A near-infrared survey of the entire R Coronae Australis cloud

Accurately quantifying the impact of radiation feedback in star formation is challenging. To address this complex problem, we employ deep-learning techniques known as denoising diffusion probabilistic models (DDPMs) to predict the interstellar radiation field (ISRF) strength based on three-band dust emission at 4.5, 24, and 250 μm. We adopt magnetohydrodynamic simulations from the STARFORGE project that model star formation and giant molecular cloud (GMC) evolution. We generate synthetic dust emission maps matching observed spectral energy distributions in the Monoceros R2 (MonR2) GMC. We train DDPMs to estimate the ISRF using synthetic three-band dust emission. The dispersion between the predictions and true values is within a factor of 0.1 for the test set. We extended our assessment of the diffusion model to include new simulations with varying physical parameters. While there is a consistent offset observed in these out-of-distribution simulations, the model effectively constrains the relative intensity to within a factor of 2. Meanwhile, our analysis reveals a weak correlation between the ISRF solely derived from dust temperature and the actual ISRF. We apply our trained model to predict the ISRF in MonR2, revealing a correspondence between intense ISRF, bright sources, and high dust emission, confirming the model’s ability to capture ISRF variations. Our model robustly predicts radiation feedback distribution, even in complex, poorly constrained ISRF environments like those influenced by nearby star clusters. However, precise ISRF predictions require an accurate training data set mirroring the target molecular cloud’s unique physical conditions.

We report a discovery of young stellar objects associated with a molecular cloud at the edge of the optical disk of our Galaxy. This cloud is denoted as Cloud 2 in the list by Digel et al., and it is one of the most distant molecular clouds from the Galactic center known to date, with a probable distance of 15-19 kpc. We found seven red near-infrared (NIR) sources associated with this cloud. Based on our NIR observations and the far-infrared/radio data in the literature, we conclude that most sources are likely to be members of Cloud 2. The geometry of ionized gas, IRAS sources, NIR sources, and molecular cloud suggests that MR 1, an isolated early B-type star near Cloud 2, has triggered the star formation activity in Cloud 2. Our results show that ongoing star formation is present in Cloud 2 and that active star formation can occur in the farthest regions of the Galaxy, where the molecular gas density is extremely low, perturbation from the spiral arms is very small, and the metallicity is similar to that for irregular dwarf galaxies. Cloud 2 is an excellent laboratory in which to study the details of the star formation process in an environment that is similar to that in the early stage of the formation of the Galactic disk.

We have performed a census of the young stellar populations near the Corona Australis molecular cloud using photometric and kinematic data from several sources, particularly Gaia EDR3, and spectroscopy of hundreds of candidate members. We have compiled a catalog of 393 members of Corona Australis, (39 at >M6), 293 (36) of which are spectroscopically classified for the first time in this work. We find that Corona Australis can be described in terms of two stellar populations, a younger one (a few megayears) that is partially embedded in the cloud (the Coronet Cluster) and an older one (∼15 Myr) that surrounds and extends beyond the cloud (Upper Corona Australis). These populations exhibit similar space velocities, and we find no evidence for distinct kinematic populations in Corona Australis, in contrast to a recent study based on Gaia DR2. The distribution of spectral types in Corona Australis reaches a maximum at M5 (∼0.15 M ⊙), indicating that the initial mass function has a similar characteristic mass as other nearby star-forming regions. Finally, we have compiled mid-infrared photometry from the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope for the members of Corona Australis, and we have used those data to identify and classify their circumstellar disks. Excesses are detected for 122 stars, one-third of which are reported for the first time in this work.

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.

We uncover the H2 flows in the Corona Australis molecular cloud and in\nparticular identify the flows from the Coronet cluster. Near-infrared H2 v=1--0\nS(1), 2.12micron-line, narrow-band imaging survey of the R CrA cloud core was\ncarried out. We identify the best candidate-driving source for each outflow by\ncomparing the flow properties, available proper motions, and the\nknown/estimated properties of the driving sources. We also adopted the\nthumbrule of outflow power as proportional to source luminosity and inversely\nproportional to the source age to reach a consensus.\n Results: Continuum-subtracted, narrow-band images reveal several new\nMolecular Hydrogen emission-line Objects (MHOs). Together with previously known\nMHOs and Herbig-Haro objects we catalog at least 14 individual flow components\nof which 11 appear to be driven by the RCrA aggregate members. The flows\noriginating in the Coronet cluster have lengths of ~0.1-0.2 pc. Eight out of\nnine submillimeter cores mapped in the Coronet cluster region display embedded\nstars driving an outflow component. Roughly 80% of the youngest objects in the\nCoronet are associated with outflows. The MHO flows to the west of the Coronet\ndisplay lobes moving to the west and vice-versa, resulting in nondetections of\nthe counter lobe in our deep imaging. We speculate that these counterflows may\nbe experiencing a stunting effect in penetrating the dense central core.\n Conclusions:Although this work has reduced the ambiguities for many flows in\nthe Coronet region, one of the brightest H2 feature (MHO2014) and a few fainter\nfeatures in the region remain unassociated with a clear driving source. The\nflows from Coronet, therefore, continue to be interesting targets for future\nstudies.\n

Context. In star-forming regions like Taurus-Auriga, it has been found that most young stars are born as multiples, which theories of star formation should definitely take into account. The R CrA star-forming region has a small dark cloud with quite a number of protostars, T Tauri stars, and some Herbig Ae/Be stars, plus a number of weak-line T Tauri stars around the cloud found by ROSAT follow-up observations. Aims. We would like to detect multiples among the young stars in and around the R CrA cloud in order to investigate multiplicity in this region. Methods. We performed interferometric and imaging observations with the speckle camera SHARP I at the ESO 3.5 m NTT and adaptive optics observation with ADONIS at the ESO 3.6 m telescope, all in the near-infrared bands JHK obtained in the years 1995, 2000, and 2001. Results. We found 13 new binaries among the young stars in CrA between 0.13 arcsec (the diffraction limit) and 6 arcsec (set as an upper separation limit to avoid contamination by chance alignments). While most multiples in CrA are binaries, there are also one quadruple (TY CrA), and one triple (HR 7170) which may form a quintuple together with the binary HR 7169. One of the newly detected companions with a large magnitude difference found near the M3-5 type T Tauri star [MR 81] Hα 17 could be a brown dwarf or an infrared companion with an edge-on disk. Among seven Herbig Ae/Be stars in CrA, six are multiple. Conclusions. The multiplicity frequency in CrA is as high as in similar star forming regions. By comparing with the period distribution of main-sequence stars and extrapolating to separations not probed in this survey, we conclude that the companion-star frequency is (95 ± 23)%; i.e. the average number of companions per primary is 0.95.

We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg^2 field including the Corona Australis (CrA) star-forming region. At a distance of 130 pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include sources in the well-studied Coronet cluster as well as distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from the literature are also added to the list, and a total of 116 candidate YSOs in CrA are compiled. Based on these YSO candidates, the star formation rate is computed to be 12 M_o Myr^-1, similar to that of the Lupus clouds. A clustering analysis was also performed, finding that the main cluster core, consisting of 68 members, is elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc and mean surface density of 150 pc^-2. In addition, we analyze outflows and jets in CrA by means of new CO and H_2 data. We present 1.3 mm interferometric continuum observations made with the Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712 (IRAS 32). We also present multi-epoch H_2 maps and detect jets and outflows, study their proper motions, and identify exciting sources. The Spitzer and ISAAC/VLT observations of IRAS 32 show a bipolar precessing jet, which drives a CO (2-1) outflow detected in the SMA observations. There is also clear evidence for a parsec-scale precessing outflow, E-W oriented, and originating in the SMA 2 region, likely driven by SMA 2 or IRS 7A.

We have calculated bolometric temperature (Tbol) and bolometric luminosity (Lbol) for 383 young stellar objects (YSOs) in five molecular clouds within 200 pc in Corona Australis (CrA), Ophiuchus (Oph), Taurus (Tau), Chamaeleon (Cha), and Lupus (Lup). We used Tbol, Lbol, and bolometric luminosity-temperature (BLT) diagrams to characterize and compare the overall-star-formation activity of the clouds on a self-consistent basis. The main results are the following: (1) the YSO populations in the clouds can be differentiated by the fraction of their low-Tbol sources, which increases systematically from Lup and Cha to Tau and to Oph and CrA. This trend is interpreted as increasing current star-forming activity in the same order; (2) the clouds with higher cold source fractions also seem to have higher bright source fractions; (3) In the BLT diagram, the CrA and Oph sources are more uniformly distributed while the Cha and Lup sources are aggregated near the zero-age mainsequence (ZAMS). Tau sources appear to be an intermediate case. Taurus also seems to contain more cold (Tbol < 1000 K) and low-luminosity (Lbol < 1 L?) sources than the other complexes; (4) the YSOs show a characteristic distribution in the median BLT diagram. This distribution is qualitatively consistent with the early YSO evolution from a protostar to a pre-main-sequence star and provides a unique observational test to star-formation models; (5) for Lup pre-main-sequence stars, the ratio of their Tbol to Teff increases during their approach to the ZAMS. This increase can be explained by the disk and envelope dissipation during the pre-main-sequence evolution; (6) the most active star-forming clouds (Oph and CrA) also have denser molecular cores as measured by C18O J = 1-0 line emission, suggesting that the star formation occurs in the densest parts of the molecular clouds; and (7) we find an anti-correlation between Tbol and C18O emission for the class 0 and I Tau sources (Tbol < 650 K). This shows that Tbol measures the intrinsic redness of YSOs, rather than their disk-envelope orientation. The disk orientation may have a more important effect on Tbol of the pre-main-sequence stars.

Aims. We report the investigation results of the structure and content of a molecular cloud surrounding the source IRAS 05168+3634 (also known as Mol 9). Methods. We present a photometric analysis using the data of J, H, K UKIDSS, [3.6], [4.5] μm Spitzer-IRAC and 3.4, 4.6, 12, 22 μm WISE databases. A multi-color criteria was used to identify the candidates of young stellar objects (YSOs) in the molecular cloud; in addition to IRAS 05168+3634, there are four IRAS sources embedded in the same molecular cloud. Color–magnitude diagrams and the K luminosity function (KLF) were used to determine the basic parameters of stellar objects (spectral classes, masses, ages). To study the YSOs with longer wavelength photometry the radiative transfer models were used. Results. Based on color–color and color–magnitude diagrams, we identified a rich population of embedded YSO candidates with infrared excess (Class 0/I and Class II) and their characteristics in a quite large molecular cloud located in a region of 24 arcmin radius. The molecular cloud includes 240 candidates of YSOs within the radii of subregions around five IRAS sources. The local distribution of identified YSOs in the molecular cloud frequently shows elongation and subclustering. The observed young subregions and parental molecular cloud morphologies are similar, especially when only the youngest Class I/0 sources are considered. The color–magnitude diagrams of the subregions suggest a very young stellar population. We construct the KLF of the subregions except for the IRAS 05162+3639 region and it shows unusually low values for α slope: 0.12–0.21. According to the values of the slopes of the KLFs, the age of the subregions can be estimated at 0.1–3 Myr. The spectral energy distributions (SEDs) are constructed for 45 Class I and 75 Class II evolutionary stage YSOs and the received parameters of these YSOs are well correlated with the results obtained by other methods. According to the results of SED fitting tool, the sources IRAS 05184+3635, IRAS 05177+3636, and IRAS 05162+3639 can be classified as Class I evolutionary stage objects. IRAS 05168+3634 and IRAS 05156+3643 can be classified as flat-spectrum objects.

Context. The Magellanic Bridge is a tidal feature located between the Magellanic Clouds, containing young stars formed in situ. Its proximity allows high-resolution studies of molecular gas, dust, and star formation in a tidal low-metallicity environment. Aims. Our goal is to characterize gas and dust emission in Magellanic Bridge A, the source with the highest 870 μm excess of emission found in single-dish surveys. Methods. Using the ALMA telescope including the Morita Array, we mapped a 3′ field of view centered on the Magellanic Bridge A molecular cloud, in 1.3 mm continuum emission and 12CO(2−1) line emission at subparsec resolution. This region was also mapped in continuum at 870 μm and in 12CO(2−1) line emission at ~6 pc resolution with the APEX telescope. To study its dust properties, we also use archival Herschel and Spitzer data. We combine the ALMA and APEX 12CO(2−1) line cubes to study the molecular gas emission. Results. Magellanic Bridge A breaks up into two distinct molecular clouds in dust and 12CO(2−1) emission, which we call North and South. Dust emission in the North source, according to our best parameters from fitting the far-infrared fluxes, is ≈3 K colder than in the South source in correspondence to its less developed star formation. Both dust sources present large submillimeter excesses in LABOCA data: according to our best fits the excess over the modified blackbody (MBB) fit to the Spitzer/Herschel continuum is E(870 μm) ~ 7 and E(870 μm) ~ 3 for the North and South sources, respectively. Nonetheless, we do not detect the corresponding 1.3 mm continuum with ALMA. Our limits are compatible with the extrapolation of the MBB fits, and therefore we cannot independently confirm the excess at this longer wavelength. The 12CO(2−1) emission is concentrated in two parsec-sized clouds with virial masses of around 400 and 700 M⊙. Their bulk volume densities are n(H2) ~ 0.7−2.6 × 103 cm−3, higher than typical bulk densities of Galactic molecular clouds. The 12CO luminosity to H2 mass conversion factor αCO is 6.5 and 15.3 M⊙ (K km s−1 pc2)−1 for the North and South clouds, calculated using their respective virial masses and 12CO(2−1) luminosities. Gas mass estimates from our MBB fits to dust emission yields masses M ~ 1.3 × 103 M⊙ and 2.9 × 103 M⊙ for North and South, respectively, a factor of ~4 higher than the virial masses we infer from 12CO.

We present the results of infrared (IR; 2.5–160 μm) observations of the supernova remnant (SNR) Kes 17 based on the data obtained with the AKARI and Spitzer satellites. We first detect bright continuum emission of its western shell in the mid- and far-IR wavebands together with its near-IR molecular line emission. We also detect hidden mid-IR emission of its southern shell after subtraction of the background emission in this region. The far-IR luminosity of the western shell is ∼8100 L☉, which makes Kes 17 one of the few SNRs of significant far-IR emission. The fittings of the spectral energy distribution indicate the existence of two dust components: ∼79 K (hot) and ∼27 K (cold) corresponding to the dust masses of ∼6.2 × 10−4 M☉ and ∼6.7 M☉, respectively. We suggest that the hot component represents the dust emission of the material swept up by the SNR to its western and southern boundaries, compatible with the distribution of radio continuum emission overlapping the mid-IR emission in the western and southern shells. The existence of hot (∼2000 K), shocked dense molecular gas revealed by the near-IR molecular line emission in the western shell, on the other hand, suggests that the cold dust component represents the dust emission related to the interaction between the SNR and nearby molecular gas. The excitation conditions of the molecular gas appear to be consistent with those from shocked, clumpy admixture gas of different temperatures. We discuss three possibilities for the origin of the bright far-IR emission of the cold dust in the western shell: the emission of dust in the inter-clump medium of shocked molecular clouds, the emission of dust in evaporating flows of molecular clouds engulfed by hot gas, and the emission of dust of nearby molecular clouds illuminated by radiative shocks.

We use young clusters and giant molecular clouds (GMCs) in the galaxies M33 and M31 to constrain temporal and spatial scales in the star formation process. In M33, we compare the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) catalogue of 1214 clusters with ages measured via colour–magnitude diagram (CMD) fitting to 444 GMCs identified from a new 35 pc resolution Atacama Large Millimeter/submillimeter Array (ALMA) 12CO(2–1) survey. In M31, we compare the Panchromatic Hubble Andromeda Treasury (PHAT) catalogue of 1249 clusters to 251 GMCs measured from a Combined Array for Research in Millimeter-wave Astronomy (CARMA) 12CO(1–0) survey with 20 pc resolution. Through two-point correlation analysis, we find that young clusters have a high probability of being near other young clusters, but correlation between GMCs is suppressed by the cloud identification algorithm. By comparing the positions, we find that younger clusters are closer to GMCs than older clusters. Through cross-correlation analysis of the M33 cluster data, we find that clusters are statistically associated when they are ≤10 Myr old. Utilizing the high precision ages of the clusters, we find that clusters older than ≈18 Myr are uncorrelated with the molecular interstellar medium (ISM). Using the spatial coincidence of the youngest clusters and GMCs in M33, we estimate that clusters spend ≈4–6 Myr inside their parent GMC. Through similar analysis, we find that the GMCs in M33 have a total lifetime of ≈11–15 Myr. We also develop a drift model and show that the above correlations can be explained if the clusters in M33 have a 5–10 km s−1 velocity dispersion relative to the molecular ISM.

The measurement and assessment of dust emissions from different landforms are important to understand the atmospheric loading of PM10 (particulate matter ≤10 μm aerodynamic diameter) and to assess natural sources of dust; however, the methodology and technique for determining the dust still present significant research challenges. In the past, specialized field observation and field wind tunnel studies have been used to understand the dust emission. A series of wind tunnel tests were carried out to identify natural sources of dust and measure the magnitudes of dust emissions from different landforms. The method used in this study allowed the measurement of the PM10 emission rate using a laboratory based environmental boundary layer wind tunnel. Results indicated that PM10 emissions demonstrated strong temporal variation and were primarily driven by aerodynamic entrainment. Sand dunes, playa, and alluvial fans had the largest dust emission rates (0.8–5.4 mg/(m2•s)) while sandy gravel, Gobi desert and abandoned lands had the lowest emission rates (0.003–0.126 mg/(m2•s)). Dust emissions were heavily dependent on the surface conditions, especially the availability of loose surface dust. High dust emissions were a result of the availability of dustparticle materials for entrainment while low dust emissions were a result of surface crusts and gravel cover. Soil surface property (surface crusts and gravel cover) plays an important role in controlling the availability of dust-sized particles for entrainment. The dust emission rate depended not only on the surface conditions but also on the friction velocity. The emission rate of PM10 varies as a power function of the friction velocity. Although dynamic abrasion processes have a strong influence on the amount of dust entrainment, aerodynamic entrainment may provide an important mechanism for dust emissions. Large volumes of dust entrained by aerodynamic entrainment cannot only occur at low shear velocity without saltation, but may dominate the entrainment process in many arid and semi-arid environments. So it may also be responsible for large magnitude dust storms. Playa and alluvial fan landforms, prior to developing a surface crust, may be the main sources of dust storms in Qinghai Province.

Aims. Using the speckle camera SHARP at the 3.5 m ESO NTT, Kohler and collaborators found an object ∼3.5 mag fainter in K only 1.3 �� north-east of the T Tauri star [MR81] Hα17 in the Corona Australis (CrA) star-forming region, which could be either a brown dwarf or a T Tauri star with an edge-on disk. We attempt to study this faint object in detail. Methods. We acquired deep VLT NACO near-infrared images at three epochs to determine, whether [MR81] Hα17 and the nearby faint object are comoving and to measure the infrared colors of both objects. We obtained optical and infrared spectra of both objects with the VLT using FORS and ISAAC, respectively, to determine spectral types and temperatures as well as ages and masses. Results. The T Tauri star [MR81] Hα17 and the faint nearby object have a projected separation of 1369.58 mas, i.e. 178 AU at 130 pc. They share the same proper motion (∼5σ), so that they most certainly form a bound binary pair. The apparently fainter component [MR81] Hα17 NE has a spectral type of M2e, while the apparently brighter component [MR81] Hα17 SW, the previously known T Tauri star, has a spectral type of M4-5e. We can identify a nearly edge-on disk around [MR81] Hα17 NE by visual inspection, which has a diameter of at least 30 to 50 AU. We are able to detect strong emission lines in [MR81] Hα17 NE, which are almost certainly due to ongoing accretion. The NE object is detectable only by means of its scattered light. Conclusions. If both objects are co-eval (2–3 Myr) and located at the same distance (∼130 pc as CrA), then the apparently fainter [MR81] Hα17 NE is more massive (primary) component with a nearly edge-on disk and the apparently brigther component [MR81] Hα17 SW is less massive (companion). Both are low-mass T Tauri stars with masses of ∼0.5 and 0.23 ± 0.05 M� , respectively.

Optimized approach for developing soil fugitive dust emission inventory in "2+26" Chinese cities