Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4541c Report Date: 09-May-96:19:41 Version: ********** Check-in Date: ********** 1.Proposal Title: CEPHEID MASSES -CYC3-HIGH ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID COOL STARS GO 3 Long Term yrs Sub Category PULSATING STARS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Erika Hr Bohm-vitense 3760 USA ------------------------------------------------------------------------------------ 7. Abstract For 2 decades the "Cepheid mass problem" has persisted: Mass determinations from standard evolutionary tracks and those from pulsation theory gave conflicting values. The luminosity of a Cepheid of given mass depends sensitively on the amount of convective overshoot above the core of the main sequence progenitor. Hence a good mass determination for the Cepheid with known luminosity will measure the amount of convective core overshoot. This knowledge is important for interpretation of HR diagrams of populous clusters in the LMC and especially for age determinations. It is also necessary for the understanding of the mixing processes in stars. IUE observations have revealed a number of Cepheid binaries with blue companions, whose orbits have now been determined by groundbased observations. We propose to measure the orbital radial velocities of 5 blue Cepheid companions on GHRS spectra for wavelengths shorter than 2000 A. The ratios of the orbital velocities for the binaries provide the mass ratios for the stars. The effective temperature of the companion can be determined from its energy distribution. For main sequence stars this also determines its mass. With GHRS spectra the orbital velocity ratio and thereby the mass ratio can be determined with an accuracLy of +/- 10 %. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 11.99 par: 0 10. Num targs pri: 7 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ 12. Special sched req: Time Critical obs. ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4541c PI: Erika Hr Bohm-vitense Proposal Title: CEPHEID MASSES -CYC3-HIGH ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Erika Hr Bohm-Vitense 3760 U.S.A. Nancy R Evans INST. SPACE & TERRESTRIAL CANADA SCIENCE, NORTH YORK Kenneth G Carpenter 2856 U.S.A. ------------------------------------------------------------------------------------ 3. Description of proposed observations. The purpose of this proposal is to measure the orbital velocities of the main sequence companions of 5 classical Cepheids. We would like to observe each target twice. The observations are spread out over several observing cycles in order to observe most targets both at maximum and at minimum orbital velocity. The highest accuracy will be achieved if the observations can be done close to the middle of the observing windows given. We plan to use the GHRS with the 2" aperture and the Echelle B at 1722 A for the observations for S Mus B which has the brightest companion. For the comparison star HD 66591 the same instrument configuration has to be used. We want to use the G200M grating at 1860 A for the other stars. The stars HD 65456 and HD 139129 are standard stars for comparison with the other Cepheid companions. The G200M grating at 1860 A has to be used for those. These stars should also be observed twice to be sure that we measure the same velocity. We would like the standard stars to be observed once during cycle 3 and the second time during cycle 4. We would like a wavelength calibration before and after each stellar observation. We need to break up the exposures into subexposures of not more than 5 minutes duration each in order to avoid geomagnetic smearing They will then be aligned by cross-correlation and co-added. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. We need the UV capabilities and the large collection area of HST. The Cepheid companions can only be seen in the ultraviolet because in the optical their light is drowned by the light of the luminous Cepheid. Because of the temperature difference between the components ,the hotter main sequence companions dominate, however, for wavelengths shorter than 2000 A. Companion velocities can therefore be measured only on UV spactra. The companions (except for S Mus B) are too faint to be observed with IUE at high resolution, needed for radial velocity measurements. Orbits for all program stars have been determined from the ground. In some cases we are working with collaborators to obtain additional velocity data to improve the orbits. We have also observed all the program stars in low resolution with IUE to determine the spectral types and the UV absolute fluxes for the companions. For S Mus, V636 Sco, and U Aql we have also attempted to measure the companion velocities. For S Mus and SU Cyg we have demonstrated that the cross-correlation technique works well to measure velocity differences between the Cepheid and the companion. The velocity differences are uncertain by about +/- 2.5 km/sec. The companion velocity becomes more uncertain because the somewhat uncertain Cepheid velocity (pulsation+orbit) has to be subtracted. With IUE we have been able to measure absolute velocities with an accuracy of about +/ - 5 km/sec. We have estimated the exposure times from the fluxes on the IUE spectra, which are available for all the target stars. Count rates have been computed by Carpenter based on grating sensitivities and experience with observations. A signal to noise ratio of 15 is adequate for a reliable radial velocity measured by cross-correlation techniques. In addition we will be able to examine the companion spectra, which have not been observed at high resolution before. As discussed above, we plan to observe at least two standard stars to be used as primary velocity comparisons. To obtain the necessary wavelength accuracy wavelength calibration exposures will have to be taken before and after the stellar observations. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. In order to achieve the highest possible accuracy for the orbital velocity ratio, we need to observe the companions at phases near orbital radial velocity extrema. The orbits are typically a few years. Specific scheduling requests are detailed in Table 3. Generally a window of several months is available, which should assure that spacekraft constraints will not preclude our orbital requirements. Highest accuracy will be achieved in the middle of the windows. We stress that the selected intervals are set by orbital mechanics. If the length of a HST cycle should change, we require the requested times of observation even if they shift to a different cycle. In order to obtain an accuracy in the mass determination of 10% (which we consider necessary for a significant result), we require a velocity accuracy of 2 km/sec. In order to obtain this accuracy, a wavelength calibration is required before and after each stellar exposure. In addition, we intend to break the long exposures up into a series of short exposures to avoid geomagnetic smearing. These will then be aligned by cross- correlation and co-added. By the combination of the spectra, wavelength calibrations, and an aperture map the 0.2 diode wavelength accuracy should be possible within the large science aperture, on which the exposure times are based. Page 4 ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. In order to obtain an accuracy in the mass determination of +/-10% (which we consider necessary for a significant result), we require a velocity accuracy of 2 km/sec. This corresponds to a wvalength accuracy of 0.2 diode or better with the G200M grating. We believe that this can be obtained because of the results of Carpenter et al. (May 1991,HST Workshop) on the emission line spectrum of alpha Tau. In order to obtain this accuracy a wavelength calibration is required before and after each stellar exposure. In addition we intend to break the long exposures up into a series of short exposures to avoid geomagnetic smearing. These will then be aligned by cross-correlation and co-added. By the combination of the spectra, wavelength calibrations, and an aperture map the 0.2 diode wavelength accuracy should be possible within the large science aperture, on which the exposure times are based. ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. The first step in reducing the HST spectra is to cross-correlate them. The absolute wavelength scale can then be determined from the wavelength calibrations. The velocities will be determined in three ways as described above. The primary determination will be to cross- correlate the program spectra with the spectra of the standard stars with known velocities to determine the velocity difference between them. In addition we will cross-correlate the two spectra of the companions taken at minimum and maximum orbital radial velocity to measure the velocity amplitude. Since we then measure velocity differences any systematic errors will cancel.The methods should agree. Any difference will alert us to an incomplete understanding of a spectral region which has not previously been used for high precision velocity measurements. The measured companion velocity will then be ratioed with the Cepheid orbital velocity at the same phase to give the inverse mass ratio. Since the effective temperature of the main sequence companion is known from the IUE measured energy distribution the mass of the companion can be determined very accurately,( +/- 2% according to Anderson 1991). (Small evolutionary corrections for the main sequence companion, which has a much smaller mass than the Cepheid, can be applied, knowing the age of the Cepheid). The orbital velocity ratio gives the inverse mass ratio of the binary components. The mass of the Cepheid can thus be derived. ------------------------------------------------------------------------------------ 11. Address Information Name: ERIKA HR BOHM-VITENSE Category: PI Institution: 3760 Address: ASTRONOMY DEPARTMENT FM-20 UNIVERSITY OF WASHINGTON City: SEATTLE State: WA Zip Code: 98195 Country: U.S.A. Telephone: (206) 543 4858 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4541c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD106111 A;147;175;178; RA= 12H 12M 47.23S +/- 0.5", 2000 V=11.0 1 V=8.9+/-1, TYPE=B5V HR4645 S-MUS 134;111 DEC= -70D 09' 6.0" +/- 1.0", 1 B-V=0.07+/-0.1 -B PLATE-ID=05ZX 2 E(B-V)=0.24+/-0.04 3 F-CONT(1722)=3.2+/-0.2E-12 Comments: WE OBSERVE THE B5V COMPANION OF THE F8II CEPHEID S-MUS THE CEPHEID MAGNITUDE IS 6.7+/-1 FOR THE CEPHEID B-V=0.5+/0.1 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J 1950.00 -0.0020 +/- 0.0001 -0.0200 +/- 0.0100 0.0200 +/- 0.0030 ------------------------------------------------------------------------------------------------------------------------------------ 2 HD66591 A;111 RA= 08H 00M 20.00S +/- 1.0", 2000 V=22.0 1 V=4.82+/-0.02, TYPE=B3V HR3159 DEC= -63D 34' 03.2" +/- 1.0" 1 B-V=-0.17+/-0.02 2 E(B-V)=0.0 3 F-CONT(1722)=5.0E-10 Comments: THIS IS A VELOCITY CALIBRATION STAR FOR THE OBSERVATIONS OF S-MUS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J 1950.00 0.0010 +/- 0.0000 0.0200 +/- 0.0100 0.0040 +/- 0.0010 ------------------------------------------------------------------------------------------------------------------------------------ 3 HD91595 Y- A;147;175;178;134; RA= 10H 33M 10.90S +/- 1.0", 2000 V=-14.1 1 V=11.9+/-1 CAR-B 112 DEC= -58D 29' 55.7" +/- 1 B-V=0.09+/-0.05 1.0", 2 E(B-V)=0.08+/-0.05 3 F-CONT(1860)=1.0E-13 Comments: WE WANT TO OBSERVE THE B9V COMPANION OF THE CEPHEID Y CAR THE CEPHEID HAS V=7.5+/- 1 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J 1950.00 0.0001 +/- 0.0000 0.0000 +/- 0.0000 0.0000 +/- 0.0000 ------------------------------------------------------------------------------------------------------------------------------------ 4 HD172167 A,123 RA=18H36M56.3S+/-0.1S, 2000.00 V=-14.0 1 V=0.02+/-0.02, TYPE=A0V HR7001 ALPHA DEC=+38D47'01"+/-1" 1 B-V=0.01 -LYRAE 2 E(B-V)=0.0 3 F-CONT(1860)=5.5E-9 Comments: THIS IS A CALIBRATION STAR TO MEASURE THE RADIAL VELOCITY OF Y-CAR-B Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J 1950.00 0.0171 +/- 0.0006 0.2900 +/- 0.0300 0.1200 +/- 0.0100 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4541c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD106111 HRS ACQ 2.0 MIRROR-N2 LOCATE=YES 1 1.8S 1 1 ONBOARD ACQ FOR BRIGHT=RETURN 2.000 SEARCH-SIZE=3 SEQ 1 - 5 CYCLE 3/1-45 AT 22-NOV-93+/-50D Comments: USE STEP-TIME = 0.2 SEC. EXPECT ROUGHLY 50000.CTS/0.2S ------------------------------------------------------------------------------------------------------------------------------------ 2 HD106111 HRS ACQ/ 2.0 MIRROR-N2 1 20.4S 1 1 PEAKUP Comments: STEP-TIME = 0.2 SEC ------------------------------------------------------------------------------------------------------------------------------------ 3 WAVE HRS ACCUM SC2 ECH-B 1722.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 4 NO SLEW SEQ 2-5 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 4 HD106111 HRS ACCUM 2.0 ECH-B 1722.0 STEP-PATT=7 5 5.0M 15 2 1 FP-SPLIT=NO Comments: S/N IS FOR SUM OF 5 EXP'S. ------------------------------------------------------------------------------------------------------------------------------------ 5 WAVE HRS ACCUM SC2 ECH-B 1722.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 4 NO SLEW ------------------------------------------------------------------------------------------------------------------------------------ 11 HD91595 HRS ACQ 2.0 MIRROR-N2 LOCATE=YES 1 1.8S 1 1 ONBOARD ACQ FOR BRIGHT=RETURN 12.000 SEARCH-SIZE=3 SEQ 11-15 AT 14-JUL-93+/-20D Comments: USE STEP-TIME = 200 MSEC. EXPECT ROUGHLY 2938 CTS/200MS ------------------------------------------------------------------------------------------------------------------------------------ 12 HD91595 HRS ACQ/ 2.0 MIRROR-N2 1 20.4S 1 1 PEAKUP Comments: STEP-TIME = 200 MSEC ------------------------------------------------------------------------------------------------------------------------------------ 13 WAVE HRS ACCUM SC2 G200M 1860.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 14 NO SLEW SEQ 12-15 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 14 HD91595 HRS ACCUM 2.0 G200M 1860.0 STEP-PATT=5 5 5.0M 15 2 1 FP-SPLIT=NO Comments: S/N IS FOR SUM OF 5 EXP'S. ------------------------------------------------------------------------------------------------------------------------------------ 15 WAVE HRS ACCUM SC2 G200M 1860.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 14 NO SLEW ------------------------------------------------------------------------------------------------------------------------------------ 15.2 HD91595 HRS ACQ/ 2.0 MIRROR-N2 1 20.4S 1 1 PEAKUP Comments: STEP-TIME = 200 MSEC ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4541c [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 15.5 WAVE HRS ACCUM SC2 G200M 1860.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 15.6 NO SLEW SEQ 15.2-15.7 NON- INT ------------------------------------------------------------------------------------------------------------------------------------ 15.6 HD91595 HRS ACCUM 2.0 G200M 1860.0 STEP-PATT=5 5 5.0M 15 2 1 FP-SPLIT=NO Comments: S/N IS FOR SUM OF 5 EXP'S. ------------------------------------------------------------------------------------------------------------------------------------ 15.7 WAVE HRS ACCUM SC2 G200M 1860.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 15.6 NO SLEW ------------------------------------------------------------------------------------------------------------------------------------ 31 HD66591 HRS ACQ 2.0 MIRROR-A2 LOCATE=YES 1 1.8S 1 1 ONBOARD ACQ FOR BRIGHT=RETURN 32.000 SEARCH-SIZE=3 SEQ 31 - 35 Comments: USE STEP-TIME = 200 MSEC. EXPECT 12000 CTS/200MS ------------------------------------------------------------------------------------------------------------------------------------ 32 HD66591 HRS ACQ/ 2.0 MIRROR-A2 1 20.4S 1 1 PEAKUP Comments: STEP-TIME = 200 MSEC ------------------------------------------------------------------------------------------------------------------------------------ 33 WAVE HRS ACCUM SC2 ECH-B 1722.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 34 NO SLEW SEQ 32-35 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 34 HD66591 HRS ACCUM 2.0 ECH-B 1722.0 STEP-PATT=7 2 27.2S 15 2 1 FP-SPLIT=NO Comments: S/N IS FOR SUM OF 2 EXP'S. ------------------------------------------------------------------------------------------------------------------------------------ 35 WAVE HRS ACCUM SC2 ECH-B 1722.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 34 NO SLEW ------------------------------------------------------------------------------------------------------------------------------------ 41 HD172167 HRS ACQ 2.0 MIRROR-A2 LOCATE=YES 1 1.8S 1 1 ONBOARD ACQ FOR BRIGHT=RETURN 42.000 SEARCH-SIZE=3 SEQ 41-45 Comments: USE STEP-TIME = 200 MSEC. EXPECT >>>> CTS/200MS ------------------------------------------------------------------------------------------------------------------------------------ 42 HD172167 HRS ACQ/ 2.0 MIRROR-A2 1 20.4S 1 1 PEAKUP Comments: STEP-TIME = 200 MSEC ------------------------------------------------------------------------------------------------------------------------------------ 43 WAVE HRS ACCUM SC2 G200M 1860.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 44 NO SLEW SEQ 42-45 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 44 HD172167 HRS ACCUM 2.0 G200M 1860.0 STEP-PATT=3 2 3.2S 15 2 1 FP-SPLIT=NO Comments: S/N IS FOR SUM OF 5 EXP'S. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4541c [ 8] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 45 WAVE HRS ACCUM SC2 G200M 1860.0 STEP-PATT=3 1 30.0S 1 CALIB FOR 44 NO SLEW ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4541c [ 9] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters LOCATE=YES BRIGHT=RETURN SEARCH-SIZE=3 STEP-PATT=3 STEP-PATT=7 FP-SPLIT=NO STEP-PATT=5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 11.99 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category PULSATING STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2.000; SEQ 1 - 5; CYCLE 3/1-45; AT 22-NOV-93+/-50D CALIB FOR 4 NO SLEW; SEQ 2-5 NON-INT; CALIB FOR 4 NO SLEW ONBOARD ACQ FOR 12.000; SEQ 11-15; AT 14-JUL-93+/-20D; CALIB FOR 14 NO SLEW; SEQ 12-15 NON-INT; CALIB FOR 14 NO SLEW CALIB FOR 15.6 NO SLEW; SEQ 15.2-15.7 NON-INT; CALIB FOR 15.6 NO SLEW ONBOARD ACQ FOR 32.000; SEQ 31 - 35 CALIB FOR 34 NO SLEW; SEQ 32-35 NON-INT; CALIB FOR 34 NO SLEW ONBOARD ACQ FOR 42.000; SEQ 41-45; CALIB FOR 44 NO SLEW; SEQ 42-45 NON-INT; CALIB FOR 44 NO SLEW ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 ECH-B G200M MIRROR-A2 ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD106111 HR4645 S-MUS-B HD66591 HR3159 HD91595 Y-CAR-B HD172167 HR7001 ALPHA-LYRAE ------------------------------------------------------------------------------------------------------------------------------------