Showing papers in "Publications of the Astronomical Society of the Pacific in 2014"
TL;DR: The K2 mission as discussed by the authors uses an innovative way of operating the Kepler spacecraft to observe target fields along the ecliptic for the next 2-3 years, with an estimated photometric precision near 400 ppm in a single 30 minute observation.
Abstract: The K2 mission will make use of the Kepler spacecraft and its assets to expand upon Kepler's groundbreaking discoveries in the fields of exoplanets and astrophysics through new and exciting observations. K2 will use an innovative way of operating the spacecraft to observe target fields along the ecliptic for the next 2-3 years. Early science commissioning observations have shown an estimated photometric precision near 400 ppm in a single 30 minute observation, and a 6-hr photometric precision of 80 ppm (both at V = 12). The K2 mission offers long-term, simultaneous optical observation of thousands of objects at a precision far better than is achievable from ground-based telescopes. Ecliptic fields will be observed for approximately 75 days enabling a unique exoplanet survey which fills the gaps in duration and sensitivity between the Kepler and TESS missions, and offers pre-launch exoplanet target identification for JWST transit spectroscopy. Astrophysics observations with K2 will include studies of young open clusters, bright stars, galaxies, supernovae, and asteroseismology.
1,672 citations
TL;DR: In this paper, a technique for generating photometric light curves from pixel-level data obtained with the two-wheeled extended Kepler mission, K2, was presented, which accounts for the nonuniform pixel response function of the Kepler detectors by correlating flux measurements with the spacecraft's pointing and removing the dependence.
Abstract: The original Kepler mission achieved high photometric precision thanks to ultrastable pointing enabled by use of four reaction wheels. The loss of two of these reaction wheels reduced the telescope's ability to point precisely for extended periods of time, and as a result, the photometric precision has suffered. We present a technique for generating photometric light curves from pixel-level data obtained with the two-wheeled extended Kepler mission, K2. Our photometric technique accounts for the nonuniform pixel response function of the Kepler detectors by correlating flux measurements with the spacecraft's pointing and removing the dependence. When we apply our technique to the ensemble of stars observed during the Kepler Two-Wheel Concept Engineering Test, we find improvements over raw K2 photometry by factors of 2-5, with noise properties qualitatively similar to Kepler targets at the same magnitudes. We find evidence that the improvement in photometric precision depends on each target's position in the Kepler field of view, with worst precision near the edges of the field. Overall, this technique restores the median-attainable photometric precision within a factor of two of the original Kepler photometric precision for targets ranging from 10th to 15th magnitude in the Kepler bandpass, peaking with a median precision within 35% to that of Kepler for stars between 12th and 13th magnitude in the Kepler bandpass.
584 citations
TL;DR: In this paper, a multiscale MAP (MSMAP) algorithm was proposed to further minimize the number of targets for which PDC-MAP fails to perform admirably.
Abstract: The previous presearch data conditioning algorithm, PDC-MAP, for the Kepler data processing pipeline performs very well for the majority of targets in the Kepler field of view. However, for an appreciable minority, PDC-MAP has its limitations. To further minimize the number of targets for which PDC-MAP fails to perform admirably, we have developed a new method, called multiscale MAP, or msMAP. Utilizing an overcomplete discrete wavelet transform, the new method divides each light curve into multiple channels, or bands. The light curves in each band are then corrected separately, thereby allowing for a better separation of characteristic signals and improved removal of the systematics.
439 citations
TL;DR: The Exoplanet Orbit Database (EOD) as discussed by the authors is a database of robustly-detected exoplanets that compiles orbital, transit, host star, and other parameters reported in the peer-reviewed literature.
Abstract: The Exoplanet Orbit Database (EOD) compiles orbital, transit, host star, and other parameters of robustly-detected exoplanets reported in the peer-reviewed literature. The EOD can be navigated through the Exoplanet Data Explorer (EDE) plotter and table, available on the World Wide Web at exoplanets.org. The EOD contains data for 1492 confirmed exoplanets as of 2014 July. The EOD descends from a table provided by Butler and coworkers in 2002 and the Catalog of Nearby Exoplanets (Butler and coworkers in 2006), and the first complete documentation for the EOD and the EDE was presented by Wright and coworkers in 2011. In this work, we describe our work since then. We have expanded the scope of the EOD to include secondary eclipse parameters and asymmetric uncertainties and expanded the EDE to include the sample of over 3000 Kepler Objects of Interest (KOIs) and other real planets without good orbital parameters (such as many of those detected by microlensing and imaging). Users can download the latest version of the entire EOD as a single comma separated value file from the front page of exoplanets.org.
344 citations
California Institute of Technology1, Harvard University2, Cornell University3, European Space Research and Technology Centre4, Grinnell College5, Massachusetts Institute of Technology6, Max Planck Society7, Ames Research Center8, Goddard Space Flight Center9, Space Telescope Science Institute10, Steward Health Care System11, University of California, Santa Cruz12, University of Chicago13, University of Geneva14, University of Maryland, College Park15, Université de Montréal16, University of Exeter17
TL;DR: The potential of the James Webb Space Telescope (JWST) to revolutionize our knowledge of the physical properties of exoplanets through transit observations was discussed in a workshop held on March 14, 2014 as discussed by the authors.
Abstract: This article summarizes a workshop held on March, 2014, on the potential of the James Webb Space Telescope (JWST) to revolutionize our knowledge of the physical properties of exoplanets through transit observations. JWST’s unique combination of high sensitivity and broad wavelength coverage will enable the accurate measurement of transits with high signal-to-noise ratio (S/N). Most importantly, JWST spectroscopy will investigate planetary atmospheres to determine atomic and molecular compositions, to probe vertical and horizontal structure, and to follow dynamical evolution, i.e., exoplanet weather. JWST will sample a diverse population of planets of varying masses and densities in a wide variety of environments characterized by a range of host star masses and metallicities, orbital semi-major axes, and eccentricities. A broad program of exoplanet science could use a substantial fraction of the overall JWST mission.
330 citations
TL;DR: The Dragonfly Telephoto Array as discussed by the authors is a robotic imaging system optimized for the detection of extended ultra-low surface brightness structures, which is capable of imaging extended structures to surface brightness levels below μB = 30 mag arcsec-2 in ~10 h integrations.
Abstract: We describe the Dragonfly Telephoto Array, a robotic imaging system optimized for the detection of extended ultra-low surface brightness structures. The array consists of eight Canon 400 mm f/2.8 L IS II USM telephoto lenses coupled to eight science-grade commercial CCD cameras. The lenses are mounted on a common framework and are coaligned to simultaneously image the same position on the sky. The system provides an imaging capability equivalent to a 0.4 m aperture f/1.0 refractor with a 2.6° × 1.9° field of view. The system is driven by custom software for instrument control and robotic operation. Data is collected with noncommon optical paths through each lens, and with careful tracking of sky variations in order to minimize systematic errors that limit the accuracy of background estimation and flat-fielding. The system has no obstructions in the light path, optimized baffling, and internal optical surfaces coated with a new generation of antireflection coatings based on subwavelength nanostructures. As a result, the array's point-spread function has a factor of ~10 less scattered light at large radii than well-baffled reflecting telescopes. The Dragonfly Telephoto Array is capable of imaging extended structures to surface brightness levels below μB = 30 mag arcsec-2 in ~10 h integrations (without binning or foreground star removal). This is considerably deeper than the surface brightness limit of any existing wide-field telescope. At present, no systematic errors limiting the usefulness of much longer integration times have been identified. With longer integrations (50-100 h), foreground star removal, and modest binning, the Dragonfly Telephoto Array is capable of probing structures with surface brightnesses below μB = 32 mag arcsec-2. The detection of structures at these surface brightness levels may hold the key to solving the "missing substructure" and "missing satellite" problems of conventional hierarchical galaxy formation models. The Dragonfly Telephoto Array is therefore executing a fully automated multiyear imaging survey of a complete sample of nearby galaxies in order to undertake the first census of ultrafaint substructures in the nearby universe.
214 citations
TL;DR: BRITE-Constellation as mentioned in this paper is an international nanosatellite mission to monitor photometrically, in two colours, the brightness and temperature variations of stars generally brighter than mag(V) ≈ 4 with precision and time coverage not possible from the ground.
Abstract: BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, the brightness and temperature variations of stars generally brighter than mag(V) ≈ 4 with precision and time coverage not possible from the ground. The current mission design consists of six nanosats (hence Constellation): two from Austria, two from Canada, and two from Poland. Each 7 kg nanosat carries an optical telescope of aperture 3 cm feeding an uncooled CCD. One instrument in each pair is equipped with a blue filter; the other with a red filter. Each BRITE instrument has a wide field of view (≈24°), so up to about 15 bright stars can be observed simultaneously, sampled in 32 × 32 pixels sub-rasters. Photometry of additional fainter targets, with reduced precision but thorough time sampling, will be possible through onboard data processing. The BRITE sample is dominated by the most intrinsically luminous stars: massive stars seen at all evolutionary stages, and evolved medium-mass stars at the very end of their nuclear burning phases. The goals of BRITE-Constellation are to (1) measure p- and g-mode pulsations to probe the interiors and ages of stars through asteroseismology; (2) look for varying spots on the stars surfaces carried across the stellar disks by rotation, which are the sources of co-rotating interaction regions in the winds of the most luminous stars, probably arising from magnetic subsurface convection; and (3) search for planetary transits.
183 citations
TL;DR: In this article, a barycentric correction with an rms of 1 cm s-1 is proposed for the Doppler detection of true Earth analogs, which is an order of magnitude better than necessary for the detection of accurate Earth analog.
Abstract: The goal of this paper is to establish the requirements of a barycentric correction with an rms of 1 cm s-1, which is an order of magnitude better than necessary for the Doppler detection of true Earth analogs (~9 cm s-1). We describe the theory and implementation of accounting for the effects on precise Doppler measurements of motion of the telescope through space, primarily from rotational and orbital motion of the Earth, and the motion of the solar system with respect to target star (i.e., the "barycentric correction"). We describe the minimal algorithm necessary to accomplish this and how it differs from a naive subtraction of velocities (i.e., a Galilean transformation). We demonstrate the validity of code we have developed from the California Planet Survey code via comparison with the pulsar timing package, TEMPO2. We estimate the magnitude of various terms and effects, including relativistic effects, and the errors associated with incomplete knowledge of telescope position, timing, and stellar position and motion. We note that chromatic aberration will create uncertainties in the time of observation, which will complicate efforts to detect true Earth analogs. Our code is available for public use and validation.
164 citations
TL;DR: The Automated Planet Finder (APF) as discussed by the authors is a facility purpose-built for the discovery and characterization of extrasolar planets through high-cadence Doppler velocimetry of the reflex barycentric accelerations of their host stars.
Abstract: The Automated Planet Finder (APF) is a facility purpose-built for the discovery and characterization of extrasolar planets through high-cadence Doppler velocimetry of the reflex barycentric accelerations of their host stars. Located atop Mount Hamilton, the APF facility consists of a 2.4 m telescope and its Levy spectrometer, an optical echelle spectrometer optimized for precision Doppler velocimetry. APF features a fixed-format spectral range from 374–970 nm, and delivers a “throughput” (resolution × slit width product) of 114,000″, with spectral resolutions up to 150,000. Overall system efficiency (fraction of photons incident on the primary mirror that are detected by the science CCD) on blaze at 560 nm in planet-hunting mode is 15%. First-light tests on the radial-velocity (RV) standard stars HD 185144 and HD 9407 demonstrate sub-meter-per-second precision (rms per observation) held over a 3 month period. This paper reviews the basic features of the telescope, dome, and spectrometer, and gives...
146 citations
TL;DR: PolarBase as mentioned in this paper is an evolving database that contains all stellar data collected with the ESPaDOnS and NARVAL high-resolution spectropolarimeters, in their reduced form, as soon as they become public.
Abstract: PolarBase is an evolving database that contains all stellar data collected with the ESPaDOnS and NARVAL high-resolution spectropolarimeters, in their reduced form, as soon as they become public. As of early 2014, observations of 2000 stellar objects throughout the Hertzsprung-Russell diagram are available. Intensity spectra are available for all targets, and the majority of the observations also include simultaneous spectra in circular or linear polarization, with the majority of the polarimetric measurements being performed only in circularly polarized light (Stokes V). Observations are associated with a cross-correlation pseudoline profile in all available Stokes parameters, greatly increasing the detectability of weak polarized signatures. Stokes V signatures are detected for more than 300 stars of all masses and evolutionary stages, and linear polarization is detected in 35 targets. The detection rate in Stokes V is found to be anticorrelated with the stellar effective temperature. This unique set of Zeeman detections offers the first opportunity to run homogeneous magnetometry studies throughout the H-R diagram. The Web interface of PolarBase is available at http://polarbase.irap.omp.eu.
123 citations
TL;DR: In this paper, optical and near-infrared UBVRIJHK photometry of stars in the Galactic globular cluster M4 (NGC 6121) based upon a large corpus of observations obtained mainly from public astronomical archives is presented.
Abstract: We present optical and near-infrared UBVRIJHK photometry of stars in the Galactic globular cluster M4 (NGC 6121) based upon a large corpus of observations obtained mainly from public astronomical archives. We concentrate on the RR Lyrae variable stars in the cluster, and make a particular effort to accurately reidentify the previously discovered variables. We have also discovered two new probable RR Lyrae variables in the M4 field: one of them by its position on the sky and its photometric properties is a probable member of the cluster, and the second is a probable background (bulge?) object. We provide accurate equatorial coordinates for all 47 stars identified as RR Lyraes, new photometric measurements for 46 of them, and new period estimates for 45. We have also derived accurate positions and mean photometry for 34 more stars previously identified as variable stars of other types, and for an additional five non-RR Lyrae variable stars identified for the first time here. We present optical and near-infrared color-magnitude diagrams for the cluster and show the locations of the variable stars in them. We present the Bailey (period-amplitude) diagrams and the period-frequency histogram for the RR Lyrae stars in M4 and compare them to the corresponding diagrams for M5 (NGC 5904). We conclude that the RR Lyrae populations in the two clusters are quite similar in all the relevant properties that we have considered. The mean periods, pulsation-mode ratios, and Bailey diagrams of these two clusters show support for the recently proposed "Oosterhoff-neutral" classification.
TL;DR: In this paper, the spectral energy distributions (SEDs) of redshifted Ia supernovae in the rest frame are compared to the CALSPEC reference standard spectrophotometry.
Abstract: The measurement of precise absolute fluxes for stellar sources has been pursued with increased vigor since the discovery of dark energy and the realization that its detailed understanding requires accurate spectral energy distributions (SEDs) of redshifted Ia supernovae in the rest frame. The flux distributions of spectrophotometric standard stars were initially derived from the comparison of stars to laboratory sources of known flux but are now mostly based on calculated model atmospheres. For example, pure hydrogen white dwarf (WD) models provide the basis for the HST CALSPEC archive of flux standards. The basic equations for quantitative spectrophotometry and photometry are explained in detail. Several historical lab-based flux calibrations are reviewed; and the SEDs of stars in the major online astronomical databases are compared to the CALSPEC reference standard spectrophotometry. There is good evidence that relative fluxes from the visible to the near-IR wavelength of ~2.5 μm are currently accurate to 1% for the primary reference standards, and new comparisons with lab flux standards show promise for improving that precision.
TL;DR: In this paper, the first on-sky demonstration of speckle nulling was achieved at the Subaru Telescope in the context of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) Project.
Abstract: This paper presents the first on-sky demonstration of speckle nulling, which was achieved at the Subaru Telescope in the context of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) Project. Despite the absence of a high-order high-bandwidth closed-loop AO system, observations conducted with SCExAO show that even in poor-to-moderate observing conditions, speckle nulling can be used to suppress static and slow speckles even in the presence of a brighter dynamic speckle halo, suggesting that more advanced high-contrast imaging algorithms developed in the laboratory can be applied to ground-based systems.
TL;DR: The Palomar Transient Factory (PTF) is a multiepochal robotic survey of the northern sky that acquires data for the scientific study of transient and variable astrophysical phenomena.
Abstract: The Palomar Transient Factory (PTF) is a multiepochal robotic survey of the northern sky that acquires data for the scientific study of transient and variable astrophysical phenomena. The camera and telescope provide for wide-field imaging in optical bands. In the five years of operation since first light on 2008 December 13, images taken with Mould-R and SDSS-g′ camera filters have been routinely acquired on a nightly basis (weather permitting), and two different Hα filters were installed in 2011 May (656 and 663 nm). The PTF image-processing and data-archival program at the Infrared Processing and Analysis Center (IPAC) is tailored to receive and reduce the data, and, from it, generate and preserve astrometrically and photometrically calibrated images, extracted source catalogs, and co-added reference images. Relational databases have been deployed to track these products in operations and the data archive. The fully automated system has benefited by lessons learned from past IPAC projects and comprises advantageous features that are potentially incorporable into other ground-based observatories. Both off-the-shelf and in-house software have been utilized for economy and rapid development. The PTF data archive is curated by the NASA/IPAC Infrared Science Archive (IRSA). A state-of-the-art custom Web interface has been deployed for downloading the raw images, processed images, and source catalogs from IRSA. Access to PTF data products is currently limited to an initial public data release (M81, M44, M42, SDSS Stripe 82, and the Kepler Survey Field). It is the intent of the PTF collaboration to release the full PTF data archive when sufficient funding becomes available.
TL;DR: POET as mentioned in this paper is a tool for calculating the evolution of circular-aligned planetary orbits due to the tidal dissipation in the host star, which can be used to estimate the angular momentum of the stellar convective envelope by the tidal coupling.
Abstract: We make publicly available an efficient, versatile, easy-to-use-and-extend tool for calculating the evolution of circular-aligned planetary orbits due to the tidal dissipation in the host star. This mode fully accounts for the evolution of the angular momentum of the stellar convective envelope by the tidal coupling, the transfer of angular momentum between the stellar convective and radiative zones, the effects of the stellar evolution on the tidal dissipation efficiency and stellar core and envelope spins, the loss of stellar convective zone angular momentum to a magnetically launched wind, and frequency-dependent tidal dissipation. This is only a first release and further development is under way to allow calculating the evolution of inclined and eccentric orbits, with the latter including the tidal dissipation in the planet and its feedback on planetary structure. Considerable effort has been devoted to providing extensive documentation detailing both the usage and the complete implementation details, in order to make it as easy as possible for independent groups to use and/or extend the code for their purposes. POET represents a significant improvement over some previous models for planetary tidal evolution and so has many astrophysical applications. In this article, we describe and illustrate several key examples.
TL;DR: In this article, the authors proposed the coronagraphic low-order wavefront sensor (CLOWFS), which uses a partially reflective focal plane mask to measure pointing errors for Lyot-type coronagraphs.
Abstract: High performance coronagraphic imaging of faint structures around bright stars at small angular separations requires fine control of tip, tilt, and other low order aberrations. When such errors occur upstream of a coronagraph they result in starlight leakage, which reduces the dynamic range of the instrument. This issue has been previously addressed for occulting coronagraphs by sensing the starlight before or at the coronagraphic focal plane. One such solution, the coronagraphic low order wave-front sensor (CLOWFS), uses a partially reflective focal plane mask to measure pointing errors for Lyot-type coronagraphs. To deal with pointing errors in low inner working angle phase mask coronagraphs which do not have a reflective focal plane mask, we have adapted the CLOWFS technique. This new concept relies on starlight diffracted by the focal plane phase mask being reflected by the Lyot stop towards a sensor which reliably measures low order aberrations such as tip and tilt. This reflective Lyot-based wavefront sensor is a linear reconstructor which provides high sensitivity tip-tilt error measurements with phase mask coronagraphs. Simulations show that the measurement accuracy of pointing errors with realistic post adaptive optics residuals are ≈10-2λ/D per mode at λ = 1.6 μm for a four quadrant phase mask. In addition, we demonstrate the open loop measurement pointing accuracy of 10-2λ/D at 638 nm for a four quadrant phase mask in the laboratory.
TL;DR: In this paper, the authors compare the observed transit durations of transiting exoplanets to a synthetic distribution generated from the known eccentricities of radial velocity (RV) discovered ex-oplanets and find that the Kepler and RV distributions differ at a statistically significant level.
Abstract: The Kepler mission discovery of candidate transiting exoplanets (KOIs) enables a plethora of ensemble analyses of the architecture and properties of exoplanetary systems. We compare the observed transit durations of KOIs to a synthetic distribution generated from the known eccentricities of radial velocity (RV) discovered exoplanets. We find that the Kepler and RV distributions differ at a statistically significant level. We identify three related systematic trends that are likely due to errors in stellar radii, which in turn affect the inferred exoplanet radii and the distribution thereof, and prevent a valid analysis of the underlying ensemble eccentricity distribution. First, 15% of KOIs have transit durations >20% longer than the transit duration expected for an edge-on circular orbit, including 92 KOIs with transit durations >50% longer, when only a handful of such systems are expected. Second, the median transit duration is too long by up to ∼25%. Random errors of < 50% in the stellar radius are not adequate to account for these two trends. We identify that incorrect estimates of stellar metallicity and extinction could account for these anomalies, rather than astrophysical effects such as eccentric exoplanets improbably transiting near apastron. Third, we find that the median transit duration is correlated with stellar radius, when no such trend is expected. All three effects are still present, although less pronounced, when considering only multiple transiting KOI systems which are thought to have a low false-positive rate. Improved stellar parameters for KOIs are necessary for the validity of future ensemble tests of exoplanetary systems found by Kepler.
TL;DR: In this article, a single-mode fiber Fabry-Perot (FFP) interferometer is used for high precision radial velocity (RV) spectrographs.
Abstract: We discuss the ongoing development of single-mode fiber Fabry-Perot (FFP) Interferometers as precise astrophotonic calibration sources for high precision radial velocity (RV) spectrographs. FFPs are simple, inexpensive, monolithic units that can yield a stable and repeatable output spectrum. An FFP is a unique alternative to a traditional etalon, as the interferometric cavity is made of single-mode fiber rather than an air-gap spacer. This design allows for excellent collimation, high spectral finesse, rigid mechanical stability, insensitivity to vibrations, and no need for vacuum operation. The device we have tested is a commercially available product from Micron Optics.10 Our development path is targeted toward a calibration source for the Habitable-Zone Planet Finder (HPF), a near-infrared spectrograph designed to detect terrestrial-mass planets around low-mass stars, but this reference could also be used in many existing and planned fiber-fed spectrographs as we illustrate using the Apache Point Observatory Galactic Evolution Experiment (APOGEE) instrument. With precise temperature control of the fiber etalon, we achieve a thermal stability of 100 μK and associated velocity uncertainty of 22 cm s-1. We achieve a precision of ≈2 m s-1 in a single APOGEE fiber over 12 hr using this new photonic reference after removal of systematic correlations. This high precision (close to the expected photon-limited floor) is a testament to both the excellent intrinsic wavelength stability of the fiber interferometer and the stability of the APOGEE instrument design. Overall instrument velocity precision is 80 cm s-1 over 12 hr when averaged over all 300 APOGEE fibers and after removal of known trends and pressure correlations, implying the fiber etalon is intrinsically stable to significantly higher precision.
TL;DR: In this article, the authors propose to use citizen science data for training machine learning systems, and show experimental results demonstrating that machine learning system can be trained with citizen scientists data, but the performance of machine learning depends on the quality of the data, which can be improved by using samples that have a high degree of agreement between the citizen scientists.
Abstract: The increasing importance of digital sky surveys collecting many millions of galaxy images has reinforced the need for robust methods that can perform morphological analysis of large galaxy image databases. Citizen science initiatives such as Galaxy Zoo showed that large data sets of galaxy images can be analyzed effectively by nonscientist volunteers, but since databases generated by robotic telescopes grow much faster than the processing power of any group of citizen scientists, it is clear that computer analysis is required. Here, we propose to use citizen science data for training machine learning systems, and show experimental results demonstrating that machine learning systems can be trained with citizen science data. Our findings show that the performance of machine learning depends on the quality of the data, which can be improved by using samples that have a high degree of agreement between the citizen scientists. The source code of the method is publicly available.
TL;DR: In this article, the authors present an analysis of the meteorological data collected at Dome A, Antarctica by the Kunlun Automated Weather Station, including temperatures and wind speeds at eight elevations above the snow surface between 0 m and 14.5 m.
Abstract: We present an analysis of the meteorological data collected at Dome A, Antarctica by the Kunlun Automated Weather Station, including temperatures and wind speeds at eight elevations above the snow surface between 0 m and 14.5 m. The average temperatures at 2 m and 14.5 m are -54 degrees C and -46 degrees C, respectively. We find that a strong temperature inversion existed at all heights for more than 70% of the time, and the temperature inversion typically lasts longer than 25 hr, indicating an extremely stable atmosphere. The temperature gradient is larger at lower elevations than at higher elevations. The average wind speed was 1.5 ms(-1) at 4 m elevation. We find that the temperature inversion is stronger when the wind speed is lower, and the temperature gradient decreases sharply at a specific wind speed for each elevation. The strong temperature inversion and low wind speed result in a shallow and stable boundary layer with weak atmospheric turbulence above it, suggesting that Dome A should be an excellent site for astronomical observations. All the data from the weather station are available for download.
TL;DR: In this paper, the authors describe the measured performance characteristics that most directly affect scientific observations including read noise, total noise, dark current, quantum efficiency (QE), and image persistence.
Abstract: ESA and NASA recently selected two 5 μm cutoff Teledyne H2RG sensor chip assemblies (SCA) for flight on the James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec). These HgCdTe SCAs incorporate Teledyne's "improved barrier layer" design that eliminates the degradation that affected earlier JWST H2RGs. The better indium barrier, together with other design changes that Teledyne phased in from other programs over the years, has improved the performance and reliability of JWST's SCAs. In this article, we describe the measured performance characteristics that most directly affect scientific observations including read noise, total noise, dark current, quantum efficiency (QE), and image persistence. As part of measuring QE, we inferred the quantum yield over the full NIRSpec pass band of λ = 0.6-5 μm and found that it exceeds unity for photon energies Eγ > (2.65 ± .2)Eg, where Eg is the HgCdTe bandgap energy. This corresponds to λ 2 μm for NIRSpec's 5 μm cutoff HgCdTe.
TL;DR: In this article, the authors developed a more efficient and uniform grating with a weighted average efficiency at λ = 1.310 μm of 78.0% ± 1.6%, with field variation of only 2.2%.
Abstract: OSIRIS is a near-infrared integral field spectrograph operating behind the adaptive optics system at W. M. Keck Observatory. While OSIRIS has been a scientifically productive instrument to date, its sensitivity has been limited by a grating efficiency that is less than half of what was expected. The spatially averaged efficiency of the old grating, weighted by error, is measured to be 39.5% ± 0.8% at λ = 1.310 μm, with a large field-dependent variation of 11.7% due to efficiency variation across the grating surface. Working with a new vendor, we developed a more efficient and uniform grating with a weighted average efficiency at λ = 1.310 μm of 78.0% ± 1.6%, with field variation of only 2.2%. This is close to double the average efficiency and 5 times less variation across the field. The new grating was installed in 2012 December, and on-sky OSIRIS throughput shows an average factor of 1.83 improvement in sensitivity between 1 and 2.4 μm. We present the development history, testing, and implementation of this new near-infrared grating for OSIRIS and report on the comparison with the predecessors. The higher sensitivities are already having a large impact on scientific studies with OSIRIS.
TL;DR: In this article, the authors used data from the science verification period of the DES to characterize the effects of electric fields transverse to the surface of the CCDs, with diverse origins such as doping gradients, guard rings around the imaging area of the sensor, and physical stresses on the silicon lattice.
Abstract: Photogenerated charge in thick, back-illuminated, fully-depleted CCDs is transported by electric fields from the silicon substrate to the collecting well at the front gate of the CCDs. However, electric fields transverse to the surface of the CCD—with diverse origins such as doping gradients, guard rings around the imaging area of the sensor, and physical stresses on the silicon lattice—displace this charge, effectively modifying the pixel area and producing noticeable signals in astrometric and photometric measurements. We use data from the science verification period of the Dark Energy Survey (DES) to characterize these effects in the Dark Energy Camera (DECam) CCDs. The transverse fields mainly manifest as concentric rings (''tree rings'') and bright stripes near the boundaries of the detectors (''edge distortions'') with relative amplitudes of about 1% and 10% in the flat-field images, respectively. Their nature as pixel size variations is confirmed by comparing their photometric and astrometric signatures. Using flat-field images from DECam, we derive templates in the five DES photometric bands (grizY) for the tree rings and the edge distortions as a function of their position in each DECam detector. These templates can be directly incorporated into the derivation of photometric and astrometric solutions, helping to meet the DES photometric and astrometric requirements.
TL;DR: In this paper, the authors review what observations and theoretical models of Lyα emission and Lyα and Mg ii absorption have told us about the interstellar, circumgalactic, and intergalactic medium in the context of galaxy formation and evolution.
Abstract: Lyα emission, Lyα absorption, and Mg ii absorption are powerful tracers of neutral hydrogen. Hydrogen is the most abundant element in the universe and plays a central role in galaxy formation via gas accretion and outflows, as well as being the precursor to molecular clouds, the sites of star formation. Since 21 cm emission from neutral hydrogen can only be directly observed in the local universe, we rely on Lyα emission, and Lyα and Mg ii absorption to probe the physics that drive galaxy evolution at higher redshifts. Furthermore, these tracers are sensitive to a range of hydrogen densities that cover the interstellar medium, the circumgalactic medium, and the intergalactic medium, providing an invaluable means of studying gas physics in regimes where it is poorly understood. At high-redshift, Lyα emission line searches have discovered thousands of star-forming galaxies out to z = 7. The large Lyα scattering cross-section makes observations of this line sensitive to even very diffuse gas outside of galaxies. Several thousand more high-redshift galaxies are known from damped Lyα absorption lines and absorption by the Mg ii doublet in quasar and GRB spectra. Mg ii, in particular, probes metal-enriched neutral gas inside galaxy haloes in a wide range of environments and redshifts (0.1 < z < 6.3), including the so-called redshift desert. Here, we review what observations and theoretical models of Lyα emission and Lyα and Mg ii absorption have told us about the interstellar, circumgalactic, and intergalactic medium in the context of galaxy formation and evolution.
TL;DR: In this article, the authors present spectrograph design details and initial radial velocity results from the PRL optical fiber-fed high-resolution cross-dispersed echelle spectrogram (PARAS), which has recently been commissioned at the Mount Abu 1.2 m telescope in India.
Abstract: We present spectrograph design details and initial radial velocity results from the PRL optical fiber-fed high-resolution cross-dispersed echelle spectrograph (PARAS), which has recently been commissioned at the Mount Abu 1.2 m telescope in India. Data obtained as part of the postcommissioning tests with PARAS show velocity precision better than 2 m s-1 over a period of several months on bright RV standard stars. For observations of σ Dra, we report 1.7 m s-1 precision for a period of 7 months, and for HD 9407, we report 2.1 m s-1 over a period of 2 months. PARAS is capable of single-shot spectral coverage of 3800-9500 A at a resolution of ~67,000. The RV results were obtained between 3800 and 6900 A using simultaneous wavelength calibration with a thorium-argon (ThAr) hollow cathode lamp. The spectrograph is maintained under stable conditions of temperature with a precision of 0.01-0.02° C (rms) at 25.55° C and is enclosed in a vacuum vessel at pressure of 0.1 ± 0.03 mbar. The blaze peak efficiency of the spectrograph between 5000 and 6500 A, including the detector, is ~30%; it is ~25% with the fiber transmission. The total efficiency, including spectrograph, fiber transmission, focal ratio degradation (FRD), and telescope (with 81% reflectivity) is ~7% in the same wavelength region on a clear night with good seeing conditions. The stable point-spread function (PSF), environmental control, existence of a simultaneous calibration fiber, and availability of observing time make PARAS attractive for a variety of exoplanetary and stellar astrophysics projects. Future plans include testing of octagonal fibers for further scrambling of light and extensive calibration over the entire wavelength range up to 9500 A using thorium-neon (ThNe) or uranium-neon (UNe) spectral lamps. Thus, we demonstrate how such highly stabilized instruments, even on small aperture telescopes, can contribute significantly to the ongoing radial velocity searches for low-mass planets around bright stars.
TL;DR: A review of the recent work on LGRB host galaxies can be found in this paper, where the authors consider the many new questions that are poised to be pursued in the coming years.
Abstract: Long-duration gamma-ray bursts (LGRBs) are the signatures of extraordinarily high-energy events occurring in our universe. Since their discovery, we have determined that these events are produced during the core-collapse deaths of rare young massive stars. The host galaxies of LGRBs are an excellent means of probing the environments and populations that produce their unusual progenitors. In addition, these same young stellar progenitors make LGRBs and their host galaxies valuable, potentially powerful tracers of star formation and metallicity at high redshifts. However, properly utilizing LGRBs as probes of the early universe requires a thorough understanding of their formation and the host environments that they sample. This review looks back at some of the recent work on LGRB host galaxies that has advanced our understanding of these events and their cosmological applications, and considers the many new questions that we are poised to pursue in the coming years.
TL;DR: In this paper, the authors calculated the success rate of HST Cycles 11 through 21 as a function of the gender of the Principal Investigator (PI) and found that proposals with male PI have a higher success rate, with the disparity greatest for Cycle 12 and 18.
Abstract: Proposal success rates are calculated for HST Cycles 11 through 21 as a function of the gender of the Principal Investigator (PI). In each cycle, proposals with male PIs have a higher success rate, with the disparity greatest for Cycles 12 and 18. The offsets are small enough that they might be ascribed to chance for any single cycle, but the consistent pattern suggests the presence of a systematic effect. Closer inspection of results from Cycles 19, 20, and 21 shows that the systematic difference does not appear to depend on the geographic origin of the proposal nor does it depend on the gender distribution on the review panels. Segregating proposals by the seniority of the PI, the success rates by gender for more recent graduates (Ph.D. since 2000) are more closely comparable. There is also a correlation between success by gender and the average seniority of the review panel for Cycles 19 and 20, but not Cycle 21. We discuss these results and some consequent changes to the proposal format and additions to the HST TAC orientation process.
TL;DR: In this article, the results of the atmospheric optical turbulence (OT) measurements performed atop Mount Shatdzhatmaz at the installation site of new 2.5 m telescope of the Sternberg Astronomical Institute were presented.
Abstract: We present the results of the atmospheric optical turbulence (OT) measurements performed atop Mount Shatdzhatmaz at the installation site of new 2.5 m telescope of the Sternberg Astronomical Institute. Nearly 300,000 vertical OT profiles from the ground up to an altitude of 23 km were obtained in the period of 2007 November-2013 June 2 with the combined multiaperture scintillation sensor (MASS) and differential image motion monitor (DIMM) instrument. The medians of the main OT characteristics, computed over the whole dataset are as follows: the integral seeing β0 = 0.96'', the free-atmosphere seeing βFA = 0.43'', and the isoplanatic angle θ0 = 2.07''. The median atmospheric time constant is τ0 = 6.57 ms. The revealed long-term variability of these parameters on scales of months and years implies the need to take it into account in astroclimatic campaign planning. For example, the annual variation in the monthly θ0 estimate amounts to 30%, while the time constant τ0 changes by a factor of 2.5. Evaluation of the potential of Mount Shatdzhatmaz in terms of high angular resolution observations indicates that in October-November, this site is as good as the best of studied summits in the world.
TL;DR: The Atacama Astronomical Park offers an opportunity for national and international projects to settle within its boundaries, gain access to an extremely dry site that is suitable for observations over a broad spectral range, especially in the millimeter to mid-infrared wavelengths, and benefit from operational and logistical support within a secure legal framework.
Abstract: The area of Chajnantor, at more than 5000 m altitude in northern Chile, offers unique atmospheric and operational conditions which arguably make it the best site in the world for millimeter, submillimeter, and mid-infrared observatories. Long-term monitoring of the precipitable water vapor (PWV) column on the Chajnantor plateau has shown its extreme dryness with annual median values of 1.1 mm. Simultaneous measurements of PWV on the Chajnantor plateau (5050 m) and on Cerro Chajnantor (5612 m) show that the latter is around 36% lower under normal atmospheric conditions and up to 80% lower than the plateau in the presence of temperature inversion layers. Recently, the Government of Chile has consolidated the creation of the Parque Astronomico de Atacama (Atacama Astronomical Park), an initiative of the Chilean Commission for Science and Technology (CONICYT). This new park offers an opportunity for national and international projects to settle within its boundaries, gain access to an extremely dry site that is suitable for observations over a broad spectral range, especially in the millimeter to mid-infrared wavelengths, and benefit from operational and logistical support within a secure legal framework.
TL;DR: In this article, the authors present DAMEWARE (DAta Mining & Exploration Web Application REsource): a general purpose, web-based, distributed data mining environment developed for the exploration of large data sets, and finely tuned for astronomical applications.
Abstract: Astronomy is undergoing a methodological revolution triggered by an unprecedented wealth of complex and accurate data. The new panchromatic, synoptic sky surveys require advanced tools for discovering patterns and trends hidden behind data which are both complex and of high dimensionality. We present DAMEWARE (DAta Mining & Exploration Web Application REsource): a general purpose, web-based, distributed data mining environment developed for the exploration of large data sets, and finely tuned for astronomical applications. By means of graphical user interfaces, it allows the user to perform classification, regression, or clustering tasks with machine learning methods. Salient features of DAMEWARE include its ability to work on large datasets with minimal human intervention, and to deal with a wide variety of real problems such as the classification of globular clusters in the galaxy NGC1399; the evaluation of photometric redshifts; and, finally, the identification of candidate Active Galactic Nuclei in multiband photometric surveys. In all these applications, DAMEWARE allowed us to achieve better results than those attained with more traditional methods. With the aim of providing potential users with all needed information, in this paper we briefly describe the technological background of DAMEWARE, give a short introduction to some relevant aspects of data mining, followed by a summary of some science cases and, finally, provide a detailed description of a template use case.