The reduction and analysis of spectra of B stars

1. The reduction and analysis of spectra of B stars Majda Smole and Sanja Tomić Menthor:Michaela Kraus

2. Ondřejov Observatory • 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.

3. Ondřejov Observatory B1 HD2905 (kap Cas) B9 HD202850 (sig Cyg)

4. Reduction of the spectra • 1. subtracting the over-scan, bias and flat-fielding • 2. wavelengths calibration • 3. telluric and heliocentric correction

5. Subtracting the over-scan • 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

6. Subtracting the bias • 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

7. Flat-fielding • 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 flat-field in IRAF

8. Wavelength calibration • 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. Example of lamp in IRAF

9. Telluric correction • 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.

10. Heliocentric correction • 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

11. Analysis of the spectra • 1. Identication of lines • 2. Calculating radial velocities • 3. Determination of period of pulsation

12. Identication of lines • NIST Atomic Spectra Database a) encyclopedias of lines expected for our stars b) ionisation energies c) solar abundances

13. Calculating radial velocities • Once we knew both theoretical and measured line proles we were able to calculate radial velocities. • λm=λth*(1+V/c)

14. HD2905 (kap Cas) Hα He I

15. HD202850 (sig Cyg) Hα He I

16. HD202850 (sig Cyg) Si II 6347Å Si II 6371Å

17. Determination of period of pulsation • 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.

18. Determination of period of pulsation Si II 6347Å Si II 6371Å

19. Results • 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.

20. References • 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 fromline profile variations with the moment method. A&A, 1992. • Charlotte E. Moore, Ionization potentials and Ionization Limits Derived from theanalyses 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 theOB 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.

21. Thank you!