Optical Spectroscopy of the Surface Population of the rho Ophiuchi Molecular Cloud: The First Wave of Star Formation

We present the results of optical spectroscopy of 139 stars obtained with the Hydra multi-object spectrograph. The objects extend over a 1.3 square degree area surrounding the main cloud of the rho Oph complex. The objects were selected from narrowband images to have H alpha in emission. Using the presence of strong H alpha emission, lithium absorption, location in the Hertzsprung-Russell diagram, or previously reported x-ray emission, we were able to identify 88 objects as young stars associated with the cloud. Strong H alpha emission was confirmed in 39 objects with line widths consistent with their origin in magnetospheric accretion columns. Two of the strongest emission-line objects are young, x-ray emitting brown dwarf candidates with M8 spectral types. Comparisons of the bolometric luminosities and effective temperatures with theoretical models suggest a medianage for this population of 2.1 Myr which is signifcantly older than the ages derived for objects in the cloud core. It appears that these stars formed contemporaneously with low mass stars in the Upper Scorpius subgroup, likely triggered by massive stars in the Upper-Centaurus subgroup.Comment: 35 pages of postscript which includes seven figures (some of which are multi-panel) and four postscript tables. Astronomical Journal (in press

Low-Mass Star Formation and the Initial Mass Function in the Rho Ophiuchi Cloud Core

We have obtained moderate-resolution (R=800-1200) K-band spectra for ~100 stars within and surrounding the cloud core of rho Oph. We have measured spectral types and continuum veilings and have combined this information with results from new deep imaging. The IMF peaks at about 0.4 M_sun and slowly declines to the hydrogen burning limit with a slope of ~-0.5 in logarithmic units (Salpeter is +1.35). Our lower limits on the numbers of substellar objects demonstrate that the IMF probably does not fall more steeply below the hydrogen burning limit, at least down to ~0.02 M_sun. We then make the first comparison of mass functions of stars and pre-stellar clumps (Motte, Andre, & Neri) measured in the same region. The similar behavior of the two mass functions in rho Oph supports the suggestion of Motte et al. and Testi & Sargent that the stellar mass function in young clusters is a direct product of the process of cloud fragmentation. After considering the effect of extinction on the SED classifications of the sample, we find that ~17% of the rho Oph stars are Class I, implying ~0.1 Myr for the lifetime of this stage. In spectra separated by two years, we observe simultaneous variability in the Br gamma emission and K-band continuum veiling for two stars, where the hydrogen emission is brighter in the more heavily veiled data. This behavior indicates that the disk may contribute significantly to continuous K-band emission, in contrast to the proposal that the infalling envelope always dominates. Our detection of strong 2 micron veiling (r_K=1-4) in several Class II and III stars, which should have disks but little envelope material, further supports this proposition.Comment: 35 pages, 14 figures, accepted to Ap

A Search for Close Binaries in the Rho Ophiuchus Star-Forming Region

We have carried out a new, near-infrared speckle imaging survey of 19 members of the young stellar population in the nearby (d=140 pc), Rho Ophiuchi cloud core. Results for four binary and one newly discovered triple system are reported. Data for all known multiple systems among the pre-main-sequence population of Rho Oph are tabulated. We define a "restricted binary fraction", Fbr, and a "restricted companion fraction", Fcr, as counting only those systems most detectable in the present and previous high-resolution near-infrared imaging surveys, having separations between 0.1-1.1 arcsec and K-band magnitude differences, Delta K < 3. Analysis of all the available multiplicity data results in updated values of Fbr=Fcr=24%+/-11% for the Ophiuchus pre-main-sequence population. These values are consistent with the values in the Taurus star-forming region, and Fcr is in excess by a factor of 2 relative to the Main Sequence at the 1-sigma level.Comment: 21 pages, 6 figures, 4 table

The deuteron: structure and form factors

A brief review of the history of the discovery of the deuteron in provided. The current status of both experiment and theory for the elastic electron scattering is then presented.Comment: 80 pages, 33 figures, submited to Advances in Nuclear Physic

Can environment or allergy explain international variation in prevalence of wheeze in childhood?

Asthma prevalence in children varies substantially around the world, but the contribution of known risk factors to this international variation is uncertain. The International Study of Asthma and Allergies in Childhood (ISAAC) Phase Two studied 8–12 year old children in 30 centres worldwide with parent-completed symptom and risk factor questionnaires and aeroallergen skin prick testing. We used multilevel logistic regression modelling to investigate the effect of adjustment for individual and ecological risk factors on the between-centre variation in prevalence of recent wheeze. Adjustment for single individual-level risk factors changed the centre-level variation from a reduction of up to 8.4% (and 8.5% for atopy) to an increase of up to 6.8%. Modelling the 11 most influential environmental factors among all children simultaneously, the centre-level variation changed little overall (2.4% increase). Modelling only factors that decreased the variance, the 6 most influential factors (synthetic and feather quilt, mother’s smoking, heating stoves, dampness and foam pillows) in combination resulted in a 21% reduction in variance. Ecological (centre-level) risk factors generally explained higher proportions of the variation than did individual risk factors. Single environmental factors and aeroallergen sensitisation measured at the individual (child) level did not explain much of the between-centre variation in wheeze prevalence

Liquid Radiation Treatments and Environmental Challenges in Georgia

მოცემული ნაშრომი იკვლევს რადიოაქტიურ ნარჩენებთან უსაფრთხო მოპყრობის ძირითად მოთხოვნებს, რომელიც შემუშვებულია საერთაშორისო სტანდარტების მოთხოვნით და საქართველოში არსებული რეალური სიტუაციის გათვალისწინებით. დღემდე ატომური ენერგიის საერთაშორისო სააგენტოს გამოცემული აქვს მრავალი დოკუმენტი, სადაც განხილულია რადიოაქტიურ ნარჩენებთან მოპყრობის დროს უსაფრთხოების საკითხები. ნაშრომი შეისწავლის ტექნოლოგიურ ხაზს თხევადი რადიაოაქტიური ნარჩენების წარმოქმნის მომენტიდან გარემოში ჩაშვებამდე.ნაშრომის აქტუალობა მდგომარეობს იმაში რომ, მედიცინის ეს უახლესი მიმართულება სულ ერთეული წლებია საქართველოში დამკვიდრდა.რაც მოითხოვს რადიაციული უსაფრთხოებას შემდგომ განვითარებას და მოდერნიზაციას.The present work investigates the main demands of safe treatment of radioactive residues which have been worked out by the International standards and with allowance of real situation existing in Georgia. Till the present time the International Agency of atomic energy has published many documents in which there are considered the issues of safety during treatment with radioactive residues. The work studies the technological line from the moment of formation of liquid radioactive residues till the discharge in the environment. The actuality of the work lies in the fact that this most new direction of the medicine has been established in Georgia only since few years which requires the further development and modernization of the radiation safety