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2010 CFHT Users Meeting
November 16-18, 2010
ASIAA Auditorium, Taipei, Taiwan

Poster Presentation

Time resolved spectrocsopic analysis of the roAp star 33 Lib

Author(s): M. Sachkov (INASAN), M. Hareter (Vienna University), T. Ryabchikova (INASAN, Vienna University), G. Wade (Department of Physics, Royal Military College of Canada), O. Kochukhov (Uppsala University), W.W. Weiss (Vienna University)

Presenter: Gregg Wade (Royal Military College)

Spectroscopy provides 3D resolution of modes in rapidly-oscillating Ap (roAp) stars and allows us to search for pulsational frequencies that are undetectable photometrically. On the other hand, space photometry provides a very high precision measurement of pulsation frequencies and enables an accurate phasing of multi-site spectroscopic data. A combination of simultaneous spectroscopic and photometric data represents the most sophisticated asteroseismic dataset for any roAp star.

In 2009 the roAp star 33 Lib became the target of an intense observing campaign, that combined ground-based spectroscopy and the space photometry obtained with the MOST satellite. We collected 780 spectra with the ESPaDOnS spectrograph attached at the 3.6-m CFHT telescope and 374 spectra obtained with FIES spectrograph attached at the 2.56-m NOT telescope to perform time-resolved spectroscopy of 33 Lib. In addition, we used 111 UVES spectra (2004) from the ESO archive to check mode stability.

Frequency analysis of the new radial velocity (RV) measurements based on the ESPaDOnS and FIES data confirmed previously the reported frequency pattern (two frequencies: 2.015, 1.769 mHz and the first harmonic of the main frequency) and revealed an additional frequency at 1.991 mHz, which was not resolved before (in 2004) in 2 hours of monitoring with UVES. 33 Lib is one of a few roAp stars in which different spectral lines show different sets of frequencies. The lines of the rare-earth elements (REE) have the richest frequency spectrum. These lines are formed in the upper atmospheric layers. All three independent frequencies found in the RV analysis of Pr and Nd lines, while only two frequencies appear in the RV variation of the Halpha core and only one frequency is resolved by photometry and by the RV variations of other lines formed deeper in the atmosphere.

The results of our analysis show that the amplitudes of the newly derived frequency, as well as of the frequency at 1.769 mHz, drop faster with atmospheric depth than does the amplitude of the principal frequency at 2.015 mHz, thus explaining their non-detection in the photospheric layers. This phenomenon was first discovered by Kurtz et al. (MNRAS, 370, 1274, 2006) in the atmosphers of few roAp stars. 33 Lib is one of only two roAp stars with a detected pulsation node in the upper atmosphere. Simultaneous spectroscopic and photometric monitoring allow us to derive the phase lag between the maxima of luminosity and RV variations of lines of different chemical species. This phase lag is the same as in the roAp star 10 Aql - another object with the detected pulsation node in the atmosphere. The new frequency solution fits perfectly the RV variations from 2004 and 2009 observational sets, providing a strong support to the p-mode stability in
33 Lib for at least 5 years.

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