17488( 8) - 10-Sep-2024 14:19:25 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17488 Version: 8 Check-in Time: 10-Sep-2024 14:19:25 STScI Edit Number: 1 Title Unraveling the mystery of the rare 2175 A extinction bump in the SMC ------------------------------------------------------------------------------------ Type Cycle GO 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Petia Yanchulova Merica-Jones Space Telescope Science Institute Y CoI: Dr. Karl D. Gordon Space Telescope Science Institute N CoI: Dr. Marjorie Decleir Space Telescope Science Institute - ESA N CoI: Dr. Karin Marie Sandstrom University of California - San Diego N CoI: Dr. Dries Van De Putte The University of Western Ontario N ------------------------------------------------------------------------------------ Abstract Understanding the properties of dust extinction is fundamental to answer questions ranging from how dust grains form to what drives galaxy evolution. The dust extinction curve at ultraviolet (UV) wavelengths is known to vary widely in the Local Group and beyond, but the reason is still not fully understood. It is an open question how, and physical conditions of the interstellar medium (ISM) may affect extinction curve features such as the far-UV rise and the properties of the 2175A bump. The Small Magellanic Cloud (SMC) is key to studying such variations since it is our best nearby analog to low-metallicity and high-redshift observations, there are plenty of observations of its ISM, and spatially-resolved individual stars and dust/gas complexes enable analyzing correlations between environment and dust extinction properties. The limited number of high-quality SMC UV extinction curve measurements needs to be supplemented with new targeted measurements of sightlines in a variety of ISM physical conditions. We propose to measure UV extinction curves and the HI column densities of a carefully selected sample of 6 reddened, hot stars to evaluate the dependence on environment of the 2175A bump and the FUV rise. These stars have a high probability of a strong bump in their extinction curves based on modeling their spectral energy distributions from an existing large photometric survey in the SMC Southwest Bar. Our proposed sample will triple the UV extinction curve database of SMC sightlines with a strong bump from 3 to 9 improving the statistical significance of correlations of bump properties with environment. ------------------------------------------------------------------------------------ Observations Description ------------------------ HST STIS is the most suitable instrument for our proposed observations. We propose to obtain STIS low-resolution spectra with the 52x2 slit and the G140L grating (to measure the FUV extinction curve rise and obtain Ly-alpha to measure the HI column density) and the G230L grating (to measure the properties of the 2175 A feature). STIS will be able to perform the observations significantly faster than COS. Our targets have 17.62 <= F475W <= 19.47 mag and extinction in the V band of 0.91 <= AV <= 1.6. These correspond to V-band magnitudes from 17.54 to 19.43 mag. We require a S/N of ~ 10 at R = 10 since from previous STIS UV spectra work we know these criteria will allow us to measure the detailed properties of the bump and the strength of the FUV rise. Using the STIS exposure time calculator, we find that the faintest object will 17488( 8) - 10-Sep-2024 14:19:25 - [ 2] require a 2452s/2407s exposure in G230L/G140L respectively. This and two other objects will require 2 orbits each when taking into consideration the instrument overheads. Our brightest object will require 271s/424s in G230L/G140L respectively, which along with two other bright objecrs will require one orbit each. In total, for the 6 targets in our sample we request 9 HST orbits. ------------------------------------------------------------------------------------ 17488( 8) - 10-Sep-2024 14:19:25 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SMIDGE-S1 EXT-STAR, B0-B2 III-I RA=00H45M17.5392S +/- 0.2", J2000 V = 17.62 +/- 0.02 DEC=-73D23'44.05" +/- 0.2" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 2 SMIDGE-S2 EXT-STAR, B3-B5 V-IV RA=00H45M10.1400S, J2000 V = 18.06 +/- 0.02 DEC=-73D21'0.29" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 3 SMIDGE-S3 EXT-STAR, B3-B5 V-IV RA=00H46M23.9256S +/- 0.2", J2000 V = 17.96 +/- 0.02 DEC=-73D16'38.24" +/- 0.2" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 4 SMIDGE-S4 EXT-STAR, B0-B2 V-IV RA=00H46M26.7980S +/- 0.2", J2000 V = 17.99 +/- 0.001 DEC=-73D20'20.45" +/- 0.2" Reference Frame: ICRS Comments: replaced original S4 which was located in the N13 nebula due to bright UV sources and extended emission nearby. The new target is brighter and is does not appear to have other bright nearby objects of concern. ------------------------------------------------------------------------------------------------------------------------------------ 5 SMIDGE-S5 EXT-STAR, B3-B5 V-IV RA=00H46M6.4704S +/- 0.2", J2000 V = 18.275 +/- 0.002 DEC=-73D17'28.98" +/- 0.2" Reference Frame: ICRS Comments: Replaced SMIDGE-S5 with a star with similar parameters for the science proposed, and better observation parameters: J004606.4704-731728.978 Target is 9.4" away from a brighter object with V=17.7 mag. Is within or close to 5" away from objects with V=19.7 mag and 19.1 mag, resepctively. log(T) = 4.14 dex; log(g) = 3.52 dex; Av = 1.15; Rv = 2.74; => E(B-V) =~ 0.38 ------------------------------------------------------------------------------------------------------------------------------------ 6 SMIDGE-S6 EXT-STAR, B0-B2 V-IV RA=00H45M19.8960S +/- 0.2", J2000 V = 18.35 +/- 0.002 DEC=-73D22'13.80" +/- 0.2" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 7 2MASS-J00462 EXT-STAR, K III-I RA=00H46M27.2030S, J2000 V = 17.090 720-7321013 DEC=-73D21'1.40" Reference Frame: ICRS Comments: 2MASS J00462720-7321013 1 00 46 27.203 -73 21 01.40 RGB*_Candidate MIR|NIR|RB? B= 18.390 V=17.090 J=14.966 H=14.247 K=14.269 ------------------------------------------------------------------------------------------------------------------------------------ 17488( 8) - 10-Sep-2024 14:19:25 - [ 4] Visit: 01 (s1) 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 SMIDGE-S1 STIS/CCD ACQ F28X50LP MIRROR 1 27.8 S (27.8 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMIDGE-S1 STIS/NUV ACCUM 52X2 G230L 2376 1 221.9 S -MAMA see below (807.9 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SMIDGE-S1 STIS/FUV ACCUM 52X2D1 G140L 1425 1 322.6 S -MAMA see below (908.6 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 | ------------------------------------------------------------------------------------------------------------------------------------ SMIDGE-S1 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SMIDGE-S1 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 807.9 S -MAMA SMIDGE-S1 3 STIS/FUV ACCUM 52X2D1 G140L 1425 none none none none 1 908.5999 -MAMA 99999999 9 S 17488( 8) - 10-Sep-2024 14:19:25 - [ 5] Visit: 02 (s2) 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 SMIDGE-S2 STIS/CCD ACQ F28X50LP MIRROR 1 57 S (57 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMIDGE-S2 STIS/NUV ACCUM 52X2 G230L 2376 1 488 S -MAMA see below (720 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SMIDGE-S2 STIS/FUV ACCUM 52X2D1 G140L 1425 1 646 S -MAMA see below (878 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 | ------------------------------------------------------------------------------------------------------------------------------------ SMIDGE-S2 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SMIDGE-S2 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 720.0 S -MAMA SMIDGE-S2 3 STIS/FUV ACCUM 52X2D1 G140L 1425 none none none none 1 878.0 S -MAMA 17488( 8) - 10-Sep-2024 14:19:25 - [ 6] Visit: 03 (s3) 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 SMIDGE-S3 STIS/CCD ACQ F28X50LP MIRROR 1 35 S (35 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMIDGE-S3 STIS/NUV ACCUM 52X2 G230L 2376 1 660 S -MAMA see below (736 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SMIDGE-S3 STIS/FUV ACCUM 52X2D1 G140L 1425 1 874 S -MAMA see below (950 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 | ------------------------------------------------------------------------------------------------------------------------------------ SMIDGE-S3 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SMIDGE-S3 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 736.0 S -MAMA SMIDGE-S3 3 STIS/FUV ACCUM 52X2D1 G140L 1425 none none none none 1 950.0 S -MAMA 17488( 8) - 10-Sep-2024 14:19:25 - [ 7] Visit: 04 (s4) 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 2MASS-J0046 STIS/CCD ACQ F28X50LP MIRROR 1 12 S (12 2720-732101 S) 3 ------------------------------------------------------------------------------------------------------------------------------------ 2 SMIDGE-S4 STIS/NUV ACCUM 52X2 G230L 2376 1 244 S -MAMA see below (2199 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SMIDGE-S4 STIS/FUV ACCUM 52X2D1 G140L 1425 1 371 S -MAMA see below (2736 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2MASS-J00462720-732 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 1013 SMIDGE-S4 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 2199.0 S -MAMA SMIDGE-S4 3 STIS/FUV ACCUM 52X2D1 G140L 1425 none none none none 2 2736.0 S -MAMA 17488( 8) - 10-Sep-2024 14:19:25 - [ 8] Visit: 05 (s5) 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 SMIDGE-S5 STIS/CCD ACQ F28X50LP MIRROR 1 9 S (9 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMIDGE-S5 STIS/NUV ACCUM 52X2 G230L 2376 1 1678 S -MAMA see below (2239 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SMIDGE-S5 STIS/FUV ACCUM 52X2D1 G140L 1425 1 2179 S -MAMA see below (2708 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 | ------------------------------------------------------------------------------------------------------------------------------------ SMIDGE-S5 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SMIDGE-S5 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 2239.0 S -MAMA SMIDGE-S5 3 STIS/FUV ACCUM 52X2D1 G140L 1425 none none none none 2 2708.0 S -MAMA 17488( 8) - 10-Sep-2024 14:19:25 - [ 9] Visit: 06 (s6) 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 SMIDGE-S6 STIS/CCD ACQ F28X50LP MIRROR 1 59 S (59 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMIDGE-S6 STIS/NUV ACCUM 52X2 G230L 2376 1 1069 S -MAMA see below (2039 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SMIDGE-S6 STIS/FUV ACCUM 52X2D1 G140L 1425 1 1190 S -MAMA see below (2708 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 | ------------------------------------------------------------------------------------------------------------------------------------ SMIDGE-S6 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SMIDGE-S6 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 2039.0 S -MAMA SMIDGE-S6 3 STIS/FUV ACCUM 52X2D1 G140L 1425 none none none none 2 2708.0 S -MAMA 17488( 8) - 10-Sep-2024 14:19:25 - [ 10] Summary Form for Proposal 17488 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X2, 52X2D1, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names 2MASS-J00462720-7321013, SMIDGE-S1, SMIDGE-S2, SMIDGE-S3, SMIDGE-S4, SMIDGE-S5, SMIDGE-S6 ------------------------------------------------------------------------------------------------------------------------------------