0 Assigned ID: 511 ----- Attempting Submission 1 (Fri Apr 11 14:58:33 GMT 2014) ----- HST Phase I Proposal 511 (omcen_22.apt) successfully submitted. ----- Attempting Submission 2 (Fri Apr 11 18:55:08 GMT 2014) ----- The finding chart for V5 provided in Phase1 was wrong, please use the version e-mailed to the Contact Scientist for any necessary checks. Since both targets are in omega Cen the BOT as well as the charts generated by the APT are not useful. However, we cleared both fields of FUV bright objects out to 20" (see proposal description) 1872712692 ----- Attempting Submission 1 (Thu Jul 24 09:10:16 GMT 2014) ----- We request far-UV spectroscopy for the hottest and the coolest members of the recently discovered class of rapid subdwarf O pulsators on the Extreme Horizontal Branch (EHB) in omega Centauri. Our main aim is to derive reliable temperature estimates and thus map the location of the omega Cen EHB instability strip in the Teff-log g plane. Current estimates based on optical spectroscopy suggest the pulsators to be clustered around 50,000 K, which is distinctly cooler than the red edge of the predicted instability strip. We suspect that this discrepancy is due, at least in part, to the known problem of the temperatures being significantly underestimated from optical spectroscopy (compared to the more realistic values from FUV spectroscopy) for very hot stars. Given the successful pulsational modeling of the cooler (~31,000 K) rapid subdwarf B pulsators found among the Galactic field population, the inability to reproduce the omega Cen pulsators would point towards fundamental differences between the two EHB populations. On the other hand, if we are able to reconcile the predicted and observed instability regions for the omega Cen pulsators, this will open them up to exploitation via asteroseismology. Asteroseismology has proven to be a very powerful tool for determining the internal stellar structure in the subdwarf B pulsators, providing valuable constraints on competing evolutionary scenarios. In light of the currently raging debate as to the origin of EHB stars particularly in Globular Clusters, the prospect of applying asteroseismology to EHB stars in a Globular Cluster for the first time is highly enticing. We will obtain COS/G140L FUV spectroscopy for two known omega Cen pulsators (V1 and V5) with the main aim of pinning down their effective temperatures as well as metal abundances (primarily C,N,O). Each of the targets will be placed in the COS primary science aperture (no orientation restrictions) and requires one visit of 2 orbits each. Each of the two visits encompasses a FUV PEAKXD and PEAKD acquisition followed by four exposures on-source (FP-POS=1,2,3,4). The availability of ACS photometry covering both fields implies a good astrometric accuracy (~0.2"), allowing us to skip the SEARCH step during acquisition. Given an orbital visibility of (2x) 57 minutes we can expect to get a total of 5336 s integration time on-source for each of our two targets (1209 s per exposure for FP-POS1,2 and 1459 s for FP-POS3,4). According to the COS ETC this yields a S/N~30-40 per spectral resolution element in the 1120-1550 A wavelength range. The resolving power (R~3000) is sufficient to resolve the lines and distinguish the metal lines arising from interstellar absorption (notably CIV at 1548,1550 A) from the redshifted stellar lines. Since omega Cen has a well-measured velocity of 230 km/s, the stellar lines will be shifted by ~1 A in the wavelength range of interest, more than the ~0.5 A spectral resolution achieved. At B~18.5 (U~16.9) our targets are faint enough to observe in TIMETAG mode and pose no safety issues (the count rate over the entire detector is <600/s according to the COS ETC). The buffer time is larger than the exposure time for all exposures. Since our two pointings are in omega Cen, the BOT is not useful for determining whether the observations are safe. However, we carefully checked the surrounding area with the help of ACS/435W, WFPC2/F218W and UIT FUV data. All the surrounding stars falling in the COS apertures (~1") are main sequence or red giant stars with T < 5000 K and (B-R) > 1 that will have negligible FUV fluxes compared to our sdO targets. For V1, there are no objects brighter than U=16 within 15", and the UIT (lamda_eff=1615 A) data for omega Cen show no other FUV bright objects within 20" (see left panel of Fig. 5 in the proposal). For V5, there is one bright star with U~15.3 (m218_AB ~ 17.4) at a distance of ~6" from V5 (see the finding chart emailed to Charles Proffitt, the Contact Scientist - note that the chart provided in the right hand panel of Fig. 5 in the proposal is wrong). However, this star is significantly cooler than V5 (m218_AB-V = 1.85 vs m218_AB-V=-0.72 for V5) and is therefore expected to be fainter in the FUV. From doing simple counts statistics on the UIT FUV image, we estimate that this star has only 90% of the flux of V5 at 1615 A and is therefore not problematic from a safety point of view. There are no other FUV bright stars within 20". Our observations are not affected by the change in COS lifetime position, i.e. it would be o.k. to have one visit executed before the change and one after. HOT STARS 12 Regular false true false false false SUPPORTED STAR SDO The target star should be the brightest object in the FOV in the FUV OMEGA-CEN-V1 J2000 J2000 U=16.81, spectral type sdO STAR SDO The target star should be the brightest object in the FOV in the FUV. There is another star with ~90% of the FUV flux of V5 about 6" to the North-East of V5, but that should fall outside of the COS field and not influence the observations. OMEGA-CEN-V5 J2000 J2000 U=16.96, spectral type sdO COS/FUV Spectroscopic No No G140L 1105 COS/FUV Spectroscopic No No G140L 1105 1406192884264 The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. FUV spectroscopy of V1 (Tic-Visit :proposal-id 13707 :visit-id "01" :proposal-version -1 :trans-version "20140605" :date "24-Jul-2014 11:08:03.0" :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 191456 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13707 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13707 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3024 :al-overhead-at-end 0 :internal-dur-at-end 76 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13707 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3135 :al-overhead-at-end 0 :internal-dur-at-end 414 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) false 2 0 1406192872664 The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. FUV spectroscopy of V5 (Tic-Visit :proposal-id 13707 :visit-id "02" :proposal-version -1 :trans-version "20140605" :date "24-Jul-2014 11:07:52.0" :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 191456 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13707 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13707 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3024 :al-overhead-at-end 0 :internal-dur-at-end 76 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13707 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3135 :al-overhead-at-end 0 :internal-dur-at-end 414 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) true 2 0