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High-resolution, millimeter observations of disks at the protoplanetary stage reveal substructures such as gaps, rings, arcs, spirals, and cavities. While many protoplanetary disks host such substructures, only a few at the younger protostellar stage have shown similar features. We present a detailed search for early disk substructures in ALMA 1.3 and 0.87~mm observations of ten protostellar disks in the Ophiuchus star-forming region. Of this sample, four disks have identified substructure, two appear to be smooth disks, and four are considered ambiguous. The structured disks have wide Gaussian-like rings ($\sigma_R/R_{\mathrm{disk}}\sim0.26$) with low contrasts ($C<0.2$) above a smooth disk profile, in comparison to protoplanetary disks where rings tend to be narrow and have a wide variety of contrasts ($\sigma_R/R_{\mathrm{disk}}\sim0.08$ and $C$ ranges from $0-1$). The four protostellar disks with the identified substructures are among the brightest sources in the Ophiuchus sample, in agreement with trends observed for protoplanetary disks. These observations indicate that substructures in protostellar disks may be common in brighter disks. The presence of substructures at the earliest stages suggests an early start for dust grain growth and, subsequently, planet formation. The evolution of these protostellar substructures is hypothesized in two potential pathways: (1) the rings are the sites of early planet formation, and the later observed protoplanetary disk ring-gap pairs are secondary features, or (2) the rings evolve over the disk lifetime to become those observed at the protoplanetary disk stage., Comment: Accepted by ApJ, 22 pages, 10 figures

We present the results from an Atacama Large Millimeter/Submillimeter Array (ALMA) 1.3 mm continuum and $^{12}$CO ($J=2-1$) line survey spread over 10 square degrees in the Serpens star-forming region of 320 young stellar objects, 302 of which are likely members of Serpens (16 Class I, 35 Flat spectrum, 235 Class II, and 16 Class III). From the continuum data, we derive disk dust masses and show that they systematically decline from Class I to Flat spectrum to Class II sources. Grouped by stellar evolutionary state, the disk mass distributions are similar to other young ($<3$ Myr) regions, indicating that the large scale environment of a star-forming region does not strongly affect its overall disk dust mass properties. These comparisons between populations reinforce previous conclusions that disks in the Ophiuchus star-forming region have anomalously low masses at all evolutionary stages. Additionally, we find a single deeply embedded protostar that has not been documented elsewhere in the literature and, from the CO line data, 15 protostellar outflows which we catalog here., Comment: 14 pages, 9 figures, 3 tables, accepted to ApJ

The complex organic molecules (COMs) detected in star-forming regions are the precursors of the prebiotic molecules that can lead to the emergence of life. By studying COMs in more evolved protoplanetary disks we can gain a better understanding of how they are incorporated into planets. This paper presents ALMA band 7 observations of the dust and ice trap in the protoplanetary disk around Oph IRS 48. We report the first detection of dimethyl ether (CH3OCH3) in a planet-forming disk and a tentative detection of methyl formate (CH3OCHO). We determined column densities for the detected molecules and upper limits on non-detected species using the CASSIS spectral analysis tool. The inferred column densities of CH3OCH3 and CH3OCHO with respect to methanol (CH3OH) are of order unity, indicating unusually high abundances of these species compared to other environments. Alternatively, the 12CH3OH emission is optically thick and beam diluted, implying a higher CH3OH column density and a smaller emitting area than originally thought. The presence of these complex molecules can be explained by thermal ice sublimation, where the dust cavity edge is heated by irradiation and the full volatile ice content is observable in the gas phase. This work confirms the presence of oxygen-bearing molecules more complex than CH3OH in protoplanetary disks for the first time. It also shows that it is indeed possible to trace the full interstellar journey of COMs across the different evolutionary stages of star, disk, and planet formation., Comment: Accepted to A&A - 20th Jan 2022

WL 17 is a young transition disk in the Ophiuchus L1688 molecular cloud complex. Even though WL 17 is among the brightest disks in L1688 and massive enough to expect dust self-scattering, it was undetected in polarization down to ALMA's instrument sensitivity limit. Such low polarization fractions could indicate unresolved polarization within the beam or optically thin dust emission. We test the latter case by combining the high sensitivity 233 GHz Stokes I data from the polarization observations with previous ALMA data at 345 GHz and 100 GHz. We use simple geometric shapes to fit the observed disk visibilities in each band. Using our simple models and assumed dust temperature profiles, we estimate the optical depth in all three bands. The optical depth at 233 GHz peaks at $\tau_{233} \sim 0.3$, which suggests the dust emission may not be optically thick enough for dust self-scattering to be efficient. We also find the higher sensitivity 233 GHz data show substructure in the disk for the first time. The substructure appears as brighter lobes along the major axis, on either side of the star. We attempt to fit the lobes with a simple geometric model, but they are unresolved in the 233 GHz data. We propose that the disk may be flared at 1 mm such that there is a higher column of dust along the major axis than the minor axis when viewed at an inclination. These observations highlight the strength of high sensitivity continuum data from dust polarization observations to study disk structures., Comment: Accepted to ApJ, 13 pages, 6 figures

The origin of the inner dust cavities observed in transition discs remains unknown. The segregation of dust and size of the cavity is expected to vary depending on which clearing mechanism dominates grain evolution. We present the results from the Discs Down Under program, an 8.8 mm continuum Australia Telescope Compact Array (ATCA) survey targeting 15 transition discs with large (> 20 au) cavities, and compare the resulting dust emission to Atacama Large millimetre/sub-millimetre Array (ALMA) observations. Our ATCA observations resolve the inner cavity for 8 of the 14 detected discs. We fit the visibilities and reconstruct 1D radial brightness models for 10 sources with a S/N > 5sigma. We find that, for sources with a resolved cavity in both wavebands, the 8.8 mm and sub-mm brightness distributions peak at the same radius from the star. We suggest that a similar cavity size for 8.8 mm and sub-mm dust grains is due to a dust trap induced by the presence of a companion., Comment: 18 pages, 11 figures

We present the first ALMA survey of protoplanetary discs at 3 mm, targeting 36 young stellar objects in the Lupus star-forming region with deep observations (sensitivity 20-50 microJy/beam) at ~0.35" resolution (~50 au). Building on previous ALMA surveys at 0.89 and 1.3 mm that observed the complete sample of Class II discs in Lupus at a comparable resolution, we aim to assess the level of grain growth in the relatively young Lupus region. We measure 3 mm integrated fluxes, from which we derive disc-averaged 1-3 mm spectral indices. We find that the mean spectral index of the observed Lupus discs is $\alpha_\mathrm{1-3 mm}=2.23\pm0.06$, in all cases $\alpha_\mathrm{1-3 mm}<3.0$, with a tendency for larger spectral indices in the brightest discs and in transition discs. Furthermore, we find that the distribution of spectral indices in Lupus discs is statistically indistinguishable from that of the Taurus and Ophiuchus star-forming regions. Assuming the emission is optically thin, the low values $\alpha_\mathrm{1-3 mm}\leq 2.5$ measured for most discs can be interpreted with the presence of grains larger than 1 mm. The observations of the faint discs in the sample can be explained without invoking the presence of large grains, namely through a mixture of optically thin and optically thick emission from small grains. However, the bright (and typically large) discs do inescapably require the presence of millimeter-sized grains in order to have realistic masses. Based on a disc mass argument, our results challenge previous claims that the presence of optically thick sub-structures may be a universal explanation for the empirical millimeter size-luminosity correlation observed at 0.89 mm., Comment: MNRAS Accepted; 12 pages, 5 figures, 2 tables. Machine-readable tables available at https://zenodo.org/record/4756282

Protoplanetary disk surveys by the Atacama Large Millimeter/sub-millimeter Array (ALMA) are now probing a range of environmental conditions, from low-mass star-forming regions like Lupus to massive OB clusters like $\sigma$ Orionis. Here we conduct an ALMA survey of protoplanetary disks in $\lambda$ Orionis, a ~5 Myr old OB cluster in Orion, with dust mass sensitivities comparable to the surveys of nearby regions (~0.4 $M_\oplus$). We assess how massive OB stars impact planet formation, in particular from the supernova that may have occurred ~1 Myr ago in the core of $\lambda$ Orionis; studying these effects is important as most planetary systems, including our Solar System, are likely born in cluster environments. We find that the effects of massive stars, in the form of pre-supernova feedback and/or a supernova itself, do not appear to significantly reduce the available planet-forming material otherwise expected at the evolved age of $\lambda$ Orionis. We also compare a lingering massive "outlier" disk in $\lambda$ Orionis to similar systems in other evolved regions, hypothesizing that these outliers host companions in their inner disks that suppress disk dispersal to extend the lifetimes of their outer primordial disks. We conclude with numerous avenues for future work, highlighting how $\lambda$ Orionis still has much to teach us about perhaps one of the most common types of planet-forming environments in the Galaxy., Comment: 21 pages, 8 figures, 3 tables. Accepted to AAS Journals

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of a protoplanetary disk around the T Tauri star Sz~84 and analyses of the structures of the inner cavity in the central region of the dust disk. Sz~84's spectral energy distribution (SED) has been known to exhibit negligible infrared excess at $\lambda \lesssim$10~$\mu$m due to the disk's cavity structure. Analyses of the observed visibilities of dust continuum at 1.3~mm and the SED indicate that the size of the cavity in the disk of large (millimeter size) dust grains is 8~au in radius and that in the disk of small (sub-micron size) dust grains is 60~au in radius. Furthermore, from the SED analyses, we estimate that the upper limit mass of small dust grains at $r<$60~au is less than $\sim$10$^{-3}$~$M_{\rm earth}$, which is $\lesssim$0.01~\% of the total (small~$+$~large) dust mass at $r<$60~au. These results suggest that large dust grains are dominant at $r<$60~au, implying that dust grains efficiently grow with less efficient fragmentation in this region, potentially due to weak turbulence and/or stickier dust grains. The balance of grain growth and dust fragmentation is an important factor for determining the size of large dust grains in protoplanetary disks, and thus Sz~84 could serve as a good testbed for investigations of grain growth in such disks., Comment: 22 pages, 11 figures

The protoplanetary disk around Ophiuchus IRS 48 shows an azimuthally asymmetric dust distribution in (sub-)millimeter observations, which is interpreted as a vortex, where millimeter/centimeter-sized particles are trapped at the location of the continuum peak. In this paper, we present 860 $\mu$m ALMA observations of polarized dust emission of this disk. The polarized emission was detected toward a part of the disk. The polarization vectors are parallel to the disk minor axis, and the polarization fraction was derived to be $1-2$\%. These characteristics are consistent with models of self-scattering of submillimeter-wave emission, which indicate a maximum grain size of $\sim100$ $\mu$m. However, this is inconsistent with the previous interpretation of millimeter/centimeter dust particles being trapped by a vortex. To explain both, ALMA polarization and previous ALMA and VLA observations, we suggest that the thermal emission at 860 $\mu$m wavelength is optically thick ($\tau_{\rm abs}\sim7.3$) at the dust trap with the maximum observable grain size of $\sim100$ $\mu$m rather than an optically thin case with $\sim$ cm dust grains. We note that we cannot rule out that larger dust grains are accumulated near the midplane if the 860 $\mu$m thermal emission is optically thick., Comment: 22 pages, 17 figures, accepted for publication in ApJ

Protoplanetary disks in dense, massive star-forming regions are strongly affected by their environment. How this environmental impact changes over time is an important constraint on disk evolution and external photoevaporation models. We characterize the dust emission from 179 disks in the core of the young (0.5 Myr) NGC 2024 cluster. By studying how the disk mass varies within the cluster, and comparing these disks to those in other regions, we aim to determine how external photoevaporation influences disk properties over time. Using the Atacama Large Millimeter/submillimeter Array, a 2.9' x 2.9' mosaic centered on NGC 2024 FIR 3 was observed at 225 GHz with a resolution of 0.25'', or ~100 AU. The imaged region contains 179 disks identified at IR wavelengths, seven new disk candidates, and several protostars. The overall detection rate of disks is $32 \pm 4\%$. Few of the disks are resolved, with the exception of a giant (R = 300 AU) transition disk. Serendipitously, we observe a millimeter flare from an X-ray bright young stellar object (YSO), and resolve continuum emission from a Class 0 YSO in the FIR 3 core. Two distinct disk populations are present: a more massive one in the east, along the dense molecular ridge hosting the FIR 1-5 YSOs, with a detection rate of $45 \pm 7\%$. In the western population, towards IRS 1, only $15 \pm 4\%$ of disks are detected. NGC 2024 hosts two distinct disk populations. Disks along the dense molecular ridge are young (0.2 - 0.5 Myr) and partly shielded from the far ultraviolet radiation of IRS 2b; their masses are similar to isolated 1 - 3 Myr old SFRs. The western population is older and at lower extinctions, and may be affected by external photoevaporation from both IRS 1 and IRS 2b. However, it is possible these disks had lower masses to begin with., Comment: Accepted for publication in A&A; 19 pages, 13 figures. Key results shown in Fig. 8 & 10

GW Ori is a hierarchical triple system which has a rare circumtriple disk. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.3 mm dust continuum and 12CO J=2-1 molecular gas emission of the disk. For the first time, we identify three dust rings in the disk at ~46, 188, and 338 AU, with estimated dust mass of ~70-250 Earth masses, respectively. To our knowledge, the outer ring in GW Ori is the largest dust ring ever found in protoplanetary disks. We use visibility modelling of dust continuum to show that the disk has misaligned parts and the innermost dust ring is eccentric. The disk misalignment is also suggested by the CO kinematics modelling. We interpret these substructures as evidence of ongoing dynamical interactions between the triple stars and the circumtriple disk., Comment: 17 pages, 3+3 figures, 2 tables; accepted by ApJL on 2020-04-29

Transition disks with large inner dust cavities are thought to host massive companions. However, the disk structure inside the companion orbit and how material flows toward an actively accreting star remain unclear. We present a high resolution continuum study of inner disks in the cavities of 38 transition disks. Measurements of the dust mass from archival Atacama Large Millimeter/Submillimeter Array observations are combined with stellar properties and spectral energy distributions to assemble a detailed picture of the inner disk. An inner dust disk is detected in 18 of 38 disks in our sample. Of the 14 resolved disks, 9 are significantly misaligned with the outer disk. The near-infrared excess is uncorrelated with the mm dust mass of the inner disk. The size-luminosity correlation known for protoplanetary disks is recovered for the inner disks as well, consistent with radial drift. The inner disks are depleted in dust relative to the outer disk and their dust mass is uncorrelated with the accretion rates. This is interpreted as the result of radial drift and trapping by planets in a low $\alpha$ ($\sim 10^{-3}$) disk, or a failure of the $\alpha$-disk model to describe angular momentum transport and accretion. The only disk in our sample with confirmed planets in the gap, PDS 70, has an inner disk with a significantly larger radius and lower inferred gas-to-dust ratio than other disks in the sample. We hypothesize that these inner disk properties and the detection of planets are due to the gap having only been opened recently by young, actively accreting planets., Comment: 31 pages, 14 figures, accepted for publication in the Astrophysical Journal, minor corrections

Star formation involves the flow of gas and dust within molecular clouds into protostars and young stellar objects (YSOs) due to gravity. Along the way, these flows are shaped significantly by many other mechanisms, including pressure, turbulent motions, magnetic fields, stellar feedback, jets, and angular momentum. How all these mechanisms interact nonlinearly with each other on various length scales leads to the formation and evolution of substructures within clouds, including filaments, clumps, cores, disks, outflows, the protostars/YSOs themselves, and planets. In this white paper, prepared for the 2020 Long Range Plan panel which will recommend Canada's future directions for astronomy, we describe the observational and theoretical leadership in the star formation field that Canada's vibrant community has demonstrated over the past decade. Drawing from this extensive background, we identify five key questions that must be addressed for further progress to be made in understanding star formation in the next decade. Addressing these questions will improve our understanding of the dynamics of the dense gas and the role of the magnetic field in star formation, the optical properties of the dust used to trace mass and magnetic fields, the sources of variability in star-forming objects on short timescales, and the physical processes that specifically promote the clustering of stars. We further highlight key facilities in which Canada should become involved to continue making progress in this field. Single-dish facilities we recommend include LSST, trans-atmospheric far-infrared telescopes like BLAST-TNG and SPICA, and ground-based telescopes like JCMT, GBT, and CCAT-p. Interferometric facilities we recommend include ALMA, ngVLA, and SKA1., Comment: 11 pages, a contributed white paper prepared for Canada's 2020 Long Range Plan decadal process

We present a characterization of the protostar embedded within the BHR7 dark cloud, based on both photometric measurements from the near-infrared to millimeter and interferometric continuum and molecular line observations at millimeter wavelengths. We find that this protostar is a Class 0 system, the youngest class of protostars, measuring its bolometric temperature to be 50.5~K, with a bolometric luminosity of 9.3~L$_{\odot}$. The near-infrared and \textit{Spitzer} imaging show a prominent dark lane from dust extinction separating clear bipolar outflow cavities. Observations of $^{13}$CO ($J=2\rightarrow1$), C$^{18}$O ($J=2\rightarrow1$), and other molecular lines with the Submillimeter Array (SMA) exhibit a clear rotation signature on scales $<$1300~AU. The rotation can be traced to an inner radius of $\sim$170~AU and the rotation curve is consistent with an R$^{-1}$ profile, implying that angular momentum is being conserved. Observations of the 1.3~mm dust continuum with the SMA reveal a resolved continuum source, extended in the direction of the dark lane, orthogonal to the outflow. The deconvolved size of the continuum indicates a radius of $\sim$100~AU for the continuum source at the assumed distance of 400~pc. The visibility amplitude profile of the continuum emission cannot be reproduced by an envelope alone and needs a compact component. Thus, we posit that the resolved continuum source could be tracing a Keplerian disk in this very young system. If we assume that the continuum radius traces a Keplerian disk (R$\sim$120~AU) the observed rotation profile is consistent with a protostar mass of 1.0~$M_{\odot}$., Comment: 36 pages; 11 Figures, 2 Tables; Accepted to ApJ

The $\sigma$ Orionis cluster is important for studying protoplanetary disk evolution, as its intermediate age ($\sim$3-5 Myr) is comparable to the median disk lifetime. We use ALMA to conduct a high-sensitivity survey of dust and gas in 92 protoplanetary disks around $\sigma$ Orionis members with $M_{\ast}\gtrsim0.1 M_{\odot}$. Our observations cover the 1.33 mm continuum and several CO $J=2-1$ lines: out of 92 sources, we detect 37 in the mm continuum and six in $^{12}$CO, three in $^{13}$CO, and none in C$^{18}$O. Using the continuum emission to estimate dust mass, we find only 11 disks with $M_{\rm dust}\gtrsim10 M_{\oplus}$, indicating that after only a few Myr of evolution most disks lack sufficient dust to form giant planet cores. Stacking the individually undetected continuum sources limits their average dust mass to 5$\times$ lower than that of the faintest detected disk, supporting theoretical models that indicate rapid dissipation once disk clearing begins. Comparing the protoplanetary disk population in $\sigma$ Orionis to those of other star-forming regions supports the steady decline in average dust mass and the steepening of the $M_{\rm dust}$-$M_{\ast}$ relation with age; studying these evolutionary trends can inform the relative importance of different disk processes during key eras of planet formation. External photoevaporation from the central O9 star is influencing disk evolution throughout the region: dust masses clearly decline with decreasing separation from the photoionizing source, and the handful of CO detections exist at projected separations $>1.5$ pc. Collectively, our findings indicate that giant planet formation is inherently rare and/or well underway by a few Myr of age., Comment: 16 pages, 9 figures; published in AJ; The full machine readable tables can be obtained by downloading and extracting the gzipped tar source file listed under "Other formats."

We report ALMA Cycle 2 observations of 230 GHz (1.3 mm) dust continuum emission, and $^{12}$CO, $^{13}$CO, and C$^{18}$O J = 2-1 line emission, from the Upper Scorpius transitional disk [PZ99] J160421.7-213028, with an angular resolution of ~0".25 (35 AU). Armed with these data and existing H-band scattered light observations, we measure the size and depth of the disk's central cavity, and the sharpness of its outer edge, in three components: sub-$\mu$m-sized "small" dust traced by scattered light, millimeter-sized "big" dust traced by the millimeter continuum, and gas traced by line emission. Both dust populations feature a cavity of radius $\sim$70 AU that is depleted by factors of at least 1000 relative to the dust density just outside. The millimeter continuum data are well explained by a cavity with a sharp edge. Scattered light observations can be fitted with a cavity in small dust that has either a sharp edge at 60 AU, or an edge that transitions smoothly over an annular width of 10 AU near 60 AU. In gas, the data are consistent with a cavity that is smaller, about 15 AU in radius, and whose surface density at 15 AU is $10^{3\pm1}$ times smaller than the surface density at 70 AU; the gas density grades smoothly between these two radii. The CO isotopologue observations rule out a sharp drop in gas surface density at 30 AU or a double-drop model as found by previous modeling. Future observations are needed to assess the nature of these gas and dust cavities, e.g., whether they are opened by multiple as-yet-unseen planets or photoevaporation., Comment: 34 pages (single column), 13 figures, ApJ in press

An era has started in which gas and dust can be observed independently in protoplanetary disks, thanks to the recent surveys with ALMA. The first near-complete high-resolution disk survey in both dust and gas in a single star-forming region has been carried out in Lupus, finding surprisingly low gas/dust ratios. The goal of this work is to fully exploit CO isotopologues observations in Lupus, comparing them with physical-chemical model results, in order to obtain gas masses for a large number of disks. We have employed physical-chemical models to analyze continuum and CO isotopologues observations of Lupus disks, including isotope-selective processes and freeze-out. Employing also the ALMA 13CO-only detections, disk gas masses have been calculated for a total of 34 sources, expanding the sample of 10 disks studied by Ansdell et al. (2016), where also C18O was detected. We confirm that overall gas-masses are very low, often smaller than 1 $M_{\rm J}$, if volatile carbon is not depleted. Accordingly, global gas/dust ratios predominantly between 1 and 10. Low CO-based gas masses and gas/dust ratios may indicate rapid loss of gas, or alternatively chemical evolution, e.g. via sequestering of carbon from CO to more complex molecules, or carbon locked up in larger bodies. Current ALMA observations cannot distinguish between these two hypotheses. We have simulated both scenarios, but chemical model results do not allow us to rule out one of the two. Assuming that all Lupus disks have evolved mainly due to viscous processes over the past few Myr, the observed correlation between the current mass accretion rate and dust mass found by Manara et al. (2016) implies a constant gas-to-dust ratio, which is close to 100 based on the observed $M_{\rm disk}/\dot{M}_{\rm acc}$ ratio. This in turn points to a scenario in which carbon depletion is responsible for the low CO isotopologue line luminosities., Comment: 11 pages, 9 figures, A&A accepted

Understanding disk evolution and dissipation is essential for studies of planet formation. Transition disks, i.e., disks with large dust cavities and gaps, are promising candidates of active evolution. About two dozen SED-selected candidates have been confirmed to have dust cavities through millimeter interferometric imaging, but this sample is biased towards the brightest disks. The Spitzer surveys of nearby low-mass star forming regions have resulted in more than 4000 Young Stellar Objects (YSOs). Using color criteria we have selected a sample of ~150 candidates, and an additional 40 candidates and known transition disks from the literature. The Spitzer data were complemented by new observations at longer wavelengths, including new JCMT and APEX submillimeter photometry, and WISE and Herschel-PACS mid and far-infrared photometry. Furthermore, optical spectroscopy was obtained and stellar types were derived for 85% of the sample, including information from the literature. The SEDs were fit to a grid of RADMC-3D disk models with a limited number of parameters: disk mass, inner disk mass, scale height and flaring, and disk cavity radius, where the latter is the main parameter of interest. A large fraction of the targets possibly have dust cavities based on the SED. The derived cavity sizes are consistent with imaging/modeling results in the literature, where available. Trends are found with Ldisk/Lstar and stellar mass and a possible connection with exoplanet orbital radii. A comparison with a previous study where color observables are used (Cieza et al. 2010) reveals large overlap between their category of planet-forming disks and our transition disks with cavities. A large number of the new transition disk candidates are suitable for follow-up observations with ALMA., Comment: accepted for publication by A&A

NGC 1333 IRAS 4A and IRAS 4B sources are among the best studied Stage 0 low-mass protostars which are driving prominent bipolar outflows. Most studies have so far concentrated on the colder parts (T<30K) of these regions. The aim is to characterize the warmer parts of the protostellar envelope in order to quantify the feedback of the protostars on their surroundings in terms of shocks, UV heating, photodissociation and outflow dispersal. Fully sampled large scale maps of the region were obtained; APEX-CHAMP+ was used for 12CO 6-5, 13CO 6-5 and [CI] 2-1, and JCMT-HARP-B for 12CO 3-2 emissions. Complementary Herschel-HIFI and ground-based lines of CO and its isotopologs, from 1-0 upto 10-9 (Eu/k 300K), are collected at the source positions. Radiative-transfer models of the dust and lines are used to determine temperatures and masses of the outflowing and UV-heated gas and infer the CO abundance structure. Broad CO emission line profiles trace entrained shocked gas along the outflow walls, with typical temperatures of ~100K. At other positions surrounding the outflow and the protostar, the 6-5 line profiles are narrow indicating UV excitation. The narrow 13CO 6-5 data directly reveal the UV heated gas distribution for the first time. The amount of UV-heated and outflowing gas are found to be comparable from the 12CO and 13CO 6-5 maps, implying that UV photons can affect the gas as much as the outflows. Weak [CI] emission throughout the region indicates a lack of CO dissociating photons. Modeling of the C18O lines indicates the necessity of a "drop" abundance profile throughout the envelope where the CO freezes out and is reloaded back into the gas phase, thus providing quantitative evidence for the CO ice evaporation zone around the protostars. The inner abundances are less than the canonical value of CO/H_2=2.7x10^-4, indicating some processing of CO into other species on the grains., Comment: 20 pages, 22 figures, Accepted by A&A

Gas-phase complex organic molecules are commonly detected toward high-mass protostellar hot cores. Detections toward low-mass protostars and outflows are comparatively rare, and a larger sample is key to investigate how the chemistry responds to its environment. Guided by the prediction that complex organic molecules form in CH3OH-rich ices and thermally or non-thermally evaporate with CH3OH, we have identified three sight-lines in the Serpens core - SMM1, SMM4 and SMM4-W - which are likely to be rich in complex organics. Using the IRAM 30m telescope, narrow lines (FWHM of 1-2 km s-1) of CH3CHO and CH3OCH3 are detected toward all sources, HCOOCH3 toward SMM1 and SMM4-W, and C2H5OH not at all. Beam-averaged abundances of individual complex organics range between 0.6 and 10% with respect to CH3OH when the CH3OH rotational temperature is applied. The summed complex organic abundances also vary by an order of magnitude, with the richest chemistry toward the most luminous protostar SMM1. The range of abundances compare well with other beam-averaged observations of low-mass sources. Complex organic abundances are of the same order of magnitude toward low-mass protostars and high-mass hot cores, but HCOOCH3 is relatively more important toward low-mass protostars. This is consistent with a sequential ice photochemistry, dominated by CHO-containing products at low temperatures and early times., Comment: 20 pages, including 5 figures. Accepted for publication in ApJ