12172( 3) - 28-Apr-2011 10:15:22 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12172 Version: 3 Check-in Time: 28-Apr-2011 10:15:22 STScI Edit Number: 0 Title Is the Extraordinary Super Star Cluster NGC 3125-1 an Imposter? ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Claus Leitherer Space Telescope Science Institute CoI: Dr. Rupali Chandar University of Toledo N CoI: Dr. Aida H. Wofford Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract We propose a short, 4 orbit COS+STIS spectroscopic program to observe the extraordinary super star cluster in the local starburst galaxy NGC 3125. The cluster has the strongest He II 1640 emission ever observed in a starburst region in the local universe. This line is the tell-tale sign of Wolf-Rayet stars, the evolved descendants of very massive O stars. Taken at face value, the anomalous He II 1640 line indciates a Wolf-Rayet population that is very different from other starburst regions. However, previous attempts to interpret the observational data of the super star cluster were hampered by the low resolution of the ultraviolet spectra and the lack of co-spatial panchromatic data. As a result, the suggestion of the extraordinary nature of this super star cluster is still not unambiguous. The proposed program will settle the matter. We will test the upper initial mass function from several angles: the N V and Si IV stellar wind-lines, the elusive O V line associated with the hottest, most massive stars, and the ionizing radiation as probed by recombination lines. We will determine the dust redening with three independent methods: the SED, the Balmer decrement, and the He II 4686/1640 ratio. The STIS long-slit capabilities will allow us to perform a comparative study with a nearby super star cluster in the host galaxy. The ultraviolet spectrum of the super star cluster may be the missing link between local starbursts and star-forming galaxies at cosmological redshift. The UV spectra of the two classes of objects are rather similar, except for the He II 1640 line, which is much stronger at high redshift. Detailed observations of NGC 3125 may help shed light on understanding the details of star-formation at high redshift. ------------------------------------------------------------------------------------ Observations Description ------------------------ There are two visits. The first 2-orbit visit will use COS and the G130M grating for an observation of NGC 3125-1. The cluster is almost point-like and has F(1300) = 2e-15, as observed before with STIS. This will make it an easy target acquisition taking about 10 min, including all overheads. The remainder of the first orbit and the full second orbit will then yield close to 5000 s of science exposure time. The resulting S/N per resolution element will be about 10. The second 2-orbit visit will be with STIS using all four low-resolution gratings. This visit will be done at a specific orientation in order to obtain spectra of NGC 3125-1 and NGC 3125-2 simultaneously. The two clusters have a separation of 11arcsec. NGC 3125-2 has not been observed spectroscopically with HST but archival FOC images suggest roughly equal 2200 ? fluxes of the two 12172( 3) - 28-Apr-2011 10:15:22 - [ 2] clusters. We will acquire on NGC 3125-1, as this has previously been demonstrated to be successful. A 20 sec CCD image with the F28x50LP aperture will be taken for the acquisition. The rest of the first orbit and the full second orbit will be filled with G750L, G430L, G230L, and G140L exposures using the 52x2 aperture. Exposure times of 2300 s and 700 s with the G140L and G230L gratings, respectively, will result in S/N = 15. An S/N in excess of 30 will be achieved within less than 5 min with the G430L and G750L. Since the science exposure times for the CCD spectroscopy are short, we request that they be combined with the MAMA observations in the same visit. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12172( 3) - 28-Apr-2011 10:15:22 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3125-1 GALAXY, STARBURST RA=10H06M33.2800S +/- 0.1", J2000 V = 1113 V = 13.0 +/- 0.5 F(1300) = 2e-15 DEC=-29D56'6.80" +/- 0.1" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 12172( 3) - 28-Apr-2011 10:15:22 - [ 4] Visit: 01 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 NGC3125-1 COS/NUV ACQ/IMA PSA MIRRORA 1 30 S GE ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3125-1 COS/FUV TIME-TA PSA G130M 1300 BUFFER-TIME=1500, FP-POS=3 1 2549 S G ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC3125-1 COS/FUV TIME-TA PSA G130M 1318 BUFFER-TIME=1500, FP-POS=3 1 2971 S G ------------------------------------------------------------------------------------------------------------------------------------ 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 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE NGC3125-1 2 COS/FUV TIME-TA PSA G130M 1300 none none none none 1 N/A G NGC3125-1 3 COS/FUV TIME-TA PSA G130M 1318 none none none none 2 N/A G 12172( 3) - 28-Apr-2011 10:15:22 - [ 5] Visit: 02 Visit Requirements: ORIENT 349D TO 350 D 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 NGC3125-1 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3125-1 STIS/CCD ACCUM 52X2 G750L 7751 CR-SPLIT=3 1 120 S POS TARG null, 6.5 ------------------------------------------------------------------------------------------------------------------------------------ 3 CCDFLAT STIS/CCD ACCUM 0.2X0.2 G750L 7751 2 DEF ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC3125-1 STIS/CCD ACCUM 52X2 G430L 4300 CR-SPLIT=3 1 240 S SAME POS AS 2 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC3125-1 STIS/NUV ACCUM 52X2 G230L 2376 1 808 S SAME POS AS 2 -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC3125-1 STIS/FUV ACCUM 52X2 G140L 1425 1 2967 S SAME POS AS 2 -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 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 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A NGC3125-1 2 STIS/CCD ACCUM 52X2 G750L 7751 none none none 1 1 N/A NGC3125-1 2 STIS/CCD ACCUM 52X2 G750L 7751 none none none 2 1 N/A NGC3125-1 2 STIS/CCD ACCUM 52X2 G750L 7751 none none none 3 1 N/A CCDFLAT 3 STIS/CCD ACCUM 0.2X0.2 G750L 7751 none none 1 none 1 N/A CCDFLAT 3 STIS/CCD ACCUM 0.2X0.2 G750L 7751 none none 2 none 1 N/A NGC3125-1 4 STIS/CCD ACCUM 52X2 G430L 4300 none none none 1 1 N/A NGC3125-1 4 STIS/CCD ACCUM 52X2 G430L 4300 none none none 2 1 N/A NGC3125-1 4 STIS/CCD ACCUM 52X2 G430L 4300 none none none 3 1 N/A NGC3125-1 5 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 1 N/A -MAMA NGC3125-1 6 STIS/FUV ACCUM 52X2 G140L 1425 none none none none 2 N/A -MAMA 12172( 3) - 28-Apr-2011 10:15:22 - [ 6] Summary Form for Proposal 12172 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, 52X2, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV, STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT, BUFFER-TIME=1500, CR-SPLIT=3, FP-POS=3 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 349D TO 350 D, POS TARG null, 6.5, SAME POS AS 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G130M, G140L, G230L, G430L, G750L, MIRROR, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names CCDFLAT, NGC3125-1 ------------------------------------------------------------------------------------------------------------------------------------