scholarly journals Asteroseismic observations of OB stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 433-444 ◽  
Author(s):  
Peter De Cat ◽  
Katrien Uytterhoeven ◽  
Juan Gutiérrez-Soto ◽  
Pieter Degroote ◽  
Sergio Simón-Díaz
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Space Missions ◽  
High Order ◽  
Be Stars ◽  
B Stars ◽  
Ob Stars ◽  
Pulsating Stars ◽  
Different Types

AbstractThe region of the hot end of the main-sequence is hosting pulsating stars of different types and flavours. Pulsations are not only observed for Slowly pulsating B stars (mid to late B-type stars; high order g-modes) and β Cephei stars (early B-type stars; low order p/g-modes) but are also causing variability in Be stars and OB-supergiants. In this review we give an overview of the asteroseismic observations that are currently available for these types of stars. The first asteroseismic results were solely based on ground-based observations. Recently, the arrival of space-based data gathered by space missions like most, corot and kepler has led to important discoveries for massive stars, highlighting their excellent asteroseismic potential. We show that, despite the unprecedented precision of the space-based data, there is still a clear need for ground-based follow-up observations.

scholarly journals Spectroscopic Hα and Hγ survey of field Be stars: 2004–2009

2010 ◽  
Vol 6 (S272) ◽  
pp. 290-291
Author(s):  
Erika D. Grundstrom ◽  
Douglas R. Gies ◽  
Christina Aragona ◽  
Tabetha S. Boyajian ◽  
E. Victor Garcia ◽  
...  
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Line Emission ◽  
Circumstellar Disks ◽  
Circumstellar Disk ◽  
Sequence Evolution ◽  
Be Stars ◽  
B Stars ◽  
Significant Variability ◽  
The Universe

AbstractMassive O- and B-type stars are “cosmic engines” in the Universe and can be the dominant source of luminosity in a galaxy. The class of Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity. We find that 90% of the observed stars show some variability with 8% showing significant variability over the 5-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while ~20% of the sample consists of known binaries, we find that another 15–30% of the sample shows indications of binarity.

scholarly journals Asteroseismic Diagnostics for Semi-Convection in B Stars in the Era of K2

2014 ◽  
Vol 9 (S307) ◽  
pp. 182-187
Author(s):  
Ehsan Moravveji
Keyword(s):  
High Precision ◽  
Main Sequence ◽  
Massive Stars ◽  
Mixing Process ◽  
B Stars ◽  
Ob Stars ◽  
Slow Mixing

AbstractSemi-convection is a slow mixing process in chemically-inhomogeneous radiative interiors of stars. In massive OB stars, it is important during the main sequence. However, the efficiency of this mixing mechanism is not properly gauged yet. Here, we argue that asteroseismology of β Cep pulsators is capable of distinguishing between models of varying semi-convection efficiencies. We address this in the light of upcoming high-precision space photometry to be obtained with theKeplertwo-wheel mission for massive stars along the ecliptic.

scholarly journals Chromospheres, Coronae, and Mass Loss in Stars Hotter than the Sun

1980 ◽  
Vol 5 ◽  
pp. 525-531 ◽  
Author(s):  
Theodore P. Snow
Keyword(s):  
Mass Loss ◽  
Main Sequence ◽  
Emission Lines ◽  
Be Stars ◽  
Main Sequence Stars ◽  
B Stars ◽  
X Ray ◽  
Ob Stars ◽  
F Stars ◽  
Simple Dependence

AbstractReviews of the mass-loss characteristics of OB stars have been published recently, and the present review therefore emphasizes the A and F stars and very recent results on O and B stars. For the F stars, chromospheric indicators are present in the form of emission lines, seen in visible and ultraviolet wavelengths. Winds are present in A supergiants, but not in main sequence stars, although at least a few of the latter are X-ray sources, indicating the possible existence of coronae. Most OB supergiants are X-ray sources as well, indicating, along with the presence of super-ionization, that these stars have coronae. On the main sequence, the O stars and some B stars (including Be stars in many cases) have mass loss with highly-ionized species in the wind. The winds in the O and B stars are commonly variable. The mass-loss rates do not show a simple dependence on luminosity, contrary to the predictions for radiatively-driven winds.

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 New Results on Pulsating OB Stars

1995 ◽  
Vol 155 ◽  
pp. 44-55 ◽  
Author(s):  
Paweł Moskalik
Keyword(s):  
Data Model ◽  
Physical Mechanism ◽  
High Order ◽  
Early Type ◽  
Instability Strip ◽  
Model Calculations ◽  
B Stars ◽  
Ob Stars ◽  
Early Type Stars ◽  
Theoretical Results

AbstractUntil very recently the physical mechanism driving oscillations in β Cep and other early type stars has been a mystery. The breakthrough came with the publication of new OPAL and OP opacity data. Model calculations with the new opacities have demonstrated that the pulsations are driven by the familiar K-mechanism, acting in the metal opacity bump at T ≈ 2 × 105K. The mechanism excites the low order p- and g-modes in the upper part of the instability strip and the high order g-modes in the lower part of the strip. The theoretical instability domains agree well with the observed domains of the β Cep and the SPB stars. In this review I present these recent theoretical results and discuss their consequences for our understanding of B stars pulsations.

scholarly journals Pulsations of Ob-Stars: New Observations

1998 ◽  
Vol 185 ◽  
pp. 347-354 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Main Sequence ◽  
Physical Parameters ◽  
Be Stars ◽  
Instability Strip ◽  
Ob Stars ◽  
Analysis Strategies ◽  
The Galaxy ◽  
Order Line ◽  
Nonradial Pulsation ◽  
Radial Pulsations

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

scholarly journals Main-sequence broadening, Be stars, and stellar rotation inhand χ Persei

1994 ◽  
Vol 162 ◽  
pp. 151-152
Author(s):  
J. Denoyelle ◽  
C. Aerts ◽  
C. Waelkens
Keyword(s):  
Main Sequence ◽  
Large Fraction ◽  
Variable Stars ◽  
Theoretical Studies ◽  
Be Stars ◽  
Stellar Rotation ◽  
B Stars ◽  
Fundamental Parameters ◽  
Magnitude Diagram ◽  
Double Cluster

The double cluster h andxPersei is one of the richest clusters containing early-B stars, and therefore is important for observational and theoretical studies on the fundamental parameters of massive stars. The colour-magnitude diagram of the double cluster shows an important scatter (see Figure 1). It has long been known thathandxPersei are extremely rich in Be stars (Slettebak 1968). Our previous contention (Waelkens et al. 1990) that the large-amplitude variable stars we discovered are also Be stars, could be confirmed for a few objects. Rotation velocities for stars inhandxPersei are usually high, which is not surprising in view of the large fraction of Be stars.

scholarly journals Pulsation among TESS A and B stars and the Maia variables

2020 ◽  
Vol 493 (4) ◽  
pp. 5871-5879
Author(s):  
L A Balona ◽  
D Ozuyar
Keyword(s):  
Main Sequence ◽  
Large Fraction ◽  
Single Mode ◽  
Distinct Region ◽  
Low Frequencies ◽  
B Stars ◽  
High Frequencies ◽  
Pulsating Stars ◽  
Scuti Stars

ABSTRACT Classification of over 50 000 TESS stars in sectors 1–18 has resulted in the detection of 766 pulsating main-sequence B stars as well as over 5000 δ Scuti, 2300 γ Doradus, and 114 roAp candidates. Whereas it has been assumed that high-frequency pulsations among B-type main-sequence stars are confined to the early B-type β Cephei stars, the observations indicate that high frequencies are to be found over the whole B-star range, eventually merging with δ Scuti stars. The cool B stars pulsating in high frequencies are called Maia variables. It is shown that Maia variables are not rapidly rotating and thus cannot be β Cephei pulsators that appear to have lower temperatures due to gravity darkening. In the region where β Cephei variables are found, the proportion of pulsating stars is larger and amplitudes are higher and a considerable fraction pulsate in a single mode and low rotation rate. There is no distinct region of slowly pulsating B stars (SPB stars). Stars pulsating solely in low frequencies are found among all B stars. At most, only one-third of B stars appear to pulsate. These results, as well as the fact that a large fraction of A and B stars show rotational modulation, indicate a need for a revision of current ideas regarding stars with radiative envelopes.

scholarly journals Core Overshoot and Nonrigid Internal Rotation of Massive Stars: Current Status from Asteroseismology

2007 ◽  
Vol 3 (S250) ◽  
pp. 237-244 ◽  
Author(s):  
Conny Aerts
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Rotation Frequency ◽  
Current Status ◽  
Structure Parameters ◽  
B Stars ◽  
Surface Rotation ◽  
Oscillation Modes ◽  
Drastic Increase ◽  
Core Rotation

AbstractSeismic estimates of core overshoot have been derived from extensive high-precision photometric and spectroscopic ground-based (multisite) campaigns for five main-sequence B-type stars. For three of these, the ratio of the near-core rotation frequency to the surface rotation frequency could be estimated as well, from the identified oscillation modes. We summarise these seismic results obtained for B stars. Now that the technique of asteroseismology was proven to work for probing the interior of massive stars, we expect a drastic increase in the precision of the structure parameters from the space missions CoRoT and Kepler, as well as from currently ongoing ground-based campaigns, in the coming years.

scholarly journals Mixing of CNO-cycled matter in pulsationally and magnetically active massive stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 26-31 ◽  
Author(s):  
Norbert Przybilla ◽  
Maria-Fernanda Nieva
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Comprehensive Analysis ◽  
Line Formation ◽  
High Quality ◽  
Analysis Strategies ◽  
Magnetic Stars ◽  
Larger Sample ◽  
Magnetic Nature

AbstractWe report on the abundances of helium, carbon, nitrogen and oxygen in a larger sample of Galactic massive stars of ~7-20 M⊙ near the main sequence, composed of apparently normal objects, pulsators of β-Cephei- and SPB-type, and magnetic stars. High-quality spectra are homogeneously analysed using sophisticated non-LTE line-formation and comprehensive analysis strategies. All the stars follow a previously established tight trend in the N/C-N/O ratio and show normal helium abundances, tracing the nuclear path of the CNO-cycles quantitatively. A correlation of the strength of the mixing signature with the presence of magnetic fields is found. In conjunction with low rotation velocities this implies that magnetic breaking is highly efficient for the spin-down of some massive stars. We suggest several objects for follow-up spectropolarimetry, as the mixing signature indicates a possible magnetic nature of these stars.

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