arXiv subjects

Y. C. Unruh

Publications and source records attributed to Y. C. Unruh.

39 records · Page 3Linked to original sources

arXiv2000

Magnetospheric Accretion and Winds on the T Tauri Star SU Aurigae: Multi-Spectral Line Variability and Cross-Correlation Analysis

SU Aurigae is a T Tauri star that was well monitored during the MUSICOS 96 multi-site campaign. We present the results of the spectroscopic analysis of the circumstellar environment of this star, particularly of the Halpha, Hbeta, Na I D and He I D3 line profiles. The signatures of modulated outflows and mass accretion events are analysed, as well as transient spectral features. We compute the cross-correlation function (CCF) of several pairs of (velocity bins in) spectral lines to better investigate the profiles' temporal variability. We found increasing time lags between the variability of He I D3, Na I D and Hbeta. We propose this may be understood in terms of azimuthal distortion of the magnetic field lines due to the different rotation rates of the star and the disk. We find the slightly blueshifted absorption features in Halpha, Hbeta and Na I D to be anti-correlated with the accretion flow signatures. We propose that the transient absorption features in the blue wings of Halpha, Hbeta and Na I D (signatures of mass outflows), and flare brightenings are related to the disruption of distorted magnetospheric field lines.

astro-ph↗

arXiv1999

Spectral Line Variability in the Circumstellar Environment of the Classic al T Tauri Star SU Aurigae

SU Aurigae is a classical T Tauri star of spectral type G2. This star was one of the scientific targets of the MUSICOS 96 multi-site campaign that provided a wealth of high resolution cross-dispersed spectral data with a good continuous time coverage. We present the results of the analysis of the complex circumstellar environment of this star, with particular regard to magnetospheric models, in which the accretion from the disk is channelled onto the star along magnetic field lines. The signatures of modulated outflows and mass accretion events are present in the spectra, as well as transient spectral features. We computed auto-correlation and cross-correlation functions to better investigate the source of the profiles' variability. The comparison of the profiles of different spectral lines allows us to study the footprints of events effectively observed at different distances from the stellar surface.

astro-ph↗

arXiv1998

Optical and UV observations of a strong flare in the young, single K2-dwarf LQ Hya

We present high resolution optical echelle spectra and IUE observations during a strong flare on 1993 December 22 in the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The initial impulsive phase of the flare, which started sometime between 2:42 UT and 4:07 UT, was characterized by strong optical continuum enhancement and blue-shifted emission lines with broad wings. The optical chromospheric lines reached their maximum intensity at $\approx$5:31 UT, by which time the blue-shift vanished and the optical continuum enhancement had sharply decreased. Thereafter, the line emission slowly decreased and the lines red-shift in a gradual phase that lasted at least two more hours. The Mg II lines behaved similarly. Quiescent C IV flux levels were not recovered until 21 hours later, though a data gap and a possible second flare make the interpretation uncertain. In addition to the typically flare-enhanced emission lines (e.g., H_alpha and H_beta), we observe He I D_3 going into emission, plus excess emission (after subtraction of the quiescent spectrum) in other He I and several strong neutral metal lines (e.g., Mg I b). Flare enhancement of the far UV continuum generally agrees with a Si I recombination model. We estimate the total flare energy, and discuss the broad components, asymmetries, and Doppler shifts seen in some of the emission lines.

astro-ph↗