2012 programme

Second Variable Stars South Colloquium

Tom Richards, Convenor

Following the very successful inaugural colloquium in Wellington in 2009, VSSC2 will be held on Friday, April 6th, as the curtain-raiser for NACAA XXV. Whether you’re an active variable star observer and researcher, or considering getting involved in variable star work, or just curious about this rich and important field, you are warmly invited to attend and contribute.

The colloquium will have a mix of oral presentations, short workshops, posters and discussions, with the accent on informality. Some presentations will report on VSS projects such as the outstanding work being done exploring DSLR cameras for variable star work, and the innovative pro-am SPADES exoplanet project.

But the southern hemisphere variable star activities are much wider than just VSS, and contributions are especially encouraged from outside VSS. There’s a good deal more about VSSC2 on the front page of the November 2011 Newsletter of VSS, which you can download from www.variablestarssouth.org > Community > Newsletters. If you’d like to make a presentation of any sort, you’ll find the guidelines there. Please email me your proposal, as set out there, before the end of January. And do feel free to contact me with any queries or suggestions

Speaker	Title	Duration (min)	Abstract
SESSION 1
David Benn	VStar: the next generation	60	Vstar, the free, open source variable star visualisation and analysis tool has expanded and matured since the NACAA 2010 workshop. New features, bug fixes, and user interface changes will be covered and some of the uses to which it has been put will be summarised. Planned future development  will be outlined. Attendees may find it useful to bring their laptops with Vstar (download free from http://www.aavso.org/vstar-overview
Mark Blackford	How to get started in DSLR Photometry	30	Surprisingly good photometry is possible using a basic DSLR camera and telephoto lens providing appropriate procedures are followed. DSLR's are well suited to imaging the relatively under observed bright low amplitude variables that are difficult for visual and CCD observers to study. Usable exposure times range from a few seconds for untracked cameras to several minutes for cameras on tracking mounts. Hardware and software considerations and factors influencing the choice of target variables will be discussed. Examples of image calibration and photometric measurement procedures will be given. Variable Stars South currently have two projects utilising DSLR cameras and would like to encourage more people to contribute to these. Audience participation during the presentation is encouraged.
SESSION 2
David Moriarty	CCD Photometry Contributions to the SPADES Project: 1 Updating GCVS Ephemeris Elements	20	The search for planets around detached eclipsing systems (SPADES) is a project to which I have been contributing since May 2011. Several of the target stars that I observed did not show any change around the times when minima had been predicted in ephemerides using the GCVS elements, and for many of those for which minima were observed, the times differed from predictions. In order to prepare for productive observing schedules in the future of this >5 year research programme. I aimed to check, and where necessary, update the ephemeris elements in the first season of observations. As an example, the GCVS elements for V775 Centauri were not correct, with the stated period being double the period that I observed, and confirmed by finding a primary on 2011-09-04 and a much shallower secondary on 2011-09-07. In contrast, the period given in the GCVS for AA Crucis was half the actual period. In planning observing runs for the SPADES targets, we need to compare ephemeris data based on the GCVS, the Krakow Ephemeris calculator, D. Motl’s Ephemerides programme, the O-C Gateway and ASAS phase plots (the latter two linked via the AAVSO VSX web site).
Margaret Streamer	The 2011 Eruption of T Pyxidis	30	In early April, 2011, the recurrent nova, T Pyxidis, unexpectedly went into outburst (the prediction was for 2052). Southern hemisphere observers were well placed to participate in a thorough observational campaign.23 Australian and New Zealand observers submitted results to the database of the American Association of Variable Star Observers. Observational techniques included visual, CCD and DSLR photometry. Rod Stubbings caught a short-duration pre-eruption rise, 13 days before the main eruption, followed by Linnolt (Hawaii) alerting the world to the start of the main eruption. This was confirmed by visual observers, Alan Plummer and Steve Kerr. Peter Nelson, Rolf Carstens and Margaret Streamer acquired time series photometry in multiple bands of the initial rise. The speed of the initial rise was 9 mag/day, representing a uniformly expanding shell. T Pyx finally peaked around magnitude 6.5. The decline to mag 11 initially showed numerous small flare-ups before following a steadier decline after about 140 days back to quiescence (mag ~15.5). The results and interpretations of this rare event will be presented, based on a paper by Brad Schaefer (Louisiana State University), with co-authors including Rod Stubbings, Alan Plummer, Steve Kerr, Peter Nelson, Tom Richards, Rolf Carstens and myself.
Tom Richards & Simon O’Toole	SPADES: progress, problems and prognosis	20	The SPADES Project (Search for Planets Around Detached Eclipsing Stars) now has collected data on 46 target binaries. This paper will outline the goals and methods of the project, provide an overview of the data we have collected, and discuss the issues arising for the project from a review of that data.
David Moriarty	CCD Photometry Contributions to the SPADES Project: 2 CCD Imaging Issues	20	For many target stars in the SPADES project that I observed in 2011, the derived magnitudes were close to the expected values, without applying transformation coefficients, whereas for some they were noticeably different. In the case of VX Normae, when a small change was made in the position of the stars on the CCD chip, derived magnitudes differed by about 0.4 mag. and the differences altered when different comparison stars were used, yet full calibrations were applied that should have minimised effects such as vignetting. This raises questions for discussion about imaging technique and whether transformations that take into account variations in seeing should be applied as part of the SPADES project.
SESSION 3
Alan Plummer	Observing the Observers, Through the Light Curve of Eta Carinae	30	A light curve carries more information than simple brightness. The historical light curve of eta Carinae gives insights into the European exploration of the southern seas, the establishing of the first southern observatories at Saint Helena and the Cape of Good Hope, and highlights the colonisation of South Africa, Australia, and New Zealand. This story is told—briefly—by looking at the people who made these historically important estimates.
Tom Richards	Finding and Using your Transformation Coefficients	40	Transformation Coefficients are the numbers that correct the colour photometry measures made on your idiosyncratic imaging system, aligning them with the “standard system” of star colours. Most variable star photometry requires colour filters and transformed colour data, but the business of acquiring your TCs seems difficult, and how you apply them to your observations obscure. This tutorial will try to explain why they matter, how you use them in practice, and how you find out what yours are.
Tom Richards	VSS discussion	20	To wrap up the colloquium, an open discussion on what VSS is doing and where it should be going. My role is to listen, yours is to talk.

Tom Richards
Director, VSS