Zusammenfassung
Eleven irregular variable stars have been observed whose physical
characteristics seem much alike and yet are sufficiently
different from other known classes of variables to warrant the
recognition of a new * type of variable stars whose prototype is
T Tauri. The distinctive characteristics are: (1) irregular
light- variations of about 3 mag., (2) spectral type F5-GS with
emission lines resembling the solar chromo- sphere, (3) low
luminosity, and (4) association with dark or bright nebulosity.
The stars included are RW Aur, TJY Aur, R CrA, S CrA, RU Lup, R
Mon, ,T Tau, RY Tau, UX Tau, UZ Tau, and XZ Tau. They are
situated in or near the Milky Way dark clouds in the direction
either of the center or of the anticenter of the galaxy. The
light-curves.-The total light-changes are about 3 mag., the
variations being extremely irregu- lar as to range and time. The
light-curves are not unique. The individual variables.-The
spectrographic observations of the variables are described and
the significant features of the spectra pointed out. Discussion
of th speclra.-The spectral types of the T Tauri stars are
estimated to be between F5 and G5, although for many of them the
absorption lines generally used in classification are lacking. A
small variation of type with phase was found for T Tau and RY
Tau. Bright hydrogen has been found in all stars of the group,
and bright Caii (H and K) in all except R CrA. Most of the stars
show an emission spectrum composed of many bright lines of low
excitation. The strongest lines are those of Can, H, Fe ii, Cai,
Sr ii, Fe I, and Ti ii. The identification and relative maximum
intensifies of 160 lines of the differ- ent stars are shown in
Table 16. The intensity of the emission spectrum varies greatly
from time to time in each star, the bright lines becoming more
prominent at maximum light of the variable. The lines X 4063 and
X 4132 of the a3F-y3F ° multiplet of Fe i are
greatly enhanced in strength in the stars showing strong
emission spectra. This distortion is probably the result of
fluorescent effects. The marked similarity of the bright-line
spectrum of the T Tauri stars to that of the upper solar
chromosphere is shown in Table 17. Absolute magnitudes and color
indices.-Spectroscopic absolute magnitudes of three stars of the
group, together with meager indirect evidence, indicate that the
T Tauri stars are dwarfs of the main sequence. Color indlices
for five stars show some color excess, which is probably the
result of selective absorption by surrounding
nebu˜osity. Radial velocilies.-Radial-velocity
measures from absorption lines are difficult when the emission
spectrum is present. Lack of agreement in the measures of both
absorption and emission spectra indi- cates irregular
atmospheric motions. In the mean the emission lines are
displaced toward the violet with respect to the absorption lines
