Majda Smole and Sanja TomićMenthor:Michaela Kraus

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)

1. subtracting the over-scan, bias and flat-fielding

2. wavelengths calibration

3. telluric and heliocentric correction

The over-scan is region of the CCD chip that is not exposed to the light.

The over-scan need to be subtracting from all images (bias, flat-fields, lamps and raw spectra).

IRAF task fit1d

Example of bias in IRAF

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 flat-field 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).

Example of lamp in IRAF

In order to use wavelenghts instead of pixels we had to identify lines in arc spectra (Thorium-Argon lamp).

Identify task in IRAF The calibrated arc

spectrum can be used to wavelenght calibrate the object spectra.

Refspec and dispcor tasks in IRAF.

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.

To make heliocentric correction we

needed to obtain list of heliocentric speeds

for our spectra.

λcor=λobs*(1+Vhelio/c)

Exemple of spectra after heliocentriccorrection

1. Identication of lines

2. Calculating radial velocities

3. Determination of period of pulsation

NIST Atomic Spectra Database

a) encyclopedias of lines expected for our stars

b) ionisation energies

c) solar abundances

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

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

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.