Magnetic-field measurements of T Tauri stars in the Orion Nebula cluster

We present an analysis of high-resolution ($R \sim 50,000$) 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 $\sim 10^{-11}$ \Msol yr$^{-1}$ 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