Abstract. Let α ∈ (0, 1) be an irrational, and [0; a1, a2, · · · ] the continued fraction expansion of α. Let Hα,V be the one-dimensional Schrödinger operator with Sturm potential of frequency α. Suppose the potential strength V is large enough and (ai)i≥1 is bounded. We prove that the spectral generating bands possess properties of bounded distortion, bounded covariation and there exists Gibbs...

Wereport high resolution spectroscopic observations of the Hα line profile for a sample of 32 bright giant stars with spectral type between F3 II and G5 II. By studying the link between the Hα behavior and the stellar rotation in such class of luminosity we have found no clear evidence that the rotational discontinuity established around F9 II is related with the Hα profiles. No emission featur...

The Universidad Complutense de Madrid (UCM) Survey is a long-term project aiming at finding and analysing star-forming galaxies detected by their Hα emission in Schmidt objective-prism plates. The instrumental set-up limits the volume of the Universe surveyed to a redshift z ∼< 0.045. So far we have discovered several hundred emission-line galaxies (ELGs) undergoing star formation at a wide ran...

We present the optical spectra of the periodic radio star LSI +61◦303 with intermediate dispersion. The Hα emission line profile and its variation are analyzed. Variability in LSI +61◦303 is observed on different timescales. During our observations the equivalent width (EW) of Hα line showed long-term variability that is likely to be associated with the 4-year period. We suggest that the long-t...

From Hα images of a carefully selected sample of 57 relatively large, Northern spiral galaxies with low inclination, we study the distribution of the Hα emission in the circumnuclear and nuclear regions. At a resolution of around 100 parsec, we find that the nuclear Hα emission in the sample galaxies is often peaked, and significantly more often so among AGN host galaxies. The circumnuclear Hα ...

We analyze the Hα spectral variability of the rapidly-rotating K1-dwarf LQ Hya using high-resolution Hα spectra recorded during April-May 2000. Chromospheric parameters were computed from the Hα profile as a function of rotational phase. We find that all these parameters vary in phase, with a higher chromospheric electron density coinciding with the maximum Hα emission. We find a clear rotation...

Abstract We report on the results of our simultaneous observations three large stellar flares with soft X-rays (SXRs) and an Hα emission line from two binary systems RS CVn type. The energies released in X-ray emissions during were 1036–1038 1035–1037 erg, respectively. This renders set as first successful X-ray/Hα above 1035 erg; although coverage was limited, $\sim\! 10\%$ e-folding time deca...

Since the Hα and UV fluxes from galaxies are sensitive to stellar populations of ages < 10 and ≈ 10 yr respectively, their ratio f(Hα)/f(UV) provides us with a tool to study the recent t ≤ 10 yr star formation history of galaxies, an exercise that we present here applied to 98 galaxies in 4 nearby clusters (Virgo, Coma, Abell 1367 and Cancer). The observed f(Hα)/f(UV) ratio is ∼ a factor of two...

Context. Young close binaries clear central cavities in their surrounding circumbinary disk from which the stars can still accrete material. This process takes place within the very first astronomical units, and is still not well constrained as the observational evidence has been gathered, until now, only by means of spectroscopy. Aims. The young object HD 200775 (MWC 361) is a massive spectros...