| Abstract : | The GROWTH-India Telescope (GIT) is a wide-field fully autonomous telescope for time-domain astronomy, set up as a part of the international “Global Relay of Observatories Watching Transients Happen” (GROWTH) network. One of the key science goals of GROWTH is the study of solar system objects - in particular, Near Earth Objects (NEOs) and Potentially Hazardous Asteroids (PHAs) that may disrupt human civilization. The detection and accurate astrometry of such fast-moving near-Earth objects (NEOs) has been a far-standing challenge for the NEO follow-up community. Their fast apparent motion results in streaks in sidereal images, thus affecting the telescope’s limiting magnitude, i.e. reducing the target’s signal-to-noise ratio and chances of detection. In order to boost the signal from faint objects, GIT uses non-sidereal tracking such that the target remains a point source in the image, but stars become elongated streaks, making it difficult to perform standard astrometry. No existing astrometry software is configured to detect such elongated stars. We present Astreaks, a streaking source detection algorithm, to obtain accurate astrometry of NEOs in non-sidereal data. The pipeline uses a precise background estimation technique that appropriately captures the background variations while also considering the presence of elongated sources in the field. Further, we methodically compute the Streak Spread Function (SSF) of elongated sources by convolving the PSF over the streaks. A catalogue of sources detected in the background subtracted image is used to generate a synthetic image that imitates a sidereal image, generating the SSF scaled point sources at the mid-time of the exposure. The astrometry solution of this synthetic image gives the astrometric measurements of the minor planet. We validate the astrometric accuracy of Astreaks on non-sidereal tracked images for more than a hundred observed NEOs with the GROWTH-India Telescope. |
