Browsing by Subject "methods : data analysis"

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Finding Ultracool Brown Dwarfs With MegaCam On CFHT: Method And First Results
(2008-06) Delorme, P.; Willott, C. J.; Forveille, T.; Delfosse, X.; Reyle, C.; Bertin, E.; Albert, L.; Artigau, E.; Robin, A. C.; Allard, F.; Doyon, R.; Hill, G. J.; Hill, G. J.
Aims. We present the first results of a wide field survey for cool brown dwarfs with the MegaCam camera on the CFHT telescope, the Canada-France Brown Dwarf Survey, hereafter CFBDS. Our objectives are to find ultracool brown dwarfs and to constrain the field-brown dwarf mass function thanks to a larger sample of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i' and z' images using optimised psf-fitting within Source Extractor, and follow them up with pointed near-infrared imaging on several telescopes. Results. We have so far analysed over 350 square degrees and found 770 brown dwarf candidates brighter than z'(AB) = 22.5. We currently have J-band photometry for 220 of these candidates, which confirms 37% as potential L or T dwarfs. Some are among the reddest and farthest brown dwarfs currently known, including an independent identification of the recently published ULAS J003402.77-005206.7 and the discovery of a second brown dwarf later than T8, CFBDS J005910.83-011401.3. Infrared spectra of three T dwarf candidates confirm their nature, and validate the selection process. Conclusions. The completed survey will discover similar to 100 T dwarfs and similar to 500 L dwarfs or M dwarfs later than M8, approximately doubling the number of currently known brown dwarfs. The resulting sample will have a very well-defined selection function, and will therefore produce a very clean luminosity function.
First-Year Spectroscopy For The Sloan Digital Sky Survey-II Supernova Survey
(2008-05) Zheng, Chen; Romani, Roger W.; Sako, Masao; Marriner, John; Bassett, Bruce; Becker, Andrew; Choi, Changsu; Cinabro, David; DeJongh, Fritz; Depoy, Darren L.; Dilday, Ben; Doi, Mamoru; Frieman, Joshua A.; Garnavich, Peter M.; Hogan, Craig J.; Holtzman, Jon; Im, Myungshin; Jha, Saurabh; Kessler, Richard; Konishi, Kohki; Lampeitl, Hubert; Marshall, Jennifer L.; McGinnis, David; Miknaitis, Gajus; Nichol, Robert C.; Prieto, Jose L.; Riess, Adam G.; Richmond, Michael W.; Schneider, Donald P.; Smith, Mathew; Takanashi, Naohiro; Tokita, Kouichi; Van der Heyden, Kurt; Yasuda, Naoki; Assef, Roberto J.; Barentine, John; Bender, Ralf; Blandford, Roger D.; Bremer, Malcolm; Brewington, Howard; Collins, Chris A.; Crotts, Arlin; Dembicky, Jack; Eastman, Jason; Edge, Alastair; Elson, Ed; Eyler, Michael E.; Filippenko, Alexi V.; Foley, Ryan J.; Frank, Stephan; Goobar, Ariel; Harvanek, Michael; Hopp, Ulrich; Ihara, Yutaka; Kahn, Steven; Ketzeback, William; Kleinman, Scott J.; Kollatschny, Wolfram; Krzesinski, Jurek; Leloudas, Giorgos; Long, Daniel C.; Lucey, John; Malanushenko, Elena; Malanushenko, Viktor; McMillan, Russet J.; Morgan, Christopher W.; Morokuma, Tomoki; Nitta, Atsuko; Ostman, Linda; Pan, Kaike; Romer, A. Kathy; Saurage, Gabrelle; Schlesinger, Katie; Snedden, Stephanie A.; Sollerman, Jasper; Stritzinger, Maximillian; Watson, Linda C.; Watters, Shannon; Wheeler, J. Craig; York, Donald; Barentine, John; Wheeler, J. Craig
This paper presents spectroscopy of supernovae (SNe) discovered in the first season of the Sloan Digital Sky Survey-II SN Survey. This program searches for and measures multi-band light curves of SNe in the redshift range z = 0.05-0.4, complementing existing surveys at lower and higher redshifts. Our goal is to better characterize the SN population, with a particular focus on SNe Ia, improving their utility as cosmological distance indicators and as probes of dark energy. Our SN spectroscopy program features rapid-response observations using telescopes of a range of apertures, and provides confirmation of the SN and host-galaxy types as well as precise redshifts. We describe here the target identification and prioritization, data reduction, redshift measurement, and classification of 129 SNe Ia, 16 spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first season. We also describe our efforts to measure and remove the substantial host-galaxy contamination existing in the majority of our SN spectra.
GEMS : Galaxy Fitting Catalogs and Testing Parametric Galaxy Fitting Codes : GALFIT and GIM2D
(2007-10) Haeussler, Boris; McIntosh, Daniel H.; Barden, Marco; Bell, Eric F.; Rix, Hans-Walter; Borch, Andrea; Beckwith, Steven V. W.; Caldwell, John A. R.; Heymans, Catherine; Jahnke, Knud; Jogee, Shardha; Koposov, Sergey E.; Meisenheimer, Klaus; Sanchez, Sebastian F.; Somerville, Rachel S.; Wisotzki, Lutz; Wolf, Christian; Caldwell, John A. R.
In the context of measuring the structures of intermediate-redshift galaxies with HST ACS surveys, we tune, test, and compare two widely used fitting codes (GALFIT and GIM2D) for fitting single-component Sersic models to both simulated and real galaxy data. Our study focuses on the GEMS survey with the sensitivity of typical HST survey data, and we include our final catalog of fit results for all 41,495 objects detected in GEMS. Using simulations, we find that fitting accuracy depends sensitively on galaxy profile shape. Exponential disks are well fit and have small measurement errors, whereas fits to de Vaucouleurs profiles show larger uncertainties owing to the large amount of light at large radii. Both codes provide reliable fits with little systematic error for galaxies with effective surface brightnesses brighter than that of the sky; the formal uncertainties returned by these codes significantly underestimate the true uncertainties (as estimated using the simulations). We find that GIM2D suffers significant systematic errors for spheroids with close companions owing to the difficulty of effectively masking out neighboring galaxy light; there appears to be no work-around to this important systematic in GIM2D's current implementation. While this crowding error affects only a small fraction of galaxies in GEMS, it must be accounted for in the analysis of deeper cosmological images or of more crowded fields with GIM2D. In contrast, GALFIT results are robust to the presence of neighbors because it can simultaneously fit the profiles of multiple companions as well as the galaxy of interest. We find GALFIT's robustness to nearby companions and factor of greater than or similar to 20 faster runtime speed are important advantages over GIM2D for analyzing large HST ACS data sets.
The Milky Way Tomography With SDSS. II. Stellar Metallicity
(2008-09) Ivezic, Zeljko; Sesar, Branimir; Juric, Mario; Bond, Nicholas; Dalcanton, Julianne; Rockosi, Constance M.; Yanny, Brian; Newberg, Heidi J.; Beers, Timothy C.; Prieto, Carlos Allende; Wilhelm, Ron; Lee, Young Sun; Sivarani, Thirupathi; 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; Munn, Jeffrey A.; Pier, Jeffrey R.; Quinn, Tom; Hawley, Suzanne; Anderson, Scott; Kiuchi, Furea; Chen, Alex; Bushong, James; Sohi, Harkirat; Haggard, Daryl; Kimball, Amy; Barentine, John; Brewington, Howard; Harvanek, Mike; Kleinman, Scott; Krzesinski, Jurek; Long, Dan; Nitta, Atsuko; Snedden, Stephanie; Lee, Brian; Harris, Hugh; Brinkmann, Jonathan; Schneider, Donald P.; York, Donald G.; Prieto, Carlos Allende
Using effective temperature and metallicity derived from SDSS spectra for similar to 60,000 F- and G-type main-sequence stars (0.2 < g - r < 0.6), we develop polynomial models for estimating these parameters from the SDSS u - g and g - r colors. These photometric estimates have similar error properties as those determined from SDSS spectra. We apply this method to SDSS photometric data for over 2 million F/G stars and measure the unbiased metallicity distribution for a complete volume-limited sample of stars at distances between 500 pc and 8 kpc. The metallicity distribution can be exquisitely modeled using two components with a spatially varying number ratio, which correspond to disk and halo. The two components also possess the kinematics expected for disk and halo stars. The metallicity of the halo component is spatially invariant, while the median disk metallicity smoothly decreases with distance from the Galactic plane from -0.6 at 500 pc to -0.8 beyond several kiloparsecs. The absence of a correlation between metallicity and kinematics for disk stars is in a conflict with the traditional decomposition in terms of thin and thick disks. We detect coherent substructures in the kinematics-metallicity space, such as the Monoceros stream, which rotates faster than the LSR, and has a median metallicity of [Fe/H] = -0.95, with an rms scatter of only similar to 0.15 dex. We extrapolate our results to the performance expected from the Large Synoptic Survey Telescope (LSST) and estimate that LSST will obtain metallicity measurements accurate to 0.2 dex or better, with proper-motion measurements accurate to similar to 0.5 mas yr(-1), for about 200 million F/G dwarf stars within a distance limit of similar to 100 kpc (g < 23.5).