41 research outputs found
The Origin of B-Type Runaway Stars: Non-LTE Abundances as a Diagnostic
There are two accepted mechanisms to explain the origin of runaway OB-type
stars: the Binary Supernova Scenario (BSS), and the Cluster Ejection Scenario
(CES). In the former, a supernova explosion within a close binary ejects the
secondary star, while in the latter close multi-body interactions in a dense
cluster cause one or more of the stars to be ejected from the region at high
velocity. Both mechanisms have the potential to affect the surface composition
of the runaway star. TLUSTY non-LTE model atmosphere calculations have been
used to determine atmospheric parameters and carbon, nitrogen, magnesium and
silicon abundances for a sample of B-type runaways. These same analytical tools
were used by Hunter et al. (2009) for their analysis of 50 B-type open cluster
Galactic stars (i.e. non-runaways). Effective temperatures were deduced using
the silicon-ionization balance technique, surface gravities from Balmer line
profiles and microturbulent velocities derived using the Si spectrum. The
runaways show no obvious abundance anomalies when compared with stars in the
open clusters. The runaways do show a spread in composition which almost
certainly reflects the Galactic abundance gradient and a range in the
birthplaces of the runaways in the Galactic disk. Since the observed Galactic
abundance gradients of C, N, Mg and Si are of a similar magnitude, the
abundance ratios (e.g., N/Mg) are, as obtained, essentially uniform across the
sample
Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption
The structure and properties of the diffuse interstellar medium (ISM) on
small scales, sub-au to 1 pc, are poorly understood. We compare interstellar
absorption-lines, observed towards a selection of O- and B-type stars at two or
more epochs, to search for variations over time caused by the transverse motion
of each star combined with changes in the structure in the foreground ISM. Two
sets of data were used: 83 VLT- UVES spectra with approximately 6 yr between
epochs and 21 McDonald observatory 2.7m telescope echelle spectra with 6 - 20
yr between epochs, over a range of scales from 0 - 360 au. The interstellar
absorption-lines observed at the two epochs were subtracted and searched for
any residuals due to changes in the foreground ISM. Of the 104 sightlines
investigated with typically five or more components in Na I D, possible
temporal variation was identified in five UVES spectra (six components), in Ca
II, Ca I and/or Na I absorption-lines. The variations detected range from 7\%
to a factor of 3.6 in column density. No variation was found in any other
interstellar species. Most sightlines show no variation, with 3{\sigma} upper
limits to changes of the order 0.1 - 0.3 dex in Ca II and Na I. These
variations observed imply that fine-scale structure is present in the ISM, but
at the resolution available in this study, is not very common at visible
wavelengths. A determination of the electron densities and lower limits to the
total number density of a sample of the sightlines implies that there is no
striking difference between these parameters in sightlines with, and sightlines
without, varying components.Comment: 19 pages, 11 figures, accepted for publication in MNRA
The birth place of the type Ic Supernova 2007gr
We report our attempts to locate the progenitor of the peculiar type Ic SN
2007gr in HST pre-explosion images of the host galaxy, NGC 1058. Aligning
adaptive optics Altair/NIRI imaging of SN 2007gr from the Gemini (North)
Telescope with the pre-explosion HST WFPC2 images, we identify the SN position
on the HST frames with an accuracy of 20 mas. Although nothing is detected at
the SN position we show that it lies on the edge of a bright source, 134+/-23
mas (6.9 pc) from its nominal centre. Based on its luminosity we suggest that
this object is possibly an unresolved, compact and coeval cluster and that the
SN progenitor was a cluster member, although we note that model profile fitting
favours a single bright star. We find two solutions for the age of this assumed
cluster; 7-/+0.5 Myrs and 20-30 Myrs, with turn-off masses of 28+/-4 Msun and
12-9 Msun respectively. Pre-explosion ground-based K-band images marginally
favour the younger cluster age/higher turn-off mass. Assuming the SN progenitor
was a cluster member, the turn-off mass provides the best estimate for its
initial mass. More detailed observations, after the SN has faded, should
determine if the progenitor was indeed part of a cluster, and if so allow an
age estimate to within ~2 Myrs thereby favouring either a high mass single star
or lower mass interacting binary progenitor.Comment: 12 pages, 3 figures, resolution of fig 1. has been reduced, some
revision based on referee's comments, Accepted ApJL 27 Nov 200
An unusually large gaseous transit in a debris disc
We present the detection of an unusually large transient gas absorption in several ionized species in the debris disc star HD 37306 using high-resolution optical spectra. We have been analysing a large sample of debris discs searching for circumstellar gas absorptions aiming to determine the frequency of gas in debris discs. HD 37306 stood out showing remarkably broad absorptions superimposed on to several photospheric Ca II, Fe II, and Ti II lines. The observed absorptions, unlike typical exocometary transits, lasted for at least eight days. Here, we analyse simultaneous spectroscopic and photometric data of the event and evaluate different scenarios that might explain the observed features. We conclude that the most likely scenario might be an exocometary break-up releasing a significant amount of gas close to the star, producing an occulting `ring'/`torus' shape
Using CRISPR/Cas9 genome editing in tomato to create a gibberellin-responsive dominant dwarf DELLA allele
The tomato PROCERA gene encodes a DELLA protein, and loss-of-function mutations derepress growth. We used CRISPR/Cas9 and a single guide RNAs (sgRNA) to target mutations to the PROCERA DELLA domain, and recovered several loss-of-function mutations and a dominant dwarf mutation that carries a deletion of one amino acid in the DELLA domain. This is the first report of a dominant dwarf PROCERA allele. This allele retains partial responsiveness to exogenously applied gibberellin. Heterozygotes show an intermediate phenotype at the seedling stage, but adult heterozygotes are as dwarfed as homozygotes
The EDIBLES Survey. VII. A survey of C2 and C3 in interstellar clouds
We carried out a sensitive survey of C and C using the EDIBLES data
set. We also expanded our searches to C, C, and CC
isotopologue in the most molecule-rich sightlines.
We fit synthetic spectra generated following a physical excitation model to
the C (2-0) Phillips band to obtain the C column density () as well
as the kinetic temperature () and number density () of the
host cloud. The C molecule was measured through its
(000-000) electronic origin band system. We simulated the excitation of this
band with a double-temperature Boltzmann distribution.
We present the largest combined survey of C and C to date in which
the individual transitions can be resolved. In total we detected C in 51
velocity components along 40 sightlines, and C in 31 velocity components
along 27 sightlines. The two molecules are detected in the same velocity
components. We find a very good correlation between (C) and (C)
with Pearson and an average (C)/(C) ratio of
15.51.4. A comparison with the behaviour of the C DIBs shows that
there are no clear differences among sightlines with and without detection of
C and C. This is in direct contrast to the better-studied non-C
DIBs who have reduced strengths in molecule-rich environments. We also identify
for the first time the (2), (3), and (4) transitions of the
CC (2-0) Phillips band in a stacked average spectrum, and
estimate the isotopic ratio of carbon C/C as 798. Our search
for the C and C optical bands was unsuccessful.Comment: 31 pages, 23 figures. To appear in A&
Exploring the Origin and Fate of the Magellanic Stream with Ultraviolet and Optical Absorption
(Abridged) We present an analysis of ionization and metal enrichment in the
Magellanic Stream (MS), the nearest gaseous tidal stream, using HST/STIS and
FUSE ultraviolet spectroscopy of two background AGN, NGC 7469 and Mrk 335. For
NGC 7469, we include optical spectroscopy from VLT/UVES. In both sightlines the
MS is detected in low-ion and high-ion absorption. Toward NGC 7469, we measure
a MS oxygen abundance [O/H]_MS=[OI/HI]=-1.00+/-0.05(stat)+/-0.08(syst),
supporting the view that the Stream originates in the SMC rather than the LMC.
We use CLOUDY to model the low-ion phase of the Stream as a photoionized plasma
using the observed Si III/Si II and C III/C II ratios. Toward Mrk 335 this
yields an ionization parameter log U between -3.45 and -3.15 and a gas density
log (n_H/cm^-3) between -2.51 and -2.21. Toward NGC 7469 we derive sub-solar
abundance ratios for [Si/O], [Fe/O], and [Al/O], indicating the presence of
dust in the MS. The high-ion column densities are too large to be explained by
photoionization, but also cannot be explained by a single-temperature
collisional-ionization model (equilibrium or non-equilibrium). This suggests
the high-ion plasma is multi-phase. Summing over the low-ion and high-ion
phases, we derive conservative lower limits on the ratio N(total H II)/N(H I)
of >19 toward NGC 7469 and >330 toward Mrk 335, showing that along these two
directions the vast majority of the Stream has been ionized. The presence of
warm-hot plasma together with the small-scale structure observed at 21 cm
provides evidence for an evaporative interaction with the hot Galactic corona.
This scenario, predicted by hydrodynamical simulations, suggests that the fate
of the MS will be to replenish the Galactic corona with new plasma, rather than
to bring neutral fuel to the disk.Comment: Accepted for publication in ApJ. 18 pages, 7 figures, all in colo
Mepivacaine versus Bupivacaine Spinal Anesthesia for Early Postoperative Ambulation.
BACKGROUND: Early ambulation after total hip arthroplasty predicts early discharge. Spinal anesthesia is preferred by many practices but can delay ambulation, especially with bupivacaine. Mepivacaine, an intermediate-acting local anesthetic, could enable earlier ambulation than bupivacaine. This study was designed to test the hypothesis that patients who received mepivacaine would ambulate earlier than those who received hyperbaric or isobaric bupivacaine for primary total hip arthroplasty.
METHODS: This randomized controlled trial included American Society of Anesthesiologists Physical Status I to III patients undergoing primary total hip arthroplasty. The patients were randomized 1:1:1 to 52.5 mg of mepivacaine, 11.25 mg of hyperbaric bupivacaine, or 12.5 mg of isobaric bupivacaine for spinal anesthesia. The primary outcome was ambulation between 3 and 3.5 h. Secondary outcomes included return of motor and sensory function, postoperative pain, opioid consumption, transient neurologic symptoms, urinary retention, intraoperative hypotension, intraoperative muscle tension, same-day discharge, length of stay, and 30-day readmissions.
RESULTS: Of 154 patients, 50 received mepivacaine, 53 received hyperbaric bupivacaine, and 51 received isobaric bupivacaine. Patient characteristics were similar among groups. For ambulation at 3 to 3.5 h, 35 of 50 (70.0%) of patients met this endpoint in the mepivacaine group, followed by 20 of 53 (37.7%) in the hyperbaric bupivacaine group, and 9 of 51 (17.6%) in the isobaric bupivacaine group (P \u3c 0.001). Return of motor function occurred earlier with mepivacaine. Pain and opioid consumption were higher for mepivacaine patients in the early postoperative period only. For ambulatory status, 23 of 50 (46.0%) of mepivacaine, 13 of 53 (24.5%) of hyperbaric bupivacaine, and 11 of 51 (21.5%) of isobaric bupivacaine patients had same-day discharge (P = 0.014). Length of stay was shortest in mepivacaine patients. There were no differences in transient neurologic symptoms, urinary retention, hypotension, muscle tension, or dizziness.
CONCLUSIONS: Mepivacaine patients ambulated earlier and were more likely to be discharged the same day than both hyperbaric bupivacaine and isobaric bupivacaine patients. Mepivacaine could be beneficial for outpatient total hip arthroplasty candidates if spinal is the preferred anesthesia type
Very accurate cryogenic mechanisms for CRIRES+
After 5 years of operation on the VLT, a large upgrade of CRIRES (the ESO Cryogenic InfraRed Echelle Spectrograph) was decided mainly in order to increase the efficiency. Using a cross dispersion design allows better wavelength coverage per exposure. This means a complete re-design of the cryogenic pre-optic which were including a predispersion stage with a large prism as dispersive element. The new design requires a move of the entrance slit and associated decker toward the first intermediate focal plane right behind the window. Implement 2 functions with high positioning accuracy in a pre-defined and limited space was a real challenge. The design and the test results recorded in the ESO Cryogenic Test Facility are reported in this paper. The second critical function is the grating wheel which positions the 6 cross disperser gratings into the beam. The paper describes the design of the mechanism which includes a detente system in order to guaranty the 5 arc sec positioning reproducibility requested. The design includes also feedback system, based on switches, in order to ensure that the right grating is in position before starting a long exposure. The paper reports on the tests carried out at cryogenic temperature at the sub-system level. It also includes early performances recorded in the instrument along the first phases of the system test
The ESO Diffuse Interstellar Bands Large Exploration Survey EDIBLES: I. Project description, survey sample and quality assessment
The carriers of the diffuse interstellar bands (DIBs) are largely unidentified molecules ubiquitously present in the interstellar medium (ISM). After decades of study, two strong and possibly three weak near-infrared DIBs have recently been attributed to the C+ 60 fullerene based on observational and laboratory measurements. There is great promise for the identification of the over 400 other known DIBs, as this result could provide chemical hints towards other possible carriers. In an effort to systematically study the properties of the DIB carriers, we have initiated a new large-scale observational survey: the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES). The main objective is to build on and extend existing DIB surveys to make a major step forward in characterising the physical and chemical conditions for a statistically significant sample of interstellar lines-of-sight, with the goal to reverse-engineer key molecular properties of the DIB carriers. EDIBLES is a filler Large Programme using the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope at Paranal, Chile. It is designed to provide an observationally unbiased view of the presence and behaviour of the DIBs towards early-spectraltype stars whose lines-of-sight probe the diffuse-to-translucent ISM. Such a complete dataset will provide a deep census of the atomic and molecular content, physical conditions, chemical abundances and elemental depletion levels for each sightline. Achieving these goals requires a homogeneous set of high-quality data in terms of resolution (R ~ 70 000 – 100 000), sensitivity (S/N up to 1000 per resolution element), and spectral coverage (305–1042 nm), as well as a large sample size (100+ sightlines). In this first paper the goals, objectives and methodology of the EDIBLES programme are described and an initial assessment of the data is provided