1,152 research outputs found
The abundance of boron in evolved A- and B-type stars
Boron abundances in A- and B-type stars may be a successful way to track evolutionary effects in these hot stars. The light elements -- Li, Be, and B -- are tracers of exposure to temperatures more moderate than those in which the H-burning CN-cycle operates. Thus, any exposure of surface stellar layers to deeper layers will affect these light element abundances. Li and Be are used in this role in investigations of evolutionary processes in cool stars, but are not observable in hotter stars. An investigation of boron, however, is possible through the B II 1362=C5 resonance line. We have gathered high resolution spectra from the IUE database of A- and B-type stars near 10~M_\odot for which nitrogen abundances have been determined (by Gies & Lambert, 1992, and Venn 1995). The B II 1362=C5 line is blended throughout the temperature range of this program, requiring spectrum syntheses to recover the boron abundances. For no star could we synthesize the 1362=C5 region using the meteoritic/solar boron abundance of log(B) =3D 2.88 (Anders & Grevesse 1989); a lower boron abundance was necessary which may reflect evolutionary effects (e.g., mass loss or mixing near the main-sequence), the natal composition of the star forming regions, or a systematic error in the analyses (e.g., non-LTE effects). Regardless of the initial boron abundance, and despite the possibility of non-LTE effects, it seems clear that boron is severely depleted in some stars. It may be that the nitrogen and boron abundances are anticorrelated, as would be expected from mixing between the H-burning and outer stellar layers. If, as we suspect, a residue of boron is present in the A-type supergiants, we may exclude a scenario in which mixing occurs continuously between the surface and the dee
Testing Rotational Mixing Predictions with New Boron Abundances in Main Sequence B-type Stars
(Abridged) New boron abundances for seven main-sequence B-type stars are
determined from HST STIS spectroscopy around the BIII 2066A line. Boron
abundances provide a unique and critical test of stellar evolution models that
include rotational mixing since boron is destroyed in the surface layers of
stars through shallow mixing long before other elements are mixed from the
stellar interior through deep mixing. Boron abundances range from 12+log(B/H) =
1.0 to 2.2. The boron abundances are compared to the published values of their
stellar nitrogen abundances (all have 12+log(N/H) < 7.8, i.e., they do not show
significant CNO-mixing) and to their host cluster ages (4 to 16 Myr) to
investigate the predictions from models of massive star evolution with
rotational mixing effects (Heger & Langer 2000). Only three stars (out of 34)
deviate from the model predictions, including HD36591, HD205021, and HD30836.
These three stars suggest that rotational mixing could be more efficient than
currently modelled at the highest rotation rates.Comment: 10 figures, 7 tables; accepted for publication in the Astrophysical
Journa
The Pristine survey II: a sample of bright stars observed with FEROS
Extremely metal-poor (EMP) stars are old objects formed in the first Gyr of
the Universe. They are rare and, to select them, the most successful strategy
has been to build on large and low-resolution spectroscopic surveys. The
combination of narrow- and broad band photometry provides a powerful and
cheaper alternative to select metal-poor stars. The on-going Pristine Survey is
adopting this strategy, conducting photometry with the CFHT MegaCam wide field
imager and a narrow-band filter centred at 395.2 nm on the CaII-H and -K lines.
In this paper we present the results of the spectroscopic follow-up conducted
on a sample of 26 stars at the bright end of the magnitude range of the Survey
(g<=15), using FEROS at the MPG/ESO 2.2 m telescope. From our chemical
investigation on the sample, we conclude that this magnitude range is too
bright to use the SDSS gri bands, which are typically saturated. Instead the
Pristine photometry can be usefully combined with the APASS gri photometry to
provide reliable metallicity estimates.Comment: AN accepte
SUN-221 Psychological factors and clinical outcomes in adults with advanced chronic kidney disease not on renal replacement therapy
Takeaway food consumption, diet quality and abdominal obesity in young adults
Background - Takeaway food consumption is associated with a higher BMI and poorer diet quality in the USA but little is known about the association in Australians.Objective - To examine if takeaway food consumption is associated with abdominal obesity and poorer diet quality in young Australian adults.Design - A national sample of 1,277 men and 1,585 women aged 26-36 completed a self-administered questionnaire on demographic and lifestyle factors, a 127 item food frequency questionnaire, and usual frequency of fruit, vegetable and takeaway food consumption. Dietary intake was compared with the dietary recommendations of the Australian Guide to Healthy Eating. A pedometer was worn for seven days. Waist circumference was measured and moderate abdominal obesity was defined as ≥94 cm for men and ≥80 cm for women. Prevalence ratios (PR) were calculated using log binomial regression with eating takeaway food once a week or less as the reference group.Outcomes - Consumption of takeaway food twice a week or more was reported by more men (37.9%) than women (17.7%). Participants eating takeaway food at least twice a week were less likely to meet the guidelines for vegetables (P<0.05 men and women), fruit (P<0.001 men and women), dairy (P<0.01 men and women), extra foods (P=0.001 men and women), breads and cereals (P<0.05 men only), lean meats and alternatives (P<0.05 women only) and overall met significantly fewer dietary guidelines (P<0.001 men and women) than participants eating takeaway less than twice per week. After adjusting for confounding variables (age, physical activity, TV viewing, and employment status) consuming takeaway food twice a week or more was associated with a 31% higher prevalence of moderate abdominal obesity in men (PR 1.31; 95% CI: 1.07, 1.61) and a 25% higher prevalence in women (PR 1.25; 95% CI: 1.04, 1.50).Conclusion - Eating takeaway food twice a week or more was associated with poorer diet quality and a higher prevalence of moderate abdominal obesity in both young men and young women.<br /
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