Engineering topics

Garcia, M. R.

Publications and source records attributed to Garcia, M. R..

9 records

NASA NTRS1997

Using the Tycho catalogue for AXAF: Guiding and aspect reconstruction for half-arcsecond X-ray images

The Advanced X-ray Astrophysics Facility (AXAF) will carry a high resolution mirror, two imaging detectors, and two sets of transmission gratings. The Tycho catalog from the Hipparcos mission will serve as a primary part of the AXAF Guide and Aspect Star Catalog (AGASC). The incorporation of Tycho into AGASC will provide: accurate positions and magnitudes for target acquisition and guidance; the necessary colors for magnitude transformations to the AXAF aspect camera system; high internal astrometric accuracy for half-arcsecond, post-facto image reconstruction; and an external astrometric system.

Green, P. J.↗

NASA NTRS1992

X-rays from the eclipsing pulsar 1957+20

The detection of soft X-rays of about 1 keV energy from the eclipsing pulsar PSR1957+20 is reported. This high-energy radiation should be a valuable diagnostic of the wind in this recycled pulsar system. Possible sources of the X-ray emission are the interstellar nebula driven by the pulsar wind, the interaction between the pulsar and its evaporating companion, and the pulsar itself. The small apparent size of the X-ray object argues against the first of these possibilities and suggests that the X-rays are produced within the binary.

Fruchter, A. S.↗

NASA NTRS1992

The infrared counterpart of GX 13 + 1

A bright (K = 12) IR source is discovered which is likely the counterpart to the bright galactic-bulge X-ray source GX 13 + 1. Observations with the MMT IR photometer and the Rochester IR Array camera at the IRTF allow determination of the source position to about 0.7 arcsec, allow the IR colors to be measured, and show no variability on a 1-yr timescale. Four possible sources for the IR emission are considered and it is most likely due to a K-giant secondary. The discovery of a late-type giant secondary in GX 13 + 1 is contrary to the expectation that low-mass X-ray binaries which show quasi-periodic oscillations (QPO) have giant companions, while those which do not show QPO (like GX 13 + 1) have dwarf secondaries. The relation between the size of the scattered X-ray halo and the Av inferred from the IR observations is compared to that found in other X-ray sources.

Garcia, M. R.↗

NASA NTRS1990

Observations of Cygnus X-2 with IUE - Ultraviolet results from a multiwavelength campaign

IUE observations of Cyg X-2 obtained during June and October 1988 are reported and analyzed, with reference to data from simultaneous X-ray and radio observations and the predictions of theoretical models. The results are presented in extensive tables and graphs and characterized in detail. The UV flux is shown to increase monotonically as the X-ray emission moves along the Z-shaped trajectory from the horizontal to the flaring branch and the estimated mass accretion rate increases from about 6 x 10 to the -9th to 1.6 x 10 to the -8th solar mass/yr. Model calculations indicate that X-ray illumination of the accretion disk accounts for at least 80 percent of the observed UV emission, with 20 percent or less from the X-ray-heated surface of the companion star and less than 1 percent from the cool surface.

Vrtilek, S. D.↗

NASA NTRS1989

Observations of Cygnus X-2 with IUE: Ultraviolet results from a multiwavelength campaign

The observations of the low-mass x ray binary, Cyg X-2, taken with the International Ultraviolet Explorer (IUE) in a campaign conducted in June and October of 1988 are reported. A direct relationship between the strength of the UV continuum and line emission and the placement of the x ray spectrum in one of three branches of the so-called Z-shaped curve is found by comparison with simultaneous x ray observations. All three previously known x ray spectral states are detected; the UV continuum and line emission increase monotonically along the Z with the least emission in the horizontal branch, and the most in the flaring branch. Emission lines due to HeII, CIV, NIII, NIV, NV, SiIV, and MgII are observed.

Vrtilek, S. D.↗

NASA NTRS1988

Simultaneous X-ray and radio observations of GX 13 + 1

The results of simultaneous X-ray and radio observations of GX 13 + 1, intrinsically one of the brightest Galactic bulge X-ray sources, are presented and possible models are discussed. No evidence is found for correlated X-ray and radio flux density variations. The variation of the 6-20 cm wavelength spectral index from +0.5 to -1.0 indicates that the radio flux is probably produced by a nonthermal emission mechanism. Application of an equipartition synchrotron model to the data suggests that the radio emission originates in a region with a magnetic field of about 1 gauss. If the radio flux density variations are due to injection of relativistic electrons, the equivalent nonthermal particle energy is 10 to the 36th - 10 to the 41st ergs/s.

Garcia, M. R.↗

NASA NTRS1986

Spectroscopic orbits of symbiotic stars - Preliminary results

The present search for radial velocity variations due to orbital motions in symbiotic stars involved observations of 17 such stars at approximately 1-month intervals, as well as of radial velocity variations in the M-giant primary in nine stars. The observed radial velocity curves are commensurate with those expected from a group of binaries having random sin i and about 20 km/sec orbital velocities. Four of the orbital periods thus suggested for seven stars confirm previously known photometric periods, while one confirms a previously known orbital period and two are completely new. Knowledge of the orbits allows identification of those symbiotics that are close to filling their Roche lobes.

Garcia, M. R.↗

NASA NTRS1986

Development of the EXITE detector - A new imaging detector for 20 - 300 keV astronomy

The development and testing of a detector to be used in the Energetic X-ray Imaging Telescope Experiment (EXITE) are reported. It consists of a 34 cm diameter NaI(Tl) crystal coupled directly to a single large image intensifier tube with associated silicon PIN diode readout. The measured spatial and energy resolutions at 122 keV are 6mm (FWHM) and 9 percent (FWHM), respectively. This energy resolution is about 50 percent better than that of any previously flown hard X-ray experiment. These resolutions decrease with the square root of the energy of the incident X-ray, indicating that they are determined by the number of photons emitted in the NaI(Tl) scintillator light flash.

Garcia, M. R.↗

NASA NTRS1986

The energetic X-ray imaging telescope experiment (EXITE)

A new position-sensitive scintillation detector (NaI(Tl)), coded mask, and precision pointing system (resolution less than 1 arcmin) are being developed for balloon-borne imaging and spectral studies of cosmic X-ray sources in the 20-300 keV band. The scientific objectives of EXITE, as well as the general design of the detector, telescope and balloon gondola systems are presented.

Grindlay, J. E.↗