Nearby Alpha Centauri contains the two best characterized G and K dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved angular diameters, and well understood co-evolutionary state. Alpha Cen A & B also have the best studied stellar X-ray activity cycles, extending back to the 1970’s. Present proposal is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual HRC-I pointings in Cycles 13-15, as solar twin A is expected to be rising to cycle maximum from an extended coronal recession. STIS E140M spectra will support and leverage the broad-band X-ray measurements by probing subcoronal dynamics and providing a low-T boundary condition for DEM modeling, with connection to HRC through the FUV Fe XII coronal forbidden line. The STIS observations are straightforward. Alpha Cen falls in the HST Continuous Viewing Zone numerous times during the year, allowing the two stars to be captured in a single visit of just two orbits. Two such visits (four orbits total), about six months apart, are contemplated for Cycle 20, compatible with the semiannual pointings by Chandra. There is no need to strictly coordinate the FUV and X-ray visits, because the FUV Fe XII coronal forbidden line can tie the STIS observation into the X-ray framework. In each HST/STIS visit, the binary companions are observed sequentially, beginning with Alp Cen A, the brighter of the two stars. The target is acquired with the CCD and F25ND5, followed by a 4.3 ks exposure with the E140M-1425 medium-res echelle through the photometric slot (0.2′′ ×0.2′′ ), which delivers R∼40,000 and good sensitivity (peak S/N∼ 60 per resol at the tops of the important Si IV and C IV resonance lines). The observation is split into three subexposures to mitigate instrumental drifts. The exposure depth is sufficient to capture the key Fe XII λ1242 coronal forbidden line, which as mentioned earlier is used to tie the STIS FUV measurements into the X-ray timeline. Following the E140M exposure, a ~5" offset manuever is performed to Alp Cen B, and a peak-up is performed in dispersed light (G430L) with the 0.3x0.05ND filtered slit to precisely locate the target. This particular slit was chosen because the default peak-up sweeps out a sufficient area (0.3"x0.3") to capture the B component, given that the time-dependent separation of the binary companions is accurately known (to the 0.1" level; based on five years of measurements by Chandra HRC-I). After the peak-up, a second 4.3 ks E140M exposure through the photometric aperture is obtained on B. Given that the AB orbital separation is changing relatively rapidly in the present epoch, Alp Cen B was specified as two separate targets, with different offsets, to reflect the orbital evolution over the six months between the two STIS visits. COOL STARS 12 false 0.0 0.0 false false false false SUPPORTED STAR G V-IV The target coords for epoch 2011.997 were measured directly from a high-precision Chandra HRC-I image, and include the parallactic shift at that time. The effective proper motion of Alpha Cen A was determined from the best-fit track of that component, based on most recent two years of HRC-I measurements (the orbit is near periaston, where the apparent proper motion of both companions is most affected by the orbital component). The coords (advanced slightly to epoch 2012.0) and PMs differ minimally from those cited in SIMBAD, even though the catelogue values were measured in an earlier epoch when the relative orbital motion was different. ALP-CEN-A J2000 J2000 FUV peak fluxes are 5E-12 per Angstrom (excluding Lyman-alpha, which is ~ 8E-11) STAR G V-IV ALP-CEN-B J2000 STAR G V-IV ALP-CEN-B J2000 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. This is first CVZ opportunity roughly 6 months after visit 2 of program 12758 (of which this is second year continuation) (Tic-Visit :proposal-id 13060 :visit-id "10" :proposal-version -1 :trans-version "20120604" :date "04-Jul-2012 14:27:02.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 488704 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13060 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :cvz T :proposal-id 13060 :visit-id "10" :orbit-number 1 :pcs-time 333 :si-vis-utilization 10773 :al-overhead-at-end 0 :internal-dur-at-end 375 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 0 :low-sky "N" :pcs-visibility 0 :pcs-gap 0 ) true 2 0 Castelli and Kurucz Models:G2V;Time to Saturation (for a single exposure) = 2.3 seconds ; Optimum SNR = 179 input=StarCAT ETC file for ALP-CEN-A; Exposure time= 4.3 ks at wavelength 1393.80 Å gives: SNR = 58 (per resol); Brightest Pixel (at 1215.40 Å)= 1.8 cps; peak S/N~200 at Lyman-alpha dispersed light peak-up assuming Castelli-Kurucz Models K0V, V=1.33 mag: at wavelength 5000 Å in 0.1 s, SNR ~ 15 (per resol); Time to Saturation (for a single exposure) ~ 60 seconds. ETC calculation done with 52x0.05 slit, then scaled to 0.3x0.05ND aperture by factor 0.001 (ND=3), as verified by comparing throughputs indicated by separate ETC TARG ACQ runs (without disperser) with ND ap and clear apertures. ETC run is for ALP-CEN-A, which has very similar spectrum to ALP-CEN-B in observed flux densities The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13060 :visit-id "11" :proposal-version -1 :trans-version "20120604" :date "04-Jul-2012 14:27:05.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 488704 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13060 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :cvz T :proposal-id 13060 :visit-id "11" :orbit-number 1 :pcs-time 333 :si-vis-utilization 10773 :al-overhead-at-end 0 :internal-dur-at-end 375 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 0 :low-sky "N" :pcs-visibility 0 :pcs-gap 0 ) true 2 0 Castelli and Kurucz Models:G2V;Time to Saturation (for a single exposure) = 2.3 seconds ; Optimum SNR = 179 input=StarCAT ETC file for ALP-CEN-A; Exposure time= 4.3 ks at wavelength 1393.80 Å gives: SNR = 58 (per resol); Brightest Pixel (at 1215.40 Å)= 1.8 cps; peak S/N~200 at Lyman-alpha dispersed light peak-up assuming Castelli-Kurucz Models K0V, V=1.33 mag: at wavelength 5000 Å in 0.1 s, SNR ~ 15 (per resol); Time to Saturation (for a single exposure) ~ 60 seconds. ETC calculation done with 52x0.05 slit, then scaled to 0.3x0.05ND aperture by factor 0.001 (ND=3), as verified by comparing throughputs indicated by separate ETC TARG ACQ runs (without disperser) with ND ap and clear apertures. ETC run is for ALP-CEN-A, which has very similar spectrum to ALP-CEN-B in observed flux densities