Subaru Seminars



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The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Subaru seminar organizers (Tomonori Usuda, Kumiko S. Usuda, Naoyuki Tamura) by email : (please change"_at" to @).

October 28th, Wednesday at 10:30 am

" Be-shell stars and the near UV spectroscopy of hydrogen "

Tomokazu Kogure (Kyoto University)

In near UV region (λλ3400 ~4000Å) Be-shell stars show two remarkable features (1) the appearance of sharp absorption lines in the Balmer higher members (H10 to even H37) and (2) strong Balmer discontinuity as compared to that of normal B stars. Both features reveal the existence of an optically thick region in front of the stellar disk. Based on the absorption line analysis we can estimate the optical depth τ(Hα) and the fractional area β of this region relative to the stellar disk (Kogure and Leung 2007). Balmer discontinuity increases in the shell phase serving as an indicator of the shell activity (Moujtahid et al. 1998). Long-term variation of shell activity in both features is compared in two cases of Be-shell stars, Pleione and EW Lacertae. In both stars it is found that when the optical depth τ(Hα) is high, the discontinuity is also high. In addition, remarkable results are (1) shell activity occurs even in slowly rotating stars with small V sin i, and (2) the covering fractional area β often reaches as high as unity From these behaviors, we suggest that Be-shell stars are not necessarily the equator-on stars surrounded by vertically thin disk-like envelopes. Instead, the optically thick region often expands sufficiently high from the equatorial plane, and shell activity occasionally appears in Be stars with smaller inclination angles. (Kogure, T. and Leung, K. C. 2007, Astrophysics of Emission Line Stars Springer, Chapters 4 and 5 / Moujtahid, A. et al. 1998, A&A, S.129, 289)

" Three years photometric and spectroscopic observations of Nova V1280 Sco "

Kozo Sadakane (Osaka Kyoiku University)

We have continuously monitored Nova V1280 Sco (Nova Sco 2007 #1) at Osaka Kyoiku University since its explosion (2007, February). The observed light curve shows some unusual features. Its V (visual) and y (yellow) magnitudes remain bright (around 10 mag.) 800 days after the optical maximum. The bright y magnitude indicates that the Nova is still dominated by the continuous radiation. In 2009, we observed the Nova with the High Dispersion Spectrograph (HDS) of the Subaru telescope in order to examine the nature of the continuous radiation. Unexpectedly, we have discovered highly blue-shifted (from -900 to -650 km/s) multiple sharp absorption components of the Na I D2 and D1 lines. Some of the sharp components had deepened during the two months period from 2009 May to July. We discuss the origin of the mysterious absorptions observed in V1280 Sco.

Seminars are also held at JAC, CFHT, and IfA.

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