119187994
Bolometric luminosity variations in the luminous blue variable AFGL2298
Aims. We characterise the variability in the physical properties of the luminous blue variable AFGL 2298 (IRAS 18576+0341) between 1989−2008. Methods. In conjunction with published data from 1989−2001, we have undertaken a long term (2001−2008) near-IR spectroscopic and photometric observational campaign for this star and utilise a non-LTE model atmosphere code to interpret these data. Results. We find AFGL 2298 to have been highly variable during the two decades covered by the observational datasets. Photometric variations of ≥1.6 mag have been observed in the JHK wavebands; however, these are not accompanied by correlated changes in near-IR colour. Non-LTE model atmosphere analysis of 4 epochs of K band spectroscopy obtained between 2001−7 suggests that the photometric changes of AFGL 2298 were driven by expansion and contraction of the stellar photosphere accompanied by comparatively small changes in the stellar temperature (ΔT∗ ∼ 4.5 kK). Unclumped mass loss rates throughout this period were modest and directly comparable to those of other highly luminous (candidate) LBVs. However, the main finding of this analysis was that the bolometric luminosity of AFGL 2298 appears to have varied by at least a factor of ∼2 between 1989−2008, with it being one of the most luminous stars in the Galaxy during maximum. Comparison to other LBVs that have undergone non bolometric luminosity conserving “eruptions” shows such events to be heterogeneous, with AFGL 2298 the least extreme example. These results – and the diverse nature of both the quiescent LBVs and associated ejecta – may offer support to the suggestion that more than one physical mechanism is responsible for such behaviour.
17962299
The G305 star‐forming complex: wide‐area molecular mapping of NH3 and H2O masers
The definitive version can be found at : http://onlinelibrary.wiley.com/ Copyright Royal Astronomical Society
17044411
Multiple stellar generations in massive star forming complexes
The formation of massive stars is an outstanding problem in stellar evolution. However, it is expected that they are (predominantly) born in heirarchical environments within massive young clusters, which in turn are located within larger star forming complexes that reflect the underlying structure of the natal molecular cloud. Initial observations of such regions suggest that multiple generations of stars and proto-stars are present, necessitating a multiwavelength approach to yield a full (proto-)stellar census; in this contribution we provide an overview of just such an observational approach for Galactic examples, focusing on the G305 complex.
59319613
NGC 300 X-1 is a Wolf-Rayet/black hole binary
ABSTRACT We present VLT/FORS2 time-series spectroscopy of the Wolf-Rayet star #41 in the Sculptorgroup galaxy NGC300. We conﬁrm a physical association with N GC300 X–1, since radialvelocity variations of the He II λ4686 line indicate an orbital period of 32.3 ± 0.2 hr whichagrees at the 2σ level with the X-ray period from Carpano et al. We measure a radial velocitysemi-amplitudeof 267±8kms −1 , fromwhicha mass functionof 2.6±0.3 M ⊙ is obtained.Arevised spectroscopic mass for the WN-type companionof 26 +7−5 M ⊙ yields a black hole massof 20 ±4 M ⊙ for a preferred inclination of 60−75 ◦ . If the WR star provides half of the mea-sured visual continuum ﬂux, a reduced WR (black hole) mass of 15 +4−2.5 M ⊙ (14.5 +3−2.5 M ⊙ )would be inferred.As such, #41/NGC300 X–1 represents only the second extragalactic Wolf-Rayet plus black-hole binary system, after IC10 X–1. In addition, the compact object respon-sible for NGC300 X–1 is the second highest stellar-mass black hole known to date, exceededonly by IC10 X–1.Key words: (galaxies:)individual:NGC 300– Stars: Wolf-Rayet – X-rays: binaries – X-rays:individual: NGC300 X–1
9792700
Radio emission from the massive stars in the Galactic Super Star Cluster Westerlund 1
Aims. Current mass-loss rate estimates imply that main sequence line-driven winds are not suffi cient to strip away the H-rich envelope to yield Wolf-Rayet (WR) stars. The rich transitional population of the young massive cluster Westerlund 1 (Wd 1) provides an ideal laboratory to observe and constrain mass-loss processes throughout the transitional phase of stellar evolution. Methods. We present an analysis of deep radio continuum observations of Wd 1 obtained with the Australia Telescope Compact Array at four frequency bands that permit investigation of the intrinsic characteristics of the radio emission. Results. We detect 18 cluster members, a sample dominated by the cool hypergiants, with additional detections amongst the hotter OB supergiants and WR stars. The radio properties of the sample are diverse, with thermal, non-thermal and composite thermal/non
119435357
The identification of the optical/IR counterpart of the 15.8-s transient X–ray pulsar XTE J1946+274
We report on the discovery of the optical/IR counterpart of the 15.8 s transient X-ray pulsar XTE J1946+274. We re-analyzed archival BeppoSAX observations of XTE J1946+274 obtaining a new refined position (a circle with 22 00 radius at 90% confidence level). Based on this new position we carried out optical and infra-red (IR) follow-up observations. Within the new error circle we found a relatively optical faint (B= 18:6) IR bright (H= 12:1) early type reddened star (V R= 1:6). The optical spectra show strong H and H emission lines. The IR photometric observations of the field confirm the presence of an IR excess for the H-emitting star (K = 11:6, J H = 0:6) which is likely surrounded by a circumstellar envelope. Spectroscopic and photometric data indicate a B0-1V-IVe spectral-type star located at a distance of 8-10 kpc and confirm the Be-star/X-ray binary nature of XTE J1946+274.
8018008
An evidence based time-frequency search method for gravitational waves from pulsar glitches
We review and expand on a Bayesian model selection technique for the detection of gravitational waves from neutron star ring-downs associated with pulsar glitches. The algorithm works with power spectral densities constructed from overlapping time segments of gravitational wave data. Consequently, the original approach was at risk of falsely identifying multiple signals where only one signal was present in the data. We introduce an extension to the algorithm which uses posterior information on the frequency content of detected signals to cluster events together. The requirement that we have just one detection per signal is now met with the additional bonus that the belief in the presence of a signal is boosted by incorporating information from adjacent time segments.
9176350
Inference on inspiral signals using LISA MLDC data
In this paper, we describe a Bayesian inference framework for the analysis of data obtained by LISA. We set up a model for binary inspiral signals as defined for the Mock LISA Data Challenge 1.2 (MLDC), and implemented a Markov chain Monte Carlo (MCMC) algorithm to facilitate exploration and integration of the posterior distribution over the nine-dimensional parameter space. Here, we present intermediate results showing how, using this method, information about the nine parameters can be extracted from the data.
18080099
The third generation of gravitational wave observatories and their science reach
Large gravitational wave interferometric detectors, like Virgo and LIGO, demonstrated the capability to reach their design sensitivity, but to transform these machines into an effective observational instrument for gravitational wave astronomy a large improvement in sensitivity is required. Advanced detectors in the near future and third-generation observatories in more than one decade will open the possibility to perform gravitational wave astronomical observations from the Earth. An overview of the possible science reaches and the technological progress needed to realize a third-generation observatory are discussed in this paper. The status of the project Einstein Telescope (ET), a design study of a third-generation gravitational wave observatory, will be reported.
18473016
The Einstein Telescope: a third-generation gravitational wave observatory
Advanced gravitational wave interferometers, currently under realization, will soon permit the detection of gravitational waves from astronomical sources. To open the era of precision gravitational wave astronomy, a further substantial improvement in sensitivity is required. The future space-based Laser Interferometer Space Antenna and the third-generation ground-based observatory Einstein Telescope (ET) promise to achieve the required sensitivity improvements in frequency ranges. The vastly improved sensitivity of the third generation of gravitational wave observatories could permit detailed measurements of the sources' physical parameters and could complement, in a multi-messenger approach, the observation of signals emitted by cosmological sources obtained through other kinds of telescopes. This paper describes the progress of the ET project which is currently in its design study phase.
1028791
Report on the first round of the Mock LISA Data Challenges
The Mock LISA Data Challenges (MLDCs) have the dual purpose of fostering the development of LISA data analysis tools and capabilities, and demonstrating the technical readiness already achieved by the gravitational-wave community in distilling a rich science payoff from the LISA data output. The first round of MLDCs has just been completed: nine challenges consisting of data sets containing simulated gravitational-wave signals produced either by galactic binaries or massive black hole binaries embedded in simulated LISA instrumental noise were released in June 2006 with deadline for submission of results at the beginning of December 2006. Ten groups have participated in this first round of challenges. All of the challenges had at least one entry which successfully characterized the signal to better than 95% when assessed via a correlation with phasing ambiguities accounted for. Here, we describe the challenges, summarize the results and provide a first critical assessment of the entries.