Abstract Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations with 0 . ″ 1 resolution have revealed characteristic substructures in circumstellar disks around young Class I sources, providing clues to the early stages of morphological disk evolution. In this paper, we applied PRIISM imaging to ALMA archival Band 6 continuum data of the circumstellar disk around the Class I protostar CrA IRS 2, located in the Corona Australis molecular cloud, which is associated with an extended gas ring attributed to magnetic flux advection driven by interchange instability. The dust continuum image, with 1.5 times higher spatial resolution than conventional imaging, revealed for the first time an early-phase circumstellar disk with both inner central hole and outer ring-gap structures, making CrA IRS 2 the youngest system known to exhibit such features based on its bolometric temperature of T bol = 235 K. To examine planet–disk interaction as one possible origin of the outer ring-gap structure, we found the measured depth and width to be consistent with planet–disk interaction models, suggesting the existence of a giant planet with a mass of 0.1–1.8 M Jup . The additional mechanism required for rapid planet formation could be the magnetic flux dissipation driven by the interchange instability, which suppresses magnetorotational-instability-driven turbulence and extends the dead zone, allowing efficient dust growth and the early formation of planets. This system thus provides new insight into how substructures and planet formation can emerge during the early, accreting phase of disk evolution.

Measuring the properties of disks around Class 0/I protostars is crucial for understanding protostellar assembly and early planet formation. We present high-resolution (~7.5 au) ALMA continuum observations at 1.3 and 3 mm of 16 disks around Class 0/I protostars across multiple star-forming regions (Taurus, Ophiuchus, and Corona Australis) and a variety of multiplicities. Our observations show a wide range of deconvolved disk sizes (~2–100 au) and the presence of circumbinary disks (CBDs) in all binaries with separations <100 au. The measured properties show similarities to Class II disks, including (a) low spectral index values ( α disks = 2.1 −0.3 +0.5 ) that increase with disk radius, (b) 3 mm disk sizes only marginally smaller than at 1.3 mm (<10%), and (c) radial intensity morphologies well described by modified self-similar profiles. However, there are some key differences: (i) the α 1.3-3 mm values increase monotonically with radius but exceed two only at the disk edge; (ii) higher brightness temperatures, T b , comparable to or higher than the predicted midplane temperatures due to irradiation; and (iii) an approximately ten times higher luminosity at a given size compared to the Class II disks. Together, the results confirm significant optical depth in the observed Class 0/I disks, most with T bol < 200 K, at both 1.3 and 3 mm. Assuming fully optically thick disks at these wavelengths can explain the higher luminosities compared with Class II disks, but the most compact (≲40 au) disks also require higher temperatures, suggesting additional heating from viscous accretion. Taking into account the high optical depths, most disk dust masses are estimated in the range 30–900 M ⊕ (or 0.01–0.3 M ⊙ in gas), with some disks potentially reaching marginal gravitational instability. Based on the elevated T b 1.3 mm , the median location of the water iceline is ~3 au, but this location can extend to more than 10–20 au for the hottest disks in the sample. The CBDs exhibit lower optical depths at both wavelengths and hence higher spectral index values ( τ 3 mm ≲ 1, α CBD = 3.0 −0.3 +0.2 ), dust masses of ~10 2 M ⊕ , and dust emissivity indices of β CBD ~ 1.5 (two Class 0 CBDs) and ~1 (one Class I CBD), suggesting substantial grain growth only in the more evolved CBD. The high optical depths inferred from our analysis provide a compelling explanation for the apparent scarcity of dust substructures in the younger Class 0/I disks at ~1 mm despite the mounting evidence of early planet formation.

Abstract We present an overview of the final data release (DR2) from the Green Bank Ammonia Survey (GAS). GAS is a large program at the Green Bank Telescope to map all Gould Belt star-forming regions with A V ≳ 7 mag visible from the Northern Hemisphere in emission from NH 3 and other key molecular tracers. This final release includes the data for all the regions observed: Heiles Cloud 2 and B18 in Taurus; Barnard 1, Barnard 1-E, IC 348, NGC 1333, L1448, L1451, and Per7/34 in Perseus; L1688 and L1689 in Ophiuchus; Orion A (North and South) and Orion B in Orion; Cepheus; B59 in Pipe; Corona Australis East and West; IC 5146; and Serpens Aquila and MWC297 in Serpens. Similar to what was presented in GAS DR1, we find that the NH 3 emission and dust continuum emission from Herschel correspond closely. We find that the NH 3 emission is generally extended beyond the typical 0.1 pc length scales of dense cores, and we find that the transition between coherent core and turbulent cloud is a common result. This shows that the regions of coherence are common throughout different star-forming regions, with a substantial fraction of the high column density regions displaying subsonic nonthermal velocity dispersions. We produce maps of the gas kinematics, temperature, and NH 3 column densities through forward modeling of the hyperfine structure of the NH 3 (1,1) and (2,2) lines. We show that the NH 3 velocity dispersion, σ v , and gas kinetic temperature, T K , vary systematically between the regions included in this release, with an increase in both the mean value and spread of σ v and T K with increasing star formation activity. The data presented in this paper are publicly available via doi: 10.11570/24.0091 .

Context. Cosmic rays drive several key processes for the chemistry and dynamical evolution of star-forming regions. Their effect is quantified mainly by means of the cosmic-ray ionisation rate ζ2. Aims. We aim to obtain a sample of ζ2 measurements in 20 low-mass, starless cores embedded in different parental clouds in order to assess the average level of ionisation in this kind of source and to investigate the role of the environment in this context. The warmest clouds in our sample are Ophiuchus and Corona Australis, where star formation activity is higher than in the Taurus cloud and the other isolated cores we targeted. Methods. We computed ζ2 using an analytical method based on the column density of ortho-H2D+, the CO abundance, and the deuteration level of HCO+. To estimate these quantities, we analysed new, high-sensitivity molecular line observations obtained with the Atacama Pathfinder Experiment (APEX) single-dish telescope and archival continuum data from Herschel. Results. We report ζ2 estimates in 17 cores in our sample and provide upper limits on the three remaining sources. The values span almost two orders of magnitude, from 1.3 × 10−18 s−1 to 8.5 × 10−17 s−1. Conclusions. We find no significant correlation between ζ2 and the core’s column densities N(H2). On the contrary, we find a positive correlation between ζ2 and the core’s temperature, estimated via Herschel data: cores embedded in warmer environments present higher ionisation levels. The warmest clouds in our sample are Ophiuchus and Corona Australis, where star formation activity is higher than in the other clouds we targeted. The higher ionisation rates in these regions support the scenario that low-mass protostars in the vicinity of our targeted cores contribute to the re-acceleration of local cosmic rays.

To date, the quantification of the on-sky motion for interstellar clouds has relied on proxies such as young stellar objects (YSOs) and masers. We present the first direct measurement of an interstellar cloud proper motion using the VISTA Star Formation Atlas (VISIONS) multi-epoch infrared images of the Corona Australis star-forming region. Proper motions are extracted by tracking the morphology of extended structures in the cloud complex based on image registration techniques implemented in SimpleITK. Our determined values ( μ α * ∼ +15 mas yr −1 , μ δ ∼ −30 mas yr −1 ) are in good agreement with those obtained for YSOs and young stellar clusters in the region. This study demonstrates the potential of image registration for directly mapping the kinematics of nearby molecular clouds, opening a new window into the study of cloud dynamics.

Context. The substellar initial mass function (IMF) and the formation mechanisms of brown dwarfs (BDs) remain key open questions in star formation theory. A detailed census and characterization of the IMF in a large number of star-forming regions are essential for constraining these processes. Aims. We identify and spectroscopically confirm very low-mass members of the Corona Australis (CrA) star-forming region to refine its substellar census, determine its low-mass IMF, and compare it to other clusters. Methods. Using deep I-band photometry from Suprime-Cam/Subaru and data from the VISTA Hemisphere Survey (VHS), we identified low-mass BD candidates in CrA. We subsequently conducted near-infrared spectroscopic follow-up of 173 of these candidates with KMOS/VLT, and we also obtained optical spectra for eight kinematic candidate members identified via Gaia data using FLOYDS/LCO. Results. The kinematic candidates observed with optical spectroscopy are confirmed as low-mass stellar members with spectral types M1 to M5. In contrast, all 173 BD candidates observed with KMOS are identified as contaminants. Although the follow-up yielded no new substellar members, it places strong constraints on the number of undetected substellar objects in the region. Combined with literature data, this enables us to derive the substellar IMF, which is consistent with a single power-law slope of α = 0.95 ± 0.06 in the range 0.01–1 M⊙ or α = 0.33 ± 0.19 in the range 0.01–0.1 M⊙. The star-to-BD ratio in CrA is ∼2. We also provide updated IMFs and star-to-BD ratios for Lupus 3 and Cha I from the SONYC survey, reflecting revised distances from Gaia. Finally, we estimate surface densities and median far-ultraviolet fluxes for six star-forming regions and clusters to characterize their environments and compare their substellar populations as a function of environmental properties. Conclusions. The IMF and star-to-BD ratio show no clear dependence on stellar density or ionizing flux from the massive stars. A combined effect in which one factor enhances and the other suppresses BD formation also appears unlikely.

Abstract The viability of the star count (Wolf) method is assessed as a means of constraining the near-infrared (NIR) extinction law toward the Corona Australis molecular cloud. Using deep JHK S photometry from the VISIONS survey, extinction maps with 1′ spatial resolution are constructed. The derived extinction ratios are A J /A H = 1.73 ± 0.07, A H / A K S = 1.70 ± 0.11 , and A J / A K S = 3.02 ± 0.22 , which are consistent with Galactic literature means. Assuming a power-law form (A λ ∝ λ −α ) for the NIR extinction law, we derive indices of α ≈ 2.0 across all wavelength combinations, with no statistically significant wavelength dependence throughout the NIR wavelength range. While spatial variations in extinction properties are tentatively observed across the cloud, concerns persist regarding the impact of photometric completeness, and the role of reference field selection. Continued research is required to refine the approach, and scrutinize the veracity of potential extinction law variations over a more expansive region of sky.

Abstract To investigate the interstellar medium (ISM) and Galactic cosmic rays (CRs) in the solar neighborhood, we analyzed γ-ray data by the Fermi Large Area Telescope (LAT) for five nearby molecular cloud regions. Our data include the MBM/Pegasus (MBM 53, 54, 55 clouds and Pegasus loop), R CrA (R Coronae Australis clouds), Chamaeleon (Chamaeleon clouds), Cep/Pol (Cepheus and Polaris flare), and Orion (Orion clouds) regions. The ISM templates are constructed by a component decomposition of the 21 cm H i line, the Planck dust emission model, and the carbon monoxide (CO) 2.6 mm line. Through γ-ray data analysis the ISM gas is successfully decomposed into non-local H i, narrow-line and optically thick H i, broad-line and optically thin H i, CO-bright H2, and CO-dark H2 for all five regions. CR intensities evaluated by the γ-ray emissivity of broad H i agree well with a model based on directly measured CR spectra at the Earth, with a gradient giving a higher CR intensity toward the inner Galaxy at the 10% level in ∼500 pc. The ratio of CO-dark H2 to CO-bright H2 anticorrelates with the H2 mass traced by the CO 2.6 mm line, and reaches 5–10 for small systems of ∼1000 solar mass.

Context. Pre-stellar cores are the birthplaces of Sun-like stars and represent the initial conditions for the assembly of protoplanetary systems. Due to their short lifespans, they are rare. As part of recent efforts to increase the number of such sources identified in the solar neighbourhood, we have selected a sample of 40 starless cores from the publicly available core catalogues of the Herschel Gould Belt survey. In this work, we focus on a source that stands out for its high central density: Corona Australis 151. Aims. We used molecular lines that trace dense gas (n ≳ 106 cm−3) to confirm the exceptionally high density of this object, study its physical structure, and understand its evolutionary stage. Methods. We detected the N2H+ 3 − 2 and 5 − 4 transitions and the N2D+ 3 − 2, 4 − 3, and 6 – 5 lines with the Atacama Pathfinder EXperiment (APEX) telescope. We used the Herschel continuum data to infer a spherically symmetric model of the core’s density and temperature. This was used as input to perform a non-local-thermodynamic-equilibrium radiative transfer to fit the five observed lines. Results. Our analysis confirms that this core is characterised by very high densities (a few × 107 cm−3 at the centre) and cold temperatures (8 − 12 K). We inferred a high deuteration level of N2D+/N2H+ = 0.50, indicative of an advanced evolutionary stage. In the large bandwidth covered by the APEX data, we detected several other deuterated species, including CHD2OH, D2CO, and ND3. We also detected multiple sulphurated species that present broader lines with signs of high-velocity wings. Conclusions. High-angular resolution observations will be necessary to unveil the evolutionary stage of Cra 151. The detection of a compact emission at 70 μm does not exclude that the source is a first hydrostatic core or in a very early stage of the protostellar phase. The observation of high-velocity wings and the fact that the linewidths of N2H+ and N2D+ become larger with increasing frequency can be interpreted as either an indication of supersonic infall motions developing in the central parts of a very evolved pre-stellar core or the signature of outflows from a very low luminosity object.

The TW Hydrae Association (TWA) is a young local association (YLA) about 50 pc from the Sun, offering a unique opportunity to study star and planet formation processes in detail. We characterized TWA’s location, kinematics, and age, investigating its origin within the Scorpius-Centaurus (Sco-Cen) OB association. Using Gaia DR3 astrometric data and precise ground-based radial velocities, we identified substructures within TWA, tentatively dividing them into TWA-a and TWA-b. Sco-Cen’s massive cluster σ Cen (15 Myr, 1805 members) may have influenced TWA’s formation. The alignment of σ Cen, TWA-a, and TWA-b in 3D positions, velocities, and ages resembles patterns in regions such as Corona Australis, suggesting that TWA is part of a cluster chain from sequential star formation induced by massive stars in Sco-Cen. TWA’s elongation in the opposite direction to that produced by Galactic differential rotation indicates its shape is still influenced by its formation processes and will dissipate in less than 50 Myr due to Galactic forces. These findings unveil the nature of YLAs and low-mass clusters in a new light. We propose that clusters such as ϵ Chamaeleontis, η Chamaeleontis, and TWA were forged by stellar feedback from massive stars in Sco-Cen, while others–such as β Pictoris, Carina, Columba, and Tucana-Horologium–are older and formed differently. Remarkably, all these YLAs and Sco-Cen are part of the α Persei cluster family, a vast kiloparsec-scale star formation event active over the past 60 Myr. This suggests that YLAs are the smallest stellar structures emerging from major star formation episodes and should be common in the Milky Way. Crucially, their formation in regions with intense stellar feedback may have influenced planet formation in these systems.

ABSTRACT We present 450 and 850 $\mu$m James Clerk Maxwell Telescope (JCMT) observations of the Corona Australis (CrA) molecular cloud taken as part of the JCMT Gould Belt Legacy Survey (GBLS). We present a catalogue of 39 starless and protostellar sources, for which we determine source temperatures and masses using SCUBA-2 450 $\mu$m/850 $\mu$m flux density ratios for sources with reliable 450 $\mu$m detections, and compare these to values determined using temperatures measured by the Herschel Gould Belt Survey (HGBS). In keeping with previous studies, we find that SCUBA-2 preferentially detects high-volume-density starless cores, which are most likely to be prestellar (gravitationally bound). We do not observe any anticorrelation between temperature and volume density in the starless cores in our sample. Finally, we combine our SCUBA-2 and Herschel data to perform SED fitting from 160–850 $\mu$m across the central Coronet region, thereby measuring dust temperature T, dust emissivity index $\beta$, and column density $N({\rm H}_2)$ across the Coronet. We find that $\beta$ varies across the Coronet, particularly measuring $\beta = 1.55 \pm 0.35$ in the colder starless SMM-6 clump to the north of the B star R CrA. This relatively low value of $\beta$ is suggestive of the presence of large dust grains in SMM-6, even when considering the effects of $T\!-\!\beta$ fitting degeneracy and $^{12}$CO contamination of SCUBA-2 850 $\mu$m data on the measured $\beta$ values.

We explore the kinematics and star formation history of the Scorpius Centaurus (Sco-Cen) OB association following the initial identification of sequential, linearly aligned chains of clusters. Building upon our characterization of the Corona Australis (CrA) chain, we now analyze two additional major cluster chains that exhibit similar characteristics: the Lower Centaurus Crux (LCC) and Upper Scorpius (Upper Sco) chains. All three cluster chains display distinct sequential patterns in (1) the 3D spatial distribution, (2) age, (3) velocity, and (4) mass. The Upper-Sco chain is the most massive and complex cluster chain, possibly consisting of two or more overlapping subchains. We discuss the possible formation of cluster chains and argue for a scenario where feedback from the most massive star formation episode 15 Myr ago initiated the formation of these spatio-temporal cluster sequences. Our results identify cluster chains as a distinct type of stellar structure with well-defined physical properties, formed in environments capable of sustaining stellar feedback over timescales of 5–10 Myr. We find that around 40% of the stellar population in Sco-Cen formed due to triggered star formation, with 35% forming along the three cluster chains. We conclude that cluster chains could be common structures in OB associations, particularly in regions that have similar natal environments as Sco-Cen. Beyond their significance for star formation and stellar feedback, they appear to be promising laboratories for chemical enrichment and the transport of elements from one generation to the next in the same star-forming region.

The author analyses an asterism identified by the Toba of western Formosa (Argentina) and the symbolism associated with it. Specifically, the article concerns Qolá, the celestial formation that forms the western constellation Corona Australis as well as certain stars that belong to the constellation of Sagittarius. The word Qolá also refers to a type of necklace worn by Toba leaders that – together with other insignias – represents their social rank and emblazons their prestige.

We surveyed nearly all the embedded protostars in seven nearby clouds (Corona Australis, Aquila, Chamaeleon I and II, Ophiuchus North, Ophiuchus, Serpens) with the Atacama Large Millimeter/submillimeter Array at 1.3 mm observations with a resolution of 0.″1. This survey detected 184 protostellar disks, 90 of which were observed at a resolution of 14–18 au, making it one of the most comprehensive high-resolution disk samples across various protostellar evolutionary stages to date. Our key findings include the detection of new annular substructures in two Class I and two flat-spectrum sources, while 21 embedded protostars exhibit distinct asymmetries or substructures in their disks. We find that protostellar disks have a substantially large variability in their radii across all evolutionary classes. In particular, the fraction of large disks with sizes above 60 au decreases as the protostar evolves from Class 0 to Class I. Compiling the literature data, we discovered an increasing trend of the gas disk radii to dust disk radii ratio (R gas,Kep/R mm) with increasing bolometric temperature (T bol). Our results indicate that the dust and gas disk radii decouple during the early Class I stage. However, in the Class 0 stage, the dust and gas disk sizes are similar, which allows for a direct comparison between models and observational data at the earliest stages of protostellar evolution. We show that the distribution of radii in the 52 Class 0 disks in our sample is in high tension with various disk formation models, indicating that protostellar disk formation remains an unsolved question.

We report Atacama Large Millimeter/submillimeter Array/Atacama Compact Array observations of a high-density region of the Corona Australis cloud forming a young star cluster, and the results of resolving internal structures. In addition to embedded Class 0/I protostars in the continuum, a number of complex dense filamentary structures are detected in the C18O and SO lines by the 7 m array. These are substructures of the molecular clump that are detected by the total power array as extended emission. We identify 101 and 37 filamentary structures with widths of a few thousand astronomical units in C18O and SO, respectively, which are called feathers. The typical column density of the feathers in C18O is about 1022 cm−2, and the volume density and line mass are ∼105 cm−3 and a few M ☉ pc−1, respectively. This line mass is significantly smaller than the critical line mass expected for cold and dense gas. These structures have complex velocity fields, indicating a turbulent interior. The number of feathers associated with Class 0/I protostars is only ∼10, indicating that most of them do not form stars but rather are transient structures. The formation of feathers can be interpreted as a result of colliding gas flow because the morphology is well reproduced by MHD simulations, and this is supported by the presence of H i shells in the vicinity. The colliding gas flows may accumulate gas and form filaments and feathers, and trigger the active star formation of the R CrA cluster.

Context. The Cryogenic IR echelle Spectrometer (CRIRES) instrument at the Very Large Telescope (VLT) was in operation from 2006 to 2014. Great strides in characterizing the inner regions of protoplanetary disks were made using CRIRES observations in the L- and M-band at this time. The upgraded instrument, CRIRES+, became available in 2021 and covers a larger wavelength range simultaneously. Aims. Here, we present new CRIRES+ Science Verification data of the binary system S Coronae Australis (S CrA). We aim to characterize the upgraded CRIRES+ instrument for disk studies and provide new insight into the gas in the inner disk of the S CrA N and S systems. Methods. We analyze the CRIRES+ data taken in all available L- and M-band settings, providing spectral coverage from 2.9 to 5.5 μm. Results. We detect emission from 12CO (v = 1−0, v = 2−1, and v = 3−2), 13CO (v = 1−0), hydrogen recombination lines, OH, and H2O in the S CrA N disk. In the fainter S CrA S system, only the12 CO v = 1−0 and the hydrogen recombination lines are detected. The 12CO v = 1−0 emission in S CrA N and S shows two velocity components, a broad component coming from ~0.1 au in S CrA N and ~0.03 au in S CrA S and a narrow component coming from ~3 au in S CrA N and ~5 au in S CrA S. We fit local thermodynamic equilibrium slab models to the rotation diagrams of the two S CrA N velocity components and find that they have similar column densities (~8×1016−4×1017 cm−2), but that the broad component is coming from a hotter and narrower region. Conclusions. Two filter settings, M4211 and M4368, provide sufficient wavelength coverage for characterizing CO and H2O at ~5 μm, in particular covering low- and high-J lines. CRIRES+ provides spectral coverage and resolution that are crucial complements to low-resolution observations, such as those with JWST, where multiple velocity components cannot be distinguished.

Context. The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. Aims. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. Methods. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH3OH, H2CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Results. Methanol emission reveals an arc-like structure at ∼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 H2CO, 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 H2 column density of ∼7 × 1021 cm−2, a mass of ∼9 × 10−3 M⊙, and a lower limit on the dust spectral index of 1.4. Conclusions. 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.

We study the kinematics of the recently discovered Corona Australis (CrA) chain of clusters by examining the 3D space motion of its young stars using Gaia DR3 and APOGEE-2 data. While we observe linear expansion between the clusters in the Cartesian XY directions, the expansion along Z exhibits a curved pattern. To our knowledge, this is the first time such a nonlinear velocity–position relation has been observed for stellar clusters. We propose a scenario to explain our findings, in which the observed gradient is caused by stellar feedback, accelerating the gas away from the Galactic plane. A traceback analysis confirms that the CrA star formation complex was located near the central clusters of the Scorpius Centaurus (Sco-Cen) OB association 10–15 Myr ago. It contains massive stars and thus offers a natural source of feedback. Based on the velocity of the youngest unbound CrA cluster, we estimate that a median number of about two supernovae would have been sufficient to inject the present-day kinetic energy of the CrA molecular cloud. This number agrees with that of recent studies. The head-tail morphology of the CrA molecular cloud further supports the proposed feedback scenario, in which a feedback force pushed the primordial cloud from the Galactic north, leading to the current separation of 100 pc from the center of Sco-Cen. The formation of spatially and temporally well-defined star formation patterns, such as the CrA chain of clusters, is likely a common process in massive star-forming regions.

We present a variability and morphological classification study of TESS light curves for T Tauri star candidates in the Orion, IC 348, γ Velorum, Upper Scorpius, Corona Australis, and Perseus OB2 regions. We propose 11 morphological classes linking brightness variation behaviors with possible physical or geometric phenomena present in T Tauri stars, and develop a supervised machine-learning algorithm to automate the classification among these. Our algorithm optimizes and compares the true positive rate (recall) among k-nearest neighbors, classification trees, random forests, and support vector machines. This is done characterizing light curves with features depending on time, periodicity, and magnitude distribution. Binary and multiclass classifiers are trained and interpreted in a way that allows our final algorithm to have single or mixed classes. In the testing sample, the algorithm assigns mixed classes to 27% of the stars, reaching up to five simultaneous classes. A catalog of 3672 T Tauri star candidates is presented, along with their possible period estimations, predicted morphological classes, and visually revised ones. The cross-validation estimated performance of the final classifiers is reported. Binary classifiers surpass multiclass recall values for classes with less representation in the training sample. Support vector machines and random forest classifiers obtain better recalls. For comparison, another performance estimation of the final classifiers is calculated using the revised classes of our testing sample, indicating that this performance excels in singled classed stars, which happens in about 75% of the testing sample.

Context. During the journey from the cloud to the disc, the chemical composition of the protostellar envelope material can be either preserved or processed to varying degrees depending on the surrounding physical environment. Aims. This works aims to constrain the interplay of solid (ice) and gaseous methanol (CH3OH) in the outer regions of protostellar envelopes located in the Coronet cluster in Corona Australis (CrA), and assess the importance of irradiation by the Herbig Ae/Be star R CrA. CH3OH is a prime test case as it predominantly forms as a consequence of the solid-gas interplay (hydrogenation of condensed CO molecules onto the grain surfaces) and it plays an important role in future complex molecular processing. Methods. We present 1.3 mm Submillimeter Array (SMA) and Atacama Pathfinder Experiment (APEX) observations towards the envelopes of four low-mass protostars in the Coronet cluster. Eighteen molecular transitions of seven species were identified. We calculated CH3OH gas-to-ice ratios in this strongly irradiated cluster and compared them with ratios determined towards protostars located in less irradiated regions such as Serpens SVS 4 in Serpens Main and the Barnard 35A cloud in the λ Orionis region. Results. The CH3OH gas-to-ice ratios in the Coronet cluster vary by one order of magnitude (from 1.2 × 10−4 to 3.1 × 10−3) which is similar to less irradiated regions as found in previous studies. We find that the CH3OH gas-to-ice ratios estimated in these three regions are remarkably similar despite the different UV radiation field intensities and formation histories. Conclusions. This result suggests that the overall CH3OH chemistry in the outer regions of low-mass envelopes is relatively independent of variations in the physical conditions and hence that it is set during the prestellar stage.