828 research outputs found
A Direct Measurement of the Total Gas Column Density in Orion KL
The large number of high-J lines of C^(18)O available via the Herschel Space Observatory provide an unprecedented ability to model the total CO column density in hot cores. Using the emission from all the observed lines (up to J = 15-14), we sum the column densities in each individual level to obtain the total column after correcting for the population in the unobserved states. With additional knowledge of source size, V_(LSR), and line width, and both local thermodynamic equilibrium (LTE) and non-LTE modeling, we have determined the total C^(18)O column densities in the Extended Ridge, Outflow/Plateau, Compact Ridge, and Hot Core components of Orion KL to be 1.4 Ă 10^(16) cm^(â2), 3.5 Ă 10^(16) cm^(â2), 2.2 Ă 10^(16) cm^(â2), and 6.2 Ă 10^(16) cm^(â2), respectively. We also find that the C^(18)O/C^(17)O abundance ratio varies from 1.7 in the Outflow/Plateau, 2.3 in the Extended Ridge, 3.0 in the Hot Core, and to 4.1 in the Compact Ridge. This is in agreement with models in which regions with higher ultraviolet radiation fields selectively dissociate C^(17)O, although care must be taken when interpreting these numbers due to the size of the uncertainties in the C^(18)O/C^(17)O abundance ratio
HERSCHEL OBSERVATIONS OF EXTRA-ORDINARY SOURCES: H2S AS A PROBE OF DENSE GAS AND POSSIBLY HIDDEN LUMINOSITY TOWARD THE ORION KL HOT CORE
We present Herschel/HIFI observations of the light hydride H2S obtained from the full spectral scan of the Orion Kleinmann-Low nebula (Orion KL) taken as part of the Herschel Observations of EXtra-Ordinary Sources GT (guaranteed time) key program. In total, we observe 52, 24, and 8 unblended or slightly blended features from H2 32S, H2 34S, and H2 33S, respectively. We only analyze emission from the so-called hot core, but emission from the plateau, extended ridge, and/or compact ridge are also detected. Rotation diagrams for ortho and para H2S follow straight lines given the uncertainties and yield T rot = 141 ± 12 K. This indicates H2S is in local thermodynamic equilibrium and is well characterized by a single kinetic temperature or an intense far-IR radiation field is redistributing the population to produce the observed trend. We argue the latter scenario is more probable and find that the most highly excited states (E up gsim 1000 K) are likely populated primarily by radiation pumping. We derive a column density, N tot(H2 32S) = 9.5 ± 1.9 Ă 1017 cmâ2, gas kinetic temperature, T kin = 120 K, and constrain the H2 volume density, gsim 9 Ă 10 7 cmâ3, for the H2S emitting gas. These results point to an H2S origin in markedly dense, heavily embedded gas, possibly in close proximity to a hidden self-luminous source (or sources), which are conceivably responsible for Orion KL's high luminosity. We also derive an H2S ortho/para ratio of 1.7 ± 0.8 and set an upper limit for HDS/H2S of <4.9 Ă 10 â3
Prognostic factors of atrial fibrillation following elective coronary artery bypass grafting: the impact of quantified intraoperative myocardial ischemia
<p>Abstract</p> <p>Background</p> <p>Atrial fibrillation (AF) occurs in 28-33% of the patients undergoing coronary artery revascularization (CABG). This study focuses on both pre- and peri-operative factors that may affect the occurrence of AF. The aim is to identify those patients at higher risk to develop AF after CABG.</p> <p>Patients and methods</p> <p>Two patient cohorts undergoing CABG were retrospectively studied. The first group (group A) consisted of 157 patients presenting AF after elective CABG. The second group (group B) consisted of 191 patients without AF postoperatively.</p> <p>Results</p> <p>Preoperative factors presenting significant correlation with the incidence of post-operative AF included: 1) age > 65 years (p = 0.029), 2) history of AF (p = 0.022), 3) chronic obstructive pulmonary disease (p = 0.008), 4) left ventricular dysfunction with ejection fraction < 40% (p = 0.015) and 5) proximal lesion of the right coronary artery (p = 0.023). The intraoperative factors that appeared to have significant correlation with the occurrence of postoperative AF were: 1) CPB-time > 120 minutes (p = 0.011), 2) myocardial ischemia index < 0.27 ml.m<sup>2</sup>/Kg.min (p = 0.011), 3) total positive fluid-balance during ICU-stay (p < 0.001), 4) FiO<sub>2</sub>/PO<sub>2 </sub>> 0, 4 after extubation and during the ICU-stay (p = 0.021), 5) inotropic support with doses 15-30 ÎŒg/Kg/min (p = 0.016), 6) long ICU-stay recovery for any reason (p < 0.001) and perioperative myocardial infarction (p < 0.001).</p> <p>Conclusions</p> <p>Our results suggest that the incidence of post-CABG atrial fibrillation can be predicted by specific preoperative and intraoperative measures. The intraoperative myocardial ischemia can be sufficiently quantified by the myocardial ischemia index. For those patients at risk we would suggest an early postoperative precautionary anti-arrhythmic treatment.</p
Follow-Up Observations of PTFO 8-8695: A 3 MYr Old T-Tauri Star Hosting a Jupiter-mass Planetary Candidate
We present Spitzer 4.5\micron\ light curve observations, Keck NIRSPEC radial
velocity observations, and LCOGT optical light curve observations of
PTFO~8-8695, which may host a Jupiter-sized planet in a very short orbital
period (0.45 days). Previous work by \citet{vaneyken12} and \citet{barnes13}
predicts that the stellar rotation axis and the planetary orbital plane should
precess with a period of days. As a consequence, the observed
transits should change shape and depth, disappear, and reappear with the
precession. Our observations indicate the long-term presence of the transit
events ( years), and that the transits indeed do change depth, disappear
and reappear. The Spitzer observations and the NIRSPEC radial velocity
observations (with contemporaneous LCOGT optical light curve data) are
consistent with the predicted transit times and depths for the $M_\star = 0.34\
M_\odot$ precession model and demonstrate the disappearance of the transits. An
LCOGT optical light curve shows that the transits do reappear approximately 1
year later. The observed transits occur at the times predicted by a
straight-forward propagation of the transit ephemeris. The precession model
correctly predicts the depth and time of the Spitzer transit and the lack of a
transit at the time of the NIRSPEC radial velocity observations. However, the
precession model predicts the return of the transits approximately 1 month
later than observed by LCOGT. Overall, the data are suggestive that the
planetary interpretation of the observed transit events may indeed be correct,
but the precession model and data are currently insufficient to confirm firmly
the planetary status of PTFO~8-8695b.Comment: Accepted for publication in The Astrophysical Journa
The European Large Area ISO Survey II: mid-infrared extragalactic source counts
We present preliminary source counts at 6.7um and 15um from the Preliminary
Analysis of the European Large Area ISO survey, with limiting flux densities of
\~2mJy at 15um & ~1mJy at 6.7um. We separate the stellar contribution from the
extragalactic using identifications with APM sources made with the likelihood
ratio technique. We quantify the completeness & reliability of our source
extraction using (a) repeated observations over small areas, (b) cross-IDs with
stars of known spectral type, (c) detections of the PSF wings around bright
sources, (d) comparison with independent algorithms. Flux calibration at 15um
was performed using stellar IDs; the calibration does not agree with the
pre-flight estimates, probably due to effects of detector hysteresis and
photometric aperture correction. The 6.7um extragalactic counts are broadly
reproduced in the Pearson & Rowan-Robinson model, but the Franceschini et al.
(1997) model underpredicts the observed source density by ~0.5-1 dex, though
the photometry at 6.7um is still preliminary. At 15um the extragalactic counts
are in excellent agreement with the predictions of the Pearson & Rowan-Robinson
(1996), Franceschini et al. (1994), Guiderdoni et al. (1997) and the evolving
models of Xu et al. (1998), over 7 orders of magnitude in 15um flux density.
The counts agree with other estimates from the ISOCAM instrument at overlapping
flux densities (Elbaz et al. 1999), provided a consistent flux calibration is
used. Luminosity evolution at a rate of (1+z)^3, incorporating mid-IR spectral
features, provides a better fit to the 15um differential counts than (1+z)^4
density evolution. No-evolution models are excluded, and implying that below
around 10mJy at 15um the source counts become dominated by an evolving
cosmological population of dust-shrouded starbursts and/or active galaxies.Comment: MNRAS in press. 14 pages, uses BoxedEPS (included). For more
information on the ELAIS project see http://athena.ph.ic.ac.uk
The type IIb SN 2008ax: spectral and light curve evolution
We present spectroscopy and photometry of the He-rich supernova (SN) 2008ax.
The early-time spectra show prominent P-Cygni H lines, which decrease with time
and disappear completely about two months after the explosion. In the same
period He I lines become the most prominent spectral features. SN 2008ax
displays the ordinary spectral evolution of a type IIb supernova. A stringent
pre-discovery limit constrains the time of the shock breakout of SN 2008ax to
within only a few hours. Its light curve, which peaks in the B band about 20
days after the explosion, strongly resembles that of other He-rich
core-collapse supernovae. The observed evolution of SN 2008ax is consistent
with the explosion of a young Wolf-Rayet (of WNL type) star, which had retained
a thin, low-mass shell of its original H envelope. The overall characteristics
of SN 2008ax are reminiscent of those of SN 1993J, except for a likely smaller
H mass. This may account for the findings that the progenitor of SN 2008ax was
a WNL star and not a K supergiant as in the case of SN 1993J, that a prominent
early-time peak is missing in the light curve of SN 2008ax, and that Halpha is
observed at higher velocities in SN 2008ax than in SN 1993J.Comment: 10 pages, including 8 figures and 4 tables. Accepted for publication
in MNRA
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