Discovery of 28 pulsars using new techniques for sorting pulsar candidates

Modern pulsar surveys produce many millions of candidate pulsars, far more than can be individually inspected. Traditional methods for filtering these candidates, based upon the signal-to-noise ratio of the detection, cannot easily distinguish between interference signals and pulsars. We have developed a new method of scoring candidates using a series of heuristics which test for pulsar-like properties of the signal. This significantly increases the sensitivity to weak pulsars and pulsars with periods close to interference signals. By applying this and other techniques for ranking candidates from a previous processing of the Parkes Multi-beam Pulsar Survey, 28 previously unknown pulsars have been discovered. These include an eccentric binary system and a young pulsar which is spatially coincident with a known supernova remnant.Comment: To be published in Monthly Notices of the Royal Astronomical Society. 11 pages, 9 figure

An Optical Study of Two VY Sculptoris-Type Cataclysmic Binary Stars: V704 And and RX J2338+431

We report observations of the known cataclysmic variable star (CV) V704 And, and also confirm that the optical counterpart of the ROSAT Galactic Plane Survey source RX J2338+431 is a heretofore-neglected CV. Photometric and spectroscopic observations from MDM Observatory show both systems to be novalike variables that exhibit dips of 4-5 magnitudes from their mean brightnesses, establishing them as members of the VY~Scl subclass. From high-state emission-line radial velocities, we determine orbital periods of 0.151424(3) d (3.63 hr) for V704 And and 0.130400(1) d (3.13 hr) for RX J2338+431. In V704 And, we find that the H-alpha emission-line measures cluster into distinct regions on a plot of equivalent width versus full width at half-maximum, which evidently correspond to high, intermediate, and low photometric states. This allows us to assign spectra to photometric states when contemporaneous photometry is not available, an apparently novel method that may be useful in studies of other novalikes. Our low-state spectra of RX J2338+431 show features of an M-type secondary star, from which we estimate a distance of 890 +- 200 pc, in good agreement with the Gaia DR2 parallax.Comment: Accepted for Astronomical Journa

Discovery of hydroxyl and water masers in R Aquarii and H1-36 Arae

We present the first results from an all-sky maser-line survey of symbiotic Miras. Interferometric spectral-line observations of R Aqr and H1-36 Arae have revealed a 22-GHz water maser in the former and 1612-MHz hydroxyl and weak 22-GHz water maser emission from the latter. H1-36 has thus become the first known symbiotic OH/IR star. We have also detected weak OH line emission from the vicinity of R Aqr, but we note that there are small discrepencies between the OH- and H2O-line velocities and positions. These detections demonstrate unequivocally that dust can shield some circumstellar hydroxyl and water molecules from dissociation, even in systems which possess intense local sources of UV. Finally, we discuss some of the implications of these observations. The narrow profile of the water maser in R Aqr means that there may finally be an opportunity to determine the system's orbital parameters. We also point out that high resolution synthesis observations may trace the distribution of dust in H1-36 and R Aqr, possibly throwing light on the mass-loss process in symbiotic Miras and placing constraints on the amount of collimation experienced by UV radiation from their hot, compact companions.Comment: 7 pages; no figures attached; LaTex (MN style); postscript figures via anonymous ftp in /users/ers on astro.caltech.edu; University of Toronto pre-print; ERSRJI

Discovery of a bright eclipsing cataclysmic variable

We report on the discovery of J0644+3344, a bright deeply eclipsing cataclysmic variable (CV) binary. Spectral signatures of both binary components and an accretion disk can be seen at optical wavelengths. The optical spectrum shows broad H I, He I, and He II accretion disk emission lines with deep narrow absorption components from H I, He I, Mg II and Ca II. The absorption lines are seen throughout the orbital period, disappearing only during primary eclipse. These absorption lines are either the the result of an optically-thick inner accretion disk or from the photosphere of the primary star. Radial velocity measurements show that the H I, He I, and Mg II absorption lines phase with the the primary star, while weak absorption features in the continuum phase with the secondary star. Radial velocity solutions give a 150+/-4 km/s semi-amplitude for the primary star and 192.8+/-5.6 km/s for the secondary. The individual stellar masses are 0.63-0.69 Mdot for the primary and 0.49-0.54 Mdot for the secondary. The bright eclipsing nature of this binary has helped provide masses for both components with an accuracy rarely achieved for CVs. This binary most closely resembles a nova-like UX UMa or SW Sex type of CV. J0644+3344, however, has a longer orbital period than most UX UMa or SW Sex stars. Assuming an evolution toward shorter orbital periods, J0644+3344 is therefore likely to be a young interacting binary. The secondary star is consistent with the size and spectral type of a K8 star, but has an M0 mass.Comment: 10 pages, 13 figure, accepted for publication in A&

Binary-induced magnetic activity? Time-series echelle spectroscopy and photometry of HD123351 = CZ CVn

We present a first and detailed study of the bright and active K0IV-III star HD 123351. The star is found to be a single-lined spectroscopic binary with a period of 147.8919+-0.0003 days and a large eccentricity of e=0.8086+-0.0001. The rms of the orbital solution is just 47 m/s, making it the most precise orbit ever obtained for an active binary system. The rotation period is constrained from long-term photometry to be 58.32+-0.01 days. It shows that HD 123351 is a very asynchronous rotator, rotating five times slower than the expected pseudo-synchronous value. Two spotted regions persisted throughout the 12 years of our observations. Four years of Halpha, CaII H&K and HeI D3 monitoring identifies the same main periodicity as the photometry but dynamic spectra also indicate that there is an intermittent dependence on the orbital period, in particular for Ca ii H&K in 2008. Line-profile inversions of a pair of Zeeman sensitive/insensitive iron lines yield an average surface magnetic-flux density of 542+-72 G. The time series for 2008 is modulated by the stellar rotation as well as the orbital motion, such that the magnetic flux is generally weaker during times of periastron and that the chromospheric emissions vary in anti-phase with the magnetic flux. We also identify a broad and asymmetric lithium line profile and measure an abundance of log n(Li) = 1.70+-0.05. The star's position in the H-R diagram indicates a mass of 1.2+-0.1 Msun and an age of 6-7 Gyr. We interpret the anti-phase relation of the magnetic flux with the chromospheric emissions as evidence that there are two magnetic fields present at the same time, a localized surface magnetic field associated with spots and a global field that is oriented towards the (low-mass) secondary component

An Extended Double Row Layout Problem

The double row layout problem (DRLP) seeks to determine optimal machine locations on either side of an aisle, where the objective has been defined as the minimization of material ow cost among ma- chines while meeting machine clearance constraints. In this paper, we extend existing DRLP formulations in two respects. First, we consider the minimization of layout area besides the usual material ow cost objective. Second, we present a mixed integer linear programming formulation that permits non-zero aisle widths. This new formulation also includes new constraints that eliminate layout \mirroring, thus reducing the solution space significantly and thus solution times. Although small-scale problems may be solved optimally by commercial integer programming solvers, solution times are highly sensitive to the number of machines in a layout. A tabu search heuristic is shown to work well for moderately-sized problems. Numerical examples demonstrating the impact of both ow and area objectives, as well as aisle widths, are included

A Statistical Survey of Peculiar L and T Dwarfs in SDSS, 2MASS, and WISE

We present the final results from a targeted search for brown dwarfs with unusual near-infrared colors. From a positional cross-match of SDSS, 2MASS and WISE, we have identified 144 candidate peculiar L and T dwarfs. Spectroscopy confirms that 20 of the objects are peculiar or are candidate binaries. Nine of the 420 objects in our sample are young ($\lesssim$200 Myr; 2.1%) and another 8 (1.9%) are unusually red with no signatures of youth. With a spectroscopic $J-K_s$ color of 2.58 $\pm$ 0.11 mag, one of the new objects, the L6 dwarf 2MASS J03530419+0418193, is among the reddest field dwarfs currently known and is one of the reddest objects with no signatures of youth known to date. We have also discovered another potentially very low gravity object, the L1 dwarf 2MASS J00133470+1109403, and independently identified the young L7 dwarf 2MASS J00440332+0228112, first reported by Schneider and collaborators. Our results confirm that signatures of low gravity are no longer discernible in low to moderate resolution spectra of objects older than $\sim$200 Myr. The 1.9% of unusually red L dwarfs that do not show other signatures of youth could be slightly older, up to $\sim$400 Myr. In this case a red $J-K_s$ color may be more diagnostic of moderate youth than individual spectral features. However, its is also possible that these objects are relatively metal-rich, and so have an enhanced atmospheric dust content.Comment: 27 pages, 7 figures, 5 tables, accepted to A

The ESPRI project: astrometric exoplanet search with PRIMA I. Instrument description and performance of first light observations

The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for the discovery and study of planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years and to detect their barycentric motions due to orbiting planets. We present the operation principle, the instrument's implementation, and the results of a first series of test observations. A comprehensive overview of the instrument infrastructure is given and the observation strategy for dual-field relative astrometry is presented. The differential delay lines, a key component of the PRIMA facility which was delivered by the ESPRI consortium, are described and their performance within the facility is discussed. Observations of bright visual binaries are used to test the observation procedures and to establish the instrument's astrometric precision and accuracy. The data reduction strategy for astrometry and the necessary corrections to the raw data are presented. Adaptive optics observations with NACO are used as an independent verification of PRIMA astrometric observations. The PRIMA facility was used to carry out tests of astrometric observations. The astrometric performance in terms of precision is limited by the atmospheric turbulence at a level close to the theoretical expectations and a precision of 30 micro-arcseconds was achieved. In contrast, the astrometric accuracy is insufficient for the goals of the ESPRI project and is currently limited by systematic errors that originate in the part of the interferometer beamtrain which is not monitored by the internal metrology system. Our observations led to the definition of corrective actions required to make the facility ready for carrying out the ESPRI search for extrasolar planets.Comment: 32 pages, 39 figures, Accepted for publication in Astronomy and Astrophysic

Faint warm debris disks around nearby bright stars explored by AKARI and IRSF

Context: Debris disks are important observational clues for understanding planetary-system formation process. In particular, faint warm debris disks may be related to late planet formation near 1 AU. A systematic search of faint warm debris disks is necessary to reveal terrestrial planet formation. Aims: Faint warm debris disks show excess emission that peaks at mid-IR wavelengths. Thus we explore debris disks using the AKARI mid-IR all-sky point source catalog (PSC), a product of the second generation unbiased IR all-sky survey. Methods : We investigate IR excess emission for 678 isolated main-sequence stars for which there are 18 micron detections in the AKARI mid-IR all-sky catalog by comparing their fluxes with the predicted fluxes of the photospheres based on optical to near-IR fluxes and model spectra. The near-IR fluxes are first taken from the 2MASS PSC. However, 286 stars with Ks<4.5 in our sample have large flux errors in the 2MASS photometry due to saturation. Thus we have measured accurate J, H, and Ks band fluxes, applying neutral density (ND) filters for Simultaneous InfraRed Imager for Unbiased Survey (SIRIUS) on IRSF, the \phi 1.4 m near-IR telescope in South Africa, and improved the flux accuracy from 14% to 1.8% on average. Results: We identified 53 debris-disk candidates including eight new detections from our sample of 678 main-sequence stars. The detection rate of debris disks for this work is ~8%, which is comparable with those in previous works by Spitzer and Herschel. Conclusion: The importance of this study is the detection of faint warm debris disks around nearby field stars. At least nine objects have a large amount of dust for their ages, which cannot be explained by the conventional steady-state collisional cascade model.Comment: 17 pages, 21 figures, accepted for publication in Astronomy and Astrophysic