0 Assigned ID: 259 ----- Attempting Submission 1 (Thu Apr 04 20:13:43 GMT 2019) ----- HST Phase I Proposal 259 (rgwinds.apt) successfully submitted. Receipt: # 259-1 Changed ACQ observation to use the F25ND5 filter. Changed from ACCUM to TIME-TAG mode. -67821887 ----- Attempting Submission 1 (Fri Jul 19 18:28:56 GMT 2019) ----- HST Phase II Proposal 15904 (rgwinds_phase2_v1.apt) successfully submitted. Receipt: # 15904-1 ----- Attempting Submission 2 (Mon Sep 23 19:55:45 GMT 2019) ----- Spatially Resolving the Winds of Red Giant Stars We propose to use long-slit STIS/G140M spectroscopy to spatially resolve red giant winds for the first time. Specifically, we will study the H I Lyman-alpha wind scattering around two red giant stars, Alpha Tau (K5 III) and Gamma Cru (M3.5 III). This project is stimulated by the very recent realization that in existing STIS/E140M spectra of these giants and others, the Lyman-alpha emission is to a large extent uniformly filling the 0.2x0.2 arcsecond STIS aperture, especially for the M giants. The only obvious way to explain this surprising result is to propose that H is actually ionized close to the stars, only becoming neutral far from the star (>10 R_star). Such a picture could dramatically alter our understanding of red giant winds, potentially increasing mass loss rate estimates for such stars by over an order of magnitude. Our proposed new observations will determine exactly how far the Lyman-alpha scattering region truly extends around K and M giants. In combination with constraints on the winds from existing STIS echelle spectra, we will be able to make more accurate mass loss rate measurements, involving better constrained assessments of wind temperature and ionization structure. Finally, as these winds are known to be variable, we could potentially be able to detect and study spatial structure in red giant winds for the first time. We propose to observe the Lyman-alpha lines of alpha Tau (K5 III) and gamma Cru (M3.5 III) for 4 orbits each with the G140M grating (1222 setting) through the 52" x 0.2" long slit. Both targets are comfortably in compliance with STIS/MAMA bright object limits, as verfied using both Table 13.44 in the STIS Instrument Handbook and the online STIS exposure time calculator. After acquisition and overheads are considered, we expect our 4-orbit G140M exposures to amount to about 180 minutes of total exposure per target. This information can be combined with the Lyman-alpha scattering model shown in Figure 4 to estimate expected signal-to-noise (S/N) for our planned observations, as a function of distance along the slit. The STIS exposure time calculator predicts S/N=10 for a surface brightness of sigma_lambda=2e-13 ergs/cm2/s/A/arcsec2, corresponding to distances from the star of roughly 20 AU (0.98") and 30 AU (1.11") for alpha Tau and gamma Cru, respectively, according to Figure 4. These two distances correspond to roughly 85 R_* for both stars, meaning that it is entirely possible that we may actually be able to detect scattered wind emission at >100 R_* from each star. The exposure time calculator suggests a detectable S/N=3 down to sigma_lambda=2.5e-14 ergs/cm2/s/A/arcsec2, though at that point the limiting factor may be the brightness of the extended wings of the PSF of the bright emission from close to the star. We considered using the 0.5" occulting bar available with the 52" x 0.2" slit in order to block the stellar chromospheric flux, but ultimately decided against it. The PSF wings of the chromospheric emission will be a potentially significant contaminant for the circumstellar wind-scattered flux in which we are interested. Blocking this emission would simplify the analysis and maximize the spatial extent to which we might detect the scattered flux, but it would also obscure the spatial flux profile close to the star, which is a region that is very much of interest. Thus, we ultimately decided not to use the occulter, meaning we will have to utilize deconvolution procedures to derive a true spatial flux profile from the observed one, which is convolved with the spatial PSF. We note that there is already a G140M Lyman-alpha spectrum of a white dwarf (WD1056-384) in the HST archives made through the 52" x 0.2" long slit, which will provide an excellent empirical point source PSF for our purposes. Dr. Brian Wood has extensive experience in the analysis of UV observations from HST. Dr. Graham Harper is an expert on observational and theoretical studies of red giants and supergiants, particularly their winds. Dr. Hans Mueller has a long history of studying solar/stellar winds and their interactions with the ISM. Stellar Physics 6 false false true false false false false SUPPORTED STAR K III-I WIND ALPHA-TAU ALDEBARAN J2000 J2000 TYPE=K5III, F-LINE(1216)=4.7+/-0.5E-11, W-LINE(1216)=2.5 STAR M III-I WIND GAMMA-CRU J2000 J2000 TYPE=M3.5III, F-LINE(1216)=1.2+/-0.2E-11, W-LINE(1216)=3.0 STIS/FUV-MAMA Spectroscopic No No G140M 1222 STIS/FUV-MAMA Spectroscopic No No G140M 1222 /tmp/OPVisit3543638495010727683.xml The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15904 :visit-id "01" :proposal-version -1 :trans-version "20190514" :date "23-Sep-2019 15:52:45.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 904928 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15904 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15904 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2763 :al-overhead-at-end 0 :internal-dur-at-end 178 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3156 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15904 :visit-id "01" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2854 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3156 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15904 :visit-id "01" :orbit-number 3 :pcs-time 302 :si-vis-utilization 2854 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3156 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15904 :visit-id "01" :orbit-number 4 :pcs-time 302 :si-vis-utilization 2854 :al-overhead-at-end 0 :internal-dur-at-end 622 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3156 :pcs-gap 0 ) true 4 0 /tmp/OPVisit2828366298969189321.xml The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. 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