109 research outputs found
Water, O2 and Ice in Molecular Clouds
We model the temperature and chemical structure of molecular clouds as a
function of depth into the cloud, assuming a cloud of constant density n
illuminated by an external FUV (6 eV < E < 13.6 eV) flux G_0 (scaling factor in
multiples of the local interstellar field). Extending previous
photodissociation region models, we include the freezing of species, simple
grain surface chemistry, and desorption (including FUV photodesorption) of
ices. We also treat the opaque cloud interior with time-dependent chemistry.
Here, under certain conditions, gas phase elemental oxygen freezes out as water
ice and the elemental C/O abundance ratio can exceed unity, leading to complex
carbon chemistry. Gas phase H2O and O2 peak in abundance at intermediate depth
into the cloud, roughly A_V~3-8 from the surface, the depth proportional to
ln(G_0/n). Closer to the surface, molecules are photodissociated. Deeper into
the cloud, molecules freeze to grain surfaces. At intermediate depths
photodissociation rates are attenuated by dust extinction, but photodesorption
prevents total freezeout. For G_0 < 500, abundances of H2O and O2 peak at
values ~10^(-7), producing columns ~10^(15) per cm^2, independent of G_0 and n.
The peak abundances depend primarily on the product of the photodesorption
yield of water ice and the grain surface area per H nucleus. At higher values
of G_0, thermal desorption of O atoms from grains enhances the gas phase H2O
peak abundance and column slightly, whereas the gas phase O2 peak abundance
rises to ~10^(-5) and the column to ~2x10^(16) per cm^2. We present simple
analytic equations for the abundances as a function of depth which clarify the
dependence on parameters. The models are applied to observations of H2O, O2,
and water ice in a number of sources, including B68, NGC 2024, and Rho Oph.Comment: 70 pages including 17 figure
Laboratory and tentative interstellar detection of trans-methyl formate using the publicly available Green Bank Telescope PRIMOS survey
The rotational spectrum of the higher-energy trans conformational isomer of
methyl formate has been assigned for the first time using several pulsed-jet
Fourier transform microwave spectrometers in the 6-60 GHz frequency range. This
species has also been sought toward the Sagittarius B2(N) molecular cloud using
the publicly available PRIMOS survey from the Green Bank Telescope. We detect
seven absorption features in the survey that coincide with laboratory
transitions of trans-methyl formate, from which we derive a column density of
3.1 (+2.6, -1.2) \times 10^13 cm-2 and a rotational temperature of 7.6 \pm 1.5
K. This excitation temperature is significantly lower than that of the more
stable cis conformer in the same source but is consistent with that of other
complex molecular species recently detected in Sgr B2(N). The difference in the
rotational temperatures of the two conformers suggests that they have different
spatial distributions in this source. As the abundance of trans-methyl formate
is far higher than would be expected if the cis and trans conformers are in
thermodynamic equilibrium, processes that could preferentially form
trans-methyl formate in this region are discussed. We also discuss measurements
that could be performed to make this detection more certain. This manuscript
demonstrates how publicly available broadband radio astronomical surveys of
chemically rich molecular clouds can be used in conjunction with laboratory
rotational spectroscopy to search for new molecules in the interstellar medium.Comment: 40 pages, 7 figures, 4 tables; accepted for publication in Ap
Accuracy in local staging of prostate cancer by adding a three-dimensional T2-weighted sequence with radial reconstructions in magnetic resonance imaging.
BACKGROUND: The evidence supporting the use of magnetic resonance imaging (MRI) in prostate cancer detection has been established, but its accuracy in local staging is questioned. PURPOSE: To investigate the additional value of multi-planar radial reconstructions of a three-dimensional (3D) T2-weighted (T2W) MRI sequence, intercepting the prostate capsule perpendicularly, for improving local staging of prostate cancer. MATERIAL AND METHODS: Preoperative, bi-parametric prostate MRI examinations in 94 patients operated between June 2014 and January 2015 where retrospectively reviewed by two experienced abdominal radiologists. Each patient was presented in two separate sets including diffusion-weighted imaging, without and with the 3D T2W set that included radial reconstructions. Each set was read at least two months apart. Extraprostatic tumor extension (EPE) was assessed according to a 5-point grading scale. Sensitivity and specificity for EPE was calculated and presented as receiver operating characteristics (ROC) with area under the curve (AUC), using histology from whole-mount prostate specimen as gold standard. Inter-rater agreement was calculated for the two different reading modes using Cohen's kappa. RESULTS: The AUC for detection of EPE for Readers 1 and 2 in the two-dimensional (2D) set was 0.70 and 0.68, respectively, and for the 2D + 3D set 0.62 and 0.65, respectively. Inter-rater agreement (Reader 1 vs. Reader 2) on EPE using Cohen's kappa for the 2D and 2D + 3D set, respectively, was 0.42 and 0.17 (i.e. moderate and poor agreement, respectively). CONCLUSION: The addition of 3D T2W MRI with radial reconstructions did not improve local staging in prostate cancer
CO2 Ice toward Low-luminosity, Embedded Protostars: Evidence for Episodic Mass Accretion via Chemical History
We present Spitzer IRS spectroscopy of CO2 ice bending mode spectra at 15.2
micrometer toward 19 young stellar objects with luminosity lower than 1 Lsun (3
with luminosity lower than 0.1 Lsun). Ice on dust grain surfaces can encode the
history of heating because pure CO2 ice forms only at elevated temperature, T >
20 K, and thus around protostars of higher luminosity. Current internal
luminosities of YSOs with L < 1 Lsun do not provide the conditions needed to
produce pure CO2 ice at radii where typical envelopes begin. The presence of
detectable amounts of pure CO2 ice would signify a higher past luminosity. Many
of the spectra require a contribution from a pure, crystalline CO2 component,
traced by the presence of a characteristic band splitting in the 15.2
micrometer bending mode. About half of the sources (9 out of 19) in the low
luminosity sample have evidence for pure CO2 ice, and six of these have
significant double-peaked features, which are very strong evidence of pure CO2
ice. The presence of the pure CO2 ice component indicates that the dust
temperature, and hence luminosity of the central star/accretion disk system,
must have been higher in the past. An episodic accretion scenario, in which
mixed CO-CO2 ice is converted to pure CO2 ice during each high luminosity
phase, explains the presence of pure CO2 ice, the total amount of CO2 ice, and
the observed residual C18O gas.Comment: Accepted for publication in ApJ, total 24 pages, 14 figure
Chemistry in a gravitationally unstable protoplanetary disc
Until now, axisymmetric, alpha-disc models have been adopted for calculations
of the chemical composition of protoplanetary discs. While this approach is
reasonable for many discs, it is not appropriate when self-gravity is
important. In this case, spiral waves and shocks cause temperature and density
variations that affect the chemistry. We have adopted a dynamical model of a
solar-mass star surrounded by a massive (0.39 Msun), self-gravitating disc,
similar to those that may be found around Class 0 and early Class I protostars,
in a study of disc chemistry. We find that for each of a number of species,
e.g. H2O, adsorption and desorption dominate the changes in the gas-phase
fractional abundance; because the desorption rates are very sensitive to
temperature, maps of the emissions from such species should reveal the
locations of shocks of varying strengths. The gas-phase fractional abundances
of some other species, e.g. CS, are also affected by gas-phase reactions,
particularly in warm shocked regions. We conclude that the dynamics of massive
discs have a strong impact on how they appear when imaged in the emission lines
of various molecular species.Comment: 10 figures and 3 tables, accepted for publication in MNRA
First Detection of Near-Infrared Line Emission from Organics in Young Circumstellar Disks
We present an analysis of high-resolution spectroscopy of several bright T
Tauri stars using the VLT/CRIRES and Keck/NIRSPEC spectrographs, revealing the
first detections of emission from HCN and C2H2 in circumstellar disks at
near-infrared wavelengths. Using advanced data reduction techniques we achieve
a dynamic range with respect to the disk continuum of ~500 at 3 microns,
revealing multiple emission features of H2O, OH, HCN, and C2H2. We also present
stringent upper limits for two other molecules thought to be abundant in the
inner disk, CH4 and NH3. Line profiles for the different detected molecules are
broad but centrally peaked in most cases, even for disks with previously
determined inclinations of greater than 20 degrees, suggesting that the
emission has both a Keplerian and non-Keplerian component as observed
previously for CO emission. We apply two different modeling strategies to
constrain the molecular abundances and temperatures: we use a simplified
single-temperature LTE slab model with a Gaussian line profile to make line
identifications and determine a best-fit temperature and initial abundance
ratios, and we compare these values with constraints derived from a detailed
disk radiative transfer model assuming LTE excitation but utilizing a realistic
temperature and density structure. Abundance ratios from both sets of models
are consistent with each other and consistent with expected values from
theoretical chemical models, and analysis of the line shapes suggests the
molecular emission originates from within a narrow region in the inner disk (R
< 1 AU).Comment: Accepted to the Astrophysical Journa
The Spitzer Survey of Interstellar Clouds in the Gould Belt. III. A Multi-Wavelength View of Corona Australis
We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg^2
field including the Corona Australis (CrA) star-forming region. At a distance
of 130 pc, CrA is one of the closest regions known to be actively forming
stars, particularly within its embedded association, the Coronet. Using the
Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include
sources in the well-studied Coronet cluster as well as distributed throughout
the molecular cloud. Twelve of the YSOs discussed are new candidates, one of
which is located in the Coronet. Known YSOs retrieved from the literature are
also added to the list, and a total of 116 candidate YSOs in CrA are compiled.
Based on these YSO candidates, the star formation rate is computed to be 12 M_o
Myr^-1, similar to that of the Lupus clouds. A clustering analysis was also
performed, finding that the main cluster core, consisting of 68 members, is
elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc
and mean surface density of 150 pc^-2.
In addition, we analyze outflows and jets in CrA by means of new CO and H_2
data. We present 1.3 mm interferometric continuum observations made with the
Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712
(IRAS 32). We also present multi-epoch H_2 maps and detect jets and outflows,
study their proper motions, and identify exciting sources. The Spitzer and
ISAAC/VLT observations of IRAS 32 show a bipolar precessing jet, which drives a
CO (2-1) outflow detected in the SMA observations. There is also clear evidence
for a parsec-scale precessing outflow, E-W oriented, and originating in the SMA
2 region, likely driven by SMA 2 or IRS 7A.Comment: Accepted for publication in ApJS. 112 pages, 42 figures (quality
reduced), 13 tables. Full resolution version can be found at
http://www.cfa.harvard.edu/~dpeterson/CrA/CrA_highres.pd
A novel approach in the treatment of neuroendocrine gastrointestinal tumors: Additive antiproliferative effects of interferon-γ and meta-iodobenzylguanidine
BACKGROUND: Therapeutic options to effectively inhibit growth and spread of neuroendocrine gastrointestinal tumors are still limited. As both meta-iodobenzylguanidine (MIBG) and interferon-γ (IFNγ) cause antineoplastic effects in neuroendocrine gastrointestinal tumor cells, we investigated the antiproliferative effects of the combination of IFNγ and non-radiolabeled MIBG in neuroendocrine gut STC-1 and pancreatic carcinoid BON tumor cells. METHODS AND RESULTS: IFNγ receptors were expressed in both models. IFNγ dose- and time-dependently inhibited the growth of both STC-1 and of BON tumor cells with IC(50)-values of 95 ± 15 U/ml and 135 ± 10 U/ml, respectively. Above 10 U/ml IFNγ induced apoptosis-specific caspase-3 activity in a time-dependent manner in either cell line and caused a dose-dependent arrest in the S-phase of the cell cycle. Furthermore, IFNγ induced cytotoxic effects in NE tumor cells. The NE tumor-targeted drug MIBG is selectively taken up via norepinephrine transporters, thereby specifically inhibiting growth in NE tumor cells. Intriguingly, IFNγ treatment induced an upregulation of norepinephrine transporter expression in neuroendocrine tumors cells, as determined by semi-quantitative RT-PCR. Co-application of sub-IC(50 )concentrations of IFNγ and MIBG led to additive growth inhibitory effects, which were mainly due to increased cytotoxicity and S-phase arrest of the cell cycle. CONCLUSION: Our data show that IFNγ exerts antiproliferative effects on neuroendocrine gastrointestinal tumor cells by inducing cell cycle arrest, apoptosis and cytotoxicity. The combination of IFNγ with the NE tumor-targeted agent MIBG leads to effective growth control at reduced doses of either drug. Thus, the administration of IFNγ alone and more so, in combination with MIBG, is a promising novel approach in the treatment of neuroendocrine gastrointestinal tumors
JWST Reveals Excess Cool Water near the Snow Line in Compact Disks, Consistent with Pebble Drift
Previous analyses of mid-infrared water spectra from young protoplanetary disks observed with the Spitzer-IRS found an anticorrelation between water luminosity and the millimeter dust disk radius observed with ALMA. This trend was suggested to be evidence for a fundamental process of inner disk water enrichment proposed decades ago to explain some properties of the solar system, in which icy pebbles drift inward from the outer disk and sublimate after crossing the snow line. Previous analyses of IRS water spectra, however, were uncertain due to the low spectral resolution that blended lines together. We present new JWST-MIRI spectra of four disks, two compact and two large with multiple radial gaps, selected to test the scenario that water vapor inside the snow line is regulated by pebble drift. The higher spectral resolving power of MIRI-MRS now yields water spectra that separate individual lines, tracing upper level energies from 900 to 10,000 K. These spectra clearly reveal excess emission in the low-energy lines in compact disks compared to large disks, demonstrating an enhanced cool component with T ≈ 170–400 K and equivalent emitting radius R
eq ≈ 1–10 au. We interpret the cool water emission as ice sublimation and vapor diffusion near the snow line, suggesting that there is indeed a higher inward mass flux of icy pebbles in compact disks. Observation of this process opens up multiple exciting prospects to study planet formation chemistry in inner disks with JWST
The kinematics and excitation of infrared water vapor emission from planet-forming disks: results from spectrally-resolved surveys and guidelines for JWST spectra
This work presents water emission spectra at wavelengths covered by JWST
(2.9-12.8 m) as spectrally-resolved with high resolving powers (R =
30,000-100,000) using ground-based spectrographs. Two new surveys with iSHELL
and VISIR are combined with previous spectra from CRIRES and TEXES to cover
parts of multiple ro-vibrational and rotational bands observable within
telluric transmission bands, for a total of 85 disks and spectra.
The general expectation of a range of regions and excitation conditions traced
by infrared water spectra is for the first time supported by the combined
kinematics and excitation as spectrally resolved at multiple wavelengths. The
main findings from this analysis are: 1) water lines are progressively narrower
going from the ro-vibrational bands at 2-9 m to the rotational lines at 12
m, and partly match a broad (BC) and narrow (NC) emission components,
respectively, as extracted from ro-vibrational CO spectra; 2) rotation diagrams
of resolved water lines from upper level energies of 4000-9500 K show
curvatures indicative of optically thick emission ( cm)
from a range of excitation temperatures ( 800-1100 K); 3) the new 5
m spectra demonstrate that slab model fits to the rotational lines at m strongly over-predict the ro-vibrational emission bands at m,
implying non-LTE excitation. We discuss these findings in the context of a
emission from a disk surface and a molecular inner disk wind, and provide a
list of detailed guidelines to support the analysis and interpretation of
spectrally-unresolved JWST spectra.Comment: Posted on arXiv as submitted to AJ, for immediate access by teams
working on the analysis of JWST spectr
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