ECLIPSING DWARF NOVAE PROGRAMME: 2001 NOVEMBER UPDATE

Bill Worraker

PROGRESS SINCE 2000 SEPTEMBER

Progress in the last 14 months has been limited, not least because of attention being diverted to other projects, namely time-series photometry of U Gem during the winter (2001 January to April) when it was in the later stages of a long period of quiescence, and of WZ Sge, which in 2001 July underwent an impressive outburst lasting several weeks. Another high-priority target for time-series photometry, IP Peg, has undergone prime-time outbursts in 2000 October and in 2001 October.

The only photometry undertaken and submitted for the EDNe project during this period has been on CY Lyr (2.5 hours by Graham Salmon, 2000 October and 1.5 hours by Roger Pickard, 2001 July), on AR And (4 hours by David Boyd, 2000 November) and on V516 Cyg (4.1 hours by Nick James, 2001 October). Although there is no sign of eclipses in any of these stars, further time-series photometry will be needed before we can be certain that these stars are not eclipsing systems.

However, sufficient time-series photometric data from previous years has been submitted by Tonny Vanmunster (CBA Belgium) to cover at least three orbits of the following systems, all of which have turned out to be non-eclipsers: V1504 Cyg, V844 Her, QY Per (from the ROP, or Recurrent Objects Programme), RZ Sge, SW UMa (formerly ROP) and BC UMa (ROP). These are all therefore dropped from the programme.

No new stars are being added to the programme at this point, but suggestions for new additions will be welcome - they must be stars which have not previously been covered in the programme, they must not be on the Recurrent Objects Programme (since dwarf novae on the ROP are automatically regarded as targets for this programme), they should be relatively poorly observed to date, and should be expected to reach magnitude 15 visual when in outburst.

HOW YOU CAN PARTICIPATE IN THE PROGRAMME EVEN WITHOUT A TELESCOPE!

When this programme was set up two years ago, an initial target list of dwarf novae was published, the idea being to alert interested observers when stars on the list were detected in outburst, thus giving them the opportunity of doing time-series photometry in order to check for the occurrence of eclipses [see Variable Star Circular 102, December 1999, pp.11-14]. In most cases the stars on the target list were selected as not being the brightest, most familiar dwarf novae and not already being known to exhibit eclipses, yet expected to reach visual magnitude 15 or brighter during outbursts. The thinking behind this choice was that, in the case of the better-known systems, published photometry probably already existed which was sufficient to show whether or not they underwent eclipses.

Since the long-term aim of this project is to check every possible dwarf nova down to the magnitude 15 limit, it is important to be able to give a defensible answer as to whether or not eclipses occur even for the better-known systems. Instead of adding these systems to the list of observing targets, I propose to make use of published photometry as follows:

(1) If you are interested in contributing to the programme through literature searching, contact me to register your interest;

(2) I will suggest a particular dwarf nova in the 'brighter, better-known' category, e.g. SS Cyg, Z Cam, RU Peg, VW Hyi;

(3) You should then search for a suitable paper or papers of professional standard which contain sufficient information to decide whether the star of interest undergoes eclipses. I envisage two ways whereby this question will normally be settled, viz (i) a clear statement by the author or authors to the effect that, from the data presented, there is either no sign of eclipses in the orbital light curve, or there is a clear eclipse signature; (ii) a light curve or curves from which it is evident (just by looking) whether eclipses are occurring or not. If you are relying on light curves it is important to allow for the occurrence of superhumps, which are frequently seen in SU UMa stars in outburst, and which are distinct in origin from eclipses. Please also remember that the policy in this programme is to require three orbits' worth of photometric data on a star before deciding finally whether it exhibits eclipses;

(4) Once an appropriate paper has been found, send me details of the reference and of the text and/or figures relevant to the eclipsing/non-eclipsing question. It is also worth noting whether the star was in outburst or in quiescence at the time of the reported observations. I can then add your dwarf nova to the list of objects assessed for the occurrence of eclipses. If you are interested in looking up further objects, I can then assign you another, and so on. Everyone participating in this way can expect to be recognised in resulting publications in the same way as observers who submit photometric data.

The obvious next question is how to go about searching the literature. If you have no relevant books or papers to hand, a good way to start is to log into the Harvard astrophysics database at http://adswww.harvard.edu. Abstracts of papers in most recognised astronomical and astrophysical publications are listed here, and searches can be made using either keywords or an object name. Users should beware, however, that searches often produce misleadingly generous results, i.e. many of the abstracts listed only have a tenuous link to the subject of interest.

Having selected an abstract of real interest, the problem is then to extract the information required, viz. photometric light curves or statements about the eclipsing or non-eclipsing status of the star under investigation. Normally such information is not found in abstracts, and the full paper has to be consulted. Recent papers (up to about 5 years old) published in the major journals (e.g. Monthly Notices of the Royal Astronomical Society, Astronomy and Astrophysics etc) are not generally available online, so if you do not have access to a suitable university library it may be necessary to request an offprint from the main author (a technique I have not found very useful in practice). A possible alternative is to download preprints from a site such as http://xxx.soton.ac.uk/archive/astro-ph, which I understand carries preprints of about 50% of the papers appearing in the refereed literature. Older papers are generally easier to obtain - either from one of the authors, through a local university library or astrophysics group, or even through a public library.

I am confident that if only a small number of people are willing to participate in this way, we can soon establish the eclipsing/non-eclipsing status of many dwarf novae without telescopes or clear skies. This will neatly complement the efforts of observers doing time-series photometry of more obscure stars and move the programme rapidly forward.

Please get in touch!

My contact details are given on the main page for this project.