We cross-match high-precision astrometric data from Gaia DR2 with accurate multiband photometry from the Dark Energy Survey (DES) DR1 to confidently measure proper motions for nine stellar streams in ...the DES footprint: Aliqa Uma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana III, and Turranburra. We determine low-confidence proper-motion measurements for four additional stellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for a misalignment between stream tracks and the systemic proper motion of streams that may suggest a systematic gravitational influence from the Large Magellanic Cloud (LMC). These proper motions, when combined with radial velocity measurements, will allow for detailed orbit modeling that can be used to constrain properties of the LMC and its effect on nearby streams, as well as global properties of the Milky Way's gravitational potential.
Sympatric ocelots (Leopardus pardalis) and bobcats (Lynx rufus) in South Texas show substantial overlap in body size, food habits, and habitat use. Consequently, we explore whether temporal niche ...partitioning may explain ocelot and bobcat coexistence. We investigated the influence of sun angle, lunar illumination, and maximum diurnal temperature on temporal movement rates of sympatric ocelots (n = 8) and bobcats (n = 6) using a combination of high-frequency GPS locations and bi-axial accelerometer data. We demonstrated that accelerometer data could be used to predict movement rates, providing a nearly continuous measure of animal activity and supplementing GPS locations. Ocelots showed a strong nocturnal activity pattern with the highest movement rates at night whereas bobcats showed a crepuscular activity pattern with the highest movement rates occurring around sunrise and sunset. Although bobcat activity levels were lower during the day, bobcat diurnal activity was higher than ocelot diurnal activity. During warmer months, bobcats were more active on nights with high levels of lunar illumination. In contrast, ocelots showed the highest nocturnal activity levels during periods of low lunar illumination. Ocelots showed reduced diurnal activity on hotter days. Our results indicate that ocelot and bobcat coexistence in South Texas can be partially explained by temporal niche partitioning, although both felids showed periods of overlapping activity during nocturnal and crepuscular periods.
Most proxy records used for reconstruction of Holocene climate of Amazonia are unable to quantitatively distinguish between the effect of temperature and rainfall amounts.
We present a new isotope ...technique applied to a ∼
13,500 yr stalagmite archive from Peruvian Amazonia. By analysing the coupled isotope composition of fossil dripwater trapped in stalagmite fluid inclusions, and that of the calcite hosting the fluid inclusions, we were able to calculate independent paleotemperatures and rainfall amounts.
This stalagmite record shows that Holocene climate variation was controlled by orbitally-forced Southward migration of the Inter Tropical Convergence Zone. While temperature remained constant, isotope variation of rainwater, reflected in fluid inclusion water
δ
18O composition, suggests a ∼
15–30% increase in convective rainfall through the Holocene.
A comparison of the low-land Peruvian fluid inclusion record with the high Andean Huascaran ice core record shows a constant ∼
12‰ offset of
δ
18O curves for the Holocene, suggesting that Andean vertical temperature gradients (lapse rates) did not vary much over the last 9000 years. During the Younger Dryas interval, however, the offset of
δ
18O values was much higher than in the Holocene. This may be attributed to a relative drop in air temperatures in the highlands (higher lapse rate), caused by long distance teleconnections to climate perturbations in the North Atlantic.
In a wider perspective, fluid inclusion isotope analysis drastically improves paleotemperature reconstructions based on speleothem calcite
δ
18O data, because it provides the
δ
18O value of drip water through time, which is usually the most important unknown in paleotemperature equations.
Heightened concern over endocrine-disrupting chemicals is driven by the hypothesis that they could reduce reproductive success and affect wildlife populations, but there is little evidence for this ...expectation. The pharmaceutical ethynylestradiol ( EE2) is a potent endocrine modulator and is present in the aquatic environment at biologically active concentrations. To investigate impacts on reproductive success and mechanisms of disruption, we exposed breeding populations (n = 12) of zebrafish (Danio rerio) over multiple generations to environmentally relevant concentrations of EE2. Life-long exposure to 5 ng/ L EE2in the F1generation caused a 56% reduction in fecundity and complete population failure with no fertilization. Conversely, the same level of exposure for up to 40 days in mature adults in the parental F0generation had no impact on reproductive success. Infertility in the F1generation after life-long exposure to 5 ng/ L EE2was due to disturbed sexual differentiation, with males having no functional testes and either undifferentiated or intersex gonads. These F1males also showed a reduced vitellogenic response when compared with F0males, indicating an acclimation to EE2exposure. Depuration studies found only a partial recovery in reproductive capacity after 5 months. Significantly, even though the F1males lacked functional testes, they showed male-pattern reproductive behavior, inducing the spawning act and competing with healthy males to disrupt fertilization. Endocrine disruption is therefore likely to affect breeding dynamics and reproductive success in group-spawning fish. Our findings raise major concerns about the population-level impacts for wildlife of long-term exposure to low concentrations of estrogenic endocrine disruptors.
We describe the model for mapping from sky brightness to the digital output of the Dark Energy Camera (DECam) and the algorithms adopted by the Dark Energy Survey (DES) for inverting this model to ...obtain photometric measures of celestial objects from the raw camera output. This calibration aims for fluxes that are uniform across the camera field of view and across the full angular and temporal span of the DES observations, approaching the accuracy limits set by shot noise for the full dynamic range of DES observations. The DES pipeline incorporates several substantive advances over standard detrending techniques, including principal-components-based sky and fringe subtraction; correction of the "brighter-fatter" nonlinearity; use of internal consistency in on-sky observations to disentangle the influences of quantum efficiency, pixel-size variations, and scattered light in the dome flats; and pixel-by-pixel characterization of instrument spectral response, through combination of internal-consistency constraints with auxiliary calibration data. This article provides conceptual derivations of the detrending/calibration steps, and the procedures for obtaining the necessary calibration data. Other publications will describe the implementation of these concepts for the DES operational pipeline, the detailed methods, and the validation that the techniques can bring DECam photometry and astrometry within 2 mmag and 3 mas, respectively, of fundamental atmospheric and statistical limits. The DES techniques should be broadly applicable to wide-field imagers.
Photometric Characterization of the Dark Energy Camera Bernstein, G. M.; Abbott, T. M. C.; Armstrong, R. ...
Publications of the Astronomical Society of the Pacific,
05/2018, Letnik:
130, Številka:
987
Journal Article
Recenzirano
Odprti dostop
We characterize the variation in photometric response of the Dark Energy Camera (DECam) across its 520 Mpix science array during 4 years of operation. These variations are measured using high ...signal-to-noise aperture photometry of >107 stellar images in thousands of exposures of a few selected fields, with the telescope dithered to move the sources around the array. A calibration procedure based on these results brings the rms variation in aperture magnitudes of bright stars on cloudless nights down to 2-3 mmag, with <1 mmag of correlated photometric errors for stars separated by ≥20″. On cloudless nights, any departures of the exposure zeropoints from a secant airmass law exceeding 1 mmag are plausibly attributable to spatial/temporal variations in aperture corrections. These variations can be inferred and corrected by measuring the fraction of stellar light in an annulus between 6″ and 8″ diameter. Key elements of this calibration include: correction of amplifier nonlinearities; distinguishing pixel-area variations and stray light from quantum-efficiency variations in the flat fields; field-dependent color corrections; and the use of an aperture-correction proxy. The DECam response pattern across the 2° field drifts over months by up to 9 mmag, in a nearly wavelength-independent low-order pattern. We find no fundamental barriers to pushing global photometric calibrations toward mmag accuracy.
PDF
