7478( 9) - 09/03/98 11:56 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7478 Version: 9 Check-in Date: 27-Mar-1998 13:50:41 1.Proposal Title: The Mass of the Classical Cepheid ADS 14859 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Nancy R. Evans Harvard Smithsonian Center for Astrophysics CoI: Otto Franz Lowell Observatory N CoI: Richard Walker US Naval Observatory, Flagstaff N CoI: Derck Massa Hughes STX N CoI: Brian Mason CHARA, Georgia State University N ------------------------------------------------------------------------------------ 5. Abstract The determination of accurate masses for Cepheid variable stars is required for quantitative understanding of these primary distance indicators, and also the related questions of the accuracy of evolutionary calculations and the role played by massive stars in galactic evolution. The system ADS 14859 = HR 8157 = V1334 Cyg provides a unique opportunity to determine a Cepheid mass because it has a visual binary orbit. The system consists of a wide pair (AB) discovered by Hough (1887), and a newly discovered close system (Aa, b) which consists of the Cepheid (Aa) and a yet uncharacterized companion (Ab). No mass information will be available, however, without the proposed HST FGS and STIS observations, particularly of the Ab star which cannot be observed from the ground. From the STIS observations we will determine the temperature and infer the mass of Ab. Combining this mass with the sum of all three masses of the system derived from the visual orbit and the mass of B from IUE observations provides the mass of the Cepheid (Aa). In addition, the FGS observations (POS mode) of the Aa, b system can provide its inclination, and hence the sum of the two masses of that system, and ultimately the Cepheid mass. Furthermore, the short period system (Aa, b) should be resolvable with the improved FGS in TRANS mode. Thus, the combination of these observations will provide determinations of the Cepheid mass from both the close and wide orbits. ------------------------------------------------------------------------------------ 7478( 9) - 09/03/98 11:56 - [ 2] Observations Description ------------------------ STIS: Because ADS 14859 is too bright for the G140 L, we propose to use the G140 M in the following way. The maximum flux from ADS 14859 in the 1190 to 1750 Angstrom region is 1.1 * 10^-11, leading to the count rates shown in Figure 3. Both the maximum flux and the count rate are within the bright limits, as is the global spectroscopic count rate of less than 12, 000 counts per sec. We shall use the prime scan settings which cover the region in 55 Angstrom steps. For a single setting, an integration of 3 minutes gives between 360 and 4320 counts per 0.05 Angstrom element, for a S/N between 19 and 66. Because the MAMA is a photon counting device (not background or read noise limited), Poisson statistics are preserved in rebinning. Rebinning from 0.05 Angstrom to 1 Angstrom pixels increases the S/N by a factor of 4.5. For the comparison with either IUE spectra of MK spectral standard stars or theoretical models, this is sufficient. During the first orbit we estimate 9 minutes for a Guide Star Acquisition, and 8 minutes for a STIS target acquisition, which allows 6 spectra of 3 minutes each to be obtained involving 5 grating moves (estimated to take 3 minutes). No peakup is required, since the observation is to be in slitless mode, selected so that no flux will be lost from the two components of the wide orbit. We have discussed the acquisition with the StSci staff, and the standard STIS acquisition will provide our needed accuracy of a few tenths of an arc sec. The second orbit allows for a Guide Star Reacquisition (6 minutes) and the remaining 5 spectra and 4 grating moves. The remaining additional time in the 2 orbits will be used to obtain stronger spectra in the 1300 Angstrom region where the strong lines can be used (unbinned) to determine the wavelength zeropoint since the spectra are slitless. (The orientation of the two spectra are well known from the ground- based orbit. The image obtained as part of the standard acquisition, however, will be useful additional information in locating the two spectral components.) beginfigure plotfiddlemassa.ps8cm07575-270-290 captionThe count rate for the STIS G140 M grating for ADS 14859. endfigure FGS: All astrometric observations will made with FGS3 (PRIME) in a combination of POS and TRANS modes. With POS we will observe the Cepheid system through F5ND, and nearby astrometric reference stars through F583W (CLEAR). TRANS mode will be used with F5ND to observe the Cepheid system only. Each set of combined POS and TRANS mode observations will require one orbit. Because the ground-based spectroscopic orbit provides the time of nodal passage (no foreshortening of the orbit) we can select the times of maximum and minimum foreshortening to determine the orbital inclination. Maximum foreshortening occurs during the first month of HST Cycle 7; minimum foreshortening occurs in Cycle 8. Theoretically the third phase (maximum foreshortening) in Cycle 9 provides enough information to determine the inclination, but it will be highly desirable to repropose for the fourth phase in Cycle 10 to confirm the result. Since this phase is the second observation with minimum foreshortening, it will also provide a significantly improved determination to the semi-major axis of the short period orbit, which is itself enough to provide a Cepheid mass, although not with as high an accuracy as the spectroscopic orbit (in combination with other data supplied from this proposal). As discussed above, we will consider using the FGS-1R if the improvement in performance is as large as expected. Real Time Justification ----------------------- The FGS observations are time critical because the most accurate determination of the inclination requires selecting appropriate orbital phases. The window is approximately two months at the beginning of Cycle 7. The STIS observations are also time critical because a roll angle such that the separation between the B and (Aa + Ab) components is perpendicular to the spectral dispersion is required to resolve the wide system. As discussed in the proposal, subtantial preparation for this project has been undertaken, including observations for most of this century. The CHARA group will continue to observe the visual orbit regularly, and both instrumental improvements and the orbital phase itself (moving beyond periastron) guarantees a continually improving orbit. In addition, the ground-based spectroscopic orbit of the short period binary has been obtained as well as IUE spectral information about the temperature and velocity of the hottest star in the system (component B). Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7478( 9) - 09/03/98 11:56 - [ 3] Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7478( 9) - 09/03/98 11:56 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ADS14859 STAR, Cepheid, RA=21H 19M 22.22S +/- .008S, J2000 V = -2.0 V = 5.9+/-0.1 Composite Spectral Type DEC=38D 14' 14.4" +/- .1" B-V = 0.50+/-0.1 E(B-V) = 0.07+/-0.02 F-CONT(1300)=1.2+/-.1e-11 Comments: This is a triple system. The primary (brightest in V) is a Cepheid with a hot companion. This means V can vary by +/- 0.1 mag. The third star is another hot star (late B) offset approximately 0.05" South of the primary. The aim of the observation is to get resolved spectra of the two hot stars. 2 ADS14859-2- CALIBRATION, RA=21H 19M 27.742S +/- .1S, J2000 V = 12.29+/-0.2 REF ASTROMETRIC DEC=+38D 14' 27.38" +/- 1" 3 ADS14859-3- CALIBRATION, RA=21H 19M 28.966S +/- .1S, J2000 V = 13.74+/-0.2 REF ASTROMETRIC DEC=+38D 13' 24.13" +/- 1" 4 ADS14859-4- CALIBRATION, RA=21H 19M 23.590S +/- .1S, J2000 V = 14.28+/-0.2 REF ASTROMETRIC DEC=+38D 11' 33.40" +/- 1" 5 ADS14859-5- CALIBRATION, RA=21H 19M 15.727S +/- .1S, J2000 V = 13.59+/-0.2 REF ASTROMETRIC DEC=+38D 14' 38.54" +/- 1" 6 ADS14859-6- CALIBRATION, RA=21H 19M 23.834S +/- .1S, J2000 V = 12.33+/-0.2 REF ASTROMETRIC DEC=+38D 18' 1.91" +/- 1" 7478( 9) - 09/03/98 11:56 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENTation 170D TO 180D BETWEEN 20-JUL-97 AND 20-AUG-97 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 ADS14859 FGS POS 3 F5ND 1 20 S POS TARG 0.0, 0.0;MAX DUR 20S SEQ 10-120 NON-INT Comments: OBSERVATION MAY BE TRUNCATED TO SATISFY MONITORING SPACING REQUIREMENTS ------------------------------------------------------------------------------------------------------------------------------------ 20 ADS14859-2- FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 30 ADS14859-3- FGS POS 3 F583W 1 40 S MAX DUR 40S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 40 ADS14859-4- FGS POS 3 F583W 1 60 S MAX DUR 60S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 50 ADS14859-5- FGS POS 3 F583W 1 40 S MAX DUR 40S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 60 ADS14859-6- FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 65 ADS14859-2- FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 70 ADS14859 FGS TRANS 3 F5ND SCANS=16,STEP-SIZE=1 1 560 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 75 ADS14859-2- FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 80 ADS14859 FGS POS 3 F5ND 1 20 S MAX DUR 20S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 85 ADS14859-6- FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 90 ADS14859-5- FGS POS 3 F583W 1 40 S MAX DUR 40S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 95 ADS14859-4- FGS POS 3 F583W 1 60 S MAX DUR 60S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 100 ADS14859-3- FGS POS 3 F583W 1 40 S MAX DUR 40S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 110 ADS14859-2- FGS POS 3 F583W 1 20 S MAX DUR 20S; SAME POS AS REF 10 ------------------------------------------------------------------------------------------------------------------------------------ 7478( 9) - 09/03/98 11:56 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 120 ADS14859 FGS POS 3 F5ND 1 20 S MAX DUR 20S; SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 7478( 9) - 09/03/98 11:56 - [ 7] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: The purpose of the observation is to spatially resolve the two hot stars in the system. The line joining the stars which must be perpendicular to the dispersion direction is at an angle of 10 East of North. The required roll is thus 10 + 45 deg (with a tolerance of +/- 15 deg). The separation of the two hot stars is approximately 0.05 arc sec. The Cepheid (primary with the two hot stars as companions) dominates the system in the visual region. An orientation 180 degrees from the one specified is equally acceptable. For our slitless spectra, we do not need automatic wavecals. We discussed the situation with Dr. S. Hulbert who investigated the problem and said we could omit the wavcals. The RPS2 software gives us an error for this reason, however this is how we want to proceed. Added, Feb., 1998: The FGS observation failed to resolve the Cepheid and the distant companion. Therefore we requested to replace the STIS spectrum with an FOC image. This is the observation discussed below. The target is to be heavily filtered in order that the count rate remain linear. The filter combination (F140W + F170M + F6ND) convolved with the composite spectrum of the triple system results in flux between 1600 and 2000 AA. The Cepheid will make a negligible contribution to the resulting image. The aim is to look for the two hot stars, and thus obtain the first direct measure of the light from the third star in the system. The exposure is to be taken in 3 pieces because thermal drift during the orbit may cause a shift in focus. In addition, one of the exposures is to be offset slightly in order to sample an independent part of the flat field. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 320 ADS14859 FOC/96 IMAGE 512X512 F140W, CHECK-FILTER=YES 1 660 S MAX DUR 12M F170M, F6ND ------------------------------------------------------------------------------------------------------------------------------------ 330 ADS14859 FOC/96 IMAGE 512X512 F140W, CHECK-FILTER=YES 1 660 S MAX DUR 12M F170M, F6ND ------------------------------------------------------------------------------------------------------------------------------------ 340 ADS14859 FOC/96 IMAGE 512X512 F140W, CHECK-FILTER=YES 1 660 S POS TARG +0.1,+0.1 F170M, F6ND ------------------------------------------------------------------------------------------------------------------------------------ 7478( 9) - 09/03/98 11:56 - [ 8] Summary Form for Proposal 7478 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 3 512X512 ------------------------------------------------------------------------------------------------------------------------------------ Configurations FGS FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes POS TRANS IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCANS=16 STEP-SIZE=1 CHECK-FILTER=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENTation 170D TO 180D BETWEEN 20-JUL-97 AND 20-AUG-97 POS TARG 0.0, 0.0;MAX DUR 20S SEQ 10-120 NON-INT MAX DUR 20S; SAME POS AS 10 MAX DUR 40S; SAME POS AS 10 MAX DUR 60S; SAME POS AS 10 MAX DUR 12M POS TARG +0.1,+0.1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F5ND F583W F140W,F170M,F6ND ------------------------------------------------------------------------------------------------------------------------------------ Target Names ADS14859 ADS14859-2-REF ADS14859-3-REF ADS14859-4-REF ADS14859-5-REF ADS14859-6-REF ------------------------------------------------------------------------------------------------------------------------------------