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

s of recently accepted papers Detection of Molecular Hydrogen Orbiting a “Naked” T Tauri Star Jeffrey S. Bary, David A. Weintraub and Joel H. Kastner 1 Vanderbilt University, P.O. Box 1807, Station B, Nashville, TN 37235, USA 2 Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA E-mail contact: jeff.bary@vanderbilt.edu Astronomers have established that for a few million years newborn stars possess disks of orbiting gas and dust. Such disks, which are likely sites of planet formation, appear to disappear once these stars reach ages of 5-10 × 10 yr; yet, ≥ 10 yr is thought necessary for giant planet formation. If disks dissipate in less time than is needed for giant planet formation, such planets may be rare and those known around nearby stars would be anomalies. Herein, we report the discovery of H2 gas orbiting a weak-lined T Tauri star heretofore presumed nearly devoid of circumstellar material. We estimate that a significant amount of H2 persists in the gas phase, but only a tiny fraction of this mass emits in the near-infrared. We propose that this star possesses an evolved disk that has escaped detection thus far because much of the dust has coagulated into planetesimals. This discovery suggests that the theory that disks are largely absent around such stars should be reconsidered. The widespread presence of such disks would indicate that planetesimals can form quickly and giant planet formation can proceed to completion before the gas in circumstellar disks disperses. Accepted by Astrophysical Journal Letters Variability of Southern T Tauri Stars (VASTT) III: The Continuum Flux Changes of the TW Hya Bright Spot Celso Batalha, Natalie M. Batalha, Silvia H.P. Alencar, Dalton F. Lopes and Eduardo S. Duarte 1 Observatório Nacional/CNPq, Rua General José Cristino, 77, Rio de Janeiro, RJ 20920-400, Brazil 2 NASA Ames Research Center, Planetary Systems Branch, Moffett Field, CA 94035-1000, USA 3 Universidade de São Paulo, IAG, Departamento de Astronomia, Rua do Matão, 1226, São Paulo, 05508-900, Brazil E-mail contact: celso@on.br We have collected low resolution spectrophotometric data of the classical T Tauri star TW Hya in an effort to detect and to follow the excess continuum emission (veiling) and the line changes at λ < 5100 Å. The de-veiled and calibrated flux distribution resembles that of a 30 Myr K7-M1 star, of radius R/R = 0.8, mass M/M = 0.7 and log g = 4.5. The anticorrelation between the veiling (in the B-band) and the observed Balmer jump, found by previous authors based on large samples of classical T Tauri stars, is confirmed in TW Hya. The line emission luminosities of the H, CaII and HeI lines correlate with one another throughout the series, supporting the claims that the bulk of the line emission is formed in a single region or their growth is controlled by a common mechanism. Surprisingly, the line emission fluxes do not correlate with the veiling at 4250 Å (B-band). The line luminosities are in general less than 1% of the continuum luminosities. The veiling time series presents a cyclic behavior at 4.4 ± 0.4 days. We collected all of the archival photometric data and analyzed the B-band observations using different algorithms. We found solutions at either the 4.4-day timescale