Magnetic activity and differential rotation in the young Sun-like stars KIC 7985370 and KIC 7765135

Aims. We present a detailed study of the two Sun-like stars KIC 7985370 and KIC 7765135, to determine their activity level, spot distribution, and differential rotation. Both stars were previously discovered by us to be young stars and were observed by the NASA Kepler mission. Methods. The fundamental stellar parameters (vsini, spectral type, T_eff, log g, and [Fe/H]) were derived from optical spectroscopy by comparison with both standard-star and synthetic spectra. The spectra of the targets allowed us to study the chromospheric activity based on the emission in the core of hydrogen Hα and Ca ii infrared triplet (IRT) lines, which was revealed by the subtraction of inactive templates. The high-precision Kepler photometric data spanning over 229 days were then fitted with a robust spot model. Model selection and parameter estimation were performed in a Bayesian manner, using a Markov chain Monte Carlo method. Results. We find that both stars are Sun-like (of G1.5 V spectral type) and have an age of about 100–200 Myr, based on their lithium content and kinematics. Their youth is confirmed by their high level of chromospheric activity, which is comparable to that displayed by the early G-type stars in the Pleiades cluster. The Balmer decrement and flux ratio of their Ca ii-IRT lines suggest that the formation of the core of these lines occurs mainly in optically thick regions that are analogous to solar plages. The spot model applied to the Kepler photometry requires at least seven persistent spots in the case of KIC 7985370 and nine spots in the case of KIC 7765135 to provide a satisfactory fit to the data. The assumption of the longevity of the star spots, whose area is allowed to evolve with time, is at the heart of our spot-modelling approach. On both stars, the surface differential rotation is Sun-like, with the high-latitude spots rotating slower than the low-latitude ones. We found, for both stars, a rather high value of the equator-to-pole differential rotation (dΩ ≈ 0.18 rad d^-1), which disagrees with the predictions of some mean-field models of differential rotation for rapidly rotating stars. Our results agree instead with previous works on solar-type stars and other models that predict a higher latitudinal shear, increasing with equatorial angular velocity, that can vary during the magnetic cycle.

The challenges of safeguarding and securing cultural heritage materials during violent conflict in Nigeria.

Almost every community, country and continent is experiencing a form of conflict, war or disaster. These wars have claimed lives, antiquities, heritage materials, contemporary Arts, Galleries, Museums, Archives, Monuments andHeritage sites. The aim of this study is to explore the challenges of safeguarding cultural heritage material during violent conflict in Nigeria bearing in mind the two UNESCO world heritage sites in Nigeria: Sukur kingdom and Osun Oshogbo sacred Grove. The outcome of this study will help the policy makers to address the challenges of safeguarding cultural heritage materials in times of conflicts, bridge the gap on the existing literature concerning the safeguarding of cultural heritage materials in times of conflict and to make a modest contribution to the existing body of knowledge on cultural heritage protection in Nigeria in particular and other parts of the world in general. This study relies on both primary and secondary sources using questionnaire and oral interview to elicit information from selected relevant cultural agencies, journalists and scholars in the field of art and culture. Relevant literature and documents on the challenges of safeguarding and securing of cultural heritage materials during conflicts were reviewed. The data gathered from the questionnaires and the oral interview is presented in frequency tabular form to give precise and comprehensive insight into the study findings. Notable among the challenges were insecurity and lack of professionalism in the field of cultural heritage profession. The study also revealed that governments are not enforcing the global laws and conventions for the protection of cultural heritage materials in times of violent conflict. The communities where these materials are located have little or no knowledge about the import of these materials and do not take part in securing them in the event of conflict. It is crucial that we place high value on heritage materials since they are inextricably linked with our identity and where we come from. It is strongly recommended that Cultural Heritage Institutions should involve as much as possible the local communities living around the sites by creating awareness educating and encouraging them to take ownership of the Sites located within their communities. They must ensure that the site is safeguarded against all forms of threat. Items of heritage value are not often considered in most disaster management plans therefore there is the need to consider heritage as priority just as the protection of lives and property.