Jennifer Milburn

Speckle nulling wavefront control for Palomar and Keck

We present a speckle nulling code currently being used for high contrast imaging at the Palomar and Keck telescopes. The code can operate in open and closed loop and is self-calibrating, requiring no system model and minimal hand-coded parameters. Written in a modular fashion, it is straightforward to port to different instruments. It has been used with systems operating in the optical through thermal infrared, and can deliver nearly an order of magnitude improvement in raw contrast. We will be releasing this code to the public in the near future.

CHIMERA: a wide-field, multi-colour, high-speed photometer at the prime focus of the Hale telescope

The Caltech HIgh-speed Multi-colour camERA (CHIMERA) is a new instrument that has been developed for use at the prime focus of the Hale 200-inch telescope. Simultaneous optical imaging in two bands is enabled by a dichroic beam splitter centred at 567 nm, with Sloan u′ and g′ bands available on the blue arm and Sloan r′, i′ and z_s bands available on the red arm. Additional narrow-band filters will also become available as required. An electron multiplying CCD (EMCCD) detector is employed for both optical channels, each capable of simultaneously delivering sub-electron effective read noise under multiplication gain and frame rates of up to 26 fps full frame (several 1000 fps windowed), over a fully corrected 5 × 5 arcmin field of view. CHIMERA was primarily developed to enable the characterization of the size distribution of sub-km Kuiper Belt Objects via stellar occultation, a science case that motivates the frame-rate, the simultaneous multi-colour imaging and the wide field of view of the instrument. In addition, it also has unique capability in the detection of faint near-Earth asteroids and will be used for the monitoring of short-duration transient and periodic sources, particularly those discovered by the intermediate Palomar Transient Factory (iPTF), and the upcoming Zwicky Transient Facility (ZTF).

FLITECAM: early commissioning results

We present a status report and early commissioning results for FLITECAM, the 1-5 micron imager and spectrometer for SOFIA (the Stratospheric Observatory for Infrared Astronomy). In February 2014 we completed six flights with FLITECAM mounted in the FLIPO configuration, a co-mounting of FLITECAM and HIPO (High-speed Imaging Photometer for Occultations; PI Edward W. Dunham, Lowell Observatory). During these flights, the FLITECAM modes from ~1-4 μm were characterized. Since observatory verification flights in 2011, several improvements have been made to the FLITECAM system, including the elimination of a light leak in the FLITECAM filter wheel enclosure, and updates to the observing software. We discuss both the improvements to the FLITECAM system and the results from the commissioning flights, including updated sensitivity measurements. Finally, we discuss the utility of FLITECAM in the FLIPO configuration for targeting exoplanet transits.

FLITECAM: current status and results from observatory verification flights

This paper describes the current status of FLITECAM, the near-infrared (1 - 5 μm) camera and spectrometer for NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA). Due to a change in schedule FLITECAM’s delivery was advanced, allowing it to be co-mounted with the HIPO instrument and used on four flights in October 2011 for observatory verification. Although not part of FLITECAM’s commissioning time, some preliminary performance characteristics were determined. Image size as a function of wavelength was measured prior to the installation of active mass dampers on the telescope. Preliminary grism spectroscopy was also obtained. In addition, FLITECAM was used to measure the emissivity of the telescope and warm optics in the co-mounted configuration. New narrow band filters were added to the instrument, including a Paschen alpha filter for line emission. Results are illustrated.

The Zwicky Transient Facility Camera

The Zwicky Transient Facility Camera (ZTFC) is a key element of the ZTF Observing System, the integrated system of optoelectromechanical instrumentation tasked to acquire the wide-field, high-cadence time-domain astronomical data at the heart of the Zwicky Transient Facility. The ZTFC consists of a compact cryostat with large vacuum window protecting a mosaic of 16 large, wafer-scale science CCDs and 4 smaller guide/focus CCDs, a sophisticated vacuum interface board which carries data as electrical signals out of the cryostat, an electromechanical window frame for securing externally inserted optical filter selections, and associated cryo-thermal/vacuum system support elements. The ZTFC provides an instantaneous 47 deg2 field of view, limited by primary mirror vignetting in its Schmidt telescope prime focus configuration. We report here on the design and performance of the ZTF CCD camera cryostat and report results from extensive Joule-Thompson cryocooler tests that may be of broad interest to the instrumentation community.

Know the Star, Know the Planet. IV. A Stellar Companion to the Host Star of the Eccentric Exoplanet HD 8673b

HD 8673 hosts a massive exoplanet in a highly eccentric orbit (e = 0.723). Based on two epochs of speckle interferometry a previous publication identified a candidate stellar companion. We observed HD 8673 multiple times with the 10 m Keck II telescope, the 5 m Hale telescope, the 3.63 m Advanced Electro-Optical System telescope, and the 1.5 m Palomar telescope in a variety of filters with the aim of confirming and characterizing the stellar companion. We did not detect the candidate companion, which we now conclude was a false detection, but we did detect a fainter companion. We collected astrometry and photometry of the companion on six epochs in a variety of filters. The measured differential photometry enabled us to determine that the companion is an early M dwarf with a mass estimate of 0.33–0.45 M_☉. The companion has a projected separation of 10 AU, which is one of the smallest projected separations of an exoplanet host binary system. Based on the limited astrometry collected, we are able to constrain the orbit of the stellar companion to a semimajor axis of 35–60 AU, an eccentricity ≤0.5, and an inclination of 75°–85°. The stellar companion has likely strongly influenced the orbit of the exoplanet and quite possibly explains its high eccentricity.

The Zwicky transient facility robotic observing system (Conference Presentation)

The transient universe is fast becoming one of the most important research areas in astronomy. Finding objects that change, either quickly or periodically, has opened up new understanding of the cosmos around us, and brought up new questions that require further investigation. The Zwicky Transient Facility (ZTF) has been developed to observe as much of the sky as possible at a rapid rate, in order to expand the regime of time domain measurement to shorter intervals and detect changes in the sky more quickly. ZTF is a fully automated system, composed of the Samuel Oschin 48-inch (1.2m) telescope at Palomar Observatory (P48), the mosaic camera constructed by Caltech, a filter exchange system, associated sensors and electrical systems, and the Robotic Observing Software (ROS) that controls the operation of the entire system. P48 is a 70 year old telescope that has been upgraded with new hardware, electronics, and a modern telescope control system to allow it to move quickly and accurately across the sky under robotic control. The ZTF mosaic camera is a custom system composed of 16 6Kx6K pixel CCDs, creating a mosaic camera with over 576 million pixels that can image 47 square degrees down to a magnitude of 20.5 in a 30 second exposure. The filter exchange system uses a Kuka robotic arm to grab the 400x450mm filters out of a storage closet and place them onto the front of the mosaic camera, where they are held in place by electromagnets and locking pins. A full sensor system monitors the health of the camera dewar and environment of the observatory; a separate weather station monitors the outside environment. Other subsystems control the motion of the Hexapod that the mosaic camera is mounted on, the top end shutter, and remote switching of power, Managing all of these subsystems is ROS, which is the automated control software that runs ZTF observations. ROS is based on the Robo-AO control system, with improved automation procedures and expanded capabilities to handle the operations required for ZTF. ROS consists of 31 separate software daemons spread across 5 computer systems (4 to control the mosaic camera, 1 for robotic operation); the robotic control daemon is able to manage all daemons, as well as start and stop their operation as necessary. Watchdog daemons intervene in case of robotic system problems, and each daemon has an internal watchdog that can fix or kill the daemon in case of difficulties; if a daemon dies the robotic system automatically restarts it. ROS controls the start of observations and morning shut down, handles weather monitoring and safely stopping in case of bad weather, and responds to problems in the observing sequence by fixing them or stopping operations and sending a message for help. All calibration measurements are done automatically at the beginning of the night; if the calibrations are interrupted they are completed after observations finish in the morning. A queue system determines the observation priority and revises the order of observations dynamically to optimize observational efficiency. ROS is able to operate with less than 15 second overhead between each standard ZTF observation (with a 7.5 degree slew); this is achieved by reading out thee mosaic camera during telescope slew, then transferring and writing FITS data files during the next exposure. FITS headers are kept synchronized through daemons that gather all relevant FITS header information and distribute that to the camera computers. ROS is able to produce more than 80 mosaic science images per hour in standard survey mode; each mosaic is a total of 380MB compressed, so the system produces more than 30GB of data on disk per hour that have to be transferred off the mountain. A new data transfer system synchronizes the compressed FITS data files to the data analysis servers in Pasadena, CA in parallel with the observing system; images are in place for the data analysis pipelines in less than a minute after the ZTF shutter closes. This presentation will discuss the development and execution of the ZTF observing software, as well as analyze the observational behavior and efficiency of the system during the first few months of on-sky science observations.

WIRC+Pol: low-resolution near-infrared spectropolarimeter

WIRC+Pol is a newly commissioned low-resolution (R 100), near-infrared (J and H bands) spectropolarimetry mode of the Wide-field InfraRed Camera (WIRC) on the 200-inch Hale Telescope at Palomar Observatory. The instrument utilizes a novel polarimeter design based on a quarter-wave plate and a polarization grating (PG), which provides full linear polarization measurements (Stokes I, Q, and U ) in one exposure with no need for a polarimetric modulator. The PG also has high transmission across the J and H bands. The instrument is situated at the prime focus of an equatorially mounted telescope. As a result, the system only has one reflection in the light path and the instrument does not rotate with respect to the sky, which provides minimal and stable telescope induced polarization. A data reduction pipeline has been developed for WIRC+Pol to produce linear polarization measurements from observations, allowing, e.g., real-time monitoring of the signal-to-noise ratio of ongoing observations. WIRC+Pol has been on-sky since February 2017. Results from the first year commissioning data show that the instrument has a high dispersion efficiency as expected from the polarization grating. We discuss instrumental systematics we have uncovered in the data, their potential causes, along with calibrations that are necessary to eliminate them. We demonstrate the polarimetric stability of the instrument with RMS variation at 0.2% level over 30 minutes for a bright standard star (J = 8.7). While the spectral extraction is photon noise limited, polarization calibration between sources remain limited by systematics.

Aligning the ZTF science focal plane using stellar images

The Zwicky Transient Facility (ZTF) is a next-generation, optical, synoptic survey that leverages the success of the Palomar Transient Factory (PTF). ZTF has a large science focal plane (SFP) that needs to be aligned such that all portions of the CCDs are simultaneously placed in focus to optimize the survey’s efficiency. The SFP consists of 16 large, wafer-scale science CCDs, which are mosaicked to achieve 47 deg2 field of view. The SFP is aligned by repositioning each CCD based on the measured height map, which is a map of the camera’s z position at which each portion of the CCD is in focus. This height map is measured using on-sky stellar images in order to recreate the optical path that will be used throughout the survey. We present our technique for placing the SFP in focus, which includes two different methods to measure the height map of the SFP. The first method measures the height at which a star is in focus by fitting a parabola to each star’s photometric width as the star is moved in and out of focus. The second method measures the height by decomposing a defocused star into its image moments. We will discuss the strengths and limitations of each method and their outputs. By repositioning the CCDs, we were able to reduce the standard deviation of the height map from 33 to 14microns, which improved the survey’s speed by ∼ 81%.

PULSE: The Palomar Ultraviolet Laser for the Study of Exoplanets

The Palomar Ultraviolet Laser for the Study of Exoplanets (PULSE) will dramatically expand the science reach of PALM-3000, the facility high-contrast extreme adaptive optics system on the 5-meter Hale Telescope. By using an ultraviolet laser to measure the dominant high spatial and temporal order turbulence near the telescope aperture, one can increase the limiting natural guide star magnitude for exquisite correction from mV < 10 to mV < 16. Providing the highest near-infrared Strehl ratios from any large telescope laser adaptive optics system, PULSE uniquely enables spectroscopy of low-mass and more distant young exoplanet systems, essential to formulating a complete picture of exoplanet populations.