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NASA NTRS1984

Infrared observations of galactic bulge X-ray sources

Nine unidentified galactic bulge X-ray sources, the recently identified X-ray burster MXB 1728-34, and two optically identified sources (Sco X-1 and MXB 1735-44) were observed with the NASA 3 m Infrared Telescope Facility. The data constrain both the presence of diffuse infrared sources near the X-ray positions and the flux of possible infrared counterparts. None of the nine unidentified sources lies within obscured globular clusters, although there is marginal evidence for diffuse infrared emission near 4U 1822-00 and 4U 1916-05. This implies that at most two additional luminous galactic bulge X-ray sources lie within undiscovered, obscured globular clusters. No infrared counterparts were detected for unidentified sources; the limits derived are consistent with all of the sources observed being similar to the low mass X-ray binary Sco X-1.

Hertz, P.↗
NASA NTRS1984

Inflow of halo gas from the direction of the Galactic north pole

A far-UV echelle spectrum has been obtained of the UV-bright star vZ1128 in the globular cluster M3. This cluster lies in a direction 11 deg off the Galactic north pole at a distance of about 10 kpc. Only the usually strong interstellar lines are recognizable in the faint spectrum, and they show absorption at velocities from near +40 km/s to -100 km/s. Since in the direction observed the line-of-sight component of the Milky Way rotation is negligible, the detected velocities demonstrate for this direction the motion of gas from the Milky Way halo toward the disk. Gas returning to the disk in a galactic fountainlike flow may explain the observations.

De Boer, K. S.↗
NASA NTRS1985

The 8.3 and 12.4 micron imaging of the Galactic Center source complex with the Goddard infrared array camera

A 30 x 30 arcsec field at the Galactic Center (1.5 x 1.5 parsec) was mapped at 8.3 microns and 12.41 microns with high spatial resolution and accurate relative astrometry, using the 16 x 16 Si:Bi accumulation mode charge injection device Goddard infrared array camera. The design and performance of the array camera detector electronics system and image data processing techniques are discussed. Color temperature and dust opacity distributions derived from the spatially accurate images indicate that the compact infrared sources and the large scale ridge structure are bounded by warmer, more diffuse material. None of the objects appear to be heated appreciably by internal luminosity sources. These results are consistent with the model proposing that the complex is heated externally by a strong luminosity source at the Galactic Center, which dominates the energetics of the inner few parsecs of the galaxy.

Gezari, D. Y.↗
NASA NTRS1985

On galactic origin of cosmic rays with energy up to 10(19) eV

The experimental data on ultrahigh energy cosmic ray anisotropy are considered. In supposed models of galactic magnetic field the main characteristics of expected anisotropy are estimated and are compared with the experimental data. It is shown that particles with energy up to 10 to the 19th power eV are of galactic origin.

Efimov, N. N.↗
NASA NTRS1985

the role of shock waves in modulation of galactic cosmic rays

The understanding of modulation of the galactic cosmic rays has considerably progressed by the exploration by space probes of major heliospheric structures, such as the Corotating Interaction Regions, the neutral sheet, and the compression regions of intense heliospheric magnetic fields. Also relevant in this context were the detections in the outer heliosphere of long lasting Forbush type decreases of cosmic ray intensity. The results of recent theoretical studies on the changes in intensity and energy, at different location from the Sun, induced by the passage of shocks across the heliosphere are presented. In this version of the research, the simplest cases of modulation of uGV and 2GV particles by single or several shocks during periods of positive and negative solar field polarity are reviewed. The results of the theoretical aspects of the search is reported. The comparison of the theoretical predictions with space probe data allows conclusions to be drawn on the role of shocks on the modulation on both the 11 and 22 year galactic cosmic ray cycles in the outer heliosphere and on the plausibility of the models and parameters used.

Gall, R.↗
NASA NTRS1985

Influence of the source distribution on the age distribution of galactic cosmic rays

The age distribution of galactic cosmic rays in the diffusion approximation is calculated. The influence of the scale height of the spatial source distribution on the mean age of particles arriving at the solar system is discussed. The broader the source distribution with respect to the galactic plane, the longer the mean age. This result provides a natural explanation for the shorter mean age of secondary cosmic rays compared to primary cosmic rays necessary for the understanding of the observed secondary/primary ratio.

Lerche, I.↗
NASA NTRS1985

RR Lyrae stars and the distant Galactic halo - Distribution, chemical composition, kinematics, and dynamics

Published observational data on 29 outer-Galactic-halo RR Lyr stars (Saha, 1984, and Saha and Oke, 1984) and from other surveys are analyzed to characterize the mass distribution, chemical composition, kinematics, and dynamics of the outer Galaxy (up to galactocentric radius R = 40 kpc). The results are presented in graphs and tables and discussed. Findings reported include a rapid fall-off of RR Lyr density at R = 25 kpc, Fe/H varying from -1.0 to -2.2 (with two stars at -0.5), no net Fe/H gradient in the far halo, and Galactic mass (from dynamical computations) about 3 x 10 to the 11th solar mass within R = 25 kpc.

Saha, A.↗
NASA NTRS1984

Ultraviolet studies of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330 and the Galactic cluster NGC 6530

High-resolution and low-resolution IUE spectra of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330, and the young Galactic cluster NGC 6530 are investigated. Temperatures and luminosities are determined. In the LMC and SMC clusters, the most luminous stars are evolved stars on the horizontal supergiant branch, while in NGC 6530 the stars are all still on the main sequence. Extinction laws were determined. They confirm the known differences between LMC and Galactic extinctions. No mass loss was detected for the evolved B stars in the LMC and SMC clusters, while the high-luminosity stars in NGC 6530 show P Cygni profiles.

Boehm-Vitense, E.↗
NASA NTRS1983

Effects of line width and spatial extent on measurements of the 0.51 MeV Galactic center line

Over the past 15 years, a number of measurements have been made of positron-electron annihilation radiation from the Galactic Center region. The results after 1979 show a significant decrease in measured flux intensity from that previously observed with the same instruments. This is probably due to time variations; however, the contributions of a spatially extended and/or energy-broadened component should also be considered. The entire data set is consistent with a time variable point source plus a distribution along the Galactic Disk. There is no strong evidence for a component broadened in energy.

Dunphy, P. P.↗
NASA NTRS1983

An electron-positron jet model for the Galactic center

High energy observations of the galactic center on the subparsec scale seem to be consistent with electron-positron production in the form of relativistic jets. These jets could be produced by an approximately 1,000,000 solar mass black hole dynamo transporting pairs away from the massive core. An electomagnetic cascade shower would develop first from ambient soft protons and then nonlinearly, the shower using itself as a scattering medium. This is suited to producing, cooling and transporting pairs to the observed annihilation region. It is possible the center of our galaxy is a miniature version of more powerful active galactic nuclei that exhibit jet activity.

Burns, M. L.↗
NASA NTRS1985

Optical emission-line properties of evolved galactic supernova remnants

New optical spectrophotometric data are presented for the supernova remnants CTB 1, OA 184, VRO 42.05.01, S147, the Monoceros Loop, G206.9 + 2.3, and G65.3 + 5.7. These data are combined with published spectral data to study some of the general properties of evolved galactic supernova remnants. It is found that (1) O I and O II forbidden line strengths, when used in conjunction with the usual H-alpha S II forbidden line ratio test, provide an excellent additional diagnostic for discriminating remnants from H II regions; (2) the line ratios H-alpha forbidden line N II, H-alpha forbidden line S II, and forbidden line S II 6717/6731 A generally do not vary substantially among the filaments of an individual remnant; and (3) the observed correlation of forbidden line N II/H-alpha with S II forbidden line 6717/6731 A in remnants is the result of observational selection rather than of evolutionary effects. A galactic nitrogen abundance gradient of d log (N/H)/dR = -0.088 dex/kpc, which is in agreement with that derived from H II regions. However, no abundance gradients for oxygen or sulfur are indicated from the remnant data.

Fesen, R. A.↗
NASA NTRS1985

Radio and infrared observations of OH/IR stars at the tangential point and near the galactic center

Unambiguous infrared identifications of a sample of OH/IR stars in the galactic disk and in the vicinity of the galactic center are presented. Simultaneous OH and broadband infrared photometric measurements are used to derive quantitative relations between the infrared and OH fluxes and the properties of the circumstellar shells, providing observational evidence that these stars represent an evolutionary sequence of increasing mass loss rate. These relations are used to explain the observed time variations of the silicate absorption feature with changing bolometric luminosity in OH/IR stars. It appears that the ratio of the OH flux to the number of pump photons is not constant, but is also a function of the mass loss rate.

Baud, B.↗
NASA NTRS1985

Ultraviolet absorption by highly ionized halo gas near the Galactic center

Initial results are presented for a program to survey highly ionized gas in the Milky Way disk and halo. High-resolution IUE (International Ultraviolet Explorer) far-UV spectra were obtained for 12 stars at galactocentric distances less than 6 kpc. The stars are 0.7-2.2 kpc away from the plane. Most of the spectra contain exceedingly strong and broad interstellar absorption lines of weakly and highly ionized atoms. In addition to the normally strong lines of Si IV and C IV, strong interstellar NV lines have been detected in the spectra of eight stars. The detection of NV absorption (amounting to more than 10 times the predicted NV) provides an important new constraint on models for the origin of Galactic halo gas. A Galactic fountain operating in the presence of known UV and EUV radiation might explain the observations.

Savage, B. D.↗
NASA NTRS1985

Galactic bulge X-ray burst sources from disrupted globular clusters?

The origin of the bright galactic bulge X-ray sources, or GX sources, is unclear despite intensive study for the past 15 years. It is suggested that the fact that many (or most) of the GX sources are X-ray burst sources (GXRBS) and are otherwise apparently identical to the luminous X-ray sources found in globular cluster cores implies that they too may have a globular cluster origin. The possibility that the compact X-ray binaries found in globulars are ejected is constrained by observations of CVs in and out of clusters. The GXRBS are instead hypothesized to have been formed by capture processes in globular clusters which have now largely been disrupted by repeated tidal stripping and shocking in the galactic plane. A statistical analysis of the 12 GXRBS which have precise positions from Einstein and/or optical (or radio) observations indicate that it is probably significant that a bright, of less than about 19, G or K star is found within the error circle (3 arcmin radius) in four cases. These may be surviving giants in a disrupted globular cluster core. Implications for globular cluster evolution and the GXRBS themselves are discussed.

Grindlay, J. E.↗
NASA NTRS1985

Estimated number of field stars toward Galactic globular clusters and Local Group Galaxies

Field star densities are estimated for 89 fields with /b/ greater than 10 degrees based on the Galaxy model of Bahcall and Soneira (1980, 1984; Bahcall et al. 1985). Calculated tables are presented for 76 of the fields toward Galactic globular clusters, and 16 Local Group Galaxies in 13 fields. The estimates can be used as an initial guide for planning both ground-based and Space Telescope observations of globular clusters at intermediate-to-high Galactic latitudes.

Ratnatunga, K. U.↗
NASA NTRS1986

Electromagnetic dissociation effects in galactic heavy-ion fragmentation

Methods for calculating cross sections for the breakup of galactic heavy ions by the Coulomb fields of the interacting nuclei are presented. By using the Weizsacker-Williams method of virtual quanta, estimates of electromagnetic dissociation cross sections for a variety of reactions applicable to galactic cosmic ray shielding studies are presented and compared with other predictions and with available experimental data.

Norbury, J. W.↗
NASA NTRS1986

Using the IRAS data to search in the asteroid belt for any potential evidence of galactic colonization

The end product of the biological evolution seems to be the appearance of technological civilizations, which are characterized by superior technology that supercedes biological capabilities. The Search for Extraterrestrial Intelligence (SETI) has gained scientific recognition in recent years. The concept of galactic colonization is debated extensively, with opinions ranging from the impossible to the inevitable, but without a clear resolution. Answers can be obtained only with experimental tests and not with endless debates. A search for large space colonies in the asteroid belt, an ideal source of raw materials for a spaceborne civilization, is a test of the galactic colonization theory. The catalogue of solar system objects obtained form the Infrared Astronomy Satellite (IRAS) observations at 12, 25, 60, and 100 microns, is an ideal source for such a search. The catalog is expected to be ready at the end of 1985 and will contain more than 10,000 objects.

Papagiannis, M. D.↗
NASA NTRS1986

Galactic cosmic ray composition

An assessment is given of the galactic cosmic ray source (GCRS) elemental composition and its correlation with first ionization potential. The isotopic composition of heavy nuclei; spallation cross sections; energy spectra of primary nuclei; electrons; positrons; local galactic reference abundances; comparison of solar energetic particles and solar coronal compositions; the hydrogen; lead; nitrogen; helium; and germanium deficiency problems; and the excess of elements are among the topics covered.

Meyer, J. P.↗