15,705 research outputs found
Northern JHK Standard Stars for Array Detectors
We report J, H and K photometry of 86 stars in 40 fields in the northern
hemisphere. The fields are smaller than or comparable to a 4x4 arcmin
field-of-view, and are roughly uniformly distributed over the sky, making them
suitable for a homogeneous broadband calibration network for near-infrared
panoramic detectors. K magnitudes range from 8.5 to 14, and J-K colors from
-0.1 to 1.2. The photometry is derived from a total of 3899 reduced images;
each star has been measured, on average, 26.0 times per filter on 5.5 nights.
Typical errors on the photometry are about 0.012.Comment: 10 pages including 3 figures, one separate figure on four pages. The
finding chart of the AS-30 field and a few coordinates have been corrected.
GIF finding charts can also be found at
http://www.arcetri.astro.it/~hunt/std.htm
Star-forming dwarf galaxies in the Virgo cluster: the link between molecular gas, atomic gas, and dust
We present CO(1-0) and CO(2-1) observations of a sample of 20
star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with
oxygen abundances ranging from 12 + log(O/H) ~ 8.1 to 8.8. CO emission is
observed in ten galaxies and marginally detected in another one. CO fluxes
correlate with the FIR 250 m emission, and the dwarfs follow the same
linear relation that holds for more massive spiral galaxies extended to a wider
dynamical range. We compare different methods to estimate H2 molecular masses,
namely a metallicity-dependent CO-to-H2 conversion factor and one dependent on
H-band luminosity. The molecular-to-stellar mass ratio remains nearly constant
at stellar masses <~ 10 M, contrary to the atomic hydrogen
fraction, M/M, which increases inversely with M. The flattening
of the M/M ratio at low stellar masses does not seem to be related
to the effects of the cluster environment because it occurs for both
HI-deficient and HI-normal dwarfs. The molecular-to-atomic ratio is more
tightly correlated with stellar surface density than metallicity, confirming
that the interstellar gas pressure plays a key role in determining the balance
between the two gaseous components of the interstellar medium. Virgo dwarfs
follow the same linear trend between molecular gas mass and star formation rate
as more massive spirals, but gas depletion timescales, , are not
constant and range between 100 Myr and 6 Gyr. The interaction with the Virgo
cluster environment is removing the atomic gas and dust components of the
dwarfs, but the molecular gas appears to be less affected at the current stage
of evolution within the cluster. However, the correlation between HI deficiency
and the molecular gas depletion time suggests that the lack of gas
replenishment from the outer regions of the disc is lowering the star formation
activity.Comment: 19 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Color Transformations for the 2MASS Second Incremental Data Release
Transformation equations are presented to convert colors and magnitudes
measured in the AAO, ARNICA, CIT, DENIS, ESO, LCO (Persson standards), MSSSO,
SAAO, and UKIRT photometric systems to the photometric system inherent to the
2MASS Second Incremental Data Release. The transformations have been derived by
comparing 2MASS photometry with published magnitudes and colors for stars
observed in these systems. Transformation equations have also been derived
indirectly for the Bessell & Brett (1988) and Koornneef (1983) homogenized
photometric systems.Comment: To appear in AJ, May 200
Shoot growth of woody trees and shrubs is predicted by maximum plant height and associated traits
1. The rate of elongation and thickening of individual branches (shoots) varies across plant species. This variation is important for the outcome of competition and other plant-plant interactions. Here we compared rates of shoot growth across 44 species from tropical, warm temperate, and cool temperate forests of eastern Australia.2. Shoot growth rate was found to correlate with a suite of traits including the potential height of the species, xylem-specific conductivity, leaf size, leaf area per xylem cross-section, twig diameter (at 40 cm length), wood density and modulus of elasticity.3. Within this suite of traits, maximum plant height was the clearest correlate of growth rates, explaining 50 to 67% of the variation in growth overall (p p 4. Growth rates were not strongly correlated with leaf nitrogen or leaf mass per unit leaf area.5. Correlations between growth and maximum height arose both across latitude (47%, p p p p < 0.0001), reflecting intrinsic differences across species and sites
Morphology of the 12-micron Seyfert Galaxies: II. Optical and Near-Infrared Image Atlas
We present 263 optical and near-infrared (NIR) images for 42 Seyfert 1s and
48 Seyfert 2s, selected from the Extended 12-micron Galaxy Sample.
Elliptically-averaged profiles are derived from the images, and isophotal radii
and magnitudes are calculated from these. We also report virtual aperture
photometry, that judging from comparison with previous work, is accurate to
roughly 0.05mag in the optical, and 0.07mag in the NIR. Our B-band isophotal
magnitude and radii, obtained from ellipse fitting, are in good agreement with
those of RC3. When compared with the B band, V, I, J, and K isophotal diameters
show that the colors in the outer regions of Seyferts are consistent with the
colors of normal spirals. Differences in the integrated isophotal colors and
comparison with a simple model show that the active nucleus+bulge is stronger
and redder in the NIR than in the optical. Finally, roughly estimated Seyfert
disk surface brightnesses are significantly brighter in B and K than those in
normal spirals of similar morphological type.Comment: 17 pgs including figures; Table 2 is a separate file. Complete Figure
1 is available by contacting the authors. Accepted for publication in ApJ
The âcultured rainforestsâ of Borneo
Borneo has a 50,000-year record of ' interactions with rainforest on the coastal lowlands assembled especially by the interdisciplinary investigation of the archaeology and palaeoecology of the Niah Caves on the coastal plain of Sarawak (Barker et al., 2007; Barker, 2013). More recent work by many of the same team in the interior of Borneo, in the Kelabit Highlands of Sarawak, has combined those approaches with ethnography and anthropology to investigate recent and present-day, as well as past, human-rainforest interactions. In combination, the two projects indicate that the present-day rainforests of Borneo are the product of a deep ecological history related to both natural factors such as climate change and cultural factors such as how different groups of people chose to extract their livelihoods from the forest, including in ways that do not have simple analogies with the subsistence activities of present-day rainforest foragers and farmers in Borneo.Sarawak Museum, Arts and Humanities Research Board (APN10872), Arts and Humanities Research Council (APN12333, APN16175, E5105741), Association of Southeast Asianists UK, British Academy, British Academy's Committee for Southeast Asian Studies, Natural Environment Research Council (Radiocarbon Facility)This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.quaint.2016.08.01
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Evolution of the eyes of vipers with and without infrared-sensing pit organs
We examined lens and brille transmittance, photoreceptors, visual pigments, and visual opsin gene sequences of viperid snakes with and without infrared-sensing pit organs. Ocular media transmittance is high in both groups. Contrary to previous reports, small as well as large single cones occur in pit vipers. Non-pit vipers differ from pit vipers in having a twotiered retina, but few taxa have been examined for this poorly understood feature. All vipers sampled express rh1, sws1 and lws visual opsin genes. Opsin spectral tuning varies but not in accordance with the presence/absence of pit organs, and not always as predicted from gene sequences. The visual opsin genes were generally under purifying selection, with positive selection at spectral tuning amino acids in RH1 and SWS1 opsins, and at retinal pocket stabilization sites in RH1 or LWS (and without substantial differences between pit and nonpit vipers). Lack of evidence for sensory trade-off between viperid eyes (in the aspects examined) and pit organs might be explained by the high degree of neural integration of vision and infrared detection; the latter representing an elaboration of an existing sense with addition of a novel sense organ, rather than involving the evolution of a wholly novel sensory system
Extreme Water Velocities: Topographical Amplification of Wave-Induced Flow in the Surf Zone of Rocky Shores
Water velocities as high as 25 m s-1 have been recorded in the surf zone of wave-swept rocky shores-velocities more than twice the phase speed of the breaking waves with which they are associated. How can water travel twice as fast as the waveform that initially induces its velocity? We explore the possibility that the interaction of a wave with the local topography of the shore can greatly amplify the water velocities imposed on intertidal plants and animals. Experiments in a laboratory wave tank show that interactions between bores refracted by a prowlike beach can produce jets in which the velocity is nearly twice the bore\u27s phase speed. This velocity can be further amplified by a factor of 1.3-1.6 if the jet strikes a vertical wall. This type of topographically induced amplification of water velocity could result in substantial spatial variation in wave-induced hydrodynamic forces and might thereby help to explain the patchwork nature of disturbance that is characteristic of intertidal communities
Harnack inequality for fractional sub-Laplacians in Carnot groups
In this paper we prove an invariant Harnack inequality on
Carnot-Carath\'eodory balls for fractional powers of sub-Laplacians in Carnot
groups. The proof relies on an "abstract" formulation of a technique recently
introduced by Caffarelli and Silvestre. In addition, we write explicitly the
Poisson kernel for a class of degenerate subelliptic equations in product-type
Carnot groups
Corridors of barchan dunes: stability and size selection
Barchans are crescentic dunes propagating on a solid ground. They form dune
fields in the shape of elongated corridors in which the size and spacing
between dunes are rather well selected. We show that even very realistic models
for solitary dunes do not reproduce these corridors. Instead, two instabilities
take place. First, barchans receive a sand flux at their back proportional to
their width while the sand escapes only from their horns. Large dunes
proportionally capture more than they loose sand, while the situation is
reversed for small ones: therefore, solitary dunes cannot remain in a steady
state. Second, the propagation speed of dunes decreases with the size of the
dune: this leads -- through the collision process -- to a coarsening of barchan
fields. We show that these phenomena are not specific to the model, but result
from general and robust mechanisms. The length scales needed for these
instabilities to develop are derived and discussed. They turn out to be much
smaller than the dune field length. As a conclusion, there should exist further
- yet unknown - mechanisms regulating and selecting the size of dunes.Comment: 13 pages, 13 figures. New version resubmitted to Phys. Rev. E.
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