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Population II (population + ii)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Evolutionary models for two hyper-iron-poor low-mass stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
Gregory J. Harris
ABSTRACT The possible origin of two low-mass hyper-iron-poor (HIP) stars, HE0107-5240 and HE1327-2326 are investigated. The three scenarios tested are as follows. (i) The star forms metal free (Population III) and accretes metals throughout its lifetime. (ii) A Population III binary star system forms, and the lower mass star accretes metals from the higher mass star during its asymptotic giant branch phase. (iii) An HIP Population II star is formed and evolves with no further pollution. Using the ng-elms code, stellar evolution models of these three scenarios are computed and fitted to the observed colours. Models are computed at 0.8 and 0.7 M,, and for several metal accretion rates. It is not possible to unambiguously identify the origin, evolutionary stage or mass for either star with the present observational data. Our evolutionary models indicate that HE0107,5240 is either a red giant or a subgiant close to the base of the red giant branch. In line with the study of Aoki et al., HE1327,2326 is found to be either a main-sequence or a subgiant star. If HE1327,2326 is a main-sequence star the fits indicate that it must have a mass less than 0.8 M,; if the star is assumed to have an age of around 12.5 Gyr it will have a mass closer to 0.7 M,. Main-sequence low-mass model Population III stars which have been polluted with metals are found to closely resemble Population II stars. However, the case is different for subgiants. The polluted and unpolluted Population III subgiants have luminosity up to twice that of a comparable Population II model. If HE1327,2326 is a subgiant, its distance is measured and if its mass can be reasonably well constrained, it should be possible to determine if it is a Population II or III star. [source]

Searching for the reionization sources

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2007
T. Roy Choudhury
ABSTRACT Using a reionization model simultaneously accounting for a number of experimental data sets, we investigate the nature and properties of reionization sources. Such a model predicts that hydrogen reionization starts at z, 15, is initially driven by metal-free (Population III) stars, and is 90 per cent complete by z, 8. We find that a fraction f, > 80 per cent of the ionizing power at z, 7 comes from haloes of mass M < 109 M, predominantly harbouring Population III stars; a turnover to a Population II dominated phase occurs shortly after, with this population, residing in M > 109 M, haloes, yielding f,, 60 per cent at z= 6. Using Lyman-break broad-band dropout techniques, J -band detection of sources contributing to 50 per cent (90 per cent) of the ionizing power at z, 7.5 requires reaching a magnitude J110,AB= 31.2 (31.7), where , 15 (30) (Population III) sources arcmin,2 are predicted. We conclude that z > 7 sources tentatively identified in broad-band surveys are relatively massive (M, 109 M,) and rare objects which are only marginally (,1 per cent) adding to the reionization photon budget. [source]

Scaling and root planing, systemic metronidazole and professional plaque removal in the treatment of chronic periodontitis in a Brazilian population II , microbiological results

JOURNAL OF CLINICAL PERIODONTOLOGY, Issue 4 2005
L. H. Carvalho
Abstract Objective: The current investigation evaluated changes in levels and proportions of 39 bacterial species in subgingival plaque samples after scaling and root planing (SRP) alone or in combination with systemic metronidazole and/or professional cleaning in subjects with chronic periodontitis. Methods: Forty-four adult subjects (mean age 45±6 years) with periodontitis were randomly assigned in four treatment groups, a control (C, n=10) that received SRP and placebo and three test groups treated as follows: T1 (n=12): SRP and metronidazole (M, 400 mg tid) for 10 days; T2 (n=12): SRP, weekly professional supragingival plaque removal for 3 months (PC) and placebo; and T3 (n=10): SRP, M and PC. Subgingival plaque samples were taken from seven sites per subject at baseline and 90 days post-therapy. Counts of 39 subgingival species were determined using checkerboard DNA,DNA hybridization. Significance of differences over time was determined using the Wilcoxon signed ranks test and among groups using ancova. Results: The mean counts of the majority of the species were reduced post-therapy in the 4 treatment groups. Counts (× 105±SEM) of Porphyromonas gingivalis, Tannerella forsythensis and Treponema denticola were significantly reduced in groups T2 and T3. Levels of beneficial species, such as some Actinomyces species, Veillonella parvula, Streptococcus sanguis, Streptococcus oralis and Streptococcus gordonii were minimally affected in levels when the combined therapy was applied (T3). Mean proportions of red complex species decreased from 18.4% at baseline to 3% at 90 days post-therapy in group T3 (p<0.01), from 25.8% to 2.3% in group T2 (p<0.01), from 17.7% to 5.6% in group T1 (p<0.05) and from 19.4% to 8.8% in group C (NS). Proportions of the suspected periodontal pathogens from the orange complex were also markedly reduced in groups T2 and T3. Conclusions: All treatments reduced counts and proportions of red complex species. Adjunctive therapy appeared to have a greater effect and also affected members of the orange complex. [source]

Transferability and characterization of nine microsatellite markers for the tropical tree species Tabebuia roseo-alba

MOLECULAR ECOLOGY RESOURCES, Issue 1 2009
JULIANA MASSIMINO FERES
Abstract Microsatellite loci that were previously developed in the tropical tree Tabebuia aurea were used for the genetic analysis of Tabebuia roseo-alba populations. Nine of 10 simple sequence repeat markers were amplified, and the polymorphism was assessed in 58 individuals sampled from two stands in southeastern Brazil. All loci were polymorphic with Mendelian inheritance. The allele numbers were high, ranging from 5 to 13 in population I and 3 to 7 in population II, with means of 8.9 and 5.5, respectively. We conclude that these markers can be efficiently used for parentage and gene-flow studies. [source]