9049( 3) - 04/13/01 09:45 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9049 Version: 3 Check-in Date: 13-Apr-2001 09:45:01 1.Proposal Title: Boron in G64-12: Higher Big Bang Lithium or Signature of the Nu-Process? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Constantine Deliyannis Indiana University System CoI: Prof. Ann Boesgaard University of Hawaii N ------------------------------------------------------------------------------------ 5. Abstract The extremely metal-poor ( Fe/H ~ -3.3 ) star G64-12 shows a remarkable lithium (Li) abundance that is about 2 times larger than those seen in other warm metal-poor stars, from which the Big Bang Li abundance is inferred. This star's enhanced Li has resulted from either 1. Galactic Li enrichment from a lower Big Bang value, or 2. stellar depletion from a higher Big Bang value, with significant cosmological implications. We argue against two of the three prominent mechanisms of Galactic Li enrichment, leaving the theoretical Nu-process in Type II supernovae as the sole viable mechanism. This mechanism's crisp signature is the concomitant production of copious amounts of boron (B); if the Nu-process enriched the material out which G64- 12 formed with the extra Li observed today, then this star should also exhibit a large detectable B overabundance. B in G64-12 can only be observed from space, using HST/STIS. If this star's STIS-based B abundance lies above the established B-Fe trend, this would be the first observational evidence for the Nu-process. But if its B abundance lies near the B-Fe trend, this would provide direct evidence that G64-12 is an elusive fossil of a Big Bang Li abundance about 0.3 dex above currently favored values, providing consistency in standard Big Bang Nucleosynthesis between Li and D (but not 4He). EITHER RESULT would be of fundamental importance to Astronomy. ------------------------------------------------------------------------------------ 9049( 3) - 04/13/01 09:45 - [ 2] Observations Description ------------------------ Additional comments during Phase II. NOTE: It is desirable to schedule the four Visits as close to each other as possible. For the E230M observations, we employ a setting of 2415A, rather than the 2415A setting indicated in Phase I. The reason is that the setting at 2415A will allow us to also observe the boron lines neat 2090A. Thus, we will be able to check on the boron abundance derived from the 2497A lines; i.e. we get twice the info for free has worked on 2090A data from previous HST cycle(s) and has kindly volunteered to give us his line list. Using RPS2 and the exposure time calculator, we have verfied that our ACK and ACK/PEAK exposures are within acceptable tolerances. Original Phase I comments. A single STIS observation will be made of G64-12, using the E230M grating, which should yield similar performance as the instrumental setup utilized during our previous GHRS boron observations. The STIS data will include the 2500 Angstrom region, which contains the B I resonance lines at Lambda2496.8 and Lambda2497.7. Our previous experience has verified that S/N~50 is needed to derive accurate abundances in metal-poor stars from the weak B lines (e.g., Duncan et al. 1997). For the present purposes, namely to distinguish between a normal B abundance and a much, MUCH higher value, we can economize on spacecraft orbits; S/N~25 will more than suffice. We also know (e.g., from detecting very weak B features even in very metal-poor stars) that R~30, 000 will allow us to analyze the spectra successfully, despite moderate blending of the B I features. To determine exposure times, we have used a combination of \ a) absolute fluxes at 2500 Angstrom as reported by Cacciari et al. (1985, A&AS, 61, 407) which we calibrated to take into account the dependence of 2500 Angstrom flux on T_ eff and the differences in V magnitude), \ b) our experience from previous HST Cycles in observing B in metal-poor stars, and c) the STIS Exposure Time Calculator. Our orbit calculations include adequate allowances for target acquisition, peak ups, etc. Note that the Lambda2500 B I region in low mass stars has been calibrated carefully in previous studies (ours and those of others) involving HST spectra of stars with a variety of stellar parameters (Procyon, two low gravity Hyades giants, the red giants Beta Gem and Arcturus, and the high gravity halo dwarf Gmb 1830), as well as new studies utilizing high resolution, high S/N UV solar spectra (Cunha & Smith 1999, ApJ, 512, 1006). Furthermore, the absolute boron abundance scale is now well-established (Cunha, Smith, Boesgaard, & Lambert 2000, ApJ, 530, 939). Given, \ a) the availability of these quality linelists with suitably calibrated atomic data, and \ b) our considerable experience with the synthesizing stellar spectra to compare with high resolution observational data, the path from the observations to reliable abundance determinations is a straightforward one. We propose to observe the Li-rich star G64-12. The Li- rich star's Boron content will be compared to the mean B-Fe trend as defined in our previous (GHRS) studies of the origin and evolution of Galactic B (Duncan et al. 1997). Cosmic ray interactions have been shown to produce a constant B/Be ratio of ~15, as predicted (Duncan et al. 1997, Prantzos et al. 1993; Ramaty et al. 1996). If the B in G64-12 also originated from cosmic ray production, its abundance should agree with that of the mean B-Fe trend; but, if the B and extra Li in G64-12 were instead produced by the Nu-process, then it should have a much higher B abundance the mean B-Fe trend (see Figure 2). Our extensive Be studies with Keck/HIRES, and our and others' studies based on other telescopes all find that the Be-Fe trend in normal dwarfs is tight. The B -Fe relation, based on our previous HST results, also seems to be tight. This facilitates detection of the excess B in (potentially) B-rich stars such as our candidates. A digression regarding a fine detail for G 64-12: Stromgren--beta photometry suggests this star is slightly reddened. If we (conservatively) ignore the reddening, then G 64-12 has the same T_ eff as G 64-37, a star of similar low metallicity and high dwarf-like gravity. Even then, our Keck spectra (Fig. 3) show that the Li abundance in G 64-12 is still nearly TWICE that of G 64-37. Even in this conservative case, the corresponding Nu-process B would still be far above the mean trend, and easy to detect (labeled ``very conservative low limit'' in Figures 2 and 4). Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9049( 3) - 04/13/01 09:45 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 G64-12 STAR, F3-F9 RA=13H 40M 2.63S +/- 0.0029", J2000 V=+441 V = 11.47+/-0.004 DEC=-00D 02' 18.0" +/- 0.0017" TYPE=F8V B-V = +0.38+/-0.01 E(B-V) = 0.02+/-0.02 U-B = -0.23 Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1991.25 -0.01538 -0.08032 0.0 9049( 3) - 04/13/01 09:45 - [ 4] Visit: 01 Visit Priority: 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 G64-12 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 11 G64-12 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 1 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 12 G64-12 STIS/N ACCUM 0.2X0.0 E230M 2415 1 33 M UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 13 G64-12 STIS/N ACCUM 0.2X0.0 E230M 2415 4 48 M EXPAND UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9049( 3) - 04/13/01 09:45 - [ 5] Visit: 02 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 20 G64-12 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 21 G64-12 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 1 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 22 G64-12 STIS/N ACCUM 0.2X0.0 E230M 2415 1 33 M UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 23 G64-12 STIS/N ACCUM 0.2X0.0 E230M 2415 4 48 M EXPAND UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9049( 3) - 04/13/01 09:45 - [ 6] Visit: 03 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 30 G64-12 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 31 G64-12 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 1 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 32 G64-12 STIS/N ACCUM 0.2X0.0 E230M 2415 1 33 M UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 33 G64-12 STIS/N ACCUM 0.2X0.0 E230M 2415 4 48 M EXPAND UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9049( 3) - 04/13/01 09:45 - [ 7] Visit: 04 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 40 G64-12 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 41 G64-12 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 1 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 42 G64-12 STIS/N ACCUM 0.2X0.0 E230M 2415 1 33 M UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 43 G64-12 STIS/N ACCUM 0.2X0.0 E230M 2415 3 48 M EXPAND UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9049( 3) - 04/13/01 09:45 - [ 8] Summary Form for Proposal 9049 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.06 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements EXPAND ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names G64-12 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2415 ------------------------------------------------------------------------------------------------------------------------------------