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Viewing Angle Effects

In the model line profiles, produced by Hartmann, Calvet, Muzerolle and co-workers discussed above, one important factor for the appearance of a redshifted absorption feature in the profiles is the viewing angle, the other being the temperature of the underlying accretion shock. High inclinations and high enough temperatures in the accretion shock imply the production of a redshifted absorption (as the accreting material is seen in absorption against the shock). Bouvier et al. (1995) compute inclinations, i, for several T Tauri stars from observed rotational periods and vsini measurements. This allows one to check for any pattern in the distribution of inclination angles for each type of line profile. For the 7 stars displaying an IPC Pa Beta line profile with inclinations in Bouvier et al. (1995) one finds 5 stars with i between 30o and 60o, 1 star with i smaller than 30o and 1 star with that angle larger than 60o. For the 8 stars with Type I profiles with inclinations in Bouvier et al., the distributions are as follows: 1 star with i smaller than 30o, 3 stars for which i is between 30o and 60o and 4 stars for which i is larger than 60o. The results for the Br Gamma line profiles are as follows: for the 2 stars with IPC lines and inclinations in Bouvier et al. one has an i between 30o and 60o and the other has i larger than 60o; for the 7 stars with Type I profiles, 1 has i smaller than 30o, 3 have i between 30o and 60o and the other 3 stars have i larger than 60o. These distributions do not show any clear separation in inclination angle for stars with IPC and with Type I line profiles. The IPC line profiles tend to occur in systems with i between 30o and 60o but rarely above 60o. This is a result obtained from a relatively small number of stars and should be regarded with caution. It is a somewhat surprising result since the magnetospheric accretion model predicts redshifted absorption at high latitudes, nearly polar in fact. As before, such a result is another indication that the magnetospheric accretion model envisioned so far is still only a rough approximation of the way in which matter accretes onto the star. It should be stressed again that the presence of a redshifted absorption is not only sensitive to the inclination angle but also to the temperature of the accretion shock. The latter is not observationally constrained well enough for individual objects. The logical step of performing an observational check by looking at the accretion shock temperature for individual stars and the presence of IPC line profiles is therefore not possible.



next up previous contents
Next: Multiple Systems Up: Discussion Previous: The Type I

Daniel Folha
Fri Aug 28 11:53:21 BST 1998