SIMBAD references

We present time series spectrophotometric observations of GQ Lupi, a typical representative of the YY Orionis subgroup of T Tauri stars that show conspicuous inverse P Cygni profiles. The data set consists of 32 exposures taken over five and eight consecutive nights of 1998 May and July, respectively, and covers the spectral range of 3100 Å<λ<5100 Å. 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 λ>4600 Å. The Balmer continuum slope indicates that the spectral energy distribution is governed by a gas of temperature greater than that of the stellar photosphere. The variability of the Balmer continuum flux has the largest amplitude. Flux increases in the B band are accompanied by concurrent flux increases in the U band. The contrary is not always verified.

The excess of continuum emission (veiling) for each exposure is computed throughout the spectral format. We find a tight anticorrelation between the veiling and the observed Balmer jump. We report the largest inverse P Cygni profile ever observed at this resolution: the depth of the Hβ absorption component is nearly twice the height of the peak emission. Surprisingly, this absorption vanishes a few nights later. The time series of the redward absorption component behaves similarly to the veiling time series: the progressive weakening of the redward absorption is closely followed by a similar weakening of the excess continuum emission. If the absorption component is deveiled, the correlation strengthens. Thus, large/small redward absorption=large/small veiling=small/large Balmer jump.

We model the emitting region by a gas of uniform temperature and density, each of the 32 exposures acting as a snapshot of such a region for a given stellar rotational phase. We explore models of temperature greater than 5000 K and number of hydrogen atoms N_H larger than 10¹³ cm^–3, extending the gas spectral energy distribution up to the blackbody of a given temperature. The resulting 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.