안녕하십니까.

세종대학교 이재우 교수님의 초청으로 진행되는 Chris Sneden (University of Texas at Austin) 교수님의 특별 세미나를 공지드립니다. 세미나는 온라인 형식으로 진행됩니다.

연사 : Prof. Chris Sneden (University of Texas at Austin)

호스트: 이재우 (세종대학교)

장소 : 비대면 세미나

일시 : 8월 12일 (금) 오전 10:30 

접속주소 : https://us02web.zoom.us/j/84597516884?pwd=OHVjOEQra1lSZ242K2tOZWY4T2Nzdz09

제목: The Active Chromospheres of Lithium-Rich Red Giant Stars

초록: 

We have discovered a new observational feature of the rare lithium-rich G-K red giant stars: many of them have very strong neutral helium 10830 A absorption transitions in their spectra.  Most red giants have small Li abundances, but about 1% have surface Li contents that are much larger than predicted from normal stellar evolution events.  He I 10830 absorption provides a surprising new piece of evidence for this puzzle.  While over 90% of the (normal) Li-poor giants have weak He I absorption lines, more than half of the Li-rich stars have deep, very broad 10830 features.  The noble gas helium cannot generate detectable spectroscopic absorption in the photospheres of cool red giants; any 10830 A feature must arise in the hot, disturbed outer chromospheres of these stars. Almost all Li-rich, helium-active giants appear to be red clump or red horizontal-branch objects; very few seem to be on the first-ascent red giant branch. The Li-He combination most probably results from lithium generation and envelope mixing during the otherwise unobservable helium flash.  The Li-rich, He-strong stars are ones who must have experienced this internal cataclysm recently. But some of the Li-rich giants obviously are members of binary stellar systems or are experiencing rapid rotation.  We probably are witnessing "young" helium-burning horizontal branch stars whose outer envelopes are trying to recover from the helium flash, maybe while simultaneously struggling with the disruptive influence of a companion.

진행언어 : 영어

오희영 드림.

Dear all,

On August 12 (Fri) 10:30 am, there will be special seminar by Prof. Chris Sneden (University of Texas at Austin).

Speaker : Prof. Chris Sneden (University of Texas at Austin)

Host: Jae-Woo Lee (Sejong University)

Place : Online Seminar

Schedule : August 12 (Fri) 10:30 am 

Access: https://us02web.zoom.us/j/84597516884?pwd=OHVjOEQra1lSZ242K2tOZWY4T2Nzdz09

Title: The Active Chromospheres of Lithium-Rich Red Giant Stars

Abstract: 

We have discovered a new observational feature of the rare lithium-rich G-K red giant stars: many of them have very strong neutral helium 10830 A absorption transitions in their spectra.  Most red giants have small Li abundances, but about 1% have surface Li contents that are much larger than predicted from normal stellar evolution events.  He I 10830 absorption provides a surprising new piece of evidence for this puzzle.  While over 90% of the (normal) Li-poor giants have weak He I absorption lines, more than half of the Li-rich stars have deep, very broad 10830 features.  The noble gas helium cannot generate detectable spectroscopic absorption in the photospheres of cool red giants; any 10830 A feature must arise in the hot, disturbed outer chromospheres of these stars. Almost all Li-rich, helium-active giants appear to be red clump or red horizontal-branch objects; very few seem to be on the first-ascent red giant branch. The Li-He combination most probably results from lithium generation and envelope mixing during the otherwise unobservable helium flash.  The Li-rich, He-strong stars are ones who must have experienced this internal cataclysm recently. But some of the Li-rich giants obviously are members of binary stellar systems or are experiencing rapid rotation.  We probably are witnessing "young" helium-burning horizontal branch stars whose outer envelopes are trying to recover from the helium flash, maybe while simultaneously struggling with the disruptive influence of a companion.

Language : This talk will be given in English.

Regards,

Heeyoung Oh