IRAS16293E revisited : a prestellar core under influence.
IRAS16293E is a prestellar core located in the vicinity of a well-known multiple class 0 system and a lesser known class I object. The west side of the core is heated by the protostars, mostly via the mechanical interaction of their outflows. Previous studies have revealed a strong DCO$^+$ peak, a ND$_3$ peak and a dust peak, all misaligned. Strong H$_2$D$^+$ and a tentative detection of D$_2$H$^+$ have also been reported towards the DCO$^+$ peak. Though a temperature gradient has been invoked for this source, two studies have advocated constant temperatures for the dust (16 K) and the gas (12 K). Given the high density derived by the different authors, the discrepancy between the gas and dust temperatures is not expected and this led us to completely reconsider this source.
By gathering archival information about dust at many wavelengths and fresh IRAM 30-m N$_2$H$^+$ and N$_2$D$^+$ observations plus a number of molecular observations from various archives, we can present a new picture of this core. We trace the outflows, report the discovery of a new one, and estimate their velocities. We identify several temperature components (including a very cold component down to 8 K), as well as the expected temperature gradient away from the protostars. We map higher turbulence in the interaction region between the core and the outflows and we measure the column densities of two deuterated species (N$_2$D$^+$ and DCO$^+$). A coherent picture emerges from this study and the misalignments are explained. Indeed, the emission peaks reveal primarily warmer gas or dust but do not trace the peak column densities which are situated further east.
This work illustrates our recent finding that even Herschel 500 $\mu$m channel cannot reveal the cold dust hidden in the cores and only a multi-wavelength study combining both dust and molecular observations can help to disentangle complicated star-forming environments like IRAS16293E. It will be the basis to re-interpret the observations of many species detected in this exceptional prestellar core.