STELLAR PULSATIONS ACROSS THE HR DIAGRAM: Part II

The peculiar outburst of the star baptized Sakurai’s Object (SO) is a conceivable example of a late He shell flash in a post-AGB object. The new source of nuclear energy forces such objects toward high luminosities and eventually low effective temperatures; they cross the HR diagram in a comparable fashion as FG Sge did in the past - i.e., they move noticeably on the HR diagram on human timescales. From monitoring campaigns of SO during the last year, first estimates of its cooling rate were derived and in particular cyclic light variability was established. We present first results from attempts to model stellar envelopes appropriate for SO. As we hypothesize the light variability to be attributable to stellar pulsations, we aim at constraining the basic stellar parameters based on stability analyses of our envelope models. Radial, nonadiabatic stability computations provided predictions of the modal content which should be observable as SO evolves. The particular components in such mode spectra of SO as they are to appear in the coming years should indeed help to constrain basic stellar parameters such as mass and luminosity.

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Two Aspects of Using Hipparcos Data for Studying Multiperiodic Stellar Pulsations

International Astronomical Union Colloquium ◽

10.1017/s0252921100057043 ◽

2000 ◽

Vol 176 ◽

pp. 46-49

Author(s):

M. Jerzykiewicz

Keyword(s):

Effective Temperature ◽

Hydrogen Burning ◽

Stellar Pulsations ◽

Scuti Star ◽

Frequency Ratios ◽

Hipparcos Parallax ◽

Multicolor Photometry ◽

Hr Diagram

AbstractTwo aspects of using Hipparcos data for studying multiperiodic stellar pulsations involve (1) deriving frequencies of multiperiodic pulsators from Hipparcos Epoch Photometry, and (2) using Hipparcos parallaxes together with other data, such as the frequencies, frequency ratios and multicolor photometry, to identify pulsation modes. Details are examined by looking at the δ Scuti star DK Virginis. From Hipparcos Epoch Photometry, two frequencies are derived. These frequencies are then verified by showing that they also fit all available ground-based observations of the star. In addition, Hipparcos parallax and a photometric effective temperature are used to compare the position of DK Vir in the HR diagram with evolutionary tracks. The star turns out to be at the end of core-hydrogen-burning stage of its evolution or slightly beyond, with a mass of 2.2 M⊙, or somewhat smaller. The observed frequencies indicate that the two detected modes are p3 and p2, while the relatively large photometric amplitudes imply ℓ ≲ 2.

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Stellar Pulsations Across the HR Diagram: Part 1

Annual Review of Astronomy and Astrophysics ◽

10.1146/annurev.aa.33.090195.000451 ◽

1995 ◽

Vol 33 (1) ◽

pp. 75-113 ◽

Cited By ~ 92

Author(s):

Alfred Gautschy ◽

Hideyuki Saio

Keyword(s):

Stellar Pulsations ◽

Hr Diagram

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Meridional Circulation, Turbulence, and Diffusion Processes in Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100080477 ◽

1976 ◽

Vol 32 ◽

pp. 109-116 ◽

Cited By ~ 1

Author(s):

S. Vauclair

Keyword(s):

Convection Zone ◽

Diffusion Processes ◽

Meridional Circulation ◽

Diffusion Time ◽

Work In Progress ◽

First Results ◽

Stellar Envelopes ◽

And Diffusion ◽

Turbulence And Diffusion ◽

Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

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The Metallicity Distribution of Late Type Dwarfs

Highlights of Astronomy ◽

10.1017/s1539299600022292 ◽

1998 ◽

Vol 11 (1) ◽

pp. 571-571

Author(s):

M. Haywood ◽

J. Palasi ◽

A. Gómez ◽

L. Meillon Dasgal

Keyword(s):

Star Formation Rate ◽

Formation Rate ◽

Angular Separation ◽

Stellar Populations ◽

Late Type ◽

Limited Sample ◽

Hipparcos Catalogue ◽

Galactic Stellar Populations ◽

Metallicity Distribution ◽

Hr Diagram

The Hipparcos catalogue provides an accurate and extensive sampling of the solar neighbourhood HR diagram. The morphology of this diagram depends on selection criteria of the catalogue such as the limiting magnitude, angular separation and on the characteristics of the stellar populations near the sun (space density, metallicity, star formation rate, etc). Since the Hipparcos data are so accurate, one needs to model precisely the different selection bias and, at the same time, parametrize models of the galactic stellar populations with sufficient flexibility that as much information as possible can be grasped from the catalogue. Comparisons between our model and the Hipparcos catalogue will be presented elsewhere. Since the quantity of information contained in the Hipparcoscatalogue is so important, models ought to be complex, and external contraints, obtained prior to any general comparison with the model, are welcome. A major factor that influences the distribution of the stars in the HR diagram is the metallicity. For the late type stars, the metallicity distribution can be best studied by re-analysing a volume-limited sample of stars from the catalogue.

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Towards an Improved Model of the Galaxy

Highlights of Astronomy ◽

10.1017/s1539299600022280 ◽

1998 ◽

Vol 11 (1) ◽

pp. 570-570

Author(s):

Johan Holmberg ◽

Lennart Lindegren ◽

Chris Flynn

Keyword(s):

Three Dimensional ◽

Direct Determination ◽

Galactic Structure ◽

Open Clusters ◽

Selection Effects ◽

Observational Errors ◽

Red Giant ◽

Improved Model ◽

First Time ◽

Hr Diagram

We use the Hipparcos survey to derive an improved model of the local galactic structure. The availability of parallaxes for all the stars permits direct determination of stellar distributions, eliminating the basic indeterminacy of classical methods based on star counts. Hipparcos gives for the first time a truly three-dimensional view of the solar vicinity, and a complete, homogeneous and highly accurate set of magnitudes and colours. This means that new techniques can be applied in the treatment of the data which place strong constraints on a model that tries to describe the local Galactic structure. Here we investigate how well a static model of low complexitycan describe the Hipparcos observations. The interpretation of the Hipparcos data is complicated by various observational errors and selection effects that are hard to treat correctly. We do not try to correct the data, but instead use a model and subject this model to the same observational errors and selection effects. A model catalogue is created that can be compared with the observed catalogue directly in the observational domain, thereby eliminating the effects from various biases. Many features in the HR diagram are for the first time seen in field stars thanks to Hipparcos, such as the slanted red giant clump, previously seen in rich old open clusters such as Berkeley 18. This and other features ofthe observed HR diagram are well reproduced by the model thanks to the rather detailed modelling of the joint Mv/B — V distribution. Actually, separate distributions were derived for the three different components, disk, thick disk and halo, using the kinematic characteristics of the components to discriminate between them.

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Luminosity Calibration of Giants and Supergiants, G0–M5

Symposium - International Astronomical Union ◽

10.1017/s0074180900055108 ◽

1973 ◽

Vol 54 ◽

pp. 68-77

Author(s):

Ph. C. Keenan

Keyword(s):

Calibration Curves ◽

Hr Diagram

Calibration curves giving Mv for stars of luminosity classes III, II, Ib, Iab and 0 are derived and shown graphically in the HR diagram. There are serious gaps in which the calibration needs to be improved.

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Constraints on pre-main-sequence evolution from stellar pulsations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313014221 ◽

2013 ◽

Vol 9 (S301) ◽

pp. 137-144

Author(s):

M. P. Casey ◽

K. Zwintz ◽

D. B. Guenther

Keyword(s):

Stellar Evolution ◽

Main Sequence ◽

Sequence Evolution ◽

B Stars ◽

Stellar Pulsations ◽

Pms Stars

AbstractPulsating pre-main-sequence (PMS) stars afford the earliest opportunity in the lifetime of a star to which the concepts of asteroseismology can be applied. PMS stars should be structurally simpler than their evolved counterparts, thus (hopefully!) making any asteroseismic analysis relatively easier. Unfortunately, this isn't necessarily the case. The majority of these stars (around 80) are δ Scuti pulsators, with a couple of γ Doradus, γ Doradus – δ Scuti hybrids, and slowly pulsating B stars thrown into the mix. The majority of these stars have only been discovered within the last ten years, with the community still uncovering the richness of phenomena associated with these stars, many of which defy traditional asteroseismic analysis.A systematic asteroseismic analysis of all of the δ Scuti PMS stars was performed in order to get a better handle on the properties of these stars as a group. Some strange results have been found, including one star pulsating up to the theoretical acoustic cut-off frequency of the star, and a number of stars in which the most basic asteroseismic analysis suggests problems with the stars' positions in the Hertzsprung-Russell diagram. From this we get an idea of the\break constraints — or lack thereof — that these results can put on PMS stellar evolution.

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