0Assigned ID: 7453
----- Attempting Submission 1 (Thu Apr 16 16:26:12 GMT 2026) -----
HST Phase I Proposal 7453 successfully submitted.
Receipt: # 7453-1
----- Attempting Submission 2 (Thu Apr 16 20:29:24 GMT 2026) -----
HST Phase I Proposal 7453 successfully submitted.
Receipt: # 7453-2
----- Attempting Submission 3 (Thu Apr 16 22:59:39 GMT 2026) -----
HST Phase I Proposal 7453 successfully submitted.
Receipt: # 7453-3Could not connect to APT Status Server
MERGING RULE VIOLATED DURING AUTOMATIC MERGING0----- Attempting Submission 1 (Wed Aug 12 08:01:54 GMT 2026) -----I couldn't find the solution to error in visit 3 as nothing evident popped up.Probing the Existence of the Elusive Ultracompact White Dwarf Binaries in a Dense Globular ClusterGlobular clusters (GCs) are believed to be important factories of exotic binaries that harbor stellar remnants, which formation is enhanced due to dynamical interactions because of their high stellar densities. One of the populations expected to be abundant in GCs is the one of accreting double white dwarfs (or AM CVns). These are binaries with orbital periods between 5-70 min which lack H. However, not a single AM CVn has been confirmed yet in any GC, raising concerns about their existance in those very dense environments. This proposal aims to monitor in UV and narrow filter the low extinction and high stellar density globular cluster NGC 6752 to identify AM CVns via their transient behavior and photometric excesses. Using this innovative technique we will test dynamical formation and evolutionary models of these binaries in GCs. We will also compare their characteristics to the known population of AM CVns in the Galactic disk. Should the discovery of an upper limit on the identification rate be lower than anticipated, it would challenge the current understanding of GCs as efficient factories of compact binaries, particularly those containing white dwarfs. The study of white dwarf binaries in GCs will also have implications for the gravitational wave source detection in GCs with missions like LISA.Our goal is to identify blue transients in the cluster, especially those which are He-rich. The program is composed of 14 orbits divided in 9 visits.
Visits 1 and 2 have 3 orbits each, visit 4 has 2 orbits and the remaining 6 have one orbit each.
The primaries of the first 2 orbits of visits 1 and 2, and the first orbit of visit 3 are devoted to the filters F469N and F475W to detect helium. We took 2 images per filter per orbit to remove artifacts. We dedicated more time to the narrow filter F469N which has a very low transmission. We obtained around 1800s total per orbit in the filter F469N and 440s in the wider filter F475W. We think that despite having an exposure of 1000s in the narrow filter, its low transmission will prevent saturation.
For the primaries in the UV (visits 1-9) we use the F225W and F275W filters on the UVIS channel of WFC3 in order to overcome the stellar crowding. We point at the center of the cluster. In order to remove cosmic rays and other artifacts we obtain 2 images per filter for a total of 4 per orbit. In orbits 1-9 each F225W observation has an exposure of 700s or less and the F275W observations have 600s or less, optimized to obtain the similar signal-to-noise. For the primaries, the strategy is the same for each of the 9 visits.
We simultaneously obtain parallel observations with the WFC on the ACS. We are using 3 filters: F435W, F635W and F658N. Due to dumping and maneuver times to cover the chip gaps, we accomodate 4 parallel images per orbit. Our statrategy is to obtain 2 images in 2 different filters every orbit, alternating between the F435W and F658N filters between visits. This help us to remove cosmic rays and other artifacts each orbit, giving us reliable colors of the sources identified. For the first parallel visit we use the combination F625W and F435W, with longer exposures in F435W because it is the bluer filter. The total exposure times per orbit are around 320s for F625W and 630s for F435W, each divided in 2 observations.
For the second parallel visit we use the combination F625W and F658N. In this case we give more weight to the narrow filter. Total exposure times are around 320s in F625W and 670s in F658N, divided in 2 observations each. Our third and fourth observations are similar to our first and second one, respectively. The rest repeat the pattern.
We set up our dithers as POS-TARGS. We use similar values to the ones given by the WFC3-UVIS-MOSAIC-LINE strategy, which according to the documentation (section "C.2 WFC3 Patterns" of the WFC3 handbook) steps the gap on both detectors and it is used for full-frame WFC3-UVIS with ACS-WFC in parallel. The values used are X=1.446 arcsec, Y=2.926 arcsec and were set after the second primary observation in each visit.
No timing restrictions for the first visit are placed. However, subsequent visits must be scheduled between 10-25 days from the previous one.
We give a post flash of 17-20 e-/pix for each WFC3-UVIS images to account for the increasing CTE looses on the detector, as was recommended by the documentaion (ISR 2020-08: Strategies for Mitigation of CTE Losses in WFC3/UVIS) .The team members of this proposal are experts on the study of compact binaries in globular clusters (GCs).
They have made important contributions to the field using data taken at different wavelengths. All of them have
several published papers on compact binaries in GCs, including several papers based on HST data.
They have obtained approved HST proposals as PI to study compact binaries in UV and optical in globular clusters.
Dr. L.E. Rivera Sandoval has expertise reducing and analyzing UV HST WFC3 and ACS data, the prime instruments and
wavelengths requested in this proposal. She has carried out NUV studies of compact binaries in 47 Tuc, leading
to the discovery of the first AM CVn candidate in that cluster as well as doubled the number of cataclysmic variables known there. She has multiple first-author papers published on UV data taken with HST data. She has been PI of 4 HST proposals to study globular clusters.
Prof. T. J. Maccarone has expertise in X-ray observations for understanding the populations of X-ray binaries in
the field and in star clusters, and in correlating X-ray source properties with multiwavelength properties. He is also PI of multiple HST data sets.
Dr. Manuel Pichardo Marcano has expertise working with HST data of globular clusters, and in particular, reducing and analyzing optical and near-ultraviolet data. He has worked on a survey to search for compact binaries and variable sources in NGC 6397. This led to the discovery of new exotic white dwarf binaries in NGC 6397, like the first magnetic extremely-low mass white dwarf in any globular cluster. He has also worked on the variability of AM CVns in the Galaxy.Stellar Populations and the Interstellar MediumStellar Physics and Stellar Types6falsetruefalsefalsefalsefalsefalseSUPPORTEDSTELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000WFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF275WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NWFC3/UVISImagingNoNoF469NWFC3/UVISImagingNoNoF475WWFC3/UVISImagingNoNoF469NWFC3/UVISImagingNoNoF475WWFC3/UVISImagingNoNoF469NWFC3/UVISImagingNoNoF475WWFC3/UVISImagingNoNoF469NWFC3/UVISImagingNoNoF475WWFC3/UVISImagingNoNoF469NWFC3/UVISImagingNoNoF475WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658NACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF625WACS/WFCImagingNoNoF658N/private/var/folders/st/rq1t3ycd4fn78w66l9d2w9fs7b2w78/T/OPVisit7111769856037050893.xmlTiming link suitability includes constraints ([02 After 01 by 10.0 to 25.0 days])The scheduling data was generated by CASM 34.2.CASM was run in Phase II mode.(Tic-Visit
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