22 research outputs found
A spectroscopic analysis of the chemically peculiar star HD207561
In this paper we present a high-resolution spectroscopic analysis of the
chemically peculiar star HD207561. During a survey programme to search for new
roAp stars in the Northern hemisphere, Joshi et al. (2006) observed significant
photometric variability on two consecutive nights in the year 2000. The
amplitude spectra of the light curves obtained on these two nights showed
oscillations with a frequency of 2.79 mHz [P~6-min]. However, subsequent
follow-up observations could not confirm any rapid variability. In order to
determine the spectroscopic nature of HD207561, high-resolution spectroscopic
and spectro-polarimetric observations were carried out. A reasonable fit of the
calculated Hbeta line profile to the observed one yields the effective
temperature (Teff) and surface gravity (log g) as 7300 K and 3.7 dex,
respectively. The derived projected rotational velocity (vsin i) for HD207561
is 74 km/sec indicative of a relatively fast rotator. The position of HD207561
in the H-R diagram implies that this is slightly evolved from the main-sequence
and located well within the delta-Scuti instability strip. The abundance
analysis indicates the star has slight under-abundances of Ca and Sc and mild
over-abundances of iron-peak elements. The spectro-polarimetric study of
HD207561 shows that the effective magnetic field is within the observational
error of 100 gauss (G). The spectroscopic analysis revealed that the star has
most of the characteristics similar to an Am star, rather than an Ap star, and
that it lies in the delta-Scuti instability strip; hence roAp pulsations are
not expected in HD207561, but low-overtone modes might be excited.Comment: 8 pages, 7 figures, 3 tables. Accepted for pubblication in MNRA
Statistics of Magnetic Fields for OB Stars
Based on an analysis of the catalog of magnetic fields, we have investigated
the statistical properties of the mean magnetic fields for OB stars. We show
that the mean effective magnetic field of a star can be used as a
statistically significant characteristic of its magnetic field. No correlation
has been found between the mean magnetic field strength and
projected rotational velocity of OB stars, which is consistent with the
hypothesis about a fossil origin of the magnetic field. We have constructed the
magnetic field distribution function for B stars, , that has a
power-law dependence on with an exponent of . We have
found a sharp decrease in the function F for {\cal B}\lem 400 G
that may be related to rapid dissipation of weak stellar surface magnetic
fields.Comment: 22 pages, 7 figures, accepted Astronomy Letters, 2010, vol.36, No.5,
pp.370-379, contact E-mail: [email protected]
Comprehensive study of the magnetic stars HD 5797 and HD 40711 with large chromium and iron overabundances
We present the results of a comprehensive study of the chemically peculiar
stars HD 5797 and HD 40711. The stars have the same effective temperature, Teff
= 8900 K, and a similar chemical composition with large iron (+1.5 dex) and
chromium (+3 dex) overabundances compared to the Sun. The overabundance of
rare-earth elements typically reaches +3 dex. We have measured the magnetic
field of HD 5797. The longitudinal field component Be has been found to vary
sinusoidally between -100 and +1000 G with a period of 69 days. Our estimate of
the evolutionary status of the stars suggests that HD 5797 and HD 40711, old
objects with an age t \approx 5 \times 108 yr, are near the end of the core
hydrogen burning phase.Comment: 26 pages, 5 Encapsulated Postscript figure
Statistics of magnetic field measurements in OBA stars and the evolution of their magnetic fields
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim We review the measurements of magnetic fields of OBA stars. Based on these data, we confirm that magnetic fields are distributed according to a lognormal law with mean log B = − 0.5 (B in kG) with a standard deviation σ = 0.5. The shape of the magnetic field distribution (MFD) is similar to that for neutron stars. This finding favors the hypothesis that the magnetic field of a neutron star is determined mainly by the magnetic field of its predecessor, namely the massive OB star. Further, we model the evolution of an ensemble of magnetic massive stars in the Galaxy. We use our own population synthesis code to obtain the distribution of stellar radii, ages, masses, temperatures, effective magnetic fields, and magnetic fluxes from the pre-main-sequence (PMS) via zero-age main sequence (ZAMS) up to the terminal-age main sequence stages. A comparison of the MFD obtained in our model with that obtained from the recent measurements of the stellar magnetic field allows us to conclude that the evolution of magnetic fields of massive stars is slow if not absent. The shape of the real MFD shows no indications of the magnetic desert proposed previously. Based on this finding, we argue that the observed fraction of magnetic stars is determined by physical conditions at the PMS stage of stellar evolution