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The enigmatic young object : Walker 90/V590 Monocerotis

Pérez, M. R. and McCollum, B. and van den Ancker, M. E. and Joner, M. D. (2008) The enigmatic young object : Walker 90/V590 Monocerotis. Astronomy and Astrophysics, 486 (2). pp. 533-544. ISSN 0004-6361.

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Aims. We assess the evolutionary status of the intriguing object Walker 90/V590 Mon, which is located about 20 arcmin northwest of the Cone Nebula near the center of the open cluster NGC 2264. This object, according to its most recent optical spectral type determination (B7), which we confirmed, is at least 3 mag too faint in V for the cluster distance, but it shows the classical signs of a young pre-main sequence object, such as highly variable H emission, Mg II emission, IR excess, UV continuum, and optical variability. Methods. We analyzed a collection of archival and original data on Walker 90, covering 45 years including photometry, imaging, and spectroscopic data ranging from ultraviolet to near-infrared wavelengths. Results. According to star formation processes, it is expected that, as this object clears its primordial surroundings, it should become optically brighter, show a weakening of its IR excess and present decreasing line emissions. This behavior is supported by our observations and analysis, but timescales are expected to be longer than the one observed here. Based on photometric data secured in 2007, we find Walker 90 at its brightest recorded optical magnitude √(12.47 ± 0.06). We document an evolution in spectral type over the past five decades (from A2/A3 to currently B7 and as early as B4), along with a decrease in the near-infrared K fluxes. From near-infrared VISIR images secured in 2004, Walker 90 appears as a point source placing an upper limit of < 0.1" for its diameter. Evidence of turbulent inflows is found in rapidly changing inverse P-Cygni profiles in the lower Balmer lines, with a broadening of ±400 km s-1 in Hα and a redshifted component in Hβ with a terminal velocity of ~600 km s-1. The measured steep UV continuum fluxes (mimicking a star as early as B4), added to a tentative identification of N V emission, suggest a strong non-photospheric component, typically of fluxes arising from a thermally inhomogeneous accretion disk. We detect a well defined 2200 Å bump, indicative of dense material in the line-of-sight. We conclude that many observational features are explained if W90 is a flared disk system, surrounded by an inclined optically thick accretion disk.

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Additional Information:© ESO 2008. Received 8 April 2008. Accepted 17 May 2008. This research has made use of the Simbad database, operated at CDS, Strasbourg, France. This work is based in part on observations made with the Spitzer Space Telescope operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation We thank the Palomar Observatory for the generous assignment of time for the Echelle observations. We thank Dr. Derck Massa for providing the color figures (Figs. 10 and 12), which utilize his IUE NEWSIPS flux calibration corrections. We also acknowledge the use of the SAAO facilities and thanks to Dr. C. D. Laney for some of the IR observations and BVRcIc photometry of standard stars in the W90 field. We finally thank the support by the US Department of Energy, through the Los Alamos Laboratory-Directed Research and Development (LDRD 20080085DR) funds, used to complete the analysis work included in this paper (LA-UR-08-2165). We also thank the anonymous referee for his comments which helped us to improve the presentation and to clarify key points.
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University of Massachusetts and the Infrared Processing and Analysis CenterUNSPECIFIED
US Department of EnergyUNSPECIFIED
Los Alamos Laboratory-Directed Research and DevelopmentLDRD 20080085DR
Los Alamos Laboratory-Directed Research and DevelopmentLA-UR-08-2165
Subject Keywords:stars: pre-main sequence – stars: evolution – stars: emission line be stars; planetary systems; protoplanetary disks
Issue or Number:2
Record Number:CaltechAUTHORS:20090603-145800757
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14360
Deposited By: Ruth Sustaita
Deposited On:25 Jun 2009 19:08
Last Modified:03 Oct 2019 00:49

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