Widening of Protostellar Outflows: an Infrared Outflow Survey in Low
  Luminosity Objects
  We present an outflow survey toward 20 Low Luminosity Objects (LLOs), namely
protostars with an internal luminosity lower than 0.2 Lsun. Although a number
of studies have reported the properties of individual LLOs, the reasons for
their low luminosity remain uncertain. To answer this question, we need to know
the evolutionary status of LLOs. Protostellar outflows are found to widen as
their parent cores evolve, and therefore, the outflow opening angle could be
used as an evolutionary indicator. The infrared scattered light escapes out
through the outflow cavity and highlights the cavity wall, giving us the
opportunity to measure the outflow opening angle. Using the
Canada-France-Hawaii Telescope, we detected outflows toward eight LLOs out of
20 at Ks band, and based on archival Spitzer IRAC1 images, we added four
outflow-driving sources from the remaining 12 sources. By fitting these images
with radiative transfer models, we derive the outflow opening angles and
inclination angles. To study the widening of outflow cavities, we compare our
sample with the young stellar objects from Arce & Sargent 2006 and Velusamy et
al. 2014 in the plot of opening angle versus bolometric temperature taken as an
evolutionary indicator.Our LLO targets match well the trend of increasing
opening angle with bolometric temperature reported by Arce & Sargent and are
broadly consistent with that reported by Velusamy et al., suggesting that the
opening angle could be a good evolutionary indicator for LLOs. Accordingly, we
conclude that at least 40% of the outflow-driving LLOs in our sample are young
Class 0 objects.
