Transcript The reduction and analysis of spectra of B stars

Majda Smole and Sanja Tomić
Menthor:Michaela Kraus
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B1 star HD2905 (kap Cas)
B9 star HD202850 (sig Cyg)
We were given raw spectra obtained via
observations starting from 15.8.2009. to
19.3.2011.
Our task was to reduce spectra and then to
analyse it.
B1 HD2905 (kap Cas)
B9 HD202850 (sig Cyg)
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1. subtracting the over-scan, bias and flatfielding
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2. wavelengths calibration
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3. telluric and heliocentric correction
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The over-scan is region of the CCD chip that is not
exposed to the light.
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The over-scan need to be subtracting from all images
(bias, flat-fields, lamps and raw spectra).
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IRAF task fit1d
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Bias frame is dark
frame with almost
zero second exposure.
Bias images are
combined into one
masterbias (imcombine
task).
Imarith task for
subtracting the bias
from all images.
Example of bias in IRAF
A CCD chip exposed to
an uniform light
does not produce
equally uniform image.
 Several flat-fields are
combined into one
master-flat
(imcombine task).
 Images need to be
devided by master-flat
(imarith task).
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Example of flat-field in IRAF
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In order to use
wavelenghts instead of
pixels we had to
identify lines in arc
spectra (ThoriumArgon lamp).
Identify task in IRAF
The calibrated arc
spectrum can be used
to wavelenght calibrate
the object spectra.
Refspec and dispcor
tasks in IRAF.
Example of lamp in IRAF
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Telluric correction is used for removing
absorption and emission of the Earth's
atmosphere.
To do so it is necessary to use fast rotating
comparison star with well known spectra.
We used Regulus and HR7880.
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To make heliocentric
correction we
needed to obtain list
of heliocentric speeds
for our spectra.
λcor=λobs*(1+Vhelio/c)
Exemple of spectra after heliocentric
correction
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1. Identication of lines
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2. Calculating radial velocities
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3. Determination of period of pulsation
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NIST Atomic Spectra Database
a) encyclopedias of lines expected for our stars
b) ionisation energies
c) solar abundances
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Once we knew both theoretical and measured
line proles we were able to calculate radial
velocities.
λm=λth*(1+V/c)
Hα
He I
Hα
He I
Si II 6347Å
Si II 6371Å
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After plotting we saw that there is some
periodical change in radial velocities for some
lines, so the next step was to determine their
period and to fit the sine curve trough the
data.
To determine period of pulsation for
HD202850 we used silicone lines.
Si II 6347Å
Si II 6371Å
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For HD202850 (sig Cyg) we got the
periodicity of 1.59h.
For kap Cas we did not have enough data to
conclude anything.
Our results support the hypothesis that
HD202850 has pulsating atmosphere.
P.North and S.Paltani, HD37151: A new "slowly pulsating B star".
A&A,1994.
 C. Aerts, M. De Pauw and C. Waelkens, Mode identication of pulsating
stars from line profile variations with the moment method.
A&A, 1992.
 Charlotte E. Moore, Ionization potentials and Ionization Limits Derived
from the analyses of Optical spectra. 1970.
 M. Asplund, N. Grevesse and A. J. Sauval, The solar chemical
composition.
 D. J. Lennon, P. L. Dufton and A. Fitzsimmons, Galactic B-supergiants.
A&A,1992.
 N.R. Walborn and E.L. Fitzpatrick, Contemporary optical spectral
classication of the OB stars. A digital atlas. PASP, 1990.
 N. Markova and J. Puls, Bright OB stars in the galaxy. A&A, 2008.
 P.A. Crowther, D.J. Lennon and N.R. Walborn, Physical parameters and
wind properties
 of galactic early B supergiants. A&A, 2006.
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