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PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

We present the first results from the SuperWASP Variable Stars (SVS) citizen science project. The photometry archive of the Wide Angle Search for Planets has previously been searched for periodic variations and the results of this search formed the basis of the SVS project on the Zooniverse. The SVS project asks volunteers to visually inspect light curve plots and categorize each one according to a broad classification scheme. Results from the first two years of SVS have now been published online as the SuperWASP Variable Star Photometry Archive (VeSPA). The archive can be browsed online, downloaded in full, or queried, filtered, and sorted to export a refined set of results. An interactive light curve viewer also allows any light curve to be folded at a user-defined period. Analysis of citizen science results and development of VeSPA features are both ongoing. Updated results will be published every six months.

We present the first analysis of results from the SuperWASP Variable Stars Zooniverse project, which is aiming to classify 1.6 million phase-folded light curves of candidate stellar variables observed by the SuperWASP all sky survey with periods detected in the SuperWASP periodicity catalogue. The resultant data set currently contains $>$1 million classifications corresponding to $>$500,000 object-period combinations, provided by citizen scientist volunteers. Volunteer-classified light curves have $\sim$89 per cent accuracy for detached and semi-detached eclipsing binaries, but only $\sim$9 per cent accuracy for rotationally modulated variables, based on known objects. We demonstrate that this Zooniverse project will be valuable for both population studies of individual variable types and the identification of stellar variables for follow up. We present preliminary findings on various unique and extreme variables in this analysis, including long period contact binaries and binaries near the short-period cutoff, and we identify 301 previously unknown binaries and pulsators. We are now in the process of developing a web portal to enable other researchers to access the outputs of the SuperWASP Variable Stars project., Comment: Accepted for publication in MNRAS, 13 pages, 16 figures, 4 tables

Amateur astronomers can make useful contributions to the study of comets. They add temporal coverage and multi-scale observations which can aid the study of fast-changing, and large-scale comet features. We document and review the amateur observing campaign set up to complement the Rosetta space mission, including the data submitted to date, and consider the campaign's effectiveness in the light of experience from previous comet amateur campaigns. We report the results of surveys of campaign participants, the amateur astronomy community, and schools who participated in a comet 46P observing campaign. We draw lessons for future campaigns which include the need for: clarity of objectives; recognising the wider impact campaigns can have on increasing science capital; clear, consistent, timely and tailored guidance; easy upload procedures with in-built quality control; and, regular communication, feedback and recognition., Comment: 32 pages, 8 figures To be published in The AAS Planetary Science Journal A'Hearn Symposium Focus Issue

It is well established that late-type main-sequence stars display a relationship between X-ray activity and the Rossby number, $Ro$, the ratio of rotation period to the convective turnover time. This manifests itself as a saturated regime (where X-ray activity is constant) and an unsaturated regime (where X-ray activity anti-correlates with the Rossby number). However, this relationship breaks down for the fastest rotators. We cross-correlated SuperWASP visually classified photometric light curves and ASAS-SN automatically classified photometric light curves with XMM-Newton X-ray observations to identify 3,178 stars displaying a photometrically defined rotational modulation in their light curve and corresponding X-ray observations. We fitted a power-law to characterise the rotation-activity relation of 900 main-sequence stars. We identified that automatically classified rotationally modulated light curves are not as reliable as visually classified light curves for this work. We found a power-law index in the unsaturated regime of G- to M-type stars of $\beta=-1.84\pm0.18$ for the SuperWASP catalogue, in line with the canonical value of $\beta=-2$. We find evidence of supersaturation in the fastest rotating K-type stars, with a power-law index of $\beta_{s}=1.42\pm0.26$., Comment: Accepted for publication in PASA. 14 pages, 12 figures, 3 tables

Some highly irradiated close-in exoplanets orbit stars showing anomalously low stellar chromospheric emission. We attribute this to absorption by circumstellar gas replenished by mass loss from ablating planets. Here we report statistics validating this hypothesis. Among ~3000 nearby, bright, main sequence stars ~40 show depressed chromospheric emission indicative of undiscovered mass-losing planets. The Dispersed Matter Planet Project uses high precision, high cadence radial velocity measurements to detect these planets. We summarise results for two planetary systems (DMPP-1 and DMPP-3) and fully present observations revealing a Mp sin i = 0.469 M$_{\rm J}$ planet in a 5.207 d orbit around the $\gamma$-Doradus pulsator HD 11231 (DMPP-2). We have detected short period planets wherever we have made more than 60 RV measurements, demonstrating that we have originated a very efficient method for detecting nearby compact planetary systems. Our shrouded, ablating planetary systems may be a short-lived phase related to the Neptunian desert: i.e. the dearth of intermediate-mass planets at short orbital periods. The circumstellar gas facilitates compositional analysis; allowing empirical exogeology in the cases of sublimating rocky planets. Dispersed Matter Planet Project discoveries will be important for establishing the empirical mass-radius-composition relationship(s) for low mass planets., Comment: Accepted for publication by Nature Astronomy on 12th November 2019 (Main article, Methods and Supplementary Information; 42 pages, 15 figures, 5 tables)

Estimates of population abundance are fundamental to wildlife management and conservation, but are difficult to obtain across large geographic scales and for cryptic species. We used a state-space model with age-at-harvest data in a Bayesian framework to model American black bear (Ursus americanus) abundance and demographic parameters in four management zones in Wisconsin from 2011-2017. We had limited demographic data available from the population, and relied upon a) the model, b) age-at-harvest data, and c) informative prior distributions from a literature review. The estimated posterior means and distributions for abundance and demographic parameters from our models were reasonable for each management zone, and indicated a decreasing trend in zones A and B, and a generally stable trend in zones C and D. The age-at-harvest data updated the posterior distribution and means for initial population size, harvest season survival, and non-harvest season survival, with a notable increase in precision for the survival values. A strength of the model for managers is the formalized process for providing biologically supported information as prior distributions to transparently accommodate expert opinion with measures of confidence when estimating wildlife populations, which can then be updated by the age-at-harvest data and model structure. The integration of prior information and age-at-harvest state-space models in a Bayesian framework efficiently leverage all available information for making zone-specific abundance estimates for the management of harvested species. This may create more informative data for decision-makers when setting harvest quotas, and could lead to more effective monitoring, conservation, and management of cryptic carnivore species., Comment: 1 table, 2 figures

A semi analytic framework for simulating the effects of atmospheric seeing in Adaptive Optics systems on an 8-m telescope is developed with the intention of understanding the origin of the wind-butterfly, a characteristic two-lobed halo in the PSF of AO imaging. Simulations show that errors in the compensated phase on the aperture due to servo-lag have preferential direction orthogonal to the direction of wind propagation which, when Fourier Transformed into the image plane, appear with their characteristic lemniscate shape along the wind direction. We develop a metric to quantify the effect of this aberration with the fractional standard deviation in an annulus centered around the PSF, and use telescope pointing to correlate this effect with data from an atmospheric models, the NOAA GFS. Our results show that the jet stream at altitudes of 100-200 hPa (equivalently 10-15 km above sea level) is highly correlated (13.2$\sigma$) with the strong butterfly, while the ground wind and other layers are more or less uncorrelated., Comment: 13 pages, 8 figures, Proceedings of SPIE 10703-230

The Gemini Planet Imager (GPI), a coronagraphic adaptive optics instrument designed for spectroscopy of extrasolar planets, had first light in 2013[13]. After five years, GPI has observed more than 500 stars, producing an extensive library of science images and associated telemetry that can be analyzed to determine performance predictors. We will present a summary of on-sky performance and lessons learned. The two most significant factors determining bright star contrast performance are atmospheric coherence time and the presence of dome seeing. With a possible move to Gemini North, we are planning potential upgrades including a pyramid-sensor based AO system with predictive control; we will summarize upgrade options and the science they would enable., Comment: To appear in Proceedings of the SPIE 10703 (Adaptive Optics Systems VI)

The Gemini Planet Imager (GPI) is the dedicated high-contrast imaging facility, located on Gemini South, designed for the direct detection and characterization of young Jupiter mass exoplanets. In 2019, Gemini is considering moving GPI from Gemini South to Gemini North. Analysis of GPI's as-built performance has highlighted several key areas of improvement to its detection capabilities while leveraging its current capabilities as a facility class instrument. We present the proposed upgrades which include a pyramid wavefront sensor, broadband low spectral resolution prisms and new apodized-pupil Lyot coronagraph designs all of which will enhance the current science capabilities while enabling new science programs., Comment: 14 pages, 6 figures, 1 table

We explore KLIP forward modeling spectral extraction on Gemini Planet Imager coronagraphic data of HR 8799, using PyKLIP and show algorithm stability with varying KLIP parameters. We report new and re-reduced spectrophotometry of HR 8799 c, d, and e in H & K bands. We discuss a strategy for choosing optimal KLIP PSF subtraction parameters by injecting simulated sources and recovering them over a range of parameters. The K1/K2 spectra for HR 8799 c and d are similar to previously published results from the same dataset. We also present a K band spectrum of HR 8799 e for the first time and show that our H-band spectra agree well with previously published spectra from the VLT/SPHERE instrument. We show that HR 8799 c and d show significant differences in their H & K spectra, but do not find any conclusive differences between d and e or c and e, likely due to large error bars in the recovered spectrum of e. Compared to M, L, and T-type field brown dwarfs, all three planets are most consistent with mid and late L spectral types. All objects are consistent with low gravity but a lack of standard spectra for low gravity limit the ability to fit the best spectral type. We discuss how dedicated modeling efforts can better fit HR 8799 planets' near-IR flux and discuss how differences between the properties of these planets can be further explored., Comment: Accepted to AJ, 25 pages, 16 Figures

Recent studies have shown that attackers can force deep learning models to misclassify so-called "adversarial examples": maliciously generated images formed by making imperceptible modifications to pixel values. With growing interest in deep learning for security applications, it is important for security experts and users of machine learning to recognize how learning systems may be attacked. Due to the complex nature of deep learning, it is challenging to understand how deep models can be fooled by adversarial examples. Thus, we present a web-based visualization tool, Adversarial-Playground, to demonstrate the efficacy of common adversarial methods against a convolutional neural network (CNN) system. Adversarial-Playground is educational, modular and interactive. (1) It enables non-experts to compare examples visually and to understand why an adversarial example can fool a CNN-based image classifier. (2) It can help security experts explore more vulnerability of deep learning as a software module. (3) Building an interactive visualization is challenging in this domain due to the large feature space of image classification (generating adversarial examples is slow in general and visualizing images are costly). Through multiple novel design choices, our tool can provide fast and accurate responses to user requests. Empirically, we find that our client-server division strategy reduced the response time by an average of 1.5 seconds per sample. Our other innovation, a faster variant of JSMA evasion algorithm, empirically performed twice as fast as JSMA and yet maintains a comparable evasion rate. Project source code and data from our experiments available at: https://github.com/QData/AdversarialDNN-Playground, Comment: 5 pages. {I.2.6}{Artificial Intelligence} ; {K.6.5}{Management of Computing and Information Systems}{Security and Protection}. arXiv admin note: substantial text overlap with arXiv:1706.01763

We set out to compile a catalogue of RRab pulsating variables in the SuperWASP archive and identify candidate Blazhko effect objects within this catalogue. We analysed their light curves and power spectra for correlations in their common characteristics to further our understanding of the phenomenon. Pulsation periods were found for each SWASP RRab object using PDM techniques. Low frequency periodic signals detected in the CLEAN power spectra of RRab stars were matched with modulation sidebands and combined with pairs of sidebands to produce a list of candidate Blazhko periods. A novel technique was used in an attempt to identify Blazhko effect stars by comparing scatter at different parts of the folded light curve. Pulsation amplitudes were calculated based on phase folded light curves. The SuperWASP RRab catalogue consists of 4963 objects of which 3397 are previously unknown. We discovered 983 distinct candidates for Blazhko effect objects, 613 of these being previously unknown in the literature as RR Lyrae stars, and 894 are previously unknown to be Blazhko effect stars. Correlations were investigated between the scatter of points on the light curve, the periods and amplitudes of the objects' pulsations, and those of the Blazhko effect. A statistical analysis has been performed on a large population of Blazhko effect stars from the wide-field SuperWASP survey. No correlations were found between the Blazhko period and other parameters including the Blazhko amplitude, although we confirmed a lower rate of occurrence of the Blazhko effect in long pulsation period objects., Comment: Includes Note added in Press re: CRTS cross-match

With growing interest in adversarial machine learning, it is important for machine learning practitioners and users to understand how their models may be attacked. We propose a web-based visualization tool, Adversarial-Playground, to demonstrate the efficacy of common adversarial methods against a deep neural network (DNN) model, built on top of the TensorFlow library. Adversarial-Playground provides users an efficient and effective experience in exploring techniques generating adversarial examples, which are inputs crafted by an adversary to fool a machine learning system. To enable Adversarial-Playground to generate quick and accurate responses for users, we use two primary tactics: (1) We propose a faster variant of the state-of-the-art Jacobian saliency map approach that maintains a comparable evasion rate. (2) Our visualization does not transmit the generated adversarial images to the client, but rather only the matrix describing the sample and the vector representing classification likelihoods. The source code along with the data from all of our experiments are available at \url{https://github.com/QData/AdversarialDNN-Playground}., Comment: 8 pages; 3 figures

Using the Gemini Planet Imager (GPI) located at Gemini South, we measured the near-infrared (1.0-2.4 micron) spectrum of the planetary companion to the nearby, young star $\beta$ Pictoris. We compare the spectrum obtained with currently published model grids and with known substellar objects and present the best matching models as well as the best matching observed objects. Comparing the empirical measurement of the bolometric luminosity to evolutionary models, we find a mass of $12.9\pm0.2$ $\mathcal{M}_\mathrm{Jup}$, an effective temperature of $1724\pm15$ K, a radius of $1.46\pm0.01$ $\mathcal{R}_\mathrm{Jup}$, and a surface gravity of $\log g = 4.18\pm0.01$ [dex] (cgs). The stated uncertainties are statistical errors only, and do not incorporate any uncertainty on the evolutionary models. Using atmospheric models, we find an effective temperature of $1700-1800$ K and a surface gravity of $\log g = 3.5$-$4.0$ [dex] depending upon model. These values agree well with other publications and with "hot-start" predictions from planetary evolution models. Further, we find that the spectrum of $\beta$ Pic b best matches a low-surface gravity L2$\pm$1 brown dwarf. Finally comparing the spectrum to field brown dwarfs we find the the spectrum best matches 2MASS J04062677-381210 and 2MASS J03552337+1133437., Comment: 21 pages, 11 figures, Accepted to AJ

During the first-light run of the Gemini Planet Imager (GPI) we obtained K-band spectra of exoplanets HR 8799 c and d. Analysis of the spectra indicates that planet d may be warmer than planet c. Comparisons to recent patchy cloud models and previously obtained observations over multiple wavelengths confirm that thick clouds combined with horizontal variation in the cloud cover generally reproduce the planets' spectral energy distributions. When combined with the 3 to 4 um photometric data points, the observations provide strong constraints on the atmospheric methane content for both planets. The data also provide further evidence that future modeling efforts must include cloud opacity, possibly including cloud holes, disequilibrium chemistry, and super-solar metallicity., Comment: Accepted for publication in ApJ

The Lick Observatory's Shane 3-meter telescope has been upgraded with a new infrared instrument (ShARCS - Shane Adaptive optics infraRed Camera and Spectrograph) and dual-deformable mirror adaptive optics (AO) system (ShaneAO). We present first-light measurements of imaging sensitivity in the Ks band. We compare measured results to predicted signal-to-noise ratio and magnitude limits from modeling the emissivity and throughput of ShaneAO and ShARCS. The model was validated by comparing its results to the Keck telescope adaptive optics system model and then by estimating the sky background and limiting magnitudes for IRCAL, the previous infra-red detector on the Shane telescope, and comparing to measured, published results. We predict that the ShaneAO system will measure lower sky backgrounds and achieve 20\% higher throughput across the $JHK$ bands despite having more optical surfaces than the current system. It will enable imaging of fainter objects (by 1-2 magnitudes) and will be faster to reach a fiducial signal-to-noise ratio by a factor of 10-13. We highlight the improvements in performance over the previous AO system and its camera, IRCAL., Comment: 13 pages, 5 figures, SPIE Astronomical Telescopes + Instrumentation, Montreal 2014

Deformable mirrors with very high order correction generally have smaller dynamic range of motion than what is required to correct seeing over large aperture telescopes. As a result, systems will need to have an architecture that employs two deformable mirrors in series, one for the low-order but large excursion parts of the wavefront and one for the finer and smaller excursion components. The closed-loop control challenge is to a) keep the overall system stable, b) avoid the two mirrors using control energy to cancel each other's correction, c) resolve actuator saturations stably, d) assure that on average the mirrors are each correcting their assigned region of spatial frequency space. We present the control architecture and techniques for assuring that it is linear and stable according to the above criteria. We derived the analytic forms for stability and performance and show results from simulations and on-sky testing using the new ShaneAO system on the Lick 3-meter telescope., Comment: 11 pages, 4 figures, Presented SPIE Astronomical Telescopes and Instrumentation Conference, paper #9148-174

A new high-order adaptive optics system is now being commissioned at the Lick Observatory Shane 3-meter telescope in California. This system uses a high return efficiency sodium beacon and a combination of low and high-order deformable mirrors to achieve diffraction-limited imaging over a wide spectrum of infrared science wavelengths covering 0.8 to 2.2 microns. We present the design performance goals and the first on-sky test results. We discuss several innovations that make this system a pathfinder for next generation AO systems. These include a unique woofer-tweeter control that provides full dynamic range correction from tip/tilt to 16 cycles, variable pupil sampling wavefront sensor, new enhanced silver coatings developed at UC Observatories that improve science and LGS throughput, and tight mechanical rigidity that enables a multi-hour diffraction- limited exposure in LGS mode for faint object spectroscopy science., Comment: 11 pages, 10 figures. Presented at SPIE Astronomical Telescopes + Instrumentation conference, paper 9148-76

We describe the design and first-light early science performance of the Shane Adaptive optics infraRed Camera-Spectrograph (ShARCS) on Lick Observatory's 3-m Shane telescope. Designed to work with the new ShaneAO adaptive optics system, ShARCS is capable of high-efficiency, diffraction-limited imaging and low-dispersion grism spectroscopy in J, H, and K-bands. ShARCS uses a HAWAII-2RG infrared detector, giving high quantum efficiency (>80%) and Nyquist sampling the diffraction limit in all three wavelength bands. The ShARCS instrument is also equipped for linear polarimetry and is sensitive down to 650 nm to support future visible-light adaptive optics capability. We report on the early science data taken during commissioning., Comment: 9 pages, 7 figures. Presented at SPIE Astronomical Telescopes + Instrumentation conference, paper 9148-118

Using the recently installed Gemini Planet Imager (GPI), we have taken the first H-band spectrum of the planetary companion to the nearby young star beta Pictoris. GPI is designed to image and provide low-resolution spectra of Jupiter sized, self-luminous planetary companions around young nearby stars. These observations were taken covering the H-band (1.65 microns). The spectrum has a resolving power of $\sim$ 45 and demonstrates the distinctive triangular shape of a cool substellar object with low surface gravity. Using atmospheric models, we find an effective temperature of $1650 \pm 50$ K and a surface gravity of $\log(g) = 4.0 \pm 0.25$ (cgs units). These values agree well with predictions from planetary evolution models for a gas giant with mass between 10 and 12 $M_{\rm Jup}$ and age between 10 and 20 Myrs., Comment: 8 pages, 5 figures, submitted to ApJL

Micro-electro-mechanical systems (MEMS) technology can provide for deformable mirrors (DMs) with excellent performance within a favorable economy of scale. Large MEMS-based astronomical adaptive optics (AO) systems such as the Gemini Planet Imager are coming on-line soon. As MEMS DM end-users, we discuss our decade of practice with the micromirrors, from inspecting and characterizing devices to evaluating their performance in the lab. We also show MEMS wavefront correction on-sky with the "Villages" AO system on a 1-m telescope, including open-loop control and visible-light imaging. Our work demonstrates the maturity of MEMS technology for astronomical adaptive optics., Comment: 14 pages, 15 figures, Invited Paper, SPIE Photonics West 2012

Adaptive Optics (AO) is a new and rapidly expanding field of instrumentation, yet astronomers, vision scientists, and general AO practitioners are largely unfamiliar with the root technologies crucial to AO systems. The AO Summer School (AOSS), sponsored by the Center for Adaptive Optics, is a week-long course for training graduate students and postdoctoral researchers in the underlying theory, design, and use of AO systems. AOSS participants include astronomers who expect to utilize AO data, vision scientists who will use AO instruments to conduct research, opticians and engineers who design AO systems, and users of high-bandwidth laser communication systems. In this article we describe new AOSS laboratory sessions implemented in 2006-2009 for nearly 250 students. The activity goals include boosting familiarity with AO technologies, reinforcing knowledge of optical alignment techniques and the design of optical systems, and encouraging inquiry into critical scientific questions in vision science using AO systems as a research tool. The activities are divided into three stations: Vision Science, Fourier Optics, and the AO Demonstrator. We briefly overview these activities, which are described fully in other articles in these conference proceedings (Putnam et al., Do et al., and Harrington et al., respectively). We devote attention to the unique challenges encountered in the design of these activities, including the marriage of inquiry-like investigation techniques with complex content and the need to tune depth to a graduate- and PhD-level audience. According to before-after surveys conducted in 2008, the vast majority of participants found that all activities were valuable to their careers, although direct experience with integrated, functional AO systems was particularly beneficial., Comment: Published in ASP Conference Proceedings: Learning from Inquiry in Practice, 436, 2010, L. Hunter and A. Metevier, eds

We present a comparative study of the thermal emission of the transiting exoplanets WASP-1b and WASP-2b using the Spitzer Space Telescope. The two planets have very similar masses but suffer different levels of irradiation and are predicted to fall either side of a sharp transition between planets with and without hot stratospheres. WASP-1b is one of the most highly irradiated planets studied to date. We measure planet/star contrast ratios in all four of the IRAC bands for both planets (3.6-8.0um), and our results indicate the presence of a strong temperature inversion in the atmosphere of WASP-1b, particularly apparent at 8um, and no inversion in WASP-2b. In both cases the measured eclipse depths favor models in which incident energy is not redistributed efficiently from the day side to the night side of the planet. We fit the Spitzer light curves simultaneously with the best available radial velocity curves and transit photometry in order to provide updated measurements of system parameters. We do not find significant eccentricity in the orbit of either planet, suggesting that the inflated radius of WASP-1b is unlikely to be the result of tidal heating. Finally, by plotting ratios of secondary eclipse depths at 8um and 4.5um against irradiation for all available planets, we find evidence for a sharp transition in the emission spectra of hot Jupiters at an irradiation level of 2 x 10^9 erg/s/cm^2. We suggest this transition may be due to the presence of TiO in the upper atmospheres of the most strongly irradiated hot Jupiters., Comment: 10 pages, submitted to ApJ

To date, classical mass renormalization has been invoked in all tube-based self-force calculations, thus following the method introduced in Dirac's 1938 calculation of the electromagnetic self-force for the classical radiating electron. In this paper a new tube method is described that does not rely on a mass renormalization procedure. As a result, exact self-force calculations become possible for classical radiating systems of finite size. A new derivation of the Lorentz-Dirac equation is given and the relationship between the new tube method and the classical mass renormalization procedure is explained. It is expected that a similar tube method could be used to obtain rigorous results in the gravitational self-force problem., Comment: 21 pages, 2 figures. An accompanying Mathematica notebook is available at http://124.178.231.75/sfcalc

Cataclysmic Variables are a distinct class of interacting binaries, transferring mass from a donor star to a degenerate accretor, a white dwarf. We here review X-ray observations of these systems, with some emphasis on what has been achieved in the last decade., Comment: 40 pages, 10 figures; minor updates to text. To appear in Compact Stellar X-Ray Sources, eds. W.H.G. Lewin and M. van der Klis, Cambridge University Press

We present optical spectroscopy and optical and infrared photometry of the counterpart to the transient X-ray source KS 1947+300. The counterpart is shown to be a moderately reddened V=14.2 early-type Be star located in an area of low interstellar absorption slightly above the Galactic plane. Changes in brightness are accompanied by correlated reddening of the source, as is expected in this kind of object. From intermediate resolution spectroscopy, we derive a spectral type B0Ve. If the intrinsic luminosity of the star is normal for its spectral type, KS 1947+300 is situated at a distance of ~10 kpc, implying that its X-ray luminosity at the peak of the spring 2000 X-ray outburst was typical of Type II outbursts in Be/X-ray transients. KS 1947+300 is thus the first Be/X-ray recurrent transient showing Type II outbursts which has an almost circular orbit., Comment: 7 pages, 5 figures, uses new A&A format (included). Accepted for publication in A&A

We report on the identification of the optical/IR counterpart of the 29.5-s transient X-ray pulsar GS 1843+009. We re-analysed an archival ROSAT HRI observation of GS 1843+009, obtaining a new refined position. The optical and IR follow-up observations carried out for the new error circle allowed us to find a relatively faint (V=20.9) and variable early type reddened star (V-R=2.1). The optical spectra show the Balmer and Paschen series in emission, while the IR observations confirm the presence of a flux excess (H=13.2, J-H=0.54), suggesting that the star is surrounded by a circumstellar envelope. Spectroscopic and photometric data together indicate a B0-B2 IV-Ve spectral-type star located at a distance of > 10kpc confirming the Be-star/X-ray binary nature of GS 1843+009., Comment: 6 pages (3 figures included). Accepted for publication in A&A

We describe numerical techniques used in the construction of our 4th order evolution for the full Einstein equations, and assess the accuracy of representative solutions. The code is based on a null gauge with a quasi-spherical radial coordinate, and simulates the interaction of a single black hole with gravitational radiation. Techniques used include spherical harmonic representations, convolution spline interpolation and filtering, and an RK4 "method of lines" evolution. For sample initial data of "intermediate" size (gravitational field with 19% of the black hole mass), the code is accurate to 1 part in 10^5, until null time z=55 when the coordinate condition breaks down., Comment: Latex, 38 pages, 29 figures (360Kb compressed)