9762( 8) - 11/14/03 15:42 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9762 Version: 8 Check-in Date: 14-Nov-2003 15:41:05 1.Proposal Title: Verifying the White Dwarf Mass-Radius Relation with Sirius B ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 12 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Dr. Martin Adrian Barstow University of Leicester CoI: Dr. Jay B. Holberg University of Arizona N CoI: Dr. Howard E. Bond Space Telescope Science Institute N CoI: Dr. Matthew Burleigh University of Leicester N CoI: Dr. Detlev G. Koester Universitat Kiel N CoI: Dr. Ivan Hubeny NASA Goddard Space Flight Center N ------------------------------------------------------------------------------------ 5. Abstract We propose timely STIS observations of Sirius B, that will provide fundamental astrophysical data on this very important, but difficult to study, white dwarf. High quality spectra of the Balmer line region will provide accurate, modern measurements of its gravitational redshift, effective temperature, surface gravity and absolute flux. From these measurements, precise determinations of the spectroscopic mass and radius can be made, that will approach a 1% uncertainty. At this level, it will be possible to: 1) directly compare the spectroscopic and astrometric masses at a comparable level of accuracy, 2) precisely test the theoretical mass-radius relation for a 1 solar mass white dwarf, 3) distinguish between thick and thin H layer masses and 4) confirm the widely used method of estimating white dwarf masses from the Balmer lines. The only existing Balmer line observations of Sirius B are those of Greenstein et al. (1971) from the days of photographic plates. The increasing separation of the components now permits STIS observations at a time when new astrometric and far UV observations are available. ------------------------------------------------------------------------------------ 9762( 8) - 11/14/03 15:42 - [ 2] Observations Description ------------------------ We require STIS observations of Sirius B to obtain a complete Balmer series spectrum, including Ha. The spectra will be obtained using the combined G430L and G750M gratings with the CCD detector. The G430L grating provides complete coverage of the Balmer line series from H?, yielding a resolution of 5.4?, well-matched to the requirement for determination of accurate Teff and log g (see Bergeron et al. 1992). The current estimate of the gravitational redshift is ~90km s-1, hence the G430L grating does not yield adequate resolution (170km s-1 per pixel) for a sufficiently accurate radial velocity measurement. We will obtain a single G750M exposure, centered on Ha for this purpose. The 0.56?/pixel spectral resolution of the grating translates into 30km/s in velocity space and cross-correlation techniques can be used to improve the accuracy beyond this by a factor 10. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- Since Sirius has a very close, bright main sequence companion ( ------------------------------------------------------------------------------------ 9762( 8) - 11/14/03 15:42 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SIRIUSB STAR, DA RA=06H45M9.01S +/- 0.1", DEC=- J2000 V = - V = 8.44+/-0.06 16D43'4.4" +/- 0.1", PLATE- 8.53 ID=06LC Coordinate Source: HST_IMAGE Comments: Position and proper motion have been determined from WFPC2 images of Sirius B taken in October 2001, 2002, and 2003, and have been corrected for annual parallax. Note that this results in an "effective" p.m. for Sirius B that includes its orbital motion around Sirius A, and this p.m. will not be the same as the p.m. of the center of mass of the binary. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2003.786 0.0304 -0.6087 0.379 9762( 8) - 11/14/03 15:42 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 66.0D TO 76.0 D ORIENT 246.0D TO 256.0 D On Hold Comments: Additional Comments: The ORIENTs are used to place Sirius B halfway between the diffraction spikes from Sirius A. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SIRIUSB STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 0.2 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 2 SIRIUSB STIS/C ACCUM 52X0.2 G430L 4300 GAIN=4,CR-SPLIT=NO 3 3.5 S CD ------------------------------------------------------------------------------------------------------------------------------------ 3 SIRIUSB STIS/C ACCUM 52X0.2 G750M 6581 GAIN=4,CR-SPLIT=NO 3 30 S CD ------------------------------------------------------------------------------------------------------------------------------------ 4 SIRIUSB STIS/C ACCUM 52X0.2 G230MB 1854 GAIN=4,CR-SPLIT=NO 3 235 S CD ------------------------------------------------------------------------------------------------------------------------------------ 5 SIRIUSB STIS/C ACCUM 52X0.2 G230MB 2794 GAIN=4,CR-SPLIT=NO 3 50 S CD ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 01 1 none none none none 1 tbd 01 2 none none 1 none 1 tbd 01 2 none none 2 none 1 tbd 01 2 none none 3 none 1 tbd 01 3 none none 1 none 1 tbd 01 3 none none 2 none 1 tbd 01 3 none none 3 none 1 tbd 01 4 none none 1 none 1 tbd 01 4 none none 2 none 1 tbd 01 4 none none 3 none 1 tbd 01 5 none none 1 none 1 tbd 01 5 none none 2 none 1 tbd 01 5 none none 3 none 1 tbd 9762( 8) - 11/14/03 15:42 - [ 5] Summary Form for Proposal 9762 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50OII 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT CR-SPLIT=NO GAIN=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 66.0D TO 76.0 D ORIENT 246.0D TO 256.0 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430L G750M G230MB ------------------------------------------------------------------------------------------------------------------------------------ Target Names SIRIUSB ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4300 6581 1854 2794 ------------------------------------------------------------------------------------------------------------------------------------