NELIOTA: The wide-field, high-cadence, lunar monitoring system at the prime focus of the Kryoneri telescope

Abstract

We present the technical specifications and first results of the ESA-funded, lunar monitoring project "NELIOTA" (NEO Lunar Impacts and Optical TrAnsients) at the National Observatory of Athens, which aims to determine the size-frequency distribution of small Near-Earth Objects (NEOs) via detection of impact flashes on the surface of the Moon. For the purposes of this project a twin camera instrument was specially designed and installed at the 1.2 m Kryoneri telescope utilizing the fast-frame capabilities of scientific Complementary Metal-Oxide Semiconductor detectors (sCMOS). The system provides a wide field-of-view (17.0 ×14.4 ) and simultaneous observations in two photometric bands (R and I), reaching limiting magnitudes of 18.7 mag in 10 sec in both bands at a 2.5 signal-to-noise level. This makes it a unique instrument that can be used for the detection of NEO impacts on the Moon, as well as for any astronomy projects that demand high-cadence multicolor observations. The wide field-of-view ensures that a large portion of the Moon is observed, while the simultaneous, high-cadence, monitoring in two photometric bands makes possible, for the first time, the determination of the temperatures of the impacts on the Moon's surface and the validation of the impact flashes from a single site. Considering the varying background level on the Moon's surface we demonstrate that the NELIOTA system can detect NEO impact flashes at a 2.5 signal-to-noise level of ∼ 12.4 mag in the I-band and R-band for observations made at low lunar phases (∼ 0.1). We report 31 NEO impact flashes detected during the first year of the NELIOTA campaign. The faintest flash was at 11.24 mag in the R-band (about two magnitudes fainter than ever observed before) at lunar phase 0.32. Our observations suggest a detection rate of 1.96×10 −7 events km −2 h −1 .

Impacts on the Moon: Analysis methods and size distribution of impactors

“…A.5), duration and the calibrated peak magnitudes in R and I bands. Unfortunately, as it is derived by Xilouris et al (2018) and Liakos et al (2020), the reported magnitudes and errors on the NELIOTA database are approximate, while some selenographic coordinates are possibly reported incorrectly (swapped longitude and latitude).…”

“…In this work we follow the same assumptions and methodology that are described in details by Avdellidou & Vaubaillon (2019) and here we remind the main steps. According to Xilouris et al (2018) the NELIOTA magnitudes R and I are calibrated in the Cousins system and the R − I colour is described by the the following equations:…”

“…As of December 1 st 2020 there have been detected, by NELIOTA's double camera system, 112 confirmed LIFs in about 167 hours of observations since February 1 st 2017, giving a rate of 1 flash every 1.5 hours of observations. Extensive details on the instrumentation, the observational method and calibration techniques are given by Xilouris et al (2018) and Bonanos et al (2018). The NELIOTA website 1 provides data for the date and time of each event (Tab.…”

“…These observations have been performed by small and moderate telescopes from the ground with the aim to derive the impact flux of cm-to dm-sized meteoroids (Suggs et al, 2014;Ait Moulay Larbi et al, 2015;Bonanos et al, 2018;Avdelli-dou & Vaubaillon, 2019). In parallel, several detection and analysis techniques have been developed depending on the specific observational setup (single or double camera systems) and the scientific goals of the teams (Bouley et al, 2012;Madiedo et al, 2015b;Xilouris et al, 2018). In a few cases NASA's Lunar Reconnaissance Orbiter (LRO) has detected these impact craters on the lunar surface (Suggs et al, 2014;Robinson et al, 2015;Ortiz et al, 2015).…”

LOCATION, ORBIT AND ENERGY OF A METEOROID IMPACTING THE MOON DURING THE LUNAR ECLIPSE OF JANUARY 21, 2019 & TESTING THE WEAK EQUIVALENCE PRINCIPLE WITH COSMOLOGICAL GAMMA RAY BURSTS

“…MIDAS was the first of such monitor system confirming the L1-21J event. More recently, the NEO Lunar Impacts and Optical TrAnsients, NELIOTA saw the first light [22]. To date at least 55 flashes have been registered by the NELIOTA team, most of them produced by sporadic impactors and some by geminids.…”