138 research outputs found
The Data Processing Pipeline for the Herschel-HIFI Instrument
The HIFI data processing pipeline was developed to systematically process
diagnostic, calibration and astronomical observations taken with the HIFI
science instrumentas part of the Herschel mission. The HIFI pipeline processed
data from all HIFI observing modes within the Herschel automated processing
environment, as well as, within an interactive environment. A common software
framework was developed to best support the use cases required by the
instrument teams and by the general astronomers. The HIFI pipeline was built on
top of that and was designed with a high degree of modularity. This modular
design provided the necessary flexibility and extensibility to deal with the
complexity of batch-processing eighteen different observing modes, to support
the astronomers in the interactive analysis and to cope with adjustments
necessary to improve the pipeline and the quality of the end-products. This
approach to the software development and data processing effort was arrived at
by coalescing the lessons learned from similar research based projects with the
understanding that a degree of foresight was required given the overall length
of the project. In this article, both the successes and challenges of the HIFI
software development process are presented. To support future similar projects
and retain experience gained lessons learned are extracted.Comment: 18 pages, 5 figure
Diagnosing shock temperature with NH and HO profiles
In a previous study of the L1157 B1 shocked cavity, a comparison between
NH(1-) and HO(1--1) transitions showed a
striking difference in the profiles, with HO emitting at definitely higher
velocities. This behaviour was explained as a result of the high-temperature
gas-phase chemistry occurring in the postshock gas in the B1 cavity of this
outflow. If the differences in behaviour between ammonia and water are indeed a
consequence of the high gas temperatures reached during the passage of a shock,
then one should find such differences to be ubiquitous among chemically rich
outflows. In order to determine whether the difference in profiles observed
between NH and HO is unique to L1157 or a common characteristic of
chemically rich outflows, we have performed Herschel-HIFI observations of the
NH(1-0) line at 572.5 GHz in a sample of 8 bright low-mass outflow
spots already observed in the HO(1--1) line within
the WISH KP. We detected the ammonia emission at high-velocities at most of the
outflows positions. In all cases, the water emission reaches higher velocities
than NH, proving that this behaviour is not exclusive of the L1157-B1
position. Comparisons with a gas-grain chemical and shock model confirms, for
this larger sample, that the behaviour of ammonia is determined principally by
the temperature of the gas.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Societ
Water distribution in shocked regions of the NGC1333-IRAS4A protostellar outflow
We present the study of the H2O spatial distribution at two bright shocked
regions along IRAS4A, one of the strongest H2O emitters among the Class 0
outflows. We obtained Herschel-PACS maps of the IRAS4A outflow and HIFI
observations of two shocked positions. The largest HIFI beam of 38 arcsec at
557 GHz was mapped in several key water lines with different upper energy
levels, to reveal possible spatial variations of the line profiles. We detect
four H2O lines and CO (16-15) at the two selected positions. In addition,
transitions from related outflow and envelope tracers are detected. Different
gas components associated with the shock are identified in the H2O emission. In
particular, at the head of the red lobe of the outflow, two distinct gas
components with different excitation conditions are distinguished in the HIFI
emission maps: a compact component, detected in the ground-state water lines,
and a more extended one. Assuming that these two components correspond to two
different temperature components observed in previous H2O and CO studies, the
excitation analysis of the H2O emission suggests that the compact (about 3
arcsec) component is associated with a hot (T~1000 K) gas with densities
~(1-4)x10^5 cm^{-3}, whereas the extended one (10-17 arcsec) traces a warm
(T~300-500 K) and dense gas (~(3-5)x10^7 cm^{-3}). Finally, using the CO
(16-15) emission observed at R2, we estimate the H2O/H2 abundance of the warm
and hot components to be (7-10)x10^{-7} and (3-7)x10^{-5}. Our data allowed us,
for the first time, to resolve spatially the two temperature components
previously observed with HIFI and PACS. We propose that the compact hot
component may be associated with the jet that impacts the surrounding material,
whereas the warm, dense, and extended component originates from the compression
of the ambient gas by the propagating flow.Comment: 13 pages, 11 figures. Accepted for publication in Astronomy and
Astrophysic
Mapping water in protostellar outflows with Herschel: PACS and HIFI observations of L1448-C
We investigate on the spatial and velocity distribution of H2O along the
L1448 outflow, its relationship with other tracers, and its abundance
variations, using maps of the o-H2O 1_{10}-1_{01} and 2_{12}-1_{01} transitions
taken with the Herschel-HIFI and PACS instruments, respectively. Water emission
appears clumpy, with individual peaks corresponding to shock spots along the
outflow. The bulk of the 557 GHz line is confined to radial velocities in the
range \pm 10-50 km/s but extended emission associated with the L1448-C extreme
high velocity (EHV) jet is also detected. The H2O 1_{10}-1_{01}/CO(3-2) ratio
shows strong variations as a function of velocity that likely reflect different
and changing physical conditions in the gas responsible for the emissions from
the two species. In the EHV jet, a low H2O/SiO abundance ratio is inferred,
that could indicate molecular formation from dust free gas directly ejected
from the proto-stellar wind. We derive averaged Tkin and n(H2) values of about
300-500 K and 5 10^6 cm-3 respectively, while a water abundance with respect to
H2 of the order of 0.5-1 10^{-6} along the outflow is estimated. The fairly
constant conditions found all along the outflow implies that evolutionary
effects on the timescales of outflow propagation do not play a major role in
the H2O chemistry. The results of our analysis show that the bulk of the
observed H2O lines comes from post-shocked regions where the gas, after being
heated to high temperatures, has been already cooled down to a few hundred K.
The relatively low derived abundances, however, call for some mechanism to
diminish the H2O gas in the post-shock region. Among the possible scenarios, we
favor H2O photodissociation, which requires the superposition of a low velocity
non-dissociative shock with a fast dissociative shock able to produce a FUV
field of sufficient strength.Comment: 16 pages, 13 figures, accepted for publication on Astronomy &
Astrophysic
The CHESS survey of the L1157-B1 shock: the dissociative jet shock as revealed by Herschel--PACS
Outflows generated by protostars heavily affect the kinematics and chemistry
of the hosting molecular cloud through strong shocks that enhance the abundance
of some molecules. L1157 is the prototype of chemically active outflows, and a
strong shock, called B1, is taking place in its blue lobe between the
precessing jet and the hosting cloud. We present the Herschel-PACS 55--210
micron spectra of the L1157-B1 shock, showing emission lines from CO, H2O, OH,
and [OI]. The spatial resolution of the PACS spectrometer allows us to map the
warm gas traced by far-infrared (FIR) lines with unprecedented detail. The
rotational diagram of the high-Jup CO lines indicates high-excitation
conditions (Tex ~ 210 +/- 10 K). We used a radiative transfer code to model the
hot CO gas emission observed with PACS and in the CO (13-12) and (10-9) lines
measured by Herschel-HIFI. We derive 20010^5 cm-3. The CO
emission comes from a region of about 7 arcsec located at the rear of the bow
shock where the [OI] and OH emission also originate. Comparison with shock
models shows that the bright [OI] and OH emissions trace a dissociative J-type
shock, which is also supported by a previous detection of [FeII] at the same
position. The inferred mass-flux is consistent with the "reverse" shock where
the jet is impacting on the L1157-B1 bow shock. The same shock may contribute
significantly to the high-Jup CO emission.Comment: 7 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
The GUAPOS project: III. Characterization of the O- and N-bearing complex organic molecules content and search for chemical differentiation
Context. The G31.41+0.31 Unbiased ALMA sPectral Observational Survey (GUAPOS) project targets the hot molecular core (HMC) G31.41+0.31 (G31) to reveal the complex chemistry of one of the most chemically rich high-mass star-forming regions outside the Galactic center (GC). Aims. In the third paper of the project we present a study of nine O-bearing (CH3OH, 13CH3OH, CH318OH, CH3CHO, CH3OCH3, CH3COCH3, C2H5OH, aGgâČ-(CH2OH)2, and gGgâČ-(CH2OH)2) and six N-bearing (CH3CN,13CH3CN, CH313CN, C2H3CN, C2H5CN, and C2H513CN) complex organic molecules toward G31. The aim of this work is to characterize the abundances in G31 and to compare them with the values estimated in other sources. Moreover, we searched for a possible chemical segregation between O-bearing and N-bearing species in G31, which hosts four compact sources as seen with higher angular resolution data. In the discussion we also include the three isomers of C2H4O2 and the O- and N-bearing molecular species NH2CHO, CH3NCO, CH3C(O)CH2, and CH3NHCHO, which were analyzed in previous GUAPOS papers. Methods. Observations were carried out with the interferometer ALMA and cover the entire Band 3 from 84 to 116 GHz (âŒ32 GHz bandwidth) with an angular resolution of 1.2âł Ă 1.2âł (âŒ4400 au Ă 4400 au) and a spectral resolution of âŒ0.488 MHz (âŒ1.3- 1.7 km s-1). The transitions of the 14 molecular species were analyzed with the tool SLIM of MADCUBA to determine the physical parameters of the emitting gas. Moreover, we analyzed the morphology of the emission of the molecular species. Results. The values of abundances with respect to H2 in G31 range from 10-6 to 10-10 for the different species. We compared the abundances with respect to methanol of O-bearing, N-bearing, and O- and N-bearing COMs in G31 with 27 other sources, including other hot molecular cores inside and outside the GC, hot corinos, shocked regions, envelopes around young stellar objects, and quiescent molecular clouds, and with chemical models. Conclusions. From the comparison with other sources there is not a unique template for the abundances in hot molecular cores, pointing toward the importance of the thermal history for the chemistry of the various sources. The abundances derived from the chemical models are in good agreement, within a factor of 10, with those of G31. From the analysis of the maps we derived the peak positions of all the molecular species toward G31. Different species peak at slightly different positions, and this, together with the different central velocities of the lines obtained from the spectral fitting, point to chemical differentiation of selected O-bearing species
Excitation of the molecular gas in the nuclear region of M82
We present high resolution HIFI spectroscopy of the nucleus of the
archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4
fine-structure lines are detected. Besides showing the effects of the overall
velocity structure of the nuclear region, the line profiles also indicate the
presence of multiple components with different optical depths, temperatures and
densities in the observing beam. The data have been interpreted using a grid of
PDR models. It is found that the majority of the molecular gas is in low
density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and
a relatively low UV radiation field (GO = 10^2). The remaining gas is
predominantly found in clouds with higher densities (n=10^5 cm^-3) and
radiation fields (GO = 10^2.75), but somewhat lower column densities
(N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1%
relative surface filling) component, with an even higher density (n=10^6 cm^-3)
and UV field (GO = 10^3.25). These results show the strength of multi-component
modeling for the interpretation of the integrated properties of galaxies.Comment: Accepted for publication in A&A Letter
The GUAPOS project:III. Characterization of the O- and N-bearing complex organic molecules content and search for chemical differentiation
The G31.41+0.31 Unbiased ALMA sPectral Observational Survey (GUAPOS) project
targets the hot molecular core (HMC) G31.41+0.31 (G31), to unveil the complex
chemistry of one of the most chemically rich high-mass star-forming regions
outside the Galactic Center (GC). In the third paper of the project, we present
a study of nine O-bearing (CHOH, CHOH, CHOH, CHCHO,
CHOCH, CHCOCH , CHOH, aGg'-(CHOH), and
gGg'-(CHOH)) and six N-bearing (CHCN, CHCN,
CHCN, CHCN, CHCN, and CHCN) complex
organic molecules toward G31. The aim of this work is to characterize the
abundances in one of the most chemically-rich hot molecular cores outside the
GC and to search for a possible chemical segregation between O-bearing and
N-bearing species in G31, which hosts four compact sources as seen with higher
angular resolution data. Observations were carried out with the interferometer
ALMA and covered the entire Band 3 from 84 to 116 GHz ( GHz bandwidth)
with an angular resolution of (). The spectrum
has been analyzed with the tool SLIM of MADCUBA to determine the physical
parameters of the emitting gas. Moreover, we have analyzed the morphology of
the emission of the molecular species. We have compared the abundances w.r.t
methanol of COMs in G31 with other twenty-seven sources, including other hot
molecular cores inside and outside the Galactic Center, hot corinos, shocked
regions, envelopes around young stellar objects, and quiescent molecular
clouds, and with chemical models. Different species peak at slightly different
positions, and this, together with the different central velocities of the
lines obtained from the spectral fitting, point to chemical differentiation of
selected O-bearing species.Comment: accepted for publication in A&A, 39 page
Water emission from the chemically rich outflow L1157
In the framework of the Herschel-WISH key program, several ortho-H2O and
para-H2O emission lines, in the frequency range from 500 to 1700 GHz, were
observed with the HIFI instrument in two bow-shock regions (B2 and R) of the
L1157 cloud. The primary aim is to analyse water emission lines as a diagnostic
of the physical conditions in the blue (B2) and red-shifted (R) lobes to
compare the excitation conditions. A total of 5 ortho- and para-H216O plus one
o-H218O transitions were observed in B2 and R with a wide range of excitation
energies (27 K<=Eu<=215 K). The H2O spectra, observed in the two shocked
regions, show that the H2O profiles are markedly different in the two regions.
In particular, at the bow-shock R, we observed broad (~30 km s-1 with respect
to the ambient velocity) red-shifted wings where lines at different excitation
peak at different red-shifted velocities. The B2 spectra are associated with a
narrower velocity range (~6 km s-1), peaking at the systemic velocity. The
excitation analysis suggests, for B2, low values of column density NH2O
<=5{\times}1013 cm-2, a density range of 105 <=nH2 <=107 cm-3, and warm
temperatures (>=300 K). The presence of the broad red-shifted wings and
multiple peaks in the spectra of the R region, prompted the modelling of two
components. High velocities are associated with relatively low temperatures
(~100K),NH2O{\simeq}5{\times}1012-5{\times}1013 cm-2 and densities
nH2{\simeq}106-108 cm-3.Lower velocities are associated with higher excitation
conditions with Tkin>=300 K, very dense gas (nH2 ~108 cm-3) and low column
density (NH2O<5{\times}1013 cm-2).Comment: 9 pages, 8 figures, A&A in pres
Herschel observations in the ultracompact HII region Mon R2: Water in dense Photon-dominated regions (PDRs)
Mon R2, at a distance of 830 pc, is the only ultracompact HII region (UC HII)
where the photon-dominated region (PDR) between the ionized gas and the
molecular cloud can be resolved with Herschel. HIFI observations of the
abundant compounds 13CO, C18O, o-H2-18O, HCO+, CS, CH, and NH have been used to
derive the physical and chemical conditions in the PDR, in particular the water
abundance. The 13CO, C18O, o-H2-18O, HCO+ and CS observations are well
described assuming that the emission is coming from a dense (n=5E6 cm-3,
N(H2)>1E22 cm-2) layer of molecular gas around the UC HII. Based on our
o-H2-18O observations, we estimate an o-H2O abundance of ~2E-8. This is the
average ortho-water abundance in the PDR. Additional H2-18O and/or water lines
are required to derive the water abundance profile. A lower density envelope
(n~1E5 cm-3, N(H2)=2-5E22 cm-2) is responsible for the absorption in the NH
1_1-0_2 line. The emission of the CH ground state triplet is coming from both
regions with a complex and self-absorbed profile in the main component. The
radiative transfer modeling shows that the 13CO and HCO+ line profiles are
consistent with an expansion of the molecular gas with a velocity law, v_e =0.5
x (r/Rout)^{-1} km/s, although the expansion velocity is poorly constrained by
the observations presented here.Comment: 4 pages, 5 figure
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