615 research outputs found
Resolving Stellar Populations outside the Local Group: MAD observations of UKS2323-326
We present a study aimed at deriving constraints on star formation at
intermediate ages from the evolved stellar populations in the dwarf irregular
galaxy UKS2323-326. These observations were also intended to demonstrate the
scientific capabilities of the multi-conjugated adaptive optics demonstrator
(MAD) implemented at the ESO Very Large Telescope as a test-bench of adaptive
optics (AO) techniques. We perform accurate, deep photometry of the field using
J and Ks band AO images of the central region of the galaxy. The near-infrared
(IR) colour-magnitude diagrams clearly show the sequences of asymptotic giant
branch (AGB) stars, red supergiants, and red giant branch (RGB) stars down to
~1 mag below the RGB tip. Optical-near-IR diagrams, obtained by combining our
data with Hubble Space Telescope observations, provide the best separation of
stars in the various evolutionary stages. The counts of AGB stars brighter than
the RGB tip allow us to estimate the star formation at intermediate ages.
Assuming a Salpeter initial mass function, we find that the star formation
episode at intermediate ages produced ~6x10^5 M_sun of stars in the observed
region.Comment: 4 pages, 4 figures, Accepted for publication in A&A Letter
MCAO near-IR photometry of the Globular Cluster NGC 6388: MAD observations in crowded fields
Deep photometry of crowded fields, such as Galactic Globular Clusters, is
severely limited by the actual resolution of ground-based telescopes. On the
other hand, the Hubble Space Telescope does not provide the near-infrared (NIR)
filters needed to allow large color baselines. In this work we aim at
demonstrating how ground based observations can reach the required resolution
when using Multi-Conjugated Adaptive Optic (MCAO) devices in the NIR, such as
the experimental infrared camera (MAD) available on the VLT. This is
particularly important since these corrections are planned to be available on
all ground--based telescopes in the near future. We do this by combining the
infrared photometry obtained by MAD/VLT with ACS/HST optical photometry of our
scientific target, the bulge globular cluster NGC 6388, in which we imaged two
fields. In particular, we constructed color-magnitude diagrams with an
extremely wide color baseline in order to investigate the presence of multiple
stellar populations in this cluster. From the analysis of the external field,
observed with better seeing conditions, we derived the deepest optical-NIR CMD
of NGC 6388 to date. The high-precision photometry reveals that two distinct
sub-giant branches are clearly present in this cluster. We also use the CMD
from the central region to estimate the distance ((m-M)=15.33) and the
reddening (E(B-V)=0.38) for this cluster. We estimate the age to be ~11.5+/-
1.5 Gyr. The large relative-age error reflects the bimodal distribution of the
SGB stars. This study clearly demonstrates how MCAO correction in the NIR bands
implemented on ground based telescopes can complement the high-resolution
optical data from HST.Comment: 9 pages, 10 figures. Accepted for publication on A. &
The organic aquaculture sector in Italy: a Delphi evaluation of the market potentialities
The paper draws out the possibilities of development and increase of organic farmed fish in Italy, evaluating both technical and economic aspects, for breeding, market, political, regulatory and environmental issues. The survey has been conducted using the Delphi technique, in three rounds with a panel of national experts. The analysis offers interesting insights and useful suggestions addressed to the organic aquaculture sector.
Authors chose Delphi methodology according to the paper’s objective: the study is in fact aimed at exploring the evolution dynamics (positive or absent) for a less-developed market like the one of the Italian organic fish. This method allows to create a forecast by collecting and evaluating experts’ opinions about the organic fish market; these experts are divided in homogeneous groups and selected as privileged observers of the phenomenon
Ground-based CCD astrometry with wide field imagers. IV. An improved Geometric Distortion Correction for the Blue prime-focus Camera at the LBT
High precision astrometry requires an accurate geometric distortion solution.
In this work, we present an average correction for the Blue Camera of the Large
Binocular Telescope which enables a relative astrometric precision of ~15 mas
for the B_Bessel and V_Bessel broad-band filters. The result of this effort is
used in two companion papers: the first to measure the absolute proper motion
of the open cluster M67 with respect to the background galaxies; the second to
decontaminate the color-magnitude diagram of M67 from field objects, enabling
the study of the end of its white dwarf cooling sequence. Many other
applications might find this distortion correction useful.Comment: 13 pages, 11 figures, 4 tables. accepted for publication on Astronomy
and Astrophysic
Observations of Isolated Neutron Stars with the ESO Multi-Conjugate Adaptive Optics Demonstrator
High-energy observations have unveiled peculiar classes of isolated neutron
stars which, at variance with radio pulsars, are mostly radio silent and not
powered by the star rotation. Among these objects are the magnetars,
hyper-magnetized neutron stars characterized by transient X-ray/gamma-ray
emission, and neutron stars with purely thermal, and in most cases stationary,
X-ray emission (a.k.a., X-ray dim isolated neutron stars or XDINSs). While
apparently dissimilar in their high-energy behavior and age, both magnetars and
XDINSs have similar periods and unusually high magnetic fields. This suggests a
tantalizing scenario where the former evolve into the latter.Discovering so far
uninvestigated similarities between the multi-wavelength properties of these
two classes would be a further step forward to establish an evolutionary
scenario. A most promising channels is the near infrared (NIR) one, where
magnetars are characterized by a distinctive spectral flattening with respect
to the extrapolation of the soft X-ray spectrum.We observed the two XDINSs RX
J0420.0-5022 and RX J1856.5-3754 with the Multi-Conjugate Adaptive Optics
Demonstrator (MAD) at the Very Large Telescope (VLT) as part of the instrument
guaranteed time observations program, to search for their NIR counterparts.
Both RX J1856.5-3754 and RX J0420.0-5022 were not detected down to K_s ~20 and
Ks ~21.5, respectively. In order to constrain the relation between XDINSs and
magnetars it would be of importance to perform deeper NIR observations. A good
candidate is 1RXS J214303.7+065419 which is the XDINS with the highest inferred
magnetic field.Comment: Accepted for publication in Astronomy and Astrophysic
MAD Adaptive Optics Imaging of High Luminosity Quasars: A Pilot Project
We present near-IR images of five luminous quasars at z~2 and one at z~4
obtained with an experimental adaptive optics instrument at the ESO Very Large
Telescope. The observations are part of a program aimed at demonstrating the
capabilities of multi-conjugated adaptive optics imaging combined with the use
of natural guide stars for high spatial resolution studies on large telescopes.
The observations were mostly obtained under poor seeing conditions but in two
cases. In spite of these non optimal conditions, the resulting images of point
sources have cores of FWHM ~0.2 arcsec. We are able to characterize the host
galaxy properties for 2 sources and set stringent upper limits to the galaxy
luminosity for the others. We also report on the expected capabilities for
investigating the host galaxies of distant quasars with adaptive optics systems
coupled with future Extremely Large Telescopes. Detailed simulations show that
it will be possible to characterize compact (2-3 kpc) quasar host galaxies for
QSOs at z = 2 with nucleus K-magnitude spanning from 15 to 20 (corresponding to
absolute magnitude -31 to -26) and host galaxies that are 4 mag fainter than
their nuclei.Comment: 19 pages, 12 figures, accepted for pubblication in The Astronomical
Journa
On the radio and NIR jet of PKS 2155-304 and its close environment
PKS 2155-304 is one of the brightest BL Lac object in the sky and a very well
studied target from radio to TeV bands. We report on high-resolution (~ 0.12
arcsec) direct imaging of the field of PKS 2155-304 using adaptive optics
near-IR observations in J and Ks bands obtained with the ESO multi-conjugate
adaptive optic demonstrator (MAD) at the Very Large Telescope. These data are
complemented with archival VLA images at various frequencies to investigate the
properties of the close environment of the source. We characterized the faint
galaxies that form the poor group associated to the target. No radio emission
is present for these galaxies, while an old radio jet at ~ 20 kpc from the
nucleus of PKS 2155-304 and a jet-like structure of ~ 2 kpc (~ 1 arcsec) in the
eastern direction are revealed. No counterparts of these radio jets are found
in the NIR or in archival Chandra observations.Comment: 10 pages, 7 figures, accepted for publication in The Astronomical
Journa
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