! Proposal 6716, submission 1 ! PI: Theodore Stecher ! Received Sun Feb 11 18:20:16 EST 1996 ! From: fanelli@trifle.gsfc.nasa.gov ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6716,v 6.1 1997/03/19 16:08:14 pepsa Exp $ ! ! 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 ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: archive-0844.stecher.prop ! Date generated: Fri Dec 22 18:20:31 EST 1995 ! Proposal_Information ! Section 4 Title: The Pattern of Massive Star Formation in Nearby Irregular and Amorphous Galaxies Proposal_Category: GO Scientific_Category: STELLAR POPULATIONS Cycle: 6 Investigators PI_name: Theodore Stecher PI_Institution: NASA Goddard Space Flight Center CoI_Name: Michael Fanelli CoI_Institution: NASA Goddard Space Flight Center & Hughes-STX Corp Contact: Y CoI_Name: William Waller CoI_Institution: NASA Goddard Space Flight Center & Hughes-STX Corp CoI_Name: Robert Hill CoI_Institution: NASA Goddard Space Flight Center & Hughes-STX Corp CoI_Name: Denise Smith CoI_Institution: NASA Goddard Space Flight Center & NRC CoI_Name: Susan Neff CoI_Institution: NASA Goddard Space Flight Center CoI_Name: Robert O'Connell CoI_Institution: U. of Virginia Abstract: We propose to obtain deep WFPC2 images in far-UV (~1700 A), U, V, and I bandpasses of the stellar populations in four nearby galaxies known from their observed FUV luminosities to be forming massive (OB) stars. Our primary goals are to determine the total intensity and spatial distribution of recent (t < 100 Myr), massive star formation, to confirm the suspected presence of ``super star-clusters'', and to measure their basic properties. We will utilize the superior spatial resolution of HST to completely determine the young stellar populations in these systems. Extinction, ages, IMFs, radiative and kinetic luminosities for the star cluster population will be derived by comparing observed colors with those obtained from evolutionary synthesis models of young starbursts. We have carefully chosen our sample based on their measured FUV flux and morphology as found in images recently obtained with the Ultraviolet Imaging Telescope (UIT), and their ability to be resolved on parsec scales with HST. These data will allow us to map the spatial pattern of massive star formation and derive detailed star formation histories. The proposed observations will provide fundamental insight into the physics of massive star formation on galactic scales, and serve as a template for understanding massive star formation in more distant systems. Questions ! Free format text (please update) Observing_Description: Targets: We intend to obtain HST images of the UV and visible continua of the targets, thereby identifying and characterizing their massive stellar populations. We have carefully selected the following galaxies using the criteria described below. 1. NGC 4214, v(sun) = 298 km/s, D = 4.2 Mpc, 0.1"= 2.0 pcs 2. NGC 4449, v(sun) = 255 km/s, D = 3.4 Mpc, 0.1"= 1.6 pcs 3. NGC 5253, v(sun) = 271 km/s, D = 3.6 Mpc, 0.1"= 1.7 pcs 4. NGC 1510, v(sun) = 789 km/s, D = 10.5 Mpc, 0.1"= 5.1 pcs Selection Criteria: To carry out the proposed investigation, we have selected targets based on these criteria: 1) Systems known to be actively forming OB stars at the present epoch from ground and space-based multiwavelength data. Their observed FUV luminosities span a narrow range, -17 < M(FUV) < -19 , implying that the global level of massive star formation is similar within a factor of 5. 2) Intermediate luminosity (mass). To probe massive star formation within a small range of mass, we have selected objects with -16.8 > M(B) > -18.3. These systems are neither dwarfs (e.g., 1 Zw 18), or massive systems like the Milky Way Galaxy. Additionally, the selected targets span a narrow range in mean gas-phase abundance; all are moderately metal-poor with respect to solar abundance. 3) The sample is UV-bright. This criterion insures that we can directly probe the OB star population. All four targets were detected in FUV images obtained with the UIT during the Astro-2 mission. Low extinctions are implied by these data, which will reduce systematic uncertainties in derived population parameters. Equally important, we minimize the exposure times needed for FUV photometry. 4) Distances ~< 10 Mpc. The targets must be sufficiently nearby to resolve structure in the UV-bright knots. The host galaxies contain suspected compact star clusters from lower resolution, ground-based optical imaging studies. Using this criteria, we chose two systems which are highly resolved into numerous clusters and associations: NGC 4214 and NGC 4449, and two amorphous systems: NGC 5253 and NGC 1510. NGC 4214 and NGC 4449 are members of a small set of nearby, optically bright, large (5' < d_25 < 10') irregular galaxies. Both systems have been the subject of numerous investigations exploring the structure, dynamics, stellar populations, interstellar medium, and evolutionary state of irregular galaxies. We feel they are among the best candidates for high spatial resolution imaging with HST, to completely describe the morphology, intensity, and history of their young stellar populations. For similar reasons, NGC 5253 and NGC 1510 are among the best candidates for understanding the physical nature of amorphous systems. The UIT observations have demonstrated that these two objects are bright in the far-UV, unlike M82, another nearby amorphous system, which was undetected in similar exposures. The observations proposed here will produce a dataset fully describing the massive star content for these systems: sizes, ages, total mass, and spatial distribution within the galaxy. We will then combine this dataset with complementary data obtained through our own (described below) and other sources. The combined dataset will be used to explore the relationship between recently formed massive stars, the interstellar medium, and the underlying older stellar population. Target Descriptions A brief description of the far-UV morphology of the selected targets as observed with the UIT. NGC 4214: FUV images show an exceptionally bright knot [m(1500A) ~11.8], located near the optically defined center, and a well-defined population of 40-50 fainter knots extending over 3-4 arcminutes (Neff etal. 1995). An archival HST/FOC image indicates that the core knot is compact, but the FOC field does not include any of the other structures seen in the UIT data. NGC 4449 has a total FUV luminosity comparable to NGC 4214, and a comparable system of bright knots (Hill etal ApJ430, 568 1994). The brightest FUV knot is ~1' from the nucleus. NGC 5253 displays an elliptical light distribution in the FUV, unresolved into knots at the ~2'' resolution of UIT. Optically, the underlying galaxy which is not detected in the FUV image, shows a more symmetric morphology than either NGC 4214 or NGC 4449. NGC 1510 is an elliptical companion to the SB(r)a galaxy NGC 1512 (separation ~5'). An ellipsoidal UV-bright core is seen in the UIT image without resolution into knots. Filters & Exposure Times We propose to obtain broad-band images in 4 continuum filters: F170W, F336W, F555W, and F814W. The latter three filters approximate the U,V and I bandpasses; F170W best matches the FUV filter response of the UIT data. A large spectral baseline is essential for deriving accurate extinction and cluster ages. To estimate the exposure times needed we have modeled these knots as 5 Myr clusters and derived the expected FUV, U, V, and I-band magnitudes. Exposure times were estimated by modeling the clusters as both point and partially resolved sources. We also calculated expected S/N ratios for individual stars, using an early-O dwarf and a B0 supergiant as a typical source. We examined models with a range of extinction values. The exposure time estimates are derived for the WFC mode. For a single early-O star, M(V) = -5.5, and M(FUV) = -10.0. For the assumed distances, the expected unextincted FUV magnitudes of this stellar type are 18.1 (NGC 4214), 17.6 (NGC 4449), and 17.8 (NGC 5253). For a 5 Myr old star cluster with M(V) ~ -13, typical of the super star clusters described by Whitmore & Schweizer (1995) and O'Connell et al. (1995), M(FUV) ~ -16. Assuming a modest extinction of 1 mag in the FUV, E(B-V) = 0.12, the expected FUV magnitude of a cluster of this luminosity at the adopted distances would be 13.2 (NGC 4214), 12.7 (NGC 4449), 12.8 (NGC 5253), and 14.9 (NGC 1510). Observed integrated FUV magnitudes for the knots in NGC 4214 span the range 11.8 to ~17 mags, similar values are found in NGC 4449. Our planned exposure sequence for each pointing will be: 800secs for F170W, 520secs for F336W, 200secs for F555W, and 200s for F814W. The observed angular extent in the FUV is 4.1' by 3.0' for NGC 4449 and 7.0' by 5.6' for NGC 4214. To fully characterize their global masssive star populations, two pointings are necessary for NGC 4214 and NGC 4449. We choose the F170W filter for maximum FUV sensitivity. Assuming that the UV-bright sources have spectra bluer than an A0 star, the potential red leak from this filter should not significantly affect photometry of these sources. Real_Time_Justification: All of the targets are nearby galaxies-- extended objects which will fill the entire WFPC2 FOV with sources. Since these systems are larger in angular extent than the FOV and display irregular morphologies, the orientation of the WFPC2 FOV is critical to the science objectives of this proposal. We have iterated possible orientation ranges with the RPS2 software, to determine the maximum range which is acceptable. We believe the orient angles specified below in the visit requirements fields are the best compromise between scheduling flexibility as determined by RPS2, and our desire for very well defined aperture placements. In particular, we were awarded two orbits each for two targets (NGC 4214 and NGC 4449) for the explicit purpose of mapping massive star formation in these objects-- this requires roughly orthogonal aperture orientations. Calibration_Justification: Additional_Comments: The proposed HST observations are one element in a coordinated program of ground and space-based multiwavelength data which we are collecting to explore the global properties of massive star formation in nearby systems. These data include deep, wide-field satellite UV, optical and near-IR images (1-3" resolution) obtained by our group, and archival data derived from NASA mission databases (IRAS, ROSAT). Fixed_Targets ! Section 5.1 Target_Number: 01 Target_Name: NGC4214-nuc Alternate_Names: Description: GALAXY,MAGELLANIC IRREGULAR,STARBURST,HOTSPOT Position: RA=12H 15M 39.78S +/- 0.1S, DEC=36D 19' 37.5" +/- 1", Equinox: J2000 RV_or_Z: V = +298 Flux: surf(V) = 20.5 +/- 0.2 surf(1500) = 18.7 +/- 0.5 B-V = 0.18 U-B = -0.4 Comments: V-band SB and optical colors refer to aperture of ~30 FUV SB refers to 10 aperture Target_Number: 02 Target_Name: NGC4214-pos2 Alternate_Names: Description: GALAXY,MAGELLANIC IRREGULAR,STARBURST,HOTSPOT Position: RA=12H 15M 39.78S +/- 0.1S, DEC=36D 19' 34.0" +/- 2", Equinox: J2000 RV_or_Z: V = +298 Flux: surf(V) = 20.5 +/- 0.2 surf(1500) = 18.7 +/- 0.5 B-V = 0.18 U-B = -0.4 Comments: V-band SB and optical colors refer to aperture of ~30 FUV SB refers to 10 aperture Target_Number: 03 Target_Name: NGC4449-nuc Alternate_Names: Description: GALAXY,MAGELLANIC IRREGULAR,STARBURST,HOTSPOT Position: RA=12H 28M 11.50S +/- 0.12S, DEC=44D 05' 41.0" +/- 2", Equinox: J2000 RV_or_Z: V = +255 Flux: surf(V) = 18.8 +/- 0.2 surf(1500) = 18.9 +/- 0.3 B-V = 0.31 U-B = -0.35 Comments: V surface brightness and optical colors refer to aperture = 22. FUV surface brightness refers to 10. Target_Number: 04 Target_Name: NGC4449-pos2 Alternate_Names: Description: GALAXY,MAGELLANIC IRREGULAR,STARBURST,HOTSPOT Position: RA=12H 28M 09.55S +/- 0.1S, DEC=44D 05' 12.0" +/- 2", Equinox: J2000 RV_or_Z: V = +255 Flux: surf(V) = 18.8 +/- 0.2 surf(1500) = 18.9 +/- 0.3 B-V = 0.31 U-B = -0.35 Comments: V surface brightness and optical colors refer to aperture = 22. FUV surface brightness refers to 10. Target_Number: 05 Target_Name: NGC5253 Alternate_Names: Description: GALAXY,Amorphous IRREGULAR,STARBURST,HOTSPOT Position: RA=13H 39M 55.9S +/- 0.13S, DEC=-31D 38' 41.0" +/- 2", Equinox: J2000 RV_or_Z: V = +271 Flux: surf(V) = 18.3 +/- 0.2 surf(1500) = 18.3 +/- 0.5 B-V = -0.21 U-B = -0.54 Comments: V band surface brightness and optical colors refer to an aperture = 5.5. FUV surface brightness is within a 10.0 aperture. Target_Number: 06 Target_Name: NGC1510 Alternate_Names: Description: GALAXY,AMORPHOUS IRREGULAR,STARBURST,HOTSPOT Position: RA=04H 03M 32.65S +/- 0.1S, DEC=-43D 24' 01.4" +/- 2", Equinox: J2000 RV_or_Z: V = +798 Flux: surf(V) = 19.3 +/- 0.2 surf(1500) = 20.3 +/- 0.5 B-V = 0.28 V-R = -0.04 Comments: V band surface brightness and optical colors refer to an aperture = 11. FUV surface brightness refers to a 10 aperture. Visits Visit_Number: 01 Visit_Requirements: ORIENT 285.0D to 355.0D On_Hold_Comments: Visit_Comments: Optimum orientation = 330.0D Exposure_Number: 01 Target_Name: NGC4214-nuc Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F170W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 800s Special_Requirements: Comments: Exposure_Number: 02 Target_Name: NGC4214-nuc Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 520s Special_Requirements: Comments: Exposure_Number: 03 Target_Name: NGC4214-nuc Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Exposure_Number: 04 Target_Name: NGC4214-nuc Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Visit_Number: 02 Visit_Requirements: ORIENT 105.0D to 205.0D On_Hold_Comments: Visit_Comments: Optimum orientation = 155.0D Exposure_Number: 05 Target_Name: NGC4214-pos2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F170W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 800s Special_Requirements: Comments: Exposure_Number: 06 Target_Name: NGC4214-pos2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 520s Special_Requirements: Comments: Exposure_Number: 07 Target_Name: NGC4214-pos2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Exposure_Number: 08 Target_Name: NGC4214-pos2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Visit_Number: 03 Visit_Requirements: ORIENT 175.0D to 265.0D On_Hold_Comments: Visit_Comments: Optimum orientation = 210.0D Exposure_Number: 09 Target_Name: NGC4449-nuc Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F170W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 800s Special_Requirements: Comments: Exposure_Number: 10 Target_Name: NGC4449-nuc Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 520s Special_Requirements: Comments: Exposure_Number: 11 Target_Name: NGC4449-nuc Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Exposure_Number: 12 Target_Name: NGC4449-nuc Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Visit_Number: 04 Visit_Requirements: ORIENT 315.0D to 95.0D On_Hold_Comments: Visit_Comments: Optimum orientation = 20D Exposure_Number: 13 Target_Name: NGC4449-pos2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F170W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 800s Special_Requirements: Comments: Exposure_Number: 14 Target_Name: NGC4449-pos2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 520s Special_Requirements: Comments: Exposure_Number: 15 Target_Name: NGC4449-pos2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Exposure_Number: 16 Target_Name: NGC4449-pos2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Visit_Number: 05 Visit_Requirements: ORIENT 350.0D to 100.0D On_Hold_Comments: Visit_Comments: An alternate orientation is equally acceptable, using orient 170.0D to 280.0D. Optimum orient = 45.0D or 215.0D. Long `axis' of WFPC2 (from PC1 to opposite side of WF3) should be oriented along the major axis of the target. Exposure_Number: 17 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F170W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 800s Special_Requirements: Comments: Exposure_Number: 18 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 520s Special_Requirements: Comments: Exposure_Number: 19 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Exposure_Number: 20 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: PC1-fix Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Visit_Number: 06 Visit_Requirements: ORIENT 60.0D to 160.0D On_Hold_Comments: Visit_Comments: Optimum orientation = 110.0D Exposure_Number: 21 Target_Name: NGC1510 Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F170W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 800s Special_Requirements: Comments: Exposure_Number: 22 Target_Name: NGC1510 Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F336W Wavelength: Optional_Parameters: CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 520s Special_Requirements: Comments: Exposure_Number: 23 Target_Name: NGC1510 Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Exposure_Number: 24 Target_Name: NGC1510 Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 200s Special_Requirements: Comments: Data_Distribution Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 Ship_To: PI_Address ! STSCI or PI_Address or Ship_Via: UPS ! UPS (2-day) or OVERNIGHT Recipient_Email: ! Needed if Ship_To: is not PI_Address