Showing papers in "Publications of the Astronomical Society of the Pacific in 2008"

The Keck Planet Search: Detectability and the Minimum Mass and Orbital Period Distribution of Extrasolar Planets

Abstract: . We analyze 8 years of precise radial velocity measurements from the Keck Planet Search, characterizing the detection threshold, selection effects, and completeness of the survey. We first carry out a systematic search for planets, by assessing the false-alarm probability associated with Keplerian orbit fits to the data. This allows us to understand the detection threshold for each star in terms of the number and time baseline of the observations, and the underlying “noise” from measurement errors, intrinsic stellar jitter, or additional low-mass planets. We show that all planets with orbital periods P 20 m s-1 K > 20 m s - 1 , and eccentricities e ≲ 0.6 e ≲ 0.6 have been announced, and we summarize the candidates at lower amplitudes and longer orbital periods. For the remaining stars, we calculate upper limits on the velocity amplitude of a companion. For orbital periods less than the duration of the observations, these are typically ...

GROND-a 7-channel imager

Abstract: .We describe the construction of GROND, a 7-channel imager, primarily designed for rapid observations of gamma-ray burst afterglows. It allows simultaneous imaging in the Sloan g′r′i′z′g′r′i′z′ and near-infrared JHKJHK bands. GROND was commissioned at the MPI/ESO 2.2 m telescope at La Silla (Chile) in April 2007, and first results of its performance and calibration are presented.

Design Considerations for a Ground-Based Transit Search for Habitable Planets Orbiting M Dwarfs

Abstract: By targeting nearby M dwarfs, a transit search using modest equipment is capable of discovering planets as small as 2 R⊕ in the habitable zones of their host stars. The MEarth Project, a future transit search, aims to employ a network of ground-based robotic telescopes to monitor M dwarfs in the northern hemisphere with sufficient precision and cadence to detect such planets. Here we investigate the design requirements for the MEarth Project. We evaluate the optimal bandpass, and the necessary field of view, telescope aperture, and telescope time allocation on a star-by-star basis, as is possible for the well-characterized nearby M dwarfs. Through these considerations, 1976 late M dwarfs (R < 0.33 R⊙) emerge as favorable targets for transit monitoring. Based on an observational cadence and on total telescope time allocation tailored to recover 90% of transit signals from planets in habitable zone orbits, we find that a network of 10 30 cm telescopes could survey these 1976 M dwarfs in less than three years. A null result from this survey would set an upper limit (at 99% confidence) of 17% for the rate of occurrence of planets larger than 2 R⊕ in the habitable zones of late M dwarfs, and even stronger constraints for planets lying closer than the habitable zone. If the true occurrence rate of habitable planets is 10%, the expected yield would be 2.6 planets.

The Pulsating White Dwarf Stars

Abstract: We present a summary of what is currently known about the three distinct families of isolated pulsating white dwarfs. These are the GW Vir stars (He/C/O-atmosphere stars with Teff 120,000 K), the V777 Her stars (He-atmosphere, Teff 25,000 K), and the ZZ Ceti stars (H-atmosphere, Teff 12,000 K), all showing multiperiodic luminosity variations caused by low-order and low-degree g-mode instabilities. We also provide, in an Appendix, a very brief overview of the newly found evidence in favor of the existence of a fourth category of oscillating white dwarfs bearing strong similarities with these families of pulsators. We begin our survey with a short historical introduction, followed by a general discussion of pulsating white dwarfs as compact pulsators. We then discuss the class properties of these objects, including an updated census. We next focus on the instability domains for each family of pulsators in the log g - Teff diagram, and present their time-averaged properties in more detail. This is followed by a section on excitation physics, i.e., the causes of the pulsational instabilities, with emphasis on the common properties of the different types of pulsator. We then discuss the time-dependent properties of the pulsating white dwarfs featuring, among other things, a brief "picture tour" across the ZZ Ceti instability strip. We next review the methods used to infer or constrain the angular geometry of a pulsation mode in a white dwarf. These include multicolor photometry and time-resolved spectroscopy, the exploitation of the nonlinear features in the observed light curves, and rotational splitting. We also consider basic adiabatic asteroseismology starting with a discussion of the reaction of the period spectrum to variations of model parameters. We next review the various asteroseismological inferences that have so far been claimed for white dwarfs. We also discuss the potential of exploiting the rates of period change. We finally provide some concluding remarks, including a list with several suggestions for future progress in the field.

DAOSPEC: An Automatic Code for Measuring Equivalent Widths in High-Resolution Stellar Spectra*

Abstract: DAOSPEC is a Fortran code for measuring equivalent widths of absorption lines in stellar spectra with minimal human involvement. It works with standard FITS-format files and it is designed for use with high-resolution (R > 15,000) and high signal-to-noise-ratio (S/N > 30) spectra that have been binned on a linear wavelength scale. First, we review the analysis procedures that are usually employed in the literature. Next, we discuss the principles underlying DAOSPEC and point out similarities and differences with respect to conventional measurement techniques. Then, experiments with artificial and real spectra are discussed to illustrate the capabilities and limitations of DAOSPEC, with special attention given to the issues of continuum placement, radial velocities, and the effects of strong lines and line crowding. Finally, quantitative comparisons with other codes and with results from the literature are also presented.

MegaPipe: The MegaCam Image Stacking Pipeline at the Canadian Astronomical Data Centre

Abstract: . This paper describes the MegaPipe image processing pipeline at the Canadian Astronomical Data Centre. The pipeline combines multiple images from the MegaCam mosaic camera on Canada-France-Hawaii Telescope (CFHT) and combines them into a single output image. MegaPipe takes as input detrended MegaCam images and does a careful astrometric and photometric calibration on them. The calibrated images are then resampled and combined into image stacks. The astrometric calibration of the output images is accurate to within 0.15″ relative to external reference frames and 0.04″ internally. The photometric calibration is good to within 0.03 mag. The stacked images and catalogs derived from these images are available through the CADC Web site.

Revised bolometric corrections and interstellar extinction coefficients for the ACS and WFPC2 photometric systems

Abstract: We present extensive tables of bolometric corrections and interstellar extinction coefficients for the WFPC2 and ACS (both WFC and HRC) photometric systems. They are derived from synthetic photometry applied to a database of spectral energy distributions covering a large range of effective temperatures, surface gravity, and metal content. Carbon stars are also considered. The zero points take into consideration the new high-accuracy Vega fluxes from Bohlin. These tables are employed to transform Padova isochrones into WFPC2 and ACS photometric systems using interstellar extinction coefficients on a star-to-star basis. All data are available either in tabular form or via an interactive web interface in the case of the isochrones. Preliminary tables for the WFC3 camera are also included in the database.

Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest

Abstract: Precision astrometry at microarcsecond accuracy has applications for a wide range of astrophysical problems. This paper is a study of the science questions that can be addressed using an instrument with flexible scheduling that delivers parallaxes at about 4 μas on targets as faint as V = 20, and differential accuracy of 0.6 μas on bright targets. The science topics are drawn primarily from the team key projects, selected in 2000, for the Space Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities of this mission to illustrate the importance of the next level of astrometric precision in modern astrophysics. SIM PlanetQuest is currently in the detailed design phase, having completed in 2005 all of the enabling technologies needed for the flight instrument. It will be the first space-based long-baseline Michelson interferometer designed for precision astrometry. SIM PlanetQuest will contribute strongly to many astronomical fields, including stellar and galactic astrophysics, planetary systems around nearby stars, and the study of quasar and AGN nuclei. Using differential astrometry SIM PlanetQuest will search for planets with masses as small as Earth orbiting in the “habitable zone” around the nearest stars, and could discover many dozen if Earth-like planets are common. It will characterize the multiple-planet systems that are now known to exist, and it will be able to search for terrestrial planets around all of the candidate target stars in the Terrestrial Planet Finder and Darwin mission lists. It will be capable of detecting planets around young stars, thereby providing insights into how planetary systems are born and how they evolve with time. Precision astrometry allows the measurement of accurate dynamical masses for stars in binary systems. SIM PlanetQuest will observe significant numbers of very high- and low-mass stars, providing stellar masses to 1%, the accuracy needed to challenge physical models. Using precision proper-motion measurements, SIM PlanetQuest will probe the Galactic mass distribution, and, through studies of tidal tails, the formation and evolution of the Galactic halo. SIM PlanetQuest will contribute to cosmology through improved accuracy of the Hubble constant. With repeated astrometric measurements of the nuclei of active galaxies, SIM PlanetQuest will probe the dynamics of accretion disks around supermassive black holes, and the relativistic jets that emerge from them.

Obit: A Development Environment for Astronomical Algorithms

Abstract: Obit is a development environment for astronomical algorithms. It implements multiple "native" data formats including FITS and AIPS. The shared data model with AIPS means almost complete interoperability, allowing algorithmic development in a production environment. The Obit package supports both prepackaged, compiled tasks and a python interface to the major class functionality to allow rapid prototyping using python scripts. Developed features are predominantly radio astronomical, but support for astronomical images and tables is generic and should allow a wider range of applications. The design is intended to be readily extensible. An example is given that explores the effect of "CLEAN bias" in the VLA Low-Frequency Sky Survey and compares its method of CLEAN to an automated CLEAN window selection scheme that should reduce the bias. This technique shows much promise for reducing this systematic effect.

The Apache Point Observatory Lunar Laser-ranging Operation: Instrument Description and First Detections

Abstract: A next-generation lunar laser-ranging apparatus using the 35 m telescope at the Apache Point Observatory in southern New Mexico has begun science operation The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) has achieved 1m mrange precision to the moon, which should lead to ap- proximately 1 order-of-magnitude improvements in several tests of fundamental properties of gravity We briefly outline the scientific goals, and then give a detailed discussion of the APOLLO instrumentation

A Scalable Correlator Architecture Based on Modular FPGA Hardware, Reuseable Gateware, and Data Packetization

Abstract: . A new generation of radio telescopes is achieving unprecedented levels of sensitivity and resolution, as well as increased agility and field of view, by employing high-performance digital signal-processing hardware to phase and correlate signals from large numbers of antennas. The computational demands of these imaging systems scale in proportion to BMN2 B M N 2 , where B B is the signal bandwidth, M M is the number of independent beams, and N N is the number of antennas. The specifications of many new arrays lead to demands in excess of tens of PetaOps per second. To meet this challenge, we have developed a general-purpose correlator architecture using standard 10-Gbit Ethernet switches to pass data between flexible hardware modules containing Field Programmable Gate Array (FPGA) chips. These chips are programmed using open-source signal-processing libraries that we have developed to be flexible, scalable, and chip-independent. This work reduces the time and cost of implementing a wide range of...

Nighttime Optical Turbulence Vertical Structure above Dome C in Antarctica

Abstract: . During the austral winter 2005, the first astronomical site testing campaign were performed at Dome C, in Antarctica. Thirty-five meteorological balloons equipped with microthermal sensors were used to sense the vertical profile of the optical turbulence intensity C N 2 above Dome C up to 20 km. All the profiles of the 2005 campaign are statistically analyzed. We provide the median C N 2 profiles and the mean potential temperature, mean horizontal wind speed, and mean direction profiles for the three seasons covered by this campaign (autumn, winter, and beginning of the spring). The structure of the optical turbulence in the atmosphere above Dome C is analyzed and compared with the well-known median C N 2 profiles of midlatitude sites. Of the whole optical turbulence, 80% lies within the first 33 m above the ground and 9% in the upper part of the boundary layer, between 33 m and 1 km above the ground. The remaining 11% are in the free atmosphere. This is an extreme situation when compared with “...

PuMa-II: A Wide Band Pulsar Machine for the Westerbork Synthesis Radio Telescope

Abstract: The Pulsar Machine II (PuMa-II) is the new flexible pulsar processing back-end system at the Westerbork Synthesis Radio Telescope (WSRT), specifically designed to take advantage of the upgraded WSRT. The instrument is based on a computer cluster running the Linux operating system, with minimal custom hardware. A maximum of 160 MHz analog bandwidth sampled as 8 × 20 MHz subbands with 8-bit resolution can be recorded on disks attached to separate computer nodes. Processing of the data is done in the additional 32 nodes allowing near real time coherent dedispersion for most pulsars observed at the WSRT. This has doubled the bandwidth for pulsar observations in general, and has enabled the use of coherent dedispersion over a bandwidth 8 times larger than was previously possible at the WSRT. PuMa-II is one of the widest bandwidth coherent dedispersion machines currently in use and has a maximum time resolution of 50 ns. The system is now routinely used for high-precision pulsar timing studies, polarization studies, single pulse work, and a variety of other observational work.

The Beginning and Evolution of the Universe

Abstract: We review the current standard model for the evolution of the Universe from an early inflationary epoch to the complex hierarchy of structure seen today. We summarize and provide key references for the following topics: observations of the expanding Universe; the hot early Universe and nucleosynthesis; theory and observations of the cosmic microwave background; Big Bang cosmology; inflation; dark matter and dark energy; theory of structure formation; the cold dark matter model; galaxy formation; cosmological simulations; observations of galaxies, clusters, and quasars; statistical measures of large-scale structure; and measurement of cosmological parameters. We conclude with discussion of some open questions in cosmology. This review is designed to provide a graduate student or other new worker in the field an introduction to the cosmological literature.

Photometry using the Infrared Array Camera on the Spitzer Space Telescope

Abstract: We present several corrections for point-source photometry to be applied to data from the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. These corrections are necessary because of characteristics of the IRAC arrays and optics and the way the instrument is calibrated in flight. When these corrections are applied, it is possible to achieve a ~2% relative photometric accuracy for sources of adequate signal-to-noise ratio in an IRAC image.

2DPHOT: A Multi-Purpose Environment for the Two-Dimensional Analysis of Wide-Field Images

Abstract: We describe 2DPHOT, a general-purpose analysis environment for source detection and analysis in deep wide-field images. 2DPHOT is an automated tool to obtain both integrated and surface photometry of galaxies in an image, to perform reliable star-galaxy separation with accurate estimates of contamination at faint flux levels, and to estimate completeness of the image catalog. We describe the analysis strategy on which 2DPHOT is based, and provide a detailed description of the different algorithms implemented in the package. This new environment is intended as a dedicated tool to process the wealth of data from wide-field imaging surveys. To this end, the package is complemented by 2DGUI, an environment that allows multiple processing of data using a range of computing architectures.

Calibrated griz magnitudes of Tycho stars: All-sky photometric calibration using bright stars

Abstract: Photometric calibration to ~5% level is frequently needed at arbitrary celestial location. However, existing all-sky astronomical catalogs do not reach this accuracy, and time consuming photometric calibration procedures are required. I fitted the Hipparcos B-T and V-T magnitudes, along with the 2MASS J, H, and K magnitudes of Tycho-2-catalog stars with stellar spectral templates. From the best-fit spectral template derived for each star, I calculated its synthetic SDSS griz magnitudes and constructed an all-sky catalog of griz magnitudes of bright stars (V ≾ 12). Testing this method on SDSS photometric-telescope observations, I find that the photometric accuracy, for a single star, is usually about 0.12, 0.12, 0.10, and 0.08 mag (1 σ), for the g, r, i, and z-bands, respectively. However, by using ~10 such stars, the typical errors per calibrated field (systematic + statistical) can be reduced to about 0.04, 0.03, 0.02, and 0.02 mag, in the g, r, i, and z-bands, respectively. Therefore, in cases for which several calibration stars can be observed in the field of view of an instrument, accurate photometric calibration is possible.

XPOL—the Correlation Polarimeter at the IRAM 30-m Telescope

Abstract: XPOL, the first correlation polarimeter at a large-millimeter telescope, uses a flexible digital correlator to measure all four Stokes parameters simultaneously, i.e., the total power I, the linear polarization components Q and U, and the circular polarization V. The versatility of the back end provides adequate bandwidth for efficient continuum observations as well as sufficient spectral resolution (40 kHz) for observations of narrow lines. We demonstrate that the polarimetry-specific calibrations are handled with sufficient precision, in particular the relative phase between the Observatory's two orthogonally linearly polarized receivers. The many facets of instrumental polarization are studied at 3 mm wavelength in all Stokes parameters: on-axis with point sources and off-axis with beam maps. Stokes Q, which is measured as the power difference between the receivers, is affected by instrumental polarization at the 1.5% level. Stokes U and V, which are measured as cross-correlations, are very minimally affected (maximum sidelobes 0.6% [U] and 0.3% [V]). These levels critically depend on the precision of the receiver alignment. They reach these minimum levels set by small ellipticities of the feed horns when alignment is optimum (0.3''). A second critical prerequisite for low polarization sidelobes turned out to be the correct orientation of the polarization splitter grid. Its cross-polarization properties are modeled in detail. XPOL observations are therefore limited only by receiver noise in Stokes U and V even for extended sources. Systematic effects set in at the 1.5% level in observations of Stokes Q. With proper precautions, this limitation can be overcome for point sources. Stokes Q observations of extended sources are the most difficult with XPOL.

Spectrophotometry with Hectospec, the MMT's Fiber-Fed Spectrograph

Abstract: The spectrophotometric calibration of surveys is a significant, but often neglected, issue when measuring the history of star formation by combining spectroscopic surveys conducted with different instruments. We describe techniques for photometric calibration of optical spectra obtained with the MMT's fiber-fed spectrograph, Hectospec. The atmospheric dispersion compensation prisms built into the MMT's f/5 wide-field corrector effectively eliminate errors due to differential refraction and simplify the calibration procedure. The procedures that we describe here are applicable to all 220,000+ spectra obtained to date with Hectospec because the instrument response is stable. We estimate the internal error in the Hectospec measurements by comparing duplicate measurements of ~1500 galaxies. For a sample of 400 galaxies in the Smithsonian Hectospec Lensing Survey (SHELS) with a median z = 0.10, we compare line and continuum fluxes measured by Hectospec through a 1.5'' diameter optical fiber with those measured by the Sloan Digital Sky Survey (SDSS) through a 3'' diameter optical fiber. Agreement of the [O II] and Hα SHELS and SDSS line fluxes, after scaling by the R-band flux in the different apertures, suggests that the spatial variation in star-formation rates over a 1.5 to 3 kpc radial scale is small. The median ratio of the Hectospec and SDSS spectra, smoothed over 100 A scales, is remarkably constant to ~5% over the range of 3850 to 8000 A. Offsets in the ratio of the median [O II] and Hα fluxes, the equivalent width of Hδ and the continuum index d4000 are a few percent, small compared with other sources of scatter. We also explore the impact of atmospheric absorption. Observing redward of 6500 A, it is impossible to remove the effects of atmospheric absorption perfectly because the variation of absorption with wavelength is not resolved by a moderate dispersion spectrograph. Thus measurements of spectral line fluxes including Hα, and derived physical quantities including star-formation rates, may have sizable systematic errors where the redshifted spectral features land on strong atmospheric absorption troughs.

First Speckle Interferometry at SOAR Telescope with Electron-Multiplication CCD

Abstract: A simple camera with electron-multiplication CCD, fast frame rate, and a pixel scale of 15 mas is described. This instrument was tested at the SOAR 4-m telescope in the speckle-interferometry regime. The data were processed by the standard speckle algorithm permitting derivation of binary-star parameters. We observed 29 objects with separations from 21 mas to 1.32'', mostly southern binaries with known orbits. Some pairs require orbit revision. Two spectroscopic binaries HIP 9631 and HIP 11072 and the astrometric binary κ For are resolved for the first time, while three objects were unresolved.

The Large-Grained Dust Coma of 174P/Echeclus

Abstract: On 2005 December 30, Y.-J. Choi and P. R. Weissman discovered that the formerly dormant Centaur 2000 EC98 was in strong outburst. Previous observations by P. Rousselot et al. spanning a 3-year period indicated a lack of coma down to the 27 mag arcsec 2 level.We present Spitzer Space Telescope MIPS observations of this newly active Centaur--now known as 174P/Echeclus (2000 EC98)--or 60558 Echeclus--taken in 2006 late February. The images show strong signal at both the 24 and 70 micron bands and reveal an extended coma about 2' in diameter. Analyses yield estimates of the coma signal contribution that are in excess of 90% of the total signal in the 24 micron band. Dust production estimates ranging from 1.7-4 x 10(exp 2) kg/s are on the order of 30 times that seen in other Centaurs. Simultaneous visible-wavelength observations were also obtained with Palomar Observatory's 200-inch telescope, the 1.8-m Vatican Advanced Technology Telescope, the Bohyunsan Optical Astronomy Observatory (BOAO) 1.8-m telescope, and Table Mountain Observatory's 0.6-m telescope, revealing a coma morphology nearly identical to the mid-IR observations. The grain size distribution derived from the data yields a log particle mass power-law with slope parameter (alpha) = -0.87 +/- 0.07, and is consistent with steady cometary-activity, such as that observed during the Stardust spacecraft's encounter at 81P/Wild 2, and not with an impact driven event, such as that caused by the Deep Impact experiment.

Near-Infrared Monitoring of Ultracool Dwarfs: Prospects for Searching for Transiting Companions

Abstract: . Stars of late-M and L spectral types, collectively known as ultracool dwarfs (UCDs), may be excellent targets for searches for extrasolar planets. Owing to their small radii, the signal from an Earth-size planet transiting a UCD is, in principle, readily detectable. We present results from a study designed to evaluate the feasibility of using precise near-infrared (NIR) photometry to detect terrestrial extrasolar planets orbiting UCDs. We used the Peters Automated Infrared Imaging Telescope (PAIRITEL) to observe a sample of 13 UCDs over a period of 10 months. We consider several important systematic effects in NIR differential photometry and develop techniques for generating photometry with a precision of 0.01 mag and long-term stability. We simulate the planet detection efficiency of an extended campaign to monitor a large sample of UCDs with PAIRITEL. We find that both a targeted campaign with a single telescope lasting several years and a campaign making use of a network of telescopes distrib...

χ Values for Blue Emission Lines in M Dwarfs

Abstract: . We compute χ χ values for blue emission lines in active M dwarfs. Using flux-calibrated spectra from nearby M dwarfs and spectral M dwarf templates from SDSS, we derive analytical relations that describe how the χ χ values for the Ca II H and K as well as the Hβ, Hγ, Hδ, Hϵ, and H8 Balmer emission lines vary as a function of spectral type and color. These derived values are important for numerous M dwarf studies where the intrinsic luminosity of emission lines cannot be estimated due to uncertain distances and/or non-flux-calibrated spectra. We use these results to estimate the mean properties of blue emission lines in active-field M dwarfs from SDSS.

GHαFaS: Galaxy Hα Fabry-Perot System for the William Herschel Telescope

Abstract: GHαFaS, a new Fabry-Perot system, is now available at the William Herschel Telescope (WHT). It was mounted, for the first time, at the Nasmyth focus of the 4.2-m WHT on La Palma in 2007 July. Using modern technology, with a spectral resolution of the order R ~ 15,000, and with a seeing-limited spatial resolution, GHαFaS will provide a new look at the Hα-emitting gas over a 4.8' circular field in the nearby universe. Many science programs can be done on a 4.2-m class telescope in world-class seeing conditions with a scanning Fabry-Perot. Not only galaxies but H II regions, planetary nebulae, supernova remnants, and the diffuse interstellar medium are subjects for which unique data can be aquired rapidly. Astronomers from the Laboratoire d'Astrophysique Experimentale (LAE) in Montreal, the Laboratoire d'Astrophysique de Marseille (LAM-OAMP), and the Instituto de Astrofisica de Canarias (IAC), have inaugurated GHαFaS by studying in detail the dynamics of some nearby spiral galaxies. A robust set of state-of-the-art tools for reducing and analyzing the data cubes obtained with GHαFaS has also been developed.

SDSS 1507+52: A Halo Cataclysmic Variable? 1

Abstract: We report a photometric and spectroscopic study of the peculiar cataclysmic variable SDSS 1507+52. The star shows very deep eclipses on the 67-minute orbital period, and those eclipses are easily separable into white-dwarf and hot-spot components. This leads to tight constraints on binary parameters, with M1 = 0.83(8) M⊙, M2 = 0.057(8) M⊙, R1 = 0.0097(9) R⊙, R2 = 0.097(4) R⊙, q = 0.069(2), and i = 83.18(13)°. Such numbers suggest possible membership among the WZ Sge stars, a common type of dwarf nova. The spectroscopic behavior (strong and broad H emission, double-peaked and showing a classic rotational disturbance during eclipse) is also typical. But the star's orbital period is shockingly below the "period minimum" of ~77 minutes that is characteristic of hydrogen-rich CVs; producing such a strange binary will require some tinkering with the theory of cataclysmic-variable evolution. The proper motion is also remarkably high for a star of its distance, which we estimate from photometry and trigonometric parallax as 230 ± 40 pc. This suggests a transverse velocity of 164 ± 30 km s-1—uncomfortably high if the star belongs to a Galactic-disk population. These difficulties with understanding its evolution and space velocity can be solved if the star belongs to a Galactic-halo population.

Robotic Observations of the Sky with TAROT: 2004–2007

Abstract: The TAROTs (Telescopes a Action Rapide pour les Objets Transitoires; Rapid Action Telescopes for Transient Objects) are two fully robotic observatories designed to observe the early transient optical counterpart of gamma-ray bursts (GRBs). As their occurrence is rare, we also use TAROT to observe various other celestial objects: RR Lyrae stars, minor planets and supernovae. In this paper, we describe the telescopes, their networking, and the data-processing methods used.

Further Studies of the Local Environmental Dependence of Galaxy Properties

Abstract: Using the three-dimensional galaxy local density in a comoving sphere with a radius of the distance to the fifth nearest galaxy for each galaxy, we construct two samples at both extremes of density from the volume-limited Main galaxy sample of the Sixth Data Release of the Sloan Digital Sky Survey (SDSS DR6). It is found that the sample at low density has a higher proportion of faint, blue, and late-type galaxies and a lower proportion of luminous, red, and early-type galaxies than the sample at high density. We also measure the projected local density , which is computed from the distance to the fifth nearest neighbor within a redshift slice ± 1000 km s-1 of each galaxy, and come to the same conclusions. In addition, we note that there is no significant difference between the mean luminosity and the mean colors of two samples (< 1 σ), which is consistent with the conclusion obtained by Deng and colleagues in 2007.

A Pathfinder Instrument for Precision Radial Velocities in the Near-Infrared

Abstract: Original article can be found at : http://www.journals.uchicago.edu/ Copyright Astronomical Society of the Pacific

CN Bimodality at Low Metallicity : The Globular Cluster M53

Abstract: We present low resolution UV-blue spectroscopic observations of red giant stars in the globular cluster M53 ([Fe/H] = -1.84), obtained to study primordial abundance variations and deep mixing via the CN and CH absorption bands. The metallicity of M53 makes it an attractive target: a bimodal distribution of 3883 A CN band strength is common in moderate- and high-metallicity globular clusters ([Fe/H]≥-1.6) but unusual in those of lower metallicity ([Fe/H] ≤ -2.0). We find that M53 is an intermediate case, and has a broad but not strongly bimodal distribution of CN band strength, with CN and CH band strengths anticorrelated in the less-evolved stars. Like many other globular clusters, M53 also exhibits a general decline in CH band strength and [C/Fe] abundance with rising luminosity on the red giant branch.

Time-resolved optical photometry of the ultracompact binary 4U 0614+091

Abstract: . We present a detailed optical study of the ultracompact X-ray binary 4U 0614+091. We have used 63 hr of time-resolved optical photometry taken with three different telescopes (IAC80, NOT, and SPM) to search for optical modulations. The power spectra of each data set reveals sinusoidal modulations with different periods, which are not always present. The strongest modulation has a period of 51.3 minutes, a semiamplitude of 4.6 mmag, and is present in the IAC80 data. The SPM and NOT data show periods of 42 minutes and 64 minutes, respectively, but with much weaker amplitudes, 2.6 mmag and 1.3 mmag, respectively. These modulations arise from either X-ray irradiation of the inner face of the secondary star and/or a superhump modulation from the accretion disk, or quasi-periodic modulations in the accretion disk. It is unclear whether these periods/quasi-periodic modulations are related to the orbital period; however, the strongest period of 51.3 minutes is close to earlier tentative orbital periods....