arXiv subjects

N. Sakai

Publications and source records attributed to N. Sakai.

At least 19 recordsLinked to original sources

arXiv2026

FAUST XXXI. Grain properties and variability of three sources in GSS 30

To advance our understanding of dust properties in class 0/I young stellar objects, it is crucial to resolve their structures at multiple wavelengths and investigate how grain growth and environmental effects shape their spectral properties. We present 0.5 arcsec resolution ALMA observations of the GSS 30 complex at 1.2-3.0 mm from the FAUST large programme, achieving a linear resolution of 69 au. We analyse the dust continuum emission and perform modelling to constrain dust properties and disk structures. For IRS3, the spectral index increases radially from 2.0 at the centre to 2.5 at the disk edge, while decreasing to 1.6-1.8 along the outflow direction. The asymmetric low-alpha region towards the northeastern blueshifted lobe may result from cold outer envelope dust obscuring warmer inner regions. SED fitting suggests maximum grain sizes of tens of microns and a dust mass of 650-1510 M_earth. IRS1 is associated with an extended north-eastern structure, which may represent an outflow-disk complex, a trailing structure linked to a circumbinary disk, or a gas streamer accreting onto IRS1. The central IRS1 shows alpha < 0.8, consistent with marginally optically thick free-free emission. IRS2 displays brightness variations over 420 s, and multi-epoch comparison suggests a flare lasting tens of minutes, likely caused by magnetic activity in the protostar. Our results highlight the importance of environmental effects, including dust obscuration and streamer structures, in shaping the observed properties of young disks, and reveal millimetre variability associated with possible protostellar magnetic flares.

astro-ph.SR↗

arXiv2026

Characterizing the physical and chemical properties of the Class I protostellar system Oph-IRS 44. Binarity, infalling streamers, and accretion shocks

(Abridged) In the low-mass star formation process, theoretical models predict that material from the infalling envelope could be shocked as it encounters the outer regions of the disk. Nevertheless, only a few protostars show evidence of these shocks at the disk-envelope interface, and the main formation path of shocked-related species is still unclear. We present new ALMA observations of IRS 44, a Class I source that has previously been associated with accretion shocks, taken at high angular resolution (0.1"). We target multiple molecular transitions of CO, H2CO, and simple sulfur-bearing species. In continuum emission, the binary nature of IRS 44 is observed for the first time at sub-millimeter wavelengths. Infalling signatures are seen for the CO line and the emission peaks at the edges of the continuum emission around IRS 44 B, the same region where bright SO and SO2 emission is seen. Weak CS and H2CO emission is observed, while OCS, H2S, and H2CS transitions are not detected. IRS 44 B seems to be more embedded than IRS 44 A, indicating a non-coeval formation scenario or the rejuvenation of source B due to late infall. CO emission is tracing the outflow component at large scales, infalling envelope material at intermediate scales, and two infalling streamer candidates are identified at disk scales. Infalling streamers might produce accretion shocks when they encounter the outer regions of the infalling-rotating envelope. These shocks heat the dust and release S-bearing species as well as promoting a lukewarm chemistry in the gas phase. With the majority of carbon locked in CO, there is little free C available to form CS and H2CS in the gas, leaving an oxygen-rich environment. The high column densities of SO and SO2 might be a consequence of two processes: direct thermal desorption from dust grains and gas-phase formation due to the availability of O and S.

astro-ph.SR↗

arXiv2025

FAUST. XXVIII. High-Resolution ALMA Observations of Class 0/I Disks: Structure, Optical Depths, and Temperatures

We present high-resolution (~7.5 au) ALMA observations at 1.3 and 3 mm of 16 disks around Class 0/I protostars across multiple star-forming regions and a variety of multiplicities, showing a range of disk sizes (~2-100 au) and including circumbinary disks (CBDs) in binaries with separations <100 au. The disk properties show similarities to Class II disks, including (a) low spectral index (SI) values (alpha=2.1) that increase with disk radius, (b) 3 mm disk sizes only marginally smaller than at 1.3 mm (<10%), and (c) radial intensity profiles well described by modified self-similar profiles. We also find key differences: (i) SI values increasing with radius, but exceeding 2 only at the disk edge (ii) higher brightness temperatures Tb, in some cases higher than the predicted temperatures due to irradiation, and (iii) ~10x higher luminosity at a given size compared to the Class II disks. These results confirm significant optical depth in the observed Class 0/I disks, at both 1.3 and 3 mm, helping to explain their higher luminosities, but higher temperatures are also required for the most compact (< 40 au) disks, suggesting additional viscous heating. Considering optical depth, most disk dust masses are estimated in the range 30-900 Mearth (0.01-0.3 Msun in gas), resulting in some disks reaching marginal gravitational instability. The median location of the water iceline is ~3 au, but it can extend beyond 10-20 au for the hottest disks. CBDs exhibit lower optical depths at both wavelengths and hence higher SI values (alpha=3.0), dust masses of 100 Mearth, and beta~1.5 (2 Class 0 CBDs) and beta~1 (1 Class I CBD), suggesting substantial grain growth only in the more evolved CBD. The inferred high optical depths provide a compelling explanation for the apparent scarcity of dust substructures in the younger disks at ~ 1 mm, despite mounting evidence for early planet formation (ABRIDGED).

astro-ph.SR↗

arXiv2025

The factors that influence protostellar multiplicity II. Gas temperature and mass in Perseus with APEX

Protostellar multiplicity is a common outcome of the star formation process. To fully understand the formation and evolution of these systems, the physical parameters of the molecular gas together with the dust must be systematically characterized. Using observations of molecular gas tracers, we characterize the physical properties of cloud cores in the Perseus molecular cloud (average distance of 295 pc) at envelope scales (5000-8000 AU). We used Atacama Pathfinder EXperiment (APEX) and Nobeyama 45m Radio Observatory (NRO) observations of DCO$^+$, H$_2$CO and c-C$_3$H$_2$ in several transitions to derive the physical parameters of the gas toward 31 protostellar systems in Perseus. Gas kinetic temperature was obtained from DCO$^+$, H$_2$CO and c-C$_3$H$_2$ line ratios. Column densities and gas masses were then calculated for each species and transition. Gas kinetic temperature and gas masses were compared with bolometric luminosity, envelope dust mass, and multiplicity to search for statistically significant correlations. Gas kinetic temperature derived from DCO$^+$, H$_2$CO and c-C$_3$H$_2$ line ratios have average values of 14 K, 26 and 16 K, respectively, with a range of 10-26 K for DCO$^+$ and c-C$_3$H$_2$. The gas kinetic temperature obtained from H$_2$CO line ratios have a range of 13-82 K. Column densities of all three molecular species are on the order of 10$^{11}$ to 10$^{14}$ cm$^{-2}$, resulting in gas masses of 10$^{-11}$ to 10$^{-9}$ M$_{\odot}$. Statistical analysis of the physical parameters finds: i) similar envelope gas and dust masses for single and binary protostellar systems; ii) multiple (>2 components) protostellar systems tend to have slightly higher gas and dust masses than binaries and single protostars; iii) a continuous distribution of gas and dust masses is observed regardless of separation between components in protostellar systems.

astro-ph.GA↗

arXiv2025

FAUST XXVI. The dust opacity spectral indices of protostellar envelopes bridge the gap between interstellar medium and disks

The sub-millimetre dust opacity spectral index is a critical observable to constrain dust properties, such as the maximum grain size of an observed dust population. It has been widely measured at galactic scales and down to protoplanetary disks. However, because of observational and analytical challenges, quite a gap exists in measuring dust properties in the envelopes that feed newborn protostars and their disks. To fill this gap, we use sensitive dust continuum emission data at 1.2 and 3.1 mm from the ALMA FAUST Large Program and constrain the dust opacity millimetre spectral index around a sample of protostars. Our high-resolution data, along with a more refined methodology with respect to past efforts, allow us to disentangle disk and envelope contributions in the uv-plane, and thus measure spectral indices for the envelopes uncontaminated by the optically thick emission of the inner regions. First, we find that the young disks are small and optically thick. Secondly, we measure the dust opacity spectral index at envelope scales for n=11 sources: the beta of n=9 sources had never been constrained in the literature. We effectively double the number of sources for which the dust opacity spectral index beta has been measured at these scales. Third, combining the available literature measurements with our own (total n=18), we show how envelope spectral indices distribute between ISM-like and disk-like values, bridging the gap in the inferred dust evolution. Finally, we statistically confirm a significant correlation between beta and the mass of protostellar envelopes, previously suggested in the literature. Our findings indicate that the dust optical properties smoothly vary from the ISM, through envelopes and all the way down to disks. Multi-wavelength surveys are needed to further this study and make more general claims on dust evolution in its pathway from cloud to disks.

astro-ph.SR↗

arXiv2025

FAUST XXIV. Large dust grains in the protostellar outflow cavity walls of the Class I binary L1551 IRS5

Planet formation around young stars requires the growth of interstellar dust grains from mm-sized particles to km-sized planetesimals. Numerical simulations have shown that large ($\sim$mm-sized) grains found in the inner envelope of young protostars could be lifted from the disc via winds. However we are still lacking unambiguous evidence for large grains in protostellar winds/outflows. We investigate dust continuum emission in the envelope of the Class I binary L1551 IRS5 in the Taurus molecular cloud, aiming to identify observational signatures of grain growth, such as variations in the dust emissivity index ($\beta_{\rm mm}$). In this context, we present new, high-angular resolution (50 au), observations of thermal dust continuum emission at 1.3 mm and 3 mm in the envelope ($\sim$3000 au) of L1551 IRS5 , obtained as part of the ALMA-FAUST Large Program. We analyse dust emission along the cavity walls of the CO outflow, extended up to $\sim$1800 au. We find an H$_2$ volume density $>2\times10^5$ cm$^{-3}$, a dust mass of $\sim$58 M$_\oplus$, and $\beta_{\rm mm}$<1, implying the presence of grains $\sim$10$^3$ times larger than the typical ISM sizes. We provide the first spatially resolved observational evidence of large grains within an outflow cavity wall. Our results suggest that these grains have been transported from the inner disc to the envelope by protostellar winds and may subsequently fall back into the outer disc by gravity and/or via accretion streamers. This cycle provides longer time for grains to grow, playing a crucial role in the formation of planetesimals.

astro-ph.GA↗

arXiv2025

FAUST XXV. A potential new molecular outflow in [BHB2007] 11

During the early stages of star formation, accretion processes such as infall from the envelope and molecular streamers, and ejection of matter through winds and jets take place simultaneously. The Class 0/I binary [BHB2007] 11 shows evidence for accretion and ejection at the scales of the circumbinary disk and the inner close binary. Recent H$_2$CO observations showed two elongated structures with hints of outflowing motion almost perpendicular to the main CO outflow, which is launched from the circumbinary disk. With the aim of verifying the nature of these elongated structures, we analyze the line emission of H$^{13}$CO$^+$, CCH, c-C$_3$H$_2$ and SiO observed with ALMA within the Large Program FAUST. These molecules trace material moving at velocities close to the ambient cloud velocity. The images of H$^{13}$CO$^+$, CCH, c-C$_3$H$_2$ show the elongated structures, whose gas kinematics are consistent with outflowing motions and with rotation in the opposite sense to the main CO outflow. The derived mass loss rate from these large-scale structures is $(1.8\pm0.5)\times10^{-6}M_{\odot}\textrm{ yr}^{-1}$, in agreement with those measured in outflows driven by Class 0/I protostars. The SiO image reveals compact emission close to the binary system, with a slight elongation aligned with the larger-scale structures. This suggests that SiO is released from the sputtering of dust grains in the shocked material at the base of the potential new outflow, with a relative abundance of $\geq(0.11-2.0)\times10^{-9}$. However, higher angular and spectral resolution observations are needed to accurately estimate the outflow launching radius and its powering source. Given the location and the abundance of the SiO emission, we propose that the second outflow may be launched from inside the circumbinary disk, likely by the less massive companion, which is actively accreting material from its surroundings.

astro-ph.GA↗

arXiv2025

FAUST-XXII. Deuteration in the VLA1623-2417 protostellar hot-corinos, cavities, and streamers

The study of deuterium fractionation is a valuable tool for reconstructing our chemical history from the early prestellar stages to the formation of planets. In the context of the ALMA Large Programme FAUST, we observed formaldehyde, H$_2$CO, and its singly and doubly deuterated forms, HDCO and D$_2$CO, towards the protostellar cluster VLA1623-2417, on scales of ~ 2000 - 50 au. Formaldehyde probes the inner envelopes of the protostars VLA1623A, B, and W, the rotating cavities opened by the VLA1623A outflow, and several streamers. The HDCO and D$_2$CO emissions are observed towards VLA1623A, in its outflow cavities, and in one of the streamers. We estimate the gas temperature from the HDCO lines: T~ 125 K towards VLA1623A, indicating hot-corino emission, lower temperatures in the outflow cavities (20 - 40 K), and in the streamers ($\le15$ K). The D$_2$CO lines also trace the flattened envelope of VLA1623A, where H$_2$CO and HDCO are fainter. This may be due to D$_2$CO formation on dust grains in the cold prestellar phase, and subsequent photodesorption caused by the enhanced UV flux from two nearby B stars. We inferred the molecular deuteration: [HDCO]/[H$_2$CO] ~ 0.16, ~ 0.07 - 0.13, and ~ 0.3; [D$_2$CO]/[H$_2$CO] ~ 0.003, ~ 0.05 - 0.13, and ~ 0.03 in the hot corino, in the outflow cavities, and in the streamer, respectively. The spatial distribution of D$_2$CO, which points to formation on dust grains, and the similar values of [HDCO]/[H$_2$CO] and [D$_2$CO]/[H$_2$CO] in the components of the system, suggest that deuterium fractionation occurs at the prestellar stage and is then inherited, mostly unaltered, in the protostellar phase.

astro-ph.SR↗

arXiv2025

FAUST XX. The chemical structure and temperature profile of the IRAS 4A2 hot corino at 20-50 au

Young low-mass protostars often possess hot corinos, compact, hot and dense regions bright in interstellar Complex Organic Molecules (iCOMs). Besides of their prebiotic role, iCOMs can be used as a powerful tool to characterize the chemical and physical properties of hot corinos. Using ALMA/FAUST data we aim to explore the iCOMs emission at < 50 au scale around the Class 0 prototypical hot corino IRAS 4A2. We imaged IRAS 4A2 in six abundant, common iCOMs (CH$_3$OH, HCOOCH$_3$, CH$_3$CHO, CH$_3$CH$_2$OH, CH$_2$OHCHO, and NH$_2$CHO), and derived their emitting size. The column density and gas temperature for each species were derived at 1$\sigma$ from a multi-line analysis by applying a non-LTE approach for CH$_3$OH, and LTE population or rotational diagram analysis for the other iCOMs. Thanks to the unique estimates of the absorption from foreground millimeter dust toward IRAS 4A2, we derived for the first time unbiased gas temperatures and column densities. We resolved the IRAS 4A2 hot corino finding evidence for a chemical spatial distribution in the inner 50 au, with the outer emitting radius increasing from ~ 22-23 au for NH$_2$CHO and CH$_2$OHCHO, followed by CH$_3$CH$_2$OH (~ 27 au), CH$_3$CHO (~ 28 au), HCOOCH$_3$ (~ 36 au), and out to ~ 40 au for CH$_3$OH. Combining our estimate of the gas temperature probed by each iCOM with their beam-deconvolved emission sizes, we inferred the gas temperature profile of the hot corino on scales of 20-50 au in radius, finding a power-law index $q$ of approximately -1. We observed, for the first time, a chemical segregation in iCOMs of the IRAS 4A2 hot corino, and derived the gas temperature profile of its inner envelope. The derived profile is steeper than when considering a simple spherical collapsing and optically-thin envelope, hinting at a partially optically-thick envelope or a gravitationally unstable disk-like structure.

astro-ph.EP↗

arXiv2024

FAUST. XVIII. Evidence for annular substructure in a very young Class 0 disk

When the planet formation process begins in the disks surrounding young stars is still an open question. Annular substructures such as rings and gaps in disks are intertwined with planet formation, and thus their presence or absence is commonly used to investigate the onset of this process. Current observations show a limited number of disks surrounding protostars exhibiting annular substructures, all of them in the Class I stage. The lack of observed features in most of these sources may indicate a late emergence of substructures, but it could also be an artifact of these disks being optically thick. To mitigate the problem of optical depth, we investigate substructures within a very young Class 0 disk characterized by a low inclination using observations at longer wavelengths. We use 3 mm ALMA observations tracing dust emission at a resolution of 7 au to search for evidence of annular substructures in the disk around the deeply embedded Class 0 protostar Oph A SM1. The observations reveal a nearly face-on disk (i$\sim$16$^{\circ}$) extending up to 40 au. The radial intensity profile shows a clear deviation from a smooth profile near 30 au, which we interpret as the presence of either a gap at 28 au or a ring at 34 au with Gaussian widths of $σ=1.4^{+2.3}_{-1.2}$ au and $σ=3.9^{+2.0}_{-1.9}$ au, respectively. The 3 mm emission at the location of the possible gap or ring is determined to be optically thin, precluding the possibility that this feature in the intensity profile is due to the emission being optically thick. Annular substructures resembling those in the more evolved Class I and II disks could indeed be present in the Class 0 stage, earlier than previous observations suggested. Similar observations of embedded disks in which the high optical depth problem can be mitigated are clearly needed to better constrain the onset of substructures in the embedded stages.

astro-ph.SR↗

arXiv2024

The factors that influence protostellar multiplicity I: Gas temperature, density, and mass in Perseus with Nobeyama

Protostellar multiplicity is common at all stages and mass ranges. However, the factors that determine the multiplicity of protostellar systems have not been systematically characterized through their molecular gas. Nobeyama 45m Radio Observatory OTF maps of HCN, HNC, HCO$^+$, and N$_2$H$^+$ (J = 1--0) toward five subregions in Perseus, complemented with single pointing APEX observations of HNC (J = 4--3) are used to derive physical parameters of the dense gas. Both observations have angular resolutions of $\sim$18", equivalent to $\sim$5000 AU scales at the distance of Perseus. Kinetic gas temperature is derived from the $I$(HCN)/$I$(HNC) J = 1--0 ratio, and H$_2$ density is obtained from the HNC J=4--3/J=1--0 ratio. These parameters are used to obtain the N$_2$H$^+$ and HCO$^+$ gas masses. The inferred and derived parameters are compared to source parameters. Inferred mean kinetic gas temperature ($I$(HCN)/$I$(HNC) J=1--0 ratio; ranging between 15 and 26 K), and H$_2$ volumetric density (HNC J=4--3/J=1--0; 10$^5$ -- 10$^6$ cm$^{-3}$) do not show correlations with multiplicity in Perseus. The derived gas and dust masses, 1.3 to 16 $\times~10^{-9}$ M$_{\odot}$ for the N$_2$H$^+$ gas mass, 0.1 to 25 M$_{\odot}$ for envelope dust masses (850 $\mu$m), and 0.8 to 10 $\times~10^{-10}$ M$_{\odot}$ for the HCO$^+$ gas mass, are correlated to multiplicity and number of protostellar components. The warm gas masses are a factor of 16 lower than the cold gas masses. This work shows that gas and dust mass is correlated to multiplicity at $\sim$5000 AU scales in Perseus. Higher order multiples tend to have higher gas and dust masses in general, while close binaries (separations $\leq$7") and single protostars have similar gas and dust mass distributions. On the other hand, H$_2$ density and kinetic gas temperature do not show any correlation with multiplicity.

astro-ph.GA↗

arXiv2024

FAUST XVII: Super deuteration in the planet forming system IRS 63 where the streamer strikes the disk

Recent observations suggest that planets formation starts early, in protostellar disks of $\le10^5$ yrs, which are characterized by strong interactions with the environment, e.g., through accretion streamers and molecular outflows. To investigate the impact of such phenomena on disk physical and chemical properties it is key to understand what chemistry planets inherit from their natal environment. In the context of the ALMA Large Program Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars (FAUST), we present observations on scales from ~1500 au to ~60 au of H$_2$CO, HDCO, and D$_2$CO towards the young planet-forming disk IRS~63. H$_2$CO probes the gas in the disk as well as in a large scale streamer (~1500 au) impacting onto the South-East (SE) disk side. We detect for the first time deuterated formaldehyde, HDCO and D$_2$CO, in a planet-forming disk, and HDCO in the streamer that is feeding it. This allows us to estimate the deuterium fractionation of H$_2$CO in the disk: [HDCO]/[H$_2$CO]$\sim0.1-0.3$ and [D$_2$CO]/[H$_2$CO]$\sim0.1$. Interestingly, while HDCO follows the H$_2$CO distribution in the disk and in the streamer, the distribution of D$_2$CO is highly asymmetric, with a peak of the emission (and [D]/[H] ratio) in the SE disk side, where the streamer crashes onto the disk. In addition, D$_2$CO is detected in two spots along the blue- and red-shifted outflow. This suggests that: (i) in the disk, HDCO formation is dominated by gas-phase reactions similarly to H$_2$CO, while (ii) D$_2$CO was mainly formed on the grain mantles during the prestellar phase and/or in the disk itself, and is at present released in the gas-phase in the shocks driven by the streamer and the outflow. These findings testify on the key role of streamers in the build-up of the disk both concerning the final mass available for planet formation and its chemical composition.

astro-ph.EP↗

arXiv2024

FAUST XV. A disk wind mapped by CH$_3$OH and SiO in the inner 300 au of the NGC 1333 IRAS 4A2 protostar

Context. Understanding the connection between outflows, winds, accretion and disks in the inner protostellar regions is crucial for comprehending star and planet formation process. Aims. We aim to we explore the inner 300 au of the protostar IRAS 4A2 as part of the ALMA FAUST Large Program. Methods. We analysed the kinematical structures of SiO and CH$_3$OH emission with 50 au resolution. Results. The emission arises from three zones: i) a very compact and unresolved region ($<$50 au) dominated by the ice sublimation zone, at $\pm$1.5 km s$^{-1}$ with respect to vsys, traced by methanol; ii) an intermediate region (between 50 au and 150 au) traced by both SiO and CH$_3$OH, between 2 and 6 km s$^{-1}$ with respect to vsys, with an inverted velocity gradient (with respect to the large scale emission), whose origin is not clear; iii) an extended region ($>$150 au) traced by SiO, above 7 km s$^{-1}$ with respect to vsys, and dominated by the outflow. In the intermediate region we estimated a CH$_3$OH/SiO abundance ratio of about 120-400 and a SiO/H$_2$ abundance of 10$^{-8}$. We explored various possibilities to explain the origin of this region such as, rotating disk/inner envelope, jet on the plane of the sky/precessing, wide angle disk wind. Conclusions. We propose that CH$_3$OH and SiO in the inner 100 au probe the base of a wide-angle disk wind. The material accelerated in the wind crosses the plane of the sky, giving rise to the observed inverted velocity gradient, and sputtering the grain mantles and cores releasing CH$_3$OH and SiO. This is the first detection of a disk wind candidate in SiO, and the second ever in CH$_3$OH.

astro-ph.SR↗

arXiv2024

FAUST XIII. Dusty cavity and molecular shock driven by IRS7B in the Corona Australis cluster

The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH$_3$OH, H$_2$CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Methanol emission reveals an arc-like structure at $\sim$1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H$_2$CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H$_2$ column density of $\sim$7$\times$10$^{21}$ cm$^{-2}$, a mass of $\sim$9$\times$10$^{-3}$ M$_\odot$, and a lower limit on the dust spectral index of $1.4$. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues.

astro-ph.GA↗

arXiv2024

FAUST XI: Enhancement of the complex organic material in the shocked matter surrounding the [BHB2007] 11 protobinary system

iCOMs are species commonly found in the interstellar medium. They are believed to be crucial seed species for the build-up of chemical complexity in star forming regions as well as our own Solar System. Thus, understanding how their abundances evolve during the star formation process and whether it enriches the emerging planetary system is of paramount importance. We use data from the ALMA Large Program FAUST to study the compact line emission towards the [BHB2007] 11 proto-binary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disk has previously been detected. More than 45 CH3OCHO lines are clearly detected, as well as 8 CH3OCH3 transitions , 1 H2CCO transition and 4 t-HCOOH transitions. We compute the abundance ratios with respect to CH3OH for CH3OCHO, CH3OCH3, H2CCO, t-HCOOH (as well as an upper limit for CH3CHO) through a radiative transfer analysis. We also report the upper limits on the column densities of nitrogen bearing iCOMs, N(C2H5CN) and N(C2H3CN). The emission from the detected iCOMs and their precursors is compact and encompasses both protostars, which are separated by only 0.2" (~ 28 au). The integrated intensities tend to align with the Southern filament, revealed by the high spatial resolution observations of the dust emission at 1.3 mm. A PV and 2D analysis are performed on the strongest and uncontaminated CH3OCH3 transition and show three different spatial and velocity regions, two of them being close to 11B (Southern filament) and the third one near 11A. All our observations suggest that the detected methanol, as well as the other iCOMs, are generated by the shocked gas from the incoming filaments streaming towards [BHB2007] 11A and 11B, respectively, making this source one of the few where chemical enrichment of the gas caused by the streaming material is observed.

astro-ph.SR↗

arXiv2024

FAUST XII. Accretion streamers and jets in the VLA 1623--2417 protocluster

The ALMA interferometer has played a key role in revealing a new component of the Sun-like star forming process: the molecular streamers, i.e. structures up to thousands of au long funneling material non-axisymmetrically to disks. In the context of the FAUST ALMA LP, the archetypical VLA1623-2417 protostellar cluster has been imaged at 1.3 mm in the SO(5$_6$--4$_5$), SO(6$_6$--5$_5$), and SiO(5--4) line emission at the spatial resolution of 50 au. We detect extended SO emission, peaking towards the A and B protostars. Emission blue-shifted down to 6.6 km s$^{-1}$ reveals for the first time a long ($\sim$ 2000 au) accelerating streamer plausibly feeding the VLA1623 B protostar. Using SO, we derive for the first time an estimate of the excitation temperature of an accreting streamer: 33$\pm$9 K. The SO column density is $\sim$ 10$^{14}$ cm$^{-2}$, and the SO/H$_2$ abundance ratio is $\sim$ 10$^{-8}$. The total mass of the streamer is 3 $\times$ 10$^{-3}$ $Msun$, while its accretion rate is 3--5 $\times$ 10$^{-7}$ Msun yr$^{-1}$. This is close to the mass accretion rate of VLA1623 B, in the 0.6--3 $\times$ 10$^{-7}$ Msun yr$^{-1}$ range, showing the importance of the streamer in contributing to the mass of protostellar disks. The highest blue- and red-shifted SO velocities behave as the SiO(5--4) emission, the latter species detected for the first time in VLA1623-2417: the emission is compact (100-200 au), and associated only with the B protostar. The SO excitation temperature is $\sim$ 100 K, supporting the occurrence of shocks associated with the jet, traced by SiO.

astro-ph.SR↗

arXiv2023

FAUST IX. Multi-band, multi-scale dust study of L1527 IRS. Evidence for dust properties variations within the envelope of a Class 0/I YSO

Early dust grain growth in protostellar envelopes infalling on young discs has been suggested in recent studies, supporting the hypothesis that dust particles start to agglomerate already during the Class 0/I phase of young stellar objects (YSOs). If this early evolution were confirmed, it would impact the usually assumed initial conditions of planet formation, where only particles with sizes $\lesssim 0.25 μ$m are usually considered for protostellar envelopes. We aim to determine the maximum grain size of the dust population in the envelope of the Class 0/I protostar L1527 IRS, located in the Taurus star-forming region (140 pc). We use Atacama Large millimetre/sub-millimetre Array (ALMA) and Atacama Compact Array (ACA) archival data and present new observations, in an effort to both enhance the signal-to-noise ratio of the faint extended continuum emission and properly account for the compact emission from the inner disc. Using observations performed in four wavelength bands and extending the spatial range of previous studies, we aim to place tight constraints on the spectral ($α$) and dust emissivity ($β$) indices in the envelope of L1527 IRS. We find a rather flat $α\sim$ 3.0 profile in the range 50-2000 au. Accounting for the envelope temperature profile, we derive values for the dust emissivity index, 0.9 < $β$ < 1.6, and reveal a tentative, positive outward gradient. This could be interpreted as a distribution of mainly ISM-like grains at 2000 au, gradually progressing to (sub-)millimetre-sized dust grains in the inner envelope, where at R=300 au, $β$ = 1.1 +/- 0.1. Our study supports a variation of the dust properties in the envelope of L1527 IRS. We discuss how this can be the result of in-situ grain growth, dust differential collapse from the parent core, or upward transport of disc large grains.

astro-ph.SR↗

arXiv2023

The Perseus ALMA Chemical Survey (PEACHES). III. Sulfur-bearing species tracing accretion and ejection processes in young protostars

(Abridged) Sulfur chemistry is poorly understood in the process of low-mass star and planet formation, where the main carriers of sulfur are still unknown. Despite the fact that simple S-bearing molecules are usually detected toward embedded sources, large surveys of S-bearing molecules with high angular resolution and sensitive observations are currently lacking. The goal of this work is to present an unbiased survey of simple sulfur-bearing species in protostars and provide new statistics. In addition, we investigate the role of S-bearing molecules in accretion processes and the connection between (non-)detection of complex organic molecules (COMs) and S-related species. We present the observations of sulfur-bearing species that are part of the Perseus ALMA Chemical Survey (PEACHES). We analyzed a total of 50 Class 0/I sources with an average angular resolution of about 0.6" (~180 au) in ALMA band 6. We present detection rates for CS, SO, 34SO, and SO2. The SO/34SO ratio is lower than the canonical value of 22 and the lowest values are found for those sources rich in COMs. This ratio, therefore, seems to be a good tracer of the inner high-density envelope. The detection of multiple COMs seems to be related to the presence of collimated outflows and SO2 emission seems to trace the warm gas in those sources where CH3OH is also detected. The SO2 abundances toward the PEACHES sample are, on average, two orders of magnitude lower than values from the Ophiuchus star-forming region and comparable with sources in Taurus, suggesting that the sulfur depletion in the gas-phase could depend on the external UV radiation. Finally, the SO2 emission detected in different evolutionary stages seems to arise from different physical mechanisms: high column density of warm material in Class 0 sources, shocks in Class I/II, and exposure to UV radiation from the protostar in more evolved Class II disks.

astro-ph.SR↗