Optical microvariability (OM, small amplitude variations in time scales from minutes to hours) in radio-quiet quasars (RQQ) may be as frequent as in radio-loud...
Spectroscopic classification of a complete sample of astrometrically-selected quasar candidates using Gaia DR2
Here we explore the efficiency and fidelity of a purely astrometric selection of quasars as point sources with zero proper motions in the Gaia data release 2...
Spectroscopy and polarimetry of the gravitationally lensed quasar SDSS J1004+4112 with the 6m SAO RAS telescope
Context. We present new spectroscopic and polarimetric observations of the gravitational lens SDSS J1004+4112 taken with the 6 m telescope of the Special...
Spectroscopy of the Lens Galaxy of Q0957+561A,B: Implications of a Possible Central Massive Dark Object
We present new long-slit William Herschel Telescope spectroscopic observations of the lens galaxy G1 associated with the double-imaged QSO 0957+561A,B. The...
Star formation rates in luminous quasars at 2 < z < 3
We investigate the relation between star formation rates (dot{{M}}_s) and AGN properties in optically selected type 1 quasars at 2 z 3 using data from...
Stars and brown dwarfs in the σ Orionis cluster. III. OSIRIS/GTC low-resolution spectroscopy of variable sources
Context. Although many studies have been performed so far, there are still dozens of low-mass stars and brown dwarfs in the young σ Orionis open cluster without...
Statistics of Microlensing Caustic Crossings in Q 2237+0305: Peculiar Velocity of the Lens Galaxy and Accretion Disk Size
We use the statistics of caustic crossings induced by microlensing in the lens system Q 2237+0305 to study the lens galaxy peculiar velocity. We calculate the...
The massive black holes found at the centers of most nearby galaxies including our own, are believed to be the ashes of the fuel that powered quasars early in...
Stellar mass fraction and quasar accretion disk size in SDSS J1004+4112 from photometric follow-up
The gravitational lens SDSS J1004+4112 was the first discovered system where a background quasar is lensed by a galaxy cluster instead of a single galaxy. We...