Cosmogenic nuclides in the Košice meteorite: Experimental investigations and Monte Carlo simulations

Results of nondestructive gamma‐ray analyses of cosmogenic radionuclides (⁷Be, ²²Na, ²⁶Al, ⁴⁶Sc, ⁴⁸V, ⁵⁴Mn, ⁵⁶Co, ⁵⁷Co, ⁵⁸Co, and ⁶⁰Co) in 19 fragments of the Ko?ice meteorite are presented and discussed. The activities varied mainly with position of fragments in the meteoroid body, and with fluxes of cosmic‐ray particles in the space affecting radionuclides with different half‐lives. Monte Carlo simulations of the production rates of ⁶⁰Co and ²⁶Al compared with experimental data indicate that the pre‐atmospheric radius of the meteoroid was 50 ± 5 cm. In two Ko?ice fragments, He, Ne, and Ar concentrations and isotopic compositions were also analyzed. The noble‐gas cosmic‐ray exposure age of the Ko?ice meteorite is 5–7 Myr, consistent with the conspicuous peak (or doublet peak) in the exposure age histogram of H chondrites. One sample likely contains traces of implanted solar wind Ne, suggesting that Ko?ice is a regolith breccia. The agreement between the simulated and observed ²⁶Al activities indicate that the meteoroid was mostly irradiated by a long‐term average flux of galactic cosmic rays of 4.8 particles cm^?2 s^?1, whereas the short‐lived radionuclide activities are more consistent with a flux of 7.0 protons cm^?2 s^?1 as a result of the low solar modulation of the galactic cosmic rays during the last few years before the meteorite fall.     

New CCD photometric investigation of the early-type overcontact binary BH Cen in the young star-forming Galactic cluster IC 2944

BH Cen is a short-period early-type binary with a period of 0.792 din the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A_3 = 0.024 d and a period of P_3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M_2 = 2.8×10~(-6) M_⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M_⊙at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.     

Prediction of deuterium abundance in comets

Using a chemical scheme based on ion-molecule reactions in cool interstellar clouds, the possibility of a deuterium enrichment of volatile material in comets is discussed. It is assumed that the hydrogen-containing molecules are deuterated before accretion and condensation on the coremantle dust particles from which the cometesimals are formed. The D/H ratio in comets may be enhanced in respect to the average value by a factor of 10². Therefore comets are not promising objects for testing the primordial deuterium abundance.     

Protosolar nebula and composition of comets

Comets seem to be composed of matter, which is supposed to have the same molecular composition as protosolar nebula. Although there are no unbiased evidence that cometary nuclei retain the molecular composition inherited from the protosolar cloud, the observed properties of comets indicate that there is at least a resemblance between cometary composition and the material properties of dense interstellar clouds. Therefore the origin of comets could be searched in the cold stages of the protosolar nebula and molecular abundances of grain mantles in this nebula may be similar to those in the cometary dust. It is suggested that comets may contain pristine, virtually unaltered protosolar material and their study might be very relevant way to more information about processes in early stages of the solar nebula. Our knowledge about composition of the cometary nucleus is still relatively scarce, but we can partly deduce it from data obtained either by ground-based spectroscopy or by in situ mass spectrometry from space experiments. Most important were the discovery of fluffy CHON particles composed partly or even completely from compounds containing light elements. No consensus concerning the presence of interstellar pristine matter in comet has been reached from various approaches to determine the relationship between comets and interstellar grains. Most of these studies are based on infrared spectroscopy. Another method is the comparison on the chemical models of the protosolar nebula with the volatile compounds of the cometary nuclei. Both gas-phase and grain-surface chemistry are considered and initial gas-phase atomic abundances are assumed to be protosolar. The cometary matter is certainly not identical with the typical material of dense interstellar cool dense clouds, but it is closer to it than any other type of matter in solar system so far accessible to us. The data from comets combined with models of chemical evolution of matter in environment similar as prevailed the early stage of presolar nebula may at least impose constrains on the condition for comet formation. Here presented study is a preliminary contribution to such studies.     

On Methods for the Light Curves Extrema Determination

We present two methods for the determination of moments of extrema and their errors appropriate for the analysis of light variations of variable objects. The method I is suitable for determination of times of extrema of non-periodical variables or objects, whose light curves vary. The method II is apt for O-C analyses of objects whose light curves are more or less repeating. Both methods are displayed on the analysis of BL Cam light variations and compared with the Kwee-van Woerden method.     

The basic cycle of solar activity and the global magnetic field and active phenomena distribution

We have compared the latitudinal distributions of polar faculae, green coronal emission maxima, prominences and of a new index of enhanced geomagnetic recurrence with the distribution of magnetic fields during the cycles Nos. 20 and 21.We did not find a distinct high-latitude initial stage of an extended cycle in the corona, prominences and polar faculae distribution. On the contrary, it seems that the polar faculae and their following polarity magnetic fields represent the last evolutionary phase of a magnetic activity cycle lasting 15–17 years. The enhanced recurrent geomagnetic activity seems to be related to the old cycle fields.All studied phenomena clearly display two types of latitudinal distribution: the polar belts, into which the old following polarity fields have been transported from the equatorial belt where both the polarities developin situ simultaneously, but in which the leading polarity fields only remain, crossing the equator during the minimum of activity, to play the same role on the opposite hemispheres in the new cycle.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.