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M. de Groot, Senior Research Associate

Dr Mart de Groot continued his research into the behaviour of Luminous Blue Variables (LBVs):

1.

In collaboration with Drs Van Genderen (Leiden, Holland) and Sterken (Brussels, Belgium) papers XV and XVI in the series `Light Variations of Massive Stars' were published. These dealt with the brightness variations of several massive stars in the two nearest neighbour galaxies, namely six stars (R85, R99, R103, R110, R123 and R128) in the Large Magellanic Cloud (LMC) and two (R42 and R45) in the Small Magellanic Cloud (SMC). Several of these stars were identified as genuine LBVs, pulsation periods were determined for all of them, and theoretical models were discussed.

2.

As a part of the same collaboration, paper II in the series `Cyclicities in the light variations of LBVs' was published. It dealt with R40 in the SMC which was found to be subject to normal SDor (slow pulsation-like) phases.

3.

Also in the same collaboration, another paper on the brightness variations of one of the brightest stars in our Galaxy, $\eta$Carinae, was completed. This confirmed earlier findings, and also allowed refinement of the previous model in terms of the complicated interaction of the colliding winds from the two stars present in this binary and the hot luminous disk around one of them.

4.

Research on the peculiar LBV PCygni continued with regular observations done by the Automatic Photoelectric Telescope Service in Arizona. An investigation in collaboration with Dr Markova of the Bulgarian National Observatory and Dr Scuderi of the Catania Astrophysical Observatory (Italy) into the behaviour of PCygni's spectral lines, especially in relation to the star's brightness variations, was started and almost concluded. This should be published by the end of 1999.

5.

On the invitation of the Editor of Space Science Reviews, an article reviewing our present knowledge of PCygni was written in collaboration with Dr Israelian from the Astrophysical Institute of the Canaries, Spain. At the time of writing this report it has been accepted for publication.

6.

In preparation for a study of the brightness variations of PCygni during the last 50 years, many observations were collected from a variety of sources and subjected to detailed analysis to arrive at a set of data that is as homogeneous as possible; this is not an easy task when so many different observers and instruments are involved!

7.

Two summer students from QUB worked on a project to investigate a possible correlation between the behaviour of a selected number of spectral lines and the simultaneous photometric variations of PCygni. Some tentative conclusions were drawn, but these need further investigation as under item 4. Two further summer students, grant-aided under the Nuffield scheme, worked on different data sets of LBVs to find (quasi-)periods in a number of them, supporting research related to that under point 1 above.

8.

PUS: On the invitation of the Curaçao Astronomy Club the total solar eclipse of 1998 February 26 was observed, and two lectures delivered on the origin and future of the Universe. Four extensive radio interviews about the eclipse were given for three different radio stations, for a total of 4 hours 45 minutes.