9105( 5) - 10/15/01 16:51 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9105 Version: 5 Check-in Date: 15-Oct-2001 16:50:37 1.Proposal Title: Determination of the Distances and Masses of 3 Galactic Cepheids ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Derck Massa Emergent Information Technologies, Inc. CoI: Dr. Nancy Evans Smithsonian Astrophysical Observatory N ------------------------------------------------------------------------------------ 5. Abstract We propose to continue a successful observing strategy which enabled us to accurately measure angular separations < 10^-2'' with the FOC for binaries with Cepheid primaries and main sequence B or A star secondaries (our accuracy should improve to ~10^-3'' with STIS). Once measurements are available at two carefully selected phases and these are combined with spectroscopic orbits, the angular information will enable the masses and distances for the binaries to be determined from Newton's laws and Euclidean geometry. The distances determinations amount to bypassing two rungs of the cosmic distance ladder: the moving-cluster distance to the Hyades and main sequence fitting of clusters containing Cepheids. The mass determinations will provide the first direct dynamical mass measurements for Cepheids, providing sorely needed quantitative information on this poorly understood stage of massive star evolution. ------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 2] Observations Description ------------------------ Program stars: The binary Cepheids selected for observation are U Aql (HD 183344), AW Per (HD 30282) and W Sgr (HD 164975). Table 1 list some properties of these systems: their maximum expected separations, orbital periods, magnitudes, color excesses, and the spectral types and magnitudes of the hot secondaries. Optical spectroscopic orbits are available for the primaries and UV spectroscopy exists for U Aql (Evans, et al. 1998, ApJ 494, 768). The AW Per system has the largest separation, but the longest orbital period. Consequently, observations will have to be spaced more than 5 years apart to obtain the 2 distinct orbital positions needed to determine sin i, and hence the full orbital solution. However, since this was our only definitive detection with the FOC, our primary reason for observing it with STIS is to verify the FOC results. Furthermore, the separation in Cycle 10 is the largest it will be for a decade, so it is particularly important to have an accurate measurement at this epoch. For U Aql and W Sgr, the orbital periods are relatively short, with 1/4 of a period being less than 2 years in each case. Therefore, we are requesting time to perform both sets of observations needed to determine sin i at this time. For U Aql, maximum separation is expected to occur during 2001 December (in Cycle 10) and minimum separation in 2002 October (Cycle 11). For W Sgr, maximum separation occurs in January 2002 (Cycle 10), and the minimum is expected in June 2003 (Cycle 11). Our FOC observation of U Aql marginally resolved the system with Theta_0 = 0.0047''. This was only a 2 Sigma result, because the FOC systematics were so large. As explained above, we expect to be able to control and characterize any systematic effects in the STIS observations. In this case, the centroid accuracy will be limited by the random errors which (see Centroid Accuracy subsection) are expected to be ~10^- 4''. This should be more than adequate to resolve both U Aql and W Sgr (see, Table 1). Description of the observations: All observations will use the NUV MAMA and the G230L grating. They will be performed in the slitless mode, and the F25NDQ1 neutral density filter will have to be used for the W Sgr observation. As pointed out above, the STIS MAMA detector has several advantages over the FOC. The observing sequence will proceed as follows: guide star acquisition (6 min), STIS target acquisition to get the target within 0.1'' of a known location on the detector (6 min), a 10 min exposure (10 min + 8 min overhead), a small angle maneuver to displace the target 0.05'' perpendicular to the dispersion (10 sec), a second 10 min exposure (10 min + 1 min overhead), a small angle maneuver to displace the target 0.05'' perpendicular to the dispersion in the other direction (10 sec), a third 10 min exposure (10 min + 1 min overhead). All of these observations can be performed in a single orbit. The telescope will then be rolled in one direction and the sequence repeated (new guide stars must be acquired after each roll). Finally, the telescope will be rolled in the other direction and the sequence repeated a final time. Thus, we require 3 orbits for each visit. The three different different roll angles will change the position angle of the binary relative to the dispersion and enable us to determine the position angle and separation of the system. The small displacements will be used to assess the impact of localized residual geometric distortions on the centroid measurements. Finally, the entire sequence must be repeated a second time once the binary orbit has changed sufficiently so that the orbital inclination factor, sin i, can be determined. Table 1 lists the signal-to-noise values (determined with the STIS on-line exposure time calculator) for a resolution element obtained in a 10 min STIS exposure at 1700 Angstrom and 3000 Angstrom. These correspond to the minimum and maximum S/N in the spectra. Centroid Accuracy: The counts needed to centroid to an accuracy Sigma Theta (Lambda) can be estimated for an instrument whose spread function perpendicular to the dispersion is a Gaussian with FWHM=Alpha. A single count is equivalent to one estimate of the center of the spectrum drawn from a sample with an RMS dispersion Sigma =Alpha sqrt8 ln 2 = 0.42 Alpha. Therefore, N samples (counts) determine the centroid to an accuracy of Sigma Theta (Lambda )=frac0.42Alpha sqrtN(Lambda) (3). Equation (3) gives the counts needed over a wavelength band to obtain the desired accuracy. A typical STIS FWHM is <=q 0.045'' and the minimum number of counts obtained over a spectral resolution element is 30^2 in one 10 min exposure and we will obtain 3 of these. Therefore, the poorest precision we will obtain is ~4*10^-4'', and this is for a single resolution element. In all, there are 512 independent resolution elements which will be combined to determine a single measurement of Delta Theta through the use of eq (2). Therefore, random noise in the angular separation determinations should be <=q 10^-4'', and not a limiting factor for our observations. Real Time Justification ----------------------- To unambiguously determine the separation and position angle of the system, it must be observed with the dispersion oriented in different directions on the sky. Optimally, this would span 120 deg. The telescope can be rolled by +/-60 deg during a brief portion of the year. However, should such a scheduling request prove too difficult, roll angles of +/-30 deg (which span 60 deg) would be acceptable, and are relatively easy to schedule. To provide the best measurement of sin i, the binaries must be observed near their expected minimum and maximum separations. Since the periods are relatively long, the timing is not very stringent, but the systems should be observed within the months listed in Table 2. Table 2 System Minimum Maximum U Aql 2002 October 2001 December W Sgr 2003 June 2002 January Together, these constraints require us to observe our targets not only at specific times in their orbits but also at specific times of the year so that the HST anti-Sun angle is sufficiently large to allow us to roll the spacecraft. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 U-AQL STAR, Cepheid RA=19H 29M 21.36S +/-0.03S, DEC= J2000 V = 6.90+/-0.76 -07D 02' 38.6" +/-0.3" B-V = 0.95+/-0.20 F-CONT(2400)=30+/-3e-15 Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE 2 W-SGR STAR, Cepheid RA=18H 05M 01.22S +/-0.02S, DEC= J2000 V = 5.09+/-0.85 -29D 34' 48.3" +/-0.2" B-V = 0.7+/-0.3 F-CONT(2400)=10+/-2e-14 Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE 3 AW-PER STAR, Cepheid RA=04H 47M 46.32S +/-0.03S, J2000 V = 7.39+/-0.22 DEC=+36D 43' 22.1" +/-0.3" B-V = 0.9+/-0.1 F-CONT(2400)=10+/-2e-14 Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE 9105( 5) - 10/15/01 16:51 - [ 4] Visit: 01 Visit Priority: Visit Requirements: GROUP 1-3 WITHIN 5H; BETWEEN 10-JUN-2002 AND 10-JUL-2002; SCHED 100%; PERIOD 7.02393D AND ZERO-PHASE JD2450101.356 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 U-AQL STIS/C ACQ F28X50L MIRROR 1 0.1 S PHASE 0.2 TO 0.85 CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 3 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 27D TO 30D FROM 1; SCHED 100%; PERIOD 7.02393D AND ZERO-PHASE JD2450101.356 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 ------------------------------------------------------------------------------------------------------------------------------------ 5 U-AQL STIS/C ACQ F28X50L MIRROR 1 0.1 S PHASE 0.2 TO 0.85 CD P ------------------------------------------------------------------------------------------------------------------------------------ 6 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 6] Visit: 03 Visit Priority: Visit Requirements: ORIENT -30D TO -27D FROM 1; SCHED 100%; PERIOD 7.02393D AND ZERO-PHASE JD2450101.356 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 ------------------------------------------------------------------------------------------------------------------------------------ 9 U-AQL STIS/C ACQ F28X50L MIRROR 1 0.1 S PHASE 0.2 TO 0.85 CD P ------------------------------------------------------------------------------------------------------------------------------------ 10 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 11 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 12 U-AQL STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 7] Visit: 04 Visit Priority: Visit Requirements: GROUP 4-6 WITHIN 5H; BETWEEN 16-NOV-2001 AND 10-DEC-2001; SCHED 100% 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 AW-PER STIS/C ACQ F28X50L MIRROR 1 0.1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 21 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 23 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 24 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 8] Visit: 05 Visit Priority: Visit Requirements: ORIENT 29D TO 30D FROM 4; SCHED 100% 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 ------------------------------------------------------------------------------------------------------------------------------------ 25 AW-PER STIS/C ACQ F28X50L MIRROR 1 0.1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 26 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 27 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 28 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 9] Visit: 06 Visit Priority: Visit Requirements: ORIENT -30D TO -29D FROM 4; SCHED 100% 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 ------------------------------------------------------------------------------------------------------------------------------------ 29 AW-PER STIS/C ACQ F28X50L MIRROR 1 0.1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 30 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 31 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 32 AW-PER STIS/N ACCUM 25MAMA G230L 2376 1 10 M POS TARG 0, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 10] Visit: 07 Visit Priority: Visit Requirements: GROUP 7-9 WITHIN 5H; BETWEEN 01-JUN-2002 AND 01-AUG-2002; PERIOD 7.594904D AND ZERO-PHASE JD2443374.772; SCHED 100% 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 ------------------------------------------------------------------------------------------------------------------------------------ 41 W-SGR STIS/C ACQ F28X50L MIRROR 1 0.1 S PHASE 0.3 TO 0.8 CD P ------------------------------------------------------------------------------------------------------------------------------------ 42 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, 0.0 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 43 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 44 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 11] Visit: 08 Visit Priority: Visit Requirements: ORIENT 29D TO 30D FROM 7; PERIOD 7.594904D AND ZERO-PHASE JD2443374.772; SCHED 100% 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 ------------------------------------------------------------------------------------------------------------------------------------ 45 W-SGR STIS/C ACQ F28X50L MIRROR 1 0.1 S PHASE 0.3 TO 0.8 CD P ------------------------------------------------------------------------------------------------------------------------------------ 46 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, 0.0 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 47 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 48 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 12] Visit: 09 Visit Priority: Visit Requirements: ORIENT -30D TO -29D FROM 7; PERIOD 7.594904D AND ZERO-PHASE JD2443374.772; SCHED 100% 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 ------------------------------------------------------------------------------------------------------------------------------------ 49 W-SGR STIS/C ACQ F28X50L MIRROR 1 0.1 S PHASE 0.3 TO 0.8 CD P ------------------------------------------------------------------------------------------------------------------------------------ 50 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, 0.0 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 51 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, 0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 52 W-SGR STIS/N ACCUM F25NDQ1 G230L 2376 1 10 M POS TARG 4.3, -0.10 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9105( 5) - 10/15/01 16:51 - [ 13] Summary Form for Proposal 9105 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 25MAMA F25NDQ1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 1-3 WITHIN 5H; BETWEEN 10-JUN-2002 AND 10-JUL-2002; SCHED 100%; PERIOD 7.02393D AND ZERO-PHASE JD2450101.356 PHASE 0.2 TO 0.85 POS TARG 0, 0.10 POS TARG 0, -0.10 ORIENT 27D TO 30D FROM 1; SCHED 100%; PERIOD 7.02393D AND ZERO-PHASE JD2450101.356 ORIENT -30D TO -27D FROM 1; SCHED 100%; PERIOD 7.02393D AND ZERO-PHASE JD2450101.356 GROUP 4-6 WITHIN 5H; BETWEEN 16-NOV-2001 AND 10-DEC-2001; SCHED 100% ORIENT 29D TO 30D FROM 4; SCHED 100% ORIENT -30D TO -29D FROM 4; SCHED 100% GROUP 7-9 WITHIN 5H; BETWEEN 01-JUN-2002 AND 01-AUG-2002; PERIOD 7.594904D AND ZERO-PHASE JD2443374.772; SCHED 100% PHASE 0.3 TO 0.8 POS TARG 4.3, 0.0 POS TARG 4.3, 0.10 POS TARG 4.3, -0.10 ORIENT 29D TO 30D FROM 7; PERIOD 7.594904D AND ZERO-PHASE JD2443374.772; SCHED 100% ORIENT -30D TO -29D FROM 7; PERIOD 7.594904D AND ZERO-PHASE JD2443374.772; SCHED 100% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names U-AQL AW-PER W-SGR ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2376 ------------------------------------------------------------------------------------------------------------------------------------