76 research outputs found
Velocity resolved [CII], [CI], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities
The [CII]158um line is one of the dominant cooling lines in star-forming
active regions. The commonly assumed clumpy UV-penetrated cloud models predict
a [CII] line profile similar to that of CO. However, recent spectral-resolved
observations show that they are often very different, indicating a more complex
origin of the line emission including the dynamics of the source region. The
aim of our study is to investigate the physical properties of the star-forming
ISM in the Large Magellanic Cloud (LMC) by separating the origin of the
emission lines spatially and spectrally. In this paper, we focus on the
spectral characteristics and the origin of the emission lines, and the phases
of carbon-bearing species in the N159 star-forming region in the LMC. We mapped
a 4'x(3-4)' region in N159 in [CII]158um and [NII]205um with the GREAT on board
SOFIA, and in CO(3-2), (4-3), (6-5), 13CO(3-2), and [CI]3P1-3P0 and 3P2-3P1
with APEX. The emission of all transitions observed shows a large variation in
the line profiles across the map and between the different species. At most
positions the [CII] emission line profile is substantially wider than that of
CO and [CI]. We estimated the fraction of the [CII] integrated line emission
that cannot be fitted by the CO line profile to be 20%-50%. We derived the
relative contribution from C+, C, and CO to the column density in each velocity
bin. The contribution from C+ dominates the velocity range far from the
velocities traced by the dense molecular gas, and the region located between
the CO cores of N159 W and E. We estimate the contribution of the ionized gas
to the [CII] emission using the ratio to the [NII] emission to be < 19% to the
[CII] emission at its peak position, and <15% over the whole observed region.
Using the integrated line intensities, we present the spatial distribution of
I([CII])/I(FIR). (abridged for arXiv)Comment: 16 pages with 14 figures, accepted for publication in A&
GREAT/SOFIA atmospheric calibration
The GREAT observations need frequency-selective calibration across the
passband for the residual atmospheric opacity at flight altitude. At these
altitudes the atmospheric opacity has both narrow and broad spectral features.
To determine the atmospheric transmission at high spectral resolution, GREAT
compares the observed atmospheric emission with atmospheric model predictions,
and therefore depends on the validity of the atmospheric models. We discusse
the problems identified in this comparison with respect to the observed data
and the models, and describe the strategy used to calibrate the science data
from GREAT/SOFIA during the first observing periods.Comment: 14 pages, 4 figure
A 490 GHz planar circuit balanced Nb-AlO-Nb quasiparticle mixer for radio astronomy: Application to quantitative local oscillator noise determination
This article presents a heterodyne experiment which uses a 380-520 GHz planar
circuit balanced Nb--Nb
superconductor-insulator-superconductor (SIS) quasiparticle mixer with 4-8 GHz
instantaneous intermediate frequency (IF) bandwidth to quantitatively determine
local oscillator (LO) noise. A balanced mixer is a unique tool to separate
noise at the mixer's LO port from other noise sources. This is not possible in
single-ended mixers. The antisymmetric IV characteristic of a SIS mixer further
helps to simplify the measurements. The double-sideband receiver sensitivity of
the balanced mixer is 2-4 times the quantum noise limit over the
measured frequencies with a maximum LO noise rejection of 15 dB. This work
presents independent measurements with three different LO sources that produce
the reference frequency but also an amount of near-carrier noise power which is
quantified in the experiment as a function of the LO and IF frequency in terms
of an equivalent noise temperature . In a second experiment we use only
one of two SIS mixers of the balanced mixer chip, in order to verify the
influence of near-carrier LO noise power on a single-ended heterodyne mixer
measurement. We find an IF frequency dependence of near-carrier LO noise power.
The frequency-resolved IF noise temperature slope is flat or slightly negative
for the single-ended mixer. This is in contrast to the IF slope of the balanced
mixer itself which is positive due to the expected IF roll-off of the mixer.
This indicates a higher noise level closer to the LO's carrier frequency. Our
findings imply that near-carrier LO noise has the largest impact on the
sensitivity of a receiver system which uses mixers with a low IF band, for
example superconducting hot-electron bolometer (HEB) mixers.Comment: 13 pages, 8 figures, 2 tables, see manuscript for complete abstrac
Structure of the W3A Low Density Foreground Region
We present analysis of OI 63 micron and CO = 5-4 and 8-7 multi-position
data in the W3A region and use it to develop a model for the extended
low-density foreground gas that produces absorption features in the OI and
= 5-4 CO lines. We employ the extinction to the exciting stars of the
background HII region to constrain the total column density of the foreground
gas. We have used the Meudon PDR code to model the physical conditions and
chemistry in the region employing a two-component model with high density layer
near the HII region responsible for the fine structure line emission, and an
extended low density foreground layer. The best-fitting total proton density,
constrained largely by the CO lines, is (H) = 250 cm in the
foreground gas, and 510 cm in the material near the HII
region. The absorption is distributed over the region mapped in W3A, and is not
restricted to the foreground of either the embedded exciting stars of the HII
region or the protostar W3 IRS5. The low-density material associated with
regions of massive star formation, based on an earlier study by Goldsmith et
al. (2021), is quite common, and we now see that it is extended over a
significant portion of W3A. It thus should be included in modeling of fine
structure line emission, including interpreting low-velocity resolution
observations made with incoherent spectrometer systems, in order to use these
lines as accurate tracers of massive star formation
CCAT-prime: a novel telescope for submillimeter astronomy
The CCAT-prime telescope is a 6-meter aperture, crossed-Dragone telescope,
designed for millimeter and sub-millimeter wavelength observations. It will be
located at an altitude of 5600 meters, just below the summit of Cerro
Chajnantor in the high Atacama region of Chile. The telescope's unobscured
optics deliver a field of view of almost 8 degrees over a large, flat focal
plane, enabling it to accommodate current and future instrumentation fielding
>100k diffraction-limited beams for wavelengths less than a millimeter. The
mount is a novel design with the aluminum-tiled mirrors nested inside the
telescope structure. The elevation housing has an integrated shutter that can
enclose the mirrors, protecting them from inclement weather. The telescope is
designed to co-host multiple instruments over its nominal 15 year lifetime. It
will be operated remotely, requiring minimum maintenance and on-site activities
due to the harsh working conditions on the mountain. The design utilizes
nickel-iron alloy (Invar) and carbon-fiber-reinforced polymer (CFRP) materials
in the mirror support structure, achieving a relatively temperature-insensitive
mount. We discuss requirements, specifications, critical design elements, and
the expected performance of the CCAT-prime telescope. The telescope is being
built by CCAT Observatory, Inc., a corporation formed by an international
partnership of universities. More information about CCAT and the CCAT-prime
telescope can be found at www.ccatobservatory.org.Comment: Event: SPIE Astronomical Telescope + Instrumentation, 2018, Austin,
Texas, USA; Proceedings Volume 10700, Ground-based and Airborne Telescopes
VII; 107005X (2018
SOFIA FEEDBACK Survey: The Pillars of Creation in [C II] and Molecular Lines
We investigate the physical structure and conditions of photodissociation
regions (PDRs) and molecular gas within the Pillars of Creation in the Eagle
Nebula using SOFIA FEEDBACK observations of the [C II] 158 micron line. These
observations are velocity resolved to 0.5 km s and are analyzed
alongside a collection of complimentary data with similar spatial and spectral
resolution: the [O I] 63 micron line, also observed with SOFIA, and rotational
lines of CO, HCN, HCO, CS, and NH. Using the superb spectral
resolution of SOFIA, APEX, CARMA, and BIMA, we reveal the relationships between
the warm PDR and cool molecular gas layers in context of the Pillars' kinematic
structure. We assemble a geometric picture of the Pillars and their
surroundings informed by illumination patterns and kinematic relationships and
derive physical conditions in the PDRs associated with the Pillars. We estimate
an average molecular gas density cm
and an average atomic gas density cm
and infer that the ionized, atomic, and molecular phases are in pressure
equilibrium if the atomic gas is magnetically supported. We find pillar masses
of 103, 78, 103, and 18 solar masses for P1a, P1b, P2, and P3 respectively, and
evaporation times of 1-2 Myr. The dense clumps at the tops of the pillars
are currently supported by the magnetic field. Our analysis suggests that
ambipolar diffusion is rapid and these clumps are likely to collapse within
their photoevaporation timescales.Comment: 42 pages, 16 figures. Accepted for publication in The Astronomical
Journa
First detection of the atomic O18 isotope in the mesosphere and lower thermosphere of Earth
In the lower atmosphere of Earth, oxygen contains a higher fraction of the heavy O18 isotope than ocean water does (Dole effect). This isotopic enrichment is a signature of biological activity, set by the equilibrium between oxygenic photosynthesis and respiratory metabolisms in terrestrial and oceanic ecosystems. While the mixing between stratospheric and tropospheric oxygen leads to a slow isotopic homogenization, little is known about the isotopic oxygen enrichment in the mesosphere and thermosphere of Earth. In situ measurements from rocket-borne air samplers are limited to altitudes below the mesopause, while higher layers have only been accessible through the analysis of the oxidation of ancient cosmic spherules. Here we report the detection of the far-infrared fine-structure lines (3P1<-3P2 and 3P0<-3P1) of O18 in absorption against the Moon, and determine the O16/O18 ratio in atomic oxygen from the mesosphere and lower thermosphere in absorption. After correcting for isotopic exchange between atomic and molecular oxygen, our values for the bulk O16/O18 ratio of 468 and 382 in February and November 2021, respectively, fall significantly below that found in solar wind samples (530±2), and encompass, within uncertainties, the corresponding ratios pertaining to the Dole effect in the troposphere (487), and those found in stratospheric ozone (429 to 466). We show that with existing technology, future, more sensitive measurements will allow us to monitor deviations from isotopic homogeneity in the mesosphere and lower thermosphere of Earth by remote sensing. We demonstrate that the collisional excitation of the fine-structure levels of the P3 ground-state triplet of O18 may compete with isotopic exchange reactions, implying a deviation from the Boltzmann distribution that would be established under local thermodynamic equilibrium
The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO)
AST/RO, a 1.7 m diameter telescope for astronomy and aeronomy studies at
wavelengths between 200 and 2000 microns, was installed at the South Pole
during the 1994-1995 Austral summer. The telescope operates continuously
through the Austral winter, and is being used primarily for spectroscopic
studies of neutral atomic carbon and carbon monoxide in the interstellar medium
of the Milky Way and the Magellanic Clouds. The South Pole environment is
unique among observatory sites for unusually low wind speeds, low absolute
humidity, and the consistent clarity of the submillimeter sky. Four heterodyne
receivers, an array receiver, three acousto-optical spectrometers, and an array
spectrometer are installed. A Fabry-Perot spectrometer using a bolometric array
and a Terahertz receiver are in development. Telescope pointing, focus, and
calibration methods as well as the unique working environment and logistical
requirements of the South Pole are described.Comment: 57 pages, 15 figures. Submitted to PAS
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