425 research outputs found
Far-infrared photometric observations of the outer planets and satellites with Herschel-PACS
We present all Herschel PACS photometer observations of Mars, Saturn, Uranus,
Neptune, Callisto, Ganymede, and Titan. All measurements were carefully
inspected for quality problems, were reduced in a (semi-)standard way, and were
calibrated. The derived flux densities are tied to the standard PACS photometer
response calibration, which is based on repeated measurements of five fiducial
stars. The overall absolute flux uncertainty is dominated by the estimated 5%
model uncertainty of the stellar models in the PACS wavelength range between 60
and 210 micron. A comparison with the corresponding planet and satellite models
shows excellent agreement for Uranus, Neptune, and Titan, well within the
specified 5%. Callisto is brighter than our model predictions by about 4-8%,
Ganymede by about 14-21%. We discuss possible reasons for the model offsets.
The measurements of these very bright point-like sources, together with
observations of stars and asteroids, show the high reliability of the PACS
photometer observations and the linear behavior of the PACS bolometer source
fluxes over more than four orders of magnitude (from mJy levels up to more than
1000 Jy). Our results show the great potential of using the observed solar
system targets for cross-calibration purposes with other ground-based,
airborne, and space-based instruments and projects. At the same time, the PACS
results will lead to improved model solutions for future calibration
applications.Comment: 25 pages, 11 figures, 11 table
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
Preparation for the Solar system observations with Herschel: Simulation of Jupiter observations with PACS
Observations of the water inventory as well as other chemically important
species on Jupiter will be performed in the frame of the guaranteed time key
project of the Herschel Space Observatory entitled "Water and related chemistry
in the Solar system". Among other onboard instruments, PACS (Photodetector
Array Camera and Spectrometer) will provide new data of the spectral atlas in a
wide region covering the far-infrared and submillimetre domains, with an
improved spectral resolution and a higher sensitivity compared to previous
observations carried out by Cassini/CIRS (Composite InfraRed Spectrometer) and
by ISO (Infrared Space Observatory). In order to optimise the observational
plan and to prepare for the data analysis, we have simulated the expected
spectra of PACS Jupiter observations. Our simulation shows that PACS will
promisingly detect several H2O emission lines. As PACS is capable of spatially
resolving the Jovian disk, we will be able to discern the external oxygen
sources in the giant planets by exploring the horizontal distribution of water.
In addition to H2O lines, some absorption lines due to tropospheric CH4, HD,
PH3 and NH3 lines will be observed with PACS. Furthermore, owing to the high
sensitivity of the instrument, the current upper limit on the abundance of
hydrogen halides such as HCl will be also improved.Comment: to be published in Planetary and Space Scienc
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
The effects of star formation on the low-metallicity ISM: NGC4214 mapped with Herschel/PACS spectroscopy
We present Herschel/PACS spectroscopic maps of the dwarf galaxy NC4214
observed in 6 far infrared fine-structure lines: [C II] 158mu, [O III] 88mu, [O
I] 63mu, [O I] 146mu, [N II] 122mu, and [N II] 205mu. The maps are sampled to
the full telescope spatial resolution and reveal unprecedented detail on ~ 150
pc size scales. We detect [C II] emission over the whole mapped area, [O III]
being the most luminous FIR line. The ratio of [O III]/[C II] peaks at about 2
toward the sites of massive star formation, higher than ratios seen in dusty
starburst galaxies. The [C II]/CO ratios are 20 000 to 70 000 toward the 2
massive clusters, which are at least an order of magnitude larger than spiral
or dusty starbursts, and cannot be reconciled with single-slab PDR models.
Toward the 2 massive star-forming regions, we find that L[CII] is 0.5 to 0.8%
of the LTIR . All of the lines together contribute up to 2% of LTIR . These
extreme findings are a consequence of the lower metallicity and young,
massive-star formation commonly found in dwarf galaxies. These conditions
promote large-scale photodissociation into the molecular reservoir, which is
evident in the FIR line ratios. This illustrates the necessity to move to
multiphase models applicable to star-forming clusters or galaxies as a whole.Comment: Accepted for publication in the A&A Herschel Special Issu
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