86 research outputs found
Impact of Sodium Layer variations on the performance of the E-ELT MCAO module
Multi-Conjugate Adaptive Optics systems based on sodium Laser Guide Stars may
exploit Natural Guide Stars to solve intrinsic limitations of artificial
beacons (tip-tilt indetermination and anisoplanatism) and to mitigate the
impact of the sodium layer structure and variability. The sodium layer may also
have transverse structures leading to differential effects among Laser Guide
Stars. Starting from the analysis of the input perturbations related to the
Sodium Layer variability, modeled directly on measured sodium layer profiles,
we analyze, through a simplified end-to-end simulation code, the impact of the
low/medium orders induced on global performance of the European Extremely Large
Telescope Multi-Conjugate Adaptive Optics module MAORY.Comment: 7 pages, 5 figures, SPIE conference Proceedin
Massive Star cluster formation under the microscope at z=6
We report on a superdense star-forming region with an effective radius (R_e)
smaller than 13 pc identified at z=6.143 and showing a star-formation rate
density \Sigma_SFR~1000 Msun/yr/kpc2 (or conservatively >300 Msun/yr/kpc2).
Such a dense region is detected with S/N>40 hosted by a dwarf extending over
440 pc, dubbed D1 (Vanzella et al. 2017b). D1 is magnified by a factor
17.4+/-5.0 behind the Hubble Frontier Field galaxy cluster MACS~J0416 and
elongated tangentially by a factor 13.2+/-4.0 (including the systematic
errors). The lens model accurately reproduces the positions of the confirmed
multiple images with a r.m.s. of 0.35", and the tangential stretch is well
depicted by a giant multiply-imaged Lya arc. D1 is part of an interacting
star-forming complex extending over 800 pc. The SED-fitting, the very blue
ultraviolet slope (\beta ~ -2.5, F(\lambda) ~ \lambda^\beta) and the prominent
Lya emission of the stellar complex imply that very young (< 10-100 Myr),
moderately dust-attenuated (E(B-V)<0.15) stellar populations are present and
organised in dense subcomponents. We argue that D1 (with a stellar mass of 2 x
10^7 Msun) might contain a young massive star cluster of M < 10^6 Msun and
Muv~-15.6 (or m_uv=31.1), confined within a region of 13 pc, and not dissimilar
from some local super star clusters (SSCs). The ultraviolet appearance of D1 is
also consistent with a simulated local dwarf hosting a SSC placed at z=6 and
lensed back to the observer. This compact system fits into some popular
globular cluster formation scenarios. We show that future high spatial
resolution imaging (e.g., E-ELT/MAORY-MICADO and VLT/MAVIS) will allow us to
spatially resolve light profiles of 2-8 pc.Comment: 21 pages, 14 figures, 1 table, MNRAS accepte
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
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
Laser Guide Stars for Extremely Large Telescopes: Efficient Shack-Hartmann Wavefront Sensor Design using Weighted center-of-gravity algorithm
Over the last few years increasing consideration has been given to the study
of Laser Guide Stars (LGS) for the measurement of the disturbance introduced by
the atmosphere in optical and near-infrared astronomical observations from the
ground. A possible method for the generation of a LGS is the excitation of the
Sodium layer in the upper atmosphere at approximately 90 km of altitude. Since
the Sodium layer is approximately 10 km thick, the artificial reference source
looks elongated, especially when observed from the edge of a large aperture.
The spot elongation strongly limits the performance of the most common
wavefront sensors. The centroiding accuracy in a Shack-Hartmann wavefront
sensor, for instance, decreases proportionally to the elongation (in a photon
noise dominated regime). To compensate for this effect a straightforward
solution is to increase the laser power, i.e. to increase the number of
detected photons per subaperture. The scope of the work presented in this paper
is twofold: an analysis of the performance of the Weighted Center of Gravity
algorithm for centroiding with elongated spots and the determination of the
required number of photons to achieve a certain average wavefront error over
the telescope aperture.Comment: 10 pages, 14 figure
The jet of the BL Lac object PKS 0521 -365 in the near-IR : MAD adaptive optics observations
BL Lac objects are low--power active nuclei exhibiting a variety of peculiar
properties that are caused by the presence of a relativistic jet and
orientation effects.
We present here adaptive optics near-IR images at high spatial resolution of
the nearby BL Lac object PKS 0521-365, which is known to display a prominent
jet both at radio and optical frequencies. The observations were obtained in
Ks--band using the ESO multi-conjugated adaptive optics demonstrator at the
Very Large Telescope. This allowed us to obtain images with 0.1 arcsec
effective resolution. We performed a detailed analysis of the jet and its
related features from the near-IR images, and combined them with images
previously obtained with HST in the R band and by a re-analysis of VLA radio
maps. We find a remarkable similarity in the structure of the jet at radio,
near-IR, and optical wavelengths. The broad--band emission of the jet knots is
dominated by synchrotron radiation, while the nucleus also exhibits a
significant inverse Compton component. We discovered the near-IR counterpart of
the radio hotspot and found that the near-IR flux is consistent with being a
synchrotron emission from radio to X-ray. The bright red object (red-tip),
detached but well aligned with the jet, is well resolved in the near-IR and has
a linear light profile. Since it has no radio counterpart, we propose that it
is a background galaxy not associated with the jet. The new adaptive optics
near-IR images and previous observations at other frequencies allow us to study
the complex environment around the remarkable BL Lac object PKS 0521-365. These
data exemplify the capabilities of multi conjugate adaptive optics observations
of extragalactic extended sources.Comment: accepted for publication in Astronomy and Astrophysics 9 pages. A & A
2009, in pres
Deep into the core of dense star clusters: An astrometric and photometric test case for ELT
We present a novel analysis of a young star cluster in the Large Magellanic cloud, R136- like, as seen by the Extremely Large Telescope (ELT). The main aim of this study is to quantify precision and accuracy of stellar proper motion measurements in crowded field when using an ELT working at its diffraction limit. This can serve as a reference study for future development of ELT scientific cases. In particular, we investigate our future ability to detect the dynamical signature of intermediate-mass black holes (IMBHs) with mass ∼104 M⊙ through detailed measurements of stellar proper motions. We have simulated two N-body dynamical cluster models with and without an IMBH. For each model, we have chosen two snapshots temporally spaced by 5 yr. Stellar fluxes in IJHK filters and star positions have been used to create ELT mock images for both single- and multiconjugate adaptive optics observing modes following the requierements given by ESO technical specifications for the first light imager. These images have been analysed using a classical software for seeing-limited data reduction, DAOPHOT/ALLSTAR. We make accurate photometry till the very faint pre-main-sequence stars, i.e. depending on the adaptive optics (AO) mode, magnitudes down to K ∼ 24 mag (singleconjugate AO) or K ∼ 22 mag (multiconjugate AO) in a total integration time of 20 min on target. Although DAOPHOT suite of programs is not devoted to precise astrometry, the astrometric accuracy is impressive, reaching few μas yr-1 or km s-1. In these assumptions, we are able to detect the IMBH signature at the centre of the cluster
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
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