225 research outputs found
Near-Infrared Spectroscopy of Carbon-Enhanced Metal-Poor Stars. I. A SOAR/OSIRIS Pilot Study
We report on an abundance analysis for a pilot study of seven Carbon-Enhanced
Metal-Poor (CEMP) stars, based on medium-resolution optical and near-infrared
spectroscopy. The optical spectra are used to estimate [Fe/H], [C/Fe], [N/Fe],
and [Ba/Fe] for our program stars. The near-infrared spectra, obtained during a
limited early science run with the new SOAR 4.1m telescope and the Ohio State
Infrared Imager and Spectrograph (OSIRIS), are used to obtain estimates of
[O/Fe] and 12C/13C. The chemical abundances of CEMP stars are of importance for
understanding the origin of CNO in the early Galaxy, as well as for placing
constraints on the operation of the astrophysical s-process in very
low-metallicity Asymptotic Giant Branch (AGB) stars.
This pilot study includes a few stars with previously measured [Fe/H],
[C/Fe], [N/Fe],[O/Fe], 12C/13C, and [Ba/Fe], based on high-resolution optical
spectra obtained with large-aperture telescopes. Our analysis demonstrates that
we are able to achieve reasonably accurate determinations of these quantities
for CEMP stars from moderate-resolution optical and near-infrared spectra. This
opens the pathway for the study of significantly larger samples of CEMP stars
in the near future. Furthermore, the ability to measure [Ba/Fe] for (at least
the cooler) CEMP stars should enable one to separate stars that are likely to
be associated with s-process enhancements (the CEMP-s stars) from those that do
not exhibit neutron-capture enhancements (the CEMP-no stars).Comment: 27 pages, including 5 tables, 6 figures, accepted for publication in
The Astronomical Journa
Sakurai's Object: characterizing the near-infrared CO ejecta between 2003 and 2007
We present observations of Sakurai's Object obtained at 1â5 ÎŒm between 2003 and 2007. By fitting a radiative transfer model to an echelle spectrum of CO fundamental absorption features around 4.7 ÎŒm, we determine the excitation conditions in the line-forming region. We find 12C/13C = 3.5+2.0â1.5, consistent with CO originating in ejecta processed by the very late thermal pulse, rather than in the pre-existing planetary nebula. We demonstrate the existence of 2.2 Ă 10â6â€MCO†2.7 Ă 10â6 Mâ of CO ejecta outside the dust, forming a high-velocity wind of 500 ± 80 km sâ1. We find evidence for significant weakening of the CO band and cooling of the dust around the central star between 2003 and 2005. The gas and dust temperatures are implausibly high for stellar radiation to be the sole contributor
What Therapists Learn from Psychotherapy Clients: Effects on Personal and Professional Lives
While considerable research has examined how clients learn from psychotherapists, there is only sparse literature on what therapists learn from their therapy clients. In a qualitative, exploratory study, nine researchers interviewed 61 psychologists from across North America in order to see what psychotherapists may have learned and how they have been affected by their clients both personally and professionally. Participants responded to nine open-ended questions on learning about life-lessons, relationships, ethical decision-making, coping, courage, wisdom, psychopathology, personality, cultural differences, lifespan development and more. Participantsâ richly elaborated responses were coded thematically and narrative data illustrates the most frequent themes. Therapists reported learning a great deal across each of the questions, consistently expressing respect for their clients\u27 resilience, courage and moral sensibilities
Modeling the spectrum of V4334 Sgr (Sakurai's Object)
Theoretical spectral energy distributions were computed for a grid of
hydrogen-deficient and carbon-rich model atmospheres of T(eff) in the range of
5000-6250 K and log g = 1.0 - 0.0 by the technique of opacity sampling, taking
into account continuous, molecular band and atomic line absorption. These
energy distributions were compared with the spectrum of V4334 Sgr (Sakurai's
object) of April, 1997 in the wavelength interval 300-1000 nm. We show that (1)
the shape of the theoretical spectra depends strongly on T(eff) but only very
weakly on the hydrogen abundance; (2) the comparison of the observed and
computed spectra permits to estimate T(eff) approximately 5500 K for V4334 Sgr
in April, 1997, and its interstellar reddening (plus a possible circumstellar
contribution) E(B-V) approximately 0.70.Comment: 7 pages, 8 figures, LaTeX, accepted by Astronomy and Astrophysic
The evolutionary status of the semiregular variable QYSge
Repeated spectroscopic observations made with the 6m telescope of yielded new
data on the radial-velocity variability of the anomalous yellow supergiant
QYSge. The strongest and most peculiar feature in its spectrum is the complex
profile of NaI D lines, which contains a narrow and a very wide emission
components. The wide emission component can be seen to extend from -170 to +120
km/s, and at its central part it is cut by an absorption feature, which, in
turn, is split into two subcomponents by a narrow (16km/s at r=2.5) emission
peak. An analysis of all the Vr values leads us to adopt for the star a
systemic velocity of Vr=-21.1 km/s, which corresponds to the position of the
narrow emission component of NaI. The locations of emission-line features of
NaI D lines are invariable, which point to their formation in regions that are
external to the supergiant's photosphere. Differential line shifts of about
10km/s are revealed. The absorption lines in the spectrum of QYSge have a
substantial width of FWHM~45 km/s. The method of model atmospheres is used to
determine the following parameters: Teff=6250K, lg g=2.0, and microturbulence
Vt=4.5km/s. The metallicity of the star is found to be somewhat higher than the
solar one with an average overabundance of iron-peak elements of [Met/H]=+0.20.
The star is found to be slightly overabundant in carbon and nitrogen,
[C/Fe]=+0.25, [N/Fe]=+0.27. The alpha-process elements Mg, Si, and Ca are
slightly overabundant [alpha/H]=+0.12. The strong sodium excess, [Na/Fe]=+0.75,
is likely to be due to the dredge-up of the matter processed in the NeNa cycle.
Heavy elements of the s-process are underabundant relative to the Sun. On the
whole, the observed properties of QYSge do not give grounds for including this
star into the group of RCrB or RVTau-type type objects.Comment: 29 pages, 8 figures, 4 tables; accepted by Astrophys. Bulleti
Dosing of Ceftriaxone and Metronidazole for Children With Severe Acute Malnutrition
Infants and young children with severe acute malnutrition (SAM) are treated with empiric broadâspectrum antimicrobials. Parenteral ceftriaxone is currently a secondâline agent for invasive infection. Oral metronidazole principally targets small intestinal bacterial overgrowth. Children with SAM may have altered drug absorption, distribution, metabolism, and elimination. Population pharmacokinetics of ceftriaxone and metronidazole were studied, with the aim of recommending optimal dosing. Eightyâone patients with SAM (aged 2â45 months) provided 234 postdose pharmacokinetic samples for total ceftriaxone, metronidazole, and hydroxymetronidazole. Ceftriaxone protein binding was also measured in 190 of these samples. A threeâcompartment model adequately described free ceftriaxone, with a MichaelisâMenten model for concentration and albuminâdependent protein binding. A oneâcompartment model was used for both metronidazole and hydroxymetronidazole, with only 1% of hydroxymetronidazole predicted to be formed during firstâpass. Simulations showed 80âmg/kg once daily of ceftriaxone and 12.5âmg/kg twice daily of metronidazole were sufficient to reach therapeutic targets
The evolutionary state of Miras with changing pulsation periods
Context: Miras are long-period variables thought to be in the asymptotic
giant branch (AGB) phase of evolution. In about one percent of known Miras, the
pulsation period is changing. It has been speculated that this changing period
is the consequence of a recent thermal pulse in these stars. Aims: We aim to
clarify the evolutionary state of these stars, and to determine in particular
whether or not they are in the thermally-pulsing (TP-)AGB phase. Methods: One
important piece of information that has been neglected so far when determining
the evolutionary state is the presence of the radio-active s-process element
technetium (Tc). We obtained high-resolution, high signal-to-noise-ratio
optical spectra of a dozen prominent Mira variables with changing pulsation
period to search for this indicator of TPs and dredge-up. We also use the
spectra to measure lithium (Li) abundances. Furthermore, we establish the
evolutionary states of our sample stars by means of their present-day periods
and luminosities. Results: Among the twelve sample stars observed in this
programme, five were found to show absorption lines of Tc. BH Cru is found to
be a carbon-star, its period increase in the past decades possibly having
stopped by now. We report a possible switch in the pulsation mode of T UMi from
Mira-like to semi-regular variability in the past two years. R Nor, on the
other hand, is probably a fairly massive AGB star, which could be true for all
meandering Miras. Finally, we assign RU Vul to the metal-poor thick disk with
properties very similar to the short-period, metal-poor Miras. Conclusions: We
conclude that there is no clear correlation between period change class and Tc
presence. The stars that are most likely to have experienced a recent TP are BH
Cru and R Hya, although their rates of period change are quite different.Comment: 11 pages, 7 figures, 2 tables; accepted for publication in A&
s-Process Nucleosynthesis in Carbon Stars
We present the first detailed and homogeneous analysis of the s-element
content in Galactic carbon stars of N-type. Abundances of Sr,Y, Zr (low-mass
s-elements, or ls) and of Ba, La, Nd, Sm and Ce (high-mass s-elements, hs) are
derived using the spectral synthesis technique from high-resolution spectra.
The N-stars analyzed are of nearly solar metallicity and show moderate
s-element enhancements, similar to those found in S stars, but smaller than
those found in the only previous similar study (Utsumi 1985), and also smaller
than those found in supergiant post-AGB stars. This is in agreement with the
present understanding of the envelope s-element enrichment in giant stars,
which is increasing along the spectral sequence M-->MS-->S-->SC-->C during the
AGB phase. We compare the observational data with recent -process
nucleosynthesis models for different metallicities and stellar masses. Good
agreement is obtained between low mass AGB star models (M < 3 M_o) and
s-elements observations. In low mass AGB stars, the 13C(alpha, n)16O reaction
is the main source of neutrons for the s-process; a moderate spread, however,
must exist in the abundance of 13C that is burnt in different stars. By
combining information deriving from the detection of Tc, the infrared colours
and the theoretical relations between stellar mass, metallicity and the final
C/O ratio, we conclude that most (or maybe all) of the N-stars studied in this
work are intrinsic, thermally-pulsing AGB stars; their abundances are the
consequence of the operation of third dredge-up and are not to be ascribed to
mass transfer in binary systems.Comment: 31 pages, 10 figures, 6 tables. Accepted in Ap
Peculiarities and variations in the optical spectrum of the post-AGB star V448Lac=IRAS22223+4327
Repeated observations with high spectral resolution acquired in 1998-2008 are
used to study the temporal behavior of the spectral line profiles and velocity
field in the atmosphere and circumstellar envelope of the post-AGB star
V448Lac. Asymmetry of the profiles of the strongest absorption lines with
low-level excitation potentials less 1eV and time variations of these profiles
have been detected, most prominently the profiles of the resonance lines of
BaII, YII, LaII, SiII. The peculiarity of these profiles can be explained using
a superposition of stellar absorption line and shell emission lines. Emission
in the (0;1) 5635A Swan band of the C2 molecule has been detected in the
spectrum of V448Lac for the first time. The core of the Halpha line displays
radial velocity variations with an amplitude ~8 km/s. Radial velocity
variations displayed by weakest metallic lines with lower amplitudes, 1-2 km/s,
may be due to atmospheric pulsations. Differential line shifts, 0 -- 8 km/s,
have been detected on various dates. The position of the molecular spectrum is
stationary in time, indicating a constant expansion velocity of the
circumstellar shell, Vexp=15.2 km/s, as derived from the C2 and NaI lines.Comment: 19 pages, 8 figures, 1 tabl
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