Are the Luminosities of RR Lyrae Stars Affected by Second Parameter Effects?

There is a serious discrepancy between the distance to the LMC derived from the Cepheid Period-Luminosity relation and that obtained by using the Galactic calibration for the luminosity of RR Lyrae stars. It is suggested that this problem might be due to the fact that second parameter effects make it inappropriate to apply Galactic calibrations to RR Lyrae variables in the Magellanic Clouds, i.e. Mv(RR) could depend on both [Fe/H] and on one or more second parameters.Comment: 10 pages as uuencoded compressed Postscript. Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.htm

N-body simulations with two-orders-of-magnitude higher performance using wavelets

Noise is a problem of major concern for N-body simulations of structure formation in the early Universe, of galaxies and plasmas. Here for the first time we use wavelets to remove noise from N-body simulations of disc galaxies, and show that they become equivalent to simulations with two orders of magnitude more particles. We expect a comparable improvement in performance for cosmological and plasma simulations. Our wavelet code will be described in a following paper, and will then be available on request.Comment: Mon. Not. R. Astron. Soc., in press. The interested reader is strongly recommended to ignore the low-resolution Fig. 3 (and Fig. 4), and to download the full-resolution paper (700 kb) from http://www.oso.chalmers.se/~romeo/Paper_VI.ps.g

Rotating solenoidal perfect fluids of Petrov type D

We prove that aligned Petrov type D perfect fluids for which the vorticity vector is not orthogonal to the plane of repeated principal null directions and for which the magnetic part of the Weyl tensor with respect to the fluid velocity has vanishing divergence, are necessarily purely electric or locally rotationally symmetric. The LRS metrics are presented explicitly.Comment: 6 pages, no figure

Detection of CO in Triton's atmosphere and the nature of surface-atmosphere interactions

Triton possesses a thin atmosphere, primarily composed of nitrogen, sustained by the sublimation of surface ices. The goal is to determine the composition of Triton's atmosphere and to constrain the nature of surface-atmosphere interactions. We perform high-resolution spectroscopic observations in the 2.32-2.37 $\mu$m range, using CRIRES at the VLT. From this first spectroscopic detection of Triton's atmosphere in the infrared, we report (i) the first observation of gaseous methane since its discovery in the ultraviolet by Voyager in 1989 and (ii) the first ever detection of gaseous CO in the satellite. The CO atmospheric abundance is remarkably similar to its surface abundance, and appears to be controlled by a thin, CO-enriched, surface veneer resulting from seasonal transport and/or atmospheric escape. The CH$_4$ partial pressure is several times larger than inferred from Voyager. This confirms that Triton's atmosphere is seasonally variable and is best interpreted by the warming of CH$_4$-rich icy grains as Triton passed southern summer solstice in 2000. The presence of CO in Triton's atmosphere also affects its temperature, photochemistry and ionospheric composition. An improved upper limit on CO in Pluto's atmosphere is also reported.Comment: 11 pages, including 4 figures and 2 on-line figures Astronomy and Astrophysics, in press (accepted March 13, 2010

Purely radiative perfect fluids

We study `purely radiative' (div E = div H = 0) and geodesic perfect fluids with non-constant pressure and show that the Bianchi class A perfect fluids can be uniquely characterized --modulo the class of purely electric and (pseudo-)spherically symmetric universes-- as those models for which the magnetic and electric part of the Weyl tensor and the shear are simultaneously diagonalizable. For the case of constant pressure the same conclusion holds provided one also assumes that the fluid is irrotational.Comment: 12 pages, minor grammatical change

Exploring the spatial, temporal, and vertical distribution of methane in Pluto's atmosphere

High-resolution spectra of Pluto in the 1.66 um region, recorded with the VLT/CRIRES instrument in 2008 (2 spectra) and 2012 (5 spectra), are analyzed to constrain the spatial and vertical distribution of methane in Pluto's atmosphere and to search for mid-term (4 year) variability. A sensitivity study to model assumptions (temperature structure, surface pressure, Pluto's radius) is performed. Results indicate that (i) no variation of the CH4 atmospheric content (column-density or mixing ratio) with Pluto rotational phase is present in excess of 20 % (ii) CH4 column densities show at most marginal variations between 2008 and 2012, with a best guess estimate of a ~20 % decrease over this time frame. As stellar occultations indicate that Pluto's surface pressure has continued to increase over this period, this implies a concomitant decrease of the methane mixing ratio (iii) the data do not show evidence for an altitude-varying methane distribution; in particular, they imply a roughly uniform mixing ratio in at least the first 22-27 km of the atmosphere, and high concentrations of low-temperature methane near the surface can be ruled out. Our results are also best consistent with a relatively large (> 1180 km) Pluto radius. Comparison with predictions from a recently developed global climate model GCM indicates that these features are best explained if the source of methane occurs in regional-scale CH4 ice deposits, including both low latitudes and high Northern latitudes, evidence for which is present from the rotational and secular evolution of the near-IR features due to CH4 ice. Our "best guess" predictions for the New Horizons encounter in 2015 are: a 1184 km radius, a 17 ubar surface pressure, and a 0.44 % CH4 mixing ratio with negligible longitudinal variations.Comment: 21 pages, 6 figure

Globular Cluster Systems of Early-Type Galaxies

Properties of 53 globular cluster systems are investigated. Strong correlations are found between parent galaxy luminosity and both the slope of the radial density profile for clusters and the width of the cluster color (metallicity) distribution. These correlations are in the sense that the most luminous early-type galaxies are embedded in cluster systems that have the shallowest radial gradients and exhibit the broadest color distributions. The data suggest a scenario in which luminous early-type galaxies have a more complex evolutionary history than fainter ones. A problem with the interpretation of the present data is that it is difficult (or impossible) to disentangle the strongly correlated effects of high parent galaxy luminosity, presence of a core or boxy isophotes, and shallow radial cluster density gradients.Comment: Contains complete Table 1 which had been truncated. To appear in the Astrophysical Journal. Also available at http://www.hia.nrc.ca/eprints.htm

Shear-free perfect fluids with a solenoidal electric curvature

We prove that the vorticity or the expansion vanishes for any shear-free perfect fluid solution of the Einstein field equations where the pressure satisfies a barotropic equation of state and the spatial divergence of the electric part of the Weyl tensor is zero.Comment: 9 page

Shearfree perfect fluids with solenoidal magnetic curvature and a gamma-law equation of state

We show that shearfree perfect fluids obeying an equation of state p=(gamma -1) mu are non-rotating or non-expanding under the assumption that the spatial divergence of the magnetic part of the Weyl tensor is zero.Comment: 11 page

Shapley-Ames Galaxies in the Blue and Infrared

The Shapley-Ames Catalog of 1276 galaxies with B < 12.5 is compared with the Sanders et al. all sky sample of the 629 galaxies with 60 m flux density > 5.24 Jy. The fraction of Shapley-Ames galaxies that are visible in the IR is found to increase from 0.006 for E or E/S0 galaxies to 0.384 for Sc galaxies. The subset of Shapley-Ames galaxies that are detected in the IR has a median blue luminosity that is ~0.8 mag fainter than that of all Shapley-Ames galaxies. Most of this difference is due to the fact that late-type galaxies (which contain dust and hot stars) are systematically less luminous in blue light than are early-type galaxies. Within individual stages along the Hubble sequence no significant differences are found between the luminosity distributions in blue light of galaxies that were detected in the infrared and those that were not. However, our data show a puzzling exception (significant at 99.9%) for SBc galaxies. For reasons that are not understood Shapley-Ames SBc galaxies, that are visible in the IR, are more luminous in blue light than those SBc galaxies that are not detected in the infrared. An other peculiarity of the data is that Shapley-Ames Sc galaxies galaxies are (at 99.6% confidence) more luminous than objects of type SBc .Comment: 11 pages. no figures. To be published in the Astronomical Journa