Analysis of the HST Ultraviolet Spectra for T Tauri Stars: RY Tau and HD115043

Details Analysis of the HST Ultraviolet Spectra for T Tauri Stars: RY Tau and HD115043 Analysis of the HST Ultraviolet Spectra for T Tauri Stars: RY Tau and HD115043

Publishing date

Sep 2000

URL

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000astl...26..589l&link_type=abstract

Journals

Astronomy Letters, vol. 26, p. 589-599 (2000)

Science

Astronomy and Astrophysics

Field

Astronomy

Additional info 2

14

Type

Scientific paper

Abstract

The ultraviolet spectra of the stars RY Tau and HD115043 from the Hubble Space Telescope are analyzed. RY Tau belongs to the classical T Tauri stars, while HD115043 is a young (t ~ 3 x 10^8 years), chromospherically active star. The most intense emission lines were identified, and their fluxes were measured. Low-resolution spectra of RY Tau and HD115043 in the wavelength range 1160-1760 A exhibit almost the same set of emission lines. However, first, the luminosity of RY Tau in these lines is approximately a factor of 300 higher than that of HD115043, and, second, the relative line intensities differ greatly. The intensity ratio of the CIV lambda 1550, SiIV lambda 1400, and NV lambda 1240 doublet components is close to 1:2 in the spectra of both stars. Judging by the continuum energy distribution, the spectral type of RY Tau is later than that of HD115043. Synchronous flux variability in the CIV lambda 1550 and HeII lambda 1640 lines in a time of ~ 20 min was detected in RY Tau. The flux rise in these lines was accompanied by a redshift of the intensity peak in the profiles by ~ 50 km/s. Intermediate-resolution spectra are used to study line profiles in the spectrum of RY Tau. In particular, the profiles of (optically thin) SiIII lambda 1892 and CIII lambda 1909 lines were found to be asymmetric and about 300 km/s in width. The (optically thick) CIV lambda 1550 doublet lines have similar profiles. The MgII lambda 2800 doublet lines are also asymmetric, but their shape is different: they consist of a broad (approximately 750 km/s at the base) emission component on which an interstellar absorption line shifted from the line symmetry center by about 20 km/s is superimposed. The intensity ratio of the MgII lambda 2800 doublet components is approximately equal to 1.4. Whether there are molecular hydrogen lines in the spectrum of RY Tau is still an open question. It is shown that the emission lines in the ultraviolet spectrum of RY Tau cannot originate in a hydrostatically equilibrium chromosphere. It is argued that quasi-steady accretion of circumstellar matter is responsible for the emission.

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