IRAS 4B Research Articles

Tracking the Ice Mantle History in the Solar-type Protostars of NGC 1333 IRAS 4

To understand the origin of the diversity observed in exoplanetary systems, it is crucial to characterize the early stages of their formation, represented by solar-type protostars. Likely, the gaseous chemical content of these objects directly depends on the composition of the dust-grain mantles formed before the collapse. Directly retrieving the ice mantle composition is challenging, but it can be done indirectly by observing the major components, such as NH3 and CH3OH at centimeter wavelengths, once they are released into the gas phase during the warm protostellar stage. We observed several CH3OH and NH3 lines toward three Class 0 protostars in NGC 1333 (IRAS 4A1, IRAS 4A2, and IRAS 4B), at high angular resolution (1″; ∼300 au) with the VLA interferometer at 24–26 GHz. Using a non-LTE LVG analysis, we derived a similar NH3/CH3OH abundance ratio in the three protostars (≤0.5, 0.015–0.5, and 0.003–0.3 for IRAS 4A1, 4A2, and 4B, respectively). Hence, we infer they were born from precollapse material with similar physical conditions. Comparing the observed abundance ratios with astrochemical model predictions, we constrained the dust temperature at the time of the mantle formation to be ∼17 K, which coincides with the average temperature of the southern NGC 1333 diffuse cloud. We suggest that a brutal event started the collapse that eventually formed IRAS 4A1, 4A2, and 4B, which, therefore, did not experience the usual prestellar core phase. This event could be the clash of a bubble with NGC 1333 South, which has previously been evoked in the literature.

Erratum: “The JCMT BISTRO Survey: Magnetic Fields Associated with a Network of Filaments in NGC 1333” (2020, ApJ, 899, 28)

In the published article, we presented high-resolution polarimetry data obtained by using JCMT SCUBA-2/POL-2, and compared them with the larger-scale magnetic structure observed by Planck (Planck Collaboration et al. 2020). There was a miscalculation in the analysis of the Planck data for comparison, and the mean position angle of the Planck magnetic field should be corrected from -40° ± 7° to -48° ± 6°. Thus, we replace the descriptions in the published article as follows. In Section 4.2, paragraph 3, the second sentence should read: differences between the orientations of IRAS 4A, IRAS 4B, and IRAS 2A are not statistically significant, but they do show significantly different orientations from those of the global B-field observed by Planck (-48° ± 6°; Section 4.1). In Section 4.1, paragraph 3, the second line should read: Planck B-field orientation shows a smoothly and slowly varying field distribution with a position angle of -48° ± 6° in our observed NGC 1333 area. Accordingly, we replace Figures 4, 5, 9, 10, and 17 to reflect the correct Planck data. As described above, this error of modest magnitude is related only to our derivation of the Planck polarization angle, and the JCMT observation results are unaffected. Therefore, all conclusions drawn in the published article are unchanged even after the above correction is applied. The 1 pc scale magnetic field observed by Planck shows a smooth distribution, and the interstellar magnetic field in molecular clouds increases the complexity significantly on the scale of less than 1 pc.

The prebiotic molecular inventory of Serpens SMM1

Aims. Methyl isocyanate (CH3NCO) and glycolonitrile (HOCH2CN) are isomers and prebiotic molecules that are involved in the formation of peptide structures and the nucleobase adenine, respectively. These two species are investigated to study the interstellar chemistry of cyanides (CN) and isocyanates (NCO) and to gain insight into the reservoir of interstellar prebiotic molecules. Methods. ALMA observations of the intermediate-mass Class 0 protostar Serpens SMM1-a and ALMA-PILS data of the low-mass Class 0 protostar IRAS 16293B are used. Spectra are analysed with the CASSIS line analysis software package in order to identify and characterise molecules. Results. CH3NCO, HOCH2CN, and various other molecules are detected towards SMM1-a. HOCH2CN is identified in the PILS data towards IRAS 16293B in a spectrum extracted at a half-beam offset position from the peak continuum. CH3NCO and HOCH2CN are equally abundant in SMM1-a at [X]/[CH3OH] of 5.3 × 10−4 and 6.2 × 10−4, respectively. A comparison between SMM1-a and IRAS 16293B shows that HOCH2CN and HNCO are more abundant in the former source, but CH3NCO abundances do not differ significantly. Data from other sources are used to show that the [CH3NCO]/[HNCO] ratio is similar in all these sources within ~10%. Conclusions. The new detections of CH3NCO and HOCH2CN are additional evidence for a large interstellar reservoir of prebiotic molecules that can contribute to the formation of biomolecules on planets. The equal abundances of these molecules in SMM1-a indicate that their formation is driven by kinetic processes instead of thermodynamic equilibrium, which would drive the chemistry to one product. HOCH2CN is found to be much more abundant in SMM1-a than in IRAS 16293B. From the observational data, it is difficult to indicate a formation pathway for HOCH2CN, but the thermal Strecker-like reaction of CN− with H2CO is a possibility. The similar [CH3NCO]/[HNCO] ratios found in the available sample of studied interstellar sources indicate that these two species are either chemically related or their formation is affected by physical conditions in the same way. Both species likely form early during star formation, presumably via ice mantle reactions taking place in the dark cloud or when ice mantles are being heated in the hot core. The relatively high abundances of HOCH2CN and HNCO in SMM1-a may be explained by a prolonged stage of relatively warm ice mantles, where thermal and energetic processing of HCN in the ice results in the efficient formation of both species.

The ALMA-PILS survey: first detection of the unsaturated 3-carbon molecules Propenal (C2H3CHO) and Propylene (C3H6) towards IRAS 16293–2422 B

Context.Complex organic molecules with three carbon atoms are found in the earliest stages of star formation. In particular, propenal (C2H3CHO) is a species of interest due to its implication in the formation of more complex species and even biotic molecules.Aims.This study aims to search for the presence of C2H3CHO and other three-carbon species such as propylene (C3H6) in the hot corino region of the low-mass protostellar binary IRAS 16293–2422 to understand their formation pathways.Methods.We use ALMA observations in Band 6 and 7 from various surveys to search for the presence of C3H6and C2H3CHO towards the protostar IRAS 16293–2422 B (IRAS 16293B). The identification of the species and the estimates of the column densities and excitation temperatures are carried out by modeling the observed spectrum under the assumption of local thermodynamical equilibrium.Results.We report the detection of both C3H6and C2H3CHO towards IRAS 16293B, however, no unblended lines were found towards the other component of the binary system, IRAS 16293A. We derive column density upper limits for C3H8, HCCCHO,n-C3H7OH,i-C3H7OH, C3O, and cis-HC(O)CHO towards IRAS 16293B. We then use a three-phase chemical model to simulate the formation of these species in a typical prestellar environment followed by its hydrodynamical collapse until the birth of the central protostar. Different formation paths, such as successive hydrogenation and radical-radical additions on grain surfaces, are tested and compared to the observational results in a number of different simulations, to assess which are the dominant formation mechanisms in the most embedded region of the protostar.Conclusions.The simulations reproduce the abundances within one order of magnitude from those observed towards IRAS 16293B, with the best agreement found for a rate of 10−12cm3s−1for the gas-phase reaction C3+ O → C2+ CO. Successive hydrogenations of C3, HC(O)CHO, and CH3OCHO on grain surfaces are a major and crucial formation route of complex organics molecules, whereas both successive hydrogenation pathways and radical-radical addition reactions contribute to the formation of C2H5CHO.

Constraints of the Formation and Abundances of Methyl Carbamate, a Glycine Isomer, in Hot Corinos

Abstract Methyl carbamate CH3OC(O)NH2 is an isomer of glycine. Quantum chemical analyses show that methyl carbamate is a more stable isomer than glycine. Because of this, there could be a higher chance for methyl carbamate to exist in the interstellar medium (ISM) as compared to glycine. Despite immense searches, until now glycine has not been detected in the ISM; therefore, it is worthwhile to search its isomer methyl carbamate. In this paper, we present the constraints of methyl carbamate formation under the interstellar conditions. Large complex organic molecules are favorably produced in hot-corino environments of low-mass protostars. We for the first time carried out astrochemical modeling focusing on the formation of methyl carbamate in physical conditions similar to hot-corino objects. Consequently, we examined ALMA archival data for existing spectral line observations toward hot corinos NGC 1333 IRAS 4A2 and IRAS 16293B. Within the common spectral range toward these sources, we found three features are possibly related to the spectral transitions of methyl carbamate and consequently estimate the upper limit of column densities. Results of chemical modeling are consistent with the observational upper limit of estimated column density/abundance toward the sources. This may hint the validation of the proposed formation mechanism. Future observations using a telescope like ngVLA may confirm the presence of MC toward the hot corinos.

Probing the temperature structure of optically thick discs using polarized emission of aligned grains

ABSTRACT Polarized continuum emission from aligned grains in discs around young stellar objects can be used to probe the magnetic field, radiation anisotropy, or drift between dust and gas, depending on whether the non-spherical grains are aligned magnetically, radiatively, or mechanically. We show that it can also be used to probe another key disc property – the temperature gradient – along sightlines that are optically thick, independent of the grain alignment mechanism. We first illustrate the technique analytically using a simple 1D slab model, which yields an approximate formula that relates the polarization fraction to the temperature gradient with respect to the optical depth τ at the τ = 1 surface. The formula is then validated using models of stellar irradiated discs with and without accretion heating. The promises and challenges of the technique are illustrated with a number of Class 0 and I discs with ALMA dust polarization data, including NGC 1333 IRAS4A1, IRAS 16293B, BHB 07-11, L1527, HH 212, and HH 111. We find, in particular, that the sightlines passing through the near-side of a highly inclined disc trace different temperature gradient directions than those through the far-side, which can lead to a polarization orientation on the near-side that is orthogonal to that on the far-side, and that the HH 111 disc may be such a case. Our technique for probing the disc temperature gradient through dust polarization can complement other methods, particularly those using molecular lines.

The ALMA-PILS survey: propyne (CH3CCH) in IRAS 16293–2422

Context. Propyne (CH3CCH), also known as methyl acetylene, has been detected in a variety of environments, from Galactic star-forming regions to extragalactic sources. These molecules are excellent tracers of the physical conditions in star-forming regions, allowing the temperature and density conditions surrounding a forming star to be determined. Aims. This study explores the emission of CH3CCH in the low-mass protostellar binary, IRAS 16293–2422, and examines the spatial scales traced by this molecule, as well as its formation and destruction pathways. Methods. Atacama Large Millimeter/submillimeter Array (ALMA) observations from the Protostellar Interferometric Line Survey (PILS) were used to determine the abundances and excitation temperatures of CH3CCH towards both protostars. This data allows us to explore spatial scales from 70 to 2400 au. This data is also compared with the three-phase chemical kinetics model MAGICKAL, to explore the chemical reactions of this molecule. Results. CH3CCH is detected towards both IRAS 16293A and IRAS 16293B, and is found the hot corino components, one around each source, in the PILS dataset. Eighteen transitions above 3σ are detected, enabling robust excitation temperatures and column densities to be determined in each source. In IRAS 16293A, an excitation temperature of 90 K and a column density of 7.8 × 1015 cm−2 best fits the spectra. In IRAS 16293B, an excitation temperature of 100 K and 6.8 × 1015 cm−2 best fits the spectra. The chemical modelling finds that in order to reproduce the observed abundances, both gas-phase and grain-surface reactions are needed. The gas-phase reactions are particularly sensitive to the temperature at which CH4 desorbs from the grains. Conclusions. CH3CCH is a molecule whose brightness and abundance in many different regions can be utilised to provide a benchmark of molecular variation with the physical properties of star-forming regions. It is essential when making such comparisons, that the abundances are determined with a good understanding of the spatial scale of the emitting region, to ensure that accurate abundances are derived.

Synthesis of solid-state complex organic molecules through accretion of simple species at low temperatures

AbstractComplex organic molecules (COMs) have been detected in the gas-phase in cold and lightless molecular cores. Recent solid-state laboratory experiments have provided strong evidence that COMs can be formed on icy grains through ‘non-energetic’ processes. In this contribution, we show that propanal and 1-propanol can be formed in this way at the low temperature of 10 K. Propanal has already been detected in space. 1-propanol is an astrobiologically relevant molecule, as it is a primary alcohol, and has not been astronomically detected. Propanal is the major product formed in the C2H2 + CO + H experiment, and 1-propanol is detected in the subsequent propanal + H experiment. ALMA observations towards IRAS 16293-2422B are discussed and provide a 1-propanol:propanal upper limit of < 0.35–0.55, which are complemented by computationally-derived activation barriers in addition to the performed laboratory experiments.

Dust Polarization toward Embedded Protostars in Ophiuchus with ALMA. II. IRAS 16293-2422

Abstract We present high-resolution (∼35 au) ALMA Band 6 1.3 mm dust polarization observations of IRAS 16293. These observations spatially resolve the dust polarization across the two protostellar sources and toward the filamentary structures between them. The dust polarization and inferred magnetic field have complicated structures throughout the region. In particular, we find that the magnetic field is aligned parallel to three filamentary structures. We characterize the physical properties of the filamentary structure that bridges IRAS 16293A and IRAS 16293B and estimate a magnetic field strength of 23–78 mG using the Davis-Chandrasekhar-Fermi method. We construct a toy model for the bridge material assuming that the young stars dominate the mass and gravitational potential of the system. We find that the expected gas flow to each star is of comparable order to the Alfvén speed, which suggests that the field may be regulating the gas flow. We also find that the bridging material should be depleted in ∼103 yr. If the bridge is part of the natal filament that formed the stars, then it must have accreted new material. Alternatively, the bridge could be a transient structure. Finally, we show that the 1.3 mm polarization morphology of the optically thick IRAS 16293B system is qualitatively similar to dust self-scattering. Based on similar polarization measurements at 6.9 mm, we propose that IRAS 16293B has produced a substantial population of large dust grains with sizes between 200 and 2000 μm.

The ALMA-PILS survey: complex nitriles towards IRAS 16293–2422

Context. Complex organic molecules are readily detected in the inner regions of the gaseous envelopes of forming protostars. Their detection is crucial to understanding the chemical evolution of the Universe and exploring the link between the early stages of star formation and the formation of solar system bodies, where complex organic molecules have been found in abundance. In particular, molecules that contain nitrogen are interesting due to the role nitrogen plays in the development of life and the compact scales such molecules have been found to trace around forming protostars. Aims. The goal of this work is to determine the inventory of one family of nitrogen-bearing organic molecules, complex nitriles (molecules with a –C≡N functional group) towards two hot corino sources in the low-mass protostellar binary IRAS 16293–2422. This work explores the abundance differences between the two sources, the isotopic ratios, and the spatial extent derived from molecules containing the nitrile functional group. Methods. Using data from the Protostellar Interferometric Line Survey (PILS) obtained with ALMA, we determine abundances and excitation temperatures for the detected nitriles. We also present a new method for determining the spatial structure of sources with high line density and large velocity gradients – Velocity-corrected INtegrated emission (VINE) maps. Results. We detect methyl cyanide (CH3CN) as well as five of its isotopologues, including CHD2CN, which is the first detection in the interstellar medium (ISM). We also detect ethyl cyanide (C2H5CN), vinyl cyanide (C2H3CN), and cyanoacetylene (HC3N). We find that abundances are similar between IRAS 16293A and IRAS 16293B on small scales except for vinyl cyanide which is only detected towards the latter source. This suggests an important difference between the sources either in their evolutionary stage or warm-up timescales. We also detect a spatially double-peaked emission for the first time in molecular emission in the A source, suggesting that this source is showing structure related to a rotating toroid of material. Conclusions. With high-resolution observations, we have been able to show for the first time a number of important similarities and differences in the nitrile chemistry in these objects. These illustrate the utility of nitriles as potential tracers of the physical conditions in star-forming regions.

Evolutionary status of dense cores in the NGC 1333 IRAS 4 star-forming region

Protostellar evolution, following the formation of the protostar is becoming reasonably well characterized, but the evolution from a prestellar core to a protostar is not well known, although the first hydrostatic core (FHSC) must be a pivotal step. NGC 1333 IRAS 4C is a potentially very young object, that we directly compare with the nearby Class 0 IRAS 4A and IRAS 4B. Observational constraints are provided by spectral imaging from the JCMT Spectral Legacy Survey (330-373 GHz) and continuum and line observations from CARMA. We present integrated intensity and velocity maps of several species, including CO, H2CO and CH3OH. The velocity of an observed outflow, the degree of CO depletion, the deuteration of DCO+/HCO+ and gas kinetic temperatures are observational signatures that we present. We report differences between the three sources in four aspects: a) the kinetic temperature is much lower towards IRAS 4C, b) the line profiles of the detected species show strong outflow activity towards IRAS 4A and IRAS 4B but not towards IRAS 4C, c) the HCN/HNC is < 1 towards IRAS 4C, which confirms the cold nature of the source, d) the degree of CO depletion and the deuteration are the lowest towards the warmest of the sources, IRAS 4B. IRAS 4C seems to be in a different evolutionary state than the IRAS 4A and IRAS 4B sources. We can probably exclude the FHSC stage due to the relatively low Lsmm/Lbol (~6\%) and we investigate the earliest accretion phase of Class 0 stage and the transition between Class 0 to Class I. Our results do not show a consistent scenario for either case, with the major issue being the absence of outflow activity and the cold nature of IRAS 4C. The number of FHSC candidates in Perseus is ~10 times higher than current models predict, which suggests that the lifespan of these objects is greater than 1000 years, possibly due to an accretion rate lower than 4x10^-5 msun/yr.

Characterizing shock waves in molecular outflow sources: the interpretation of Herschel and Spitzer observations of NGC 1333 IRAS 4B

Characterizing shock waves in molecular outflow sources: the interpretation of Herschel and Spitzer observations of NGC 1333 IRAS 4B

Herschel/HIFI observations of high-JCO lines in the NGC 1333 low-mass star-forming region

Herschel-HIFI observations of high-J lines (up to J_u=10) of 12CO, 13CO and C18O are presented toward three deeply embedded low-mass protostars, NGC 1333 IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. The spectrally-resolved HIFI data are complemented by ground-based observations of lower-J CO and isotopologue lines. The 12CO 10-9 profiles are dominated by broad (FWHM 25-30 km s^-1) emission. Radiative transfer models are used to constrain the temperature of this shocked gas to 100-200 K. Several CO and 13CO line profiles also reveal a medium-broad component (FWHM 5-10 km s^-1), seen prominently in H2O lines. Column densities for both components are presented, providing a reference for determining abundances of other molecules in the same gas. The narrow C18O 9-8 lines probe the warmer part of the quiescent envelope. Their intensities require a jump in the CO abundance at an evaporation temperature around 25 K, thus providing new direct evidence for a CO ice evaporation zone around low-mass protostars.

MAGNETIC FIELDS AND INFALL MOTIONS IN NGC 1333 IRAS 4

We present single-dish 350 μm dust continuum polarimetry as well as HCN and HCO^+ J = 4 → 3 rotational emission spectra obtained on NGC 1333 IRAS 4. The polarimetry indicates a uniform field morphology over a 20 radius from the peak continuum flux of IRAS 4A, in agreement with models of magnetically supported cloud collapse. The field morphology around IRAS 4B appears to be quite distinct, however, with indications of depolarization observed toward the peak flux of this source. Inverse P Cygni profiles are observed in the HCN J = 4 → 3 line spectra toward IRAS 4A, providing a clear indication of infall gas motions. Taken together, the evidence gathered here appears to support the scenario that IRAS 4A is a cloud core in a critical state of support against gravitational collapse.

Time‐Resolved AU‐Scale Jets Traced by Masers in the IRAS 4A/B Regions of NGC 1333

We present results of VLBI observations of the water masers associated with IRAS 4A and IRAS 4B in the NGC 1333 star-forming region taken in four epochs over a two month period. Both objects have been classified as extremely young sources, and each source is known to be a multiple system. Using the Very Long Baseline Array, we detected 35 masers in epoch I, 40 masers in epoch II, 35 in epoch III, and 24 in epoch IV. Only one identified source in each system is associated with these masers. These data are used to calculate proper motions for the masers and trace the jet outflows within 100 AU of IRAS 4A2 and IRAS 4BW. In IRAS 4A2 there are two groups of masers, one near the systemic cloud velocity and one redshifted. They expand linearly away from each other at velocities of 53 km s−1. In IRAS 4BW, masers are observed in two groups that are blueshifted and redshifted relative to the cloud velocity. They form complex linear structures with a thickness of 3 mas (1 AU at a distance of 320 pc) that expand linearly away from each other at velocities of 78 km s−1. Neither of the jet outflows traced by the maser groups align with the larger scale outflows. We suggest the presence of unresolved companions to both IRAS 4A2 and 4BW.

IRAS 16293-2422B: A Compact, Possibly Isolated Protoplanetary Disk in a Class 0 Object

Theoretical arguments suggest that protoplanetary disks around young stars should start small and grow with the addition of high angular momentum material to reach the radii of several hundred AUs that characterize the disks around optically visible T Tauri stars. Examples of much more compact disks, with radii much less than 100 AU, have been found around some very young stars, but in all cases tidal truncation from a near binary companion provides a ready explanation for the small disk size. We report here an example of a compact, possibly isolated disk around the class 0 object IRAS16293-2422B, which is thought to be among the youngest protostars known. This disk has a Gaussian half power radius of only $\sim$8 AU, and a detailed, self-consistent, accretion disk model indicates an outer radius of only 26 AU. This discovery supports the notion that protoplanetary disks start small and grow with time, although other explanations for the compact size cannot be ruled out, including gravitational instability in its outer parts and tidal truncation from the close approach of a now distant stellar companion.

High Angular Resolution Observations of Maser Kinematics Near Low Mass Young Stellar Objects

With the advent of new correlators and dedicated arrays, spectral line VLBI is entering its ascendancy as a probe of a variety of interesting astrophysical environments. One of the most interesting environments where spectroscopic VLBI techniques are valuable are the regions directly coincident with forming stars. In these sources, water maser emission is observed when the outflowing jets of material interact with the surrounding medium. Observations of these water masers dramatically reveal the innermost regions of the star formation process at or below the 1-AU scale.We have found that the water masers clearly trace the jets at these scales. The masers show space motions on the order of 60 to 100 kms−1 and form within a few AU of the exciting protostar. By observing the distributions and motions of the water masers associated with these objects, we may be able to address in greater detail the collimation mechanism of the jets seen in these protostars.In this brief poster proceeding, we provide a summary image of the water masers associated with SVS13, the driving source for the HH 7-11 objects. We have also mapped the masers associated with IRAS 16293-2422, IRAS 05413-0104, IRAS 4A and IRAS 4B, both in the NGC 1333 star forming region. For further information on these sources, please contact any of the authors directly.

NGC 1333 IRAS 4: Further Multiplicity Revealed with the CSO-JCMT Interferometer

Single-dish submillimeter continuum observations showed that IRAS 4 in the NGC 1333 region of the L1450 molecular cloud is a 30'' separation binary protostellar system. The components are designated as 4A and 4B, and are believed to be very young and deeply embedded. Our observations with the CSO-JCMT Interferometer at λ = 0.84 mm show that components 4A and 4B are both multiple systems; the visibility curve for IRAS 4A is well fitted by a 18 binary whose components are consistent in size and flux with dusty accretion disks. IRAS 4B appears to show even higher multiplicity, since it is not fitted well by either single or binary models. We conclude that IRAS 4 is a hierarchical quadruple, or higher order, embedded protostellar system.