0 Assigned ID: 5193 ----- Attempting Submission 1 (Mon Mar 25 16:25:14 GMT 2024) ----- HST Phase I Proposal 5193 successfully submitted. Receipt: # 5193-1 Initial Submission. -746071226 ----- Attempting Submission 1 (Wed Jul 31 16:11:37 GMT 2024) ----- Stellar Rotation and Winds for Old Sun-like Stars We propose to use STIS to study the H I Lyman-alpha spectra of four nearby old Sun-like coronal GK stars, to search for signs of astrospheric absorption. The Lyman-alpha astrospheric absorption signature is currently the only means of detecting the coronal winds of cool main sequence stars, and HST is the only observatory that has ever been capable of observing it. The project will allow us to explore the future of our own Sun's wind. In addition, one of our targets, HD 166620, appears to have an interrupted activity cycle, possibly analogous to the "Maunder minimum" state that the Sun went through in the 1600s. Thus, the HD 166620 data could tell us what the solar wind was like then. A particular area of scientific interest is the phenomenon of "weakened magnetic braking", recently discovered from analyses of Kepler data, indicating a significant change in stellar rotation evolution at late stellar ages. All of our chosen targets have existing or expected ground-based spectropolarimetric constraints, which when combined with HST mass loss measurements will allow us to determine if the weakened magnetic braking is due to dramatically weaker winds or fundamental changes in stellar magnetic morphology. Table 1 in the proposal lists the 4 GK dwarfs that we plan to observe with STIS for 1-2 orbits each. Note that COS cannot be used for Lyman-alpha studies due to obscuration by geocoronal Lyman-alpha caused by the large COS aperture, so STIS is our only option. Our project is focused on detecting and measuring astrospheric absorption in the H I Ly-alpha line, but confidence in this analysis is significantly improved with information provided by observations of the MgII h & k lines near 2800 A, so we will be obtaining an E230H spectrum of the 2574-2851A wavelength range for each of our targets, through the 0.2"x0.09" aperture. Such an observation already exists for Tau Ceti, so we will not make the E230H exposure for this star. The Mg II lines provide two benefits. The first is that the ISM Mg II absorption lines are much narrower than the ISM H I and D I lines, allowing us to discern multiple velocity components in the ISM towards our stars, which we can then account for in our analysis of the Lyman-alpha line. The second benefit is that the Mg II emission lines are highly opaque chromospheric lines like Lyman-alpha, and so provide useful guidance for what the intrinsic stellar Lyman-alpha lines should look like. This is useful considering that the stellar Lyman-alpha profile is always greatly obscured by the broad ISM absorption (see Figure 2). After the E230H exposure (if done), the rest of the observing time will be used for an E140M spectrum of the 1150-1700 A wavelength range through the 0.2"x0.2" aperture, which will contain the primary line of interest: H I Ly-alpha at 1216 A. All but one of our targets are comfortably in compliance with STIS/MAMA bright object limits, as verified using both Table 13.45 in the STIS Instrument Handbook and the online STIS exposure time calculator. The exception is Beta Hyi. The E230H exposure for this star exceeds the total image count rate limit unless we replace the 0.2"X0.09" aperture with the tiny 0.1"x0.03" slit. The E230H observation will provide the highest resolution (R= \lambda/\Delta\lambda = 110,000) spectrum of the Mg II lines. After target acquisition we will perform an ACQ/PEAK peakup observation to accurately center the target in the narrow 0.2"x 0.09" slit (or the smaller slit for Beta Hyi), thereby maximizing the accuracy of our wavelength calibration, important for both this spectrum and the following E140M spectrum. The E140M grating does not have quite the resolution of E230H, but its R=45,800 resolution is good enough to study the H I Ly-alpha line profile in the detail that we require. Previous studies provide many examples of Mg II and Ly-alpha spectra of inactive GK dwarfs (Wood et al. 2021). The chromospheric Mg II and H I Ly-alpha lines are very bright even for inactive GK dwarfs, so we have high confidence that we can acquire high-quality Mg II and Ly-alpha spectra in only 2 orbits, or just 1 in the case of Tau Ceti where we do not need Mg II. The PI, Dr. Brian Wood, has extensive experience in the analysis of stellar UV spectra taken by HST, including the study of astrospheric Lyman-alpha absorption that is the subject of this proposal. Co-I Hans Mueller has an extensive background in modeling the wind/ISM interaction regions of the Sun and stars, which is necessary to interpret any detected astrospheric absorption in the HST data. Co-I Seth Redfield has an extensive background studying the local ISM, including the analysis of ISM absorption lines observed in HST spectra. Co-I Travis Metcalfe is an expert in stellar angular momentum evolution, including the research on weakened magnetic braking that is motivating this proposal. Stellar Physics and Stellar Types 6 false true false false false false SUPPORTED STAR G V-IV This object was generated by the targetselector and retrieved from the SIMBAD database. GJ71 TAU-CETI J2000 J2000 G8-V, B-V=0.72 STAR G V-IV This object was generated by the targetselector and retrieved from the SIMBAD database. GJ19 BETA-HYI J2000 J2000 G0-V, B-V=0.62 STAR K V-IV GJ764 SIGMA-DRA J2000 J2000 K0-V, B-V=0.78 STAR K V-IV This object was generated by the targetselector and retrieved from the SIMBAD database. GJ706 J2000 J2000 K2-V, B-V=0.87 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/NUV-MAMA Spectroscopic No No E230H 2713 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/NUV-MAMA Spectroscopic No No E230H 2713 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/NUV-MAMA Spectroscopic No No E230H 2713 STIS/FUV-MAMA Spectroscopic No No E140M 1425 The scheduling data was generated by CASM 32.1.1. 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