214 research outputs found
Carbon Stars in the Hamburg/ESO Survey: Abundances
We have carried out a detailed abundance analysis for a sample of 16 carbon
stars found among candidate extremely metal-poor (EMP) stars from the
Hamburg/ESO Survey. We find that the Fe-metallicities for the cooler C-stars
(Teff ~ 5100K) have been underestimated by a factor of ~10 by the standard HES
survey tools. The results presented here provided crucial supporting data used
by Cohen et al (2006) to derive the frequency of C-stars among EMP stars.
C-enhancement in these EMP C-stars appears to be independent of
Fe-metallicity and approximately constant at ~1/5 the solar C/H. The mostly low
C12/C13 ratios (~4) and the high N abundances in many of these stars suggest
that material which has been through proton burning via the CN cycle comprises
most of the stellar envelope. C-enhancement is associated with strong
enrichment of heavy nuclei beyond the Fe-peak for 12 of the 16 stars. The
remaining C-stars from the HES, which tend to be the most Fe-metal poor, show
no evidence for enhancement of the heavy elements. Very high enhancements of
lead are detected in some of the C-stars with highly enhanced Ba. (We show
that) the s-process is responsible for the enhancement of the heavy elements
for the majority of the C-stars in our sample.
We suggest that both the s-process rich and Ba-normal C-stars result from
phenomena associated with mass transfer in binary systems. This leads directly
to the progression from C-stars to CH stars and then to Ba stars as the
Fe-metallicity increases. (abridged and slightly edited to shorten)Comment: AJ, in press, submitted 13 Dec, 2005, accepted 21 March 200
EPICA Dome C electronic control system
AbstractA new deep drill has been developed within the framework of the European Programme for Ice Coring in Antarctica (EPICA). Several versions of the EPICA drill exist. The version used at Dome Concordia (75Ë06'1" S, 123Ë23'71" E) was operated with a new electronic control system developed by the Ente per le Nuove tecnologie, l'Energia e l'Ambiente (ENEA) Research Center in Brasimone, Italy. This electronic control system was used for the first time during the 1997/98 Antarctic summer season
Spectroscopic Study of IRAS 19285+0517(PDS 100): A Rapidly Rotating Li-Rich K Giant
We report on photometry and high-resolution spectroscopy for IRAS 19285+0517.
The spectral energy distribution based on visible and near-IR photometry and
far-IR fluxes shows that the star is surrounded by dust at a temperature of
250 K. Spectral line analysis shows that the star is a K
giant with a projected rotational velocity = 9 2 km s.
We determined the atmospheric parameters: = 4500 K, log =
2.5, = 1.5 km s, and [Fe/H] = 0.14 dex. The LTE abundance
analysis shows that the star is Li-rich (log (Li) = 2.50.15),
but with essentially normal C, N, and O, and metal abundances. Spectral
synthesis of molecular CN lines yields the carbon isotopic ratio
C/C = 9 3, a signature of post-main sequence evolution and
dredge-up on the RGB. Analysis of the Li resonance line at 6707 \AA for
different ratios Li/Li shows that the Li profile can be fitted best
with a predicted profile for pure Li. Far-IR excess, large Li abundance,
and rapid rotation suggest that a planet has been swallowed or, perhaps, that
an instability in the RGB outer layers triggered a sudden enrichment of Li and
caused mass-loss.Comment: To appear in AJ; 40 pages, 9 figure
Long-Slit Observations of Extended C II 1335 Emission Around V854 Centauri and RY Sagittarii
We have obtained long-slit far-ultraviolet (1150--1730 A) spectra of the R
Coronae Borealis (RCB) stars V854 Cen and RY Sgr, near maximum light and
pulsational phase zero, with the Space Telescope Imaging Spectrograph (STIS) on
Hubble Space Telescope (HST). The far-UV spectrum of each star shows a
photospheric continuum rising steeply toward longer wavelengths, and a
prominent emission feature at C II 1335. RY Sgr displays a second, but fainter,
emission attributed to Cl I 1351 (which is radiatively fluoresced by C II
1335), but Cl I is weak or absent in V854 Cen. Most surprisingly, the C II
emission of V854 Cen is significantly extended along the slit by +/- 2.5
arcsec, about 6 x 10^3 AU at the distance of the star. The C II feature of RY
Sgr exhibits no such gross extension. Nevertheless, subtle broadenings of the C
II emissions beyond the point response profile suggests inner clouds of radius
\~0.1 arcsec (250 AU) around both stars. V854 Cen is only the third RCB star
after R CrB and UW Cen known to have a resolved shell.Comment: 15 pages, 2 figures, (Figure 1 is a jpeg file), ApJ, in pres
Spectropolarimetry of R Coronae Borealis in 1998--2003: Discovery of Transient Polarization at Maximum Brightness
We present an extended optical spectropolarimetry of R CrB from 1998 January
to 2003 September. The polarization was almost constant in the phase of maximum
brightness, being consistent with past observations. We detected, however,
temporal changes of polarization ( %) in 2001 March and August, which
were the first detection of large polarization variability in R CrB near
maximum brightness. The amplitude and the position angle of the `transient
polarization' were almost constant with wavelength in both two events. There
was a difference by about 20 degrees in the position angle between the two
events. Each event could be explained by light scattering due to short-lived
dust puff occasionally ejected off the line of sight. The flatness of the
polarization against the wavelength suggests that the scatterer is a mixture of
dust grains having various sizes. The rapid growth and fading of the transient
polarization favors the phenomenological model of dust formation near the
stellar photosphere (e.g., within two stellar radii) proposed for the time
evolution of brightness and chromospheric emission lines during deeply
declining periods, although the fading timescale can hardly be explained by a
simple dispersal of expanding dust puff with a velocity of km s
. Higher expansion velocity or some mechanism to destroy the dust grains
should be needed.Comment: 22 pages, 10 figures, accepted for publication in A
Winds in R Coronae Borealis Stars
We present new spectroscopic observations of the He I 10830 line in
R Coronae Borealis (RCB) stars which provide the first strong evidence that
most, if not all, RCB stars have winds. It has long been suggested that when
dust forms around an RCB star, radiation pressure accelerates the dust away
from the star, dragging the gas along with it. The new spectra show that nine
of the ten stars observed have P-Cygni or asymmetric blue-shifted profiles in
the He I 10830 line. In all cases, the He I line indicates a mass
outflow - with a range of intensity and velocity. Around the RCB stars, it is
likely that this state is populated by collisional excitation rather than
photoionization/recombination. The line profiles have been modeled with an SEI
code to derive the optical depth and the velocity field of the helium gas. The
results show that the typical RCB wind has a steep acceleration with a terminal
velocity of \Vinf = 200-350 \kms and a column density of N
cm in the He I 10830 line. There is a possible relationship
between the lightcurve of an RCB star and its He I 10830 profile.
Stars which have gone hundreds of days with no dust-formation episodes tend to
have weaker He I features. The unusual RCB star, V854 Cen, does not follow this
trend, showing little or no He I absorption despite high mass-loss activity.
The He I 10830 line in R CrB itself, which has been observed at four
epochs between 1978 and 2001, seems to show a P-Cygni or asymmetric
blue-shifted profile at all times whether it is in decline or at maximum light.Comment: 14 pages, 4 figures, ApJ in pres
CRIRES-POP: A library of high resolution spectra in the near-infrared
New instrumental capabilities and the wealth of astrophysical information
extractable from the near-infrared wavelength region have led to a growing
interest in the field of high resolution spectroscopy at 1-5 mu. We aim to
provide a library of observed high-resolution and high signal-to-noise-ratio
near-infrared spectra of stars of various types throughout the
Hertzsprung-Russell diagram. This is needed for the exploration of spectral
features in this wavelength range and for comparison of reference targets with
observations and models.
High quality spectra were obtained using the CRIRES near-infrared
spectrograph at ESO's VLT covering the range from 0.97 to 5.3 mu at high
spectral resolution. Accurate wavelength calibration and correction for of
telluric lines were performed by fitting synthetic transmission spectra for the
Earth's atmosphere to each spectrum individually. We describe the observational
strategy and the current status and content of the library which includes 13
objects. The first examples of finally reduced spectra are presented. This
publication will serve as a reference paper to introduce the library to the
community and explore the extensive amount of material.Comment: accepted for publication in A&A; see also the project webpage
http://www.univie.ac.at/crirespo
A theoretical introduction to âCombinatory SYBRÂźGreen qPCR Screeningâ, a matrix-based approach for the detection of materials derived from genetically modified plants
The detection of genetically modified (GM) materials in food and feed products is a complex multi-step analytical process invoking screening, identification, and often quantification of the genetically modified organisms (GMO) present in a sample. âCombinatory qPCR SYBRÂźGreen screeningâ (CoSYPS) is a matrix-based approach for determining the presence of GM plant materials in products. The CoSYPS decision-support system (DSS) interprets the analytical results of SYBRÂźGREEN qPCR analysis based on four values: the Ct- and Tm values and the LOD and LOQ for each method. A theoretical explanation of the different concepts applied in CoSYPS analysis is given (GMO Universe, âPrime number tracingâ, matrix/combinatory approach) and documented using the RoundUp Ready soy GTS40-3-2 as an example. By applying a limited set of SYBRÂźGREEN qPCR methods and through application of a newly developed âprime numberâ-based algorithm, the nature of subsets of corresponding GMO in a sample can be determined. Together, these analyses provide guidance for semi-quantitative estimation of GMO presence in a food and feed product
Early postoperative weight loss predicts maximal weight loss after sleeve gastrectomy and Roux-en-Y gastric bypass
Background
Previous studies show that âpoor respondersâ to Roux-en-Y gastric bypass (RYGBP) may be identified on the basis of early postoperative weight loss. Early identification of poor responders could allow earlier provision of postoperative behavioural and/or intensive lifestyle interventions and enhance their maximal weight loss. Our aim was to investigate whether early postoperative weight loss predicts the maximal weight loss response after RYGBP and sleeve gastrectomy (SG).
Methods
We undertook a retrospective cross-sectional study of 1,456 adults who underwent either RYGBP (n = 918) or SG (n = 538) as a primary procedure in one of two European centres. Postoperative weight loss was expressed as weight loss velocity (WLV) and percentage weight loss. Linear regression analyses were performed to determine the association of early postoperative weight loss with maximal %WL, including adjustment for baseline variables.
Results
There was marked variability in maximal %WL following both RYGBP (mean 32.9 %, range 4.1â60.9 %) and SG (mean 26.2 %, range 1.1â58.3 %). WLV 3â6 months postoperatively was more strongly associated with maximal %WL (r 2 = 0.32 for RYGBP and r 2 = 0.26 for SG, P < 0.001 for both) than either WLV 0â6 weeks or 6 weeks to 3 months postoperatively (r 2 = 0.14 and 0.10 for RYGBP, respectively; r 2 = 0.18 and 0.21 for SG, respectively; P < 0.001 for all). Multiple linear regression analysis, including baseline variables of age, sex, preoperative BMI, type 2 diabetes, ethnicity, and bariatric centre, revealed that 3â6 month WLV was an independent predictor of maximal %WL in both SG and RYGBP groups (standardised ÎČ-coefficients 0.51 and 0.52, respectively; P < 0.001 for both).
Conclusions
There is a marked variability in weight loss response following RYGBP and SG. Early postoperative weight loss can be used to identify patients whose predicted weight loss trajectories are suboptimal. Early targeting of poor responders with more intensive postoperative lifestyle and behavioural support could potentially enhance their weight loss response
SYBRÂźGreen qPCR methods for detection of endogenous reference genes in commodity crops: a step ahead in combinatory screening of genetically modified crops in food and feed products
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