71 research outputs found
Operations and Performance of the PACS Instrument 3He Sorption Cooler on board of the Herschel Space Observatory
A 3He sorption cooler produced the operational temperature of 285mK for the
bolometer arrays of the Photodetector Array Camera and Spectrometer (PACS)
instrument of the Herschel Space Observatory. This cooler provided a stable
hold time between 60 and 73h, depending on the operational conditions of the
instrument. The respective hold time could be determined by a simple functional
relation established early on in the mission and reliably applied by the
scientific mission planning for the entire mission. After exhaustion of the
liquid 3He due to the heat input by the detector arrays, the cooler was
recycled for the next operational period following a well established automatic
procedure. We give an overview of the cooler operations and performance over
the entire mission and distinguishing in-between the start conditions for the
cooler recycling and the two main modes of PACS photometer operations. As a
spin-off, the cooler recycling temperature effects on the Herschel cryostat 4He
bath were utilized as an alternative method to dedicated Direct Liquid Helium
Content Measurements in determining the lifetime of the liquid Helium coolant.Comment: 34 pages, 13 figures, accepted in Experimental Astronom
Impacts of The Radiation Environment At L2 On Bolometers Onboard The Herschel Space Observatory
We present the effects of cosmic rays on the detectors onboard the Herschel
satellite. We describe in particular the glitches observed on the two types of
cryogenic far- infrared bolometer inside the two instruments PACS and SPIRE.
The glitch rates are also reported since the launch together with the SREM
radiation monitors aboard Herschel and Planck spacecrafts. Both have been
injected around the Lagrangian point L2 on May 2009. This allows probing the
radiation environment around this orbit. The impacts on the observation are
finally summarized.Comment: 8 pages, 13 figures, 2 images, Author Keywords: Bolometers, Infrared
detectors, cryogenics, radiation effects, submillimeter wave technology IEEE
Terms: Bolometers, Detectors, Instruments, Picture archiving and
communication systems, Protons, Silicon, Space vehicles; Radiation and Its
Effects on Components and Systems (RADECS), 2011 12th European Conference.
Conference location: Sevilla. Date of Conference: 19-23 Sept. 2011. Session
H: Radiation Environment: Space, Atmospheric and Terrestrial (PH2
Complex spectral line profiles resulting from cryogenic deformation of the SINFONI/SPIFFI diffraction gratings
The integral field spectrograph, spectrometer for infrared faint field imaging (SPIFFI), has complex line profile shapes that vary with wavelength and pixel scale, the origins of which have been sought since the instrument construction. SPIFFI is currently operational as part of SINFONI at the Very Large Telescope (VLT) and will be upgraded and incorporated into the VLT instrument enhanced resolution imager and spectrograph (ERIS). We conducted an investigation of the line profiles based on the measurements we could take with the instrument calibration unit, as well as laboratory measurements of spare SPIFFI optical components. Cryogenic measurements of a spare SPIFFI diffraction grating showed significant periodic deformation. These measurements match the cryogenic deformation expected from bimetallic bending stress based on a finite element analysis of the lightweighted grating blank. The periodic deformation of the grating surface gives rise to satellite peaks in the diffraction pattern of the grating. An optical simulation including the cryogenic grating deformation reproduces the behavior of the SPIFFI line profiles with both wavelength and pixel scale as measured with the instrument calibration unit. The conclusion is that cryogenic deformation of the diffraction gratings is responsible for the nonideal line profiles, and that the diffraction gratings should be replaced during the upgrade for optimal instrument performance.ISSN:2329-4221ISSN:2329-412
The Pointing System of the Herschel Space Observatory. Description, Calibration, Performance and Improvements
We present the activities carried out to calibrate and characterise the
performance of the elements of attitude control and measurement on board the
Herschel spacecraft. The main calibration parameters and the evolution of the
indicators of the pointing performance are described, from the initial values
derived from the observations carried out in the performance verification phase
to those attained in the last year and half of mission, an absolute pointing
error around or even below 1 arcsec, a spatial relative pointing error of some
1 arcsec and a pointing stability below 0.2 arsec. The actions carried out at
the ground segment to improve the spacecraft pointing measurements are
outlined. On-going and future developments towards a final refinement of the
Herschel astrometry are also summarised. A brief description of the different
components of the attitude control and measurement system (both in the space
and in the ground segments) is also given for reference. We stress the
importance of the cooperation between the different actors (scientists, flight
dynamics and systems engineers, attitude control and measurement hardware
designers, star-tracker manufacturers, etc.) to attain the final level of
performance.Comment: 28 pages, 8 figures, accepted for publication in Experimental
Astronom
ISO observations of far-infrared rotational emission lines of water vapor toward the supergiant star VY Canis Majoris
We report the detection of numerous far-infrared emission lines of water
vapor toward the supergiant star VY Canis Majoris. A 29.5 - 45 micron grating
scan of VY CMa, obtained using the Short Wavelength Spectrometer (SWS) of the
Infrared Space Observatory (ISO) at a spectral resolving power of approximately
2000, reveals at least 41 spectral features due to water vapor that together
radiate a total luminosity ~ 25 solar luminosities. In addition to pure
rotational transitions within the ground vibrational state, these features
include rotational transitions within the (010) excited vibrational state. The
spectrum also shows the doublet Pi 1/2 (J=5/2) <-- doublet Pi 3/2 (J=3/2) OH
feature near 34.6 micron in absorption. Additional SWS observations of VY CMa
were carried out in the instrument's Fabry-Perot mode for three water
transitions: the 7(25)-6(16) line at 29.8367 micron, the 4(41)-3(12) line
31.7721 micron, and the 4(32)-3(03) line at 40.6909 micron. The higher spectral
resolving power of approximately 30,000 thereby obtained permits the line
profiles to be resolved spectrally for the first time and reveals the "P Cygni"
profiles that are characteristic of emission from an outflowing envelope.Comment: 11 pages (inc. 2 figures), LaTeX, uses aaspp4.sty, accepted for
publication in ApJ Letter
The Infrared Continuum Spectrum of VY CMa
We combine spectra of VY CMa obtained with the short- and long-wavelength
spectrometers, SWS and LWS, on the Infrared Space Observatory to provide a
first detailed continuum spectrum of this highly luminous star. The
circumstellar dust cloud through which the star is observed is partially
self-absorbing, which makes for complex computational modeling. We review
previous work and comment on the range of uncertainties about the physical
traits and mineralogical composition of the modeled disk. We show that these
uncertainties significantly affect the modeling of the outflow and the
estimated mass loss. In particular, we demonstrate that a variety of quite
diverse models can produce good fits to the observed spectrum. If the outflow
is steady, and the radiative repulsion on the dust cloud dominates the star's
gravitational attraction, we show that the total dust mass-loss rate is yr, assuming that the star is at a distance of
1.5 kpc. Several indications, however, suggest that the outflow from the star
may be spasmodic. We discuss this and other problems facing the construction of
a physically coherent model of the dust cloud and a realistic mass-loss
analysis
ERIS: revitalising an adaptive optics instrument for the VLT
ERIS is an instrument that will both extend and enhance the fundamental
diffraction limited imaging and spectroscopy capability for the VLT. It will
replace two instruments that are now being maintained beyond their operational
lifetimes, combine their functionality on a single focus, provide a new
wavefront sensing module that makes use of the facility Adaptive Optics System,
and considerably improve their performance. The instrument will be competitive
with respect to JWST in several regimes, and has outstanding potential for
studies of the Galactic Center, exoplanets, and high redshift galaxies. ERIS
had its final design review in 2017, and is expected to be on sky in 2020. This
contribution describes the instrument concept, outlines its expected
performance, and highlights where it will most excel.Comment: 12 pages, Proc SPIE 10702 "Ground-Based and Airborne Instrumentation
for Astronomy VII
The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI
The GRAVITY instrument has been revolutionary for near-infrared
interferometry by pushing sensitivity and precision to previously unknown
limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer
(VLTI) in GRAVITY+, these limits will be pushed even further, with vastly
improved sky coverage, as well as faint-science and high-contrast capabilities.
This upgrade includes the implementation of wide-field off-axis
fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser
guide stars in an upgraded facility. GRAVITY+ will open up the sky to the
measurement of black hole masses across cosmic time in hundreds of active
galactic nuclei, use the faint stars in the Galactic centre to probe General
Relativity, and enable the characterisation of dozens of young exoplanets to
study their formation, bearing the promise of another scientific revolution to
come at the VLTI.Comment: Published in the ESO Messenge
The infrared spectrum of Neptune at 3.5-4.1 microns: Search for H<SUB>3</SUB><SUP>+</SUP> and evidence for recent meteorological variations
International audienc
The infrared spectrum of Neptune at 3.5-4.1 microns: Search for H<SUB>3</SUB><SUP>+</SUP> and evidence for recent meteorological variations
International audienc
- …