9054( 2) - 02/08/01 10:41 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9054 Version: 2 Check-in Date: 08-Feb-2001 10:40:27 1.Proposal Title: Star Formation Triggers and Chemical Reprocessing in I Zw 18 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Thomas Brown Catholic University of America CoI: Sara R. Heap Goddard Space Flight Center N CoI: Ivan Hubeny Goddard Space Flight Center N CoI: Thierry Lanz Goddard Space Flight Center N ------------------------------------------------------------------------------------ 5. Abstract I Zw 18 is a blue compact galaxy (BCD) with the smallest known abundance of heavy elements yet observed. Although it is currently undergoing an intense period of star formation, debate continues to focus on the presence of any older generations of stars in this system. If its star formation history is truly restricted to the last 50 Myr, the existence of I Zw 18 demonstrates that the formation of galaxies can be delayed until the present epoch. This galaxy may represent a local template for the young galaxies that will be observed with NGST at high redshift, and as such it is essential that we understand its evolutionary status. Narrow-band imaging and spectroscopy have focused on the ionized gas in this galaxy. Broad-band imaging has resolved the brighter stellar populations, but due to the uncertain distance of I Zw 18 and its high level of crowding, interpretation of this imaging has been disputed. We propose a spatially resolved far-UV spectroscopic map of this critically important galaxy. Our data will investigate how star formation propagates across a starbursting galaxy, determine if heavy elements have been incorporated into the young hot stars or instead have been blown out of the galaxy, extend our understanding of mass loss and stellar winds to very low metallicity, and create a template for metal-poor starbursts observed at high redshift. ------------------------------------------------------------------------------------ 9054( 2) - 02/08/01 10:41 - [ 2] Observations Description ------------------------ Our proposed STIS observations aim to map the star formation history of I Zw 18 as a function of position within the galaxy. To obtain our spectroscopic map, we will step the 52" x 0.5" slit across the galaxy, placing it at seven positions, with two orbits per position, with the slit parallel to the major axis of the galaxy. The two orbits for each position will have different offsets along the axis of the slit, to allow masking of hot pixels, defective pixels, and pixels shadowed by the repeller wire. Each orbit will be split into four spectroscopic exposures, to allow correction for any drift in the pointing. We will also use 2 orbits to obtain the first far-UV image of the I Zw 18 main body, and another 2 orbits to obtain a near-UV image at the same spatial resolution and pixel sampling. The large-aperture IUE and GHRS spectra, combined with the FOC and WFPC2 near-UV images, demonstrate that the target is safe to image with the STIS MAMAs without violating local or global bright object limits. We will use the images to determine the angle of incidence of each star/cluster within the slit and hence, to make a zero-point adjustment in the wavelength scale of the source. The net result of the reduction will be a set of >100 registered spectra, each tagged with (x, y) position, far-UV magnitude and UV color. The spectra can then be coadded for the scientific task at hand. These coadded spectra will have a higher resolution than would be expected from a wide-slit observation, because the sources are near-point sources, and their spectra are registered. The images will also serve to create a UV CMD of the clusters. We have split the images into short exposures so that portions with higher background can be excluded if necessary. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- In visits 2, 3, and 4, pos-targs are used to step the slit across the main body of the galaxy. The slit is parallel to the major axis of the galaxy. Pos-targs perpendicular to the slit are used to create the mosaic (7 positions), while pos-targs along the slit are used to remove hot pixels, defective pixels, and pixels shadowed by the repeller wire. These pos-targs generate "feasibility diagnostics" because they are larger than the slit size, but we are not moving the object out of the slit; we are scanning across an extended object to create a mosaic. ------------------------------------------------------------------------------------ 9054( 2) - 02/08/01 10:41 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 IZW18-OFFSET STAR RA=09H 34M 6.29S +/- 0.3", J2000 V = 15.21+/-0.40 DEC=55D 14' 37.6" +/- 0.3", PLATE-ID=0009 Coordinate Source: GUIDE_STAR_CATALOG Comments: V mag is from DSS Quick Northern V. The star is in the GSC. 2 IZW18 GALAXY, STARBURST, RA-OFF=-4.1232S+/- 0.01S, DEC- J2000 SURF(V) = 20.4+/-0.1 GALAXY, DWARF COMPACT OFF=-11.858"+/- 0.01", FROM 1, B-V = -0.03+/-0.04 PLATE-ID=0009 E(B-V) = 0.03+/-0.01 SURF-CONT(1200)=4+/-1e-15 SURF-CONT(2000)=1+/-0.25e-15 SURF-CONT(3000)=0.5+/-0.13e-15 TYPE=B0V Coordinate Source: HST_IMAGE Comments: Optical surface brightness comes from WFPC2 F555W imaging. Broadband color comes from van Zee et al. 1998, AJ, 115:1000. Extinction comes from Schlegel et al. 1998, ApJ, 500:525. UV fluxes come from far-UV and near-UV spectrscopy with IUE and GHRS through 10"x20" and 2"x2" apertures. 9054( 2) - 02/08/01 10:41 - [ 4] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Imaging visit Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 IZW18-OFFSE STIS/C ACQ 50CCD MIRROR ACQTYPE=POINT 1 0.5 S T CD ------------------------------------------------------------------------------------------------------------------------------------ 20 IZW18 STIS/F ACCUM F25SRF2 MIRROR 8 5 M POS TARG 0, 0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 IZW18 STIS/F ACCUM F25SRF2 MIRROR 8 6 M POS TARG 0,-0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 40 IZW18 STIS/N ACCUM F25QTZ MIRROR 8 6 M POS TARG 0,-0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 50 IZW18 STIS/N ACCUM F25QTZ MIRROR 8 6 M POS TARG 0, 0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9054( 2) - 02/08/01 10:41 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 190D TO 190.5D ORIENT 10D TO 11D On Hold Comments: Additional Comments: Spectroscopic visit. Scan perpendicular to slit in 0.5" steps through the central 5 positions, from - to + pos-targ. Position along slit is also offset by 0.25". Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 IZW18-OFFSE STIS/C ACQ 50CCD MIRROR ACQTYPE=POINT 1 0.5 S T CD ------------------------------------------------------------------------------------------------------------------------------------ 20 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 10 M POS TARG -1.0, 0.25 UV-MAM A Comments: Position 2a of 7 slit positions. -X----- ------------------------------------------------------------------------------------------------------------------------------------ 30 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG -0.5, 0.25 UV-MAM A Comments: Position 3a of 7 slit positions. --X---- ------------------------------------------------------------------------------------------------------------------------------------ 40 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG 0.0, 0.25 UV-MAM A Comments: Position 4a of 7 slit positions. ---X--- ------------------------------------------------------------------------------------------------------------------------------------ 50 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG 0.5, 0.25 UV-MAM A Comments: Position 5a of 7 slit positions. ----X-- ------------------------------------------------------------------------------------------------------------------------------------ 60 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG 1.0, 0.25 UV-MAM A Comments: Position 6a of 7 slit positions. -----X- ------------------------------------------------------------------------------------------------------------------------------------ 9054( 2) - 02/08/01 10:41 - [ 6] Visit: 03 Visit Priority: Visit Requirements: SAME ORIENT AS 02 On Hold Comments: Additional Comments: Spectroscopic visit. Scan perpendicular to slit in 0.5" steps through the central 5 positions, from + to - pos-targ. Position along slit is also offset by -0.25". Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 IZW18-OFFSE STIS/C ACQ 50CCD MIRROR ACQTYPE=POINT 1 0.5 S T CD ------------------------------------------------------------------------------------------------------------------------------------ 20 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 10 M POS TARG 1.0,-0.25 UV-MAM A Comments: Position 6b of 7 slit positions. -----X- ------------------------------------------------------------------------------------------------------------------------------------ 30 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG 0.5,-0.25 UV-MAM A Comments: Position 5b of 7 slit positions. ----X-- ------------------------------------------------------------------------------------------------------------------------------------ 40 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG 0.0,-0.25 UV-MAM A Comments: Position 4b of 7 slit positions. ---X--- ------------------------------------------------------------------------------------------------------------------------------------ 50 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG -0.5,-0.25 UV-MAM A Comments: Position 3b of 7 slit positions. --X---- ------------------------------------------------------------------------------------------------------------------------------------ 60 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG -1.0,-0.25 UV-MAM A Comments: Position 2b of 7 slit positions. -X----- ------------------------------------------------------------------------------------------------------------------------------------ 9054( 2) - 02/08/01 10:41 - [ 7] Visit: 04 Visit Priority: Visit Requirements: SAME ORIENT AS 02 On Hold Comments: Additional Comments: Spectroscopic visit. Scan perpendicular to slit to obtain outermost positions. Position along slit is also offset by 0.25" and -0.25". Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 IZW18-OFFSE STIS/C ACQ 50CCD MIRROR ACQTYPE=POINT 1 1 S T CD ------------------------------------------------------------------------------------------------------------------------------------ 20 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 10 M POS TARG -1.5, 0.25 UV-MAM A Comments: Position 1a of 7 slit positions. X------ ------------------------------------------------------------------------------------------------------------------------------------ 30 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG -1.5,-0.25 UV-MAM A Comments: Position 1b of 7 slit positions. X------ ------------------------------------------------------------------------------------------------------------------------------------ 40 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG 1.5,-0.25 UV-MAM A Comments: Position 7b of 7 slit positions. ------X ------------------------------------------------------------------------------------------------------------------------------------ 50 IZW18 STIS/F ACCUM 52X0.5 G140L 1425 4 11 M POS TARG 1.5, 0.25 UV-MAM A Comments: Position 7a of 7 slit positions. ------X ------------------------------------------------------------------------------------------------------------------------------------ 9054( 2) - 02/08/01 10:41 - [ 8] Summary Form for Proposal 9054 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD F25SRF2 F25QTZ 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG 0, 0.25 POS TARG 0,-0.25 ORIENT 190D TO 190.5D ORIENT 10D TO 11D POS TARG -1.0, 0.25 POS TARG -0.5, 0.25 POS TARG 0.0, 0.25 POS TARG 0.5, 0.25 POS TARG 1.0, 0.25 SAME ORIENT AS 02 POS TARG 1.0,-0.25 POS TARG 0.5,-0.25 POS TARG 0.0,-0.25 POS TARG -0.5,-0.25 POS TARG -1.0,-0.25 POS TARG -1.5, 0.25 POS TARG -1.5,-0.25 POS TARG 1.5,-0.25 POS TARG 1.5, 0.25 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names IZW18-OFFSET IZW18 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------