Spectroscopic Studies Of The Stellar Atmospheres Of Iota Herculis
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Date
2015-08
Authors
MD. SAID, NOOR MASDIANA
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Abstract
This study on iota Herculis, a B3 IV star, has three purposes: 1) Correlation
between microturbulence and nonradial pulsations, 2) Correlation between subphotospheric
iron convection zone (FeCZ) and the fluctuations of central depth of S II
(5453.810 Å) line profile, and 3) Determination of the pulsation periods of iota Herculis.
This research was conducted using 144 spectra of iota Herculis taken from the archive
data of Haute Provence Observatory (ELODIE), France, and 47 spectra from the archive
data of Ritter Observatory, United States of America. Our first objective was to compare
the curves of microturbulent velocities with the curves of heliocentric radial velocities
(HRV) of iota Herculis which we assumed to be nonradial pulsations velocities. For both
archives data, the measurements of microturbulent velocities and HRV were done using
the full width at half maximum of the line profile for Doppler broadening and the
rvidlines subroutine of IRAF software respectively. Both sets of curves of HRV and
microturbulent velocities showed an identical pattern, that is, the HRV curves will
increase when the microturbulent velocity curves increase and vice versa. The second
objective was to compare the graphs between the fluctuations of the central depth of S II
line profile (obtained using IRAF) with the fluctuations of microturbulent velocities. The
central depth of S II line profile became deeper with the increasing microturbulent
velocities and vice versa. The pulsation periods of iota Herculis for the archive data of
Ritter Observatory were obtained by using the Phase Dispersion Minimization (PDM)
technique. We found two pulsation periods of iota Herculis; the 112.9 days period which
is close to the orbital period of 112.7175 days observed by Kodaira (1971), and the 1 day
period which is similar to the pulsation period observed by Smith (1981). From the data
analysis, we have derived three conclusions: (1) The correlation between microturbulence
and nonradial pulsations in iota Herculis is due to the gravity waves which drive the
nonradial pulsations and induce the microturbulence, (2) The sub-photospheric iron
convection zones (FeCZ) are related to the microturbulence phenomenon, stellar
temperature, and the fluctuations of the central depth of S II line profile of this star and
(3) The 1 day pulsation period that we found has led us to a confirmation that iota
Herculis can be considered as a Slowly Pulsating B-type star (SPB).
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Keywords
Spectroscopic Studies Of The Stellar Atmospheres , Of Iota Herculis