574 research outputs found
The evolution of M 2-9 from 2000 to 2010
M 2-9, the Butterfly nebula, is an outstanding representative of extreme
aspherical flows. It presents unique features such as a pair of high-velocity
dusty polar blobs and a mirror-symmetric rotating pattern in the inner lobes.
Imaging monitoring of the evolution of the nebula in the past decade is
presented. We determine the proper motions of the dusty blobs, which infer a
new distance estimate of 1.3+-0.2 kpc, a total nebular size of 0.8 pc, a speed
of 147 km/s, and a kinematical age of 2500 yr. The corkscrew geometry of the
inner rotating pattern is quantified. Different recombination timescales for
different ions explain the observed surface brightness distribution. According
to the images taken after 1999, the pattern rotates with a period of 92+-4 yr.
On the other hand, the analysis of images taken between 1952 and 1977 measures
a faster angular velocity. If the phenomenon were related to orbital motion,
this would correspond to a modest orbital eccentricity (e=0.10+-0.05), and a
slightly shorter period (86+-5 yr). New features have appeared after 2005 on
the west side of the lobes and at the base of the pattern. The geometry and
travelling times of the rotating pattern support our previous proposal that the
phenomenon is produced by a collimated spray of high velocity particles (jet)
from the central source, which excites the walls of the inner cavity of M 2-9,
rather than by a ionizing photon beam. The speed of such a jet would be
remarkable: between 11000 and 16000 km/s. The rotating-jet scenario may explain
the formation and excitation of most of the features observed in the inner
nebula, with no need for additional mechanisms, winds, or ionization sources.
All properties point to a symbiotic-like interacting binary as the central
source of M 2-9.Comment: Accepted for publication on Astronomy and Astrophysics (10 pages, 8
figures
Organizational culture and climate as moderators of enhanced outreach for persons with serious mental illness: results from a cluster-randomized trial of adaptive implementation strategies
Abstract
Background
Organizational culture and climate are considered key factors in implementation efforts but have not been examined as moderators of implementation strategy comparative effectiveness. We investigated organizational culture and climate as moderators of comparative effectiveness of two sequences of implementation strategies (Immediate vs. Delayed Enhanced Replicating Effective Programs [REP]) combining Standard REP and REP enhanced with facilitation on implementation of an outreach program for Veterans with serious mental illness lost to care at Veterans Health Administration (VA) facilities nationwide.
Methods
This study is a secondary analysis of the cluster-randomized Re-Engage implementation trial that assigned 3075 patients at 89 VA facilities to either the Immediate or Delayed Enhanced REP sequences. We hypothesized that sites with stronger entrepreneurial culture, task, or relational climate would benefit more from Enhanced REP than Standard REP. Veteran- and site-level data from the Re-Engage trial were combined with site-aggregated measures of entrepreneurial culture and task and relational climate from the 2012 VA All Employee Survey. Longitudinal mixed-effects logistic models examined whether the comparative effectiveness of the Immediate vs. Delayed Enhanced REP sequences were moderated by culture or climate measures at 6 and 12Â months post-randomization. Three Veteran-level outcomes related to the engagement with the VA system were assessed: updated documentation, attempted contact by coordinator, and completed contact.
Results
For updated documentation and attempted contact, Veterans at sites with higher entrepreneurial culture and task climate scores benefitted more from Enhanced REP compared to Standard REP than Veterans at sites with lower scores. Few culture or climate moderation effects were detected for the comparative effectiveness of the full sequences of implementation strategies.
Conclusions
Implementation strategy effectiveness is highly intertwined with contextual factors, and implementation practitioners may use knowledge of contextual moderation to tailor strategy deployment. We found that facilitation strategies provided with Enhanced REP were more effective at improving uptake of a mental health outreach program at sites with stronger entrepreneurial culture and task climate; Veterans at sites with lower levels of these measures saw more similar improvement under Standard and Enhanced REP. Within resource-constrained systems, practitioners may choose to target more intensive implementation strategies to sites that will most benefit from them.
Trial registration
ISRCTN:
ISRCTN21059161
. Date registered: April 11, 2013.https://deepblue.lib.umich.edu/bitstream/2027.42/144775/1/13012_2018_Article_787.pd
Light echoes reveal an unexpectedly cool Eta Carinae during its 19th-century Great Eruption
Eta Carinae (Eta Car) is one of the most massive binary stars in the Milky
Way. It became the second-brightest star in the sky during its mid-19th century
"Great Eruption," but then faded from view (with only naked-eye estimates of
brightness). Its eruption is unique among known astronomical transients in that
it exceeded the Eddington luminosity limit for 10 years. Because it is only 2.3
kpc away, spatially resolved studies of the nebula have constrained the ejected
mass and velocity, indicating that in its 19th century eruption, Eta Car
ejected more than 10 M_solar in an event that had 10% of the energy of a
typical core-collapse supernova without destroying the star. Here we report the
discovery of light echoes of Eta Carinae which appear to be from the 1838-1858
Great Eruption. Spectra of these light echoes show only absorption lines, which
are blueshifted by -210 km/s, in good agreement with predicted expansion
speeds. The light-echo spectra correlate best with those of G2-G5 supergiant
spectra, which have effective temperatures of ~5000 K. In contrast to the class
of extragalactic outbursts assumed to be analogs of Eta Car's Great Eruption,
the effective temperature of its outburst is significantly cooler than allowed
by standard opaque wind models. This indicates that other physical mechanisms
like an energetic blast wave may have triggered and influenced the eruption.Comment: Accepted for publication by Nature; 4 pages, 4 figures, SI: 6 pages,
3 figures, 5 table
Bolometric luminosity variations in the Luminous Blue Variable AFGL2298
We characterise the variability in the physical properties of the luminous
blue variable AFGL2298 between 1989-2008. In conjunction with published data
from 1989-2001, we have undertaken a long term (2001-2008) near-IR
spectroscopic and photometric observational campaign for this star and utilise
a non-LTE model atmosphere code to interpret these data. We find AFGL2298 to
have been highly variable during the two decades covered by the observational
datasets. Photometric variations of >1.6 mag have been observed in the JHK
wavebands; however, these are not accompanied by correlated changes in near-IR
colour. Non-LTE model atmosphere analysis of 4 epochs of K band spectroscopy
obtained between 2001-7 suggests that the photometric changes were driven by
expansion and contraction of the stellar photosphere accompanied by
comparatively small changes in the stellar temperature. Unclumped mass loss
rates throughout this period were modest and directly comparable to those of
other highly luminous LBVs. However, the bolometric luminosity of AFGL2298
appears to have varied by at least a factor of ~2 between 1989-2008, with it
being one of the most luminous stars in the Galaxy during maximum. Comparison
to other LBVs that have undergone non bolometric luminosity conserving
`eruptions' shows such events to be heterogeneous, with AFGL2298 the least
extreme example. These results - and the diverse nature of both the quiescent
LBVs and associated ejecta - may offer support to the suggestion that more than
one physical mechanism is responsible for such behaviour. [ABRIDGED]Comment: 12 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst. I The reflection nebula
Aims: The recent outburst of the young eruptive star V1647 Orionis has
produced a spectacular appearance of a new reflection nebula in Orion (McNeil's
nebula). We present an optical/near infrared investigation of McNeil's nebula.
This analysis is aimed at determining the morphology, temporal evolution and
nature of the nebula and its connection to the outburst.
Method: We performed multi epoch B, V, R, I, z, and K imaging of McNeil's
nebula and V1647 Ori as well as K_S imaging polarimetry. The multiband imaging
allows us to reconstruct the extinction map inside the nebula. Through
polarimetric observations we attempt to disentangle the emission from the
nebula from that of the accretion disk around V1647 Ori. We also attempt to
resolve the small spatial scale structure of the illuminating source.
Results: The energy distribution and temporal evolution of McNeil's nebula
mimic that of the illuminating source. The extinction map reveals a region of
higher extinction in the direction of V1647 Ori. Excluding foreground
extionction, the optical extinction due to McNeil's nebula in the direction of
V1647 Ori is A_V ~ 6.5 mag. The polarimetric measurement shows a compact high
polarization emission around V1647 Ori. The percentage of K_S band linear
polarization goes from 10 -- 20 %. The vectors are all well aligned with a
position angle of 90 +/- 9 degree East of North. This may correspond to the
orientation of a possible accretion disk around V1647 Ori. These findings
suggest that the appearance of McNeil's nebula is due to reflection of light by
pre-existing material in the surroundings of V1647 Ori. We also report on the
discovery of a new candidate brown dwarf or protostar in the vicinity of V1647
Ori as well as the presence of clumpy structure within HH 22A.Comment: 8 pages, 7 figures, in pres
Observed Consequences of Presupernova Instability in Very Massive Stars
This chapter concentrates on the deaths of very massive stars, the events
leading up to their deaths, and how mass loss affects the resulting death. The
previous three chapters emphasized the theory of wind mass loss, eruptions, and
core collapse physics, but here we emphasize mainly the observational
properties of the resulting death throes. Mass loss through winds, eruptions,
and interacting binaries largely determines the wide variety of different types
of supernovae that are observed, as well as the circumstellar environments into
which the supernova blast waves expand. Connecting these observed properties of
the explosions to the initial masses of their progenitor stars is, however, an
enduring challenge and is especially difficult for very massive stars.
Superluminous supernovae, pair instability supernovae, gamma ray bursts, and
"failed" supernovae are all end fates that have been proposed for very massive
stars, but the range of initial masses or other conditions leading to each of
these (if they actually occur) are still very certain. Extrapolating to infer
the role of very massive stars in the early universe is essentially
unencumbered by observational constraints and still quite dicey.Comment: 39 pages, 5 figures, to appear as chapter in the book "Very Massive
Stars in the Local Universe", ed. J. Vin
Luminous Blue Variable eruptions and related transients: Diversity of progenitors and outburst properties
We present new light curves and spectra for a number of extragalactic optical
transients or "SN impostors" related to giant eruptions of LBVs, and we provide
a comparative discussion of LBV-like giant eruptions known to date. New data
include photometry and spectroscopy of SNe1999bw, 2000ch, 2001ac, 2002bu,
2006bv, and 2010dn. SN2010dn resembles SN2008S and NGC 300-OT, whereas SN2002bu
shows spectral evolution from a normal LBV at early times to a twin of these
cooler transients at late times. SN2008S, NGC300-OT, and SN2010dn appear to be
special cases of a broader eruptive phenomenon where the progenitor star was
enshrouded by dust. Examining the full sample, SN impostors have range of
timescales from a day to decades, potentially suffering multiple eruptions. The
upper end of the luminosity distribution overlaps with the least luminous SNe.
The low end of the luminosity distribution is poorly defined, and a distinction
between various eruptions is not entirely clear. We discuss observational clues
concerning winds or shocks as the relevant mass-loss mechanism, and we evaluate
possible ideas for physical mechanisms. Although examples of these eruptions
are sufficient to illustrate their diversity, their statistical distribution
will benefit greatly from upcoming transient surveys. Based on the distribution
of eruptions, we propose that SN1961V was not a member of this class of
impostors, but was instead a true core-collapse SNIIn preceded by a giant LBV
eruption. (abridged)Comment: 36(!) journal pages, 16 figures. submitted to MNRAS on october 12.
coments welcome. updated reference
The Type Ic Supernova 1994I in M51: Detection of Helium and Spectral Evolution
We present a series of spectra of SN 1994I in M51, starting 1 week prior to maximum brightness. The nebular phase began about 2 months after the explosion; together with the rapid decline of the optical light, this suggests that the ejected mass was small. Although lines of He I in the optical region are weak or absent, consistent with the Type Ic classification, we detect strong He I λ10830 absorption during the first month past maximum. Thus, if SN 1994I is a typical Type Ic supernova, the atmospheres of these objects cannot be completely devoid of helium. The emission-line widths are smaller than predicted by the model of Nomoto and coworkers, in which the iron core of a low-mass carbon-oxygen star collapses. They are, however, larger than in Type Ib supernovae
Estimating the effect of a rare timeâdependent treatment on the recurrent event rate
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143592/1/sim7626_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143592/2/sim7626.pd
Galactic-Scale Outflow and Supersonic Ram-Pressure Stripping in the Virgo Cluster Galaxy NGC 4388
The Hawaii Imaging Fabry-Perot Interferometer (HIFI) on the University of
Hawaii 2.2m telescope was used to map the Halpha and [O III] 5007 A
emission-line profiles across the entire disk of the edge-on Sb galaxy NGC
4388. We confirm a rich complex of highly ionized gas that extends ~4 kpc above
the disk of this galaxy. Low-ionization gas associated with star formation is
also present in the disk. Evidence for bar streaming is detected in the disk
component and is discussed in a companion paper (Veilleux, Bland-Hawthorn, &
Cecil 1999; hereafter VBC). Non-rotational blueshifted velocities of 50 - 250
km/s are measured in the extraplanar gas north-east of the nucleus. The
brighter features in this complex tend to have more blueshifted velocities. A
redshifted cloud is also detected 2 kpc south-west of the nucleus. The velocity
field of the extraplanar gas of NGC 4388 appears to be unaffected by the
inferred supersonic (Mach number M ~ 3) motion of this galaxy through the ICM
of the Virgo cluster. We argue that this is because the galaxy and the high-|z|
gas lie behind a Mach cone with opening angle ~ 80 degrees. The shocked ICM
that flows near the galaxy has a velocity of ~ 500 km/s and exerts insufficient
ram pressure on the extraplanar gas to perturb its kinematics. We consider
several explanations of the velocity field of the extraplanar gas. Velocities,
especially blueshifted velocities on the N side of the galaxy, are best
explained as a bipolar outflow which is tilted by > 12 degrees from the normal
to the disk. The observed offset between the extraplanar gas and the radio
structure may be due to buoyancy or refractive bending by density gradients in
the halo gas. Velocity substructure in the outflowing gas also suggests an
interaction with ambient halo gas.Comment: 29 pages including 5 figures, Latex, requires aaspp4.sty, to appear
in ApJ, 520 (July 20, 1999 issue
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