Katherine C. Roth

Johns Hopkins University, Baltimore, MD, United States

Are you Katherine C. Roth?

Claim your profile

Publications (46)133.46 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the first Far-Ultraviolet Spectroscopic Explorer measurements of diffuse O VI (λλ1032, 1038) emission from the general diffuse interstellar medium outside of supernova remnants or superbubbles. We observed a 30'' × 30'' region of the sky centered at l = 3150 and b = -413. From the observed intensities (2930 ± 290 [random] ± 410 [systematic] and 1790 ± 260 [random] ± 250 [systematic] photons cm-2 s-1 sr-1 in λλ1032 and 1038, respectively), derived equations, and assumptions about the source location, we calculate the intrinsic intensity, electron density, thermal pressure, and emitting depth. The intensities are too large for the emission to originate solely in the Local Bubble. Thus, we conclude that the Galactic thick disk and lower halo also contribute. High-velocity clouds are ruled out because there are none near the pointing direction. The calculated emitting depth is small, indicating that the O VI-bearing gas fills a small volume. The observations can also be used to estimate the cooling rate of the hot interstellar medium and to constrain models. The data also yield the first intensity measurement of the C II 3s 2S1/2-2p 2P3/2 emission line at 1037 Å and place upper limits on the intensities of ultraviolet line emission from C I, C III, Si II, S III, S IV, S VI, and Fe III.
    The Astrophysical Journal 12/2008; 560(2):730. DOI:10.1086/322478 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Far Ultraviolet Spectroscopic Explorer spectra of the white dwarf stars G191-B2B, GD 394, WD 2211-495, and WD 2331-475 cover the absorption features out of the ground electronic states of N I, N II, N III, O I, and Ar I in the far-ultraviolet, providing new insights on the origin of the partial ionization of the local interstellar medium (LISM) and, for the case of G191-B2B, the interstellar cloud that immediately surrounds the solar system. Toward these targets the interstellar abundances of Ar I, and sometimes N I, are significantly below their cosmic abundances relative to H I. In the diffuse interstellar medium, these elements are not likely to be depleted onto dust grains. Generally, we expect that Ar should be more strongly ionized than H (and also O and N, whose ionizations are coupled to that of H via charge-exchange reactions) because the cross section for the photoionization of Ar I is very high. Our finding that Ar I/H I is low may help to explain the surprisingly high ionization of He in the LISM found by other investigators. Our result favors the interpretation that the ionization of the local medium is maintained by a strong extreme-ultraviolet flux from nearby stars and hot gases, rather than an incomplete recovery from a past, more highly ionized condition.
    The Astrophysical Journal 12/2008; 538(1):L81. DOI:10.1086/312786 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The metal-deficient starburst galaxy I Zw 18 has been observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) in a search for H2 molecules. The spectrum obtained with an aperture covering the full galaxy shows no absorption lines of diffuse H2 at the radial velocity of the galaxy. The upper limit for the diffuse H2 column density is found to be very low, N(H2) 1015 cm-2 (10 σ), unlike our Galaxy where H2 is generally present for even low H I column densities. Although the H I column density here is as high as N(H I) ≈ 2 × 1021 cm-2, we observe 2N(H2)/N(H I) 10-6. We cannot exclude the possibility that some H2 could be in very dense, small, and discrete clumps that cannot be detected with the present observation. However, the remarkable absence of diffuse H2 in this metal-poor galaxy can be explained by the low abundance of dust grains (needed to form this molecule from H atoms), the high ultraviolet flux, and the low density of the H I cloud surrounding the star-forming regions. Thus, having eliminated diffuse H2 as a significant contributor to the total mass, it appears that the gas of the galaxy is dominated by H I and that the high dynamical mass is not composed of cold and diffuse baryonic dark matter.
    The Astrophysical Journal 12/2008; 538(1):L77. DOI:10.1086/312797 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) have been used to determine the column densities of D I, N I, and O I along seven sight lines that probe the local interstellar medium (LISM) at distances from 37 to 179 pc. Five of the sight lines are within the Local Bubble, and two penetrate the surrounding H I wall. Reliable values of N(H I) were determined for five of the sight lines from Hubble Space Telescope (HST) data, International Ultraviolet Explorer (IUE) data, and published Extreme Ultraviolet Explorer (EUVE) measurements. The weighted mean of D I/H I for these five sight lines is (1.52 ± 0.08) × 10-5 (1 σ uncertainty in the mean). It is likely that the D I/H I ratio in the Local Bubble has a single value. The D I/O I ratio for the five sight lines within the Local Bubble is (3.76 ± 0.20) × 10-2. It is likely that O I column densities can serve as a proxy for H I in the Local Bubble. The weighted mean for O I/H I for the seven FUSE sight lines is (3.03 ± 0.21) × 10-4, comparable to the weighted mean (3.43 ± 0.15) × 10-4 reported for 13 sight lines probing larger distances and higher column densities. The FUSE weighted mean of N I/H I for five sight lines is half that reported by Meyer and colleagues for seven sight lines with larger distances and higher column densities. This result combined with the variability of O I/N I (six sight lines) indicates that at the low column densities found in the LISM, nitrogen ionization balance is important. Thus, unlike O I, N I cannot be used as a proxy for H I or as a metallicity indicator in the LISM.
    The Astrophysical Journal Supplement Series 12/2008; 140(1):3. DOI:10.1086/339133 · 14.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on measurements of interstellar O VI, H2, P II, Si II, Ar I, and Fe II absorption along the line of sight to Sk -67°05, a B0 Ia star in a diffuse H II region in the western edge of the Large Magellanic Cloud (LMC). We find log N(O ) = 14.40 ± 0.04 in the Milky Way component and, using the C IV column density from previous IUE observations, N(C )/N(O ) = 1.00 ± 0.16, a value similar to other halo measurements made with the Far Ultraviolet Spectroscopic Explorer. In the LMC component, log N(O ) = 13.89 ± 0.05 and N(C )/N(O ) < 0.4 (3 σ), since only an upper limit on N(C IV) is available. Along this sight line, the LMC is rich in molecular hydrogen [log N(H2) = 19.50 ± 0.08]; in the Milky Way, log N(H2) = 14.95 ± 0.08. A two-component fit for the excitation temperature of the molecular gas in the LMC gives T01 = 59 ± 5 K for J = 0, 1 and Tex = 800 ± 330 K for J = 3, 4, 5. For the Milky Way, T01 = 99 K; no excitation temperature could be determined for the higher rotational states. The Milky Way and LMC gas-phase [Fe/P] abundances are ~0.6 and ~0.7 dex lower, respectively, than solar system abundances. These values are similar to [Fe/Zn] measurements for the Milky Way and LMC toward SN 1987A.
    The Astrophysical Journal 12/2008; 538(1):L39. DOI:10.1086/312800 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the sight line toward the Seyfert 1 galaxy Markarian 876, which passes through high-velocity cloud (HVC) complex C. This sight line demonstrates the ability of FUSE to measure ionic absorption lines in Galactic HVCs. High-velocity absorption is clearly seen in both members of the O VI doublet. This is the first detection of O VI in a neutral hydrogen HVC. One component of HVC complex C is resolved in multiple Fe II lines from which we derive N(Fe II)/N(H I) = 0.48 (Fe/H)☉. This value of N(Fe II)/N(H I) implies that the metallicity of complex C along this sight line may be higher than that along the Mrk 290 sight line (0.1 solar) found by Wakker et al. On the other hand, if the metallicity of complex C is also 0.1 solar along this line of sight, the observed value of N(Fe II)/N(H I) suggests there may be a significant amount of H+ along the line of sight. In any case, little, if any, iron can be depleted into dust grains if the intrinsic metallicity of complex C is subsolar. Absorption from complex C is also seen in C II, N I, and N II, and upper limits based on nondetections can be determined for Ar I, P II, and Fe III. Although molecular hydrogen in the Milky Way is obvious in the FUSE data, no H2 absorption is seen in the HVC to a limit N(H2) < 2.0 × 1014 cm-2. Future FUSE observations of extragalactic objects behind Galactic HVCs will allow us to better constrain models of HVC origins.
    The Astrophysical Journal 12/2008; 538(1):L35. DOI:10.1086/312801 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed by an extensive period of calibration and characterization as part of the preparation for normal satellite operations. Major tasks carried out during this period include the initial coalignment, focusing, and characterization of the four instrument channels and a preliminary measurement of the resolution and throughput performance of the instrument. We describe the results from this test program and present preliminary estimates of the on-orbit performance of the FUSE satellite based on a combination of these data and prelaunch laboratory measurements.
    The Astrophysical Journal 12/2008; 538(1):L7. DOI:10.1086/312794 · 6.28 Impact Factor
  • J. T. Lauroesch · D. M. Meyer · K. C. Roth
    [Show abstract] [Hide abstract]
    ABSTRACT: We have recently obtained long slit echelle observations of high velocity NaI absorption toward the core of the galaxy M81 using the Kitt Peak National Observatory 4-meter telescope. Our observations probe the neutral gas toward the core of the galaxy with a spatial resolution of 1" and a spectral resolution of 9 km/s, and we detect NaI absorption stretching more than 425 pc from the core. Previous observations of NaI toward the core of M81 and along the sightline to SN 1993J in M81 have shown absorption due to neutral gas at high positive velocities which is not associated with published HI 21cm emission at these positions. The NaI absorption toward the core is at velocities consistent with gas in the halo of M81 which has been tidally striped from M82. Our NaI data shows that this gas varies significantly in optical depth and in velocity over scales of
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) have been used to determine the column densities of D I, O I, and N I along seven sight lines that probe the local interstellar medium (LISM) at distances from 37 pc to 179 pc. Five of the sight lines are within the Local Bubble and two penetrate the surrounding H I wall. Reliable values of N(H I) were determined for five of the sight lines from HST data, IUE data, and published EUVE measurements. The weighted mean of D I/H I for these five sight lines is (1.52 +/- 0.08) x10-5 (1 sigma uncertainty in the mean). It is likely that the D I/H I ratio in the Local Bubble has a single value. The D I/O I ratio for the five sight lines within the Local Bubble is (3.76 +/- 0.20) x10-2. It is likely that the O I column densities can serve as a proxy for H I in the Local Bubble. The weighted mean for O I/H I for the seven FUSE sight lines is (3.03 +/-0.21) x10-4, comparable to the weighted mean (3.43 +/- 0.15) x10-4 reported for 13 sight lines probing larger distances and higher column densities (Meyer et al. 1998, Meyer 2001). The FUSE weighted mean of N I/H I for the five sight lines is half that reported by Meyer et al. (1997) for seven sight lines with larger distances and higher column densities. This result combined with the variability of O I/N I (six sight lines) indicates that at the low column densities found in the LISM, nitrogen ionization balance is important. Thus, unlike O I, N I cannot be used as a proxy for H I or as a metallicity indicator in the LISM. Subject Headings: cosmology: observations- ISM: abundances- ISM: evolution - Galaxy:abundances-Ultraviolet:ISM
  • [Show abstract] [Hide abstract]
    ABSTRACT: We propose to obtain high resolution observations of the interstellar Na I absorption toward the central 73 arcsec x 121 arcsec of the Andromeda Galaxy (M31) and the core of its nearby (24.3 arcmin separation) satellite galaxy M32 utilizing the 4 arcsec spatial resolution and 27 arcsec x 43 arcsec field of the DensePak array on the WIYN telescope. Recent observations with this instrumentation have revealed that the interstellar clouds toward the globular clusters M15 and M92 exhibit significant small-scale Na I structure. Although the M15 and M92 cloud maps are similar in terms of their smallest-scale variations, the M92 clouds do not exhibit the larger-scale, higher-amplitude structure characteristic of the M15 clouds. M31 provides a unique opportunity to further study such patterns in that its surface brightness is high enough to afford DensePak coverage of an area that is 9 times greater than that of our previous M15 and M92 observations. Such coverage will afford an examination of the Na I structure over a wider range in scale and may allow us to better distinguish the contributions of turbulence and actual H I structure to the observed Na I variations.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Far Ultraviolet Spectroscopic Explorer spectra of the white dwarf stars G191-B2B, GD 394, WD 2211#495, and WD 2331#475 cover the absorption features out of the ground electronic states of N i,Nii,Niii,Oi, and Ar i in the far-ultraviolet, providing new insights on the origin of the partial ionization of the local interstellar medium (LISM) and, for the case of G191-B2B, the interstellar cloud that immediately surrounds the solar system. Toward these targets the interstellar abundances of Ar i, and sometimes N i, are significantly below their cosmic abundances relative to H i. In the diffuse interstellar medium, these elements are not likely to be depleted onto dust grains. Generally, we expect that Ar should be more strongly ionized than H (and also O and N, whose ionizations are coupled to that of H via charge-exchange reactions) because the cross section for the photoionization of Ar i is very high. Our finding that Ar i/H i is low may help to explain the surprisingly high ionization of He in the LISM found by other investigators. Our result favors the interpretation that the ionization of the local medium is maintained by a strong extreme-ultraviolet flux from nearby stars and hot gases, rather than an incomplete recovery from a past, more highly ionized condition.
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report Far Ultraviolet Spectroscopic Explorer (FUSE) measurements of diffuse O VI (lambda lambda 1032,1038) emission from the southern sky toward l = 315.0o and b = -41.3o. There are no known point sources, supernova remnants, or superbubbles in this directions and the soft X-ray maps indicate that this region is representative of the southern sky. The expected sources for the observed emission are the Local Bubble and gaseous Galactic halo, though in the latter case, the flux may be attenuated by roughly 50%. The O VI surface brightnesses in the 1032 and 1038 Å components from this direction are 2900 +/- 270 and 1900 +/- 260 photons cm-2 sec-1 sr-1, respectively. We derive the electron density and thermal pressure of the emitting plasma from an isothermal model and estimates of the O VI column density for the Local Bubble and Galactic halo. We conclude that the observed flux is too bright to have originated entirely in the Local Bubble, hence the Galactic halo must have produced most of the flux. We also measured the C II* surface brightness and placed upper limits on the surface brightnesses of ultraviolet emission lines of C I, C III, Si II, S III, S IV, S I, and Fe II.
  • K. C. Roth · D. M. Meyer · J. T. Lauroesch
    [Show abstract] [Hide abstract]
    ABSTRACT: We present high-resolution (R=20,000) integral field spectra of the Na I absorption toward the nucleus of the nearby spiral galaxy M81 (NGC 3031) obtained in April 2000 with the WIYN 3.5-m telescope and the DensePak fiber optic bundle. Our DensePak map covers the central 27 x 43 arcsec of M81 at a spatial resolution of 4 arcsec which corresponds to a projected length scale of 63 pc at the distance of the galaxy (3.25 Mpc). These data were intended to explore the spatial extent of high-velocity (v = 110-130 km/s) gas seen in Na I, Mg I and Mg II absorption toward SN 1993J by Bowen et al. (1994), which they proposed is due to tidal material associated with interactions between M81 and nearby M82 (Yun, Ho & Lo 1993). No H I gas at these velocities has been detected in 21 cm interferometry maps near the position of SN 1993J (2.6 arcmin SW of the M81 nucleus). Our Na I map of the M81 core shows no evidence of the strong absorption seen at v = 110-130 km/s toward SN 1993J. However, our map does reveal a strong Na I component at v = 220 km/s in several fibers that appears to trace a filamentary structure running from the SW to the NE across the M81 nuclear region. The origin and distance of this filament are unknown. No H I gas at v = 220 km/s has previously been detected in 21 cm studies of the core. At the location of SN 1993J, Bowen et al. measured weak Mg II absorption at this velocity but found no evidence of corresponding Na I absorption. The only known H I gas that corresponds to this velocity in the M81 group are the H I streamers found around M82 by Yun, Ho, & Lo that they interpreted as tidally disrupted M82 disk material.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is now making high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 angstroms). Its high effective area, low background, and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. In this paper, we describe the on- orbit performance of the FUSE satellite during its first nine months of operation, including measurements of sensitivity and resolution.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report empirical determinations of atomic oscillator strengths, or f-values, for 11 ground-state transitions of Fe II in the wavelength range 1050 to 1150 Ang. We use ultraviolet absorption line observations of interstellar material towards stars in the Galaxy and the Magellanic Clouds taken with Copernicus, the Goddard High Resolution Spectrograph on-board the Hubble Space Telescope, and the Far Ultraviolet Spectroscopic Explorer. We derive absolute oscillator strengths by a combination of the apparent optical depth, component fitting, and curve-of-growth fitting techniques. Our derived oscillator strengths are generally in excellent agreement with recent theoretical calculations by Raassen & Uylings using the orthogonal operator technique. However, we identify three of the eleven transitions studied here whose f-values seem to be incompatible with these calculations, by as much as a factor of two. We suggest revisions to these f-values based upon our analysis. Comment: To appear in the Astrophysical Journal. 31 pages, including 8 embedded tables and 10 embedded figures. Also available at http://fuse.pha.jhu.edu/~howk/Papers/
    The Astrophysical Journal 07/2000; 544(2). DOI:10.1086/317263 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the sightline toward the Seyfert 1 galaxy Markarian 876, which passes through high velocity cloud (HVC) complex C. This sight line demonstrates the ability of FUSE to measure ionic absorption lines in Galactic HVCs. High velocity absorption is clearly seen in both members of the O VI doublet. This is the first detection of O VI in a neutral hydrogen HVC. One component of HVC complex C is resolved in multiple Fe II lines from which we derive N(Fe II)/N(H I)=0.48 (Fe/H)_solar. This value of N(Fe II)/N(H I) implies that the metallicity of complex C along this sightline may be higher than that along the Mrk 290 sightline (0.1 solar) found by Wakker et al. (1999). On the other hand, if the metallicity of complex C is also 0.1 solar along this line of sight, the observed value of N(Fe II)/(N(H I) suggests there may be a significan t amount of H+ along the line of sight. In any case, little, if any, iron can be depleted into dust grains if the intrinsic metallicity of complex C is subsolar. Absorption from complex C is also seen in C II, N I, and N II, and upper limits based on non-detections can be determined for Ar I, P II, and Fe III. Although molecular hydrogen in the Milky Way is obvious in the FUSE data, no H_2 absorption is seen in the high velocity cloud to a limit N(H_2)<2.0x10^14 cm^-2. Future FUSE observations of extragalactic objects behind Galactic high velocity clouds will allow us to better constrain models of HVC origins.
  • Source
    David V. Bowen · Katherine C. Roth · David M. Meyer · J. Chris Blades
    [Show abstract] [Hide abstract]
    ABSTRACT: We have observed SN 1998S which exploded in NGC 3877, with the Utrecht Echelle Spectrograph (6-7 km s-1 FWHM) at the William Herschel Telescope and with the E230M echelle of the Space Telescope Imaging Spectrograph (8 km s-1 FWHM) aboard the Hubble Space Telescope. Both data sets were obtained at two epochs, separated by 19 (optical) and 7 days (UV data). From our own Galaxy we detect interstellar absorption lines of Ca II K, Fe II lambdalambda2600, 2586, 2374, 2344, Mg I lambda2852, and probably Mn II lambda2576, at vLSR=-95 km s-1 arising from the outer edge of the High Velocity Cloud Complex M. We derive gas-phase abundances of [Fe/H]=-1.4 and [Mn/H]=-1.0, values which are very similar to warm disk clouds found in the local ISM. This is the first detection of manganese from a Galactic HVC, and we believe that the derived gas-phase abundances argue against the HVC material having an extragalactic origin. At the velocity of NGC 3877 we detect interstellar Mg I lambda2852, Mn II lambdalambda2576, 2594, 2606, Ca II K and Na I D2, D1 absorption lines, spanning a velocity range of -102 to +9 km s-1 from the systemic velocity of the galaxy (910 km s-1). Surprisingly, the component at -102 km s-1 is seen to increase by a factor of >~1 dex in N(Na I) between 1998 March 20 and April 8, and in N(Mg I) between 1998 April 4 and April 11. Unusually, our data also show narrow Balmer, He I, and metastable UV Fe II P Cygni profiles, with a narrow absorption component superimposed on the bottom of the profile's absorption trough. Both the broad and narrow components of the optical lines are seen to increase substantially in strength between March 20 and April 8. The broad absorption covers ~350 km s-1 and is seen in Mg II lambdalambda2796, 2803 absorption as well, although there is no evidence of narrow Mg II emission forming a P Cygni profile. There is some suggestion that this shelf has decreased in strength over 7 days between April 4 and April 11. Most of the low-ionization absorption can be understood in terms of gas corotating with the disk of NGC 3877, provided the supernova is at the back of the disk as we observe it, and the H I disk is of a similar thickness to our own Galaxy. However, the variable component seen in all the other lines, and the accompanying emission which forms the classic P Cygni profiles, most likely arise in slow-moving circumstellar outflows originating from the red supergiant progenitor of SN 1998S. Based in part on observations obtained with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Aeronautics and Space Administration, NAS5-26555.
    The Astrophysical Journal 06/2000; 536(1):225-238. DOI:10.1086/308913 · 6.28 Impact Factor
  • David M. Meyer · James T. Lauroesch · Katherine C. Roth
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose to obtain high resolution observations of the interstellar Na I D absorption toward the bright cores of seven globular clusters and galaxies utilizing the 4 arcsec spatial sampling and 27 arcsec x 43 arcsec field of the DensePak fiber bundle in tandem with the WIYN telescope. Recent observations with this instrumentation have revealed that the intermediate-velocity halo cloud (IVC) toward the globular M15 exhibits significant small-scale structure with sixteenfold variations in the Na I column density across the DensePak field. Our proposed observations will determine if the small-scale Na I structure observed in the halo (and local) gas toward M15 is common in other sightlines through the Galactic halo. If such structure reflects H I and is common in other halo clouds, its impact on derived parameters like metallicity would have been missed in the highest resolution (~1 arcmin) H I 21 cm emission studies of these clouds. The maps of local ISM Na I structure toward our 7 targets will also provide an important two-dimensional perspective on the ubiquitous single-axis Na I variations observed toward nearby binary stars.
  • Source
    Katherine C. Roth · James M. Bauer
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the detection of the 1560 A and 1657 A ground-state C I absorption features in the z(abs)=1.6748 system toward the QSO PKS 1756+237. We find no associated C I* lines with a resulting 3-sigma excitation temperature upper-limit of T(ex) <= 8.54 (+0.65,-0.56) K, which is consistent with the predicted CMBR temperature of T(CMBR)=7.291 K. Because the redshifted CMBR populates the J=1 level and leaves little room for additional local excitation through either collisions or UV pumping, our data place 2-3 times more stringent limits on particle densities and UV fields than existing Copernicus observations of similar column density sightlines in the Milky Way. We also detect several Ni II lines and the weak Fe II 1611 A line. From the Ni/Fe column density ratio we find evidence for dust at a dust-to-metals ratio similar to that seen toward warm Galactic disk clouds. Based on these findings and supported by our Ly-alpha spectrum we propose to reclassify this system as a damped Ly-alpha absorber. Comment: 12 pages, 3 figures, to appear in Ap. J. Letters. For further information and associated images see http://www.ifa.hawaii.edu/~kroth/PKS1756.html
    The Astrophysical Journal 02/1999; 515(2). DOI:10.1086/311974 · 6.28 Impact Factor

Publication Stats

910 Citations
133.46 Total Impact Points

Institutions

  • 2000–2008
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, MD, United States
    • Gemini Observatory
      Hilo, Hawaii, United States
    • The Royal Observatory, Edinburgh
      Edinburgh, Scotland, United Kingdom
  • 1999
    • Honolulu University
      Honolulu, Hawaii, United States
  • 1989–1995
    • Northwestern University
      • Department of Physics and Astronomy
      Evanston, Illinois, United States
  • 1993
    • Space Telescope Science Institute
      Baltimore, Maryland, United States