variable star data online
TRANSCRIPT
Pickard et al.: Variable star database
A&G • June 2012 • Vol. 53 3.19
The Variable Star Section of the British Astronomical Association is the oldest established variable star observing group
in the world, with observations dating back to 1888. Our database comprises more than 2 mil-lion observations, both visual and CCD, cover-ing at least 2000 stars with contributions from more than 900 observers. Around 30 stars have more than 10 000 observations each.
Computers became established in many homes in the 1990s, and had a big effect on amateur astronomy. Dave McAdam, the BAA VSS Sec-retary at that time, created a database of many of the visual observations made by members; for the first time light curves and data tables could be created quickly for any given star. The database also contained information about the sequences used by observers, allowing observa-tions to be re-reduced as new sequences of com-parison stars became available. This data was then made available to researchers on a request basis, but everyone involved in the early years could see the value of a downloadable database.
The next technological advance came with CCD observations, which required differ-ent information to be recorded. In the early 2000s Andrew Wilson created a new database for CCD data. Initially this recorded a single comparison star along with a check star and, of course, the variable star itself. Modifications mean that it is now able to record an unlim-ited number of comparison stars to cope with ensemble photometry, where many comparison stars are used in order to deduce a more accurate magnitude. Ideally observers submit instrumen-tal magnitudes, to allow re-reduction of obser-vations. However, the database also accepts simple derived magnitudes of the variable star only, although it is expected that observers sub-mit a magnitude error estimate.
The task of making this database available to web users has been long and hard. BAA VSS officers worked in their spare time not only to make historical observations available in a suit-able format, but also to do the same for recent data, both in visual and CCD forms. As well as the data being available in a downloadable for-mat, we needed to ensure that we had a graphic representation of a particular star’s behaviour, in the form of a light curve. This light curve needed to be in a format that allowed manipula-tion, so that different time sections of the data could be viewed, as well as the full plot. We also needed search facilities, especially as these days a variable star can have several designations, and we wanted observer details to be included. In short, we worked to make a database that
included every possible piece of information to meet the requirements of researchers.
Finally, after years of work behind the scenes, the database went live on 1 January 2012. The data is freely available to view or download from http://britastro.org/~vssdb.
While an achievement in itself, this is merely phase 1 of a complete overhaul of the BAA VSS databases. Phase 2 will allow observers to sub-mit observations online. Once this has hap-pened then the old visual and CCD databases will be decommissioned. The online database also has the ability to store the PEP (Photoelec-tric Photometry) observations, which are cur-rently not held within any central database. It is expected that the PEP observations will be added at some point over the next few years.
Measurement re-reductionThe BAA VSS database has the unique ability to re-reduce magnitudes. This is immensely use-ful when sequence magnitudes are updated with improved photometry. This is made possible by two critical factors: the database records both the full magnitude e.g. “b(2)v(3)c”, and the sequence magnitudes. This means that observations span-ning many years using different sequences can be re-reduced to give results based on the same modern sequence of magnitudes. This capability is built into both the visual and CCD databases, though it does rely on observers submitting the full estimate and not simply a magnitude, a requirement insisted upon by the VSS.
BAA VSS observing programmesThe section organizes the observations of the many stars its members monitor in this way:
● The Telescopic Programme consists mainly of Miras, eruptives, cataclysmic variables (CVs) and other types.● The Binocular Programme, of mainly red semi-regular stars.● The Recurrent Objects Programme gener-ally covers under-observed CVs with periods in excess of one year.● The Eclipsing Binary Programme is mainly for visual and (PEP) observers, but CCD and camera (DSLR: digital single lens reflex) obser-vations are now starting to be made.● The Nova/Supernova Search Programmes are run in conjunction with the Deep Sky Section of the BAA and The Astronomer magazine. More than 240 supernovae discoveries have been made by UK amateurs.● The Eclipsing Dwarf Novae Programme was set up to discover eclipses in these objects.● The Identification, Classification and Correc-tion of Errors Programme (ICCE) also checks discoveries of new variables. ● The CCD Programme is relatively new and is designed to help those with CCDs to obtain scientific results; it covers mainly CVs.
SummaryFurther improvements will be made to the online database, but one aspect that is already being worked on is to link it to the inter national database of the American Association of Vari-able Star Observers (AAVSO). We hope that this will benefit not only variable star researchers but also both organizations.
The online database is a great advance on what had been available, where the interested researcher had to contact the Director who would then download the observations and email them. However, it has always been dif-ficult to monitor who has been using the data; now that it is free to download this is even more difficult. Therefore, we ask that the BAA VSS is acknowledged in publications where the data are used, by including the following note (or similar): “The BAAVSS database is acknowl-edged as the (part) source of data on which this article was based.” We hope the new online database will prove to be useful to the scientific community at large, both amateur and profes-sional, but if you have queries please feel free to contact the Director or the Database Secretary. ●
Roger Pickard, Director BAAVSS ([email protected]); Andy Wilson, Database Secretary ([email protected]); Gary Poyner, Recurrent Objects Co-ordinator ([email protected])
Variable star data onlineRoger Pickard, Andy Wilson
and Gary Poyner describe the online database of the British
Astronomical Association Variable Star Section, a treasure trove of observations stretching
back nearly 125 years.
Screenshot of the light curve for c Cyg with some observation methods omitted.