Variable Star Section Circular 75
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The British Astronomical Association VARIABLE STAR SECTION ISSN 0267-9272 Office: Burlington House, Piccadilly, London, W1V 9AG Section Officers Director Tristram Brelstaff, 3 Malvern Court, Addington Road, Reading, Berks, RG1 5PL Tel: 0734-268981 Assistant Director Storm R Dunlop 140 Stocks Lane, East Wittering, Chichester, West Sussex, P020 8NT Tel: 0243-670354 Telex: 9312134138 (SD G) Email: CompuServe:100015,1610 JANET:SDUNLOP@UK. AC. SUSSEX.STARLINK Secretary Melvyn D Taylor, 17 Cross Lane, Wakefield, West Yorks, WF2 8DA Tel: 0924-374651 Chart John Toone, Hillside View, 17 Ashdale Road, Secretary Cressage, Shrewsbury, SY5 6DT Nova/Supernova Guy M Hurst, 16 Westminster Close, Kempsho+-+· Rise, Secretary Basingstoke, Hants, RG22 4PP Tel & Fax: 0256-471074 Telex: 9312111261 (TA G) Email: Telecom Gold/DialCom:10074:MIK2885 JANET: GMH0UK. AC. RUTHERFORD. STARLINK. ASTROPHYS ICS STARLINK :RLSAC: :GMH Pro-Am Liaison Roger D Pickard, 28 Appletons, Hadlow, Kent, TN11 0DT Committee Tel: 0732-850663 Secretary Email: Telecom Gold 10074:MIK3229 Computer Dave McAdam, 33 Wrekin View, Madeley, Telford, Secretary Shropshire, TF7 5HZ Tel: 0952-432048 Email: Telecom Gold 10087:YQQ587 Eclipsing Binary Director Secretary Circulars Editor Director Circulars Assistant Director Subscriptions Telephone Alert Numbers Nova and Supernova First phone Nova/Supernova Secretary. If only Discoveries answering machine response then try the following: Denis Buczynski 0524-68530 Glyn Marsh 0772-690502 Martin Mobberley 0245-75297 (weekdays) 0284-828431 (weekends) Variable Star Gary Poyner 021-3504312 Alerts Email: JANET:[email protected] STARLINK :BHVAD: :GP For subscription rates and charges for charts and other publications see inside back cover SUBSCRIPTION RENEWALS WARMING! This Circular, number 75, has been issued out of sequence - numbers 73 and 74 will follow soon after, at the end of February. This might create problems if your subscription has nearly run out. The number of Circulars that you still have to come is indicated by the part of the serial number following the '/' on your address label. If you have fewer than 2 left then you should renew your subscription as soon as possible or else you might miss a Circular. If you are in doubt, then renew anyway. A Word from the New Director I was going to take this opportunity to outline all my plans and ideas for the Section but there isn't enough space (or time) left, so that will have to wait until later. However, I should point out that I have taken over the editing of the Circulars myself. This is not intended to be a criticism, implied or otherwise, of the work of the previous editor, Storm Dunlop; it is just that I think that this will be the most effective way that I can do my job of Director (those of you who used to get the Variable Star Observer may know what I mean). Storm will continue to handle subscriptions and act as Assist ant Director. FG Sagittae FG Sge is a quite extraordinary variable star. It was discovered in 1943 by Hoffmeister who classified it as an irregular variable. In 1960, Richter noticed that earlier photographs showed its brightness increasing, almost linearly, from the 1890's. In 1890 its photographic magnitude ««as 13.7, in 1960 it was 10.0, and the rise continued to a maximum of 9.4 in 1967. By the summer of 1992, the photographic magnitude had fallen back to 11.2 but this was accompanied by the star becoming redder and so the visual magnitude remained at about 9.4 between the late 1960's and the early 1990's. This light-curve, alone, would be enough to make a star an abject of interest but, in the case of FG Sge, it comes with three other peculiarities which make it into a unique abject. Firstly, FG is at the centre of a small planetary nebula, discovered by Henize and designated He 1-5. This nebula is probably made up of material ejected by FG several thousand years ago. It is almost certainly not derived from the latest outburst. Secondly, FG has shown a systematic change in spectral type over the past few decades. In 1955 Henize classified it as B4I; in 1967 it was A5Ia; in 1972, F5Ip; and during the 1980's the classifications range from F6-7I to K0-2Ib, according to the region of the spectrum used. This indicates a rapid cooling and expansion of the atmosphere of the star. This is the sort of behaviour that would be expected of a star in which a new set of nuclear reactions had just been ignited. This would cause the star to move from the top-left hand corner of the Hertzsprung-Russell over to the right-hand side. In doing so, it «lould take it through the Instability Strip, which leads on to the next peculiarity of FG Sge. Thirdly, at maximum, FG Sge has shown semiregular pulsations with an amplitude of a few tenths of a magnitude and a period ranging from 10 - 20 days in 1962 up to 140 days in 1990. This general increase in period is what would be expected if the pulsations were occurring in an atmosphere which was expanding and becoming more tenuous. I. As if all this wasn't enough, in August 1992 FG suffered a sudden fade which, by the end of September, had taken it to mag 13.5 visual. This is about the same as it was back in 1390, when it started out on its slow rise from obscurity! Guinan et al (IAU Circular No 5632, 1992) suggest that the fade might have been causedby dust forming in an ejected shell, rather as happens with R CrB-type variables. According to Gary Poyner, FG was still near mag 13.5 in the middle of January (several reports of the star being at mag 12 have appeared but these are almost certainly just the result of confusion with a nearby star). The accompanying light-curve is taken from Jurcsik (IBVS 3775, 1992). It rather nicely shows the last of the pulsations, which occurred in 1990. By 1991, well before the onset of the fade, the pulsations had apparently ceased. This cessation of the pulsations may well be assoc iated with the ejection of the shell. FG Sge is not on the VSS Program but charts based on the AAVSO one can be found in Volume 8 of The Webb Society Deep-Sky Observer's Handbook and in The Astronomer 29, 115 (1992). In both cases you will also require the extension chart given in The Astronomer 29, 138 (1992) when FG is at minimum. Hungarian Variable Star Meeting The Variable Star Section of the Hungarian Astronomical Association held its 27th meeting at the new observatory at Szeged. The Section has close contacts with the professionals (and amateurs) who work at Szeged. The Director of the new observatory, Karoly Szatmary, has made much use of their results in his research. He recently published a paper in Astrophysics and Space Science which was based on their observations of Y Lyncis. Also at the meeting, Tibor Hegedus reported on an astronomical visit he had recently made to Spain and spoke on his plans for an Eclipsing Binary Subsection. The most striking presentation was given by Laszlo Kiss and Gabor Kaszas who displayed about one hundred light-curves, plotted by computer, using Hungarian data from the past two decades. Attila Hizser talked about the American variable star observer and AAVSO stalwart, Clinton B Ford, who died last year. Apparently, much else went on at the meeting, as well , but’the above was all that was included in the English language summary included in with the December 1992 issue of 'Meteor'. 2. VSS Computerization: Progress to the End of 1992 Dave MeAdam The rate of computer entries increased during the latter part of 1992 with results from 1991 being keyed in as well as earlier records. A few observers continued to submit their observations on floppy disks or via electronic mail. 173411 observations have now been entered. These are in the form of 1032 files, each file containing all the observations of a given star for a partic ular year. Twenty-seven people have helped in the data entry. The follow ing table lists their names and the number of observations they have entered: Data Entry Totals to the End of 1992 H Joy 55506 I Howard-Duff 1673 D McAdam 29935 S R Dunlop 1594 G A V Coady 26229(1) B Rye 1577 M J Carson-Rowland 17441 V Garvey 1313 G Poyner 7953 G M Hurst 1215 P Dean 5103 T Brelstaff 1137 J C Fairweather 3764 J Moran 941 N L HcAdam 3295 E J W West 725 The Crayford Group 3098(2) — -J J Howarth 533 D Lloyd 2948 H Collins 385 G Ramsey 2510 D Gill 247 P White 2336 - ' R D Pickard 81 E Clancy 1844 A 0 Hiller 28 Notes: (1) G A V Coady entered over 40000 observations in the early 1980's. Unfortunately, many of these were entered again before all of his work became available. r\J (2) The Crayford Group consisted of A 0 Hiller, R D Pickard, V Stoneham and R Whiting working together as a team. The grand total is very encouraging, being over 8% of the estimated 2 million backlog. Apart from Coady's work and a proportion of some other individual totals, most of the observations were entered in the last 10 months of 1992. If more help is available with keying past records, we can look forward to dealing with a major part of the backlog on a realistic timescale.