%ADASS_PROCEEDINGS_FORM%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % \documentclass[11pt,twoside]{article} % Leave intact \usepackage{adassconf} % If you have the old LaTeX 2.09, and not the current LaTeX2e, comment % out the \documentclass and \usepackage lines above and uncomment % the following: %\documentstyle[11pt,twoside,adassconf]{article} \begin{document} % Leave intact %----------------------------------------------------------------------- % Paper ID Code %----------------------------------------------------------------------- % Enter the proper paper identification code. The ID code for your % paper is the session number associated with your presentation as % published in the official conference proceedings. You can % find this number locating your abstract in the printed proceedings % that you received at the meeting or on-line at the conference web % site; the ID code is the letter/number sequence proceeding the title % of your presentation. % % This will not appear in your paper; however, it allows different % papers in the proceedings to cross-reference each other. Note that % you should only have one \paperID, and it should not include a % trailing period. % \paperID{P2-7} %% Corrected! %%%% ID=P2-7 %----------------------------------------------------------------------- % Paper Title %----------------------------------------------------------------------- % Enter the title of the paper. % \title{A Comparison of Large All-Sky Catalogs} %----------------------------------------------------------------------- % Authors of Paper %----------------------------------------------------------------------- % Enter the authors followed by their affiliations. The \author and % \affil commands may appear multiple times as necessary. List each % author by giving the first name or initials first followed by the % last name. Authors with the same affiliations should grouped % together. % % Try to limit the front matter to no more than three \author % commands. Group authors with the same affiliations. Too many % \author commands fills the first page of the paper with little % actual text. \author{D.\ J.\ Mink, W.\ R.\ Brown, M.\ J.\ Kurtz} \affil{Smithsonian Astrophysical Observatory, Cambridge, MA 02138} %----------------------------------------------------------------------- % Contact Information %----------------------------------------------------------------------- % This information will not appear in the paper but will be used by % the editors in case you need to be contacted concerning your % submission. Enter your name as the contact along with your email % address. \contact{Doug Mink} \email{dmink@cfa.harvard.edu} %----------------------------------------------------------------------- % Author Index Specification %----------------------------------------------------------------------- % Specify how each author name should appear in the author index. The % \paindex{ } should be used to indicate the primary author, and the % \aindex for all other co-authors. You MUST use the following % syntax: % % SYNTAX: \aindex{LASTNAME, F. M.} % % where F is the first initial and M is the second initial (if % used). This guarantees that authors that appear in multiple papers % will appear only once in the author index. \paindex{Mink, D. J.} \aindex{Brown, W. R.} \aindex{Kurtz, M. J.} %----------------------------------------------------------------------- % Author list for page header %----------------------------------------------------------------------- % Please supply a list of author last names for the page header. in % one of these formats: % % EXAMPLES: % \authormark{LASTNAME} % \authormark{LASTNAME1 \& LASTNAME2} % \authormark{LASTNAME1, LASTNAME2, ... \& LASTNAMEn} % \authormark{LASTNAME et al.} % % Use the "et al." form in the case of seven or more authors, or if % the preferred form is too long to fit in the header. \authormark{Mink, Brown, \& Kurtz} %----------------------------------------------------------------------- % Subject Index keywords %----------------------------------------------------------------------- % Enter up to 6 keywords describing your paper. These will NOT be % printed as part of your paper; however, they will be used to % generate the subject index for the proceedings. There is no % standard list; however, you can consult the indices for past ADASS % proceedings (http://iraf.noao.edu/ADASS/adass.html). \keywords{catalogs, world coordinate systems, image: astrometry} %----------------------------------------------------------------------- % Abstract %----------------------------------------------------------------------- % Type abstract in the space below. Consult the User Guide and Latex % Information file for a list of supported macros (e.g. for typesetting % special symbols). Do not leave a blank line between \begin{abstract} % and the start of your text. \begin{abstract} % Leave intact % Accurate positions are needed to compare observations of objects made % at various wavelengths, such as are to be found in the Virtual Observatory. % New instruments for ground-based observing, such as multi-fiber spectrographs, % also need very accurate positions for objects fainter than those already % catalogued. Recent large catalogs have revolutionized our ability to do astrometry with CCD images. The recently published FITS World Coordinate System standard has provided a standard way of parameterizing that astrometry, and the WCSTools and SExtractor software packages allow the automation of the ``plate-fitting" process. % As part of a survey to be conducted with one of these new spectrographs, we We have amassed 1728 15$\arcmin \times 30\arcmin$ CCD images of a portion of the northern sky. After matching image point sources to objects in each of the catalogs and fitting world coordinate systems to them using the IMWCS program, we find mean residuals between observed and catalog star positions of between 0$\farcs$09 and 0$\farcs$25 for the latest catalogs. \end{abstract} %----------------------------------------------------------------------- % Main Body %----------------------------------------------------------------------- % Place the text for the main body of the paper here. You should use % the \section command to label the various sections; use of % \subsection is optional. Significant words in section titles should % be capitalized. Sections and subsections will be numbered % automatically. \section{Introduction} In the last few years, several motivations for acquiring sub-arcsecond astrometry of faint astronomical sources have arisen. Surveys and studies of specific objects at radio and X-ray wavelengths require exact optical or infrared positions to identify optical counterparts. Small aperture spectroscopes such as the 300-fiber MMT Hectospec require input positions better than a half arcsecond. The usual method of acquiring positions for faint, uncatalogued objects is to match the brighter stars in a CCD image to one of the deep catalogs which have been developed over the past 20 years by the Space Telescope Science Institute, the U.S. Naval Observatory, and the 2 Micron All Sky Survey. Table 1 shows the history of those large catalogs. At the same time, standards and software for associating image pixels with sky positions as world coordinate systems have been developed, culminating in two papers (Greisen \& Calabretta 2002, Calabretta \& Greisen 2002) and a software package which utilizes Calabretta's WCSLIB with real images (Mink 1997, Mink 1999, Mink 2002). As more and more optical images were matched to catalogs, the question of the accuracy of the positions of objects in the catalogs arose. We set out to compare how well various catalogs fit a large set of images. \begin{table} \begin{center} \caption{Growing Astronomical Catalogs \label{P2-7:T2.7-tbl-1}} \scriptsize \begin{tabular}{clcl} \tableline \tableline Year &Catalog &Number of Sources &Reference\nl \tableline 1989 &HST Guide Star Catalog (GSC I) &25,541,952 &Lasker et al. 1990 \nl 1996 &USNO-A1.0 Catalog &488,006,860 &Monet 1996 \nl 1998 &USNO-A2.0 Catalog &526,280,881 &Monet 1998 \nl 2001 &GSC II Catalog (2.2.01) &998,402,801 &McLean et al. 2000 \nl 2002 &USNO-B1.0 Catalog &1,036,366,767 &Monet et al. 2003 \nl 2003 &2MASS Point Source Catalog &470,992,970 &Cutri et al. 2003 \nl 2003 &USNO UCAC2 Catalog &48,366,996 &Zacharias et al. 2000\nl \tableline \end{tabular} \end{center} \end{table} \section{Data and Analysis} As part of the CfA Century Survey of galaxies (Geller et al. 1997), 1728 15 by 30 arcminute CCD images of a portion of the northern sky over the north galactic pole were taken as 216 exposures by the 8-detector, one-degree-square MOSAIC camera (Muller et al. 1998) on the KPNO 0.9 m telescope in 1998 December and 1999 January and processed as described in Brown et al. 2001. A correction was made for distortion across the wide field and a world coordinate system was fit to objects in the images found by SExtractor (Bertin \& Arnouts 1998) using WCSTools and the GSC-I catalog. The resulting image catalogs, with image coordinates and approximate right ascension and declination, became the raw data for our study. The uniformity of the images and the fact that they cover a portion of the sky well away from the dense star fields of the galactic plane made them ideal for automatic star matching. Unix shell scripts written for each catalog set up an initial FITS header for each of the 1728 images with the center being the mean position of the objects found in that image. The WCSTools imwcs program was then run on each image. The IMWCS program fits the same number of brightest catalog objects and brightest image objects limited by whichever there were fewer of; with these wide field images, the number of catalog objects in the field was usually the limit. The IMWCS program fit all eight parameters of the FITS WCS tangent plane projection to all of the catalog-image matches in the field. The program made three additional iterations per image following an intial fit. The second fit used the refined parameters which might have changed the position and size of the catalog section to be matched. In the two final passes, the tolerance in the catalog-image match was reduced by half each time to eliminate both bad matches and objects whose catalog positions did not match their actual positions. The goodness of a fit for an image is judged by the mean radial offset between the position of the objects in the image mapped to sky coordinates through the fit world coordinate system and the catalog position of the closest object, which is almost always within one arcsecond. \section{Results} The means of the individual image offsets were used to compare how well each catalog matched the sky as captured by our 1728 CCD images. The GSC-I was used as a baseline, despite the fact that it matched 25 or more stars in only 353 of the 1728 images. Figure 1 shows the distribution of mean Catalog-Image positions in arcseconds. Table 2 shows how many catalog stars were found in each images as a range and an average, how many catalog stars were fit to image stars, as a range and an average for each catalog and the range of mean (Observed-Catalog) radial offsets per image, and the mean and standard deviation of that mean for the entire data set. \begin{figure} \epsscale{.50} \plotone{P2-7_f1a.eps} \plotone{P2-7_f1b.eps} \plotone{P2-7_f1c.eps} \plotone{P2-7_f1d.eps} \plotone{P2-7_f1e.eps} \plotone{P2-7_f1f.eps} \caption{Distribution of image-catalog radial offsets.} \label{P2.7-fig-1} \end{figure} \begin{table}[h] \caption{Fits of Various Catalogs to 1728 Images. \label{P2.7-tbl-3}} \begin{center}\scriptsize \begin{tabular} {lcrrrrr} \tableline \tableline Catalog & \multicolumn{2}{c}{Catalog Stars} & \multicolumn{2}{c}{Matches fit} & \multicolumn{2}{c}{Image-Catalog (arcsec)} \nl &Range &Mean &Range &Mean &Range &Mean(Sigma) \nl \tableline GSC-I &26-61 &35.78 &25-64 &34.16 &0.168-0.654 &0.321(0.085) \nl USNO-A2.0 &119-454 &258.52 &78-353 &189.10 &0.301-0.457 &0.368(0.024) \nl GSC-II &90-752 &226.73 &87-378 &179.16 &0.123-0.343 &0.196(0.043) \nl 2MASS PSC &93-365 &171.06 &86-331 &153.26 &0.154-0.347 &0.220(0.024) \nl B1.0/id=2 &136-1125 &586.50 &51-661 &418.47 &0.182-0.523 &0.267(0.030) \nl B1.0/id=3 &136-957 &528.38 &62-653 &382.16 &0.181-0.479 &0.251(0.029) \nl B1.0/id=4 &136-654 &365.13 &116-555 &309.98 &0.155-0.430 &0.223(0.023) \nl B1.0/id=5 &109-409 &227.89 &98-375 &205.14 &0.136-0.326 &0.192(0.021) \nl UCAC2 &40-72 &51.52 &40-69 &48.80 &0.054-0.159 &0.091(0.015) \nl \tableline \end{tabular} \end{center} \end{table} The GSC-I based on plates from the 1980's does better than the USNO-A2.0 which is based on plates from the 1950's, probably due to the motions of stars in the intervening years, though the shorter exposures of the GSC-I may also have given better centers. The more recent GSC-II, 2MASS PSC, and USNO-B1.0 catalogs all are based on the Tycho-2 astrometric reference catalog (H\o g, et al. 2000), and give similar results. When the USNO-B1.0 gave worse results than expected, it was filtered by the number of plates (POSS I red and blue, POSS II red and blue, and N) on which the object was found. Thus the most recent catalogs all cluster around 0$\farcs$2 mean offset. Only 303 images were fit to the recently-released UCAC2 catalog which covers our field, but it is incomplete, so the automatic matching algorithm does not work perfectly. The mean offset was 0$\farcs$1, tightly clustered as the standard deviation and Figure 1 show, half that of the other catalogs. This shows that detector nonlinearity is not an issue above 0$\farcs$1, at least for these CCDs, and that there is room for improvement in the astrometry of current deep all sky catalogs. % Finally, we have a little acknowledgments section. \acknowledgments This project makes use of several publicly available catalogs. The 2MASS PSC is from the Two Micron All Sky Survey, a joint project of the University of Massachusetts and IPAC at Caltech, funded by NASA and the NSF. The GSC-II is a joint project of the Space Telescope Science Institute, operated by AURA for NASA under contract NAS5-26555 and the Osservatorio Astronomico di Torino, which is supported by the Italian Council for Research in Astronomy, with additional support is provided by ESO, ST-ECF, the International GEMINI project, and ESA's Astrophysics Division. The GSC-I was produced at the Space Telescope Science Institute under U.S. Government grants based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The USNO A and B-1.0 catalogs were provided by Dave Monet and Steve Levine of the U.S. Naval Observatory at Flagstaff on 21 CDROMs and one 128-gigabyte disk drive, respectively. A beta version of the UCAC2 and a good discussion of limiting factors in CCD astrometry were kindly provided by Norbert Zacharias of the U.S. Naval Observatory at Flagstaff. % That's the end of the main body of the paper. Now we will have some % back matter. % %----------------------------------------------------------------------- % References %----------------------------------------------------------------------- % Now comes the reference list. Since we typed out the citations ourselves, % the reference list is enclosed in a "references" environment. Each % new reference begins with a \reference command which sets up the proper % indentation. Typography that may be required in the reference list by % the editorial staff must be included by the author. % % Observe the "standard" order for bibliographic material: author name(s), % publication year, journal name, volume, and page number for articles. % Some journal names are available as macros; see the package % instructions for a listing of which ones have been "macro-ized". % % There is no need to engage in any other typographic manipulation. % % List your references below within the reference environment % (i.e. between the \begin{references} and \end{references} tags). % Each new reference should begin with a \reference command which sets % up the proper indentation. Observe the following order when listing % bibliographical information for each reference: author name(s), % publication year, journal name, volume, and page number for % articles. Note that many journal names are available as macros; see % the User Guide for a listing "macro-ized" journals. % % Note the following are some of the tricks that can be used: % % o \& is used to format an ampersand symbol (&). % o \'e and \`e puts an accent agu and accent grave, respectively, % over the letter e. See the User Guide for details on % formatting special characters. % o "\ " after a period prevents LaTeX from interpreting the period % as an end of a sentence. % o \aj is a macro that expands to "Astron. J." See the User Guide % for a full list of journal macros % o \adassviii is a macro that expands to the full title, editor, % and publishing information for the ADASS VIII conference % proceedings. Such macros are defined for ADASS conferences I % through X. % o When referencing a paper in the current volume, use the % \adassviii and \paperref macros. The argument to \paperref is % the paper ID code for the paper you are referencing. See the % note in the "Paper ID Code" section above for details on how to % determine the paper ID code for the paper you reference. % \vspace*{-2ex} %% TO AVOID last ref. on next page \begin{references} \vspace*{-1ex} %% TO AVOID last ref. on next page \reference Bertin, E. \& Arnouts, S. 1998, \aaps 117, 393 \reference Brown, W. R. et al. 2001, \aj, 122, 714 \reference Calabretta, M. R. \& Greisen, E. W. 2002, \aap, 395, 1077 \reference Cutri, et al. 2003, VizieR On-line Data Catalog: II/246. \reference Geller, M. J., et al. 1997, \aj, 114, 2205 \reference Greisen, E. \& Calabretta, M. 2002, \aap, 395, 1061 \reference H\o g, E., et al. 2000, \aap 355, L27 %%% added FO \reference Lasker, B. M., Sturch, C. R., McLean, B. J., Russell, J. L., Jenkner, H., \& Shara, M. M. 1990, \aj, 99, 2019 \reference McLean, B. J., Greene, G. R., Lattanzi, M. G., Pirenne, B. 2000, \adassix, 145 \reference Mink, D. J. 1997, \adassvi, 249 \reference Mink, D. J. 1999, \adassviii, 498 \reference Mink, D. J. 2002, \adassxi, 169 \reference Monet, D. G. 1996, \baas, 28, 905 (abstract) \reference Monet, D. G. 1998, \baas, 30, 1427 (abstract) \reference Monet, D. G. et al. 2003, \aj, 125, 984 \reference Muller, G. P., Reed, R., Armandroff, T., Boroson, T. A., \& Jacoby, G. H. 1998, Proc. SPIE, 3355, 577 \reference Zacharias, N., et al. 2000, \aj, 120, 2131 \end{references} % Do not place any material after the references section \end{document} % Leave intact