0 Assigned ID: 228 ----- Attempting Submission 1 (Thu Apr 06 14:11:49 GMT 2017) ----- For the best data quality, it is strongly recommended that the maximum number of allowed FP-POS positions is used when observing at a given COS CENWAVE setting. See full description for details. For the best data quality, it is strongly recommended that the maximum number of allowed FP-POS positions is used when observing at a given COS CENWAVE setting. See full description for details. For the best data quality, it is strongly recommended that the maximum number of allowed FP-POS positions is used when observing at a given COS CENWAVE setting. See full description for details. For the best data quality, it is strongly recommended that the maximum number of allowed FP-POS positions is used when observing at a given COS CENWAVE setting. See full description for details. For the best data quality, it is strongly recommended that the maximum number of allowed FP-POS positions is used when observing at a given COS CENWAVE setting. See full description for details. For the best data quality, it is strongly recommended that the maximum number of allowed FP-POS positions is used when observing at a given COS CENWAVE setting. See full description for details. For the best data quality, it is strongly recommended that the maximum number of allowed FP-POS positions is used when observing at a given COS CENWAVE setting. See full description for details. Run auto-adjust to fix 60 s overrun in every orbit. -1072004688 ----- Attempting Submission 1 (Wed Jul 19 18:58:22 GMT 2017) ----- ----- Attempting Submission 2 (Fri Aug 18 19:04:02 GMT 2017) ----- ----- Attempting Submission 3 (Wed Oct 25 21:10:31 GMT 2017) ----- ----- Attempting Submission 4 (Wed Dec 12 20:52:01 GMT 2018) ----- I'm ignoreing the following warnings: FP-POS splitting: in 12315 we used only FP-POS = 2,3,4, because in FP-POS=1 the Si IV 1393.76 Ang line will very close to the edge of the detector so that is potentially difficult to the fit the continuum on that side of the line. I'm preparing the observations with just FP-POS=2,3,4, but please let me know if you disagree. Testing our scenario of a failed wind for TW Hya Young, accreting low-mass stars show strong, broad and asymmetric FUV emission lines. When multiple observations of the same wavelength region exist, we often see that the flux and profile of these lines change strongly between the observations. Observationally, this is poorly characterized, and theoretically, neither the lines profiles nor their variability can be explained. In 2011 we tried to remedy this situation by monitoring the classical Tauri star TW Hya for 10 orbits with HST/COS. At the time, the literature suggested that the variability could be due to a hot stellar wind and thus we distributed the observations over one month, which would have been the appropriate time scale. As it turns out, this assumption appears to have been wrong. The data we received clearly shows that no hot wind is present and that all variability happens on much shorter time scales. In this proposal, we show that we have done a thorough analysis of the existing data and we have a model to explain it. Now, we ask for additional monitoring of TW Hya to cover the time scale of a few hours - as we now know this is the relevant time scale to understand the variability. We propose to observe the variability of the FUV emission lines in CTTS. With a distance of only 57 pc (Wichmann et al. 1998) TW Hya is the closest bright CTTS and it has a larger FUV flux than any other star of this class, thus it is the prime target to study variability. The large effective area of COS makes this project possible in a reasonable number of orbits. Because of its proximity TW Hya is also the best-studied CTTS (e.g. it has been observed for 700 ks with X-ray gratings on Chandra). We observed TW Hya before in ProgID 12315. The observations here largely copy that setup, so we are confident that there are no safety risks etc to the instrument. We concentrate here on the C IV doublet at 1548/1550 Ang the brightest hot FUV line, which we will observe with the G160M grating, set on central wavelength 1577 Ang. Several other important features are covered in the wavelength range of this grating: i) Si IV 1392/1403 Ang is a second hot ion line we will use for comparison. ii) Si ii 1527/1533 Ang, He II 1640 Ang and C I 1656 A probe the presence of cooler material. iii) Between the lines we obtain a continuum measurement to calculate the mass accretion rate. Unlike our existing observation we will expose in the G160M grating for the entire orbit to better sample the variability (in the previous observations the half of each orbit was spend on NUV exposures). We ask for 7 HST orbits unevenly spaced over about 1.5 days. Each orbit will have an identical layout of observations with target acquisition and four G160M exposures at different FP-SPLIT positions to reduce fixed-pattern noise. According to the ETC TW Hya can be observed in the ACQ/IMAGE mode, if the BOA is used. Thus the target acquisition including initial acquisition, exposures and spacecraft motion requires about 10 min out of 55 min usable orbit time at TW Hya's declination. The existing data (Program ID 12315) shows that the signal-to-noise ratio is very good and there are no safety risks to the instrument. Stellar Physics 6 false false true false false false 0.2 true SUPPORTED STAR T TAURI STAR NO Target coordiantes and propoer motions have been updated to GAIA values. J2000 J2000 COS/FUV Spectroscopic No No G160M 1577 COS/FUV Spectroscopic No No G160M 1577 COS/FUV Spectroscopic No No G160M 1577 COS/FUV Spectroscopic No No G160M 1577 COS/FUV Spectroscopic No No G160M 1577 COS/FUV Spectroscopic No No G160M 1577 COS/FUV Spectroscopic No No G160M 1577 Timing link suitability includes constraints ([02 After 01 by 0.1 to 0.2 days] [03 After 01 by 0.4 to 0.5 days] [04 After 01 by 0.6 to 0.7 days] [05 After 01 by 0.9 to 0.9 days] [06 After 01 by 1.1 to 1.1 days] [07 After 01 by 1.3 to 1.3 days]) The scheduling data was generated by CASM 26.2.2. 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