New short period stellar pulsators at large Galactocentric distances

Gavin Ramsay, Ralf Napiwotzki, Thomas Barclay, Pasi Hakala, Stephen Potter, Mark Cropper

Figure 3. The light curves of our blue candidate stellar pulsators identified in our survey and which had an amplitude less than 0.2 mag.

ABSTRACT

We report the discovery of 31 blue, short period, pulsators made using data taken as part of the Rapid Temporal Survey (RATS). We find they have periods between 51òÀÓ83 mins and full-amplitudes between 0.05òÀÓ0.65 mag. Using the period-luminosity relationship for short period pulsating stars we determine their distance. Assuming they are pulsating in either the fundamental or first over-tone radial mode the ma- jority are located at a distance greater than 3kpc, with several being more than 20 kpc distant. Most stars are at least 1 kpc from the Galactic plane, with three being more than 10 kpc. One is located in the direction of the Galactic anti-center and has Galactocentric distance of òÈ®30 kpc and is òÈ®20 kpc below the plane: they are therefore potential tracers of Galactic structure. We have obtained low-resolution spectra for a small number our targets and find they have temperatures between 7200òÀÓ7900K and a metal content less than Solar. The colours of the pulsators and the spectral fits to those stars for which we have spectra indicate that they are either SX Phe or δ Scuti stars. We estimate the number of SX Phe stars in our Galaxy and find significantly fewer per unit mass than reported in massive globular clusters or dwarf spheroidal galaxies.

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Last Revised: 2011 June 20th