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Session 49 - Young Stellar Objects.
Display session, Tuesday, January 14
HR 5999 is one of the nearest Herbig Ae stars (d=130 pc). The star is apparently viewed through its circumstellar disk and thus represents a young \beta Pic analog in both stellar characteristics and in system inclination. Previous UV and optical studies have noted the presence of variable, high velocity, accreting gas with profiles similar to \beta Pic. Like other Herbig Ae/Be stars, the accreting gas species seen toward HR 5999 include neutral, atomic gas with comparatively short photoionization lifetimes in the stellar radiation field. Together with the large observed velocities, the presence of such species indicates that we view material recently sublimated from unseen, solid bodies which are plausibly on star-grazing orbits. UV spectra indicate that the acreting gas contains dissociation products of silicates, mildly refractory material including Zn II, and volatiles, as has also been demonstrated for the Herbig Be star HD 100546. The IUE data for HR 5999 suggest comparable covering factors for the silicon dissociation products, indicating that the silicates more closely resemble those seen in the \beta Pic disk. We present the results of coordinated ISO SWS (2.5-45 \mum) and IUE observations made in August 1996, and compare the HR 5999 data with similar observations for other Herbig Ae/Be stars.
This study was supported by NASA Contracts S78611Z and NASW 4756 to Eureka Scientific. IUE data analysis was carried out at the IUE Data Analysis Center located in the Laboratory for Astronomy amp; Solar Physics, NASA/GSFC. ISO data analysis was carried out at the Infrared Processing amp; Analysis Center located at Caltech.
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