5856( 0) - 07/18/95 18:19 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5856 Version: ********** Check-in Date: ********** 1.Proposal Title: ABUNDANCES OF VERY HEAVY ELEMENTS IN THE EARLY GALAXY. II. ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Cool Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: JOHN COWAN UNIVERSITY OF OKLAHOMA CoI: CHRIS SNEDEN UNIVERSITY OF TEXAS N CoI: JAMES TRURAN UNIVERSITY OF CHICAGO N ------------------------------------------------------------------------------------ 6. Abstract We propose to search for spectral lines indicating the presence of the very heavy elements platinum, iridium, bismuth and osmium in a very old, metal-poor halo star, and to determine the relative abundances of these elements. These elements, synthesized in stellar interiors by r(apid) and s(low) neutron capture processes, have never before been detected in metal-poor stars because their only strong lines lie in the ultraviolet spectral region. The abundances of these r- and s-process nucleosynthesis products in halo stars will serve to provide important constraints both on the early history and chemical evolution of the Galaxy and, indirectly, on the age of the Galaxy and the universe. ------------------------------------------------------------------------------------ 5856( 0) - 07/18/95 18:19 - [ 2] Observations Description ------------------------ We will measure the abundances of the heavy r-process elements Os,Ir, Pt and the s-process element Bi in the extreme Population II star HD 126238 in an attempt to understand more about the early history and age of the Galaxy. Specifically, we will obtain spectra for all four of these elements, which have spectral lines in the ultraviolet, with wavelengths near 3000 Angstroms, in this very metal-poor halo giant. In these observations, we will determine the abundances of the r- and s-process elements in HD 126238, which is more metal- rich (Fe/H = -1.7; Gratton and Sneden 1991, 1994) than HD 122563, another metal -poor halo giant which we observed with HST in Cycle 4. Among the heavier neutron-capture elements, Gratton and Sneden (1994) show that the abundance pattern of the Sr-Y-Zr group is nearly identical in the two stars: Sr/Fe = +0.01, Y/Fe = -0.36, and Zr/Fe = +0.08, with uncertainties of +/- 0.10 for each of these abundance ratios. Obviously, this suggests that the lines of the Pt-Ir -Os-Bi group ought to be 10 times stronger in HD 126238 than in HD 122563. The abundances of the heavier Ba-...-Dy group in HD 126238 are in their solar mix with respect to Fe, strikingly different than in HD 122563. We will use the SSA, grating 270M, and 4 substeps per diode to achieve an ultimate resolution of 50,000 while capturing about 45 Angstrom \ of spectrum per integration. The resolution requirement is due to the crowded spectral region near 3000 Angstrom \ in these stars, and the spectral coverage requirement, aside from increasing the number of candidate lines available per integration, will aid considerably in the setting of continua for our spectrum syntheses. The 270M grating is a better choice than ECH-B for it does not have the pronounced dropoff in throughput over short wavelength intervals that the short-order echelle grating does, and the larger spectral coverage allows at least two very heavy element transitions to be observed with each integration. For HD 126238, a comparison of its UBV colors and effective temperature with those of HD 122563 (for example, although its V magnitude is 1.5 greater than that of HD 122563, it is 400K warmer so that its U is only 1.2 greater) indicates that its 3000 Angstrom \ flux is about .40 that of HD 122563. The total observing time of 13 orbits will allow us to achieve the necessary S/N ratio (= 50), and thus to determine the abundances the very heavy elements in HD 126238. Comparisons of the abundances in this very old star with the earlier stellar abundance determinations from Cycle 4 will provide a measure of the chemical evolution of the Galaxy. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 5856( 0) - 07/18/95 18:19 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5856( 0) - 07/18/95 18:19 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD126238 STAR,GIANT O,K III-I, RA = 14H 25M 30.03S +/- 0.05S, J2000 V = V = 7.70 DEC = -43D 38' 35.7" +/- 0.5", +252.2 B-V = 8.5 E-1 PLATE-ID = 011M U-B = 1.9 E-1 F-CONT(2650.0) = 2.0 E-13 F-CONT(3000.0) = 6.0 E-13 Comments: Coords are from GSC. FLUX AT 2650A IS A LOWER LIMIT TO STAR'S FLUX, FROM THE IUE SPECTRUM OF GUSTAFSSON ET AL (1980,A&A) OF THE METAL-POOR GIANT HD122563, ADJUSTED FOR THE MAGNITUDE DIFFERENCES BETWEEN HD122563 AND OUR TARGET HD126238. THE FLUX AT 3000A IS INTERPOLATED BETWEEN THE 2650A FLUX AND THE "U" BANDPASS FLUX. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1976.412 0.0024 -0.118 0.0 5856( 0) - 07/18/95 18:19 - [ 5] Visit: 01 Visit Requirements: 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 HD126238 HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN 1 1.8S ONBOARD ACQ FOR 20 Comments: STEP_TIME=0.2S; EXPECT 7500 COUNTS IN STEP- TIME TARGET IS METAL-POOR, SO UV MAGS ARE SLIGHTLY UNCERTAIN ------------------------------------------------------------------------------------------------------------------------------------ 20 HD126238 HRS ACQ/PEA 0.25 MIRROR-N2 SEARCH-SIZE=5 1 10S ONBOARD ACQ FOR 30-60 KUP Comments: STEP-TIME=0.4S ------------------------------------------------------------------------------------------------------------------------------------ 30 HD126238 HRS ACCUM 0.25 G270M 3060.0 COMB=FOUR, FP- 6 1817.6S SPLIT=STD, STEP -PATT=3 Comments: TOTAL EXPOSURE=10905.6S--BREAK UP TO AVOID DRIFT DUE TO GIMP; S/N IS PER SUBSTEP; WANT HIGH S/N IN EACH SUBSTEP FOR DECONVOLUTION. ------------------------------------------------------------------------------------------------------------------------------------ 60 HD126238 HRS ACCUM 0.25 G270M 2915.0 COMB=FOUR, FP- 6 1817.6S SPLIT=STD, STEP -PATT=3 Comments: TOTAL EXPOSURE=10905.6S--BREAK UP TO AVOID DRIFT DUE TO GIMP; S/N IS PER SUBSTEP; WANT HIGH S/N IN EACH SUBSTEP FOR DECONVOLUTION. ------------------------------------------------------------------------------------------------------------------------------------ 70 HD126238 HRS ACQ/PEA 0.25 MIRROR-N2 SEARCH-SIZE=3 1 3.6S ONBOARD ACQ FOR 90 KUP Comments: STEP-TIME=0.4S ------------------------------------------------------------------------------------------------------------------------------------ 90 HD126238 HRS ACCUM 0.25 G270M 2833.0 COMB=FOUR, FP- 5 2560S SPLIT=STD, STEP -PATT=3 Comments: TOTAL EXPOSURE=12800S--BREAK UP TO AVOID DRIFT DUE TO GIMP; S/N IS PER SUBSTEP; WANT HIGH S/N IN EACH SUBSTEP FOR DECONVOLUTION. ------------------------------------------------------------------------------------------------------------------------------------ 5856( 0) - 07/18/95 18:19 - [ 6] Summary Form for Proposal 5856 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=5 STEP-PATT=3 FP-SPLIT=STD SEARCH-SIZE=3 COMB=FOUR ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Cool Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 20 ONBOARD ACQ FOR 30-60 ONBOARD ACQ FOR 90 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G270M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD126238 ------------------------------------------------------------------------------------------------------------------------------------