Letters of Intent received in 2018

LoI 2020-2046
Non-GA Symposium: New Avenues in Variability Science from Legacy Data

Topics

Long-term variability throughout the cosmos
Preserving and accessing heritage information for new science
Rapid access to variability data across decades
Photographic plate digitization

((Editors: Elizabeth Griffin, [address as above]
((Dr Wayne Osborn,
((Central University Michigan
((Mount Pleasant, Michigan, USA

Rationale

Summary: The huge new surveys planned or commencing are expected to yield prolific information about variable objects throughout the cosmos, from galaxies to transiting planets. But those advances in knowledge will be limited to, and inescapably biased by, the time-spans which modern surveys can cover. Astronomy's heritage data reach back significantly further in time, but the data are photographic, so are inaccessible to modern analyses that require data to be digital. Through intense digitization, the DASCH project at Harvard (completion 2020) is providing access for the first time to a century of photographic data and has already revealed numerous new variables and transients on a variety of time-scales. Treating all significant plate collections similarly will increase the cadence for available data, fill gaps, and render access to the historical data easy and rapid, thereby serving the whole of our science. The Symposium will seek to match the potential of individual plate collections to the requirements of different scientific topics, and will draw up an Action Plan to effect accurate and efficient digitization that brings these inherited data into the reach of modern analyses. Doing so will establish collaborations throughout astronomy's sub-disciplines.
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Astrophysics - the archetypal observational science - is built upon pyramids of data collected with numerous instruments, technologies and techniques, from sites in many different areas of the globe. Assiduous observing has shown that everything actually changes at some level, manner or time-scale. Those changes contain clues to detailed intricacies of stellar formation and evolution, yet new surveys are still adding new questions, new rates of change, and querying the frequencies of such changes. These are indeed exciting and profitable sources for investigating the detailed nature of the universe. Yet modern observing can only probe back in time as far as its electronic archives of data extend - at most up to 20 years - leaving very serious gaps in our knowledge as to how changes occur over significantly longer time-scales. The volumes in the DASCH and AAVSO databases illustrate some of the very many fascinating changes that have been occurring during the pre-digital decades, but there are few spectroscopic follow-ups to assist with interpretations. Studies of the past activity of the Sun will also benefit enormously from examining historical records of its spectra, yet it has never been attempted methodically. These are core matters for the Symposium to discuss.

Astronomy has an exceedingly rich accumulation of inherited observations - direct images and spectra, well documented, well ordered, and generally well preserved, and the envy of almost all the other natural sciences. The great majority were taken as part of individual research projects; relatively few were acquired purely through surveys. The long time-spans between those observations and modern ones can yield exciting new information about variability, of a nature not otherwise yet encountered (e.g., AGB stars at the He flash; historical observations of comets leading to accurate orbits and to quantifying non-gravitational perturbations). Combined information from sunspot drawings, geomagnetic and ionospheric activity and galactic cosmic rays will be a tremendous boost to the burgeoning study of “space weather”. These inherited observations belong to the whole astronomical community; estimated numbers range from 4 to 7 million. The motivation for keeping them in the first place was the declared intention to make them available to any bona fide researcher. That objective continues, whether as physical plates or as strings of digitized information. Plates are also valued as historical artefacts; many bear pointers to cultural evolution, and are ideal for public outreach.

To convert a physical record, encoded in light-sensitive grains embedded in gelatin, into readable digits requires a purpose-built machine and the application of a theory which was well understood as long ago as 1890. Organizing and implementing that “digitization” (and the auxiliary steps needed, from cleaning the backsides of every plate to processing the digital images into a rapid-access database), is all that prevents the astronomical community from analyzing variability across many decades rather than just a few years. However, universal changes in detector technology mean that only a few astronomers today understand the correct procedures for photographic plates, or can recall the original projects for which a set of plates was exposed. Moreover, plates that belong to the community are in effect the responsibility of no-one. With the notable exceptions of DASCH at Harvard and the new Chinese scanner now operational in Shanghai, most observatories have fewer options for scanning now than they had 40+ years ago when they could - and did – make graphical recordings of spectra, or measured stellar images photometrically or astrometrically.

Time is not on our side. The plates themselves age, though slowly, but the associated meta-data (log-books and other records) are ageing rapidly and soon many will be no longer readable. Both plates and records are vulnerable to damage or destruction by natural hazards (flooding, fire, earthquakes), and - worse - to human ignorance. The extant wisdom in the community will also be lost before long, as people retire or disappear from the scene. A comprehensive Catalogue of data is clearly a matter of high priority, and to which each Observatory can contribute but may only be motivated to do so if part of an international scheme. The time to act is therefore NOW. The action will start by establishing a meaningful conversation between experts in time-domain studies and their attendant requirements for broader expansion, and experts who understand the full potential of different plate archives. An IAU Symposium is an ideal forum for such a meeting; it will command the respect of the community which needs to be represented, and it will enable the attendance of all who need to attend, without the drawback of insufficient resources for travel. The Symposium will also provide a forum for planning closer involvement of students and scientists from developing countries. Most are familiar with digital activities, and could become engaged in deep-machine learning, the preservation and evaluation of both digitized and analogue materials, and other tasks that are central to the overall project.

The timing is propitious. DASCH will have completed the scanning of its entire plate collection by 2020, and the scientific results will be becoming available. DASCH provides rapid access to the most complete (full sky) and deep coverage (B 14-17) of a century of data and has already revealed numerous new variables and transients on a variety of time-scales. Its discoveries of nearly countless new variables, a great many new dwarf novae, and unidentifiable objects will spark enormous interest in the potential of every other plate archive. But the meeting should be no later than 2020. IAU GA XXX (2018) accepted a new Resolution that not only encourages efforts to make archived plate materials accessible to the community but also stresses the fact that this has got to be done before it is too late.

This Symposium will be organized as an intense discussion forum, with more sessions being devoted to break-out consultations than to formal plenary talks. Time will be devoted to details of new science that has been made possible only through access to archived plates, and to learning details of the scientific information which Harvard [DASCH] and Shanghai have extracted from their plate collections. At a number of critical junctures the participants will be challenged to make realistic decisions regarding methods and routes to pursue, criteria to apply, where and when to engage unskilled assistance, publicity, and acceptable time-scales for achieving full digital access to historical data. The meeting will also discuss “best practice”, both in handling plates and in digitizing them, bearing in mind the different kinds or modes of data which various new science topics will need, and will devote time to defining the best models for carrying out the tasks of digitization. The model(s) finally selected will point the way to possible funders.

The location is under discussion. Holding the meeting at Shanghai Astronomical Observatory will provide an important opportunity to see a new design of plate-scanner and its attendant team in operation; equally, holding it at Harvard will demonstrate how a fully working scanner and comprehensive analysis system can be created.