ORion Alma New GEneration Survey (ORANGES) I. Dust continuum and
  free-free emission of OMC-2/3 filament protostars
  The spectral energy distribution (SED) in the millimetre (mm) to centimetre
(cm) range is a useful tool for characterising the dust in protostellar
envelopes as well as free-free emission from the protostar and outflow. 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. We focus here on the OMC-2/3 solar-type protostars,
which are bounded by nearby HII regions and which are, therefore, potentially
affected by the high-UV illumination. We aim to understand whether the
small-scale structure ($\leq$1000 au) and the evolutionary status of these
solar-type protostars are affected by the nearby HII regions, as is the case
for the large-scale ($\leq$10$^4$ au) gas chemical composition. We used ALMA in
the 1.3 mm band (246.2 GHz) to image the continuum of 16 OMC-2/3 solar-type
protostars, with an angular resolution of 0.25$''$ (100 au). We completed our
data with archival data from the VANDAM survey of Orion Protostars at 333 and
32.9 GHz, respectively, to construct the dust SED, extract several dust
parameters and to assess whether free-free emission is contaminating their dust
SED in the cm range. From the mm to cm range dust SED, we found low dust
emissivity spectral indexes ($\beta < 1$) 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.
Finally, we did not find any dependence of the source dust parameters on their
location in the OMC-2/3 filament. Our results show that the small-scale dust
properties of the OMC-2/3 protostars are not affected by the high- UV
illumination from the nearby HII regions.
