0 Assigned ID: 6603 ----- Attempting Submission 1 (Thu Apr 10 18:48:15 GMT 2025) ----- The South field was relocated to the star SO 1036 (BG-ORI) which is a stronger candidate: it is a confirmed proplyd in H2 (JWST) oriented toward σ Ori and shows the full suite of expected forbidden lines (Mauco et al. 2025). 524009220 ----- Attempting Submission 1 (Wed Aug 13 20:35:10 GMT 2025) ----- HST Phase II Proposal 18093 successfully submitted. Receipt: # 18093-1 ----- Attempting Submission 2 (Thu Aug 14 12:26:28 GMT 2025) ----- HST Phase II Proposal 18093 successfully submitted. Receipt: # 18093-2 ----- Attempting Submission 3 (Tue Aug 19 14:33:08 GMT 2025) ----- HST Phase II Proposal 18093 successfully submitted. Receipt: # 18093-3 ----- Attempting Submission 4 (Tue Aug 19 14:46:22 GMT 2025) ----- ----- Attempting Submission 5 (Wed Feb 04 20:35:42 GMT 2026) ----- ----- Attempting Submission 6 (Wed Jul 01 23:04:15 GMT 2026) ----- Photoevaporating disks in the final evolution phase: Probing Sigma Orionis with HST/WFC3 The evolutionary pathways of protoplanetary disks differ depending on the surrounding environment. Theoretical models and observational evidence point to external photoevaporation by OB stars playing a significant role in the evolution of planet-forming disks in clusters. As the majority of exoplanet we know did form in such environments, it is mandatory to better understand this process. The effect of external photoevaporation is a depletion of the disk outside-in, severely shortening disk lifetimes. Previous studies have focused on analysing externally-induced disk winds in young (<1-2 Myr) star-forming regions and in high radiation fields. Here we aim to target the intermediate age (3-5 Myr) and milder radiation field Sigma Orionis cluster, a region with disks that have never been imaged in visible light with HST or other high spatial resolution instruments before. We propose, for the first time, to resolve the final stages of disk dissipation caused by photoevaporation with the UVIS camera of HST/WFC3 in three narrow-band filters, tuned to reveal the cocoon around the targets, tell-tale proxy of ongoing external photoevaporation from the massive stars at the center of the cluster. We will thus measure the size of the ionization fronts, and infer the mass loss rates in the winds. These observations will allow us to determine key diagnostics necessary to constrain external photoevaporation models at a later stage of disk evolution and at lower incident radiation than previously observed. We plan to observe with HST four fields which include the best ten candidates for detecting a proplyd structure based on their optical emission lines. In the same fields, several other targets known to have disks through ALMA detections (Ansdell et al. 2017) are included. Therefore, we will be able to detect additional proplyds, if any. This sample will cover a range of G0 ~10^3 - 10^5, allowing us to test external photoevaporation models in a wide range of (relatively low) G0, at ages older than previously studied. Each field will be observed with WFC3/UVIS using three narrow-band filters, F656N (Halpha), F631N ([OI]), and F658N ([NII]). These are chosen to spatially resolve ionization fronts and proplyd tails. WFC3/UVIS provides the best sampling, largest FoV, and has the required narrow-band filters. Using WFC3 instead of ACS leads to a better spatial resolution, thanks to the better pixel size, to higher sensitivity, and gives the possibility to use the best narrow band filters for our observations. The HST diffraction limit in Halpha is ~70 mas, which means we will be able to spatially resolve structures as small as ~30 AU for a distance of ~400pc to sigma-Orionis. Each observation in each filter will be done using one orbit to account for ~1600 s on target plus overheads (6.5 minutes acquisition plus dithering overheads). Indeed, the targets are visible for 52 minutes during the orbit, which are then covered by the exposure and the overheads. The exposure time estimate is based on the observations by Bally et al. (2012), which are reported by Kim et al. (2016) to be appropriate to detect proplyds. We will use short sub-exposures of length between ~400 s and then combine the various subexposures to get to the final deep image. Between exposures, we will perform a dither pattern. This will be planned with particular attention to recovering the spatial resolution, accounting for the fact that the PSF is slightly undersampled. This will also be important for the mitigation of image defects. The short exposures are needed to avoid saturation, which happens after 3600 s on our targets but could happen on shorter exposures for other stars in the field of view. In particular, the field including the massive sigma-Ori star will be observed adding two shorter exposures (30s), one at the beginning and one at the end of the 4 dithers, and positioning the massive star in the region between the two CCDs to avoid saturation. For the rest of the fields (without the massive star SOri) we choose dithering pattern parameters such that they fill the chip gap. The observations will not have to be scheduled in consecutive orbits, we will be able to combine data in the different filters also taken with time separation between them. However, consecutive observations in the three filters allow for minimizing the telescope overheads. The team comprises experts of studies of proplyds in the ONC and in other star-forming regions (Vicente, Haworth, Manara, Robberto, Aru, Winter), and of external photoevaporation using spectra (Mauco) and models (Facchini, Haworth, Ballabio). Also experts on protoplanetary disks evolution are also present (Miotello, Rosotti, Ansdell, Alcala). The analysis will be carried out by the PhD student M.L. Aru, supervised by C. Manara and K. Mauco and with the technical support on the analysis of the HST data from M. Robberto, who has led several HST program to study young stars in the Orion Nebula Cluster (e.g., Robberto et al. 2013). M.L. Aru is currently carrying out a PhD Thesis to study proplyds in the ONC using VLT/MUSE data, and is in close contact with modelers to learn how to interpret the data. Complementary data from VLT/X-Shooter and Magellan/MIKE is available from the works of K. Mauco (Mauco et al. 2023, 2025) who will assist during the analysis of the HST data. Exoplanets and Exoplanet Formation Stellar Populations and the Interstellar Medium 6 false false false false false false false SUPPORTED STAR PRE-MAIN SEQUENCE STAR NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR PRE-MAIN SEQUENCE STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR PRE-MAIN SEQUENCE STAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR PRE-MAIN SEQUENCE STAR This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. J2000 WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F631N WFC3/UVIS Imaging No No F658N WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F673N WFC3/UVIS Imaging No No F658N WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F658N WFC3/UVIS Imaging No No F631N WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F658N WFC3/UVIS Imaging No No F631N POS-TARG DITHER 0.173 This pattern is to be used in the field where the sigma-Ori massive star is (Left Field). We do not want to fill the chip gap. We want to position the massive star between the chip gap LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 2 false POS-TARG DITHER 2 This pattern is to be used in the fields without the sigma-Ori massive star (Right, North, and South Fields). We do want to fill the chip gap. LINE 0.8 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 3 false The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit10957715771036264597.xml (Tic-Visit :proposal-id 18093 :visit-id "01" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:04.0" :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 1732496 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2359 :al-overhead-at-end 129 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit15859687504753463954.xml (Tic-Visit :proposal-id 18093 :visit-id "02" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:04.0" :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 1732496 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2359 :al-overhead-at-end 129 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit7528969635476155389.xml (Tic-Visit :proposal-id 18093 :visit-id "03" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:04.0" :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 1732496 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2359 :al-overhead-at-end 129 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit15731703048533026038.xml (Tic-Visit :proposal-id 18093 :visit-id "04" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:04.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit9922486702574669762.xml (Tic-Visit :proposal-id 18093 :visit-id "05" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:05.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit4010098427588674396.xml (Tic-Visit :proposal-id 18093 :visit-id "06" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:05.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit6506719181918971077.xml (Tic-Visit :proposal-id 18093 :visit-id "07" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:05.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "07" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit11620392371275178521.xml (Tic-Visit :proposal-id 18093 :visit-id "08" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:05.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "08" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /private/var/folders/8z/_1d47x0s14qg372ggznn730r0000gn/T/OPVisit9957493063132613002.xml (Tic-Visit :proposal-id 18093 :visit-id "09" :proposal-version -1 :trans-version "20260319" :date "01-Jul-2026 15:58:05.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "09" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /Users/karina/Observing_Proposals/HST/OP-cache/18093_new_fields-v10.xml (Tic-Visit :proposal-id 18093 :visit-id "10" :proposal-version -1 :trans-version "20260319" :date "01-Jun-2026 16:14:45.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "10" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /Users/karina/Observing_Proposals/HST/OP-cache/18093_new_fields-v11.xml (Tic-Visit :proposal-id 18093 :visit-id "11" :proposal-version -1 :trans-version "20260319" :date "01-Jun-2026 16:14:48.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "11" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 34.1. CASM was run in Phase II mode. /Users/karina/Observing_Proposals/HST/OP-cache/18093_new_fields-v12.xml (Tic-Visit :proposal-id 18093 :visit-id "12" :proposal-version -1 :trans-version "20260319" :date "01-Jun-2026 16:13:41.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18093 :visit-id "12" :obset-id "12" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18093 :visit-id "12" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2219 :al-overhead-at-end 125 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0