SPECTRAL VARIABILITY OF SOUTHERN T TAURI STARS GQ Lupi

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1 SPECTRAL VARIABILITY OF SOUTHERN T TAURI STARS GQ Lupi Seperuelo, E. esduarte@on.br Batalha, C. celso@on.br Lopes, D. dalton@on.br Abstract We present veiling and emission lines fluxes measurements for the T Tauri GQ Lupi, observed during eighteen consecutive nights in February of 1999 at ESO 1.52m telescope and with Boller & Chivens spectrograph, in the ESO-ON agreement. The veiling showed a variation through the nights with period of about twelve days, the same result found with Batalha, Lopes, Batalha (2001), BLB, one year early observations. The emission line fluxes correlate each other, indicating that they are forming in a commom region. But, the inverse P Cygni profile, that one year early was very strength (BLB), disapear in our observations. Muzerolle, Calvet & Hartmann (2001), MCH, reported theoretical lines profiles for diferent values of spot temperature, acretion rate and the disk inclination. We are comparing our observed profiles with MCH theoretical profiles to obtain the better configuration of GQ Lupi star and to try explain the ciclic behaviour of the veiling. Introduction GQ Lupi belongs to the YY Orionis stars subclass in which the main feature is the presence of inverse P Cygni profiles (IPC) (Walker, 1972). 1

2 2 It shows photometric variability correlated to the line emission shapes (Bertout et al., 1982). Recently, Batalha, Lopes, & Batalha (2001) reported a series of spectrophotometric observation of GQ Lupi. They found a veiling variability, correlations between veiling and Hβ equivalent width as well an intense IPC. In this work, we report a series of spectrophotometric observations of this star. We analyze the veiling and emission lines variabilities and started comparisons between the theoretical profiles computed by Muzerolle, Calvet, & Hartmann (2001) with the observed ones. 1. Observations The observations were made in eighteen consecutive nights on February 1999 in La Silla, with a Boller & Chivens spectrograph attached to the 1.52m telescope. We have used gratings 26 (600 lines/mm) and 32 (1200 lines/mm). The spectral range was 4200Å to 6200Å and 3500Å to 7200Å, respectively. The data were reduced following the standard procedure. We observed the standard stars Hiltner 600 and CD Veiling For determining the veiling we used the method based on direct comparison between the photosferic lines profiles selected in the standard star (M1 from Jacoby, Hunter, & Christian, 1998). and in the T Tauri star (Basri & Batalha, 1990). We selected iron and calcium lines. 3. Results 3.1 Veiling We compute the average veiling for each night. Then we made a periodogram analysis using the Scargle periodogram estimator (1982) updated by Horne & Baliunas (1986). The analysis yield a period of days with FAP of 0.05 (see figure 1). BLB reported veiling measurements for GQ Lupi star made six months early than ours. We did the same analysis for their days measurements and we found a period of days with FAP of The same was done for the fluxes in V band published by Covino et al. (1992) and the period found was with FAP of Correlations We measured the integrated fluxes for the Balmer series lines, He I (4462Å and 5876Å) and Ca II (H & K). Firstly, the line emission fluxes do not correlate with the average veiling (see figure 2). Secondly, we

3 Spectral Variability Of Southern T Tauri Stars 3 Figure 1. Veiling Time variability. The veiling showed a periodic behavior through the eighteen consecutive nights. look for correlations between lines fluxes. The line emission fluxes of H, Ca II, and He I 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 that their growth is controlled by a common mechanism (See figure 3). 3.3 Hβ profiles We have compared the observed Hβ profiles with the theoretical profiles from a table of model line fluxes obtained on-line at models.html, yielded by Muzerolle, Calvet, & Hartmann (2001). Initially, we use the chi-square method to obtain the theoretical profile that fit the observed one and the main parameters like temperature, accretion rate, magnetosphere size and thickness. In figure 4 we can see the observed Hβ variability through the eighteen nights. This and the other lines results will be presented in forthcoming paper.

4 4 Figure 2. Correlations between average veiling and line emissions. Figure 3. fluxes. Correlations between line emissions. We found correlations between line 4. Conclusions - We found a veiling variability with period of days. This result agree with the photometric variation reported by Covino et al. (1992) and the veiling variability reported by BLB.

5 Spectral Variability Of Southern T Tauri Stars 5 Figure 4. Hβ time variability profiles. Hβ didnt show the IPC like in BLB. - Comparing our new observations to those of BLB, it is clear that GQ Lupi was undergoing different accretion phase: lower veiling and almost none signature of IPC; - As found before, there are positive line-to-line correlations, favoring the magnetic accretion hypothesis; - We can not find any line-to-veiling correlation. It is noteworthy that in this run we didn t observe the absorption component in Hβ line ; References Basri, G.,Batalha, C. 1990, ApJ, 363, 654 Batalha, C., Batalha, N. M., Alencar, S. H. P., Lopes, D. F., Duarte, E. S. 2002, ApJ, 580, 343 Batalha, C., Lopes, D. F., Batalha, N. M. 2001, ApJ, 548, 377 Covino, E., Terranegra, L., Franchini, M., Chavarria-K., C., Stalio, R. 1992, A&AS, 94, 273 Hartmann, L., Hewett, R., Calvet, N. 1994, ApJ, 426, 669 Horne, J. H.; Baliunas, S. L. 1986, ApJ, 302, 757H Jacoby, G. H., Hunter, D. A., Christian, C. A. 1998, ycat., 3092 Muzerolle, J., Calvet, N., Hartmann, L. 1998, ApJ, 492, 743 Muzerolle, J., Calvet, N., Hartmann, L. 2001, ApJ, 550, 944 Muzerolle, J., Hartmann, L., Calvet, N. 1998, AJ, 116, 455 Scargle, J. D. 1982, ApJ, 263, 835S