8333( 6) - 10/11/99 11:23 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8333 Version: 6 Check-in Date: 02-Mar-1999 13:26:37 1.Proposal Title: Pox 186: A Nearby Protogalaxy? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Michael Corbin University of Arizona CoI: Dr. William Vacca NASA/IRTF N ------------------------------------------------------------------------------------ 5. Abstract Blue Compact Dwarf Galaxies (BCDGs) typically consist of clusters of early-type stars embedded in older, evolved stellar populations similar in size and shape to normal dwarf ellipticals. However, deep ground-based CCD images of one faint BCDG, Pox 186, reveal a very compact (~ 5" diameter) structure with no evidence of an underlying older population. Optical spectroscopy of this object also indicates that a large number of Wolf-Rayet stars are present, which implies that a burst of star formation must have occurred very recently (<=sssim 10^7 years ago). It has thus been suggested that Pox 186 is a protogalaxy, forming its very first generation of stars. Further investigation of this possibility requires the high angular resolution and ultraviolet spectral coverage that only HST can provide. Using WFPC2, we propose to image the galaxy in the U, V, and I bands, in order to better test for the presence of an underlying evolved population and to reveal any substructure in its star-forming regions. Using STIS, we will obtain low-resolution ultraviolet spectra of the galaxy for combination with ground-based spectra covering the optical through near infrared. This will allow us to determine its spectral energy distribution, metallicity, and dust content, which will in turn constrain its age and star formation history. ------------------------------------------------------------------------------------ 8333( 6) - 10/11/99 11:23 - [ 2] Observations Description ------------------------ The integrated V-band magnitude of Pox 186 is 17.0, and it has a circular apprearance with a radius of approximately 2.5". This gives a surface brightness of approximately 20.2 mag arcsec^-2. Using the WFPC2 exposure estimator for the PC, we find that, approximating the galaxy to have an overall continuum shape similar to an O5 star, images with S/N values ~ 10 per pixel can be obtained within approximately one orbit (~ 25 - 80 minutes, allowing for overheads) for each of the F336W, F555W, and F814W filters. We thus request three orbits for the WFPC2 observations, to be divided equally among these filters. Long integrations are also necessary to go at least as deep as the ground-based images of the galaxy, which were obtained from 30 - 60 minute integrations with a 1.5m telescope. For the spectroscopy, we wish to cover the full ultraviolet spectral range of STIS, at no less than ~ 10 Angstrom resolution. While it would be best to also obtain the object's optical and near -IR spectra with STIS, it is simply too faint, under the above assumption about its continuum shape, to be observed at such resolution with HST. We thus plan to obtain optical/IR spectra from the ground with a larger telescope. The UV observations require the NUV MAMA and grating G230L, and the FUV MAMA and grating G140L, with the 52x0.5 slit. We find from the STIS exposure time calculator that achieving a S/N ratio ~ 10 in the continuum with these configurations requires integration times of approximately 2500s and 2000s, respectively. This will require a single orbit per configuration. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: NO Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8333( 6) - 10/11/99 11:23 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 POX186 GALAXY, PROTOGALAXY RA=13H 25M 48.5S +/- 0.1S, DEC=- J2000 Z=0.0039 SURF(V) = 20.2+/-1.0 11D 36' 37.7" +/- 1" SURF(1425)=3e-15 SURF(2375)=8.3e-16 8333( 6) - 10/11/99 11:23 - [ 4] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 POX186 WFPC2 IMAGE PC1 F336W 1 1500 S ------------------------------------------------------------------------------------------------------------------------------------ 2 POX186 WFPC2 IMAGE PC1 F555W 1 600 S ------------------------------------------------------------------------------------------------------------------------------------ 3 POX186 WFPC2 IMAGE PC1 F814W 1 5400 S ------------------------------------------------------------------------------------------------------------------------------------ 8333( 6) - 10/11/99 11:23 - [ 5] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 POX186 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE , 1 100 S ONBOARD ACQ FOR 2 CD P DIFFUSE-CENTER=FLUX-CENTROID , CHECKBOX = 9 ------------------------------------------------------------------------------------------------------------------------------------ 2 POX186 STIS/F ACCUM 52X0.5 G140L 1425 3 700 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 3 POX186 STIS/N ACCUM 52X0.5 G230L 2376 3 700 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8333( 6) - 10/11/99 11:23 - [ 6] Summary Form for Proposal 8333 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 F28X50LP 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE DIFFUSE-CENTER=FLUX-CENTROID CHECKBOX = 9 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F336W F555W F814W MIRROR G140L G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names POX186 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2376 ------------------------------------------------------------------------------------------------------------------------------------