arXiv subjects

J. Canto

Publications and source records attributed to J. Canto.

21 records · Page 2Linked to original sources

arXiv2002

Radio Continuum Observations towards Optical and Molecular Outflows

We present multi-frequency VLA continuum observations towards 8 star forming regions with molecular and optical outflows: L1489, HH 68-69, HH 94-95, NGC 2264D, L1681B, L778, MWC 1080 and V645 Cyg. We detect three thermal radio jets, L1489, YLW 16A in L1681B and NGC 2264D VLA 7, associated with molecular and/or HH outflows. The L1489 and NGC 2264D VLA 7 thermal radio jets appear elongated in the direction of the larger scale outflow. We report the first tentative detection of a non-thermal radio jet, L778 VLA 5, associated with a low mass Class I protostar and powering a molecular outflow. For HH68-69, HH 94-95 and the molecular outflow in NGC 2264D we could not identify a candidate of the exciting source of these outflows. The radio emission associated with V645 Cyg is quite extended, ~0.1 pc, and time variable. We detect three radio sources in the MWC 1080 that could be associated with YSOs.

astro-ph↗

arXiv2000

Photoevaporating flows from the cometary knots in the Helix nebula (NGC 7293)

We explain the Ha emission of the cometary knots in the Helix Nebula (NGC 7293) with an analytical model that describes the emission of the head of the globules as a photoevaporated flow produced by the incident ionizing radiation of the central star.We compare these models with the Ha emission obtained from the HST archival images of the Helix Nebula. From a comparison of the Ha emission with the predictions of the analytical model we obtain a rate of ionizing photons from the central star of about 5e45 s^-1, which is consistent with estimates based on the total Hb flux of the nebula. We also model the tails of the cometary knots as a photoevaporated wind from a neutral shadow region produced by the diffuse ionizing photon field of the nebula. A comparison with the HST images allows us to obtain a direct determination of the value of the diffuse ionizing flux. We compare the ratio of diffuse to direct stellar flux as a function of radius inside an HII region with those obtained from the observational data through the analytical tail and head wind model. The agreement of this model with the values determined from the observations of the knots is excellent.

astro-ph↗

arXiv1997

Does Turbulent Pressure Behave as a Logatrope?

We present numerical simulations of an isothermal turbulent gas undergoing gravitational collapse, aimed at testing for ``logatropic'' behavior of the form $P_t \sim \log ρ$, where $P_t$ is the ``turbulent pressure'' and $ρ$ is the density. To this end, we monitor the evolution of the turbulent velocity dispersion $σ$ as the density increases during the collapse. A logatropic behavior would require that $σ\propto ρ^{-1/2}$, a result which, however, is not verified in the simulations. Instead, the velocity dispersion increases with density, implying a polytropic behavior of $P_t$. This behavior is found both in purely hydrodynamic as well as hydromagnetic runs. For purely hydrodynamic and rapidly-collapsing magnetic cases, the velocity dispersion increases roughly as $σ\propto ρ^{1/2}$, implying $P_t\sim ρ^2$, where $P_t$ is the turbulent pressure. For slowly-collapsing magnetic cases the behavior is close to $σ\propto ρ^{1/4}$, which implies $P_t \sim ρ^{3/2}$. We thus suggest that the logatropic ``equation of state'' may represent only the statistically most probable state of an ensemble of clouds in equilibrium between self-gravity and kinetic support, but does not adequately represent the behavior of the ``turbulent pressure'' within a cloud undergoing a dynamic compression due to gravitational collapse. Finally, we discuss the importance of the underlying physical model for the clouds (in equilibrium vs. dynamic) on the results obtained.

astro-ph↗