10400( 4) - 12/08/04 10:57 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10400 Version: 4 Check-in Date: 08-Dec-2004 15:56:03 1.Proposal Title: Unravelling NGC 3125-1: The Most Extreme Wolf-Rayet Star Cluster Known in the Local Universe ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance GO 13 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Rupali Chandar Space Telescope Science Institute CoI: Dr. Claus Leitherer Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract Based on cycle 10 STIS UV spectroscopy, we have recently discovered a star cluster, NGC 3125-1, which has the strongest known He II 1640 emission (of stellar origin) in the local universe. The number of implied WR stars is more than an order of magnitude higher than for any other well-studied giant HII region. Because strong He II 1640 emission has been discovered in the composite spectra of redshift 3 Lyman Break Galaxies, NGC 3125-1 potentially provides a unique opportunity to study a nearby object with direct implications for the stellar populations observed in the early universe. In order to understand the origin of this anomalously strong WR feature, we propose to obtain the first high resolution imaging of NGC 3125-1, at wavelengths from the far ultraviolet through the near infrared. This will allow us to simultaneously place it in the context of more familiar objects, such as R136 in 30 Doradus, while also unravelling the physics responsible for the observed UV spectral signature. ------------------------------------------------------------------------------------ 10400( 4) - 12/08/04 10:57 - [ 2] Observations Description ------------------------ The science goals of this program require broadband imaging from the far-UV to the near infrared, as well as narrowband Halpha and Paschen alpha imaging. For the far-UV imaging, we use the ACS/SBC. We calculated exposure times for NGC3125-1 based on observed UV flux from STIS spectroscopy, and find it similar to that for He2-10-1, a cluster which is at a comparable distance and has available archival images which we can use to estimate exposure times. Using the STIS FUV/MAMA+F25QTZ filter, requires roughly 50 minutes to achieve a S/N of 30 for our target objects. Scaling by the throughput (from the ACS instrument handbook), we can achieve the needed depth in the UV in a single orbit. We have also checked to ensure that the field does not violate brightness limits. The ACS/SBC field is centered on a UV luminous cluster, NGC3125-1, for which there is archival FOC imaging and for which we have previously obtained STIS longslit UV spectra. The FOC imaging shows that NGC3125-1 is the most luminous source within its field of view. Because the ACS/SBC has a larger field of view than the FOC, we searched the GSC2.2 source list with a 3.0 arcmin radius (much larger than the SBC field of view), and found that NGC3125-1 is indeed the most luminous source in the field of view. Next, we checked that NGC3125-1 itself does not violate brightness limits. The cluster is resolved in our longslit STIS spectrum, and our calculations show that we may be missing up to 1/2 the flux. We uploaded the extracted spectrum, assumed all the flux was coming from a point source, and then ran the ACS ETC for the F150LP filter for the SBC. No brightness violation occurred. As a final check, we also uploaded our extracted spectrum of a much brighter cluster, NGC4214-1. This spectrum contains roughly an order of magnitude more flux than NGC3125-1. Again, the ACS/SBC ETC shows that with for the F150LP filter, there is no brightness violation, even for NGC4214-1, which has much higher flux than our target cluster, NGC3125-1. For optical imaging, we use ACS/HRC to achieve the highest possible resolution. Again using archival optical images of He2-10 and accounting for a factor of 3 difference in QE between WFPC2 and ACS (at 6500 Ang), we need about 20 minutes in Halpha. Based on the age-dating techniques we have developed using a combination of broad and narrow band filters, the U and B bands, combined with redder filters are crucial for age dating. For young single stellar populations with ages of 10 Myr and younger, we assume an intrinsic U-B=-1 and B-V=0. Assuming E(B-V) similar to that found for NGC3125-1 (from STIS spectroscopy), we can detect young clusters in the U band down to M_V=-7 in 1200 s. Similar parameters give B band exposure times of 900 s. For the V band, where we will do our detection and make size measurements, we require deeper images, and a minimum S/N of 25. This gives an exposure time of 1200 s. These add up to roughly 75 minutes, which can be easily accomodated in 2 orbits, including overhead. We will also include I band imaging, to increase the number of datapoints used for age dating. In the infrared, we require Paschen alpha and continuum imaging, to allow us to discover highly obscured young clusters. Each NICMOS observation will consist of images taken in a narrowband filter centered on Paschen alpha (F187N) and a matgching continuum exposure in the companion narrowband filter (F190W). We use NIC2 for its optimal compromise between angular resolution and field-of-view. Each set of NICMOS exposures is taken in a 4-position dither pattern to maximize recovery of spatial information and reject CRs and CR-persistence. We base exposure times on the typical Paschen alpha line surface brightness of starburst galaxies at comparable distances to NGC3125, from the SNAP-9360 10400( 4) - 12/08/04 10:57 - [ 3] images. The NICMOS ETC shows that 4 exposures of minimum 500 s each in F187N and F190N will achieve S/N=8-10 per resolution element for the continuum subtracted line emission, which is sufficient for our needs. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10400( 4) - 12/08/04 10:57 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3125 GALAXY, STARBURST RA=10H06M33.3000S +/- 0.1", J2000 V = 13.5 DEC=-29D56'8.00" +/- 0.5", PLATE-ID=01O0 Coordinate Source: HST_IMAGE 10400( 4) - 12/08/04 10:57 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type NIC-SPIRAL-DITH Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.8 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 0.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type ACS-HRC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 1.9 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 5.85 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 Primary_Pattern Secondary_Pattern Pattern_Type ACS-HRC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 1.9 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 5.85 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 10400( 4) - 12/08/04 10:57 - [ 6] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3125 ACS/HRC ACCUM HRC F658N CR-SPLIT=NO 1 800 S PATTERN 2 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3125 ACS/HRC ACCUM HRC F435W CR-SPLIT=NO 1 900 S PATTERN 2 2 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC3125 ACS/HRC ACCUM HRC F555W CR-SPLIT=NO 1 550 S PATTERN 3 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC3125 ACS/HRC ACCUM HRC F814W CR-SPLIT=NO 1 400 S PATTERN 2 4 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC3125 ACS/HRC ACCUM HRC F330W CR-SPLIT=NO 1 900 S PATTERN 2 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC3125 1 ACS/HRC ACCUM HRC F658N 1 none none none 1 N/A NGC3125 1 ACS/HRC ACCUM HRC F658N 2 none none none 1 N/A NGC3125 2 ACS/HRC ACCUM HRC F435W 1 none none none 1 N/A NGC3125 2 ACS/HRC ACCUM HRC F435W 2 none none none 2 N/A NGC3125 3 ACS/HRC ACCUM HRC F555W 1 none none none 2 N/A NGC3125 3 ACS/HRC ACCUM HRC F555W 2 none none none 2 N/A NGC3125 3 ACS/HRC ACCUM HRC F555W 3 none none none 2 N/A NGC3125 4 ACS/HRC ACCUM HRC F814W 1 none none none 3 N/A NGC3125 4 ACS/HRC ACCUM HRC F814W 2 none none none 3 N/A NGC3125 5 ACS/HRC ACCUM HRC F330W 1 none none none 3 N/A NGC3125 5 ACS/HRC ACCUM HRC F330W 2 none none none 3 N/A 10400( 4) - 12/08/04 10:57 - [ 7] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3125 NIC2 MULTIAC NIC2-FIX F187N SAMP-SEQ=STEP64,NSAMP=18 1 DEF PATTERN 1 1 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3125 NIC2 MULTIAC NIC2-FIX F190N SAMP-SEQ=STEP64,NSAMP=18 1 DEF PATTERN 1 2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC3125 1 NIC2 MULTIAC NIC2-FIX F187N 1 none none none 1 N/A CUM NGC3125 1 NIC2 MULTIAC NIC2-FIX F187N 2 none none none 1 N/A CUM NGC3125 1 NIC2 MULTIAC NIC2-FIX F187N 3 none none none 1 N/A CUM NGC3125 1 NIC2 MULTIAC NIC2-FIX F187N 4 none none none 1 N/A CUM NGC3125 2 NIC2 MULTIAC NIC2-FIX F190N 1 none none none 2 N/A CUM NGC3125 2 NIC2 MULTIAC NIC2-FIX F190N 2 none none none 2 N/A CUM NGC3125 2 NIC2 MULTIAC NIC2-FIX F190N 3 none none none 2 N/A CUM NGC3125 2 NIC2 MULTIAC NIC2-FIX F190N 4 none none none 2 N/A CUM 10400( 4) - 12/08/04 10:57 - [ 8] Summary Form for Proposal 10400 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC NIC2-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO SAMP-SEQ=STEP64 NSAMP=18 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 2 1 PATTERN 2 2 PATTERN 3 3 PATTERN 2 4 PATTERN 2 5 PATTERN 1 1 PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F658N F435W F555W F814W F330W F187N F190N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC3125 ------------------------------------------------------------------------------------------------------------------------------------