DEUTERIUM AND THE LOCAL INTERSTELLAR-MEDIUM - PROPERTIES FOR THE PROCYON AND CAPELLA LINES OF SIGHT

We present Goddard High-Resolution Spectrograph observations of the in terstellar H I and D I Ly alpha lines and the Mg II and Fe II resonanc e lines formed along the lines of sight toward the nearby stars Procyo n (3.5 pc, l = 214 degrees, b = 13 degrees) and Capella (12.5 pc, l = 163 degrees, b = 5 degrees). New observations of Capella were obtained at orbital phase 0.80, when the radial velocities of the intrinsic Ly alpha emission lines of each star were nearly reversed from those of the previous observations at phase 0.26 (analyzed by Linsky et al.). S ince the intrinsic Ly alpha line of the Capella system-the ''continuum '' against which the interstellar absorption is measured-has different shapes at phases 0.26 and 0.80, we can derive both the intrinsic stel lar profiles and the interstellar absorption lines more precisely by j ointly analyzing the two data sets. We derive interstellar parameters from the simultaneous analysis of the two data sets as follows: (D/H)( LISM) = (1.60 +/- 0.09 [+0.05, -0.10 systematic error]) x 10(-5), temp erature T = 7000 +/- 500 [+/-400 systematic error] K, and microturbule nce xi = 1.6 +/- 0.4 [and +/-0.2 systematic error] km s(-1). (All rand om errors determined in this paper are +/-2 sigma.) For the analysis o f the Procyon line of sight, we first assumed that the intrinsic Ly al pha line profile is a broadened solar profile, but this assumption doe s not lead to a good fit to the observed D I line profile for any valu e of D/H. We then assumed that (D/H)(LISM) = 1.6 x 10(-5), the same va lue as for the Capella line of sight, and we modified the broadened so lar profile to achieve agreement between the simulated and observed li ne profiles. The resulting asymmetric intrinsic stellar line profile i s consistent with the shapes of the scaled Mg II line profiles. We bel ieve therefore that the Procyon data are consistent with (D/H)(LISM) = 1.6 x 10(-5), but the uncertainty in the intrinsic Ly alpha emission- line profile does not permit us to conclude that the D/H ratio is cons tant in the local interstellar medium (LISM). The temperature and turb ulence in the Procyon line of sight are T = 6900 +/- 80 (+/-300 system atic error) K and xi = 1.21 +/- 0.27 km s(-1). These properties are si milar to those of Capella, except that the gas toward Procyon is divid ed into two velocity components separated by 2.6 km s(-1) and the Proc yon line of sight has a mean neutral hydrogen density that is a factor of 2.4 larger than that of the Capella line of sight. This suggests t hat the first 5.3 pc along the Capella line of sight lies within the l ocal cloud and the remaining 7.2 pc lies in the hot gas surrounding th e local cloud. We propose that n(HI) = 0.1065 +/- 0.0028 cm(-2) be ado pted for the neutral hydrogen density within the local cloud and that xi = 1.21 +/- 0.27 km s(-1) be adopted for the nonthermal motions. The existence of different second velocity components toward the nearby s tars Procyon and Sirius provides the first glimpse of a turbulent clou dlet boundary layer between the local cloud and the surrounding hot in terstellar gas. We speculate that what is often called ''turbulence'' may instead be velocity shear within the local cloud that is not a rig id comoving structure. We also derive gas phase abundances of iron and magnesium in the Procyon line of sight and the abundance of oxygen in the Capella line of sight. Within the context of standard big bang nu cleosynthesis, our observed value of(D/H)(LISM) leads to 0.042 less th an or equal to Omega(B) h(50)(2) less than or equal to 0.09, depending on the assumed model for Galactic chemical evolution of deuterium. Ou r lower limit (D/H)(LISM) greater than or equal to 1.41 x 10(-5) provi des a hard lower limit to the primordial D abundance and thus a hard u pper limit on Omega(B) h(50)(2) less than or equal to 0.125. These lim its are independent of Galactic chemical evolution models and only ass ume that D is destroyed with time.