Engine inlet distortion in a 9.2 percent scale vectored thrust STOVL model in ground effect

Advanced Short Takeoff/Vertical Landing (STOVL) aircraft which can operate from remote locations, damaged runways, and small air capable ships are being pursued for deployment around the turn of the century. To achieve this goal, NASA Lewis Research Center, McDonnell Douglas Aircraft, and DARPA defined a cooperative program for testing in the NASA Lewis 9- by 15-foot low speed wind tunnel (LSWT) to establish a database for hot gas ingestion, one of the technologies critical to STOVL. Results are presented which show the engine inlet distortions (both temperature and pressure) in a 9.2 percent scale vectored thrust STOVL model in ground effects. Results are shown for the forward nozzle splay angles of 0 degrees, -6 degrees, and 18 degrees. The model support system had 4 degrees of freedom, heated high pressure air for nozzle flow, and a suction system exhaust for inlet flow. The headwind (freestream) velocity was varied from 8 to 23 knots

A Young Planet Search in Visible and IR Light: DN Tau, V836 Tau, and V827 Tau

In searches for low-mass companions to late-type stars, correlation between radial velocity variations and line bisector slope changes indicates contamination by large starspots. Two young stars demonstrate that this test is not sufficient to rule out starspots as a cause of radial velocity variations. As part of our survey for substellar companions to T Tauri stars, we identified the ~2 Myr old planet host candidates DN Tau and V836 Tau. In both cases, visible light radial velocity modulation appears periodic and is uncorrelated with line bisector span variations, suggesting close companions of several M_Jup in these systems. However, high-resolution, infrared spectroscopy shows that starspots cause the radial velocity variations. We also report unambiguous results for V827 Tau, identified as a spotted star on the basis of both visible light and infrared spectroscopy. Our results suggest that infrared follow up observations are critical for determining the source of radial velocity modulation in young, spotted stars.Comment: Accepted for publication in the Astrophysical Journal Letter

Accretion-powered Stellar Winds as a Solution to the Stellar Angular Momentum Problem

We compare the angular momentum extracted by a wind from a pre-main-sequence star to the torques arising from the interaction between the star and its Keplerian accretion disk. We find that the wind alone can counteract the spin-up torque from mass accretion, solving the mystery of why accreting pre-main-sequence stars are observed to spin at less than 10% of break-up speed, provided that the mass outflow rate in the stellar winds is ~10% of the accretion rate. We suggest that such massive winds will be driven by some fraction $\epsilon$ of the accretion power. For observationally constrained typical parameters of classical T-Tauri stars, $\epsilon$ needs to be between a few and a few tens of percent. In this scenario, efficient braking of the star will terminate simultaneously with accretion, as is usually assumed to explain the rotation velocities of stars in young clusters.Comment: Accepted by ApJ Letter

El Niño and the delayed action oscillator

We study the dynamics of the El Niño phenomenon using the mathematical model of delayedaction oscillator (DAO). Topics such as the influence of the annual cycle, global warming, stochastic influences due to weather conditions and even off-equatorial heat-sinks can all be discussed using only modest analytical and numerical resources. Thus the DAO allows for a pedagogical introduction to the science of El Niño and La Niña while at the same time avoiding the need for large-scale computing resources normally associated with much more sophisticated coupled atmosphere-ocean general circulation models. It is an approach which is ideally suited for student projects both at high school and undergraduate level

Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph

From observations collected with the ESPaDOnS spectropolarimeter, we report the discovery of magnetic fields at the surface of the mildly accreting classical T Tauri star V2129 Oph. Zeeman signatures are detected, both in photospheric lines and in the emission lines formed at the base of the accretion funnels linking the disc to the protostar, and monitored over the whole rotation cycle of V2129 Oph. We observe that rotational modulation dominates the temporal variations of both unpolarized and circularly polarized line profiles. We reconstruct the large-scale magnetic topology at the surface of V2129 Oph from both sets of Zeeman signatures simultaneously. We find it to be rather complex, with a dominant octupolar component and a weak dipole of strengths 1.2 and 0.35 kG, respectively, both slightly tilted with respect to the rotation axis. The large-scale field is anchored in a pair of 2-kG unipolar radial field spots located at high latitudes and coinciding with cool dark polar spots at photospheric level. This large-scale field geometry is unusually complex compared to those of non-accreting cool active subgiants with moderate rotation rates. As an illustration, we provide a first attempt at modelling the magnetospheric topology and accretion funnels of V2129 Oph using field extrapolation. We find that the magnetosphere of V2129 Oph must extend to about 7R* to ensure that the footpoints of accretion funnels coincide with the high-latitude accretion spots on the stellar surface. It suggests that the stellar magnetic field succeeds in coupling to the accretion disc as far out as the corotation radius, and could possibly explain the slow rotation of V2129 Oph. The magnetospheric geometry we derive produces X-ray coronal fluxes typical of those observed in cTTSs.Comment: MNRAS, in press (18 pages, 17 figures

Corn as a Grazing Crop: An Option for Extending the Grazing Season in Kentucky

Grazing is the cheapest way to feed cattle on a cost per pound of nutrient basis. However, producers with limited land resources in Kentucky have been able to use commodities or grain by-products to increase cattle numbers due to low cost and availability of these inputs. Extending the grazing season is one solution that would enable producers to reduce cost and expand production with little or no impact on the environment

The Angular Momentum Evolution of 0.1-10 Msun Stars From the Birthline to the Main Sequence

(Abridged) Projected rotational velocities (vsini) have been measured for a sample of 145 stars with masses between 0.4 and >10 Msun (median mass 2.1 Msun) located in the Orion star-forming complex. These measurements have been supplemented with data from the literature for Orion stars with masses as low as 0.1 Msun. The primary finding from analysis of these data is that the upper envelope of the observed values of angular momentum per unit mass (J/M) varies as M^0.25 for stars on convective tracks having masses in the range ~0.1 to ~3 Msun. This power law extends smoothly into the domain of more massive stars (3 to 10 Msun), which in Orion are already on the ZAMS. This result stands in sharp contrast to the properties of main sequence stars, which show a break in the power law and a sharp decline in J/M with decreasing mass for stars with M <2 Msun. A second result of our study is that this break is seen already among the PMS stars in our Orion sample that are on radiative tracks, even though these stars are only a few million years old. A comparison of rotation rates seen for stars on either side of the convective-radiative boundary shows that stars do not rotate as solid bodies during the transition from convective to radiative tracks.Comment: to appear in Ap

Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546

[Abridged] We present the first simultaneous radio, X-ray, ultraviolet, and optical spectroscopic observations of the M8.5 dwarf TVLM513-46546, with a duration of 9 hours. These observations are part of a program to study the origin of magnetic activity in ultracool dwarfs, and its impact on chromospheric and coronal emission. Here we detect steady quiescent radio emission superposed with multiple short-duration, highly polarized flares; there is no evidence for periodic bursts previously reported for this object, indicating their transient nature. We also detect soft X-ray emission, with L_X/L_bol~10^-4.9, the faintest to date for any object later than M5, and a possible weak X-ray flare. TVLM513-46546 continues the trend of severe violation of the radio/X-ray correlation in ultracool dwarfs, by nearly 4 orders of magnitude. From the optical spectroscopy we find that the Balmer line luminosity exceeds the X-ray luminosity by a factor of a few, suggesting that, unlike in early M dwarfs, chromospheric heating may not be due to coronal X-ray emission. More importantly, we detect a sinusoidal H-alpha light curve with a period of 2 hr, matching the rotation period of TVLM513-46546. This is the first known example of such Balmer line behavior, which points to a co-rotating chromospheric hot spot or an extended magnetic structure, with a covering fraction of about 50%. This feature may be transitory based on the apparent decline in light curve peak during the four observed maxima. From the radio data we infer a large scale steady magnetic field of ~100 G, in good agreement with the value required for confinement of the X-ray emitting plasma. The radio flares, on the other hand, are produced in a component of the field with a strength of ~3 kG and a likely multi-polar configuration.Comment: 13 pages, 4 figure