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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
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NASA NTRS1990

A catalogue of QSOs and link stars for the HST link of the Hipparcos reference frame

A list of bright (less than 17 mag) southern QSOs and bright (less than 11 mag) stars that may be suitable for the Hubble Space Telescope link between the Hipparcos astrometric reference frame and the VLBI extragalactic frame is presented. The QSOs have been selected from various lists of radio objects and identifications. The stars have been selected from the Strasbourg (CDS) data base and from the Preliminary Second Cape Photographic Catalog, and supplemented with stars measured from the SERC IIIa-J Schmidt survey. These QSOs and stars have been included in the Hipparcos and HST schedule of observations.

White, Graeme L.↗
NASA NTRS1991

HST imaging of the inner 3 arcseconds of NGC 1068 in the light of forbidden O III 5007 A

The Planetary Camera aboard HST has been used to obtain a high spatial resolution forbidden O III 5007 A image of the nucleus of the barred spiral galaxy NGC 1068. This image shows more detail than any previously published images and resolves the NLR into several distinct clouds arranged in an apparently conical geometry. The individual emission-line regions appear to be resolved with sizes of 0.1-0.2 arcsec. There is a strong apparent correspondence between the 1.3 cm radio structure and several of the forbidden O III 5007 A clouds, although there are also bright emission-line clouds for which there are no radio counterparts. In particular, the radio 'triple' of Ulvestad et al. (1987) appears to correspond directly to the forbidden O III 5007 A clouds A-D. It is concluded that the distribution of the clouds is consistent with ionization core models. The hidden nucleus is located somewhere in the southern radio component and may be coincident with the H2O megamaser.

Evans, I. N.↗
NASA NTRS1991

The postcollapse core of M15 imaged with the HST planetary camera

It is shown here that, despite the severe spherical aberration present in the HST, the Wide Field/Planetary Camera (WFPC) images still present useful high-resolution information on M15, the classic candidate for a cluster with a collapsed core. The stars in M15 have been resolved down to the main-sequence turnoff and have been subtracted from the images. The remaining faint, unresolved stars form a diffuse background with a surprisingly large core with r(c) = 0.13 pc. The existence of a large core interior to the power-law cusp may imply that M15 has evolved well past maximum core collapse and may rule out the presence of a massive central black hole as well.

Lauer, Tod R.↗
NASA NTRS1991

HST observations of 3C 66B - A double-stranded optical jet

The central region of the synchrotron jet in 3C 66B imaged with ultrahigh spatial resolution by the Faint Object Camera on the HST is discussed. A close correspondence between the general characteristics of the smoothed optical image and the radio map is observed, implying that the young and old relativistic particles occupy similar regions to within about 130 pc. Focus is placed on the double-stranded filamentary nature of the jet, and it is speculated that this could reflect edge-brightening effects due to enhanced radiation from a skinlike structure surrounding the jet. It is noted that the similarity of optical and radio morphologies points to the fact that localized particle acceleration occurs along the jet; however, the filamentary structure and a low filling factor of radiation agree with a model in which the electrons are accelerated within the nucleus and are transported along the jet in a channel having low magnetic field.

Macchetto, F.↗
NASA NTRS1992

HST observations of the inner coma of Comet Levy 1990c

Data reduction procedures which will make it possible to model the nucleus of future targets of cometary space missions were tested on the basis of observations of Comet Levy 1990c by the HST on September 27, 1990. Faint hemispherical shells expanding in the coma, which is structured as a sunward fan deflected by solar radiation pressure, were observed. The Eddington fountain model makes it possible to infer the ejection times of the expanding shells and the initial velocity of the dust. Three shells ejected at time intervals of 11.5 and 12.5 h with an initial velocity of 0.35 km/s were observed for dust grains of 3-micron size. The lag angle of the fan is between 10 and 15 deg, thus suggesting a time delay of the most active sublimation of 1 h after midday. The observed time periodicities suggest a nucleus rotating in 24 h with a surface characterized by two active areas placed almost exactly in opposite hemispheres, even if a longer rotation period and a more complex nucleus topography can be excluded.

Fulle, M.↗
NASA NTRS1993

Discovery of new objects in the Orion nebula on HST images - Shocks, compact sources, and protoplanetary disks

We have reduced and analyzed a set of narrow-band HST images of a portion of M42 south of the Trapezium. Many new emission-line sources were found, some quite long but so narrow that they are not seen on ground-based images. These include thin shells which are high-ionization shocks. The structure around Orion HH 3 is resolved into multiple components. Slit spectroscopy data establish the high expansion velocities of all these regions. The other objects seen are compact sources. Although some had been detected in VLA surveys and several had been seen from the ground optically, the new images show previously undetected structure and clearly establish that most are protoplanetary disks, which are neutral disks surrounding low-mass pre-main-sequence stars and are ionized from the outside by Theta sup 1 C and Theta sup 2 A Ori.

O'Dell, C. R.↗
NASA NTRS1993

HST imaging of hydrogen-poor ejecta in Abell 30 and Abell 78 - Wind-blown cometary structures

HST Faint Object Camera images of hydrogen-poor gas in the planetary nebulae A30 and A78 have revealed remarkable 'cometary' structures in the O III 5007-A forbidden line. Most of these cometary structures, consisting of compact (0.15-0.5 arcsec) knots with radial tails several arcsec in length, are located in an equatorial plane in both nebulae. In addition, two bright, compact (0.3 arcsec) polar knots are present in A30, one of them forming a bow shock. Corresponding polar features in A78 are more diffuse. The central stars of both nebulae have energetic winds which are most likely responsible for the 'cometary' knot morphology. We interpret this morphology in terms of dense (several thousand electrons per cu cm) H-poor condensations whose outer expanding layers are swept outward by stellar winds. Photoionization modeling indicates that while dense knot cores are mostly heated by atomic photoionization, expanding tenuous gas is heated by photoelectrons ejected from abundant dust grains. Our models predict steep temperature gradients for which there is observational evidence and possible abrupt phase transitions in the expanding gas.

Borkowski, Kazimierz J.↗
NASA NTRS1990

STS-31 HST Deploy Sim in SMS and MOCR

This video shows the crew on a simulated middeck during the Hubble Space Telescope (HST) deploy simulation. Intercut from the MOCR is included.

Source record↗
NASA NTRS1992

HST PSF simulation using Tiny Tim

Tiny Tim is a program which simulates Hubble Space Telescope imaging camera PSF's. It is portable (written and distributed in C) and is reasonably fast. It can model the WFPC, WFPC 2, FOC, and COSTAR corrected FOC cameras. In addition to aberrations such as defocus and spherical, it also includes WFPC obscuration shifting, mirror zonal error maps, and jitter. The program has been used at a number of sites for deconvolving HST images. Tiny Tim is available via anonymous ftp on stsci.edu in the directory software/tinytim.

Krist, J. E.↗
NASA NTRS1994

Ellipticals with kinematically distinct cores : HST imaging of the nuclear structure of IC 1459

The elliptical galaxy IC 1459 has one of the strongest counter-rotating core components of any observed elliptical. Here we present Hubble Space Telescope (HST) Planetary Camera images of the center of IC 1459. Before deconvolution, our V band images reveal a bright point source at the galaxy nucleus, and dust near the nucleus. After removal of the central point source, deconvolution and model fitting, we show that the central starlight profile is better fit by a 'cusp' model than an isothermal core model. The photometric properties of the stellar light are comparable to those of other ellipticals without counter-rotating core components. There is an indication of a central stellar disk, although its detection is complicated by the extensive dust. Although the velocity field of the emission-line gas is ordered, the dust distribution is very irregular, and indicates nonequilibrium motions. The irregular dust distribution suggests that material is currently infalling and may be fueling the active nucleus. There is no direct evidence which relates the dust and gas to the peculiar stellar kinematics.

Forbes, Duncan A.↗
NASA NTRS1994

HST images of very compact blue galaxies at z approximately 0.2

We present the results of Hubble Space Telescope (HST) Wide-Field Camera (WFC) imaging of seven very compact, very blue galaxies with B less than or equal to 21 and redshifts z approximately 0.1 to 0.35. Based on deconvolved images, we estimate typical half-light diameters of approximately 0.65 sec, corresponding to approximately 1.4 h(exp -1) kpc at redshifts z approximately 0.2. The average rest frame surface brightness within this diameter is mu(sub v) approximately 20.5 mag arcsec(exp -2), approximately 1 mag brighter than that of typical late-type blue galaxies. Ground-based spectra show strong, narrow emission lines indicating high ionization; their very blue colors suggest recent bursts of star-formation; their typical luminosities are approximately 4 times fainter than that of field galaxies. These characteristics suggest H II galaxies as likely local counterparts of our sample, though our most luminous targets appear to be unusually compact for their luminosities.

Koo, David C.↗
NASA NTRS1994

Narrowband HST imagery of the young planetary nebula Henize 1357

We present Hubble Space Telescope (HST) Planetary Camera observations showing the first optically resolved images of the planetary nebula Henize 1357 . The small size of this object has heretofore precluded optical investigations of its morphology. In H-beta, He 3-1357 appears to have an equatorial ring of enhanced density tilted approximately 56 deg from our line of sight. In addition, there are bubbles of gas above and below the ring with areas of decreased brightness near the poles where a fast stellar wind has broken through the red giant envelope. He 3-1357 has been evolving very rapidly, becoming a planetary nebula only within the past few decades. Assuming a distance of 5.6 kpc, the radius of the nebula is 0.02 pc, implying an expansion age of 2650 yr, although it has been ionized for no more than 40 yr. The H-beta flux is now 5.8 x 10(exp -11) ergs/sq cm/s which implies an ionized mass of 0.2 solar mass, log L*/solar luminosity = 3.7, and a core mass of 0.59 solar mass.

Bobrowsky, M.↗
NASA NTRS1994

Ultraviolet spectra of HZ Herculis/Hercules X-1 from HST: Hot gas during total eclipse of the neutron star

The Faint Object Spectrograph (FOS) aboard Hubble Space Telescope (HST) has been used in the UV to observe the prototypical X-ray pulsar Her X-1 and its companion HZ Her. Optical spectra were also obtained contemporaneously at the Kitt Peak National Observatory (KPNO) 2.1 m. The FOS spectra encompass the 1150-3300 A range near binary orbital phases 0.5 (X-ray maximum) and at 0.0 (mid-X-ray eclipse). The maximum light spectra show strong, narrow C III, N V, O V, Si IV + O IV), N IV), C IV, He II, and N IV emission lines, extending previous IUE results; the O III lambda 3133 Bowen resonance line is also prominent, confirming that the Bowen mechanism is the source of the strong lambda lambda 4640, 4650 emission complex, also seen at maximum light. Most remarkable, however, are the minimum light spectra, where the object is too faint for reasonable observations from IUE. Despite the total eclipse of the X-ray-emitting neutron star, our spectra show strong emission at N V lambda 1240, S IV + O IV) whose emission dominates the UV light at phase 0.0 might be associated with the 'accretion disk corona,' it is more likely the source is somewhat less hot (but extended) gas above and around the disk, or perhaps circumstellar material such as a stellar wind.

Anderson, Scott F.↗
NASA NTRS1994

HST eclipse mapping of dwarf nova OY Carinae in quiescence: An 'Fe II curtain' with Mach approx. = 6 velocity dispersion veils the white dwarf

Hubble Space Telescope (HST) observations of the eclipsing dwarf nova OY Car in its quiescent state are used to isolate the ultraviolet spectrum (1150-2500 A at 9.2 A Full Width at Half Maximum (FWHM) resolution) of the white dwarf, the accretion disk, and the bright spot. The white dwarf spectrum has a Stark-broadened photospheric L(alpha) absorption, but is veiled by a forest of blended Fe II features that we attribute to absorption by intervening disk material. A fit gives T(sub w) approx. = 16.5 x 10(exp 3) K for the white dwarf with a solar-abundance, log g = 8 model atmosphere, and T approx. = 10(exp 4) K, n(sub e) approx. = 10(exp 13)/cu cm, N(sub H) approx. = 10(exp 22) sq cm, and velocity dispersion delta V approx. = 60 km/s for the veil of homogeneous solar-abundance local thermodynamic equilibrium (LTE) gas. The veil parameters probably measure characteristic physical conditions in the quiescent accretion disk or its chromosphere. The large velocity dispersion is essential for a good fit; it lowers (chi square)/778 from 22 to 4. Keplerian shear can produce the velocity dispersion if the veiling gas is located at R approx. = 5 R(sub W) with (delta R)/R approx. = 0.3, but this model leaves an unobscured view to the upper hemisphere of the white dwarf, incompatible with absorptions that are up to 80% deep. The veiling gas may be in the upper atmosphere of the disk near its outer rim, but we then require supersonic (Mach approx. = 6) but sub-Keplerian (delta V/V(sub Kep) approx. = 0.07) velocity disturbances in this region to produce both the observed radial velocity dispersion and vertical motions sufficient to elevate the gas to z/R = cos i = 0.12. Such motions might be driven by the gas stream, since it may take several Kepler periods to reestablish the disk's vertical hydrostatic equilibrium. The temperature and column density of the gas we see as Fe II absorption in the ultraviolet are similar to what is required to produce the strong Balmer jump and line emissions seen in optical spectra of OY Car and similar quiescent dwarf novae. The outer accretion disk is detected at mid-eclipse with a spectrum that rises from 0.05 to 0.3 mJy between 2000 and 2500 A, consistent with combinations of cool blackbodies, blended Fe II emission lines, and Balmer continuum emission. The total disk flux density is 0.5 mJy at 2500 A, and this shallow disk eclipse implies a roughly flat surface brightness distribution. The bright spot, somewhat bluer than the disk, has a flux density rising from 0.05 to 0.15 mJy between 1600 and 2500 A. The C IV emission line has a broad shallow eclipse, but the radial velocity variations observed during the eclipse do not clearly distinguish between a disk or wind origin. The only possible indications of boundary layer emission are fast UV flares that appear to arise from near the central object -- not from the bright spot.

Horne, Keith↗
NASA NTRS1994

The HST quasar absorption line key project. 9: An emission-line study of PG 2251+113

We present Hubble Space Telescope (HST) and quasi-simultaneous ground-based observations of the z = 0.3252 QSO PG 2251+113. We find a correlation between line widths and the critical density for de-excitation of the forbidden emission lines observed in this object. We can show that this correlation also applies to the semiforbidden and possibly also the permitted lines which arise in the broad emission-line region. While this result was predicted from statistical studies, it has never previously been shown to hold in detail in any individual object. This relationship between the narrow and broad emission-line regions may help constrain dynamical models of both regions. We examine the implications of this result for a simple radial infall model of the emitting gas developed to explain the origin of narrow-line profiles.

Espey, Brian R.↗
NASA NTRS1994

HST images of nearby luminous quasars

Strong upper limits are placed on the visual-band brightness of galactic hosts for four luminous, radioquiet quasars with redshifts between 0.16 and 0.24 that were studied with the Hubble Space Telescope (HST's) Wide Field/Planetary Camera 2 (WFPC2). Typical upper limits on the luminosities of galactic hosts are approximately 1.4 mag fainter than L* for spirals and approximately 0.5 mag fainter than L* for ellipticals. The galactic hosts of the quasars are more than a magnitude and a half fainter than the median integrated absolute magnitude of Seyfert galaxies. If the detection limits are determined using featureless simulated galaxies instead of observed galaxy images, then the detection limits for spirals are 0.5-1.0 mag less stringent. These results are consistent with the hypothesis that the quasar phenomenon corresponds to the early stages of galaxy formation, before extensive star formation occurs.

Bahcall, John N.↗
NASA NTRS1994

Narrowband HST images of M87: Evidence for a disk of ionized gas around a massive black hole

We present Hubble Space Telescope Wide Field/Planetary Camera-2 (HST WFPC2) narrowband H-alpha + (N II) images of M87 which show a small disk of ionized gas with apparent spiral structure surrounding the nucleus of M87. The jet projects approximately 19.5 deg from the minor axis of the disk, which suggests that the jet is approximately normal to the disk. In a companion Letter, Harms et al. measure the radial velocities at r = +/- 0.25 sec along a line perpendicular to the jet, showing that one side of the disk is approaching at 500 +/- 50 km/s and the other side of the disk is receding at 500 +/- 50 km/s. Absorption associated with the disk and the sense of rotation imply that the apparent spiral arms trail the rotation. The observed radial velocites corrected for a 42 deg inclination of the disk imply rotation at +/- 750 km/s. Analysis of velocity measurements at four positions near the nucleus gives a total mass of approximately 2.4 +/- 0.7 x 10(exp 9) solar mass within 18 pc of the nucleus, and a mass-to-light ratio (M/L)(sub I) = 170. We conclude that there is a disk of ionized gas feeding a massive black hole in the center of M87.

Ford, Holland C.↗
NASA NTRS1994

HST FOS spectroscopy of M87: Evidence for a disk of ionized gas around a massive black hole

Using the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST) to observe the central region of M87, we have obtained spectra covering approximately 4600-6800 A at a spectral dispersion approximately 4.4 A per resolution element through the .26 sec diameter entrance aperture. One spectrum was obtained centered on the nucleus of M87 and two centered 0.25 sec off the nucleus at position angles of 21 deg and 201 deg, thus sampling the anticipated major axis of the disklike structure (described in a companion Letter) expected to lie approximately perpendicular to the axis of the M87 jet. Pointing errors for these observations are estimated to be less than 0.02 sec. Radial velocities of the ionized gas in the two positions 0.25 sec on either side of the nucleus are measured to be approx. equals +/- 500 km/s relative to the M87 systemic velocity. These observations plus emission-line spectra obtained at two additional locations near the nucleus show the ionized gas to be in Keplerian rotation about a mass M = (2.4 +/- 0.7) x 10(exp 9) solar mass within the inner 0.25 sec of M87. Our results provide strong evidence for the presence of a supermassive nuclear black hole in M87.

Harms, Richard J.↗