Variability of Southern T Tauri Stars (VASTT). III. The Continuum Flux Changes of the TW Hydrae Bright Spot

We present time series spectrophotometric observations of GQ Lupi, a typical representative of the YY Ori subgroup of T Tauri stars that show conspicuous inverse PCygni profiles. The data set consists of 32 exposures taken over 5 and 8 consecutive nights of May and July 1998, respectively, and covers the spectral range of 3100 AA~ $< lambda < 5100 $ AA. The region redward and next to the Balmer jump varies significantly on a night-to-night basis and the amplitude of such variability decreases sharply at $lambda >$ 4600 AA. The Balmer continuum slope indicates that the spectral energy distribution is governed by a gas of temperature greater than that of the stellar photosphere. We find an anticorrelation between the veiling and the observed Balmer jump. The time series of the redward absorption component behaves similarly to the veiling time series. We model the emitting region by a gas of uniform temperature and density. The models indicate that the gas densities and the respective temperatures are strongly anticorrelated. In addition, the model time series show that the increase in the gas density is mirrored by an increase of the projected emitting area (filling factor). Large/small gas densities and filling factors are characterized by high/low observed veiling. As the accretion rate fades from night-to-night, the observed veiling decreases, as does the gas density and the total projected emitting area.Comment: 26 pages, 14 postscript figures, ApJ accepte