# Presentation: 816807

## BERYLLIUM IN THE OLDEST STARSAnn Merchant Boesgaard, Emily M. Levesque, Jeffrey A. RichInstitute for Astronomy, University of Hawaii

**ABSTRACT**

**Beryllium, oxygen and iron abundances have been determined in 51 halo dwarf stars with [Fe/H] between -0.9 and -3.5. The spectra were obtained at high resolution (~48,000) and high signal-to-noise (80-150) with the upgraded HIRES on the Keck-I 10-m telescope. These spectra have been used to determine the stellar parameters: temperature, log g and [Fe/H]. The Be abundances have been found by spectrum synthesis of the Be II doublet at 3130.4 and 3131.1 A. Our sample also includes 5 stars observed with HDS on the Subaru 8-m telescope**
**(Boesgaard & Novicki 2006) and 14 stars reanalyzed from Boesgaard et al. (1999) with the latest version of MOOG. Newly determined O abundances are found from three OH lines in the UV. We show the relationships between Be and [Fe/H], [O/H], and [O/Fe] and [Be/Fe] vs. [Fe/H] for the whole sample to trace**
**the Galactic evolution of these elements. In addition we subdivide sample into accretive and dissipative populations to examine possible differences.**

**OBSERVATIONS**

**   ****ANALYSIS   **

**RESULTS AND CONCLUSIONS – cont.**

**Sample of the spectrum synthesis used to find Be abundances.   The black dots are the data.  The best fit model is the blue line.  The red lines are plus and minus a factor of two in Be.**

**Sample of the spectrum synthesis used  to**
** ****find O abundances from the UV OH lines.  **
**The black dots are the data.  The blue line is**
** ****the best fit, while the red lines are**** a factor **
**of ±2 in oxygen.**

**2. Is there a **_**plateau **_**in the Be abundance at low metallicity, analogous to the Li plateau, as suggested by Primas et al. 2000?**

**The abundance of Be as A(Be) = log N(Be/H) +12.00 vs. [Fe/H].  Red points are from Subaru HDS, blue from reanalyzed 1999 HIRES data, the others are from newHIRES data.  The slope is ~1.**

**Be as normalized to Fe to compare with [Fe/H].  This shows no trend.  **
**The slope of  -0.05 ± 0.04 is consistent with 0.0.**

**Oxygen abundances from 3 UV OH lines gives [O/H] to compare with A(Be).  The slope is ~1.**

**[Fe/H] compared to A(Be).****The slope is again ~1.**

**There is a uniform increase in A(Be) = log N(Be/H) +12.00 with [Fe/H] with a slope of about 1.  Similarly, there is an increase of A(Be) with [O/H] with a slope of about 1.  All 3 elements appear to increase together as the Galaxy evolves.**

**1.  How does the Beryllium abundance evolve **
**over time in the Galaxy as measured by its growth with Iron and with Oxygen? **

**RESULTS AND CONCLUSIONS**

**The evidence is not convincing for**
**a difference in the Be vs [O/Fe] relations for the two different populations of stars. **

**Following Gratton et al. (2003) and Pasquini et al (2005) we divided our sample into two subsets: the dissipative component and the accreted component. **
** **
**“****Dissipative”**** stars: formed in the early collapse of the Galaxy identified by Eggen, Lyndon-Bell and Sandage (1962).**
**   **
**“****Accretive”**** stars:  formed in the material of the infalling protogalactic fragments which were accreted after the initial collapse (Searle and Zinn 1978).  **
**The dissipative stars take part in the general rotation of the Galaxy, while the accreted stars are non-rotating or counter-rotating.   The definition  for dissipative stars is that they have **
**R****apo ****< 15 kpc   **_**and**_**   v****rot****  > 40 km/s.**** **

**A plot of [O/Fe] vs A(Be) for the two subgroups, as labeled.  The line is the model of the thick disk from  Pasquini et al. (2005), in good agreement with the dissipative component.**

**This work has been supported by **
**NSF grant AST05-05899 to AMB**

**     ****WHY BERYLLIUM?    **

**Beryllium is synthesized only by high-energy spallation reactions of p or n with atoms of CNO. **
**2. It has only one stable isotope, ****9****Be.**
**3. There are minimal effects due to non-LTE.**
**4. It traces the history of formation of massive stars and early supernovae production.**

**No, there is no evidence for a plateau as might have occurred via  nucleosynthesis in some inhomogeneous Big Bang models.**

**3.  Are the Beryllium abundance patterns different in halo star populations that are “dissipative” vs. “accreted,” as suggested by Pasquini et al. 2005?**

**References:**
**Boesgaard et al. 1999, AJ, 117, 1549**
**Boesgaard & Novicki 2006, ApJ, 641, 1122**
**Eggen et al. 1962,ApJ, 136,748**
**Gratton et al. 2003, A&A, 436, 57**
**Pasquini et al. 2005, A&A,406, 131**
**Primas et al. 2000, A&A, 364, 42**
**Primas et al. 2000, A&A,362, 666**
**Searle & Zinn 1978, ApJ, 225, 357**

**Keck HIRES Spectra                   14 Stars**
**Keck Upgraded Hires Spectra   32 Stars**
**Subaru HDS spectra                     5 Stars**
**Resolution:     ~48,000;     S/N: ~100-150**