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NASA NTRS1979

IUE observations of the quasar 3C 273

IUE observations indicate that the spectrum of 3C 273 is similar to that of other large-redshift quasars. There is a large excess of flux in the range 2400 A to 5300 A, which encompasses the Balmer jump region but which does not appear to be explainable by Balmer emission. The intensity ratio of Lyman-alpha to H-beta is 5.5, in agreement with other measures and a factor 6 smaller than the recombination value. The only absorption lines in the spectrum are due to our Galaxy. There is marginal evidence for a depression of the continuum shortward of the Lyman-alpha emission line, but the errors are too large to warrant any conclusion that 3C 273 has a rich absorption-line spectrum such as that seen in large-redshift quasars. The absence of emission and absorption lines of Fe II leads to the conclusion that resonance fluorescence probably produces the visual Fe II emission lines.

Boggess, A.↗
NASA NTRS2001

The Lyman-Alpha Forest in the Lensed Quasar Q0957+561 and the Characteristic Dimension of the Absorbing Clouds

Far-ultraviolet spectra of the gravitational lens components Q0957+561 A and 9 were obtained with the Hubble Space Telescope Faint Object Spectrograph (FOS) at five equally spaced epochs, one every two weeks. We confirm the flux variability of the quasar's Lyman-alpha and 0 VI emission lines reported by Dolan et al. (1995) in IUE spectra. The fluxes in these lines vary on a time scale of weeks in the observer's rest frame, independently of each other and of the surrounding continuum. The individual spectra of each image were co-added to investigate the properties of the Lyman-alpha forest along the two lines of sight to the quasar. Absorption lines having equivalent width W > 0.3 A in the observer's frame not previously identified by Michalitsianos et al. (1997) as interstellar lines, metal lines, or higher order Lyman lines were taken to be Ly-alpha forest lines. The existence of each line in this consistently selected set was then verified by its presence in two archival FOS spectra with -1.5 times higher signal to noise than our co-added spectra. Ly-alpha forest lines with W > 0.3 A appear at 41 distinct wavelengths in the spectra of the two images. one absorption line in the spectrum of image A has no counterpart in the spectrum of image B and one line in image B has no counterpart in image A. Based on the separation of the lines of sight over the redshift range searched for Ly-forest lines, the density of the absorbing clouds in the direction of Q0957+561 must change significantly over a distance R = 160 (+120, -70)/ h(sub 50) kpc in the simplified model where the absorbers are treated as spherical clouds and the characteristic dimension, R, is the radius. (We adopt H(sub 0) = 50 h(sub 50) km/s/ kpc, q(sub 0) = 1/2, and lambda = 0 throughout the paper.) The 95% confidence interval on R extends from (50 - 950)/h(sub 50) kpc We show in the Appendix that the fraction of Ly-alpha forest lines that appear in only one spectrum can be expressed as a rapidly converging power series in 1/r, where r the ratio of the radius of the cloud to the separation of the two lines of sight at the redshift of the cloud. This power series can be rewritten to give r in terms of the fraction of Ly-forest wavelengths that appear in the spectrum of only one image. A simple linear approximation to the solution that everywhere agrees with the power series solution to better than 0.8% for r > 2 is derived in the Appendix.

Dolan, Joseph↗
NASA NTRS1980

Velocity structure in long period variable star atmospheres

A regression analysis of the dependence of absorption line velocities on wavelength, line strength, excitation potential, and ionization potential is presented. The method determines the region of formation of the absorption lines for a given data and wavelength region. It is concluded that the scatter which is frequently found in velocity measurements of absorption lines in long period variables is probably the result of a shock of moderate amplitude located in or near the reversing layer and that the frequently observed correlation of velocity with excitation and ionization are a result of the velocity gradients produced by this shock in the atmosphere. A simple interpretation of the signs of the coefficients of the regression analysis is presented in terms of preshock, post shock, or across the shock, together with criteria for evaluating the validity of the fit. The amplitude of the reversing layer shock is estimated from an analysis of a series of plates for four long period variable stars along with the most probable stellar velocity for these stars.

Pilachowski, C.↗
NASA NTRS2001

First Detection of a Foreground Damped Ly-Alpha Absorber Along a GRB Line of Sight?

We present a VLT spectrum of the optical afterglow of GRB 991216, taken 1.5 days after the burst, and HST (Hubble Space Telescope) imaging of the host galaxy, obtained four months later. The spectrum contains three metal absorption-line systems with redshifts z = 1.024, z = 0.803, and z = 0.771, where the highest redshift most likely reflects the distance to the host galaxy. For the z = 1.024 and z = 0.803 systems we tentatively detect MgI which suggests a dense environment at these redshifts. This and the strength of the z = 0.803 Fe lines indicate that this system very likely is a damped Ly-alpha absorber (DLA), which would be the first foreground DLA to be detected along a GRB afterglow sight line. The HST images are consistent with these findings: they show two blobs of light, one underneath the projected OT position, the presumed host galaxy, and the other 0.6" away, which is probably responsible for the absorption lines at z = 0.803. The lowest redshift system can be explained by either one of the two galaxies that are located roughly 2" away from the transient. Including these newly found systems, the total number of DLAS and Lyman limit systems along GRB afterglow sight lines is consistent with the number expected from QSO (quasi-stellar object) absorption line studies. We expect early spectroscopy of GRB afterglows to significantly increase the number of detected foreground absorption systems, and we discuss some advantages over QSO lines of sight.

Vreeswijk, P. M.↗
DOE OSTI2025

DESI Mg II Absorbers: Extinction Characteristics and Quasar Redshift Accuracy

In this paper, we study how absorption-line systems affect the spectra and redshifts of quasi-stellar objects (QSOs), using catalogs of Mg II absorbers from the early data release and first data release of the Dark Energy Spectroscopic Instrument. We determine the reddening effect of an absorption system by fitting an unreddened template spectrum to a sample of 50,674 QSO spectra that contain Mg II absorbers. We find that reddening caused by intervening absorbers (v off > 3500 km s −1 ) has an average color excess of $\overline{E(B-V)}$ = 0.04 mag. We find that the E(B − V) tends to be greater for absorbers at low redshifts, or those having Mg II absorption lines with higher equivalent widths, but shows no clear trend with v off for intervening systems. However, the $\overline{E(B-V)}$ of associated absorbers, those at v off < 3500 km s −1 , shows a strong trend with v off , increasing rapidly with decreasing v off and peaking (∼0.15 mag) around v off = 0 km s −1 . We demonstrate that Mg II absorbers impact redshift estimation for QSOs by investigating the distributions of v off for associated absorbers. We find that at z > 1.5, these distributions broaden and bifurcate in a nonphysical manner. In an effort to mitigate this effect, we mask pixels associated with the Mg II absorption lines and recalculate the QSO redshifts. We find that we can recover voff populations in better agreement with those for z < 1.5 absorbers and in doing so typically shift background QSO redshifts by Δz ≈ ± 0.005.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Absorption filaments toward the massive clump G0.253+0.016

ALMA HCO{sup +} observations of the infrared dark cloud G0.253+0.016 located in the central molecular zone of the Galaxy are presented. The 89 GHz emission is area-filling, optically thick, and sub-thermally excited. Two types of filaments are seen in absorption against the HCO{sup +} emission. Broad-line absorption filaments (BLAs) have widths of less than a few arcseconds (0.07-0.14 pc), lengths of 30-50 arcsec (1.2-1.8 pc), and absorption profiles extending over a velocity range larger than 20 km s{sup –1}. The BLAs are nearly parallel to the nearby G0.18 non-thermal filaments and may trace HCO{sup +} molecules gyrating about highly ordered magnetic fields located in front of G0.253+0.016 or edge-on sheets formed behind supersonic shocks propagating orthogonal to our line of sight in the foreground. Narrow-line absorption filaments (NLAs) have line widths less than 20 km s{sup –1}. Some NLAs are also seen in absorption in other species with high optical depth, such as HCN, and occasionally in emission where the background is faint. The NLAs, which also trace low-density, sub-thermally excited HCO{sup +} molecules, are mostly seen on the blueshifted side of the emission from G0.253+0.016. If associated with the surface of G0.253+0.016, the kinematics of the NLAs indicate that the cloud surface is expanding. The decompression of entrained, milli-Gauss magnetic fields may be responsible for the re-expansion of the surface layers of G0.253+0.016 as it recedes from the Galactic center following a close encounter with Sgr A.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

Probing Pre-Galactic Metal Enrichment with High-Redshift Gamma-Ray Bursts

We explore high-redshift gamma-ray bursts (GRBs) as promising tools to probe pre-galactic metal enrichment. We utilize the bright afterglow of a Population III (Pop III) GRB exploding in a primordial dwarf galaxy as a luminous background source, and calculate the strength of metal absorption lines that are imprinted by the first heavy elements in the intergalactic medium (IGM). To derive the GRB absorption line diagnostics, we use an existing highly resolved simulation of the formation of a first galaxy which is characterized by the onset of atomic hydrogen cooling in a halo with virial temperature approximately greater than10(exp 4) K.We explore the unusual circumburst environment inside the systems that hosted Pop III stars, modeling the density evolution with the self-similar solution for a champagne flow. For minihalos close to the cooling threshold, the circumburst density is roughly proportional to (1 + z) with values of about a few cm(exp −3). In more massive halos, corresponding to the first galaxies, the density may be larger, n approximately greater than100 cm(exp −3). The resulting afterglow fluxes are weakly dependent on redshift at a fixed observed time, and may be detectable with the James Webb Space Telescope and Very Large Array in the near-IR and radio wavebands, respectively, out to redshift z approximately greater than 20. We predict that the maximum of the afterglow emission shifts from near-IR to millimeter bands with peak fluxes from mJy to Jy at different observed times. The metal absorption line signature is expected to be detectable in the near future. GRBs are ideal tools for probing the metal enrichment in the early IGM, due to their high luminosities and featureless power-law spectra. The metals in the first galaxies produced by the first supernova (SN) explosions are likely to reside in low-ionization stages (C II, O I, Si II and Fe II). We show that, if the afterglow can be observed sufficiently early, analysis of the metal lines may distinguish whether the first heavy elements were produced in a pair-instability supernova or a core-collapse (Type II) SN, thus constraining the initial mass function of the first stars.

Metal↗
NASA NTRS1983

Ultraviolet studies of nova-like variables with the IUE

KQ Mon is a new UX UMa-type nova-like variable. Optical spectra taken in 1978 reveal very shallow Balmer absorption lines and He I (wavelength 4471) absorption. There was no evidence of orbital variations but the appearance of the optical spectrum and the presence of low amplitude flickering suggested a strong similarity to CD-42 degrees 14462 (=V3885 Sgr) and other members of the UX UMa class. KQ Mon was observed at low dispersion with the IUE satellite. Six spectra taken with the short wavelength prime (SWP) camera are dominated by strong broad absorption lines due to N V, O I, Si III, Si IV, C IV, He II, N IV, and A1 III. There is little evidence of orbital phase modulation over the time baseline of the observations. Unlike UV observations of other UX UMa-type objects, KQ Mon exhibits no emission lines or P Cygni-type profiles and the velocity displacements appear to be smaller, suggesting the absence of a hot, high velocity wind characterizing other UX UMa stars. The relationship of KQ Mon to other UX UMa disk stars is discussed and a model is suggested to explain their observed properties and the lack of major outbursts.

Guinan, E. F.↗
NASA NTRS1983

Gamma-ray burst high time-resolution spectral observations made with the Solar Maximum Mission

The gamma-ray bursts of April 19 and 21, 1980, and March 1, 1981, are characterized on the basis of observations obtained at 25-500 keV and time resolution 128 msec using the hard-X-ray-burst spectrometer of the SMM satellite. The data are presented graphically, and the parameters determined by fitting three theoretical models to the data for each phase (rising phase, decay phase, and valleys between pulses) are given in tables. Models used are thin thermal bremsstrahlung with or without absorption lines, thermal synchrotron with or without absorption lines, and power law with exponential cutoff.

Desai, U. D.↗
NASA NTRS1995

A Hubble Space Telescope study of the underlying white dwarf in the dwarf nova VW Hydri during quiescence

We have analyzed a far-ultraviolet spectrum of the dwarf nova VW Hyi obtained during quiescence with the Hubble Space Telescope Faint Object Spectrograph (HST FOS). The observation occurred 10 days after the return to optical quiescence from a superoutburst of VW Hyi. The spectrum reveals a very strong Stark-broadened Ly-alpha absorption with narrow geocoronal emission, and a very rich metallic absorption-line spectrum dominated by strong resonance absorption features of singly and doubly ionized silicon and carbon, the first solid identification of metallic absorption features arising in the accreted atmosphere of the white dwarf. We confirm the reported low-resolution IUE detection of the underlying white dwarf photosphere by Mateo & Szkody. A synthetic spectral analysis with hot, high-gravity LTE model atmospheres yields a best-fit model with the following parameters: T(sub eff) = 22,000 +/- 1000 K, log g = 8.0 +/- 0.3, with chemical abundances for oxygen of 0.3 times solar, for nitrogen of 5 times solar, and for all other heavy elements of 0.15 times solar. Based upon our absorption-line measurements of the observations at different orbital phases, we find no conclusive evidence of equivalent width variations with orbital phase. In the absence of any significant reduction of the white dwarf's core mass by past nova explosions, its lower limit cooling age is approximately 50 million years.

Sion, Edward M.↗
NASA NTRS1974

Optical measurement of static temperature and hydroxyl radical profiles in a hydrogen-fueled supersonic combustor

Profiles of static temperature and hydroxyl radical concentration were measured in a two-dimensional supersonic combustor test section 22.8 cm downstream of hydrogen injection. A high-pressure gas generator supplied vitiated air to the test section at Mach 2.44, atmospheric pressure, and a total temperature of about 2240 K. Room-temperature hydrogen was injected through a 0.40-cm step slot at Mach 1 and matched pressure. The measurements utilized a noninterfering spectral line absorption technique in which narrow ultraviolet emission lines of the hydroxyl electronic transition are absorbed by the broader absorption lines in the combustion gas. Comparison of the measured temperature profiles with theoretical calculations showed good agreement.

Gaugler, R. E.↗
NASA NTRS1984

The distribution of interstellar matter toward Tycho's supernova remnant and its relation to distance estimates

Observations of interstellar absorption lines in the spectra of five stars in the direction of Tycho's Supernova Remnant are presented. The profiles show significant absorption at large negative velocities, - 50 to - 60 km/s (LSR). This information, together with the distances of the background stars, permits limiting distances to be assigned to the corresponding velocity components in the H I 21-cm line absorption spectrum of the supernova remnant itself. The 21-cm absorption line data for Tycho's Supernova Remnant are entirely consistent with a distance as small as 2 kpc. Distances based upon simple kinematic models of galactic rotation can be confused by well-known noncircular motions in this direction. The interstellar line data also reveal a relatively high column density of CO toward HD 108.

Black, J. H.↗
NASA NTRS1989

Zonal Winds Between 25 and 120 Km Retrieved from Solar Occultation Spectra

Atmospheric winds at heights between 25 and 120 km have been retrieved with precisions of 5/ms from the Doppler shifts of atmospheric absorption lines measured from a satellite-borne instrument. Lines of the upsilon 3 CO2 and upsilon 2 H2O rotation-vibration bands caused by gases in the instrument allowed the instrumental frequency scale to be absolutely calibrated so that accurate relative speeds could be obtained. By comparing the positions of both sets of instrumental lines the calibration of the frequency scale was determined to be stable to a precision of less than 2 x 10(-5) cm during the course of each occultation. It was found that the instrumental resolution of 0.015 cm after apodization, the signal to noise ratio of about 100 and stable calibration allowed relative speeds to be determined to a precision of 5 ms or better by using small numbers of absorption lines between 1600 and 3200 cm. Absolute absorption line positions were simultaneously recovered to precisions of 5 x 10(-5) cm or better. The wind speed profiles determined from four sunset occultations and one sunrise occultation show remarkable similarities in the magnitudes and directions of the zonal wind velocities as functions of height. These wind profiles appear to be manifestations of atmospheric tides.

Vancleef, Garrett Warren↗
NASA NTRS1988

The small molecular cloud toward HD 169454

Optical absorption line observations of the B1 supergiant HD 169454 reveal the presence of an intervening translucent interstellar cloud. Millimeter wavelength observations of CO emission show that the absorption lines can be attributed to a well-defined cloud approximately 18 by 22 min in extent at the same radial velocity as the C2 and CN absorption lines. The map of the CO emission shows three large condensations and evidence of unresolved structure on smaller scales. Various procedures for determining the cloud mass are compared. The estimated mass is 7-14 M solar masses if the cloud lies at the distance (D about 125 pc) of an extended atomic cloud at the same radial velocity, and is 250-500 M solar masses if the kinematic distance (D about 750 pc) is adopted. The dynamical state of the cloud is examined. The composition and structure of the cloud are discussed with reference to detailed theoretical models and the properties of other interstellar clouds.

Jannuzi, Buell T.↗
DOE OSTI2022

The 2175 Å bump features in FeLoBAL quasars: One indicator of MW-like dust in the nuclear region of quasars

To investigate the properties of dust in the nuclear region of quasars, we explored the extinction curves of the iron low-ionisation broad absorption line (FeLoBAL) quasar SDSS J163004.29+311957.6 and its two analogues. The parametrised extinction curves indicated the Milky Way-like 2175 Å bump features in underlying extinction, which are similar to those seen in the Local Group and in a subset of high-redshift star-forming galaxies. Compared to the bump features in the Large Magellanic Cloud (LMC), the detections in this work are much closer to those in the Milky Way (MW). These bump features, as well as those in the high- and low-ionisation broad absorption line (BAL) quasars with 2175 Å bumps, are probably the counterpart of the 2175 Å bump features in the quasar environment. This type of dust grain is generally small, easily disrupted by high-energy photons, and has difficulty surviving in the radiation field of the active galactic nucleus. However, due to the presence of absorption-line outflows, the 2175 Å bump feature in quasars, which should be rare, is seen many times in BAL quasars. The shielding effect of outflow clouds allows the MW-like dust grains to be assembled or extends the survival period in the quasar nuclear region. The process and physical and chemical conditions deserve further observational study and investigation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Probing outflows in z = 1 ∼ 2 galaxies through Fe II/Fe II* multiplets

We report on a study of the 2300-2600 Å Fe II/Fe II* multiplets in the rest-UV spectra of star-forming galaxies at 1.0 < z < 2.6 as probes of galactic-scale outflows. We extracted a mass-limited sample of 97 galaxies at z ∼ 1.0-2.6 from ultra-deep spectra obtained during the GMASS spectroscopic survey in the GOODS South field with the Very Large Telescope and FORS2. We obtain robust measures of the rest equivalent width of the Fe II absorption lines down to a limit of W{sub r} > 1.5 Å and of the Fe II* emission lines to W{sub r} > 0.5 Å. Whenever we can measure the systemic redshift of the galaxies from the [O II] emission line, we find that both the Fe II and Mg II absorption lines are blueshifted, indicating that both species trace gaseous outflows. We also find, however, that the Fe II gas has generally lower outflow velocity relative to that of Mg II. We investigate the variation of Fe II line profiles as a function of the radiative transfer properties of the lines, and find that transitions with higher oscillator strengths are more blueshifted in terms of both line centroids and line wings. We discuss the possibility that Fe II lines are suppressed by stellar absorptions. The lower velocities of the Fe II lines relative to the Mg II doublet, as well as the absence of spatially extended Fe II* emission in two-dimensional stacked spectra, suggest that most clouds responsible for Fe II absorption lie close (3 ∼ 4 kpc) to the disks of galaxies. We show that the Fe II/Fe II* multiplets offer unique probes of the kinematic structure of galactic outflows.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Weighing the Low-Redshift Lyman-alpha Forest

In 2003-2004, our FUSE research group prepared several major surveys of the amount of baryonic matter in the intergalactic medium (IGM), using the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. These surveys include measurements of the Lyman-alpha absorption line of neutral hydrogen (H I), the far-ultraviolet (1032,1038 Angstrom) doublet of highly ionized oxygen ( O VI), the higher Lyman-series lines (Ly-beta, Ly-gamma, etc) of H I, and the 977 Angstrom line of c III. As an overview, our FUSE spectroscopic studies, taken together with data from the Hubble Space Telescope, show that approximately 30% of the normal matter is contained in intergalactic hydrogen gas clouds (the Lyman-alpha forest). Another 5-10% resides in hotter gas at temperatures of 10(exp 5) to 10(exp 6) K, visible in 0 VI and C III absorption. Along with the matter attributed to galaxies, we have now accounted for approximately HALF of all the baryonic matter in the universe. Where is the other half? That matter my exist in even hotter gas, invisible through the ultraviolet absorption lines, but perhaps detectable through X-ray absorption lines of more highly ionized oxygen and neon.

Shull, Mike↗
NASA NTRS1991

Evidence for a thermally unstable shock wave in the Vela supernova remnant

The emission and absorption line signatures of supernova remnant shock waves provide complementary diagnostic capabilities. This paper presents IUE spectra of the nebulosity and new spectra of HD 72088. Models of the emission and absorption lines from shocked gas are used to derive a shock velocity and elemental depletions. There is evidence from the absorption-line strengths and widths for thermally unstable cooling behind a 150 km/s shock. The shock velocity and swept-up column density estimates of Wallerstein and Balick (1990) are confirmed, and evidence is found for a nonthermal contribution to the pressure.

Raymond, John C.↗