Petar Goulev, Milcho Tsvetkov, Renate Budell

►Spectral observations of the Sun

►Discovered Helium in the Sun (1868)

►Nature of Sunspots and Solar Flares

►Determined the temperature of the Sun

► Founder of scientific journal “Nature”

►6,000 glass negatives►Size: 81 x 30 mm

or 164 x 81 mm►Dates from 1880’s – 1950’s

(Solar Physics Observatory, Norman Lockyer Observatory)

►Spectra of individual stars & clusters

►Spectra of Comets and Novae

Reproduced from “The Chemistry of the Sun” (1887)  

►A couple of two large refractors one of them fitted with an objective prisms.

►Made to Lockyer's specification (in 1885)

► In this second telescope starlight is split by a 52-degree prism in front of the objective lens

Collection of plates of all the known elements, Collection of plates of all the known elements, which Lockyer used to identify atoms present which Lockyer used to identify atoms present in the Sun.in the Sun.

A collection of spectra of 36 metallic elements A collection of spectra of 36 metallic elements made in 1874-1879 remains in our archivesmade in 1874-1879 remains in our archives

Edward Edward FranklanFranklandd

►Antique plate

►Modern Plate

► This plate This plate contains the contains the spectra of spectra of 25 stars.25 stars.

►The timeframe in which the scanning could be done is essential

►Gelatine loses its properties►Remaining fixing bath may destroy silver

►The chemical technology wasn’t developed in the beginning of the last century

►Underexposed ►Underdeveloped►Faint as maximum density is below 1

►Every transportation is a risk►Furthermore the cost is very high and practically unaffordable

►Microdensitometer►Photometric Data System (PDS) - PDS 1010► Joyce Loebl

►Custom-designed scanner ►Digital Access to a Sky Century @ Harvard (DASCH)►Super Cosmos

► Flatbed ScannerWe used three different scanners manufactured by Epson ►Expression 10000►Expression 1640XL ►Perfection V700

►Advantages►Density mode D = 5.2►Resolution 5 µm in

important for precise position of spectra lines

►Weakness►depth of focus only few

µm therefore bending of plates with long spectra could be unfocused

►Advantages►Scan more plates at once►Automatically focus with large depths up to 1

mm

►Weaknesses►Maximum density D ≤ 3 ► Spatial resolution 12 µm► Density mode is impossible

►Advantages ►Large focus depths up to 1 mm ►Lowest cost

►Weaknesses►Maximum density D ≤ 3 ►No Autofocus

►The problem with the historical plates is the low contrast and is better to use a transmission mode.

►PDS image is sharper, however flatbed scanner has a better contrast ratio

► For further and precise study of the absorption lines optimal resolution is required

► Flatbed scanner should be used for a initial scanning of a spectral collection

►Microdensitometer scanner could be used only if the precise study is required

►The scanning has to be done sooner rather than later as the quality of the plates deteriorate.

►Some organisation would need a support to perform the scanning process.

► Matching the referent spectral lines with the spectral plates require a specialised software, and could be difficult to achieve.

► There is a necessity of a specialised spectral database with meets the requirements of storing such data

► The owners of spectral plates archives have to be made aware of how important is to come forward, digitalise their plates and make them accessible on-line.

► Thank you for your attention► Благодаря за вниманието► Хвала вам на пажњи

► With our presentation we would like to start a discussion for the future of the spectral plates stored into public and private archives across Europe and even worldwide.