We report here on an ongoing investigation of US astronomical plate archives and tests of the suitability of transportable scanning devices for in situ digitization of archival astronomical plates

Hudec , Lukáš

Hudec , René

Digital Library of the Czech Technical University in Prague

Acta Polytechnica 53(1):23–26, 2013 © Czech Technical University in Prague, 2013available online at http://ctn.cvut.cz/ap/FINDING HIDDEN TREASURES: INVESTIGATIONS IN USASTRONOMICAL PLATE ARCHIVESRené Hudeca,b,∗, Lukáš Hudecba Astronomical Institute, Academy of Sciences of the Czech Republic, Ondřejov, Czech Republicb Czech Technical University in Prague, Faculty of Electrical Engineering, Prague, Czech Republic∗ corresponding author: rhudec@asu.cas.czAbstract. We report here on an ongoing investigation of US astronomical plate archives and tests ofthe suitability of transportable scanning devices for in situ digitization of archival astronomical plates.Keywords: astronomical data archives, astronomical photography, astronomical photographic archives.1. IntroductionThere are numerous important astronomical platearchives in the USA, including plate collections thatare little known to the community and that have beenlittle investigated in the past. Within the frameworkof a Czech-US collaborative project, we have recentlyanalysed some of them, obtaining test scans with theuse of a portable digitizing device. Digitization isa necessary step for an extended evaluation of theplate data using dedicated programs and powerfulcomputers.2. The plate archivesThe US astronomical archival plate collections that werecently visited include those housed in the following14 institutions:(1.) Carnegie Observatories Pasadena, CA;(2.) Lick Observatory, CA;(3.) Yerkes Observatory, WI;(4.) Mt Palomar Observatory, CA;(5.) PARI, Rosman, NC (which has a collection ofplates from many observatories);(6.) KPNO Tucson, AZ;(7.) CFHT Waimea, HI;(8.) IfA Manoa, HI;(9.) USNO Flagstaff, AZ;(10.) USNO Washington, DC;(11.) Steward Observatory Tucson, AZ;(12.) NMSU, Las Cruces, NM;(13.) Rosemary Hill Observatory, University of Florida,Gainesville, FL;(14.) Leander McCormick Observatory, University ofVirginia, Charlottesville, VA.Our estimate is that there are more than 1 millionastronomical archival plates in these archives. Weperformed a quality check and analyzed these plateFigure 1. Digitizing plates with a transportabledevice in the plate vault of the Steward Observatory,Tuscon, AZ. This digitization technique can be usedeven in very small rooms.archives with emphasis on their scientific, historicaland cultural value, which we have found to be enor-mous.3. Transportable digitizing deviceMost of the plate archives that we visited have no platescanners and lack modern instrumentation in general.As our study includes plate digitization, it was neces-sary to find a solution. Since we were going to travelfrom Europe to the US by air, the obvious option wasa transportable digitization device based on a digitalcamera with a high-quality lens and a stable tripod.This solution has the following advantages over othertechniques: the device is easily transportable, andoffers much faster scanning and higher repeatabilitythan commercial flatbed scanners, because there areno moving scanner parts. The equipment that weused was as follows: Camera: 21 MPx Canon EOS 5D23R. Hudec, L. Hudec Acta PolytechnicaFigure 2. Storage of archival plates at the McCormickObservatory.Mark II, Lenses: Canon EF 24–70 f/2.8 L USM andCanon 70–200mm F4, a stable tripod, and a FomeiLP-310 professional photographic light table. Morerecently, we have been working on the design and de-velopment of a better custom-made light table basedon highly homogeneous LED illumination, and alsoa further improved camera and lens. The recordedimages are then corrected for lens image distortionsand for other effects, in order to store research-gradedigital images.4. General pictureAfter visiting the 14 US plate collections mentionedabove, we offer a (subjective) list of the major prob-lems found in these archives:(1.) The list of US plate collections provided by Dr.Wayne Osborn (Robbins and Osborn, 2009) wasfound to be incomplete. We have found valuableplate collections with plates from important tele-scopes that are not listed, e.g. the two Hawaiiplate collections in Manoa (Institute of Astronomy)and in Waimea (Canada-France Hawaii TelescopeCFHT). Some plate archives have been completelyhidden, as their home institutes were in some ex-treme cases not even aware that they have platestacks.(2.) In numerous collections, only a very rough esti-mate of the number of plates can be given, as noexact information about the total number of plates,etc., is available. Usually, the real number of platesis higher than the previously available estimate. Ingeneral, it is very difficult to give the exact num-ber of plates, due to lack of observation logs andinadequate organization of the plate archives.(3.) In many cases, there is no contact person respon-sible for the plate archive, and it is difficult to makecontact. In some places, it is even difficult to getaccess. This situation very has a serious adverseeffect on efforts to exploit these plate collections forscientific purposes.Figure 3. Example of metadata on the plate en-velope (McCormick Observatory plate archive). Innumerous US plate archives, the plate envelopes arethe only source of metadata information.(4.) For some archives, no information is available,not even an approximate number of plates. Inmany archives, no plate logs are available; theyhave either been removed or are lost. The onlyavailable information is what is written on the platesor on the envelopes (in some cases, there is noteven adequate information on the envelope). Weguess that there were originally observation logs, butthat these were later separated from the plates andarchived in a different location. Example: CarnegieObservatories Pasadena (nearly 0.5 million plates),where the logs are probably located in the atticabove the library, with difficult access.(5.) Damaged plates in some archives (mostly due toa partly-released or even complete released emulsionlayer), probably due to improper storage (or changesin humidity/temperature over time). We point outhowever that even these plates can be restored usingsuitable chemical methods and procedures.(6.) Lack of electronic records — no lists of plates,the only information is on the plates and/or plateenvelopes(7.) Many of the archives that we visited suffer frominadequate funding, lack of devices, e.g. no scanners.(8.) We have revealed that many plates have beenremoved from their home: these plates are usuallyscattered in private homes and offices, or are be-ing kept by observers (often abroad). Numerousplates taken at US observatories have been foundin European plate archives.24vol. 53 no. 1/2013 Finding Hidden Treasures: Investigations in US Astronomical Plate ArchivesFigure 4. Historical plate evaluation instruments at the McCormick Observatory: blink microscope (left) and thePDS machine (right).Figure 5. Example of a digitized direct plate(blazar program, full area), Rosemary Hill Observa-tory.Nevertheless, we found highly valuable plates al-most everywhere, and the quality of the plates (andhence their scientific potential) is mostly high or evenvery high, in comparison with the plates in Europeanarchives. This is true both for direct images andfor spectral images (taken with an objective prism).In addition to stellar images, some of the archivesthat we visited also include extensive collections of so-lar images (e.g. Carnegie Observatories in Pasadena)and/or planetary images (unique collection in LasCruces). The storage conditions were found to varyfrom archive to archive, from proper temperature andhumidity conditions, to less proper conditions. Themain degradation sources found in the plate collec-tions were high levels of humidity and probably alsotemperature variation, resulting in partial or com-plete release of the emulsion layer. The scientificuse of the plate archives is negatively impacted bypoor access to the plates at some places, and also bythe fact that the plates have in most cases not yetbeen cataloged.Figure 6. Example of a digitized low-dispersion spec-tral plate (small selected area), McCormick Observa-tory. This is one of many plates taken with a 10-inchCooke camera and an objective prism for the longspectral survey program (lasting over 20 years) set upby A. Vyssotsky.5. Suggested strategyOur suggested strategy for data mining and platedigitization in US plate archives is as follows.(1.) Digitize the plate archives using a fast and trans-portable scanning device, as described above. Thisscanning method is fast and inexpensive. Theseare important considerations, as the archives arescattered and there are very large numbers ofplates.(2.) Create electronic catalogs.(3.) Include these catalogs into search programs likeWFPD, operated by our Bulgarian colleagues (e.g.Tsvetkov et al., 2005, and Tsvetkov, 2009).6. SummaryFourteen US astronomical plate archives were visitedwithin the AMVIS Czech-US collaborative project.The quality of the plates and their scientific, histori-cal and cultural value were investigated for possible25R. Hudec, L. Hudec Acta Polytechnicainclusion in the US astronomical plate repository atPARI, NC. Some of these archives (CFHT Waimeaand IfA Manoa) were unknown to the astronomicalcommunity before our study.Selected plates were digitized using a transportablescanning device. All the archives that we visited haveplates that are scientifically valuable, and in manycases unique. The plates are however mostly hiddenfrom the astronomical community, and the plates havenot yet been catalogued.The total number of plates is higher than expected– in many of the locations, the actual number of platesis unknown. As no catalogs exist, the real numberof plates is very difficult to estimate, but for surethe places that we visited have more than a millionphotographic plates in their collections.AcknowledgementsWe acknowledge grants 102/08/0997 and 205/08/1207from the Grant Agency of the Czech Republic, and fromMSMT Project ME09027. This work is based on collabo-ration with Thurburn Barker and Mike Castelaz, PARI,within the framework of a collaborative Czech-US plateproject.References[1] Hudec, R. et al., Acta Polytechnica 1(52), 2012.[2] Hudec, R. Astrophysics with Astronomical PlateArchives, in Exploring the Cosmic Frontier:Astrophysical Instruments for the 21st Century. ESOAstrophysics Symposia, European SouthernObservatory series. Edited by Andrei P. Lobanov, J.Anton Zensus, Catherine Cesarsky and Phillip J.Diamond. Series editor: Bruno Leibundgut, ESO. ISBN978-3-540-39755-7. Published by Springer-Verlag, Berlinand Heidelberg, Germany, 2007, p.79[3] Hudec, R., An introduction to the world’s large platearchives, Acta Historica Astronomiae, vol. 6, p. 28-40,1999.[4] Tsvetkov M. et al., Proc. IV Serbian-BulgarianAstronomical Conference, Publ. Astron. Soc. RudjerBoskovic No 5, 303-308, 2005.[5] Tsvetkov, M. Making Astronomical PhotographicData Available: The European Perspective, PreservingAstronomy’s Photographic Legacy: Current State andthe Future of North American Astronomical Plates.ASP Conference Series, Vol. 410. Edited by WayneOsborn and Lee Robbins. San Francisco: AstronomicalSociety of the Pacific, 15, 2009.[6] Robbins, L.; Osborn, W., Preserving Astronomy’sPhotographic Legacy: Current State and the Future ofNorth American Astronomical Plates. ASP ConferenceSeries, Vol. 410, Appendix B and C. Edited by WayneOsborn and Lee Robbins. San Francisco: AstronomicalSociety of the Pacific, 2009.26

Finding Hidden Treasures: Investigations in US Astronomical Plate Archives

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