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Title: The progenitor mass of the Type IIP supernova SN 2004et from late-time spectral modelling
Authors: Anders Jerkstrand, Claes Fransson, Kate Maguire, Stephen Smartt, Mattias Ergon, Jason Spyromilio

SN 2004et is one of the nearest and best-observed Type IIP supernovae, with a progenitor detection as well as good photometric and spectroscopic observational coverage well into the nebular phase. Based on nucleosynthesis from stellar evolution/explosion models we apply spectral modelling to analyse its 140-700 day evolution from ultraviolet to mid-infrared. We find a M_ZAMS= 15 solar mass progenitor star (with an oxygen mass of 0.8 solar masses) to satisfactorily reproduce [O I] 6300, 6364 {\AA} and other emission lines of carbon, sodium, magnesium, and silicon, while 12 solar mass and 19 solar mass models under- and overproduce most of these lines, respectively. This result is in fair agreement with the mass derived from the progenitor detection, but in disagreement with hydrodynamical modelling of the early-time light curve. From modelling of the mid-infrared iron-group emission lines, we determine the density of the "Ni-bubble" to rho(t) = 7E-14*(t/100d)^-3 g cm^-3, corresponding to a filling factor of f = 0.15 in the metal core region (V = 1800 km/s). We also confirm that silicate dust, CO, and SiO emission are all present in the spectra.

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Title: Dust and the type II-plateau supernova 2004et
Authors: Rubina Kotak (1), Peter Meikle (2), Duncan Farrah (3), Christopher Gerardy (4), Ryan Foley (5), Schuyler van Dyk (6), Claes Fransson (7), Peter Lundqvist (7), Jesper Sollerman (7,8), Robert Fesen (9), Alex Filippenko (5), Seppo Mattila (10), Anja Andersen (8), Peter Hoeflich (4), Monica Pozzo (11), J. Craig Wheeler (12) ((1) Queen's Uni. Belfast; (2) Imperial College London; (3) Uni. of Sussex; (4) Florida State Uni.; (5) Berkeley; (6) Spitzer Science Center; (7) Stockholm University; (8) DARK Cosmology Centre; (9) Dartmouth College; (10) Tuorla Observatory; (11) UCL; (12) Uni. of Texas)

We present mid-infrared (MIR) observations of the Type II-Plateau supernova, SN 2004et, obtained with the Spitzer Space Telescope between days 64 and 1240 post-explosion. Late-time optical spectra are also presented. For the period 300-795 days post-explosion, we argue that the spectral energy distribution of SN 2004et comprises (a) a hot component due to emission from optically thick gas, as well as free-bound radiation (b) a warm component due to newly-formed, radioactively-heated dust in the ejecta, and (c) a cold component due to an IR echo from the interstellar medium dust of the host galaxy, NGC 6946. We reveal the first-ever spectroscopic evidence for silicate dust formed in the ejecta of a recent supernova. This is supported by our detection of a large, but declining, mass of SiO. However, we conclude that the mass of directly-detected ejecta dust grew to no more than a few times 10^(-4) Msun. We also provide evidence that the ejecta dust formed in co-moving clumps of fixed size. We argue that, after about 2 years post-explosion the appearance of wide square-shaped optical line profiles was due to the impact of the ejecta on the progenitor circumstellar medium and that the subsequent formation of a cool, dense shell was responsible for a later rise in the MIR flux. This study demonstrates the rich, many-faceted ways in which a typical core-collapse supernova and its progenitor can produce and/or interact with dust grains. It also adds to the growing weight of evidence that the mass of grains produced in supernova ejecta can be only a minor contributor to the total mass of cosmic dust.

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NGC 6946
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Title: The Detection of Molecular Gas in the Outskirts of NGC 6946
Authors: Jonathan Braine, Annette M. N. Ferguson, Frank Bertoldi, Christine D. Wilson

We present the results of a search for molecular gas emission via the CO line in the far outer disk of the nearby spiral, NGC 6946. The positions targeted were chosen to lie on or near previously-identified outer disk HII regions. Molecular gas was clearly detected out to 1.3 R_{25}, with a further tentative detection at 1.4 R_{25}. The CO detections show excellent agreement with the HI velocities and imply beam-averaged column densities of 0.3-9 x 10^{20} cm^{-2} and molecular gas masses of (2-70) x 10^{5} M_{\sun} per 21'' beam (560pc). We find evidence for an abrupt decrease in the molecular fraction at the edge of the optical disk, similar to that seen previously in the azimuthally-averaged areal star formation rate. Our observations provide new constraints on the factors that determine the presence and detectability of molecular gas in the outskirts of galaxies, and suggest that neither the HI column, the metallicity or the local heating rate alone plays a dominant role.

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Title: The patterns speeds of NGC 6946
Authors: Silvia Toonen, Kambiz Fathi, Jesús Falcón-Barroso, John Beckman, Tim de Zeeuw

We study the kinematics of the barred spiral galaxy NGC 6946 by investigating the velocity field from H-alpha Fabry-Perot observations, determined the pattern speed of the bar by using the Tremaine-Weinberg method, and find a main pattern speed of 21.7 (+4.0,-0.8) km/s/kpc. Our data clearly suggest the presence of an additional pattern with a pattern speed more than twice that of the large pattern in this galaxy. We use the epicycle approximation to deduce the location of the resonance radii and subsequently determine the pattern speed between the radii, and find that inside the Inner Lindblad Resonance radius, a bar-like system has evolved.

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Supernova 2004et
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Title: Chandra Observations of SN 2004et and the X-ray Emission of Type IIp Supernovae
Authors: J. Rho, T. H. Jarrett, N. N. Chugai, R. A. Chevalier

We report the X-ray detection of the Type II-plateau supernova SN 2004et in the spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The position of the X-ray source was found to agree with the optical position within ~0.4 arcsec. Chandra also surveyed the region before the 2004 event, finding no X-ray emission at the location of the progenitor. For the post-explosion observations, a total of 202, 151, and 158 photons were detected in three pointings, each ~29 ks in length, on 2004 October 22, November 6, and December 3, respectively. The spectrum of the first observation is best fit by a thermal model with a temperature of kT=1.3 keV and a line-of-sight absorption of N_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is ~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard and soft counts on the first and third epochs indicates a softening over this time, although there is an insufficient number of photons to constrain the variation of temperature and absorption by spectral fitting. We model the emission as arising from the reverse shock region in the interaction between the supernova ejecta and the progenitor wind. For a Type IIP supernova with an extended progenitor, the cool shell formed at the time of shock wave breakout from the star can affect the initial evolution of the interaction shell and the absorption of radiation from the reverse shock. The observed spectral softening might be due to decreasing shell absorption. We find a pre-supernova mass loss rate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which is in line with expectations for a Type IIP supernova.

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