Target P2023-V6: There is no need or capability to test the scheduling of observations of moving targets in Phase I. This warning will go away the next time the proposal is loaded. Version 0 Submission 460191684 Assigned ID: 5214 ----- Attempting Submission 1 (Mon Mar 25 18:26:18 GMT 2024) ----- HST Phase I Proposal 5214 successfully submitted. Receipt: # 5214-1 The warning is due to a moving target, resulting in an inability of the tool to test the scheduling. This submission uses the latest JPL orbital solution, V6, with observations obtained in October 2024. This submission also changes the dither point spacing from 0.24" to the standard 0.145" recommended in the WFC3 Handbook (Appendix C.2). -1156735648 ----- Attempting Submission 1 (Fri Aug 02 20:04:21 GMT 2024) ----- ----- Attempting Submission 2 (Wed Nov 13 15:21:37 GMT 2024) ----- The discovery of the transient Jupiter co-orbital comet P/2019 LD2 (ATLAS) drew significant interest. Not only will LD2 transition between being a Centaur and a Jupiter Family Comet (JFC) in 2063, the first time this process can be observed as it happens, it is also very active for its large heliocentric distance. We propose HST WFC3 observations of the newly discovered transient Jupiter co-orbital comet P/2023 V6 (PANSTARRS), the second such object known. Despite similar modern orbits, V6 is significantly (15x) less active than LD2 and most JFCs as determined via dust production measurements at the same heliocentric distance. As such, this suggests a correspondinly smaller nucleus size. If the nuclei are similar in size, we interpret these differences in activity as evolutionary, with V6 having lost a significant fraction of its near-surface ice compared to LD2 by previously being warmer. We will observe P/2023 V6 witht F350LP filter for two orbits of HST (a total of 2000s of exposure) to measure the nucleus size using HST's stable PSF and separate the weak dust coma from the nuclear contribution. If our hypothesis about V6's size is proven, this would be more evidence that LD2 is a pristine and ice-rich object, and thus it may display very strong activity when it becomes a JFC. We will use our observattion to delineate the differences between V6 and LD2 to discuss the interpretation of cometary activity at large heliocentric distances. This has significant repercussions for our understanding of the end state of JFCs, as well as the small end of the cratering record of the Galilean Satellites. We will execute a short and highly impactful campaign to image the inner coma of P/2023 V6 (PANSTARRS) with WFC3 on the Hubble Space Telescope. The primary objective is to measure or constrain the size of this comet so as to contextualize the strength of its activity.To do so we will obtain 4 370s exposures of the F350LP filter per orbit for two consecutive orbits, for 8 total exposures, to reach a limiting magnitude of V=28 in ~2960s. The only relevant size scale to compare to V6 is the nuclear radius upper estimate from Kareta et al., 2021 of LD2, r< 1.2 km. V6 is a relatively condensed comet whose coma was about ~5 arcseconds across in November 2023. The spatial distribution of reflected light from V6's nucleus and coma will be compared against models of the WFC3 350LP PSF (e.g., with the software TinyTim (Krist, Hook, and Stoehr 2011) so as to understand the likely size of the object's nucleus. In the following paragraphs, we outline our sensitivity requirements, the proposed observations high scientific utility in the event of a non-detection, and our observing strategy. At the distance of ~5 AU during our observational window (within a month of opposition of on January 4, 2025) this corresponds to a 5-sigma detection of a 100-m nucleus, approximately three times smaller than the smallest expected size of V6. Using the exposure time calculator for WFC3, we are able to obtain an SNR~10 detection of an LD2-sized nucleus (V~23) in just 44.7s on target in a 0.3"-radius circular aperture. If LD2 and V6 have the same activity strength, and thus V6 is approximately 4x smaller, then 1794.6s on target is sufficient. A non-detection of the nucleus at this level would be striking; it would indicate that V6 is far smaller than expected and yet still active out at Jupiter's orbit. This finding would have massive implications for the size frequency and compositions of the Galilean impactor population. With our 2-orbit allocation we are able to obtain nearly 3000s of exposure time, more than enough to accomplish our science goals. To mitigate cosmic ray effects and other artifacts and improve sampling of the PSF we will dither each exposure (Dither pattern WFC3-UVIS-DITHER-LINE), placing V6 on the UVIS2-2K2C subarray. We will use a combination of Tiny Tim and DOLPHOT (Dolphin 2000, Dolphin 2016\footnote{http://americano.dolphinsim.com/dolphot/}) to model the PSF, which is not explicitly recommended by the WFC3 Instrument handbook (see 6.11.4). However, the F350LP filter does not have a publicly available PSF on the WFC3 PSF website. We also expect background dust coma contribution of V6 to substantially weaker than nucleus reflectance at the high angular resolution of HST WFC3, and as such do not expect substantial effort to be made to correct for dust distributions. 1-Observation Plan We will use the WFC3-UVIS-DITHER-LINE Pattern for a single, 2-orbit visit, with four dithers per orbit. Each dither will be a 370s exposure, for a total of 1480s per orbit and 2960 s cumulatively. 2-Observing Constraints The current observational arc for V6 is relatively short, leading to 3-sigma uncertainties of ~200'' in right ascension and ~18'' in declination near opposition in January 2025. We want to execute our visit within 30 days of opposition, between December 4, 2024 and February 4, 2025. We will maintain our own cadence of ground-based observations throughout 2024 to increase the arc length, submit astrometry to improve the orbital solution on Horizons, and narrow the positional uncertainties prior to execution of Cycle 32 orbits. These updates will be submitted as updated targets in the APT. However, given the 160" FOV of WFC3 we anticipate that the ephemeris uncertainties will be will within the FOV with only a few additional arc measurements in the fall of 2024. Co-PI John Noonan (Auburn U.) is a postdoctoral scholar with WFC3 and Far Ultraviolet (FUV) comet observation experience with HST, and is an expert in the analysis and interpretation of cometary and Centaur spectra and images. Co-PI Theodore Kareta (Lowell Obs.) is a postdoctoral researcher with WFC3 and extensive ground-based imaging experience, and is an expert in the analysis and interpretation of images and spectroscopy of various kinds of Solar System small bodies. Solar System Astronomy 6 false false false false false false false false SUPPORTED SOLAR SYSTEM COMET Active Jupiter co-orbital object P/2023 V6 TYPE=COMET,Q=4.383193965570757,E=0.1806836940613261,I=3.974862309687347 ,O=190.0079195419479,W=194.4890868749891,T=22-DEC-2022:23:19:23,TTimeScale=TDB,EQUINOX=J2000,EPOCH=03-DEC-2023:00:00:00,EpochTimeScale=TDB EARTH WFC3/UVIS Imaging No No F350LP POS-TARG DITHER 0.145 LINE false false 4 46.84 WFC3-UVIS-DITHER-LINE 1 false 1731510889105 /private/var/folders/3h/3p9m4q0s69xctgx7_b4s4gp80000gs/T/OPVisit7454944501267681929.xml Using ephemeris for target 17795-01-P2023-V6-JPLV6 ephemeris data for target 17795-01-P2023-V6-JPLV6 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 24.214 to 26.089. ephemeris interval: 24.305 to 26.305 The scheduling data was generated by CASM 32.1.3. CASM was run in Phase II mode. 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