Molecular shells in IRC+10216: Evidence for non-isotropic and episodic mass loss enhancement

We report high angular-resolution VLA observations of cyanopolyyne molecules HC$_3$N and HC$_5$N from the carbon rich circumstellar envelope of IRC+10216. The observed low-lying rotational transitions trace a much more extended emitting region than seen in previous observations at higher frequency transitions. We resolve the hollow quasi-spherical distribution of the molecular emissions into a number of clumpy shells. These molecular shells coincide spatially with dust arcs seen in deep optical images of the IRC+10216 envelope, allowing us to study for the first time the kinematics of these features. We find that the molecular and dust shells represent the same density enhancements in the envelope separated in time by $\sim$120 to $\sim$360 yrs. From the angular size and velocity spread of the shells, we estimate that each shell typically covers about 10% of the stellar surface at the time of ejection. The distribution of the shells seems to be random in space. The good spatial correspondance between HC$_3$N and HC$_5$N emissions is in qualitative agreement with a recent chemical model that takes into account the presence of density-enhanced shells. The broad spatial distribution of the cyanopolyyne molecules, however, would necessitate further study on their formation.Comment: 16 pages, 5 figures, accepted for publication in Ap

Dynamics of horizontal-like maps in higher dimension

We study the regularity of the Green currents and of the equilibrium measure associated to a horizontal-like map in C^k, under a natural assumption on the dynamical degrees. We estimate the speed of convergence towards the Green currents, the decay of correlations for the equilibrium measure and the Lyapounov exponents. We show in particular that the equilibrium measure is hyperbolic. We also show that the Green currents are the unique invariant vertical and horizontal positive closed currents. The results apply, in particular, to Henon-like maps, to regular polynomial automorphisms of C^k and to their small pertubations.Comment: Dedicated to Professor Gennadi Henkin on the occasion of his 65th birthday, 37 pages, to appear in Advances in Mat

Dense molecular clumps in the envelope of the yellow hypergiant IRC+10420

The circumstellar envelope of the hypergiant star IRC+10420 has been traced as far out in SiO J=2-1 as in CO J = 1-0 and CO J = 2-1, in dramatic contrast with the centrally condensed (thermal) SiO- but extended CO-emitting envelopes of giant and supergiant stars. Here, we present an observation of the circumstellar envelope in SiO J=1-0 that, when combined with the previous observation in {\sioii}, provide more stringent constraints on the density of the SiO-emitting gas than hitherto possible. The emission in SiO peaks at a radius of $\sim$2\arcsec\ whereas that in SiO J=2-1 emission peaks at a smaller radius of $\sim$1\arcsec, giving rise to their ring-like appearances. The ratio in brightness temperature between SiO J=1-0 and SiO J=2-1 decreases from a value well above unity at the innermost measurable radius to about unity at radius of $\sim$2\arcsec, beyond which this ratio remains approximately constant. Dividing the envelope into three zones as in models for the CO J = 1-0 and CO J = 2-1 emission, we show that the density of the SiO-emitting gas is comparable with that of the CO-emitting gas in the inner zone, but at least an order of magnitude higher by comparison in both the middle and outer zones. The SiO-emitting gas therefore originates from dense clumps, likely associated with the dust clumps seen in scattered optical light, surrounded by more diffuse CO-emitting interclump gas. We suggest that SiO molecules are released from dust grains due to shock interactions between the dense SiO-emitting clumps and the diffuse CO-emitting interclump gas.Comment: Accepted for publication in Ap

Multiple Radial Cool Molecular Filaments in NGC 1275

We have extended our previous observation (Lim et al. 2008) of NGC1275 covering a central radius of ~10kpc to the entire main body of cool molecular gas spanning ~14kpc east and west of center. We find no new features beyond the region previously mapped, and show that all six spatially-resolved features on both the eastern and western sides (three on each side) comprise radially aligned filaments. Such radial filaments can be most naturally explained by a model in which gas deposited "upstream" in localized regions experiencing an X-ray cooling flow subsequently free falls along the gravitational potential of PerA, as we previously showed can explain the observed kinematics of the two longest filaments. All the detected filaments coincide with locally bright Halpha features, and have a ratio in CO(2-1) to Halpha luminosity of ~1e-3; we show that these filaments have lower star formation efficiencies than the nearly constant value found for molecular gas in nearby normal spiral galaxies. On the other hand, some at least equally luminous Halpha features, including a previously identified giant HII region, show no detectable cool molecular gas with a corresponding ratio at least a factor of ~5 lower; in the giant HII region, essentially all the pre-existing molecular gas may have been converted to stars. We demonstrate that all the cool molecular filaments are gravitationally bound, and without any means of support beyond thermal pressure should collapse on timescales ~< 1e6yrs. By comparison, as we showed previously the two longest filaments have much longer dynamical ages of ~1e7yrs. Tidal shear may help delay their collapse, but more likely turbulent velocities of at least a few tens km/s or magnetic fields with strengths of at least several ~10uG are required to support these filaments.Comment: 52 pages, 11 figures. Accepted to Ap