2,731 research outputs found
Predicting Stellar Angular Diameters from , , , Photometry
Determining the physical properties of microlensing events depends on having
accurate angular sizes of the source star. Using long-baseline optical
interferometry we are able to measure the angular sizes of nearby stars with
uncertainties . We present empirically derived relations of angular
diameters that are calibrated using both a sample of dwarfs/subgiants and a
sample of giant stars. These relations are functions of five color indices in
the visible and near-infrared, and have uncertainties of 1.8-6.5% depending on
the color used. We find that a combined sample of both main-sequence and
evolved stars of A-K spectral types is well fit by a single relation for each
color considered. We find that in the colors considered, metallicity does not
play a statistically significant role in predicting stellar size, leading to a
means of predicting observed sizes of stars from color alone.Comment: 8 pages, 1 figure, accepted for publication in MNRA
Turning Earth into Venus: A Stochastic Model of Possible Evolutions of Terrestrial Topography
Venus may have had both an Earth-like climate as well as extensive water
oceans and active (or incipient) plate tectonics for an extended interval of
its history. The topographical power spectrum of Venus provides important clues
to the planet's past evolution. By drawing detailed contrast with the strong
low-order odd- dominated global topography of Earth, we demonstrate that the
relatively flat Venusian topography can be interpreted to have arisen from the
transition from active terrestrial-like plate tectonics to the current stagnant
lid configuration at a time million years before
present. This scenario is plausible if loss of oceans and the attendant
transition to a CO-dominated atmosphere were accompanied by rapid
continental-scale erosion, followed by gradual lava resurfacing at an outflow
rate 1 km yr. We study Venus' proposed topographical
relaxation with a global diffusion-like model that adopts terrestrial erosion
rates scaled to account for the increased rainfall and temperatures that would
accompany a planet-wide transition from an Earth-like climate to the runaway
greenhouse climate that could ultimately yield present-day Venus, with an
estimate of Myr if the global erosion operated as
efficiently as that of a typical bedrock river basin on Earth.Comment: 17 pages, 4 figures, submitted to AAS Journal
A new specimen of Dicynodon traquairi (Newton) (Synapsida: Anomodontia) from the Late Permian (Tartarian) of northern Scotland
A recently discovered natural mould of a complete, almost undistorted, skull and lower jaw of a dicynodont (c. 237mmoverall length),
in a block of Upper Permian sandstone (= Dicynodon Assemblage Zone: Hopeman Sandstone Formation) from Clashach Quarry,
Hopeman, Morayshire, is described using novel techniques, including Computed Tomography scanning (CT), Magnetic Resonance
Imaging (MRI) and rapid-prototype modelling. It is assigned to the taxon Dicynodon traquairi (Newton, 1893). When compared with
Dicynodon lacerticeps Owen, 1845, it is distinguished principally by having the pineal opening sunk deeply between the diverging
parietals, subparallel pterygoid rami narrowly separated, with no transverse flanges, and in addition, a deeply grooved lower jaw
symphysis. The southern African fauna lived on river flats in a higher (southern) palaeolatitude than the possibly desert-dwelling
Scottish species. The Hopeman Sandstone Formation is of the same age as the better-known Cutties Hillock Sandstone Formation,
whose fauna is briefly discussed and reviewed
On elliptic factors in real endoscopic transfer I
This paper is concerned with the structure of packets of representations and
some refinements that are helpful in endoscopic transfer for real groups. It
includes results on the structure and transfer of packets of limits of discrete
series representations. It also reinterprets the Adams-Johnson transfer of
certain nontempered representations via spectral analogues of the
Langlands-Shelstad factors, thereby providing structure and transfer compatible
with the associated transfer of orbital integrals. The results come from two
simple tools introduced here. The first concerns a family of splittings of the
algebraic group G under consideration; such a splitting is based on a
fundamental maximal torus of G rather than a maximally split maximal torus. The
second concerns a family of Levi groups attached to the dual data of a
Langlands or an Arthur parameter for the group G. The introduced splittings
provide explicit realizations of these Levi groups. The tools also apply to
maps on stable conjugacy classes associated with the transfer of orbital
integrals. In particular, they allow for a simpler version of the definitions
of Kottwitz-Shelstad for twisted endoscopic transfer in certain critical cases.
The paper prepares for spectral factors in twisted endoscopic transfer that are
compatible in a certain sense with the standard factors discussed here. This
compatibility is needed for Arthur's global theory. The twisted factors
themselves will be defined in a separate paper.Comment: 48 pages, to appear in Progress in Mathematics, Volume 312,
Birkha\"user. Also renumbering to match that of submitted versio
Planet Eclipse Mapping with Long-Term Baseline Drifts
High precision lightcurves combined with eclipse mapping techniques can
reveal the horizontal and vertical structure of a planet's thermal emission and
the dynamics of hot Jupiters. Someday, they even may reveal the surface maps of
rocky planets. However, inverting lightcurves into maps requires an
understanding of the planet, star and instrumental trends because they can
resemble the gradual flux variations as the planet rotates (ie. partial phase
curves). In this work, we simulate lightcurves with baseline trends and assess
the impact on planet maps. Baseline trends can be erroneously modeled by
incorrect astrophysical planet map features, but there are clues to avoid this
pitfall in both the residuals of the lightcurve during eclipse and sharp
features at the terminator of the planet. Models that use a Gaussian process or
polynomial to account for a baseline trend successfully recover the input map
even in the presence of systematics but with worse precision for the m=1
spherical harmonic terms. This is also confirmed with the ThERESA eigencurve
method where fewer lightcurve terms can model the planet without correlations
between the components. These conclusions help aid the decision on how to
schedule observations to improve map precision. If the m=1 components are
critical, such as measuring the East/West hotspot shift on a hot Jupiter,
better characterization of baseline trends can improve the m=1 terms'
precision. For latitudinal North/South information from the remaining mapping
terms, it is preferable to obtain high signal-to-noise at ingress/egress with
more eclipses.Comment: AJ, accepted, 22 page
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