18091( 2) - 31-Jul-2025 19:28:55 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18091 Version: 2 Check-in Time: 31-Jul-2025 19:28:55 STScI Edit Number: 0 Title An Exciting New Population of Luminous Point Sources in Nearby Galaxies ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Jimmy A. Irwin University of Alabama Y CoI: Dr. Rosanne Di Stefano Smithsonian Institution Astrophysical N Observatory CoI: Mr. Mustafa Muhibullah University of Alabama N ------------------------------------------------------------------------------------ Abstract An exciting new class of X-ray emitters with no detectable emission above 0.3 keV has recently been discovered within galaxies observed with early archival Chandra ACIS-S data, dubbed 'hypersoft' X-ray sources. Within the narrow 0.15-0.3 keV X-ray bandpass these sources emit up to 1e38 erg/s with bolometric luminosities potentially as high as 1e40 erg/s. The estimated blackbody temperatures of these source are constrained to be below 21 eV (250, 000 K), making them strong EUV, and potentially FUV emitters detectable with HST. The available X-ray data indicate the sources are not persistent over ~5 year time scales. Previous WFC3/UVIS/F225W observations of large, nearby elliptical galaxies taken in 2009 have found FUV-bright point sources in those galaxies that we suggest are the FUV tails of hypersoft X-ray sources. We propose WFC3/UVIS/F225W re-observations of two of those nearby large elliptical galaxies known to possess hypersoft X-ray sources to search for variable FUV-bright sources that have turned off (or on) since the initial 2009 F225W observations that would be strong evidence for a new, unrecognized very high bolometric luminosity class of objects in galaxies. ------------------------------------------------------------------------------------ Observations Description ------------------------ Our observations are designed to mimic the WFPC3/UVIS/F225W observations of HST program (11583; PI: Bregman) of the galaxies NGC4697 and NGC3379 as much as possible. We plan for four exposures (to eliminate cosmic rays) covering two orbits each for each of the galaxies in the F225W filter. This led to individual exposure times of ~1220 seconds (and four exposures per galaxy). We choose the pattern type as WFC3-UVIS-DITHER-BOX, with UVIS-CENTER as the aperture, and CR-SPLIT=NO to match Program 11583. Since Program 11583 did not increase the flash level, we did not either. ------------------------------------------------------------------------------------ 18091( 2) - 31-Jul-2025 19:28:55 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4697 GALAXY, ELLIPTICAL RA=12H48M35.8981S, J2000 V = 10.55 +/- 0.02 DEC=-05D48'2.48" Reference Frame: Other: SIMBAD Extended: YES Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3379 GALAXY, ELLIPTICAL RA=10H47M49.6000S, J2000 V = 9.76 DEC=+12D34'53.87" Reference Frame: Other: SIMBAD Extended: YES Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 18091( 2) - 31-Jul-2025 19:28:55 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18091( 2) - 31-Jul-2025 19:28:55 - [ 4] Visit: 01 (NGC4697) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4697 WFC3/UVI ACCUM UVIS-CENT F225W CR-SPLIT=NO 1 1230 S PATTERN 1 1 S ER (4900 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC4697 1 WFC3/UVI ACCUM UVIS-CEN F225W 1 none none none 1 N/A S TER NGC4697 1 WFC3/UVI ACCUM UVIS-CEN F225W 2 none none none 1 N/A S TER NGC4697 1 WFC3/UVI ACCUM UVIS-CEN F225W 3 none none none 2 1220.0 S S TER NGC4697 1 WFC3/UVI ACCUM UVIS-CEN F225W 4 none none none 2 1220.0 S S TER 18091( 2) - 31-Jul-2025 19:28:55 - [ 5] Visit: 02 (NGC3379) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3379 WFC3/UVI ACCUM UVIS-CENT F225W CR-SPLIT=NO 1 1230 S PATTERN 1 1 S ER see below (4896 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC3379 1 WFC3/UVI ACCUM UVIS-CEN F225W 1 none none none 1 1229.0 S S TER NGC3379 1 WFC3/UVI ACCUM UVIS-CEN F225W 2 none none none 1 1229.0 S S TER NGC3379 1 WFC3/UVI ACCUM UVIS-CEN F225W 3 none none none 2 1219.0 S S TER NGC3379 1 WFC3/UVI ACCUM UVIS-CEN F225W 4 none none none 2 1219.0 S S TER 18091( 2) - 31-Jul-2025 19:28:55 - [ 6] Summary Form for Proposal 18091 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS-CENTER ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F225W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC3379, NGC4697 ------------------------------------------------------------------------------------------------------------------------------------