We report results of a spectroscopic campaign carried out at the 10 m Gran Telescopio Canarias for a sample of 22 BL Lac objects detected (or candidates) at TeV...
On the redshift of the very high-energy gamma-ray BL Lac object S2 0109+22
The determination of the redshift of extragalactic gamma-ray sources is of fundamental importance for the interpretation of their emission models and...
On the relation between active-region lifetimes and the autocorrelation function of light curves
Rotational modulation of stellar light curves due to dark spots encloses information on spot properties and, thus, on magnetic activity. In particular, the...
On the relation between the coronal line emission and the infrared/X-ray emission in Seyfert galaxies
The relation between the X-ray, the coronal line and the infrared (IR) emissions in a sample of the brightest known Seyfert galaxies is analysed. A close...
On the relation between the intensities of bright features and the local background in sunspot umbrae
A photometric study of umbral bright features (umbral dots, clusters of umbral dots, bright grains of light bridges) in sunspots is presented. It is based on...
On the relation between the IR continuum and the active galactic nucleus in Seyfert galaxies
A sample of the brightest known Seyfert galaxies from the CfA sample is analyzed on the basis of ISO photometric and spectroscopic data. Regardless of the...
On the relation between the Schmidt and Kennicutt-Schmidt star formation laws and its implications for numerical simulations
When averaged over large scales, star formation in galaxies is observed to follow the empirical Kennicutt-Schmidt (KS) law for surface densities above a...
On the Relative Distances of ω Centauri and 47 Tucanae
We present precise optical and near-infrared ground-based photometry of two globular clusters (GCs): ω Cen and 47 Tuc. These photometric catalogs are unbiased...
On the Reliability of Microvariability Tests in Quasars
Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to...