Fig. 3: The shell star HR 5999 unveiJed. An artist's impression.Courtesy Mrs. M. Moesman.

derived. It is shown in Fig. 2 as an extension of the visualpart of the law. Compared to the normal extinction law ofinterstellar matter, the behaviour of the UV circumstellarlaw is completely different. The 2200 A bump is somewhatlower and shifted towards larger wavelengths Further­more, at about 1800 A it is very much lower, resemblingthat for the star (J Sco reported by Savage.

The Spectrum

A study was made of the red and blue spectral plates(12 A/mm) of HR 5999 taken in May 1978. Many lines ofH I, Ca I, Fe I1 and Ti 1I are present and are composed of abroad photospheric component and several blue-shiftedshell components. There are, however, lines which arepurely photospheric (e.g. Mg II), 4481) whereas other lineshave only shell components (Na 1 D). The H-alpha line is inemission and has variable double structure. This variationappears to be in antiphase with the brightness changes ofthe star. Low resolution IUE spectra, taken also in May1978, show in the short wavelength range (A< 2000 A) thepresence of emission lines of 0 I, C 11, C IV and probablyAI 11; in the long wavelength range (2000 A < A < 3000 A)there are indications of strong and broad absorptionfeatures. A steep drop-off of the continuum at about1800 Ais in agreement with the spectral type A7 derivedearlier from the red and blue plates. High resolution IUEspectra of the long wavelength region, taken more recentlyby Hack and Selvelli, reveal the presence of many shelllines from multiplets of Fe 11, Cr 11 and Mn 11 in absorptionand strong emission of the Mg 11 A 2800 doublet with adouble structure, comparable with that of H-alpha.

The radial velocities of the shell components on the blueand red plates vary in time between -40 and -5 km/s, moreor less in phase with the variation of the dust extinction.Because of the large width of photospheric lines theirradial velocites are more difficult to determine. The valuesvary between -20 and +20 km/so

Although many details of the spectra are still beingstudied, the spectral data support our believe in theexistence of a hot emission shell (C IV emission line)around the star, surrounded by a cooler, less dense shellregion, where the shell absorption components are formedand in wh ich the circumstellar dust is embedded. If this is

true, one can imagine that the dust extinction andpolarization variations are the result of changes in thecharacter of the dust grains due to perturbations in thephotosperic or hot shell region, which are propagatedoutward supersonically through the cooler dusty surround­ings. The cause and the characteristics of the perturba­tions are not yet clear, but the existence of instabilities inthe shell of HR 5999 can be expected in view of theevolutionary stage of this pre-main-sequence star.

A Supernova Discovered at La SillaDr. Andre B. Muller from ESO recently described (The

Messenger No. 19, p. 29, 1979) a new system allowing aneasy and efficient monitoring of galaxies for the detectionof supernovae. Using this system, H.E. Schuster discov­ered a supernova in NGC 1255 on December 30,1980 (lAUCircular No. 3559, 1981). At the time of discovery itsmagnitude was 17. This was the first supernova found onLa Silla.

Thanks to the kind collaboration of Visiting AstronomersDr. W. Seitter and Dr. H. Duerbeck, an immediate follow-upwas carried out, showing that it was a type 11 supernova.

P. V.

ESO/ESA Workshop on "Optical Jetsin Galaxies"

With the aim of encouraging European cooperation andcoordination in the use of the Space Telescope within somefields of research, ESO and ESA have arranged aseries ofworkshops on the use of the Space Telescope andcoordinated ground-baserJ observations. The second ofthese workshops, entitled "Optlcal Jets in Galaxies", tookplace in the auditorium of the new ESO Headquarters inGarching on February 18-19, 1~81.

Thanks to active contributions from 50 participants fromdifferent institutions in Europe and the USA, the meetingwas very successful. Optical, radio and ultraviolet observa­tions of jets were discussed in great detail. One of theresults of the meeting is that the Space Telescope isexpected to playa key role in the study of jets because ofhigh resolution and UV sensitivity. The workshop pro­ceedings will be published in a short time by the ESAPress. M. T.

ALGUNOS RESUMENES

Observaciones "Speckle" en infrarrojorealizadas con una cämara de television

En principio, los grandes telescopios, como el de 3.6 mde la ESO, tienen una resolucion angular mejor que0.1 segundo de arco, vale decir, que detalles asi depequenos pueden ser vistos; pero comunmente este no esel caso. Las mejores fotografias tomadas con grandestelescopios pocas veces muestran detalles mas pequenosque 1 segundo de arco (un segundo de arco es laseparacion angular de dos puntos separados por unmilimetro a una distancia de 200 metros); esto se debe ala presencia de la atmosfera que es turbulenta, y estaturbulencia produce una imagen borrosa dei objeto.

27

J. van Paradijs: Simultaneous Optical/X-ray Bursts 1

Tentative Time-table of Council Sessions and Committee Meetings. . . . . . 3

Applications for Observing Time at La Silla . . . . . . . . . . . . . . . . . . . . . . 4

Ph. Lamy and S. Koutchmy: Infrared Imaging and Speckle Observationswith a TV Camera 5

International Symposium on X-ray Astronomy 6

H.-A. Ott: Circumstellar Emission and Variability among SouthernSupergiants 7

Visiting Astronomers 9

N. Bergvall: The Drama of Galaxies in Close Interaction . . . . . . . . . . . . . . .. 11

Announcement of an ESO Conference on "Scientific Importance ofHigh Angular Resolution at Infrared and Optical Wavelengths" . . . . . . .. 14

List of Preprints Published at ESO Scientific Group 14

Personnel Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15

G. Courtes, J. P. Sivan, J. Boulesteix and H. Petit: The lonized Gas of M33 asSeen with a 6 m, F/1 Telescope 15

N. Kappelmann and H. Mauder: Cyclic Variations of T Tauri Stars 18

J. Bergeron: MR 2251-178: A Nearby QSO in a Cluster of Galaxies andEmbedded in a Giant H 11 Envelope 19

A. Hayli, F. Bertola and M. Capaccioli: The Dynamics of Elliptical Galaxies 21

P.S. The and H.R.E. Tjin A Djie: The Pre-Main-Sequence Shell StarHR 5999 Unveiled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 25

A Supernova Discovered at La Silla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 27

ESO/ESA Workshop on "Optical Jets in Galaxies" . . . . . . . . . . . . . . . . . . .. 27

Aigunos Resumenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 27

28

Los astr6nomos denominan esto"seeing"; y ellos se sienten bastantecontentos cuando el "seeing" se redu­ce a un segundo de arco. Hace aproxi­madamente 10 afios, un astr6nomofrances, Dr. Antoine Labeyrie, not6 queexposiciones de extremadamente cor­ta duraci6n (de s610 algunas centesi­mas de segundos) de estrellas brillan­tes muestran detalles (liamados"speckles") que son tan pequefioscomo la resoluci6n te6rica dei telesco­pio, y desarroll6 una tecnica (interfero­metria speckle) que permite extraer lainformaci6n que contiene un gran nu­mero de fotografias de corta exposi­ci6n de un solo objeto.

En el campo optico esta tecnica esusada hoy en dia por un gran numerode grupos en todo el mundo. Reciente­mente los Drs. P. Lamy y S. Koutchmyhan realizado con exito varios tests enLa Silla que mostraron que esta tecni­ca tambien puede ser aplicada en elinfrarrojo (a 1.6 ~lm).

EI gas ionizado de M33visto con un telescopiode 6m

Generalmente las regiones de hi­drogeno ionizado (H 11) en una galaxiason fuentes que emiten solo algunaslineas de muy baja intensidad. La mejormanera para obtener fotografias deta­Iladas de las estructuras de hidrogeno

Contents

ionizado en galaxias cercanas es usarun filtro de interferencia angosto paraseleccionar una de las lineas masintensas, en combinaci6n con un re­ductor focal para aumentar la ilumina­ci6n dei plano focal en el foco de ungran telescopio.

Debido a su gran extension angulary a su favorable inclinacion, M33 esuna de las galaxias mas apropiadaspara investigar las estructuras de H 11.

Cuando fue observada por primeravez por el Dr. Courtes y sus colabora­dores con el telescopio de 1.93 m deHaute-Provence, usando un filtro deinterferencia angosto y un reductorfocal, se hizo evidente que se requeriauna mayor resolucion angular parapoder obtener mas detalles de lasestructuras de hidr6geno ionizado. Yaque la resoluci6n angular aumenta conel tamafio dei telescopio, el reductorfocal dei Dr. Courtes fue adaptado alfoco primario dei telescopio de 6 m enla montafia dei Caucaso, cerca deZelentchuk en la Uni6n Sovietica.

En las paginas 16 Y 17 se puedenapreciar dos fotografias tomadas coneste instrumento, que es el telescopiooptico mas grande en el mundo. Ellasmuestran mas detalles que cualquierotra fotografia tomada antes de lamisma region y mas estudios serannecesarios para entender el origen delas varias estructuras que se puedenapreciar en las placas.