2,557 research outputs found
Multiband Comparative Study of Optical Microvariability in RL vs. RQ Quasars
We present the results of an optical multi-band (BVR) photometric monitoring
program of 22 core-dominated radio-loud quasars (CRLQs) and 22 radio-quiet
quasars (RQQs). The aim was to compare the properties of microvariability in
both types of quasars. We detected optical microvariability in 5 RQQs and 4
CRLQs. Our results confirm that microvariability in RQQs may be as frequent as
in CRLQs. In addition we compare microvariability duty cycles in different
bands. Finally, the implications for the origin of the microvariations are
briefly discussed.Comment: 17 pages, 14 figures, Accepted for publication in the Astronomical
Journa
Photometric and spectroscopic study of the intermediate-age open cluster NGC 2355
In this paper we analyse the evolutionary status and properties of the old
open cluster NGC 2355, located in the Galactic anticentre direction, as a part
of the long term programme BOCCE. NGC 2355 was observed with LBC@LBT using the
Bessel , , and filters. The cluster parameters have been obtained
using the synthetic colour-magnitude diagram (CMD) method, as done in other
papers of this series. Additional spectroscopic observations with FIES@NOT of
three giant stars were used to determine the chemical properties of the
cluster. Our analysis shows that NGC 2355 has metallicity slightly less than
solar, with [Fe/H] dex, age between 0.8 and 1 Gyr, reddening
in the range 0.14 and 0.19 mag, and distance modulus of about 11 mag.
We also investigated the abundances of O, Na, Al, , iron-peak, and
neutron capture elements, showing that NGC 2355 falls within the abundance
distribution of similar clusters (same age and metallicity). The Galactocentric
distance of NGC~2355 places it at the border between two regimes of metallicity
distribution; this makes it an important cluster for the study of the chemical
properties and evolution of the disc.Comment: 20 pages, 11 figures, Accepted on MNRA
Large Binocular Telescope observations of PSR J2043+2740
We present the results of deep optical imaging of the radio/-ray
pulsar PSR J2043+2740, obtained with the Large Binocular Telescope (LBT). With
a characteristic age of 1.2 Myr, PSR J2043+2740 is one of the oldest (non
recycled) pulsars detected in -rays, although with still a quite high
rotational energy reservoir ( erg
s). The presumably close distance (a few hundred pc), suggested by the
hydrogen column density ( cm),
would make it a viable target for deep optical observations, never attempted
until now. We observed the pulsar with the Large Binocular Camera of the LBT.
The only object (V=25.440.05) detected within ~3" from the pulsar radio
coordinates is unrelated to it. PSR J2043+2740 is, thus, undetected down to
V~26.6 (3-), the deepest limit on its optical emission. We discuss the
implications of this result on the pulsar emission properties.Comment: 4 pages, 3 figures, accepted for publication on MNRA
Results from the Blazar Monitoring Campaign at the Whipple 10m Gamma-ray Telescope
In September 2005, the observing program of the Whipple 10 m gamma-ray
telescope was redefined to be dedicated almost exclusively to AGN monitoring.
Since then the five Northern Hemisphere blazars that had already been detected
at Whipple are monitored routinely each night that they are visible. Thanks to
the efforts of a large number of multiwavelength collaborators, the first year
of this program has been very successful. We report here on the analysis of
Markarian 421 observations taken from November, 2005 to May, 2006 in the
gamma-ray, X-ray, optical and radio bands.Comment: 4 pages; contribution to the 30th International Cosmic Ray
Conference, Merida, Mexico, July 200
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