0 Assigned ID: 6124 ----- Attempting Submission 1 (Mon Apr 07 11:46:10 GMT 2025) ----- HST Phase I Proposal 6124 successfully submitted. Receipt: # 6124-1 ----- Attempting Submission 2 (Tue Apr 08 12:10:12 GMT 2025) ----- HST Phase I Proposal 6124 successfully submitted. Receipt: # 6124-2 0 ----- Attempting Submission 1 (Sat Jul 26 15:34:46 GMT 2025) ----- Measuring the Accretion Rate for the Least Massive Known Brown Dwarf with a Circumstellar Disk A Cycle 3 JWST program has searched for free-floating brown dwarfs down to the mass of Jupiter in the nearby star-forming cluster IC 348 (5 Myr, 300 pc). Those observations have discovered a brown dwarf that has an estimated mass of 2 Jupiter masses and that exhibits excess emission at 3-5 um from a circumstellar disk, making it the least massive known brown dwarf with a disk. We propose to use UV imaging with HST to measure the disk's accretion, which is a vital component of any effort to model the disk and constrain its properties. Using the accretion rate measured with HST, we will develop a model that fits the IR excess emission detected by JWST, which will provide an estimate of the inner radius of the disk. The accretion rate will also facilitate the modeling of any other future observations of the disk, such as JWST spectroscopy at 5-15 um and ALMA millimeter continuum measurements. Ultimately, this system represents a unique opportunity to study disk accretion and planet formation in an extreme, unexplored regime of stellar mass. We will obtain WFC3/UVIS images in the F336W filter of a point source (a brown dwarf) within a cluster of young stars. In each of 10 orbits, we will obtain one 1230 s exposure at each position in a two-point dither pattern. To mitigate CTE losse, a post flash of 13 electrons per pixel will be applied to each exposure, which should raise the background to the desired level of 20 electrons per pixel according to the ETC. The target will be observed at the UVIS2-C512C-CTE aperture, which also should mitigate CTE losses. The 10 orbits are divided among 10 visits. The ORIENT and timing of the visits are unconstrained. Kevin Luhman and Catarina Alves de Oliveira have extensive experience identifying brown dwarfs that have circumstellar disks in star-forming regions using IR photometry from Spitzer, WISE, and JWST. Catherine Espaillat is a leading expert in modeling accretion disks around young stars and is a member of the ULLYSES Scientific Advisor Committee. Luhman and Alves de Oliveira will design the phase II observations and reduce the data. Espaillat will model the data and estimate the accretion rate. Stellar Physics and Stellar Types Exoplanets and Exoplanet Formation 6 false true false false false false SUPPORTED STAR BROWN DWARF NO J2000 J2000 The scheduling data was generated by CASM 33.0. CASM was run in Phase I mode. WFC3/UVIS Imaging No No F336W POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 1 false /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v01.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "01" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:25:25.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v02.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "02" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:28:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v03.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "03" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:28:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v04.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "04" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:28:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v05.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "05" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:28:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v06.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "06" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:28:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v07.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "07" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:28:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "07" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v08.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "08" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:28:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "08" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v09.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18067 :visit-id "09" :proposal-version -1 :trans-version "20250624" :date "26-Jul-2025 11:28:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 577488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18067 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18067 :visit-id "09" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2604 :al-overhead-at-end 124 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 1 0 /Users/kll207/prop/hst/cycle33/ic348/phase2/OP-cache/prop-v10.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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