Proposal_Information Title: Determination of the Distances and Masses of 2 Galactic Cepheids Proposal_Category: GO Scientific_Category: COOL STARS Cycle: 6 Investigators PI_Name: Derck Massa PI_Institution: Applied Research Corporation CoI_Name: Nancy Evans CoI_Institution: Smithsonian Astrophysical Observatory Contact: 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. Questions Observing_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: Fixed_Targets Target_Number: 1 Target_Name: HD183344 Alternate_Names: U-AQL Description: STAR, CEPHEID Position: RA=19H 29M 21.42S +/- 0.3",DEC=-7D 2' 38.5" +/- 0.3" Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: V = 6.5+/-0.4 B-V = 1.04+/-0.2 E(B-V) = 0.35+/-0.03 F(1550)=50+/-5e-15 Comments: Coordinates are from Hipparcos INCA Target_Number: 2 Target_Name: HD30282 Alternate_Names: AW-PER Description: STAR, CEPHEID Position: RA=4H 47M 46.322S +/- 0.3",DEC=36D 43' 22.11" +/- 0.3" Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: V = 7.5+/-0.4 B-V = 1.08+/-0.2 E(B-V) = 0.52+/-0.03 F(1550)=12+/-2e-14 Comments: Coordinates are from Hipparcos INCA Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: GROUP 1-3 WITHIN 10 H ORIENT 265D TO 266D On_Hold_Comments: Visit_Comments: Exposure_Number: 10 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG 0,-1.2 MIN DUR MAX DUR Comments: Exposure_Number: 12 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG -0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 15 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG 0.7,0 MIN DUR MAX DUR Comments: Visit_Number: 02 Visit_Requirements: ORIENT 236D TO 236D On_Hold_Comments: Visit_Comments: Exposure_Number: 20 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG 0,-1.2 MIN DUR MAX DUR Comments: Exposure_Number: 22 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG -0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 25 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG 0.7,0 MIN DUR MAX DUR Comments: Visit_Number: 03 Visit_Requirements: ORIENT 206D TO 207D On_Hold_Comments: Visit_Comments: Exposure_Number: 30 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG 0,-1.2 MIN DUR MAX DUR Comments: Exposure_Number: 32 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG -0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 35 Target_Name: HD183344 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 590 S Special_Requirements: POS TARG 0.7,0 MIN DUR MAX DUR Comments: Visit_Number: 04 Visit_Requirements: GROUP 4-6 WITHIN 10 H On_Hold_Comments: Visit_Comments: Exposure_Number: 40 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG 0,-1.2 MIN DUR MAX DUR Comments: Exposure_Number: 42 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG -0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 45 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG 0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 47 Target_Name: INTFLAT Config: FOC/96 Opmode: RESEAU Aperture: 512X1024 Sp_Element: CLEAR Wavelength: Optional_Parameters: PIXEL=25X25,LED=GREEN-2,LED-STEP=64 Number_of_Iterations: 1 Time_Per_Exposure: 600S Special_Requirements: Comments: Visit_Number: 05 Visit_Requirements: ORIENT 29D TO 30D FROM 4 On_Hold_Comments: Visit_Comments: Exposure_Number: 50 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG 0,-1.2 MIN DUR MAX DUR Comments: Exposure_Number: 52 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG -0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 55 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG 0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 57 Target_Name: INTFLAT Config: FOC/96 Opmode: RESEAU Aperture: 512X1024 Sp_Element: CLEAR Wavelength: Optional_Parameters: PIXEL=25X25,LED=GREEN-2,LED-STEP=64 Number_of_Iterations: 1 Time_Per_Exposure: 600S Special_Requirements: Comments: Visit_Number: 06 Visit_Requirements: ORIENT -30D TO -29D FROM 4 On_Hold_Comments: Visit_Comments: Exposure_Number: 60 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG 0,-1.2 MIN DUR MAX DUR Comments: Exposure_Number: 62 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG -0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 65 Target_Name: HD30282 Config: FOC/96 Opmode: IMAGE Aperture: 512X1024 Sp_Element: PRISM2,F175W,F195W Wavelength: Optional_Parameters: CHECK-FILTER=YES Number_of_Iterations: 1 Time_Per_Exposure: 616 S Special_Requirements: POS TARG 0.7,0 MIN DUR MAX DUR Comments: Exposure_Number: 67 Target_Name: INTFLAT Config: FOC/96 Opmode: RESEAU Aperture: 512X1024 Sp_Element: CLEAR Wavelength: Optional_Parameters: PIXEL=25X25,LED=GREEN-2,LED-STEP=64 Number_of_Iterations: 1 Time_Per_Exposure: 600S Special_Requirements: Comments: Data_Distribution ! 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