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Bernacca, P. L.

Publications and source records attributed to Bernacca, P. L..

8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

The FAST Hipparcos data reduction consortium - Overview of the reduction software

The main features of the data analysis methods adopted by FAST in the calibration and processing of the Hipparcos data are discussed. The structure of the data reduction software is examined, and the actual processing and evaluation are presented. Attention is given to the first look task, the calibration task, data preparation, attitude determination, the great circle reduction, synthesis treatment, iterations, data management and command software, and follow-up and evaluation activities.

Kovalevsky, J.↗
NASA NTRS1979

Optical observations of X-ray bursts from MXB 1837 + 05

Optical observations of the X-ray burst source MXB 1837 + 05 (Ser X-1) made at different observatories are discussed. Six X-ray bursts were detected with SAS-3 X-ray Observatory during these observations, but no simultaneous optical signals were seen during or after any of these bursts. For an assumed burst duration of 10 sec, the 3-sigma upper limits of the ratio of the detected energy in an optical burst to that in an X-ray burst range from 3 x 10 to the minus fifth to 6 x 10 to the minus fifth.

Bernacca, P. L.↗
NASA NTRS1976

Periodic flickering in the optical spectrum of HZ Herculis

Photometric observations of HZ Herculis in the ultraviolet with a time resolution of 5 seconds are discussed. The existence of periodic flickering with a time scale of 115 to 130 seconds is observed. The amplitude modulation is about 3 to 6 percent, larger than that associated with the erratic white flickering. The flickering, either erratic or periodic, occurs, but not always, near orbital phase 0.5, irrespective of the on and off parts of the X-ray cycle.

Bernacca, P. L.↗
NASA NTRS1972

A search for He-weak stars in very young clusters.

Spectral classification has been carried out for B-type stars in Ori OBl Ib, NGC 2362, IC 5146 and NGC 2264. Six stars with weak helium lines for their UBV colors were found in Ori OBl Ib, one in NGC 2362 which might be helium variable, and none in IC 5146. The star Walker No 109 (B6V) in NGC 2264 is a helium variable which has developed an outstanding absorption feature between 4144 and 4156 A.

Bernacca, P. L.↗
NASA NTRS1972

Ultraviolet observations of weak-helium stars

Ultraviolet filter photometry aboard OAO-2 has been carried out for the weak helium stars 3 Cen A, 3 Sco, HD 144334, HD 21699, HD 144844, alpha Scl, HR 8535, HR 8770 and HD 144661. The flux distribution is compared with that of B3 to B8 main sequence and giant stars in terms of color-color diagrams. When allowance is made for line blocking shortward of 2800 A that most of the weak helium stars have normal fluxes in good agreement with their ground-based colors. The star alpha Scl is a light and spectrum variable. The strengthening of Ti II and Sr II lines around 2400 A appears to redistribute flux longward of the Balmer discontinuity. The flux distribution indicates an effective temperature about 1500 K higher than previously determined.

Bernacca, P. L.↗
NASA NTRS1971

Statistical studies in stellar rotation 2: A method of analyzing rotational coupling in double stars and an introduction to its applications

The correlation between the equatorial velocities of the components of double stars is studied from a statistical standpoint. A theory of rotational correlation is developed and discussed with regard to its applicability to existing observations. The theory is then applied to a sample of visual binaries which are the least studied for rotational coupling. Consideration of eclipsing systems and spectroscopic binaries is limited to show how the degrees of freedom in the spin parallelism problem can be reduced. The analysis lends support to the existence of synchronism in closely spaced binaries.

Bernacca, P. L.↗