21 research outputs found
An asteroseismic study of the Beta Cephei star Theta Ophiuchi: photometric results
We have carried out a three-site photometric campaign for the Beta Cephei
star Theta Ophiuchi from April to August 2003. 245 hours of differential
photoelectric uvy photometry were obtained during 77 clear nights. The
frequency analysis of our measurements resulted in the detection of seven
pulsation modes within a narrow frequency interval between 7.116 and 7.973 c/d.
No combination or harmonic frequencies were found. We performed a mode
identification of the individual pulsations from our colour photometry that
shows the presence of one radial mode, one rotationally split l=1 triplet and
possibly three components of a rotationally split l=2 quintuplet. We discuss
the implications of our findings and point out the similarity of the pulsation
spectrum of Theta Ophiuchi to that of another Beta Cephei star, V836 Cen.Comment: 8 pages, 6 figure
An asteroseismic study of the beta Cephei star beta Canis Majoris
We present the results of a detailed analysis of 452 ground-based
high-resolution high S/N spectroscopic measurements spread over 4.5 years for
beta Canis Majoris with the aim to determine the pulsational characteristics of
this star, and to use them to derive seismic constraints on the stellar
parameters. We determine pulsation frequencies in the SiIII 4553 Angstrom line
with Fourier methods. We identify the m-value of the modes by taking into
account the photometric identifications of the degrees l. To this end we use
the moment method together with the amplitude and phase variations across the
line profile. The frequencies of the identified modes are used for a seismic
interpretation of the structure of the star. We confirm the presence of the
three pulsation frequencies already detected in previous photometric datasets:
f_1 = 3.9793 c/d (46.057 microHz), f_2 = 3.9995 c/d (46.291 microHz) and f_3 =
4.1832 c/d (48.417 microHz). For the two modes with the highest amplitudes we
unambiguously identify (l_1,m_1) = (2,2) and (l_2,m_2) = (0,0). We cannot
conclude anything for the third mode identification, except that m_3 > 0. We
also deduce an equatorial rotational velocity of 31 +/- 5 Km/s for the star. We
show that the mode f_1 must be close to an avoided crossing. Constraints on the
mass (13.5 +/- 0.5 Msun), age (12.4 +/- 0.7 Myr) and core overshoot (0.20 +/-
0.05 H_P) of beta CMa are obtained from seismic modelling using f_1 and f_2.Comment: Accepted for publication in A&
An asteroseismic study of the Beta Cephei star Theta Ophiuchi: spectroscopic results
We present the results of a detailed analysis of 121 ground-based
high-resolution high S/N spectroscopic measurements spread over 3 years 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 days with an eccentricity of 0.1670. After removing the
orbit we determined two frequencies for the primary in the residual radial
velocities: f1 = 7.1160 c/d and f2 = 7.4676 c/d. We also found the presence of
f3 = 7.3696 c/d by means of a two dimensional frequency search across the Si
III 4567 A profiles. We identified the m-value of the main mode with frequency
f1 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 (l1,m1) = (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 Teff = 24000 K and log g = 4.1, which is
consistent with photometrically determined values.Comment: 8 pages, 6 figure
Catalog of Galactic Beta Cephei Stars
We present an extensive and up-to-date catalog of Galactic Beta Cephei stars.
This catalog is intended to give a comprehensive overview of observational
characteristics of all known Beta Cephei stars. 93 stars could be confirmed to
be Beta Cephei stars. For some stars we re-analyzed published data or conducted
our own analyses. 61 stars were rejected from the final Beta Cephei list, and
77 stars are suspected to be Beta Cephei stars. A list of critically selected
pulsation frequencies for confirmed Beta Cephei stars is also presented. We
analyze the Beta Cephei stars as a group, such as the distributions of their
spectral types, projected rotational velocities, radial velocities, pulsation
periods, and Galactic coordinates. We confirm that the majority of these stars
are multiperiodic pulsators. We show that, besides two exceptions, the Beta
Cephei stars with high pulsation amplitudes are slow rotators. We construct a
theoretical HR diagram that suggests that almost all 93 Beta Cephei stars are
MS objects. We discuss the observational boundaries of Beta Cephei pulsation
and their physical parameters. We corroborate that the excited pulsation modes
are near to the radial fundamental mode in frequency and we show that the mass
distribution of the stars peaks at 12 solar masses. We point out that the
theoretical instability strip of the Beta Cephei stars is filled neither at the
cool nor at the hot end and attempt to explain this observation
PHASES Differential Astrometry and Iodine Cell Radial Velocities of the kappa Pegasi Triple Star System
kappa Pegasi is a well-known, nearby triple star system. It consists of a
``wide'' pair with semi-major axis 235 milli-arcseconds, one component of which
is a single-line spectroscopic binary (semi-major axis 2.5 milli-arcseconds).
Using high-precision differential astrometry and radial velocity observations,
the masses for all three components are determined and the relative
inclinations between the wide and narrow pairs' orbits is found to be 43.8 +/-
3.0 degrees, just over the threshold for the three body Kozai resonance. The
system distance is determined to 34.60 +/- 0.21 parsec, and is consistent with
trigonometric parallax measurements.Comment: Accepted for publication in ApJ, complete versions of tables 2 and 4
can be found at http://stuff.mit.edu/~matthew1/kapPegTables
The new orbital elements and properties of epsilon Persei
Contains fulltext :
35168.pdf (publisher's version ) (Open Access)A detailed analysis of a large collection of electronic spectra from three observatories, together with radial velocities published earlier, were used to derive a new ephemeris and improved orbital elements for the ε Per binary. Observations covering a time interval of about 37 000 days (101.3 years) can be reconciled with a constant orbital period of 1406916000004. The high orbital eccentricity of 0.5550.009 was also confirmed. New spectral observations confirm that there is a periodic variation of the systemic velocity. Together with new evidence from astrometric observations (also analyzed here), they confirm the existence of a third body in the system with an orbital period of about 9600 days (26.3 years), rather than 4156 days, as reported earlier. Application of the disentangling technique to the Hα spectra with good ratios did not allow detection of spectral lines of either the secondary or tertiary components. For plausible inclinations between 30° and 90°, the observed mass function implies a mass of the secondary , if a primary mass is adopted of 13.52.0 . Attempts to detect the third body via interferometric observations should continue in spite of this first negative result.A detailed analysis of a large collection of electronic spectra from three observatories, together with radial velocities published earlier, were used to derive a new ephemeris and improved orbital elements for the ε Per binary. Observations covering a time interval of about 37 000 days (101.3 years) can be reconciled with a constant orbital period of 1406916000004. The high orbital eccentricity of 0.5550.009 was also confirmed. New spectral observations confirm that there is a periodic variation of the systemic velocity. Together with new evidence from astrometric observations (also analyzed here), they confirm the existence of a third body in the system with an orbital period of about 9600 days (26.3 years), rather than 4156 days, as reported earlier. Application of the disentangling technique to the Hα spectra with good ratios did not allow detection of spectral lines of either the secondary or tertiary components. For plausible inclinations between 30° and 90°, the observed mass function implies a mass of the secondary , if a primary mass is adopted of 13.52.0 . Attempts to detect the third body via interferometric observations should continue in spite of this first negative result