Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei

We report a detection of water in emission in the spectrum of the M2 supergiant atar mu Cep (M2Ia) observed by the Short Wavelength Spectrometer (SWS) aboard Infrared Space Observatory (ISO) and now released as the ISO Archives. The emission first appears in the 6 micron region (nu2 fundamental) and then in the 40 micron region (pure rotation lines) despite the rather strong dust emission. The intensity ratios of the emission features are far from those of the optically thin gaseous emission. Instead, we could reproduce the major observed emission features by an optically thick water sphere of the inner radius about two stellar radii (1300Rsun), Tex = 1500K, and Ncol (H2O) = 3.0E+20/cm2. This model also accounts for the H2O absorption bands in the near infrared (1.4, 1.9, and 2.7 micron) as well. The detection of water in emission provides strong constraints on the nature of water in the early M supergiant stars, and especially its origin in the outer atmosphere is confirmed against other models such as the large convective cell model. We finally confirm that the early M supergiant star is surrounded by a huge optically thick sphere of the warm water vapor, which may be referred to as MOLsphere for simplicity. Thus, the outer atmosphere of M supergiant stars should have a complicated hierarchical and/or hybrid structure with at least three major constituents including the warm MOLsphere (T about 1.0E+3K) together with the previously known hot chromosphere (T about 1.0E+4K) and cool expanding gas-dust envelope (T about 1.0E+2K).Comment: 14 pages, 5 postscript figures, to appear in ApJ

Water vapor on supergiants. The 12 micron TEXES spectra of mu Cephei

Several recent papers have argued for warm, semi-detached, molecular layers surrounding red giant and supergiant stars, a concept known as a MOLsphere. Spectroscopic and interferometric analyses have often corroborated this general picture. Here, we present high-resolution spectroscopic data of pure rotational lines of water vapor at 12 microns for the supergiant mu Cephei. This star has often been used to test the concept of molecular layers around supergiants. Given the prediction of an isothermal, optically thick water-vapor layer in Local Thermodynamic Equilibrium around the star (MOLsphere), we expected the 12 micron lines to be in emission or at least in absorption but filled in by emission from the molecular layer around the star. Our data, however, show the contrary; we find definite absorption. Thus, our data do not easily fit into the suggested isothermal MOLsphere scenario. The 12 micron lines, therefore, put new, strong constraints on the MOLsphere concept and on the nature of water seen in signatures across the spectra of early M supergiants. We also find that the absorption is even stronger than that calculated from a standard, spherically symmetric model photosphere without any surrounding layers. A cool model photosphere, representing cool outer layers is, however, able to reproduce the lines, but this model does not account for water vapor emission at 6 microns. Thus, a unified model for water vapor on mu Cephei appears to be lacking. It does seem necessary to model the underlying photospheres of these supergiants in their whole complexity. The strong water vapor lines clearly reveal inadequacies of classical model atmospheres.Comment: Accepted for publication in the Astrophysical Journa

Extrasolar Giant Planets under Strong Stellar Irradiation

We investigate the effects on extrasolar giant planets [EGPs] of intense irradiation by their parent stars, describing the issues involved in treating the model atmosphere problem correctly. We treat the radiative transfer in detail, allowing the flux from the parent star to interact with all relevant depths of the planetary atmosphere, with no need for a pre-assumed albedo. We present a low-resolution optical and near-IR spectrum of a close-in EGP, focusing on the differences from an isolated planet. In our dust-free planetary atmospheres we find that Rayleigh scattering increases the EGP's flux by orders of magnitude shortward of the CaII H&K doublet (393 nm), and the spectral features of the parent star are exactly reflected. In the optical and near-IR the thermal absorption of the planet takes over, but the absorption features are changed by the irradiation. The inclusion of dust increases the reflected flux in the blue; the stellar spectral lines can be seen blueward of H-beta (486 nm).Comment: 14 pages, 4 figures, LaTex, accepted in ApJ

Dust in the Photospheric Environment: Unified Cloudy Models of M, L, and T Dwarfs

We address the problem of how dust forms and how it could be sustained in the static photospheres of cool dwarfs for a long time. In the cool and dense gas, dust forms easily at the condensation temperature, T_cond, and the dust can be in detailed balance with the ambient gas so long as it remains smaller than the critical radius, r_cr. However, dust will grow larger and segregate from the gas when it will be larger than r_cr somewhere at the lower temperature, which we refer to as the critical temperature, T_cr. Then, the large dust grains will precipitate below the photosphere and only the small dust grains in the region of T_cr < T < T_cond can be sustained in the photosphere. Thus a dust cloud is formed. Incorporating the dust cloud, non-grey model photo- spheres in radiative-convective equilibrium are extended to T_eff as low as 800K. Observed colors and spectra of cool dwarfs can consistently be accounted for by a single grid of our cloudy models. This fact in turn can be regarded as supporting evidence for our basic assumption on the cloud formation.Comment: 50 pages with 14 postscript figures, to be published in Astrophys.

The Evolution of L and T Dwarfs in Color-Magnitude Diagrams

We present new evolution sequences for very low mass stars, brown dwarfs and giant planets and use them to explore a variety of influences on the evolution of these objects. We compare our results with previous work and discuss the causes of the differences and argue for the importance of the surface boundary condition provided by atmosphere models including clouds. The L- to T-type ultracool dwarf transition can be accommodated within the Ackerman & Marley (2001) cloud model by varying the cloud sedimentation parameter. We develop a simple model for the evolution across the L/T transition. By combining the evolution calculation and our atmosphere models, we generate colors and magnitudes of synthetic populations of ultracool dwarfs in the field and in galactic clusters. We focus on near infrared color- magnitude diagrams (CMDs) and on the nature of the ``second parameter'' that is responsible for the scatter of colors along the Teff sequence. Variations in metallicity and cloud parameters, unresolved binaries and possibly a relatively young population all play a role in defining the spread of brown dwarfs along the cooling sequence. We find that the transition from cloudy L dwarfs to cloudless T dwarfs slows down the evolution and causes a pile up of substellar objects in the transition region, in contradiction with previous studies. We apply the same model to the Pleiades brown dwarf sequence. Taken at face value, the Pleiades data suggest that the L/T transition occurs at lower Teff for lower gravity objects. The simulated populations of brown dwarfs also reveal that the phase of deuterium burning produces a distinctive feature in CMDs that should be detectable in ~50-100 Myr old clusters.Comment: Accepted for publication in the ApJ. 52 pages including 20 figure

Infrared Spectra and Visibilities as Probes of the Outer Atmospheres of Red Supergiant Stars

In the light of the recent results of the stellar interferometry, we examine the nature of the extra molecular layer outside the photosphere of red super- giant stars, so far studied mostly with the use of the infrared spectra. Although the visibility data are more direct probes of the spatial structure of the outer atmosphere, it is essential that they are analyzed in combination with the spectral data of a wide spectral coverage. In the case of the M2 supergiant mu Cephei, several sets of data, both spectra and visibilities, strongly suggested the presence of an extra-molecular layer, and its basic parameters are estimated to be: excitation temperature T_ex = 1600 K, column densities of CO and H2O N_col = 3.0d+20/cm2, and inner radius R_in = 2.0R*. The result shows reasonable agreement with the one based on the infrared spectra alone, and this may be because the infrared spectra already include some information on the spatial structure of the outer atmosphere. It is important, however, that the model inferred from the spectra is now fully supported with the recent visibility data. In the case of the M2 supergiant alpha Orionis, the infrared spectra and visibilities show a consistent picture in that its molecular layer is closer to the photosphere (R_in = 1.3R*) with higher gas temperature (T_ex = 2250 K) and lower gas column density (N_col = 1.0d+20/cm2), compared with that of mu Cephei. Some controversy on the interpretation of the mid infrared data of alpha Orionis can be reconciled.Comment: 47 pages, 14 Postscript figures, to be published in the Astrophysical Journa

Coefficient of Restitution for Viscoelastic Spheres: The Effect of Delayed Recovery

The coefficient of normal restitution of colliding viscoelastic spheres is computed as a function of the material properties and the impact velocity. From simple arguments it becomes clear that in a collision of purely repulsively interacting particles, the particles loose contact slightly before the distance of the centers of the spheres reaches the sum of the radii, that is, the particles recover their shape only after they lose contact with their collision partner. This effect was neglected in earlier calculations which leads erroneously to attractive forces and, thus, to an underestimation of the coefficient of restitution. As a result we find a novel dependence of the coefficient of restitution on the impact rate.Comment: 11 pages, 2 figure

A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres

The atmospheres of substellar objects contain clouds of oxides, iron, silicates, and other refractory condensates. Water clouds are expected in the coolest objects. The opacity of these `dust' clouds strongly affects both the atmospheric temperature-pressure profile and the emergent flux. Thus any attempt to model the spectra of these atmospheres must incorporate a cloud model. However the diversity of cloud models in atmospheric simulations is large and it is not always clear how the underlying physics of the various models compare. Likewise the observational consequences of different modeling approaches can be masked by other model differences, making objective comparisons challenging. In order to clarify the current state of the modeling approaches, this paper compares five different cloud models in two sets of tests. Test case 1 tests the dust cloud models for a prescribed L, L--T, and T-dwarf atmospheric (temperature T, pressure p, convective velocity vconv)-structures. Test case 2 compares complete model atmosphere results for given (effective temperature Teff, surface gravity log g). All models agree on the global cloud structure but differ in opacity-relevant details like grain size, amount of dust, dust and gas-phase composition. Comparisons of synthetic photometric fluxes translate into an modelling uncertainty in apparent magnitudes for our L-dwarf (T-dwarf) test case of 0.25 < \Delta m < 0.875 (0.1 < \Delta m M 1.375) taking into account the 2MASS, the UKIRT WFCAM, the Spitzer IRAC, and VLT VISIR filters with UKIRT WFCAM being the most challenging for the models. (abr.)Comment: 22 pages, 17 figures, MNRAS 2008, accepted, (minor grammar/typo corrections

Increasing the Adaptive Capacity of Indigenous People to Environmental Change: The Potential Use of an Innovative, Web-Based, Collaborative-Geomatics Informatics Tool to Reduce the Degree of Exposure of First Nations Cree to Hazardous Travel Routes

The arctic and subarctic regions of Canada are experiencing amplified climate change impacts, which are disproportionately impacting Canadian indigenous populations’ ability to safely travel on land to acquire resources. Less predictable and more dangerous travel conditions are impacting not only the health and safety of individuals but also the traditional lifestyles that are vital to the cultural well-being of these indigenous communities. The University of Waterloo’s Computer Systems Group has developed a novel decision-support tool termed “Collaborative-Geomatics.” This web-based informatics tool can allow for the community to monitor, in real-time, the safety of travel routes. Using handheld GPS tracking systems, the utility of the geomatics system to present real-time travel conditions was carried out in a Canadian First Nations community, located along the Western James Bay coast. The results of this study showed that the collaborative-geomatics tool offers the potential to monitor and store information on the safety of travel routes, helping to promote adaptive capacity and aid in knowledge transfer within arctic and subarctic indigenous communities

The Spectrum of the Brown Dwarf Gliese 229B

We present a spectrum of the cool (T_eff = 900 K) brown dwarf Gliese 229B. This spectrum, with a relatively high signal-to-noise ratio per spectral resolution element (> 30), spans the wavelength range from 0.837 microns to 5.0 microns. We identify a total of four different major methane absorption features, including the fundamental band at 3.3 microns, at least four steam bands, and two neutral cesium features. We confirm the recent detection of carbon monoxide (CO) in excess of what is predicted by thermochemical equilibrium calculations. Carbon is primarily involved in a chemical balance between methane and CO at the temperatures and pressures present in the outer parts of a brown dwarf. At lower temperatures, the balance favors methane, while in the deeper, hotter regions, the reaction reverses to convert methane into CO. The presence of CO in the observable part of the atmosphere is therefore a sensitive indicator of vertical flows. The high signal-to-noise ratio in the 1 to 2.5 microns region permits us to place constraints on the quantity of dust in the atmosphere of the brown dwarf. We are unable to reconcile the observed spectrum with synthetic spectra that include the presences of dust. The presence of CO but lack of dust may be a clue to the location of the boundaries of the outer convective region of the atmosphere: The lack of dust may mean that it is not being conveyed into the photosphere by convection, or that it exists in patchy clouds. If the dust is not in clouds, but rather sits below the outer convective region, we estimate that the boundary between outer convective and inner radiative layers is between 1250 K and 1600 K, in agreement with recent models.Comment: 15 pages, 8 figure