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We discuss the v sin i distributions of main sequence B stars in galactic clusters in relation to stellar luminosity and to cluster metallicity. We show that evolutionary effects and/or dependence of initial v sin i distribution on stellar mass are important, so that a much larger sample and a wider metallicity range are required to detect any possible metallicity effect beyond doubt.
We report the discovery of non-radial pulsations with at least 4 periods in the B7V star HD 37151. This result is based on 465 photometric measurements spanning 12 years. In addition, 30 high-resolution spectra were taken in the Mgii λ4481 region: they show a small projected rotational velocity and slight variations of the line profiles. Although this star was once classified B8Vp(Si), all available data show it is a normal B7V star. It is the second coolest SPB star found to date.
We present new observations of projected rotational velocities of main sequence B stars in the galactic clusters NGC 2439, NGC 3293, NGC 3766, NGC 4755, NGC 7160 and h & χ Persei. 257 stars have been observed with three instruments, 207 of which are presented here. Projected rotational velocities have been determined by least-squares fit to synthetic spectra. Our v sin i scale is compared with that of Slettebak et al. (1975).
Lithium in cool magnetic CP stars in still poorly studied and estimations of the Li abundance in these stars are scarce. There is some evidence of variability of the LiI 6708 Â line, but this variability has not been studied systematicaly. Even the identification of the 6708 Â line with the LiI resonance doublet is still in doubt. This problem is important in the broader context of the Li abundance in various types of stars, as well as for deeper undersfanding of the magnetic star phonomenon itself. The reason for fhis is that the Li abundance in very sensitive to evolutionary status of the stars and their properties, such as the character and intensity of mixing processes.
Looking in the literature for short period variations of Ap stars, we found the puzzling case of HD 24975. Used as a comparison star by Weiss (1978), it had been found then to present variations with a peak-to-peak amplitude of 0.01 in U, B and V with a period of about 45mn, but with no clear correlation between the three passbands.
HD 24975 has the same spectral type A2 as 21 Com which seems to present photometric variations with P ⋍ 31mn and Δ V < 0,02m (Percy, 1973, 1975). Both stars are near the blue edge of the δ Scuti instability strip in the HR diagram. The lack of photo metric data, however, prevented the precise location of HD 24975 from being found on the HR diagram.
The evolutionary state of CP Stars is defined using members of open clusters. It is confirmed that all CP stars belong to the main sequence, if the case of Horizontal-Branch Stars is omitted. The frequency of CP Stars as a function of age has been reconsidered: it is found constant for the CP2 stars, but significantly increasing with age for the CP1 (Am) stars.
Geneva photometry of the important and relatively well known Ap star 53 Cam (HR 3109, HD 65339) is presented. These 27 data, which cover rather evenly the rotational phase interval, are compared with the photometric data in ten bandpasses published by Musielok et al. (1980). They allow to show that at least four “null-wavelength regions” occur between 3400 and 7800 Å.
Photometrically determined gravities for field and cluster Ap stars, together with published periods, show that conservation of angular momentum alone is responsible for the observed increase of the periods with age. New photometric periods of a few cluster stars are presented which independently confirm this result. No outstanding change with age of the amplitude of lightcurves is noted.
The magnetic field investigations of the rapidly-oscillating (ro)Ap star ϒ Equ show a very long magnetic (rotational) period of about 74 years (Leroy et al. 1994; Bychkov & Shtol 1997). No significant changes of radial velocities were detected during the history of investigations of this star. Recently, Scholz et al. (1997) (hereafter S97) reported a rapid increase of radial velocity (RV) of ϒ Equ from the mean value of -16.81 km s−1 up to a maximum at -4.28 km s−1 within the interval JD 2449608 – JD 2450356, and suggested that ϒ Equ is a long-period binary star with high eccentricity. Such a probable discovery of binary motion of ϒ Equ is very interesting, since it opens the possibility to compare asteroseismic parameters of the star with those obtained from the binary orbit.
Making use of detached eclipsing binaries with B-type components discovered by the OGLE and MACHO teams in the SMC and in the LMC, we give the value of the fractional radius above which circularization occurs. This critical radius is around 0.24 to 0.26, regardless of the mass, surface gravity or metallicity, and is consistent with that found by Giuricin et al. (1984) for galactic binaries. These empirical facts are shown to be consistent with Zahn’s (1975) theory of tidal dissipation. This work confirms and extends that of North & Zahn (2003), thanks to a sample of 448 binaries taken from the recent OGLE catalogue of 2580 eclipsing binaries in the LMC (Wyrzykowski et al. 2003) and a more homogeneous interpretation of the lightcurves of the 148 SMC binaries.
The quest for accurate fundamental parameters (M, R, Teff log g, v sin i) of CP stars has been a lasting problem ever since the nature and origin of these stars has been discussed. The main reason for the difficulty lies in the anomalous colours of these stars, linked with their abundance anomalies which are responsible for complicated blocking and backwarming effects. In the following, we review the Teff determinations proposed so far, and show how the Hipparcos results improve the radius and log g determinations of nearby Ap stars.
New angular diameter determinations for the bright southern F8 supergiant δ CMa enable the bolometric emergent flux and effective temperature of the star to be determined with improved accuracy. The spectral flux distribution and bolometric flux have been determined from published photometry and spectrophotometry and combined with the angular diameter to derive the bolometric emergent flux ℱ = (6.50 ± 0.24) × 107 Wm−2 and the effective temperature Teff = 5818 ± 53 K. The new value for the effective temperature is compared with previous interferometric and infrared flux method determinations. The accuracy of the effective temperature is now limited by the uncertainty in the bolometric flux rather than by the uncertainty in the angular diameter.
A new beam-combination and detection system has been installed in the Sydney University Stellar Interferometer working at the red end of the visual spectrum (λλ 500–950 nm) to complement the existing blue-sensitive system (λλ 430–520 nm) and to provide an increase in sensitivity. Dichroic beam-splitters have been introduced to allow simultaneous observations with both spectral systems, albeit with some restriction on the spectral range of the longer wavelength system (λλ 550–760 nm). The blue system has been upgraded to allow remote selection of wavelength and spectral bandpass, and to enable simultaneous operation with the red system with the latter providing fringe-envelope tracking. The new system and upgrades are described and examples of commissioning tests presented. As an illustration of the improvement in performance the measurement of the angular diameter of the southern F supergiant δ CMa is described and compared with previous determinations.
The Sydney University Stellar Interferometer (SUSI) has been used to make a new determination of the angular diameter of Sirius A. The observations were made at an effective wavelength of 694.1 nm and the new value for the limb-darkened angular diameter is 6.048 ± 0.040 mas (± 0.66%). This new result is compared with previous measurements and is found to be in excellent agreement with a conventionally calibrated measurement made with the European Southern Observatory's Very Large Telescope Interferometer (VLTI) at 2.176 μm (but not with a second globally calibrated VLTI measurement). A weighted mean of the SUSI and first VLTI results gives the limb-darkened angular diameter of Sirius A as 6.041 ± 0.017 mas (± 0.28%). Combination with the Hipparcos parallax gives the radius equal to 1.713 ± 0.009 R⊙. The bolometric flux has been determined from published photometry and spectrophotometry and, combined with the angular diameter, yields the emergent flux at the stellar surface equal to (5.32 ± 0.14) × 108 W m−2 and the effective temperature equal to 9845 ± 64 K. The luminosity is 24.7 ± 0.7 L⊙.
Objective: Several studies have provided prevalence estimates of posttraumatic stress disorder (PTSD) related to the September 11, 2001 (9/11) attacks in broadly affected populations, although without sufficiently addressing qualifying exposures required for assessing PTSD and estimating its prevalence. A premise that people throughout the New York City area were exposed to the attacks on the World Trade Center (WTC) towers and are thus at risk for developing PTSD has important implications for both prevalence estimates and service provision. This premise has not, however, been tested with respect to DSM-IV-TR criteria for PTSD. This study examined associations between geographic distance from the 9/11 attacks on the WTC and reported 9/11 trauma exposures, and the role of specific trauma exposures in the development of PTSD.
Methods: Approximately 3 years after the attacks, 379 surviving employees (102 with direct exposures, including 65 in the towers, and 277 with varied exposures) recruited from 8 affected organizations were interviewed using the Diagnostic Interview Schedule/Disaster Supplement and reassessed at 6 years. The estimated closest geographic distance from the WTC towers during the attacks and specific disaster exposures were compared with the development of 9/11–related PTSD as defined by the Diagnostic and Statistical Manual, Fourth Edition, Text Revision.
Results: The direct exposure zone was largely concentrated within a radius of 0.1 mi and completely contained within 0.75 mi of the towers. PTSD symptom criteria at any time after the disaster were met by 35% of people directly exposed to danger, 20% of those exposed only through witnessed experiences, and 35% of those exposed only through a close associate’s direct exposure. Outside these exposure groups, few possible sources of exposure were evident among the few who were symptomatic, most of whom had preexisting psychiatric illness.
Conclusions: Exposures deserve careful consideration among widely affected populations after large terrorist attacks when conducting clinical assessments, estimating the magnitude of population PTSD burdens, and projecting needs for specific mental health interventions.
(Disaster Med Public Health Preparedness. 2011;5:S205-S213)