Context. Despite the low cosmic abundance of deuterium (D/H ∼ 10 −5 ), high degrees of deuterium fractionation in molecules are observed in star-forming regions with enhancements that can reach 13 orders of magnitude, a level that current models have difficulty accounting for. Aims. Multi-isotopologue observations are a very powerful constraint for chemical models. The aim of our observations is to understand the processes that form the observed high abundances of methanol and formaldehyde in low-mass protostellar envelopes (gas-phase processes? chemistry on the grain surfaces?), as well as to better constrain the chemical models.Methods. With the IRAM 30 m single-dish telescope, we observed deuterated formaldehyde (HDCO and D 2 CO) and methanol (CH 2 DOH, CH 3 OD, and CHD 2 OH) towards a sample of seven low-mass class 0 protostars. Using population diagrams, we then derived the fractionation ratios of these species (abundance ratio between the deuterated molecule and its main isotopologue) and compared them to the predictions of grain chemistry models. Results. These protostars show a similar level of deuteration as in IRAS 16293−2422, where doubly-deuterated methanol -and even triply-deuterated methanol -were first detected. Our observations point to the formation of methanol on the grain surfaces, while formaldehyde formation cannot be fully pinned down. While none of the scenarii can be excluded (gas-phase or grain chemistry formation), they both seem to require abstraction reactions to reproduce the observed fractionations.

Accurate measurements of the physical structure of protoplanetary discs are critical inputs for planet formation models. These constraints are traditionally established via complex modelling of continuum and line observations. Instead, we present an empirical framework to locate the CO isotopologue emitting surfaces from high spectral and spatial resolution ALMA observations. We apply this framework to the disc surrounding IM Lupi, where we report the first direct, i.e. model independent, measurements of the radial and vertical gradients of temperature and velocity in a protoplanetary disc. The measured disc structure is consistent with an irradiated self-similar disc structure, where the temperature increases and the velocity decreases towards the disc surface. We also directly map the vertical CO snow line, which is located at about one gas scale height at radii between 150 and 300 au, with a CO freeze-out temperature of 21 ± 2 K. In the outer disc (> 300 au), where the gas surface density transitions from a power law to an exponential taper, the velocity rotation field becomes significantly sub-Keplerian, in agreement with the expected steeper pressure gradient. The sub-Keplerian velocities should result in a very efficient inward migration of large dust grains, explaining the lack of millimetre continuum emission outside of 300 au. The sub-Keplerian motions may also be the signature of the base of an externally irradiated photo-evaporative wind. In the same outer region, the measured CO temperature above the snow line decreases to ≈ 15 K because of the reduced gas density, which can result in a lower CO freeze-out temperature, photo-desorption, or deviations from local thermodynamic equilibrium.

Context. Understanding the formation mechanisms of protoplanetary disks and multiple systems and also their pristine properties are key questions for modern astrophysics. The properties of the youngest disks, embedded in rotating infalling protostellar envelopes, have largely remained unconstrained up to now. Aims. We aim to observe the youngest protostars with a spatial resolution that is high enough to resolve and characterize the progenitors of protoplanetary disks. This can only be achieved using submillimeter and millimeter interferometric facilities. In the framework of the IRAM Plateau de Bure Interferometer survey CALYPSO, we have obtained subarcsecond observations of the dust continuum emission at 231 GHz and 94 GHz for a sample of 16 solar-type Class 0 protostars. Methods. In an attempt to identify disk-like structures embedded at small scales in the protostellar envelopes, we modeled the dust continuum emission visibility profiles using Plummer-like envelope models and envelope models that include additional Gaussian disk-like components.Results. Our analysis shows that in the CALYPSO sample, 11 of the 16 Class 0 protostars are better reproduced by models including a disk-like dust continuum component contributing to the flux at small scales, but less than 25% of these candidate protostellar disks are resolved at radii > 60 au. Including all available literature constraints on Class 0 disks at subarcsecond scales, we show that our results are representative: most (> 72% in a sample of 26 protostars) Class 0 protostellar disks are small and emerge only at radii < 60 au. We find a multiplicity fraction of the CALYPSO protostars < ∼ 57% ± 10% at the scales 100-5000 au, which generally agrees with the multiplicity properties of Class I protostars at similar scales. Conclusions. We compare our observational constraints on the disk size distribution in Class 0 protostars to the typical disk properties from protostellar formation models. If Class 0 protostars contain similar rotational energy as is currently estimated for prestellar cores, then hydrodynamical models of protostellar collapse systematically predict a high occurrence of large disks. Our observations suggest that these are rarely observed, however. Because they reduce the centrifugal radius and produce a disk size distribution that peaks at radii < 100 au during the main accretion phase, magnetized models of rotating protostellar collapse are favored by our observations.

We present far-infrared (57−196 µm) spectra of 21 protostars in the Orion molecular clouds. These were obtained with the Photodetector Array Camera and Spectrometer (PACS) onboard the Herschel Space observatory, as part of the Herschel Orion Protostar Survey (HOPS) program. We analyzed the emission lines from rotational transitions of CO, involving rotational quantum numbers in the range J up = 14−46, using PACS spectra extracted within a projected distance of 2000 AU centered on the protostar. The total luminosity of the CO lines observed with PACS (L CO ) is found to increase with increasing protostellar luminosity (L bol ). However, no significant correlation is found between L CO and evolutionary indicators or envelope properties of the protostars such as bolometric temperature, T bol or envelope density. The CO rotational (excitation) temperature implied by the line ratios increases with increasing rotational quantum number J, and at least 3−4 rotational temperature components are required to fit the observed rotational diagram in the PACS wavelength range. The rotational temperature components are remarkably invariant between protostars and show no dependence on L bol , T bol or envelope density, implying that if the emitting gas is in local thermodynamic equillibrium, the CO emission must arise in multiple temperature components that remain independent of L bol over two orders of magnitudes. The observed CO emission can also be modeled as arising from a single temperature gas component or from a medium with a power-law temperature distribution; both of these require sub-thermally excited molecular gas at low densities (n(H 2 ) 10 6 cm −3 ) and high temperatures (T 2000 K). Our results suggest that the contribution from photodissociation regions (PDRs), produced along the envelope cavity walls from UV-heating, is unlikely to be the dominant component of the CO emission observed with PACS. Instead, the 'universality' of the rotational temperatures and the observed correlation between L CO and L bol can most easily be explained if the observed CO emission originates in shock-heated, hot (T 2000 K), sub-thermally excited (n(H 2 ) 10 6 cm −3 ) molecular gas. Post-shock gas at these densities is more likely to be found within the outflow cavities along the molecular outflow or along the cavity walls at radii several 100−1000 AU.

Complex organic molecules have previously been discovered in solar type protostars, raising the questions of where and how they form in the envelope. Possible formation mechanisms include grain mantle evaporation, interaction of the outflow with its surroundings or the impact of UV/X-rays inside the cavities. In this Letter we present the first interferometric observations of two complex molecules, CH 3 CN and HCOOCH 3 , towards the solar type protostar IRAS16293-2422. The images show that the emission originates from two compact regions centered on the two components of the binary system. We discuss how these results favor the grain mantle evaporation scenario and we investigate the implications of these observations for the chemical composition and physical and dynamical state of the two components. Subject headings: ISM: abundances -ISM: individual (IRAS16293) -ISM: molecules -stars: formation 0 Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

Abstract. We present a survey of the formaldehyde emission in a sample of eight Class 0 protostars obtained with the IRAM and JCMT millimeter telescopes. The range of energies of the observed transitions allows us to probe the physical and chemical conditions across the protostellar envelopes. The data have been analyzed with three different methods with increasing level of sophistication. We first analyze the observed emission in the LTE approximation, and derive rotational temperatures between 11 and 40 K, and column densities between 1 and 20 × 10 13 cm −2 . Second, we use a LVG code and derive higher kinetic temperatures, between 30 and 90 K, consistent with subthermally populated levels and densities from 1 to 6 × 10 5 cm −3 . The column densities from the LVG modeling are within a factor of 10 with respect to those derived in the LTE approximation. Finally, we analyze the observations based upon detailed models for the envelopes surrounding the protostars, using temperature and density profiles previously derived from continuum observations. We approximate the formaldehyde abundance across the envelope with a jump function, the jump occurring when the dust temperature reaches 100 K, the evaporation temperature of the grain mantles. The observed formaldehyde emission is well reproduced only if there is a jump of more than two orders of magnitude, in four sources. In the remaining four sources the data are consistent with a formaldehyde abundance jump, but the evidence is more marginal (≤2 σ). The inferred inner H 2 CO abundance varies between 1 × 10 −8 and 6 × 10 −6 . The absolute values of the jump in the H 2 CO abundance are uncertain by about one order of magnitude, because of the uncertainties in the density, ortho to para ratio, temperature and velocity profiles of the inner region, as well as the evaporation temperature of the ices. We discuss the implications of these jumps for our understanding of the origin and evolution of ices in low mass star forming regions. Finally, we give predictions for the submillimeter H 2 CO lines, which are particularly sensitive to the abundance jumps.

We present a study of dense molecular gas kinematics in seventeen nearby protostellar systems using single-dish and interferometric molecular line observations. The non-axisymmetric envelopes around a sample of Class 0/I protostars were mapped in the N 2 H + (J = 1 → 0) tracer with the IRAM 30m, CARMA and PdBI as well as NH 3 (1,1) with the VLA. The molecular line emission is used to construct line-center velocity and linewidth maps for all sources to examine the kinematic structure in the envelopes on spatial scales from 0.1 pc to ∼1000 AU. The direction of the large-scale velocity gradients from single-dish mapping is within 45 • of normal to the outflow axis in more than half the sample. Furthermore, the velocity gradients are often quite substantial, the average being ∼2.3 km s −1 pc −1 . The interferometric data often reveal small-scale velocity structure, departing from the more gradual large-scale velocity gradients. In some cases, this likely indicates accelerating infall and/or rotational spin-up in the inner envelope; the median velocity gradient from the interferometric data is ∼10.7 km s −1 pc −1 . In two systems, we detect high-velocity HCO + (J = 1 → 0) emission inside the highestvelocity N 2 H + emission. This enables us to study the infall and rotation close to the disk and estimate the central object masses. The velocity fields observed on large and small-scales are more complex than would be expected from rotation alone, suggesting that complex envelope structure enables other dynamical processes (i.e. infall) to affect the velocity field. 1 Based on observations carried out with the IRAM 30m Telescope and IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).-5with 20kHz channels and in 2009 we used 40 MHz with 20kHz channels; see Table 2 the list of sources observed and more detail.We conducted our observations using frequency-switched on-the-fly (OTF) mapping mode. The maps varied in size depending on the extent of the source being observed, most being 3 × 3 . Most maps were integrated down to at least σ T ∼ 150mK for the N 2 H + (J = 1 → 0) transition, noise levels for each map are listed in Table 2. We mapped the sources by scanning in the northsouth direction and again in the east-west direction to minimize striping in the final map. The scan legs were stepped by 5 and we repeated the maps to gain a higher signal-to-noise ratio. Calibration scans were taken about every 10 minutes between scan legs and the final maps took approximately 2 hours to complete. Pointing was checked about every two hours, azimuth and elevation offsets were typically ±5 ; the pointing offset remained stable, typically within ∼2 during an observation. These values agree well with the rms pointing accuracy of ∼2 .

We report the detection of complex molecules (HCOOCH 3 , HCOOH and CH 3 CN), signposts of a "hot core" like region, toward the low mass, Class 0 source NGC1333-IRAS4A. This is the second low mass protostar where such complex molecules have been searched for and reported, the other source being IRAS16293-2422. It is therefore likely that compact (few tens of AUs) regions of dense and warm gas, where the chemistry is dominated by the evaporation of grain mantles, and where complex molecules are found, are common in low mass Class 0 sources. Given that the chemical formation timescale is much shorter than the gas hot core crossing time, it is not clear whether the reported complex molecules are formed on the grain surfaces (first generation molecules) or in the warm gas by reactions involving the evaporated mantle constituents (second generation molecules). We do not find evidence for large differences in the molecular abundances, normalized to the formaldehyde abundance, between the two solar type protostars, suggesting perhaps a common origin.