Opihi NASA InfraRed Telescope Facility(IRTF), Institute for Astronomy, University of Hawaii

Introduction

Opihi is a 17" finderscope for the IRTF, mounted on the IRTF telescope. Opihi will have a wide 0.5 degree square field of view and be able to reach 20th magnitude in about 1 minute. Opihi's main goal is to recover newly discovered asteroids, where uncertainty in the ephemeris is much larger than the FOV of MORIS/SpeX, and the uncertainty in the non-sidereal rates makes guiding difficult. Opihi will enable us to find the target, update the ephemeris, and point MORIS/SpeX to the target.

When not being used to find asteroids, Opihi will run autonomously to monitor the sky tranparency, and provide live images of the sky to the IRTF observer. Since the wavelength coverage of SpeX and Opihi overlap at i-band, Opihi images can be used to flux calibrate SpeX spectra, provided that the target is bright enough at i-band and SpeX is being used in prism or SXD modes.

Opihi is for night time use only. The aperture cover will be kept closed during daylight hours to avoid damage to the system.

Opihi consists of:

• 17" Planewave CDK telescope
• 2k x 2k Andor iKon-L 936 CCD Camera
• Filter wheel with standard SDSS filters
• Linux based computer system running custom IRTF acquition software
• OpihiExarata: a software package for data reduction and image processing

Measured Specs

• Field of View: 0.54 degrees (32')
• Pixel scale: 0.94" / pixel
• Filter wheel positions: SDSS g', r', i', z', clear, blank
• Sensitivity: mag 20.1 (clear), 1 min exposure, S/N=60, quarter moon

Opihi Modes

• Asteroid finder: Manual camera and filter control
• Visible photometry: Manual camera and filter control
• Flux calibration: z-band, user set exposure time, images at 1 minute cadence
• Sky Monitoring: z-band, default exposure time, images at 1 minute cadence
• Guider: TBD

Project Status

• As of Jun 12, 2023...
• 'Opihi is now being offered under shared risk and can be used for asteroid acquisition, absolute flux calibration of SpeX data, optical photometry, and general purpose imaging! We welcome suggestions from any observers who have used or are interested in using 'Opihi.
• Zero point monitoring is fully functional. Check the "Monitor" tab. The automatic mode of 'Opihi successfully ran for a full night and is now used for nightly zeropoint monitoring. Manual mode is also fully functional but has not yet been incorporated as part of standard procedure with our TOs.
• An observing manual and other documentation have been posted to the "Observers Documents" tab.
• As of Jun 10, 2022...

Figure 1: A four-color image of M65 and M66 shown in the entire 32' FOV of Opihi. An illumination frame was created by summing ten 30 s clear exposures. The colors were determined by one 60 s exposure through each of the four filters. Each of the exposures was individually processed (flat field and dark + bias subtraction) before being compiled into a single color image.
• Photometric performance has been measured; data used to create color images (Fig. 1)
• Measured maximum flexure of ~1'

Figure 2: 2022 HP1 visual detection, circled in red, via an A-B subtraction of two 90 s exposures. Guiding was done with MORIS using non-sidereal rates. Background stars can be seen as residual streaks.
• Successful 20th magnitude asteroid detection (Fig. 2)
• Tested ephemeris propagation by locating an asteroid in IRTF's FOV half an hour after the last observation with Opihi
• TO DO: improve software frontend and test on a new object from the MPC's NEO confirmation page
• First Light! Feb 19, 2022