6689( 16) - 07/18/97 15:43 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6689 Version: 16 Check-in Date: 18-Jul-1997 15:42:34 1.Proposal Title: Determination of the Distances and Masses of 2 Galactic Cepheids ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COOL STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Derck Massa HUGHES STX CoI: Nancy Evans Smithsonian Astrophysical Observatory N ------------------------------------------------------------------------------------ 6. Abstract We propose an observing strategy which could accurately measure angular separations ~ 10^-3 for binaries with Cepheid primaries and main sequence B or A star secondaries. When combined with available spectroscopic orbits, the spatial 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 information on this poorly understood stage of massive star evolution. ------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 2] Observations Description ------------------------ Program stars: The binary Cepheids selected for observation are the 7.0 day Cepheid U Aql and the 6.4 day Cepheid AW Per. Table 1 list some properties of these systems -- their expected separations, orbital periods, magnitudes, color excesses, and the spectral types and magnitudes of the hot secondaries. Both primaries have optical spectroscopic orbits available. The AW Per system has the advantage of a larger expected separation, but it suffers from a large orbital period. Consequently, we will have to space observations over at least 5 years in order to obtain the 2 distinct orbital positions needed to determine sin i, and hence the full orbital solution. However, we know from the optical spectroscopic orbit (Welch & Evans, 1989, AJ, 97, 1153) that the system is close to periastron, so high precision HST observations would be particularly valuable. The expected separation of the U Aql system, on the other hand, is considerably less (but still well within our expected accuracy) and in this case the period is relatively short. Should the proposed observations be successful, we could return for the concluding observation of this system during the next cycle. Furthermore, a UV spectroscopic orbit of its secondary is almost completed under another HST program. It seems, therefore, reasonable to observe both systems. Table 1 System | Secondary | Cnt rates Name DTheta Period V E(B-V)| V Sp Ty | max min mean U Aql 0.008'' 5.1 yrs 6.5 0.35 | 10.8 A0 V | 1.0 0.3 0.5 AW Per 0.048 35.9 yrs 7.6 0.52 | 10.1 B8 V | 0.7 0.3 0.4 Description of the observations: All observations will be performed with the F/96 (actually F/151) FOC camera, the NUVOP objective prism, and both the F175W and F195W filters in order to obtain acceptable count rates. Table 1 lists the minimum, maximum and mean total expected count rates for each system at a given wavelength (i.e., integrated over all pixels in a 1 pixel wide strip across the dispersion). The maximum count rates per pixel will be roughly one fifth of the values listed. The observations of each system will entail a sequence of 3 pairs of 20 min FOC exposures obtained at three different roll angles. The different roll angles will change the position angle of the binary relative to the dispersion by 90^o. The set of 3 observations will enable us to determine the position angle and separation of the system, and to determine the effects of any residual distortion. This procedure is more efficient than setting up a second set of observations on a single, standard star to calibrate the residual distortions. Exposure Times: The counts needed to centroid to an accuracy Sig_Theta(Lam) 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 sqrt(8ln2) =0.42Alpha . Therefore, N samples (counts) determine the centroid to an accuracy of Sig_Theta (Lambda )=0.42Alpha/sqrt[N(Lambda)]. (3) Equation (3) gives the counts needed over a wavelength band to obtain the desired accuracy. Because a typical FOC FWHM is <= 0.045", we will need 357 counts to obtain 0.001" accuracy at a single wavelength. With both the F175W and F195W filters in place, the lowest total count rate at any wavelength for either of our systems is 0.3 cnts s^-1. Thus, we can accumulate enough counts to centroid each wavelength of the spectrum to 0.001" with a 20 min exposure. Furthermore, 512 such measurements will be combined to determine a single measurement of Delta Theta through the use of eq (2). Therefore, we propose that each visit consist of 3 pairs of 20 min exposures: one pair at a roll of -45^o, another pair at 0^o, and a final pair at +45^o. Since the rolls can be accomplished during the occulted portion of the orbit, we will require 3 orbits for each star, 6 altogether. In addition, 1 orbit will be needed for each set of observations for interactive acquisiton, which is required for all FOC observations of bright objects. 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 90^o. The telescope can be rolled by this amount during a brief portion of the year when the target is in the anti-solar direction. However, should such a scheduling request prove too difficult, roll angles of +/- 30^o (which span 60^o) would be acceptable and are relatively easy to schedule. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD183344 STAR, CEPHEID RA=19H 29M 21.42S +/- 0.3",DEC=- J2000 V = 6.5+/-0.4 7D 2' 38.5" +/- 0.3" B-V = 1.04+/-0.2 E(B-V) = 0.35+/-0.03 F(1550)=50+/-5e-15 Comments: Coordinates are from Hipparcos INCA 2 HD30282 STAR, CEPHEID RA=4H 47M 46.322S +/- J2000 V = 7.5+/-0.4 0.3",DEC=36D 43' 22.11" +/- 0.3" B-V = 1.08+/-0.2 E(B-V) = 0.52+/-0.03 F(1550)=12+/-2e-14 Comments: Coordinates are from Hipparcos INCA 6689( 16) - 07/18/97 15:43 - [ 5] Visit: 01 Visit Requirements: GROUP 1-3 WITHIN 10 H ORIENT 265D TO 266D 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG 0,-1.2 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 12 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG -0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 15 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG 0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 6] Visit: 02 Visit Requirements: ORIENT 236D TO 236D 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 ------------------------------------------------------------------------------------------------------------------------------------ 20 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG 0,-1.2 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 22 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG -0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 25 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG 0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 7] Visit: 03 Visit Requirements: ORIENT 206D TO 207D 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 ------------------------------------------------------------------------------------------------------------------------------------ 30 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG 0,-1.2 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 32 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG -0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 35 HD183344 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 590 S POS TARG 0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 8] Visit: 04 Visit Requirements: GROUP 4-6 WITHIN 10 H 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 ------------------------------------------------------------------------------------------------------------------------------------ 40 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG 0,-1.2 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 42 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG -0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 45 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG 0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 47 INTFLAT FOC/96 RESEAU 512X102 CLEAR PIXEL=25X25,LED=GREEN-2, 1 600 S 4 LED-STEP=64 ------------------------------------------------------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 9] Visit: 05 Visit Requirements: ORIENT 29D TO 30D FROM 4 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 ------------------------------------------------------------------------------------------------------------------------------------ 50 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG 0,-1.2 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 52 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG -0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 55 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG 0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 57 INTFLAT FOC/96 RESEAU 512X102 CLEAR PIXEL=25X25,LED=GREEN-2, 1 600 S 4 LED-STEP=64 ------------------------------------------------------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 10] Visit: 06 Visit Requirements: ORIENT -30D TO -29D FROM 4 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 ------------------------------------------------------------------------------------------------------------------------------------ 60 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG 0,-1.2 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 62 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG -0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 65 HD30282 FOC/96 IMAGE 512X102 PRISM2, CHECK-FILTER=YES 1 616 S POS TARG 0.7,0 MIN DUR 4 F175W, MAX DUR F195W ------------------------------------------------------------------------------------------------------------------------------------ 67 INTFLAT FOC/96 RESEAU 512X102 CLEAR PIXEL=25X25,LED=GREEN-2, 1 600 S 4 LED-STEP=64 ------------------------------------------------------------------------------------------------------------------------------------ 6689( 16) - 07/18/97 15:43 - [ 11] Summary Form for Proposal 6689 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE RESEAU ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CHECK-FILTER=YES LED-STEP=64 LED=GREEN-2 PIXEL=25X25 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 1-3 WITHIN 10 H ORIENT 265D TO 266D POS TARG 0,-1.2 MIN DUR MAX DUR POS TARG -0.7,0 MIN DUR MAX DUR POS TARG 0.7,0 MIN DUR MAX DUR ORIENT 236D TO 236D ORIENT 206D TO 207D GROUP 4-6 WITHIN 10 H ORIENT 29D TO 30D FROM 4 ORIENT -30D TO -29D FROM 4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements PRISM2,F175W,F195W CLEAR ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD183344 HD30282 INTFLAT ------------------------------------------------------------------------------------------------------------------------------------