A dynamical study of the circumstellar gas in UX Orionis

We present the results of a high spectral resolution (== 49 000) study of the circumstellar (CS) gas around the intermediate mass, pre-main sequence star UX Ori. The results are based on a set of 10 ´ echelle spectra covering the spectral range 3800-5900 A, monitoring the star on time scales of months, days and hours. A large number of transient blueshifted and redshifted absorption features are detected in the Balmer and in many metallic lines. A multigaussian fit is applied to determine for each transient absorption the velocity,v, dispersion velocity,v, and the parameter R, which provides a measure of the absorption strength of the CS gas. The time evolution of those parameters is presented and discussed. A comparison of intensity ratios among the transient absorptions suggests a solar-like composition of the CS gas. This confirms previous results and excludes a very metal-rich environment as the cause of the transient features in UX Ori. The features can be grouped by their similar velocities into 24 groups, of which 17 are redshifted and 7 blueshifted. An analysis of the velocity of the groups allows us to identify them as signatures of the dynamical evolution of 7 clumps of gas, of which 4 represent accretion events and 3 outflow events. Most of the events decelerate at a rate of tenths of m s 2 , while 2 events accelerate at approximately the same rate; one event is seen experiencing both an acceleration and a deceleration phase and lasts for a period of few days. This time scale seems to be the typical duration of outflowing and infalling events in UX Ori. The dispersion velocity and the relative aborption strength of the features do not show drastic changes during the lifetime of the events, which suggests they are gaseous blobs preserving their geometrical and physical identity. These data are a very useful tool for constraining and validating theoretical models of the chemical and physical conditions of CS gas around young stars; in particular, we suggest that the simultaneous presence of infalling and outflowing gas should be investigated in the context of detailed magnetospheric accretion models, similar to those proposed for the lower mass T Tauri stars.

[1]  B. Rodgers,et al.  Spectroscopic Variability of the UXOR Star RR Tauri , 2002 .

[2]  A. Natta,et al.  Optical spectra of five UX Orionis-type stars , 2001 .

[3]  C. Eiroa,et al.  EXPORT: Optical photometry and polarimetry of Vega-type and pre-main sequence stars , 2001, astro-ph/0110641.

[4]  A. Harris,et al.  EXPORT: Spectral classification and projected rotational velocities of Vega-type and pre-main sequence stars , 2001 .

[5]  Diagnostics for accretion disks around UX Ori stars based on Balmer, Paschen, and Brackett Lines , 2001 .

[6]  L. Hartmann,et al.  Emission-Line Diagnostics of T Tauri Magnetospheric Accretion. II. Improved Model Tests and Insights into Accretion Physics , 2001 .

[7]  A. Lagrange,et al.  Falling Evaporating Bodies around Herbig stars. A theoretical study , 2001 .

[8]  A. Harris,et al.  EXPORT: Near-IR observations of Vega-type and pre-main sequence stars , 2001 .

[9]  A. Natta,et al.  An Interesting Episode of Accretion Activity in UX Orionis , 2000 .

[10]  A. Boss,et al.  Protostars and Planets VI , 2000 .

[11]  H. C. Stempels,et al.  VALD{2: Progress of the Vienna Atomic Line Data Base ? , 1999 .

[12]  L. Hartmann,et al.  Accretion processes in star formation , 1999 .

[13]  Robert Winglee,et al.  Time-dependent Accretion by Magnetic Young Stellar Objects as a Launching Mechanism for Stellar Jets , 1997 .

[14]  G. Basri,et al.  The Line Profile Variability of SU Aurigae , 1995 .

[15]  A. Natta,et al.  Formation of double-peaked lines in stochastic winds of T tauri stars , 1993 .

[16]  N. Voshchinnikov,et al.  The investigations of ‘zodiacal light’ of isolated AE-Herbig stars with non-periodic Algol-type minima , 1991 .

[17]  R. Kurucz Model atmospheres for G, F, A, B, and O stars , 1979 .