1,238 research outputs found
Protostellar accretion traced with chemistry: Comparing synthetic C18O maps of embedded protostars to real observations
Context: Understanding how protostars accrete their mass is a central
question of star formation. One aspect of this is trying to understand whether
the time evolution of accretion rates in deeply embedded objects is best
characterised by a smooth decline from early to late stages or by intermittent
bursts of high accretion.
Aims: We create synthetic observations of deeply embedded protostars in a
large numerical simulation of a molecular cloud, which are compared directly to
real observations. The goal is to compare episodic accretion events in the
simulation to observations and to test the methodology used for analysing the
observations.
Methods: Simple freeze-out and sublimation chemistry is added to the
simulation, and synthetic CO line cubes are created for a large number
of simulated protostars. The spatial extent of CO is measured for the
simulated protostars and compared directly to a sample of 16 deeply embedded
protostars observed with the Submillimeter Array. If CO is distributed over a
larger area than predicted based on the protostellar luminosity, it may
indicate that the luminosity has been higher in the past and that CO is still
in the process of refreezing.
Results: Approximately 1% of the protostars in the simulation show extended
CO emission, as opposed to approximately 50% in the observations,
indicating that the magnitude and frequency of episodic accretion events in the
simulation is too low relative to observations. The protostellar accretion
rates in the simulation are primarily modulated by infall from the larger
scales of the molecular cloud, and do not include any disk physics. The
discrepancy between simulation and observations is taken as support for the
necessity of disks, even in deeply embedded objects, to produce episodic
accretion events of sufficient frequency and amplitude.Comment: Accepted for publication in A&A, 11 pages, 8 figures; v2 contains
minor updates to the languag
Isometric Gaussian Process Latent Variable Model for Dissimilarity Data
We present a probabilistic model where the latent variable respects both the
distances and the topology of the modeled data. The model leverages the
Riemannian geometry of the generated manifold to endow the latent space with a
well-defined stochastic distance measure, which is modeled locally as Nakagami
distributions. These stochastic distances are sought to be as similar as
possible to observed distances along a neighborhood graph through a censoring
process. The model is inferred by variational inference based on observations
of pairwise distances. We demonstrate how the new model can encode invariances
in the learned manifolds.Comment: ICML 202
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