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  • 1
    Publication Date: 2019-07-12
    Description: The present study examines eight new echelle spectra of HD 72127A found between 1981 and 1988 near the Ca II K line, along with four similar spectra near the Na I D lines. In addition to the unrivaled intensity and width of this interstellar K line formed at a distance of not more than 500 pc, which were previously discovered by Thackeray (1974), the spectra show clearly the unique temporal variability of the interstellar absorption along this light path, which was reported in an earlier study by Hobbs et al. (1982). The new results strengthen further the hypothesis that the interstellar absorption toward this star occurs predominantly in the disturbed gas located within the SNR, in which the interstellar grains have been largely destroyed. The variable interstellar lines were found to consist of at least 120 components at the K line and of at least eight generally corresponding components at the D lines. The total column densities summed over all of these interstellar clouds varied irregularly by about 45 percent in five and about 38 percent in ten years, respectively.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 378; 586-598
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  • 2
    Publication Date: 2019-07-12
    Description: Due to dielectric recombination, neutral magnesium represents an important tracer for the warm low-density gas around the solar system. New Mg I 2852 absorption-line data from IUE are presented, including detections in a few stars within 40 pc of the sun. The absence of detectable Mg I in Alpha CMa and other stars sets limits on the combined size and electron density of the interstellar cloud which gives rise to the local interstellar wind. For a cloud radius greater than 1 pc and density of 0.1/cu cm, the local cloud has a low fractional ionization, n(e)/n(tot) less than 0.05, if magnesium is undepleted, equilibrium conditions prevail, the cloud temperature is 11,750 K, and 80 percent of the magnesium in the sightline is Mg II.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 357; 514-523
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  • 3
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    In:  Other Sources
    Publication Date: 2019-07-12
    Description: Abundances of Si(+), S(+), Cr(+), Mn(+), Fe(_), and Zn(+) are considered for two absorption-line systems in the spectrum of the QSO PKS 0528 - 250. Zinc and sulfur are underabundant, relative to H, by a factor of 10 compared to their solar and Galactic interstellar abundances. The silicon-, chromium-, iron-, and nickel-to-hydrogen ratios are less than the solar values and comparable to the local interstellar ratios. A straightforward interpretation is that nucleosynthesis in these high-redshift systems has led to only about one-tenth as much heavy production as in the gas clouds around the sun, and that the amount of the observed underabundances attributable to grain depletion is small. The dust-to-gas ratio in these clouds is less than 8 percent of the Galactic value.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 343; L37-L40
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  • 4
    Publication Date: 2019-07-12
    Description: Echelle spectra of beta Pictoris have been obtained in the region of the Ca II 8542A line which arises from the metastable 3d 2D5/2 level. A narrow, weak, circumstellar absorption line is seen at the stellar radial velocity. A simple theory is developed of the radiative pumping of the metastable levels of the Ca II ions by the radiation from the star at the H and K lines. The relatively large fractional population, N3(Ca II)/N1(Ca II) of roughly 0.05, observed for the metastable level then requires that the calcium absorbers be largely concentrated within about 1 AU of the star. This result confirms two previous, independent estimates of the location of this gas. A time-variable circumstellar component of the 8542A line also is found at an infall velocity of about 15 km/s.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 334; L41-L44
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  • 5
    Publication Date: 2019-07-12
    Description: A procedure designed to obtain increased sensitivity from high-dispersion IUE spectra by using a flat-field spectrum to remove nonrandom noise due to the response pattern of the SEC vidicon detector is described. Application of this procedure to spectra of Rho Oph and Beta(1) Sco near the spin-forbidden interstellar 2325 line of C II yields 2 sigma upper limits on absorption of W (lambda) not greater than about 4 mA. The resulting depletion of carbon from the interstellar gas toward Rho Oph exceeds a factor of 1.4.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 98; 857-861
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  • 6
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    In:  Other Sources
    Publication Date: 2019-07-12
    Description: Observations at a resolving power or a velocity resolution are reported of the interstellar D(sub 1) line of Na I in the spectra of Gamma Cas, Delta Ori, Epsilon Ori, Pi Sco, Delta Cyg, and Alpha Cyg. An echelle grating was used in a double-pass configuration with a CCD detector in the coude spectrograph of the 2.7 m reflector at McDonald Observatory. At least 42 kinematically distinct clouds are detected along the light paths to the five more distant stars, in addition to a single cloud seen toward Delta Cyg. The absorption lines arising in 13 of the clouds are sufficiently narrow and unblended to reveal clearly resolved hyperfine structure components split by 1.05 km/s. An additional 13 clouds apparently show comparably narrow, but more strongly blended, lines. For each individual cloud, upper limits T(sub max) and (v sub t) (sub max) on the temperature and the turbulent velocity, respectively, are derived by fitting the observing lines with theoretical absorption profiles.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 368; 426-431
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  • 7
    Publication Date: 2019-07-12
    Description: In an attempt to determine the distances to four high-latitude molecular clouds (HLCs), echelle spectra near the Na I D lines, accurate MK spectral types, and photoelectric photometry for 25 nearby stars have been obtained. Fairly firm distance limits may be placed on MBM 40 (d smaller than or equal to 140 pc) and MBM 53 (d greater than or equal to 110 pc and less than or equal to 155 pc), based on the presence or absence of strong interstellar Na I absorption towards stars projected on or near those HLCs. Weak interstellar absorption lines observed toward many of the stars located near MBM 54 and 55 make the distances to those clouds less certain (about 265 pc for both). Interstellar CH absorption at 4300 A was detected in the spectrum of HD 218662, located behind MBM 53 with a CH column density of 2.1 x 10 to the 13th per sq cm, thus implying a CH abundance comparable to that observed in other molecular clouds. Morphological and velocity agreement among CO emission, the Na I absorption, the 100 micron infrared cirrus emission, and the 21 cm H I emission near these HLCs suggest a close association of the interstellar material responsible for those phenomena.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 346; 232-242
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  • 8
    Publication Date: 2019-07-12
    Description: The paper presents echelle spectra recorded at the D lines of Na I for three stars projected on the high-latitude molecular cloud MBM 16 at l = 172 deg, b = -38 deg. The A stars HD 21142 at about 95 pc and HD 21134 at about 240 pc show strong D-line absorption at the same velocities as the CO emission observed at these positions. The distance to MBM 16 therefore is in the range of 60 to 95 pc. MBM 16 is only 11 deg away from MBM 12, previously placed by the same method at distance of about 65 pc. Consideration is given to the relationship between clouds 12 and 16 and the local hot low-density interstellar gas.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 327; 356-363
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  • 9
    Publication Date: 2019-07-13
    Description: Spectra recorded at 1150-1600 A with an instrumental resolution near 16 km/s were obtained with the Goddard High-Resolution Spectrograph on board the HST. The gaseous interstellar abundances of five heavy elements along the light paths to 23 Ori, 15 Mon, 1 Sco, Pi Sco, and Pi Aqr were determined from the observations. The 1400.450 A line of Sn II was detected and identified toward three stars; at Z = 50, tin is the first element from the fifth row of the periodic table to be identified in the interstellar medium. One spectral line of each of Cu II (Z = 29) and Ga II (Z = 31), three lines of Ge II (Z = 32), and two lines of Kr I (Z = 36) were also detected toward some or all of the five stars. The depletions of these five heavy elements generally decrease monotonically with increasing atomic number toward each of the six stars, and tin is generally undepleted within the observational errors. The depletions of 26 elements from the interstellar gas in an average dense interstellar cloud appear to correlate with the elemental 'nebular' condensation temperatures more closely than with the first ionization potentials.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal - Part 1 (ISSN 0004-637X); 411; 2; p. 750-755.
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  • 10
    Publication Date: 2019-06-27
    Description: Diffuse-band data have been collected from the literature and reduced statistically to a common measurement system, enabling correlation analyses to be made with a larger quantity of data than previously possible. A full listing of the catalogued data is presented, along with some discussion of the correlations. One important application of such studies is the identification of cases of peculiar diffuse-band behavior, and a table is given showing all cases of band strengths deviating by more than twice the mean dispersion from the best-fit correlations. This table may be useful in planning further observations.
    Keywords: ASTRONOMY
    Type: Astronomical Journal; 82; Feb. 197
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