VLT - Infrared Integral Field Spectrometer Observations of Molecular Hydrogen Lines in the Knots in the Planetary Nebula NGC 7293 the Helix Nebula - AstrophysicsReport as inadecuate




VLT - Infrared Integral Field Spectrometer Observations of Molecular Hydrogen Lines in the Knots in the Planetary Nebula NGC 7293 the Helix Nebula - Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: Knots are commonly found in nearby planetary nebulae PNe and star formingregions. Within PNe, knots are often found to be associated with the brightestparts of the nebulae and understanding the physics involved in knots may revealthe processes dominating in PNe. As one of the closest PNe, the Helix NebulaNGC 7293 is an ideal target to study such small-scale ~300 AU structures.We have obtained infrared integral spectroscopy of a comet-shaped knot in theHelix Nebula using SINFONI on the Very Large Telescope at high spatialresolution 50-125 mas. With spatially resolved 2 micron spectra, we find thatthe H2 rotational temperature within the cometary knots is uniform. Therotational-vibrational temperature of the cometary knot situated in theinnermost region of the nebula, 2.5 arcmin away from the central star, is 1800K, higher than the temperature seen in the outer regions 5-6 arcmin from thecentral star of the nebula 900 K, showing that the excitation temperaturevaries across the nebula. The obtained intensities are reasonably well fittedwith 27 km s-1 C-type shock model. This ambient gas velocity is slightly higherthan the observed HeII wind velocity of 13 km s-1. The gas excitation canalso be reproduced with a PDR photo dominant region model, but this requiresan order of magnitude higher UV radiation. Both models have limitations,highlighting the need for models that treats both hydrodynamical physics andthe PDR.



Author: M. Matsuura 1,2,3, A.K. Speck 4, M.D. Smith 5, A.A. Zijlstra 3,6, S. Viti 7, K.T.E. Lowe 8, M. Redman 9, C.J. Wareing 3, E. Lagad

Source: https://arxiv.org/



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