Browsing by Subject "methods: data analysis"

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The Bolocam Galactic Plane Survey. XII. Distance Catalog Expansion Using Kinematic Isolation Of Dense Molecular Cloud Structures With (Co)-C-13(1-0)
(2015-01) Ellsworth-Bowers, Timothy P.; Rosolowsky, Erik; Glenn, Jason; Ginsburg, Adam; Evans, Neal J.; Battersby, Cara; Shirley, Yancy L.; Svoboda, Brian; Evans, Neal J.
We present an expanded distance catalog for 1710 molecular cloud structures identified in the Bolocam Galactic Plane Survey (BGPS) version 2, representing a nearly threefold increase over the previous BGPS distance catalog. We additionally present a new method for incorporating extant data sets into our Bayesian distance probability density function (DPDF) methodology. To augment the dense-gas tracers (e.g., HCO+ (3-2), NH3(1,1)) used to derive line-of-sight velocities for kinematic distances, we utilize the Galactic Ring Survey (GRS) (CO)-C-13(1-0) data to morphologically extract velocities for BGPS sources. The outline of a BGPS source is used to select a region of the GRS (CO)-C-13 data, along with a reference region to subtract enveloping diffuse emission, to produce a line profile of (CO)-C-13 matched to the BGPS source. For objects with a HCO+ (3-2) velocity, approximate to 95% of the new O-13C(1-0) velocities agree with that of the dense gas. A new prior DPDF for kinematic distance ambiguity (KDA) resolution, based on a validated formalism for associating molecular cloud structures with known objects from the literature, is presented. We demonstrate this prior using catalogs of masers with trigonometric parallaxes and Hii regions with robust KDA resolutions. The distance catalog presented here contains well-constrained distance estimates for 20% of BGPS V2 sources, with typical distance uncertainties less than or similar to 0.5 kpc. Approximately 75% of the well-constrained sources lie within 6 kpc of the Sun, concentrated in the Scutum-Centaurus arm. Galactocentric positions of objects additionally trace out portions of the Sagittarius, Perseus, and Outer arms in the first and second Galactic quadrants, and we also find evidence for significant regions of interarm dense gas.
The Bolocam Galactic Plane Survey: Survey Description and Data Reduction
(2011-01) Aguirre, James E.; Ginsburg, Adam G.; Dunham, Miranda K.; Drosback, Meredith M.; Bally, John; Battersby, Cara; Bradley, Eric Todd; Cyganowski, Claudia; Dowell, Darren; Evans, Neal J., II; Glenn, Jason; Harvey, Paul; Rosolowsky, Erik; Stringfellow, Guy S.; Walawender, Josh; Williams, Jonathan P.; Dunham, Miranda K.; Evans, Neal J., II
We present the Bolocam Galactic Plane Survey (BGPS), a 1.1 mm continuum survey at 33 '' effective resolution of 170 deg(2) of the Galactic Plane visible from the northern hemisphere. The BGPS is one of the first large area, systematic surveys of the Galactic Plane in the millimeter continuum without pre-selected targets. The survey is contiguous over the range-10.5 <= l <= 90.5, vertical bar b vertical bar <= 0.5. Toward the Cygnus X spiral arm, the coverage was flared to vertical bar b vertical bar <= 1.5 for 75.5 <= l <= 87.5. In addition, cross-cuts to vertical bar b vertical bar <= 1.5 were made at l = 3, 15, 30, and 31. The total area of this section is 133 deg(2). With the exception of the increase in latitude, no pre-selection criteria were applied to the coverage in this region. In addition to the contiguous region, four targeted regions in the outer Galaxy were observed: IC1396 (9 deg(2), 97.5 <= l <= 100.5, 2.25 <= b <= 5.25), a region toward the Perseus Arm (4 deg(2) centered on l = 111, b = 0 near NGC 7538), W3/4/5 (18 deg(2), 132.5 <= l <= 138.5), and Gem OB1 (6 deg(2), 187.5 <= l <= 193.5). The survey has detected approximately 8400 clumps over the entire area to a limiting non-uniform 1s noise level in the range 11-53 mJy beam(-1) in the inner Galaxy. The BGPS source catalog is presented in a previously published companion paper. This paper details the survey observations and data reduction methods for the images. We discuss in detail the determination of astrometric and flux density calibration uncertainties and compare our results to the literature. Data processing algorithms that separate astronomical signals from time-variable atmospheric fluctuations in the data timestream are presented. These algorithms reproduce the structure of the astronomical sky over a limited range of angular scales and produce artifacts in the vicinity of bright sources. Based on simulations, we find that extended emission on scales larger than about 5'.9 is nearly completely attenuated (>90%) and the linear scale at which the attenuation reaches 50% is 3'.8. Comparison with other millimeter-wave data sets implies a possible systematic offset in flux calibration, for which no cause has been discovered. This presentation serves as a companion and guide to the public data release (http://irsa.ipac.caltech.edu/Missions/bolocam.html) through NASA's Infrared Processing and Analysis Center (IPAC) Infrared Science Archive (IRSA). New data releases will be provided through IPAC-IRSA with any future improvements in the reduction. The BGPS provides a complementary long-wavelength spectral band for the ongoing ATLASGAL and Herschel-SPIRE surveys, and an important database and context for imminent observations with SCUBA-2 and ALMA.
The Chemical Abundances Of Stars In The Halo (CASH) Project. II. A Sample Of 14 Extremely Metal-Poor Stars
(2011-11) Hollek, Julie K.; Frebel, Anna; Roederer, Ian U.; Sneden, Christopher; Shetrone, Matthew; Beers, Timothy C.; Kang, Sung-Ju; Thom, Christopher; Hollek, Julie K.; Sneden, Christopher; Shetrone, Matthew
We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R similar to 15,000) and corresponding high-resolution (R similar to 35,000) Magellan Inamori Kyocera Echelle spectra. The stars span a metallicity range from [Fe/H] from -2.9 to -3.9, including four new stars with [Fe/H] < -3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]< -3. We also find four neutron-capture-enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H] less than or similar to -3.0) of the brightest stars included in CASH and are used to calibrate a newly developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire similar to 500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manual analysis from a high-resolution spectrum.
The Mass of the Black Hole in Arp 151 from Bayesian Modeling of Reverberation Mapping Data
(2011-06) Brewer, Brendon J.; Treu, Tommaso; Pancoast, Anna; Barth, Aaron J.; Bennert, Vardha N.; Bentz, Misty C.; Filippenko, Alexei V.; Greene, Jenny E.; Malkan, Matthew A.; Woo, Jong-Hak; Greene, Jenny E.
Supermassive black holes are believed to be ubiquitous at the centers of galaxies. Measuring their masses is extremely challenging yet essential for understanding their role in the Formation and evolution of cosmic structure. We present a direct measurement of the mass of a black hole in an active galactic nucleus (Arp 151) based on the motion of the gas responsible for the broad emission lines. By analyzing and modeling spectroscopic and photometric time series, we find that the gas is well described by a disk or torus with an average radius of 3.99 +/- 1.25 light days and an opening angle of 68.9(-17.2)(+21.4) deg, viewed at an inclination angle of 67.8 +/- 7.8 deg (that is, closer to face-on than edge-on). The black hole mass is inferred to be 10(6.51 +/- 0.28) M-circle dot. The method is fully general and can be used to determine the masses of black holes at arbitrary distances, enabling studies of their evolution over cosmic time.
The Milky Way Tomography With SDSS. III. Stellar Kinematics
(2010-06) Bond, Nicholas A.; Ivezic, Zeljko; Sesar, Branimir; Juric, Mario; Munn, Jeffrey A.; Kowalski, Adam; Loebman, Sarah; Roskar, Rok; Beers, Timothy C.; Dalcanton, Julianne; Rockosi, Constance M.; Yanny, Brian; Newberg, Heidi J.; Prieto, Carlos Allende; Wilhelm, Ron; Lee, Young Sun; Sivarani, Thirupathi; Majewski, Steven R.; Norris, John E.; Bailer-Jones, Coryn A. L.; Fiorentin, Paola Re; Schlegel, David; Uomoto, Alan; Lupton, Robert H.; Knapp, Gillian R.; Gunn, James E.; Covey, Kevin R.; Smith, J. Allyn; Miknaitis, Gajus; Doi, Mamoru; Tanaka, Masayuki; Fukugita, Masataka; Kent, Steve; Finkbeiner, Douglas; Quinn, Tom R.; Hawley, Suzanne; Anderson, Scott; Kiuchi, Furea; Chen, Alex; Bushong, James; Sohi, Harkirat; Haggard, Daryl; Kimball, Amy; McGurk, Rosalie; Barentine, John; Brewington, Howard; Harvanek, Mike; Kleinman, Scott; Krzesinski, Jurek; Long, Dan; Nitta, Atsuko; Snedden, Stephanie; Lee, Brian; Pier, Jeffrey R.; Harris, Hugh; Brinkmann, Jonathan; Schneider, Donald P.; Prieto, Carlos Allende
We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r < 20 and proper-motion measurements derived from Sloan Digital Sky Survey (SDSS) and POSS astrometry, including similar to 170,000 stars with radial-velocity measurements from the SDSS spectroscopic survey. Distances to stars are determined using a photometric-parallax relation, covering a distance range from similar to 100 pc to 10 kpc over a quarter of the sky at high Galactic latitudes (|b| > 20 degrees). We find that in the region defined by 1 kpc < Z < 5 kpc and 3 kpc < R < 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (< 100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.
The Planet Search Programme At The Eso Ces And Harps IV. The Search For Jupiter Analogues Around Solar-Like Stars
(2013-04) Zechmeister, M.; Kurster, M.; Endl, M.; Lo Curto, G.; Hartman, H.; Nilsson, H.; Henning, T.; Hatzes, A. P.; Cochran, W. D.; Endl, M.; Cochran, W. D.
Context. In 1992 we began a precision radial velocity survey for planets around solar-like stars with the Coude Echelle Spectrograph and the Long Camera (CES LC) at the 1.4m telescope in La Silla (Chile) resulting in the discovery of the planet iota Hor b. We have continued the survey with the upgraded CES Very Long Camera (VLC) and the HARPS spectrographs, both at the 3.6m telescope, until 2007. Aims. In this paper we present additional radial velocities for 31 stars of the original sample with higher precision. The observations cover a time span of up to 15 years and permit a search for Jupiter analogues. Methods. The survey was carried out with three different instruments/instrument configurations using the iodine absorption cell and the ThAr methods for wavelength calibration. We combine the data sets and perform a joint analysis for variability, trends, and periodicities. We compute Keplerian orbits for companions and detection limits in case of non-detections. Moreover, the HARPS radial velocities are analysed for correlations with activity indicators (CaII H&K and cross-correlation function shape). Results. We achieve a long-term RV precision of 15 m/s (CES+LC, 1992-1998), 9 m/s (CES+VLC, 1999-2006), and 2.8 m/s (HARPS, 2003-2009, including archive data), respectively. This enables us to confirm the known planetary signals in iota Hor and HR 506 as well as the three known planets around HR 3259. A steady RV trend for epsilon Ind A can be explained by a planetary companion and calls for direct imaging campaigns. On the other hand, we find previously reported trends to be smaller for beta Hyi and not present for alpha Men. The candidate planet epsilon Eri b was not detected despite our better precision. Also the planet announced for HR 4523 cannot be confirmed. Long-term trends in several of our stars are compatible with known stellar companions. We provide a spectroscopic orbital solution for the binary HR 2400 and refined solutions for the planets around HR 506 and iota Hor. For some other stars the variations could be attributed to stellar activity, as e.g. the magnetic cycle in the case of HR 8323. Conclusions. The occurrence of two Jupiter-mass planets in our sample is in line with the estimate of 10% for the frequency of giant planets with periods smaller than 10 yr around solar-like stars. We have not detected a Jupiter analogue, while the detections limits for circular orbits indicate at 5 AU a sensitivity for minimum mass of at least 1M(Jup) (2M(Jup)) for 13% (61%) of the stars.
Radial Velocity Observations And Light Curve Noise Modeling Confirm That Kepler-91B Is A Giant Planet Orbiting A Giant Star
(2015-02) Barclay, Thomas; Endl, Michael; Huber, Daniel; Foreman-Mackey, Daniel; Cochran, William D.; MacQueen, Phillip J.; Rowe, Jason F.; Quintana, Elisa V.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.
Kepler-91b is a rare example of a transiting hot Jupiter around a red giant star, providing the possibility to study the formation and composition of hot Jupiters under different conditions compared to main-sequence stars. However, the planetary nature of Kepler-91b, which was confirmed using phase-curve variations by Lillo-Box et al., was recently called into question based on a re-analysis of Kepler data. We have obtained ground-based radial velocity observations from the Hobby-Eberly Telescope and unambiguously confirm the planetary nature of Kepler-91b by simultaneously modeling the Kepler and radial velocity data. The star exhibits temporally correlated noise due to stellar granulation which we model as a Gaussian Process. We hypothesize that it is this noise component that led previous studies to suspect Kepler-91b to be a false positive. Our work confirms the conclusions presented by Lillo-Box et al. that Kepler-91b is a 0.73 +/- 0.13 M-Jup planet orbiting a red giant star.
Searches For High-Frequency Variations In The B-8 Solar Neutrino Flux At The Sudbury Neutrino Observatory
(2010-02) Aharmim, B.; Ahmed, S. N.; Anthony, A. E.; Barros, N.; Beier, E. W.; Bellerive, A.; Beltran, B.; Bergevin, M.; Biller, S. D.; Boudjemline, K.; Boulay, M. G.; Burritt, T. H.; Cai, B.; Chan, Y. D.; Chauhan, D.; Chen, M.; Cleveland, B. T.; Cox, G. A.; Dai, X.; Deng, H.; Detwiler, J.; DiMarco, M.; Doe, P. J.; Doucas, G.; Drouin, P. L.; Duba, C. A.; Duncan, F. A.; Dunford, M.; Earle, E. D.; Elliott, S. R.; Evans, H. C.; Ewan, G. T.; Farine, J.; Fergani, H.; Fleurot, F.; Ford, R. J.; Formaggio, J. A.; Gagnon, N.; Goon, J. T. M.; Graham, K.; Guillian, E.; Habib, S.; Hahn, R. L.; Hallin, A. L.; Hallman, E. D.; Harvey, Paul J.; Hazama, R.; Heintzelman, W. J.; Heise, J.; Helmer, R. L.; Hime, A.; Howard, C.; Howe, M. A.; Huang, M.; Jamieson, B.; Jelley, N. A.; Keeter, K. J.; Klein, J. R.; Kormos, L. L.; Kos, M.; Kraus, C.; Krauss, C. B.; Kutter, T.; Kyba, C. C. M.; Law, J.; Lawson, I. T.; Lesko, K. T.; Leslie, J. R.; Levine, I.; Loach, J. C.; MacLellan, R.; Majerus, S.; Mak, H. B.; Maneira, J.; Martin, R.; McCauley, N.; McDonald, A. B.; McGee, S.; Miller, M. L.; Monreal, B.; Monroe, J.; Morissette, B.; Nickel, B. G.; Noble, A. J.; O'Keeffe, H. M.; Oblath, N. S.; Gann, G. D. O.; Oser, S. M.; Ott, R. A.; Peeters, S. J. M.; Poon, A. W. P.; Prior, G.; Reitzner, S. D.; Rielage, K.; Robertson, B. C.; Robertson, R. G. H.; Schwendener, M. H.; Secrest, J. A.; Seibert, S. R.; Simard, O.; Sinclair, D.; Skensved, P.; Sonley, T. J.; Stonehill, L. C.; Tesic, G.; Tolich, N.; Tsui, T.; Tunnell, C. D.; Van Berg, R.; VanDevender, B. A.; Virtue, C. J.; Wall, B. L.; Waller, D.; Tseung, H. W. C.; Wark, D. L.; Watson, P. J. S.; West, N.; Wilkerson, J. F.; Wilson, J. R.; Wouters, J. M.; Wright, A.; Yeh, M.; Zhang, F.; Zuber, K.; Anthony, A. E.; Huang, M.; Klein, J. R.; Seibert, S. R.
We have performed three searches for high-frequency signals in the solar neutrino flux measured by the Sudbury Neutrino Observatory, motivated by the possibility that solar g-mode oscillations could affect the production or propagation of solar B-8 neutrinos. The first search looked for any significant peak in the frequency range 1-144 day(-1), with a sensitivity to sinusoidal signals with amplitudes of 12% or greater. The second search focused on regions in which g-mode signals have been claimed by experiments aboard the Solar and Heliospheric Observatory satellite, and was sensitive to signals with amplitudes of 10% or greater. The third search looked for extra power across the entire frequency band. No statistically significant signal was detected in any of the three searches.
The SEGUE Stellar Parameter Pipeline. III. Comparison With High-Resolution Spectroscopy Of SDSS/SEGUE Field Stars
(2008-11) Prieto, Carlos Allende; Sivarani, Thirupathi; Beers, Timoth C.; Lee, Young Sun; Koesterke, Lars; Shetrone, Matthew; Sneden, Christopher; Lambert, David L.; Wilhelm, Ronald; Rockosi, Constance M.; Lai, David K.; Yanny, Brian; Ivans, Inese I.; Johnson, Jennifer A.; Aoki, Wako; Bailer-Jones, Coryn A. L.; Fiorentin, Paola Re; Koesterke, Lars; Shetrone, Matthew D.; Sneden, Christopher; Lambert, David L.
We report high-resolution spectroscopy of 125 field stars previously observed as part of the Sloan Digital Sky Survey and its program for Galactic studies, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). These spectra are used to measure radial velocities and to derive atmospheric parameters, which we compare with those reported by the SEGUE Stellar Parameter Pipeline (SSPP). The SSPP obtains estimates of these quantities based on SDSS ugriz photometry and low-resolution (R similar to 2000) spectroscopy. For F- and G-type stars observed with high signal-to-noise ratios (S/Ns), we empirically determine the typical random uncertainties in the radial velocities, effective temperatures, surface gravities, and metallicities delivered by the SSPP to be 2.4 km s(-1), 130 K (2.2%), 0.21 dex, and 0.11 dex, respectively, with systematic uncertainties of a similar magnitude in the effective temperatures and metallicities. We estimate random errors for lower S/N based on numerical simulations.
Toward Early-Warning Detection Of Gravitational Waves From Compact Binary Coalescence
(2012-04) Cannon, Kipp; Cariou, Romain; Chapman, Adrian; Crispin-Ortuzar, Mireia; Fotopoulos, Nickolas; Frei, Melissa; Hanna, Chad; Kara, Erin; Keppel, Drew; Liao, Laura; Privitera, Stephen; Searle, Antony; Singer, Leo; Weinstein, Alan; Frei, Melissa
Rapid detection of compact binary coalescence (CBC) with a network of advanced gravitational-wave detectors will offer a unique opportunity for multi-messenger astronomy. Prompt detection alerts for the astronomical community might make it possible to observe the onset of electromagnetic emission from CBC. We demonstrate a computationally practical filtering strategy that could produce early-warning triggers before gravitational radiation from the final merger has arrived at the detectors.
The VIRUS-P Exploration Of Nearby Galaxies (VENGA): Survey Design, Data Processing, And Spectral Analysis Methods
(2013-05) Blanc, Guillermo A.; Weinzirl, Tim; Song, Mimi M.; Heiderman, Amanda; Gebhardt, Karl; Jogee, Shardha; Evans, Neal J.; van den Bosch, Remco C. E.; Luo, Rongxin; Drory, Niv; Fabricius, Maximilian; Fisher, David; Hao, Lei; Kaplan, Kyle; Marinova, Irina; Vutisalchavakul, Nalin; Yoachim, Peter; Weinzirl, Tim; Song, Mimi M.; Heiderman, Amanda; Gebhardt, Karl; Jogee, Shardha; Evans, Neal J.
We present the survey design, data reduction, and spectral fitting pipeline for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies. Targets span a wide range in Hubble type, star formation activity, morphology, and inclination. The VENGA data cubes have 5 ''.6 FWHM spatial resolution, similar to 5 angstrom FWHM spectral resolution, sample the 3600 angstrom-6800 angstrom range, and cover large areas typically sampling galaxies out to similar to 0.7R(25). These data cubes can be used to produce two-dimensional maps of the star formation rate, dust extinction, electron density, stellar population parameters, the kinematics and chemical abundances of both stars and ionized gas, and other physical quantities derived from the fitting of the stellar spectrum and the measurement of nebular emission lines. To exemplify our methods and the quality of the data, we present the VENGA data cube on the face-on Sc galaxy NGC 628 (a.k.a. M 74). The VENGA observations of NGC 628 are described, as well as the construction of the data cube, our spectral fitting method, and the fitting of the stellar and ionized gas velocity fields. We also propose a new method to measure the inclination of nearly face-on systems based on the matching of the stellar and gas rotation curves using asymmetric drift corrections. VENGA will measure relevant physical parameters across different environments within these galaxies, allowing a series of studies on star formation, structure assembly, stellar populations, chemical evolution, galactic feedback, nuclear activity, and the properties of the interstellar medium in massive disk galaxies.