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Recent observations have demonstrated that very-low mass stars and brown dwarfs are capable of sustaining strong magnetic fields despite their cool and neutral atmospheres. These kG field strengths are inferred based on strong highly circularly polarized GHz radio emission, a consequence of the electron cyclotron maser instability. Crucially, these observations imply the existence of energetic non-thermal electron populations, associated with strong current systems, as are found in the auroral regions of the magnetized planets of the Solar System. Intense auroral electron precipitation will lead to electron collisions with the H$_{2}$ gas that should ultimately generate the ion H$_{3}^{+}$. With this motivation, we targeted a sample of ultracool dwarfs, known to exhibit signatures associated with aurorae, in search of the K-band emission features of H$_{3}^{+}$ using the Keck telescopes on Mauna Kea. From our sample of 9 objects, we found no clear indication of H$_{3}^{+}$ emission features in our low-medium resolution spectra (R$\sim$3600). We also modeled the impact of an auroral electron beam on a brown dwarf atmosphere, determining the depth at which energetic beams deposit their energy and drive particle impact ionization. We find that the H$_{3}^{+}$ non-detections can be explained by electron beams of typical energies $\gtrsim$2-10~keV, which penetrate deeply enough that any H$_{3}^{+}$ produced is chemically destroyed before radiating energy through its infrared transitions. Strong electron beams could further explain the lack of UV detections, and suggest that most or nearly all of the precipitating auroral energy must ultimately emerge as thermal emissions deep in brown dwarf atmospheres., Comment: accepted to ApJ

Occultations provide indirect sensitivity to the number density of small Kuiper Belt objects (KBOs) too faint to directly detect telescopically. We present results from the Caltech HI-speed Multicolor camERA (CHIMERA) survey with the Palomar Hale Telescope, which monitored stars over the central 5'x5' of the M22 globular cluster along the ecliptic plane for serendipitous occultations by kilometer-scale KBOs over 63 hr across 24 nights at a 33 Hz frame rate simultaneously in i' and g'. We adapted dense-field photometry and occultation template fitting techniques to this dataset, finding a 95% confidence upper limit on the occultation rate corresponding to an ecliptic sky density of <10^7 deg^-2 of >1 km diameter classical KBOs. We discuss a few of the occultation-like light curve signatures at the edge of the sensitivity limit responsible for setting the upper bounds, and their likely nonviability as true occultations., Comment: 13 pages, 7 figures, 1 table; AJ, in press

We report a detection of a faint near-Earth asteroid (NEA), which was done using our synthetic tracking technique and the CHIMERA instrument on the Palomar 200-inch telescope. This asteroid, with apparent magnitude of 23, was moving at 5.97 degrees per day and was detected at a signal-to-noise ratio (SNR) of 15 using 30 sec of data taken at a 16.7 Hz frame rate. The detection was confirmed by a second observation one hour later at the same SNR. The asteroid moved 7 arcseconds in sky over the 30 sec of integration time because of its high proper motion. The synthetic tracking using 16.7 Hz frames avoided the trailing loss suffered by conventional techniques relying on 30-sec exposure, which would degrade the surface brightness of image on CCD to an approximate magnitude of 25. This detection was a result of our 12-hour blind search conducted on the Palomar 200-inch telescope over two nights on September 11 and 12, 2013 scanning twice over six 5.0 deg x 0.043 deg fields. The fact that we detected only one NEA, is consistent with Harris's estimation of the asteroid population distribution, which was used to predict the detection of 1--2 asteroids of absolute magnitude H=28--31 per night. The design of experiment, data analysis method, and algorithms for estimating astrometry are presented. We also demonstrate a milli-arcsecond astrometry using observations of two bright asteroids with the same system on Apr 3, 2013. Strategies of scheduling observations to detect small and fast-moving NEAs with the synthetic tracking technique are discussed.

We present an approach that significantly increases the sensitivity for finding and tracking small and fast near Earth asteroids (NEA's). This approach relies on a combined use of a new generation of high-speed cameras which allow short, high frame-rate exposures of moving objects, effectively "freezing" their motion, and a computationally enhanced implementation of the "shift-and-add" data processing technique that helps to improve the signal to noise ratio (SNR) for detection of NEA's. The SNR of a single short exposure of a dim NEA is insufficient to detect it in one frame, but by computationally searching for an appropriate velocity vector, shifting successive frames relative to each other and then co-adding the shifted frames in post-processing, we synthetically create a long-exposure image as if the telescope were tracking the object. This approach, which we call "synthetic tracking," enhances the familiar shift-and-add technique with the ability to do a wide blind search, detect, and track dim and fast-moving NEA's in near real time. We discuss also how synthetic tracking improves the astrometry of fast moving NEA's. We apply this technique to observations of two known asteroids conducted on the Palomar 200-inch telescope and demonstrate improved SNR and 10-fold improvement of astrometric precision over the traditional long exposure approach. In the past 5 years, about 150 NEA's with absolute magnitudes H=28 (~10 m in size) or fainter have been discovered. With an upgraded version of our camera and a field of view of (28 arcmin)^2 on the Palomar 200-inch telescope, synthetic tracking could allow detecting up to 180 such objects per night, including very small NEAs with sizes down to 7 m., Comment: 26 pages, 9 figures, aastex