113 research outputs found
Magnetic-field measurements of T Tauri stars in the Orion Nebula cluster
We present an analysis of high-resolution () infrared K-band
echelle spectra of 14 T Tauri stars in the Orion Nebula Cluster. We model
Zeeman broadening in three magnetically sensitive \ion{Ti}{1} lines near $2.2\
\mu$m and consistently detect kilogauss-level magnetic fields in the stellar
photospheres. The data are consistent in each case with the entire stellar
surface being covered with magnetic fields, suggesting that magnetic pressure
likely dominates over gas pressure in the photospheres of these stars. These
very strong magnetic fields might themselves be responsible for the
underproduction of X-ray emission of T Tauri stars relative to what is expected
based on main-sequence star calibrations. We combine these results with
previous measurements of 14 stars in Taurus and 5 stars in the TW Hydrae
association to study the potential variation of magnetic-field properties
during the first 10 million years of stellar evolution, finding a steady
decline in total magnetic flux with age.Comment: 34 pages, 17 figures, published in ApJ, 2011, 729, 8
How Hot is the Wind from TW Hydrae?
It has recently been suggested that the winds from Classical T Tauri stars in
general, and the wind from TW Hya in particular, reaches temperatures of at
least 300,000 K while maintaing a mass loss rate of \Msol
yr or larger. If confirmed, this would place strong new requirements on
wind launching and heating models. We therefore re-examine spectra from the
Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and
spectra from the Far Ultraviolet Spectroscopic Explorer satellite in an effort
to better constrain the maximum temperature in the wind of TW Hya. We find
clear evidence for a wind in the \ion{C}{2} doublet at 1037 \AA and in the
\ion{C}{2} multiplet at 1335 \AA. We find no wind absorption in the \ion{C}{4}
1550 \AA doublet observed at the same time as the \ion{C}{2} 1335 \AA line or
in observations of \ion{O}{6} observed simultaneously with the \ion{C}{2} 1037
\AA line. The presence or absence of \ion{C}{3} wind absorption is ambiguous.
The clear lack of a wind in the \ion{C}{4} line argues that the wind from TW
Hya does not reach the 100,000 K characteristic formation temperature of this
line. We therefore argue that the available evidence suggests that the wind
from TW Hya, and probably all classical T Tauri stars, reaches a maximum
temperature in the range of 10,000 -- 30,000 K.Comment: 17 pages, 3 figures, Figure 1 in 2nd version fixes a small velocity
scaling error and new revision adds a reference to an additional paper
recently foun
Starspot-induced optical and infrared radial velocity variability in T Tauri star Hubble 4
We report optical (6150 Ang) and K-band (2.3 micron) radial velocities
obtained over two years for the pre-main sequence weak-lined T Tauri star
Hubble I 4. We detect periodic and near-sinusoidal radial velocity variations
at both wavelengths, with a semi-amplitude of 1395\pm94 m/s in the optical and
365\pm80 m/s in the infrared. The lower velocity amplitude at the longer
wavelength, combined with bisector analysis and spot modeling, indicates that
there are large, cool spots on the stellar surface that are causing the radial
velocity modulation. The radial velocities maintain phase coherence over
hundreds of days suggesting that the starspots are long-lived. This is one of
the first active stars where the spot-induced velocity modulation has been
resolved in the infrared.Comment: Accepted for publication in The Astrophysical Journa
Bipolar jets produced by a spectroscopic binary
We present evidence that the spectroscopically identified bipolar jets of the
pre-main sequence binary KH 15D are a common product of the whole binary
system, rather than being launched from either star individually. They may be
launched from the innermost part of the circumbinary disk (CBD) or may result
from the merging of two outflows driven by the individual stars. This evidence
is based on high-resolution H-alpha and [OI] 6300A line profiles obtained
during eclipse phases of this nearly edge-on system. The occultation of star A
(the only currently visible star) by the disk strongly suppresses the stellar
H-alpha and continuum emission and allows one to study the faint redshifted and
blueshifted emission components of the bipolar jets. The strongest evidence for
jet production by the whole binary system comes from the observed radial
velocity symmetry of the two jet components relative to the systemic velocity
of the binary, in combination with current accretion models from the CBD onto a
binary system.Comment: ApJ Letters, in press [6 pages
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