The Be Star Newsletter, Volume 40 - September 2011
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Ca II K line profile in the latest Be-epoch of PleioneJun-ichi Katahira1, Kazutoshi Inoue2, Yoshihito Kawabata3, and Tetuya Kawabata4
Pleione (28 Tau, HD23862; B8IVe) is a well-known classical Be star in the Pleiades cluster, and has a high rotational velocity V sin i of almost 300 km s-1 (Chauville et al. 2001). During the past 80 years, this star has shown three times the successive formation of the equatorial circumstellar disk with a period of about 34 years, which started at 1938, 1972 and 2005, respectively (Hirata 1995, Tanaka et al. 2007). After the beginning of circumstellar disk formation, Pleione usually develops a Be-shell phase and a subsequent Be phase. Gulliver (1977) found a wide and shallow profile of Ca II K line just before the beginning of Be-shell phase at 1972, and concluded that the appearance of a weak and broad component of Ca II K line is a precursor of new disk formation. In 2002 March we started on monitoring the Ca II K line to find a new disk formation at the Bisei Astronomical Observatory (BAO). Before finding a wide and shallow profile of Ca II K line at 2005 December (Tanaka et al. 2007), we have observed the Ca II K line of Pleione three times, when we had the similar feature as Gulliver (1977) observed at the previous Be phase in 1969–1970, and recognized no existence of the wide and shallow feature. However, from the obtained three profiles we now suppose that the Ca II K line had an emission component in the late epoch of the previous Be phase. In the following we report the profiles of the Ca II K line in the late Be epoch of Pleione, together with the high-dispersion observations, and discuss a variation of the profile in 2000–2004. The observations at the BAO were carried out with a mid-dispersion spectrograph of spectral resolution power of about 10000, attached to the folded Cassegrain focus of 101cm reflector. The detector was a LN2-cooled AstroCam4200 CCD, by which a 400 Å region was obtained. We got two frames of the Ca II K line spectral region with the exposure time of 600 s on 2002 March 19, three frames with the 600 s exposure on 2003 November 16, and three frames with the 1200 s exposure on 2004 December 21, respectively. The obtained Ca II K profiles are plotted in Fig. 1a. The S/N ratio of the profiles is estimated to be in 280–380. For the profiles in the previous years, the high-dispersion profiles of the Ca II K line in 2000–2002 are obtained from the ELODIE library v3.1 (Prugniel et al. 2007). For each observation epoch in the database the original profiles are processed by a simple averaging method, and the resultant mean profile is renormalized as to the modified continuum level of a straight line to obtain the final profile of Ca II K line. In addition, the profile on 2003 September 27 is taken from the SMOKA database (Baba et al. 2002), which was observed by the High Dispersion Echelle spectrograph (HIDES). These profiles are drawn in Fig. 1b, where we tentatively add a synthetic photospheric spectrum to see the photospheric and circumstellar contributions. According to the stellar fundamental parameters of Chauville et al. (2001), the synthetic one is simulated by the 'SPTOOL' soft based on the ATLAS9 (released by Y. Takeda, National Astronomical Observatory of Japan), and that is renormalized at the intensity-levels of the far wings of the Ca II K line to match the profiles presented here.
Figure 1. (a) Ca II K line profiles observed with the mid-dispersion spectrograph at the Bisei Astronomical Observatory (BAO) in 2002 March– 2004 December. (b) Ca II K line profiles from high-dispersion in 2000 January–2003 September. The data are taken from ELODIE library v3.1 (Prugniel et al. 2007) in 2000–2002, and SMOKA database (Baba et al. 2002) in 2003. The swells on both sides of interstellar component are indicated by upward arrows. In Fig. 1 we find the interstellar component of the Ca II K line at a glance, and recognize the existence of the swells of profile on both sides of the interstellar component (indicated by upward arrows in the figures). The synthetic photospheric spectrum suggests that the swells of Ca II K lines mostly fill the photospheric component, and that the photospheric component is traced only at a 3930.5 Å region of the wing. Especially in 2000, a structure of the swells above the photosperic component has a marked characteristic, i.e., the blueward swell is very stronger than the redward one. So, a similar profile among the Fe II emission lines (V ≫ R) is easily found in the ELODIE spectra in 2000. Moreover, it is noted that the Na I D resonance lines have almost same emission features as the Ca II K line in spite of the severe contamination of the atmospheric lines. These may show a reality of the swells of Ca II K line. To see an overall variation of Ca II K profile in 2000–2004, we make a convolution of high-dispersion profiles plotted in Fig. 1b, with a Gaussian function estimated from a comparison spectrum of BAO. The resultant profiles are plotted in Fig. 2a together with the BAO profiles. The convoluted synthetic spectrum is also added. We notice that there is some tendency for the ratio of the blueward to redward swell intensities to vary between 2000 and 2004, i.e., the blueward swell intensity is stronger than the redward swell intensity in 2000, and the intensities of two swells are nearly equal in 2004.
Figure 2. (a) Ca II K line profiles from the convoluted high-dispersion (red lines) and mid-dispersion in 2000–2004. Upward arrows show the swells on the both sides of the interstellar component. (b) V/R variation of strong Fe II emission lines and the change of the intensity ratio of Ca II K swell-components. The data sources are given in the text. Since such a tendency for the two swell intensities of Ca II K profile is similar to the V/R variation of the double peak emission intensities of the Fe II lines in 2000–2004, we compare a variation of intensity-ratio of two swells of Ca II K with the V/R variation of Fe II lines. In Fig. 2b the values of intensity-ratio for two swells of Ca II K line are plotted over the V/R variation of eight strong Fe II emission lines. The intensity ratios for the swells of Ca II K are directly read out from Fig. 2a without a correction of the photospheric component. The data for the Fe II emission intensities are obtained from Iliev (2000), Saad et al. (2006), Rivinius et al. (2006), the archived data referred in Fig. 1b, and our observations at the BAO. As the time variation for the ratio of the swell intensities of Ca II K line in Fig. 2b is alike to the V/R variation of the Fe II emission lines, we think that the swells on both sides of the Ca II K interstellar component are composed of the double emission components. If such an imagination is real, the observations plotted in Fig. 1 firstly show an appearance of the emission component of Ca II K in the late Be epoch. And, an emission component of Ca II K line may be formed in the circumstellar disk together with the emission component of Fe II lines. We discussed a reliability for an existence of the Ca II K emission in the late Be phase from the profiles plotted in Fig. 1. As the number of the reported profiles is small, a confirmation of the emission component may be not sufficient. Perhaps, because of its weakness of an emission intensity, the emission may be overlooked until now. We earnestly propose to research the spectral data-archive observed in the previous Be phase. References: Baba, H., Yasuda, N., Ichikawa, S., et al. 2002, eds. D. A. Bohlender, D. Durand, & T. H. Handley, ASP Conference Series, Vol. 281, 298 Chauville, J., Zorec, J., Ballereau, D, et al. 2001, A&A, 378, 861 Gulliver, A.F. 1977, ApJS, 35, 441 Hirata, R. 1995, PASJ, 47, 195 Iliev, L. 2000, eds. M. A. Smith, H. F. Henrichs, & J. Fabregat, ASP Conference Series, Vol.214, 566 Prugniel, P., Soubiran, C., Koleva, M., & Le Borgne, D. 2007, arXiv:astrp-ph/0703658V1 Rivinius, Th., Štefl, S., & Baade, D. 2006, A&A, 459, 137 Saad, S. M., Kubát, J., Korčáková, D., et al. 2006, A&A, 450, 427 Tanaka, K., Sadakane, K., Narusawa, S., et al. 2007, PASJ, 59, L35 |