Variability of Young Massive Stars in the Arches Cluster
K. Markakis, A.Z. Bonanos, G. Pietrzynski, L. Macri, K.Z. Stanek
aa r X i v : . [ a s t r o - ph . S R ] S e p Active OB stars: structure, evolution, mass lossand critical limitsProceedings IAU Symposium No. 272, 2010C. Neiner, G. Wade, G. Meynet & G. Peters c (cid:13) Variability of Young Massive Stars in theArches Cluster
K. Markakis , A.Z. Bonanos , G. Pietrzynski L. Macri K.Z.Stanek National Observatory of Athens, Institute of Astronomy & Astrophysics,I. Metaxa & Vas. Pavlou St., P. Penteli 15236, Athens, Greece [email protected] , [email protected] K.M. & A.Z.B. acknowledge support from the IAU and the European Commissionfor an FP7 Marie Curie International Reintegration Grant. Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, PolandUniversidad de Concepci´on, Departamento de Astronomia, Casilla 160-C, Concepci´on, Chile Department of Physics & Astronomy, Texas A&M University, College Station, TX77842-4242, USA The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
Abstract.
We present preliminary results of the first near-infrared variability study of theArches cluster, using adaptive optics data from NIRI/Gemini and NACO/VLT. The goal isto discover eclipsing binaries in this young (2.5 ± Keywords.
Galaxy: center, infrared: Stars, open clusters and associations: individual (Archescluster), binaries: eclipsing, stars: variables, stars: Wolf-Rayet
1. Introduction
One of the most important questions is how massive can the most massive stars in theUniverse be today. In other words what is the upper limit of the Initial Mass Function inthe Universe. The Arches Cluster provides us with a unique opportunity to address thisquestion because it has all the criteria of the ideal place to look at for massive eclipsingbinary systems. It lies near the Galactic Center which is a very dense region that benefitsthe formation of massive stars and the cluster itself is very young which can guaranteethat its stars will not have evolved significantly.
2. Datasets & Reduction
We used two datasets in the K s band. The first dataset was obtained with Gemini’sNIRI infrared camera which consisted of 16 observations of 30 and 1 second exposuresrespectively covering 8 nights from April to July of 2006. The NIRI data are pendinga linearity correction. The second dataset was obtained with the VLT’s NACO infraredcamera and consisted of 46 observations of 20 seconds exposures each covering 31 nightsfrom June of 2008 to March of 2009. The reduction of the NIRI images was performedwith the IRAF † Gemini v1.9 package while the reduction of the NACO images wasperformed via the NACO reduction pipeline, based on ESO’s Common Pipeline Library. † IRAF is distributed by the NOAO, which are operated by the Association of Universitiesfor Research in Astronomy, Inc., under cooperative agreement with the NSF.
3. Image Subtraction & Photometry
We used the image subtraction package ISIS (Alard & Lupton 1998, Alard 2000), whichis optimal for detecting variables in crowded fields, together with IRAF’s DAOPHOT(Stetson 1987) package on the reference image from ISIS. Although ISIS allows for aspatially variable PSF it doesn’t provide us with an accurate PSF model due to theanisoplanatic effects introduced by the imperfect correction of atmospheric turbulenceby the adaptive optics. The light curve presented below has been obtained with ISIS andits overall shape strongly suggests that this may be a contact eclipsing binary. In orderto obtain more accurate photometry and confirm our result, we are currently using theStarFinder code (Diolaiti et al. 2000a). StarFinder was designed to extract an empiricalPSF from the image, that also takes into account the anisoplanatic effects caused by theadaptive optics.
4. Preliminary results
We present the light curve of an eclipsing binary candidate in the Arches cluster fromthe NACO data, which corresponds to the second star in the catalog of Figer et al. (2002).It has a 10.49 day period and is likely in a contact configuration. This candidate eclipsingbinary has a spectral type of WN7 (Blum et al. 2001). It has also been identified as radiosource AR10 with a mass loss rate of the order of 1.9 x 10 − M ⊙ yr − (Lang et al. 2001b)and as X-Ray source A6, probably associated with the close pair of radio sources AR6and AR10 (Wang et al. 2006). Finally it has an initial mass greater than 120 M ⊙ (Figeret al. 2002).Figure 1: K s − band light curve of the candidate eclipsing binary in the Arches cluster. References
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