The Swiss Ambassador and Consul GeneralVisit ESO

book will make the volume even moreuseful.

The work is weil underway. The pain­staking reproduction of the photographshas been accomplished under the closesupervision of C. Madsen, the transla­tion of the English original text into Ger­man has been completed and the textsfor the English and German editions areat the typesetters. Negotiations withlicence publishers are taking place in theUK, France, Italy, Spain, The Nether­lands, Denmark and the Soviet Union.Even the difficult question of the maintitle has been solved in two of thelanguages.

"Entdeckungen am Südhimmel" and"Exploring the Southern Sky" will bepublished in May 1987, a correspondingFrench edition will be out a few monthslater.

ESO Pictorial Atlas is Underway

The Swiss Ambassador to the FederalRepublic of Germany, His ExcellencyMr. Charles Müller, and the Swiss Con­sul General in Munieh, Mr. Kurt Weite,visited the ESO Headquarters on Oc­tober 14, 1986 for information about

Right on time for ESO's 25th anniver­sary, Springer-Verlag will publish a pic­torial atlas of the southern sky authoredby S. Laustsen, C. Madsen and R. M.West. It would appear to be the first timethat one of the leading astronomical in­stitutions has endorsed such an as­tronomical picture book for the generalaudience. It will present 237 photo­graphs (including 90 large-size colourand an approximately 120 cm long fold­ing plate) in an unprecedented quality ofreproduction and printing.

ESO and its current projects. The pic­ture was taken during a demonstrationof the ESO MIDAS image processingsystem (from lett to right: Preben Gros­b01, the Consul General, Klaus Banse,the Ambassador).

Part 1 of the book is devoted tophotographs taken with ESO telescopeson La Silla and showing extragalacticphenomena. Numerous objects insidethe Milky Way Galaxy are described inpart 2, and part 3 presents pictures ofminor bodies in the solar system with anemphasis on the latest pictures of Com­et Halley. The fourth and last part of thebook gives a portrait of ESO as an as­tronomical research institution. A com­prehensive glossary and indexes ofplate data and objects shown in the

ESO Press Releases

The following Press Releases havebeen published since the last issue ofthe Messenger. The distribution listnow contains about 350 addresses ofeditors, science journalists and others,who contribute to the dissemination ofnews about science. Members of thepress are welcome to apply for inclusionto the ESO Information and Photo­graphie Service.PR 08/86: The ESO Very Large Tele­

scope: One More Step Towards Real­ity (4 October).

PR 09/86: First Accurate Determinationof the Sizes of Pluto and its Moon(5 November).

PR 10/86: Long Lost Planet FoundAgain (4 December).

Wide Angle Photography of the Milky Wayc. MAOSEN, ESD, and S. LAUSTSEN, Institute of Astronomy, Aarhus

Introduction

Since astronomers began to usephotography on a scientific basis, anumber of pictures of the Milky Wayband, or large parts thereof, has beenmade. Barnard (1890, 1927) produced aseries of fine Milky Way photos. Laterattempts by Rodgers, Whiteoak et al.(1960), Schmidt-Kaler and Schlosser(1972), Sivan (1974) and others resultedin impressive pictures, either in the formof panoramas or extreme wide-fieldviews, mostly in weil defined (narrow)

12

spectral bands. The most famous de­pietion of the Milky Way, however, is nota photograph but a drawing made byhand. This was made by M. and T. Kes­ku la at Lund Observatory, and it hasbecome the standard representation ofthe Milky Way band in textbooks.

A new panorama has recently beenproduced at ESO. This panorama differsin some respects from most previousimages of the Milky Way band. With nofilter being used and the emulsion sensi­tive to visual light, the general impres­sion of the panorama is similar to the

impression when watehing the MilkyWay on the night sky.

As explained below, the resolution isof the order of 1 arcminute, or about thesame as that of the unaided human eye.However, 11th magnitude stars are visi­ble on the panorama. The full panoramais currently being reproduced for use ina forthcoming book with the title "Ex­ploring the Southern Sky". Here it willappear as a four-page spread with atotal length of approximately 120 cm,and it is our hope that in general it willserve educational purposes.

Selecting the Instrumentation

The photographic plate provides anideal detector for large-field survey workin the Milky Way. The surface brightnessof the Milky Way is easy to reach withthe speed of standard spectroscopicplates. In addition the combination ofhigh resolution and a large field is ofimportance. To obtain a wide field ofview, observers have either built specialinstruments or resorted to more or lessstandard off-the-shelf camera equip­men!. We feit that the lalter possibilityshould be investigated, although it wasevident that the choice would be verylimited. A survey of the market led us totest the Hasselblad SWC camera at theESO optical laboratory.

The SWC camera is fitted with a CarlZeiss Biogon 1 : 4,5/38 mm lens. Thislens covers 72° (horizontally) at a platesize of 56 x 56 mm2. This gives a scaleof 1 mm = 1°17', or l' = 0.013 mm. Thelens itself exhibits a minimal distortion(barrel distortion, 0.3 % at r = 30 mm).From k = 8 (k describing the nominalaperture), the lens is practically free ofcoma, a particularly annoying problemin connection with wide-angle photo­graphy of point objects. However at k~ 8, the light collecting area becomesprohibitively smalI, requiring excessiveexposure times. The lens has liltle vig­netting, although the cos4 law (decreaseof illumination by oblique rays due to thegeometry of image formation by lensesand the compression of the exit pupil foroblique rays) obviously leads to anoticeable light fall-off towards theedges of the field.

As far as resolution is concerned, acalculation on the basis of Rayleighs'sLimit (0 = 1.22 Ald radians), assuming awavelength of 5500 A, gives a theoreti­cal minimum resolution angle at fullaperture (1 : 4.5/38 mm = 8.44 mm) ofnot less than 16:3. However, a complexrefractor consisting of a large number oflens elements can hardly be expected toyield such a resolution in practice, dueto lens aberrations leading to a reduc­tion of contras!. In fact, the effectiveresolution was measured to be of theorder of 1'.

Overall, the performance of the lenswith respect to chromatic aberration,astigmatism and curvature of fieldturned out to be fully acceptable, andfollowing careful sampling of a numberof lenses on the optical test bench, acamera was selected for practical testson the sky.

Which Emulsion?

Keeping the optical performance ofthe lens in mind, we initially chose the

Kodak Technical Pan TP-2425 emulsionfor our tests. This emulsion, which wasbased on the Kodak Solar Flare Patrolfilm, reportedly has aresolution of400 I/mm (at a test-object contrast of1000 : 1) and 125 I/mm (at TOC 1.6 : 1)with development in POTA.

The spectral sensitivity extends to ap­prox. 7000 A, and with an increasedred-sensitivity (peak sensitivity falling inthe UV, in red around 6500 Aand againaround 6800 A) this of course impliesthat galactic emission nebulae will showup very weil.

This emulsion can be developed tofairly high y-values (2.8-3.8 in Kodak0-19), which is necessary to achieve agood detection of faint objects.

The TP-2415 is a rather slow material.Fortunately, however, it is fairly easy tohypersensitize. Everhardt (1980), Westet al. (1981) and others have reportedspeed increases up to 8.9 times by bak­ing in forming gas.

At the time of our tests the TP 2415was available in the form of 35 mm and4 x 5" sheet film. We therefore chose touse (cut-down) sheet film in Hasselbladsheet film holders.

Initial Sky Tests

The first sky tests were carried out ata private observatory at Herrsching,Ammersee, in southern Germany. Withthe camera mounted at the top end of asmall telescope, and the lalter beingused for tracking and guiding, the filmwas exposed for 60 min. at full aperture,which was deemed necessary in spite ofsome residual coma. Stars of mv = 11were recorded with aresolution of 1'. Itturned out, however, that the film did not(always) stay flat in its holder during theexposure, thus leading to a partial defo­cussing. It was therefore ultimately de­cided to abandon the TP 2415 (proper)in favour of the Kodak 153-01 emulsion,which is the TP-2415 emulsion coatedon glass. The main photographiccharacterics are more or less the same,with the main differences being some­what lower sensitivity and a slightly dif­ferent characteristic curve. For the finalobservations, the 153-01 was exposedfor 90 min. following 8 hrs baking informing gas at 60°C.

The Observations

The northern part of the Milky Waywas photographed from the Obser­vatorio dei Rocque de los Muchachoson the isle of La Palma, using the 60 cmreflector of the Royal Swedish Academyas tracking instrument carrying our tinycamera.

The southern part as weil as the MilkyWay centre was photographed from La

Silla in March 1985. Here, the 40 cmGPO was used. In addition to the platesneeded for the panorama, a few otherplates were obtained, including someplates of the twin Magellanic Cloudstogether with the Milky Way, shown inthe 1984 ESO Annual Report.

Printing the Panorama

Following the successful completionof the observations, the work started onprinting the panorama. The final picturecomprises 8 individual pictures. Each ofthese pictures originally exhibited differ­ing sky background densities, partly dueto the natural vignetting and partly be­cause of varying zenith distance. To re­duce these effects as much as possiblethe field actually used was limited to alittle more than 45 x 60°. Each platewas enlarged onto a copy film of24 x 24 cm2 and, during the copyingphase, flat field masks were used tocompensate the inherent vignelting.Each frame was fitted with a thin line tomark the galactic equator, and finallythe copy films were printed onto photo­graphic paper. Ouring the enlargementand final printing, enlargement factorswere carefully chosen in order not tointroduce additional distortion.

Finally the 8 prints were merged toform the panorama. Care was taken toensure a good fit, wh ich however wasonly possible along a narrow bandaround the galactic equator. While thecamera field is flat, the distances in thesky are measured along great circles ona sphere. The plates consequently ex­hibit a "varying" scale, and some ob­jects unavoidably appear twice alongthe edges of the merged images.

Acknowledgements

Our thanks are due to B. Buzzoni ofthe ESO optical laboratory (Garching),the staff of the Technical ResearchSupport at La Silla, Mr. P. Stältmeyer(Herrsching, FRG), P. Corbern and thestaff of the Swedish Telescope on LaPalma. Furthermore, we should like tothank Messrs. James Polack NS (Oen­mark) and J.A. Lundberg of VictorHasselblad AB (Sweden) for their assis­tance.

One ot the plates used tor the panorama isreproduced on the tollowing two pages. Itshows the central bulge ot the Milky Way withits myriad of stars. The central part of thegalaxy is of course hidden behind the ex­tended dust clouds in the galactic disko Thefield shown here covers approximately70 x 50°. The coma is of course visible in theouter regions of this image. In the panorama,only around 45° of each field is used, thusminimizing the effect of this aberration. ~

13

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From the forthcoming ESO book "Exploring the Southern Sky": Cometary globules in the Gum Nebula. Reproduced from a plate obtained withthe ESO Schmidt telescope for the ESO/SRC Atlas of the Southem Sky.

17