Engineering topics

Kreidl, T. J.

Publications and source records attributed to Kreidl, T. J..

9 records

NASA NTRS1994

ROSAT observations of the black hole candidate V404 Cygni in quiescence

V404 Cyg was detected with the ROSAT PSPC in a 16 ks observation 1265 days after the 1989 May outburst. This is the first unambiguous detection of a soft X-ray transient or X-ray nova black hole candidate in quiescence. The observed X-ray spectrum is extremely soft and can be described equally well by either a blackbody, power-law, or a thermal bremsstrahlung continuum. The best-fit blackbody spectrum is characterized by a temperature of 0.2 keV. A significant amount of absorption, both along the line of sight and intrinsic to the V404 Cyg system, is required to understand the observations. The 0.2-2.4 keV light curve of V404 Cyg exhibits substantial variability on timescales of less than a day. Assuming a distance of 3.5 kpc, the quiescent X-ray luminosity of V404 Cyg is 8 x 10(exp 33) ergs/s, nearly two orders of magnitude larger than the upper such as Cen X-4. The lack of a significant hard X-ray luminosity in quiescence, the presence of a large and cold neutral region in the accretion disk, and a low-mass accretion rate suggests that an accretion disk instability might account for the outburst of V404 Cyg.

Wagner, R. Mark↗

NASA NTRS1992

Periodic photometric variability of the black hole binary V404 Cygni

Periodic variations of V404 Cyg having a period of 6.474 +/- 0.005 d with a full amplitude of 0.2 mag were discovered with CCD photometry, in the I band, of the compact star. The light curve consists of two maxima and two minima per cycle, and the shape suggests that it is due to ellipsoidal variations of the secondary star which is tidally distorted by the presence of the massive compact object. It is proposed that the secondary is a 1 solar mass K0 IV star with MV of about 2.5 mag at a distance of about 3.5 kpc. It is suggested that if the secondary star is nearly filling its Roche lobe, then the orbital inclination must be about 60 deg. If the inclination is as high as 80 deg, then the secondary star fills about 90 percent of the Roche lobe. These limits imply a compact star mass of 8-12 solar masses and thus strengthen the evidence that the compact star is extremely massive and possibly a black hole.

Wagner, R. M.↗

NASA NTRS1989

Disk-integrated photometry of Neptune at methane-band and continuum wavelengths

The present disk-integrated photometry of Neptune, which was obtained in 1986 and 1987, is used to study the diurnal and short-term variability; the fact that this photometry was obtained from high-resolution CCD images allows the discrete cloud features' causing of the rotational lightcurve seen at methane-band wavelengths to be definitively demonstrated. A quiescent state of the Neptune atmosphere is suggested by the planet's 8900 A reflectivity in the absence of bright clouds, appears to have remained nearly constant over the observational period.

Hammel, H. B.↗

NASA NTRS1989

The 1989 outburst of V404 Cygni: A very unusual x ray nova

On May 22, 1989, the Japanese Ginga Team discovered a new x ray source that was cataloged as GS 2023+338. This source was subsequently identified as coincident in position with a previously known nova cataloged as V404 Cygni. Its last recorded outburst was in 1938 when it rose to about 12th mag. Spectroscopic data were obtained and confirmed the nature of the outburst. Additional ground based data were obtained by us at CTIO and the VLA. The x ray behavior of this object was reported to be very unusual and it reached a peak of about 17 crab about one week after discovery. Since then it has varied widely in magnitude at all wavelengths at which it has been studied. A brief summary of the observations that were obtained up to the time of the meeting and shortly thereafter is presented.

Wagner, R. M.↗

NASA NTRS1988

US 943 - A 19th mag eclipsing cataclysmic variable with a period of 2 hr 3.8 min

The high-latitude, V equals about 19.5, blue variable star US 943 is found to be an eclipsing binary with an orbital period of 2.06 hr. The light curve is dominated by an orbital hump which has an amplitude of 0.9 mag in V and is centered about 0.17 orbital cycles before the 1.5-mag deep eclipse. There is evidence that the eclipse has at least two components. The overall appearance of the star is that of a dwarf nova in quiescence, a conclusion that is supported by the observation of a subsequent bright state (V equals about 15) suggesting a dwarf nova outburst.

Howell, S. B.↗

NASA NTRS1986

Planetary research at Lowell Observatory

Narrowband CCD profiles of C2 and grains in several comets (including P/Halley and P/Giacobini-Zinner) were performed. Rotational light curves were made of Comet P/Arend-Rigaux (visible and infrared) yielding the size, shape, albedo, and rotation period of the nucleus. Production rates were measured as a function of heliocentric distance for OH, CN, and C2 in P/Giacobini-Zinner and for OH, NH, CN, C3, and C2 in P/Halley. Detection and measurement was made of forbidden (O I) lines near 6300 and 5577 A in P/Halley, permitting the production rate of oxygen from CO to be distinguished from that from H2O. Identification of C-12C-13 lines in cometary spectra indicating a possible enrichment of C-13 over the telluric value was made. An assessment of techniques for detecting (determining the existence of) a trans-Neptunian comet belt is included.

Baum, W. A.↗

NASA NTRS1986

The size, shape, density, and albedo of Ceres from its occultation of BD+8 deg 471

The occultation of BD+8 degrees 471 by Ceres on 13 November 1984 was observed photoelectrically at 13 sites in Mexico, Florida, and the Caribbean. These observations indicate that Ceres is an oblate spheroid having an equatorial radius of 479.6 + or - 2.4 km and a polar radius of 453.4 + or - 4.5 km. The mean density of this minor planet is 2.7 gm/cubic cm + or - 5%, and its visual geometric albedo is 0.070. While the surface appears globally to be in hydrostatic equilibrium, firm evidence of real limb irregularities is seen in the data.

Millis, R. L.↗

NASA NTRS1984

Clouds above the Martin Limb: Viking observations

Whenever Viking Orbiter images included the limb of Mars, they recorded one or more layers of clouds above the limb. The height above the limb and the brightness (reflectivity) of these clouds were determined in a selected group of these images. Normalized individual brightness profiles of three separate traverses across the limb of each image are shown. The most notable finding is that some of these clouds can be very high. Many reach heights of over 60 km, and several are over 70 km above the limb. Statistically, the reflectivity of the clouds increases with phase angle. Reflectivity and height both appear to vary with season, but the selected images spanned only one Martian year, so the role of seasons cannot be isolated. Limb clouds in red-filter images tend to be brighter than violet-filter images, but both season and phase appear to be more dominant factors. Due to the limited sample available, the possible influences of latitude and longitude are less clear. The layering of these clouds ranges from a single layer to five or more layers. Reflectivity gradients range from smooth and gentle to steep and irregular.

Martin, L. J.↗

NASA NTRS1981

Subtleties in the flat-fielding of charge-coupled device /CCD/ images

Astronomical photometry with CCDs will often involve relatively low signal levels (less than 1000 charge carriers per pixel), at which nonlinear effects sometimes become significant. These effects will probably play a role in the processing of Space Telescope data. The problem apparently arises because signal charges are not read out equally completely from all columns and all pixels. It is shown that, although a first-order correction can be made by subtracting a low-level flat field from all frames before conventional processing, higher accuracy can be achieved by modeling the response with a nonlinear function.

Baum, W. A.↗