Abstract
To date, about two dozen low-mass embedded protostars exhibit rich spectra with lines of complex organic molecules (COMs). These protostars seem to possess a different enrichment in COMs. ...However, the statistics of COM abundance in low-mass protostars are limited by the scarcity of observations. This study introduces the Perseus ALMA Chemistry Survey (PEACHES), which aims at unbiasedly characterizing the chemistry of COMs toward the embedded (Class 0/I) protostars in the Perseus molecular cloud. Of the 50 embedded protostars surveyed, 58% of them have emission from COMs. 56%, 32%, and 40% of the protostars have CH
3
OH, CH
3
OCHO, and N-bearing COMs, respectively. The detectability of COMs depends neither on the averaged continuum brightness temperature, a proxy of the H
2
column density, nor on the bolometric luminosity and the bolometric temperature. For the protostars with detected COMs, CH
3
OH has a tight correlation with CH
3
CN, spanning more than two orders of magnitude in column densities normalized by the continuum brightness temperature, suggesting a chemical relation between CH
3
OH and CH
3
CN and a large chemical diversity in the PEACHES samples at the same time. A similar trend with more scatter is also found between all identified COMs, which hints at a common chemistry for the sources with COMs. The correlation between COMs is insensitive to the protostellar properties, such as the bolometric luminosity and the bolometric temperature. The abundance of larger COMs (CH
3
OCHO and CH
3
OCH
3
) relative to that of smaller COMs (CH
3
OH and CH
3
CN) increases with the inferred gas column density, hinting at an efficient production of complex species in denser envelopes.
Abstract
The origin of complex organic molecules (COMs) in young Class 0 protostars has been one of the major questions in astrochemistry and star formation. While COMs are thought to form on icy ...dust grains via gas-grain chemistry, observational constraints on their formation pathways have been limited to gas-phase detection. Sensitive mid-infrared spectroscopy with JWST enables unprecedented investigation of COM formation by measuring their ice absorption features. Mid-infrared emission from disks and outflows provide complementary constraints on the protostellar systems. We present an overview of JWST/Mid-Infrared Instrument (MIRI) Medium Resolution Spectroscopy (MRS) and imaging of a young Class 0 protostar, IRAS 15398−3359, and identify several major solid-state absorption features in the 4.9–28
μ
m wavelength range. These can be attributed to common ice species, such as H
2
O, CH
3
OH, NH
3
, and CH
4
, and may have contributions from more complex organic species, such as C
2
H
5
OH and CH
3
CHO. In addition to ice features, the MRS spectra show many weaker emission lines at 6–8
μ
m, which are due to warm CO gas and water vapor, possibly from a young embedded disk previously unseen. Finally, we detect emission lines from Fe
ii
, Ne
ii
, S
i
, and H
2
, tracing a bipolar jet and outflow cavities. MIRI imaging serendipitously covers the southwestern (blueshifted) outflow lobe of IRAS 15398−3359, showing four shell-like structures similar to the outflows traced by molecular emission at submillimeter wavelengths. This overview analysis highlights the vast potential of JWST/MIRI observations and previews scientific discoveries in the coming years.
Abstract
Previous observations have shown that the ≲10 au, ≳400 K hot inner disk of the archetypal accretion outburst young stellar object, FU Ori, is dominated by viscous heating. To constrain dust ...properties in this region, we have performed radio observations toward this disk using the Karl G. Jansky Very Large Array in 2020 June–July, September, and November. We also performed complementary optical photometric monitoring observations. We found that the dust thermal emission from the hot inner disk mid-plane of FU Ori has been approximately stationary and the maximum dust grain size is ≳1.6 mm in this region. If the hot inner disk of FU Ori, which is inward of the 150–170 K water snowline, is turbulent (e.g., corresponding to a Sunyaev & Shakura viscous
α
t
≳ 0.1), or if the actual maximum grain size is still larger than the lower limit we presently constrain, then as suggested by the recent analytical calculations and the laboratory measurements, water-ice-free dust grains may be stickier than water-ice-coated dust grains in protoplanetary disks. Additionally, we find that the free–free emission and the Johnson
B-
and
V
-band magnitudes of these binary stars were brightening in 2016–2020. The optical and radio variability might be related to the dynamically evolving protostellar- or disk-accretion activities. Our results highlight that the hot inner disks of outbursting objects are important laboratories for testing models of dust grain growth. Given the active nature of such systems, to robustly diagnose the maximum dust grain sizes, it is important to carry out coordinated multiwavelength radio observations.
Models of Rotating Infall for the B335 Protostar Evans II, Neal J.; Yang, Yao-Lun; Green, Joel D. ...
Astrophysical journal/The Astrophysical journal,
02/2023, Volume:
943, Issue:
2
Journal Article
Peer reviewed
Open access
Abstract
Models of the protostellar source, B335, are developed using axisymmetric three-dimensional models to resolve conflicts found in one-dimensional models. The models are constrained by a large ...number of observations, including ALMA, Herschel, and Spitzer data. Observations of the protostellar source B335 with ALMA show redshifted absorption against a central continuum source indicative of infall in the HCO
+
and HCN
J
= 4 → 3 transitions. The data are combined with a new estimate of the distance to provide strong constraints to three-dimensional radiative transfer models including a rotating, infalling envelope, outflow cavities, and a very small disk. The models favor ages since the initiation of collapse between 3 × 10
4
and 4 × 10
4
yr for both the continuum and the lines, resolving a conflict found in one-dimensional models. The models underpredict the continuum emission seen by ALMA, suggesting an additional component such as a pseudo-disk. The best-fitting model is used to convert variations in the 4.5
μ
m flux in recent years into a model for a variation of a factor of 5–7 in luminosity over the last 8 yr.
Cyanobacteria are model organisms for photosynthesis and are attractive for biotechnology applications. To aid investigation of genotype-phenotype relationships in cyanobacteria, we develop an ...inducible CRISPRi gene repression library in Synechocystis sp. PCC 6803, where we aim to target all genes for repression. We track the growth of all library members in multiple conditions and estimate gene fitness. The library reveals several clones with increased growth rates, and these have a common upregulation of genes related to cyclic electron flow. We challenge the library with 0.1 M L-lactate and find that repression of peroxiredoxin bcp2 increases growth rate by 49%. Transforming the library into an L-lactate-secreting Synechocystis strain and sorting top lactate producers enriches clones with sgRNAs targeting nutrient assimilation, central carbon metabolism, and cyclic electron flow. In many examples, productivity can be enhanced by repression of essential genes, which are difficult to access by transposon insertion.
The collapse of a protostellar envelope results in the growth of a protostar and the development of a protoplanetary disk, playing a critical role during the early stages of star formation. ...Characterizing the gas infall in the envelope constrains the dynamical models of star formation. We present unambiguous signatures of infall, probed by optically thick molecular lines, toward an isolated embedded protostar, BHR 71 IRS1. The three-dimensional radiative transfer calculations indicate that a slowly rotating infalling envelope model following the "inside-out" collapse reproduces the observations of both HCO + J = 4 → 3 and CS J = 7 → 6 lines, as well as the low-velocity emission of the HCN J = 4 → 3 line. The envelope has a model-derived age of 12,000 3000 yr after the initial collapse. The envelope model underestimates the high-velocity emission at the HCN J = 4 → 3 and H13CN J = 4 → 3 lines, where outflows or a Keplerian disk may contribute. The ALMA observations serendipitously discover the emission of complex organic molecules (COMs) concentrated within a radius of 100 au, indicating that BHR 71 IRS1 harbors a hot corino. Eight species of COMs are identified, including CH3OH and CH3OCHO, along with H2CS, SO2 and HCN v2 = 1. The emission of methyl formate and 13C-methanol shows a clear velocity gradient within a radius of 50 au, hinting at an unresolved Keplerian rotating disk.
Abstract
In protostellar cores, sulfur species are effective probes for the energetic environments, such as shocked regions. With the majority of sulfur depleted on dust grains, sulfur-bearing ...molecules could be liberated back to gas phase by shocks associated with accretion and outflow activities. Therefore, the gas-phase abundance of these molecules may be correlated to the change of dust properties, which can be investigated through polarization observations. Here we present a comparison study of sulfur species and dust polarization at ∼100 au scale for nine protostars in the Perseus Molecular Cloud. Overall, the emission of sulfur-bearing molecules correlates with the high and disordered polarization in the extended continuum of eight sources, indicating intense physical conditions (e.g., high temperature) and/or change of dust properties within these regions, while no clear correlation is seen for Per-emb-14. For the more evolved sources with clear disk structures (Per-emb-50 and −18), the enhanced SO/SO
2
emission overlaps with the stark contrast of polarization in the shocked regions near the centrifugal barriers. In the six sources with more extended CS and SO emission, such as Per-emb-11 and -5, the polarization enhancement correlates with the outer edge of outflow cavities and other filaments probed by sulfur-bearing molecules, revealing soft shocks along the outflows and envelopes. Such comparison studies could provide additional diagnostics of the physical properties and activities in star-forming processes, especially for the shocked regions.
Abstract
Understanding the chemical past of our Sun and how life appeared on Earth is no mean feat. The best strategy we can adopt is to study newborn stars located in an environment similar to the ...one in which our Sun was born and assess their chemical content. In particular, hot corinos are prime targets because recent studies have shown correlations between interstellar complex organic molecules abundances from hot corinos and comets. The ORion ALMA New GEneration Survey aims to assess the number of hot corinos in the closest and best analog to our Sun’s birth environment, the OMC-2/3 filament. In this context, we investigated the chemical nature of 19 solar-mass protostars and found that 26% of our sample sources show warm methanol emission indicative of hot corinos. Compared to the Perseus low-mass star-forming region, where the PErseus ALMA CHEmistry Survey detected hot corinos in ∼60% of the sources, the hot corinos seem to be relatively scarce in the OMC-2/3 filament. While this suggests that the chemical nature of protostars in Orion and Perseus is different, improved statistics is needed in order to consolidate this result. If the two regions are truly different, this would indicate that the environment is likely playing a role in shaping the chemical composition of protostars.
Isolated Massive Star Formation in G28.20-0.05 Law, Chi-Yan; Tan, Jonathan C.; Gorai, Prasanta ...
Astrophysical journal/The Astrophysical journal,
11/2022, Volume:
939, Issue:
2
Journal Article
Peer reviewed
Open access
Abstract
We report high-resolution 1.3 mm continuum and molecular line observations of the massive protostar G28.20-0.05 with Atacama Large Millimeter/submillimeter Array. The continuum image reveals ...a ring-like structure with 2000 au radius, similar to morphology seen in archival 1.3 cm Very Large Array observations. Based on its spectral index and associated H30
α
emission, this structure mainly traces ionized gas. However, there is evidence for ∼30
M
⊙
of dusty gas near the main millimeter continuum peak on one side of the ring, as well as in adjacent regions within 3000 au. A virial analysis on scales of ∼2000 au from hot core line emission yields a dynamical mass of ∼80
M
⊙
. A strong velocity gradient in the H30
α
emission is evidence for a rotating, ionized disk wind, which drives a larger-scale molecular outflow. An infrared spectral energy distribution (SED) analysis indicates a current protostellar mass of
m
*
∼ 40
M
⊙
forming from a core with initial mass
M
c
∼ 300
M
⊙
in a clump with mass surface density of Σ
cl
∼ 0.8 g cm
−2
. Thus the SED and other properties of the system can be understood in the context of core accretion models. A structure-finding analysis on the larger-scale continuum image indicates G28.20-0.05 is forming in a relatively isolated environment, with no other concentrated sources, i.e., protostellar cores, above ∼1
M
⊙
found from ∼0.1 to 0.4 pc around the source. This implies that a massive star can form in relative isolation, and the dearth of other protostellar companions within the ∼1 pc environs is a strong constraint on massive star formation theories that predict the presence of a surrounding protocluster.
We report new Atacama Large Millimeter/submillimeter Array Band 3 (86-100 GHz; ∼80 mas angular resolution) and Band 4 (146-160 GHz; ∼50 mas angular resolution) observations of the dust continuum ...emission toward the archetypal and ongoing accretion burst young stellar object FU Ori, which simultaneously covered its companion, FU Ori S. In addition, we present near-infrared (2-2.45 m) observations of FU Ori taken with the General Relativity Analysis via VLT InTerferometrY (GRAVITY; ∼1 mas angular resolution) instrument on the Very Large Telescope Interferometer (VLTI). We find that the emission in both FU Ori and FU Ori S at (sub)millimeter and near-infrared bands is dominated by structures inward of ∼10 au radii. We detected closure phases close to zero from FU Ori with VLTI/GRAVITY, which indicate the source is approximately centrally symmetric and therefore is likely viewed nearly face-on. Our simple model to fit the GRAVITY data shows that the inner 0.4 au radii of the FU Ori disk has a triangular spectral shape at 2-2.45 m, which is consistent with the H2O and CO absorption features in a 10−4 M yr−1, viscously heated accretion disk. At larger (∼0.4-10 au) radii, our analysis shows that viscous heating may also explain the observed (sub)millimeter and centimeter spectral energy distribution when we assume a constant, ∼10−4 M yr−1 mass inflow rate in this region. This explains how the inner 0.4 au disk is replenished with mass at a modest rate, such that it neither depletes nor accumulates significant masses over its short dynamic timescale. Finally, we tentatively detect evidence of vertical dust settling in the inner 10 au of the FU Ori disk, but confirmation requires more complete spectral sampling in the centimeter bands.
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