Constraints on chemical evolution models from QSOALS abundances

Models of the formation and early chemical evolution of our Galaxy are guided and constrained by our knowledge of abundances in globular cluster stars and halo field stars. The abundance patterns identified in halo and disk stars should be discernible in absorption lines of gas clouds in forming galaxies which are accidentally lying in front of background QSO's. Conversely, the ensemble of QSO absorption line systems (QSOALS) at each redshift may suggest a detailed model for the formation of our Galaxy that is testable using abundance patterns in halo stars

Lunar Photo Study, Phase 4 Final Report, 30 Nov. 1967 - 30 Nov. 1968

Lunar photo stud

The Physical Characteristics of the Small-Scale Interstellar Structure towards Mu Crucis

We present HST/GHRS echelle observations of multiple interstellar lines of CI, MgI, CrII, and ZnII towards both stars in the mu Cru binary system. Despite large differences in the profiles of the neutral species, no significant variations between the stars are seen in the CrII and ZnII line profiles. In particular, the ZnII absorption observed at -8.6 km/sec towards mu Cru is constant despite greatly enhanced columns of the neutral species at this velocity towards mu^1 Cru. An analysis of the fine-structure excitation of CI in this cloud implies that the density is n_H < 250 cm^{-3}. From the lack of variation in the (optical) NaI D2 line profiles towards mu^1 and mu^2 Cru in spectra taken 21 months apart, we can place a lower limit to the size of the structures of ~10 AU. These results are discussed in the context of recent radio and optical studies of apparently pervasive high density small-scale interstellar structure.Comment: 10 pages, 2 figures, to appear in the Astrophysical Journal (Letters

Observations of Small Scale ISM Structure in Dense Atomic Gas

We present high resolution (R~170,000) Kitt Peak National Observatory Co'ude Feed telescope observations of the interstellar KI 7698 angstrom line towards 5 multiple star systems with saturated NaI components. We compare the KI absorption line profiles in each of the two (or three) lines of sight in these systems, and find significant differences between the sight-lines in 3 out of the 5 cases. We infer that the small scale structure traced by previous NaI observations is also present in at least some of the components with saturated NaI absorption lines, and thus the small scale structures traced by the neutral species are occurring at some level in clouds of all column densities. We discuss the implications of that conclusion and a potential explanation by density inhomogeneities

A Na I Absorption Map of the Small-Scale Structure in the Interstellar Gas Toward M15

Using the DensePak fiber optic array on the KPNO WIYN telescope, we have obtained high S/N echelle spectra of the Na I D wavelength region toward the central 27" x 43" of the globular cluster M15 at a spatial resolution of 4". The spectra exhibit significant interstellar Na I absorption at LSR velocities of +3 km/s (LISM component) and +68 km/s (IVC component). Both components vary appreciably in strength on these scales. The derived Na I column densities differ by a factor of 4 across the LISM absorption map and by a factor of 16 across the IVC map. Assuming distances of 500 pc and 1500 pc for the LISM and IVC clouds, these maps show evidence of significant ISM structure down to the minimum scales of 2000 AU and 6000 AU probed in these absorbers. The smallest-scale N(Na I) variations observed in the M15 LISM and IVC maps are typically comparable to or higher than the values found at similar scales in previous studies of interstellar Na I structure toward binary stars. The physical implications of the small and larger-scale Na I features observed in the M15 maps are discussed in terms of variations in the H I column density as well as in the Na ionization equilibrium.Comment: 11 pages, 3 figures, accepted for publication in ApJ Letter

A Cold Nearby Cloud Inside the Local Bubble

The high-latitude Galactic H I cloud toward the extragalactic radio source 3C 225 is characterized by very narrow 21 cm emission and absorption indicative of a very low H I spin temperature of about 20 K. Through high-resolution optical spectroscopy, we report the detection of strong, very narrow Na I absorption corresponding to this cloud toward a number of nearby stars. Assuming that the turbulent H I and Na I motions are similar, we derive a cloud temperature of 20 (+6, -8) K (in complete agreement with the 21 cm results) and a line-of-sight turbulent velocity of 0.37+/-0.08 km/s from a comparison of the H I and Na I absorption linewidths. We also place a firm upper limit of 45 pc on the distance of the cloud, which situates it well inside the Local Bubble in this direction and makes it the nearest-known cold diffuse cloud discovered to date.Comment: 11 pages, 3 figures, accepted for publication in ApJ Letter

Small-Scale Interstellar Na I Structure Toward M92

We have used integral field echelle spectroscopy with the DensePak fiber-optic array on the KPNO WIYN telescope to observe the central 27" x 43" of the globular cluster M92 in the Na I D wavelength region at a spatial resolution of 4". Two interstellar Na I absorption components are evident in the spectra at LSR velocities of 0 km/s (Cloud 1) and -19 km/s (Cloud 2). Substantial strength variations in both components are apparent down to scales limited by the fiber-to-fiber separations. The derived Na I column densities differ by a factor of 4 across the Cloud 1 absorption map and by a factor of 7 across the Cloud 2 map. Using distance upper limits of 400 and 800 pc for Cloud 1 and Cloud 2, respectively, the absorption maps indicate structure in the ISM down to scales of 1600 and 3200 AU. The fiber-to-fiber Na I column density differences toward M92 are comparable to those found in a similar study of the ISM toward the globular cluster M15. Overall, the structures in the interstellar components toward M92 have significantly lower column densities than those toward M15. We interpret these low column density structures as small-scale turbulent variations in the gas and compare them to the larger-scale, higher column density variations toward M15, which may be the hallmarks of actual H I structures.Comment: 9 pages, 2 figures, accepted for publication in ApJ Letter