Low-ionization structures in planetary nebulae: confronting models with observations

Around 50 PNe are presently known to possess "small-scale" low-ionization structures (LISs). We consider here jets, jet-like, symmetrical and non-symmetrical LISs and present a detailed comparison of the existing model predictions with the observational morphological and kinematical properties. We find that nebulae with LISs appear indistinctly spread among all morphological classes of PNe, indicating that the processes leading to the formation of LISs are not necessarily related to those responsible for the asphericity of the large-scale morphological components of PNe. We show that both the observed velocities and locations of most non-symmetrical LISs can be reasonably well reproduced assuming either fossil condensations originated in the AGB wind or in-situ instabilities. The jet models proposed to date (HD and MHD interacting winds or accretion-disk collimated winds) appear unable to account simultaneously for the kinematical ages and the angle between the jet and the symmetry axes of the nebulae. The linear increase in velocity observed in several jets favors MHD confinement compared to pure HD interacting wind models. On the other hand, we find that the formation of jet-like systems characterized by relatively low expansion velocities cannot be explained by any of the existing models. Finally, the knots which appear in symmetrical and opposite pairs of low velocity could be understood as the survival of fossil (symmetrical) condensations formed during the AGB phase or as structures that have experienced substantial slowing down by the ambient medium.Comment: 21 pages including 5 tables. To appear in ApJ 547, Jan 2001. Also available at http://www.iac.es/publicaciones/preprints.htm

German evidence and consensus‐based (S3) guideline: Vaccination recommendations for the prevention of HPV‐associated lesions

Anogenital and oropharyngeal infections with human papilloma viruses (HPV) are common. Clinically manifest disease may significantly impact quality of life; the treatment of HPV-associated lesions is associated with a high rate of recurrence and invasive neoplasms, such as cervical, anal, vulvar, penile, and oropharyngeal cancers, which are characterized by significant morbidity and mortality. Vaccination against HPV is an effective and safe measure for the primary prevention of HPV-associated lesions, but immunization rates are still low in Germany. The present publication is an abridged version of the German evidence and consensus-based guideline "Vaccination recommendations for the prevention of HPV-associated lesions", which is available on the website of the German Association of the Scientific Medical Societies (AWMF). On the basis of a systematic review with meta-analyses, a representative panel developed and agreed upon recommendations for the vaccination of different populations against HPV. In addition, consensus-based recommendations were developed for specific issues relevant to everyday practice. Based on current evidence and a representative expert consensus, these recommendations are intended to provide guidance in a field in which there is often uncertainty and in which both patients and health care providers are sometimes confronted with controversial and emotionally charged points of view

The planet in M4: implications for planet formation in globular clusters

We consider the formation and evolution of the planetary system PSR B1620-26 in the globular cluster M4. We propose that as M4 is a very-low metallicity environment the standard model of planet formation around main-sequence stars through the accretion of gas onto metallic rocky cores should not be applied. Consequently the previously suggested methods for formation are unlikely. We propose that the planet formed through the interaction of a passing star with a circumbinary disc during the common-envelope phase of the inner binary's evolution. This formation route is favoured by dense stellar systems such as globular clusters.Comment: 8 pages, 2 figures, MNRAS accepte

Young stars and brown dwarfs surrounding Alnilam (eps Ori) and Mintaka (del Ori)

Aims: We look for new regions for the search of substellar objects. Methods: Two circular areas, 45 arcmin-radius each, centred on the young massive star systems Alnilam and Mintaka in the Orion Belt, have been explored. The regions are very young (less than 10 Ma), have low extinction, and are neighbours to sigma Orionis (~3 Ma), a young open cluster very rich in brown dwarfs and planetary-mass objects. We have used Virtual Observatory tools, the astro-photometric Tycho-2, DENIS and 2MASS catalogues, 10 control fields at similar galactic latitudes, and X-ray, mid-infrared and spectroscopic data from the literature. Results: We have compiled exhaustive lists of known young stars and new candidate members in the Ori OB1b association, and of fore- and background sources. A total of 136 stars display features of extreme youth, like early spectral types, lithium in absorption, or mid-infrared flux excess. Other two young brown dwarf and 289 star candidates have been identified from an optical/near-infrared colour-magnitude diagram. We list additional 74 known objects that might belong to the association. This catalogue can serve as an input for characterisation of the stellar and high-mass substellar populations in the Orion Belt. Finally, we have investigated the surface densities and radial distributions of young objects surrounding Alnilam and Mintaka, and compared them with those in the sigma Orionis cluster. We report a new open cluster centred on Mintaka. Conclusions: Both regions can be analogs to the sigma Orionis cluster, but more massive, more extended, slightly older, and less radially concentrated.Comment: Accepted for publication in A&A. It will be published on line in Sect. 14 (Catalogs and data). Tables in Appendix A will soon be available at the CD