Assigned ID: 28 ----- Attempting Submission 1 (Thu Feb 18 14:40:28 GMT 2010) ----- minor coordinate update ----- Attempting Submission 1 (Fri Jul 09 16:27:33 GMT 2010) ----- HST Phase II Proposal 12172 (C18 NGC3125_PhaseII.apt) successfully submitted. ----- Attempting Submission 2 (Wed Apr 27 11:48:59 GMT 2011) ----- warning for same pos; it is understood and may be ignored Is the Extraordinary Super Star Cluster NGC 3125-1 an Imposter? 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.
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 Å fluxes of the two 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. UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE 12 false 0.0 0.0 false false false false SUPPORTED GALAXY STARBURST This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 10 06 33.3500 -29 56 6.82 J2000 F(1300) = 2e-15 COS/FUV Spectroscopic No No G130M 1309 STIS/CCD Spectroscopic No No G750L 7751 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/FUV-MAMA Spectroscopic No No G140L 1425 The scheduling data was generated by CASM 19.0. CASM was run in Phase II mode. C:\Users\claus\AppData\Local\Temp\OPVisit929116292537912123.xml (Tic-Visit :proposal-id 12172 :visit-id "01" :proposal-version -1 :trans-version "20100902" :date "27-Apr-2011 07:46:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 313184 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12172 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12172 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2914 :al-overhead-at-end 0 :internal-dur-at-end 97 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12172 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3035 :al-overhead-at-end 0 :internal-dur-at-end 428 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 19.0. CASM was run in Phase II mode. C:\Users\claus\AppData\Local\Temp\OPVisit5045611982233299029.xml (Tic-Visit :proposal-id 12172 :visit-id "02" :proposal-version -1 :trans-version "20100902" :date "27-Apr-2011 07:47:23.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 375952 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12172 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12172 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2924 :al-overhead-at-end 0 :internal-dur-at-end 115 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12172 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3035 :al-overhead-at-end 241 :internal-dur-at-end 321 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 2 0