Recent mass balance of the Purogangri Ice Cap, central Tibetan Plateau, by means of differential X-band SAR interferometry

Due to their remoteness, altitude and harsh climatic conditions, little is known about the glaciological parameters of ice caps on the Tibetan Plateau. This study presents a geodetic mass balance estimate of the Purogangri Ice Cap, Tibet's largest ice field between 2000 and 2012. We utilized data from the actual TerraSAR-X mission and its add-on for digital elevation measurements and compared it with elevation data from the Shuttle Radar Topography Mission. The employed data sets are ideal for this approach as both data sets were acquired at X-band at nearly the same time of the year and are available at a fine grid spacing. In order to derive surface elevation changes we employed two different methods. The first method is based on differential synthetic radar interferometry while the second method uses common DEM differencing. Both approaches revealed a slightly negative mass budget of −44 ± 15 and −38 ± 23 mm w.eq. a⁻¹ (millimeter water equivalent) respectively. A slightly negative trend of −0.15 ± 0.01 km² a⁻¹ in glacier extent was found for the same time period employing a time series of Landsat data. Overall, our results show an almost balanced mass budget for the studied time period. Additionally, we detected one continuously advancing glacier tongue in the eastern part of the ice cap

Habitat amount and ambient temperature dictate patterns of anuran diversity along a subtropical elevational gradient

Aim: Patterns of diversity along elevational gradients are driven by species characteristics but remain poorly understood. Filling this gap is imperative given the deteriorating conservation status of anurans worldwide. Here, we examine frog diversity and species composition along a sharp subtropical elevational gradient and assess the degree to which these are determined by environmental and spatial predictors. Location: An extensive southern Brazilian Atlantic Forest elevational gradient ranging from 300 to 1,800 m above sea level. Methods: We sampled 38 ponds and used structural equation modelling to examine the direct and indirect effects of area, climate, habitat amount, habitat complexity and productivity on frog species richness and abundance. We also applied joint species distribution models to investigate the importance of these predictors on frog species composition using species distribution and co-occurrence along the elevational gradient. Results: We recorded 12,636 individuals of 41 frog species. Frog species richness was highest at intermediate elevations, showing a hump-shaped pattern. Frog abundance was highest at lowlands and decreased towards higher elevations. We found support for only the habitat amount hypothesis in explaining overall species richness. Although temperature had a positive influence on productivity and frog abundance, neither predictors were related to species richness. Species composition diverged markedly between lowland and highland frog assemblages, which was mainly attributed to differences in ambient temperature. Main conclusion: Elevations containing more extensive natural habitat areas retained the most species-rich frog assemblages. The mid-elevational peak is likely attributed to lowland habitat (1,400 masl). The entire elevational gradient is, however, critical in maintaining anuran species diversity as lowland assemblages are distinct from those at mid- to high elevations. Our study also shows that anthropogenic habitat loss has a decisive effect on montane frog diversity, reinforcing the need to effectively protect these areas

Invasive compute balancing for applications with shared and hybrid parallelization

This is the author manuscript. The final version is available from the publisher via the DOI in this record.Achieving high scalability with dynamically adaptive algorithms in high-performance computing (HPC) is a non-trivial task. The invasive paradigm using compute migration represents an efficient alternative to classical data migration approaches for such algorithms in HPC. We present a core-distribution scheduler which realizes the migration of computational power by distributing the cores depending on the requirements specified by one or more parallel program instances. We validate our approach with different benchmark suites for simulations with artificial workload as well as applications based on dynamically adaptive shallow water simulations, and investigate concurrently executed adaptivity parameter studies on realistic Tsunami simulations. The invasive approach results in significantly faster overall execution times and higher hardware utilization than alternative approaches. A dynamic resource management is therefore mandatory for a more efficient execution of scenarios similar to our simulations, e.g. several Tsunami simulations in urgent computing, to overcome strong scalability challenges in the area of HPC. The optimizations obtained by invasive migration of cores can be generalized to similar classes of algorithms with dynamic resource requirements.This work was supported by the German Research Foundation (DFG) as part of the Transregional Collaborative Research Centre ”Invasive Computing” (SFB/TR 89)

An empirical temperature calibration for the Delta a photometric system. II. The A-type and mid F-type star

With the Delta a photometric system, it is possible to study very distant galactic and even extragalactic clusters with a high level of accuracy. This can be done with a classical color-magnitude diagram and appropriate isochrones. The new calibration presented in this paper is a powerful extension. For open clusters, the reddening is straightforward for an estimation via Isochrone fitting and is needed in order to calculate the reddening-free, temperature sensitive, index (g1-y)0. As a last step, the calibration can be applied to individual stars. Because no a-priori reddening-free photometric parameters are available for the investigated spectral range, we have applied the dereddening calibrations of the Stromgren uvbybeta system and compared them with extinction models for the Milky Way. As expected from the sample of bright stars, the extinction is negligible for almost all objects. As a next step, already established calibrations within the Stromgren uvbybeta, Geneva 7-color, and Johnson UBV systems were applied to a sample of 282 normal stars to derive a polynomial fit of the third degree for the averaged effective temperatures to the individual (g1-y)0 values with a mean of the error for the whole sample of Delta T(eff) is 134K, which is lower than the value in Paper I for hotter stars. No statistically significant effect of the rotational velocity on the precision of the calibration was found.Comment: 5 pages, 2 figures, accepted by A&

Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim

Multicolor (BVRI) light curves of the eclipsing classical nova V Per are presented, and a total of twelve new eclipse timings are measured for the system. When combined with previous eclipse timings from the literature, these timings yield a revised ephemeris for the times of mid-eclipse given by HJD = 2,447,442.8260(1) + 0.107123474(3) E. The eclipse profiles are analyzed with a parameter-fitting model that assumes four sources of luminosity: a white dwarf primary star, a main-sequence secondary star, a flared accretion disk with a rim, and a bright spot at the intersection of the mass-transfer stream and the disk periphery. A matrix of model solutions are computed, covering an extensive range of plausible parameter values. The solution matrix is then explored to determine the optimum values for the fitting parameters and their associated errors. For models that treat the accretion disk as a flat structure without a rim, optimum fits require that the disk have a flat temperature profile. Although models with a truncated inner disk (R_in >> R_wd) result in a steeper temperature profile, steady-state models with a temperature profile characterized by T(r) \propto r^{-3/4} are found only for models with a significant disk rim. A comparison of the observed brightness and color at mid-eclipse with the photometric properties of the best-fitting model suggests that V Per lies at a distance of ~ 1 kpc.Comment: Accepted for publication in The Astrophysical Journal. Thirty-nine pages, including 9 figures. V2 - updated to include additional references and related discussion to previous work overlooked in the original version, and to correct a typo in the ephemeris given in the abstract. V3 - Minor typos corrected. The paper is scheduled for the 20 June 2006 issue of the ApJ. V4 - An error in equation (9) has been corrected. The results presented in the paper were not affected, as all computations were made using the correct formulation of this equatio

Optical Detection of Two Intermediate Mass Binary Pulsar Companions

We report the detection of probable optical counterparts for two Intermediate Mass Binary Pulsar (IMBP) systems, PSR J1528-3146 and PSR J1757-5322. Recent radio pulsar surveys have uncovered a handful of these systems with putative massive white dwarf companions, thought to have an evolutionary history different from that of the more numerous class of Low Mass Binary Pulsars (LMBPs) with He white dwarf companions. The study of IMBP companions via optical observations offers us several new diagnostics: the evolution of main sequence stars near the white-dwarf-neutron star boundary, the physics of white dwarfs close to the Chandrasekhar limit, and insights into the recycling process by which old pulsars are spun up to high rotation frequencies. We were unsuccessful in our attempt to detect optical counterparts of PSR J1141-6545, PSR J1157-5112, PSR J1435-6100, and PSR J1454-5846.Comment: 9 pages, 2 figures, accepted for publication in ApJ

The highly polarized open cluster Trumpler 27

We have carried out multicolor linear polarimetry (UBVRI) of the brightest stars in the area of the open cluster Trumpler 27. Our data show a high level of polarization in the stellar light with a considerable dispersion, from $P = 4$ to $P = 9.5$. The polarization vectors of the cluster members appear to be aligned. Foreground polarization was estimated from the data of some non-member objects, for which two different components were resolved: the first one associated with a dust cloud close to the Sun producing $P_{\lambda max}=1.3$ and $\theta=146$ degrees, and a second component, the main source of polarization for the cluster members, originated in another dust cloud, which polarizes the light in the direction of $\theta= 29.5$ degrees. From a detailed analysis, we found that the two components have associated values $E_{B-V} < 0.45$ for the first one, and $E_{B-V} > 0.75$ for the other. Due the difference in the orientation of both polarization vectors, almost 90 degrees (180 degrees at the Stokes representation), the first cloud ($\theta \sim 146$ degrees) depolarize the light strongly polarized by the second one ($\theta \sim 29.5$ degrees).Comment: 12 Pages, 6 Figures, 2 tables (9 Pages), accepted for publication in A

Detection of Gravitational Redshift on the Solar Disk by Using Iodine-Cell Technique

With an aim to examine whether the predicted solar gravitational redshift can be observationally confirmed under the influence of the convective Doppler shift due to granular motions, we attempted measuring the absolute spectral line-shifts on a large number of points over the solar disk based on an extensive set of 5188-5212A region spectra taken through an iodine-cell with the Solar Domeless Telescope at Hida Observatory. The resulting heliocentric line shifts at the meridian line (where no rotational shift exists), which were derived by finding the best-fit parameterized model spectrum with the observed spectrum and corrected for the earth's motion, turned out to be weakly position-dependent as ~ +400 m/s near the disk center and increasing toward the limb up to ~ +600 m/s (both with a standard deviation of sigma ~ 100 m/s). Interestingly, this trend tends to disappear when the convectiveshift due to granular motions (~-300 m/s at the disk center and increasing toward the limb; simulated based on the two-component model along with the empirical center-to-limb variation) is subtracted, finally resulting in the averaged shift of 698 m/s (sigma = 113 m/s). Considering the ambiguities involved in the absolute wavelength calibration or in the correction due to convective Doppler shifts (at least several tens m/s, or more likely up to <~100 m/s), we may regard that this value is well consistent with the expected gravitational redshift of 633 m/s.Comment: 28 pages, 12 figures, electronic materials as ancillary data (table3, table 4, ReadMe); accepted for publication in Solar Physic

A Near-Infrared (JHK) Survey of the Vicinity of the HII region NGC 7538: Evidence for a Young Embedded Cluster

We describe the results of two near infrared (K-band) imaging surveys and a three color (JHK) survey of the vicinity of NGC 7538. The limiting magnitudes are K ~ 16.5 and K ~ 17.5 mag for the K-band surveys and K ~ 15 mag for the JHK survey. We identify more than 2000 and 9000 near-infrared (NIR) sources on the images of the two K-band surveys and 786 NIR sources in the JHK survey. From color-color diagrams, we derive a reddening law for background stars and identify 238 stars with NIR excesses. Contour maps indicate a high density peak coincident with a concentration of stars with NIR excesses. We identify this peak as a young, embedded cluster and confirm this result with the K-band luminosity function, color histograms, and color-magnitude diagrams. The center of the cluster is at RA = 23:13:39.34, DEC = 61:29:18.9. The cluster radius is $\sim$ 3' ~ 2.5 pc for an adopted distance, d ~ 2.8 kpc. For d = 2.8 kpc, and reddening, E_{J-K} = 0.55 mag, the slope of the logarithmic K-band luminosity function (KLF) of the cluster, s ~ 0.32 +- 0.03, agrees well with previous results for L1630 (s = 0.34) and M17 (s = 0.26).Comment: 26 pages with 11 figures. Accepted by Astronomical Journa

A Precise Distance to IRAS 00420+5530 via H2O Maser Parallax with the VLBA

We have used the VLBA to measure the annual parallax of the H2O masers in the star-forming region IRAS 00420+5530. This measurement yields a direct distance estimate of 2.17 +/- 0.05 kpc (<3%), which disagrees substantially with the standard kinematic distance estimate of ~4.6 kpc (according to the rotation curve of Brand and Blitz 1993), as well as most of the broad range of distances (1.7-7.7 kpc) used in various astrophysical analyses in the literature. The 3-dimensional space velocity of IRAS 00420+5530 at this new, more accurate distance implies a substantial non-circular and anomalously slow Galactic orbit, consistent with similar observations of W3(OH) (Xu et al., 2006; Hachisuka et al. 2006), as well as line-of-sight velocity residuals in the rotation curve analysis of Brand and Blitz (1993). The Perseus spiral arm of the Galaxy is thus more than a factor of two closer than previously presumed, and exhibits motions substantially at odds with axisymmetric models of the rotating Galaxy.Comment: 33 pages, 12 figures; Accepted by ApJ (to appear March 2009