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Draftversion January11,2017 PreprinttypesetusingLATEXstyleemulateapjv.5/2/11 VISUALISATION OF MULTI-MISSION ASTRONOMICAL DATA WITH ESASKY Deborah Baines1, Fabrizio Giordano1, Elena Racero1, Jesu´s Salgado1, Belén Lo´pez Mart´ı1,2, Bruno Mer´ın1, Mar´ıa-Henar Sarmiento1, Rau´l Gutiérrez1, Inãki Ortiz de Landaluce1, Ignacio Leoń1, Pilar de Teodoro1, 7 Juan Gonza´lez1, Sara Nieto1, Juan Carlos Segovia1, Andy Pollock1,3, Michael Rosa1, Christophe Arviset1, 1 Daniel Lennon1, William O’Mullane1 and Guido de Marchi4. 0 Draft version January 11, 2017 2 ABSTRACT n a ESASky is a science-driven discovery portal to explore the multi-wavelength sky and visualise J and access multiple astronomical archive holdings. The tool is a web application that requires no 0 prior knowledge of any of the missions involved and gives users world-wide simplified access to the 1 highest-level science data products from multiple astronomical space-based astronomy missions plus a number of ESA source catalogues. The first public release of ESASky features interfaces for the ] visualisation of the sky in multiple wavelengths, the visualisation of query results summaries, and M the visualisation of observations and catalogue sources for single and multiple targets. This paper describesthesefeatureswithinESASky,developedtoaddressusecasesfromthescientificcommunity. I . The decisions regarding the visualisation of large amounts of data and the technologies used were h made in order to maximise the responsiveness of the application and to keep the tool as useful and p intuitive as possible. - o r Key words: astronomicaldatabases: miscellaneous – telescopes – catalogs t s a [ 1. INTRODUCTION support from many ESA mission science and technical 1 Many astronomy data centres and archiving facilities experts, andfrom the Centre de Données astronomiques deStrasbourg(CDS).ESASkyprovidesfullaccesstothe v arecurrentlyaddressingtheneedfromthescientificcom- entireskyasobservedby ESA(andother)missions,and 3 munity to provide intuitive, fast and visual access to provides a simple way to search and download multi- 3 their data holdings, with the main goal of maximising wavelength data, going beyond the individual archives 5 the exploitationofscientific data. This needcomes from boundaries. 2 a number of issues, such as the yearly exponential in- Version 1 of ESASky was released in May 2016 and 0 crease in astronomical data; the need to understand as- . tronomical objects across the full electromagnetic spec- can be found at the following URL: 1 trum and/or across the time domain; the need for easy 0 http://sky.esa.int 7 access to science-ready data (or the highest-level data 1 products) from as many astronomical observatories as This version addresses three main use cases: (i) the : possible; and to understand which observatories, if any, v explorationof the multi-wavelengthskies;(ii) the search have observed in a particular region of the sky. i andretrievalofdataforsingletargets;and(iii)thesearch X The ESAC Science Data Centre (ESDC), located at andretrievalofdataformultipletargetlists. Inaddition the European Space Astronomy Centre (ESAC) near r to the three main use cases, a fourth is also addressed: a Madrid, Spain, hosts the archives from ESA space sci- the visualisation of the sky coverage from all missions. ence missions (astronomy, planetary science and helio- This first version contains imaging data sets and cata- physics) and provides services and tools to access and loguesonly(futurereleaseswillenableretrievalofspectra retrieve ESA mission data. With this experience, and and will have special time domain explorationfeatures). to fulfill the requests from the scientific community, In this paper, we describe the visualisation features the ESDC have developed ESASky (http://sky.esa.int), within version 1 of ESASky, developed to address the a web-based data discovery portal for visualising and use cases; the technologies used to develop these fea- accessing science-ready astronomical data in collective tures;andthedecisionsmaderegardingthevisualisation astronomical archives (Mer´ın et al. 2015; Mer´ın et al. of large amounts of data, with the aim of keeping the 2016). Thetoolwasdevelopedincollaborationandwith tool as useful and intuitive as possible. Section 2 de- scribes the visualisation and exploration of the sky and 1European Space Astronomy Centre (ESAC), European section3describeshowtheresultsaresummarisedinhis- SpaceAgency(ESA),28691VillanuevadelaCanãda,Spain tograms. Sections 4 and 5 describe the visualisation of 2Saint Louis University - Madridcampus, Avenida del Valle the observationsandcataloguesrespectively,andfinally, 34,28003Madrid,Spain 3Department of Physics and Astronomy, University of the summary is given in section 6. Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK 4European Space Research and Technology Centre, Kepler- laan1,2201AZNoordwijk,TheNetherlands 2 Baines et al. 2. VISUALISATIONOFTHESKY inESASkywithanumberofstackedskies. Transparency of one or more skies will be available in the near future. Before developing ESASky, a strong user requirement was to make the tool web-based. Google Web Toolkit5 3. VISUALISATIONOFTHERESULTSSUMMARY (GWT; a development toolkit for building and optimis- To fulfill the use case to search and retrieve data for ing complex browser-based applications) was chosen as single targets, the results of a search first need to be the development technology for ESASky, the decision visualised. ESASky contains a search field that accepts being based on a feasability study by ESDC into web- coordinates (equatorial or Galactic) or an object name based technologies and on previous experience developing archives with GWT. that can be resolved by SIMBAD.7 The search region The second decision to be made was how to fulfill the displayed in ESASky is chosen by taking the size of the use case to explore multi-wavelength skies. For this, objectfromSIMBAD.Alltheavailablearchivesarethen we chose Aladin Lite (Boch & Fernique 2014) developed queried in this region (within the corner coordinates of by CDS, a lightweight version of the Aladin Sky At- the display). las (Bonnarel et al. 2000), running in the browser and Theresultsofthisqueryaresummarisedinhistograms, geared towards simple visualisation of the sky. To in- one for the observations and one for the catalogues, to tegrate Aladin Lite into the ESASky source code, we give the user a general overview of all results available. developed a GWT wrapper using the JavaScript Native The results shown are the highest-level science observa- Interface (JSNI) methods to communicate directly with tions only. The histograms are ordered by wavelength the JavaScript of Aladin Lite. (similar to the skies menu), assuming that the average Aladin Lite displays progressive multi-resolution, user does not know the specific details of every mission all-sky projections of full mission data sets using and catalogue available, but is interested in wavelength HEALPix projections (Górski et al. 2005) called Hi- regions (time domain searches will be available in a fu- erarchical Progressive Surveys (HiPS), also developed ture version). The histograms are interactive, and by by CDS (Fernique et al. 2015a). Hundreds of HiPS hoveringoverthe histogrambarstheusercanseeasum- from major astronomical surveys and observatories mary showing the number of observations and sources have been created by CDS and other institutes, foreachmissionorcataloguerespectively. Byclickingon and they can be visualised within Aladin Lite (see themissionnamesinthelegends,thehistogrambarscan http://aladin.u-strasbg.fr/hips/list for a comprehensive be hidden to better visualise others; for example, those list). As the user zooms into the sky the spatial resolu- with small numbers of observations or sources. The his- tionoftheHiPSchangesuntilthelowestlevelisreached, tograms are automatically refreshed and re-scaled when which is normally the resolution of the instrument. To one does this or when one moves to a different region keep ESASky simple and easy to use, we chose to show of the sky. These histograms are produced with the a subset of the available HiPS (some of the most well- JavaScript Highcharts8 library. Figure 1 shows an ex- known surveys and missions) and we created our own ample of the results histograms (centred on the Small HiPSfortheESAastronomymissions. Thiswasachieved Magellanic Cloud). using the Aladin/hipsgen6 code, a package used to cre- To maximise the responsiveness of the tool, a thresh- ateprogressiveHiPSmapsfromacollectionofcalibrated old is placed at a field of view (FOV) of three degrees FITS files. It should be noted that the ESA HiPS are or larger, after which the number of observations and intended forvisualisationonly andare notscience-ready catalogue sources are obtained from pre-computed ta- products and should therefore not be used to perform bles (rather than directly on the fly from the individual scientific data analysis. ESASky instead provides easy archives). These tables were created by dividing the sky access to the highest-level data products from each mis- (represented as a sphere) into equal area HiPS pixels, sion (see section 4). ESA astronomy mission HiPS have with each pixel containing a pre-computed number of been created for the Akari, EXOSAT, Herschel, Hub- observations and sources per mission and catalogue re- ble SpaceTelescope (HST),INTEGRAL, InfraredSpace spectively. Anapproximatecountisthencalculatedfrom Observatory (ISO), Planck and XMM-Newton missions thepre-computedtablesanddisplayedintheresultshis- andareavailablethroughESASky(seethe“skies/HiPS” tograms. Thesetablesareupdatedregularlyformissions section of the online ESASky help for details, accessible still in operation (such as HST and XMM-Newton). from http://sky.esa.int). 4. VISUALISATION OFTHEOBSERVATIONS The HiPS are available to visualise through ESASky via the skies menu and are displayed in the Equatorial Inversion1ofESASky,imagingobservationsareavail- system (J2000) by default (the user can also choose the ablefromtheESAHerschel,HST,INTEGRAL,ISOand Galacticcoordinatesystem). Theskiesmenuwaschosen XMM-Newton missions and from the JAXA SUZAKU to be mission agnostic, and groups the skies (HiPS) by mission (see http://sky.esa.int help for details). Details wavelength regions, from γ-ray to radio. The skies can on the observations are loaded in ESASky via the sum- be stacked above the menu and played through using maryhistogramsby clickingonthe histogrambars. The video style buttons to aid the user exploration experi- archives are queried in the region displayed, a results ence. The user can also modify the colour of the skies table is provided per mission, and the footprints of each usingthecolourmapoptions: greyscale,rainbow,EOSB, observationaredisplayedonthesky(orinthecaseofIN- Planckand reverse. Figure 1 shows the skies menu open TEGRAL, the central pointing positions are displayed; see below for details). 5 http://www.gwtproject.org 7 http://simbad.u-strasbg.fr/simbad/ 6 http://aladin.u-strasbg.fr/hips/ 8 http://www.highcharts.com Visualisation of multi-mission astronomical data with ESASky 3 Figure 1. ESASkyvisualisingthecentreoftheSmallMagellanicCloudasseenintheopticalwiththeDigitizedSkySurvey(DSS2). The skies menu is open in the top left of the tool and includes a number of stacked skies. Results histograms are shown towards the bottom ofthetoolwithanexampleofhoveringoverabartodisplaythenumberofavailableobservations(inthiscasefortheHST).Observation footprintsareshownforHerschel(cyan),HST(yellow),ISO(red),XMM-Newton(X-ray: darkblue;ultraviolet: purple),SUZAKU(blue), andpointingsforINTEGRAL(lightbluecrosses). The footprints for each observation are generated by The results table can also be downloaded, either the missions and obtained from the individual mission as a comma-separated value (CSV) file or a VOTable archives. In the case where no footprints were available (Ochsenbein et al. 2009) file and it can be sent via (ISO and XMM-Newton), we generated the footprints the Simple Application Messaging Protocol (SAMP; using the ST-ECFFootprint Finder9 code, with support Taylor et al. 2015; Taylor et al. 2012) to SAMP en- from the instrument experts. In ESASky, each mission abled tools (such as TOPCAT; Taylor 2005). In ad- hasadifferentcolouredfootprinttoeasilydistinguishone dition to providing the column metadata, the product mission from another in the sky. url, postcard url and the footprint coordinates are also The results of a query are summarised in a table per provided for each observation. Finally, for nearly all the mission,whereeachrowisaseparateobservation. Meta- missions, the imaging data can also be sent via SAMP datasuchastheobservationIDnumber,theinstrument, to SAMP enabled image visualisation tools, such as the coordinates,amongstothers,aredisplayedinthe ta- DS9 (Joye & Mandel 2003) and Aladin (Bonnarel et al. ble, as chosenby the missionexperts. The observational 2000). data themselves (and also the catalogue data) remain in In the case of the ESA INTEGRAL γ-ray mission, a their corresponding archives, and ESASky provides the differentapproachwasneededtodisplaytheobservations user with access to download the data products from from the IBIS (Imager on Board the INTEGRAL Satel- thesearchives. Forallmissions,directlinksareavailable lite;Ubertini et al. 2003)instrument. ThetotalFOVof ◦ ◦ to the image previews. In the case of HST and XMM- the instrument (down to zero response) is 29.1 x 29.4 . Newton, a link is provided(via the observationID) that It is not helpful to the user to visualise the whole foot- opens the corresponding archive results page for each print on the sky for two reasons: (i) because the instru- specific observation. Users can then explore further in ment sensitivity decreases towards the edge of the FOV thearchivestoobtainmoredetailedinformationforeach and (ii) because the footprints cover such a large area observation. AsimilarlinkisprovidedforSUZAKU,and of the sky, and in some regions there are many point- we plan on extending this to other archives in future re- ings close to one another, it visually becomes confusing leases. what regions have been observed. Instead, we display the central coordinates of each pointing as a (light blue) 9 http://hla.stsci.edu/Footprintfinder/FootprintFinder.html 4 Baines et al. Figure 2. ESASkyvisualisingNGC6357asseeninthefar-infraredwiththeHerschelPACSRGBHiPS.Themulti-targetmenuisopenin thetopleftofthetoolandincludesanuploadedtargetlistfileandtext. TheresultstableforHerschelisshowntowardsthebottomofthe tool,selectingonerow(inblue)highlightstheobservationfootprintonthesky. ObservationfootprintsareshownforHerschel(cyan),HST (yellow),ISO(red),XMM-Newton(X-ray: darkblue;ultraviolet: purple;optical: orange),SUZAKU(blue),andpointingsforINTEGRAL (lightbluecrosses). Catalogue sourcesareshownfromtheGaiaTGAScatalogue (Michaliketal. 2015;orangesquares). cross. Figures 1 and 2 include examples of INTEGRAL be opened for the same mission, or catalogue, and dif- pointings visualised on the sky. ferent targets. In addition, text and comments can be The number of footprints displayed on the sky is lim- added to the target list file, which are then displayed ited to a few thousand (this number is optimised per in ESASky below the target list. This is a useful fea- mission), again in order to maximise the performance ture for users to keep notes on specific objects of inter- of the tool. Above this threshold, a multi-order cover- est, as well as being useful for education purposes: users age map (MOC; Fernique et al. 2015b) for each mission can be taken on a tour of astronomical objects in multi- is displayed. A MOC is a HEALPix pixelization of the wavelength skies. Figure 2 shows an example target list coverage maps of complete surveys or missions and is and text displayed in ESASky. a simple way to map regions of the sky into hierarchi- cally grouped predefined cells. For all the ESA missions 5. VISUALISATIONOFCATALOGUES in ESASky, we created MOCs simultaneously with the Version 1 of ESASky provides the visualisation of 11 HiPSmapsusing the HIPSGENcode withinAladin(see ESAmissioncatalogues,fromtheGaia,Hipparcos,HST, Lo´pez Mart´ı et al. 2016 for more details on the MOCs INTEGRAL, Planck and XMM-Newton missions (see created for ESASky). Visualising the MOCs of every http://sky.esa.int help for details). The catalogues vary missionprovidesafastandeasywaytocomparemission in sizes, from just a few thousand rows, to tens of mil- coverages against one another over the entire sky, and lions of rows (in the case of the Hubble Source Catalog, addressesthe use case to visualise the sky coveragefrom HSC; Whitmore et al. 2016). Two main issues occur all missions. when visualising such large catalogues: (i) the speed of To fulfill the use case to search and retrieve data for the tool decreases; and (ii) the user can be overloaded multipletargetlists,ESASkyallowstheusertouploada with visual information and individual sources can’t be textfilecontainingalistoftargets,eithernamesresolved resolved. To prevent this we apply two filters, firstly, a by SIMBAD or a list of coordinates. Once loaded, the warning is given to refine the search by using a smaller target list appears in the tool and is interactive: targets FOV when there are more than 50,000 sources in the can be selected and the sky will reload, centred on the FOV. Secondly, in the case of more than 2000 sources target; or one can play through the list of targets and in the FOV, ESASky orders them by magnitude or flux viewthesummaryofresults;ormultipleresultstabscan andshowsthebrightest2000. Anexceptiontothisisfor Visualisation of multi-mission astronomical data with ESASky 5 the HSC, where the 2000 displayed sources are ordered MOC, TAP, STC-S, SAMP, VOTable etc. These pro- bythemostobservedsources(the NumImagesvalue). A tocols play an essential part in the tool, enhance the higher NumImage value provides a higher confidence in user experience, and have helped to increase the speed themagnitudevaluesandcaneliminate artifactspresent at which we have been able to develop ESASky. in the catalogue. The next major release of ESASky will include the re- Aswiththeobservations,thecataloguesareloadedvia trievalofspectroscopicdata,linkstomoreofthemission the interactive histograms. A choice was made by the catalogues and improvements in some of the visualisa- ESA mission specialists on the most important columns tionfunctionalities. Afterthis,futurefunctionalitieswill todisplaywithinthe resultstablepercatalogue. Forthe include spectral visualisation and special time domain majority of catalogues, these columns are source name, exploration features. right ascension, declination, flux or magnitude, errors and source flags, but other columns are also shown de- Acknowledgements: Weacknowledgetheexcellentsup- pending on the type of catalogue (for example, proper portfromtheexpertscienceandtechnicalstaffatESAC motionsandparallaxforHipparcosandTGAS).ESASky and CDS. In particular, we acknowledge the follow- provides interaction between the results table and the ing people: Mark Allen, Bruno Altieri, Ruben A´lvarez, sky, and vice versa, i.e. clicking on a row in the results Guillaume Belanger, Thomas Boch, Tama´s Budavári, tablewillhighlightthe sourceonthe skyandclickingon Javier Castellanos, Xavier Dupac, Daniel Durand, Ken the sourceon the sky will highlightthe results table row Ebisawa, Matthias Ehle, Pilar Esquej, Pierre Fernique, and will bring up a summary box. The summary box Pedro Garc´ıa Lario, Krzysztof Górski, Jonas Haase, provides the source name, coordinates, which catalogue JohnHoar,PeterKretschmar,ErikKuulkers,RenéLau- (results tab name) it belongs to, and links to SIMBAD, reijs, Nora Loiseau, Marcos Lo´pez-Caniego, Alejandro the NASA/IPAC Extragalactic Database10 (NED), and Lorca, Anthony Marston, Antonella Nota, Göran Pil- theVizieRphotometryviewer11,wheresearchesareper- bratt,RobertoPrieto,PedroRodr´ıguez,MiguelSańchez- formed centred on the source coordinates. As with the Portal,MariaSantos-Lleo,NorbertSchartel,JanTauber, observations, the catalogues can be downloaded or sent IvanValtchanovandEvaVerdugo. ESASkymakesuseof toaVOapplicationviaSAMP.Inthecaseofthe XMM- AladinLite, developedatCDS,StrasbourgObservatory, Newton3XMM-DR6catalogue(Rosen et al. 2016),one France (Boch & Fernique 2014). This work also bene- can obtain further catalogue information via a link in fited from experience gained from projects supported by the results table which opens the XMM-Newton Science the Mission Operation Division of ESA’s Directorate of Archive results for each source. We plan to provide this Science. functionality for all catalogues in the near future. REFERENCES 6. SUMMARY As a response to our archive users, we have developed Boch,T.&Fernique,P.2014,ASPC,485,277 ESASky, a web-based science-driven discovery portal to Bonnarel,F.,Fernique,P.,Bienaymé,O.,etal.2000, A&AS,143, visualise and access multiple astronomical archive hold- 33 ings. The first public release of ESASky features inter- Fernique,P.,Allen,M.G.,Boch,T.,etal.2015a,A&A,578,A114 Fernique,P.,Boch,T.,Donaldson,T.,etal.2015b,ArXiv faces for the visualisation of the sky in multiple wave- e-prints[arXiv:1505.02937] lengths,thevisualisationofqueryresultssummaries,and Górski,K.M.,Hivon,E.,Banday,A.J.,etal.2005,ApJ,622,759 the visualisation of observations and catalogue sources Joye,W.A.&Mandel,E.2003, ASPC,295,489 for single and multiple targets. This version addresses LópezMart´ı,B.,Mer´ın,B.,Racero,E.,etal.2017,A&A,in use cases from the scientific community, such as the ex- preparation. Mer´ın,B.,etal.2017,A&A,inpreparation. ploration of multi-wavelength skies; searching and re- Mer´ın,B.,Salgado,J.,Giordano,F.,etal.2015,ArXive-prints trieving data for single targets; searching and retrieving [arXiv:1512.00842] dataformultipletargetlists;andvisualisingtheskycov- Michalik,D.,Lindegren,L.&Hobbs,D.2015,A&A,574,115 erage from all missions. Ochsenbein,F.,Williams,R.,Davenhall,C.,etal.2009, IVOA Inadditiontoaddressingtheusecases,thechoicesthat Recommendation, ArXive-prints[arXiv:1110.0524] Rosen,S.R.,Webb,N.A.,Watson,M.G.,etal.2016,A&A,590, were made on the visualisation technologies and tech- 1 niques used were for four main reasons: (i) to maximise Taylor,M.B.,Boch,T.&Taylor,J.2015,A&C,11,81 theresponsivenessoftheapplication;(ii)tokeepthetool Taylor,M.,Boch,T.,Fitzpatrick,M.,etal.2012,IVOA simple and intuitive; (iii) to not overload the user with Recommendation, ArXive-prints[arXiv:1110.0528] too much visual information; and (iv) to enhance the Taylor,M.B.2005,ASPC,347,29 Ubertini,P.,Lebrun,F.,DiCocco,G.,etal.2003,A&A,411, user experience. L131 ESASky(andtheunderlyingESAastronomyarchives) Whitmore,B.C.,Allam,S.S.,Budava´ri,T.,etal.2016,AJ,151, makes use of many International Virtual Observatory 134 Alliance12 (IVOA) protocols and notes, such as HiPS, 1101 hhttttpps:/:///vnizeide.ri.pua-sct.craalstbegc.hfr.e/dvuizier/sed/ 12 http://ivoa.net