|CO emission from a molecular knot in the Cas A supernova remnant
|Supernovae play a key role in the dust budget of galaxies producing dust from freshly synthesized elements in their ejecta and processing dust in their strong shocks both in the local and in the early Universe. Key to understanding the importance of the dust formed in supernova ejecta for this budget is to quantify the effects of the reverse shock in supernova remnants in processing ejecta dust, particularly for the dense knots where newly formed dust is best protected (shock velocity scales inversely with the square root of the density). Observations of molecules provide an ideal tool to determine the characteristics of dense knots processed by the reverse shock. We propose to measure five high J pure rotational lines of CO from a knot in the supernova remnant Cas A using PACS in spectroscopy mode. Bright ro-vibrational emission from CO molecules has been discovered in the near- and mid-IR by Spitzer, Akari, and Palomar but the low spectral resolution, Akari, 4.6 micron spectrum has insufficient resolution to determine the characteristics of the emitting gas, except that the emission originates from warm (virgul2000K) and dense (&amp;gt;5x10^5 cm^-3) gas being processed by the reverse shock. The proposed PACS spectroscopy observations are designed to accurately determine the excitation of CO and thereby the density, temperature, and mass of emitting CO in this knot. These are key to understanding the preshock conditions and shock velocity for this knot. Dense knots in the supernova ejecta are the best place for dust and molecules formed in supernova ejecta to survive processing by the reverse shock because the shock velocity is much lower than in the interclump medium and hence we expect them to play a key role in seeding the ISM with supernova-produced dust. The results of these observations will form the basis for studies of the effects of the reverse shock in dense ejecta clumps using our dust processing shock models.
|CO rotational line emission from a dense knot in Cassiopeia A. Evidence for active post-reverse-shock chemistry . Wallström Sofia H. J. et al. . Astronomy & Astrophysics, Volume 558, id.L2, 4 pp. . 558 . 10.1051/0004-6361/201322576 . 2013A&A...558L...2W ,
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2012, OT2_atielens_2, SPG v14.2.0. https://doi.org/10.5270/esa-c949dkd