Realistic Line Models for Pulsating B Stars

1980 ◽  
Vol 4 (1) ◽  
pp. 80-83
Author(s):  
P. A. Stamford ◽  
R. D. Watson
Keyword(s):  
Detailed Examination ◽  
Stellar Disk ◽  
Stellar Winds ◽  
Line Profiles ◽  
Stellar Rotation ◽  
B Stars ◽  
Pulsating Stars ◽  
Velocity Gradients ◽  
Expanding Atmospheres ◽  
Realistic Line

Spectral line profiles in pulsating stars are affected by the interplay of a number of velocity fields. In addition to the basic velocities associated with the pulsation mode, the complications of stellar rotation, atmospheric velocity gradients, stellar winds and varying scales of turbulence may also be present. Initial modelling for line profiles in variables assumed a constant ‘intrinsic profile’ which was integrated over the limb-darkened stellar disk. This approach has been used even in recent work for nonradial pulsations (Stamford and Watson 1977; Kubiak 1978) because of computational ease. Employing an LTE analysis to predict centre-to-limb profile variations, which are then integrated over the disk, represents an improvement on this. This has been done, for example, by Parsons (1972) for radial pulsations in cepheids and by Smith (1978) for nonradial oscillations in B stars. Mihalas (1979) has recently made an even more detailed examination of profiles in expanding atmospheres which involved consideration of velocity gradients, departures from LTE and rotation.

scholarly journals Spectroscopic Measurements of Stellar Rotation

1995 ◽  
Vol 10 ◽  
pp. 403-406
Author(s):  
Dainis Dravins
Keyword(s):  
Rigid Body ◽  
Fourier Transforms ◽  
Stellar Disk ◽  
Radial Pulsation ◽  
Line Profiles ◽  
Stellar Rotation ◽  
Temporal Aspect ◽  
Rotating Star ◽  
Single Epoch ◽  
Profile Change

This section title is identical to that of the first paper where the broadening of absorption lines in response to stellar rotation was discussed: Abney (1877).More accurate measurements now reveal also the details of stellar line shapes, making it possible to segregate the signatures of rotational and other broadening mechanisms: e.g. Gray (1992) and Smith & Gray (1976). To determine the rotation, fits can be made to line profiles (e.g. Anders et al., 1993), to their Fourier transforms (e.g. Dravins et al. 1990;Smith & Gray 1976), or to extended spectral regions (e.g. Kurucz et al. 1977).This review, however, concerns issues for [single-epoch] spectroscopic observations only, no temporal aspect will be discussed.What is observed is a rotationally broadened profile, the accuracy begins to get limited by the incomplete physical understanding of stellarline profiles and of the nature of stellar rotation. In order to disentangle the rotational broadening from other effects, one needs to know the ‘intrinsic’ (i.e. rotationally unbroadened) profile of the non-rotating star. How does this profile change with latitude and longitude across the stellar disk? What effects besides rotation are broadening the lines? What about mass loss, radial pulsation, non-radial oscillations, magnetic fields, spots, etc.? And the star might not even rotate as a rigid body, but perhaps differentially with respect to latitude and/or atmospheric height. All this has to be deduced from the often blended lines in complex spectra.

scholarly journals Inverse tides in pulsating binary stars

2020 ◽  
Vol 501 (1) ◽  
pp. 483-490
Author(s):  
Jim Fuller
Keyword(s):  
Binary Stars ◽  
Close Binary ◽  
Close Binaries ◽  
Spin Orbit ◽  
Misalignment Angle ◽  
Stellar Rotation ◽  
Transfer Energy ◽  
Pulsating Stars ◽  
Mode Amplitude ◽  
Rotation Periods

ABSTRACT In close binary stars, the tidal excitation of pulsations typically dissipates energy, causing the system to evolve towards a circular orbit with aligned and synchronized stellar spins. However, for stars with self-excited pulsations, we demonstrate that tidal interaction with unstable pulsation modes can transfer energy in the opposite direction, forcing the spins of the stars away from synchronicity, and potentially pumping the eccentricity and spin–orbit misalignment angle. This ‘inverse’ tidal process only occurs when the tidally forced mode amplitude is comparable to the mode’s saturation amplitude, and it is thus most likely to occur in main-sequence gravity mode pulsators with orbital periods of a few days. We examine the long-term evolution of inverse tidal action, finding the stellar rotation rate can potentially be driven to a very large or very small value, while maintaining a large spin–orbit misalignment angle. Several recent asteroseismic analyses of pulsating stars in close binaries have revealed extremely slow core rotation periods, which we attribute to the action of inverse tides.

scholarly journals K2 space photometry reveals rotational modulation and stellar pulsations in chemically peculiar A and B stars

2018 ◽  
Vol 616 ◽  
pp. A77 ◽  
Author(s):  
D. M. Bowman ◽  
B. Buysschaert ◽  
C. Neiner ◽  
P. I. Pápics ◽  
M. E. Oksala ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Intrinsic Variability ◽  
B Stars ◽  
Pulsating Stars ◽  
Chemically Peculiar ◽  
Large Scale Magnetic Field ◽  
Peculiar Stars ◽  
Show Evidence ◽  
Chemically Peculiar Stars

Context. The physics of magnetic hot stars and how a large-scale magnetic field affects their interior properties is largely unknown. Few studies have combined high-quality observations and modelling of magnetic pulsating stars, known as magneto-asteroseismology, primarily because of the dearth of detected pulsations in stars with a confirmed and well-characterised large-scale magnetic field. Aims. We aim to characterise observational signatures of rotation and pulsation in chemically peculiar candidate magnetic stars using photometry from the K2 space mission. Thus, we identify the best candidate targets for ground-based, optical spectropolarimetric follow-up observations to confirm the presence of a large-scale magnetic field. Methods. We employed customised reduction and detrending tools to process the K2 photometry into optimised light curves for a variability analysis. We searched for the periodic photometric signatures of rotational modulation caused by surface abundance inhomogeneities in 56 chemically peculiar A and B stars. Furthermore, we searched for intrinsic variability caused by pulsations (coherent or otherwise) in the amplitude spectra of these stars. Results. The rotation periods of 38 chemically peculiar stars are determined, 16 of which are the first determination of the rotation period in the literature. We confirm the discovery of high-overtone roAp pulsation modes in HD 177765 and find an additional 3 Ap and Bp stars that show evidence of high-overtone pressure modes found in roAp stars in the form of possible Nyquist alias frequencies in their amplitude spectra. Furthermore, we find 6 chemically peculiar stars that show evidence of intrinsic variability caused by gravity or pressure pulsation modes. Conclusions. The discovery of pulsations in a non-negligible fraction of chemically peculiar stars make these stars high-priority targets for spectropolarimetric campaigns to confirm the presence of their expected large-scale magnetic field. The ultimate goal is to perform magneto-asteroseismology and probe the interior physics of magnetic pulsating stars.

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 Ubiquitous C IV 1550 Variability in B and Be Stars

1987 ◽  
Vol 92 ◽  
pp. 286-288 ◽  
Author(s):  
G. Sonneborn ◽  
M.P. Garhart ◽  
C.A. Grady
Keyword(s):  
Time Scale ◽  
High Dispersion ◽  
Be Stars ◽  
Line Profiles ◽  
Standard Star ◽  
B Stars ◽  
Short And Long Term ◽  
Resonance Transitions ◽  
Long Term Behavior

Studies of line profile variability of the ultraviolet 1550 Angstrom resonance transitions of C IV in Be stars (Sonneborn et al. 1986; Grady, et al. 1986a,b) have prompted an investigation into the short- and long-term behavior of the C IV lines in other types of B stars. We present examples of two well-studied Be stars, Omega Orionis and 66 Ophiuchi, and two non-Be stars, Beta Cephei and the standard star Zeta Cassiopeiae. Zeta Cas is also known to be a 53 Per variable (see Cox 1983). The IUE SWP high-dispersion spectra of Beta Cep and Zeta Cas have been obtained from the IUE archives. It has been known for some years that the C IV line profiles in Beta Cep vary in a time scale of several days (Fishel and Sparks, 1980). However, it came as a surprise to discover C IV variability in Zeta Cas. Available data allow us to set an upper limit of several months for the time scale of Zeta Cas C IV variability. The principal difference between the C IV variability in Be and non-Be stars appears to be the magnitude and velocity range of the effect.

scholarly journals Stellar Winds and Mass-Loss Rates from Be Stars

1982 ◽  
Vol 98 ◽  
pp. 377-385 ◽  
Author(s):  
Theodore P. Snow
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Stellar Winds ◽  
Be Stars ◽  
Line Profiles ◽  
Sample Group ◽  
Show Evidence ◽  
Acceleration Zone ◽  
Low Levels ◽  
Loss Rates

Resonance-line profiles of SiIII and SiIV lines in 22 B and Be stars have been analyzed in the derivation of mass-loss rates. Of the 19 known Be or shell stars in the sample group, all but one show evidence of winds. It is argued that for stars of spectral type B1.5 and later, SiIII and SiIV are the dominant stages of ionization, and this conclusion, together with theoretical fits to the line profiles, leads to mass-loss rates between 10-11 and 3 × 10-9 for the stars. The rate of mass loss does not correlate simply with stellar parameters, and probably is variable with time. The narrow FeIII shell lines often seen in the ultraviolet spectra of Be stars may arise at low levels in the wind, below the strong acceleration zone. The mass-loss rates from Be stars are apparently insufficient to affect stellar evolution.

scholarly journals Magnetic braking of supermassive stars through winds

2019 ◽  
Vol 623 ◽  
pp. L7 ◽  
Author(s):  
L. Haemmerlé ◽  
G. Meynet
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Formation Process ◽  
Magnetic Coupling ◽  
Rotation Velocity ◽  
Stellar Surface ◽  
Stellar Winds ◽  
Stellar Rotation ◽  
Magnetic Braking ◽  
The Magnetic Field

Context. Supermassive stars (SMSs) are candidates for being progenitors of supermassive quasars at high redshifts. However, their formation process requires strong mechanisms that would be able to extract the angular momentum of the gas that the SMSs accrete. Aims. We investigate under which conditions the magnetic coupling between an accreting SMS and its winds can remove enough angular momentum for accretion to proceed from a Keplerian disc. Methods. We numerically computed the rotational properties of accreting SMSs that rotate at the ΩΓ-limit and estimated the magnetic field that is required to maintain the rotation velocity at this limit using prescriptions from magnetohydrodynamical simulations of stellar winds. Results. We find that a magnetic field of 10 kG at the stellar surface is required to satisfy the constraints on stellar rotation from the ΩΓ-limit. Conclusions. Magnetic coupling between the envelope of SMSs and their winds could allow for SMS formation by accretion from a Keplerian disc, provided the magnetic field is at the upper end of present-day observed stellar fields. Such fields are consistent with primordial origins.

scholarly journals A search for variable subdwarf B stars in TESS full frame images – I. Variable objects in the southern ecliptic hemisphere

2020 ◽  
Vol 499 (4) ◽  
pp. 5508-5526
Author(s):  
S K Sahoo ◽  
A S Baran ◽  
S Sanjayan ◽  
J Ostrowski
Keyword(s):  
Preliminary Analysis ◽  
Variable Stars ◽  
Eclipsing Binaries ◽  
Spectral Classification ◽  
B Stars ◽  
Mode Identification ◽  
Pulsating Stars ◽  
Subdwarf B Stars ◽  
Amplitude Spectra

ABSTRACT We report the results of our search for pulsating subdwarf B stars in full frame images, sampled at 30 min cadence and collected during Year 1 of the TESS mission. Year 1 covers most of the southern ecliptic hemisphere. The sample of objects we checked for pulsations was selected from a subdwarf B stars data base available to public. Only two positive detections have been achieved, however, as a by-product of our search we found 1807 variable objects, most of them not classified, hence their specific variability class cannot be confirmed at this stage. Our preliminary discoveries include: 2 new subdwarf B (sdB) pulsators, 26 variables with known sdB spectra, 83 non-classified pulsating stars, 83 eclipsing binaries (detached and semidetached), a mix of 1535 pulsators and non-eclipsing binaries, two novae, and 77 variables with known (non-sdB) spectral classification. Among eclipsing binaries we identified two known HW Vir systems and four new candidates. The amplitude spectra of the two sdB pulsators are not rich in modes, but we derive estimates of the modal degree for one of them. In addition, we selected five sdBV candidates for mode identification among 83 pulsators and describe our results based on this preliminary analysis. Further progress will require spectral classification of the newly discovered variable stars, which hopefully include more subdwarf B stars.

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