THE 2000 MEETING OF THE VARIABLE STAR SECTION TRISTRAM BRELSTAFF The 2000 Meeting of the BAA Variable Star Section was held at the Humphrey Rooms in Northampton on Saturday the 14th of October. Bob Marriott opened the meeting by welcoming the Section on behalf of the hosts, the Northampton Natural History Society, and then handed over to the BAA VSS Director, Roger Pickard. Roger said that there was a particularly packed program because everyone who he had asked to speak had eventually said yes. He then introduced the first speaker of the day. Alex Vincent's talk, 'Maxima and Minima of Eclipsing Binaries' consisted of a series of slides of various eclipsing binaries at maximum and minimum. These included naked-eye stars such as Beta Per, Beta Lyr, W UMa, Epsilon & Zeta Aur, and Lamba Tau, and also fainter ones such as RZ and TV Cas, Z Vul, RW Tau, and V1016 Ori. The naked-eye stars were captured on 30 second undriven exposures with a 50mm lens and the fainter ones on 1-2 minute exposures with a 135mm lens. V1016 Ori showed no visible difference between maximum and minimum because it is part of a multiple system (the Trapezium) but for all the other stars the eclipses showed up clearly (even Zeta Aur). In answer to a question for John Toone, Alex said the film he used was Fujichrome 400 and to another from Nick James he said he had not yet 'blinked' his slides for new variables, but was going to try it. The second speaker was Tony Markham and his talk was entitled 'The times they are a-changin', a reference to the times of minimum of eclipsing binary stars. Tony is the BAA VSS Eclipsing Binary Secretary and the Director of the Variable Star Section of the Society for Popular Astronomy (SPA VSS). He started of by asking why eclipsing binaries are not more popular amongst variable star observers. The answers, he suggested, were that eclipsing binaries have a reputation for predictability (and presumably are therefore unexciting), that several hours of observations are required each evening to get useful results, and that you really need to use predictions to plan your observations of them. Tony went on to explain the light elements of eclipsing binaries. These are often expressed as Min = JD + PxE where JD is the Julian date of an eclipse observed in the past, P is the period between eclipses, and E is the number of periods elapsed since the observed eclipse. The General Catalogue of Variable Stars (GCVS) lists values of JD and P for each eclipsing binary and these can be used to predict the times of future eclipses or to determine the phase of a given observation. The calculations involved are easy using a PC - Tony said he uses a spreadsheet program to do them. Tony then showed a phase diagram (a plot of magnitude against phase) of visual observation of u Her. This showed rather large scatter, but taking means reveals the shape of the light-curve much better. He went on to show phase diagrams for RZ Cas, U Cep & Beta Lyr. Diagrams for different years show clear systematic changes in the phase of mid eclipse relative to the GCVS light elements (these are the times that are 'a-changin'). For example, in 1996 the eclipse of U Cep was at phase 0.035 (ie, 2 hours later than predicted) but in 1999 it was at phase 0.045 (2.5 hours late). Tony went on to explain why eclipses might not occur at the predicted phase (phase 0.00). Firstly, the GCVS elements might be wrong: the JD part of the light elements could be in error, which would give a constant error in the predictions; the P part could be slightly wrong, giving a systematically varying error in the predictions; the P part could be multiple of the true period; or the P part could be completely wrong due to a transcription error. Secondly, the period of the star could be truly changing. This might be due to mass-transfer within or mass-loss from the system. It might also be due to the gravitational effect of a third star in the system. To be useful, predictions should be based on the latest available light elements. The GCVS elements are often rather old, but a good source of recent light elements is the Krakow Yearbook (SAC). Tony uses these as the basis for the predictions in the BAA VSS Circulars and the BAA VSS web pages. The predictions in the Circulars only cover a small number of large-amplitude stars, but the web pages include predictions for many more. Charts are available for around 130 stars on the BAA VSS Eclipsing Binary Program and 20 are downloadable from the web pages. Observations should be submitted to Dave McAdam in the same way as Main Program observations. In the discussion, Norman Walker pointed out the need for fairly frequent timings of minimum in order to distinguish between smooth and discontinuous period changes. Andy Hollis also stressed the need for continuity in observational coverage. Norman Walker said that the timing of eclipsing binary minima was still of scientific value, for example, in the Wolf-Rayet eclipsing binaries, whose periods are not changing in the way expected from the mass-loss known to be occurring in these stars. Gary Poyner said that the SPA VSS produce lots of eclipsing binary observations and asked what can be done to get BAA VSS members to do more. Albert Zijlstra mentioned the possibility of period changes due to relativistic effects and pointed out that the planet Mercury had once had a 'period problem'. The next speaker was Guy Hurst, the Editor of The Astronomer magazine, whose subject was 'Is Astronomical Bias the Enemy of the Modern Variable Star Observer?'. He started off by reviewing various sources of error in variable star observing. Misidentification of the variable or comparison stars is a common problem, especially with fainter stars, and there is even a need for astrometry of some cataclysmic variables at maximum to allow them to be unambiguously identified at minimum. The Purkinje effect is another common source of errors because we often have to compare a red variable with white comparison stars. Its effects vary with the instrument and with the part of the eye used to make the estimates. Transcription errors during recording or reduction are also probably fairly common and the former are more likely if you are recording from distant memory. Cold, tiredness and other distractions also make errors more likely. Comparison star sequences can encourage errors if they labelled in wrong order and the use of Johnson V magnitudes can introduce small errors because they do not match visual magnitudes precisely. Guy went on to mention position-angle error (ideally you should have the variable and comparison horizontal in your field of view when you compare them), dark adaption (allow at least 15 minutes and use only a dim red light), and averted vision (you should bring the variable and comparison in turn to the middle of your field of view when estimating). He then talked about bias and the influence of observer expectations. As an example he mentioned that R CrB can fade as far as mag 7.0 before some people stop recording it at mag 6.0. Observing too frequently can lead to errors because the memory of previous observations is still fresh in the mind. So can hearing of other people's results over the phone or internet. Guy said he was especially aware of this as he is often asked to confirm other people's discoveries. Chart quality can also influence errors. The older BAA VSS charts tend to show the comparison star magnitudes, which can encourage bias, but the newer ones don't. As mentioned above, if the comparison star sequence is labelled in the wrong order it can result in observers 'forcing' their estimates to 'fit' the sequence. Inadequate plotting of faint stars (Guy mentioned over-reliance on Guide Star Catalog) can also lead to mistakes when the variable is faint. The presence of 'secondary variable stars' on charts drawn up for other variables can also introduce errors as these often have poor identifications and poor comparison stars. The way you record and reduce your observations can also influence errors. Observations should preferably be recorded as soon as they are made. However, some observers apparently wait until end of the observing session before recording them. Guy also warned against the habit of recording the 'usual estimate'. Also, if you reduce your observations on the same night then there is the possibility of introducing bias. Over the past few years the internet has had a big effect on the quality of variable star observations. Observations presented on the internet tend to contain lots of errors. They often appear to be inadequately checked and most lack details, such as the instrument used, that can be used to assess their quality. Guy also mentioned what he called the 'trigger effect' in which one observer reports a change in a particular star on the internet and then the observations of other observers tend to follow suit. He showed a light-curve of V705 Cas (Nova 1993) in which a long interval of constancy was followed by a sudden drop of about 1.0 mag which he thought might be a result of this 'trigger effect'. He also suspected that some of the spikes on the fade of V723 Cas (Nova 1995) might be of similar origin. Discoveries of novae, supernovae and other variable stars are often announced on inadequate evidence. There have even been cases of 'discoveries' being submitted to the GCVS on the basis of only 2 photos. There is also a widespread tendency to accept small-amplitude changes too readily. Confirmations of discoveries are often made and reported without due care, for instance, several people 'confirmed' a 'nova' which turned out to be Mars. Also, some people seem to believe that any star near a galaxy must be a supernova. In the discussion, Bill Worraker said had a particularly galling experience when he recently made a negative observation of a particular cataclysmic only to have Gary Poyner phone up an hour later saying someone had discovered it in outburst. Norman Walker said the visual observations have errors (rms) as large as 0.5 mag and that some people are trying to use then to detect variations that are just too small. However, Gary Poyner pointed out that Bjorn Granslo had detected 0.2 mag superhumps and that this had been confirmed by CCD photometry. Nick James was worried that bias invalidates our ability to take averages of observations, which is a basic assumption of collaborative variable star observing. Andy Hollis said that W Cyg is regarded as beginners object but Doug Saw said the observations of it show so much scatter that he could summarise each year's observations by drawing a straight line through them. Mike Peel added that we really need a long series of observations for each star but that this is difficult to get for novae. Don Pollacco (Queen's University Belfast) then got up to speak on 'Highly Evolved Low/Intermediate Mass Stars'. He started off by asking 'What is an R CrB star?'. There is the spectroscopic definition: a hydrogen-deficient supergiant star, and there is the photometric definition: a star which shows long intervals of stability with occasional steep declines followed by slower recoveries. While these definitions are good for R CrB itself, they are not so good for some other R CrB stars. For example, V854 Cen, a star that was only named as a variable star in 1983, is mag 7 at max but has spent most of the last century at mag 14 or fainter. It also shows hydrogen lines in its spectrum. Don then asked 'What is going on in R CrB stars?'. He showed some images of UW Cen, a very active R CrB star that is surrounded by a nebula, the structure of which has changed significantly in just 6 years. This is probably due to dust clouds close to the star moving and casting shadows on the nebula. The current physical model has R CrB stars as unstable stars that eject 'puffs' of material, 3 or 4 at a time. When a puff is ejected in our line of sight we see the star 'eclipsed'. We even see the equivalent of the solar corona spectrum. There are currently two competing evolutionary models for R CrB stars and both are difficult to test. The first model has them as merged white dwarfs, but the only real evidence in favour of this is that no R CrB stars are known to be binaries. The second has them as highly evolved single stars, almost white dwarfs, that undergo instabilities similar to nova explosions. These instabilities may be similar to those seen in the outbursts of Sakurai's Object and in Nova 1918 No2 Aql. Sakurai's Object (V4334 Sgr) underwent a nova-like outburst in 1995, reaching mag 10 in 1996. It is currently at mag 25 but is somewhat brighter in infra-red. At first it was thought to be a nova but then it was shown to be hydrogen-deficient, like an R CrB star. In 1995 its spectrum was like that of a nova with Teff=7000K but it cooled rapidly to 3500K within only a few months. During this time the star expanded and its outer layers were ejected obscuring our line of sight. It is also surrounded by ionisation nebula but the star has been too cool during the recent outburst to produce such ionisation. It must therefore have been much hotter in the past, probably something like a white dwarf. So, in just 7 years Sakurai's Object appears to have evolved from something close to a white dwarf into something close to a red supergiant. Nova 1918 No2 Aql (V605 Aql) was a distinctly odd nova, showing no emission lines in its spectrum at maximum. Instead, it looked just like a late-type star. In the early 1970's the nova remnant was identified with the central star of the planetary nebula Abell 58. It is now mag 22, shows Wolf-Rayet features in its spectrum, and is hot enough to ionise the nebula. The nebula itself is hydrogen-deficient. A thermal pulse mechanism similar to that used to explain Sakurai's Object and Nova 1918 No2 Aql is probably at work in R CrB stars. In Don's opinion this explanation is preferable to the merged white dwarf scenario, which he regards as 'trendy'. In the discussion, Gary Poyner pointed out that the R CrB stars V482 Cyg and DY Per had both been proposed as possible binaries. Don answered that neither star had been confirmed as a binary, and that V482 Cyg might not even be R CrB star. He went on to explain that R CrB stars are not very well defined as a class and are rather heterogeneous. For example, most are cool stars but some are hot. In all, only about 30 are known and only 5 of those have been well studied. They are rarer than supernovae. The next speaker was Bill Worraker who spoke on 'Progress in Searching for Eclipsing Dwarf Novae'. He said that he was going to report the the results so far of a collaborative photometry project to detect eclipses in dwarf novae not previously known to show them. Eclipses are important for our understanding of dwarf novae because they allow us to probe the structure of the accretion disk and other parts of the system. The photometry must cover at least one whole orbital cycle in order to demonstrate the presence or absence of eclipses, but Bill said that he would prefer 3 orbital cycles coverage. There are 5 observers participating in the project. Nine stars have been dropped from the program because they are now known not to show eclipses, and 3 new stars (AR And, CY Lyr and LL Lyr) have been added. Bill then showed a CCD light-curve of IY UMa, obtained during its Sep 2000 outburst, in which it showed 1.3 mag deep asymmetric eclipses along with 0.6 mag superhumps. Next he showed CCD light-curves by Nick James of TZ Per (during Jan 2000), QY Per (Jan 2000), GX Cas (Aug 2000), and by Salmon and Boyd of V844 Her (Jul 2000). TZ Per showed no significant variations and the other three stars showed superhumps of 0.2-0.3 mag, but none of them showed any evidence for eclipses. So far, the project has produced results for 13 stars, all of which have turned out to be non-eclipsing, which suggests that eclipsing dwarf novae are rarer than expected. This conclusion is supported by data in the Downes and Shara Catalog which lists 386 dwarf novae of which fewer than 20 are known to eclipse. Bill then enumerated and examined the assumptions on which the expected number of eclipsing dwarf novae rested: 1. The standard model for dwarf novae holds. 2. Eclipses will occur if the orbital inclination is greater than 70 degrees. 3. The orbital planes are randomly distributed in space. 4. There are no significant selection effects in the discovery of dwarf novae that are related to the orbital inclination. 5. Any eclipses will still be visible during outburst. 6. Under-observation is the main reason for the small number of known eclipsing dwarf novae. Regarding point 4, he explained that there appears to be no significant correlation between the orbital inclination and the outburst amplitude. In summing up, he said that if further data confirms the shortfall in the number of eclipsing dwarf novae then this would be important because it would would reveal a hole in our understanding of these stars. Alternatively, if further data contradicts the shortfall then this would also be important because it would mean that more eclipsing dwarf novae have been discovered. As well as getting further observations of more stars, Bill suggested that search of a literature for published photometry would also be useful. The first talk after lunch was by Paul van Cauteren and was entitled 'V1162 Ori, a Mono- or Multiperiodic Delta Scuti Star?'. Paul has an observatory 10km south of Brussels equipped with a 40cm f5 Newtonian and an ST7 CCD camera. He had originally intended to use the CCD to observe dwarf novae but had tried a Delta Scuti star as a test object. When he showed his results to Patricia Lampens of the Royal Observatory Belgium, she was so impressed that she suggested he continued observing these stars. Delta Scuti stars are A - F main sequence and giant stars showing small-amplitude, short-period pulsations, some with two or more periods simultaneously. The variability of V1162 Ori was discovered by Lampens in 1985. She found it to be a Delta Scuti star with an amplitude of 0.18 mag and a single period of 0.08d. This discovery was confirmed by Poretti et al. but in 1998, Hintz et al. published results that suggested that the star showed not one but two periods. In 1999, Arencroft and Sterken organised an observing campaign in order to investigate this. Paul took part in this campaign, obtaining his first light-curve on 1999 Oct 17. As well as the designated comparison star, Paul also observed several check stars in making his observations, and one of these check stars, star 3, he found to be varying with an amplitude of about 0.015 mag. Other participants in the campaign soon confirmed this and showed it to be another Delta Scuti star. The variations in star 3 then slowly damped down until Paul started to have doubts but, to his relief, the variations eventually came back again. Paul and Patricia announced the discovery that star 3 was a new multiperiodic Delta Scuti star in IBVS 4849 (Van Cauteren & Lampens, 2000). The amplitude was given as 0.014 mag, the period as 0.073d, and the mean mag as 10.26. In IBVS 4857 (Lampens & Van Cauteren, 2000) they proposed that the multiperiodicity claimed for V1162 Ori by Hintz et al. was in fact due to them having used star 3 as their comparison star. Further observations by other observers from around the world have since confirmed these conclusions. Paul finished his talk by warning CCD observers to be careful to check their comparison stars! In the subsequent discussion Roger Pickard said that he also had come across a new Delta Scuti star. This one was in the field of an eclipsing binary which he had been observing with the Jack Ells APT. Coel Hellier (Keele University) then got up to speak about 'Linking Amateur Cataclysmic Variable Observations to Professional Work'. He began by showing a light-curve of SS Cyg which, he said, had been under observation for over 100 years but which was still well worth observing now. He illustrated this by describing how AAVSO visual observations had been used to aid the interpretation of satellite-based extreme ultraviolet and X-ray observations of an outburst of SS Cyg. The visual observations were used to fix the time of the start of the visual outburst. About 1 day later the X-rays started to rise but they then peaked and fell back again to the normal level by the 2nd day, which was when the ultraviolet outburst started. The proposed interpretation of this behaviour was that on day 0 the accretion disk started to expand inwards towards the surface of the white dwarf, emitting more and more visual light as it heated up. By day 1 the corona between the disk and the white dwarf has also heated up enough to start to emit X-rays and the X-ray outburst began. By day 2 the inner edge of the disk reached the white dwarf's surface and became hot enough to emit in the ultraviolet, and the gap occupied by the X-ray emitting corona disappeared and the X-ray outburst came to an end. Amateur observers are also useful for alerting professionals to rare and unusual phenomena in cataclysmic variables. For instance, the star EX Hya shows infrequent short low-amplitude outbursts. But amateur alerts allowed X-ray observations and CTIO photometry which showed the evolution of the eclipse shape during outburst. Subsequent modelling reproduced the shapes of the eclipses rather well. Amateur alerts will also be required if professionals are going to be able to study the very short duration outbursts reported in TV Col (a 2 mag outburst lasting only 5-6 hours) and EX Hya (a 3 mag outburst lasting less than 24 hours according to RASNZ observers). The echo outburst phenomenon was discovered by amateurs. In 1996-7 a superoutburst of EG Cnc was immediately followed by 6 short outbursts. Coel has a pet theory for them. During an SU UMa type superoutburst the disk becomes eccentric and precesses which causes the superhumps. In EG Cnc the disk may have remained eccentric after the superoutburst had finished and the mass flow inward was increased by the resultant tidal effects, triggering the repeated echo outbursts. The transition from normal to late superhumps in SU UMa stars has been well covered by Joe Patterson's professional-amateur collaboration the Center for Backyard Astrophysics (CBA). Coel showed some of their results for DV UMa (which also shows eclipses). He also mentioned ER UMa stars, that is, SU UMa stars with very short superoutburst periods of only about 20d. These stars pose serious theoretical problems - it is hard to get the models to drop out of outburst fast enough. VY Scl stars are cataclysmic variables that show extended low states during which they drop to several magnitudes fainter than normal. The standard cataclysmic variable model suggests that there should be repeated outbursts at the start of low state, but this is not what is observed. Coel suggested that the high mass transfer rate in these stars heats up the white dwarf so much that it prevents disk material from falling in and triggering outbursts. However, more data is needed on these stars, especially in their low states. TT Ari is one of the brightest VY Scl stars, being about mag 15 when in its low state. Some novae, such as Nova Aql 1999 No2, show repeated dwarf-nova like outbursts on their decline and there is no really convincing model for this phenomenon. One speculative possibility is that dust starts forming in the nova and then disperses again. Professionals again need amateur alerts and good observational coverage of this behaviour. In the discussion, Gary Poyner mentioned that MV Lyr is a very active TT Ari star. Bob Marriott said the audience should look out for Coel's book on Cataclysmic Variable Stars published by Springer. Coel added that it was written as an introductory book and was not as hard a read as Brian Warner's book on the same subject. Next, John Howarth of Crayford Manor House Astronomical Society got up to talk on 'Regularity in Semiregular Variables'. He started off by stating he was going to use BAA data to demonstrate that SRb stars may be more regular than is usually thought. Then he then briefly described the 'AMPSCAN' analysis techniques in which sine and cosine components of the variation are determined at various frequencies over a 'moving window' through the data. These components are then used to produce plots that show how the phase and the amplitude of the oscillation have varied with time. He compared results obtained with this technique with the O-C diagram for BAA observations of the Mira star Chi Cyg for 1891-2000. The O-C varies roughly sinusoidally with a period of 40 years. The AMPSCAN phase diagram shows a similar shape but with less scatter. This is to be expected because the phase diagram uses information from the whole light-curve but the O-C diagram only uses the times of maximum and minimum. The BAA observations of R Leo give similar results, that is, the AMPSCAN phase closely tracks the O-C diagram. However, it is in the analysis of SRb stars, which often have two periods, that the AMPSCAN method comes into its own. Multiple periods can be rather difficult to sort out by O-C analysis alone. W Cyg data for 1899-2000 shows two periods of 130d and 234d which have different amplitudes at different times. AMPSCAN shows that there is no clear correlation between the amplitudes of these two periods. U Boo data for 1918-2000 shows only a single period of 202d. The AMPSCAN phase and amplitude plots are much more stable than those for W Cyg. This is rather unusual for an SRb star. ST Cam data for 1981-2000 shows two periods of 205d and 370d. The AMPSCAN plots show both the phase and amplitude of these are relatively stable except when the amplitude is small, that is, when the errors in the phase are large. John went on to show results for RY Dra (main period of 1000d), AF Cyg (periods of 96d and 167d) and UU Aur (periods of 233d and 440d with very steady phase). In the discussion, Albert Zijlstra said that the results shown seem to suggest that double periods might tend to be in antiphase with each other. The last talk before the tea break was by Albert Zijlstra of UMIST (University of Manchester Institute of Science and Technology) who spoke on 'The Mira and Semiregular Period-Luminosity Relations'. However, he started off by talking first about planetary nebulae. Planetary nebulae have masses of about 0.2 solar masses and are expanding at about 25 km/s. Their central stars are hot white dwarfs of around 1 solar mass. If you run their evolution back in time, the nebula falls back on to the central star and you get something that looks very like a Mira star. Mira stars are pulsating red giants with periods of 200-500d and amplitudes greater than 2.5 mags. Closely related to them are the OH/IR stars which have periods of 700-3000d and are only visible in the infra-red. There are also the semiregular (SR) variables which can be split into two groups: the SRA stars which are really just Mira stars with amplitudes less than 2.5 mags, and the SRB stars which also have small amplitudes but are more irregular. The following evolutionary sequence has been proposed: SR -> Mira -> OH/IR -> Planetary Nebula Miras are very strange objects - they can vary by up to 10 mags within one year. Their spectra show bands of vanadium oxide and titanium oxide. Titanium oxide is actually used in sun-creams to block sunlight and the large amplitudes of Miras are mainly due to them periodically 'putting sun-cream on' to prevent visible light from getting out. However, infra-red radiation is not blocked by titanium oxide and so the infra-red amplitudes of Miras are much smaller. "Miras are pretenders - they are not as variable as they seem in visible light." The pulsations of Miras are sound waves which move out through the star, reach the surface and then move back in again. The bigger and more luminous the star the longer the sound wave takes to do this. The Mira period-luminosity (PL) relation was discovered in 1982 for Miras in the Large Magellanic Cloud (LMC) and is valid for periods less than 400d. The relation is narrow and well-defined which is odd because modelling suggests that Miras should be evolving across the line of the relation and so the relation should be broad and ill-defined. However, we do see stars evolving towards the relation - these are SR stars evolving along a separate brighter PL relation known as the Whitelock track. The local Mira stars within our own Galaxy were shown, from HIPPARCOS data a few years ago, to also fit the LMC PL relation. The local Mira star, R Doradus has been seen to switch back and forth between two periods, one of which fits the LMC Mira PL relation, and another which fits the Whitelock SR PL relation. This is rather hard to reconcile with the idea that SR stars evolve into Mira stars. Possibly there are two distinct types of SR star: the pre-Miras which are less luminous and less evolved, and the Miras with overtone pulsations, and these two types just happen to be at the same place in the period-luminosity diagram. There is also a suggestion of an intermediate sequence between the Whitelock SR and LMC Mira PL relationships. However, the evidence for this is uncertain and it may just be due to stars being assigned incorrect periods or to a systematic bias in distances derived from uncertain parallaxes. Miras are not as reqular as we tend to think. In the short-term, their light-curves do not repeat perfectly from one cycle to the next. There is even some evidence for changes on a magnitude or more within a few hours or days (possibly the result of the rapid formation of titanium oxide). In the long-term, the amplitude of V Boo has declined since 1925, the period of R Hya decreased to 1949 but has been steady since then, the period of W Hya fluctuates, and the period of Chi Cyg has been slowly increasing (in line with expected evolutionary changes) over the past couple of centuries. The outer layers of a Mira move out at about 20km/s and then move back in again, but not quite as much material moves back as moved out, and some is lost as a stellar wind. The expected velocity of this wind, 20km/s, is about the same as the expansion velocity of planetary nebulae, suggesting that the nebulae were generated by winds from their central stars when they are in their mira phase. Stronger pulsations would be expected to produce stronger stellar winds and so more mass would go into the into the nebula. Long-term variations in the pulsations of Miras should therefore produce variations in the density of the nebula. Are there any signs of this in the planetary nebulae that we can observe? Yes there are, for example, in the spherical halo of NGC 7027 there are rings which could be the result of episodic mass loss. The Egg Nebula also shows such rings. There is even a suggestion of rings in the IRAS images of the nebula around R Doradus. These is still further work to be done on analysing the long-term light-curves of Miras for period variations and on looking into historical records for SR stars that used to be Miras. Also, the reality of the intermediate PL sequence needs confirming. Albert finished with the warning: "Don't believe Don Pollacco - he is a world expert in weird objects but I believe we don't even understand the normal objects!" In the question session, John Howarth asked if there was any explanation for why, in multiply periodic stars, the longer period was often about 10 times the short one. Albert said that where the ratio P1/P2 was 1.7-1.9 this was understood as being due to overtone pulsation. Maybe these could interact to produce the longer periods. However, we really need more evidence to establish the existence of the very long periods. After the tea break, Tonny Vanmunster spoke on 'An Amateur Robotic Telescope for Variable Star Observing'. Since 1996, Tonny has been operating his own robotic observatory and has accumulated more than 82000 CCD images and more than 77 days of operation in total (far longer than the CCDs expected lifetime!). He submits his results to the CBA (Center for Backyard Astrophysics), a network of amateur and professional CCD observers coordinated by Joe Patterson of Columbia University, New York. Tonny's observatory, known as 'CBA Belgium', has a roll-off roof and holds a Celestron-14 telescope equipped with an ST7 CCD camera. In the observatory he has a PC which he uses to control the telescope and the CCD. This PC is connected to his home PC which he uses to reduce the data (in almost real-time), analyse the results, monitor the scope, monitor sky conditions, and connect to the internet. Tonny has also installed software which allows him to operate either PC from the other one. A typical observing session starts with an e-mail request from Joe Patterson for observations of a particular star. Tonny goes to the observatory, boots up the PC, starts Guide 7.0 and connects to the telescope. He then starts MIPS, an image processing program, and compares the CCD image with the chart. He checks the photometric suitability of the sky, selects a guide star for the scope and then starts his exposure program which then takes images at regular intervals through the night. Tonny then goes back into his house where he starts a program on his home PC to monitor the sky conditions. This program will raise an alarm if a certain number of consecutive blank images are recorded. He uses another program to postion the telescope at the end of the run so that it doesn't end up pointing at the Sun. Tonny also uses his image processing software to inspect the recorded images and produce preliminary light-curves before the end of the night. However, he always sends his images in to the CBA for further analysis and eventual publication. He showed some of his results for the X-ray binary RX J0909.8+1849. These images revealed, for the first time, that this system undergoes deep eclipses. In answer to a question from John Wall, Tonny said that mechanical problems prevented him from automating the closing down at the end of an observing session. To another questioner he said that he had not had any problems with the German mount near the meridian - the autoguider compensates for this. He also said that he kept a library of dark frames which he re-did every few months and, to Norman Walker, he said that his CCD was temperature controlled. The next talk was 'X-ray Transients and Microquasars' by Dr Sylvain Chaty of the Open University. Microquasars are black hole X-ray binaries with relativistic jets. They are small-scale analogues of quasars. The first one was dicovered near the centre of our own galaxy in 1992. In quasars, such as the one at the centre of M87, the black hole has the mass of several billion suns and is surrounded by an accretion disk fed by material from the host galaxy. Quasar accretion disks are heated to several thousand degrees and emit strongly at visual and ultra-violet wavelengths. The relativistic jets in quasars can be millions of parsecs long. In microquasars the black hole is only several solar masses and the accretion disk is fed by material from a companion star in a binary system. Microquasar disks are heated to several million degrees an emit strongly in X-rays. The jets of microquasars are only a few parsecs long. Because of the difference in scale, variations that would take place on a timescale of thousands of years in quasars, take place in minutes in microquasars. This makes them a lot more convenient to observe. GRS 1915+10.5 is a microquasar at a distance of about 12.5 kpc near the centre of our galaxy. It is a strong, highly variable X-ray source. In radio wavelengths it shows jets exhibiting superluminal ejection (1.25c). The connection between accretion and ejection in this object has been studied by Mirabel, Dhawan, Chaty et al. (Astronomy & Astrophysics, vol 330, pp L9-L12, 1998). The ejection events seem to occur semiperiodically. Each event starts with a drop in the X-rays which is followed, a few tens of minutes later, by a rise in the infra-red. The X-rays return, the infra-red starts to fade and the radio emission increases, peaking a few tens of minutes later. The initial drop in X-rays is interpreted as being due to the inner, X-ray emitting, part of the disk falling into the black hole. Soon afterwards a dense cloud is ejected in the jet. Initially this cloud is so dense that it emits only infra-red synchrotron radiation but, as it moves further out, it disperses and starts to emit at longer (radio) wavelengths instead. The return of the X-rays is thought to be due to the disk material moving in and reforming the X-ray emitting inner part. Studies have also been carried out on ow the outer ends of microquasar jets interact with the interstellar environment. A VLA radio image of the 1E1740.7-2942 shows two elongated radio lobes, each several parsecs long, where the jets interact with the interstellar medium. In addition, a VLA radio image of W50, the nebula around SS 433 appears to contain helical trails left by precessing jets (it is stil open whether the central object in SS 433 is a neutron star or a black hole). In GRS 1915+10.5 there are two IRAS sources symmetrically placed on opposite sides, apparently aligned with the jets, but it is not clear yet whether these are really due to the jets or not. Dr Chaty then went on to describe some work he had done with Carol Haswell (also of the Open University) on the soft X-ray transient source XTE J1859+226. In 70% of X-ray transients the central source is thought to be a black hole. XTE J1859+226 is normally at mag 23 but in October 1999 it rose to mag 15. CCD observations were made at Keele and by various amateurs. A search for periodicities with the Nordic Optical Telescope revealed a period of 24 minutes but work is in progress on a possible cause. Observations obtained with the Hubble Space Telescope and the UK Infra-red Telescope have allowed modelling of the disc during outburst. The day was rounded off with a series of short talks each lasting only only 5 minutes. First, Melvyn Taylor showed some visual observations he had made of W UMa during February and March 2000. Combining them into a phase diagram gave a minimum at about phase 0.04 relative to the elements in the Krakow Yearbook. Gary Poyner then talked about the Z And star V1413 Aql that was due to eclipse in November 2000. He reported that it was currently near max at mag 13.3 but would soon fade by about 2 magnitudes. The eclipses last about 71d with a total phase of about 21d. Next, Joel Minois of the AFOEV and SAF (Society Astronomique de France) publicised a meeting that the SAF were planning to hold at Fleurance in south-west France on 16th-18th August 2001. Peter Moreton then described a CCD camera he was building that he hoped to be offering at about £600 within a month. The CDD was a clone of the "Audine" cameras that is available in France. More details can be found at www.rockinghaminstruments.com. The VSS director, Roger Pickard, then announced that the next VSS meeting would be held at Alston Hall, Preston on 5th - 7th October 2001. It was being organised by Denis Buczynski. The cost for the weekend, including accommodation and all meals, would be about £100 per person. Finally, Roger closed the meeting by thanking Cyril Sampson for supplying the refreshments, Bob Marriott for helping organising the meeting, and all the speakers.