Showing papers in "Publications of the Astronomical Society of the Pacific in 2012"
TL;DR: In this article, a Bayesian maximum a posteriori (MAP) approach is presented, where a subset of highly correlated and quiet stars is used to generate a cotrending basis vector set, which is in turn used to establish a range of "reasonable" robust fit parameters.
Abstract: With the unprecedented photometric precision of the Kepler spacecraft, significant systematic and stochastic errors on transit signal levels are observable in the Kepler photometric data. These errors, which include discontinuities, outliers, systematic trends, and other instrumental signatures, obscure astrophysical signals. The presearch data conditioning (PDC) module of the Kepler data analysis pipeline tries to remove these errors while preserving planet transits and other astrophysically interesting signals. The completely new noise and stellar vari- ability regime observed inKepler data poses a significant problem to standard cotrending methods. Variable stars are often of particular astrophysical interest, so the preservation of their signals is of significant importance to the astrophysical community. We present a Bayesian maximum a posteriori (MAP) approach, where a subset of highly correlated and quiet stars is used to generate a cotrending basis vector set, which is in turn used to establish a range of "reasonable" robust fit parameters. These robust fit parameters are then used to generate a Bayesian prior and a Bayesian posterior probability distribution function (PDF) which, when maximized, finds the best fit that simulta- neously removes systematic effects while reducing the signal distortion and noise injection that commonly afflicts simple least-squares (LS) fitting. A numerical and empirical approach is taken where the Bayesian prior PDFs are generated from fits to the light-curve distributions themselves.
721 citations
TL;DR: The Weizmann Interactive Supernova Data Repository (WISeREP) as discussed by the authors is an SQL-based database with an interactive Web-based graphical interface for supernova data.
Abstract: We have entered an era of massive data sets in astronomy. In particular, the number of supernova (SN) discoveries and classifications has substantially increased over the years from few tens to thousands per year. It is no longer the case that observations of a few prototypical events encapsulate most spectroscopic information about SNe, motivating the development of modern tools to collect, archive, organize, and distribute spectra in general and SN spectra in particular. For this reason, we have developed the Weizmann Interactive Supernova Data Repository (WISeREP)—an SQL-based database (DB) with an interactive Web-based graphical interface. The system serves as an archive of high-quality SN spectra, including both historical (legacy) data and data that are accumulated by ongoing modern programs. The archive provides information about objects, their spectra, and related metadata. Utilizing interactive plots, we provide a graphical interface to visualize data, perform line identification of the major relevant species, determine object redshifts, classify SNe, and measure expansion velocities. Guest users may view and download spectra or other data that have been placed in the public domain. Registered users may also view and download data that are proprietary to specific programs with which they are associated. The DB currently holds more than 8000 spectra, of which more than 5000 are public; the latter include published spectra from the Palomar Transient Factory (PTF), all of the SUSPECT (Supernova Spectrum) archive, the Caltech-Core-Collapse Program (CCCP), the CfA SN spectra archive, and published spectra from the University of California, Berkeley, SNDB repository. It offers an efficient and convenient way to archive data and share it with colleagues, and we expect that data stored in this way will be easy to access, increasing its visibility, usefulness, and scientific impact. We encourage the SN community worldwide to make use of the data and tools provided by WISeREP and to contribute data to be made globally available and archived for posterity.
693 citations
TL;DR: This article introduces the completely new and significantly improved version of Presearch Data Conditioning (PDC) which was implemented in Kepler SOC version 8.0, which reliably corrects errors in the light curves while at the same time preserving planet transits and other astrophysically interesting signals.
Abstract: Kepler provides light curves of 156,000 stars with unprecedented precision. However, the raw data as they come from the spacecraft contain significant systematic and stochastic errors. These errors, which include discontinuities, systematic trends, and outliers, obscure the astrophysical signals in the light curves. To correct these errors is the task of the Presearch Data Conditioning (PDC) module of the Kepler data analysis pipeline. The original version of PDC in Kepler did not meet the extremely high performance requirements for the detection of miniscule planet transits or highly accurate analysis of stellar activity and rotation. One particular deficiency was that astrophysical features were often removed as a side effect of the removal of errors. In this article we introduce the completely new and significantly improved version of PDC which was implemented in Kepler SOC version 8.0. This new PDC version, which utilizes a Bayesian approach for removal of systematics, reliably corrects errors in the light curves while at the same time preserving planet transits and other astrophysically interesting signals. We describe the architecture and the algorithms of this new PDC module, show typical errors encountered in Kepler data, and illustrate the corrections using real light curve examples.
658 citations
TL;DR: In this article, the Kepler CDPP is calculated on a per-target basis for 3-, 6-, and 12-hr transit durations, which are now available for all Kepler observations.
Abstract: .The Kepler Mission is searching for Earth-size planets orbiting solar-like stars by simultaneously observing >160,000>160,000 stars to detect sequences of transit events in the photometric light curves. The Combined Differential Photometric Precision (CDPP) is the metric that defines the ease with which these weak terrestrial transit signatures can be detected. An understanding of CDPP is invaluable for evaluating the completeness of the Kepler survey and inferring the underlying planet population. This paper describes how the Kepler CDPP is calculated, and introduces tables of rms CDPP on a per-target basis for 3-, 6-, and 12-hr transit durations, which are now available for all Kepler observations. Quarter 3 is the first typical set of observations at the nominal length and completeness for a quarter, from 2009 September 18 to 2009 December 16, and we examine the properties of the rms CDPP distribution for this data set. Finally, we describe how to employ CDPP to calculate target completeness, ...
233 citations
TL;DR: In this article, improved photonic passbands for the UBVRI, Hipparcos Hp, and Tycho BT and VT standard systems using the extensive spectrophotometric libraries of NGSL and MILES were calculated.
Abstract: We have calculated improved photonic passbands for the UBVRI, Hipparcos Hp, and Tycho BT and VT standard systems using the extensive spectrophotometric libraries of NGSL and MILES. Using the Hp passband, we adjusted the absolute flux levels of stars in the spectrophotometric libraries so that their synthetic Hp magnitudes matched the precise Hipparcos Catalogue value. Synthetic photometry based on the renormalized fluxes was compared with the standard UBVRI, BT and VT magnitudes, and revised synthetic zero points were determined. The Hipparcos and Tycho photometry system zero points were also compared with the V-magnitude zero points of the SAAO UBVRI system, the homogenized UBV system, and the Walraven VB system. The confusion in the literature concerning broadband magnitudes, fluxes, passbands, and the choice of appropriate mean wavelengths is detailed and discussed in the Appendix.
212 citations
TL;DR: In this paper, the authors present the inner workings of a framework, based on machine-learning algorithms, that captures expert training and ground-truth knowledge about the variable and transient sky to automate the process of discovery on image differences, and the generation of preliminary science-type classifications of discovered sources.
Abstract: The rate of image acquisition in modern synoptic imaging surveys has already begun to outpace the feasibility of keeping astronomers in the real-time discovery and classification loop. Here we present the inner workings of a framework, based on machine-learning algorithms, that captures expert training and ground-truth knowledge about the variable and transient sky to automate (1) the process of discovery on image differences, and (2) the generation of preliminary science-type classifications of discovered sources. Since follow-up resources for extracting novel science from fast-changing transients are precious, self-calibrating classification probabilities must be couched in terms of efficiencies for discovery and purity of the samples generated. We estimate the purity and efficiency in identifying real sources with a two-epoch image-difference discovery algorithm for the Palomar Transient Factory (PTF) survey. Once given a source discovery, using machine-learned classification trained on PTF data, we distinguish between transients and variable stars with a 3.8% overall error rate (with 1.7% errors for imaging within the Sloan Digital Sky Survey footprint). At >96% classification efficiency, the samples achieve 90% purity. Initial classifications are shown to rely primarily on context-based features, determined from the data itself and external archival databases. In the first year of autonomous operations of PTF, this discovery and classification framework led to several significant science results, from outbursting young stars to subluminous Type IIP supernovae to candidate tidal disruption events. We discuss future directions of this approach, including the possible roles of crowdsourcing and the scalability of machine learning to future surveys such as the Large Synoptic Survey Telescope (LSST).
182 citations
California Institute of Technology1, ASTRON2, University of Sussex3, University of Hertfordshire4, University of Portsmouth5, University of Padua6, University of the Western Cape7, University of California, Davis8, University of Cambridge9, University of Lisbon10, University of California, Riverside11, McGill University12, Commonwealth Scientific and Industrial Research Organisation13, Drexel University14, Lawrence Livermore National Laboratory15, Durham University16, Spanish National Research Council17, University of Oxford18, Imperial College London19, University of Naples Federico II20, Istituto Nazionale di Fisica Nucleare21, Space Telescope Science Institute22, University of Nottingham23, University of Hawaii24, University of Calgary25, Max Planck Society26, University of Edinburgh27, University of Wisconsin-Madison28, Carnegie Institution for Science29, Commissariat à l'énergie atomique et aux énergies alternatives30, Leiden University31, Haverford College32, Liverpool John Moores University33, Leibniz Association34
TL;DR: The Spitzer Extragalactic Representative Volume Survey (SERVS) as discussed by the authors is designed to enable the study of galaxy evolution as a function of environment from z~5 to the present day, and is the first survey both large enough and deep enough to put rare objects such as luminous quasars and galaxy clusters at z>1 into their cosmological context.
Abstract: We present the Spitzer Extragalactic Representative Volume Survey (SERVS), an 18 square degrees medium-deep survey at 3.6 and 4.5 microns with the post-cryogenic Spitzer Space Telescope to ~2 microJy (AB=23.1) depth of five highly observed astronomical fields (ELAIS-N1, ELAIS-S1, Lockman Hole, Chandra Deep Field South and XMM-LSS). SERVS is designed to enable the study of galaxy evolution as a function of environment from z~5 to the present day, and is the first extragalactic survey both large enough and deep enough to put rare objects such as luminous quasars and galaxy clusters at z>1 into their cosmological context. SERVS is designed to overlap with several key surveys at optical, near- through far-infrared, submillimeter and radio wavelengths to provide an unprecedented view of the formation and evolution of massive galaxies. In this paper, we discuss the SERVS survey design, the data processing flow from image reduction and mosaicing to catalogs, as well as coverage of ancillary data from other surveys in the SERVS fields. We also highlight a variety of early science results from the survey.
181 citations
TL;DR: The Palomar Transient Factory (PTF) provides multiple epoch imaging for a large fraction of the celestial sphere as discussed by the authors, which enables the calibration of fields that are outside the SDSS footprint.
Abstract: The Palomar Transient Factory (PTF) provides multiple epoch imaging for a large fraction of the celestial sphere. Here, we describe the photometric calibration of the PTF data products that allows the PTF magnitudes to be related to other magnitude systems. The calibration process utilizes Sloan Digital Sky Survey (SDSS) r ∼ 16 mag point-source objects as photometric standards. During photometric conditions, this allows us to solve for the extinction coefficients and color terms and to estimate the camera illumination correction. This also enables the calibration of fields that are outside the SDSS footprint. We test the precision and repeatability of the PTF photometric calibration. Given that PTF is observing in a single filter each night, we define a PTF calibrated magnitude system for the R band and g band. We show that, in this system, ≈59% (47%) of the photometrically calibrated PTF R-band (g-band) data achieve a photometric precision of 0.02–0.04 mag and have color terms and extinction coefficients that are close to their average values. Given the objects’ color, the PTF magnitude system can be converted to other systems. Moreover, a night-by-night comparison of the calibrated magnitudes of individual stars observed on multiple nights shows that they are consistent to a level of ≈0.02 mag. Most of the data that were taken under nonphotometric conditions can be calibrated relative to other epochs of the same sky footprint obtained during photometric conditions. We provide a concise guide describing how to use the PTF photometric-calibration data products, as well as the transformations between the PTF magnitude system and the SDSS and Johnson-Cousins systems.
179 citations
University of Leeds1, University of Sydney2, University of Manchester3, University of Wisconsin-Madison4, National Radio Astronomy Observatory5, University of Maryland, College Park6, National Research Council7, University of Southampton8, Boston University9, University of Hertfordshire10, California Institute of Technology11, University of Jaén12, Liverpool John Moores University13, Indian Institute of Space Science and Technology14, University of Barcelona15, Max Planck Society16, Commonwealth Scientific and Industrial Research Organisation17
TL;DR: The CORNISH survey as mentioned in this paper is an arcsecond resolution radio continuum survey of the inner Galactic plane at 5GHz using the Karl G. Jansky Very Large Array (VLA).
Abstract: We describe the motivation, design and implementation of the CORNISH survey, an arcsecond resolution radio continuum survey of the inner Galactic plane at 5GHz using the Karl G. Jansky Very Large Array (VLA). It is a blind survey co-ordinated with the northern Spitzer GLIMPSE I region covering 10 o < l <65 o and |b| <1 o at similar resolution. We discuss in detail the strategy that we employed to control the shape of the synthesised beam across this survey that covers a wide range of fairly low declinations. Two snapshots separated by 4 hours in hour angle kept the beam elongation to less that 1.5 over 75% of the survey area and less than 2 over 98% of the survey. The prime scientific motivation is to provide an unbiased survey for ultra-compact H II regions to study this key phase in massive star formation. A sensitivity around 2mJy will allow the automatic distinction between radio loud and quiet mid-IR sources found in the Spitzer surveys. This survey has many legacy applications beyond star formation including evolved stars, active stars and binaries, and extragalactic sources. The CORNISH survey for compact ionized sources complements other Galactic plane surveys that target diffuse and non-thermal sources as well as atomic and molecular phases to build up a complete picture of the ISM in the Galaxy.
175 citations
TL;DR: The Kilodegree Extremely Little Telescope (KELT) project as mentioned in this paper surveys a set of 26° × 26° fields around the southern sky and targets stars in the range of 8 < V < 10 mag, searching for transits by hot Jupiters.
Abstract: The Kilodegree Extremely Little Telescope (KELT) project is a survey for new transiting planets around bright stars. KELT-South is a small-aperture, wide-field automated telescope located at Sutherland, South Africa. The telescope surveys a set of 26° × 26° fields around the southern sky and targets stars in the range of 8 < V < 10 mag, searching for transits by hot Jupiters. This article describes the KELT-South system hardware and software and discusses the quality of the observations. We show that KELT-South is able to achieve the necessary photometric precision to detect transits of hot Jupiters around solar-type main-sequence stars.
170 citations
TL;DR: It is demonstrated that the wavelength and age dependence of SPS model uncertainty translates into a redshift-dependent model uncertainty, highlighting the importance of a quantitative understanding of model differences when comparing observations with models as a function of redshift.
Abstract: We present EzGal, a flexible Python program designed to easily generate observable parameters (magnitudes, colors, and mass-to-light ratios) for arbitrary input stellar population synthesis (SPS) models. As has been demonstrated by various authors, for many applications the choice of input SPS models can be a significant source of systematic uncertainty. A key strength of EzGal is that it enables simple, direct comparison of different model sets so that the uncertainty introduced by choice of model set can be quantified. Its ability to work with new models will allow EzGal to remain useful as SPS modeling evolves to keep up with the latest research (such as varying IMFs). EzGal is also capable of generating composite stellar population models (CSPs) for arbitrary input star-formation histories and reddening laws, and it can be used to interpolate between metallicities for a given model set. To facilitate use, we have created an online interface to run EzGal and quickly generate magnitude and mass-to-light ratio predictions for a variety of star-formation histories and model sets. We make many commonly used SPS models available from the online interface, including the canonical Bruzual & Charlot models, an updated version of these models, the Maraston models, the BaSTI models, and the Flexible Stellar Population Synthesis (FSPS) models. We use EzGal to compare magnitude predictions for the model sets as a function of wavelength, age, metallicity, and star-formation history. From this comparison we quickly recover the well-known result that the models agree best in the optical for old solar-metallicity models, with differences at the ~0.1 mag level. Similarly, the most problematic regime for SPS modeling is for young ages (2 Gyr) and long wavelengths (λ 7500 A), where thermally pulsating AGB stars are important and scatter between models can vary from 0.3 mag (Sloan i) to 0.7 mag (Ks). We find that these differences are not caused by one discrepant model set and should therefore be interpreted as general uncertainties in SPS modeling. Finally, we connect our results to a more physically motivated example by generating CSPs with a star-formation history matching the global star-formation history of the universe. We demonstrate that the wavelength and age dependence of SPS model uncertainty translates into a redshift-dependent model uncertainty, highlighting the importance of a quantitative understanding of model differences when comparing observations with models as a function of redshift.
TL;DR: The Habitable Zone Gallery as mentioned in this paper is a service to the exoplanet community that provides habitable zone (HZ) information for each of the ex-oplanetary systems with known planetary orbital parameters.
Abstract: The Habitable Zone Gallery is a new service to the exoplanet community that provides habitable-zone (HZ) information for each of the exoplanetary systems with known planetary orbital parameters. The service includes a sortable table with information on the percentage of orbital phase spent within the HZ, planetary effective temperatures, and other basic planetary properties. In addition to the table, we also plot the period and eccentricity of the planets with respect to their time spent in the HZ. The service includes a gallery of known systems that plot the orbits and the location of the HZ with respect to those orbits. Also provided are animations that aid in orbit visualization and provide the changing effective temperature for those planets in eccentric orbits. Here, we describe the science motivation, the underlying calculations, and the structure of the World Wide Web site.
TL;DR: SEDfit as mentioned in this paper is a software package for spectral energy distribution fitting (SED fitting) of high-redshift photometric data, and the only one to properly treat nondetections.
Abstract: This article describes SEDfit, the earliest—but continually upgraded—software package for spectral energy distribution fitting (SED fitting) of high-redshift photometric data, and the only one to properly treat nondetections. The principles of maximum-likelihood SED fitting are described, including formulae used for fitting both detected and undetected (upper limits) photometric data. The internal mechanics of the SEDfit package are presented and several illustrative examples of its use are given. The article concludes with a discussion of several issues and caveats applicable to SED fitting in general.
TL;DR: In this article, the primary impact of exozodiacal dust on high-contrast direct imaging at optical wavelengths, such as would be performed with a coronagraph, is qualitatively assessed.
Abstract: Debris dust in the habitable zones of stars—otherwise known as exozodiacal dust—comes from extrasolar asteroids and comets and is thus an expected part of a planetary system. Background flux from the solar system’s zodiacal dust and the exozodiacal dust in the target system is likely to be the largest source of astrophysical noise in direct observations of terrestrial planets in the habitable zones of nearby stars. Furthermore, dust structures like clumps, thought to be produced by dynamical interactions with exoplanets, are a possible source of confusion. In this article, we qualitatively assess the primary impact of exozodiacal dust on high-contrast direct imaging at optical wavelengths, such as would be performed with a coronagraph. Then we present the sensitivity of previous, current, and near-term facilities to thermal emission from debris dust at all distances from nearby solar-type stars, as well as our current knowledge of dust levels from recent surveys. Finally, we address the other method of detecting debris dust, through high-contrast imaging in scattered light. This method is currently far less sensitive than thermal emission observations, but provides high spatial resolution for studying dust structures. This article represents the first report of NASA’s Exoplanet Exploration Program Analysis Group (ExoPAG).
TL;DR: The Stony Brook/SMARTS Atlas of Southern Novae as mentioned in this paper contains spectra and photometry obtained since 2003 and is available online at http://www.sunysb.astro.edu/fwalter/smARTS/NovaAtlas/.
Abstract: We introduce the Stony Brook/SMARTS Atlas of (mostly) Southern Novae. This atlas contains both spectra and photometry obtained since 2003. The data archived in this atlas will facilitate systematic studies of the nova phenomenon and correlative studies with other comprehensive data sets. It will also enable detailed investigations of individual objects. In making the data public we hope to engender more interest on the part of the community in the physics of novae. The atlas is online at http://www.astro.sunysb.edu/fwalter/SMARTS/NovaAtlas/.
TL;DR: A conceptual primer is provided to help users of the Kepler data archive understand and recognize systematic artifacts within light curves and some methods for their removal.
Abstract: The Kepler spacecraft has collected data of high photometric precision and cadence almost continuously since operations began on 2009 May 2. Primarily designed to detect planetary transits and asteroseismological signals from solar-like stars, Kepler has provided high quality data for many areas of investigation. Unconditioned simple aperture time-series photometry are however affected by systematic structure. Examples of these systematics are differential velocity aberration, thermal gradients across the spacecraft, and pointing variations. While exhibiting some impact on Kepler's primary science, these systematics can critically handicap potentially ground-breaking scientific gains in other astrophysical areas, especially over long timescales greater than 10 days. As the data archive grows to provide light curves for 10(exp 5) stars of many years in length, Kepler will only fulfill its broad potential for stellar astrophysics if these systematics are understood and mitigated. Post-launch developments in the Kepler archive, data reduction pipeline and open source data analysis software have occurred to remove or reduce systematic artifacts. This paper provides a conceptual primer for users of the Kepler data archive to understand and recognize systematic artifacts within light curves and some methods for their removal. Specific examples of artifact mitigation are provided using data available within the archive. Through the methods defined here, the Kepler community will find a road map to maximizing the quality and employment of the Kepler legacy archive.
TL;DR: Aperture Photometry Tool is software for astronomers and students interested in manually exploring the photometric qualities of astronomical images designed to allow the image data associated with aperture photometry calculations for point and extended sources to be visualized and, therefore, more effectively analyzed.
Abstract: Aperture Photometry Tool (APT) is software for astronomers and students interested in manually exploring the photometric qualities of astronomical images. It is a graphical user interface (GUI) designed to allow the image data associated with aperture photometry calculations for point and extended sources to be visualized and, therefore, more effectively analyzed. The finely tuned layout of the GUI, along with judicious use of color-coding and alerting, is intended to give maximal user utility and convenience. Simply mouse-clicking on a source in the displayed image will instantly draw a circular or elliptical aperture and sky annulus around the source and will compute the source intensity and its uncertainty, along with several commonly used measures of the local sky background and its variability. The results are displayed and can be optionally saved to an aperture-photometry-table file and plotted on graphs in various ways using functions available in the software. APT is geared toward processing sources in a small number of images and is not suitable for bulk processing a large number of images, unlike other aperture photometry packages (e.g., SExtractor). However, APT does have a convenient source-list tool that enables calculations for a large number of detections in a given image. The source-list tool can be run either in automatic mode to generate an aperture photometry table quickly or in manual mode to permit inspection and adjustment of the calculation for each individual detection. APT displays a variety of useful graphs with just the push of a button, including image histogram, x and y aperture slices, source scatter plot, sky scatter plot, sky histogram, radial profile, curve of growth, and aperture-photometry-table scatter plots and histograms. APT has many functions for customizing the calculations, including outlier rejection, pixel “picking” and “zapping,” and a selection of source and sky models. The radial-profile-interpolation source model, which is accessed via the radial-profile-plot panel, allows recovery of source intensity from pixels with missing data and can be especially beneficial in crowded fields.
TL;DR: Estimates of the measurement error are used to weight the input data such that the resulting eigenvectors are more sensitive to the true underlying signal variations rather than being pulled by heteroskedastic measurement noise.
Abstract: We present a method for performing principal component analysis (PCA) on noisy datasets with missing values. Estimates of the measurement error are used to weight the input data such that the resulting eigenvectors, when compared to classic PCA, are more sensitive to the true underlying signal variations rather than being pulled by heteroskedastic measurement noise. Missing data are simply limiting cases of weight = 0. The underlying algorithm is a noise weighted expectation maximization (EM) PCA, which has additional benefits of implementation speed and flexibility for smoothing eigenvectors to reduce the noise contribution. We present applications of this method on simulated data and QSO spectra from the Sloan Digital Sky Survey (SDSS).
TL;DR: In this paper, the authors obtained JJ-, HH-, and JHJH-band photometry of known extrasolar planet transiting systems at the 2.1m Kitt Peak National Observatory Telescope using the FLAMINGOS infrared camera between 2008 October and 2011 October.
Abstract: .We obtained JJ-, HH-, and JHJH-band photometry of known extrasolar planet transiting systems at the 2.1 m Kitt Peak National Observatory Telescope using the FLAMINGOS infrared camera between 2008 October and 2011 October. From the derived light curves we have extracted the midtransit times, transit depths and transit durations for these events. The precise midtransit times obtained help improve the orbital periods and also constrain transit-time variations of the systems. For most cases the published system parameters successfully accounted for our observed light curves, but in some instances we derive improved planetary radii and orbital periods. We complemented our 2.1 m infrared observations using CCD z′z′-band and BB-band photometry (plus two Hα filter observations) obtained with the Kitt Peak Visitor Center Telescope, and with four HH-band transits observed in 2007 October with the NSO’s 1.6 m McMath-Pierce Solar Telescope. The principal highlights of our results are (1) Our ensemble of JJ-b...
TL;DR: A ground-based photometric survey of the field targeted by the NASA Kepler mission is presented in this paper. But the survey is limited to the redder SDSS griz and D51 filters, and the typical completeness limit is U ~ 18.7, B ~ 19.3, and V ~19.1 mag.
Abstract: We present the motivations for and methods we used to create a new ground-based photometric survey of the field targeted by the NASA Kepler Mission. The survey contains magnitudes for 4,416,007 sources in one or more of the UBV filters, including 1,861,126 sources detected in all three filters. The typical completeness limit is U ~ 18.7, B ~ 19.3, and V ~ 19.1 mag, but varies by location. The area covered is 191 deg2 and includes the areas on and between the 42 Kepler CCDs, as well as additional areas around the perimeter of the Kepler field. The major significance of this survey is our addition of U to the optical bandpass coverage available in the Kepler Input Catalog, which was primarily limited to the redder SDSS griz and D51 filters. The U coverage reveals a sample of the hottest sources in the field, many of which are not currently targeted by Kepler, but may be objects of astrophysical interest.
TL;DR: The PTF photometric catalog 1.0 as mentioned in this paper contains calibrated R_PTF-filter magnitudes for ≈2.1 × 10^7 sources brighter than magnitude 19, over an area of ≈11,233 deg^2.
Abstract: We constructed a photometrically calibrated catalog of non-variable sources from the Palomar Transient Factory (PTF) observations. The first version of this catalog presented here, the PTF photometric catalog 1.0, contains calibrated R_PTF-filter magnitudes for ≈2.1 × 10^7 sources brighter than magnitude 19, over an area of ≈11,233 deg^2. The magnitudes are provided in the PTF photometric system, and the color of a source is required in order to convert these magnitudes into other magnitude systems. We estimate that the magnitudes in this catalog have a typical accuracy of about 0.02 mag with respect to magnitudes from the Sloan Digital Sky Survey. The median repeatability of our catalog’s magnitudes for stars between 15 and 16 mag, is about 0.01 mag and it is over 0.03 mag for 95% of the sources in this magnitude range. The main goal of this catalog is to provide reference magnitudes for photometric calibration of visible light observations. Subsequent versions of this catalog, which will be published incrementally online, will be extended to cover a larger sky area and will also include g_PTF-filter magnitudes, as well as variability and proper-motion information.
TL;DR: The Solar System Object Search (SSOS) at the Canadian Astronomy Data Centre as discussed by the authors allows users to search for images of moving objects by submitting either a list of observations, an object designation, a set of orbital elements, or a user-generated ephemeris for an object.
Abstract: It is very difficult to find archival images of solar system objects. While regular archive searches can find images at a fixed location, they cannot find images of moving targets. Archival images have become in- creasingly useful to extragalactic and stellar astronomers the last few years, but until now, solar system researchers have been at a disadvantage in this respect. The Solar System Object Search (SSOS) at the Canadian Astronomy Data Centre allows users to search for images of moving objects. SSOS accepts as input either a list of observations, an object designation, a set of orbital elements, or a user-generated ephemeris for an object. It then searches for images containing that object over a range of dates. The user is then presented with a list of images containing that object from a variety of archives. Initially created to search the CFHT MegaCam archive, SSOS has been extended to other telescope archives, including Gemini, Subaru/SuprimeCam, HST, several ESO instruments, and the SDSS, for a total of 6.5 million images.
TL;DR: In this article, the standardizability of Type Ia supernovae in the near-infrared (NIR) was analyzed by investigating the correlation between observed peak NIR (YJHYJH) absolute magnitude and post-maximum BB-band decline rate.
Abstract: .We analyze the standardizability of Type Ia supernovae (SNe Ia) in the near-infrared (NIR) by investigating the correlation between observed peak NIR (YJHYJH) absolute magnitude and postmaximum BB-band decline rate [Δm15(B)Δm15(B)]. A sample of 27 low-redshift SNe Ia with well-observed NIR light curves observed by the Carnegie Supernova Project (CSP) between 2004 and 2007 is used. All 27 objects have premaximum coverage in optical bands, with a subset of 13 having premaximum NIR observations as well; coverage of the other 14 begins shortly after NIR maximum brightness. We describe the methods used to derive light-curve parameters (absolute peak magnitudes and decline rates) from both spline- and template-fitting procedures, and we confirm prior findings that fitting templates to SNe Ia light curves in the NIR is problematic due to the diversity of postmaximum behavior of objects that are characterized by similar Δm15(B)Δm15(B) values, especially at high decline rates. Nevertheless, we show that N...
TL;DR: In this article, the authors present continuous, high-precision photometric monitoring data with 1 minute cadence of the dM3e flare star AD Leo with the MOST satellite.
Abstract: .We present continuous, high-precision photometric monitoring data with 1 minute cadence of the dM3e flare star AD Leo with the MOST satellite. We observed 19 flares in 5.8 days and found a flare frequency distribution that is similar to previous studies. The light curve reveals a sinusoidal modulation with a period of 2.23-0.27+0.36 days that we attribute to the rotation of a stellar spot rotating into and out of view. We see no correlation between the occurrence of flares and rotational phase, indicating that there may be many spots distributed at different longitudes or, possibly, that the modulation is caused by varying surface coverage of a large polar spot that is viewed nearly pole-on. The data show no correlation between flare energy and the time since the previous flare. We use these results to reject a simple model in which all magnetic energy is stored in one active region and released only during flares.
TL;DR: In this paper, the authors explore the detection and characterization capabilities of a 4 m space telescope plus 50 m starshade located at the Earth-Sun L2 point, known as the New Worlds Observer (NWO), and find that even without any return visits, the NWO baseline architecture (IWA = 65 mas, limiting FPB = 4 x 10(exp -11) can achieve a 95% probability of detecting and spectrally characterizing at least one habitable Earth-like planet and an expectation value of approximately 3 planets found, within the mission lifetime and delta
Abstract: As part of NASA's mission to explore habitable planets orbiting nearby stars, this article explores the detection and characterization capabilities of a 4 m space telescope plus 50 m starshade located at the Earth-Sun L2 point, known as the New Worlds Observer (NWO). Our calculations include the true spectral types and distribution of stars on the sky, an iterative target selection protocol designed to maximize efficiency based on prior detections, and realistic mission constraints. We conduct simulated observing runs for a wide range in exozodiacal background levels (epsilon = 1-100 times the local zodi brightness) and overall prevalence of Earth-like terrestrial planets (eta(sub solar halo))0.1-1). We find that even without any return visits, the NWO baseline architecture (IWA = 65 mas, limiting FPB = 4 x 10(exp -11) can achieve a 95% probability of detecting and spectrally characterizing at least one habitable Earth-like planet and an expectation value of approximately 3 planets found, within the mission lifetime and delta V budgets, even in the worst-case scenario (eta(sub solar halo) = 0.1 and = epsilon = 100 zodis for every target). This achievement requires about 1 yr of integration time spread over the 5 yr mission, leaving the remainder of the telescope time for UV-NIR general astrophysics. Cost and technical feasibility considerations point to a "sweet spot" in starshade design near a 50 m starshade effective diameter. with 12 or 16 petals, at a distance of 70,000-100,000 km from the telescope.
TL;DR: In this article, the authors present medium resolution (R = 60,000) absorption measurements of the interstellar Ca II K line observed towards five nearby A-type stars (49 Ceti, 5 Vul, ι Cyg, 2 And, and HD 223884) suspected of possessing circumstellar gas debris disks.
Abstract: We present medium resolution (R = 60,000) absorption measurements of the interstellar Ca II K line observed towards five nearby A-type stars (49 Ceti, 5 Vul, ι Cyg, 2 And, and HD 223884) suspected of possessing circumstellar gas debris disks. The stars were observed on a nightly basis during a six night observing run on the 2.1-meter Otto Struve telescope at the McDonald Observatory, Texas. We have detected nightly changes in the absorption strength of the Ca II K line observed near the stellar radial velocity in three of the stars (49 Ceti, i Cyg and HD 223884). Such changes in absorption suggest the presence of a circumstellar (atomic) gas disk around these stars. In addition to the absorption changes in the main Ca II K line profile, we have also observed weak transient absorption features that randomly appear at redshifted velocities in the spectra of 49 Ceti, 5 Vul, and 2 And. These absorption features are most probably associated with the presence of falling evaporated bodies (exo-comets) that liberate evaporating gas on their approach to the central star. This now brings the total number of systems in which exocomet activity has been observed at Ca II or Na I wavelengths on a nightly basis to seven (β Pic, HR 10, HD 85905, β Car, 49 Ceti, 5 Vul, and 2 And), with 2 And exhibiting weaker and less frequent changes. All of the disk systems presently known to exhibit either type of short-term variability in Ca II K line absorption are rapidly rotating A-type stars (V sin i > 120 km s-1). Most exhibit mid-IR excesses, and many of them are very young (< 20 Myr), thus supporting the argument that many of them are transitional objects between Herbig Ae and "Vega-like" A-type stars with more tenuous circumstellar disks. No mid-IR excess (due to the presence of a dust disk) has yet been detected around either 2 And or HD 223884, both of which have been classified as λ Bootis-type stars. This may indicate that the observed changes in gas absorption for these two stars may not be due to circumstellar activity, but may instead be associated with the stars' episodic mass loss and passage though low-density interstellar clouds.
California Institute of Technology1, Carnegie Institution for Science2, Space Telescope Science Institute3, Swinburne University of Technology4, Leiden University5, Indiana University6, University of Tokyo7, Carnegie Learning8, Institute for the Physics and Mathematics of the Universe9, University of Wyoming10
TL;DR: In this article, a narrow-band imaging program for intermediate-redshift emission-line galaxies using the newly commissioned FourStar infrared camera at the 6.5 m Magellan telescope is presented.
Abstract: We present first results from a narrowband imaging program for intermediate-redshift emission-line galaxies using the newly commissioned FourStar infrared camera at the 6.5 m Magellan telescope. To enable prompt identification of Hα emitters, a pair of custom 1% filters, which sample low-airglow atmospheric windows at 1.19 μm and 2.10 μm, is used to detect both Hα and [O II] λ3727 emission from the same redshift volume at z = 2.2. Initial observations are taken over a 130 arcmin2 area in the CANDELS-COSMOS field. The exquisite image quality resulting from the combination of the instrument, telescope, and standard site conditions (~0.55'' FWHM) allows the 1.19 μm and 2.10 μm data to probe 3σ emission-line depths down to 1.0 × 10-17 erg s-1 cm-2 and 1.2 × 10-17 erg s-1 cm-2, respectively, in less than 10 hr of integration time in each narrow band. For Hα at z = 0.8 and z = 2.2, these fluxes correspond to observed star formation rates of ~0.3 and ~4 M⊙ yr-1, respectively. We find 122 sources with a 1.19 μm excess and 136 with a 2.10 μm excess, 41 of which show an excess in both bands. The dual-narrowband technique, as implemented here, is estimated to identify 80% of z = 2.2 Hα emitters in the narrowband excess population. With the most secure such sample obtained to date, we compute constraints on the faint-end slope of the z = 2.2 Hα luminosity function. Fitting of a pure power law gives α = -1.85 ± 0.31, which is steeper than other recent estimates based on coarser selection techniques, but consistent within the typically large uncertainties that currently characterize such measurements. Combining our LF points with those at higher luminosities from other work, the slope decreases to α = -1.58 ± 0.40. These "narrow-deep" FourStar observations have been obtained as part of the larger New Hα Survey, which will combine the data with "wide-shallow" imaging through a similar narrowband filter pair with NEWFIRM at the KPNO/CTIO 4 m telescopes, to enable study of both luminous (but rare) and faint emission-line galaxies in the intermediate-redshift universe.
TL;DR: In this article, the authors present empirical scaling relations for the significance of absorption features detected in medium-resolution, far-UV spectra obtained with the Cosmic Origins Spectrograph (COS).
Abstract: We present empirical scaling relations for the significance of absorption features detected in medium-resolution, far-UV spectra obtained with the Cosmic Origins Spectrograph (COS). These relations properly account for both the extended wings of the COS line-spread function and the non-Poissonian noise properties of the data, which we characterize for the first time, and predict limiting equivalent widths that deviate from the empirical behavior by ≤ 5% when the wavelength and Doppler parameter are in the ranges of λ = 1150-1750 A and b > 10 km s-1. We have tested a number of co-addition algorithms and find the noise properties of individual exposures to be closer to the Poissonian ideal than are co-added data in all cases. For unresolved absorption lines, limiting equivalent widths for co-added data are 6% larger than limiting equivalent widths derived from individual exposures with the same signal-to-noise ratio. This ratio scales with b-value for resolved absorption lines, with co-added data having a limiting equivalent width that is 25% larger than individual exposures when b ≈ 150 km s-1.
TL;DR: In this article, the authors describe an active antenna system for HF/VHF (long wavelength) radio astronomy that has been successfully deployed 256-fold as the first station (LWA1) of the planned Long Wavelength Array.
Abstract: We describe an "active" antenna system for HF/VHF (long wavelength) radio astronomy that has been successfully deployed 256-fold as the first station (LWA1) of the planned Long Wavelength Array. The antenna system, consisting of crossed dipoles, an active balun/preamp, a support structure, and a ground screen has been shown to successfully operate over at least the band from 20 MHz (15 m wavelength) to 80 MHz (3.75 m wavelength) with a noise figure that is at least 6 dB better than the Galactic background emission-noise temperature over that band. Thus, we met the goal to design and construct a compact, inexpensive, rugged, and easily assembled antenna system that can be deployed many-fold to form numerous large individual "stations" for the purpose of building a large, long wavelength synthesis array telescope for radio astronomical and ionospheric observations.
TL;DR: The MMT and Magellan infrared spectrograph (MMIRS) as discussed by the authors is a cryogenic multiple-slit Spectrograph operating in the wavelength range 0.9-2.4 μm.
Abstract: The MMT and Magellan infrared spectrograph (MMIRS) is a cryogenic multiple-slit spectrograph operating in the wavelength range 0.9-2.4 μm. The refractive optics of MMIRS offer a 6'.9 × 6'.9 field of view for imaging with a spatial resolution of 0.2 arcsec pixel-1 on a HAWAII-2 array. For spectroscopy, MMIRS can be used with long slits up to 6'.9 long, or with custom slit masks having slitlets distributed over a 4' × 6'.9 area. A range of dispersers offer spectral resolutions of 800-3000. MMIRS is designed to be used at the f/5 foci of the MMT or Magellan Clay 6.5 m telescopes. MMIRS was commissioned in 2009 at the MMT and has been in routine operation at the Magellan Clay Telescope since 2010. MMIRS is being used for a wide range of scientific investigations from exoplanet atmospheres to Lyα emitters.