Outflow Cavity Walls Research Articles

Constraining the stellar masses and origin of the protostellar VLA 1623 system

We present ALMA Band 7 molecular line observations of the protostars within the VLA 1623 system. We detect C17O (3–2) in the circumbinary disk around VLA 1623A and the outflow cavity walls of the collimated outflow. We further detect redshifted and blueshifted velocity gradients in the circumstellar disks around VLA 1623B and VLA 1623W that are consistent with Keplerian rotation. We used the radiative transfer modelling code pdspy and simple flared disk models to measure stellar masses of 0.27 ± 0.03 M⊙, 1.9−0.2+0.3 M⊙, and 0.64 ± 0.06 M⊙ for the VLA 1623A binary, VLA 1623B, and VLA 1623W, respectively. These results represent the strongest constraints yet on stellar mass for both VLA 1623B and VLA 1623W, and the first mass measurement for all stellar components using the same tracer and methodology. We use these masses to discuss the relationship between the young stellar objects (YSOs) in the VLA 1623 system. We find that VLA 1623W is unlikely to be an ejected YSO, as has been previously proposed. While we cannot rule out that VLA 1623W is a unrelated YSO, we propose that it is a true companion star to the VLA 1623A/B system and that these stars formed in situ through turbulent fragmentation and have had only some dynamical interactions since their inception.

JWST Peers into the Class I Protostar TMC1A: Atomic Jet and Spatially Resolved Dissociative Shock Region

Outflows and winds launched from young stars play a crucial role in the evolution of protostars and the early stages of planet formation. However, the specific details of the mechanism behind these phenomena, including how they affect the protoplanetary disk structure, are still debated. We present JWST NIRSpec integral field unit observations of atomic and H2 lines from 1 to 5.1 μm toward the low-mass protostar TMC1A. For the first time, a collimated atomic jet is detected from TMC1A in the [Fe ii] line at 1.644 μm along with corresponding extended H2 2.12 μm emission. Toward the protostar, we detected spectrally broad H i and He i emissions with velocities up to 300 km s−1 that can be explained by a combination of protostellar accretion and a wide-angle wind. The 2 μm continuum dust emission, H i, He i, and O i all show emission from the illuminated outflow cavity wall and scattered line emission. These observations demonstrate the potential of JWST to characterize and reveal new information about the hot inner regions of nearby protostars; in this case, a previously undetected atomic wind and ionized jet in a well-known outflow.

Early Planet Formation in Embedded Disks (eDisk). III. A First High-resolution View of Submillimeter Continuum and Molecular Line Emission toward the Class 0 Protostar L1527 IRS

Studying the physical and chemical conditions of young embedded disks is crucial to constrain the initial conditions for planet formation. Here we present Atacama Large Millimeter/submillimeter Array observations of dust continuum at ∼0.″06 (8 au) resolution and molecular line emission at ∼0.″17 (24 au) resolution toward the Class 0 protostar L1527 IRS from the Large Program eDisk (Early Planet Formation in Embedded Disks). The continuum emission is smooth without substructures but asymmetric along both the major and minor axes of the disk as previously observed. The detected lines of 12CO, 13CO, C18O, H2CO, c-C3H2, SO, SiO, and DCN trace different components of the protostellar system, with a disk wind potentially visible in 12CO. The 13CO brightness temperature and the H2CO line ratio confirm that the disk is too warm for CO freezeout, with the snowline located at ∼350 au in the envelope. Both molecules show potential evidence of a temperature increase around the disk–envelope interface. SO seems to originate predominantly in UV-irradiated regions such as the disk surface and the outflow cavity walls rather than at the disk–envelope interface as previously suggested. Finally, the continuum asymmetry along the minor axis is consistent with the inclination derived from the large-scale (100″ or 14,000 au) outflow, but opposite to that based on the molecular jet and envelope emission, suggesting a misalignment in the system. Overall, these results highlight the importance of observing multiple molecular species in multiple transitions to characterize the physical and chemical environment of young disks.

Physical conditions for dust grain alignment in Class 0 protostellar cores

Context. High angular resolution observations of Class 0 protostars have produced detailed maps of the polarized dust emission in the envelopes of these young embedded objects. Interestingly, the improved sensitivity brought by ALMA has revealed wide dynamic ranges of polarization fractions, with specific locations harboring surprisingly large amounts of polarized dust emission. Aims. Our aim is to characterize the grain alignment conditions and dust properties responsible for the observed polarized dust emission in the inner envelopes (≤1000 au) of Class 0 protostars. Methods. We analyzed the polarized dust emission maps obtained with ALMA and compared them to molecular line emission maps of specific molecular tracers, mainly C2H, which allowed us to probe one of the key components in dust grain alignment theories: the irradiation field. Results. We show that C2H peaks toward outflow cavity walls, where the polarized dust emission is also enhanced. Our analysis provides a tentative correlation between the morphology of the polarized intensity and C2H emission, suggesting that the radiation field impinging on the cavity walls favors both the grain alignment and the warm carbon chain chemistry in these regions. We propose that shocks happening along outflow cavity walls could potentially represent an additional source of photons contributing to dust grain alignment. However, some parts of the cores, such as the equatorial planes, exhibit enhanced polarized flux, although no radiation driven chemistry is observed, for example where radiative torques are theoretically not efficient enough. This suggests that additional physical conditions, such as source geometry and dust grain evolution, may play a role in grain alignment. Conclusions. Comparing chemical processes with grain alignment physics opens a promising avenue to develop our understanding of the dust grain evolution (i.e., their origin, growth, and structure) in the interior of Class 0 protostars. The source geometry and evolution can represent important factors that set the environmental conditions of the inner envelope, determining whether the radiation field strength and spectrum can drive efficient dust grain alignment via radiative torques.

Sulphur-rich cold gas around the hot core precursor G328.2551-0.5321

Context.During the process of star formation, the dense gas undergoes significant chemical evolution leading to the emergence of a rich variety of molecules associated with hot cores and hot corinos. However, the physical conditions and the chemical processes involved in this evolution are poorly constrained; the early phases of emerging hot cores in particular represent an unexplored territory.Aims.We provide here a full molecular inventory of a massive protostellar core that is proposed to represent a precursor of a hot core. We investigate the conditions for the molecular richness of hot cores.Methods.We performed an unbiased spectral survey towards the hot core precursor associated with clump G328.2551-0.5321 between 159 GHz and 374 GHz, covering the entire atmospheric windows at 2 mm, 1.2 mm, and 0.8 mm. To identify the spectral lines, we used rotational diagrams and radiative transfer modelling assuming local thermodynamical equilibrium.Results.We detected 39 species plus 26 isotopologues, and were able to distinguish a compact (~2″), warm inner region with a temperature, T, of ~100 K, a colder, more extended envelope withT ~20 K, and the kinematic signatures of the accretion shocks that have previously been observed with ALMA. We associate most of the emission of the small molecules with the cold component of the envelope, while the molecular emission of the warm gas is enriched by complex organic molecules (COMs). We find a high abundance of S-bearing molecules in the cold gas phase, including the molecular ions HCS+and SO+. The abundance of sulphur-bearing species suggests a low sulphur depletion, with a factor of ≥1%, in contrast to low-mass protostars, where the sulphur depletion is found to be stronger. Similarly to other hot cores, the deuterium fractionation of small molecules is low, showing a significant difference compared to low-mass protostars. We find a low isotopic ratio in particular for12C/13C of ~30, and32S/34S of ~12, which are about two times lower than the values expected at the galactocentric distance of G328.2551-0.5321. We identify nine COMs (CH3OH, CH3OCH3, CH3OCHO, CH3CHO, HC(O)NH2, CH3CN, C2H5CN, C2H3CN, and CH3SH) in the warm component of the envelope, four in the cold gas, and four towards the accretion shocks.Conclusions.The presence of numerous molecular ions and high abundance of sulphur-bearing species originating from the undisturbed gas may suggest a contribution from shocked gas at the outflow cavity walls. The molecular composition of the cold component of the envelope is rich in small molecules, while a high abundance in numerous species of COMs suggests an increasing molecular complexity towards the warmer regions. The molecular composition of the warm gas is similar to that of both hot cores and hot corinos, but the molecular abundances are closer to the values found towards hot corinos than to values found towards hot cores. Considering the compactness of the warm region and its moderate temperature, we suggest that thermal desorption has not been completed towards this object yet, representing an early phase of the emergence of hot cores.

Structured velocity field in the inner envelope of B335: ALMA observations of rare CO isotopologues

Context. Studies of Class 0 objects allow to characterize the dynamical processes taking place at the onset of the star formation process and to determine the physical mechanisms responsible for the outcome of the collapse. Observations of dense gas tracers allow for the characterization of key kinematics of the gas that are directly involved in the star formation process, such as infall, outflow, and rotation. Aims. This work is aimed at investigating the molecular line velocity profiles of the Class 0 protostellar object B335 and attempts to place constraints on the infall motions happening in the circumstellar gas of the object. Methods. We present observations of C17O (1–0), C18O (1–0), and 12CO (2–1) transitions along with an analysis of spectral profiles at envelope radii between 100 and 860 au. Results. C17O emission presents a double-peaked line profile distributed in a complex velocity field. Both peaks present an offset of 0.2–1 km s−1 from the systemic velocity of the source in the probed area. The optical depth of the C17O emission has been estimated and found to be less than 1, suggesting that the two velocity peaks trace two distinct velocity components of the gas in the inner envelope. Conclusions. After discarding possible motions that could produce the complex velocity pattern, such as rotation and outflow, we conclude that infall motions are responsible for producing the velocity field. Because inside-out symmetric collapse cannot explain those observed profiles, it is suggested that these are produced by non-isotropic accretion from the envelope into the central source along the outflow cavity walls.

Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy

Water in star-forming regions: physics and chemistry from clouds to disks as probed by <i>Herschel</i> spectroscopy

Multiwavelength modelling of the circumstellar environment of the massive protostar AFGL 2591 VLA 3

ABSTRACT We have studied the dust density, temperature, and velocity distributions of the archetypal massive young stellar object (MYSO) AFGL 2591. Given its high luminosity ($L=2\times 10^5\, \mbox{L$_{\odot}$}$) and distance (d = 3.3 kpc), AFGL 2591 has one of the highest $\sqrt{L}/d$ ratio, giving better resolved dust emission than any other MYSO. As such, this paper provides a template on how to use resolved multiwavelength data and radiative transfer to obtain a well-constrained 2D axisymmetric analytic rotating infall model. We show for the first time that the resolved dust continuum emission from Herschel 70- μm observations is extended along the outflow direction, whose origin is explained in part from warm dust in the outflow cavity walls. However, the model can only explain the kinematic features from CH3CN observations with unrealistically low stellar masses (&amp;lt;15 M⊙), indicating that additional physical processes may be playing a role in slowing down the envelope rotation. As part of our three-step continuum and line fitting, we have identified model parameters that can be further constrained by specific observations. High-resolution mm visibilities were fitted to obtain the disc mass (6 M⊙) and radius (2200 au). A combination of SED and near-infrared observations were used to estimate the luminosity and envelope mass together with the outflow cavity inclination and opening angles.

A Detailed View of the Circumstellar Environment and Disk of the Forming O-star AFGL 4176

Abstract We present a detailed analysis of the disk and circumstellar environment of the forming O-type star AFGL 4176 mm1, placing results from the Atacama Large Millimeter/submillimeter Array (ALMA) into context with multiwavelength data. With ALMA, we detect seventeen 1.2 mm continuum sources within 5″ (21,000 au) of AFGL 4176 mm1. We find that mm1 has a spectral index of 3.4 ± 0.2 across the ALMA band, with &gt;87% of its 1.2 mm continuum emission from dust. The source mm2, projected 4200 au from mm1, may be a companion or a blueshifted knot in a jet. We also explore the morphological differences between the molecular lines detected with ALMA, finding 203 lines from 25 molecules, which we categorize into several morphological types. Our results show that AFGL 4176 mm1 provides an example of a forming O-star with a large and chemically complex disk, which is mainly traced by nitrogen-bearing molecules. Lines that show strong emission on the blueshifted side of the disk are predominantly oxygen-bearing, which we suggest are tracing a disk accretion shock. The molecules C34S, H2CS, and CH3CCN trace a slow wide-angle wind or dense structures in the outflow cavity walls. With the Australia Telescope Compact Array (ATCA), we detect a compact continuum source (&lt;2000 × 760 au) at 1.2 cm, associated with mm1, of which &gt;96% is from ionized gas. The ATCA NH3(1, 1) and (2, 2) emission traces a large-scale (r ∼ 0.5 pc) rotating toroid with the disk source mm1 in the blueshifted part of this structure offset to the northwest.

Determining the Physical Conditions of an Extremely Young Class 0 Circumbinary Disk around VLA 1623A

Abstract We present a detailed analysis of high-resolution C18O (2–1), SO (88–77), CO (3–2), and DCO+ (3–2) data obtained by the Atacama Large Millimeter/submillimeter Array toward a class 0 Keplerian circumbinary disk around VLA 1623A, which represents one of the most complete analyses toward a class 0 source. From the dendrogram analysis, we identified several accretion flows feeding the circumbinary disk in a highly anisotropic manner. Stream-like SO emission around the circumbinary disk reveals the complicated shocks caused by the interactions between the disk, accretion flows, and outflows. A wall-like structure is discovered south of VLA 1623B. The discovery of two outflow cavity walls at the same position traveling at different velocities suggests that the two outflows from both VLA 1623A and VLA 1623B are on top of each other in the plane of the sky. Our detailed flat and flared disk modeling shows that Cycle 2 C18O J = 2–1 data are inconsistent with the combined binary mass of 0.2 M ⊙, as suggested by early Cycle 0 studies. The combined binary mass for VLA 1623A should be modified to 0.3–0.5 M ⊙.

Understanding the Origin of the Magnetic Field Morphology in the Wide-binary Protostellar System BHR 71

Abstract We present 1.3 mm Atacama Large Millimeter/submillimeter Array observations of polarized dust emission toward the wide-binary protostellar system BHR 71 IRS1 and IRS2. IRS1 features what appears to be a natal, hourglass-shaped magnetic field. In contrast, IRS2 exhibits a magnetic field that has been affected by its bipolar outflow. Toward IRS2, the polarization is confined mainly to the outflow cavity walls. Along the northern edge of the redshifted outflow cavity of IRS2, the polarized emission is sandwiched between the outflow and a filament of cold, dense gas traced by N2D+, toward which no dust polarization is detected. This suggests that the origin of the enhanced polarization in IRS2 is the irradiation of the outflow cavity walls, which enables the alignment of dust grains with respect to the magnetic field—but only to a depth of ∼300 au, beyond which the dust is cold and unpolarized. However, in order to align grains deep enough in the cavity walls, and to produce the high polarization fraction seen in IRS2, the aligning photons are likely to be in the mid- to far-infrared range, which suggests a degree of grain growth beyond what is typically expected in very young, Class 0 sources. Finally, toward IRS1 we see a narrow, linear feature with a high (10%–20%) polarization fraction and a well-ordered magnetic field that is not associated with the bipolar outflow cavity. We speculate that this feature may be a magnetized accretion streamer; however, this has yet to be confirmed by kinematic observations of dense-gas tracers.

Rotational Desorption of Ice Mantles from Suprathermally Rotating Grains around Young Stellar Objects

Abstract Ice mantles on dust grains play a central role in astrochemistry. Water and complex organic molecules (COMs) are thought to first form on the ice mantles and subsequently are released into the gas phase due to star-formation activity. However, the critical question is whether ice mantles can survive stellar radiation when grains are being heated from to ≳100 K. In this paper, we first study the effect of suprathermal grain rotation driven by the intense radiation of young stellar objects on the ice mantles. We find that the entire ice mantles can be disrupted into small fragments by centrifugal stress before the water ice and COMs desorb via thermal sublimation. We then study the consequence of resulting ice fragments and find that tiny fragments of radius a ≲ 10 Å exhibit a transient release of COMs due to thermal spikes, whereas larger fragments can facilitate thermal sublimation at much higher rates than from the original icy grain, or the same rate but with temperatures of ∼20–40 K lower. We find that rotational desorption is efficient for hot cores/corinos from the inner to outer regions where the temperature drops to and . We discuss the implications of this mechanism for desorption of COMs and water ice in various environments, including outflow cavity walls, photodissociation regions, and protoplanetary disks. Finally, we show that very large aggregate grains can be disrupted into individual icy grains via a rotational disruption mechanism, followed by rotational desorption of ice mantles.

The Circumstellar Environment around the Embedded Protostar EC 53

Abstract EC 53 is an embedded protostar with quasi-periodic emission in the near-IR and submillimeter. We use Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution observations of continuum and molecular line emission to describe the circumstellar environment of EC 53. The continuum image reveals a disk with a flux that suggests a mass of 0.075 M ⊙, much less than the estimated mass in the envelope, and an in-band spectral index that indicates grain growth to centimeter sizes. Molecular lines trace the outflow cavity walls, infalling and rotating envelope, and/or the Keplerian disk. The rotation profile of the C17O 3–2 line emission cannot isolate the Keplerian motion clearly, although the lower limit of the protostellar mass can be calculated as 0.3 ± 0.1 M ⊙ if the Keplerian motion is adopted. The weak CH3OH emission, which is anticorrelated with the H13CO+ 4–3 line emission, indicates that the water snow line is more extended than what expected from the current luminosity, attesting to bygone outburst events. The extended snow line may persist for longer at the disk surface because the lower density increases the freeze-out timescale of methanol and water.

Mirror, mirror on the outflow cavity wall

Aims. The inner regions of high-mass protostars are often invisible in the near-infrared, obscured by thick envelopes and discs. We aim to investigate the inner gaseous disc of IRAS 11101-5829 through scattered light from the outflow cavity walls. Methods. We observed the immediate environment of the high-mass young stellar object IRAS 11101-5829 and the closest knots of its jet, HH135-136, with the integral field unit VLT/SINFONI. We also retrieved archival data from the high-resolution long-slit spectrograph VLT/X-shooter. We analysed imaging and spectroscopic observations to discern the nature of the near-infrared CO emission. Results. We detect the first three bandheads of the υ = 2−0 CO vibrational emission for the first time in this object. It is coincident with continuum and Brγ emission and extends up to ~10 000 au to the north-east and ~10 000 au to the south-west. The line profiles have been modelled as a Keplerian rotating disc assuming a single ring in local thermodynamic equilibrium. The model output gives a temperature of ~3000 K, a CO column density of ~1 × 1022 cm−2, and a projected Keplerian velocity vK sin idisc ~ 25 km s−1, which is consistent with previous modelling in other high-mass protostars. In particular, the low value of vK sin idisc suggests that the disc is observed almost face-on, whereas the well-constrained geometry of the jet imposes that the disc must be close to edge-on. This apparent discrepancy is interpreted as the CO seen reflected in the mirror of the outflow cavity wall. Conclusions. From both jet geometry and disc modelling, we conclude that all the CO emission is seen through reflection by the cavity walls and not directly. This result implies that in the case of highly embedded objects, as for many high-mass protostars, line profile modelling alone might be deceptive and the observed emission could affect the derived physical and geometrical properties; in particular the inclination of the system can be incorrectly interpreted.

Characterizing Magnetic Field Morphologies in Three Serpens Protostellar Cores with ALMA

Abstract With the aim of characterizing the dynamical processes involved in the formation of young protostars, we present high-angular-resolution ALMA dust polarization observations of the Class 0 protostellar cores Serpens SMM1, Emb 8(N), and Emb 8. With spatial resolutions ranging from 150 to 40 au at 870 μm, we find unexpectedly high values of the polarization fraction along the outflow cavity walls in Serpens Emb 8(N). We use 3 mm and 1 mm molecular tracers to investigate outflow and dense-gas properties and their correlation with the polarization. These observations allow us to investigate the physical processes involved in the radiative alignment torques (RATs) acting on dust grains along the outflow cavity walls, which experience irradiation from accretion processes and outflow shocks. The inner core of SMM1-a presents a polarization pattern with a poloidal magnetic field at the bases of the two lobes of the bipolar outflow. To the south of SMM1-a we see two polarized filaments, one of which seems to trace the redshifted outflow cavity wall. The other may be an accretion streamer of material infalling onto the central protostar. We propose that the polarized emission we see at millimeter wavelengths along the irradiated cavity walls can be reconciled with the expectations of RAT theory if the aligned grains present at &lt;500 au scales in Class 0 envelopes have grown larger than the 0.1 μm size of dust grains in the interstellar medium. Our observations allow us to constrain the magnetic field morphologies of star-forming sources within the central cores, along the outflow cavity walls, and in possible accretion streamers.

Tracing the cold and warm physico-chemical structure of deeply embedded protostars: IRAS 16293−2422 vs. VLA 1623−2417

Context. Much attention has been placed on the dust distribution in protostellar envelopes, but there are still many unanswered questions regarding the physico-chemical structure of the gas. Aims. Our aim is to start identifying the factors that determine the chemical structure of protostellar regions, by studying and comparing low-mass embedded systems in key molecular tracers. Methods. The cold and warm chemical structures of two embedded Class 0 systems, IRAS 16293−2422 and VLA 1623−2417 were characterized through interferometric observations. DCO+, N2H+, and N2D+ were used to trace the spatial distribution and physics of the cold regions of the envelope, while c-C3H2 and C2H from models of the chemistry are expected to trace the warm (UV-irradiated) regions. Results. The two sources show a number of striking similarities and differences. DCO+ consistently traces the cold material at the disk-envelope interface, where gas and dust temperatures are lowered due to disk shadowing. N2H+ and N2D+, also tracing cold gas, show low abundances toward VLA 1623−2417, but for IRAS 16293−2422, the distribution of N2D+ is consistent with the same chemical models that reproduce DCO+. The two systems show different spatial distributions c-C3H2 and C2H. For IRAS 16293−2422, c-C3H2 traces the outflow cavity wall, while C2H is found in the envelope material but not the outflow cavity wall. In contrast, toward VLA 1623−2417 both molecules trace the outflow cavity wall. Finally, hot core molecules are abundantly observed toward IRAS 16293−2422 but not toward VLA 1623−2417. Conclusions. We identify temperature as one of the key factors in determining the chemical structure of protostars as seen in gaseous molecules. More luminous protostars, such as IRAS 16293−2422, will have chemical complexity out to larger distances than colder protostars, such as VLA 1623−2417. Additionally, disks in the embedded phase have a crucial role in controlling both the gas and dust temperature of the envelope, and consequently the chemical structure.

First Results of an ALMA Band 10 Spectral Line Survey of NGC 6334I: Detections of Glycolaldehyde (HC(O)CH2OH) and a New Compact Bipolar Outflow in HDO and CS

Abstract We present the first results of a pilot program to conduct an Atacama Large Millimeter Array (ALMA) band 10 spectral line survey of the high-mass star-forming region NGC 6334I. The observations were taken in exceptional weather conditions (0.19 mm precipitable water) with typical system temperatures T sys &lt; 950 K at ∼890 GHz. A bright, bipolar north–south outflow is seen in HDO and CS emission, driven by the embedded massive protostar MM1B. This has allowed, for the first time, a direct comparison of the thermal water in this outflow to the location of water maser emission from prior 22 GHz Very Large Array observations. The maser locations are shown to correspond to the sites along the outflow cavity walls, where high-velocity gas impacts the surrounding material. We also compare our new observations to prior Herschel Heterodyne Instrument for the Far-infrared (HIFI) spectral line survey data of this field, detecting an order of magnitude more spectral lines (695 versus 65) in the Atacama Large Millimeter/submillimeter Array (ALMA) data. We focus on the strong detections of the complex organic molecule glycolaldehyde (HC(O)CH2OH) in the ALMA data that is not detected in the heavily beam-diluted HIFI spectra. Finally, we stress the need for dedicated THz laboratory spectroscopy to support and exploit future high-frequency molecular line observations with ALMA.

Sub-arcsecond Kinematic Structure of the Outflow in the Vicinity of the Protostar in L483

Abstract The bipolar outflow associated with the Class 0 low-mass protostellar source (IRAS 18148–0440) in L483 has been studied in the CCH and CS line emission at 245 and 262 GHz, respectively. Sub-arcsecond resolution observations of these lines have been conducted with ALMA. Structures and kinematics of the outflow cavity wall are investigated in the CS line, and are analyzed by using a parabolic model of an outflow. We constrain the inclination angle of the outflow to be from 75° to 90°, i.e., the outflow is blowing almost perpendicular to the line of sight. Comparing the outflow parameters derived from the model analysis with those of other sources, we confirm that the opening angle of the outflow and the gas velocity on its cavity wall correlate with the dynamical timescale of the outflows. Moreover, a hint of a rotating motion of the outflow cavity wall is found. Although the rotation motion is marginal, the specific angular momentum of the gas on the outflow cavity wall is evaluated to be comparable to or twice that of the infalling-rotating envelope of L483.

The VLA Nascent Disk And Multiplicity Survey of Perseus Protostars (VANDAM). III. Extended Radio Emission from Protostars in Perseus

Abstract Centimeter continuum emission from protostars offers insight into the innermost part of the outflows, as shock-ionized gas produces free–free emission. We observed a complete population of Class 0 and I protostars in the Perseus molecular cloud at 4.1 and 6.4 cm with resolution and sensitivity superior to previous surveys. From a total of 71 detections, eight sources exhibit resolved emission at 4.1 cm and/or 6.4 cm. In this paper, we focus on this subsample, analyzing their spectral indices along the jet and their alignment with respect to the large-scale molecular outflow. Spectral indices for fluxes integrated toward the position of the protostar are consistent with free–free thermal emission. The value of the spectral index along a radio jet decreases with distance from the protostar. For six sources, emission is well aligned with the outflow central axis, showing that we observe the ionized base of the jet. This is not the case for two sources, where we note misalignment of the emission with respect to the large-scale outflow. This might indicate that the emission does not originate in the radio jet, but rather in an ionized outflow cavity wall or disk surface. For five of the sources, the spectral indices along the jet decrease well below the thermal free–free limit of −0.1 with significance. This is indicative of synchrotron emission, meaning that high-energy electrons are being produced in the outflows close to the disk. This result can have far-reaching implications for the chemical composition of the embedded disks.

The Circumestellar Disk of the B0 Protostar Powering the HH 80-81 Radio Jet

Abstract We present subarcsecond angular resolution observations carried out with the Submillimeter Array (SMA) at 880 μm centered at the B0-type protostar GGD27 MM1, the driving source of the parsec scale HH 80-81 jet. We constrain its polarized continuum emission to ≲0.8% at this wavelength. Its submillimeter spectrum is dominated by sulfur-bearing species tracing a rotating-disk-like structure (SO and SO2 isotopologues mainly), but also shows HCN-bearing and CH3OH lines, which trace the disk and the outflow cavity walls excavated by the HH 80-81 jet. The presence of many sulfurated lines could indicate the presence of shocked gas at the disk’s centrifugal barrier or that MM1 is a hot core at an evolved stage. The resolved SO2 emission traces the disk kinematics very well and we fit the SMA observations using a thin-disk Keplerian model, which gives the inclination (47°), the inner (≲170 au) and outer (∼950–1300 au) radii, and the disk’s rotation velocity (3.4 km s−1 at a putative radius of 1700 au). We roughly estimate a protostellar dynamical mass of 4–18 . MM2 and WMC cores show, comparatively, an almost empty spectra, suggesting that they are associated with extended emission detected in previous low-angular resolution observations, and therefore indicating youth (MM2) or the presence of a less massive object (WMC).