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Oegerle, W. R.

Publications and source records attributed to Oegerle, W. R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Status of NASA's Assessment of Satellite Servicing

Following recommendations by the National Research Council, NASA's Authorization Act of 2008 (P.I. 110-422) and the Fiscal Year 2009 Omnibus Appropriations Act directed NASA to assess the feasibility of using the planned human spaceflight architecture to service existing and future observatory-class scientific spacecraft. This interest in space servicing, either with astronauts and/or with robots, reflects the decades-long success that NASA has achieved with the Space Shuttle program and the Hubble Space Telescope on behalf of the international astronomical community. This study is led by NASA Goddard Space Flight Center and will last about a year, leading to an assessment report to NASA and the science communities. We will report on the status of this study, progress toward goals, workshops, and priorities for the next few months.

Thronson, H. A.↗
NASA NTRS2006

Concept for a Large Scalable Space Telescope: In-Space Assembly

We present a conceptual design for a scalable (10-50 meter segmented filled-aperture) space observatory operating at UV-optical-near infrared wavelengths. This telescope is designed for assembly in space by robots, astronauts or a combination of the two, as envisioned in NASA s Vision for Space Exploration. Our operations concept for this-space telescope provides for assembly and check-out in an Earth Moon L2 (EML2) orbit, and transport to a Sun-Earth L2 (SEL2) orbit for science operations and routine servicing, with return to EML2 for major servicing. We have developed and analyzed initial designs for the optical, structural, thermal and attitude control systems for a 30-m aperture space telescope. We further describe how the separate components are packaged for launch by heavy lift vehicle(s) and the approach for the robot assembly of the telescope from these components.

Oegerle, W. R.↗
NASA NTRS2001

D/H Toward BD+28 4211: First FUSE Results

The atomic deuterium-to-hydrogen abundance ratio has been evaluated for the sight line toward the hot O subdwarf BD+28(sup circ) 4211. High signal-to-noise ratio (S/N is approx. 100) observations covering the wavelength range 905 to 1187 angstroms at a wavelength resolving power of lambda/Delta/lambda at approx. 20,000 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. BD+28(sup circ) 4211 is approx. 00 pc away with a total H I column density of approx. 10(exp 19)/sq cm, much higher than is typically found in the local interstellar medium (ISM). The deuterium column density was measured by analyzing several D I Lyman series transitions (Lyman delta, C, epsilon, eta, theta, iota with curve of growth and profile fitting techniques, after determining which lines were free of interference from other interstellar species and narrow stellar features. The neutral hydrogen column density was measured by an analysis of the Lyman-alpha profile using HST/Space Telescope Imaging Spectrograph (STIS) and Goddard High Resolution Spectrograph (GHRS) spectra. The stellar spectrum of BD+28(sup circ) 4211 was modelled to assist in determining the sensitivity of H I (Ly-alpha) and D I to the continuum placement and to identify stellar transitions. The D I and H I column densities, their uncertainties, and potential sources of systematic error will be presented. This work is based on data obtained for the FUSE Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U. S. participants has been provided in part by NASA contract NAS5-32985.

Sonneborne, George↗
NASA NTRS2001

FUSE Observations of Warm Gas in the Cooling Flow Clusters A1795 and A2597

We present far-ultraviolet spectroscopy of the cores of the massive cooling flow clusters Abell 1795 and 2597 obtained with FUSE. As the intracluster gas cools through 3 x 10(exp 5)K, it should emit strongly in the O VI lambda(lambda)1032,1038 resonance lines. We report the detection of O VI (lambda)1032 emission in A2597, with a line flux of 1.35 +/- 0.35 x 10(exp -15) erg/sq cm s, as well as detection of emission from C III (lambda)977. A marginal detection of C III (lambda)977 emission is also reported for A1795. These observations provide evidence for a direct link between the hot (10(exp 7) K) cooling flow gas and the cool (10(exp 4) K) gas in the optical emission line filaments. Assuming simple cooling flow models, the O VI line flux in A2597 corresponds to a mass deposition rate of approx. 40 solar mass /yr within the central 36 kpc. Emission from O VI (lambda)1032 was not detected in A1795, with an upper limit of 1.5 x 10(exp -15) erg/sq cm s, corresponding to a limit on the mass cooling flow rate of M(28 kpc) less than 28M solar mass/ yr. We have considered several explanations for the lack of detection of O VI emission in A1795 and the weaker than expected flux in A2597, including extinction by dust in the outer cluster, and quenching of thermal conduction by magnetic fields. We conclude that a turbulent mixing model, with some dust extinction, could explain our O VI results while also accounting for the puzzling lack of emission by Fe(sub XVII) in cluster cooling flows.

Oegerle, W. R.↗
NASA NTRS2001

Ultraviolet Broad Absorption Features and the Spectral Energy Distribution of the QSO PG 1351+641

We present a moderate-resolution (approximately 20 km/s) spectrum of the broad-absorption line QSO PG 1351+64 between 915-1180 angstroms, obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Additional low-resolution spectra at longer wavelengths were also obtained with the Hubble Space Telescope (HST) and ground-based telescopes. Broad absorption is present on the blue wings of C III lambda977, Ly-beta, O VI lambda-lambda-1032,1038, Ly-alpha, N V lambda-lambda-1238,1242, Si IV lambda-lambda-1393,1402, and C IV lambda-lambda-1548,1450. The absorption profile can be fitted with five components at velocities of approximately -780, -1049, -1629, -1833, and -3054 km/s with respect to the emission-line redshift of z = 0.088. All the absorption components cover a large fraction of the continuum source as well as the broad-line region. The O VI emission feature is very weak, and the O VI/Ly-alpha flux ratio is 0.08, one of the lowest among low-redshift active galaxies and QSOs. The ultraviolet continuum shows a significant change in slope near 1050 angstroms in the restframe. The steeper continuum shortward of the Lyman limit extrapolates well to the observed weak X-ray flux level. The absorbers' properties are similar to those of high-redshift broad absorption-line QSOs. The derived total column density of the UV absorbers is on the order of 10(exp 21)/s, unlikely to produce significant opacity above 1 keV in the X-ray. Unless there is a separate, high-ionization X-ray absorber, the QSO's weak X-ray flux may be intrinsic. The ionization level of the absorbing components is comparable to that anticipated in the broad-line region, therefore the absorbers may be related to broad-line clouds along the line of sight.

Zheng, W.↗
NASA NTRS2001

Ultraviolet Broad Absorption Features and the Spectral Energy Distribution of the QSO PG 1351+64

We present a moderate-resolution (approximately 20 km s(exp -1) spectrum of the mini broad absorption line QSO PG 1351+64 between 915-1180 A, obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Additional low-resolution spectra at longer wavelengths were also obtained with the Hubble Space Telescope (HST) and ground-based telescopes. Broad absorption is present on the blue wings of C III (lambda)977, Ly(beta), O VI (lambda)(lambda)1032,1038, Ly(alpha), N V (lambda)(lambda)1238,1242, Si IV (lambda)(lambda)1393,1402, and C IV (lambda)(lambda)1548,1450. The absorption profile can be fitted with five components at velocities of approximately -780, -1049, -1629, -1833, and -3054 km s(exp -1) with respect to the emission-line redshift of z = 0.088. All the absorption components cover a large fraction of the continuum source as well as the broad-line region. The O VI emission feature is very weak, and the O VI/Ly(alpha) flux ratio is 0.08, one of the lowest among low-redshift active galaxies and QSOs. The UV (ultraviolet) continuum shows a significant change in slope near 1050 A in the restframe. The steeper continuum shortward of the Lyman limit extrapolates well to the observed weak X-ray flux level. The absorbers' properties are similar to those of high-redshift broad absorption-line QSOs. The derived total column density of the UV absorbers is on the order of 10(exp 21) cm(exp -2), unlikely to produce significant opacity above 1 keV in the X-ray. Unless there is a separate, high-ionization X-ray absorber, the QSO's weak X-ray flux may be intrinsic. The ionization level of the absorbing components is comparable to that anticipated in the broad-line region, therefore the absorbers may be related to broad-line clouds along the line of sight.

Zheng, W.↗
NASA NTRS2000

FUSE Observations of O VI Absorption in the Local Interstellar Medium

We report the results of an initial Far Ultraviolet Spectroscopic Explorer (FUSE) survey of O VI Lambda 1032 absorption along the lines of sight to eleven nearby white dwarfs, ten of which are within the Local Bubble (LB; d < or approximately equal 100 pc). A goal of this survey is to investigate the possible formation of O VI in the conductive interfaces between cool (about 10(exp 4) K) clouds immersed in the presumably hot (10(exp 6) K) gas within the LB. This mechanism is often invoked to explain the widespread presence of 0 VI throughout the Galactic disk. We find no 0 VI absorption toward two stars, and the column densities along three additional sight lines are quite low; N(O VI) about 5 x 10(exp 13)/sq cm. In several directions, we observe rather broad, shallow absorption with N(O VI) about 1 - 2 x 10(exp 13)/sq cm. Models of conductive interfaces predict narrow profiles with N(OVI) > or about equal to 10(exp 13)/sq cm per interface, in the absence of a significant transverse magnetic field. Hence, our observations of weak 0 VI absorption indicate that conduction is being quenched, possibly by non-radial magnetic fields. Alternatively, the gas within the LB may not be hot. Breitschwerdt & Schmutzler have proposed a model for the LB in which an explosive event within a dense cloud created rapid expansion and adiabatic cooling, resulting in a cavity containing gas with a kinetic temperature of T about 50,000 K, but with an ionization state characteristic of much hotter gas. This model has a number of attractive features, but appears to predict significantly more O VI than we observe.

Oegerle, W. R.↗
NASA NTRS1988

Peculiar velocities of cD galaxies - MX spectroscopy of Abell 1795

Spectroscopic observations of galaxies in the Abell 1795 field have been obtained using the MX multiple-object spectrograph on the Steward Observatory 2.3 m telescope. Redshifts are presented for 46 galaxies, including 41 cluster members. It is found that the A1795 cD galaxy is not at rest in the cluster gravitational potential well; it has a peculiar radial velocity, cz, of 365 km/s, and the hypothesis that the mean cluster velocity is as large as the cD's velocity can be rejected at the 99.5 percent confidence level. This conclusion is supported by spectroscopic data for the 'cooling flow' gas found in the central region of the cluster; this gas, except for the portion coincident with the cD nucleus, lies at the velocity derived for the cluster mean. It is suggested that current models of the formation of cD galaxies are unlikely to account for the large peculiar velocities of the cD galaxies in A1795 and A2670 unless substantial subclustering is still present. However, the available data show no evidence for velocity subclustering in either A1795 or A2670.

Hill, John M.↗
NASA NTRS1987

The surface-brightness-effective-size relation for elliptical galaxies in the cores of clusters

Surface photometry of 372 elliptical galaxies has been performed using CCD images of the centers of 97 nearby rich Abell clusters. The strong correlation between surface brightness and effective size, originally found by Kormendy (1977), is clear in the data. Brightest cluster galaxies show much less scatter about the mean relation defined by these data than do lower-luminosity cluster ellipticals, and the slope of the relation is shallower for the brightest galaxies; these two results are tentative, however, because of uncertain selection and environmental effects. When combined with published central velocity dispersions, the photometry yields a relation for brightest cluster galaxies that is in good agreement with the mean relation for elliptical galaxies found by Djorgovski and Davis (1987). Use of the surface-brightness/scale-length relation to measure the lookback luminosity evolution of the stellar content in galaxies is promising.

Hoessel, J. G.↗
NASA NTRS1986

The nearby Abell clusters. I - Abell 168

As part of a large program to study the spatial and luminosity distributions of galaxies in the nearby Abell clusters, the results of a photometric study of Abell 168 are presented and compared to the previous results of Dressler (1978). The previous result is confirmed that the faint end of the luminosity function for the galaxies in the central 0.2 sq deg of this cluster is quite flat (alpha = -1.0 in the Schechter formalism). The slope of the faint end appears to be fairly normal if galaxies from a larger region (1 sq deg) are included, but this may be due to a larger than expected contribution of background galaxies. Consequently, the faint end of the luminosity function of galaxies in a 0.2 sq deg region (and possibly also in a 1 sq deg region) centered on A168 is flatter than the 'universal' luminosity function (a Schechter function with alpha = -1.25). Nevertheless, the luminosity functions for both these regions are well fit by Schechter functions. A study of the spatial distribution of galaxies indicates that the radial dependence of the projected surface density is consistent with a power law of slope - 1.01 + or - 0.09.

Oegerle, W. R.↗
NASA NTRS1985

The Palomar wedge sensitometer

A simple sensitometer for use in providing intensity calibration on photographic plates, which has been in use for many years at Palomar Observatory, is described. External comparison between reduced photographic aperture magnitudes for galaxies and CCD photometry for the same objects shows that use of this device results in proper intensity scales. The intensity scale produced using this instrument also agrees well with that produced by the KPNO spot sensitometers.

Hoessel, J. G.↗
NASA NTRS1984

Circumstellar material around rapidly rotating B stars. II - On the nature of ultraviolet shell lines in the spectra of Be and shell stars

Using high-resolution (FWHM approximately 0.05 A) ultraviolet spectral data obtained with Copernicus, the nature of shell lines in Be and shell stars. Scans were obtained for various excited fine-structure lines of Fe III, Si II, and O I. It is found that Be stars, in general, do not display shell lines in the ultraviolet, contrary to the findings of previous work at lower resolution. The only Be stars that display strong UV shell lines are the 'classical' shell stars, i.e., stars that also display shell lines in the optical region. Furthermore, it is found that the shell lines, when present, have essentially zero velocity shift with respect to the star. The resonance shell lines seen in the shell stars are generally asymmetric on the short-wavelength side, indicating that the lines are formed in a low-velocity outflowing region. The results presented here argue strongly in favor of a flattened disk structure for the shell line forming region, and against some recent scenarios involving spherical symmetry.

Oegerle, W. R.↗
NASA NTRS1983

On the presence of O I lambda 1302 emission in Be stars

The absence of UV O I emission from Be stars is investigated in terms of a model for a circumstellar disk. Observations of the O I 8446 A transition are shown to produce the UV O I triplet 1302.17, 1304.86, and 1306.02 A, which has not been seen. It is demonstrated that the total scattering optical depth in the circumstellar gas is sufficient to ensure that most photons arising from the O I 8446 A transition will be destroyed in an envelope with a density of 10 to the 12th electrons/cu cm, such as has been projected for Be stars. It is also mentioned that a flattened Be star envelope will, if viewed equator-on, will scatter more 1302 A photons from the line-of-sight, implying that Be stars observed pole-on would exhibit an enhanced 1302 A emission because the photons are scattered perpendicularly from the flattened, equatorial disk.

Oegerle, W. R.↗
NASA NTRS1982

Circumstellar material around rapidly rotating B stars. I - Nonemission-line stars

Evidence of low-velocity circumstellar material around a number of rapidly rotating nonemission-line B stars is sought. No evidence is found for circumstellar shell lines in any of the stars observed. If circumstellar material is present, then these results place constraints on the physical properties of the envelope. Furthermore, contamination of interstellar line profiles with circumstellar components in rapidly rotating non-Be stars is, in general, negligible.

Oegerle, W. R.↗
NASA NTRS1982

High resolution observations of magnesium II 2800 A in Alpha Centauri A - The density of interstellar magnesium II and the stellar chromospheric profiles

The profiles are virtually identical with the solar profiles except for the presence of an absorption feature near line center in the h and k lines of Alpha Centauri A. It is found that this absorption feature can be explained by interstellar absorption of Mg II along the line of sight. The average density of Mg II is found to be 2.75 plus or minus 0.7 x 10 to the -7th/cu cm, in good agreement with the previously determined values in the solar vicinity in the direction of Alpha CMa and Alpha Lyr.

Oegerle, W. R.↗
NASA NTRS1980

X-ray observations of the OAO1653-40 field

The region of sky containing OAO1653-40 have been observed simultaneously with the Einstein and Copernicus satellites in 1979 August. A best position of RA = 254.318 degrees, Dec = -41.577 degrees (1950) and a period of 38.019 + or - 0.009 sec were obtained for the X-ray pulsar discovered by White and Pravdo. The X-ray spectrum shows considerable photoelectric absorption with an equivalent hydrogen column density of 2.3 x 10 to the 23rd atom per sq cm. An upper limit to any 0.5-3.0 keV flux from V861 Sco of (4 + or - 1) x 10 to the -13th erg /sq cm/sec was also obtained.

Parmar, A. N.↗
NASA NTRS1980

HR 4453 - An anomalously bright UV source

Crawford et al. (1979) reported that HR 4453 has an anomalously large UV flux in the 1350-1600 A band. This paper reports results of the UV spectrophotometry of HR 4453 obtained with the Copernicus satellite. Portions of the spectrum from 1120 to 2660 A were scanned, but no stellar signal was detected in any wavelength interval. This result is consistent with both components of the binary being normal A2A stars. UV variability or a source other than HR 4453 must be invoked to explain the observations of Crawford et al.

Polidan, R. S.↗