet ~ 0.9L⊙, indicating that the jet could extract at least 25% of the gravitational energy released by the forming star.
Abstract
The shock L1157-B1 driven by the low-mass protostar L1157-mm is a unique environment to investigate the chemical enrichment due to molecules released from dust grains. IRAM-30m and Plateau ...de Bure Interferometer observations allow a census of Si-bearing molecules in L1157-B1. We detect SiO and its isotopologues and, for the first time in a shock, SiS. The strong gradient of the SiO/SiS abundance ratio across the shock (from ≥180 to ∼25) points to a different chemical origin of the two species. SiO peaks where the jet impacts the cavity walls (SiO/H2 ∼ 10−6), indicating that SiO is directly released from grains or rapidly formed from released Si in the strong shock occurring at this location. In contrast, SiS is only detected at the head of the cavity opened by previous ejection events (SiS/H2 ∼ 2 × 10−8). This suggests that SiS is not directly released from the grain cores but instead should be formed through slow gas-phase processes using part of the released silicon. This finding shows that Si-bearing molecules can be useful to distinguish regions where grains or gas-phase chemistry dominates.
Context. Deuterium fractionation is a valuable tool for understanding the chemical evolution during the process that leads to the formation of a Sun-like planetary system. Aims. Methanol is thought ...to be mainly formed during the prestellar phase, and its deuterated form keeps a memory of the conditions at that epoch. The unique combination of high angular resolution and sensitivity provided by ALMA enables us to measure methanol deuteration in the planet formation region around a Class 0 protostar and to understand its origin. Methods. We mapped both the 13CH3OH and CH2DOH distribution in the inner regions (~100 au) of the HH212 system in Orion B. To this end, we used ALMA Cycle 1 and Cycle 4 observations in Band 7 with angular resolution down to ~0.̋15. Results. We detected 6 lines of 13CH3OH and 13 lines of CH2DOH with upper level energies of up to 438 K in temperature units. We derived a rotational temperature of (171 ± 52) K and column densities of 7 × 1016 cm-2 (13CH3OH) and 1 × 1017 cm-2 (CH2DOH), respectively. This yields a D/H ratio of (2.4 ± 0.4) × 10-2, which is lower by an order of magnitude than previously measured values using single-dish telescopes toward protostars located in Perseus. Our findings are consistent with the higher dust temperatures in Orion B with respect to the temperature derived for the Perseus cloud. The emission traces a rotating structure extending up to 45 au from the jet axis, which is elongated by 90 au along the jet axis. So far, the origin of the observed emission appears to be related with the accretion disc. Only higher spatial resolution measurements will be able to distinguish between different possible scenarios, however: disc wind, disc atmosphere, or accretion shocks.
The formation of complex organic molecules (COMs) in protostellar environments is a hotly debated topic. In particular, the relative importance of the gas phase processes as compared to a direct ...formation of COMs on the dust grain surfaces is so far unknown. We report here the first high-resolution images of acetaldehyde (CH3CHO) emission towards the chemically rich protostellar shock L1157-B1, obtained at 2 mm with the IRAM Plateau de Bure interferometer. Six blueshifted CH3CHO lines with E
u = 26–35 K have been detected. The acetaldehyde spatial distribution follows the young (∼ 2000 yr) outflow cavity produced by the impact of the jet with the ambient medium, indicating that this COM is closely associated with the region enriched by iced species evaporated from dust mantles and released into the gas phase. A high CH3CHO relative abundance, 2–3 × 10−8, is inferred, similarly to what found in hot corinos. Astrochemical modelling indicates that gas phase reactions can produce the observed quantity of acetaldehyde only if a large fraction of carbon, of the order of 0.1 per cent, is locked into iced hydrocarbons.
Jets around low- and intermediate-mass young stellar objects (YSOs) contain a fossil record of the recent accretion and outflow activity of their parent star-forming systems. We aim to understand ...whether the accretion/ejection process is similar across the entire stellar mass range of the parent YSOs. To this end we have obtained optical to near-infrared spectra of HH 1042 and HH 1043, two newly discovered jets in the massive star-forming region RCW 36, using X-shooter on the ESO Very Large Telescope. HH 1042 is associated with the intermediate-mass YSO 08576nr292. Over 90 emission lines are detected in the spectra of both targets. High-velocity (up to 220 km s-1) blue- and redshifted emission from a bipolar flow is observed in typical shock tracers. Low-velocity emission from the background cloud is detected in nebular tracers, including lines from high ionization species. We applied combined optical and infrared spectral diagnostic tools in order to derive the physical conditions (density, temperature, and ionization) in the jets. The measured mass outflow rates are Ṁjet ~ 10-7M⊙ yr-1. It is not possible to determine a reliable estimate for the accretion rate of the driving source of HH 1043 using optical tracers. We measure a high accretion rate for the driving source of HH 1042 (Ṁacc ~ 10-6M⊙ yr-1). For this system the ratio Ṁjet/Ṁacc ~ 0.1, which is comparable to low-mass sources and consistent with models for magneto-centrifugal jet launching. The knotted structure and velocity spread in both jets are interpreted as fossil signatures of a variable outflow rate. While the mean velocities in both lobes of the jets are comparable, the variations in mass outflow rate and velocity in the two lobes are not symmetric. This asymmetry suggests that the launching mechanism on either side of the accretion disk is not synchronized. For the HH 1042 jet, we have constructed an interpretative physical model with a stochastic or periodic outflow rate and a description of a ballistic flow as its constituents. We have simulated the flow and the resulting emission in position–velocity space, which is then compared to the observed kinematic structure. The knotted structure and velocity spread can be reproduced qualitatively with the model. The results of the simulation indicate that the outflow velocity varies on timescales on the order of 100 yr.
The formation of protoplanetary disks is not well understood. To understand how and when these disks are formed, it is crucial to characterize the kinematics of the youngest protostars at a high ...angular resolution. Here we study a sample of 16 Class 0 protostars to measure their rotation profile at scales from 50 to 500 au and search for Keplerian rotation. We used high-angular-resolution line observations obtained with the Plateau de Bure Interferometer as part of the CALYPSO large program. From
13
CO (
J
= 2−1), C
18
O (
J
= 2−1) and SO (
N
j
= 5
6
−4
5
) moment maps, we find that seven sources show rotation about the jet axis at a few hundred au scales: SerpS-MM18, L1448-C, L1448-NB, L1527, NGC 1333-IRAS 2A, NGC 1333-IRAS 4B, and SVS13-B. We analyzed the kinematics of these sources in the
uv
plane to derive the rotation profiles down to 50 au scales. We find evidence for Keplerian rotation in only two sources, L1527 and L1448-C. Overall, this suggests that Keplerian disks larger than 50 au are uncommon around Class 0 protostars. However, in some of the sources, the line emission could be optically thick and dominated by the envelope emission. Due to the optical thickness of these envelopes, some of the disks could have remained undetected in our observations.
Context.
Class I protostars are a bridge between Class 0 protostars (≤10
5
yr old), and Class II (≥10
6
yr) protoplanetary disks. Recent studies show gaps and rings in the dust distribution of disks ...younger than 1 Myr, suggesting that planet formation may start already at the Class I stage. To understand what chemistry planets will inherit, it is crucial to characterize the chemistry of Class I sources and to investigate how chemical complexity evolves from Class 0 protostars to protoplanetary disks.
Aims.
There are two goals: (i) to perform a census of the molecular complexity in a sample of four Class I protostars, and (ii) to compare the data with the chemical compositions of earlier and later phases of the Sun-like star formation process.
Methods.
We performed IRAM-30 m observations at 1.3 mm towards four Class I objects (L1489-IRS, B5-IRS1, L1455-IRS1, and L1551-IRS5). The column densities of the detected species were derived assuming local thermodynamic equilibrium (LTE) or large velocity gradients (LVGs).
Results.
We detected 27 species: C-chains, N-bearing species, S-bearing species, Si-bearing species, deuterated molecules, and interstellar complex organic molecules (iCOMs; CH
3
OH, CH
3
CN, CH
3
CHO, and HCOOCH
3
). Among the members of the observed sample, L1551-IRS5 is the most chemically rich source. Different spectral profiles are observed: (i) narrow lines (~1 km s
−1
) towards all the sources, (ii) broader lines (~4 km s
−1
) towards L1551-IRS5, and (iii) line wings due to outflows (in B5-IRS1, L1455-IRS1, and L1551-IRS5). Narrow c-C
3
H
2
emission originates from the envelope with temperatures of 5–25 K and sizes of ~2′′−10′′. The iCOMs in L1551-IRS5 reveal the occurrence of hot corino chemistry, with CH
3
OH and CH
3
CN lines originating from a compact (~0.′′15) and warm (
T
> 50 K) region. Finally, OCS and H
2
S seem to probe the circumbinary disks in the L1455-IRS1 and L1551-IRS5 binary systems. The deuteration in terms of elemental D/H in the molecular envelopes is: ~10−70% (D
2
CO/H
2
CO), ~5−15% (HDCS/H
2
CS), and ~1−23% (CH
2
DOH/CH
3
OH). For the L1551-IRS5 hot corino we derive D/H ~2% (CH
2
DOH/CH
3
OH).
Conclusions.
Carbon chain chemistry in extended envelopes is revealed towards all the sources. In addition, B5-IRS1, L1455-IRS1, and L1551-IRS5 show a low-excitation methanol line that is narrow and centered at systemic velocity, suggesting an origin from an extended structure, plausibly UV-illuminated. The abundance ratios of CH
3
CN, CH
3
CHO, and HCOOCH
3
with respect to CH
3
OH measured towards the L1551-IRS5 hot corino are comparable to that estimated at earlier stages (prestellar cores, Class 0 protostars), and to that found in comets. The deuteration in our sample is also consistent with the values estimated for sources at earlier stages. These findings support the inheritance scenario from prestellar cores to the Class I phase when planets start forming.
Abstract
We present new Very Large Array observations, between 6.8 and 66 mm, of the edge-on Class I disk IRAS04302+2247. Observations at 6.8 mm and 9.2 mm lead to the detection of thermal emission ...from the disk, while shallow observations at the other wavelengths are used to correct for emission from other processes. The disk radial brightness profile transitions from broadly extended in previous Atacama Large Millimeter/submillimeter Array 0.9 mm and 2.1 mm observations to much more centrally brightened at 6.8 mm and 9.2 mm, which can be explained by optical depth effects. The radiative transfer modeling of the 0.9 mm, 2.1 mm, and 9.2 mm data suggests that the grains are smaller than 1 cm in the outer regions of the disk, allowing us to obtain the first lower limit for the scale height of grains emitting at millimeter wavelengths in a protoplanetary disk. We find that the millimeter dust scale height is between 1 au and 6 au at a radius 100 au from the central star, while the gas scale height is estimated to be about 7 au, indicating a modest level of settling. The estimated dust height is intermediate between less evolved Class 0 sources, which are found to be vertically thick, and more evolved Class II sources, which show a significant level of settling. This suggests that we are witnessing an intermediate stage of dust settling.
Context.
Star-forming molecular clouds are characterised by the ubiquity of intertwined filaments. The filaments have been observed in both high- and low-mass star-forming regions, and they are ...thought to split into collections of sonic fibres. The locations where filaments converge are termed hubs, and these are associated with the young stellar clusters. However, the observations of filamentary structures within hubs at distances of 75–300 pc require a high angular resolution <2″ (~ 150–600 au) that limits the number of such studies conducted so far.
Aims.
The integral shaped filament (ISF) of the Orion A molecular cloud is noted for harbouring several hubs within which no filamentary structures have been observed so far. The goal of our study is to investigate the nature of the filamentary structures within one of these hubs, which is the chemically rich hub OMC-2 FIR 4, and to analyse their emission with high density and shock tracers.
Methods.
We observed the OMC-2 FIR 4 proto-cluster using Band 6 of the Atacama Large (sub-)Millimetre Array (ALMA) in Cycle 4 with an angular resolution of ~0.26″ (100 au). We analysed the spatial distribution of dust, the shock tracer SiO, and dense gas tracers (i.e., CH
3
OH, CS, and H
13
CN). We also studied the gas kinematics using SiO and CH
3
OH maps.
Results.
Our observations for the first time reveal interwoven filamentary structures within OMC-2 FIR 4 that are probed by several tracers. Each filamentary structure is characterised by a distinct velocity as seen from the emission peak of CH
3
OH lines. They also show transonic and supersonic motions. SiO is associated with filaments and also with multiple bow-shock features. The bow-shock features have sizes between ~500 and 2700 au and are likely produced by the outflow from HOPS-370. Their dynamical ages are <800 yr. In addition, for the first time, we reveal a highly collimated SiO jet (~1°) with a projected length of ~5200 au from the embedded protostar VLA 15.
Conclusions.
Our study unveiled the previously unresolved filamentary structures as well as the shocks within OMC-2 FIR 4. The kinematics of the filamentary structures might be altered by external and/or internal mechanisms such as the wind from H II regions, the precessing jet from the protostellar source HOPS-370, or the jet from VLA 15. While the complexity of the region, coupled with the limited number of molecular lines in our dataset, makes any clear association with these mechanisms challenging, our study shows that multi-scale observations of these regions are crucial for understanding the accretion processes and flow of material that shape star formation.
Herbig Ae/Be stars are intermediate-mass pre-main sequence stars surrounded by circumstellar dust disks. Some are observed to produce jets, whose appearance as a sequence of shock fronts (knots) ...suggests a past episodic outflow variability. This “jet fossil record” can be used to reconstruct the outflow history. We present the first optical to near-infrared (NIR) spectra of the jet from the Herbig Ae star HD 163296, obtained with VLT/X-shooter. We determine the physical conditions in the knots and also their kinematic “launch epochs”. Knots are formed simultaneously on either side of the disk, with a regular interval of ~16 yr. The velocity dispersion versus jet velocity and the energy input are comparable between both lobes. However, the mass-loss rate, velocity,and shock conditions are asymmetric. We find Ṁjet/Ṁacc ~ 0.01−0.1, which is consistent with magneto-centrifugal jet launching models. No evidence of any dust is found in the high-velocity jet, suggesting a launch region within the sublimation radius (<0.5 au). The jet inclination measured from proper motions and radial velocities confirms that it is perpendicular to the disk. A tentative relation is found between the structure of the jet and the photometric variability of the central source. Episodes of NIR brightening were previously detected and attributed to a dusty disk wind. We report for the first time significant optical fadings lasting from a few days up to a year, coinciding with the NIR brightenings. These are very likely caused by dust lifted high above the disk plane, and this supports the disk wind scenario. The disk wind is launched at a larger radius than the high-velocity atomic jet, although their outflow variability may have a common origin. No significant relation between outflow and accretion variability could be established. Our findings confirm that this source undergoes periodic ejection events, which may be coupled with dust ejections above the disk plane.
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