We present 3 mm ALMA continuum and line observations at resolutions of 6.5 au and 13 au, respectively, toward the Class 0 system IRAS 16293-2422 A. The continuum observations reveal two compact ...sources toward IRAS 16293-2422 A, coinciding with compact ionized gas emission previously observed at radio wavelengths (A1 and A2), confirming the long-known radio sources as protostellar. The emission toward A2 is resolved and traces a dust disk with an FWHM size of ∼12 au, while the emission toward A1 sets a limit to the FWHM size of the dust disk of ∼4 au. We also detect spatially resolved molecular kinematic tracers near the protostellar disks. Several lines of the J = 5−4 rotational transition of HNCO, NH2CHO, and t-HCOOH are detected, with which we derived individual line-of-sight velocities. Using these together with the CS (J = 2−1), we fit Keplerian profiles toward the individual compact sources and derive masses of the central protostars. The kinematic analysis indicates that A1 and A2 are a bound binary system. Using this new context for the previous 30 yr of Very Large Array observations, we fit orbital parameters to the relative motion between A1 and A2 and find that the combined protostellar mass derived from the orbit is consistent with the masses derived from the gas kinematics. Both estimations indicate masses consistently higher (0.5 M1 M2 2 ) than previous estimations using lower-resolution observations of the gas kinematics. The ALMA high-resolution data provides a unique insight into the gas kinematics and masses of a young deeply embedded bound binary system.
Abstract
We use 3 mm continuum NOrthern Extended Millimeter Array and NH
3
Very Large Array observations toward the First Hydrostatic Core (FHSC) candidate CB 17 MMS in order to reveal the dust ...structure and gas properties to 600–1100 au scales and to constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise ratio of 9. The gas traced by NH
3
exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius ∼1800 au and a central density of ∼6 × 10
5
cm
−3
. Virial and density structure analysis reveals the core is marginally bound (
α
vir
= 0.73). The region is entirely consistent with that of a young starless core, hence ruling out CB 17 MMS as an FHSC candidate. Additionally, the core exhibits a velocity gradient aligned with the major axis, showing an arc-like structure in the position–velocity diagram and an off-center region with high velocity dispersion, caused by two distinct velocity peaks. These features could be due to interactions with the nearby outflow, which appears to deflect due to the dense gas near the NH
3
column density peak. We investigate the specific angular momentum profile of the starless core, finding that it aligns closely with previous studies of similar radial profiles in Class 0 sources. This similarity to more evolved objects suggests that motions at 1000 au scales are determined by large-scale dense cloud motions, and may be preserved throughout the early stages of star formation.
ABSTRACT
We present ALMA 3 mm molecular line and continuum observations with a resolution of ∼3.5 arcsec towards five first hydrostatic core (FHSC) candidates (L1451-mm, Per-bolo 58, Per-bolo 45, ...L1448-IRS2E, and Cha-MMS1). Our goal is to characterize their envelopes and identify the most promising sources that could be bona fide FHSCs. We identify two candidates that are consistent with an extremely young evolutionary state (L1451-mm and Cha-MMS1), with L1451-mm being the most promising FHSC candidate. Although our envelope observations cannot rule out Cha-MMS1 as an FHSC yet, the properties of its CO outflow and SED published in recent studies are in better agreement with the predictions for a young protostar. For the remaining three sources, our observations favour a pre-stellar nature for Per-bolo 45 and rule out the rest as FHSC candidates. Per-bolo 58 is fully consistent with being a Class 0, while L1448 IRS2E shows no emission of high-density tracers (NH2D and N2H+) at the location of the previously identified compact continuum source, which is also undetected in our observations. Thus, we argue that there is no embedded source at the presumptive location of the FHSC candidate L1448 IRS2E. We propose instead that what was thought to be emission from the presumed L1448 IRS2E outflow corresponds to outflow emission from a nearby Class 0 system, deflected by the dense ambient material. We compare the properties of the FHSC candidates studied in this work and the literature, which shows that L1451-mm appears as possibly the youngest source with a confirmed outflow.
Abstract
Characterizing the physical conditions at disk scales in class 0 sources is crucial for constraining the protostellar accretion process and the initial conditions for planet formation. We ...use ALMA 1.3 and 3 mm observations to investigate the physical conditions of the dust around the class 0 binary IRAS 16293–2422 A down to ∼10 au scales. The circumbinary material’s spectral index,
α
, has a median of 3.1 and a dispersion of ∼0.2, providing no firm evidence of millimeter-sized grains therein. Continuum substructures with brightness temperature peaks of
T
b
∼ 60–80 K at 1.3 mm are observed near the disks at both wavelengths. These peaks do not overlap with strong variations of
α
, indicating that they trace high-temperature spots instead of regions with significant optical depth variations. The lower limits to the inferred dust temperature in the hot spots are 122, 87, and 49 K. Depending on the assumed dust opacity index, these values can be several times higher. They overlap with high gas temperatures and enhanced complex organic molecular emission. This newly resolved dust temperature distribution is in better agreement with the expectations from mechanical instead of the most commonly assumed radiative heating. In particular, we find that the temperatures agree with shock heating predictions. This evidence and recent studies highlighting accretion heating in class 0 disks suggest that mechanical heating (shocks, dissipation powered by accretion, etc.) is important during the early stages and should be considered when modeling and measuring properties of deeply embedded protostars and disks.
Abstract
We report high-resolution ALMA observations toward a massive protostellar core C1-Sa (∼30
M
⊙
) in the Dragon infrared dark cloud. At the resolution of 140 au, the core fragments into two ...kernels (C1-Sa1 and C1-Sa2) with a projected separation of ∼1400 au along the elongation of C1-Sa, consistent with a Jeans length scale of ∼1100 au. Radiative transfer modeling using RADEX indicates that the protostellar kernel C1-Sa1 has a temperature of ∼75 K and a mass of 0.55
M
⊙
. C1-Sa1 also likely drives two bipolar outflows, one being parallel to the plane of the sky. C1-Sa2 is not detected in line emission and does not show any outflow activity but exhibits ortho-H
2
D
+
and N
2
D
+
emission in its vicinity; thus it is likely still starless. Assuming a 20 K temperature, C1-Sa2 has a mass of 1.6
M
⊙
. At a higher resolution of 96 au, C1-Sa1 begins to show an irregular shape at the periphery, but no clear sign of multiple objects or disks. We suspect that C1-Sa1 hosts a tight binary with inclined disks and outflows. Currently, one member of the binary is actively accreting while the accretion in the other is significantly reduced. C1-Sa2 shows hints of fragmentation into two subkernels with similar masses, which requires further confirmation with higher sensitivity.
Spectral lines of ammonia, NH3, are useful probes of the physical conditions in dense molecular cloud cores. In addition to advantages in spectroscopy, ammonia has also been suggested to be resistant ...to freezing onto grain surfaces, which should make it a superior tool for studying the interior parts of cold, dense cores. Here we present high-resolution NH3 observations with the Very Large Array and Green Bank Telescope toward a prestellar core. These observations show an outer region with a fractional NH3 abundance of X(NH3) = (1.975 ± 0.005) × 10−8 (±10% systematic), but it also reveals that, after all, the X(NH3) starts to decrease above a H2 column density of ≈2.6 × 1022 cm−2. We derive a density model for the core and find that the break point in the fractional abundance occurs at the density n(H2) ∼ 2 × 105 cm−3, and beyond this point the fractional abundance decreases with increasing density, following the power law n−1.1. This power-law behavior is well reproduced by chemical models where adsorption onto grains dominates the removal of ammonia and related species from the gas at high densities. We suggest that the break-point density changes from core to core depending on the temperature and the grain properties, but that the depletion power law is anyway likely to be close to n−1 owing to the dominance of accretion in the central parts of starless cores.
ABSTRACT
Deeply embedded protostars are actively fed from their surrounding envelopes through their protostellar disc. The physical structure of such early discs might be different from that of more ...evolved sources due to the active accretion. We present 1.3 and 3 mm ALMA continuum observations at resolutions of 6.5 and 12 au, respectively, towards the Class 0 source IRAS 16293−2422 B. The resolved brightness temperatures appear remarkably high, with Tb > 100 K within ∼30 au and Tb peak over 400 K at 3 mm. Both wavelengths show a lopsided emission with a spectral index reaching values less than 2 in the central ∼20 au region. We compare these observations with a series of radiative transfer calculations and synthetic observations of magnetohydrodynamic and radiation hydrodynamic protostellar disc models formed after the collapse of a dense core. Based on our results, we argue that the gas kinematics within the disc may play a more significant role in heating the disc than the protostellar radiation. In particular, our radiation hydrodynamic simulation of disc formation, including heating sources associated with gravitational instabilities, is able to generate the temperatures necessary to explain the high fluxes observed in IRAS 16293B. Besides, the low spectral index values are naturally reproduced by the high optical depth and high inner temperatures of the protostellar disc models. The high temperatures in IRAS 16293B imply that volatile species are mostly in the gas phase, suggesting that a self-gravitating disc could be at the origin of a hot corino.
Abstract
We have observed the low-mass protostellar source IRAS 15398−3359 at a resolution of 0.″2–0.″3, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST, to examine ...the presence of a hot corino in the vicinity of the protostar. We detect nine CH
3
OH lines including the high-excitation lines with upper-state energies up to 500 K. The CH
3
OH rotational temperature and the column density are derived to be
119
−
26
+
20
K and
3.2
−
1.0
+
2.5
×
10
18
cm
−2
, respectively. The beam filling factor is derived to be
0.018
−
0.003
+
0.005
, indicating that the emitting region of CH
3
OH is much smaller than the synthesized beam size and is not resolved. The emitting region of three high-excitation lines, 18
3,15
–18
2,16
, A (
E
u
= 447 K), 19
3,16
–19
2,17
, A (
E
u
= 491 K), and 20
3,17
–20
2,18
, A (
E
u
= 537 K), is located within the 50 au area around the protostar and seems to have a slight extension toward the northwest. Toward the continuum peak, we also detect one emission line from CH
2
DOH and two features of multiple CH
3
OCHO lines. These results, in combination with previous reports, indicate that IRAS 15398−3359 is a source with hybrid properties showing both hot corino chemistry rich in complex organic molecules on small scales (∼10 au) and warm carbon-chain chemistry rich in carbon-chain species on large scales (∼100–1000 au). A possible implication of the small emitting region is further discussed in relation to the origin of the hot corino activity.
Context
. Multiwavelength dust continuum and polarization observations arising from self-scattering have been used to investigate grain sizes in young disks. However, the likelihood of ...self-scattering being the polarization mechanism in embedded disks decreases for very highly optically thick disks and makes us reconsider some of the size constraints from polarization, particularly for younger and more massive disks. The 1.3 mm polarized emission detected toward the hot (≳400 K) Class 0 disk IRAS 16293-2422 B has been attributed to self-scattering, with predictions of bare grain sizes between 200 and 2000 µm.
Aims
. We aim to investigate the effects of changing the maximum grain sizes in the resultant continuum and continuum polarization fractions from self-scattering for a hot and massive Class 0 disk extracted from numerical simulations of prestellar core collapse and to compare them with IRAS 16293 B observations.
Methods
. We compared new and archival dust continuum and polarization observations at high resolution between 1.3 and 18 mm to a set of synthetic models. We developed a new publicly available tool to automate this process called Synthesizer. This tool is an easy-to-use program for generating synthetic observations from numerical simulations.
Results
. Optical depths are in the range of 130 to 2 from 1.3 to 18 mm, respectively. Predictions of significant grain growth populations, including
a
max
= 1000 µm, are comparable to the observations from IRAS 16293 B at all observed wavelengths. The polarization fraction produced by self-scattering reaches a maximum of approximately 0.1% at 1.3 mm for a maximum grain size of 100 µm, which is an order of magnitude lower than the grain size observed toward IRAS 16293 B.
Conclusions
. From comparison of the Stokes
I
fluxes, we conclude that significant grain growth could be present in the young Class 0 disk IRAS 16293 B, particularly in the inner hot region (< 10 au,
T
> 300 K) where refractory organics evaporate. The polarization produced by self-scattering in our model is not high enough to explain the observations at 1.3 and 7 mm, and such effects as dichroic extinction and polarization reversal of elongated aligned grains remain other possible but untested scenarios.
We use CARMA 3 mm continuum and molecular lines (NH2D, N2H+, HCO+, HCN, and CS) at ∼1000 au resolution to characterize the structure and kinematics of the envelope surrounding the deeply embedded ...first core candidate Per-bolo 58. The line profile of the observed species shows two distinct peaks separated by 0.4-0.6 km s−1, which most likely arise from two different optically thin velocity components rather than the product of self-absorption in an optically thick line. The two velocity components, each with a mass of ∼0.5-0.6 , overlap spatially at the position of the continuum emission and produce a general gradient along the outflow direction. We investigate whether these observations are consistent with infall in a turbulent and magnetized envelope. We compare the morphology and spectra of the N2H+ (1-0) with synthetic observations of an MHD simulation that considers the collapse of an isolated core that is initially perturbed with a turbulent field. The proposed model matches the data in the production of two velocity components, traced by the isolated hyperfine line of the N2H+ (1-0) spectra, and shows a general agreement in morphology and velocity field. We also use large maps of the region to compare the kinematics of the core with that of the surrounding large-scale filamentary structure and find that accretion from the large-scale filament could also explain the complex kinematics exhibited by this young dense core.
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