The hypergiant HR 8752 evolving through the yellow evolutionary void

Context. We study the time history of the yellow hypergiant HR 8752 based on high-resolution spectra (1973-2005), the observed MK spectral classification data, B - V- and V-observations (1918-1996) and yet earlier V-observations (1840-1918).<br>Aims. Our local thermal equilibrium analysis of the spectra yields accurate values of the effective temperature (T-eff), the acceleration of gravity (g), and the turbulent velocity (v(t)) for 26 spectra. The standard deviations average are 82 K for T-eff, 0.23 for log g, and 1.1 km s(-1) for v(t).<br>Methods. A comparison of B-V observations, MK spectral types, and T-eff-data yields E(B-V), "intrinsic" B-V, T-eff, absorption A(V), and the bolometric correction BC. With the additional information from simultaneous values of B-V, V, and an estimated value of R, the ratio of specific absorption to the interstellar absorption parameter E(B - V), the "unreddened" bolometric magnitude m(bol),(0) can be determined. With Hipparcos distance measurements of HR 8752, the absolute bolometric magnitude M-bol,M-0 can be determined.<br>Results. Over the period of our study, the value of T-eff gradually increased during a number of downward excursions that were observable over the period of sufficient time coverage. These observations, together with those of the effective acceleration g and the turbulent velocity v(t), suggest that the star underwent a number of successive gas ejections. During each ejection, a pseudo photosphere was produced of increasingly smaller g and higher v(t) values. After the dispersion into space of the ejected shells and after the restructuring of the star's atmosphere, a hotter and more compact photosphere became visible. From the B - V and V observations, the basic stellar parameters, T-eff, log M/M-circle dot, log L/L-circle dot, and log R/R-circle dot are determined for each of the observational points. The results show the variation in these basic stellar parameters over the past near-century.<br>Conclusions. We show that the atmospheric instability region in the HR-diagram that we baptize the yellow evolutionary void actually consists of two parts. We claim that the present observations show that HR 8752 is presently climbing out of the "first" instability region and that it is on its way to stability, but in the course of its future evolution it still has to go through the second potential unstable region

A VLT/FLAMES survey for massive binaries in Westerlund 1: I. First observations of luminous evolved stars

Aims. Multiwavelength observations of the young massive cluster Westerlund 1 have revealed evidence for a large number of OB supergiant and Wolf-Rayet binaries. However, in most cases these findings are based on the detection of secondary binary characteristics, such as hard X-ray emission and/or non-thermal radio spectra and hence provide little information on binary properties such as mass ratio and orbital period. To overcome this shortcoming we have initiated a long temporal baseline, multi-epoch radial velocity survey that will provide the first direct constraints on these parameters.Methods. VLT/FLAMES+GIRAFFE observations of Wd1 were made on seven epochs from late-June to early-September 2008, covering ~35 confirmed members of Wd1 and ~70 photometrically-selected candidate members. Each target was observed on a minimum of three epochs, with brighter cluster members observed on five (or, in a few cases, seven) occasions. Individual spectra cover the 8484–9001 Å range, and strong Paschen-series absorption lines are used to measure radial velocity changes in order to identify candidate binary systems for follow-up study.Results. This study presents first-epoch results from twenty of the most luminous supergiant stars in Wd1. Four new OB supergiant members of Wd1 are identified, while statistically significant radial velocity changes are detected in ~60% of the targets. W43a is identified as a short-period binary, while W234 and the newly-identified cluster member W3003 are probable binaries and W2a is a strong binary candidate. The cool hypergiants W243 and W265 display photospheric pulsations, while a number of early-mid B supergiants display significant radial velocity changes of ~15–25 km s-1 that we cannot distinguish between orbital or photospheric motion in our initial short-baseline survey. When combined with existing observations, we find 30% of our sample to be binary (6/20) while additional candidate binaries support a binary fraction amongst Wd1 supergiants in excess of ~40%, a figure that is likely to increase as further data become available

Spectroscopic monitoring of the luminous blue variable Westerlund1-243 from 2002 to 2009

The massive post-Main Sequence star W243 in the galactic starburst cluster Westerlund 1 has undergone a spectral transformation from a B2Ia supergiant devoid of emission features in 1981 to an A-type supergiant with a rich emission-line spectrum by 2002/03. We used VLT/UVES and VLT/FLAMES to obtain high-resolution spectra on six epochs in 2003/04 (UVES) and ten epochs in 2008/09 (FLAMES). These spectra are used alongside other VLT/FLAMES and NTT/EMMI spectra to follow the evolution of W243 from 2002 to 2009. W243 displays a complex, time-varying spectrum with emission lines of Hydrogen, Helium and Lyman-pumped metals, forbidden lines of Nitrogen and Iron, and a large number of absorption lines from neutral and singly-ionized metals. Many lines are complex emission/absorption blends. The LBV has a current temperature of ~8500K (spectral type A3Ia+), and displays signs of photospheric pulsations and weak episodic mass loss. Nitrogen is highly overabundant, with Carbon and Oxygen depleted, indicative of surface CNO-processed material and considerable previous mass-loss, although current time-averaged mass-loss rates are low. The emission-line spectrum forms at large radii, when material lost by the LBV in a previous mass-loss event is ionized by an unseen hot companion. Monitoring of the near-infrared spectrum suggests that the star has not changed significantly since it finished evolving to the cool state, close to the Humphreys-Davidson limit, in early 2003. [ABRIDGED]Comment: 17 pages, 16 figures, accepted for publication in Astronomy and Astrophysic

Distributed Multi-agent Video Fast-forwarding

In many intelligent systems, a network of agents collaboratively perceives the environment for better and more efficient situation awareness. As these agents often have limited resources, it could be greatly beneficial to identify the content overlapping among camera views from different agents and leverage it for reducing the processing, transmission and storage of redundant/unimportant video frames. This paper presents a consensus-based distributed multi-agent video fast-forwarding framework, named DMVF, that fast-forwards multi-view video streams collaboratively and adaptively. In our framework, each camera view is addressed by a reinforcement learning based fast-forwarding agent, which periodically chooses from multiple strategies to selectively process video frames and transmits the selected frames at adjustable paces. During every adaptation period, each agent communicates with a number of neighboring agents, evaluates the importance of the selected frames from itself and those from its neighbors, refines such evaluation together with other agents via a system-wide consensus algorithm, and uses such evaluation to decide their strategy for the next period. Compared with approaches in the literature on a real-world surveillance video dataset VideoWeb, our method significantly improves the coverage of important frames and also reduces the number of frames processed in the system.Comment: To appear at ACM Multimedia 202

IRAS 18357-0604 – an analogue of the galactic yellow hypergiant IRC +10420?

Context. Yellow hypergiants represent a short-lived evolutionary episode experienced by massive stars as they transit to and from a red supergiant phase. As such, their properties provide a critical test of stellar evolutionary theory, while recent observations unexpectedly suggest that a subset may explode as Type II supernovae.Aims. The galactic yellow hypergiant IRC +10420 is a cornerstone system for understanding this phase since it is the strongest post-RSG candidate known, has demonstrated real-time evolution across the Hertzsprung-Russell diagram and been subject to extensive mass loss. In this paper we report on the discovery of a twin of IRC +10420 - IRAS 18357-0604.Methods. Optical and near-IR spectroscopy are used to investigate the physical properties of IRAS 18357-0604 and also provide an estimate of its systemic velocity, while near- to mid-IR photometry probes the nature of its circumstellar environment.Results. These observations reveal pronounced spectral similarities between IRAS 18357-0604 and IRC +10420, suggesting comparable temperatures and wind geometries. IR photometric data reveals a similarly dusty circumstellar environment, although historical mass loss appears to have been heavier in IRC +10420. The systemic velocity implies a distance compatible with the red supergiant-dominated complex at the base of the Scutum Crux arm; the resultant luminosity determination is consistent with a physical association but suggests a lower initial mass than inferred for IRC +10420 (≲20 M⊙ versus ~40 M⊙). Evolutionary predictions for the physical properties of supernova progenitors derived from ~18–20 M⊙ stars – or ~12–15 M⊙ stars that have experienced enhanced mass loss as red supergiants – compare favourably with those of IRAS 18357-0604, which in turn appears to be similar to the the progenitor of SN2011dh; it may therefore provide an important insight into the nature of the apparently H-depleted yellow hypergiant progenitors of some Type IIb SNe

Whistleblowers as regulatory intermediaries: Instrumental and reflexive considerations in decentralizing regulation

This article frames whistleblowers as regulatory intermediaries who provide a response to the problem posed by the fragmentation of knowledge in a complex society and market economy. I identify two ways in which whistleblowers become regulatory intermediaries: The first is by remedying informational asymmetries between the regulator and the target (instrumental approach). Both in the United States and in the European Union, whistleblowers are protected on the basis of the value of the disclosed information for the advancement of regulatory objectives. The second way in which whistleblowers become regulatory intermediaries is by contributing to the development of “communities of compliance” and by enhancing the internal self-regulatory capacities of regulatory targets (reflexive approach). Creating internal channels of reporting and monitoring is perceived as a way to change the organizational culture of targets. Through the instrumentalism – reflexivity dipole, competing rationales and normative visions of regulatory intermediation become apparent: It could, on the one hand, facilitate state intervention and legal sanctions or, on the other hand, signal the aspiration to embed public and social values in private actors