14225( 2) - 22-Jul-2015 21:26:30 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14225 Version: 2 Check-in Time: 22-Jul-2015 21:26:30 STScI Edit Number: 0 Title Small Magellanic Cloud Ultraviolet Dust Extinction: A Focused Study of Four Sightlines Near a Molecular Cloud with Variable 2175 A bumps ------------------------------------------------------------------------------------ Type Cycle GO 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Karl D. Gordon Space Telescope Science Institute Y CoI: Dr. Ralph C. Bohlin Space Telescope Science Institute N CoI: Dr. Geoffrey C. Clayton Louisiana State University and A & M N College CoI: Dr. Edward L. Fitzpatrick Villanova University N CoI: Dr. Derck L. Massa Space Science Institute N CoI: Dr. Karl Misselt University of Arizona N CoI: Dr. Karin Sandstrom University of California - San Diego N ------------------------------------------------------------------------------------ Abstract We propose to obtain low-resolution STIS spectra covering the entire ultraviolet for four stars in the SMC to measure their UV extinction curves and HI columns. The SMC is the critical galaxy in which to study the strong 2175 A extinction bump as the this galaxy shows sightlines with and without this feature. This proposal will increase the number of sightlines in the SMC with high quality extinction curves showing a obvious 2175 A bump from one to three. The sightlines proposed here were previously observed by Maiz Apellaniz \& Rubio (2012) at very low resolution in the mid-UV using STIS slitless prism observations in a 25"x25" region centered on a known molecular cloud. They found two sightlines to having obvious 2175 A bumps and two sightlines with very weak to absent bumps. New observations are needed to improve the details of the mid-UV extinction curve (e.g. 2175 A bump centroid), measure the far-UV extinction curve, and measure the HI columns. We will combine these four new high quality extinction curves with the existing 16 SMC curves and use this enhanced sample to study environmental factors that influence the presence of the 2175 A bump (e.g., gas-to-dust ratio, PAH grain mass fraction, & radiation field). ------------------------------------------------------------------------------------ Observations Description ------------------------ We will obtain STIS low resolution observations in the 1150 to 3180 A wavelength range of 4 reddened SMC stars in a small region in the SMC, where small spatial scale variations in dust properties will be investigated. This will triple the number of sightlines in the SMC with well measured extinction curves having a prominent 2175 A bump. Our observational goal is to measure the full UV extinction curve of each sightline in our sample allowing the strength of the 2175 A bump and far-UV rise to be determined accurately. These features are broad (the 2175 A bump has a width of around 300-400 A) and can be well measured at a spectral resolution of 10. Our goal is to detect the signature of a 30% 2175 A depression at 3-sigma confidence. Thus, our S/N goal is 10 at a resolution of 10. STIS/MAMA 14225( 2) - 22-Jul-2015 21:26:30 - [ 2] spectroscopy with the G140L and G230L gratings and the 52x2 slit is the most efficient HST observing strategy (COS would require 2X more time). Our targets all have similar V-band brightnesses but have different amounts of dust reddening. We used the STIS ETC with the SMC Bar extinction curve (an upper limit as this gives a higher attenuation than other laws) and the appropriate stellar parameters. We have used the UV fluxes from Maiz Apellaniz & Rubio (2012). Note that we used a S/N = 1 in the STIS ETC as this should give approximately a S/N = 10 for resolution 10 (assuming the STIS resolution is 1000). Even for our faintest target, only a single orbit is needed after accounting for the overheads (guide star acq., STIS acq., 2x auto-wavecals, and necessary buffer dumps). Thus, we can get a full UV spectrum (1150-3180 A) of each of our targets in under one orbit. Given the relatively short exposure times for the brightest stars and the length of the visibility of the SMC per orbit, we have increased the exposure times to provide higher S/N detection limits as well as the ability to determine UV spectral types. We are able to use the 2x2 slit instead of the 52x2 slit to avoid any bright object issues. No bright object issues were identified using the BOT tool. We would prefer the 52x2 slit as it allows for better background/scattered light subtraction. ------------------------------------------------------------------------------------ 14225( 2) - 22-Jul-2015 21:26:30 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MR12-STAR08 EXT-STAR, B0-B2 V-IV RA=00H45M33.5628S +/- 0.3", J2000 V = 18.86 +/- 0.05 F(2200) ~ 6e-17, DEC=-73D18'30.56" +/- 0.3" F(1500) ~ 7e-17 Reference Frame: ICRS Extended: NO Comments: E(B-V) = 0.51 ------------------------------------------------------------------------------------------------------------------------------------ 2 MR12-STAR09 EXT-STAR, B3-B5 V-IV RA=00H45M35.1029S +/- 0.3", J2000 V = 18.28 +/- 0.13 F(2200) ~ 4e-16, DEC=-73D18'35.87" +/- 0.3" F(1500) ~ 5e-16 Reference Frame: ICRS Extended: NO Comments: E(B-V) = 0.20 ------------------------------------------------------------------------------------------------------------------------------------ 3 MR12-STAR10 EXT-STAR, B3-B5 V-IV RA=00H45M37.1600S +/- 0.5", J2000 V = 18.85 +/- 0.04 F(2200) ~ 1e-16, DEC=-73D18'39.95" +/- 0.5" F(1500) ~ 1e-16 Reference Frame: ICRS Comments: E(B-V) = 0.38 ------------------------------------------------------------------------------------------------------------------------------------ 4 MR12-STAR11 EXT-STAR, B3-B5 V-IV RA=00H45M34.4196S +/- 0.3", J2000 V = 18.43 +/- 0.05 F(2200) ~ 2e-16, DEC=-73D18'41.63" +/- 0.3" F(1500) ~ 3e-16 Reference Frame: ICRS Comments: E(B-V) = 0.27 ------------------------------------------------------------------------------------------------------------------------------------ 14225( 2) - 22-Jul-2015 21:26:30 - [ 4] 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 MR12-STAR08 STIS/CCD ACQ 50CCD MIRROR 1 5.5 S (5.5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 MR12-STAR08 STIS/NUV ACCUM 52X2 G230L 2376 1 700 S (700 -MAMA S) ------------------------------------------------------------------------------------------------------------------------------------ 3 MR12-STAR08 STIS/FUV ACCUM 52X2 G140L 1425 1 1547 S -MAMA (1547 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 | ------------------------------------------------------------------------------------------------------------------------------------ MR12-STAR08 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A MR12-STAR08 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 N/A -MAMA MR12-STAR08 3 STIS/FUV ACCUM 52X2 G140L 1425 none none none none 1 N/A -MAMA 14225( 2) - 22-Jul-2015 21:26:30 - [ 5] 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 MR12-STAR09 STIS/CCD ACQ 50CCD MIRROR 1 3.2 S (3.2 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 MR12-STAR09 STIS/NUV ACCUM 52X2 G230L 2376 1 780 S (780 -MAMA S) ------------------------------------------------------------------------------------------------------------------------------------ 3 MR12-STAR09 STIS/FUV ACCUM 52X2 G140L 1425 1 1477 S -MAMA (1477 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 | ------------------------------------------------------------------------------------------------------------------------------------ MR12-STAR09 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A MR12-STAR09 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 N/A -MAMA MR12-STAR09 3 STIS/FUV ACCUM 52X2 G140L 1425 none none none none 1 N/A -MAMA 14225( 2) - 22-Jul-2015 21:26:30 - [ 6] Visit: 03 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 MR12-STAR10 STIS/CCD ACQ 50CCD MIRROR 1 5.6 S (5.6 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 MR12-STAR10 STIS/NUV ACCUM 52X2 G230L 2376 1 712 S (712 -MAMA S) ------------------------------------------------------------------------------------------------------------------------------------ 3 MR12-STAR10 STIS/FUV ACCUM 52X2 G140L 1425 1 1535 S -MAMA (1535 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 | ------------------------------------------------------------------------------------------------------------------------------------ MR12-STAR10 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A MR12-STAR10 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 N/A -MAMA MR12-STAR10 3 STIS/FUV ACCUM 52X2 G140L 1425 none none none none 1 N/A -MAMA 14225( 2) - 22-Jul-2015 21:26:30 - [ 7] Visit: 04 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 MR12-STAR11 STIS/CCD ACQ 50CCD MIRROR 1 3.6 S (3.6 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 MR12-STAR11 STIS/NUV ACCUM 52X2 G230L 2376 1 800 S (800 -MAMA S) ------------------------------------------------------------------------------------------------------------------------------------ 3 MR12-STAR11 STIS/FUV ACCUM 52X2 G140L 1425 1 1455 S -MAMA (1455 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 | ------------------------------------------------------------------------------------------------------------------------------------ MR12-STAR11 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A MR12-STAR11 2 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 N/A -MAMA MR12-STAR11 3 STIS/FUV ACCUM 52X2 G140L 1425 none none none none 1 N/A -MAMA 14225( 2) - 22-Jul-2015 21:26:30 - [ 8] Summary Form for Proposal 14225 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD, 52X2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names MR12-STAR08, MR12-STAR09, MR12-STAR10, MR12-STAR11 ------------------------------------------------------------------------------------------------------------------------------------