scholarly journals Pulsation in pre-main sequence stars

2015 ◽  
Vol 11 (A29B) ◽  
pp. 552-559
Author(s):  
Konstanze Zwintz
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Theoretical Models ◽  
Oscillatory Behavior ◽  
Fundamental Parameters ◽  
Open Questions ◽  
Different Types ◽  
Model Independent ◽  
Using Data

AbstractAsteroseismology has been proven to be a successful tool to unravel details of the internal structure for different types of stars in various stages of evolution well after birth. We can now show that it has similar power for pre-main sequence (pre-MS) objects. Pre-MS stars with masses between ~1 and 6 solar masses that have recently been formed and gain their energy mainly from gravitational contraction can become vibrationally unstable during their evolution to the main sequence. Within the past ~15 years, several dozens of pulsating pre-MS stars were discovered using data obtained from ground and from space. Depending on their masses, pre-MS stars can show three different types of pulsations: (i) δ Scuti type p-mode pulsations, (ii) γ Doradus like g-mode oscillations and (iii) g-mode Slowly Pulsating B star pulsations.Our asteroseismic investigations yielded new insights into the connection between the pulsations and early stellar evolution: We revealed a relation between the stars' oscillatory behavior and their relative evolutionary stages that might lead us to a model-independent determination of the stars' fundamental parameters. With this we will be able to put constraints on theoretical models and help to answer some of the yet open questions in early stellar evolution.

scholarly journals A spectroscopic survey of FHB stars near the south galactic pole

2009 ◽  
Vol 5 (S262) ◽  
pp. 422-423
Author(s):  
Silvia Rossi ◽  
Roberto Ortiz ◽  
Ronald Wilhelm ◽  
Roberto Costa ◽  
Timothy C. Beers
Keyword(s):  
High Probability ◽  
Main Sequence ◽  
Galactic Plane ◽  
Theoretical Models ◽  
Spectral Features ◽  
Horizontal Branch ◽  
Atmospheric Parameters ◽  
The South ◽  
Medium Resolution

AbstractWe present the results of a medium-resolution spectroscopic survey of 43 field horizontal-branch (FHB) candidates carried out near the south galactic pole, selected from the original list of FHB candidates compiled by Beers et al. (2007). The observation list includes only stars classified as “high-probability” candidates, according to their 2MASS infrared colours. Atmospheric parameters of some stars have been obtained by comparing some spectral features with theoretical models provided by Kurucz (1993). A comparison between the grid of model atmospheres with some parameters of the Hδ line allowed the determination of log g, whilst [Fe/H] was estimated by the equivalent widths of the MgII 4481 and Caii lines. About 77% of the sample have been classified as FHB stars, 10% as subdwarfs, whilst the remaining 13% are probably main-sequence A-type stars far from the Galactic plane.

scholarly journals Massive star evolution revealed in the Mass-Luminosity plane

2018 ◽  
Vol 14 (S346) ◽  
pp. 480-485
Author(s):  
Erin R. Higgins ◽  
Jorick S. Vink
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Star ◽  
Main Sequence ◽  
Theoretical Models ◽  
Physical Processes ◽  
Single Star ◽  
Star Evolution ◽  
Novel Method ◽  
Massive Star Evolution

AbstractMassive star evolution is dominated by key physical processes such as mass loss, convection and rotation, yet these effects are poorly constrained, even on the main sequence. We utilise a detached, eclipsing binary HD166734 as a testbed for single star evolution to calibrate new MESA stellar evolution grids. We introduce a novel method of comparing theoretical models with observations in the ‘Mass-Luminosity Plane’, as an equivalent to the HRD (see Higgins & Vink 2018). We reproduce stellar parameters and abundances of HD166734 with enhanced overshooting (αov=0.5), mass loss and rotational mixing. When comparing the constraints of our testbed to the systematic grid of models we find that a higher value of αov=0.5 (rather than αov=0.1) results in a solution which is more likely to evolve to a neutron star than a black hole, due to a lower value of the compactness parameter.

scholarly journals Measurements of Stellar Properties through Asteroseismology: A Tool for Planet Transit Studies

2008 ◽  
Vol 4 (S253) ◽  
pp. 309-317 ◽  
Author(s):  
Hans Kjeldsen ◽  
Timothy R. Bedding ◽  
Jørgen Christensen-Dalsgaard
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Rotating Stars ◽  
Fundamental Parameters ◽  
Stellar Oscillations ◽  
Analysis Methods ◽  
Kepler Mission ◽  
Stellar Properties

AbstractOscillations occur in stars of most masses and essentially all stages of evolution. Asteroseismology is the study of the frequencies and other properties of stellar oscillations, from which we can extract fundamental parameters such as density, mass, radius, age and rotation period. We present an overview of asteroseismic analysis methods, focusing on how this technique may be used as a tool to measure stellar properties relevant to planet transit studies. We also discuss details of the Kepler Asteroseismic Investigation – the use of asteroseismology on the Kepler mission in order to measure basic stellar parameters. We estimate that applying asteroseismology to stars observed by Kepler will allow the determination of stellar mean densities to an accuracy of 1%, radii to 2–3%, masses to 5%, and ages to 5–10% of the main-sequence lifetime. For rotating stars, the angle of inclination can also be determined.

scholarly journals Comparisons between observational color-magnitude diagrams and synthetic cluster diagrams for young star clusters in the Magellanic Clouds

1984 ◽  
Vol 105 ◽  
pp. 83-87
Author(s):  
Stephen A. Becker ◽  
Grant J. Mathews ◽  
Wendee M. Brunish
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Star Clusters ◽  
Theoretical Models ◽  
Young Star ◽  
Asymptotic Giant Branch ◽  
Current Status ◽  
Large Numbers ◽  
Young Star Clusters ◽  
Convective Overshoot

Young star clusters (<3 × 108 yr) in the Maqellanic Clouds (MC) can be used to test the current status of the theory of stellar evolution as applied to intermediate and massive stars. The color-magnitude diagram of many young clusters in the MC shows, unlike the case of clusters in our Galaxy, large numbers of stars in both the main sequence and post main sequence evolutionary phases. Usina a arid of stellar evolution models, synthetic cluster H-R diagrams are constructed and compared to observed color-magnitude diagrams to determine the age, age spread, and composition for any given cluster. In addition, for those cases where the data is of high quality, detailed comparisons between theory and observation can provide a diagnostic of the accuracy of the stellar evolution models. Initial indications of these comparisons suggest that the theoretical models should be altered to include: a larger value for the mixing length parameter (α), a larger rate of mass loss during the asymptotic giant branch (AGB) phase, and possibly convective overshoot during the core burning phases.

scholarly journals EFFECTS OF RESIDUE BACKGROUND EVENTS IN DIRECT DETECTION EXPERIMENTS ON IDENTIFYING WIMP DARK MATTER

2011 ◽  
Vol 20 (08) ◽  
pp. 1453-1461 ◽  
Author(s):  
CHUNG-LIN SHAN
Keyword(s):  
Dark Matter ◽  
Direct Detection ◽  
Weakly Interacting Massive Particles ◽  
Data Sets ◽  
Model Independent ◽  
Using Data ◽  
Background Events ◽  
Matter Detection ◽  
Direct Dark Matter

We reexamine the model-independent data analysis methods for extracting properties of Weakly Interacting Massive Particles (WIMPs) by using data (measured recoil energies) from direct Dark Matter detection experiments directly and, as a more realistic study, consider a small fraction of residue background events, which pass all discrimination criteria and then mix with other real WIMP-induced signals in the analyzed data sets. In this talk, the effects of residue backgrounds on the determination of the WIMP mass as well as the spin-independent WIMP coupling on nucleons will be discussed.

scholarly journals Main Sequence Evolution, Abundance Anomalies and Particle Transport

2002 ◽  
Vol 12 ◽  
pp. 279-281
Author(s):  
Georges Michaud ◽  
Olivier Richard ◽  
Jacques Richer
Keyword(s):  
Stellar Evolution ◽  
Particle Transport ◽  
Main Sequence ◽  
Convection Zone ◽  
Accurate Determination ◽  
Atomic Diffusion ◽  
Atomic Data ◽  
Data Bases ◽  
Abundance Anomalies

AbstractThe availability of large atomic data bases has made it possible to calculate stellar evolution models taking into detailed account the abundance variations of all important contributors to opacity. In a first step, in addition to nuclear reactions, the atomic diffusion, radiative accelerations and opacity are continuously calculated during evolution taking the abundance changes of 28 species into account. This leads to the first self consistent main sequence stellar evolution models. In A and F stars (M≥ 1.5Mʘ) an iron peak convection zone is shown to appear at a temperature of 200000 K. The calculated surface abundance anomalies, that follow without any arbitrary parameter, are very similar to those observed in AmFm stars in open clusters except that they are larger by a factor of about 3. The second step, is then to introduce a competing hydrodynamical process. To reduce the calculated anomalies to the observed ones, turbulence has been introduced. It is found that the mixed zone must be about 5 times deeper than the iron convection zone. Detailed comparisons to a few AmFm stars have been carried out. The determination of the abundance anomalies of a large number of atomic species (20 to 30 are probably accessible) makes it possible to constrain stellar hydrodynamics. In clusters, the original abundances and age may be known and the accurate determination of surface abundances may constrain turbulence, mass loss and differential rotation when the required atomic data bases are available and used for the modeling of particle transport in stellar evolution.

scholarly journals Distribution patterns of polyphenols and alkaloids in instant coffee, soft and energy drinks, and tea

2013 ◽  
Vol 31 (No. 5) ◽  
pp. 483-500 ◽  
Author(s):  
N. Manchón ◽  
L. Mateo-Vivaracho ◽  
D. Arrigo M ◽  
A. García-Lafuente ◽  
E. Guillamón ◽  
...  
Keyword(s):  
Black Tea ◽  
Distribution Patterns ◽  
Energy Drinks ◽  
Soft Drinks ◽  
Instant Coffee ◽  
Different Types ◽  
Low Levels ◽  
Using Data ◽  
Phytochemical Profiles

A previously developed method of HPLC-DAD-Fl has been used for the determination of phytochemical profiles in different types of drinks: instant coffee, soft drinks, energy drinks, and different types of tea (green, white, black, and red tea). Using data on the concentrations of 20 main phytochemicals (phenolic acids, flavan-3-ols, flavonols, flavones, and alkaloids) it was possible to identify most of the sample types. Chlorogenic and caffeic acids, and caffeine are the main target compounds in instant coffee; in soft and energy drinks, only caffeine was found. Tea has a more complex phytochemical composition. Unfermented tea is mainly composed of flavan-3-ols and alkaloids, with a high caffeine concentration. Black tea is composed of alkaloids and low levels of flavan-3-ols, which are affected by oxidative reactions during the fermentation. Flavonols are present in lower concentrations in all kinds of teas. The identified phytochemical distribution patterns were used to correctly differentiate instant coffee, soft drinks, energy drinks, unfermented tea and fermented tea (within fermented tea, black tea from red tea can also be differentiated).

scholarly journals Constraints on stellar evolution theory from precise eclipsing binary data

1984 ◽  
Vol 105 ◽  
pp. 391-394
Author(s):  
J. Andersen ◽  
J.V. Clausen ◽  
H.E. J⊘rgensen ◽  
B. Nordström
Keyword(s):  
Stellar Evolution ◽  
Binary Data ◽  
Main Sequence ◽  
Theoretical Models ◽  
Stellar Structure ◽  
Sequence Evolution ◽  
Evolution Theory ◽  
Eclipsing Binary ◽  
Standard Models ◽  
Structure Calculations

Previous attempts at a detailed confrontation of eclipsing binary data with theoretical models of main-sequence evolution were faced with the choice between data of inhomogeneous (mostly low) quality for many systems (Kriz, 1969; Lacy, 1979) or accurate values of mass, radius, and temperature (or luminosity) for very few systems only (Popper et al., 1970). In addition, more detailed and homogeneous stellar structure calculations for several compositions were needed. Since 1972, a coordinated photometric and spectroscopic programme at our institute contributes to building a sufficient observational basis for such a test. Among published standard models for the range 1–10 M⊙, Hejlesen's (1980) are the most extensive, agree well with other standard models, and are presented in a format suitable for comparison with binary data. Here we can only outline a few salient new results from this study.

scholarly journals Fundamental Parameters and the Helium Content of Eclipsing Spectroscopic Binaries

1978 ◽  
Vol 80 ◽  
pp. 433-436
Author(s):  
H.E. Jørgensen
Keyword(s):  
Stellar Evolution ◽  
Stellar Atmosphere ◽  
Spectroscopic Binaries ◽  
List Type ◽  
Type Number ◽  
Helium Content ◽  
Fundamental Parameters ◽  
Effective Temperatures ◽  
Hr Diagram

Today we know accurate masses, radii, surface gravities and luminosities or effective temperatures of a very small number of stars. There are several reasons for deriving accurate parameters of stars. I shall mention only four problems:(i)checking stellar evolution calculations, particularly calculations of isochrones, using binaries,(ii)derivation of helium content in stars of different age,(iii)checking log g derived from photometry and stellar atmosphere calculations,(iv)determination of accurate positions in the HR diagram to get an independent check on calibrations of photometric systems.

scholarly journals Fundamental properties of single O stars in the MiMeS survey

2014 ◽  
Vol 9 (S307) ◽  
pp. 385-386
Author(s):  
F. Martins ◽  
A. Hervé ◽  
J.-C. Bouret ◽  
W. L. F. Marcolino ◽  
G. A. Wade ◽  
...  
Keyword(s):  
Main Sequence ◽  
Fundamental Parameters ◽  
Preliminary Results ◽  
Fundamental Properties ◽  
Cno Abundances

AbstractWe present preliminary results of the determination of fundamental parameters of single O-type stars in the MiMeS survey. We present the sample and we focus on surface CNO abundances, showing how they change as stars evolve off the zero-age main sequence.

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