TRIFFID Photometry of Globular Cluster Cores — I. Photometric Techniques and Variable Stars in M15 |
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| Authors: | Butler Shearer Redfern Colhoun O'Kane Penny Morris Griffiths & Cullum |
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| Institution: | Department of Physics, University College Galway, Galway, Ireland,;Information Technology Centre, University College Galway, Galway, Ireland,;Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX,;Department of Physics, University of Durham, South Road, Durham DHI 3LE,;Department of Physics &Astronomy, University of Leeds, Leeds LS2 9JT,;European Southern Observatory, Garching, Karl-Schwarzschild Straße 2, D-85748 Garching bei, München, Germany |
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| Abstract: | The Galway/DIAS Image Sharpening Camera, TRIFFID, has been used to make observations in two colours of the centre of the post-core-collapse globular cluster M15. We present here our analysis of the photometry in B over two seasons. We have combined the complementary qualities of the HST 's high astrometric precision and TRIFFID's extended coverage and photometric precision, to perform crowded-field photometry in the innermost region of M15. Our technique virtually eliminates the problem of extreme crowding which has hitherto hampered studies of the variable star populations in globular cluster cores, and thereby provides an extension of the HST 's capability. Candidate variables detected with the HST have been confirmed and monitored over longer periods. We show that most of these are RR Lyrae stars, and that one is a short-period Type II Cepheid (the third to be discovered in M15). Our photometric study also produced evidence of a similar number of new variables. These also appear to be RR Lyrae stars, except for a possible eclipsing system. Further data from an upgraded version of TRIFFID have recently been obtained to help to refine the light curves of all these objects. |
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| Keywords: | instrumentation: miscellaneous techniques: photometric Cepheids stars: variables: other globular clusters: general globular clusters: individual: M15 |
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