Catherine L. Imhoff

The 1993–1994 Activity of EX Lupi

EX Lupi is a classical T Tauri star (and the EXor prototype) subject to sporadic outbursts. The historic record shows that it remains at about V = 13.2 (or mpg = 14.7:) for extended periods, from which it has been observed to brighten to as much as V = 8.4 (on one occasion in 1955-1956). During 1993-1994 the star remained slightly above normal minimum, at about V = 12.8, and from that level rose to three maxima at V = 11.4 and on other occasions to about V = 12.0. At minimum light an M0 V absorption spectrum is present. At outburst this spectrum is veiled by a hot continuum (well shown by an IUE exposure), the equivalent widths of the optical-region emission lines decrease, and reverse P Cygni absorption components appear at the higher Balmer lines. The outbursts are believed to be due to episodic infall onto the M0 star.

A synoptic of H-alpha line profile in the T Tauri star SU Aurigae

We present a catalog of 106 high spectral resolution observations of the H-alpha line profile in the T Tauri star SU Aurigae, obtained during the period from 1986 October through 1990 November. The spectra were acquired during joint synoptic programs to observe selected T Tauri stars using the Hamilton Echelle Spectrometer of the Lick Observatory and the solar-stellar spectrograph at the McMath telescope of the National Solar Observatory on Kitt Peak. A restricted set of Mg II h and k line profiles was also obtained in a coordinated program involving the International Ultraviolet Explorer (IUE) satellite observatory and the McMath solar-stellar facility. Striking variability is evident on a nightly basis. A key result is that the relative intensity in the blue wing of H-alpha spanning a range of velocities bear -150 km/s is modulated at a period of 2.98 +/- 0.4 days. We identify the 2.98 day period with the rotation period of the star. We also find that the occurrence of the periodic modulation of the mass outflow is episodic and most evident during a 2 week sequence of nightly observations. We find two other intervals where the periodic spectroscopic variability is likely present, although at a lower level of significance at a lower level of significance. The variability is otherwise stochastic in nature. The Mg II resonance lines exhibit clear variability that is most pronounced in the blue wing of the k line. A comparison of the Mg II k line profile with H-alpha profiles obtained nearly simultaneous yields no apparent correlation between the variable features in each line. The profile shapes of the Mg II h and k lines are generally indicative of formation in a wind. An analysis of the principal features that appear in the H-alpha profile set suggests that the line is composed of contributions from an enhanced chromosphere; a relatively slow moving, dense, optically thick component of a stellar wind formed relatively close to the star; and an optically thin, high-velocity, expanding stellar wind located further away from the star. An investigation of possible correlations among the principal features in the series of H-alpha profiles suggests that as the density in the wind increases, the wind may become more unstable to large turbulence. This may lead to a reduction in the wind bulk velocity, thus regulating the mass-loss rate. We also find that the position of the main absorption feature which is always present in the H-alpha profiles is not correlated with its depth, indicating that optical depth and wind velocity are not correlated in the denser portions of the wind.

PB 6 and its central star

It is found that the hot nucleus of the Type I southern planetary nebula PB 6 is a member of the rare class of O VI stars. The blended O VI 3811 + 3834 emission doublet is one of the strongest seen, with an equivalent width (relative to the stellar continuum) of about 400 A. The helium, nitrogen, and carbon abundances are all very high for the core mass and the relations found by Kaler and Jacoby (1990). The Ne/O ratio, at 0.17, is close to the norm found for planetaries, which supports the high O/H, while the S/O is roughly solar.