! Proposal 6695, submission 1 ! PI: Bryan Miller ! Received Wed Jan 31 18:00:27 EST 1996 ! From: bmiller@stsci.edu ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6695,v 3.1 1996/02/08 00:05:36 pepsa Exp $ ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6695,v 3.1 1996/02/08 00:05:36 pepsa Exp $ ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Lucas ! Phone: 410-338-4716 , E-mail: lucas@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: archive-0781.miller.prop ! Date generated: Fri Dec 22 16:38:25 EST 1995 ! Proposal_Information ! Section 4 Title: The Stellar Populations in the LGS3 Dwarf Galaxy Proposal_Category: GO Scientific_Category: STELLAR POPULATIONS Cycle: 6 Investigators PI_name: Bryan Miller PI_Institution: Space Telescope Science Institute and Carnegie Institution of Washington, Department of Terrestrial Magetism CoI_Name: Myung Gyoon Lee CoI_Institution: Department of Astronomy, Seoul National University Contact: ! Y or N (designate at most one contact) CoI_Name: Paul Hodge CoI_Institution: Astronomy Department, University of Washington Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) We will study of the stellar populations in the nearby dwarf galaxy LGS3. This galaxy unique in that is has properties of both dwarf spheroidal and dwarf irregular systems, i.e. it is dominated by old or intermediate age stellar populations but it also contains a small amount of neutral hydrogen and a small young stellar population. The program is to obtain deep F555W and F814W photometry to V~27.5 to study the horizontal branch, intermediate-age main-sequence turnoff, and young main sequence. We will determine the star formation history of LGS3 has been episodic as in Carina and Leo I, or more continuous as in Local Group dwarf irregulars. The results will be important to our understanding of the morphology/density relation in nearby groups, the fate of the faint blue galaxies, and the evolution of dwarf galaxies in general. Questions ! Free format text (please update) Observing_Description: Deep WFPC2 images through filters F555W and F814W will be used to study the stellar populations and star formation histories of LGS3, a dwarf galaxy in the Local Group. The F555W and F814W bandpasses are chosen since they have good transformations to the Johnson/Cousins V and I system which is the standard for observing old stellar populations. The Cycle 4 TAC strongly recommended these filters for galaxy population studies. While it would be best to center the galaxy in the PC to take advantage of the superior resolution, the necessities of avoiding bright stars that can produce harmful scattered light and of having a large number of scheduling opportunities mean that we will need to center the galaxy in one of the wide field chips. The chip to be used as the center will depend on the orientation of the telescope at the time of the observation. For the given coordinates centering in PC1 is allowed only for orientations between 145D and 160D but according to RPS2 there are no scheduling opportunities if all 8 orbits are done in one visit. The most flexible scheduling is when the coordinates are centered in WF2 and this has been given as the default. In this case orientations between 0D and 80D are acceptable (though an offset may be needed for roll angles between 25D and 40D). Orientations between 265D and 350D are acceptable when centering in WF3, and centering in WF4 is needed for orientations between 125D and 265D. Because the majority of the stars will be in the WF chips we will incorporate a four-point dithering scheme. We use the same offset scheme as the DITHER-TYPE=BOX option but we use explicit POS TARGS so that only three spacecraft moves are needed during the entire visit. This procedure will significantly improve the undersampling of the WF PSF and therefore give more reliable magnitudes when using PSF-fitting routines. The goals of our program are to determine the morphology of the horizontal branch, to investigate the upper main sequence, and to detect the existence of a young or intermediate age turnoff. These goals can be attained with the allocated 8 orbits. The increased brightness of the stars in I is almost equally balanced by the lower system sensitivity using F814W, so 4 orbits will be given observation with each filter. Given a visibility of 53 minutes, we will have a approximately 9600 seconds of integration in each filter. Three exposures will be taken each orbit so that we will be able to unambiguously remove the cosmic rays at each dither position. The limiting magnitude in this exposure time at S/N=5 is V=27.8 according to the Exposure Time Calculator. However, dithering should allow us to push slightly fainter than this. This corresponds to M_V~3.5 for a distance modulus of 24.54 (Lee 1995, AJ, 110, 1129). The tip of the RGB is at V=21.5, so we will easily detect the horizontal branch at V=24.5. Young or intermediate age main-sequence turnoffs will be 2--3 magnitudes below the horizontal branch, and our observations will be able to detect their existence. With accurate photometry of the RGB, the horizonal branch, and the upper main sequence, we will be able to determine the star formation history of LGS3 over the last 3--5 Gyr. Real_Time_Justification: None. None. Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: LGS3 Description: GALAXY,dwarf spheroidal Position: RA=1H 03M 54.4S +/- 0.05S, DEC=21D 52' 56.2" +/- 0.5", PLATE-ID=02BD Equinox: J2000 RV_or_Z: V=-277 Flux: SURF(V)=25 Comments: ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed ! Visits ! Section 6 ! Visit_Number: ! Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! DROP TO GYRO IF NECESSARY [NO REACQuisition] ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! SCHEDulability ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN