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ULTRACAM Observations of Subdwarf B Stars

Subdwarf B stars are highly evolved stars which pulsate non-radially in several modes with different frequencies. Measurements enable astronomers to establish their overall properties and internal structure with unusual precision. In a second visit to use the phenomenal high-speed ULTRACAM photometer on the William Herschel Telescope in La Palma, Simon Jeffery teamed up with Conny Aerts (Nijmegen and Leuven) to observe one of these pulsating stars for six consecutive nights. Over 60,000 images were obtained, which when played in sequence show the star's oscillations in red, green and ultraviolet light. These observations were supported by 14 hours of observations from the brand new Faulkes Telescope North in Hawaii. The combined observations have revealed 19 pulsation frequencies including nine new ones. Moreover, groups of close multiplets give rise to complex beating patterns, and are indicative of the star's slow rotation rate. The results will enable pulsation modes to be identified and the total mass and radius of the star to be measured. Together, they will help to resolve fundamental questions about how subdwarf B stars were formed.

Figure 3: ULTRACAM light curve for PG0014+067, from 2004 August 20 to 2004 August 25 (top to bottom). The differential light curves (V-C) are shown for each filter , and (top to bottom in each panel, coloured blue, green and red respectively). The panels are labelled with the date of observation given as Julian Date (JD) . The and data are offset vertically by an arbitrary amount. These data provide evidence for 19 pulsation frequencies, including complex `beating' patterns indicative of the subluminous star's slow rotation rate.


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Next: First CCD Observations of Up: Highlights Previous: Origin of Stars   Contents