scholarly journals Pulsational instability of pre-main-sequence models from accreting protostars. I. Constraining the input physics for accretion with spectroscopic parameters and stellar pulsations

2021 ◽  
Author(s):  
T. Steindl ◽  
K. Zwintz ◽  
T. G. Barnes ◽  
M. Muellner ◽  
E. I. Vorobyov
Keyword(s):  
Main Sequence ◽  
Spectroscopic Parameters ◽  
Stellar Pulsations

scholarly journals Constraints on pre-main-sequence evolution from stellar pulsations

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.

scholarly journals The McDonald Observatory search for pulsating sdA stars

2018 ◽  
Vol 617 ◽  
pp. A6 ◽  
Author(s):  
K. J. Bell ◽  
I. Pelisoli ◽  
S. O. Kepler ◽  
W. R. Brown ◽  
D. E. Winget ◽  
...  
Keyword(s):  
Time Series ◽  
White Dwarfs ◽  
Main Sequence ◽  
Pulsating Stars ◽  
Blue Stragglers ◽  
Rr Lyrae ◽  
Stellar Pulsations ◽  
Low Mass ◽  
New Variables

Context. The nature of the recently identified “sdA” spectroscopic class of stars is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravity values between main sequence stars and isolated white dwarfs, and effective temperatures below the lower limit for He-burning subdwarfs. Most are likely products of binary stellar evolution, whether extremely low-mass white dwarfs and their precursors or blue stragglers in the halo. Aims. Stellar eigenfrequencies revealed through time series photometry of pulsating stars sensitively probe stellar structural properties. The properties of pulsations exhibited by sdA stars would contribute substantially to our developing understanding of this class. Methods. We extend our photometric campaign to discover pulsating extremely low-mass white dwarfs from the McDonald Observatory to target sdA stars classified from SDSS spectra. We also obtain follow-up time series spectroscopy to search for binary signatures from four new pulsators. Results. Out of 23 sdA stars observed, we clearly detect stellar pulsations in 7. Dominant pulsation periods range from 4.6 min to 12.3 h, with most on timescales of approximately one hour. We argue specific classifications for some of the new variables, identifying both compact and likely main sequence dwarf pulsators, along with a candidate low-mass RR Lyrae star. Conclusions. With dominant pulsation periods spanning orders of magnitude, the pulsational evidence supports the emerging narrative that the sdA class consists of multiple stellar populations. Since multiple types of sdA exhibit stellar pulsations, follow-up asteroseismic analysis can be used to probe the precise evolutionary natures and stellar structures of these individual subpopulations.

scholarly journals Asteroseismology and rotation in the main sequence

2010 ◽  
Vol 6 (S272) ◽  
pp. 509-510
Author(s):  
Andressa Jendreieck ◽  
Eduardo Janot Pacheco ◽  
Laerte B. P. de Andrade ◽  
Juan Carlos Suárez
Keyword(s):  
Main Sequence ◽  
Published Data ◽  
Stellar Rotation ◽  
Stellar Pulsations ◽  
Theoretical Predictions

AbstractIn this project, we study the effects of stellar rotation on the pulsation predictions for stars in the Main Sequence following the series δ Scu, γ Dor, SPB, Be and β Cep. The objects' rotation in this series span from a few km/s to a few hundreds of km/s. We will compare theoretical predictions yielded by the codes CESAM/FILOU with published data from the MOST and CoRoT satellites. A better diagnostic of the rotation effects on stellar pulsations will help to improve the oscillatory models.

scholarly journals Introductory Remarks on Spectroscopic Parameters

1973 ◽  
Vol 18 ◽  
pp. 73-76
Author(s):  
Helmut A. Abt
Keyword(s):  
Positive Result ◽  
Spectral Type ◽  
Spectroscopic Data ◽  
Main Sequence ◽  
Multiple Star ◽  
Spectroscopic Parameters ◽  
Multiple Systems ◽  
Visual Systems

I hope that you will excuse a relative newcomer to this field and a spectroscopist for presenting his views, which may be somewhat different than those of others. I would like to enumerate the aims of research on visual systems and the needs of the field, particularly for spectroscopic data, as I see them.I. Aims of Multiple-Star Astronomy. (1). Statistics of multiple systems. We would like to know the fraction of stars that are visually double, triple, etc. and in each case as a function of spectral type. For instance, is the frequency of visual doubles the same for Population II stars as for Population I stars? Or are the frequencies of visual doubles the same for stars off the main sequence as for their antecedents on the main sequence? For such information a negative result on duplicity is as important as a positive result, i.e. we wish to know which stars are not seen to be visually double as well as which ones are seen as doubles.

scholarly journals Radiative hydrodynamic simulations of turbulent convection and pulsations of Kepler target stars

2013 ◽  
Vol 9 (S301) ◽  
pp. 193-196
Author(s):  
Irina N. Kitiashvili
Keyword(s):  
Gravity Waves ◽  
Main Sequence ◽  
Energy Transport ◽  
Turbulence Modeling ◽  
Internal Gravity Waves ◽  
Turbulent Convection ◽  
Hydrodynamic Simulations ◽  
Stellar Pulsations ◽  
Excitation Mechanisms ◽  
Scale Turbulence

AbstractThe problem of interaction of stellar pulsations with turbulence and radiation in stellar convective envelopes is central to our understanding of excitation mechanisms, oscillation amplitudes and frequency shifts. Realistic (“ab initio”) numerical simulations provide unique insights into the complex physics of pulsation-turbulence-radiation interactions, as well as into the energy transport and dynamics of convection zones, beyond the standard evolutionary theory. 3D radiative hydrodynamics simulations have been performed for several Kepler target stars, from M- to A-class along the main sequence, using a new ‘StellarBox’ code, which takes into account all essential physics and includes subgrid scale turbulence modeling. The results reveal dramatic changes in the convection and pulsation properties among stars of different mass. For relatively massive stars with thin convective envelopes, the simulations allow us to investigate the dynamics the whole envelope convection zone including the overshoot region, and also look at the excitation of internal gravity waves. Physical properties of the turbulent convection and pulsations, and the oscillation spectrum for two of these targets are presented and discussed in this paper. In one of these stars, with mass 1.47 M⊙, we simulate the whole convective zone and investigate the overshoot region at the boundary with the radiative zone.

scholarly journals Pulsations as a mass-loss trigger in evolved hot stars

2013 ◽  
Vol 9 (S301) ◽  
pp. 217-220
Author(s):  
Michaela Kraus ◽  
Dieter H. Nickeler ◽  
Maximiliano Haucke ◽  
Lydia Cidale ◽  
Roberto Venero ◽  
...  
Keyword(s):  
Mass Loss ◽  
Main Sequence ◽  
Massive Stars ◽  
Sequence Evolution ◽  
Hot Stars ◽  
Stellar Pulsations ◽  
Pass Through ◽  
Mass Ejection

AbstractDuring their post-main sequence evolution, massive stars pass through several short-lived phases, in which they experience enhanced mass loss in the form of clumped winds and mass ejection events of unclear origin. The discovery that stars populating the blue luminous part of the Hertzsprung-Russell diagram can pulsate suggests that stellar pulsations might influence or trigger enhanced mass loss and eruptions. We present recent results for two objects in different phases: a B[e] star at the end of the main sequence and a B-type supergiant.

Chromospheric activity as a function of age in main-sequence stars

1966 ◽  
Vol 24 ◽  
pp. 40-43
Author(s):  
O. C. Wilson ◽  
A. Skumanich
Keyword(s):  
Main Sequence ◽  
The Sun ◽  
Main Sequence Stars ◽  
Tentative Conclusion ◽  
Chromospheric Activity ◽  
General Field ◽  
Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

The Infancy of Solar-Type Stars and its Relevance for the Origin of Life

1997 ◽  
Vol 161 ◽  
pp. 267-282 ◽  
Author(s):  
Thierry Montmerle
Keyword(s):  
Main Sequence ◽  
Solar Nebula ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Necessary Condition ◽  
Sequence Evolution ◽  
T Tauri ◽  
Solar Type ◽  
Optical Domain ◽  
The Origin Of Life

AbstractFor life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.

On The Radii of Ap Stars

1976 ◽  
Vol 32 ◽  
pp. 49-55 ◽  
Author(s):  
F.A. Catalano ◽  
G. Strazzulla
Keyword(s):  
Observational Data ◽  
Line Width ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Ap Stars

SummaryFrom the analysis of the observational data of about 100 Ap stars, the radii have been computed under the assumption that Ap are main sequence stars. Radii range from 1.4 to 4.9 solar units. These values are all compatible with the Deutsch's period versus line-width relation.

A large rotating structure around AB Doradus A at VLBI scale

2019 ◽  
Vol 15 (S354) ◽  
pp. 189-194
Author(s):  
J. B. Climent ◽  
J. C. Guirado ◽  
R. Azulay ◽  
J. M. Marcaide
Keyword(s):  
Magnetic Reconnection ◽  
Main Sequence ◽  
Complex Structure ◽  
Main Sequence Star ◽  
Polar Cap ◽  
Vlbi Observations ◽  
Rotating Structure ◽  
Source Structure ◽  
Expected Position

AbstractWe report the results of three VLBI observations of the pre-main-sequence star AB Doradus A at 8.4 GHz. With almost three years between consecutive observations, we found a complex structure at the expected position of this star for all epochs. Maps at epochs 2007 and 2010 show a double core-halo morphology while the 2013 map reveals three emission peaks with separations between 5 and 18 stellar radii. Furthermore, all maps show a clear variation of the source structure within the observing time. We consider a number of hypothesis in order to explain such observations, mainly: magnetic reconnection in loops on the polar cap, a more general loop scenario and a close companion to AB Dor A.

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