1,316 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
Observations of the rotational transitions of OH from the Orion molecular cloud
A summary of observed rotationally excited, far infrared OH line emissions from Orion-KL made using the Kuiper Airborne Observatory is given, together with a list of the resulting publications, talks, and lectures based on this data. In addition, a paper is appended, particularly addressing the (16)OH and (18)OH emission from Orion-KL. The first detections of the (16)OH (2)pi(1/2) to (2)pi(3/2) J = 3/2(-) to 3/2(+) rotational cross-ladder transition (53.351 micrometer) and the (18)OH (2)pi(3/2) J = 5/2(+) to 3/2(-) rotational ground-state transition (120.1719 micrometer). It is found that both of these lines exhibit a P-Cygni profile
16 x 25 Ge:Ga Detector Arrays for FIFI LS
We are developing two-dimensional 16 x 25 pixel detector arrays of both
unstressed and stressed Ge:Ga photoconductive detectors for far-infrared
astronomy from SOFIA. The arrays, based on earlier 5 x 5 detector arrays used
on the KAO, will be for our new instrument, the Far Infrared Field Imaging Line
Spectrometer (FIFI LS). The unstressed Ge:Ga detector array will cover the
wavelength range from 40 to 120 microns, and the stressed Ge:Ga detector array
from 120 to 210 microns. The detector arrays will be operated with multiplexed
integrating amplifiers with cryogenic readout electronics located close to the
detector arrays. The design of the stressed detector array and results of
current measurements on several prototype 16 pixel linear arrays are reported.
They demonstrate the feasibility of the current concept. ***This paper does not
include Figures due to astro-ph size limitations. Please download entire file
at http://fifi-ls.mpe-garching.mpg.de/spie.det.ps.gz ***Comment: 8 pages, SPIE Proceedings, Astronomical Telescopes and
Instrumentation 200
Stressed detector arrays for airborne astronomy
The development of stressed Ge:Ga detector arrays for far-infrared astronomy from the Kuiper Airborne Observatory (KAO) is discussed. Researchers successfully constructed and used a three channel detector array on five flights from the KAO, and have conducted laboratory tests of a two-dimensional, 25 elements (5x5) detector array. Each element of the three element array performs as well as the researchers' best single channel detector, as do the tested elements of the 25 channel system. Some of the exciting new science possible with far-infrared detector arrays is also discussed
CEA Bolometer Arrays: the First Year in Space
The CEA/LETI and CEA/SAp started the development of far-infrared filled bolometer arrays for space applications
over a decade ago. The unique design of these detectors makes possible the assembling of large focal planes
comprising thousands of bolometers running at 300 mK with very low power dissipation. Ten arrays of 16x16
pixels were thoroughly tested on the ground, and integrated in the Herschel/PACS instrument before launch in
May 2009. These detectors have been successfully commissioned and are now operating in their nominal environment
at the second Lagrangian point of the Earth-Sun system. In this paper we briefly explain the functioning
of CEA bolometer arrays, and we present the properties of the detectors focusing on their noise characteristics,
the effect of cosmic rays on the signal, the repeatability of the measurements, and the stability of the system
The 158 micron (CII) mapping of galaxies: Probing the atomic medium
Using the MPE/UCB Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO), we have made large scale maps of (CII) in the spiral galaxies NGC 6946, NGC 891, M83 and the peculiar elliptical Cen A, thus allowing for the first time, detailed studies of the spatial distribution of the FIR line emission in external galaxies. We find that the (CII) emission comes from a mixture of components of interstellar gas. The brightest emission is associated with the nuclear regions, a second component traces the spiral arms as seen in the nearly face on spiral galaxies NGC 6946 and M83 and the largest star forming/H2 regions contained within them, and another extended component of low brightness can be detected in all of the galaxies far from the nucleus, beyond the extent of CO emission
Physical conditions in the gas phases of the giant HII region LMC-N11 unveiled by Herschel - I. Diffuse [CII] and [OIII] emission in LMC-N11B
(Abridged) The Magellanic Clouds provide a nearby laboratory for metal-poor
dwarf galaxies. The low dust abundance enhances the penetration of UV photons
into the interstellar medium (ISM), resulting in a relatively larger filling
factor of the ionized gas. Furthermore, there is likely a hidden molecular gas
reservoir probed by the [CII]157um line. We present Herschel/PACS maps in
several tracers, [CII], [OI]63um,145um, [NII]122um, [NIII]57um, and [OIII]88um
in the HII region N11B in the Large Magellanic Cloud. Halpha and [OIII]5007A
images were used as complementary data to investigate the effect of dust
extinction. Observations were interpreted with photoionization models to infer
the gas conditions and estimate the ionized gas contribution to the [CII]
emission. Photodissociation regions (PDRs) are probed through polycyclic
aromatic hydrocarbons (PAHs). We first study the distribution and properties of
the ionized gas. We then constrain the origin of [CII]157um by comparing to
tracers of the low-excitation ionized gas and of PDRs. [OIII] is dominated by
extended emission from the high-excitation diffuse ionized gas; it is the
brightest far-infrared line, ~4 times brighter than [CII]. The extent of the
[OIII] emission suggests that the medium is rather fragmented, allowing far-UV
photons to permeate into the ISM to scales of >30pc. Furthermore, by comparing
[CII] with [NII], we find that 95% of [CII] arises in PDRs, except toward the
stellar cluster for which as much as 15% could arise in the ionized gas. We
find a remarkable correlation between [CII]+[OI] and PAH emission, with [CII]
dominating the cooling in diffuse PDRs and [OI] dominating in the densest PDRs.
The combination of [CII] and [OI] provides a proxy for the total gas cooling in
PDRs. Our results suggest that PAH emission describes better the PDR gas
heating as compared to the total infrared emission.Comment: Accepted for publication in Astronomy and Astrophysics. Fixed
inverted line ratio in Sect. 5.
Herschel PACS Spectroscopic Diagnostics of Local ULIRGs: Conditions and Kinematics in Mrk 231
In this first paper on the results of our Herschel PACS survey of local
Ultraluminous Infrared Galaxies (ULIRGs), as part of our SHINING survey of
local galaxies, we present far-infrared spectroscopy of Mrk 231, the most
luminous of the local ULIRGs, and a type 1 broad absorption line AGN. For the
first time in a ULIRG, all observed far-infrared fine-structure lines in the
PACS range were detected and all were found to be deficient relative to the far
infrared luminosity by 1 - 2 orders of magnitude compared with lower luminosity
galaxies. The deficits are similar to those for the mid-infrared lines, with
the most deficient lines showing high ionization potentials. Aged starbursts
may account for part of the deficits, but partial covering of the highest
excitation AGN powered regions may explain the remaining line deficits. A
massive molecular outflow, discovered in OH and 18OH, showing outflow
velocities out to at least 1400 km/sec, is a unique signature of the clearing
out of the molecular disk that formed by dissipative collapse during the
merger. The outflow is characterized by extremely high ratios of 18O / 16O
suggestive of interstellar medium processing by advanced starbursts.Comment: Accepted for publication in the Astronomy and Astrophysics Herschel
Special Issue, 5 pages, 4 figure
Feasibility and performances of compressed-sensing and sparse map-making with Herschel/PACS data
The Herschel Space Observatory of ESA was launched in May 2009 and is in
operation since. From its distant orbit around L2 it needs to transmit a huge
quantity of information through a very limited bandwidth. This is especially
true for the PACS imaging camera which needs to compress its data far more than
what can be achieved with lossless compression. This is currently solved by
including lossy averaging and rounding steps on board. Recently, a new theory
called compressed-sensing emerged from the statistics community. This theory
makes use of the sparsity of natural (or astrophysical) images to optimize the
acquisition scheme of the data needed to estimate those images. Thus, it can
lead to high compression factors.
A previous article by Bobin et al. (2008) showed how the new theory could be
applied to simulated Herschel/PACS data to solve the compression requirement of
the instrument. In this article, we show that compressed-sensing theory can
indeed be successfully applied to actual Herschel/PACS data and give
significant improvements over the standard pipeline. In order to fully use the
redundancy present in the data, we perform full sky map estimation and
decompression at the same time, which cannot be done in most other compression
methods. We also demonstrate that the various artifacts affecting the data
(pink noise, glitches, whose behavior is a priori not well compatible with
compressed-sensing) can be handled as well in this new framework. Finally, we
make a comparison between the methods from the compressed-sensing scheme and
data acquired with the standard compression scheme. We discuss improvements
that can be made on ground for the creation of sky maps from the data.Comment: 11 pages, 6 figures, 5 tables, peer-reviewed articl
Spectroscopic FIR mapping of the disk and galactic wind of M82 with Herschel-PACS
[Abridged] We present maps of the main cooling lines of the neutral atomic
gas ([OI] at 63 and 145 micron and [CII] at 158 micron) and in the [OIII] 88
micron line of the starburst galaxy M82, carried out with the PACS spectrometer
on board the Herschel satellite. By applying PDR modeling we derive maps of the
main ISM physical parameters, including the [CII] optical depth, at
unprecedented spatial resolution (~300 pc). We can clearly kinematically
separate the disk from the outflow in all lines. The [CII] and [OI]
distributions are consistent with PDR emission both in the disk and in the
outflow. Surprisingly, in the outflow, the atomic and the ionized gas traced by
the [OIII] line both have a deprojected velocity of ~75 km/s, very similar to
the average velocity of the outflowing cold molecular gas (~ 100 km/s) and
several times smaller than the outflowing material detected in Halpha (~ 600
km/s). This suggests that the cold molecular and neutral atomic gas and the
ionized gas traced by the [OIII] 88 micron line are dynamically coupled to each
other but decoupled from the Halpha emitting gas. We propose a scenario where
cold clouds from the disk are entrained into the outflow by the winds where
they likely evaporate, surviving as small, fairly dense cloudlets (n_H\sim
500-1000 cm^-3, G_0\sim 500- 1000, T_gas\sim300 K). We show that the UV photons
provided by the starburst are sufficient to excite the PDR shells around the
molecular cores. The mass of the neutral atomic gas in the outflow is \gtrsim
5-12x 10^7 M_sun to be compared with that of the molecular gas (3.3 x 10^8
M_sun) and of the Halpha emitting gas (5.8 x 10^6 M_sun). The mass loading
factor, (dM/dt)/SFR, of the molecular plus neutral atomic gas in the outflow is
~ 2. Energy and momentum driven outflow models can explain the data equally
well, if all the outflowing gas components are taken into account.Comment: 26 pages, 23 figures, 4 Tables, Accepted for publication in Astronomy
& Astrophysic
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