Β Cephei Stars Research Articles

A new method for the spectroscopic identification of stellar non-radial pulsation modes

We present the Fourier parameter fit method, a new method for spectroscopically identifying stellar radial and non-radial pulsation modes based on the high-resolution time-series spectroscopy of absorption-line profiles. In contrast to previous methods this one permits a quantification of the statistical significance of the computed solutions. The application of genetic algorithms in seeking solutions makes it possible to search through a large parameter space. The mode identification is carried out by minimizing chi-square, using the observed amplitude and phase across the line profile and their modeled counterparts. Computations of the theoretical line profiles are based on a stellar displacement field, which is described as superposition of spherical harmonics and that includes the first order effects of the Coriolis force. We made numerical tests of the method on a grid of different mono- and multi-mode models for 0 <= l <= 4 in order to explore its capabilities and limitations. Our results show that whereas the azimuthal order m can be unambiguously identified for low-order modes, the error of l is in the range of pm 1. The value of m can be determined with higher precision than with other spectroscopic mode identification methods. Improved values for the inclination can be obtained from the analysis of non-axisymmetric pulsation modes. The new method is ideally suited to intermediatley rotating Delta Scuti and Beta Cephei stars.

High-precision elements of double-lined spectroscopic binaries from combined interferometry and spectroscopy

We present methodology to derive high-precision estimates of the fundamental parameters of double-lined spectroscopic binaries. We apply the methods to the case study of the double-lined beta Cephei star beta Centauri. We also present a detailed analysis of beta Centauri's line-profile variations caused by its oscillations. We point out that a systematic error in the orbital amplitudes, and any quantities derived from them, occurs if the radial velocities of blended component lines are computed without spectral disentangling. This technique is an essential ingredient in the derivation of the physical parameters if the goal is to obtain a precision of only a few percent. We have devised iteration schemes to obtain the orbital elements for systems whose lines are blended throughout the orbital cycle. We find the following parameters for beta Cen: $M_1=10.7\pm 0.1 M_\odot$ and $M_2=10.3\pm 0.1 M_\odot$, an age of $(14.1\pm 0.6)\times 10^6$ years. We deduce two oscillation frequencies for the broad-lined primary of beta Centauri with degrees higher than 2. We propose that our iteration schemes be used in any future derivations of the spectroscopic orbital parameters of double-lined binaries with blended component lines to which disentangling can be successfully applied.

Inter-Division IV/V WG on Active OB Stars

Our group studies active early-type (OB) stars, with historical focus on classical Be stars, but extending in recent years to include Slowly Pulsating B-stars (SPB), Beta-Cephei stars, the strongly magnetic Bp stars, Luminous Blue Vairiable (LBV) stars, and B[e] stars. An overall goal is to understand the nature, origin, and consequences of this activity, in terms of both the stellar structure and evolution, as well as the distribution and dynamics of circumstellar material and mass outflows.

An asteroseismic study of the β Cephei star θ Ophiuchi: spectroscopic results

We present the results of a detailed analysis of 121 ground-based high-resolution, high signal-to-noise ratio spectroscopic measurements spread over 3 yr for the beta Cephei star theta Ophiuchi. We discovered theta Oph to be a triple system. In addition to the already known speckle B5 companion of the B2 primary, we showed the presence of a low-mass spectroscopic companion and we derived an orbital period of 56.71 d with an eccentricity of 0.1670. After removing the orbit we determined two frequencies for the primary in the residual radial velocities: f 1 = 7.1160 cd -1 and f 2 = 7.4676 cd -1 . We also found the presence of f 3 = 7.3696 cd -1 by means of a two-dimensional frequency search across the SiIII 4567-Aprofiles. We identified the m-value of the main mode with frequency f 1 by taking into account the photometric identifications of the degrees l. By means of the moment method and the amplitude and phase variations across the line profile, we derived (l 1 , m 1 ) = (2, -1). This result allows us to fix the mode identifications of the whole quintuplet for which three components were detected in photometry. This is of particular use for our forthcoming seismic modelling of the primary. We also determined stellar parameters of the primary by non-local thermodynamic equilibrium hydrogen, helium and silicon line profile fitting and we obtained T eff = 24000 K and logg= 4.1, which is consistent with photometrically determined values.

A photometric mode identification method, including an improved non-adiabatic treatment of the atmosphere

We present an improved version of the method of photometric mode identification of Heynderickx et al. (1994). Our new version is based on the inclusion of precise non-adiabatic eigenfunctions determined in the outer stellar atmosphere according to the formalism recently proposed by Dupret et al.(2002). Our improved photometric mode identification technique is therefore no longer dependent on ad hoc parameters for the non-adiabatic effects. It contains the complete physical conditions of the outer atmosphere of the star, provided that rotation does not play a key role. We apply our improved method to the two slowly pulsating B stars HD 74560 and HD 138764 and to the beta Cephei star EN (16) Lac. Besides identifying the degree l of the pulsating stars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on parameters such as the metallicity and the mixing-length parameter alpha (a procedure we label non-adiabatic asteroseismology).

Multiperiodicity in the light variations of the β Cephei star β Crucis

High-resolution spectroscopic observations have led recently to the discovery that the beta Cephei star beta Crucis (Mimosa) is multiperiodic with at least three non-radial pulsation modes. Data obtained by the star tracker of the WIRE satellite have now allowed us to confirm this multiperiodicity in the light variations. A total of 5 million observations covering 17 days was analyzed and the three main periods we find in this work are in perfect agreement with the results derived from the line profile variations. The photometric amplitudes are small (3, 2.7 and 0.6 millimag for the dominant modes), but this is not surprising in view of the mode identifications derived earlier from the line profiles. Additional periods of low-amplitude modes (between 0.2-0.3 mmag) are also derived, including one suggested earlier by the radial velocity data.

Analysis of Voyager spectra of the beta Cephei star nu Eridani

view Abstract Citations (4) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Analysis of Voyager Spectra of the beta Cephei Star nu Eridani Porri, A. ; Stalio, R. ; Ali, B. ; Polidan, R. S. ; Morossi, C. Abstract Voyager 500-1700 A spectrophotometric observations of the beta Cephei star nu Eri are presented and discussed. The Voyager observations were obtained in 1981 and cover six pulsation cycles of the star. These data are supplemented with a set of nine International Ultraviolet Explorer (IUE) SWP high-resolution observations covering one, earlier epoch, pulsation cycle. Light curves are derived from the Voyager data at 1055 and 1425 A. These light curves are found to be consistent in both shape and period with published optical curves. The 1055 A light curve also exhibits a phenomenon not seen in the optical curves: a small but highly significant systematic increase in the flux of the maximum light phases while maintaining a constant minimum light level over the interval of observation. Substantially larger errors in the longer wavelength data preclude discussion of this phenomenon in the 1425 A light curve. Examination of the far-UV continuum in nu Eri during this period shows that the color temperature is lower for the brighter maxima. Analysis of the far-UV continuum at maximum and minimum light yields an effective temperature difference between these two phases of 2200 + or - 750 K. Spectroscopically, three prominent features are seen in the Voyager data: a feature at 985 A mostly due to a blend of C III 977 A, H I Ly gamma 972 A, and N III 990 A; a feature at 1030 A due to H I Ly beta 1026 A and C II 1037 A; and the Si IV resonance doublet near 1400 A. A comparison of the 912-1700 A spectral region in nu Eri with a set of standard, i.e., nonpulsating stars, shows that nu Eri closely resembles the standard both in continuum shape and spectral line strengths with the possible exception of a slight flux excess between 912 and 975 A. The equivalent width of the 985 A feature is shown to vary in strength over the pulsation cycle in antiphase with the light curve and variations seen in the C IV 1548-1551 lines from the IUE data. This behavior of the 985 A feature is most likely caused by variations in the strength of the Ly gamma component of the blend. Comparisons are also made between nu Eri and the only other beta Cephei star studied in the far-UV, BW Vul, with the most notable differences between the two stars being the much larger delta(Teff) for BW Vul and the almost total absence of abnormalities in observed spectrum of nu Eri. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173898 Bibcode: 1994ApJ...424..401P Keywords: Cepheid Variables; Light Curve; Pulse Duration; Radiative Heat Transfer; Stellar Spectra; Iue; Periodic Variations; Radial Velocity; Astrophysics; STARS: VARIABLES: CEPHEIDS; STARS: INDIVIDUAL CONSTELLATION NAME: NU ERIDANI full text sources ADS | data products SIMBAD (3) MAST (1)

X-ray emission from near-main-sequence B stars

view Abstract Citations (133) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-Ray Emission from Near--Main-Sequence B Stars Cassinelli, J. P. ; Cohen, D. H. ; Macfarlane, J. J. ; Sanders, W. T. ; Welsh, B. Y. Abstract Results of a Roentgen Satellite (ROSAT) X-ray survey of 12 nearby near-main-sequence B stars are presented. Objects with very low interstellar hydrogen column density were chosen to study the soft X-ray emission properties of the stars. All of the stars were detected at the 3 sigma level. Spectral fits to seven of the stars are presented, and temperatures and source emission measures are derived. The spectra and characterized by emission from gas at a temperature of about 2 x 106 K, which is lower than that typically observed for O stars. The ratio Lx/LBol decreases sharply with spectral types later than B1, reaching values of about 10-9 at B3 V; much less than the value of 10-7 that holds for O stars and early-B stars. The survey includes four beta Cephei stars and two Be stars. Our observations are consistent with the finding that beta Cephei variables have softer spectra than other stars of the same spectral type. The X-ray emission measures for the stars are compared with upper and lower limits derived using mass loss rates and terminal velocities from line-driven wind theory. It is concluded that if shocks embedded in the winds are the source of the X-ray emission then a significant fraction of the winds in B stars must be hot. One to a few shocks can account for the observed emission measures. As a function of spectral type, there appears to be a transition in X-ray emission properties at about B1 to B1.5, with later type stars having a smaller Lx/LBol ratio. Coronal and shock models are discussed in regards to the BO V star tau Sco which has an anomalously high source temperature. Publication: The Astrophysical Journal Pub Date: February 1994 DOI: 10.1086/173683 Bibcode: 1994ApJ...421..705C Keywords: B Stars; Cepheid Variables; Emission Spectra; Main Sequence Stars; Stellar Mass; X Ray Astronomy; X Ray Spectra; Astronomical Spectroscopy; Hydrogen; Interstellar Gas; O Stars; Rosat Mission; Shock Waves; Spaceborne Astronomy; Astronomy; SHOCK WAVES; STARS: EARLY-TYPE; STARS: MASS LOSS; X-RAYS: STARS full text sources ADS | data products SIMBAD (12)

A search for Beta Cephei stars in LMC and SMC

The β Cephei instability is believed to be caused by the κ-mechanism. Model calculations, based on revised metal opacities, show this mechanism to be strongly sensitive to metallicity (e.g., Dziembowski, W. A. &amp; Pamyatnykh, A. A., 1993: MNRAS, 262, 204). It appears that [Fe/H] must be larger than the solar value in order to drive the β Cephei pulsations. For this reason, the models predict that no β Cephei stars should be found in the Magellanic Clouds. Balona (1992: MNRAS, 256, 425; 1992: ASP Conf. Ser., Vol. 30, 155; 1993: MNRAS, 260, 795) has tested this prediction by observing three young clusters in the SMC and LMC (NGC 330, NGC 2004 and NGC 2100). He found no β Cephei stars down to a magnitude of V ≈ 16; the threshold for detection of variability on time-scales of a few hours was 10 mmag. Most Galactic β Cephei stars have amplitudes greater than this, but we might expect β Cephei stars in the Magellanic Clouds (if they exist) to have smaller amplitudes, due to the different environment. To test this, we have observed two young clusters NGC 371 (SMC) and NGC 2122 (LMC) with high sensitivity.

Non-linear oscillations and beats in the Beta Canis Majoris stars

Non-linear oscillations and beats in the Beta Canis Majoris stars

Non-Linear Oscillations and Beats in the Beta Canis Majoris Stars

Notwithstanding a great number of hypotheses, suggested for explaining superpositions of the light- and of the velocity variations of the ß Canis Majoris stars, no one of these does it satisfactorily. Possibly it is due to an inadequate elaboration of the non-linearly oscillation theory. Analysis and critical evaluation of the existing hypotheses are given by Mel’nikov and Popov (1970). Our explanation consists in existence of close frequencies corresponding to various oscillation modes which are non-linearly interacting.Equations of motion of an ideal incompressible fluid under condition of preserving the equilibrium figure symmetry with respect to the equatorial plane (lateral oscillations) have the form (Baranov 1988):

Asteroseismology From The Ground

AbstractIn stars which pulsate in more than one mode, be it acoustic or gravity modes, radial or non-radial, we have a chance to study the interior structure by use of seismic techniques. Generally the greater the number of modes observable the greater the chances will be to obtain valuable direct information about the stellar interior not accessible by any other technique.The observational problem of acquiring high quality data divides the stars where seismic techniques can be applied into two groups: A group of stars with intensity amplitudes in the range of millimagnitudes and the stars with very small amplitudes around 10 μmagnitudes or less. The first group contains the white dwarfs, the rapidly oscillating Ap stars, the δ-Scuti stars and the β-Cephei stars. The modes are excited directly or indirectly by some form of к-mechanism due to an opacity source which vary from class to class. The second group is made up of stars with outer convective envelopes which generate acoustic noise that may excite resonant modes, often a very large number.This paper is a discussion of the possibilities for observing these stars with ground based techniques, and also a statement about what can not be done from the ground.

Pioneer 10 observations of the Beta Cephei stars Gamma Pegasi and Delta Ceti

The results of analyzing broad-band Pioneer 10 photometric observations of the low-amplitude pulsating Beta Cephei stars Gamma Pegasi and Delta Ceti are reported. Periods and light curve amplitudes of 3.649 + or - 0.020 hr, 0.05 + or - 0.02 mag for Gamma Peg and 3.869 + or - 0.020 hr, 0.13 + or - 0.02 mag for Delta Ceti are obtained; a power spectrum analysis of the data reveals no other periods. No evidence is found for a phase shift between the light curve maxima in the UV and visible regions. The observed amplitudes combined with published visual and near-UV data suggest a flux and temperature variability of about 200 solar luminosities and 250 K for Gamma Peg and about 600 solar luminosities and 450 K for Delta Cet. These results are compared with others obtained with satellite and ground-based instrumentation.

The nonradial oscillations of Epsilon Persei. I - A lawn-sprinkling shock

view Abstract Citations (9) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Nonradial Oscillations of Epsilon Persei. I. A Lawn-Sprinking Shock Smith, M. A. Abstract A new observational phenomenon, the detection of time-variable, extended wings of photospheric Si III lines from the large-amplitude, nonradial pulsator Epsilon Persei, is described. Computer formulations of several models to explain this phenomenon, including cycle-to-cycle amplitude variations, changes in microturbulence in the intensity model profiles, increases in the line damping or radial-tangential macroturbulence, and changes in the limb-darkening law, are considered and rejected. It is then shown that the observations can be successfully matched with a 'lawn sprinkler' model scaled from Beta Cephei star observations. This involves the vertical propagation of shocks through the star's atmosphere with the onset of each pulsation cycle. In the case of Epsilon Per, the shocks would occur locally just after the phase of maximum upward acceleration. The shock front would proceed around the star with a azimuthally traveling wave and would be confined to the equatorial regions. Publication: The Astrophysical Journal Pub Date: August 1986 DOI: 10.1086/164408 Bibcode: 1986ApJ...307..213S Keywords: Shock Waves; Stellar Oscillations; Stellar Spectra; Astronomical Models; Line Spectra; Radiation Pressure; Silicon; Stellar Mass Ejection; Stellar Winds; Astrophysics; LINE PROFILES; SHOCK WAVES; STARS: INDIVIDUAL CONSTELLATION NAME: EPSILON PERSEI; STARS: PULSATION full text sources ADS | data products SIMBAD (1) Related Materials (1) Part 2: 1987ApJ...320..768S

Beta Cephei Variables

AbstractProblems of Beta Cephei variables and of related pulsating B stars are discussed. In particular, various excitation mechanisms of both radial and nonradial oscillations so far suggested are critically examined. The present state of theory for these variables is found unsatisfactory.

Maia variables and upper-main-sequence phenomena

view Abstract Citations (18) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Maia variables and upper-main-sequence phenomena. McNamara, B. J. Abstract A sample of four stars, including Maia itself, which are located within the Maia instability strip are investigated for photometric variability. The data consist of over 1600 differential Stromgren y-magnitudes collected during 11 nights of observation. No evidence is found for variability over the 0.1-0.3-day period range suggested for Maia stars. Two stars, Merope and Atlas, do seem to show variability, but the lengths of their periods imply a closer relation to the 53 Persei stars. It is suggested that the Maia stars do not exist as a separate class of variable stars but are an extension of the 53 Persei phenomenon to cooler temperatures. Convective core overshooting is hypothesized to be the mechanism responsible for the variability of these stars. It is noted that this process has also been found to be necessary in cluster isochrone dating analyses, in the formation of the blue straggler stars, in the explanation of the apsidal motion of alpha Vir, and as the instability mechanism for the beta Canis Majoris stars. Publication: The Astrophysical Journal Pub Date: February 1985 DOI: 10.1086/162881 Bibcode: 1985ApJ...289..213M Keywords: Main Sequence Stars; Stellar Oscillations; Variable Stars; Convection; Power Spectra; Radial Velocity; Stellar Magnitude; Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (4)

An X-ray survey of beta Cephei stars

Results of an X-ray survey of beta Cephei stars carried out with the Imaging Proportional Counter are reported. Three of six surveyed beta Cephei stars observed was detected with an X-ray luminosity (LX) lying in the range (0.8 - 4.2 x 10 to the 31st erg/s. The mean value of the ratio of X-ray luminosity to bolometric luminosity for nine beta Cephei stars is found to be 8.6 x 10 to the -8th. No dependence of LX or bolometric luminosity is found on the binary or short pulsation periods of the stars, and no correlation was found between LX and the rotation velocity of the stars. It is concluded that the X-ray characteristics of the beta Cephei stars are indistinguishable from other B stars of similar luminosity. An indication was found of X-ray variations by a factor of about 2 on a time scale of about 10 min from Beta CMa.

Pulsational mode-typing in line profile variables. V - Multimodes and 'moving shells' in Nu Eridani and other Beta Cephei stars

view Abstract Citations (25) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Pulsational mode typing in line profile variables. V. Multimodes and "moving shells" in nu Eridani and other beta Cephei stars. Smith, M. A. Abstract An analysis of 31 high-resolution Reticon observations of the Si III 4567 A line reveals that most of its variations in shape are a result of nonlinear hydrodynamic processes that remain in phase with the dominant fourth (radial velocity-producing) mode. Line profile analysis shows that this fourth mode is compatible only with radial pulsation and incompatible with any nonradial pulsation mode, including any with m = 0. When the hydrodynamical effects are nearly absent from the profiles at certain times during the cycle, only one of the three nonradial modes (-m = l) is found to be of importance in describing the residual profile variations; this is in agreement with the star's presumed equator-on aspect and with energy equipartition for the triplet-modes. Several conditions imposed by the spectroscopic and photometric amplitudes of the triplet modes require the identification l = 2, and m = -2, -1, and 0. Publication: The Astrophysical Journal Pub Date: February 1983 DOI: 10.1086/160679 Bibcode: 1983ApJ...265..338S Keywords: Cepheid Variables; Line Spectra; Stellar Oscillations; Stellar Spectra; Radial Velocity; Shock Waves; Signal To Noise Ratios; Stellar Atmospheres; Astrophysics full text sources ADS | data products SIMBAD (7) Related Materials (6) Part 1: 1980ApJ...238..250C Part 2: 1980ApJ...238..667C Part 3: 1980ApJ...240..149S Part 4: 1982ApJ...254..242S Part 6: 1985ApJ...288..266S Part 7: 1986ApJ...304..728S

A PHOTOMETRIC STUDY OF EARLY-TYPE STARS.

ABSTRACT Observation data in the alpha16, Lambda9 photometric system are presented for 228 early-type O4-B8 stars of all luminosity classes. Also included are data for Be stars, B-type stars with a shell, and Beta Canis Majoris stars. The comparison with R-alpha and beta indices suggests that the alpha16 photometry is of good quality. The photometry can be used in separating different kinds of stars; when combined with the 13-color photometry, it makes possible a finer classification. The alpha16 index also provides an indication of stellar mass-loss rates, especially for supergiant stars. Preliminary He I (5876 A) measurements suggest that this line is well correlated with MK types. Be stars observed over several years also exhibit H-alpha line-strength variability. It is found that the Lambda9 index separates supergiant stars later than B2.

Infrared observations of beta Cephei and delta Scuti stars

We have made near-infrared photometric observations of nine β-Cephei and eight δ-Scuti stars inJ, H, andK bands. The observed fluxes are in good agreement with those expected according to their spectral types. We conclude that these stars do not have any anomalous emission in these near-infrared bands.