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arXiv · 0806.4453

Variable stars in the Fornax dSph Galaxy. II. Pulsating stars below the horizontal branch

Ennio Poretti·Gisella Clementini·Enrico V. Held·Claudia Greco·Mario Mateo·Luca Dell'Arciprete·Luca Rizzi·Marco Gullieuszik·Marcella Maio
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Abstract

We have carried out an intensive survey of the northern region of the Fornax dwarf spheroidal galaxy with the aim of detecting the galaxy's short--period pulsating stars (P<0.25 days). Observations collected over three consecutive nights with the Wide Field Imager of the 2.2m MPI telescope at ESO allowed us to detect 85 high-amplitude (0.20-1.00 mag in B-light) variable stars with periods in the range from 0.046 to 0.126 days, similar to SX Phoenicis stars in Galactic metal-poor stellar populations. The plots of the observed periods vs. the B and V magnitudes show a dispersion largely exceeding the observational errors. To disentangle the matter, we separated the first-overtone from the fundamental-mode pulsators and tentatively identified a group of subluminous variables, about 0.35 mag fainter than the others. Their nature as either metal-poor intermediate-age stars or stars formed by the merging of close binary systems is discussed. The rich sample of the Fornax variables also led us to reconstruct the Period-Luminosity relation for short-period pulsating stars. An excellent linear fit, M(V)=-1.83(+/-0.08)-3.65(+/-0.07) log P(fund), was obtained using 153 Delta Scuti and SX Phoenicis stars in a number of different stellar systems.

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Ennio Poretti, Gisella Clementini, Enrico V. Held, Claudia Greco, Mario Mateo, Luca Dell'Arciprete, Luca Rizzi, Marco Gullieuszik, Marcella Maio. 2008-06-27. Variable stars in the Fornax dSph Galaxy. II. Pulsating stars below the horizontal branch. https://doi.org/10.1086/591241

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