%APN3_PROCEEDINGS_FORM%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % TEMPLATE.TEX -- APN3 (2003) ASP Conference Proceedings template. % % Derived from ADASS VIII (98) ASP Conference Proceedings template % Updated by N. Manset for ADASS IX (99), F. Primini for ADASS 2000, % D.Bohlender for ADASS 2001, and H. Payne for ADASS XII and LaTeX2e. % % Use this template to create your proceedings paper in LaTeX format % by following the instructions given below. Much of the input will % be enclosed by braces (i.e., { }). The percent sign, "%", denotes % the start of a comment; text after it will be ignored by LaTeX. % You might also notice in some of the examples below the use of "\ " % after a period; this prevents LaTeX from interpreting the period as % the end of a sentence and putting extra space after it. % % You should check your paper by processing it with LaTeX. For % details about how to run LaTeX as well as how to print out the User % Guide, consult the README file. You should also consult the sample % LaTeX papers, sample1.tex and sample2.tex, for examples of including % figures, html links, special symbols, and other advanced features. % % If you do not have access to the LaTeX software or a laser printer % at your site, you can still prepare your paper following the % instructions in the User Guide. In such cases, the editors will % process the file and make any necessary editorial adjustments. % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % \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. % % EXAMPLE: \paperID{O4-1} % EXAMPLE: \paperID{P7-7} % \paperID{P3-4} %%%% ID=P3-4 %----------------------------------------------------------------------- % Paper Title %----------------------------------------------------------------------- % Enter the title of the paper. % % EXAMPLE: \title{A Breakthrough in Astronomical Software Development} % % If your title is so long as to fill the page header when you print it, % then please supply a short form as a \titlemark. % % EXAMPLE: % \title{Rapid Development for Distributed Computing, with Implications % for the Virtual Observatory} % \titlemark{Rapid Development for Distributed Computing} % \title{Spectral Data Models for the Virtual Observatory} %\titlemark{ } %----------------------------------------------------------------------- % Authors of Paper %----------------------------------------------------------------------- % Enter the authors followed by their affiliations. The \author and % \affil commands may appear multiple times as necessary (see example % below). List each author by giving the first name or initials first % followed by the last name. Authors with the same affiliations % should grouped together. % % EXAMPLE: \author{Raymond Plante, Doug Roberts, % R.\ M.\ Crutcher\altaffilmark{1}} % \affil{National Center for Supercomputing Applications, % University of Illinois Urbana-Champaign, Urbana, IL % 61801} % \author{Tom Troland} % \affil{University of Kentucky} % % \altaffiltext{1}{Astronomy Department, UIUC} % % In this example, the first three authors, "Plante", "Roberts", and % "Crutcher" are affiliated with "NCSA". "Crutcher" has an alternate % affiliation with the "Astronomy Department". The fourth author, % "Troland", is affiliated with "University of Kentucky" \author{Jonathan C.\ McDowell, Stephen Lowe, Mark Cresitello-Dittmar, Janet DePonte Evans, Ian Evans, Arnold Rots, Michael Harris} \affil{Smithsonian Astrophysical Observatory, 60 Garden St, 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{Jonathan McDowell} \email{jcm@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. % % EXAMPLE: \paindex{Crabtree, D.} % \aindex{Manset, N.} % \aindex{Veillet, C.} % % NOTE: this information is also used to build the author list that % appears in the table of contents. Authors will be listed in the order % of the \paindex and \aindex commmands. % \paindex{McDowell, J. C.} \aindex{Lowe, S.} % Remove this line if there is only one author \aindex{Cresitello-Dittmar, M.} \aindex{DePonte Evans, J.} \aindex{Evans, I.} \aindex{Rots, A. H.} \aindex{Harris, M.} %----------------------------------------------------------------------- % 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{McDowell et al.} %----------------------------------------------------------------------- % Subject Index keywords %----------------------------------------------------------------------- % Enter a comma separated list of 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 proceedings (http://adass.org/adass/proceedings/). % % EXAMPLE: \keywords{visualization, astronomy: radio, parallel % computing, AIPS++, Galactic Center} % % In this example, the author noticed that "radio astronomy" appeared % in the ADASS VII Index as "astronomy" being the major keyword and % "radio" as the minor keyword. The colon is used to introduce another % level into the index. \keywords{data: structures, software: data model, Virtual Observatory, spectroscopy} %----------------------------------------------------------------------- % 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 There is no standard way in astronomy to represent digital spectroscopic data. We present requirements for a standardized 1-dimensional spectral data model for use in the Virtual Observatory. We discuss the different kinds of spectra and the different observables used, as well as the appropriate instrumental calibrations. Our model is intended as a special case of an n-dimensional model for image and spectral data, and would incorporate the FITS spectral WCS proposal for coordinate descriptions. The problem of describing spectral data is closely related to the problems of defining bandpasses and photometric calibrations, as well as of abstract instrument descriptions such as spectral responses and efficiencies. \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. % % EXAMPLE: \section{Introduction} % ... % \subsection{Our View of the World} % ... % \section{A New Approach} % % It is recommended that you look at the sample papers, sample1.tex % and sample2.tex, for examples for formatting references, footnotes, % figures, equations, html links, lists, and other special features. \section{Introduction} A significant fraction of the public data available to the astronomical community is in the form of spectra. Although most archives store image metadata in fairly standard ways the history of archiving spectral data is much less successful. A recent survey of spectral archives (see Tody on www.ivoa.net/forum/dal) which revealed a heterogeneous collection of formats, many in ASCII tables, FITS tables, or FITS images. This is in contrast to simple sky images which, despite problems with how to represent mosaics, are mostly in some variation of FITS image extensions. The current FITS WCS proposal (Greisen et al.) for wavelength transformations is only one of the steps needed to use archived spectra interoperably. The VO will need to specify a uniform way to describe spectra. This study attempts to isolate the metadata needed for representing spectra to the VO, and proposes ways to structure this metadata. Our model separates metadata needed by applications using the idealized, generalized spectrum (pixel values, coordinates, errors, units, resolution) from metadata describing the idealized observation (sky region, observation date) and from metadata which are needed by specialized applications which deal with particular observational strategies (e.g. spectral extraction details). \section{\bf What is a spectrum?} A spectrum is the value of an observable as a function of a spectral coordinate, corrected or not for various instrumental effects. The spectral survey confirms that existing public data use the full range of possible parameters for the electromagnetic spectrum; ( see Greisen et al. 2004 for spectral coordinates in FITS). We distinguish between a theoretical spectrum sense, the energy output versus e.g. frequency, and a spectral dataset in the observer's sense, which maps such a spectrum onto an instrument. Spectral datasets often have degeneracy when two celestial axes and one spectral coordinate are projected onto two instrument coordinates. Here we describe spectra (the idealized $F(\nu)$) rather than spectral datasets. The 1-D spectrum is clearly a special case of a 1-D histogram, and our final VO scheme should unify common metadata with other 1-D histograms (e.g. lightcurves) and with n-dimensional generalizations such as the 2-D image. This case study will be used to ensure that the n-D observation model can encompass everything we need to represent a spectrum. We can identify several other kinds of `spectrum': \par - Other observables as a function of wavelength: percentage polarization, extinction coefficient. These can use the present model. \par - Arrays of spectra such as spectral-spatial data cubes. They are a simple extension if we model spatial images compatibly. \par - Spectral coordinates for particles other than photons: massless (gravitational waves) or massive (electron energies in a jet, cosmic ray spectrum). \par - Spectral coordinates not a particle property: power spectra of source variability or CMB anisotropies, Fourier transforms generally. Needs a slightly different model. %\begin{table}[ht] \begin{center} {\small \begin{tabular}{|ll|} \hline \hline Observable & Typical unit \\ \hline Energy flux Density vs $\lambda$ & erg cm$^{-2}$ s$^{-1}$~\AA$^{-1}$ \\ Energy flux Density vs $\nu$ & Jy\\ Energy flux Density vs $\log\nu$ (for SED) & Jy Hz\\ Photon flux density vs Energy & photon cm$^{-2}$ s$^{-1}$ keV$^{-1}$ \\ Luminosity (at source) & erg s$^{-1}$ \AA$^{-1}$\\ Luminosity per decade & $L_\odot$ \\ Radiation energy density & erg cm$^{-3}$ Hz$^{-1}$\\ Flux per solid angle (e.g. at source surface) & erg cm$^{-2}$ s$^{-1}$ \AA$^{-1}$ sr$^{-1}$ \\ Antenna temperature & K \\ Brightness temperature & K\\ Magnitude in given band & mag\\ AB magnitude & mag\\ Surface brightness flux density & Jy / arcsec$^2$\\ Flux per resolution element & Jy / beam \\ Surface brightness mag. & mag / arcsec$^2$ \\ Instrumental reading & ADU, count\\ Ratio of two spectra & Dimensionless\\ \hline \hline \end{tabular} \\ Table 1. An incomplete list of spectral observables } %\caption{An incomplete list of spectral observables} \end{center} %\end{table} \section{Observables} A crucial task for the VO is to standardize how data providers describe the observable. What do the pixel values represent? At the moment, if you are lucky there is a BUNIT keyword in a FITS image to at least tell you the unit, but that is not really sufficient. The VO will use tags such as Uniform Content Descriptors (UCD2, Derriere et al. 2004) to unambiguously characterize the physical concept being measured. Our spectral data model must define a standard place to store this metadata. Examples of spectral observables are listed in table 1. \section{A Partial Model} There are three main parts of our model: the dataset description, (Fig. 1), the data container description (Fig. 2), and the observation coverage description (not presented here). The complete Dataset object, a simplified version of the one presented in Cresitello-Dittmar et al. (2004), contains curation and coverage objects as well as several Data Container objects. The dataset will have at least one Data Container for the main data, and may have additional ones for a background spectrum, an exposure array, and a sensitivity array. \begin{figure}[ht] \epsscale{0.70}\plotone{P3-4_f1.eps} \caption[Dataset]{UML class diagram for the Dataset model.} \end{figure} The Data Container has a Data Storage object containing Value, Error, Quality and Resolution sub-objects. Our abstraction is that the data consists of an ordered array of values (accessed by the Index object) which may be coupled to one or more PixelMap objects locating each value in a coordinate system (Cresitello-Dittmar et al. 2004). In the spectral case, the PixelMap would provide a bijection between pixel number and the spectral coordinate. \begin{figure}[ht] \epsscale{0.62}\plotone{P3-4_f2.eps} \caption[aa]{UML class diagram for the Data Container model.} \end{figure} A simple case of such a map is a set of regularly spaced, contiguous wavelength bins. However, our abstraction also supports irregular or sparse arrays. One may in general obtain value, error, quality and resolution numbers for each pixel, although in many cases things like the resolution may be constant for all pixels; the four separate objects, accessed using the Index, hide this implementation detail. \section{Remaining Design Issues} The observable is declared with a UCD, this needs to be eloborated to fully model a Photometric System object. The resolution is grouped within the Data Container together with values and errors, but the resolution object should ideally be a line spread function at each pixel. In contrast, the sensitivity, exposure and background are treated as separate data containers for two reasons: firstly, their effects are considered to be calibrated out, and accounted for in the error object; and secondly, they often have their own error, quality and resolution information different from the main data - although we should require them to have compatible pixel maps in some sense. Alternative choices would be to include all these arrays in a single Data Storage object, or at the other extreme to consider them as separate but associated Dataset objects and replicate all the observation information. The sensitivity and exposure require care when we extend the model to a 3D energy-position cube, where practical implementations are likely to express things separably as, e.g., an on-axis energy sensitivity and a spatial sensitivity map. We need to add appropriate UCDs in the observation description for specifying that a spectrum is in the rest frame and corrected for Milky Way but not intergalactic absorption, or corrected for detector QE but not vignetting. % You can also add an acknowledgments section as indicated below. \acknowledgments We acknowledge support from NSF grant no. AST 0121296 and Cooperative Agreement AST 0122449, as well as the Chandra X-ray Center under NASA contract NAS8-39073. %----------------------------------------------------------------------- % References %----------------------------------------------------------------------- % 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 listing "macro-ized" journals. % % EXAMPLE: \reference Hagiwara, K., \& Zeppenfeld, D.\ 1986, % Nucl.Phys., 274, 1 % \reference H\'enon, M.\ 1961, Ann.d'Ap., 24, 369 % \reference King, I.\ R.\ 1966, \aj, 71, 276 % \reference King, I.\ R.\ 1975, in Dynamics of Stellar % Systems, ed.\ A.\ Hayli (Dordrecht: Reidel), 99 % \reference Tody, D.\ 1998, \adassvii, 146 % \reference Zacharias, N.\ \& Zacharias, M.\ 2003, % \adassxii, \paperref{P7.6} % % Note the following tricks used in the example above: % % o \& is used to format an ampersand symbol (&). % o \'e puts an accent agu over the letter e. See the User Guide % and the sample files 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 \adassvii is a macro that expands to the full title, editor, % and publishing information for the ADASS VII conference % proceedings. Such macros are defined for ADASS conferences I % through XI. % o When referencing a paper in the current volume, use the % \adassxii 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. % \begin{references} \reference Cresitello-Dittmar, M. et al.\ 2004, \adassxiii, \paperref{P3-6} \reference Derriere et al.\ 2004, \adassxiii, \paperref{P3-17} \reference Greisen et al., 2004, in prep. \end{references} % Do not place any material after the references section \end{document} % Leave intact