0 Assigned ID: 7790 ----- Attempting Submission 1 (Thu Apr 16 23:19:03 GMT 2026) ----- HST Phase I Proposal 7790 successfully submitted. Receipt: # 7790-1 ----- Attempting Submission 2 (Thu Apr 16 23:20:46 GMT 2026) ----- HST Phase I Proposal 7790 successfully submitted. Receipt: # 7790-2 0 ----- Attempting Submission 1 (Tue Aug 25 23:45:39 GMT 2026) ----- Building a MgII h+k age-activity relation for old main sequence stars The hunt is on for robust and widely applicable means of assessing the ages of older stars in the solar neighborhood and beyond. Past works suggest that chromospheric ultraviolet MgII emission may be a sensitive indicator of stellar age past 1 Gyr, but well-calibrated age-activity relations remain to be produced. Establishing such a relation would open up a variety of exoplanet host star and Galactic evolution research paths. We propose to obtain a solid anchoring of any putative MgII age-activity relation for Sun-like stars by combining already existing measurements with new observations of stars having well-measured ages from asteroseismology and binary companions. With the proposed dataset we will be able to assess the reliability and predictive capability of a MgII age-activity relation for main sequence stars older than roughly 1 Gyr. The proposed data will also be of great value in assessing ultraviolet properties of stars that are part of the Habitable Worlds Observatory target list. These observations will primarily obtain NUV spectra for a variety of Sun-like star targets. The experimental design borrows from past successful observations of similar stars in the same setups. NUV will use the E230M or E230H gratings depending on source brightness centered on the MgII h+k lines (emission from these transitions is the primary objective) and seek to obtain S/N of at >~10 in the MgII absorption cores. For especially bright stars where NUV exposures are short, we will fill remaining time with FUV observations using the E140M grating; the stellar continuum will not be detected in the FUV but several strong chromospheric emission lines will be present and will provide lasting archival value. Acquisition will depend on target source brightness. Most targets will follow standard acquisition protocol with imaging in the F28X50LP, F28X50OIII, or F28X50OII filters to optimally place the targets in the 0.2"x0.2" spectral aperture. The two brightest targets (gamma Pav and zeta Tuc) will initially use the narrowband OIII filter and then will peakup in a small aperture to optimally place them in their respective narrow spectral apertures. We have carefully checked that all targets will not saturate in either the NUV or FUV for the chosen aperture and exposure times and will provide signal-to-noise>~100 (without saturating) for acqusition sequences. NUV will use ACCUM mode while TIME-TAG will be used for for the FUV where we do not expect to detect stellar continuum; only emission lines will be detected and we have confirmed that the brightest emission line (Lyman-alpha) will not overwhelm the buffer for the chosen dump time. Carl Melis (PI, UC San Diego) completed his Ph.D. in Astronomy at UC Los Angeles in 2009 where he developed expertise in stellar astrophysics and planetary system formation and evolution. He has since been a post-doctoral researcher and now member of the research faculty at UC San Diego conducting a variety of projects related to stellar astrophysics, including characterizing the ages of stars of interest (e.g., see Melis et al. 2021, ApJ 923, 90). PI Melis will be the lead on this project, ensuring all data is reduced and analyzed and publications prepared. He plans to lead students in conducting this work and may support them with any awarded funds. The PI will lead students in preparing papers and submitting them, or if need be take the lead on them himself. PI Melis led students in analyzing all archival STIS data in preparation for this proposal and is currently preparing a publication on them. Stellar Physics and Stellar Types 0 false true false false false false true SUPPORTED STAR G V-IV NO GAIA-DR3-4987088807460766336 J2000 J2000 Age=1.1+/-0.1 Gyr, companion to WDJ005152.55-405952.13, mNUV=15.95 STAR K V-IV NO GAIA-DR3-4504577990890909184 J2000 J2000 Age=1.5+/-0.1 Gyr, companion to WDJ184741.53+122631.75 STAR F3-F9 NO GAIA-DR3-2125912230597714944 J2000 J2000 Age=1.9+/-0.3 Gyr, asteroseismology, mNUV=13.3 STAR F3-F9 NO GAIA-DR3-2128218559316957824 J2000 J2000 Age=2.5+/-0.6 Gyr, asteroseismology, mNUV=14.3 STAR F3-F9 NO GAIA-DR3-4900583252677355776 J2000 J2000 Age=2.9+/-0.1 Gyr, companion to WDJ002500.50-635646.91, mNUV=13.5 STAR G V-IV NO GAIA-DR3-4623036865373793408 J2000 J2000 Age=3.8+/-0.7 Gyr, asteroseismology STAR F3-F9 NO GAIA-DR3-4900108950849461248 J2000 J2000 Age=5.3+/-0.5 Gyr, asteroseismology STAR G V-IV NO GAIA-DR3-4430238051199001216 J2000 J2000 Age=5.4+/-0.7 Gyr, asteroseismology STAR F3-F9 NO GAIA-DR3-6401464693867773568 J2000 J2000 Age=5.9+/-1.0 Gyr, asteroseismology STAR G V-IV NO GAIA-DR3-5264749303462961280 J2000 J2000 Age=6.0+/-1.0 Gyr, asteroseismology STAR G V-IV NO GAIA-DR3-2052747119115620352 J2000 J2000 Age=6.6+/-0.9 Gyr, asteroseismology, mNUV=15.5 STAR K V-IV NO GAIA-DR3-2128215909315876352 J2000 J2000 Age=7.0+/-0.5 Gyr, asteroseismology, mNUV=16.05 STAR K V-IV NO 1.88" separation companion that is about 3-4 magnitudes fainter in the optical GAIA-DR3-2101486923385239808 J2000 J2000 Age=11.2+/-1.0 Gyr, asteroseismology, mNUV=15.5 STAR G V-IV NO 0.4" Delta_K=5 mag companion seen in two Keck AO epochs separated by several years V911-TAU GAIA-DR3-3313689422030650496 J2000 Age=0.7 Gyr, Hyades Sun-like star, mNUV=13.8 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230M 2561 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230M 2561 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230H 2762 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230H 2762 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230H 2762 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230H 2762 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230H 2762 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230H 2762 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230H 2762 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230H 2762 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230M 2561 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230M 2561 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. STIS/NUV-MAMA Spectroscopic No No E230M 2561 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v01.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. 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(Tic-Visit :proposal-id 18437 :visit-id "04" :proposal-version -1 :trans-version "20260618" :date "25-Aug-2026 16:02:10.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 87440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18437 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18437 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2631 :al-overhead-at-end 194 :internal-dur-at-end 319 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3011 :pcs-gap 0 ) true 1 0 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v05.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18437 :visit-id "05" :proposal-version -1 :trans-version "20260618" :date "25-Aug-2026 16:02:10.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 87440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18437 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18437 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2684 :al-overhead-at-end 194 :internal-dur-at-end 319 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3064 :pcs-gap 0 ) true 1 0 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v06.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18437 :visit-id "06" :proposal-version -1 :trans-version "20260618" :date "25-Aug-2026 16:02:11.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 87440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18437 :visit-id "06" :obset-id "A6" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18437 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2801 :al-overhead-at-end 194 :internal-dur-at-end 319 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3181 :pcs-gap 0 ) true 1 0 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v07.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. 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(Tic-Visit :proposal-id 18437 :visit-id "08" :proposal-version -1 :trans-version "20260618" :date "25-Aug-2026 16:02:11.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 243968 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18437 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18437 :visit-id "08" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2597 :al-overhead-at-end 0 :internal-dur-at-end 578 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2977 :pcs-gap 0 ) true 1 0 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v09.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18437 :visit-id "09" :proposal-version -1 :trans-version "20260618" :date "25-Aug-2026 16:02:12.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 244064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18437 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18437 :visit-id "09" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2712 :al-overhead-at-end 0 :internal-dur-at-end 440 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3092 :pcs-gap 0 ) true 1 0 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v10.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. 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(Tic-Visit :proposal-id 18437 :visit-id "11" :proposal-version -1 :trans-version "20260618" :date "25-Aug-2026 16:02:12.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 87440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18437 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18437 :visit-id "11" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2612 :al-overhead-at-end 194 :internal-dur-at-end 319 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2992 :pcs-gap 0 ) true 1 0 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v12.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18437 :visit-id "12" :proposal-version -1 :trans-version "20260618" :date "25-Aug-2026 16:02:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 87440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18437 :visit-id "12" :obset-id "12" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18437 :visit-id "12" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2631 :al-overhead-at-end 194 :internal-dur-at-end 319 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3011 :pcs-gap 0 ) true 1 0 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v13.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18437 :visit-id "13" :proposal-version -1 :trans-version "20260618" :date "25-Aug-2026 16:02:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 87440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18437 :visit-id "13" :obset-id "13" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18437 :visit-id "13" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 194 :internal-dur-at-end 319 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) true 1 0 /Users/cmelis/observing/hst/cycle34/uvageactivity/phaseii/OP-cache/uvageactivity_cycle34_phaseii-v14.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. 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