|Disentangling the water chemistry of the spectacular outflow BHR71
|At the earliest stages of low-mass star formation, observations show that mass accretion is associated with mass ejection in the form of collimated jets and bipolar outflows. The ejection activity can be traced as shocked regions, where shock waves originating from the central young stellar object (YSO) impact, and process the ambient interstellar medium (ISM) from which the star forms. This interaction generates molecular emission that is typical of the physical (temperature, density) and chemical (abundances) structure of the gas. Studying this molecular emission is the best way to understand the physical and chemical processes operating in shock regions. We propose to follow the water chemistry through one of the most spectacular and best-studied outflows in the Southern sky, BHR71. Because the water abundance is very susceptible to energetic input (both through direct formation in the gas-phase and through release from ice-coated dust grains), it is one of the best shock tracers. To trace the water chemistry accurately, velocity-resolved observations are required to disentangle different excitation regimes. Early Herschel results show that water excitation conditions resemble those of rotationally excited H2, i.e., high densities and temperatures of 300-1000 K. Currently, it is not possible to velocity-resolve rotational H2 lines. Herschel-HIFI has revealed that the water line profiles observed to date are very complex, and they look nothing like the spectra of other molecular traces. Water is therefore a unique tracer of the bulk of the shocked gas where the temperature is 300-1000 K. Given the importance of BHR71 as the most chemically rich outflow in the southern sky, that makes it a key benchmark for outflow and shock modelling with ALMA, we propose to map this outflow in a few key H2O lines with HIFI. The maps will provide legacy-value information on water and shock excitation as a function of position and velocity throughout the outflow.
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT2_lkrist01_3, SPG v14.1.0. https://doi.org/10.5270/esa-cquc3bw