Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 2474c Report Date: 09-May-96:17:08 Version: ********** Check-in Date: ********** 1.Proposal Title: ABUNDANCES OF VERY HEAVY ELEMENTS IN THE EARLY GALAXY ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID STELLAR ASTROPHYSICS GO Sub Category STELLAR ATMOSPHERES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr. John J. Cowan OKLAHOMA, UNIVERSITY OF USA 405-325-3961 ASSOC. PROFESSOR ------------------------------------------------------------------------------------ 7. Abstract We propose to search for spectral lines indicating the presence of the very heavy elements platinum, iridium and osmium in two very old, metal-poor halo stars, and to determine the elemental abundances. These lines, being weak and in the ultraviolet, have never before been detected in metal-poor stars. The abundances of these r- 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. ------------------------------------------------------------------------------------ 8. Scientific Key Words: CHEMICALLY PECULIAR STAR, NUCLEOSYNTHESIS, ABUNDANCE ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 27.00 par: 0 10. Num targs pri: 2 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 2474c PI: Dr. John J. Cowan Proposal Title: ABUNDANCES OF VERY HEAVY ELEMENTS IN THE EARLY GALAXY ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Dr. Christopher Sneden TEXAS, UNIVERSITY OF USA Dr. James W. Truran ILLINOIS, UNIVERSITY OF USA P.I. John J. Cowan OKLAHOMA, UNIVERSITY OF USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. We will measure the abundances of the heavy r-process elements Os-Ir-Pt in extreme Population II stars in an attempt to understand more about the early history of the Galaxy. Specifically, we will obtain spectra for all three of these elements, which have spectral lines in the ultraviolet, with wavelengths near 3000 A. We have chosen two very metal-poor halo giants for observations with the HST:HD 122563 and HD 108317.The star HD 122563 is the brightest very metal- poor ([Fe/H] = -2.6) star in the sky, and has been analyzed repeatedly with visual wavelength spectra (see Sneden and Parthasarathy 1983, (Ap. J., 257, 757).It is the halo star with the most completely determined heavy element abundance distribution.The star HD 108317 is slightly more metal-rich ([Fe/H] = -2.3), but more importantly this star is much more enriched in the neutron- capture very heavy elements than HD122563. A comparison of the abundance results of Gilroy et al.(1988) shows that the abundances for elements heavier than Zr are about 1 dex higher in HD 108317 than in HD 122563. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. We wish to use the High Resolution Spectrograph to obtain very high resolution spectra of Pt I lines at 2998 and 3064 A, the Ir I line at 2924 A and the Os I line at 3058 A. Our study of the relevant solar atlases and of the solar abundance studies of these elements (e. g. for Pt, see Gough, Hannaford, and Lowe 1982, J. Phys. B. 15, L431) suggests that these lines combine the best of the usual virtues of line strength and line cleanness. All other transitions of these elements are suspect on one or both of these counts, or occur at such short wavelengths that the fluxes from these cool stars are prohibitively low. Clearly the Hubble Space Telescope is necessary for our observations; the longest wavelength to be observed is 3064 A, essentially totally inaccessible from ground -based observatories. Also, we must employ one of the very high resolution echelle gratings for these observations, because a) the line crowding will be severe even in the metal-poor stars to be observed here, and b) the predicted line strengths of the Os, Ir, and Pt lines are not extremely large (see below). Page 3 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. From the figures and formulae of section 4.1.2 (HRS Instrument Handbook), and the published stellar photometry and the assumption of E(B-V)=0,the acquisition count rates should be 5E4 using mirror N2 for HD 122563. This estimate may be a bit low because this metal-poor star is likely to be anomalously bright in the uv for its B-V colors, and so a series of 200 ms exposures should produce ideal count rates for acquisition of the object. The spectrum integration times were then estimated to produce a (S/N) of about 75 in the stellar continua with a spectral resolution of 100,000 for each observation. We must use the echelle ECH- B grating for these observations to resolve our spectral features from blending transitions of other species. Therefore we used equation 4-10 to predict exposure times, taking f=0.89 for substep pattern 6 of Table 4-15, b=0.02 from the scattered light estimates of Table 4-7 and n=1 for no spectrum binning. Then to estimate s, the signal strength, we took the sensitivity estimates of the system with the ECH-B grating (4E11 to 1E12 [counts/diode/s] per [erg/cm2/s/A]) from StScI Newsletter July 1988, and multiplied by the estimated flux for the star. For HD 122563, the flux near 3000 A was determined using the broadband UBV colors and the IUE uv spectrum. Putting all these factors together, we estimate each exposure to take about 3 hours; the increased system sensitivity at the shortest wavelengths compensates for the decreased stellar fluxes. ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. The abundances will be derived by syntheses of the spectra obtained with the HST. The model atmospheres employed for the star will be those adopted by Gilroy et al. (1988).Particular attention will be paid to the abundances of ordinary metals (e. g. Fe, Ni, Ti) determined from the new uv spectra. These abundances must agree, within observation and analysis errors, to the abundances derived from the (easily analyzed) visual wavelength spectra already on hand. Then the abundances determined from the analysis of the Pt, Ir, and Os features will be compared to the abundances of the ordinary metals to ascertain the degree of enrichment of the exotic very heavy elements. We already have predicted the approximate expected strengths for the Os I, Ir I, and Pt I lines. Adopting a) model atmsophere parameters from Gilroy et al. (1988), b) recent published oscillator strengths for the lines, and c) predicted abundance ratios for these elements with respect to Ba and Eu from r-process synthesis calculations or from the solar system r-process fractions, we predict that the Pt I lines will have equivalent widths of about 20 mA, or log (W/lambda) ~ -5.2 . The Ir I and Os I equivalent widths should be about 10 mA, or log (W/lambda) ~ -5.5 . Therefore the lines of these 3 elements should be easily seen with the very high echelle resolutions to be employed here. ------------------------------------------------------------------------------------ 11. Address Information Name: JOHN J. COWAN Category: PI Institution: UNIVERSITY OF OKLAHOMA Address: DEPT. OF PHYSICS & ASTRONOMY 440 W. BROOKS, RM. 131 City: NORMAN State: OK Zip Code: 73019 Country: Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 2474c [ 4] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD122563 STAR;GIANT;CHEMICALLY RA = 14H 0M 4.55S +/- 0.01S, 1950 V = - 1 V = 6.18 +/- 0.02, B-V = +0.91 +/- BD+10D2617 PECULIAR; DEC = +9D 55' 38.8" +/- 26.0 2 0.02 SAO120251 NUCLEOSYNTHESIS:ABUNDAN 0.15" 3 TYPE = K III, E(B-V) = 0.0 CE;POPULATION II 4 F(2800) = 5 +/- 0.5 E-13 F(4400) = 1 +/- 0.1 E-11 Comments: UV FLUXES FROM GUSTAFSSON ET AL. 1980 A AND A, 89, 255. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B 1964.27 -0.0127 +/- 0.0007 -0.0710 +/- 0.0100 0.0000 +/- 0.0000 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 2474c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD122563 HRS ACQ 2.0 MIRROR-N2 FAINT=200.0 1 1.8S 100 1 1 ONBOARD ACQ FOR 2- SEARCH-SIZE=3 2 4 3 4 ------------------------------------------------------------------------------------------------------------------------------------ 2 HD122563 HRS ACCUM 0.25 ECH-B19 2997.74 FP-SPLIT=STD 3 59.46M 60 1 1 2 3 4 ------------------------------------------------------------------------------------------------------------------------------------ 3 HD122563 HRS ACCUM 0.25 ECH-B18 3061.45 FP-SPLIT=STD 3 70M 60 1 1 2 3 4 ------------------------------------------------------------------------------------------------------------------------------------ 4 HD122563 HRS ACCUM 0.25 ECH-B19 2927.5 FP-SPLIT=STD 3 59.46M 60 1 1 2 3 4 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 2474c [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FAINT=200.0 SEARCH-SIZE=3 FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 27.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR ASTROPHYSICS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category STELLAR ATMOSPHERES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2-4; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 ECH-B19 ECH-B18 ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD122563 BD+10D2617 SAO120251 ------------------------------------------------------------------------------------------------------------------------------------