A dynamical study of the circumstellar gas in UX Orionis

¹ Departamento de Física Teórica C-XI, Universidad Autónoma de Madrid, Cantoblanco 28049 Madrid, Spain
² Osservatorio Astrofisico di Arcetri, Largo Fermi 5, 50125 Firenze, Italy
³ NOAO/STIS, Goddard Space Flight Center, Code 681, NASA/GSFC, Greenbelt, MD 20771, USA
⁴ TNO/TPD-Space Instrumentation, Stieltjesweg 1, PO Box 155, 2600 AD Delft, The Netherlands
⁵ Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁶ CNRS, Institut d'Astrophysique de Paris, 98bis Bd. Arago, 75014 Paris, France
⁷ DLR Department of Planetary Exploration, Rutherfordstrasse 2, 12489 Berlin, Germany
⁸ Instituto de Astrofísica de Andalucía, Apartado de Correos 3004, 18080 Granada, Spain
⁹ LAEFF, VILSPA, Apartado de Correos 50727, 28080 Madrid, Spain
¹⁰ Department of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
¹¹ Department of Physics, Center for Astrophysics and Space Sciences, University of California San Diego, Mail Code 0424, La Jolla, CA 92093-0424, USA
¹² Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, Scotland, UK
¹³ Instituto de Astrofísica de Canarias, La Laguna 38200 Tenerife, Spain
¹⁴ Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, UK
¹⁵ Observatoire de Paris, 92195 Meudon, France
¹⁶ SRON, Universiteitscomplex “Zernike”, Landleven 12, PO Box 800, 9700 AV Groningen, The Netherlands

Corresponding author: A. Mora, alcione.mora@uam.es

Received: 14 May 2002
Accepted: 11 July 2002

Abstract

We present the results of a high spectral resolution () 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 échelle spectra covering the spectral range 3800–5900 Å, 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, , 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.