An Upper Limit for the Deuterium Abundance in the Halo Star HD 140283
Session 98 -- Activity and Abundances Near the Main Sequence
Oral presentation, Wednesday, 11, 1995, 2:00pm - 3:30pm

## [98.05] An Upper Limit for the Deuterium Abundance in the Halo Star HD 140283

D.A. Lubowich (Hofstra U. and AIP), Jay M. Pasachoff, Robert P. Galloway (Williams College), R.L. Kurucz (Cfa), Verne V. Smith (U. Texas)

Because of the possible enhanced deuterium abundance of D/H = 2.5 $10^{-4}$ (the ISM D/H = 1.65x$10^{-5}$) recently reported in quasar absorption spectra, we searched for the D$_\alpha$ line at 6561 A in the metal-poor halo star HD 140283 (G2IV, [Fe/H] = -2.6; T$_{eff}$= 5700K). We observed HD 140283 using the .9m KPNO coude feed and the 2.7m McDonald Observatory telescopes with echelle spectrographs having a resolution $\Delta\lambda$ = .05 A/pixel with S/N= 200 and $\Delta\lambda$ = .11 A/pixel with S/N = 600 respectively. We did not detect the D$_\alpha$ line and compared our results to model atmosphere calculations for this star. We estimate an upper limit of D/H $<$ 1x$10^{-5}$ which is smaller than the primordial or and Early Galactic D/H = 8x$10^{-5}$. Since D is destroyed via reactions with protons at T $>$ 5x$10^5$K, the atmospheric deuterium has probably been destroyed during the pre-main sequence convection phase. Because $^7$Li, $^9$Be, and $^{11}$B have all been detected in this star (Li/H=1.5x$10^{-10}$ and B/H=2.9x$10^{-12}$) and Li is destroyed at T $>$ 2.5x$10^6$K, the temperature at the bottom of the pre-main sequence convection zone is 1x$10^6$K $<$ T $<$ 2.5x$10^6$.K