V405 Peg (RBS 1955): A Nearby, Low-Luminosity Cataclysmic Binary

(Abridged). The cataclysmic binary V405 Peg, originally discovered as ROSAT Bright Source (RBS) 1955 (= 1RXS J230949.6+213523), shows a strong contribution from a late-type secondary star in its optical spectrum, which led Schwope et al. to suggest it to be among the nearest cataclysmic binaries. We present extensive optical observations of V405 Peg. Time-series spectroscopy shows the orbital period, Porb, to be 0.1776469(7) d (= 4.2635 hr), or 5.629 cycle/d. We classify the secondary as M3 - M4.5. Astrometry with the MDM 2.4m telescope gives a parallax 7.2 +- 1.1 milli-arcsec, and a relative proper motion of 58 mas/yr. Our best estimate of the distance yields d = 149 (+26, -20) pc. The secondary stars's radial velocity has K2 = 92 +- 3 km/s, indicating a fairly low orbital inclination if the masses are typical. Extensive I-band time-series observations in the show the system varying between a minimum brightness level of I = 14.14 and states of enhanced activity about 0.2 mag brighter. While the low-state shows an ellipsoidal modulation, an additional photometric modulation appears in the high state, with 0.1 mag amplitude and period 220-280 min. The frequency of this modulation appears to be stable for a month or so, but no single period was consistently detected from one observing season to the next. We estimate the system luminosity by combining optical measurements with the archival X-ray spectrum. The implied mass accretion rate is orders of magnitudes below the predictions for the standard angular momentum loss above the period gap. The system may possibly belong to a largely undiscovered population of hibernating CVs.Comment: 11 figures; 7 of these are .png or .jpg to save space. In press for Publications of the Astronomical Society of the Pacifi

Space‐Scale Resolved Surface Fluxes Across a Heterogeneous, Mid‐Latitude Forested Landscape

The Earth\u27s surface is heterogeneous at multiple scales owing to spatial variability in various properties. The atmospheric responses to these heterogeneities through fluxes of energy, water, carbon, and other scalars are scale-dependent and nonlinear. Although these exchanges can be measured using the eddy covariance technique, widely used tower-based measurement approaches suffer from spectral losses in lower frequencies when using typical averaging times. However, spatially resolved measurements such as airborne eddy covariance measurements can detect such larger scale (meso-β, meso-γ) transport. To evaluate the prevalence and magnitude of these flux contributions, we applied wavelet analysis to airborne flux measurements over a heterogeneous mid-latitude forested landscape, interspersed with open water bodies and wetlands. The measurements were made during the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors intensive field campaign. We ask, how do spatial scales of surface-atmosphere fluxes vary over heterogeneous surfaces across the day and across seasons? Measured fluxes were separated into smaller-scale turbulent and larger-scale mesoscale contributions. We found significant mesoscale contributions to sensible and latent heat fluxes through summer to autumn which would not be resolved in single-point tower measurements through traditional time-domain half-hourly Reynolds decomposition. We report scale-resolved flux transitions associated with seasonal and diurnal changes of the heterogeneous study domain. This study adds to our understanding of surface-atmospheric interactions over unstructured heterogeneities and can help inform multi-scale model-data integration of weather and climate models at a sub-grid scale

XMMU J100750.5+125818: A strong lensing cluster at z=1.082

We report on the discovery of the X-ray luminous cluster XMMU J100750.5+125818 at redshift 1.082 based on 19 spectroscopic members, which displays several strong lensing features. SED modeling of the lensed arc features from multicolor imaging with the VLT and the LBT reveals likely redshifts ~2.7 for the most prominent of the lensed background galaxies. Mass estimates are derived for different radii from the velocity dispersion of the cluster members, M_200 ~ 1.8 10^{14} Msun, from the X-ray spectral parameters, M_500 ~ 1.0 10^{14} Msun, and the largest lensing arc, M_SL ~ 2.3 10^{13} Msun. The projected spatial distribution of cluster galaxies appears to be elongated, and the brightest galaxy lies off center with respect to the X-ray emission indicating a not yet relaxed structure. XMMU J100750.5+125818 offers excellent diagnostics of the inner mass distribution of a distant cluster with a combination of strong and weak lensing, optical and X-ray spectroscopy.Comment: A&A, accepted for publicatio

The x-ray luminous galaxy cluster population at 0.9 < z ≲ 1.6 as revealed by the XMM-Newton Distant Cluster Project*

We present the largest sample to date of spectroscopically confirmed x-ray luminous high-redshift galaxy clusters comprising 22 systems in the range 0.9 1.3. The median system mass of the sample is M 200 ≃ 2×10 14 M ⊙, while the probed mass range for the distant clusters spans approximately (0.7-7)×10 14 M ⊙. The majority (>70%) of the x-ray selected clusters show rather regular x-ray morphologies, albeit in most cases with a discernible elongation along one axis. In contrast to local clusters, the z > 0.9 systems mostly do not harbor central dominant galaxies coincident with the x-ray centroid position, but rather exhibit significant brightest cluster galaxy (BCG) offsets from the x-ray center with a median value of about 50 kpc in projection and a smaller median luminosity gap to the second-ranked galaxy of Δm 12 ≃ 0.3 mag. We estimate a fraction of cluster-associated NVSS 1.4 GHz radio sources of about 30%, preferentially located within 1' from the x-ray center. This value suggests an increase of the fraction of very luminous cluster-associated radio sources by about a factor of 2.5-5 relative to lowz systems. The galaxy populations in z ≳ 1.5 cluster environments show first evidence for drastic changes on the high-mass end of galaxies and signs of a gradual disappearance of a well-defined cluster red-sequence as strong star formation activity is observed in an increasing fraction of massive galaxies down to the densest core regions. The presented XDCP high-z sample will allow first detailed studies of the cluster population during the critical cosmic epoch at lookback times of 7.3-9.5Gyr on the aggregation and evolution of baryons in the cold and hot phases as a function of redshift and system mass

A simple combinatorial treatment of constructions and threshold gaps of ramp schemes

We give easy proofs of some recent results concerning threshold gaps in ramp schemes. We then generalise a construction method for ramp schemes employing error-correcting codes so that it can be applied using nonlinear (as well as linear) codes. Finally, as an immediate consequence of these results, we provide a new explicit bound on the minimum length of a code having a specified distance and dual distance

An Algebraic Approach for Decoding Spread Codes

In this paper we study spread codes: a family of constant-dimension codes for random linear network coding. In other words, the codewords are full-rank matrices of size (k x n) with entries in a finite field F_q. Spread codes are a family of optimal codes with maximal minimum distance. We give a minimum-distance decoding algorithm which requires O((n-k)k^3) operations over an extension field F_{q^k}. Our algorithm is more efficient than the previous ones in the literature, when the dimension k of the codewords is small with respect to n. The decoding algorithm takes advantage of the algebraic structure of the code, and it uses original results on minors of a matrix and on the factorization of polynomials over finite fields

Togo: Thorny transition and misguided aid at the roots of economic misery

The parliamentary elections of October 2007, the first free Togolese elections since decades, were meant to correct at least partially the rigged presidential elections of 2005. Western donors considered it as a litmus test of despotic African regimes’ propensity to change towards democratization and economic prosperity. They took Togo as model to test their approach of political conditionality of aid, which had been emphasised also as corner stone of the joint EU-Africa strategy. Empirical findings on the linkage between democratization and economic performance are challenged in this paper because of its basic data deficiencies. It is open to question, whether Togo’s expected economic consolidation and growth will be due to democratization of its institutions or to the improved external environment, notably the growing competition between global players for African natural resources