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We assess the evolutionary status of the intriguing object Walker 90/V590Mon, which is located about 20 arcminutes northwest of the Cone Nebula near thecenter of the open cluster NGC 2264. This object, according to its most recentoptical spectral type determination (B7), which we confirmed, is at least 3magnitudes too faint in V for the cluster distance, but it shows the classicalsigns of a young pre-main sequence object, such as highly variable Halphaemission, Mg II emission, IR excess, UV continuum, and optical variability. Weanalyzed a collection of archival and original data on Walker 90, covering 45years including photometry, imaging, and spectroscopic data ranging fromultraviolet to near-infrared wavelengths. According to star formationprocesses, it is expected that, as this object clears its primordialsurroundings, it should become optically brighter, show a weakening of its IRexcess and present decreasing line emissions. This behavior is supported by ourobservations and analysis, but timescales are expected to be longer than theone observed here. Based on photometric data secured in 2007, we find Walker 90at its brightest recorded optical magnitude. We document an evolution inspectral type over the past five decades (from A2/A3 to currently B7 and asearly as B4), along with a decrease in the near-infrared K fluxes. Fromnear-infrared images secured in 2004, Walker 90 appears as a point sourceplacing an upper limit of 0.1 arcsec for its diameter. We conclude that manyobservational features are explained if W90 is a flared disk system, surroundedby an inclined optically thick accretion disk.

The Enigmatic Young Object: Walker 90/V590 Monocerotis