265 research outputs found
Magnesium Isotopes in Halo Stars
We have determined Mg isotope ratios in halo field dwarfs and giants in the
globular cluster M71 based on high S/N high spectral resolution (R = 10)
Keck HIRES spectra. Unlike previous claims of an important contribution from
intermediate-mass AGB stars to the Galactic halo, we find that our
Mg/Mg ratios can be explained by massive stars.Comment: Proceedings, First Stars III, July 16-20, 2007, Santa F
Happiness at Work: A Phenomenological Investigation of Clinic Managers
This study seeks to understand, through a qualitative phenomenological design, the meaning of happiness at work for clinic managers who work for a mission-driven healthcare organization. There exists many organizational dynamics that can influence happiness at work; nevertheless, for the scope of this investigation, this paper converged on three theoretical premises: (1) Positive Psychology: Happiness at work which is divided into eudemonic and hedonic happiness, (2) Intrinsic Motivation Theory: Self-determination, and (3) Extrinsic Motivation Theory: Self-determination. The evidence discovered in this study demonstrates the importance of understanding the context for what happiness at work means for management-level caregivers/employees. The clinic managers that participated in this study overwhelmingly displayed a strong sense of intrinsic motivation/eudemonic happiness, in part, because they take happiness to work and they display a strong desire to help develop and grow their respective staff. Yet the study also realized that extrinsic factors influenced their happiness at work. For example, a key extrinsic factor on the clinic manager’s happiness was his/her direct supervisor, a prime illustration, if the clinic manager’s direct supervisor fails to recognize the clinic manager’s skills/abilities and if the direct supervisor of the clinic manager was a micromanager. Notwithstanding, when clinic managers utilize their full skills and when they were able to support, encourage, and develop their direct reports, it seems that clinic managers maintained a sense of happiness at work despite any external negative experiences. Several contributions have been realized based on the findings of this study. Most interestingly, the phenomenon of happiness at work has been found to be dynamic and multidimensional
High precision abundances in the 16 Cyg binary system: a signature of the rocky core in the giant planet
We study the stars of the binary system 16 Cygni to determine with high
precision their chemical composition. Knowing that the component B has a
detected planet of at least 1.5 Jupiter masses, we investigate if there are
chemical peculiarities that could be attributed to planet formation around this
star. We perform a differential abundance analysis using high resolution (R =
81,000) and high S/N (~700) CFHT/ESPaDOnS spectra of the 16 Cygni stars and the
Sun; the latter was obtained from light reflected of asteroids. We determine
differential abundances of the binary components relative to the Sun and
between components A and B as well. We achieve a precision of about 0.005 dex
and a total error ~0.01 dex for most elements. The effective temperatures and
surface gravities found for 16 Cyg A and B are Teff = 5830+/-7 K, log g =
4.30+/-0.02 dex, and Teff = 5751+/-6 K, log g = 4.35+/-0.02 dex, respectively.
The component 16 Cyg A has a metallicity ([Fe/H]) higher by 0.047+/-0.005 dex
than 16 Cyg B, as well as a microturbulence velocity higher by 0.08 km/s. All
elements show abundance differences between the binary components, but while
the volatile difference is about 0.03 dex, the refractories differ by more and
show a trend with condensation temperature, which could be interpreted as the
signature of the rocky accretion core of the giant planet 16 Cyg Bb. We
estimate a mass of about 1.5-6 M_Earth for this rocky core, in good agreement
with estimates of Jupiter's core.Comment: ApJ Letters. Press release: http://cfht.hawaii.edu/en/news/16CygAB
Observational evidence for a broken Li Spite plateau and mass-dependent Li depletion
We present NLTE Li abundances for 88 stars in the metallicity range -3.5 <
[Fe/H] < -1.0. The effective temperatures are based on the infrared flux method
with improved E(B-V) values obtained mostly from interstellar NaI D lines. The
Li abundances were derived through MARCS models and high-quality UVES+VLT,
HIRES+Keck and FIES+NOT spectra, and complemented with reliable equivalent
widths from the literature. The less-depleted stars with [Fe/H] < -2.5 and
[Fe/H] > -2.5 fall into two well-defined plateaus of A_{Li} = 2.18 (sigma =
0.04) and A_{Li} = 2.27 (sigma = 0.05), respectively. We show that the two
plateaus are flat, unlike previous claims for a steep monotonic decrease in Li
abundances with decreasing metallicities. At all metallicities we uncover a
fine-structure in the Li abundances of Spite plateau stars, which we trace to
Li depletion that depends on both metallicity and mass. Models including atomic
diffusion and turbulent mixing seem to reproduce the observed Li depletion
assuming a primordial Li abundance A_{Li} = 2.64, which agrees well with
current predictions (A_{Li} = 2.72) from standard Big Bang nucleosynthesis.
Adopting the Kurucz overshooting model atmospheres increases the Li abundance
by +0.08 dex to A_{Li} = 2.72, which perfectly agrees with BBN+WMAP.Comment: A&A Letters, in pres
Another forbidden solar oxygen abundance: the [O I] 5577 A line
Context: Recent works with improved model atmospheres, line formation, atomic
and molecular data, and detailed treatment of blends, have resulted in a
significant downward revision of the solar oxygen abundance.
Aims: Considering the importance of the Sun as an astrophysical standard and
the current conflict of standard solar models using the new solar abundances
with helioseismological observations we have performed a new study of the solar
oxygen abundance based on the forbidden [OI] line at 5577.34 A, not previously
considered.
Methods: High-resolution (R > 500 000), high signal-to-noise (S/N > 1000)
solar spectra of the [O I] 5577.34 A line have been analyzed employing both
three-dimensional (3D) and a variety of 1D (spatially and temporally averaged
3D, Holweger & Muller, MARCS and Kurucz models with and without convective
overshooting) model atmospheres.
Results: The oxygen abundance obtained from the [OI] 5577.3 A forbidden line
is almost insensitive to the input model atmosphere and has a mean value of
A(O) = 8.71 +/- 0.02 (\sigma from using the different model atmospheres). The
total error (0.07 dex) is dominated by uncertainties in the log gf value (0.03
dex), apparent line variation (0.04 dex) and uncertainties in the continuum and
line positions (0.05 dex).
Conclusions: The here derived oxygen abundance is close to the 3D-based
estimates from the two other [OI] lines at 6300 and 6363 A, the permitted OI
lines and vibrational and rotational OH transitions in the infrared. Our study
thus supports a low solar oxygen abundance (A(O) ~ 8.7), independent of the
adopted model atmosphere.Comment: Astronomy & Astrophysics, in pres
Role of Bcl-3 in solid tumors
Bcl-3 is an established oncogene in hematologic malignancies, such as B-cell chronic lymphocytic leukemias. Nevertheless, recent research has shown that it also participates in progression of diverse solid tumors. The present review summarizes the current knowledge of Bcl3 role in solid tumors progression, including some new insights in its possible molecular mechanisms of action
2MASS J18082002-5104378: The brightest (V=11.9) ultra metal-poor star
Context. The most primitive metal-poor stars are important for studying the
conditions of the early galaxy and are also relevant to big bang
nucleosynthesis. Aims. Our objective is to find the brightest (V<14) most
metal-poor stars. Methods. Candidates were selected using a new method, which
is based on the mismatch between spectral types derived from colors and
observed spectral types. They were observed first at low resolution with EFOSC2
at the NTT/ESO to obtain an initial set of stellar parameters. The most
promising candidate, 2MASS J18082002-5104378 (V=11.9), was observed at high
resolution (R=50 000) with UVES at the VLT/ESO, and a standard abundance
analysis was performed. Results. We found that 2MASS J18082002-5104378 is an
ultra metal-poor star with stellar parameters Teff = 5440 K, log g = 3.0 dex,
vt = 1.5 km/s, [Fe/H] = -4.1 dex. The star has [C/Fe]<+0.9 in a 1D analysis, or
[C/Fe]<=+0.5 if 3D effects are considered; its abundance pattern is typical of
normal (non-CEMP) ultra metal-poor stars. Interestingly, the star has a binary
companion. Conclusions. 2MASS J1808-5104 is the brightest (V=11.9) metal-poor
star of its category, and it could be studied further with even higher S/N
spectroscopy to determine additional chemical abundances, thus providing
important constraints to the early chemical evolution of our Galaxy.Comment: A&A Letter
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