2,191 research outputs found
Three-dimensional extinction mapping using Gaussian random fields
We present a scheme for using stellar catalogues to map the three-dimensional
distributions of extinction and dust within our Galaxy. Extinction is modelled
as a Gaussian random field, whose covariance function is set by a simple
physical model of the ISM that assumes a Kolmogorov-like power spectrum of
turbulent fluctuations. As extinction is modelled as a random field, the
spatial resolution of the resulting maps is set naturally by the data
available; there is no need to impose any spatial binning. We verify the
validity of our scheme by testing it on simulated extinction fields and show
that its precision is significantly improved over previous dust-mapping
efforts. The approach we describe here can make use of any photometric,
spectroscopic or astrometric data; it is not limited to any particular survey.
Consequently, it can be applied to a wide range of data from both existing and
future surveys.Comment: 16 pages, 12 figures. Submitted for publication in MNRAS. Text
revise
Kinematic Detection of the Galactic Nuclear Disc
We report the detection of the Galactic nuclear disc in line-of-sight
kinematics of stars, measured with infrared spectroscopy from APOGEE. This
stellar component of the nuclear disc has an extent and rotation velocity V ~
120kms comparable to the gas disc in the central molecular zone. The current
data suggest that this disc is kinematically cool and has a small vertical
extent of order 50pc. The stellar kinematics suggest a truncation radius/steep
decline of the stellar disc at a galactocentric radius R ~ 150pc, and provide
tentative evidence for an overdensity at the position of the ring found in the
molecular gas disc.Comment: 6 pages, 4 figures, accepted by ApJ Letter
Reference image selection for difference imaging analysis
Difference image analysis (DIA) is an effective technique for obtaining
photometry in crowded fields, relative to a chosen reference image. As yet,
however, optimal reference image selection is an unsolved problem. We examine
how this selection depends on the combination of seeing, background and
detector pixel size. Our tests use a combination of simulated data and quality
indicators from DIA of well-sampled optical data and under-sampled
near-infrared data from the OGLE and VVV surveys, respectively. We search for a
figure-of-merit (FoM) which could be used to select reference images for each
survey. While we do not find a universally applicable FoM, survey-specific
measures indicate that the effect of spatial under-sampling may require a
change in strategy from the standard DIA approach, even though seeing remains
the primary criterion. We find that background is not an important criterion
for reference selection, at least for the dynamic range in the images we test.
For our analysis of VVV data in particular, we find that spatial under-sampling
is best handled by reversing the standard DIA procedure and convolving target
images to a better-sampled (poor seeing) reference image.Comment: 14 pages, 8 figures, 4 tables, accepted for publication in MNRA
Reduced energy availability: implications for bone health in physically active populations
Purpose: The present review critically evaluates existing literature on the effects of short- and long-term low energy availability (EA) on bone metabolism and health in physically active individuals.
Methods: We reviewed the literature on the short-term effects of low EA on markers of bone metabolism and the long-term effects of low EA on outcomes relating to bone health (bone mass, microarchitecture and strength, bone metabolic markers and stress fracture injury risk) in physically active individuals.
Results: Available evidence indicates that short-term low EA may increase markers of bone resorption and decrease markers of bone formation in physically active women. Bone metabolic marker responses to low EA are less well known in physically active men. Cross-sectional studies investigating the effects of long-term low EA suggest that physically active individuals who have low EA present with lower bone mass, altered bone metabolism (favouring bone resorption), reduced bone strength and increased risk for stress fracture injuries.
Conclusions: Reduced EA has a negative influence on bone in both the short- and long-term, and every effort should be made to reduce its occurrence in physically active individuals. Future interventions are needed to explore the effects of long-term reduced EA on bone health outcomes, while short-term low EA studies are also required to give insight into the pathophysiology of bone alterations
Marginal likelihoods of distances and extinctions to stars: computation and compact representation
We present a method for obtaining the likelihood function of distance and
extinction to a star given its photometry. The other properties of the star
(its mass, age, metallicity and so on) are marginalised assuming a simple
Galaxy model. We demonstrate that the resulting marginalised likelihood
function can be described faithfully and compactly using a Gaussian mixture
model. For dust mapping applications we strongly advocate using monochromatic
over bandpass extinctions, and provide tables for converting from the former to
the latter for different stellar types.Comment: 14 pages, 12 figures. Accepted for publication in MNRAS. Source code
is available at https://github.com/stuartsal
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