Showing papers in "Publications of the Astronomical Society of the Pacific in 2013"
TL;DR: The emcee algorithm as mentioned in this paper is a Python implementation of the affine-invariant ensemble sampler for Markov chain Monte Carlo (MCMC) proposed by Goodman & Weare (2010).
Abstract: We introduce a stable, well tested Python implementation of the affine-invariant ensemble sampler for Markov chain Monte Carlo (MCMC) proposed by Goodman & Weare (2010). The code is open source and has already been used in several published projects in the astrophysics literature. The algorithm behind emcee has several advantages over traditional MCMC sampling methods and it has excellent performance as measured by the autocorrelation time (or function calls per independent sample). One major advantage of the algorithm is that it requires hand-tuning of only 1 or 2 parameters compared to ~N2 for a traditional algorithm in an N-dimensional parameter space. In this document, we describe the algorithm and the details of our implementation. Exploiting the parallelism of the ensemble method, emcee permits any user to take advantage of multiple CPU cores without extra effort. The code is available online at http://dan.iel.fm/emcee under the GNU General Public License v2.
8,805 citations
TL;DR: The NASA Exoplanet Archive as mentioned in this paper is a database and toolset for the exoplanet community, containing properties of all published exoplanets, Kepler planet candidates, threshold-crossing events, data validation reports and target stellar parameters, light curves from the Kepler and CoRoT missions and from several ground-based surveys, and spectra and radial velocity measurements from the literature.
Abstract: .We describe the contents and functionality of the NASA Exoplanet Archive, a database and toolset funded by NASA to support astronomers in the exoplanet community. The current content of the database includes interactive tables containing properties of all published exoplanets, Kepler planet candidates, threshold-crossing events, data validation reports and target stellar parameters, light curves from the Kepler and CoRoT missions and from several ground-based surveys, and spectra and radial velocity measurements from the literature. Tools provided to work with these data include a transit ephemeris predictor, both for single planets and for observing locations, light curve viewing and normalization utilities, and a periodogram and phased light curve service. The archive can be accessed at http://exoplanetarchive.ipac.caltech.edu.
708 citations
TL;DR: Exofast as discussed by the authors is a suite of routines written in IDL that is designed to fit exoplanetary transits and radial velocity variations simultaneously or separately and characterize the parameter uncertainties and covariances with a differential evolution Markov chain Monte Carlo method.
Abstract: We present EXOFAST, a fast, robust suite of routines written in IDL that is designed to fit exoplanetary transits and radial velocity variations simultaneously or separately and characterize the parameter uncertainties and covariances with a differential evolution Markov chain Monte Carlo method. We describe how our code incorporates both data sets to derive simultaneously stellar parameters along with the transit and RV parameters, resulting in more self-consistent results on an example fit of the discovery data of HAT-P-3b that is well-mixed in under 5 minutes on a standard desktop computer. We describe in detail how our code works and outline ways in which the code can be extended to include additional effects or generalized for the characterization of other data sets—including non-planetary data sets. We discuss the pros and cons of several common ways to parameterize eccentricity, highlight a subtle mistake in the implementation of MCMC that could bias the inferred eccentricity of intrinsically circular orbits to significantly non-zero results, discuss a problem with IDL's built-in random number generator in its application to large MCMC fits, and derive a method to analytically fit the linear and quadratic limb darkening coefficients of a planetary transit. Finally, we explain how we achieved improved accuracy and over a factor of 100 improvement in the execution time of the transit model calculation. Our entire source code, along with an easy-to-use online interface for several basic features of our transit and radial velocity fitting, are available online at http://astroutils.astronomy.ohio-state.edu/exofast.
578 citations
TL;DR: The principles and algorithm of Scanamorphos are described and several examples of application are presented; it was successfully applied to P-Artemis, an instrument operating on the APEX telescope.
Abstract: Scanamorphos is public software available to postprocess scan observations performed with the Herschel photometer arrays. This postprocessing mainly consists in subtracting the total low-frequency noise (both its thermal and nonthermal components), masking high-frequency artefacts such as cosmic ray hits, and projecting the data onto a map. Although it was developed for Herschel, it is also applicable with minimal adjustment to scan observations made with some other imaging arrays subjected to low-frequency noise, provided they entail sufficient redundancy; it was successfully applied to P-Artemis, an instrument operating on the APEX telescope. Contrary to matrix-inversion softwares and high-pass filters, Scanamorphos does not assume any particular noise model, and does not apply any Fourier-space filtering to the data, but is an empirical tool using purely the redundancy built in the observations—taking advantage of the fact that each portion of the sky is sampled at multiple times by multiple bolometers. It is an interactive software in the sense that the user is allowed to optionally visualize and control results at each intermediate step, but the processing is fully automated. This paper describes the principles and algorithm of Scanamorphos and presents several examples of application.
299 citations
TL;DR: The CHIRON optical high-resolution echelle spectrometer as mentioned in this paper was designed for high throughput and stability, with the goal of monitoring radial velocities of bright stars with high precision and high cadence for the discovery of low-mass exoplanets.
Abstract: The CHIRON optical high-resolution echelle spectrometer was commissioned at the 1.5 m telescope at CTIO in 2011. The instrument was designed for high throughput and stability, with the goal of monitoring radial velocities of bright stars with high precision and high cadence for the discovery of low-mass exoplanets. Spectral resolution of R = 79 000 is attained when using a slicer with a total (including telescope and detector) efficiency of 6% or higher, while a resolution of R = 136 000 is available for bright stars. A fixed spectral range of 415–880 nm is covered. The echelle grating is housed in a vacuum enclosure and the instrument temperature is stabilized to ± 0.2°. Stable illumination is provided by an octagonal multimode fiber with excellent light-scrambling properties. An iodine cell is used for wavelength calibration. We describe the main optics, fiber feed, detector, exposure-meter, and other aspects of the instrument, as well as the observing procedure and data reduction.
259 citations
TL;DR: The Magellan Baade Spectrograph (FIRE) as mentioned in this paper is a 0.82-2.51μm echelle spectrograph for the 6.5m Magellan telescope.
Abstract: .We describe the design, construction, and commissioning of FIRE, a 0.82–2.51 μμm echelle spectrograph for the 6.5 m Magellan Baade telescope. FIRE may be operated in two modes. Its primary mode is a prism cross-dispersed echelle, which delivers R = 6000R=6000 spectra for an 0.6″ slit, with continuous wavelength coverage over the full instrument bandpass in a single setup. Alternatively, the echelle grating may be replaced with a flat mirror to obtain high-throughput R = 400R=400 longslit spectra through the prisms alone—again with full Y/J/H/KY/J/H/K coverage. This contribution outlines the details of the optical design and execution, mechanical and thermal design, detector systems, and data analysis software. We also present performance metrics from commissioning observations. These have established that the instrument is achieving its design goals, particularly with regard to throughput, as is required for observations of faint, high-redshift QSOs and the lowest mass brown dwarfs.
235 citations
TL;DR: The Dwarf Galaxy Survey (DGS) as discussed by the authors was designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially their dust and gas properties and the ISM heating and cooling processes.
Abstract: The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galaxies using 230 hr of farinfrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws from this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Z., and spans four orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 mu m with the highest sensitivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158 mu m, [OI] 63 mu m, [OI] 145 mu m, [OIII] 88 mu m, [NIII] 57 mu m, and [NII] 122 and 205 mu m have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines (J = 4-3 to J = 13-12), [NII] 205 mu m, and [CI] lines at 370 and 609 mu m. This paper describes the sample selection and global properties of the galaxies and the observing strategy as well as the vast ancillary database available to complement the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.
227 citations
TL;DR: HATSouth as discussed by the authors is the world's first network of automated and homogeneous telescopes that is capable of year-round 24-hour monitoring of positions over an entire hemisphere of the sky.
Abstract: HATSouth is the world's first network of automated and homogeneous telescopes that is capable of year-round 24 hr monitoring of positions over an entire hemisphere of the sky. The primary scientific goal of the network is to discover and characterize a large number of transiting extrasolar planets, reaching out to long periods and down to small planetary radii. HATSouth achieves this by monitoring extended areas on the sky, deriving high precision light curves for a large number of stars, searching for the signature of planetary transits, and confirming planetary candidates with larger telescopes. HATSouth employs six telescope units spread over three prime locations with large longitude separation in the southern hemisphere (Las Campanas Observatory, Chile; HESS site, Namibia; Siding Spring Observatory, Australia). Each of the HATSouth units holds four 0.18 m diameter f/2.8 focal ratio telescope tubes on a common mount producing an 8.2° × 8.2° field of view on the sky, imaged using four 4 K × 4 K CCD cameras and Sloan r filters, to give a pixel scale of 3.7'' pixel-1. The HATSouth network is capable of continuously monitoring 128 square arc degrees at celestial positions moderately close to the anti-solar direction. We present the technical details of the network, summarize operations, and present detailed weather statistics for the three sites. Robust operations have meant that on average each of the six HATSouth units has conducted observations on ~500 nights over a 2 years time period, yielding a total of more than 1 million science frames at a 4 minute integration time and observing ~10.65 hr day-1 on average. We describe the scheme of our data transfer and reduction from raw pixel images to trend-filtered light curves and transiting planet candidates. Photometric precision reaches ~6 mmag at 4 minute cadence for the brightest non-saturated stars at r ≈ 10.5. We present detailed transit recovery simulations to determine the expected yield of transiting planets from HATSouth. We highlight the advantages of networked operations, namely, a threefold increase in the expected number of detected planets, as compared to all telescopes operating from the same site.
223 citations
TL;DR: In this article, a new grid for the mass-radius relation of three-layer exoplanets within the mass range of 0.1-100 M⊕ is described.
Abstract: This article describes a new grid for the mass-radius relation of three-layer exoplanets within the mass range of 0.1-100 M⊕. The three layers are: Fe (-phase of iron), MgSiO3 (including both the perovskite phase, post-perovskite phase, and its dissociation at ultrahigh pressures), and H2O (including Ices Ih, III, V, VI, VII, X, and the superionic phase along the melting curve). We discuss the current state of knowledge about the equations of state (EOS) that influence these calculations and the improvements used in the new grid. For the two-layer model, we demonstrate the utility of contours on the mass-radius diagrams. Given the mass and radius input, these contours can be used to quickly determine the important physical properties of a planet including its p0 (central pressure), p1/p0 (core-mantle boundary pressure over central pressure), CMF (core mass fraction) or CRF (core radius fraction). For the three-layer model, a curve segment on the ternary diagram represents all possible relative mass proportions of the three layers for a given mass-radius input. These ternary diagrams are tabulated with the intent to make comparison to observations easier. How the presence of Fe in the mantle affects the mass-radius relations is also discussed in a separate section. A dynamic and interactive tool to characterize and illustrate the interior structure of exoplanets built upon models in this article is available online.
205 citations
TL;DR: The Array Camera for Optical to Near-IR Spectrophotometry (ARCONS) as discussed by the authors is the first ground-based instrument in the optical through near-IR wavelength range based on microwave kinetic inductance detectors (MKIDs).
Abstract: We present the design, construction, and commissioning results of ARCONS, the Array Camera for Optical to Near-IR Spectrophotometry. ARCONS is the first ground-based instrument in the optical through near-IR wavelength range based on microwave kinetic inductance detectors (MKIDs). MKIDs are revolutionary cryogenic detectors, capable of detecting single photons and measuring their energy without filters or gratings, similar to an X-ray microcalorimeter. MKIDs are nearly ideal, noiseless photon detectors, as they do not suffer from read noise or dark current and have nearly perfect cosmic ray rejection. ARCONS is an integral field spectrograph (IFS) containing a lens-coupled 2024 pixel MKID array yielding a 20'' × 20'' field of view and has been deployed on the Palomar 200 inch and Lick 120 inch telescopes for 24 nights of observing. We present initial results showing that ARCONS and its MKID arrays are now a fully operational and powerful tool for astronomical observations.
173 citations
TL;DR: In this paper, the authors describe several new techniques for the identification of background transit sources that are separated from their target stars, indicating an astrophysical false positive, using only Kepler photometric data.
Abstract: .The Kepler Mission was launched on 2009 March 6 to perform a photometric survey of more than 100,000 dwarf stars to search for Earth-size planets with the transit technique. The reliability of the resulting planetary candidate list relies on the ability to identify and remove false positives. Major sources of astrophysical false positives are planetary transits and stellar eclipses on background stars. We describe several new techniques for the identification of background transit sources that are separated from their target stars, indicating an astrophysical false positive. These techniques use only Kepler photometric data. We describe the concepts and construction of these techniques in detail as well as their performance and relative merits.
TL;DR: The FourStar Infrared Camera as discussed by the authors is a 4 K × 4 K near-infrared (1.0-2.4 μm) imager built for the Magellan 6.5 m Baade Telescope at Las Campanas Observatory, Chile.
Abstract: The FourStar Infrared Camera is a 4 K × 4 K near-infrared (1.0-2.4 μm) imager built for the Magellan 6.5 m Baade Telescope at Las Campanas Observatory, Chile. FourStar has an all-refractive optical system, four HAWAII-2RG detectors, and Teledyne electronics. The pixel scale of 0.159'' pixel-1 produces a 10.8' × 10.8' field of view. Ten filters are available across the Y, J, H, and Ks bands. We present the optical, mechanical, thermal, electronic, and software design choices and their associated engineering implementations. The detector readout electronics, control system, and the automatic data acquisition hardware are also described. Laboratory and on-sky performance data are presented. FourStar has excellent image quality, easily meeting the requirement of critically sampling the median seeing disk. The throughput is ≈0.5-0.6 across its wavelength coverage. Some early science results are presented.
University of Hawaii1, Johns Hopkins University2, University of Pisa3, Space Telescope Science Institute4, Princeton University5, University of Arizona6, California Institute of Technology7, Smithsonian Institution8, National Central University9, ASTRON10, Las Cumbres Observatory Global Telescope Network11
TL;DR: Pan-STARRS Moving Object Processing System (MOPS) as mentioned in this paper is a modern software package that produces automatic asteroid discoveries and identifications from catalogs of transient detections from next-generation astronomical survey telescopes.
Abstract: .We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern software package that produces automatic asteroid discoveries and identifications from catalogs of transient detections from next-generation astronomical survey telescopes. MOPS achieves >99.5%>99.5% efficiency in producing orbits from a synthetic but realistic population of asteroids whose measurements were simulated for a Pan-STARRS4-class telescope. Additionally, using a nonphysical grid population, we demonstrate that MOPS can detect populations of currently unknown objects such as interstellar asteroids. MOPS has been adapted successfully to the prototype Pan-STARRS1 telescope despite differences in expected false detection rates, fill-factor loss, and relatively sparse observing cadence compared to a hypothetical Pan-STARRS4 telescope and survey. MOPS remains highly efficient at detecting objects but drops to 80% efficiency at producing orbits. This loss is primarily due to configurable MOPS processing limits that a...
Joseph Fourier University1, University of Hawaii at Manoa2, Smithsonian Institution3, California Institute of Technology4, Kapteyn Astronomical Institute5, Spanish National Research Council6, ASTRON7, Clemson University8, Goddard Space Flight Center9, University of Maryland, College Park10, University of California, Berkeley11, Max Planck Society12, Ames Research Center13, University of Jena14, Chalmers University of Technology15, European Space Agency16, Kyoto University17, Paris Diderot University18, University of Arizona19, European Southern Observatory20, University of Hertfordshire21, University of Edinburgh22, University of Barcelona23, Katholieke Universiteit Leuven24, Open University25, Rutherford Appleton Laboratory26, University of St Andrews27
TL;DR: The Gas Survey of Protoplanetary Systems (GASPS) as discussed by the authors is a large-scale far-infrared line and continuum survey of protoplanetary disk through to young debris disk systems carried out using the ACS instrument on the Herschel Space Observatory.
Abstract: We describe a large-scale far-infrared line and continuum survey of protoplanetary disk through to young debris disk systems carried out using the ACS instrument on the Herschel Space Observatory. This Open Time Key program, known as GASPS (Gas Survey of Protoplanetary Systems), targeted similar to 250 young stars in narrow wavelength regions covering the [OI] fine structure line at 63 mu m the brightest far-infrared line in such objects. A subset of the brightest targets were also surveyed in [OI]145 mu m, [CII] at 157 mu m, as well as several transitions of H2O and high-excitation CO lines at selected wavelengths between 78 and 180 mu m. Additionally, GASPS included continuum photometry at 70, 100 and 160 mu m, around the peak of the dust emission. The targets were SED Class II-III T Tauri stars and debris disks from seven nearby young associations, along with a comparable sample of isolated Herbig AeBe stars. The aim was to study the global gas and dust content in a wide sample of circumstellar disks, combining the results with models in a systematic way. In this overview paper we review the scientific aims, target selection and observing strategy of the program. We summarise some of the initial results, showing line identifications, listing the detections, and giving a first statistical study of line detectability. The [OI] line at 63 mu m was the brightest line seen in almost all objects, by a factor of similar to 10. Overall [OI]63 mu m detection rates were 49%, with 100% of HAeBe stars and 43% of T Tauri stars detected. A comparison with published disk dust masses (derived mainly from sub-mm continuum, assuming standard values of the mm mass opacity) shows a dust mass threshold for [OI] 63 mu m detection of similar to 10(-5) M-circle dot. Normalising to a distance of 140 pc, 84% of objects with dust masses >= 10(-5) M-circle dot can be detected in this line in the present survey; 32% of those of mass 10(-6)-10(-5) M-circle dot, and only a very small number of unusual objects with lower masses can be detected. This is consistent with models with a moderate UV excess and disk flaring. For a given disk mass, [OI] detectability is lower for M stars compared with earlier spectral types. Both the continuum and line emission was, in most systems, spatially and spectrally unresolved and centred on the star, suggesting that emission in most cases was from the disk. Approximately 10 objects showed resolved emission, most likely from outflows. In the GASPS sample, [OI] detection rates in T Tauri associations in the 0.3-4 Myr age range were similar to 50%. For each association in the 5-20 Myr age range, similar to 2 stars remain detectable in [OI]63 mu m, and no systems were detected in associations with age >20 Myr. Comparing with the total number of young stars in each association, and assuming a ISM-like gas/dust ratio, this indicates that similar to 18% of stars retain a gas-rich disk of total mass similar to 1 M-Jupiter for 1-4 Myr, 1-7% keep such disks for 5-10 Myr, but none are detected beyond 10-20 Myr. The brightest [OI] objects from GASPS were also observed in [OI]145 mu m, [CII]157 mu m and CO J = 18 - 17, with detection rates of 20-40%. Detection of the [CII] line was not correlated with disk mass, suggesting it arises more commonly from a compact remnant envelope.
TL;DR: The La Silla-QUEST Low Redshift Supernova Survey (LS-QUEST) as mentioned in this paper is a part of the Southern Hemisphere Variability Survey (SVSS), which uses the 10-deg210-deg2 QUEST camera installed at the prime focus of the 1.0m Schmidt Telescope of the European Southern Observatory (ESO).
Abstract: .The La Silla-QUEST Low Redshift Supernova Survey is a part of the La Silla-QUEST Southern Hemisphere Variability Survey. The survey uses the 10 deg210 deg2 QUEST camera installed at the prime focus of the 1.0-m Schmidt Telescope of the European Southern Observatory at La Silla, Chile, and utilizes essentially all of the observing time of the telescope. The QUEST camera was installed on the ESO Schmidt telescope in 2009 after completing a 5 year variability survey in the northern hemisphere using the 1.2-m Oschin Schmidt telescope at Palomar. La Silla-QUEST started science operations in 2009 September. The low redshift supernova survey commenced in 2011 December and is planned to continue for the next 4 years. In this article we describe the instrumentation, software, operation, and performance characteristics of the survey.
Princeton University1, California Institute of Technology2, University of California, Los Angeles3, University of Toledo4, University of Virginia5, Cardiff University6, University of Chile7, Valparaiso University8, Barnard College9, California State Polytechnic University, Pomona10, University of California, Berkeley11
TL;DR: In this paper, spectra, photometry, proper motions, and distance estimates for 42 low-mass star and brown dwarf candidates discovered by the Wide-field Infrared Survey Explorer (WISE).
Abstract: In our effort to complete the census of low-mass stars and brown dwarfs in the immediate solar neighborhood, we present spectra, photometry, proper motions, and distance estimates for 42 low-mass star and brown dwarf candidates discovered by the Wide-field Infrared Survey Explorer (WISE). We also present additional follow-up information on 12 candidates selected using WISE data but previously published elsewhere. The new discoveries include 15 M dwarfs, 17 L dwarfs, five T dwarfs, and five objects of other types. Among these discoveries is a newly identified “unusually red L dwarf” (WISE J223527.07 + 451140.9), four peculiar L dwarfs whose spectra are most readily explained as unresolved L + T binary systems, and a T9 dwarf (WISE J124309.61 + 844547.8). We also show that the recently discovered red L dwarf WISEP J004701.06 + 680352.1 may be a low-gravity object and hence young and potentially low-mass (< 25 M_(Jup)).
TL;DR: The Sutherland High-speed Optical Cameras (SHOC) as mentioned in this paper have been developed for use on the South African Astronomical Observatory's (SAAO) 1.9, 1.0 and 0.75 m telescopes at Sutherland.
Abstract: Two identical new instruments, the Sutherland High-speed Optical Cameras (SHOC), have been developed for use on the South African Astronomical Observatory's (SAAO) 1.9, 1.0 and 0.75 m telescopes at Sutherland. The SHOC systems are fast-frame-rate, accurately-timed, high-quality, visible-wavelength imagers. Each system consists of a camera, global positioning system (GPS), control computer and peripherals. The primary component is an Andor iXon X3 888 UVB camera, utilizing a 1024 × 1024 pixel, frame-transfer, thermoelectrically-cooled, back-illuminated CCD. One of SHOC's most important features is that it can achieve frame rates of between 1 and 20 frames/s during normal operation (dependent on binning and subframing) with microsecond timing accuracy on each frame (achieved using frame-by-frame GPS triggering). Frame rates can be increased further, and fainter targets observed, by making use of SHOC's electron-multiplying (EM) modes. SHOC is therefore ideally suited to time domain astronomy where high frame rates and extremely accurate timing are critical. Here, we present details of the instrument components, characteristics measured during commissioning, science demonstrations, and development plans. Attention is specifically given to exploration of the signal-to-noise (S/N) parameter space as a function of EM and conventional modes. These results enable observers to optimize instrumental settings for their observations and clearly demonstrate the advantages and potential pitfalls of the EM modes.
TL;DR: An asymmetric pupil Fourier wavefront sensing (APF-WFS) was proposed in this paper, which can improve the Strehl ratio from 50% to over 90% in just a few iterations.
Abstract: This article introduces a novel wavefront sensing approach that relies on the Fourier analysis of a single conventional direct image. In the high Strehl ratio regime, the relation between the phase measured in the Fourier plane and the wavefront errors in the pupil can be linearized, as was shown in a previous work that introduced the notion of generalized closure-phase, or kernel-phase. The technique, to be usable as presented requires two conditions to be met: (1) the wavefront errors must be kept small (of the order of one radian or less), and (2) the pupil must include some asymmetry, which can be introduced with a mask, for the problem to become solvable. Simulations show that this asymmetric pupil Fourier wavefront sensing or APF-WFS technique can improve the Strehl ratio from 50% to over 90% in just a few iterations, with excellent photon noise sensitivity properties, suggesting that on-sky close loop APF-WFS is possible with an extreme adaptive optics system.
TL;DR: In this article, a two-beam waveguide-type dual-polarization sideband-separating SIS receiver was developed for searching for highly redshifted spectral lines from galaxies of unknown redshift.
Abstract: We have developed a two-beam waveguide-type dual-polarization sideband-separating SIS receiver system in the 100-GHz band for z-machine on the 45-m radio telescope at the Nobeyama Radio Observatory. The receiver is intended for astronomical use in searching for highly redshifted spectral lines from galaxies of unknown redshift. This receiver has two beams, which have 45'' of beam separation and allow for observation with the switch in the on-on position. The receiver of each beam is composed of an ortho-mode transducer and two sideband-separating SIS mixers, which are both based on a waveguide technique, and the receiver has four intermediate frequency bands of 4.0-8.0 GHz. Over the radio frequency range of 80-116 GHz, the single-sideband receiver noise temperature is lower than about 50 K, and the image rejection ratios are greater than 10 dB in most of the same frequency range. The new receiver system has been installed in the telescope, and we successfully observed a 12CO (J = 3-2) emission line toward a cloverleaf quasar at z = 2.56, which validates the performance of the receiver system. The SSB noise temperature of the system, including the atmosphere, is typically 150-300 K at a radio frequency of 97 GHz. We have begun a blind search of high-J CO toward high-z submillimeter galaxies.
TL;DR: In this article, the photometric calibration of FORCAST is described, which involves some subtleties in correction for array artifacts and uncertainties due to the airborne environment, and is able to achieve approximately 20% uncertainty in the calibration.
Abstract: FORCAST is a mid-infrared (5–40 μm) facility instrument for the Stratospheric Observatory for Infrared Astronomy (SOFIA). After achieving first light flight in 2010 May, FORCAST has completed two observatory characterization flights and thirteen science flights on SOFIA. In this paper we describe the photometric calibration of FORCAST which involves some subtleties in correction for array artifacts and uncertainties due to the airborne environment. At present FORCAST is able to achieve approximately 20% (3σ) uncertainty in the calibration.
TL;DR: In this article, the authors reported the discovery of a transiting planet with an orbital period of 1.36 days orbiting the brighter component of the visual binary star BD -07-436-07/07/436.
Abstract: .We report the discovery of a transiting planet with an orbital period of 1.36 days orbiting the brighter component of the visual binary star BD -07 436-07 436. The host star, WASP-77 A, is a moderately bright G8 VV star (V = 10.3V=10.3) with a metallicity close to solar ([Fe/H] = 0.0 ± 0.1[Fe/H]=0.0±0.1). The companion star, WASP-77 B, is a K-dwarf approximately 2 mag fainter at a separation of approximately 3″. The spectrum of WASP-77 A shows emission in the cores of the Caii H and K lines, indicative of moderate chromospheric activity. The Wide Angle Search for Planets (WASP) light curves show photometric variability with a period of 15.3 days and an amplitude of about 0.3% that is probably due to the magnetic activity of the host star. We use an analysis of the combined photometric and spectroscopic data to derive the mass and radius of the planet (1.76 ± 0.06 MJup1.76±0.06 MJup, 1.21 ± 0.02 RJup1.21±0.02 RJup). The age of WASP-77 A estimated from its rotation rate (∼1 Gyr∼1 Gyr) agrees wi...
TL;DR: In this article, the authors developed a new millimeter wave receiver system with input optics that support simultaneous observations in four bands of 22, 43, 86, and 129 GHz to facilitate calibrating tropospheric phase fluctuations for millimeter-wave VLBI observations.
Abstract: .We have developed a new millimeter wave receiver system with input optics that support simultaneous observations in four bands of 22, 43, 86, and 129 GHz to facilitate calibrating tropospheric phase fluctuations for millimeter-wave VLBI observations. In order to make simultaneous observations in four bands pointing at the same position in sky, it is crucial that errors among the beams from any misalignments should be kept small. After doing the beam alignment in the laboratory, on-site test observations were carried out so as to evaluate the performance. The result is that the beam centers of the four bands with reference to the 86 GHz beam center were aligned within 2″ over most of the elevation range of the Korean VLBI Network (KVN) 21 m telescope. Measured telescope aperture efficiencies including the multiband receiver optics are 65% at 22 GHz, 62% at 43 GHz, 57% at 86 GHz, and 38% at 129 GHz. Through this novel optics covering wide RF bandwidth effectively, we can simultaneously observe the ...
TL;DR: In this paper, the authors investigated the contribution of systematic effects on the spatial dependence of potential systematic errors to reduce the level of spurious clustering in the SDSS data and found that templates associated with stellar density, the stellar color locus, airmass, and seeing are major contaminants of the quasar maps, with seeing having the largest effect.
Abstract: Primordial non-Gaussianity of local type is predicted to lead to enhanced halo clustering on very large scales. Photometric quasars, which can be seen from cosmological redshifts z > 2 even in wide-shallow optical surveys, are promising tracers for constraining non-Gaussianity using this effect. However, large-scale systematics can also mimic this signature of non-Gaussianity. In order to assess the contribution of systematic effects, we cross-correlate overdensity maps of photometric quasars from the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6) in different redshift ranges. We find that the maps are significantly correlated on large scales, even though we expect the angular distributions of quasars at different redshifts to be uncorrelated. This implies that the quasar maps are contaminated with systematic errors. We investigate the use of external templates that provide information on the spatial dependence of potential systematic errors to reduce the level of spurious clustering in the quasar data. We find that templates associated with stellar density, the stellar color locus, airmass, and seeing are major contaminants of the quasar maps, with seeing having the largest effect. Using template projection, we are able to decrease the significance of the cross-correlation measurement on the largest scales from 9.2σ to 5.4σ. Although this is an improvement, the remaining cross-correlation suggests the contamination in this quasar sample is too great to allow a competitive constraint on f_NL by correlations internal to this sample. The SDSS quasar catalog exhibits spurious number density fluctuations of approximately 2% rms, and we need a contamination level less than 1% (0.6%) in order to measure values of f_NL less than 100 (10). Properly dealing with these systematics will be paramount for future large scale structure surveys that seek to constrain non-Gaussianity.
TL;DR: The DONUTS algorithm as mentioned in this paper was designed to fix stellar positions at the sub-pixel level for high-cadence time-series photometry, and also capable of autoguiding on defocused stars.
Abstract: We present the DONUTS autoguiding algorithm, designed to fix stellar positions at the sub-pixel level for high-cadence time-series photometry, and also capable of autoguiding on defocused stars. DONUTS was designed to calculate guide corrections from a series of science images and recentre telescope pointing between each exposure. The algorithm has the unique ability of calculating guide corrections from undersampled to heavily defocused point spread functions. We present the case for why such an algorithm is important for high precision photometry and give our results from off and on-sky testing. We discuss the limitations of DONUTS and the facilities where it soon will be deployed.
TL;DR: An introduction is presented on the methodology for producing animations and graphics with a variety of astronomical data in the software program Blender, and an example video showcasing the outlined principles and features is provided.
Abstract: Astronomical data take on a multitude of forms—catalogs, data cubes, images, and simulations. The availability of software for rendering high-quality three-dimensional graphics lends itself to the paradigm of exploring the incredible parameter space afforded by the astronomical sciences. The software program Blender gives astronomers a useful tool for displaying data in a manner used by three-dimensional (3D) graphics specialists and animators. The interface to this popular software package is introduced with attention to features of interest in astronomy. An overview of the steps for generating models, textures, animations, camera work, and renders is outlined. An introduction is presented on the methodology for producing animations and graphics with a variety of astronomical data. Examples from subfields of astronomy with different kinds of data are shown with resources provided to members of the astronomical community. An example video showcasing the outlined principles and features is provided along with scripts and files for sample visualizations.
TL;DR: In this article, medium spectral resolution (R ~ 60,000) observations of the CaII K-line (3,933 A) absorption profiles observed toward 21 nearby A-type stars thought to possess circumstellar gas debris disks were presented.
Abstract: We present medium spectral resolution (R ~ 60,000) observations of the CaII K-line (3,933 A) absorption profiles observed toward 21 nearby A-type stars thought to possess circumstellar gas debris disks. The stars were repeatedly observed over two observing runs on the 2.1 m Otto Struve telescope at the McDonald Observatory, Texas in 2011 May and 2012 November. Nightly changes in the absorption strength of the CaII K-line near the stellar radial velocity were observed in four of the stars (HD 21620, HD 110411, HD 145964 and HD 183324). This type of absorption variability indicates the presence of a circumstellar gas disk around these stars. We also have detected weak absorption features that sporadically appear with velocities in the range ± 100 km s-1 of the main circumstellar K-line in the spectra of HD 21620, HD 42111, HD 110411 and HD 145964. Due to the known presence of both gas and dust disks surrounding these four stars, these transient absorption features are most probably associated with the presence of Falling Evaporated Bodies (FEBs, or exocomets) that are thought to liberate gas on their grazing trajectory toward and around the central star. This now brings the total number of A-type stars in which the evaporation of CaII gas from protoplanetary bodies (i.e., exocomets) has been observed to vary on a nightly basis to 10 systems. A statistical analysis of the 10 A-stars showing FEB-activity near the CaII K-line compared to 21 A-type stars that exhibit no measurable variability reveals that FEB-activity occurs in significantly younger stellar systems that also exhibit chemical peculiarities. The presence of FEB-activity does not appear to be associated with a strong mid-IR excess. This is probably linked to the disk inclination angle, since unless the viewing angle is favorable the detection of time-variable absorption may be unlikely. Additionally, if the systems are more evolved then the evaporation of gas due to FEB activity could have ceased, whereas the circumstellar dust disk may still remain.
TL;DR: The Keck Interferometer (KI) as mentioned in this paper is a long-baseline near- and mid-infrared interferometer that operated from 2001 until 2012 at Mauna Kea, Hawaii.
Abstract: The Keck Interferometer (KI) combined the two 10 m W M Keck Observatory telescopes on Mauna Kea, Hawaii, as a long-baseline near- and mid-infrared interferometer Funded by NASA, it operated from 2001 until 2012 KI used adaptive optics on the two Keck telescopes to correct the individual wavefronts, as well as active fringe tracking in all modes for path-length control, including the implementation of cophasing to provide long coherent integration times KI implemented high sensitivity fringe-visibility measurements at H (16 μm), K (22 μm), and L (38 μm) bands, and nulling measurements at N band (10 μm), which were used to address a broad range of science topics Supporting these capabilities was an extensive interferometer infrastructure and unique instrumentation, including some additional functionality added as part of the NSF-funded ASTRA program This paper provides an overview of the instrument architecture and some of the key design and implementation decisions, as well as a description of all of the key elements and their configuration at the end of the project The objective is to provide a view of KI as an integrated system, and to provide adequate technical detail to assess the implementation Included is a discussion of the operational aspects of the system, as well as of the achieved system performance Finally, details on V^2 calibration in the presence of detector nonlinearities as applied in the data pipeline are provided
TL;DR: In this paper, the authors compare the performance of SExtractor and PSFEx with DAOPHOT with ALLSTAR on two kinds of simulated images, having a uniform spatial distribution of sources and an overdensity in the center, respectively.
Abstract: The scope of this article is to compare the catalog extraction performances obtained using the new combination of SExtractor with PSFEx against the more traditional and diffuse application of DAOPHOT with ALLSTAR; therefore, the paper may provide a guide for the selection of the most suitable catalog extraction software. Both software packages were tested on two kinds of simulated images, having a uniform spatial distribution of sources and an overdensity in the center, respectively. In both cases, SExtractor is able to generate a deeper catalog than DAOPHOT. Moreover, the use of neural networks for object classification plus the novel SPREAD_MODEL parameter push down to the limiting magnitude the possibility of star/galaxy separation. DAOPHOT and ALLSTAR provide an optimal solution for point-source photometry in stellar fields and very accurate and reliable PSF photometry, with robust star/galaxy separation. However, they are not useful for galaxy characterization and do not generate catalogs that are very complete for faint sources. On the other hand, SExtractor, along with the new capability to derive PSF photometry, turns out to be competitive and returns accurate photometry for galaxies also. We can report that the new version of SExtractor, used in conjunction with PSFEx, represents a very powerful software package for source extraction with performances comparable to those of DAOPHOT. Finally, by comparing the results obtained in the cases of a uniform and of an overdense spatial distribution of stars, we notice for both software packages a decline for the latter case in the quality of the results produced in terms of magnitudes and centroids.
TL;DR: In this paper, the authors presented a catalog of 1990 galaxy pairs selected from the Sloan Digital Sky Survey (SDSS) by volunteers of the Galaxy Zoo project, and highlighted subsamples which are particularly useful for retrieving such properties of the dust distribution as UV extinction, the extent perpendicular to the disk plane, and extinction in the inner parts of disks.
Abstract: Analysis of galaxies with overlapping images offers a direct way to probe the distribution of dust extinction and its effects on the background light. We present a catalog of 1990 such galaxy pairs selected from the Sloan Digital Sky Survey (SDSS) by volunteers of the Galaxy Zoo project. We highlight subsamples which are particularly useful for retrieving such properties of the dust distribution as UV extinction, the extent perpendicular to the disk plane, and extinction in the inner parts of disks. The sample spans wide ranges of morphology and surface brightness, opening up the possibility of using this technique to address systematic changes in dust extinction or distribution with galaxy type. This sample will form the basis for forthcoming work on the ranges of dust distributions in local disk galaxies, both for their astrophysical implications and as the low-redshift part of a study of the evolution of dust properties. Separate lists and figures show deep overlaps, where the inner regions of the foreground galaxy are backlit, and the relatively small number of previously-known overlapping pairs outside the SDSS DR7 sky coverage.
TL;DR: In this article, a model of the moonless natural sky brightness in the V-band was constructed from existing data on the Zodiacal Light, an airglow model based on the van Rhijn function, and integrated starlight (including diffuse galactic light) constructed from images made with the same equipment used for sky brightness observations.
Abstract: Anthropogenic sky glow (a result of light pollution) combines with the natural background brightness of the night sky when viewed by an observer on the earth's surface. In order to measure the anthropogenic component accurately, the natural component must be identified and subtracted. A model of the moonless natural sky brightness in the V-band was constructed from existing data on the Zodiacal Light, an airglow model based on the van Rhijn function, and a model of integrated starlight (including diffuse galactic light) constructed from images made with the same equipment used for sky brightness observations. The model also incorporates effective extinction by the atmosphere and is improved at high zenith angles (>80°) by the addition of atmospheric diffuse light. The model may be projected onto local horizon coordinates for a given observation at a resolution of 0.05° over the hemisphere of the sky, allowing it to be accurately registered with data images obtained from any site. Zodiacal Light and integrated starlight models compare favorably with observations from remote dark sky sites, matching within ± 8 nL over 95% of the sky. The natural airglow may be only approximately modeled, errors of up to ± 25 nL are seen when the airglow is rapidly changing or has considerable character (banding); ± 8 nL precision may be expected under favorable conditions. When subtracted from all-sky brightness data images, the model significantly improves estimates of sky glow from anthropogenic sources, especially at sites that experience slight to moderate light pollution.