Detection of Thermal Emission of XO-2b: Evidence for a Weak Temperature Inversion (2009)
Machalek, Pavel, McCullough, Peter R., Burrows, Adam, Burke, Christopher J., Hora, Joseph L., Johns-Krull, Christopher M.
We estimate flux ratios of the extrasolar planet XO-2b to its host star XO-2 at 3.6, 4.5, 5.8 and 8.0 micron with IRAC on the Spitzer Space Telescope to be 0.00081 +- 0.00017, 0.00098 +- 0.00020,...
First Magnetic Field Detection on a Class I Protostar (2009)
Johns-Krull, Christopher M., Greene, Thomas P., Doppmann, Greg W., Covey, Kevin R.
Strong stellar magnetic fields are believed to truncate the inner accretion disks around young stars, redirecting the accreting material to the high latitude regions of the stellar surface. In the...
Stellar and Circumstellar Properties of Class I Protostars (2009)
Prato, L., Lockhart, K. E., Johns-Krull, Christopher M., Rayner, John T.
We present a study of the stellar and circumstellar properties of Class I sources using low-resolution (R~1000) near-infrared K- and L-band spectroscopy. We measure prominent spectral lines and...
Magnetic Properties of Young Stars in the TW Hydrae Association (2008)
Yang, Hao, Johns-Krull, Christopher M., Valenti, Jeff A.
We present an analysis of infrared (IR) echelle spectra of five stars in the TW Hydrae Association (TWA). We model the Zeeman broadening in four magnetic-sensitive \ion{Ti}{1} lines near $2.2 \mu$m...
XO-4b: An Extrasolar Planet Transiting an F5V Star (2008)
McCullough, P. R., Burke, Christopher J., Valenti, Jeff A., Long, Doug, Johns-Krull, Christopher M., Machalek, P., ...
We report the discovery of the planet XO-4b, which transits the star XO-4 (GSC 03793-01994, V=10.7, F5V). Transits are 1.0% deep and 4.4 hours in duration. The star XO-4 has a mass of 1.32 M_sun.......
XO-5b: A Transiting Jupiter-sized Planet With A Four Day Period (2008)
Burke, Christopher J., McCullough, P. R., Valenti, Jeff A., Long, Doug, Johns-Krull, Christopher M., Machalek, P., ...
The star XO-5 (GSC 02959-00729, V=12.1, G8V) hosts a Jupiter-sized, Rp=1.15+/-0.12 Rjup, transiting extrasolar planet, XO-5b, with an orbital period of P=4.187732+/-0.00002 days. The planet mass...
The Transit Light Curve Project. IX. Evidence for a Smaller Radius of the Exoplanet XO-3b (2008)
Winn, Joshua N., Holman, Matthew J., Torres, Guillermo, McCullough, Peter, Johns-Krull, Christopher M., Latham, David W., ...
We present photometry of 13 transits of XO-3b, a massive transiting planet on an eccentric orbit. Previous data led to two inconsistent estimates of the planetary radius. Our data strongly favor the...
Reflected Light from Sand Grains in the Terrestrial Zone of a Protoplanetary Disk (2008)
Herbst, William, Hamilton, Catrina M., LeDuc, Katherine, Winn, Joshua N., Johns-Krull, Christopher M., Mundt, Reinhard, ...
We show that grains have grown to ~mm size (sand sized) or larger in the terrestrial zone (within ~3 AU) of the protoplanetary disk surrounding the 3 Myr old binary star KH 15D. We also argue that...
Reflected light from sand grains in the terrestrial zone of a protoplanetary disk (2008)
Herbst, William, Hamilton, Catrina M., Leduc, Katherine, Winn, Joshua N., Johns-Krull, Christopher M., Mundt, Reinhard, ...
In the standard model of terrestrial planet formation, the first step in the process is for interstellar dust to coagulate within a protoplanetary disk surrounding a young star, forming large grains...
XO-3b: A Massive Planet in an Eccentric Orbit Transiting an F5V Star (2007)
Johns-Krull, Christopher M., McCullough, Peter R., Burke, Christopher J., Valenti, Jeff A., Janes, K. A., Heasley, J. N., ...
We report the discovery of a massive (Mpsini = 13.02 +/- 0.64 Mjup; total mass 13.25 +/- 0.64 Mjup), large (1.95 +/- 0.16 Rjup) planet in a transiting, eccentric orbit (e = 0.260 +/- 0.017) around a...
Star Spot Induced Radial Velocity Variability in LkCa 19 (2007)
Huerta, Marcos, Johns-Krull, Christopher M., Prato, L., Hartigan, Patrick, Jaffe, D. T.
We describe a new radial velocity survey of T Tauri stars and present the first results. Our search is motivated by an interest in detecting massive young planets, as well as investigating the origin...
Characterizing the Near-UV Environment of M Dwarfs (2007)
Walkowicz, Lucianne M., Johns-Krull, Christopher M., Hawley, Suzanne L.
We report the results of our HST snapshot survey with the ACS HRC PR200L prism, designed to measure the near-UV emission in a sample of nearby M dwarfs. 33 stars were observed, spanning the mass...
XO-2b: Transiting Hot Jupiter in a Metal-rich Common Proper Motion Binary (2007)
Burke, Christopher J., McCullough, P. R., Valenti, Jeff A., Johns-Krull, Christopher M., Janes, Kenneth A., Heasley, J. N., ...
We report on a V=11.2 early K dwarf, XO-2 (GSC 03413-00005), that hosts a Rp=0.98+0.03/-0.01 Rjup, Mp=0.57+/-0.06 Mjup transiting extrasolar planet, XO-2b, with an orbital period of...
The Magnetic Fields of Classical T Tauri Stars (2007)
We report new magnetic field measurements for 14 classical T Tauri stars (CTTSs). We combine these data with one previous field determination in order to compare our observed field strengths with the...
How Hot is the Wind from TW Hydrae? (2007)
Johns-Krull, Christopher M., Herczeg, Gregory J.
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 300,000 K while maintaining a mass-loss rate of...
How hot is the wind from TW Hydrae? (2007)
Johns-Krull, Christopher M., Herczeg, Gregory J.
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 300,000 K while maintaining a mass-loss rate of...
Accurate M Dwarf Metallicities from Spectral Synthesis: A Critical Test of Model Atmospheres (2006)
Bean, Jacob L., Sneden, Christopher, Hauschildt, Peter H., Johns-Krull, Christopher M., Benedict, G. Fritz
We describe a method for accurately determining M dwarf metallicities with spectral synthesis based on abundance analyses of visual binary stars. We obtained high resolution, high signal-to-noise...
The Origins of Fluorescent H2 Emission From T Tauri~Stars (2006)
Herczeg, Gregory J., Linsky, Jeffrey L., Walter, Frederick M., Gahm, Gosta F., Johns-Krull, Christopher M.
We survey fluorescent H2 emission in HST/STIS spectra of the classical T Tauri stars (CTTSs) TW Hya, DF Tau, RU Lupi, T Tau, and DG Tau, and the weak-lined T Tauri star (WTTS) V836 Tau. From each of...
Johns-Krull, Christopher M., Valenti, Jeff A., Saar, Steven H.
High resolution optical and infrared (IR) echelle spectra of the naked (diskless) T Tauri star Hubble 4 are presented. The K band IR spectra include 4 Zeeman sensitive Ti I lines along with several...
KH 15D: A Spectroscopic Binary (2004)
Johnson, John A., Marcy, Geoffrey W., Hamilton, Catrina M., Herbst, William, Johns-Krull, Christopher M.
We present the results of a high-resolution spectroscopic monitoring program of the eclipsing pre-main-sequence star KH 15D that reveal it to be a single-line spectroscopic binary. We find that the...
Mapping the Circumstellar Environment of T Tauri with Fluorescent H_2 Emission (2003)
Walter, Frederick M., Herczeg, Gregory, Brown, Alexander, Ardila, David R., Gahm, Goesta F., Johns-Krull, Christopher M., ...
We have obtained three long-slit, far UV spectra of the pre-main sequence system T Tauri. These HST/STIS spectra show a strong and variable on-source spectrum composed of both fluoresced H_2 and...
Hamilton, Catrina M., Herbst, William, Mundt, Reinhard, Johns-Krull, Christopher M.
We present high resolution (R $\sim$ 44,000) UVES spectra of the eclipsing pre-main sequence star KH 15D covering the wavelength range 4780 to 6810 {\AA} obtained at three phases: out of eclipse,...
Transition Region Emission From Very Low Mass Stars (2003)
Hawley, Suzanne L., Johns-Krull, Christopher M.
We present results from our cycle 10 HST program to search for transition region emission in very low-mass, main-sequence stars in the spectral range M7-M9. Our program is aimed at 1) detecting...
Hamilton, Catrina M., Herbst, William, Mundt, Reinhard, Johns-Krull, Christopher M.
We present high-resolution (R~44,000) UV-Visual Echelle Spectrograph spectra of the eclipsing pre-main-sequence star KH 15D covering the wavelength range 4780-6810 Å obtained at three phases: out of...
New Tests of Magnetospheric Accretion in T Tauri Stars (2002)
Johns-Krull, Christopher M., Gafford, April D.
We examine 3 analytic theories of magnetospheric accretion onto classical T Tauri stars under the assumption that the magnetic field strength does not vary appreciably from star to star. From these...
Observations of T-Tauri Stars using HST-GHRS: II. Optical and Near UV lines (2001)
Ardila, David R., Basri, Gibor, Walter, Frederick M., Valenti, Jeff A., Johns-Krull, Christopher M.
We have analyzed GHRS data of eight Classical T Tauri stars (CTTSs) and one Weak T Tauri star (WTTS). The GHRS data consist of an spectral range 40 A wide centered on 2800 A. For 4 of the CTTS we...