AAS 201st Meeting, January, 2003
Session 20. Star Formation I
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[20.10] The Peculiar Photometric Behavior of the Young Stellar Object GW Orionis

L.E. DeWarf, E.F. Guinan (Villanova University), J.F. Sepinsky (University of Delaware), A.M. Pouch (Abington High School, PA)

Intensive long-term photometric monitoring has been carried out on the Young Stellar Object (YSO) GW Orionis (HD 244138; K3 Ve; <V> = +9.92 mag; <B-V> = +0.97). We present 5 years of UBV observations carried out with the 0.8m Four College Automatic Photoelectric Telescope (FCAPT), located in southern Arizona. GW Ori is believed to be a single-lined spectroscopic binary (Porb = 242 days; Matheiu et al., 1991, AJ, 101, 2184), in which the physical properties of the secondary component remain unknown. Mathieu et al. also observed a systemic change in the radial velocity measurements with an ~1000 day period that is attributed to a possible third component.

Our photometric data from 1992 to 1997 show variability over an ~1100 day cycle that may be correlated with the spectroscopic measurements. This variability is seen in each filter and in the photometric indices ((U-B) and (B-V)). This suggests that this modulation might be stellar in origin, as opposed to the result of some dynamical mechanism, possibly indicative of variable accretion from the circumstellar environment, magnetic activity cycles, and/or perturbations in the circumstellar disk(s). We also find some evidence for the 242 day binary periodicity in our U-filter data, but find no accompanying variability in either the B- or V-band data.

Additionally, it is evident from large infrared excesses that GW Ori is surrounded by an extensive circumprimary and possibly circumbinary disk of material. The spectral energy distribution in the optical and near-infrared wavelengths can be closely modeled by a simple two-component (stellar atmosphere + blackbody) energy distribution. We find that the observed stellar component has a temperature of order 4300 K and the mean temperature for the circumstellar component(s) is about 1350 K.

This research is supported by NSF/RUI Grant AST-93 15365, AST-00 71260, and the Delaware Space Grant College Consortium through the Undergraduate Summer Research Assistance program.

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