ORion Alma New GEneration Survey (ORANGES)

Abstract

Context. The spectral energy distribution (SED) in the millimetre to centimetre range is an extremely useful tool for characterising the dust in protostellar envelopes as well as free-free emission from the protostar and outflow. Actually, the evolutionary status of solar-type protostars is often based on their SED in the near-infrared to millimetre range. In addition, the presence or absence of free-free emission can be considered an indicator of the source evolutionary stage (Class 0/I versus Class II/III). While many studies have been carried out towards low- and high-mass protostars, little exists so far about solar-type protostars in high-mass star-forming regions, which are likely to be representatives of the conditions where the Solar System was born. Aims. In this work, we focus on the embedded solar-type protostars in the Orion Molecular Cloud (OMC) 2 and 3 filaments, which are bounded by nearby HII regions and which are, therefore, potentially affected by the high-UV illumination of the nearby OB stars. We use various dust parameters to understand whether the small-scale structure (≤1000 au) and the evolutionary status of these solar-type protostars are affected by the nearby HII regions, as is the case for the large-scale (≤104 au) gas chemical composition. Methods. We used the Atacama Large (sub-)Millimeter Array (ALMA) in the 1.3 mm band (246.2 GHz) to image the continuum of 16 young (Class 0/I) OMC-2/3 solar-type protostars, with an angular resolution of 0.25″ (100 au). We completed our data with archival data from the ALMA and VLA VANDAM survey of Orion Protostars at 333 and 32.9 GHz, respectively, to construct the dust SED and extract the dust temperature, the dust emissivity spectral index, the envelope plus disk mass of the sources and to assess whether free-free emission is contaminating their dust SED in the centimetre range. Results. From the millimetre to centimetre range dust SED, we found low dust emissivity spectral indexes (β < 1) for the majority of our source sample and free-free emission towards only 5 of the 16 sample sources. We were also able to confirm or correct the evolutionary status of the source sample reported in the literature. Finally, we did not find any dependence of the source dust parameters on their location in the OMC-2/3 filament. Conclusions. Our results show that the small-scale dust properties of the embedded OMC-2/3 protostars are not affected by the high-UV illumination from the nearby HII regions and that the formation of protostars likely takes place simultaneously throughout the filament.

The chemical nature of Orion protostars: Are ORANGES different from PEACHES? ORANGES II

“…The results of a previous single-dish study (Bouvier et al 2020) towards the same targets showed that the large scale (≤ 10 4 au) line emission is dominated by the Photo-Dissociation Region (PDR) or by the molecular cloud, rather than the protostellar envelopes. Interferometric observations are thus essential to detect hot corinos in this highly illuminated region.…”

“…They were initially 9 chosen protostellar sources based on single-dish studies (e.g. Chini et al 1997;Lis et al 1998;Nielbock et al 2003) satisfying the following three criteria: (1) detection in the (sub-)mm continuum emission; (2) estimated envelope mass ≤ 12 M ; (3) bona fide Class 0 and I protostars (see Bouvier et al 2020). The recent interferometric studies showed that most of these systems are in fact multiple systems (Tobin et al 2020;Bouvier et al 2021) which led to a total number of 19 studied targets.…”

Faust

“…As we do not know the dust temperature, T d , of the sources, we derived the dust optical depth for temperatures ranging between 100 and 500 K with steps of 10 K from 100 K to 200 K, and by steps of 20 K from 200 to 500 K, following the method described in Bouvier et al (2021). The observed 225 GHz flux provides a lower limit to T d .…”

“…The errors are calculated using the error propagation method described in Appendix C.2. ofBouvier et al (2021), and include the calibration uncertainty of 15%(Alves et al 2019) and the source size uncertainty. The left and right panels refer to 11A and 11B, respectively.…”

“…16. Dust optical depth, τ ν , at 225 GHz as function of the dust temperature, T d , derived from the observations of Alves et al (2019) and following the method described inBouvier et al (2021). The lines show τ ν as derived from Eq.…”