The stratified evolution of a cool star

A low mass star usually experiences stratification and abundance anomalies during its evolution. A 0.95 solar mass star with a metallicity Z = 0.004 is followed from the main-sequence to the Horizontal Branch (HB). On the main-sequence the larger effects of stratification may come from accretion as was suggested in relation to metallicity and planet formation. As it evolves through the giant branch, stratification appears around the hydrogen burning shell. It may create hydrodynamic instabilities and be related to abundance anomalies on the giant branch. After the He flash the star evolves to the HB. If it loses enough mass, it ends up a hot HB star (or in the field an sdB star) with effective temperatures larger than 11000 K. All sdB stars are observed to have an approximately solar iron abundance whatever their original metallicity, implying overabundances by factors of up to 100. So should the 0.95 solar mass star. How its internal hydrodynamic properties on the main sequence may influence its fate on the HB is currently uncertain.Comment: Astronomische Nachrichten - Astronomical Notes (AN) papers presented at the Cool Stars 17 conference 2012 (AN 334, issue 1-2

Abundance anomalies in pre-main-sequence stars: Stellar evolution models with mass loss

The effects of atomic diffusion on internal and surface abundances of A and F pre-main-sequence stars with mass loss are studied in order to determine at what age the effects materialize, as well as to further understand the processes at play in HAeBe and young ApBp stars. Self-consistent stellar evolution models of 1.5 to 2.8Msun with atomic diffusion (including radiative accelerations) for all species within the OPAL opacity database were computed and compared to observations of HAeBe stars. Atomic diffusion in the presence of weak mass loss can explain the observed abundance anomalies of pre-main-sequence stars, as well as the presence of binary systems with metal rich primaries and chemically normal secondaries such as V380 Ori and HD72106. This is in contrast to turbulence models which do not allow for abundance anomalies to develop on the pre-main-sequence. The age at which anomalies can appear depends on stellar mass. For A and F stars, the effects of atomic diffusion can modify both the internal and surface abundances before the onset of the MS. The appearance of important surface abundance anomalies on the pre-main-sequence does not require mass loss, though the mass loss rate affects their amplitude. Observational tests are suggested to decipher the effects of mass loss from those of turbulent mixing. If abundance anomalies are confirmed in pre-main-sequence stars they would severely limit the role of turbulence in these stars.Comment: 9 pages, 6 figures, accepeted for publicatio

Horizontal Branch evolution, metallicity and sdB stars

Context. Abundance anomalies have been observed in field sdB stars and in nearly all Horizontal Branch (HB) stars of globular clusters with Teff > 11 000K whatever be the cluster metallicity. Aims. The aim is to determine the abundance variations to be expected in sdB stars and in HB stars of metallicities Z \geq 0.0001 and what observed abundances teach us about hydrodynamical processes competing with atomic diffusion. Methods. Complete stellar evolution models, including the effects of atomic diffusion and radiative acceleration, have been computed from the zero age main-sequence for metallicities of Z0 = 0.0001, 0.001, 0.004 and 0.02. On the HB the masses were selected to cover the Teff interval from 7000 to 37000K. Some 60 evolutionary HB models were calculated. The calculations of surface abundance anomalies during the horizontal branch depend on one parameter, the surface mixed mass. Results. For sdB stars with Teff 11 000K in all observed clusters, independent of metallicity, it was found that most observed abundance anomalies (even up to ~ x 200) were compatible, within error bars, with expected abundances. A mixed mass of ~1.E-7 M\odot was determined by comparison with observations. Conclusions. Observations of globular cluster HB stars with Teff > 11 000K and of sdB stars with Teff < 37 000K suggest that most observed abundance anomalies can be explained by element separation driven by radiative acceleration occuring at a mass fraction of ~1.E-7 M\odot. Mass loss or turbulence appear to limit the separation between 1.E-7 M\odot and the surface.Comment: Accepted for publication by A&

Alien Registration- Michaud, Hazel G. (Monticello, Aroostook County)

https://digitalmaine.com/alien_docs/33977/thumbnail.jp

Male music teachers and singing fathers: effects on and correlations with kindergarten children's singing abilities

Thesis (D.M.A.)--Boston UniversityThe purpose of this study was to discover the effects, if any, of baritone and falsetto singing models on kindergarten children's singing range development and pitchmatching abilities. An additional purpose was to determine if there is a relationship between the amount of singing that fathers do with and to their children in the home and those children's singing range development and pitch-matching abilities. I investigated the following questions: (a) What effect, if any, does a male music teacher's use/nonuse of falsetto have on kindergarten children's singing range development? (b) What effect, if any, does a male music teacher's use/nonuse of falsetto have on kindergarten children's pitch-matching abilities? (c) To what extent does the amount of singing that fathers do with and to their children in the home correlate with those children's singing range development? (d) To what extent does the amount of singing that fathers do with and to their children in the home correlate with those children's pitch-matching abilities? Participants were 66 kindergarten children in four intact classrooms who received music instruction for 30 minutes once each week for 20 weeks. Two classes (n = 29) experienced a baritone vocal model during music instruction, while two classes (n = 37) experienced a falsetto vocal model during music instruction. Parents completed a revised version of the HOMES questionnaire (Brand, 1985) at the outset of the study to provide information about the children's musical home life. Vocal range development was tested using the Singing Voice Development Measure (Rutkowski, 1996). I tested pitchmatching accuracy of sol-mi patterns in a call-and-response song. Results of a MANCOVA indicated no significant differences in either pitchmatching or vocal development between the two groups; however, the results of a chi-square test indicated significantly more children in the falsetto group had success in singing over the break in the head register on the SVDM pretest (p < .00) and SVDM posttest (p = .01). The results of the HOMES indicated that the amount of singing that fathers did with and to their children in the home had multiple significant (p < .05) positive correlations with the children's scores in both pitch-matching and singing range development pre-, mid-, and post-tests. Based on the results, I recommended that male elementary music teachers consider using their falsetto ranges when teaching kindergarten children to sing in their head registers. In addition, fathers should be encouraged to sing with their children because it appears that the amount of singing fathers do with and to their children in the home positively correlates with those children's singing abilities

Scandium: A key element for understanding Am stars

{\rm Context.} Atomic diffusion is believed to cause the abundance anomalies observed in AmFm stars. However, the detailed process has still not been well-established. For instance, two possible scenarios for the diffusion theory are presently envisaged. They differ mainly by the depth from which the abundance anomalies emanate. The first scenario predicts that the abundances are modified in the superficial regions of the star, just below the hydrogen convection zone. The second scenario predicts that a much deeper extension of the mixing zone exists due to the convection caused by Fe accumulation in regions below the hydrogen convection zone. {\rm Aims.} We calculate much more accurate radiative accelerations of Sc than previously, to better understand the observed abundance anomalies of this element. We believe that it is a key element to use as a diagnostic tool for understanding AmFm stars. {\rmMethods.} The method employed to obtain these radiative accelerations is based on an interpolation from the parameters of the so-called SVP parametric method. {\rm Results.} The radiative accelerations, shown here in a typical Am stellar model, are discussed in light of the observed anomalies of Ca and Sc. Our results suggest that the deeper mixing scenario is not entirely satisfactory: the mixing zone should be deeper than what is predicted by recent models to account for observed Sc underabundances. Our results seem more compatible with the scenario where the abundances anomalies are created in the superficial regions. However, only detailed evolutionary modelling with mass loss and diffusion of all important species, including Ca and Sc, with accurate radiative accelerations, will be able to give more insight into where the source of these anomalies occur in AmFm stars.Comment: 6 pages, 3 figures, accepted for publication in A&