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تسجيل مستخدم جديدA near-infrared survey for Galactic Wolf-Rayet stars
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N. L. Homeier
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Initial results, techniques, and rationale for a near-infrared survey of evolved emission-line stars toward the Galactic Center are presented. We use images taken through narrow-band emission-line and continuum filters to select candidates for spectroscopic follow-up. The filters are optimized for the detection of Wolf-Rayet stars and other objects which exhibit emission-lines in the 2 micron region. Approximately three square degrees along the Galactic plane have been analyzed in seven narrow-filters (four emission-lines and three continuum). Four new Wolf-Rayet stars have been found which are the subject of a following paper.
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Most of the Milky Ways evolved massive stellar population is hidden from view. We can attempt to remedy this situation with near-infrared observations, and in this paper we present our method for detecting Wolf-Rayet stars in highly extincted regions
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9 arcsec and typical rms noise of 0.04 mJy/beam. Our survey of 34 WR stars resulted in 15 definite and 5 probable detections, 13 of these for the first time at radio wavelengths. All detections are unresolved. Time variations in flux are confirmed in the cases of WR98a, WR104, WR105 and WR125. WR79a and WR89 are also variable in flux and we suspect they are also non-thermal emitters. Thus, of our sample 20-30% of the detected stars are non-thermal emiters. Average mass loss rates determinations obtained excluding definite and suspected non-thermal cases give similar values for WN (all subtypes) and WC5-7 stars, while a lower value was obtained for WC8-9 stars. Uncertainties in stellar distances largely contribute to the observed scatter in mass loss rates. Upper limits to the mass loss rates were obtained in cases of undetected sources or for sources which probably show additional non-thermal emission.
We have investigated and applied machine-learning algorithms for Infrared Colour Selection of Galactic Wolf-Rayet (WR) candidates. Objects taken from the GLIMPSE catalogue of the infrared objects in the Galactic plane can be classified into different
stellar populations based on the colours inferred from their broadband photometric magnitudes ($J$, $H$ and $K_s$ from 2MASS, and the four textit{Spitzer}/IRAC bands). The algorithms tested in this pilot study are variants of the $k$-Nearest Neighbours ($k$-NN) approach, which is ideal for exploratory studies of classification problems where interrelations between variables and classes are complicated. The aims of this study are (1) to provide an automated tool to select reliable WR candidates and potentially other classes of objects, (2) to measure the efficiency of infrared colour selection at performing these tasks and, (3) to lay the groundwork for statistically inferring the total number of WR stars in our Galaxy. We report the performance results obtained over a set of known objects and selected candidates for which we have carried out follow-up spectroscopic observations, and confirm the discovery of 4 new WR stars.
We report the results of a high angular resolution near-infrared survey of dusty Wolf-Rayet stars using the Keck-1 Telescope, including new multi-wavelength images of the pinwheel nebulae WR 98a, WR 104, and WR 112. Angular sizes were measured for an
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order to investigate these uncertainties, it is useful to study massive stars just before their demise. Classical Wolf-Rayet stars represent the final end stages of stars at the upper-mass end. The multiplicity fraction of these stars was reported to be ${sim}0.4$ in the Galaxy but no correction for observational biases has been attempted. The aim of this study is to conduct a homogeneous radial-velocity survey of a magnitude-limited ($V$ $leq 12$) sample of Galactic Wolf-Rayet stars to derive their bias-corrected multiplicity properties. The present paper focuses on 12 northern Galactic carbon-rich (WC) Wolf-Rayet stars observable with the 1.2m Mercator telescope on the island of La Palma. We homogeneously measured relative radial velocities (RVs) for carbon-rich Wolf-Rayet stars using cross-correlation. Variations in the derived RVs were used to flag binary candidates. We investigated probable orbital configurations and provide a first correction of observational biases through Monte-Carlo simulations. Of the 12 northern Galactic WC stars in our sample, seven show peak-to-peak RV variations larger than 10 km s$^{-1}$, which we adopt as our detection threshold. This results in an observed spectroscopic multiplicity fraction of 0.58 with a binomial error of 0.14. In our campaign, we find a clear lack of short-period (P~$<~sim$100,d), indicating that a large number of Galactic WC binaries likely reside in long-period systems. Finally, our simulations show that at the 10% significance level, the intrinsic multiplicity fraction of the Galactic WC population is at least 0.72.
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