On the Limb Darkening, Spectral Energy Distribution, and Temperature Structure of Procyon

We have fit synthetic visibilities from 3-D (CO5BOLD + PHOENIX) and 1-D (PHOENIX, ATLAS 12) model stellar atmospheres of Procyon (F5 IV) to high-precision interferometric data from the VLTI Interferometer (K-band) and from the Mark III interferometer (500 nm and 800 nm). These data sets provide a test of theoretical wavelength dependent limb-darkening predictions. The work of Allende Prieto et al. has shown that the temperature structure from a spatially and temporally averaged 3-D hydrodynamical model produces significantly less limb darkening at 500 nm relative to the temperature structure of a 1-D MARCS model atmosphere with a standard mixing-length approximation for convection. Our direct fits to the interferometric data confirm this prediction. A 1-D ATLAS 12 model with ``approximate overshooting'' provides the required temperature gradient. We show, however, that 1-D models cannot reproduce the ultraviolet spectrophotometry below 160 nm with effective temperatures in the range constrained by the measured bolometric flux and angular diameter. We find that a good match to the full spectral energy distribution can be obtained with a composite model consisting of a weighted average of twelve 1-D model atmospheres based on the surface intensity distribution of a 3-D granulation simulation. We emphasize that 1-D models with overshooting may realistically represent the mean temperature structure of F-type stars like Procyon, but the same models will predict redder colors than observed because they lack the multicomponent temperature distribution expected for the surfaces of these stars.Comment: 24 pages, 8 figures, accepted for publication in the Astrophysical Journa

The Spectral Energy Distribution and Mass-loss Rate of the A-Type Supergiant Deneb

A stellar wind module has been developed for the PHOENIX stellar atmosphere code for the purpose of computing non-LTE, line-blanketed, expanding atmospheric structures and detailed synthetic spectra of hot luminous stars with winds. We apply the code to observations of Deneb, for which we report the first positive detections of mm and cm emission (obtained using the SCUBA and the VLA), as well a strong upper limit on the 850 micron flux (using the HHT). The slope of the radio spectrum shows that the stellar wind is partially ionized. We report a uniform-disk angular diameter measurement, 2.40 +/- 0.06 mas, from the Navy Prototype Optical Interferometer (NPOI). The measured bolometric flux and corrected NPOI angular diameter yield an effective temperature of 8600 +/- 500 K. Least-squares comparisons of synthetic spectral energy distributions from 1220 A to 3.6 cm with the observations provide estimates for the effective temperature and the mass-loss rate of 8400 +/- 100 K and 8 +/- 3 E-7 M_sun/yr, respectively. This range of mass-loss rates is consistent with that derived from high dispersion UV spectra when non-LTE metal-line blanketing is considered. We are unable achieve a reasonable fit to a typical Halpha P-Cygni profile with any model parameters over a reasonable range. This is troubling because the \ha profile is the observational basis for Wind Momentum-Luminosity Relationship.Comment: Accepted by the Astrophysical Journal, 43 pages, 23 figure

A Peer Reviewed Newspaper About_ Research Networks

How do we think about networks under post-digital conditions? What does this imply for research? Publication resulting from research workshop at Canadian Embassy in Berlin, organised in collaboration with Global Emergent Media (GEM) Lab, Concordia University and transmediale festival for art and digital culture, Berlin