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An Infrared Survey of Protostars within 500 pc with HST, Spitzer and Herschel: Measuring Feedback and the Roll of the Molecular Cloud Environment in Shaping Outflows

Presentation #237.07 in the session Young Stellar Objects.

Published onJun 29, 2022
An Infrared Survey of Protostars within 500 pc with HST, Spitzer and Herschel: Measuring Feedback and the Roll of the Molecular Cloud Environment in Shaping Outflows

We present an HST near-infrared imaging survey of protostars in multiple molecular clouds within 500 pc of the Sun. Imaging with NICMOS and WFC3 at 1.6 microns, we resolve infalling envelopes and cavities carved by outflows seen in scattered light with spacial resolutions from 30 to 100 AU. We identify over 350 protostars in these observations and catalog them into point-like, unipolar, bipolar and irregular morphologies. For sources showing outflow cavities, we apply an edge-detection code calibrated with radiative transfer models to identify the cavity/envelope boundary and measure the volume in the envelope cleared out by feedback. We compare these measurements to indicators of protostellar evolution including protostellar class and bolometric temperature. In Orion, the most well sampled region, we find no direct correlation between cavity size and SED based evolutionary indicators for Class I protostars. Furthermore, we identify more evolved sources with depleted envelopes showing narrow cavities thought previously to be only present in young protostars with dense envelopes. We extend this work to the Perseus, Lupus, Ophiuchus, Aquila, Taurus, Cepheus and Chameleon molecular clouds. Using a Monte Carlo simulation, we also show that the common point-like morphology is typically explained by protostars with thin envelopes or those seen at an inclination toward the open cavity. In Orion, we identify 20 unipolar or bipolar protostars with unexpected asymmetries seen in scattered light. By comparison with Spitzer 3.6 and 4.5 micron data and with Herschel-derived N(H) mapping of Orion, we examine the mechanisms causing this asymmetry. We find evidence that such asymmetric “broken” cavities may be often be explained by outflows expanding into regions of inhomogeneous density, and that cavities observed to be more symmetric in scattered light are located in more homogeneous environments. We find examples of protostars forming at locations offset from the centers of dense gas cores. These findings indicate that symmetries assumed in models of axisymmetrically collapsing cores are not always reflected in nature and show the influence of the larger star forming environment in shaping outflow evolution.

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