College Observatory Research Articles

Transatlantic Jesuit Encounters During the Nineteenth Century

In 1896 the Austrian-born Jesuit Johann Georg Hagen, director of the Georgetown College observatory in Washington, D.C., embarked upon a journey from the United States to Europe, from whence he had fled during Bismarck's Kulturkampf. The account of his travels, published in the Woodstock Letters, was emblematic of the Jesuit reportage that passed back and forth across the Atlantic during the nineteenth century, helping both to define and problematize Jesuit identity during the post-Restoration period. The transatlantic links between Jesuits in Europe and America, which involved the transfer of personnel (often in the wake of periods of persecution in the Old World) and commentary on affairs on both sides of the Atlantic was a source both of tension and sustenance within the Society of Jesus, and had a significant impact on the way in which the broader Catholic Church analyzed the emergence of the fledgling American Republic. Through analysis of individual Jesuit trajectories and Jesuit publications (including the Woodstock Letters in the U.S. and the Études in France), we gain insights into how the Society of Jesus attempted to negotiate the complex political and social realities of the nineteenth century. While nationality was crucial to how individual Jesuits approached this task, the process unfolded in the wider context of how the "old Society" and the "new Society" were to be reconciled and differentiated.

Project PHaEDRA: Preserving Harvard’s Early Data and Research in Astronomy

The staff of Wolbach Library, in collaboration with partners at both the Smith-sonian Institution and Harvard University, has begun a complex digitization and transcriptioneffort aimed at making a large collection of historical astronomy research more findable, accessible, interoperable, and reusable (FAIR). This collection of material was originally produced from the mid-18th century through the early 20th century by researchers at the Harvard College Observatory and was recently re-discovered in the HCO Plate Stacks holdings. The team of professionals supporting the effort to make this century and a half old science FAIR have developed a novel, distributed workflow to ensure that people can engage critically with this material to the fullest extent possible. The project’s workflow is guided by the collections as data imperative conceptual frameworks and is now being referred to as Project PHaEDRA, or Preserving Harvard’s Early Data and Research in Astronomy.

Simultaneous Multiwavelength Observations of V404 Cygni during its 2015 June Outburst Decay Strengthen the Case for an Extremely Energetic Jet-base

Abstract We present results of multiband optical photometry of the black hole X-ray binary system V404 Cyg obtained using Wheaton College Observatory’s 0.3 m telescope, along with strictly simultaneous INTEGRAL and Swift observations during 2015 June 25.15–26.33 UT, and 2015 June 27.10–27.34 UT. These observations were made during the 2015 June outburst of the source when it was going through an epoch of violent activity in all wavelengths ranging from radio to γ-rays. The multiwavelength variability timescale favors a compact emission region, most likely originating in a jet outflow, for both observing epochs presented in this work. The simultaneous INTEGRAL/Imager on Board the Integral Satellite (IBIS) 20–40 keV light curve obtained during the June 27 observing run correlates very strongly with the optical light curve, with no detectable delay between the optical bands as well as between the optical and hard X-rays. The average slope of the dereddened spectral energy distribution was roughly flat between the - and V-bands during the June 27 run, even though the optical and X-ray flux varied by >25× during the run, ruling out an irradiation origin for the optical and suggesting that the optically thick to optically thin jet synchrotron break during the observations was at a frequency larger than that of V-band, which is quite extreme for X-ray binaries. These observations suggest that the optical emission originated very close to the base of the jet. A strong emission line, probably originating in a quasi-spherical nebula around the source, also contributes significantly in the R C -band. Our data, in conjunction with contemporaneous data at other wavelengths presented by other groups, strongly suggest that the jet-base was extremely compact and energetic during this phase of the outburst.

Radial velocity measurements and orbit determination of eight single‐lined spectroscopic binary systems

Since early 2015, a new radial velocity monitoring campaign is going on at the University Observatory Jena. The aim of this project is to obtain current radial velocity measurements of selected single‐lined spectroscopic binary systems as well as to redetermine and/or constrain their orbital solutions. In this paper, we characterize the properties of the target sample of the project, describe the spectroscopic observations, data reduction, and analysis, and present the first results of the project, taken with the fiber‐linked astronomical spectrograph FLECHAS. We present 391 radial velocity measurements of eight spectroscopic binaries, which were taken within an epoch difference of 1.6 years. These radial velocities were used to determine the spectroscopic orbital elements of the observed binary systems, which exhibit orbital periods in the range between nearly one up to several dozens of days. We could constrain the orbital solutions of seven of these binary systems, and redetermine the orbital solution of φ Dra, whose orbit exhibits >4 times longer orbital period and is more eccentric than given in the 9th Catalogue of Spectroscopic Binary Orbits.

Visión urbana de la Ciudad de Choluteca en Honduras para el Año 2034

En el marco del convenio existente entre la Universidad Nacional Autónoma de Honduras y Visión Mundial, el Observatorio Universitario de Ordenamiento Territorial de la Facultad de Ciencias Espaciales desarrolló, entre los meses de junio a octubre del año 2015, un estudio de prospectiva urbana para la ciudad de Choluteca. El proyecto se desarrolló en dos fases: 1) Diagnóstico de la ciudad con recopilación de información de fuentes secundarias y datos obtenidos en gira de reconocimiento territorial, además de información resultante en talleres donde se aplicaron encuestas a los actores claves involucrados en el proceso y se hizo uso de cartografía y ortofotos de la ciudad de Choluteca; que sirvieron para identificar los principales problemas y potencialidades de la ciudad desde las dimensiones de los enfoques de ambiente, socio-economía y urbanismo e infraestructura. Así mismo se evaluaron los recursos con que cuenta la ciudad y se analizó como maximizar su potencial, teniendo como resultado final unasíntesis de problemas y potencialidades, que junto a una serie de indicadores que se determinaron permitieron conocer la situación actual que enfrenta la ciudad. Toda esta información de la fase de diagnóstico fue utilizada para generar un Modelo Urbano Actual de la ciudad de Choluteca. Posteriormente se trabajó la fase de 2) Prospectiva: donde se evaluaron las condicionantes al crecimiento de la ciudad y se construyeron los tres escenarios de prospectiva al año 2034, plasmando cartográficamente la visión futura de crecimiento tendencial, una visión de crecimiento óptima y la construcción final de un escenario intermedio construido en consenso con los actores claves que participaron en el proyecto.

The Großschwabhausen binary survey

BackgroundSince 2009, the Großschwabhausen binary survey is being carried out at the University Observatory Jena. This new imaging survey uses available time slots during photometric monitoring campaigns, caused by nonphotometric weather conditions, which often exhibit good atmospheric seeing. The goal of the project is to obtain current relative astrometric measurements of the binary systems that are listed in the Washington Visual Double Star Catalog.Materials and MethodsFor the survey we use the Refraktor‐Teleskop‐Kamera at the University Observatory Jena to take imaging data of selected visual binary systems.ResultsIn this paper, we characterize the target sample of the survey, describe the imaging observations and the astrometric measurements including the astrometric calibration, and present the relative astrometric measures of 352 binaries that could be obtained during the course of the Großschwabhausen binary survey, so far.

Harlow Shapley: The Making of an Observatory Director

In 1919, the long-serving director of the Harvard College Observatory died. When the ambitious Harlow Shapley heard the news, although only in his early 30s, he resolved, if possible, to succeed him. But a problem emerged: Shapley was enlisted to debate the size of the Galaxy at a Washington meeting, where his opponent would be a noted speaker who was sure to defeat Shapley in front of an audience that included several involved in the Harvard appointment. The article describes the steps Shapley took to avoid or restrict the confrontation, and how in the end Shapley managed to secure the post, in which he became an outstanding success.

극궤도 위성 관측을 이용한 지표면에서의 태양 복사에너지 도출

본 연구에서는 대기 상단에서 반사된 복사와 지표면에서 흡수된 복사에너지가 서로 선형 관계임을 보인 기존의 알고리즘을 MODerate resolution Imaging Spectroradiometer (MODIS) 관측 자료에 적용시킬 수 있도록 개선하여 하향 및 순 태양 복사에너지를 산출하였다. 비교 검증을 수행하기 위해 Clouds and the Earth's Radiant Energy System (CERES) 센서와 강릉원주대학교(GWNU), 미국의 Atmospheric Radiation Measurement (ARM) 관측소의 지상 일사계 자료를 사용하였다. 지구 에너지 수지와 관련하여 지표면에서의 복사에너지를 비교하기에 앞서 알고리즘을 통한 산출 결과와 CERES 자료의 대기 상단 복사에너지를 비교한 결과, 결정계수가 0.9이상을 보여 상당히 유사함을 보였지만 Root-Mean-Square-Deviation (RMSD) 값이 다소 차이가 있는 것으로 나타났고 하향과 순 태양 복사에너지도 비슷한 결과를 얻었다. 강릉원주대학교 자료와 비교한 결과, 본 연구의 알고리즘을 통해 산출된 결과가 CERES 자료보다 작은 RMSD를 보임으로서 더 높은 정확도를 보였다. 한편, ARM 관측소의 경우 하향 태양 복사에너지의 평균적인 RMSD가 CERES 자료에 비해 다소 크게 산출되었지만 순 태양 복사에너지의 경우 비슷한 결과가 나타났으며 시 공간 해상도를 고려하였을 때 상당히 유사한 경향을 보이고 있음을 확인하였다. 본 연구에서 파악된 문제점에 대한 개선을 통해 향후 지상 관측을 대신하여 위성 관측으로부터 지표면에서의 하향 및 순 태양 복사에너지 자료를 고해상도로 제공하는데 유용하게 활용될 수 있을 것으로 기대된다. In this study, the net solar radiation fluxes at the surface are retrieved by updating an existing algorithm to be applicable for MODerate resolution Imaging Spectroradiometer (MODIS) observations, in which linear relationships between the solar radiation reflected from the top of atmosphere and the net surface solar radiation are employed. The results of this study have been evaluated through intercomparison with existing Clouds and the Earth's Radiant Energy System (CERES) data products and ground-based data from pyranometers at Gangneung-Wonju National University (GWNU) and the Southern Great Plains (SGP) of observatory of Atmospheric Radiation Measurement (ARM) site. Prior to the comparison of the surface radiation energy in relation to the energy balance of the earth, the radiation energy of the upper part of the atmosphere was compared. As a result, the coefficient of determination was over 0.9, showing considerable similarity, but the Root-Mean-Square-Deviation (RMSD) value was somewhat different, and the downward and net solar-radiation energy also showed similar results. The surface solar radiation data measured from pyranometers at Gangneung-Wonju National University (GWNU) and Atmospheric Radiation Measurement (ARM) observatory are used to validate the solar radiation data produced in this study. When compared to the GWNU, The results of this study show smaller RMSD values than CERES data, showing slightly better agreements with the surface data. On the other hand, when compared with the data from ARM SGP observatory, the results of this study bear slightly larger RMSD values than those for CERES. The downward and net solar radiation estimated by the algorithm of this study at a high spatial resolution are expected to be very useful in the near future after refinements on the identified problems, especially for those area without ground measurements of solar radiation.

CTK‐II & RTK: The CCD‐cameras operated at the auxiiary telescopes of the University Observatory Jena

AbstractThe Cassegrain‐Teleskop‐Kamera (CTK‐II) and the Refraktor‐Teleskop‐Kamera (RTK) are two CCD‐imagers which are operated at the 25 cm Cassegrain and 20cm refractor auxiliary telescopes of the University Observatory Jena. This article describes the main characteristics of these instruments. The properties of the CCD‐detectors, the astrometry, the image quality, and the detection limits of both CCD‐cameras, as well as some results of ongoing observing projects, carried out with these instruments, are presented. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The synodic rotational period of asteroid 4332 Milton

The results of our new photometric observations of the main-belt asteroid 4332 Milton are presented. These observations were obtained on two successive nights in August 2012 at Çanakkale University Observatory. The bimodal light curve amplitude and period were determined to be 0.16 ± 0.01 mag and 3.295 ± 0.005 h, respectively.

RECURRING OCCULTATIONS OF RW AURIGAE BY COAGULATED DUST IN THE TIDALLY DISRUPTED CIRCUMSTELLAR DISK

ABSTRACT We present photometric observations of RW Aurigae, a Classical T Tauri system, that reveal two remarkable dimming events. These events are similar to that which we observed in 2010–2011, which was the first such deep dimming observed in RW Aur in a century’s worth of photometric monitoring. We suggested the 2010–2011 dimming was the result of an occultation of the star by its tidally disrupted circumstellar disk. In 2012–2013, the RW Aur system dimmed by ∼0.7 mag for ∼40 days and in 2014/2015 the system dimmed by ∼2 mag for >250 days. The ingress/egress duration measurements of the more recent events agree well with those from the 2010–2011 event, providing strong evidence that the new dimmings are kinematically associated with the same occulting source as the 2010–2011 event. Therefore, we suggest that both the 2012–2013 and 2014–2015 dimming events, measured using data from the Kilodegree Extremely Little Telescope and the Kutztown University Observatory, are also occultations of RW Aur A by the tidally disrupted circumstellar material. Recent hydrodynamical simulations of the eccentric fly-by of RW Aur B suggest the occulting body to be a bridge of material connecting RW Aur A and B. These simulations also suggest the possibility of additional occultations which are supported by the observations presented in this work. The color evolution of the dimmings suggest that the tidally stripped disk material includes dust grains ranging in size from small grains at the leading edge, typical of star-forming regions, to large grains, ices or pebbles producing gray or nearly gray extinction deeper within the occulting material. It is not known whether this material represents arrested planet building prior to the tidal disruption event, or perhaps accelerated planet building as a result of the disruption event, but in any case the evidence suggests the presence of advanced planet building material in the space between the two stars of the RW Aur system.

Exoplanet Transits Registered at the Universidad de Monterrey Observatory. I. HAT-P-12b, HAT-P-13b, HAT-P-16b, HAT-P-23b, and WASP-10b

Forty transits of the exoplanets HAT-P-12b, HAT-P-13b, HAT-P-16b, HAT-P-23b, and WASP-10b were recorded with the 0.36 m telescope at the Universidad de Monterrey Observatory. The images were captured with a standard Johnson-Cousins Rc and Ic and Sloan z’ filters and processed to obtain individual light curves of the events. These light curves were successfully combined for each system to obtain a resulting one of higher quality, but with a slightly larger time sampling rate. A reduction by a factor of about four in per-point scatter was typically achieved, resulting in combined light curves with a scatter of ∼1 mmag. The noise characteristics of the combined light curves were verified by comparing Allan variance plots of the residuals. The combined light curves for each system, along with radial velocity measurements from the literature when available, were modeled using a Monte Carlo method to obtain the essential parameters that characterize the systems. Our results for all these systems confirm the derived transit parameters (the planet-to-star radius ratio, ; the scaled semimajor axis, a/; the orbital inclination, i; in some cases the eccentricity, e; and argument of periastron of the orbit, ω), validating the methodology. This technique can be used by small college observatories equipped with modest-sized telescopes to help characterize known extrasolar planet systems. In some instances, the uncertainties of the essential transit parameters are also reduced. For HAT-P-23b, in particular, we derive a planet size 4.5 ± 1.0% smaller. We also derive improved linear periods for each system, useful for scheduling observations.

From Your Body Is a Space That Sees, 2016

From Your Body Is a Space That Sees, 2016 Lia Halloran (bio) Click for larger view View full resolution Lia Halloran CRATER HYPATIA, 2016 Cyanotype print, painted negative on paper, 40 x 25 in. [End Page 3] Click for larger view View full resolution Lia Halloran SPECTRA, AFTER ANTONIA MURRAY (detail), 2016 Ink on drafting film, 76 x 76 in. [End Page 5] Click for larger view View full resolution Lia Halloran PAPER DOLLS (detail), 2016 Ink on drafting film, 40 x 132 in. [End Page 27] Click for larger view View full resolution Lia Halloran SPECTRA, AFTER ANNIE JUMP CANNON, 2016 Cyanotype print, painted negative on paper, 76 x 42 in. [End Page 59] Click for larger view View full resolution Lia Halloran top: COMET, AFTER ANNIE JUMP CANNON, 2016 Cyanotype on paper, with matching negative ink on drafting film, 76 x 76 in. each Click for larger view View full resolution NEBULAE, AFTER WILLIAMINA FLEMING, 2016 Ink on drafting film, with matching positive cyanotype on paper, 76 x 76 in. each [End Page 60] Click for larger view View full resolution Lia Halloran SPECTRA, AFTER ANTONIA MURRAY, 2016 Cyanotype on paper, with matching negative ink on drafting film, 76 x 76 in. each [End Page 61] Click for larger view View full resolution Lia Halloran GLOBULAR CLUSTER, AFTER CECILIA PAYNE, 2016 Cyanotype print, painted negative on paper, 42 x 76 in. [End Page 77] Click for larger view View full resolution Lia Halloran LUNAR CRATER, AFTER CAROLINE HERSCHEL, 2016 Cyanotype print, painted negative on paper, 40 x 25 in. [End Page 101] >> Your Body Is a Space That Sees Your Body Is a Space That Sees is a series of large-scale cyanotype works inspired by the fragmented history and contributions of women in astronomy. The series offers a visual account and female-centric astronomical catalog of craters, comets, galaxies, and nebulae, drawing from narrative, visual, and historical accounts of a group of women known as “Pickering’s Harem” or the “Harvard Computers,” who worked at the Harvard Observatory starting in 1879. This little-known group of women made a significant impact in the field of astronomy by using photographic glass plates to catalogue and classify the size, brightness, and chemical content of stars. The key to unlocking the distance of the universe was discovered by one of these women, Henrietta Swan Leavitt, based on her observation of variable stars. Her discoveries provided evidence that subsequently supported Edwin Hubble’s expanding universe theories. The important contributions of these women to the fields of astronomy and astrophotography were compensated with wages less than half of what their male counterparts would have been paid. Click for larger view View full resolution Women employees of the Harvard Observatory, the “Harvard Computers,” Cambridge, Massachusetts, c. 1925. Photo courtesy of the Harvard College Observatory Harvard University houses the largest collection of astronomical glass plates in the world—over 500,000, taken between the mid-1880s and 1992, including some of the early daguerreotype of the moon. Research for this series was done in partnership with the archives at the Harvard College Observatory to identify specific plates that were studied and catalogued by the approximately eighty women in the “Harvard Computers” group. These plates serve as a reference for large paintings of the galaxies and stellar objects. Your Body Is a Space That Sees offers the experience of the night sky through the discoveries made by these astronomers. [End Page 102] The cyanotype works are created by painting stellar images on semi-transparent drafting film. They are then pressed over paper coated with light-sensitive emulsion and exposed to the sun. The resulting piece is a cyanotype print of the positive image in equal scale to its matching negative: a photographic print created without a camera. This process, which mimics early astronomical glass plates moving between transparent surfaces, is multilayered in meaning and technique: images of stars created by a star (our sun), paintings used to create a painting (light-sensitive emulsion exposed by another painting). Cliché-verre—a method that creates a photograph by painting on a glass plate used as the negative—was popular in the...

Het oudst bewaarde planetarium van Nederland: de Sphaera Movens, bijgenaamd Leidsche Sphaera. Geschiedenis en restauraties door de eeuwen heen

Around 1670 in Rotterdam a planetarium was built, depicting the Copernican configuration of the planets. In 1710 this scientific instrument was presented to Leiden University. After an intense refurbishment, the then called Sphaera incomparabilis was placed in the University library, where it could be admired until the beginning of the nineteenth century. After being housed for more than a century in the building of Leiden University Observatory, the instrument was presented in 1931 to the newly erected Museum for the History of Science and Medicine (the forerunner of the present Museum Boerhaave). In recent years the planetarium was restored. This project has triggered new research into the origin and history of the instrument, the results of which are presented in this paper.

Absolute and geometric parameters of contact binary GW Cnc

We present the results of our investigation on the geometrical and physical parameters of the W UMa type binary system GW Cnc. We analyzed the photometric data obtained in 2010 and 2011 at Ankara University Observatory (AUO) and the spectroscopic data obtained in 2010 at TUBITAK National Observatory (TUG) by using the Wilson–Devinney (2013 revision) code to obtain the absolute and geometrical parameters. We derived masses and radii of the eclipsing system to be M1=0.257M⊙,M2=0.971M⊙,R1=0.526R⊙ and R2=0.961R⊙ with an orbital inclination i(∘)=83.38±0.25 and we determined the GW Cnc system to be a W-type W UMa over-contact binary with a mass ratio of q=3.773±0.007.

Apsidal Motion Study of Close Binary System CW Cephei

New observations for the times of minimum lights of a well-known apsidal motion star CW Cephei were made using a 0.6 m wide field telescope at Jincheon station of Chungbuk National University Observatory, Korea during the 2015 observational season. We determined new times of minimum lights from these observations and analyzed O-C diagrams together with collected times of minima to study both the apsidal motion and the Light Time Effect (LTE) suggested in the system. The new periods of the apsidal motion and the LTE were calculated as 46.6 and 39.3 years, respectively, which were similar but improved accuracy than earlier ones investigated by Han et al. (2002), Erdem et al. (2004) and Wolf et al. (2006).

Optical Orbit Determination of a Geosynchronous Earth Orbit Satellite Effected by Baseline Distances between Various Ground-based Tracking Stations II: COMS Case with Analysis of Actual Observation Data

We estimated the orbit of the Communication, Ocean and Meteorological Satellite (COMS), a Geostationary Earth Orbit (GEO) satellite, through data from actual optical observations using telescopes at the Sobaeksan Optical Astronomy Observatory (SOAO) of the Korea Astronomy and Space Science Institute (KASI), Optical Wide field Patrol (OWL) at KASI, and the Chungbuk National University Observatory (CNUO) from August 1, 2014, to January 13, 2015. The astrometric data of the satellite were extracted from the World Coordinate System (WCS) in the obtained images, and geometrically distorted errors were corrected. To handle the optically observed data, corrections were made for the observation time, light-travel time delay, shutter speed delay, and aberration. For final product, the sequential filter within the Orbit Determination Tool Kit (ODTK) was used for orbit estimation based on the results of optical observation. In addition, a comparative analysis was conducted between the precise orbit from the ephemeris of the COMS maintained by the satellite operator and the results of orbit estimation using optical observation. The orbits estimated in simulation agree with those estimated with actual optical observation data. The error in the results using optical observation data decreased with increasing number of observatories. Our results are useful for optimizing observation data for orbit estimation.

DIVISION G COMMISSION 21: GALACTIC AND EXTRAGALACTIC BACKGROUNDS RADIATION

Commission 21 was one of the oldest and smallest in the IAU yet one which underwent the most evolution since its inception. It began in 1955 as Light of the Night Sky (Lumière du Ciel Nocturne) under the Presidentship of Jean Dufay (University Observatory at Lyon). As the name suggested, in the years before space observations, its focus was on observations of atmospheric light which, at the time, was the domain of astronomers. Thus the early proceedings of the Commission were dominated by reports of the daytime and nighttime emission as observed from different locations and different conditions. Our knowledge of the Earth's atmosphere is still shaped by these early observations (Meier R.R., 1991, Space Sci. Rev. 58, 1). Members of Commission 21 were key to organizing interational collaborations to set up atmospheric stations at different latitudes, including in the Souther hemisphere and in ensuring a consistent calibration between the instruments. The Commission also bought in results from Soviet scientists in an era where communication was limited by both politics and language.

Are Historical Observations “Ancient” or “Modern”?

AbstractThe demarcation between “old”, “historic” and “heritage” is fuzzy. To a large degree it depends upon purpose and usefulness, and it will always be subjective. At what point does the intrinsic value of an historic item outpace the mystique associated just with its age? When, for instance, does an “old” car become a “vintage” car? When do archived astronomical records contribute something of quantitative value to science? When can they be extricated from the realms of the museum and placed in the context of modern research?Celestial objects vary. Some do so explosively, often irreversibly; many vary periodically over time-scales from a hour or less to a century or more. Furthermore, all celestial objects change as they evolve, mostly so slowly as to be practically imperceptible, but while the general time-scale of that evolution is millions of years there are a few stages (such as the collapse from AGB towards planetary nebula and white dwarf) which happen rather suddenly, and invaluable examples of “before--after” can be found in some plate stores. Astrophysics has a comprehensive need to investigate the nature and time-scales of all types of change, especially ones which only access to its “heritage” data can describe. Surely in this day and age we have enough tools, capacity and technologies to fulfil such a basic requirement?The frustrating answer is that we do have some of the necessary tools, and most of the technologies, but as a community we lack “capacity” if that means manpower and funds. The problem is a technical one of accessing the older data in useable formats; it was generated by the universal change in detector technology from photography to electronic device, an exciting development in efficiency and scope that heralded a new era of research capability and data management, archiving and sharing, but it left pre-digital photographic data right out of the picture. Developments of that nature should have made research more inclusive, instead of the seriously exclusive picture that is currently seen. The longer the situation prevails, the greater the inertia and scepticism to be overcome. Fortunately, some of the challenges are being tackled successfully, the most productive to date being the dasch project (dasch.rc.fas.harvard.edu) at Harvard College Observatory to digitize and share all the images and objective-prism spectra from its collection (the world's biggest) of over 0.5M large plates. The DAO has commenced a programme to digitize its collection of > 16,000 high-dispersion spectra (~70% are good enough to scan and convert), and to scan plates from its larger but older Cassegrain collection of > 90,000 spectra upon request. The instrument for this Herculean task is its own PDS, now suitably upgraded to meet the demands of speed and accuracy; the DAO has also acquired and upgraded a second PDS, with which it plans to share the load. Some smaller observatories in Europe are trying with less sophisticated equipment, but the rest have not the resources to give such data transformation any priority. Despite the unquestionable advantages, it is still necessary to convince colleagues that the medium is not the message, and that the scientific need comes before technological expedience.

Circumstellar disks revealed byH/Kflux variation gradients

The variability of young stellar objects (YSO) changes their brightness and color preventing a proper classification in traditional color-color and color magnitude diagrams. We have explored the feasibility of the flux variation gradient (FVG) method for YSOs, using $H$ and $K$ band monitoring data of the star forming region RCW\,38 obtained at the University Observatory Bochum in Chile. Simultaneous multi-epoch flux measurements follow a linear relation $F_{H}=\alpha + \beta \cdot F_{K}$ for almost all YSOs with large variability amplitude. The slope $\beta$ gives the mean $HK$ color temperature $T_{var}$ of the varying component. Because $T_{var}$ is hotter than the dust sublimation temperature, we have tentatively assigned it to stellar variations. If the gradient does not meet the origin of the flux-flux diagram, an additional non- or less-varying component may be required. If the variability amplitude is larger at the shorter wavelength, e.g. $\alpha < 0$, this component is cooler than the star (e.g. a circumstellar disk); vice versa, if $\alpha > 0$, the component is hotter like a scattering halo or even a companion star. We here present examples of two YSOs, where the $HK$ FVG implies the presence of a circumstellar disk; this finding is consistent with additional data at $J$ and $L$. One YSO shows a clear $K$-band excess in the $JHK$ color-color diagram, while the significance of a $K$-excess in the other YSO depends on the measurement epoch. Disentangling the contributions of star and disk it turns out that the two YSOs have huge variability amplitudes ($\sim 3-5$\,mag). The $HK$ FVG analysis is a powerful complementary tool to analyze the varying components of YSOs and worth further exploration of monitoring data at other wavelengths.