10472( 4) - 05/12/05 08:59 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10472 Version: 4 Check-in Date: 12-May-2005 12:59:11 1.Proposal Title: SagDIG: a benchmark for understanding star formation in extreme low-metallicity galaxies ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance GO 14 ------------------------------------------------------------------------------------ 5. 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 ------------------------------------------------------------------------------------ 6. 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. ------------------------------------------------------------------------------------ 10472( 4) - 05/12/05 08:59 - [ 2] Observations Description ------------------------ In cycle12 our observational strategy was aimed at obtaining deep exposures in the F475W, F606W and F814W filters of the SagDIG dwarf Irregular Galaxy. Now, 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 dedicated to the F606W filter; 2) Orbit 2 dedicated to the F475W filter; and 3) Orbit 3 dedicated to the F814W filter. Each orbit was split in 5 deep exposures (GAIN=2, CR_SPLIT=0), using a specially designed dithering pattern. Cycle 14 observations will repeat the F814W observations. Real Time Justification ----------------------- Running the ORBIT PLANNER shows that we leave 0 seconds of unused visibility in the assigned orbit. Calibration Justification ------------------------- Additional Comments ------------------- This is the second epoch of a multi-cycle observations. To re-observe the orientation used in Cycle 12 (87.29), Cycle 14 orientaion has to be between (267.2--267.3). This leaves 2 narrow observing windows: (1) 26-27 June 2005 and (2) 22-28 March 2006. Since this second-epoch data will be used to measure the proper-motion of stars, orientation is a curcial issue and we have to reduce (to the maximum) the residual distorsion errors. 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). If the observing windows are two narrow, we can add two other orientation ranges (260.0--267.2 and 267.3--275.0) that should exapnd the observability both in June 2005 and March 2006. ------------------------------------------------------------------------------------ 10472( 4) - 05/12/05 08:59 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 2 ESO594-G004- GALAXY, MAGELLANIC RA=19H29M58.4300S +/- 0.1", J2000 V = 15.5+/-0.0 IIEPOCH IRREGULAR DEC=-17D40'49.78" +/- 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) 10472( 4) - 05/12/05 08:59 - [ 4] Visit: 01 Visit Priority: Visit Requirements: NUMBER OF GYROS 3; ORIENT 267.2D TO 267.3 D On Hold Comments: Additional Comments: The awarded single orbit in cycle 14 will enable us to measure the proper- motion of the SagDIG dwarf irregular galaxy. We therefore repeat the F184W observations, obtained in cycle 12. Thus our observing strategy is simple and straightforward: re-observe the same field of cycle12. This however forces us to use the same orientation of cycle 12 observations. An orientation range between 267.2 and 267.3 satisfies our needs, and shows an observability window around 1) 26-27 June 2005 and (2) 22-28 March 2006. If the observing windows are two narrow, we can add two other orientation ranges (260.0--267.2 and 267.3--275.0) that should exapnd the observability both in June 2005 and March 2006. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ESO594-G004 ACS/WFC ACCUM WFC F814W CR-SPLIT=NO,GAIN=2 1 410 S GS ACQ SCENARIO BASE13GO; -IIEPOCH SEQ 1-5 NON-INT Comments: The following 5 F814W ACS exposures are slightly dithered. The orientation is a serious limit because we intend to re-observe the same field observed in cycle 12, with the same orientation. ------------------------------------------------------------------------------------------------------------------------------------ 2 ESO594-G004 ACS/WFC ACCUM WFC F814W CR-SPLIT=NO,GAIN=2 1 410 S POS TARG 0.21, 0.22 -IIEPOCH ------------------------------------------------------------------------------------------------------------------------------------ 3 ESO594-G004 ACS/WFC ACCUM WFC F814W CR-SPLIT=NO,GAIN=2 1 410 S POS TARG 0.42, 0.44 -IIEPOCH ------------------------------------------------------------------------------------------------------------------------------------ 4 ESO594-G004 ACS/WFC ACCUM WFC F814W CR-SPLIT=NO,GAIN=2 1 410 S POS TARG 0.23, 0.01 -IIEPOCH ------------------------------------------------------------------------------------------------------------------------------------ 5 ESO594-G004 ACS/WFC ACCUM WFC F814W CR-SPLIT=NO,GAIN=2 1 408 S POS TARG 0.44, 0.23 -IIEPOCH ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ ESO594-G004-IIEPOC 1 ACS/WFC ACCUM WFC F814W none none none none 1 N/A H ESO594-G004-IIEPOC 2 ACS/WFC ACCUM WFC F814W none none none none 1 N/A H ESO594-G004-IIEPOC 3 ACS/WFC ACCUM WFC F814W none none none none 1 N/A H 10472( 4) - 05/12/05 08:59 - [ 5] 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 | ------------------------------------------------------------------------------------------------------------------------------------ ESO594-G004-IIEPOC 4 ACS/WFC ACCUM WFC F814W none none none none 1 N/A H ESO594-G004-IIEPOC 5 ACS/WFC ACCUM WFC F814W none none none none 1 N/A H 10472( 4) - 05/12/05 08:59 - [ 6] Summary Form for Proposal 10472 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO GAIN=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements NUMBER OF GYROS 3; ORIENT 267.2D TO 267.3 D GS ACQ SCENARIO BASE13GO; SEQ 1-5 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 F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ESO594-G004-IIEPOCH ------------------------------------------------------------------------------------------------------------------------------------