9967( 4) - 04/23/03 17:10 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9967 Version: 4 Check-in Date: 23-Apr-2003 17:08:36 1.Proposal Title: Cepheid Masses: U Aql (Cycle 12 continuation of 9146) ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 12 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Dr. Nancy R. Evans Smithsonian Institution Astrophysical Observatory CoI: Dr. Kenneth G. Carpenter NASA Goddard Space Flight Center N CoI: Dr. Francesco Kienzle Observatoire de Geneve N CoI: Dr. Richard D. Robinson Computer Sciences Corporation N CoI: Dr. Michael Albrow University of Canterbury N ------------------------------------------------------------------------------------ 5. Abstract Quantitative understanding of classical Cepheids provides confidence in their use as primary extragalactic distance indicators, as well as in the understanding of the evolution of more massive stars and more evolved stars. HST UV spectroscopy provides a unique opportunity to contribute to the dramatic improvement in the precision of fundamental stellar parameters by determining the mass of the binary Cepheid U Aql, a high-priority Cepheid mass. In this project, the orbital velocity amplitude of the hot main sequence companion is to be measured from STIS echelle spectra and combined with the orbital velocity amplitude of the Cepheid from the ground-based orbit and the mass of the main sequence companion to provide the Cepheid mass. The sensitivity of the STIS spectrograph makes possible a higher dispersion observation over a wider wavelength region than the previous GHRS medium resolution spectra. We expect the radial velocities measured from the STIS spectra to reduce the uncertainty (s.d.) in the mass of U Aql from 13% (in the previous GHRS result) to < 5%. ------------------------------------------------------------------------------------ 9967( 4) - 04/23/03 17:10 - [ 2] Observations Description ------------------------ Using the results of the orbit of U Aql A, the Cepheid is at maximum orbital velocity during the first 240 days of Cycle 12, which provides quite a broad observing window. Because the wavelength/velocity accuracy is the most important objective of this program, the following steps will be taken in making the observations to reach this goal. Both an acquisition and peakup will be done for maximum precision in the centering of the target. A GO WAVECAL will be taken at the beginning and end of each orbit through the identical science aperture as the science observations. An exposure 10 times the standard wavecal time will be requested (100 sec instead of 10 sec). These deeper WAVECALS will provide more counts in the primary reference lines at this setting, the lines 1777 and 1883 Angstrom, which only contain about 12 and 5 counts/pixel, respectively, in the default 10 second exposures. In addition, the deeper exposures will enable us to utilize a larger number of lines too faint to measure in the default AUTOWAVECALS. Standard pipeline processing and AUTOWAVECAL's produce velocities from STIS echelle spectra with an accuracy of 1.3 km/sec. Using the acquisition and WAVECAL approach above, based on STIS and DATA handbooks and discussion with STIS scientists, we should reach an accuracy of 0.2 pixels or 0.26 km sec^-1, although we have conservatively used 0.5 km sec^-1 in our mass error estimates. The exposure times were set to obtain a S/N of 10 at 1800Angstrom, which has been found to produce good velocity determinations in GHRS spectra. Two further details of the observations should be noted. Although the mean magnitude of the Cepheid (V = 6.5 mag) is listed in the observation summary, the brighter Cepheid (which is variable) makes no contribution to the flux at 1800 Angstrom. It is the companion, a B9.8 V star with V = 10.6 mag which will be observed with STIS (Evans, 1992). Second, with regard to the MAMA bright limits, IUE low resolution spectra of U Aql exist in this wavelength region. The star has a continuum/absorption line spectra with well known fluxes that do not violate the bright limits. Real Time Justification ----------------------- Time Critical: Observations are planned so that the velocity will be within 1 km sec^-1 of maximum. This is a very gentle requirement, however, in that it allows observations anytime within the first 8 months of cycle 12. Even after including HST constraints (visibility period, etc.), the scheduling window is nearly 4 months long. The observations of U Aql B will require 2 visits, which should be as close together in time as possible. Wavelength accuracy: The goal of the program is to measure the velocity of U Aql B as accurately as possible. For this reason, the observations require wavelength calibrations at the beginnning and end of each orbit that are 10 times deeper (100 sec vs 10 sec) than the default AUTOWAVECALS. None. Ground-based observations of the Cepheid orbit have already been obtained. Since it is the velocity of the companion we are measuring, the pulsation velocity of the Cepheid is not relevant, and does not need to be measured simultaneously. Calibration Justification ------------------------- 9967( 4) - 04/23/03 17:10 - [ 3] Additional Comments ------------------- ------------------------------------------------------------------------------------ 9967( 4) - 04/23/03 17:10 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD183344 STAR, B6-B9.5 V-IV, RA=19H29M21.36S +/- 0.5", DEC=- J2000 V = 6.46+/-0.5 COMPOSITE SPECTRAL 07D02'38.6" +/- 0.5" B-V = 1.02+/-0.2 TYPE, CEPHEID E(B-V) = 0.35+/-0.03 Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE Comments: The spectrum is a composite: the Cepheid (V=6.46 mag) dominates in the visible, while the B9.8 companion (V=10.6 mag) dominates the UV spectrum we are observing. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 0.0 -0.0094 0.0020 9967( 4) - 04/23/03 17:10 - [ 5] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE BETWEEN 01-JUL-2003:00:00:00 AND 01-MAR-2004:00:00:00 SEQ 01, 02 WITHIN 5 D 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 HD183344 STIS/C ACQ F25ND3 MIRROR ACQTYPE=POINT 1 1 S CD ------------------------------------------------------------------------------------------------------------------------------------ 2 HD183344 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.5 S CD K 5ND ------------------------------------------------------------------------------------------------------------------------------------ 3 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 4 HD183344 STIS/N ACCUM 0.2X0.0 E230H 1763 1 1633 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 5 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 6 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 7 HD183344 STIS/N ACCUM 0.2X0.0 E230H 1763 1 2871 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 8 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 10 HD183344 STIS/N ACCUM 0.2X0.0 E230H 1763 1 2871 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9967( 4) - 04/23/03 17:10 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 12 HD183344 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.5 S CD K 5ND ------------------------------------------------------------------------------------------------------------------------------------ 13 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 14 HD183344 STIS/N ACCUM 0.2X0.0 E230H 1763 1 1863 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 15 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 16 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 17 HD183344 STIS/N ACCUM 0.2X0.0 E230H 1763 1 2871 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 18 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9967( 4) - 04/23/03 17:10 - [ 7] Visit: 02 Visit Priority: Visit Requirements: PCS MODE FINE SEQ 01, 02 WITHIN 5 D 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 HD183344 STIS/C ACQ F25ND3 MIRROR ACQTYPE=POINT 1 1 S CD ------------------------------------------------------------------------------------------------------------------------------------ 2 HD183344 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.5 S CD K 5ND ------------------------------------------------------------------------------------------------------------------------------------ 3 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 4 HD183344 STIS/N ACCUM 0.2X0.0 E230H 1763 1 1633 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 5 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 6 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 7 HD183344 STIS/N ACCUM 0.2X0.0 E230H 1763 1 2871 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 8 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 10 HD183344 STIS/N ACCUM 0.2X0.0 E230H 1763 1 2871 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9967( 4) - 04/23/03 17:10 - [ 8] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9967( 4) - 04/23/03 17:10 - [ 9] Summary Form for Proposal 9967 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25ND3 0.2X0.05ND 0.2X0.09 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE BETWEEN 01-JUL-2003 00 00 00 AND 01-MAR-2004 00 00 00 SEQ 01, 02 WITHIN 5 D PCS MODE FINE SEQ 01, 02 WITHIN 5 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230H ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD183344 WAVE ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1763 ------------------------------------------------------------------------------------------------------------------------------------