9820( 5) - 05/07/03 08:44 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9820 Version: 5 Check-in Date: 07-May-2003 08:41:56 1.Proposal Title: SagDIG: a benchmark for understanding star formation in extreme low-metallicity galaxies ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 12 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Dr. Yazan Momany Universita di Padova CoI: Dr. R. Michael Rich University of California - Los Angeles N CoI: Dr. Ivo Saviane University of California - Los Angeles N CoI: Dr. Enrico V. Held Osservatorio Astronomico di Padova N CoI: Dr. Luigi Bedin Universita di Padova N CoI: Dr. Luca Rizzi Universita di Padova N CoI: Dr. Konrad Kuijken Universiteit Leiden N ------------------------------------------------------------------------------------ 5. Abstract A long-standing question in the field of galaxy evolution is whether metal-poor star-forming galaxies (like I ZW 18) posses a very old (>10 Gyr) stellar population. An excellent example of such a primordial galaxy is the Sagittarius dwarf irregular (SagDIG). Besides being very metal-poor, this object is exceptionally rich in atomic gas and shows evidence of propagating star formation. Such features make of SagDIG and ideal target for the study of star formation and its triggering mechanism in extremely metal-poor environments. The deep, wide-field imaging capability of ACS is able to detect an unprecedented number of the oldest stellar population. Such data will enable the construction of both the star formation and chemical enrichment history. In particular, determining the epoch of formation of the first stars in such objects places a constraint on heirarchical galaxy formation in "bottom up" cosmologies. ------------------------------------------------------------------------------------ 9820( 5) - 05/07/03 08:44 - [ 2] Observations Description ------------------------ Our cycle12 observational strategy is aimed at obtaining deep exposures in the F475W, F606W and F814W filters of the SagDIG dwarf Irregular Galaxy. On cycle14, we will repeat the F814W observations in order to decontaminate the SagDIG color-magnitude diagrams by exploiting the different parallaxes and proper motions of stars in SagDIG and the Galactic Bulge. Our cycle12 observation strategy can be summarized as follows: 1) Orbit 1 will be dedicated to the F606W filter; 2) Orbit 2 will be dedicated to the F475W filter; and 3) Orbit 3 will be dedicated to the F814W filter. Each orbit will be split in 5 deep exposures (GAIN=2, CR_SPLIT=0), using a specially designed dithering pattern. While the dithering pattern for filters F606W and F475W is designed to cover the gap between the WF1 and WF2 chips, the one employed for the F814W is specially designed to reduce (to the maximum) the residual distorsion errors ignoring the gap coverage. In fact, a 50 pixels displacements may result in a systematic positioning error as high as 0.01 pixel (of the order of our random error). Real Time Justification ----------------------- Running the ORBIT PLANNER shows that we leave less than 5 seconds of unused visibility in each of the assigned orbits. Our special scheduling requirements are those relative to the TARGET ORIENTATION REQUIREMENTS. We have defined a set of Min-Max orient. ranges in order to avoid a group of 4 bright stars, surrounding the target galaxy. The first of these Min-Max orient. ranges is our preferred. This is due to the fact that the galaxy is elongated in the East- West direction. Calibration Justification ------------------------- Additional Comments ------------------- This is the first epoch of a multi-cycle observations. To enlarge the time base-line separation of the two epochs, we request that the cycle 12 observations be scheduled as soon as possible. ------------------------------------------------------------------------------------ 9820( 5) - 05/07/03 08:44 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ESO594-G004 GALAXY, MAGELLANIC RA=19H30M0.07S +/- 0.1", DEC=- J2000 V = 15.5+/-0.0 IRREGULAR 17D40'46.42" +/- 0.1", PLATE- ID=01O4 Coordinate Source: GSC_SURVEY_PLATE Comments: This is a star-forming, dwarf irregular galaxy. Its diamaters are =2.9* 2.1 arcmin (NED) E(B-V)=0.12 mag, A_B=0.522 (Schelgel et al. 1998) 9820( 5) - 05/07/03 08:44 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 285.0D TO 300.0 D ORIENT 200.0D TO 250.0 D ORIENT 120.0D TO 185.0 D ORIENT 50.0D TO 95.0 D ORIENT 35.0D TO 40.0 D ORIENT 350.0D TO 15.0 D 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 ESO594-G004 ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 396 S SEQ 1-5 NON-INT C COMPRESSION=NONE Comments: In this exposure sequence we tie 5 exposures in the F606W filter (all to be excuted in orbit 1), each image has an: 1) exposure time of 396 sec; 2) COMPRESSION= NONE 3) CR_SPLIT=NO 4) GAIN=2 The employed dithering pattern in this orbit covers the gap. ------------------------------------------------------------------------------------------------------------------------------------ 2 ESO594-G004 ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 396 S POS TARG 2.01, 2.02 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 3 ESO594-G004 ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 396 S POS TARG 4.02, 4.04 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 4 ESO594-G004 ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 396 S POS TARG 2.03, 0.01 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 5 ESO594-G004 ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 396 S POS TARG 4.04, 2.03 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 6 ESO594-G004 ACS/WF ACCUM WFC F475W CR-SPLIT=NO,GAIN=2, 1 419 S SEQ 6-10 NON-INT C COMPRESSION=NONE Comments: In this exposures sequence we tie 5 exposures in the F475W filter (all to be excuted in orbit 2), each image has an: 1) exposure time 419 sec; 2) CR_SPLIT=NO 3) COMPRESSION=NONE 4) GAIN=2 The employed dithering pattern in this orbit covers the gap. ------------------------------------------------------------------------------------------------------------------------------------ 7 ESO594-G004 ACS/WF ACCUM WFC F475W CR-SPLIT=NO,GAIN=2, 1 419 S POS TARG 2.01, 2.02 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 8 ESO594-G004 ACS/WF ACCUM WFC F475W CR-SPLIT=NO,GAIN=2, 1 419 S POS TARG 4.02, 4.04 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 9 ESO594-G004 ACS/WF ACCUM WFC F475W CR-SPLIT=NO,GAIN=2, 1 419 S POS TARG 2.03, 0.01 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 9820( 5) - 05/07/03 08:44 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 ESO594-G004 ACS/WF ACCUM WFC F475W CR-SPLIT=NO,GAIN=2, 1 419 S POS TARG 4.04, 2.03 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 11 ESO594-G004 ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 421 S SEQ 11-15 NON-INT C COMPRESSION=NONE Comments: In this exposure sequence we tie 5 exposures in the F814W filter (all to be excuted in orbit 3), each image has an: 1) exposure time of 421 sec; 2) COPMRESION=NONE 3) GAIN=2 4) CR_SPLIT= NO The employed dithering pattern in this orbit DOES NOT COVER the gap, instead it is designed for decontamination purposes for the cycle14 observations. ------------------------------------------------------------------------------------------------------------------------------------ 12 ESO594-G004 ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 421 S POS TARG 0.21, 0.22 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 13 ESO594-G004 ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 421 S POS TARG 0.42, 0.44 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 14 ESO594-G004 ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 421 S POS TARG 0.23, 0.01 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 15 ESO594-G004 ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 421 S POS TARG 0.44, 0.23 C COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ 9820( 5) - 05/07/03 08:44 - [ 6] Summary Form for Proposal 9820 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO GAIN=2 COMPRESSION=NONE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 285.0D TO 300.0 D ORIENT 200.0D TO 250.0 D ORIENT 120.0D TO 185.0 D ORIENT 50.0D TO 95.0 D ORIENT 35.0D TO 40.0 D ORIENT 350.0D TO 15.0 D SEQ 1-5 NON-INT POS TARG 2.01, 2.02 POS TARG 4.02, 4.04 POS TARG 2.03, 0.01 POS TARG 4.04, 2.03 SEQ 6-10 NON-INT SEQ 11-15 NON-INT POS TARG 0.21, 0.22 POS TARG 0.42, 0.44 POS TARG 0.23, 0.01 POS TARG 0.44, 0.23 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W F475W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ESO594-G004 ------------------------------------------------------------------------------------------------------------------------------------