! Proposal 6536, submission 1 ! PI: Evan Skillman ! Received Thu Feb 8 11:59:51 EST 1996 ! From: eskillma@eso.org ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6536,v 7.1 1997/09/09 20:15:52 pepsa Exp $ ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6536,v 7.1 1997/09/09 20:15:52 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: Bremmer ! Phone: 410-338-4458 , E-mail: bremmer@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: archive-0383.skillman.prop ! Date generated: Fri Dec 22 15:35:03 EST 1995 ! Proposal_Information ! Section 4 Title: I Zw 18: BUILDING A MODEL Proposal_Category: GO Scientific_Category: GALAXIES & CLUSTERS Cycle: 6 Investigators PI_name: Evan Skillman PI_Institution: University of Minnesota CoI_Name: Donald Garnett CoI_Institution: University of Minnesota Contact: ! Y or N (designate at most one contact) CoI_Name: Reginald Dufour CoI_Institution: Rice University Contact: ! Y or N (designate at most one contact) CoI_Name: Robert Benjamin CoI_Institution: University of Minnesota Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) I Zw 18 is host to the lowest metallicity H II region known, and, therefore, is pivotal in studies of the chemical evolution of galaxies, the primordial He abundance, and low metallicity stellar populations. Our previous HST observations of I Zw 18 have allowed us to establish a time sequence of the recent star formation history in I Zw 18, obtain an accurate C abundance, and delineate the stellar, neutral gas, and ionized gas distributions. Here we are proposing to add WFC2 narrow- band imaging at H Beta, O II Lambda3727, and S II Lambda6717,31 to combine with our cycle 4 narrow band imaging at H Alpha\ and O III Lambda5007 in order to map the reddening and ionization structure of the ionized gas and to search for enhanced collisional excitation due to shocks. These new observations will be invaluable to our goal of producing a detailed photoionization model of the high surface brightness knots of I Zw 18 to ensure the most reliable chemical abundance determinations possible. We also propose to obtain an FOS spectrum of the SE component in order to derive a C abundance measurement. We will compare this with the C/O and C/N abundance ratios observed in the NE component. The C abundance in I Zw 18 is key to determining whether there are trends of increasing C/O and C/N with increasing O/H in dwarf star forming galaxies. Questions ! Free format text (please update) Observing_Description: The observing will be split into 5 orbits of imaging and 3 orbits of spectroscopy. The integration times are based on our previous experience with HST imaging and spectroscopy of I Zw 18. The 4 orbits of imaging will be allocated as: (1) acquisition and HBeta imaging (F487N), (2) S II imaging (F673N), (3+4) O II imaging (F375N), and (5) repositioning and HAlpha imaging in the PC (F658N). Each observation will be split into 3 integrations for cosmic-ray rejection. While the O II lines are, on average, intrinsically 5 times stronger than the S II lines, the factor of 15 greater sensitivity of the F673N filter over the F375N necessitates a longer integration for in the O II line. The small redshift of I Zw 18 places the emission lines in the highest sensitivity regions of the response curves for all four filters. We will use our cycle 4 F439W, F555W, and F675W observations to construct appropriate images for continuum subtraction. We have found this to work very well for our HAlpha and O III images. The 3 orbits of FOS spectroscopy will be allocated as: (1) acquisition and integration in G400H and G570H, (2+3) integration in G190H. We hope to detect the O III Lambda1666 line in the G190H exposure (in addition to the C III Lambda1909 line), as this allows a nearly reddening and temperature independent determination of the C/O abundance ratio (see discussion in Garnett et al.\ 1995a). However, if the Lambda1666 line is of insufficient s/n (it is very difficult to predict exactly as the UV continuum is a dominant contributor to the line measurement uncertainty), then we can still obtain an accurate C/O ratio (uncertainty less than 0.2 dex). We do this by measuring the reddening from the HAlpha/HBeta ratio, adopting the electron temperature from the ground-based observations of SK93, and measuring the Lambda1909/Lambda5007 ratio. 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: IZW18-MAINBODY Alternate_Names: MARK116 Description: GALAXY, Dwarf Compact Position: RA=09H 34M 02.04S +/- 0.05S, !specification format is DEC=+55D 14' 28.01" +/- 0.1" ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: J2000 RV_or_Z: V = +759 RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V=23.0 TYPE=B0V, E(B-V)=0.1 ! Include at least V and B-V Comments: This is a dwarf irregular galaxy Brightest stars are at V=23.0 Target_Number: 2 Target_Name: IZW18-SEHIIR Alternate_Names: MARK116 Description: EXT-MEDIUM, HII Region Position: RA-OFF = -3.9019S +/- 0.005S, !specification format is DEC-OFF = -14.346" +/- 0.05", ! RA=0H 0M 0.00S +/- 0S, FROM 3 ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: J2000 RV_or_Z: V = +759 RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: F-LINE(6563)=8.9+/-1E-15 F-LINE(5007)=6.2+/-1E-15 Comments: This is a bright ionized knot in the SE of the dwarf irregular galaxy Target_Number: 3 Target_Name: OFFSET-STAR Alternate_Names: Description: STAR, G V-IV Position: RA=09H 34M 06.220S +/- 0.005S, !specification format is DEC=+55D 14' 37.08" +/- 0.05" ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: J2000 RV_or_Z: V = 0 RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V=15.4, B-V=+0.6, TYPE=G2V Comments: This is a foreground star used for offset to the position of the bright ionized knot in the SE of the dwarf irregular galaxy for FOS spectroscopy ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 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 87D TO 107D ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! SCHEDulability ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP 1-2 WITHIN 60D ! PERIOD