16172( 3) - 09-Nov-2020 20:26:30 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16172 Version: 3 Check-in Time: 09-Nov-2020 20:26:30 STScI Edit Number: 0 Title The disappearing LBV in the low metallicity galaxy PHL293B: Collapse to a black hole? ------------------------------------------------------------------------------------ Type Cycle GO 28 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Nathan Smith University of Arizona Y CoI: Dr. Jose Groh University of Dublin, Trinity College N CoI: Mr. Andrew Allan University of Dublin, Trinity College N CoI: Dr. Jennifer Andrews University of Arizona N CoI: Mr. Eoin Farrell University of Dublin, Trinity College N CoI: Dr. Andrea Mehner European Southern Observatory - Chile N ------------------------------------------------------------------------------------ Abstract The metal-poor dwarf galaxy PHL293B (23 Mpc) contained a luminous blue variable (LBV) candidate that was identified based on its spectrum. This source was detected at roughly constant luminosity during 2001-2009, modeled as a massive LBV with log(L/Lsun)=6.4-6.7. This is similar to eta Carinae, and notably, similar to the progenitors of SN2009ip and SN2015bh. In more recent data, the source has faded beyond ground-based limits, and spectral signatures of the LBV are now gone. A massive LBV-like star at roughly 0.1 Z solar provides important clues for understanding the role of eruptive mass loss at low metallcity, and the star's recent disappearance may hold critical clues about the fate of such stars. The sudden fading in the last decade could be the result of either the end of a giant LBV eruption, or it could be the death of a very massive star when it collapsed to a black hole with no bright supernova. To rule out the second hypothesis, we would need to detect the surviving star, but ground-based data cannot do this because the source is too faint and lost in galaxy light. There are two plausible scenarios for a surviving star: (1) When the LBV eruption ended, the star faded in the optical because it got hotter, shifting its energy distribution into the UV, or (2) it faded at visual wavelengths because it formed dust, in which case the star should still be detectable in the near-IR. We propose deep imaging with WFC3 UVIS and IR to either detect the surviving star in the UV/optical/IR, or to confirm that it has vanished to deep limits. If it is gone, this would be the first secure case of a very massive star that vanished to a black hole. ------------------------------------------------------------------------------------ Observations Description ------------------------ The goal of these observations is to obtain post-event optical and near-IR magnitudes or deep upper limits of the source at the position of an LBV star that has faded beyond detectability in ground-based data (perhaps largely due to spatial resolution, as it is now indistinguishable from surropunding galaxy light from the goround). We also aim to obtain photometry of all nearby bright sources to help constrain the host environments age and/or star formation history. The UVIS observations are all set up in one visit of two orbits, but these orbits can be separated if neeeded. There are no special orients needed, although we would prefer both orbits taken at the same orient if they need to 16172( 3) - 09-Nov-2020 20:26:30 - [ 2] separated into separate visits because we are combining two exposures of F438W including one from each oribit. We are using full frame instead of sub-array because we need the whole nearby stellar population. ------------------------------------------------------------------------------------ 16172( 3) - 09-Nov-2020 20:26:30 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PHL293B-LBV EXT-STAR, BLUE RA=22H30M36.7960S, J2000 V = 22 +/- 1 STRAGGLER, ETA CARINAE DEC=-00D06'36.89" STAR, LUMINOUS BLUE VARIABLE Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 16172( 3) - 09-Nov-2020 20:26:30 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.145 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.636 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 41.788 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 16172( 3) - 09-Nov-2020 20:26:30 - [ 5] Visit: 01 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 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F606W FLASH=12 1 216 S PATTERN 1 1-2 S see below (414 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F225W FLASH=18 1 720 S S see below (1422 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F438W FLASH=18 1 280 S S see below (270 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F814W FLASH=15 1 252 S PATTERN 1 4-5 S see below (484 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F336W FLASH=18 1 680 S S see below (1340 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 PHL293B-LBV WFC3/UVI ACCUM UVIS2 F438W FLASH=18 1 280 S POS TARG S see below -3.4088166189286015E-4, (270 S) -1.425343380764952 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHL293B-LBV 1 WFC3/UVI ACCUM UVIS2 F606W 1 none none none 1 207.0 S S PHL293B-LBV 1 WFC3/UVI ACCUM UVIS2 F606W 2 none none none 1 207.0 S S PHL293B-LBV 2 WFC3/UVI ACCUM UVIS2 F225W 1 none none none 1 711.0 S S PHL293B-LBV 2 WFC3/UVI ACCUM UVIS2 F225W 2 none none none 1 711.0 S S PHL293B-LBV 3 WFC3/UVI ACCUM UVIS2 F438W none none none none 1 270.0 S S PHL293B-LBV 4 WFC3/UVI ACCUM UVIS2 F814W 1 none none none 2 242.0 S S 16172( 3) - 09-Nov-2020 20:26:30 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHL293B-LBV 4 WFC3/UVI ACCUM UVIS2 F814W 2 none none none 2 242.0 S S PHL293B-LBV 5 WFC3/UVI ACCUM UVIS2 F336W 1 none none none 2 670.0 S S PHL293B-LBV 5 WFC3/UVI ACCUM UVIS2 F336W 2 none none none 2 670.0 S S PHL293B-LBV 6 WFC3/UVI ACCUM UVIS2 F438W none none none none 2 270.0 S S 16172( 3) - 09-Nov-2020 20:26:30 - [ 7] Visit: 02 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 PHL293B-LBV WFC3/IR MULTIAC IR F125W NSAMP=12, SAMP-SEQ=STEP100 1 DEF PATTERN 2 1-2 CUM (1198.465 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 PHL293B-LBV WFC3/IR MULTIAC IR F160W NSAMP=13, SAMP-SEQ=STEP100 1 DEF CUM (1398.465 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHL293B-LBV 1 WFC3/IR MULTIAC IR F125W 1 none none none 1 N/A CUM PHL293B-LBV 1 WFC3/IR MULTIAC IR F125W 2 none none none 1 N/A CUM PHL293B-LBV 2 WFC3/IR MULTIAC IR F160W 1 none none none 1 N/A CUM PHL293B-LBV 2 WFC3/IR MULTIAC IR F160W 2 none none none 1 N/A CUM 16172( 3) - 09-Nov-2020 20:26:30 - [ 8] Summary Form for Proposal 16172 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=12, FLASH=15, FLASH=18, NSAMP=12, NSAMP=13, SAMP-SEQ=STEP100 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1-2, PATTERN 1 4-5, PATTERN 2 1-2, POS TARG -3.4088166189286015E-4, -1.425343380764952 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F125W, F160W, F225W, F336W, F438W, F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PHL293B-LBV ------------------------------------------------------------------------------------------------------------------------------------