214 research outputs found
RCW36: characterizing the outcome of massive star formation
Massive stars play a dominant role in the process of clustered star
formation, with their feedback into the molecular cloud through ionizing
radiation, stellar winds and outflows. The formation process of massive stars
is poorly constrained because of their scarcity, the short formation timescale
and obscuration. By obtaining a census of the newly formed stellar population,
the star formation history of the young cluster and the role of the massive
stars within it can be unraveled. We aim to reconstruct the formation history
of the young stellar population of the massive star-forming region RCW 36. We
study several dozens of individual objects, both photometrically and
spectroscopically, look for signs of multiple generations of young stars and
investigate the role of the massive stars in this process. We obtain a census
of the physical parameters and evolutionary status of the young stellar
population. Using a combination of near-infrared photometry and spectroscopy we
estimate ages and masses of individual objects. We identify the population of
embedded young stellar objects (YSO) by their infrared colors and emission line
spectra. RCW 36 harbors a stellar population of massive and intermediate-mass
stars located around the center of the cluster. Class 0/I and II sources are
found throughout the cluster. The central population has a median age of 1.1
+/- 0.6 Myr. Of the stars which could be classified, the most massive ones are
situated in the center of the cluster. The central cluster is surrounded by
filamentary cloud structures; within these, some embedded and accreting YSOs
are found. Our age determination is consistent with the filamentary structures
having been shaped by the ionizing radiation and stellar winds of the central
massive stars. The formation of a new generation of stars is ongoing, as
demonstrated by the presence of embedded protostellar clumps, and two exposed
jets.Comment: 18 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
The footprint of cometary dust analogues: II. Morphology as a tracer of tensile strength and application to dust collection by the Rosetta spacecraft
The structure of cometary dust is a tracer of growth processes in the
formation of planetesimals. Instrumentation on board the Rosetta mission to
comet 67P/Churyumov- Gerasimenko captured dust particles and analysed them in
situ. However, these deposits are a product of a collision within the
instrument. We conducted laboratory experiments with cometary dust analogues,
simulating the collection process by Rosetta instruments (specifically COSIMA,
MIDAS). In Paper I we reported that velocity is a key driver in determining the
appearance of deposits. Here in Paper II we use materials with different
monomer sizes, and study the effect of tensile strength on the appearance of
deposits. We find that mass transfer efficiency increases from 1 up to
10% with increasing monomer diameter from 0.3 m to 1.5 m (i.e.
tensile strength decreasing from 12 to 3 kPa), and velocities
increasing from 0.5 to 6 m/s. Also, the relative abundance of small fragments
after impact is higher for material with higher tensile strength. The
degeneracy between the effects of velocity and material strength may be lifted
by performing a closer study of the deposits. This experimental method makes it
possible to estimate the mass transfer efficiency in the COSIMA instrument.
Extrapolating these results implies that more than half of the dust collected
during the Rosetta mission has not been imaged. We analysed two COSIMA targets
containing deposits from single collisions. The collision that occurred closest
to perihelion passage led to more small fragments on the target.Comment: 13 pages, 11 figures, accepted for publication in MNRA
Design considerations of the AO module for the Gemini South multiconjugate adaptive optics system
The adaptive optics system for the Gemini South telescope, currently in the design phase, consists of several major subsystem. The largest subsystem, called the AO module, contains most of the optics and electronics and is mounted on one of the Cassegrain instrument ports. The initial system will be a conventional laser guide star AO system, but the plan is to eventually expand it to a multi-conjugate system. The system is being designed to readily add the components necessary to upgrade to a multi-conjugate system. This paper describes the design challenges encountered and solutions that were derived for the AO module design. The complexity of the multi-conjugate version is illustrated, including optical, mechanical, electronic and controls issues
Ground-layer wavefront reconstruction from multiple natural guide stars
Observational tests of ground layer wavefront recovery have been made in open
loop using a constellation of four natural guide stars at the 1.55 m Kuiper
telescope in Arizona. Such tests explore the effectiveness of wide-field seeing
improvement by correction of low-lying atmospheric turbulence with ground-layer
adaptive optics (GLAO). The wavefronts from the four stars were measured
simultaneously on a Shack-Hartmann wavefront sensor (WFS). The WFS placed a 5 x
5 array of square subapertures across the pupil of the telescope, allowing for
wavefront reconstruction up to the fifth radial Zernike order. We find that the
wavefront aberration in each star can be roughly halved by subtracting the
average of the wavefronts from the other three stars. Wavefront correction on
this basis leads to a reduction in width of the seeing-limited stellar image by
up to a factor of 3, with image sharpening effective from the visible to near
infrared wavelengths over a field of at least 2 arc minutes. We conclude that
GLAO correction will be a valuable tool that can increase resolution and
spectrographic throughput across a broad range of seeing-limited observations.Comment: 25 pages, 8 figures, to be published in Astrophys.
The footprint of cometary dust analogs: I. Laboratory experiments of low-velocity impacts and comparison with Rosetta data
Cometary dust provides a unique window on dust growth mechanisms during the
onset of planet formation. Measurements by the Rosetta spacecraft show that the
dust in the coma of comet 67P/Churyumov-Gerasimenko has a granular structure at
size scales from sub-um up to several hundreds of um, indicating hierarchical
growth took place across these size scales. However, these dust particles may
have been modified during their collection by the spacecraft instruments. Here
we present the results of laboratory experiments that simulate the impact of
dust on the collection surfaces of COSIMA and MIDAS, instruments onboard the
Rosetta spacecraft. We map the size and structure of the footprints left by the
dust particles as a function of their initial size (up to several hundred um)
and velocity (up to 6 m/s). We find that in most collisions, only part of the
dust particle is left on the target; velocity is the main driver of the
appearance of these deposits. A boundary between sticking/bouncing and
fragmentation as an outcome of the particle-target collision is found at v ~ 2
m/s. For velocities below this value, particles either stick and leave a single
deposit on the target plate, or bounce, leaving a shallow footprint of
monomers. At velocities > 2 m/s and sizes > 80 um, particles fragment upon
collision, transferring up to 50 per cent of their mass in a rubble-pile-like
deposit on the target plate. The amount of mass transferred increases with the
impact velocity. The morphologies of the deposits are qualitatively similar to
those found by the COSIMA instrument.Comment: 14 pages, 12 figures, accepted for publication in MNRA
Adaptive Optics for Astronomy
Adaptive Optics is a prime example of how progress in observational astronomy
can be driven by technological developments. At many observatories it is now
considered to be part of a standard instrumentation suite, enabling
ground-based telescopes to reach the diffraction limit and thus providing
spatial resolution superior to that achievable from space with current or
planned satellites. In this review we consider adaptive optics from the
astrophysical perspective. We show that adaptive optics has led to important
advances in our understanding of a multitude of astrophysical processes, and
describe how the requirements from science applications are now driving the
development of the next generation of novel adaptive optics techniques.Comment: to appear in ARA&A vol 50, 201
Space object identification using phase-diverse speckle
Space-object identification from ground-based telescopes is challenging because of the degradation in resolution arising from atmospheric turbulence. Phase-diverse speckle is a novel post-detection correction method that can be used to overcome turbulence-induced aberrations for telescopes with or without adaptive optics. We present a simulation study of phase-diverse speckle satellite reconstructions for the Air Force Maui Optical station 1.6-meter telescope. For a given turbulence strength, satellite reconstruction fidelity is evaluated as a function of quality and quantity of data. The credibility of this study is enhanced by reconstructions from actual compensated data collected with the 1.5-meter telescope at the Starfire Optical Range. Consistent details observed across a time series of reconstructions from a portion of a satellite pass enhance the authenticity of these features. We conclude that phase-diverse speckle can restore fine-resolution features not apparent in the raw aberrated images of space objects
The Infrared Imaging Spectrograph (IRIS) for TMT: Data Reduction System
IRIS (InfraRed Imaging Spectrograph) is the diffraction-limited first light
instrument for the Thirty Meter Telescope (TMT) that consists of a
near-infrared (0.84 to 2.4 m) imager and integral field spectrograph
(IFS). The IFS makes use of a lenslet array and slicer for spatial sampling,
which will be able to operate in 100's of different modes, including a
combination of four plate scales from 4 milliarcseconds (mas) to 50 mas with a
large range of filters and gratings. The imager will have a field of view of
3434 arcsec with a plate scale of 4 mas with many selectable
filters. We present the preliminary design of the data reduction system (DRS)
for IRIS that need to address all of these observing modes. Reduction of IRIS
data will have unique challenges since it will provide real-time reduction and
analysis of the imaging and spectroscopic data during observational sequences,
as well as advanced post-processing algorithms. The DRS will support three
basic modes of operation of IRIS; reducing data from the imager, the lenslet
IFS, and slicer IFS. The DRS will be written in Python, making use of
open-source astronomical packages available. In addition to real-time data
reduction, the DRS will utilize real-time visualization tools, providing
astronomers with up-to-date evaluation of the target acquisition and data
quality. The quicklook suite will include visualization tools for 1D, 2D, and
3D raw and reduced images. We discuss the overall requirements of the DRS and
visualization tools, as well as necessary calibration data to achieve optimal
data quality in order to exploit science cases across all cosmic distance
scales.Comment: 13 pages, 2 figures, 6 tables, Proceeding 9913-165 of the SPIE
Astronomical Telescopes + Instrumentation 201
Design considerations of the AO module for the Gemini South multiconjugate adaptive optics system
The adaptive optics system for the Gemini South telescope, currently in the design phase, consists of several major subsystem. The largest subsystem, called the AO module, contains most of the optics and electronics and is mounted on one of the Cassegrain instrument ports. The initial system will be a conventional laser guide star AO system, but the plan is to eventually expand it to a multi-conjugate system. The system is being designed to readily add the components necessary to upgrade to a multi-conjugate system. This paper describes the design challenges encountered and solutions that were derived for the AO module design. The complexity of the multi-conjugate version is illustrated, including optical, mechanical, electronic and controls issues
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