Measures of double stars (1924-1926)

Digiteeritud Euroopa Regionaalarengu Fondi rahastusel, projekti "Eesti teadus- ja õppekirjandus" (2014-2020.12.03.21-0848) raames.https://www.ester.ee/record=b2141046*es

The Futile Search for Galactic Disk Dark Matter

Several approaches have been used to search for dark matter in our galactic disk, but with mixed results: {\em maybe yes and maybe no}. The prevailing approach, integrating the Poisson-Boltzmann equation for tracer stars, has led to more definitive results: {\em yes and no}. The touchstone {\em yes} analysis of Bahcall et al. (1992) has subsequently been confirmed or refuted by various other investigators. This has been our motivation for approaching the search from a different direction: applying the Virial Theorem to extant data. We conclude that the vertical density profile of the disk is not in a state of equilbrium and, therefore, that the Poisson-Boltzmann approach is inappropriate and it thereby leads to indefensible conclusions.Comment: Accepted for publication in ApJ Letter

Krooniline mukokutaanne kandidiaas

Krooniline mukokutaanne kandidiaas on harva esinev haiguste rühm, mis kliiniliselt väljendub kroonilises või sageli korduvas Candida albicans’i põhjustatud naha, küünte ja/või limas kestade infektsioonis. Kaasuda võivad erinevad endokrinopaatiad ja autoimmuunsed kahjustused. Artiklis on kirjeldatud 3aastase tütarlapse haigusjuhtu, kellel esineb krooniline kandidiaas alates 2. elukuust. Eesti Arst 2006; 85 (4): 345–34

Stellar Evolution Constraints on the Triple-Alpha Reaction Rate

We investigate the quantitative constraint on the triple-alpha reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8 < M / Msun < 25 and in the metallicity range between Z = 0 and Z = 0.02. The revised rate has a significant impact on the evolution of low- and intermediate-mass stars, while its influence on the evolution of massive stars (M >~ 10 Msun) is minimal. We find that employing the revised rate suppresses helium shell flashes on AGB phase for stars in the initial mass range 0.8 < M / Msun < 6, which is contradictory to what is observed. The absence of helium shell flashes is due to the weak temperature dependence of the revised triple-alpha reaction cross section at the temperature involved. In our models, it is suggested that the temperature dependence of the cross section should have at least nu > 10 at T = 1 - 1.2 x 10^8 K where the cross section is proportional to T^{nu}. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than ~ 10^{-29} cm^6 s^{-1} mole^{-2} at ~ 10^{7.8} K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation. In an effort to compromise with the revised rates, we calculate and analyze models with enhanced CNO cycle reaction rates to increase the maximum luminosity of the first giant branch. However, it is impossible to reach the typical RGB tip luminosity even if all the reaction rates related to CNO cycles are enhanced by more than ten orders of magnitude.Comment: 14 pages, 8 figures, accepted by the Ap

The Frequency Distribution of Semi-major Axis of Wide Binaries. Cosmogony and Dynamical Evolution

The frequency distribution f(a) of semi-major axis of double and multiple systems, as well as their eccentricities and mass ratios, contain valuable fossil information about the process of star formation and the dynamical history of the systems. In order to advance in the understanding of these questions, we have made an extensive analysis of the frequency distribution f (a) for wide binaries (a>25 AU) in the various published catalogues, as well as in our own (Poveda et al., 1994; Allen et al., 2000; Poveda & Hernandez, 2003). Based upon all these studies we have established that the frequency f(a) is function of the age of the system and follows Oepik's distribution f(a) ~ 1/a in the range of 100 AU < a < a[c](t), where a[c](t) is a critical semi-major axis beyond which binaries have dissociated by encounters with massive objects. We argue that the physics behind the distribution f(a) ~ 1/a is a process of energy relaxation, analogous to that present in stellar clusters (secular relaxation) or in spherical galaxies (violent relaxation). The frequency distribution of mass ratios in triple systems as well as the existence of runaway stars, indicate that both types of relaxation are important in the process of binary and multiple star formation.Comment: International Astronomical Union. Symposium no. 240, held 22-25 August, 2006 in Prague, Czech Republi

Efficiency of a wide-area survey in achieving short- and long-term warning for small impactors

We consider a network of telescopes capable of scanning all the observable sky each night and targeting Near-Earth objects (NEOs) in the size range of the Tunguska-like asteroids, from 160 m down to 10 m. We measure the performance of this telescope network in terms of the time needed to discover at least 50% of the impactors in the considered population with a warning time large enough to undertake proper mitigation actions. The warning times are described by a trimodal distribution and the telescope network has a 50% probability of discovering an impactor of the Tunguska class with at least one week of advance already in the first 10 yr of operations of the survey. These results suggest that the studied survey would be a significant addition to the current NEO discovery efforts

Kriminalistikaline taktika ja tehnoloogia I osa

Sisekaitseakadeemia e-väljaannehttp://tartu.ester.ee/record=b2512090~S1*es

Über einige Karbonatgesteine im Glazialgeschiebe NW-Estlands

Digiteeritud Euroopa Regionaalarengu Fondi rahastusel, projekti "Eesti teadus- ja õppekirjandus" (2014-2020.12.03.21-0848) raames.https://www.ester.ee/record=b2332419*es

Dust and Gas as Seeds for Metal-Poor Star Formation

I address the issue of dust and gas as seeds for metal-poor star formation by reviewing what we know about star formation in nearby dwarf galaxies and its relationship to the gas and dust. I (try to) speculate on the extent to which processes in nearby galaxies mimic star formation in the early universe.Comment: To be published in "Low Metallicity Star Formation: From the First Stars to Dwarf Galaxies," Proceedings of IAU Symposium No. 255, eds. L.K. Hunt, S. Madden, & R. Schneider (Cambridge: Cambridge Univ Press