Ramon D. Wolstencroft

The enhancement of infrared emission in interacting galaxies

Selected infrared properties, based on IRAS observations, of two categories of interacting galaxy pairs from the Arp-Madore Catalogue of Southern Peculiar Galaxies and Associations are examined. For pairs of comparably sized galaxies, a strong tendency exists for pairs with the highest far-IR color temperatures to have the smallest separation. This finding implies that galaxy interactions significantly enhance the intensity or the efficiency of star formation. No trend of far-IR color temperature varying with pair separation is found for pairs consisting of a galaxy with a small companion. There are 10 times as many pairs in the sample that contain one IRAS far-IR galaxy as there are pairs for which both galaxies were detected by IRAS, thus strengthening previous conclusions that the effect of a perturbation depends strongly on the detailed geometry of the interaction. 29 references.

Zeeman Effect in the X-Ray Star Candidates HD 77581 and θ^2 Orionis

The discovery of Zeeman effects is reported in HD 77581 and THETA 2 Orionis, optical candidates for the X-ray sources Vela XR-l and 2U 0525-06, respectively. The maximum longitudinal magnetic fields recorded were -10,000 gauss in HD 77581 and + 1500 gauss in THETA 2 0ri. Various polarimetric data are also given, including evidence for a variable linear polarization in HD 77581.

Fluctuating magnetic fields in HD 153919

Circular polarization in H BETA has been observed in HD 153919. It varies over time scales as short as 10 minutes, but shows generally smaller average values over periods of 1 to 3 hours. The fluctuations are largest on the peak and trailing portions of the X-ray amplitude. Assignment of the magnetic- field strengths is in doubt because of complexities in the spectrum; present evidence is that only the underlying absorption in the Balmer lines, and presumably in the He II lines, shows Zeeman effects, the emission components being formed in regions of vanishing effective fields. Subject headings: magnetic fields polarization--X-ray sources--Zeeman effect. (auth)

Study of OB-Stars in the Large Magellanic Cloud by UBV Photometry

Preliminary results of a survey of OB stars in a region of approximately 0.75 square degrees centered on R.A. (1950) 5h 40m, Dec. (1950) --70 deg in the Large Magellanic Cloud are described. The UBV plates taken with the Curtis Schmidt telescope at Cerro Tololo were measured by GALAXY to a limiting magnitude V= 17.0m. By measuring all the stars in a small area of the plate and by studying the (U-B, B--V) diagram for each magnitude interval, it is shown that the OB stars in the LMC can be identified. Two-color and color-magnitude diagrams, and surface distribution of probable early type members in this region of the LMC are presented. Within the errors of observation no significant reddening has been detected. (auth)