Greg W. Doppmann

HIGH-RESOLUTION SPECTROSCOPY OF (Ne ii) EMISSION FROM AA Tau AND GM Aur ∗

We present high-resolution (R = 80,000) spectroscopy of [Ne II] emission from two young stars, GM Aur and AA Tau, which have moderate to high inclinations. The emission from both sources appears centered near the stellar velocity and is broader than the [Ne II] emission measured previously for the face-on disk system TW Hya. These properties are consistent with a disk origin for the [Ne II] emission we detect, with disk rotation (rather than photoevaporation or turbulence in a hot disk atmosphere) playing the dominant role in the origin of the line width. In the non-face-on systems, the [Ne II] emission is narrower than the CO fundamental emission from the same sources. If the widths of both diagnostics are dominated by Keplerian rotation, this suggests that the [Ne II] emission arises from larger disk radii on average than does the CO emission. The equivalent width of the [Ne II] emission we detect is less than that of the spectrally unresolved [Ne II] feature in the Spitzer spectra of the same sources. Variability in the [Ne II] emission or the mid-infrared continuum, a spatially extended [Ne II] component, or a very (spectrally) broad [Ne II] component might account for the differencemorexa0» in the equivalent widths.«xa0less

The TEXES Survey for H2 Emission from Protoplanetary Disks

We report the results of a search for pure rotational molecular hydrogen emission from the circumstellar environments of young stellar objects with disks using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the NASA Infrared Telescope Facility and the Gemini North Observatory. We searched for mid-infrared H2 emission in the S(1), S(2), and S(4) transitions. Keck/NIRSPEC observations of the H2 S(9) transition were included for some sources as an additional constraint on the gas temperature. We detected H2 emission from 6 of 29 sources observed: AB Aur, DoAr 21, Elias 29, GSS 30 IRS 1, GV Tau N, and HL Tau. Four of the six targets with detected emission are class I sources that show evidence for surrounding material in an envelope in addition to a circumstellar disk. In these cases, we show that accretion shock heating is a plausible excitation mechanism. The detected emission lines are narrow (~10 km s^−1), centered at the stellar velocity, and spatially unresolved at scales of 0.4, which is consistent with origin from a disk at radii 10–50 AU from the star. In cases where we detect multiple emission lines, we derive temperatures 500 K from ~1 M⊕ of gas. Our upper limits for the nondetections place upper limits on the amount of H2 gas with T > K of less than a few Earth masses. Such warm gas temperatures are significantly higher than the equilibrium dust temperatures at these radii, suggesting that the gas is decoupled from the dust in the regions that we are studying and that processes such as UV, X-ray, and accretion heating may be important.

HIGH-RESOLUTION K-BAND SPECTROSCOPY OF MWC 480 AND V1331 Cyg*

We present high-resolution (R = 25,000-35,000) K-band spectroscopy of two young stars, MWC 480 and V1331 Cyg. Earlier spectrally dispersed (R = 230) interferometric observations of MWC 480 indicated the presence of an excess continuum emission interior to the dust sublimation radius, with a spectral shape that was interpreted as evidence for hot water emission from the inner disk of MWC 480. Our spectrum of V1331 Cyg reveals strong emission from CO and hot water vapor, likely arising in a circumstellar disk. In comparison, our spectrum of MWC 480 appears mostly featureless. We discuss possible ways in which strong water emission from MWC 480 might go undetected in our data. If strong water emission is in fact absent from the inner disk, as our data suggest, the continuum excess interior to the dust sublimation radius that is detected in the interferometric data must have another origin. We discuss possible physical origins for the continuum excess.

HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF HD 100546. II. ANALYSIS OF VARIABLE ROVIBRATIONAL CO EMISSION LINES

We present observations of rovibrational CO in HD 100546 from four epochs spanning 2003 January through 2010 December. We show that the equivalent widths of the CO lines vary during this time period with the v = 1-0 CO lines brightening more than the UV fluoresced lines from the higher vibrational states. While the spectroastrometric signal of the hot band lines remains constant during this period, the spectroastrometric signal of the v = 1-0 lines varies substantially. At all epochs, the spectroastrometric signals of the UV fluoresced lines are consistent with the signal one would expect from gas in an axisymmetric disk. In 2003, the spectroastrometric signal of the v = 1-0 P26 line was symmetric and consistent with emission from an axisymmetric disk. However, in 2006 there was no spatial offset of the signal detected on the red side of the profile, and in 2010 the spectroastrometric offset was yet more strongly reduced toward zero velocity. A model is presented that can explain the evolution of the equivalent width of the v = 1-0 P26 line and its spectroastrometric signal by adding to the system a compact source of CO emission that orbits the star near the inner edge of the disk. We hypothesize that such emission may arise from a circumplanetary disk orbiting a gas giant planet near the inner edge of the circumstellar disk. We discuss how this idea can be tested observationally and be distinguished from an alternative interpretation of random fluctuations in the disk emission.

Stellar and Circumstellar Properties of the Pre-Main-Sequence Binary GV Tau from Infrared Spectroscopy

We report spatially resolved spectroscopy of both components of the low-mass pre-main-sequence binary GV Tau. High-resolution spectroscopy in the K and L bands is used to characterize the stellar properties of the binary and to explore the nature of the circumstellar environment. We find that the southern component, GV Tau S, is a radial velocity variable, possibly as a result of an unseen low-mass companion. The strong warm gaseous HCN absorption reported previously by Gibb and coworkers toward GV Tau S was not present during the epoch of our observations. Instead, we detect warm (~500 K) molecular absorption with similar properties toward the northern infrared companion, GV Tau N. At the epoch of our observations, the absorbing gas toward GV Tau N was approximately at the radial velocity of the GV Tau molecular envelope, but it was redshifted with respect to the star by ~13 km s−1. One interpretation of our results is that GV Tau N is also a binary and that most of the warm molecular absorption arises in a circumbinary disk viewed close to edge-on.

The radial velocity distribution of class I and flat-spectrum protostars

We analyze radial velocities for a sample of 31 Class I and flat-spectrum protostars in Taurus-Auriga, ? Ophiuchi, and Serpens for evidence of the global dynamical state of extremely young stellar populations buried within parental molecular clouds. Comparing the radial velocity of each protostar to that of the local CO gas, we are able to constrain the one-dimensional radial velocity dispersion of Class I and flat-spectrum objects to ~2.5 km s-1 or below. This upper limit to the protostellar velocity dispersion is consistent with the velocity dispersions of surrounding CO gas, which we measure to be ~1.4 km s-1, suggesting that the motions of protostars and local CO gas are dynamically linked and are dominated by the gravitational potential of the molecular cloud. However, the upper limit on the protostellar velocity dispersion could still allow for slightly inflated motions of protostars relative to the local molecular gas. Four of the protostars analyzed appear to have velocities more than 3 ? (7.5 km s-1) away from the central local CO gas velocity while showing spectroscopic indicators of youth and accretion such as H2 emission, H I Br? emission, or K-band continuum veiling. These radial velocity outliers may represent protostellar spectroscopic binaries or ejected cluster members.

High-resolution Near-infrared Spectroscopy of HD 100546. I. Analysis of Asymmetric Ro-vibrational OH Emission Lines

We present observations of ro-vibrational OH and CO emission from the Herbig Be star HD 100546. The emission from both molecules arises from the inner region of the disk extending from approximately 13?AU from the central star. The velocity profiles of the OH lines are narrower than the velocity profile of the [O I] ?6300 line, indicating that the OH in the disk is not cospatial with the O I. This suggests that the inner optically thin region of the disk is largely devoid of molecular gas. Unlike the ro-vibrational CO emission lines, the OH lines are highly asymmetric. We show that the average CO and average OH line profiles can be fit with a model of a disk comprised of an eccentric inner wall and a circular outer disk. In this model, the vast majority of the OH flux (75%) originates from the inner wall, while the vast majority of the CO flux (65%) originates on the surface of the disk at radii greater than 13?AU. Eccentric inner disks are predicted by hydrodynamic simulations of circumstellar disks containing an embedded giant planet. We discuss the implications of such a disk geometry in light of models of planet-disk tidal interactions and propose alternative explanations for the origin of the asymmetry.

FIRST MAGNETIC FIELD DETECTION ON A CLASS I PROTOSTAR

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 past few years, observations of strong stellar fields on T Tauri stars with field strengths in general agreement with the predictions of magnetospheric accretion theory have bolstered this picture. Currently, nothing is known about the magnetic field properties of younger, more embedded Class I young stellar objects. It is believed that protostars accrete much of their final mass during the Class I phase, but the physics governing this process remains poorly understood. Here, we use high-resolution near-infrared spectra obtained with NIRSPEC on Keck and with Phoenix on Gemini South to measure the magnetic field properties of the Class I protostar WL 17. We find clear signatures of a strong stellar magnetic field. Analysis of this data suggests a surface average field strength of 2.9 {+-} 0.43 kG on WL 17. We present our field measurements and discuss how they fit with the general model of magnetospheric accretion in young stars.

TIME-VARIABLE ACCRETION IN THE TW Hya STAR/DISK SYSTEM

We present two epochs of observations of TW Hya from the high-dispersion near-IR spectrograph ARIES at the Multiple Mirror Telescope. We detect strong emission from the Brγ transition of hydrogen, indicating an accretion rate substantially larger than previously estimated, using hydrogen line emission. The Brγ line strength varies across our two observed epochs. We also measure circumstellar-to-stellar flux ratios (i.e., veilings) that appear close to zero in both epochs. These findings suggest that TW Hya experiences episodes of enhanced accretion while the inner disk remains largely devoid of dust. We discuss several physical mechanisms that may explain these observations.

HIGH-RESOLUTION SPECTROSCOPY DURING ECLIPSE OF THE YOUNG SUBSTELLAR ECLIPSING BINARY 2MASS 0535–0546. I. PRIMARY SPECTRUM: COOL SPOTS VERSUS OPACITY UNCERTAINTIES

We present high-resolution Keck optical spectra of the very young substellar eclipsing binary 2MASS J05352184–0546085, obtained during eclipse of the lower-mass (secondary) brown dwarf. The observations yield the spectrum of the higher-mass (primary) brown dwarf alone, with negligible (~1.6%) contamination by the secondary. We perform a simultaneous fine analysis of the TiO- band and the red lobe of the K I doublet, using state-of-the-art PHOENIX DUSTY and COND synthetic spectra. Comparing the effective temperature and surface gravity derived from these fits to the empirically determined surface gravity of the primary (log g = 3.5) then allows us to test the model spectra as well as probe the prevailing photospheric conditions. We find that: (1) fits to TiO- alone imply T eff = 2500 ± 50 K; (2) at this T eff, fits to K I imply log g = 3.0, 0.5 dex lower than the true value; and (3) at the true log g, K I fits yield T eff = 2650 ± 50 K, ~150 K higher than from TiO- alone. On the one hand, these are the trends expected in the presence of cool spots covering a large fraction of the primarys surface (as theorized previously to explain the observed T eff reversal between the primary and secondary). Specifically, our results can be reproduced by an unspotted stellar photosphere with T eff = 2700 K and (empirical) log g = 3.5, coupled with axisymmetric cool spots that are 15% cooler (2300 K), have an effective log g = 3.0 (0.5 dex lower than photospheric), and cover 70% of the surface. On the other hand, the trends in our analysis can also be reproduced by model opacity errors: there are lacks in the synthetic TiO- opacities, at least for higher-gravity field dwarfs. Stringently discriminating between the two possibilities requires combining the present results with an equivalent analysis of the secondary (predicted to be relatively unspotted compared to the primary).