In terms of statistical fluctuations, stellar population synthesis models are only asymptotically correct in the limit of a large number of stars, where sampling errors become asymptotically small. When dealing with stellar clusters, starbursts, dwarf galaxies or stellar populations within pixels, sampling errors introduce a large dispersion in the

We examine seven Chandra ACIS-I observations centered on the nucleus of M31. Recent Chandra [1] and XMM results [2] have shown evidence of diffuse emission and have shown this emission to be softer than the point sources present in the nucleus. We also see a gradient in the hardness ratio with respect to radius in the diffuse emission. We will

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This book contains the lectures delivered at the XII Canary Islands Winter School of Astrophysics on Astrophysical Spectropolarimetry. It highlights how recent developments in theoretical astrophysics and astronomical instrumentation are leading an ever-growing number of astrophysicists to appreciate the enormous diagnostic potential offered by

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The pulsating PG 1159 planetary nebula central star RXJ 2117+3412 has been observed over three successive seasons of a multisite photometric campaign. The asteroseismological analysis of the data, based on the 37 identified l=1 modes among the 48 independent pulsation frequencies detected in the power spectrum, leads to the derivation of the