ALMA Observations of Asteroid 3 Juno at 60 Kilometer Resolution

We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of 0.042 arcseconds (60 km at 1.97 AU). The data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of ten consecutive images reveals continuous changes in the asteroids profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259pm4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215pm13 K, while the median over the whole surface is 197pm15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas, and lower values beyond the evening terminator. The dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. These results demonstrate ALMAs potential to resolve thermal emission from the surface of main belt asteroids, and to measure accurately their position, geometric shape, rotational period, and soil characteristics.

Subarcsecond Imaging of the NGC 6334 I(N) Protocluster: Two Dozen Compact Sources and a Massive Disk Candidate

Using the SMA and VLA, we have imaged the massive protocluster NGC6334I(N) at high angular resolution (0.5~650AU) from 6cm to 0.87mm, detecting 18 new compact continuum sources. Three of the new sources are coincident with previously-identified water masers. Together with the previously-known sources, these data bring the number of likely protocluster members to 25 for a protostellar density of ~700 pc^-3. Our preliminary measurement of the Q-parameter of the minimum spanning tree is 0.82 -- close to the value for a uniform volume distribution. All of the (nine) sources with detections at multiple frequencies have SEDs consistent with dust emission, and two (SMA1b and SMA4) also have long wavelength emission consistent with a central hypercompact HII region. Thermal spectral line emission, including CH3CN, is detected in six sources: LTE model fitting of CH3CN(J=12-11) yields temperatures of 72-373K, confirming the presence of multiple hot cores. The fitted LSR velocities range from -3.3 to -7.0 km/s, with an unbiased mean square deviation of 2.05 km/s, implying a dynamical mass of 410+-260 Msun for the protocluster. From analysis of a wide range of hot core molecules, the kinematics of SMA1b are consistent with a rotating, infalling Keplerian disk of diameter 800AU and enclosed mass of 10-30 Msun that is perpendicular (within 1 degree) to the large-scale bipolar outflow axis. A companion to SMA1b at a projected separation of 0.45 (590AU; SMA1d), which shows no evidence of spectral line emission, is also confirmed. Finally, we detect one 218.440GHz and several 229.7588GHz Class-I methanol masers.

The Digital Motion Control System for the Submillimeter Array Antennas

We describe the design and performance of the digital servo and motion control system for the 6-meter diameter parabolic antennas of the Submillimeter Array (SMA) on Mauna Kea, Hawaii. The system is divided into three nested layers operating at a different, appropriate bandwidth. (1) A rack-mounted, real-time Unix system runs the position loop which reads the high resolution azimuth and elevation encoders and sends velocity and acceleration commands at 100 Hz to a custom-designed servo control board (SCB). (2) The microcontroller-based SCB reads the motor axis tachometers and implements the velocity loop by sending torque commands to the motor amplifiers at 558 Hz. (3) The motor amplifiers implement the torque loop by monitoring and sending current to the three-phase brushless drive motors at 20 kHz. The velocity loop uses a traditional proportional-integral-derivative (PID) control algorithm, while the position loop uses only a proportional term and implements a command shaper based on the Gauss error function. Calibration factors and software filters are applied to the tachometer feedback prior to the application of the servo gains in the torque computations. All of these parameters are remotely adjustable in software. The three layers of the control system monitor each other and are capable of shutting down the system safely if a failure or anomaly occurs. The Unix system continuously relays antenna status to the central observatory computer via reflective memory. In each antenna, a Palm Vx hand controller displays system status and allows full local control of the drives in an intuitive touchscreen user interface. It can also be connected outside the cabin for convenience during antenna reconfigurations. Excellent tracking performance (0.3 arcsec rms) is achieved with this system. It has been in reliable operation on 8 antennas for over 10 years and has required minimal maintenance.