We report new non-linear pulsation models of the helium stars V652 Her and BX Cir. Linear theory has previously shown their pulsations to be due to iron-group bump instability. Recent high-resolution spectroscopic observations have provided high-precision measurements of their radial velocity curves and of their radii. Their masses remain less well

We analyze the observed properties of nested and single stellar bar systems in disk galaxies. The 112 galaxies in our sample comprise the largest matched Seyfert versus non-Seyfert galaxy sample of nearby galaxies with complete near-infrared or optical imaging sensitive to length scales ranging from tens of parsecs to tens of kiloparsecs. The

We present near-infrared 1.5-2.5μm moderate-resolution long-slit spectra of two Seyfert 1 galaxies (NGC 1097 and 1566), three Seyfert 2s (NGC 1386, 4945 and 5128) and one Seyfert 1.5 (NGC 3227), both parallel to an ionization cone or jet and perpendicular to it. The spectra are used to study the spatial extent of the line emission, integrated

We present intermediate- and low-resolution optical spectra around Hα and Li I lambda 6708 Åfor a sample of 25 low mass stars and 2 brown dwarfs with confirmed membership in the pre-main sequence stellar sigma Orionis cluster. Our observations are intended to investigate the age of the cluster. The spectral types derived for our target sample are

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We present a spectrophotometric study of short-term optical variability in the quiescent black hole X-ray transient V404 Cyg. This includes two nights of high-time-resolution Hα spectroscopy with which we resolve much of the time variability, and a further six nights of archival spectroscopy with lower time resolution but higher spectral resolution