The evolution of millimeter-sized dust in a protoplanetary disk is one of the key observable constrains on the formation of planets. In recent years, ALMA surveys of disks in nearby star-forming regions have shown a dependence of the disk mass distribution on cloud properties and environmental factors. Due to the relatively small number of regions for which these statistics are available, several key questions have so far been out of reach for observers: do disk masses vary across clouds, or are they constant? How far does the influence of massive young stars reach in different environments? How do the masses of Class II-disks compare to those of embedded objects?We present new results from the Survey of Orion Disks with ALMA (SODA), based on observations of 882 disks in the southern part of the Orion A molecular cloud. This flux-limited survey is the largest of its kind so far, and spans a large area on the sky with multiple young groups and clusters, as shown in Figure 1. We find that disk properties across the cloud are remarkably uniform, between clusters and between regions of different stellar density. However, the presence of B-stars is significant.IntroductionDifferent ALMA surveys in individual star forming regions have significantly improved our understanding of the evolution of protoplanetary disks in recent times. In particular, most of the nearby low-mass star-forming regions (SFRs) have now been observed at mm-wavelengths, as well as several SFRs hosting massive stars (e.g., Ansdell et al. 2016, Pascucci et al. 2016, Eisner et al. 2018, van Terwisga et al. 2020). These studies have provided key insight in how circumstellar matter evolves as planetary systems take shape.Observations so far have shown that disks of all masses evolve rapidy within the first few Myr of their existence (Tychoniec et al. 2020). In addition to these age effects, the disk mass distribution of populations of disks in strongly irradiated environments has also been shown to be subject to external photoevaporation. Disks decrease in mass in stronger radiation fields in regions like σ Ori and the Trapezium (Ansdell et al. 2017, Mann et al. 2014, Eisner et al. 2018), demonstrating the direct impact of extreme environments on disk evolution. Model predictions (frome.g. the FRIED grid, by Haworth et al. 2018) and observations of individual disks in low-mass SFRs have shown that even in an environment like Taurus, where the UV radiation is a factor 1000 weaker than in the Trapezium, half of the disks undergo significant mass loss.A key problem is that even with the current state-of-the-art data, the number of different star-forming regions sampled is quite small. Additionally, even in regions where complete surveys of the Class II population exist, like Lupus, stars exist in a range of environmental conditions. Our survey of Orion A, the largest of its kind so far, covers large numbers of disks in a wide variety of environments, allowing us to link disk properties to their enviroment more firmly than before.Figure 1: The 882 Class II YSOs targeted in this survey (green plus signs), and groups and clusters identified by Megeath et al. 2016 (pink crosses). The background shows the total gas and dust column as derived from Herschel continuum maps (Lombardi et al. 2014).Data reductionOur observations cover a large number of sources at low (1.4'') resolution in ALMA Band 6. This resolution is low compared to the expected disk structure. This meant we could use a high-performance computing cluster to reduce and image the data in a fraction of the time it would otherwise take, simulateously guaranteeing consistent and reproducible results.ResultsFigure 2: Disk mass distribution in the SODA sample, compared to several other well-studied nearby star-forming regions.By converting disk fluxes to masses we can compare the properties of the Orion A disks sample, both within different regions of Orion A, and between Orion A and other clouds, like Lupus and Taurus, which have been surveyed previously. As Figure 2 shows, the large number of disks in our sample allows us to determine the disk mass distribution much more accurately than previously possible. However, the large sample size also enables us to compare average disk masses between regions in Orion A, as shown in Figure 3, which shows that there are only small differences in average disk masses between areas of vastly different surface densities, even across the length of the cloud, and emphasizes the remarkable similarity between disks in Orion, Taurus, and Lupus. However, the presence of nearby B-stars is relevant for disk masses, out to scales of several parsecs, a parameter range that it was not previously possible to probe.Figure 3: Disk masses as a function of density of YSOs, across Orion A, and in Lupus, show a remarkable similarity across many orders of magnitude.

We present FEROS high-resolution (R~45000) optical spectroscopy of 34 Herbig Ae/Be star candidates with previously unknown or poorly constrained spectral types. Within the sample, 16 sources are positionally coincident with nearby (d<250 pc) star-forming regions (SFRs). All the candidates have IR excess. We determine the spectral type and luminosity class of the sources, derive their radial and rotational velocities, and constrain their distances employing spectroscopic parallaxes. We confirm 13 sources as Herbig Ae/Be stars and find one classical T Tauri star. Three sources are emission line early-type giants and may be Herbig Ae/Be stars. One source is a main-sequence A-type star. Fourteen sources are post-main-sequence giant and supergiant stars. Two sources are extreme emission-line stars. Most of the sources appear to be background stars at distances over 700 pc. We show that high-resolution optical spectroscopy is a crucial tool for distinguishing young stars from post-main sequence stars in samples taken from emission-line star catalogs based on low-resolution spectroscopy. Within the sample, 3 young stars (CD-38 4380, Hen 3-1145, and HD 145718) and one early-type luminosity class III giant with emission lines (Hen 3-416) are at distances closer than 300 pc and are positionally coincident with a nearby SFR. These 4 sources are likely to be nearby young stars and are interesting for follow-up observations at high-angular resolution. Furthermore, seven confirmed Herbig Ae/Be stars at d>700 pc (Hen 2-80, Hen 3-1121 N&S, HD 313571, MWC 953, WRAY 15-1435, and Th 17-35) are inside or close (<5') to regions with extended 8 micron continuum emission and in their 20' vicinity have astronomical sources characteristic of SFRs. These 7 sources are likely to be members of SFRs. These regions are attractive for future studies of their stellar content.

Context. Surveys of protoplanetary disks in nearby star-forming regions (SFRs) have provided important information on their demographics. However, due to their sample sizes, these surveys cannot be used to study how disk properties vary with the environment. Aims. We conduct a survey of the unresolved millimeter continuum emission of 873 protoplanetary disks identified by Spitzer in the L1641 and L1647 regions of the Orion A cloud. This is the largest such survey yet, allowing us to identify even weak trends in the median disk mass as a function of position in the cloud and cluster membership. The sample detection rates and median masses are also compared to those of nearby (&lt;300 pc) SFRs. Methods. The sample was observed with the Atacama Large Millimeter/submillimeter Array (ALMA) at 225 GHz, with a median rms of 0.08 mJy beam−1, or 1.5 M⊕. The data were reduced and imaged using an innovative parallel data processing approach. Results. We detected 58% (502/873) of the observed disks. This includes 20 disks with dust masses &gt;100 M⊕, and two objects associated with extended dust emission. By fitting a log-normal distribution to the data, we infer a median disk dust mass in the full sample of 2.2−0.2+0.2 M⊕. In L1641 and L1647, median dust masses are 2.1−0.2+0.2M⊕ and 2.6−0.5+0.4M⊕, respectively. Conclusions. The disk mass distribution of the full sample is similar to that of nearby low-mass SFRs at similar ages of 1–3 Myr. We find only weak trends in disk (dust) masses with galactic longitude and between the Young Stellar Object (YSO) clusters identified in the sample, with median masses varying by ≲50%. Differences in age may explain the median disk mass variations in our subsamples. Apart from this, disk masses are essentially constant at scales of ~100 pc. This also suggests that the majority of disks, even in different SFRs, are formed with similar initial masses and evolve at similar rates, assuming no external irradiation, with disk mass loss rates of ~10−8 M⊙ yr−1.

Most protostars have luminosities that are fainter than expected from steady accretion over the protostellar lifetime. The solution to this problem may lie in episodic mass accretion—prolonged periods of very low accretion punctuated by short bursts of rapid accretion. However, the timescale and amplitude for variability at the protostellar phase is almost entirely unconstrained. In A James Clerk Maxwell Telescope/SCUBA-2 Transient Survey of Protostars in Nearby Star-forming Regions, we are monitoring monthly with SCUBA-2 the submillimeter emission in eight fields within nearby ( &lt; 500 pc) star-forming regions to measure the accretion variability of protostars. The total survey area of ∼1.6 deg2 includes ∼105 peaks with peaks brighter than 0.5 Jy/beam (43 associated with embedded protostars or disks) and 237 peaks of 0.125–0.5 Jy/beam (50 with embedded protostars or disks). Each field has enough bright peaks for flux calibration relative to other peaks in the same field, which improves upon the nominal flux calibration uncertainties of submillimeter observations to reach a precision of ∼2%–3% rms, and also provides quantified confidence in any measured variability. The timescales and amplitudes of any submillimeter variation will then be converted into variations in accretion rate and subsequently used to infer the physical causes of the variability. This survey is the first dedicated survey for submillimeter variability and complements other transient surveys at optical and near-IR wavelengths, which are not sensitive to accretion variability of deeply embedded protostars.

SONYC -- Substellar Objects in Nearby Young Clusters -- is a survey program to investigate the frequency and properties of substellar objects in nearby star-forming regions. We present a new imaging and spectroscopic survey conducted in the young (~1 Myr), nearby (~200 pc) star-forming region Lupus 3. Deep optical and near-infrared images were obtained with MOSAIC-II and NEWFIRM at the CTIO-4m telescope, covering ~1.4 sqdeg on the sky. The i-band completeness limit of 20.3 mag is equivalent to 0.009-0.02 MSun, for Av \leq 5. Photometry and 11-12 yr baseline proper motions were used to select candidate low-mass members of Lupus 3. We performed spectroscopic follow-up of 123 candidates, using VIMOS at the Very Large Telescope (VLT), and identify 7 probable members, among which 4 have spectral type later than M6.0 and Teff \leq 3000K, i.e. are probably substellar in nature. Two of the new probable members of Lupus 3 appear underluminous for their spectral class and exhibit emission line spectrum with strong Halpha or forbidden lines associated with active accretion. We derive a relation between the spectral type and effective temperature: Teff=(4120 +- 175) - (172 +- 26) x SpT, where SpT refers to the M spectral subtype between 1 and 9. Combining our results with the previous works on Lupus 3, we show that the spectral type distribution is consistent with that in other star forming regions, as well as is the derived star-to-BD ratio of 2.0-3.3. We compile a census of all spectroscopically confirmed low-mass members with spectral type M0 or later.

We present a study of the stellar and circumstellar properties of Class I sources using low-resolution (R~1000) near-infrared K- and L-band spectroscopy. We measure prominent spectral lines and features in 8 objects and use fits to standard star spectra to determine spectral types, visual extinctions, K-band excesses, and water ice optical depths. Four of the seven systems studied are close binary pairs; only one of these systems, Haro 6-10, was angularly resolvab le. For certain stars some properties found in our analysis differ substantially from published values; we analyze the origin of these differences. We determine extinction to each source using three different methods and compare and discuss the resulting values. One hypothesis that we were testing, that extinction dominates over the K-band excess in obscuration of the stellar photospheric absorption lines, appears not to be true. Accretion luminosities and mass accretion rates calculated for our targets are highly uncertain, in part the result of our inexact knowledge of extinction. For the six targets we were able to place on an H-R diagram, our age estimates, <2 Myr, are somewhat younger than those from comparable studies. Our results underscore the value of low-resolution spectroscopy in the study of protostars and their environments; however, the optimal approach to the study of Class I sources likely involves a combination of high- and low-resolution near-infrared, mid-infrared, and millimeter wavelength observations. Accurate and precise measurements of extinction in Class I protostars will be key to improving our understanding of these objects.

Aims.We present a new continuum 3D radiative transfer code, MCFOST, based on a Monte-Carlo method. MCFOST can be used to calculate (i) monochromatic images in scattered light and/or thermal emission; (ii) polarisation maps; (iii) interferometric visibilities; (iv) spectral energy distributions; and (v) dust temperature distributions of protoplanetary disks. Methods.Several improvements to the standard Monte Carlo method are implemented in MCFOST to increase efficiency and reduce convergence time, including wavelength distribution adjustments, mean intensity calculations, and an adaptive sampling of the radiation field. The reliability and efficiency of the code are tested against a previously-defined benchmark, using a 2D disk configuration. No significant difference (no more than 10% and usually much less) is found between the temperatures and SEDs calculated by MCFOST and by other codes included in the benchmark. Results. A study of the lowest disk mass detectable by Spitzer, around young stars, is presented and the colours of “representative” parametric disks compared to recent IRAC and MIPS Spitzer colours of solar-like young stars located in nearby star-forming regions.

We have collated multiplicity data for five clusters (Taurus, Chamaeleon I,\nOphiuchus, IC348, and the Orion Nebula Cluster). We have applied the same mass\nratio (flux ratios of delta K &lt;= 2.5) and primary mass cuts (~0.1-3.0 Msun) to\neach cluster and therefore have directly comparable binary statistics for all\nfive clusters in the separation range 62-620 au, and for Taurus, Chamaeleon I,\nand Ophiuchus in the range 18-830 au. We find that the trend of decreasing\nbinary fraction with cluster density is solely due to the high binary fraction\nof Taurus, the other clusters show no obvious trend over a factor of nearly 20\nin density.\n With N-body simulations we attempt to find a set of initial conditions that\nare able to reproduce the density, morphology and binary fractions of all five\nclusters. Only an initially clumpy (fractal) distribution with an initial total\nbinary fraction of 73 per cent (17 per cent in the range 62-620 au) is able to\nreproduce all of the observations (albeit not very satisfactorily). Therefore,\nif star formation is universal the initial conditions must be clumpy and with a\nhigh (but not 100 per cent) binary fraction. This could suggest that most\nstars, including M-dwarfs, form in binaries.\n

We present the Atacama Large Millimeter/submillimeter Array Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO), a large program of the ALMA. AGE-PRO aims to systematically trace the evolution of gas disk mass and size throughout the lifetime of protoplanetary disks. It uses a carefully selected sample of 30 disks around M3-K6 stars in three nearby star-forming regions: Ophiuchus (0.5–1 Myr), Lupus (1–3 Myr), and Upper Sco (2–6 Myr). Assuming the three regions had similar initial conditions and evolutionary paths, we find the median gas disk mass appears to decrease with age. Ophiuchus disks have the highest median gas mass (6 M Jup), while the Lupus and Upper Sco disks have significantly lower median masses (0.68 and 0.44 M Jup, respectively). Notably, the gas and dust disk masses appear to evolve on different timescales. This is evidenced by the median gas-to-dust mass ratio, which decreases from 122 in the youngest disks (&lt;1 Myr) to 46 in Lupus disks, and then increases to 120 in the Upper Sco disks. The median gas disk sizes range between 74 and 110 au, suggesting that typical gas disks are much smaller than those of well-studied, massive disks. Population synthesis models suggest that magnetohydrodynamic wind-driven accretion can reproduce median disk properties across all three regions, when assuming compact disks with a declining magnetic field over time. In contrast, turbulent-driven models overestimate gas masses of &gt;1 Myr disks by an order of magnitude. Here, we discuss the program’s motivation, survey design, sample selection, observation and data calibration processes, and highlight the initial results.

In this paper we present a study of chemical abundances in six star-forming regions. Stellar parameters and metallicities are derived using high-resolution, high S/N spectra of weak-line T-Tauri stars in each region. The results show that nearby star-forming regions have a very small abundance dispersion (only 0.033 dex in [Fe/H]). The average metallicity found is slightly below that of the Sun, although compatible with solar once the errors are taken into account. The derived abundances for Si and Ni show that the observed stars have the abundances typical of Galactic thin disk stars of the same metallicity. The impact of these observations is briefly discussed in the context of the Galactic chemical evolution, local inter-stellar medium abundances, and in the origin of metal-rich stars in the solar neighbourhood (namely, stars more likely to harbour planets). The implication for future planet-search programmes around very young, nearby stars is also discussed. Based on observations collected at Paranal Observatory, eso (Chile) with the uves and flames/uves spectrographs at the VLT-Kueyen telescope (run IDs 075.C-0272(A) and 076.C-0524(A), respectively), with the feros spectrograph at the eso/mpi 2.2-m telescope (program ID 070.C-0507(A)), as well as with the sophie spectrograph at the ohp observatory, France.

Direct imaging surveys have discovered wide-orbit planetary-mass companions that challenge existing models of both star and planet formation, but their demographics remain poorly sampled. We have developed an automated binary companion point-spread function (PSF) fitting pipeline to take advantage of Spitzer's infrared sensitivity to planetary-mass objects and circum(sub)stellar disks, measuring photometry across the four Infrared Array Camera (IRAC) channels of 3.6, 4.5, 5.8, and 8.0 μm. We present PSF fitting photometry of archival Spitzer/IRAC images for 11 young, low-mass (M ∼ 0.044–0.88 M ⊙; K3.5–M7.5) members of three nearby star-forming regions (Chameleon, Taurus, and Upper Scorpius; d ∼ 150 pc; τ ∼ 1–10 Myr) that host confirmed or candidate faint companions at ρ = 1.″68–7.″31. We recover all system primaries, six confirmed, and two candidate low-mass companions in our sample. We also measure nonphotospheric [3.6]–[8.0] colors for three of the system primaries, four of the confirmed companions, and one candidate companion, signifying the presence of circumstellar or circum(sub)stellar disks. We furthermore report the confirmation of a ρ = 4.″66 (540 au) companion to [SCH06] J0359+2009 which was previously identified as a candidate via imaging over five years ago, but was not studied further. Based on its brightness (M [3.6] = 8.53 mag), we infer the companion mass to be M = 20 ± 5 M Jup given the primary’s model-derived age of 10 Myr. Our framework is sensitive to companions with masses less than 10 M Jup at separations of ρ = 300 au in nearby star-forming regions, opening up a new regime of parameter space that has yet to be studied in detail, discovering planetary-mass companions in their birth environments and revealing their circum(sub)stellar disks.

Nearby star-forming regions are ideal laboratories to study high-energy emission of different stellar populations, from very massive stars to brown dwarfs. NGC 2023 is a reflection nebula situated on the south of the Flame Nebula (NGC 2024) and at the edge of the H ii region IC 434, which also contains the Horsehead Nebula (Barnard 33). NGC 2023, NGC 2024, Barnard 33 and the surroundings of the O-type supergiant star {\zeta} Ori constitute the south part of the Orion B molecular complex. In this work, we present a comprehensive study of X-ray emitters in the region of NGC 2023 and its ?surroundings. We combine optical and infrared data to determine physical properties (mass, temperature, luminosity, presence of accretion disks) of the stars detected in an XMM-Newton observation. This study has allowed us to analyze spectral energy distribution of these stars for the first time and determine their evolutionary stage. Properties of the X-ray emitting plasma of these stars are compared to those found in other nearby star-forming regions. The results indicate that the stars that are being formed in this region have characteristics, in terms of physical properties and luminosity function, similar to those found in the Taurus-Auriga molecular complex.

Spatial correlations among protoplanetary disk orientations carry unique information on physics of multiple-star formation processes. We select five nearby star-forming regions that comprise a number of protoplanetary disks with spatially resolved images with ALMA and Hubble Space Telescope, and we search for the mutual alignment of the disk axes. Specifically, we apply the Kuiper test to examine the statistical uniformity of the position angle (PA: the angle of the major axis of the projected disk ellipse measured counterclockwise from the north) distribution. The disks located in the star-forming regions, except the Lupus clouds, do not show any signature of the alignment, supporting the random orientation. Rotational axes of 16 disks with spectroscopic measurement of PA in the Lupus III cloud, a subregion of the Lupus field, however, exhibit a weak and possible departure from the random distribution at a 2σ level, and the inclination angles of the 16 disks are not uniform as well. Furthermore, the mean direction of the disk PAs in the Lupus III cloud is parallel to the direction of its filament structure and approximately perpendicular to the magnetic field direction. We also confirm the robustness of the estimated PAs in the Lupus clouds by comparing the different observations and estimators based on three different methods, including sparse modeling. The absence of the significant alignment of the disk orientation is consistent with the turbulent origin of the disk angular momentum. Further observations are required to confirm/falsify the possible disk alignment in the Lupus III cloud.

SONYC - Substellar Objects in Nearby Young Clusters - is a survey program to investigate the frequency and properties of substellar objects with masses down to a few times that of Jupiter in nearby star-forming regions. For the ~1Myr old rho Ophiuchi cluster, in our earlier paper we reported deep, wide-field optical and near-infrared imaging using Subaru, combined with 2MASS and Spitzer photometry, as well as follow-up spectroscopy confirming three likely cluster members, including a new brown dwarf with a mass close to the deuterium-burning limit. Here we present the results of extensive new spectroscopy targeting a total of ~100 candidates in rho Oph, with FMOS at the Subaru Telescope and SINFONI at the ESO's Very Large Telescope. We identify 19 objects with effective temperatures at or below 3200 K, 8 of which are newly identified very-low-mass probable members of rho Oph. Among these eight, six objects have Teff <= 3000 K, confirming their likely substellar nature. These six new brown dwarfs comprise one fifth of the known substellar population in \rho Oph. We estimate that the number of missing substellar objects in our survey area is ~15, down to 0.003 - 0.03 MSun and for Av = 0 - 15. The upper limit on the low-mass star to brown dwarf ratio in rho Oph is 5.1 +- 1.4, while the disk fractions are ~40% and ~60% for stars and BDs, respectively. Both results are in line with those for other nearby star forming regions.

To understand low- to intermediate-mass star-formation in the nearby R CrA molecular cloud, we try to identify the stellar content that is accessible with near-infrared observations. We obtained a JHK band mosaic of 10 x 60 arcmin square covering the entire RCrA molecular cloud with unprecedented sensitivity. We present a catalogue of about 3500 near-infrared sources fainter than the saturation limit K = 10 mag, reaching K = 18mag. We analysed the extended sources by inspecting their morphology and point sources by means of colour-colour and colour-magnitude diagrams. Additionally, we compared the extinction inferred from the NIR data with the line-of-sight dust emission at 1.2 mm. Sources towards high dust emission but relatively low H-K show a projected mm-exces; these sources are either immediately surrounded by cold circumstellar material or, if too red to be a true foreground object, they are embedded in the front layer of the 1.2 mm emitting dust cloud. In both cases they are most likely associated with the cloud.