146 research outputs found
An update of the on-sky performance of the Layer-Oriented wave-front sensor for MAD
The Multi-conjugate Adaptive optics Demonstrator, MAD, successfully
demonstrated on sky the MCAO technique both in Layer Oriented and Star Oriented
modes. As results of the Guaranteed Time Observations in Layer Oriented mode
quality astronomy papers have been published. In this paper we concentrate on
the instrumentation issues and technical aspects which stay behind this
success.Comment: 12 pages, 10 figures, Proceedings of the SPIE conference "Adaptive
Optics Systems II", 27 June 2010, San Diego, California, US
GASP XIX: AGN and their outflows at the center of jellyfish galaxies
The GASP survey, based on MUSE data, is unveiling the properties of the gas
in the so-called "jellyfish" galaxies: these are cluster galaxies with
spectacular evidence of gas stripping by ram pressure. In a previous paper, we
selected the seven GASP galaxies with the most extended tentacles of ionized
gas, and based on individual diagnostic diagrams concluded that at least five
of them present clear evidence for an Active Galactic Nucleus. Here we present
a more detailed analysis of the emission lines properties in these galaxies.
Our comparison of several emission line ratios with both AGN and shock models
show that photoionization by the AGN is the dominant ionization mechanism. This
conclusion is strengthened by the analysis of luminosities, the
presence of nuclear iron coronal lines and extended ( kpc) emission line
regions ionized by the AGN in some of these galaxies. From emission line
profiles, we find the presence of outflows in four galaxies, and derive mass
outflow rates, timescales and kinetic energy of the outflows.Comment: 20 pages, 10 Figure
FORS2/VLT survey of Milky Way globular clusters I. Description of the method for derivation of metal abundances in the optical and application to NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and Terzan 8
(abridged) We have observed almost 1/3 of the globular clusters in the Milky
Way, targeting distant and/or highly reddened objects, besides a few reference
clusters. A large sample of red giant stars was observed with FORS2@VLT/ESO at
R ~ 2,000. The method for derivation of stellar parameters is presented with
application to six reference clusters. We aim at deriving the stellar
parameters effective temperature, gravity, metallicity and alpha-element
enhancement, as well as radial velocity, for membership confirmation of
individual stars in each cluster. We analyse the spectra collected for the
reference globular clusters NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and
Terzan 8. They cover the full range of globular cluster metallicities, and are
located in the bulge, disc and halo. Full spectrum fitting techniques are
applied, by comparing each target spectrum with a stellar library in the
optical region at 4560-5860 A. We employed the library of observed spectra
MILES, and the synthetic library by Coelho et al. (2005). Validation of the
method is achieved through recovery of the known atmospheric parameters for 49
well-studied stars that cover a wide range in the parameter space. We adopted
as final stellar parameters (effective temperatures, gravities, metallicities)
the average of results using MILES and Coelho et al. libraries. We identified 4
member stars in NGC 6528, 13 in NGC 6553, 10 in M 71, 5 in NGC 6558, 5 in NGC
6426 and 12 in Terzan 8. Radial velocities, Teff, log(g), [Fe/H] and
alpha-element enhancements were derived. We derived abundances for NGC 6426
from spectroscopy for the first time. The method proved to be reliable for red
giant stars observed with resolution R ~ 2,000, yielding results compatible
with high-resolution spectroscopy. The derived alpha-element abundances show
[A/Fe] vs. [Fe/H] consistent with that of field stars at the same
metallicities.Comment: 22 pages, 21 figures, accepted for publication in A&
GASP. XVI. Does cosmic web enhancement turn on star formation in galaxies?
Galaxy filaments are a peculiar environment, and their impact on the galaxy
properties is still controversial. Exploiting the data from the GAs Stripping
Phenomena in galaxies with MUSE (GASP), we provide the first characterisation
of the spatially resolved properties of galaxies embedded in filaments in the
local Universe. The four galaxies we focus on show peculiar ionised gas
distributions: Halpha clouds have been observed beyond four times the effective
radius. The gas kinematics, metallicity map and the ratios of emission line
fluxes confirm that they do belong to the galaxy gas disk, the analysis of
their spectra shows that very weak stellar continuum is associated to them.
Similarly, the star formation history and luminosity weighted age maps point to
a recent formation of such clouds. The clouds are powered by star formation,
and are characterised by intermediate values of dust absorption. We hypothesise
a scenario in which the observed features are due to "Cosmic Web Enhancement":
we are most likely witnessing galaxies passing through or flowing within
filaments that assist the gas cooling and increase the extent of the star
formation in the densest regions in the circumgalactic gas. Targeted
simulations are mandatory to better understand this phenomenon.Comment: MNRAS in press, 18 pages, 12 figure
Hierarchichal-segmented AO in order to attain wide field compensation in the visible on an 8m class telescope
We describe the preliminary optimized layout for a partially optimized
concept of an optical-8m class VLT-like 2x2 segmented camera where each channel
is assisted by an equivalent of an MCAO system where the ground layer
correction is commonly employed while the high altitude ones is performed in an
open-loop fashion. While we derive the basic relationships among the Field of
View and attainable correction with a pre-defined choice for the hardware, we
discuss sky coverage and wavefront sensing issues employing natural and
artificial references, involving the latest stateof-the-art in the development
of wavefront sensing. We show that a flexible approach allow for a compensated
Field of View that is variable and can be properly tuned matching the current
turbulence situation and the requirement in term of quality of the
compensation. A preliminary description of the overall optomechanical package
is given as well along with a rough estimates of the efforts required to
translates such a concept into reality.Comment: 6 pages, 4 figures, in AO4ELT5 Proceeding
Enhanced star formation in both disks and ram pressure stripped tails of GASP jellyfish galaxies
Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE
(GASP) program, we compare the integrated Star Formation Rate- Mass relation
(SFR-M_ast) relation of 42 cluster galaxies undergoing ram pressure stripping
("stripping galaxies") to that of 32 field and cluster undisturbed galaxies.
Theoretical predictions have so far led to contradictory conclusions about
whether ram pressure can enhance the star formation in the gas disks and tails
or not and until now a statistically significant observed sample of stripping
galaxies was lacking. We find that stripping galaxies occupy the upper envelope
of the control sample SFR-M_ast relation, showing a systematic enhancement of
the SFR at any given mass. The star formation enhancement occurs in the disk
(0.2 dex), and additional star formation takes place in the tails. Our results
suggest that strong ram pressure stripping events can moderately enhance the
star formation also in the disk prior to gas removal.Comment: ApJL in pres
GASP. XII. The variety of physical processes occurring in a single galaxy group in formation
GAs Stripping Phenomena in galaxies with MUSE (GASP) is a program aimed at
studying gas removal processes in nearby galaxies in different environments. We
present the study of four galaxies that are part of the same group (z= 0.06359)
and highlight the multitude of mechanisms affecting the spatially resolved
properties of the group members. One galaxy is passive and shows a regular
stellar kinematics. The analysis of its star formation history indicates that
the quenching process lasted for a few Gyr and that the star formation declined
throughout the disk in a similar way, consistent with strangulation. Another
galaxy is characterised by a two-component stellar disk with an extended gas
disk that formed a few 10^8 yr ago, most likely as a consequence of gas
accretion. The third member is a spiral galaxy at the edges of the group, but
embedded in a filament. We hypothesise that the compression exerted by the
sparse intergalactic medium on the dense circumgalactic gas switches on star
formation in a number of clouds surrounding the galaxy ("cosmic web
enhancement"). Alternatively, also ram pressure stripping might be effective.
Finally, the fourth galaxy is a spiral with a truncated ionised gas disk and an
undisturbed stellar kinematics. An analytical model of the galaxy's restoring
pressure, and its location and velocity within the cluster, suggest ram
pressure is the most likely physical mechanism in action. This is the first
optical evidence for stripping in groups.Comment: 19 page, 12 figure
Multiple Spatial Frequencies Pyramid WaveFront Sensing
A modification of the pyramid wavefront sensor is described. In this conceptually new class of devices, the perturbations are split at the level of the focal plane depending upon their spatial frequencies, and then measured separately. The aim of this approach is to increase the accuracy in the determination of some range of spatial frequency perturbations, or a certain classes of modes, disentangling them from the noise associated to the Poissonian fluctuations of the light coming from the perturbations outside of the range of interest or from the background in the pupil planes; the latter case specifically when the pyramid wavefront sensor is used with a large modulation. While the limits and the effectiveness of this approach should be further investigated, a number of variations on the concept are shown, including a generalization of the spatial filtering in the point-diffraction wavefront sensor. The simplest application, a generalization to the pyramid of the well-known spatially filtering in wavefront sensing, is showing promise as a significant limiting magnitude advance. Applications are further speculated in the area of extreme adaptive optics and when serving spectroscopic instrumentation where “light in the bucket” rather than Strehl performance is required
Ingot Laser Guide Stars Wavefront Sensing
We revisit one class of z-invariant WaveFront sensor where the LGS is fired
aside of the telescope aperture. In this way there is a spatial dependence on
the focal plane with respect to the height where the resonant scattering
occurs. We revise the basic parameters involving the geometry and we propose
various merit functions to define how much improvement can be attained by a
z-invariant approach. We show that refractive approaches are not viable and we
discuss several solutions involving reflective ones in what has been nicknamed
"ingot wavefront sensor" discussing the degrees of freedom required to keep
tracking and the basic recipe for the optical design.Comment: 6 pages, 4 figures, AO4ELT5 Conference Proceeding, 201
A Holographic Diffuser Generalised Optical Differentiation Wavefront Sensor
The wavefront sensors used today at the biggest World's telescopes have
either a high dynamic range or a high sensitivity, and they are subject to a
linear trade off between these two parameters. A new class of wavefront
sensors, the Generalised Optical Differentiation Wavefront Sensors, has been
devised, in a way not to undergo this linear trade off and to decouple the
dynamic range from the sensitivity. This new class of WFSs is based on the
light filtering in the focal plane from a dedicated amplitude filter, which is
a hybrid between a linear filter, whose physical dimension is related to the
dynamic range, and a step in the amplitude, whose size is related to the
sensitivity. We propose here a possible technical implementation of this kind
of WFS, making use of a simple holographic diffuser to diffract part of the
light in a ring shape around the pin of a pyramid wavefront sensor. In this
way, the undiffracted light reaches the pin of the pyramid, contributing to the
high sensitivity regime of the WFS, while the diffused light is giving a sort
of static modulation of the pyramid, allowing to have some signal even in high
turbulence conditions. The holographic diffuser zeroth order efficiency is
strictly related to the sensitivity of the WFS, while the diffusing angle of
the diffracted light gives the amount of modulation and thus the dynamic range.
By properly choosing these two parameters it is possible to build a WFS with
high sensitivity and high dynamic range in a static fashion. Introducing
dynamic parts in the setup allows to have a set of different diffuser that can
be alternated in front of the pyramid, if the change in the seeing conditions
requires it.Comment: 11 pages, 5 figure
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