138 research outputs found
Towards an automatic system for monitoring of CN2 and wind speed profiles with GeMS
Wide Field Adaptive Optics (WFAO) systems represent the more sophisticated AO
systems available today at large telescopes. A critical aspect for these WFAO
systems in order to deliver an optimised performance is the knowledge of the
vertical spatiotemporal distribution of the CN2 and the wind speed. Previous
studies (Cortes et al., 2012) already proved the ability of GeMS (the Gemini
Multi-Conjugated AO system) in retrieving CN2 and wind vertical stratification
using the telemetry data. To assess the reliability of the GeMS wind speed
estimates a preliminary study (Neichel et al., 2014) compared wind speed
retrieved from GeMS with that obtained with the atmospherical model Meso-Nh on
a small sample of nights providing promising results. The latter technique is
very reliable for the wind speed vertical stratification. The model outputs
gave, indeed, an excellent agreement with a large sample of radiosoundings (~
50) both in statistical terms and on individual flights (Masciadri et al.,
2013). Such a tool can therefore be used as a valuable reference in this
exercise of cross calibrating GeMS on-sky wind estimates with model
predictions. In this contribution we achieved a two-fold results: (1) we
extended analysis on a much richer statistical sample (~ 43 nights), we
confirmed the preliminary results and we found an even better correlation
between GeMS observations and the atmospherical model with basically no cases
of not-negligible uncertainties; (2) we evaluate the possibility to use, as an
input for GeMS, the Meso-Nh estimates of the wind speed stratification in an
operational configuration. Under this configuration these estimates can be
provided many hours in advanced with respect to the observations and with a
very high temporal frequency (order of 2 minutes or less).Comment: 12 pages, 7 figures, Proc. SPIE 9909 "Adaptive Optics Systems V",
99093B, 201
Variation around a Pyramid theme: optical recombination and optimal use of photons
We propose a new type of Wave Front Sensor (WFS) derived from the Pyramid WFS
(PWFS). This new WFS, called the Flattened Pyramid-WFS (FPWFS), has a reduced
Pyramid angle in order to optically overlap the four pupil images into an
unique intensity. This map is then used to derive the phase information. In
this letter this new WFS is compared to three existing WFSs, namely the PWFS,
the Modulated PWFS (MPWFS) and the Zernike WFS (ZWFS) following tests about
sensitivity, linearity range and low photon flux behavior. The FPWFS turns out
to be more linear than a modulated pyramid for the high-spatial order
aberrations but it provides an improved sensitivity compared to the
non-modulated pyramid. The noise propagation may even be as low as the ZWFS for
some given radial orders. Furthermore, the pixel arrangement being more
efficient than for the PWFS, the FPWFS seems particularly well suited for
high-contrast applications.Comment: 4 pages, 4 figures, accepted for publication in Optics Letters -
Version corrected for affiliation
Towards an automatic wind speed and direction profiler for Wide Field AO systems
Wide Field Adaptive Optics (WFAO) systems are among the most sophisticated AO
systems available today on large telescopes. The knowledge of the vertical
spatio-temporal distribution of the wind speed (WS) and direction (WD) are
fundamental to optimize the performance of such systems. Previous studies
already proved that the Gemini Multi-Conjugated AO system (GeMS) is able to
retrieve measurements of the WS and WD stratification using the SLODAR
technique and to store measurements in the telemetry data. In order to assess
the reliability of these estimates and of the SLODAR technique applied to such
a kind of complex AO systems, in this study we compared WS and WD retrieved
from GeMS with those obtained with the atmospherical model Meso-Nh on a rich
statistical sample of nights. It has been previously proved that, the latter
technique, provided an excellent agreement with a large sample of
radiosoundings both, in statistical terms and on individual flights. It can be
considered, therefore, as an independent reference. The excellent agreement
between GeMS measurements and the model that we find in this study, proves the
robustness of the SLODAR approach. To by-pass the complex procedures necessary
to achieve automatic measurements of the wind with GeMS, we propose a simple
automatic method to monitor nightly WS and WD using the Meso-Nh model
estimates. Such a method can be applied to whatever present or new generation
facilities supported by WFAO systems. The interest of this study is, therefore,
well beyond the optimization of GeMS performance.Comment: 9 figures, 2 tables, MNRAS accepte
Validation Through Simulations of a Cn2 Profiler for the ESO/VLT Adaptive Optics Facility
The Adaptive Optics Facility (AOF) project envisages transforming one of the
VLT units into an adaptive telescope and providing its ESO (European Southern
Observatory) second generation instruments with turbulence corrected
wavefronts. For MUSE and HAWK-I this correction will be achieved through the
GALACSI and GRAAL AO modules working in conjunction with a 1170 actuators
Deformable Secondary Mirror (DSM) and the new Laser Guide Star Facility
(4LGSF). Multiple wavefront sensors will enable GLAO and LTAO capabilities,
whose performance can greatly benefit from a knowledge about the stratification
of the turbulence in the atmosphere. This work, totally based on end-to-end
simulations, describes the validation tests conducted on a Cn2 profiler adapted
for the AOF specifications. Because an absolute profile calibration is strongly
dependent on a reliable knowledge of turbulence parameters r0 and L0, the tests
presented here refer only to normalized output profiles. Uncertainties in the
input parameters inherent to the code are tested as well as the profiler
response to different turbulence distributions. It adopts a correction for the
unseen turbulence, critical for the GRAAL mode, and highlights the effects of
masking out parts of the corrected wavefront on the results. Simulations of
data with typical turbulence profiles from Paranal were input to the profiler,
showing that it is possible to identify reliably the input features for all the
AOF modes.Comment: 15 pages, 12 figures, accepted for publication in the MNRAS Accepted
2015 January 22. Received 2015 January 21; in original form 2014 December
Haffner 16: A Young Moving Group in the Making
The photometric properties of main sequence (MS) and pre-main sequence (PMS)
stars in the young cluster Haffner 16 are examined using images recorded with
the Gemini South Adaptive Optics Imager (GSAOI) and corrected for atmospheric
blurring by the Gemini Multi-Conjugate Adapative Optics System (GeMS). A rich
population of PMS stars is identified, and comparisons with isochrones suggest
an age < 10 Myr assuming a distance modulus of 13.5 (D = 5 kpc). When compared
with the solar neighborhood, Haffner 16 is roughly a factor of two deficient in
objects with sub-solar masses. PMS objects in the cluster are also more
uniformly distributed on the sky than bright MS stars. It is suggested that
Haffner 16 is dynamically evolved, and that it is shedding protostars with
sub-solar masses. Young low mass clusters like Haffner 16 are one possible
source of PMS stars in the field. The cluster will probably evolve on time
scales of ~ 100 - 1000 Myr into a diffuse moving group with a mass function
that is very different from that which prevailed early in its life.Comment: To appear in the Publications of the Astronomical Society of the
Pacifi
GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle
Physical properties were derived for the candidate open cluster La Serena 94,
recently unveiled by the VVV collaboration. Thanks to the exquisite angular
resolution provided by GeMS/GSAOI, we could characterize this system in detail,
for the first time, with deep photometry in JHK - bands. Decontaminated
JHK diagrams reach about 5 mag below the cluster turnoff in H. The locus
of red clump giants in the colour - colour diagram, together with an extinction
law, was used to obtain an average extinction of . The
same stars were considered as standard - candles to derive the cluster
distance, kpc. Isochrones were matched to the cluster colour -
magnitude diagrams to determine its age, , and
metallicity, . A core radius of pc was
found by fitting King models to the radial density profile. By adding up the
visible stellar mass to an extrapolated mass function, the cluster mass was
estimated as M, consistent with an
integrated magnitude of and a tidal radius of
pc. The overall characteristics of La Serena 94 confirm that
it is an old open cluster located in the Crux spiral arm towards the fourth
Galactic quadrant and distant kpc from the Galactic centre. The
cluster distorted structure, mass segregation and age indicate that it is a
dynamically evolved stellar system.Comment: 16 pages, 24 figures, 2 Tables, accepted by MNRAS; corrected typo
Deep GeMS/GSAOI near-infrared observations of N159W in the Large Magellanic Cloud
Aims. The formation and properties of star clusters at the edge of H II
regions are poorly known, partly due to limitations in angular resolution and
sensitivity, which become particularly critical when dealing with extragalactic
clusters. In this paper we study the stellar content and star-formation
processes in the young N159W region in the Large Magellanic Cloud.
Methods. We investigate the star-forming sites in N159W at unprecedented
spatial resolution using JHKs-band images obtained with the GeMS/GSAOI
instrument on the Gemini South telescope. The typical angular resolution of the
images is of 100 mas, with a limiting magnitude in H of 22 mag (90 percent
completeness). Photometry from our images is used to identify candidate young
stellar objects (YSOs) in N159W. We also determine the H-band luminosity
function of the star cluster at the centre of the H II region and use this to
estimate its initial mass function (IMF).
Results. We estimate an age of 2 + or - 1 Myr for the central cluster, with
its IMF described by a power-law with an index of gamma = - 1.05 + or - 0.2 ,
and with a total estimated mass of 1300 solar mass. We also identify 104
candidate YSOs, which are concentrated in clumps and subclusters of stars,
principally at the edges of the H II region. These clusters display signs of
recent and active star-formation such as ultra-compact H II regions, and
molecular outflows. This suggests that the YSOs are typically younger than the
central cluster, pointing to sequential star-formation in N159W, which has
probably been influenced by interactions with the expanding H II bubble
Correction of distortion for optimal image stacking in Wide Field Adaptive Optics: Application to GeMS data
The advent of Wide Field Adaptive Optics (WFAO) systems marks the beginning
of a new era in high spatial resolution imaging. The newly commissioned Gemini
South Multi-Conjugate Adaptive Optics System (GeMS) combined with the infrared
camera Gemini South Adaptive Optics Imager (GSAOI), delivers quasi
diffraction-limited images over a field of 2 arc-minutes across. However,
despite this excellent performance, some variable residues still limit the
quality of the analyses. In particular, distortions severely affect GSAOI and
become a critical issue for high-precision astrometry and photometry. In this
paper, we investigate an optimal way to correct for the distortion following an
inverse problem approach. Formalism as well as applications on GeMS data are
presented.Comment: 10 pages, 6 figure
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