Bias in density estimations using strip transects in dry open-country environments in the Canary Islands

We studied bias in density estimations derived from strip transects in dry open-country in the Canary Islands. We also present some critical remarks on García-del-Rey’s (2005) paper regarding strip transects and the validity of comparisons based on population densities of birds in scrublands on Tenerife island using two different methods: territory mapping and strip transect sampling. Although strip transects with census belts of 25 m do not account for detectability, this method only slightly undervalues true density estimates, and allowed to detect more than 85% of birds present in poorly vegetated environments in the Canary Islands. Previously published works on distribution and abundance of terrestrial birds in the Canary Islands using the strip transect sampling with belts of 25 m on both sides of the observer, thus provide reliable information that only slightly underestimates true densities

Disruption of a Red Giant Star by a Supermassive Black Hole and the Case of PS1-10jh

The development of a new generation of theoretical models for tidal disruptions is timely, as increasingly diverse events are being captured in surveys of the transient sky. Recently, Gezari et al. reported a discovery of a new class of tidal disruption events: the disruption of a helium-rich stellar core, thought to be a remnant of a red giant (RG) star. Motivated by this discovery and in anticipation of others, we consider tidal interaction of an RG star with a supermassive black hole (SMBH) which leads to the stripping of the stellar envelope and subsequent inspiral of the compact core toward the black hole. Once the stellar envelope is removed the inspiral of the core is driven by tidal heating as well as the emission of gravitational radiation until the core either falls into the SMBH or is tidally disrupted. In the case of tidal disruption candidate PS1-10jh we find that there is a set of orbital solutions at high eccentricities in which the tidally stripped hydrogen envelope is accreted by the SMBH before the helium core is disrupted. This places the RG core in a portion of parameter space where strong tidal heating can lift the degeneracy of the compact remnant and disrupt it before it reaches the tidal radius. We consider how this sequence of events explains the puzzling absence of the hydrogen emission lines from the spectrum of PS1-10jh and gives rise to its other observational features.Comment: Revised version accepted for publication in ApJ, 788, 99 (12 pages, 2 figures

Framing China: The Belt and Road Initiative in Argentine national media outlets

This article studies how Argentine national media outlets reported on China’s Belt and Road Initiative (BRI) between 2013 and February 2022 (this covers the period from the launch of the BRI to Argentina’s official accession to the initiative). Based on a framing analysis of 272 articles, this study argues that national media outlets tend to reproduce two frames about the BRI: they either present it as an opportunity or as a threat. The balance between them matters when attempting to understand how media organisations shape citizens’ perceptions of China and the BRI. In the case of Argentina, even though its political and economic relations with China have become closer, reports on the BRI were quite polarised. Indeed, national media outlets’ portrayal of the BRI as an opportunity has been slightly more prevalent than negative portrayal (41% vs. 35%). However, national media firms covered the BRI in different ways. Some organisations conveyed largely positive frames, some chiefly presented negative ones, and others were more balanced. The specific editorial lines of the newspapers and their affinities to national political alliances explain these different patterns. Furthermore, although articles citing Western sources were indeed more negative about the BRI, many of the op-eds and reports criticising the BRI were produced by Argentine journalists and other local actors. Thus, Chinese academics exaggerate Western media sources’ influence on Argentina’s national media critical coverage of China while overlooking reasonable concerns about the impacts of Chinese projects

Intermediate-mass black holes in colliding clusters: Implications for lower-frequency gravitational-wave astronomy

Observations suggest that star clusters often form in binaries or larger bound groups. Therefore, mergers between two clusters are likely to occur. If these clusters both harbor an intermediate-mass black hole (IMBH; 10^{2-4} Msun) in their center, they can become a strong source of gravitational waves when the black holes merge with each other. In order to understand the dynamical processes that operate in such a scenario, one has to study the evolution of the merger of two such young massive star clusters, and more specifically, their respective IMBHs. We employ the direct-summation Nbody4 numerical tool on special-purpose GRAPE6 hardware to simulate a merger of two stellar clusters each containing 63,000 particles and a central IMBH. This allows us to study accurately the orbital evolution of the colliding clusters and the embedded massive black holes. Within ~7 Myr the clusters have merged and the IMBHs constitute a hard binary. The final coalescence happens in ~10^8 yrs. The implication of our analysis is that intermediate-mass black holes merging as the result of coalescence of young dense clusters could provide a source for the Laser Interferometer Space Antenna (LISA) space-based gravitational wave detector mission. We find that interactions with stars increase the eccentricity of the IMBH binary to about 0.8. Although the binary later circularizes by emission of gravitational waves, the residual eccentricity can be detectable through its influence on the phase of the waves if the last few years of inspiral are observed