Results 1 - 10 of 1816
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[en] We calculate simulated images of disks perturbed by embedded small planets. These 10-50 M+ bodies represent the growing cores of giant planets. We examine scattered light and thermal emission from these disks over a range of wavelengths, taking into account the wavelength-dependent opacity of dust in the disk. We also examine the effect of inclination on the observed perturbations. We find that the perturbations are best observed in the visible to mid-infrared (mid-IR). Scattered light images reflect shadows produced at the surface of perturbed disks, while the infrared images follow thermal emission from the surface of the disk, showing cooled/heated material in the shadowed/brightened regions. At still longer wavelengths in the submillimeter, the perturbation fades as the disk becomes optically thin and surface features become overwhelmed by emission closer toward the midplane of the disk. With the construction of telescopes such as TMT, GMT, and ALMA due in the next decade, there is a real possibility of observing planets forming in disks in the optical and submillimeter. However, having the angular resolution to observe the features in the mid-IR will remain a challenge.
[en] A global disk oscillation implemented in the viscous decretion disk (VDD) model has been used to reproduce most of the observed properties of the well known Be star ζ Tau. 48 Librae shares several similarities with ζ Tau—they are both early-type Be stars, display shell characteristics in their spectra, and exhibit cyclic V / R variations—but has some marked differences as well, such as a much denser and more extended disk, a much longer V / R cycle, and the absence of the so-called triple-peak features. We aim to reproduce the photometric, polarimetric, and spectroscopic observables of 48 Librae with a self-consistent model, and to test the global oscillation scenario for this target. Our calculations are carried out with the three-dimensional NLTE radiative transfer code HDUST. We employ a rotationally deformed, gravity-darkened central star surrounded by a disk whose unperturbed state is given by the VDD model. A two-dimensional global oscillation code is then used to calculate the disk perturbation and superimpose it on the unperturbed disk. A very good, self-consistent fit to the time-averaged properties of the disk is obtained with the VDD. The calculated perturbation has a period P = 12 years, which agrees with the observed period, and the behavior of the V / R cycle is well reproduced by the perturbed model. The perturbed model improves the fit to the photometric data and reproduces some features of the observed spectroscopic data. Some suggestions to improve the synthesized spectroscopy in a future work are given.
[en] We present predictions for the normalized Stokes visibilities of a Be star disk, as would be measured by an interferometric polarimeter. Using both a simple geometric model for the disk as well as a more complex radiative transfer model, we investigate, in detail, the effect of each of the model parameters on the resultant normalized Stokes visibilities. We find normalized visibility amplitudes for the total star and disk system of ∼10-2-10-3 at shorter baselines, and ∼10-3-10-4 at longer baselines, requiring, at small and moderate baselines, an accuracy for interferometric polarization observations better than ∼10-3-10-4, including all random and systematic errors. Provided this level of accuracy is attainable, we find that the Stokes Q visibility may be important both for the removal of model degeneracies present when considering the intensity alone, as well as for providing an estimate of the inclination angle of the disk.
[en] A cascade model for driven quasi-steady fluid turbulence is applied to calculation of the dissipation parameter, alpha, for a convection-accretion disk. The mode analysis is nonlocal in the vertical direction and allows arbitrary rotation curves. Nonaxisymmetric modes, nonlinear mode structure, and turbulent cascade dynamics are all treated. It is shown that proper respect of these features leads to a much larger value of alpha than would be the case in their neglect. 21 refs
[en] We present here findings for C18O depletion in eight starless cores in Taurus: TMC-2, L1498, L1512, L1489, L1517B, L1521E, L1495A-S, and L1544. We compare observations of the C18O J = 2-1 transition taken with the ALMA prototype receiver on the Heinrich Hertz Submillimeter Telescope to results of radiative transfer modeling using RATRAN. We use temperature and density profiles calculated from dust continuum radiative transfer models to model the C18O emission. We present modeling of three cores, TMC-2, L1489, and L1495A-S, which have not been modeled before, and compare our results for the five cores with published models. We find that all of the cores but one, L1521E, are substantially depleted. We also find that varying the temperature profiles of these model cores has a discernable effect, and varying the central density has an even larger effect. We find no trends with depletion radius or depletion fraction with the density or temperature of these cores, suggesting that the physical structure alone is insufficient to fully constrain evolutionary state. We are able to place tighter constraints on the radius at which C18O is depleted than the absolute fraction of depletion. As the timeline of chemical depletion depends sensitively on the fraction of depletion, this difficulty in constraining depletion fraction makes comparison with other timescales, such as the free-fall timescale, very difficult.
[en] The formal solution, in linear, nonadiabatic theory, has been obtained of the problem of the vibrational stability of a system possesing arbitrary, but steady, inviscid flows in its unperturbed (nonoscillating) state. The unperturbed system may have any geometry, but no large-scale magnetic fields are assumed. A special case is a (steadily) rotating star, where the rotation may be uniform or differential, slow or fast. This formulation may ultimately provide a new approach to the problem of the interaction (in linear theory) between stellar convection and pulsations. The formal solution is expressed in terms of certain integrals over the volume of the system. These integrals involve the nonadiabatic eigenfunctions for the oscillating system, but they may be approximated by suitable trial functions. This solution is surprisingly simple, bears considerable resemblance to previously derived formal solutions, and has a straightforward physical interpretation
[en] We report a new detection of the H-band thermal emission of CoRoT-1b and two confirmation detections of the Ks-band thermal emission of WASP-12b at secondary eclipses. The H-band measurement of CoRoT-1b shows an eclipse depth of 0.145% ± 0.049% with a 3σ percentile between 0.033% and 0.235%. This depth is consistent with the previous conclusions that the planet has an isothermal region with inefficient heat transport from day side to night side, and has a dayside thermal inversion layer at high altitude. The two Ks-band detections of WASP-12b show a joint eclipse depth of 0.299% ± 0.065%. This result agrees with the measurement of Croll and collaborators, providing independent confirmation of their measurement. The repeatability of the WASP-12b measurements also validates our data analysis method. Our measurements, in addition to a number of previous results made with other telescopes, demonstrate that ground-based observations are becoming widely available for characterization of atmospheres of hot Jupiters.