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
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
10505573
A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy ⋆
New NTT/SOFI imaging and spectroscopy of the Wolf-Rayet population in Westerlund 1 are presented. Narrow-band near-IR imaging together with follow up spectroscopy reveals four new Wolf-Rayet stars, of which three were independently identified recently by Groh et al., bringing the confirmed Wolf-Rayet content to 24 (23 excludin g source S) ‐ representing 8% of the known Galactic Wolf-Rayet population ‐ comprising 8 WC stars and 16 (15) WN stars. Revised coordinates and near-IR photometry are presented, whilst a quantitative nearIR spectral classification scheme for Wolf-Rayet stars is pr esented and applied to members of Westerlund 1. Late subtypes are dominant, with no subtypes earlier than WN5 or WC8 for the nitrogen and carbon sequences, respectively. A qualitative inspection of the WN stars suggests that most (�75%) are highly H-deficient. The Wolf-Rayet binary fraction is high (>62%), on the basis of dust emission from WC stars, in addition to a significant WN binary fraction from hard X-ray detections according to Clark et al. We exploit the large WN population of Westerlund 1 to reassess its distance (�5.0 kpc) and extinction (AKS � 0.96 mag), such that it is located at the edge of the Galactic bar, with an oxygen metallicity �60% higher than Orion. The observed ratio of WR stars to red and yellow hypergiants, N(WR)/N(RSG+YHG)� 3, favours an age of�4.5‐5.0 Myr, with individual Wolf-Rayet stars descended from progenitors of initial mass � 40 55M⊙. Qualitative estimates of current masses for non-dusty, H-free WR stars are presented, revealing 10 18M⊙, such that �75% of the initial stellar mass has been removed via stellar winds or close binary evolution. We present a revision to the cluster turn-off mass for other Milky Way clusters in which Wolf-Rayet stars are known, based upon the latest temperature calibration for OB stars. Finally, c omparisons between the observed WR population and subtype distribution in Westerlund 1 and instantaneous burst evolutionary synthesis models are presented.
119471898
SS433: The microquasar link with ulxs?
SS433 is the prototype microquasar in the Galaxy and may even be analogous to the ULX sources if the jets’ kinetic energy is taken into account. However, in spite of 20 years of study, our constraints on the nature of the binary system are extremely limited as a result of the difficulty of locating spectral features that can reveal the nature and motion of the mass donor. Newly acquired, high resolution blue spectra taken when the (precessing) disc is edge-on suggest that the binary is close to a common-envelope phase, and hence providing kinematic constraints is extremely difficult. Nevertheless, we do find evidence for a massive donor, as expected for the inferred very high mass transfer rate, and we compare SS433’s properties with those of Cyg X-3.
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.
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.
16479172
Is there potential complementarity between LISA and pulsar timing
We open the discussion into how the Laser Interferometer Space Antenna (LISA) observations of supermassive black-hole (SMBH) mergers (in the mass range ~ 106–108 M⊙) may be complementary to pulsar timing-based gravitational wave searches. We consider the toy model of determining pulsar distances by exploiting the fact that LISA SMBH inspiral observations can place tight parameter constraints on the signal present in pulsar timing observations. We also suggest, as a future path of research, the use of LISA ring-down observations from the most massive ( a few 107 M⊙) black-hole mergers, for which the inspiral stage will lie outside the LISA band, as both a trigger and constraint on searches within pulsar timing data for the inspiral stage of the merger.
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.
15980110
Inference on white dwarf binary systems using the first round Mock LISA Data Challenges data sets
We report on the analysis of selected single source data sets from the first round of the mock LISA data challenges (MLDC) for white dwarf binaries. We implemented an end-to-end pipeline consisting of a grid-based coherent pre-processing unit for signal detection and an automatic Markov Chain Monte Carlo (MCMC) post-processing unit for signal evaluation. We demonstrate that signal detection with our coherent approach is secure and accurate, and is increased in accuracy and supplemented with additional information on the signal parameters by our Markov Chain Monte Carlo approach. We also demonstrate that the Markov Chain Monte Carlo routine is additionally able to determine accurately the noise level in the frequency window of interest.
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.
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.