L. Errico

Ultraviolet spectrum of FU Ori and a “Compromise” model of the FUor

We have analyzed the Hubble Space Telescope spectrum of the young star FU Ori in the range 2300–3100 Å. The long-wavelength part of the spectrum is similar to the spectrum of a supergiant with Teff ≃ 5000–6000 K, but the range of wavelengths shorter than ≃2600 Å is dominated by radiation from a region with Teff ≃ 9000 K. We discuss the possibility of explaining these peculiarities of the spectrum, the Al II] 2669.2 emission line profile, and the results of X-ray observations for FU Ori in terms of an accretion disk model whose thickness increases as the star is approached starting from distances ≃1012 cm. Near the star, the disk has the shape of a cone in which only the part of its surface on the far (from the observer) side is visible. The suggested model is a kind of a compromise between the models of a thin α-disk and a supergiant: basically, this is an accretion model, but it resembles a supergiant in observational manifestations. Numerous absorption lines originating in the disk wind are superimposed on the disk spectrum. The wind is a cold (T ≃ 5000 K), dense (Ne ≃ 1011 cm−3) gas. The number of wind absorption lines in the ultraviolet spectrum of FU Ori increases with decreasing wavelength. This causes a rapid decline in intensity in the short-wavelength part of the spectrum. As a result, the maximum temperature in the disk estimated from low-resolution IUE spectra has been underestimated.

Variability of the Hα and Na I D line profiles in the spectrum of FU Ori

The variations of line profiles in the spectrum of FU Ori during several consecutive nights, from January 3 through January 8, 1999, have been traced for the first time in the entire history of studying this star. The variations of the Hα and Na I D line profiles are regular in pattern; at each time, the profiles of these lines were similar to a particular profile observed previously, suggesting that the phenomenon is periodic. We argue that the profile variations result from the axial rotation of the inner accretion-disk and disk-wind regions for which the temperature distribution and the wind-streamline orientation are not axisymmetric. The cause of the asymmetry could be the interaction of circumstellar matter with the stellar magnetic field if the magnetic axis is greatly inclined to the rotation axis. The possible binary nature of FU Ori seems a less likely cause of the asymmetry.

Analysis of HST and IUE ultraviolet spectra for T Tauri stars: DF Tau

AbstractWe analyze ultraviolet spectra of DF Tau, a binary system whose primary component is a classical T Tauri star. The spectra were obtained from the Hubble Space Telescope and the IUE satellite. The stellar emission in the wavelength range covered is shown to originate in an accretion shock wave. The gas infall velocity is ∼250 km s−1. The accreted-gas density is typically N0≤1011 cm−3, but it can occasionally be higher by one and a half orders of magnitude. The continuum intensity near λ=1900 Å was found to be virtually constant for such a significant change in N0. The star’s photometric variability is probably attributable to variations in accreted-gas density and velocity, as well as to variations in the area of a hot spot on the stellar surface and in its orientation relative to the observer. The mean accretion rate is

A multiple mass‐ejection by the symbiotic prototype Z And during its 2000–03 outburst

\dot M \sim 3 \times 10^{ - 9} M_ \odot yr^{ - 1}

On the Source of Optical Variability and Outflow in Z CMa System

. The interstellar extinction for DF Tau is

On the nature of the Herbig Be star V 380 Orionis

A_V \simeq 0\mathop .\limits^m 5