T Tauri Stars: GW Orionis

DeWarf and Guinan, with former undergraduate astronomy student J. Sepinsky ( NW Univ.) and A. Pouch (Abington H. S.) continue their intensive long-term photometric monitoring of the Young Stellar Object (YSO) GW Orionis (HD 244138; K3 - G5 (?) Ve; $< V >= +9.92$ mag; $< B-V >= +0.97$). They have obtained over 10 years of UBV observations carried out with the 0.8m Four College Automatic Photoelectric Telescope (FCAPT). GW Ori is possibly a single-lined spectroscopic binary $P_{\rm orb} = 242$ days), in which the physical properties of the secondary component remain unknown. There is an observed systemic change in the radial velocity measurements with an $\sim 1000$ day period that is attributed to either a third component, or possibly an asymmetric global gravitational instability (one-armed spiral density mode) in the circumstellar disk. After applying moderate reddening corrections, GW Orionis can be satisfactorily placed on the pre-main sequence evolutionary tracks, yielding a mass of about 2.5 M$_{\odot}$ and an age of approximately 3 Myrs.

Their photometric data from 1992 to 1997 show variability over an $\sim 1100$ 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). They also find some evidence for the 242 day binary periodicity in their 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 has been modeled by a simple two-component (stellar atmosphere + blackbody) energy distribution. They find that the observed stellar component has a temperature of order 6200 K and the mean temperature for the circumstellar component(s) is about 1700 K.