Showing papers in "Publications of the Astronomical Society of the Pacific in 2010"
TL;DR: In this article, the authors present a general summary of factors that must be considered in order to achieve timing precisions ranging from 15 minutes to 1 μs, and provide software tools that, in principal, allow one to calculate BJDTDB to a precision of 1 µs for any target from anywhere on Earth or from any spacecraft.
Abstract: As the quality and quantity of astrophysical data continue to improve, the precision with which certain astrophysical events can be timed becomes limited not by the data themselves, but by the manner, standard, and uniformity with which time itself is referenced. While some areas of astronomy (most notably pulsar studies) have required absolute time stamps with precisions of considerably better than 1 minute for many decades, recently new areas have crossed into this regime. In particular, in the exoplanet community, we have found that the (typically unspecified) time standards adopted by various groups can differ by as much as a minute. Left uncorrected, this ambiguity may be mistaken for transit timing variations and bias eccentricity measurements. We argue that, since the commonly-used Julian Date, as well as its heliocentric and barycentric counterparts, can be specified in several time standards, it is imperative that their time standards always be reported when accuracies of 1 minute are required. We summarize the rationale behind our recommendation to quote the site arrival time, in addition to using BJDTDB, the Barycentric Julian Date in the Barycentric Dynamical Time standard for any astrophysical event. The BJDTDB is the most practical absolute time stamp for extraterrestrial phenomena, and is ultimately limited by the properties of the target system. We compile a general summary of factors that must be considered in order to achieve timing precisions ranging from 15 minutes to 1 μs. Finally, we provide software tools that, in principal, allow one to calculate BJDTDB to a precision of 1 μs for any target from anywhere on Earth or from any spacecraft.
865 citations
TL;DR: In this paper, the authors analyzed a sample of 1266 stars drawn from the California Planet Survey targets to determine the empirical functional form describing the likelihood of a star harboring a giant planet as a function of its mass and metallicity.
Abstract: Correlations between stellar properties and the occurrence rate of exoplanets can be used to inform the target selection of future planet-search efforts and provide valuable clues about the planet-formation process. We analyze a sample of 1266 stars drawn from the California Planet Survey targets to determine the empirical functional form describing the likelihood of a star harboring a giant planet as a function of its mass and metallicity. Our stellar sample ranges from M dwarfs with masses as low as 0.2 M_⊙ to intermediate-mass subgiants with masses as high as 1.9 M_⊙. In agreement with previous studies, our sample exhibits a planet-metallicity correlation at all stellar masses; the fraction of stars that harbor giant planets scales as f ∝ 10^(1.2[Fe/H]). We can rule out a flat metallicity relationship among our evolved stars (at 98% confidence), which argues that the high metallicities of stars with planets is not likely due to convective envelope “pollution.” Our data also rule out a constant planet occurrence rate for [Fe/H] < 0, indicating that giant planets continue to become rarer at sub-Solar metallicities. We also find that planet occurrence increases with stellar mass (f ∝ M_*), characterized by a rise from 3% around M dwarfs (0.5 M_⊙) to 14% around A stars (2 M_⊙), at Solar metallicity. We argue that the correlation between stellar properties and giant planet occurrence is strong supporting evidence of the core-accretion model of planet formation.
737 citations
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Cardiff University1, University of Nottingham2, Imperial College London3, University of California, Irvine4, University of Padua5, International School for Advanced Studies6, University of Edinburgh7, University of Hertfordshire8, Centre national de la recherche scientifique9, University of Paris-Sud10, Open University11, European Southern Observatory12, Ghent University13, Goddard Space Flight Center14, University of Bonn15, California Institute of Technology16, Aix-Marseille University17, ASTRON18, Pierre-and-Marie-Curie University19, University of Oxford20, University of Crete21, Rutherford Appleton Laboratory22, Max Planck Society23, Durham University24, University of Cambridge25, Spanish National Research Council26, Space Science Institute27, University of Rome Tor Vergata28, Seoul National University29, University of Paris30, University of Central Lancashire31, University of St Andrews32, University of British Columbia33, Queen Mary University of London34, Nagoya University35, University of Leicester36, Ames Research Center37, European Space Agency38, Leiden University39
TL;DR: The Herschel ATLAS project as discussed by the authors is the largest open-time key project that will be carried out on the Herschel Space Observatory, and it will survey 570 deg2 of the extragalactic sky, 4 times larger than all the other Herschel extragala surveys combined, in five far-infrared and submillimeter bands.
Abstract: The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg2 of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands.
610 citations
TL;DR: Hi-GAL as mentioned in this paper is an open-time key project of the Herschel Space Observatory, which aims to detect the earliest phases of the formation of molecular clouds and high-mass stars.
Abstract: Hi-GAL, the Herschel infrared Galactic Plane Survey, is an Open Time Key Project of the Herschel Space Observatory. It will make an unbiased photometric survey of the inner Galactic plane by mapping a 2° wide strip in the longitude range ∣l∣ < 60° in five wavebands between 70 μm and 500 μm. The aim of Hi-GAL is to detect the earliest phases of the formation of molecular clouds and high-mass stars and to use the optimum combination of Herschel wavelength coverage, sensitivity, mapping strategy, and speed to deliver a homogeneous census of star-forming regions and cold structures in the interstellar medium. The resulting representative samples will yield the variation of source temperature, luminosity, mass and age in a wide range of Galactic environments at all scales from massive YSOs in protoclusters to entire spiral arms, providing an evolutionary sequence for the formation of intermediate and high-mass stars. This information is essential to the formulation of a predictive global model of the role of environment and feedback in regulating the star-formation process. Such a model is vital to understanding star formation on galactic scales and in the early universe. Hi-GAL will also provide a science legacy for decades to come with incalculable potential for systematic and serendipitous science in a wide range of astronomical fields, enabling the optimum use of future major facilities such as JWST and ALMA.
579 citations
California Institute of Technology1, National Radio Astronomy Observatory2, Space Telescope Science Institute3, University of Arizona4, Complutense University of Madrid5, Carnegie Institution for Science6, Seoul National University7, University of Turku8, University of Oulu9, Max Planck Society10, Centre national de la recherche scientifique11, University of Alabama12, Vassar College13, IBM14, University of La Laguna15, University of California, Riverside16, National Research Council17
TL;DR: The Spitzer Survey of Stellar Structure in Galaxies (S^4G) as mentioned in this paper is a collection of 2331 galaxies using the Infrared Array Camera (IRAC) at 3.6 and 4.5 μm.
Abstract: The Spitzer Survey of Stellar Structure in Galaxies (S^4G) is an Exploration Science Legacy Program
approved for the Spitzer post–cryogenic mission. It is a volume-, magnitude-, and size-limited (d < 40 Mpc,
|b|> 30°,m_(Bcorr) 1') survey of 2331 galaxies using the Infrared Array Camera (IRAC) at 3.6 and
4.5 μm. Each galaxy is observed for 240 s and mapped to ≥ 1:5 × D_(25). The final mosaicked images have a typical
1 σ rms noise level of 0.0072 and 0:0093 MJy sr^-1 at 3.6 and 4.5 μm, respectively. Our azimuthally averaged surface
brightness profile typically traces isophotes at μ_(3.6μm (AB)(1σ) ~ 27 mag arcsec^(-2), equivalent to a stellar mass surface
density of ~1 M_⊙pc^(-2). S^4G thus provides an unprecedented data set for the study of the distribution of mass
and stellar structures in the local universe. This large, unbiased, and extremely deep sample of all Hubble types from
dwarfs to spirals to ellipticals will allow for detailed structural studies, not only as a function of stellar mass, but also
as a function of the local environment. The data from this survey will serve as a vital testbed for cosmological
simulations predicting the stellar mass properties of present-day galaxies. This article introduces the survey and
describes the sample selection, the significance of the 3.6 and 4.5 μm bands for this study, and the data collection
and survey strategies. We describe the S^4G data analysis pipeline and present measurements for a first set of galaxies,
observed in both the cryogenic and warm mission phases of Spitzer. For every galaxy we tabulate the galaxy
diameter, position angle, axial ratio, inclination at μ_(3.6μm)(AB) = 25:5, and 26:5 mag arcsec^(-2) (equivalent to
≈μ_B(AB) = 27:2 and 28:2 mag arcsec^(-2), respectively). These measurements will form the initial S^4G catalog
of galaxy properties. We also measure the total magnitude and the azimuthally averaged radial profiles of ellipticity,
position angle, surface brightness, and color. Finally, using the galaxy-fitting code GALFIT, we deconstruct each
galaxy into its main constituent stellar components: the bulge/spheroid, disk, bar, and nuclear point source, where
necessary. Together, these data products will provide a comprehensive and definitive catalog of stellar structures,
mass, and properties of galaxies in the nearby universe and will enable a variety of scientific investigations, some of
which are highlighted in this introductory S^4G survey paper.
557 citations
Space Telescope Science Institute1, Las Cumbres Observatory Global Telescope Network2, Aarhus University3, Katholieke Universiteit Leuven4, Université Paris-Saclay5, Yale University6, University of Sydney7, University of Birmingham8, University of Porto9, Royal Observatory of Belgium10, Los Alamos National Laboratory11, University of Vienna12, Iowa State University13, Hungarian Academy of Sciences14, University of Central Lancashire15, National Center for Atmospheric Research16, Konkoly Thege Miklós Astronomical Institute17, Spanish National Research Council18, Ames Research Center19, Goddard Space Flight Center20, Harvard University21, Fermilab22
TL;DR: The first 43 days of the Kepler asteroseismology program were reported in this paper, showing that the unique capabilities of Kepler in providing a revolutionary advance in stellar astrophysics are already well in evidence.
Abstract: .Asteroseismology involves probing the interiors of stars and quantifying their global properties, such as radius and age, through observations of normal modes of oscillation. The technical requirements for conducting asteroseismology include ultrahigh precision measured in photometry in parts per million, as well as nearly continuous time series over weeks to years, and cadences rapid enough to sample oscillations with periods as short as a few minutes. We report on results from the first 43 days of observations, in which the unique capabilities of Kepler in providing a revolutionary advance in asteroseismology are already well in evidence. The Kepler asteroseismology program holds intrinsic importance in supporting the core planetary search program through greatly enhanced knowledge of host star properties, and extends well beyond this to rich applications in stellar astrophysics.
487 citations
TL;DR: In this article, the effect of charge transfer efficiency (CTE) losses in images taken with the Wide Field Channel of the Advanced Camera for Surveys (ACS) was investigated.
Abstract: We use an empirical approach to characterize the effect of charge-transfer efficiency (CTE) losses in images taken with the Wide-Field Channel of the Advanced Camera for Surveys (ACS). The study is based on profiles of warm pixels in 168 dark exposures taken between 2009 September and October. The dark exposures allow us to explore charge traps that affect electrons when the background is extremely low. We develop a model for the readout process that reproduces the observed trails out to 70 pixels. We then invert the model to convert the observed pixel values in an image into an estimate of the original pixel values. We find that when we apply this image-restoration process to science images with a variety of stars on a variety of background levels, it restores flux, position, and shape. This means that the observed trails contain essentially all of the flux lost to inefficient CTE. The Space Telescope Science Institute is currently evaluating this algorithm with the aim of optimizing it and eventually providing enhanced data products. The empirical procedure presented here should also work for other epochs (e.g., pre-SM4), though the parameters may have to be recomputed for the time when ACS was operated at a higher temperature than the current -81°C. Finally, this empirical approach may also hold promise for other instruments, such as WFPC2, STIS, the ACS's HRC, and even WFC3/UVIS.
294 citations
TL;DR: The Herschel Reference Survey (HRS) as discussed by the authors is a key project of the Herschel guaranteed time key project and will be a benchmark study of dust in the nearby universe.
Abstract: The Herschel Reference Survey is a Herschel guaranteed time key project and will be a benchmark study of dust in the nearby universe. The survey will complement a number of other Herschel key projects including large cosmological surveys that trace dust in the distant universe. We will use Herschel to produce images of a statistically-complete sample of 323 galaxies at 250, 350, and 500 μm. The sample is volume-limited, containing sources with distances between 15 and 25 Mpc and flux limits in the K band to minimize the selection effects associated with dust and with young high-mass stars and to introduce a selection in stellar mass. The sample spans the whole range of morphological types (ellipticals to late-type spirals) and environments (from the field to the center of the Virgo Cluster) and as such will be useful for other purposes than our own. We plan to use the survey to investigate (i) the dust content of galaxies as a function of Hubble type, stellar mass, and environment; (ii) the connection between the dust content and composition and the other phases of the interstellar medium; and (iii) the origin and evolution of dust in galaxies. In this article, we describe the goals of the survey, the details of the sample and some of the auxiliary observing programs that we have started to collect complementary data. We also use the available multifrequency data to carry out an analysis of the statistical properties of the sample.
279 citations
TL;DR: In this paper, the authors presented synthetic magnitudes, spectral types, and distances for 2.4 million stars, derived from synthetic photometry of a library spectrum that best matches the Tycho2 BTVT, NOMAD RN, and 2MASS JHK2/S catalog magnitudes.
Abstract: We present fitted UBVRI - ZY and u'g'r'i'z' magnitudes, spectral types, and distances for 2.4 million stars, derived from synthetic photometry of a library spectrum that best matches the Tycho2 BTVT, NOMAD RN, and 2MASS JHK2/S catalog magnitudes. We present similarly synthesized multifilter magnitudes, types, and distances for 4.8 million stars with 2MASS and SDSS photometry to g < 16 within the Sloan survey region, for Landolt and Sloan primary standards, and for Sloan northern (photometric telescope) and southern secondary standards. The synthetic magnitude zero points for BTVT, UBVRI, ZVYV, JHK2/S, JHKMKO, Stromgren uvby, Sloan u'g'r'i'z', and ugriz are calibrated on 20 CALSPEC spectrophotometric standards. The UBVRI and ugriz zero points have dispersions of 1-3%, for standards covering a range of color from -0.3 < V - I < 4.6; those for other filters are in the range of 2-5%. The spectrally matched fits to Tycho2 stars provide estimated 1σ errors per star of ~0.2, 0.15, 0.12, 0.10, and 0.08 mag, respectively, in either UBVRI or u'g'r'i'z'; those for at least 70% of the SDSS survey region to g < 16 have estimated 1σ errors per star of ~0.2, 0.06, 0.04, 0.04, and 0.05 in u'g'r'i'z' or UBVRI. The density of Tycho2 stars, averaging about 60 stars per square degree, provides sufficient stars to enable automatic flux calibrations for most digital images with fields of view of 0.5° or more. Using several such standards per field, automatic flux calibration can be achieved to a few percent in any filter, at any air mass, in most workable observing conditions, to facilitate intercomparison of data from different sites, telescopes, and instruments.
219 citations
TL;DR: A review of the research on AM CVn stars covering the last 15 yr is given, and the outlook for future research is discussed in this article, where the relative importance of the three proposed birth channels: a low-mass white dwarf donor, a helium-star donor, or a highly evolved cataclysmic variable (CV) as a donor.
Abstract: AM CVn stars are the outcome of a fine-tuned binary star evolution pathway. They are helium-rich and their binary orbital periods are less than 65 minutes. They evolve through one or two common envelope (CE) events, which are difficult to model. Observations of AM CVn stars are important to understand the CE phase. Thanks to intensive observing campaigns, the number of AM CVn stars has increased from 5 to 25 during the last 15 yr. We have witnessed long photometric campaigns, time-resolved spectroscopy, UV and X-ray observations, and progress in modeling of the internal structure of donor and accretor stars, disk structure, disk atmosphere, and their evolution. Two possible new members of the AM CVn family have orbital periods of less than 10 minutes. For these, four different models have been proposed, including one without mass transfer, driven by electricity generated by the secondary star moving in the magnetic field of the primary. Short-period AM CVn stars are among the first possible detectable sources of low-frequency gravitational wave (GW) radiation. They are also possible progenitors of a Type Ia supernova (SN Ia) and subluminous explosions, and they can produce helium novae during their evolution. From systematic searches in the Sloan Digital Sky Survey, it has been possible to estimate population densities that can be tested against population synthesis models. One important question to investigate is the relative importance of the three proposed birth channels: a low-mass white dwarf donor, a helium-star donor, or a highly evolved cataclysmic variable (CV) as a donor. A review of the research on AM CVn stars covering the last 15 yr is given, and the outlook for future research is discussed.
186 citations
University of Chicago1, African Institute for Mathematical Sciences2, University of Cape Town3, University of Delhi4, University of Portsmouth5, University of Colorado Boulder6, Fermilab7, University of Toronto8, University of Oxford9, Rutgers University10, Argonne National Laboratory11, University of Geneva12, California Institute of Technology13, University of Sussex14, Mahatma Gandhi University15, Lawrence Berkeley National Laboratory16, University of California, Berkeley17, Johns Hopkins University18, University of Pennsylvania19, University of Copenhagen20, Stockholm University21, Carnegie Institution for Science22
TL;DR: The Supernova Photometric Classification Challenge (SNPhotCC) as mentioned in this paper was the first challenge for the classification of simulated supernovae (SNe), with types (Ia, Ibc and II) selected in proportion to their expected rates.
Abstract: We report results from the Supernova Photometric Classification Challenge (SNPhotCC), a publicly released mix of simulated supernovae (SNe), with types (Ia, Ibc, and II) selected in proportion to their expected rates The simulation was realized in the griz filters of the Dark Energy Survey (DES) with realistic observing conditions (sky noise, point-spread function, and atmospheric transparency) based on years of recorded conditions at the DES site Simulations of non-Ia-type SNe are based on spectroscopically confirmed light curves that include unpublished non-Ia samples donated from the Carnegie Supernova Project (CSP), the Supernova Legacy Survey (SNLS), and the Sloan Digital Sky Survey-II (SDSS-II) A spectroscopically confirmed subset was provided for training We challenged scientists to run their classification algorithms and report a type and photo-z for each SN Participants from 10 groups contributed 13 entries for the sample that included a host-galaxy photo-z for each SN and nine entries for the sample that had no redshift information Several different classification strategies resulted in similar performance, and for all entries the performance was significantly better for the training subset than for the unconfirmed sample For the spectroscopically unconfirmed subset, the entry with the highest average figure of merit for classifying SNe Ia has an efficiency of 096 and an SN Ia purity of 079 As a public resource for the future development of photometric SN classification and photo-z estimators, we have released updated simulations with improvements based on our experience from the SNPhotCC, added samples corresponding to the Large Synoptic Survey Telescope (LSST) and the SDSS-II, and provided the answer keys so that developers can evaluate their own analysis
TL;DR: In this article, a supersampled point-spread function of the low-resolution modules of the Spitzer Space Telescope was used to perform spectral extraction of a single source and of multiple sources within the slit.
Abstract: .We present new advances in the spectral extraction of pointlike sources adapted to the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. For the first time, we created a supersampled point-spread function of the low-resolution modules. We describe how to use the point-spread function to perform optimal extraction of a single source and of multiple sources within the slit. We also examine the case of the optimal extraction of one or several sources with a complex background. The new algorithms are gathered in a plug-in called AdOpt which is part of the SMART data analysis software.
TL;DR: Easy redshift as discussed by the authors is a tool developed within the VVDS project to help in red-shift measurement from optical spectra, which is an open-source program, freely downloadable from the Pandora Web Site.
Abstract: We present EZ (Easy redshift), a tool we have developed within the VVDS project to help in red- shift measurement from optical spectra. EZ has been designed with large spectroscopic surveys in mind, and in its development particular care has been given to the reliability of the results obtained in an automatic and unsupervised mode. Nevertheless, the possibility of running it interactively has been preserved, and a graphical user interface for results inspection has been designed. EZ has been successfully used within the VVDS project, as well as the zCosmos one. In this article we describe its architecture and the algorithms used, and evaluate its performances both on simulated and real data. EZ is an open-source program, freely downloadable from the Pandora Web Site. 1
TL;DR: In this paper, an ephemeris determined from the NASA EPOXI data was used to predict a transit event in an extant Spitzer Space Telescope 8 μm data set of the known M dwarf exoplanetary system GJ 436.
Abstract: We discovered evidence for a possible additional 0.75 R_⊕ transiting planet in the NASA EPOXI observations of the known M dwarf exoplanetary system GJ 436. Based on an ephemeris determined from the EPOXI data, we predicted a transit event in an extant Spitzer Space Telescope 8 μm data set of this star. Our subsequent analysis of those Spitzer data confirmed the signal of the predicted depth and at the predicted time, but we found that the transit depth was dependent on the aperture used to perform the photometry. Based on these suggestive findings, we gathered new warm Spitzer observations of GJ 436 at 4.5 μm spanning a time of transit predicted from the EPOXI and Spitzer 8 μm candidate events. The 4.5 μm data permit us to rule out a transit at high confidence, and we conclude that the earlier candidate transit signals resulted from correlated noise in the EPOXI and Spitzer 8 μm observations. In the course of this investigation, we developed a novel method for correcting the intrapixel sensitivity variations of the 3.6 and 4.5 μm channels of the Infrared Array Camera (IRAC) instrument. We demonstrate the sensitivity of warm Spitzer observations of M dwarfs to confirm sub-Earth-sized planets. Our analysis will inform similar work that will be undertaken to use warm Spitzer observations to confirm rocky planets discovered by the Kepler mission.
University of Manchester1, Iowa State University2, Hoffmann-La Roche3, Space Telescope Science Institute4, University of Missouri5, University of Virginia6, University of California, Berkeley7, University of Arizona8, Paris Diderot University9, Katholieke Universiteit Leuven10, California Institute of Technology11, Harvard University12, National Radio Astronomy Observatory13, Nagoya University14, University College London15, Imperial College London16, Keele University17, Max Planck Society18, Cornell University19, Johns Hopkins University20, Institut d'Astrophysique de Paris21, University of Toledo22, Space Science Institute23
TL;DR: The SAGE-Spec Spitzer Legacy program as discussed by the authors is a spectroscopic follow-up to the SAGE LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope.
Abstract: The SAGE-Spec Spitzer Legacy program is a spectroscopic follow-up to the SAGE-LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope. We present an overview of SAGE-Spec and some of its first results. The SAGE-Spec program aims to study the life cycle of gas and dust in the Large Magellanic Cloud and to provide information essential to the classification of the point sources observed in the earlier SAGE-LMC photometric survey. We acquired 224.6 h of observations using the infrared spectrograph and the spectral energy distribution (SED) mode of the Multiband Imaging Photometer for Spitzer. The SAGE-Spec data, along with archival Spitzer spectroscopy of objects in the Large Magellanic Cloud, are reduced and delivered to the community. We discuss the observing strategy, the specific data-reduction pipelines applied, and the dissemination of data products to the scientific community. Initial science results include the first detection of an extragalactic 21 mu m feature toward an evolved star and elucidation of the nature of disks around RV Tauri stars in the Large Magellanic Cloud. Toward some young stars, ice features are observed in absorption. We also serendipitously observed a background quasar, at a redshift of z approximate to 0.14, which appears to be hostless.
TL;DR: In this paper, the authors report precise Doppler measurements of seven subgiants from Keck Observatory and show that all seven stars show variability in their radial velocities consistent with planet-mass companions in Keplerian orbits.
Abstract: We report precise Doppler measurements of seven subgiants from Keck Observatory. All seven stars show variability in their radial velocities consistent with planet-mass companions in Keplerian orbits. The host stars have masses ranging from 1.1 ≤ M_*/M_⊙ ≤ 1.9, radii 3.4 ≤ R_*/R_⊙ ≤ 6.1, and metallicities -0.21 ≤ [Fe/H] ≤ +0.26. The planets are all more massive than Jupiter (MP sin i > 1 M_(Jup)) and have semimajor axes a > 1 AU. We present millimagnitude photometry from the T3 0.4 m APT at Fairborn Observatory for five of the targets. Our monitoring shows these stars to be photometrically stable, further strengthening the interpretation of the observed radial velocity variability. The orbital characteristics of the planets thus far discovered around former A-type stars are very different from the properties of planets around dwarf stars of spectral type F, G, and K, and suggests that the formation and migration of planets is a sensitive function of stellar mass. Three of the planetary systems show evidence of long-term, linear trends indicative of additional distant companions. These trends, together with the high planet masses and increased occurrence rate, indicate that A-type stars are very promising targets for direct-imaging surveys.
TL;DR: In this article, the authors compare near-term and future ground-based capabilities with high-contrast imaging modes of the James Webb Space Telescope (JWST) for finding gas giant planets around nearby young stars and the closest M stars.
Abstract: .High-contrast imaging can find and characterize gas giant planets around nearby young stars and the closest M stars, complementing radial velocity and astrometric searches by exploring orbital separations inaccessible to indirect methods. Ground-based coronagraphs are already probing within 25 AU of nearby young stars to find objects as small as ∼3 MJup∼3 MJup. This paper contrasts near-term and future ground-based capabilities with high-contrast imaging modes of the James Webb Space Telescope (JWST). Monte Carlo modeling reveals that JWST can detect planets with masses as small as 0.2 MJup0.2 MJup across a broad range of orbital separations. We present new calculations for planet brightness as a function of mass and age for specific JWST filters and extending to 0.1 MJup0.1 MJup.
TL;DR: In this article, a high-resolution, low minimum sample height sonic radar (SODAR) called Snodar was used to characterize the Antarctic bound-ary thickness and structure.
Abstract: The domes, or local elevation maxima, on the Antarctic plateau provide a unique opportunity for ground-based astronomy in that the turbulent boundary layer is so thin that a telescope on a small tower can be in the free atmosphere, i.e., the portion of the atmosphere in which the turbulence is decoupled from the effect of the Earth's surface. There, it can enjoy a free atmosphere which itself appears to offer superior conditions to that of temperate sites. This breaks the problem of characterizing the turbulence at Antarctic plateau sites into two separate tasks: determining the variability, distribution and thickness of the boundary layer, and characterizing the free atmosphere. In this article we tackle the first of these tasks using a high-resolution, low minimum sample height sonic radar (SODAR) called Snodar that has been specifically designed to characterize the Antarctic bound- ary thickness and structure. Snodar delivers a vertical resolution of 0.9 m, with a minimum sampling height of 8 m. Snodar sampled the first 180 m of the atmosphere with 0.9 m resolution every 10 s at Dome A, Antarctica between 2009 February 4 and 2009 August 18. The median thickness of the boundary layer over this period was 13.9 m, with the 25th and 75th percentiles at 9.7 m and 19.7 m, respectively. The data collected from Dome A also show that, while the boundary layer can be stable for several hundred hours at a time, it can also be highly variable and must be sampled on the time scale of minutes to properly characterize its thickness.
TL;DR: In this paper, the first direct measurements of the terahertz atmospheric transmission above Dome A, the highest point on the Antarctic plateau at an elevation of 4.1 km, were presented.
Abstract: We present the first direct measurements of the terahertz atmospheric transmission above Dome A, the highest point on the Antarctic plateau at an elevation of 4.1 km. The best-quartile atmospheric transmission during the Austral winter is 80% at a frequency of 661 GHz (453 μm), corresponding to a precipitable water vapor column of 0.1 mm. Daily averages as low as 0.025 mm were observed. The Antarctic atmosphere is very stable, and excellent observing conditions generally persist for many days at a time. The exceptional conditions over the high Antarctic plateau open new far-infrared spectral windows to ground-based observation. These windows contain important spectral-line diagnostics of star formation and the interstellar medium which would otherwise only be accessible to airborne or space telescopes. Online material: color figures
Harvard University1, Curtin University2, University of Melbourne3, Commonwealth Scientific and Industrial Research Organisation4, Massachusetts Institute of Technology5, California Institute of Technology6, Australian National University7, University of California, San Diego8, Raman Research Institute9, Vassar College10, University of California, Santa Barbara11, University of Washington12, University of Western Australia13
TL;DR: The Murchison Wide-Field Array (MWA) is a low-frequency radio telescope, currently under construction, intended to search for the spectral signature of the epoch of reionization (EOR) and to probe the structure of the solar corona as mentioned in this paper.
Abstract: The Murchison Wide-Field Array (MWA) is a low-frequency radio telescope, currently under construction, intended to search for the spectral signature of the epoch of reionization (EOR) and to probe the structure of the solar corona. Sited in western Australia, the full MWA will comprise 8192 dipoles grouped into 512 tiles and will be capable of imaging the sky south of 40° declination, from 80 MHz to 300 MHz with an instantaneous field of view that is tens of degrees wide and a resolution of a few arcminutes. A 32 station prototype of the MWA has been recently commissioned and a set of observations has been taken that exercise the whole acquisition and processing pipeline. We present Stokes I, Q, and U images from two ~4 hr integrations of a field 20° wide centered on Pictoris A. These images demonstrate the capacity and stability of a real-time calibration and imaging technique employing the weighted addition of warped snapshots to counter extreme wide-field imaging distortions.
TL;DR: In this article, the effects of charge transfer inefficiency (CTI) during CCD readout on the demanding galaxy shape measurements required by studies of weak gravitational lensing were examined. But their results were limited to the p-channel CCDs.
Abstract: We examine the effects of charge transfer inefficiency (CTI) during CCD readout on the demanding
galaxy shape measurements required by studies of weak gravitational lensing. We simulate a CCD readout with CTI
such as that caused by charged particle radiation damage in space-based detectors. We verify our simulations on real
data from fully depleted p-channel CCDs that have been deliberately irradiated in a laboratory. We show that only
charge traps with time constants of the same order as the time between row transfers during readout affect galaxy shape measurements. We simulate deep astronomical images and the process of CCD readout, characterizing the effects of
CTI on various galaxy populations. Our code and methods are general and can be applied to any CCDs, once the
density and characteristic release times of their charge trap species are known. We baseline our study around p-channel
CCDs that have been shown to have charge transfer efficiency up to an order of magnitude better than several models
of n-channel CCDs designed for space applications. We predict that for galaxies furthest from the readout registers,
bias in the measurement of galaxy shapes, Δe, will increase at a rate of (2.65 ± 0.02) × 10^(-4) yr^(-1) at L2 for accumulated
radiation exposure averaged over the solar cycle. If uncorrected, this will consume the entire shape measurement
error budget of a dark energy mission surveying the entire extragalactic sky within about 4 yr of accumulated
radiation damage. However, software mitigation techniques demonstrated elsewhere can reduce this by a factor of
~10, bringing the effect well below mission requirements. This conclusion is valid only for the p-channel CCDs we
have modeled; CCDs with higher CTI will fare worse and may not meet the requirements of future dark energy
missions. We also discuss additional ways in which hardware could be designed to further minimize the impact
of CTI.
TL;DR: In this article, the authors present a framework for the analysis of direct detection planet-finding missions using space telescopes, which is coupled with a decision-modeling algorithm that allows us to automatically generate mission time lines with simple mission rules that lead to an optimized science yield.
Abstract: We present a framework for the analysis of direct detection planet-finding missions using space telescopes. This framework generates simulations of complete missions, with varying populations of planets, to produce ensembles of mission simulations, which are used to calculate distributions of mission science yields. We describe the components of a mission simulation, including the complete description of an arbitrary planetary system, the description of a planet-finding instrument, and the modeling of a target system observation. These components are coupled with a decision-modeling algorithm that allows us to automatically generate mission time- lines with simple mission rules that lead to an optimized science yield. Along with the details of our implementation of this algorithm, we discuss validation techniques and possible future refinements. We apply this analysis technique to four mission concepts whose common element is a 4 m diameter telescope aperture: an internal pupil mapping coronagraph with two different inner working angles, an external occulter, and the THEIA XPC multiple distance occulter. The focus of this study is to determine the ability of each of these designs to achieve one of their most difficult mission goals-the detection and characterization of Earthlike planets in the habitable zone. We find that all four designs are capable of detecting on the order of five Earthlike planets within a 5 yr mission, even if we assume that only one out of every 10 stars has such a planet. The designs do differ significantly in their ability to characterize the planets they find. Along with science yield, we also analyze fuel usage for the two occulter designs, and discuss the strengths and weaknesses of each of the mission concepts.
TL;DR: In this article, the authors used the Blue Channel Spectrograph (BCS) on the MMT telescope to obtain spectra to the atmospheric cutoff of quasars previously known to show at least one absorption system at z > 1.
Abstract: With the Blue Channel Spectrograph (BCS) on the MMT telescope, we have obtained spectra to the atmospheric cutoff of quasars previously known to show at least one absorption system at z > 1.6 with very strong metal lines. We refer to these absorbers as candidate metal-strong damped Lyα systems (cMSDLAs), the majority of which were culled from the Sloan Digital Sky Survey. The BCS/MMT spectra yield precise estimates of the H i column densities (NHI) of the systems through Voigt profile analysis of their Lyα transitions. Nearly all of the cMSDLAs (41/43) satisfy the NHI criterion of DLAs, 1020.3 atoms cm-2. As a population, these systems have systematically higher NHI values than DLAs chosen randomly from quasar sightlines. Combining our NHI measurements with previously measured metal column densities, we estimate metallicities for the MSDLAs. These systems have significantly higher values than randomly selected DLAs; at z ≈ 2, the MSDLAs show a median metallicity [M/H] ≈ -0.67 that is 0.6 dex higher than a corresponding control sample. This establishes MSDLAs as having among the most metal-rich gas in the high z universe. Our measurements extend the observed correlation between Si ii 1526 equivalent width and the gas metallicity to higher values. If interpreted as a mass-metallicity relation, this implies the MSDLAs are the high-mass subset of the DLA population. We demonstrate that dust in the MSDLAs reddens their background quasars, with a median shift in the spectral slope of δα = 0.29. Assuming an SMC extinction law, this implies a median reddening EB-V ≈ 0.025 mag and visual extinction AV ≈ 0.076 mag. The latter quantity yields a dust-to-gas ratio of log(AV/NHI) ≈ -22.0, very similar to estimation for the SMC. Future studies of MSDLAs offer the opportunity to study the extinction, nucleosynthesis, and kinematics of the most chemically evolved, gas-rich galaxies at high z.
TL;DR: In this paper, a multiband optical (U, B, V, I) photometry of the Carina dwarf spheroidal galaxy is presented, based on more than 4000 individual CCD images from three different ground-based telescopes.
Abstract: We present deep, accurate, and homogeneous multiband optical (U, B, V, I) photometry of the Carina dwarf spheroidal galaxy, based on more than 4000 individual CCD images from three different ground-based telescopes. Special attention was given to the photometric calibration, and the precision for the B, V, and I bands is generally better than 0.01 mag. We have performed detailed comparisons in the V, B - V, and V, B - I color-magnitude diagrams (CMDs) between Carina and three old, metal-poor Galactic globular clusters (GGCs, M53, M55, M79). We find that only the more metal-poor GCs (M55, [Fe/H] = -1.85; M53, [Fe/H] = -2.02 dex) provide a good match with the Carina giant branch. We have performed a similar comparison in the V, V - I CMD with three intermediate-age clusters (IACs) of the Small Magellanic Cloud (Kron 3, NGC 339, Lindsay 38). We find that the color extent of the subgiant branch (SGB) of the two more metal-rich IACs (Kron 3, [Fe/H] = -1.08; NGC339, [Fe/H] = -1.36 dex) is smaller than the range among Carina's intermediate-age stars. Moreover, the slope of the RGB of these two IACs is shallower than the slope of the Carina RGB. However, the ridge line of the more metal-poor IAC (Lindsay 38, [Fe/H] = -1.59 dex) agrees quite well with the Carina intermediate-age stars. These findings indicate that Carina's old stellar population is metal-poor and appears to have a limited spread in metallicity (Δ[Fe/H] = 0.2-0.3 dex). The Carina's intermediate-age stellar population can hardly be more metal-rich than Lindsay 38, and its spread in metallicity also appears modest. We also find that the synthetic CMD constructed assuming a metallicity spread of 0.5 dex for the intermediate-age stellar component predicts evolutionary features not supported by observations. In particular, red clump stars should attain colors that are redder than red giant stars, but this is not seen. These results are at odds with recent spectroscopic investigations suggesting that Carina stars cover a broad range in metallicity (Δ[Fe/H] ~ 1-2 dex). We also present a new method to estimate the metallicity of complex stellar systems using the difference in color between the red clump and the middle of the RR Lyrae instability strip. The observed colors of Carina's evolved stars indicate a metallicity of [Fe/H] = -1.70 ± 0.19 dex, which agrees quite well with spectroscopic measurements.
TL;DR: The results of the characterization of precipitable water vapor in the atmospheric column carried out in the context of identifying potential sites for the deployment of the Thirty Meter Telescope (TMT) are pre- sented as discussed by the authors.
Abstract: The results of the characterization of precipitable water vapor in the atmospheric column carried out in the context of identifying potential sites for the deployment of the Thirty Meter Telescope (TMT) are pre- sented. Prior to starting the dedicated field campaign to look for a suitable site for the TMT, candidate sites were selected based on a climatology report utilizing satellite data that considered water vapor as one of the study vari- ables. These candidate sites are all of tropical or subtropical location at geographic areas dominated by high-pressure systems. The results of the detailed on-site study, spanning a period of 4 yr, from early 2004 until the end of 2007, confirmed the global mean statistics provided in the previous reports based on satellite data, and also confirmed that all the candidate sites are exceptionally good for astronomy research. At the locations of these sites, the atmospheric conditions are such that the higher the elevation of the site, the drier it gets. However, the data analysis shows that during winter, San Pedro Martir, a site about 230 m lower in elevation than Armazones, is drier than the Armazones site. This finding is attributed to the fact that Earth's atmosphere is largely unsaturated, leaving room for regional variability; it is useful in illustrating the relevance of in situ atmospheric studies for understanding the global and seasonal variability of potential sites for astronomy research. The results also show that winter and spring are the driest seasons at all of the tested sites, with Mauna Kea (in the northern hemisphere) and Tolonchar (in the southern hemisphere) being the tested sites with the lowest precipitable water vapor in the atmospheric column and the highest atmospheric transmission in the near and mid-infrared bands. This is the tenth article in a series discussing the TMT site-testing project.
TL;DR: This work presents a versatile CS-based image reconstruction framework called SparseRI, an interesting alternative to the CLEAN algorithm, which permits a wide choice of different regularizers for interferometric image reconstruction.
Abstract: In radio interferometry, information about a small region of the sky is obtained in the form of samples in the Fourier transform domain of the desired image Since this sampling is usually incomplete, the missing information has to be reconstructed using additional assumptions about the image The emerging field of compressed sensing provides a promising new approach to this type of problem that is based on the supposed sparsity of natural images in some transform domain We present a versatile CS-based image reconstruction framework called SparseRI, an interesting alternative to the CLEAN algorithm, which permits a wide choice of different regularizers for interferometric image reconstruction The performance of our method is evaluated on simulated data as well as on actual radio interferometry measurements from the VLA, showing that our algorithm is able to reproduce the main features of the test sources The proposed method is a first step toward an alternative reconstruction approach that may be able to avoid typical artifacts like negative flux regions, to work with large fields of view and noncoplanar baselines, to avoid the gridding process, and, in particular, to produce results not far from those achievable by human-assisted processing in CLEAN through an entirely automatic algorithm, making it especially well suited for automated processing pipelines
TL;DR: Polarization gratings (PGs) have been recently developed for ultraefficient liquid crystal displays, nonmechanical optical beam steering, and telecommunication devices at optical and near-infrared wavelengths (0.4-2.0 μm).
Abstract: Polarization gratings (PGs) have been recently been developed for ultraefficient liquid crystal displays, nonmechanical optical beam steering, and telecommunication devices at optical and near-infrared wavelengths (0.4–2.0 μm). A PG simultaneously acts as both a spectroscopic and polarimetric disperser for circularly polarized light. With the use of a quarter-wave retarder (or analog) to convert linearly to circularly polarized light, these devices can be used as linear polarimetric analyzers. PGs offer high throughput and high levels of birefringence and can currently be constructed inexpensively to diameters of 150 mm, and development projects are in progress to double that size. In this article we report on the characterization of a PG sample at mid-infrared wavelengths (2–40 μm), including the birefringence, throughput, spectral response, and cold cycling survivability. We discuss these devices in the context of astronomical polarimetry, especially as the polarimetric components for a conceptual study of a SOFIA-based polarimeter.
TL;DR: In this paper, the statistical properties of the spectral kurtosis estimator were investigated and all moments of its probability density function were analytically determined, which provided a means to determine the tail probabilities of the estimator that are essential to defining the thresholds for RFI discrimination.
Abstract: Spectral kurtosis (SK) is a statistical approach for detecting and removing radio-frequency interference (RFI) in radio astronomy data. In this article, the statistical properties of the SK estimator are investigated and all moments of its probability density function are analytically determined. These moments provide a means to determine the tail probabilities of the estimator that are essential to defining the thresholds for RFI discrimination. It is shown that, for a number of accumulated spectra M≥24, the first SK standard moments satisfy the conditions required by a Pearson type IV probability density function (pdf), which is shown to accurately reproduce the observed distributions. The cumulative function (CF) of the Pearson type IV is then found, in both analytical and numerical forms, suitable for accurate estimation of the tail probabilities of the SK estimator. This same framework is also shown to be applicable to the related time-domain kurtosis (TDK) estimator, whose pdf corresponds to Pearson type IV when the number of time-domain samples is M≥46. The pdf and CF also are determined for this case.
TL;DR: In this paper, the presence of a planet with an estimated mass of 2.1 M/(Jup) orbiting the M3V star HIP 79431 was detected in Doppler surveys of M dwarfs.
Abstract: Doppler observations from Keck Observatory reveal the presence of a planet with M sin i of 2.1 M_(Jup) orbiting the M3V star HIP 79431. This is the sixth giant planet to be detected in Doppler surveys of M dwarfs and it is one of the most massive planets discovered around an M dwarf star. The planet has an orbital period of 111.7 days and an orbital eccentricity of 0.29. The host star is metal rich, with an estimated [Fe/H] = +0.4. This is the first planet to emerge from our new survey of 1600 M-to-K dwarf stars.
TL;DR: In 2008, the twenty-fourth Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to Dome A, the highest point on the Antarctic plateau as mentioned in this paper.
Abstract: In 2008 January the twenty-fourth Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to Dome A, the highest point on the Antarctic plateau. CSTAR consists of four 14.5 cm optical telescopes, each with a different filter (g, r, i, and open) and has a 4.5° × 4.5° field of view (FOV). It operates robotically as part of the Plateau Observatory, PLATO, with each telescope taking an image every ~30 s throughout the year whenever it is dark. During 2008, CSTAR 1 performed almost flawlessly, acquiring more than 0.3 million i-band images for a total integration time of 1728 hr during 158 days of observations. For each image taken under good sky conditions, more than 10,000 sources down to ~16th magnitude could be detected. We performed aperture photometry on all the sources in the field to create the catalog described herein. Since CSTAR has a fixed pointing centered on the south celestial pole (decl. = -90°), all the sources within the FOV of CSTAR were monitored continuously for several months. The photometric catalog can be used for studying any variability in these sources, and for the discovery of transient sources such as supernovae, gamma-ray bursts, and minor planets.