15086( 3) - 20-Jul-2017 15:28:35 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15086 Version: 3 Check-in Time: 20-Jul-2017 15:28:35 STScI Edit Number: 0 Title Age and mass of the star cluster around the intermediate-mass black hole HLX-1 ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Roberto Soria Curtin University Y CoI: Dr. Luca Zampieri Osservatorio Astronomico di Padova N CoI: Dr. Sean A. Farrell University of Sydney N ------------------------------------------------------------------------------------ Abstract We propose to study the optical counterpart of the intermediate-mass black hole (IMBH) HLX-1, about 3 years after its last X-ray outburst. Previous HST observations taken at epochs closer to an outburst show a variable near-UV/blue component, plus a constant red/near-IR component. The redder component probably comes from an old stellar population around the black hole; the bluer component may be a combination of emission from an irradiated accretion disk, and from a young stellar population. Their relative contributions and the age of the stellar population(s) are still subject of debate. By re-observing the system when the irradiated component is minimal, we will determine whether the near-UV/blue optical emission has declined even further and whether the red/near-IR optical emission has stayed approximately constant. This will tell us whether the optical counterpart is a massive star cluster, and place a strong upper limit to the young stellar population around the IMBH. Having determined the constant contribution of the stellar emission, we will then insert it into broad-band models of the emission in outburst, and obtain a better estimate of the accretion disk parameters, constraining formation and evolution scenarios for the IMBH. We will use the same set of filters as in previous HST observations, for direct comparison of brightness and colors: F140LP (ACS SBC); F300X, F336W, F390W, F555W, F621M, F775W (WFC3 UVIS); F105W, F160W (WFC3 IR). We request a total of 7 orbits. ------------------------------------------------------------------------------------ Observations Description ------------------------ Our proposed observations are a simple, straight-forward imaging of a point-like source, the optical counterpart of HLX-1 (likely, an unresolved star cluster), in the halo of the S0 galaxy ESO243-49. We want a broad-band coverage from the near-UV to the near-IR, to constrain the age of the stellar population and the contribution of X-ray irradiation. We will use the F140LP filter of ACS SBC, six filters of WFC3 UVIS (F300X, F336W, F390W, F555W, F775W) and two filters of WFC3 IR (F105W and F160W). This is exactly the same set of filters used for the HST observations in 2012 and 2013 (and most of them were also used in 2010), see Table 1 in the Phase I scientific justification. This will make it easy to look for variability from the previous epochs; in particular, we want to test whether there is further decrease of the near-UV/near-IR flux ratio. In 2012 and 2013, one orbit was allocated for the ACS image, and 4 orbits for 15086( 3) - 20-Jul-2017 15:28:35 - [ 2] the 8 WFC3 filters. We report on those results in Soria et al. (2017). This time we request 7 orbits instead of 5. The reasons for the increased time request are: i) we want to test whether the optical source keeps declining, as the X-ray outbursts get shorter and less frequent. We want to be able to constrain a brightness decline as small as about half a magnitude in U and V, within the uncertainties of the 2013 and 2017/8 observation. Also, in the IR filters, the source was only detected at a signal-to-noise ratio 7, because of the strong diffuse emission from the halo of ESO243-49 and the lower spatial resolution: this made it diffcult to fit the spectrum and constrain the age of the old stellar component; ii) the small increase in target visibility (56 min per orbit instead of 55) compared with 2010 and 2013 makes it just long enough to efficiently spread the six WFC3 UVIS observations over 4 orbits, with 4-point box dithering and >339s per exposure, without buffer dumps. Our suggested plan for the observations is: VISIT 1: -- orbit 1 for WFC3 IR F105W, with WFC3-IR-DITHER-BOX-MIN, 2600s; -- orbit 2 for WFC3 IR F160W, with WFC3-IR-DITHER-BOX-MIN, 2800s; VISIT 2: -- orbit 1 for ACS SBC F140LP, 4-point box dithering, 2700s of effective exposure time; -- orbit 2 for WFC3 UVIS F300X, with UV flashing and WFC3-UVIS-DITHER-BOX, approximately 1600s split into 4 exposures of 400s each. Then, the first 2 exposures in the F336W filter, also with UV flashing and dithering, about 400s each; -- orbit 3 for the last 2 exposures in the F336W filter, with UV flashing and dithering, about 400s each, total of 1600s (including those of orbit 4). Then, all 4 exposures for F390W, dithered, 400s each, total of 1600s; -- orbit 4 for WFC3 UVIS F555W, about 1600s split into 4 dithered exposures of 400s each. Then, the first 2 exposures in the F621M filter, also with dithering, about 400s each; -- orbit 5 for the last 2 dithered exposures in the F621M filter, 4000s each, total of 1600s. Then, all 4 dithered exposures for F775W, 400s each, total of 1600s. With this strategy, based on the Exposure Time Calculator and on our experience of the previous HST observations with the same set-up, we will reach signal-to-noise >10 in all filters, even if the brightness decline continues as seen between 2010 and 2013. ------------------------------------------------------------------------------------ 15086( 3) - 20-Jul-2017 15:28:35 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HLX-1 STELLAR CLUSTER, RA=01H10M28.2700S, J2000 V = 25 +/- 0.5 U=24, I=24.5 ACCRETION DISK, DEC=-46D04'22.30" GLOBULAR CLUSTER Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 15086( 3) - 20-Jul-2017 15:28:35 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-SBC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.179 Line_Spacing 0.116 Coordinate_Frame POS-TARG Pattern_Orient 20.02 Angle_Between_Sides 63.65 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 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 ------------------------------------------------------------------------------------------------------------------------------------ 15086( 3) - 20-Jul-2017 15:28:35 - [ 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 HLX-1 WFC3/IR MULTIAC IR F105W NSAMP=14, SAMP-SEQ=SPARS50 1 DEF PATTERN 2 1 CUM (2611.753 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HLX-1 WFC3/IR MULTIAC IR F160W NSAMP=15, SAMP-SEQ=SPARS50 1 DEF PATTERN 2 2 CUM (2811.754 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 | ------------------------------------------------------------------------------------------------------------------------------------ HLX-1 1 WFC3/IR MULTIAC IR F105W 1 none none none 1 N/A CUM HLX-1 1 WFC3/IR MULTIAC IR F105W 2 none none none 1 N/A CUM HLX-1 1 WFC3/IR MULTIAC IR F105W 3 none none none 1 N/A CUM HLX-1 1 WFC3/IR MULTIAC IR F105W 4 none none none 1 N/A CUM HLX-1 2 WFC3/IR MULTIAC IR F160W 1 none none none 2 N/A CUM HLX-1 2 WFC3/IR MULTIAC IR F160W 2 none none none 2 N/A CUM HLX-1 2 WFC3/IR MULTIAC IR F160W 3 none none none 2 N/A CUM HLX-1 2 WFC3/IR MULTIAC IR F160W 4 none none none 2 N/A CUM 15086( 3) - 20-Jul-2017 15:28:35 - [ 6] 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 HLX-1 ACS/SBC ACCUM SBC F140LP 1 675 S PATTERN 1 1 see below (2748 S) Comments: ACS.im.1011860 ETC run done using the well-determined Vega brightness in the U band and the best-fitting model spectrum. ACS.im.1011865 ETC run done using the observed flux density at 1500 Ang, from 2013. The two runs give essentially the same result, S/N = 10 for the requested exposure time. This is our best estimate of how the source will look like in 6 months' time. However, it could turn out to be a factor of 2 brighter or fainter, so the S/N could be ~7 or ~15. ------------------------------------------------------------------------------------------------------------------------------------ 2 HLX-1 WFC3/UVI ACCUM UVIS2 F300X FLASH=12 1 384 S PATTERN 3 2 S (1536 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 HLX-1 WFC3/UVI ACCUM UVIS2 F336W FLASH=12 1 402 S PATTERN 3 3 S see below (1571 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 HLX-1 WFC3/UVI ACCUM UVIS2 F390W FLASH=10 1 403 S PATTERN 3 4 S (1612 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 HLX-1 WFC3/UVI ACCUM UVIS2 F555W 1 402 S PATTERN 3 5 S see below (1636 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 HLX-1 WFC3/UVI ACCUM UVIS2 F621M FLASH=6 1 402 S PATTERN 3 6 S see below (1629 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 HLX-1 WFC3/UVI ACCUM UVIS2 F775W FLASH=6 1 402 S PATTERN 3 7 S see below (1612 S) ------------------------------------------------------------------------------------------------------------------------------------ 15086( 3) - 20-Jul-2017 15:28:35 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ HLX-1 1 ACS/SBC ACCUM SBC F140LP 1 none none none 1 687.0 S HLX-1 1 ACS/SBC ACCUM SBC F140LP 2 none none none 1 687.0 S HLX-1 1 ACS/SBC ACCUM SBC F140LP 3 none none none 1 687.0 S HLX-1 1 ACS/SBC ACCUM SBC F140LP 4 none none none 1 687.0 S HLX-1 2 WFC3/UVI ACCUM UVIS2 F300X 1 none none none 2 N/A S HLX-1 2 WFC3/UVI ACCUM UVIS2 F300X 2 none none none 2 N/A S HLX-1 2 WFC3/UVI ACCUM UVIS2 F300X 3 none none none 2 N/A S HLX-1 2 WFC3/UVI ACCUM UVIS2 F300X 4 none none none 2 N/A S HLX-1 3 WFC3/UVI ACCUM UVIS2 F336W 1 none none none 2 384.0 S S HLX-1 3 WFC3/UVI ACCUM UVIS2 F336W 2 none none none 2 383.0 S S HLX-1 3 WFC3/UVI ACCUM UVIS2 F336W 3 none none none 3 N/A S HLX-1 3 WFC3/UVI ACCUM UVIS2 F336W 4 none none none 3 N/A S HLX-1 4 WFC3/UVI ACCUM UVIS2 F390W 1 none none none 3 N/A S HLX-1 4 WFC3/UVI ACCUM UVIS2 F390W 2 none none none 3 N/A S HLX-1 4 WFC3/UVI ACCUM UVIS2 F390W 3 none none none 3 N/A S HLX-1 4 WFC3/UVI ACCUM UVIS2 F390W 4 none none none 3 N/A S HLX-1 5 WFC3/UVI ACCUM UVIS2 F555W 1 none none none 4 409.0 S S HLX-1 5 WFC3/UVI ACCUM UVIS2 F555W 2 none none none 4 409.0 S S HLX-1 5 WFC3/UVI ACCUM UVIS2 F555W 3 none none none 4 409.0 S S HLX-1 5 WFC3/UVI ACCUM UVIS2 F555W 4 none none none 4 409.0 S S HLX-1 6 WFC3/UVI ACCUM UVIS2 F621M 1 none none none 4 409.0 S S HLX-1 6 WFC3/UVI ACCUM UVIS2 F621M 2 none none none 4 408.0 S S HLX-1 6 WFC3/UVI ACCUM UVIS2 F621M 3 none none none 5 406.0 S S 15086( 3) - 20-Jul-2017 15:28:35 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ HLX-1 6 WFC3/UVI ACCUM UVIS2 F621M 4 none none none 5 406.0 S S HLX-1 7 WFC3/UVI ACCUM UVIS2 F775W 1 none none none 5 403.0 S S HLX-1 7 WFC3/UVI ACCUM UVIS2 F775W 2 none none none 5 403.0 S S HLX-1 7 WFC3/UVI ACCUM UVIS2 F775W 3 none none none 5 403.0 S S HLX-1 7 WFC3/UVI ACCUM UVIS2 F775W 4 none none none 5 403.0 S S 15086( 3) - 20-Jul-2017 15:28:35 - [ 9] Summary Form for Proposal 15086 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, SBC, UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/SBC, WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=10, FLASH=12, FLASH=6, NSAMP=14, NSAMP=15, SAMP-SEQ=SPARS50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 2 1, PATTERN 2 2, PATTERN 3 2, PATTERN 3 3, PATTERN 3 4, PATTERN 3 5, PATTERN 3 6, PATTERN 3 7 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F105W, F140LP, F160W, F300X, F336W, F390W, F555W, F621M, F775W ------------------------------------------------------------------------------------------------------------------------------------ Target Names HLX-1 ------------------------------------------------------------------------------------------------------------------------------------