8772( 6) - 05/12/00 09:49 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8772 Version: 6 Check-in Date: 12-May-2000 09:48:31 1.Proposal Title: The Mass of the Classical Cepheid ADS 14859 Cycle 9 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Nancy Evans Harvard-Smithsonian Center for Astrophysics CoI: Otto Franz Lowell Observatory Y 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. ------------------------------------------------------------------------------------ 8772( 6) - 05/12/00 09:49 - [ 2] Observations Description ------------------------ FGS: All astrometric observations will made with FGS1R (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. 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 ------------------- ------------------------------------------------------------------------------------ 8772( 6) - 05/12/00 09:49 - [ 3] TARGET LIST 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 Coordinate Source: PPM_STAR_CATALOGUE 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 detect all three components. Star 666 on OGF list 2 ADS14859-2- CALIBRATION, RA=21H 19M 27.742S +/- .1S, J2000 V = 12.29+/-0.2 REF ASTROMETRIC DEC=38D 14' 27.38" +/- 1" Coordinate Source: GUIDE_STAR_CATALOG Comments: Star 49 on OGF list 3 ADS14859-3- CALIBRATION, RA=21H 19M 28.966S +/- .1S, J2000 V = 13.74+/-0.2 REF ASTROMETRIC DEC=38D 13' 24.13" +/- 1" Coordinate Source: GUIDE_STAR_CATALOG Comments: Star 576 on OGF list 4 ADS14859-4- CALIBRATION, RA=21H 19M 23.590S +/- .1S, J2000 V = 14.28+/-0.2 REF ASTROMETRIC DEC=38D 11' 33.40" +/- 1" Coordinate Source: GUIDE_STAR_CATALOG Comments: Star 181 on OGF list 5 ADS14859-5- CALIBRATION, RA=21H 19M 15.727S +/- .1S, J2000 V = 13.59+/-0.2 REF ASTROMETRIC DEC=38D 14' 38.54" +/- 1" Coordinate Source: GUIDE_STAR_CATALOG Comments: Star 441 on OGF list 8772( 6) - 05/12/00 09:49 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 01-Aug-2000 AND 30-Sep-2000 SCHED 50% 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 TRANS 1 F5ND SCANS=30,STEP-SIZE=1 1 1020 S SEQ 10-130 NON-INT POS TARG 0, 0 ------------------------------------------------------------------------------------------------------------------------------------ 20 ADS14859 FGS POS 1 F5ND 1 10 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 30 ADS14859-2- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 40 ADS14859-3- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 50 ADS14859-4- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 60 ADS14859-5- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 70 ADS14859-2- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 80 ADS14859 FGS POS 1 F5ND 1 10 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 90 ADS14859-5- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 100 ADS14859-3- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 110 ADS14859-2- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 120 ADS14859-4- FGS POS 1 F583W 1 10 S SAME POS AS 10 REF ------------------------------------------------------------------------------------------------------------------------------------ 130 ADS14859 FGS POS 1 F5ND 1 10 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 8772( 6) - 05/12/00 09:49 - [ 5] Summary Form for Proposal 8772 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations FGS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes TRANS POS ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCANS=30 STEP-SIZE=1 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-Aug-2000 AND 30-Sep-2000 SCHED 50% SEQ 10-130 NON-INT POS TARG 0, 0 SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F5ND F583W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ADS14859 ADS14859-2-REF ADS14859-3-REF ADS14859-4-REF ADS14859-5-REF ------------------------------------------------------------------------------------------------------------------------------------