6690( 6) - 07/16/96 11:17 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6690 Version: 6 Check-in Date: 16-Jul-1996 11:11:43 1.Proposal Title: The Winds of Main Sequence B Stars in NGC 6231, Evidence for Shocks in Weak Winds. ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Derck Massa HUGHES STX ------------------------------------------------------------------------------------ 6. Abstract Because the main sequence B stars in NGC 6231 have abnormally strong C iv wind lines, they are the only main sequence B stars with distinct edge velocities. Although the underlying cause for the strong lines remains unknown, these stars do provide an opportunity to test two important ideas concerning B star winds: 1) that the driving ions in the winds of stars with low mass loss rates decouple from the general flow, and; 2) that shocks deep in the winds of main sequence B stars are responsible for their observed X-rays. In both of these models, the wind accelerates toward a terminal velocity, v_\infty, far greater than the observed value, shocking or decoupling well before it can attain the high v_\infty. As a result, the observable wind accelerates very rapidly, leading to wind flushing times less than 30 minutes. If these conjectures are correct, then the winds of main sequence B stars should be highly variable on time scales of minutes. Model fitting of available IUE data are consistant with the general notion of a rapidly accelerating wind, shocking well before its actual v_\infty. However, these are 5 hour exposures, so the fits are to ill-defined mean wind flows. The new GHRS observations will provide adequate spectral and temporal resolution to observe the expected variability and, thereby, verify the existance of two important astrophysical processes. ------------------------------------------------------------------------------------ 6690( 6) - 07/16/96 11:17 - [ 2] Observations Description ------------------------ The scientific goals of this program require the observation of several wind lines with a time resolution adequate to resolve a wind flushing time which may be 20 min or less. Figure 3 in the science section shows the expected accelerations in km s^-1 min^-1. We see that wind features may propagate across wind lines as rapidly as 150 km s^-1 min^-1 or more. The GHRS with its G140L grating (with its 150 km s^-1 resolution) can resolve this motion at the resolution of the grating in ~ 1 min. During this time, it is possible to achieve a signal to noise of 25:1 at half the continuum level in C iv Lambda Lambda 1550 in either CPD-41^o7719 or CPD-41^o7724. Thus, this combination is well suited for the proposed program. Unfortunately, the required sampling time is too short to switch grating positions and still fully resolve the shortest expected time scale. Therefore, two observing strategies are proposed (both using the G140L), one to time resolve features in the C iv and Si iv wind lines, and the other to examine the ionic ratios at a given time. First, the program star will be acquired and observed continuously in the RAPID mode with the grating set to cover the Si iv Lambda Lambda 1400 and C iv Lambda Lambda 1550 wind doublets (1290-1576 Angstrom). This configuration will be maintained for 2 orbits. During the first orbit, guide star and target acquisitions and will take 12 and 11 min of the available 54 min, leaving only 35 min for actual observing (the sample time will be set to 10 s, so the onboard tape recorder can be used). During the second orbit, only 6 min are needed for reacquisition, so 48 min will be available for observing. This provides a total of 83 min, roughly 4 wind flushing times, on the star. Then, while on the target, the instrument will be switched to the WSCAN mode during occultation, and 1 min exposures will be alternated between the same set up given above, and a second one (1150-1436 Angstrom) which covers Si iii Lambda 1206, N iv Lambda Lambda 1240 and Si iv. The overhead for moving grating position is only 1 min, and the read overhead is 4 min, so it will be possible to cycle through the observational sequence in 6 min, with the difference in the mean times of the two different wavelength exposures being only 2 min. This should be sufficiently close to make useful comparisons of the ionization ratios of various wind features which may appear. The 6 min cycle time will enable us to obtain 8 cycles during a single orbit. While the cycle-to- cycle time (6 min) is too long to provide full time resolution, it will help determine whether significant changes occurred during the 2 min between the 2 wavelength exposures and to apply any necessary adjustments (recall that most distinct spectral features traverse the wind lines at a somewhat slower rate than the wind flushing time). Finally, it should be pinted out that the presence of fixed pattern noise on the detector should not present a problem for the proposed RAPID observations. Because doppler shifts due to spacecraft orbital motion will be insignificant at the G140L resolution, the mapping of wavelengths to detector elements will remain effectively fixed. Since we will only be looking for changes from one spectrum to the next, noise that remains constant in detector-space, will not affect the results. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6690( 6) - 07/16/96 11:17 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: STSCI Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6690( 6) - 07/16/96 11:17 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CPD-41D7719 STAR, B0-B2 V-IV RA = 16H 54M 5.13S +/- 0.03S, J2000 V = 9.47+/-0.02 DEC = -41D 50' 7.3" +/- 0.3", B-V = 0.13+/-0.02 PLATE-ID = 06Q2 E(B-V) = 0.39+/-0.03 F(1550)=30+/-2e-13 Comments: Coordinates are from GSC 6690( 6) - 07/16/96 11:17 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CPD-41D7719 HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQuisition FOR 2-120 Comments: STEP-TIME = 5.0 S ------------------------------------------------------------------------------------------------------------------------------------ 2 CPD-41D7719 HRS RAPID 2.0 G140L 1433 SAMPLE-TIME=10.0 1 1850 S ------------------------------------------------------------------------------------------------------------------------------------ 3 CPD-41D7719 HRS RAPID 2.0 G140L 1433 SAMPLE-TIME=10.0 1 2721 S ------------------------------------------------------------------------------------------------------------------------------------ 30 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 40 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 50 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 60 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 70 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 80 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 90 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 100 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 110 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 115 CPD-41D7719 HRS WSCAN 2.0 G140L 1150-15 WAVE-STEP = DEF 1 108.8 S 76 ------------------------------------------------------------------------------------------------------------------------------------ 120 CPD-41D7719 HRS ACCUM 2.0 G140L 1300 FP-SPLIT=STD,STEP-PATT=5 1 217.6 S ------------------------------------------------------------------------------------------------------------------------------------ 6690( 6) - 07/16/96 11:17 - [ 6] Summary Form for Proposal 6690 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ RAPID WSCAN ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=3 SAMPLE-TIME=10.0 WAVE-STEP = DEF STEP-PATT=5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQuisition FOR 2-120 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N1 G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names CPD-41D7719 ------------------------------------------------------------------------------------------------------------------------------------