E140M exposure times modified for APT2023.5.1 2-OCT-2023: E140M and E230H wavecal exposures shortened (to 15s and 10s, respectively) after discussions with STScI staff. Time saved added to final E140M (Alp Cen B) of each visit. 13-FEB-2024: updated coordinates and proper motions for Alp Cen A to epoch 2025.0 for revised scheduling in SEP '24 (Visit 10) and FEB '25 (Vistit 11), and revised text to remove discussion related to the original deeper wavecal exposures (previously reverted to the defaults in Oct '23). 08-AUG-2024: modified original Visit 11 to remove CVZ and ORIENT constraints; new Visit 50 to replace failed Visit 10 (also with CVZ and ORIENT constraints removed) 1569160320 ----- Attempting Submission 1 (Mon Aug 21 20:56:54 GMT 2023) ----- HST Phase II Proposal 17405 successfully submitted. Receipt: # 17405-1 ----- Attempting Submission 2 (Fri Aug 25 17:21:45 GMT 2023) ----- ----- Attempting Submission 3 (Mon Oct 02 21:35:01 GMT 2023) ----- ----- Attempting Submission 4 (Wed Feb 14 02:52:18 GMT 2024) ----- ----- Attempting Submission 6 (Thu Aug 08 13:49:15 GMT 2024) ----- The targets are bright stars, which saturate the target confirmation charts. (Note: this is the HST part of a joint Chandra/HST project: the original Chandra proposal abstract follows.) Chandra has been tracking coronal activity cycles of late-type stars via high-contrast soft X-rays, jointly with HST to capture UV tracers. Objective is to provide fundamental observational constraints for contemporary and future studies of the underlying magnetic Dynamo, whose inner workings remain elusive. The Sun's high-energy modulations play an important "Space Weather" role in our heliosphere, as do stellar counterparts for their exoplanets. 3-year time-domain campaign (jointly with HST) is proposed for iconic Alpha Centauri, already followed by HRC-I since 2006. The Alpha Cen field also is rich in serendipitous sources, including flaring red dwarfs and several possibly cycling F-K stars. **Impact of Reduced Gyro Mode** ------------------------------------------------- Main impact of RGM would be on the CVZ orbits requested for the target Alpha Cen A+B, together with an orientation constraint for one of the ND-filtered long-slit exposures, to avoid having both stars (currently only ~8" apart) fall on the slit at the same time. If RGM becomes necessary in Cycle 30, the observing program would be modified as follows: (1) the two NUV echelle exposures would be eliminated (one of which uses the problematic long-slit); (2) the FUV exposure times would be reduced to allow the 2-orbit pointing to be carried out in non-CVZ time, to increase scheduling opportunities. The loss in science from dropping the NUV exposures would be minor, because the FUV spectral region is the highest priority in terms of its potential information content. Also, the reduced FUV exposures would have minimal impact, because the two nearby sun-like dwarfs are bright at the short wavelengths. ------------------------------------------------- Phase II Observing Description (for normal 3-gyro operations) The high southern declination Alpha Cen system falls in the HST Continuous Viewing Zone numerous times during the year, allowing the two stars to be captured in a single visit of two orbits. Two such visits are planned for Cycle 31, compatible with the semiannual pointings by Chandra. There is no need to strictly coordinate the FUV and X-ray pointings, because the FUV Fe XII 124+134 nm coronal forbidden line can tie the STIS observation into the X-ray timeline. In each STIS visit, the binary companions are observed sequentially, beginning with Alp Cen A, brighter of the two. The target is acquired with the CCD and F25ND5, followed by an exposure with the E140M-1425 medium-res echelle through the photometric slot (0.2x0.2), which delivers R=40,000 and good sensitivity (peak S/N=40 per resol at the tops of the important Si IV 140 nm and C IV 155 nm resonance doublets). A peak-up is not needed because the CCD ACQ is accurate enough for centering in the photometric slot. The exposure depth is sufficient to capture the key Fe XII coronal forbidden lines, which as mentioned earlier are used to tie the STIS FUV measurements into the X-ray time line. The combination of resolution, spectral coverage, and sensitivity of E140M for A has proven successful in previous incarnations of this program. Following the E140M exposure, a peak-up is performed with the 31x0.05NDC slit in dispersed visible light with the CCD and G430M; then an E230H-2713 exposure is taken through the ND long slit. This setting captures the key chromospheric Mg II 280 nm resonance doublet. After the Alp Cen A exposures, a 8.7" offset manuever to B is performed, followed by a CCD ACQ through F25ND5. The time-dependent separation of the binary companions is accurately known (to ~0.1"), based on the recently published ephemeris of Akeson et al. (2021, AJ, 162, 14). Similarly, the coordinates (including parallax) and proper motion of Alp Cen A were updated for Cycle 31 based on values from Akeson+2021 for 2025.0. After the CCD-ACQ of B, an E230H-2713 is taken, again to cover the important Mg II region. The 0.2x0.09 spectroscopic aperture can be used, because the previously measured Global Count Rate with this setting is below the bright limit, and B is only minimally variable in the continuum light that dominates that setting (the Mg II lines can be more variable, but do not contribute signifcantly to the total flux in that region; and do not approach the local bright limit). A peak-up ensures maximum throughput. Following the NUV exposure, an E140M-1425 exposure is taken through the 0.2x0.2 photometric aperture, to maximize sensitivity without significant loss of resolution, and minimize the influence of breathing effects. The entire FUV+NUV sequence for both stars requires two CVZ orbits. Because a tall slit is used for A, an ORIENT constraint is specified to avoid having both targets fall on the slit simultaneously, and consequently corrupt the echellegram with overlapping spectra (and possibly also violate the global limits). The constraint is not severe, however, because the NDC slit is only 0.05" wide and the separation of the stars will be 8.7" in 2025.0. A +/- 4 degree avoidance zone (+/- 0.6" pivot from B) should be sufficient to exclude B and any possible scattered light. The ORIENT avoidance zones for 2024 are listed in the Visit-level specifications (the PA of B relative to A is ~ +8 deg East of North in 2024). There are numerous CVZ windows throughout the year that satisfy the ORIENT constraint, and allow spacing the visits about 6 months apart (specified by an "After Visit" constraint). Non-standard lamp exposures, 15s with the 0.2x0.2 aperture (which accepts 3x more lamp light than the default 0.2x0.06 slit), are used to calibrate the FUV echellegrams of both stars to provide accurate zero-point wavelength shifts. The lamp output has faded over the years, and the default wavecals are no longer able to provide the desired accuracy, at least for E140M. (The NUV observations use the default wavecal exposures of 10s for the spectroscopic slit, 0.2x0.09). The non-standard FUV wavecals ensure that the dispersion properties of the spectrometer are accurately monitored, to take full advantage of STIS's ability to measure small differential velocity shifts between emission lines at different wavelengths formed in different environments in the stellar outer atmosphere, a major scientific goal of the project. All the wavecals are forced to be adjacent to the respective science exposures by a "SEQ NON-INT" pairing. Because the GO-specified wavelength calibrations can substitute for the normal brief AUTO-WAVECALs, the latter are turned off in the respective science exposures. T. Ayres is a highly experienced HST observer, especially with the STIS spectrograph, with dozens of successful programs as PI, including Large Projects in Cycles 18 and 21, alone totalling nearly 400 orbits. Stellar Physics 6 false false false false false false false false AVAILABLE STAR CORONA G V-IV NO Target coords for 2025.0 based on Akeson+2021 position in that epoch. Proper motion of Alpha Cen A derived from quadratic fit to Akeson+2021 coords 2010-2030. ALP-CEN-A J2000 J2000 STAR CORONA K V-IV NO Offset of B relative to A, for 2025.0 taken from the Akeson+2021 ephemeris. ALP-CEN-B J2000 STAR CORONA G V-IV NO Target coordinates for 2025.0 based on Akeson+2021 position of Alp Cen A in that epoch. Proper motion of Alpha Cen A derived from change in Akeson+2021 coords for Alp Cen A over reference interval 2023.0 to 2027.0 (which includes the ususal constant proper motion of the system center-of-mass, as well as the varying orbital motion of A relative to the COM over the restricted time window centered on 2025.0). The (almost negligible) influence of parallax is canceled by taking the reference times at the same fractional-year values (here, ".0"). ALP-CEN-A J2000 J2000 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 Timing link suitability includes constraints ([11 After 10 by 120.0 to 240.0 days]) The scheduling data was generated by CASM 32.1. CASM was run in Phase II mode. 1718125897704 1721333141000 90.65080499230521 (Tic-Visit :proposal-id 17405 :visit-id "10" :proposal-version -1 :trans-version "20240604" :date "11-Jun-2024 13:11:37.0" :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 489664 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17405 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :cvz T :proposal-id 17405 :visit-id "10" :orbit-number 1 :pcs-time 380 :si-vis-utilization 10480 :al-overhead-at-end 76 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 0 :low-sky "N" :pcs-visibility 0 :pcs-gap 0 ) false 2 0 Castelli-Kurucz Models G2V 5750 4.5, renormalized to vegamag = 0.01 in filter Johnson/V: SNR~140 in 0.1 s; time to saturation 0.6 s. Input=special ETC file for ALP-CEN-A from previous STIS echelle spectra; exposure time= 1.5 ks at Si IV 139 nm gives peak SNR~40 (per resol) with 0.2x0.2 aperture. No LCR or GCR issues. Dispersed light peak-up; Castelli-Kurucz Model G2V 5750 4.5, renormalized to vegamag = 0.01 in filter Johnson/V: in 0.1 s with NDA, GCR= 2780k e-. ETC GCR~135k for Castelli-Kurucz Model G2V 5750 4.5, renormalized to vegamag = 0.01 in filter Johnson/V. Measured GCR~110k for several exposures in similar setting H-2812 with NDC; H-2713 GCR should be less because NUV continuum is falling toward shorter wavelengths. Castelli-Kurucz Models K2V 4750 4.5, renormalized to vegamag = 1.33 in filter Johnson/V: SNR~74 in 0.1 s; time to saturation 1.7 s. Dispersed light peak-up; Castelli-Kurucz Models K2V 4750 4.5, renormalized to vegamag = 1.33 in filter Johnson/V: 5470k e- in 0.1 s; time to saturation 0.9 s. GCR= 73k from ETC run for Castelli-Kurucz Model K2V 4750 4.5, renormalized to vegamag = 1.33 in filter Johnson/V. Variability expected to be very low in the K-dwarf continuum, which dominates the H-2713 setting. Measured GCRs from ocre10050, ocre11050, octr10050, and od5c10050 (same setting and slit) are 126k+/-13k. Based on new FUV spectrum of ALP-CEN-B from 4 years of STIS measurements. No LCR or GCR issues. Timing link suitability includes constraints ([11 After 50 by 120.0 to 240.0 days]) The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. 1723124483587 /private/var/folders/g8/sfxwph3d1y78xbb04wh45v0c0000gn/T/OPVisit3858320155613010456.xml (Tic-Visit :proposal-id 17405 :visit-id "11" :proposal-version -1 :trans-version "20240604" :date "08-Aug-2024 09:41:23.0" :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 174832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17405 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17405 :visit-id "11" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2562 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2942 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17405 :visit-id "11" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2562 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2942 :pcs-gap 0 ) true 2 0 Castelli-Kurucz Models G2V 5750 4.5, renormalized to vegamag = 0.01 in filter Johnson/V: SNR~140 in 0.1 s; time to saturation 0.6 s. Input=special ETC file for ALP-CEN-A from previous STIS echelle spectra; exposure time= 1.5 ks at Si IV 139 nm gives peak SNR~40 (per resol) with 0.2x0.2 aperture. No LCR or GCR issues. Castelli-Kurucz Models K2V 4750 4.5, renormalized to vegamag = 1.33 in filter Johnson/V: SNR~74 in 0.1 s; time to saturation 1.7 s. Based on new FUV spectrum of ALP-CEN-B from 4 years of STIS measurements. No LCR or GCR issues. Timing link suitability includes constraints ([11 After 50 by 120.0 to 240.0 days]) The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. 1723124550792 /private/var/folders/g8/sfxwph3d1y78xbb04wh45v0c0000gn/T/OPVisit15346691899316517454.xml HOPR repeat of failed visit 10. (Tic-Visit :proposal-id 17405 :visit-id "50" :proposal-version -1 :trans-version "20240604" :date "08-Aug-2024 09:42:30.0" :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 174832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17405 :visit-id "50" :obset-id "50" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17405 :visit-id "50" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2562 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2942 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17405 :visit-id "50" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2562 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2942 :pcs-gap 0 ) true 2 0 Castelli-Kurucz Models G2V 5750 4.5, renormalized to vegamag = 0.01 in filter Johnson/V: SNR~140 in 0.1 s; time to saturation 0.6 s. Input=special ETC file for ALP-CEN-A from previous STIS echelle spectra; exposure time= 1.5 ks at Si IV 139 nm gives peak SNR~40 (per resol) with 0.2x0.2 aperture. No LCR or GCR issues. Castelli-Kurucz Models K2V 4750 4.5, renormalized to vegamag = 1.33 in filter Johnson/V: SNR~74 in 0.1 s; time to saturation 1.7 s. Based on new FUV spectrum of ALP-CEN-B from 4 years of STIS measurements. No LCR or GCR issues.