6,371 research outputs found
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 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 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-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
Measuring the Economic Value of Two Habitat Defragmentation Policy Scenarios for the Veluwe, The Netherlands
This paper offers an economic value assessment of a nature protection programme in the Veluwe. This programme involves two defragmentation scenarios: the first scenario connects the central part of the Veluwe with the IJssel river forelands in a north-eastern direction, while the second scenario is focused on defragmentation in a south-western direction, where the Rhine river forelands are located. The valuation is based on a questionnaire that was administered during face-to-face interviews in the Veluwe area and through the Internet. We employ a contingent valuation approach to assess the respondentsâ willingness to pay for the realisation of the defragmentation scenarios. It appears that the mean willingness to pay for the two defragmentation scenarios are ⏠59.7 and ⏠162.2 per respondent. These two willingness-to-pay estimates, which refer to a lump sum payment (or âonce-and-for-all paymentâ), are based on a lognormal and Weibull distribution respectively. In addition to the willingness to pay, we also estimate recreation benefits of the Veluwe. To that end, we use the travel cost technique, the purpose of which is to arrive at an estimate of the siteâs consumer surplus. According to this technique, the yearly recreational benefits are estimated between ⏠0.06 and ⏠0.45 per visitor. Whereas the former estimate is based on the fuel costs only, the latter covers also insurance and maintenance costs, and capital depreciation. Finally, we performed an aggregation of individual WTP estimates over Dutch households. With the resulting aggregate estimates we are able to compare the total costs and benefits of the two scenarios for habitat fragmentation in the Veluwe. The result of such a simple comparison turns out to critically depend on whether the mean or median estimate is used for aggregation. If aggregation of individual WTP estimates is based on mean values, then the benefits far exceed the estimated costs of defragmentation. In other words, based on an integrated economic-ecological analysis it makes sense to execute the defragmentation measures described in the scenarios. However, aggregate estimates obtained by using median values result in higher costs than aggregate estimates that are based on mean values. Even stronger, median-based estimates show that the costs of implementing scenario 2 are higher than the total benefits of this scenario.Economic value, Nature protection, Defragmentation policy, Veluwe
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