Variability of Southern T Tauri Stars. I. The Continuum and the Hβ Inverse P Cygni Profile of GQ Lupi

Abstract

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 proÐles. The data set consists of 32 exposures taken over Ðve and eight consecutive nights of 1998 May and July, respectively, and covers the spectral range of 3100The region redward and next to the Balmer jump A \ j \ 5100 A . varies signiÐcantly on a night-to-night basis, and the amplitude of such variability decreases sharply at j [ 4600 The Balmer continuum slope indicates that the spectral energy distribution is governed by a A . gas of temperature greater than that of the stellar photosphere. The variability of the Balmer continuum Ñux has the largest amplitude. Flux increases in the B band are accompanied by concurrent Ñux increases in the U band. The contrary is not always veriÐed.The excess of continuum emission (veiling) for each exposure is computed throughout the spectral format. We Ðnd a tight anticorrelation between the veiling and the observed Balmer jump. We report the largest inverse P Cygni proÐle ever observed at this resolution : the depth of the Hb 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 larger than 1013 cm~3, extending the N H 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 (Ðlling factor). Large/small gas densities and Ðlling 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.

Spectrophotometric analysis of the T Tauri star GQ Lupi A

“…Our observed Hβ profiles show a blueward asymmetric emission component whose normalized intensity varies from approximately 1.8 to 4. We do not see any redshifted absorption, but it was often observed by other authors (Bertout et al 1982;Batalha et al 2001), so we cannot discard models with IPC profiles. The NaD lines in our spectra are always seen in absorption with intensities that vary from 0.2 to 0.35.…”

“…Lines such as Hβ, He I (5876 Å) and NaD where therefore obtained during all the nights, but Hα and Ca II H & K were only included in the last 7 nights of observations with the lower resolution setup. GQ Lup A is known for showing inverse P Cygni profiles in the upper Balmer lines (Bertout et al 1982;Batalha et al 2001), which are produced when photons from the accretion shock are absorbed by the accreting material falling along magnetic field lines. Curiously, the Balmer lines did not show any inverse P Cygni profiles in our observations.…”

“…Batalha et al (2001) reported spectrophotometric observations of GQ Lup consisting of 32 medium resolution échelle spectra distributed in two periods of six and eight consecutive nights in 1998. They found variability in the veiling and in the IPC profiles.…”

An ALMA and MagAO Study of the Substellar Companion GQ Lup B∗

“…Photometric monitoring indicated that it has an inclination of  27 and a rotation period of 8.45 days (Broeg et al 2007). It is one of the most studied CTTSs due to many features indicative of active accretion onto the star from a circumstellar disk, such as brightness variations (e.g., Friedrich & Schöffel 1971;Appenzeller et al 1978;Broeg et al 2007;Donati et al 2012), inverse P-Cygni profiles (e.g., Appenzeller et al 1978;Bertout et al 1982;Batalha et al 2001), optical veiling (e.g., Batalha et al 2001;Seperuelo Duarte et al 2008), very intense magnetic field (e.g., Donati et al 2012;JohnsKrull et al 2013), and strong excess from near-to far-infrared (e.g., Mendoza 1968;Hughes et al 1994;Kessler-Silacci et al 2006;McClure et al 2012;Morales et al 2012). The accretion disk was first imaged at 1.3 mm dust continuum emission by Dai et al (2010) using the Submillimeter Array.…”

“…Both components have been shown to exhibit accretion signatures (e.g., Batalha et al 2001;Zhou et al 2014). With a ∼0 05 resolution, we resolve the primary star's accretion disk.…”