3,855 research outputs found
Searching for evidence of jet-cloud interaction in radio galaxies. First results for 3C 381
We present results of Gemini spectroscopy and Hubble Space Telescope imaging
of the 3C~381 radio galaxy. Possible ionising mechanisms for the Extended
Emission-Line Region were studied through state-of-the-art diagnostic analysis
employing line-ratios. Photoionisation from the central engine as well as
mixed-medium photoionisation models fail in reproducing both the strengths and
the behaviour of the highest-excitation lines, such as [NeV]3424, HeII, and
[OIII}]5007, which are measured at very large distances from the AGN.
Shock-ionisation models provide a better fit to the observation. Expanding
shocks with velocities higher than 500 km/s are capable of reaching the
observed intensity ratios for lines with different ionisation states and
excitation degrees. This model also provide a direct explanation of the
mechanical energy input needed to explain the high-velocity line-splitting
observed in the velocity field.Comment: 21 pages, 11 figures; to be published in Monthly Notices of the Royal
Astronomical Societ
Long-Term Optical Monitoring of Eta Carinae. Multiband light curves for a complete orbital period
The periodicity of 5.5 years for some observational events occurring in Eta
Carinae manifests itself across a large wavelength range and has been
associated with its binary nature. These events are supposed to occur when the
binary components are close to periastron. To detect the previous periastron
passage of Eta Car in 2003, we started an intensive, ground-based, optical,
photometric observing campaign. We continued observing the object to monitor
its photometric behavior and variability across the entire orbital cycle. Our
observation program consisted of daily differential photometry from CCD images,
which were acquired using a 0.8 m telescope and a standard BVRI filter set at
La Plata Observatory. The photometry includes the central object and the
surrounding Homunculus nebula. We present up-to-date results of our observing
program, including homogeneous photometric data collected between 2003 and
2008. Our observations demonstrated that Eta Car has continued increasing in
brightness at a constant rate since 1998. In 2006, it reached its brightest
magnitude (V ~ 4.7) since about 1860s. The object then suddenly reverted its
brightening trend, fading to V = 5.0 at the beginning of 2007, and has
maintained a quite steady state since then. We continue the photometric
monitoring of Eta Car in anticipation of the next "periastron passage",
predicted to occur at the beginning of 2009.Comment: Accepted by A&A. The paper contains 3 figures and 2 table
Polarimetry of an Intermediate-age Open Cluster: NGC 5617
We present polarimetric observations in the UBVRI bands of 72 stars located
in the direction of the medium age open cluster NGC 5617. Our intention is to
use polarimetry as a tool membership identification, by building on previous
investigations intended mainly to determine the cluster's general
characteristics rather than provide membership suitable for studies such as
stellar content and metallicity, as well as study the characteristics of the
dust lying between the Sun and the cluster. The obsevations were carried out
using the five-channel photopolarimeter of the Torino Astronomical Observatory
attached to the 2.15m telescope at the Complejo Astron\'omico El Leoncito
(CASLEO; Argentina. We are able to add 32 stars to the list of members of NGC
5617, and review the situation for others listed in the literature. In
particular, we find that five blue straggler stars in the region of the cluster
are located behind the same dust as the member stars are and we confirm the
membership of two red giants. The proposed polarimetric memberships are
compared with those derived by photometric and kinematical methods, with
excellent results. Among the observed stars, we identify 10 with intrinsic
polarization in their light. NGC 5617 can be polarimetrically characterized
with and . The spread in polarization
values for the stars observed in the direction of the cluster seems to be
caused by the uneven distribution of dust in front of the cluster's face.
Finally, we find that in the direction of the cluster, the interstellar medium
is apparently free of dust, from the Sun's position up to the
Carina-Sagittarius arm, where NGC 5617 seems to be located at its farthest
border
Spectroscopic observations of the cluster IC 2391
With the grating spectrograph of the Bosque Alegre telescope, which gives a dispersion of 42 A/mm, the brightest stars of the galactic cluster IC 2391 were taken,for the purpose of radial velocity measurements and for a provisional spectral classification in the MK system.Asociación Argentina de AstronomÃ
Spectroscopic observations of the cluster IC 2391
With the grating spectrograph of the Bosque Alegre telescope, which gives a dispersion of 42 A/mm, the brightest stars of the galactic cluster IC 2391 were taken,for the purpose of radial velocity measurements and for a provisional spectral classification in the MK system.Asociación Argentina de AstronomÃ
Penrose Limits, the Colliding Plane Wave Problem and the Classical String Backgrounds
We show how the Szekeres form of the line element is naturally adapted to
study Penrose limits in classical string backgrounds. Relating the "old"
colliding wave problem to the Penrose limiting procedure as employed in string
theory we discuss how two orthogonal Penrose limits uniquely determine the
underlying target space when certain symmetry is imposed. We construct a
conformally deformed background with two distinct, yet exactly solvable in
terms of the string theory on R-R backgrounds, Penrose limits. Exploiting
further the similarities between the two problems we find that the Penrose
limit of the gauged WZW Nappi-Witten universe is itself a gauged WZW plane wave
solution of Sfetsos and Tseytlin. Finally, we discuss some issues related to
singularity, show the existence of a large class of non-Hausdorff solutions
with Killing Cauchy Horizons and indicate a possible resolution of the problem
of the definition of quantum vacuum in string theory on these time-dependent
backgrounds.Comment: Some misprints corrected. Matches the version in print. To appear in
Classical & Quantum Gravit
Klossiella cobayae associated With Chronic Interstitial Nephritis in Guinea Pigs
Infection with the renal coccidian parasite K. cobayae was detected in 6 conventionally kept Dunkin-Hartley guinea pigs, submitted for routine health monitoring at The National Veterinary Intsitute, Uppsala. Chronic inflammatory lesions were microscopically observed in the kidneys and the lungs of all animals
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