7 research outputs found
Investigating the spectroscopic, magnetic and circumstellar variability of the O9 subgiant star HD 57682
Investigating the spectroscopic, magnetic and circumstellar variability of the O9 subgiant star HD 57682
The O9IV star HD 57682, discovered to be magnetic within the context of the
MiMeS survey in 2009, is one of only eight convincingly detected magnetic
O-type stars. Among this select group, it stands out due to its sharp-lined
photospheric spectrum. Since its discovery, the MiMeS Collaboration has
continued to obtain spectroscopic and magnetic observations in order to refine
our knowledge of its magnetic field strength and geometry, rotational period,
and spectral properties and variability. In this paper we report new ESPaDOnS
spectropolarimetric observations of HD 57682, which are combined with
previously published ESPaDOnS data and archival H{\alpha} spectroscopy. This
dataset is used to determine the rotational period (63.5708 \pm 0.0057 d),
refine the longitudinal magnetic field variation and magnetic geometry (dipole
surface field strength of 880\pm50 G and magnetic obliquity of 79\pm4\circ as
measured from the magnetic longitudinal field variations, assuming an
inclination of 60\circ), and examine the phase variation of various lines. In
particular, we demonstrate that the H{\alpha} equivalent width undergoes a
double-wave variation during a single rotation of the star, consistent with the
derived magnetic geometry. We group the variable lines into two classes: those
that, like H{\alpha}, exhibit non-sinusoidal variability, often with multiple
maxima during the rotation cycle, and those that vary essentially sinusoidally.
Based on our modelling of the H{\alpha} emission, we show that the variability
is consistent with emission being generated from an optically thick, flattened
distribution of magnetically-confined plasma that is roughly distributed about
the magnetic equator. Finally, we discuss our findings in the magnetospheric
framework proposed in our earlier study.Comment: 21 pages, 19 figures, Accepted for publication in MNRA
Investigating the Spectroscopic, Magnetic and Circumstellar Variability of the O9 Subgiant Star HD 57682.
The O9IV star HD 57682, discovered to be magnetic within the context of the Magnetism in Massive Stars (MiMeS) survey in 2009, is one of only eight convincingly detected magnetic O-type stars. Among this select group, it stands out due to its sharp-lined photospheric spectrum. Since its discovery, the MiMeS Collaboration has continued to obtain spectroscopic and magnetic observations in order to refine our knowledge of its magnetic field strength and geometry, rotational period and spectral properties and variability. In this paper we report new Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) spectropolarimetric observations of HD 57682, which are combined with previously published ESPaDOnS data and archival Hα spectroscopy. This data set is used to determine the rotational period (63.5708 ± 0.0057 d), refine the longitudinal magnetic field variation and magnetic geometry (dipole surface field strength of 880 ± 50 G and magnetic obliquity of 79° ± 4° as measured from the magnetic longitudinal field variations, assuming an inclination of 60°) and examine the phase variation of various lines. In particular, we demonstrate that the Hα equivalent width undergoes a double-wave variation during a single rotation of the star, consistent with the derived magnetic geometry. We group the variable lines into two classes: those that, like Hα, exhibit non-sinusoidal variability, often with multiple maxima during the rotation cycle, and those that vary essentially sinusoidally. Based on our modelling of the Hα emission, we show that the variability is consistent with emission being generated from an optically thick, flattened distribution of magnetically confined plasma that is roughly distributed about the magnetic equator. Finally, we discuss our findings in the magnetospheric framework proposed in our earlier study
Doppler tomography of the circumstellar disk of
Aims. The work is aimed at studying the circumstellar disk of the bright
classical binary Be star π Aqr.
Methods. We analysed variations of a double-peaked profile of the
Hα emission line in the spectrum of π Aqr
that was observed in many phases during ~40 orbital cycles in 2004−2013. We applied the
discrete Fourier transform (DFT) method to search for periodicity in the peak intensity
ratio (V/R). Doppler tomography was used to study the structure of the disk around the
primary.
Results. The dominant frequency in the power spectrum of the
Hα V/R ratio is 0.011873 day-1, which
corresponds to a period of 84.2(2) days and agrees with the earlier determined orbital
period of the system, Porb = 84.1 days. The V/R shows a
sinusoidal variation that is phase-locked with the orbital period. Doppler maps of all our
spectra show a non-uniform structure of the disk around the primary: a ring with the inner
and outer radii at Vin ≈ 450 km s-1 and
Vout ≈ 200 km s-1, respectively, along with an
extended stable region (spot) at Vx ≈ 225
km s-1 and Vy ≈ 100
km s-1. The disk radius of ≈65   R⊙ = 0.33 AU was
estimated by assuming Keplerian motion of a particle on a circular orbit at the disk’s
outer edge
Zerstoerungsfreie Bestimmung der Uran-235-Anreicherung in Gasultrazentrifugen-Anreicherungsanlagen
SIGLETIB: RN 5906(554) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman