6504( 6) - 11/12/96 11:37 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6504 Version: 6 Check-in Date: 12-Nov-1996 11:26:41 1.Proposal Title: Cepheid Masses ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COOL STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: ERIKA BOHM-VITENSE UNIVERSITY OF WASHINGTON CoI: Nancy R.Evans Harvard Smithsonian N CoI: Kenneth Carpenter LASP/Goddard Space Flight Center, Code 681 N CoI: Rich Robinson CSC/Goddard Space Flight Center,Code 681 N ------------------------------------------------------------------------------------ 6. Abstract This is a proposal for the fourth year of an originally three year proposal which was accepted for cycles 3, 4, 5 and 6. The aim is to determine Cepheid masses for binaries with Cepheids. For 2 decades the Cepheid ``mass problem" has persisted: Mass determinations from standard evolutionary tracks and those from pulsation theory gave conflicting results. The luminosity of a Cepheid with a given mass depends sensitively on the amount of excess mixing above the core of the main sequence progenitor. Hence a good mass determination for a Cepheid with known luminosity measures the amount of convective overshoot. This knowledge is important for the interpretation of HR diagrams of populous clusters in the LMC, especially for age determinations, and also for the understanding of mixing processes in stars. IUE observations have revealed a number of Cepheids with blue companions, whose orbits have now been determined by groundbased observations. We propose to measure the orbital radial velocities of altogether 5 companions for wavelengths shorter than 2000A. The ratio of the orbital velocity amplitudes for the binary provides the mass ratio for the stars. The effective temperature of the main sequence companion and thereby its mass is determined from its ultraviolet spectrum and energy distribution. With good GHRS spectra the velocity ratio and thereby the mass ratio can be determined with an accuracy of +/-10\%. ------------------------------------------------------------------------------------ Observations Description ------------------------ The purpose of this proposal is to measure accurate orbital velocities of main sequence companions for a representative sample of classical Cepheids, for which orbits are known. In Table 2a we list the Cepheid observations obtained so far or scheduled to be obtained during cycle 5. In Table 2b we list the observations to be taken during cycle 6. We will get the first spectrum for V636 Sco during cycle 5 and ask for the second spectrum during cycle 6. Two spectra were obtained for Y Car during cycles 3 and 4. The second one, taken shortly after the repair mission was, however, contrary to our requirements, interrupted several times, because of target of opportunity observations. The necessary wavelength calibrations were then not obtained at the appropriate times. It is a very noisy spectrum, no reliable velocities could be measured. We apply here for time to repeat this observation during cycle 6 at the same orbital phase but with an exposure time twice as long, which needs one more orbit than we asked for last year. Last year we asked for a second observation for our standard star alpha Lyrae. The observation which we obtained during cycle 4 did, however, not permit an accurate wavelength calibration, because for this very bright star the wavecal spectra were contaminated with too much scattered light. While we got a velocity calibration from a cross- correlation with a synthetic spectrum we feel that for an accurate velocity determination for the Cepheid companions (which for the remaining Cepheids all have spectral types around A0 V) we need a direct cross-correlation with a standard star with known observed radial velocity. We therefore ask to replace the alpha Lyrae observation with an observation of the A1 V star HD 72660. This star has been observed extensively by Frank Fekel and found to have constant radial velocity. This observation will take one orbit. We therefore now ask for 10 cycle 6 orbits instead of the 9 we asked for last year, and which were accepted last year for cycle 6. In Table 2c we list the observing windows for maximum orbital velocities of our targets. The middle of these windows would be the best time to observe. ------------------------------------------------------------------ Table 2a. Cepheid observation during Cycles 3 and 4 &&Spectr. &expos. &&& Star &Date &elemt. &timemin &apert. &Quality &Remark Y Car B & June 24, 93 &G200M &49 &2" &Ok & Y Car B &April 18, 94 &G200M &49 &0.2" &poor &interr. & wavecal? S Mus B & Dec. 26, 93 &Echelle B &25 &2" &OK & S Mus B & Sept. 2, 94 &Echelle B &30 &0.22" &OK V 350 Sgr & May 2, 94 &G200M &57 &0.22" &very noise & U Aql & April 4, 94 &G200M &29 &0.22" &very noisy & ----------------------------------- ------------------------------- Table 2b. Cepheid observations to be done during cycle 5 V350 Sgr &Oct. 95 &G200M &154 min &0.22" &5 & V636 Sco &July 95 &G200M &152 min &0.22" &5 & U Aql & March 96 &G200M &141 min &0.22" &5 & centerline -------------------------------------------------------------------- - Table 2c. Observing windows and exposure times for cycle 6 &Orbit &&spec. &obs. &flux &No Target &per. &per. &window &elemt. &exp. time &(1860A) &orb. V636 Sco B &6.8 d &1318 d &Oct. 15, 96 +/- 45 d &G200M &152 min &7 (-14) &5 Y Car B &3.6 d &993 d &Feb. 19, 97 +/- 24 d &G200M &120 min &1 (-13) &4 HD 72660 &Multispan2 Standard &&G200M &20 min &&1 -------------------------------------- --------------------------------- We replaced the alpha Lyrae observation with an observation of a new velocity standard. Our cycle 4 observations showed that we can not get an accurate wavelength calibration for the bright star alpha Lyrae because of the scattered light from AlphaLyrae on the wavelength calibration spectra. We plan to use the GHRS with the 0.22" aperture to avoid errors due to imperfect centering in the large entrance aperture. Since high wavelength accuracy is so important for an accurate mass determination and the success of this study we think it is worth the extra observing time. For V636 Sco and Y Car and the standard star we will use the G200M grating and observe the spectral region around 1860 Angstrom, which has strong lines, and which was used for the first spectra. The velocities will then be determined by cross- correlating the two spectra of each star and also by cross-correlating with a synthetic spectrum, which appears to give reliable velocities: The cross- correlation of the standard star spectrum of HD66591 with an appropriate synthetic spectrum gave a velocity in agreement with its optically measured radial velocity. We will acquire the targets by means of the onboard acquisition and a following PEAKUP procedure to accurately center the stars in the small entrance aperture. In order to obtain an accuracy in the mass determination of 10 percent (which we consider necessary to distinguish between different amounts of excess mixing, see Figure 3) we require a velocity accuracy of 2 km/s or better. This corresponds to a wavelength accuracy of 0.2 diodes or better. Our measurements of the first Y Car spectrum and the S Mus spectra have shown that this is possible, but accurate centering is necessary. Our estimates for the required number of orbits takes this into consideration. The long exposures will be broken up into segments of 5 to 6 min in order to minimize geomagnetic smearing. A wavelength calibration is necessary at the beginning and end of each exposure. The time for these wavelength calibrations has also been included in the estimates for the number of orbits needed. Exposures from the successive orbits will be coadded, after correcting for the wavelength shifts. Cross- correlations between them will give us some indication about the accuracy of our velocity measurements. The required exposure times were derived using the exposures from cycle 4 with a signal to noise of about 6 and aiming at a signal to noise of about 10. The relative fluxes for the different targets at the wavelength of 1860 Angstrom are known from IUE observations. For the standard star we scaled the flux from the alpha Lyrae flux according to their visual magnitudes. Real Time Justification ----------------------- We need to observe the Cepheids at the orbital phases of maximum and minimum radial velocity in order to measure the maximum possible velocity variation. For a given measuring accuracy of +/-2 km/s this will give the highest measuring accuracy for the ratio of the orbital velocities. Highest accuracy will be achieved if the observations can be done in the middle of the windows. The orbital periods are typically a few years. If the appropriate phase is missed we have to wait for several years, or miss our chance altogether if the GHRS is replaced. Additional groundbased radial velocity measurements have been and will be done for improved orbital determinations for the Cepheids. These will be continued past the time of our HST observations. Accurate spectral types for the companions, and thereby their masses, are determined from their spectra and energy distributions obtained from the IUE archives. Calibration Justification ------------------------- We need a wavelength calibration at the beginning and at the end of each exposure in order to get the wavelength accuracy needed for an accurate determination of the radial velocities. Additional Comments ------------------- Since in the end all exposures of a given target to be taken over several orbits have to be coadded we have been advised by Steve Hulbert that for a given set of wavelength calibrations the exposures should be taken without interruption, which means NON-INT, in order to achieve the velocity accuracy which is needed for a success of our program. ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: *Kenneth Carpenter*Bldg. 21/Room G22*Code 681 NASA-GSFC*Greenbelt, MD 20771 Ship Via: UPS Email: hrscarpenter@tma1.gsfc.nasa.gov , ------------------------------------------------------------------------------------ 6504( 6) - 11/12/96 11:37 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD156979 STAR, A0-A3 V-IV RA=17H 22M 46.47S +/-0.1S, DEC=- 2000 V=1.0 V = 11.4 45D 36' 51.30" +/-1" B-V = 0.15 E(B-V) = 0.20 F-CONT(1860)=7.e-14 Comments: WE WANT TO OBSERVE THE A0V COMPANION OF THE CEPHEID V636-SCO, WHICH HAS V=-6.8 +/-1, B-V=0.8 +/-0.1 Coordinates from Hipparcos/GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.001 0.00 0.001 2 HD72660- STAR, A0-A3 V-IV RA=8H 34M 01.62S +/-0.1S, DEC=- 2000 V=3.0 V = 5.81 CALIB 02D 09' 05.7" +/-1" B-V = 0.00 E(B-V) = 0.00 F-CONT(1860)=1.0e11 Comments: Coordinates from Hipparcos/GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.003 0.021 0.0 6504( 6) - 11/12/96 11:37 - [ 2] Visit: 01 Visit Requirements: PCS MODE F BETWEEN 15-SEP-96 AND 01-DEC-96 On Hold Comments: Additional Comments: VISIT 1 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 111 HD156979 HRS ACQ 2.0 MIRROR-N2 1 1.8 S ONBOARD ACQUISITION FOR 112-154 SEQ 111-115 NON-INT Comments: USE STEP-TIME = 0.2 S, VISIT 1, ORBIT 1 ------------------------------------------------------------------------------------------------------------------------------------ 112 HD156979 HRS ACQ/PEA 0.25 MIRROR-N2 1 5.0 S ONBOARD ACQ FOR 113-124 KUP Comments: STEP-TIME = 0.2 S, VISIT 1, ORBIT 1 ------------------------------------------------------------------------------------------------------------------------------------ 113 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 114 ------------------------------------------------------------------------------------------------------------------------------------ 114 HD156979 HRS ACCUM 0.25 G200M 1860 STEP-PATT=5,FP-SPLIT=NO 4 272 S ------------------------------------------------------------------------------------------------------------------------------------ 115 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 114 ------------------------------------------------------------------------------------------------------------------------------------ 122 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S SEQ 122-124 NON-INT Comments: Visit 1, Orbit 2 ------------------------------------------------------------------------------------------------------------------------------------ 123 HD156979 HRS ACCUM 0.25 G200M 1860 STEP-PATT=5,FP-SPLIT=NO 7 353.6 S ------------------------------------------------------------------------------------------------------------------------------------ 124 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: Calib FOR 123 ------------------------------------------------------------------------------------------------------------------------------------ 132 HD156979 HRS ACQ/PEA 0.25 MIRROR-N2 1 5.0 S ONBOARD ACQ FOR 133-154 KUP SEQ 132-136 NON-INT Comments: Visit 1, Orbit 3 ------------------------------------------------------------------------------------------------------------------------------------ 133 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 134 ------------------------------------------------------------------------------------------------------------------------------------ 134 HD156979 HRS ACCUM 0.25 G200M 1860 STEP-PATT=5,FP-SPLIT=NO 6 299.2 S ------------------------------------------------------------------------------------------------------------------------------------ 136 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 134 ------------------------------------------------------------------------------------------------------------------------------------ 142 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S SEQ 142-144 NON-INT Comments: CALIB FOR 143, Visit 2, Orbit 4 ------------------------------------------------------------------------------------------------------------------------------------ 143 HD156979 HRS ACCUM 0.25 G200M 1860 STEP-PATT=5,FP-SPLIT=NO 7 353.6 S ------------------------------------------------------------------------------------------------------------------------------------ 144 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 143 ------------------------------------------------------------------------------------------------------------------------------------ 6504( 6) - 11/12/96 11:37 - [ 3] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 152 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S SEQ 152-154 NON-INT Comments: CALIB FOR 153, VISIT 1, ORBIT 5 ------------------------------------------------------------------------------------------------------------------------------------ 153 HD156979 HRS ACCUM 0.25 G200M 1860 STEP-PATT=5,FP-SPLIT=NO 7 353.6 S ------------------------------------------------------------------------------------------------------------------------------------ 154 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 153 ------------------------------------------------------------------------------------------------------------------------------------ 6504( 6) - 11/12/96 11:37 - [ 4] Visit: 02 Visit Requirements: PCS MODE F On Hold Comments: Additional Comments: VISIT 2 For HD72660-CALIB Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 211 HD72660-CAL HRS ACQ 2.0 MIRROR-N2 1 1.8 S ONBOARD ACQUISITION FOR IB 213 SEQ 211-216 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 213 HD72660-CAL HRS ACQ/PEA 0.25 MIRROR-N2 1 5 S ONBOARD ACQUISITION FOR IB KUP 214-216 Comments: STEP-TIME = 0.2 S VISIT 2, ORBIT 1 ------------------------------------------------------------------------------------------------------------------------------------ 214 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 215 ------------------------------------------------------------------------------------------------------------------------------------ 215 HD72660-CAL HRS ACCUM 0.25 G200M 1860 STEP-PATT=5,FP-SPLIT=NO 3 326.4 S IB ------------------------------------------------------------------------------------------------------------------------------------ 216 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 215 ------------------------------------------------------------------------------------------------------------------------------------ 6504( 6) - 11/12/96 11:37 - [ 5] Visit: 52 Visit Requirements: PCS MODE F On Hold Comments: Additional Comments: VISIT 52 Repeat of HD72660-CALIB Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 211 HD72660-CAL HRS ACQ 2.0 MIRROR-N2 1 1.8 S ONBOARD ACQUISITION FOR IB 213 SEQ 211-216 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 213 HD72660-CAL HRS ACQ/PEA 0.25 MIRROR-N2 1 5 S ONBOARD ACQUISITION FOR IB KUP 214-216 Comments: STEP-TIME = 0.2 S VISIT 2, ORBIT 1 ------------------------------------------------------------------------------------------------------------------------------------ 214 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 215 ------------------------------------------------------------------------------------------------------------------------------------ 215 HD72660-CAL HRS ACCUM 0.25 G200M 1860 STEP-PATT=5,FP-SPLIT=NO 3 326.4 S IB ------------------------------------------------------------------------------------------------------------------------------------ 216 WAVE HRS ACCUM SC2 G200M 1860 STEP-PATT=3 1 28.8 S Comments: CALIB FOR 215 ------------------------------------------------------------------------------------------------------------------------------------ 6504( 6) - 11/12/96 11:37 - [ 6] Summary Form for Proposal 6504 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters STEP-PATT=3 FP-SPLIT=NO STEP-PATT=5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE F BETWEEN 15-SEP-96 AND 01-DEC-96 ONBOARD ACQUISITION FOR 112-154 SEQ 111-115 NON-INT ONBOARD ACQ FOR 113-124 SEQ 122-124 NON-INT ONBOARD ACQ FOR 133-154 SEQ 132-136 NON-INT SEQ 142-144 NON-INT SEQ 152-154 NON-INT PCS MODE F ONBOARD ACQUISITION FOR 213 SEQ 211-216 NON-INT ONBOARD ACQUISITION FOR 214-216 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G200M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD156979 WAVE HD72660-CALIB ------------------------------------------------------------------------------------------------------------------------------------