Croatian group MAGIC & CTA meeting Status report: Stellar occultation observations September 25, 2019 University of Zagreb - FER with MAGIC Stefan Cikota, mag. phys. University of Zagreb, Faculty of Electrical Engineering and Computing - FER • A stellar occultation occurs when the light from a star is blocked by an intervening body (such as an asteroid) Stellar from reaching an observer. Occultations • Short duration event - takes normally between a few seconds, up to ~100 seconds for distant and large objects • Used to determine physical characteristics of Small Solar System objects • Beloved for amateur astronomers S. Cikota: Stellar occultation observations by MAGIC 2 / 18 DETERMINING PHYSICAL CHARACTERISTICS Small OF SMALL SOLAR SYSTEM OBJECTS Solar • Direct observations System - large telescopes & spacecraft missions Objects • Indirect observations - Astrometry & Photometry - Occultations • Occultations allow us to estimate the objects’ size, shape, atmosphere, other features • Resolutions of a few kilometers: several orders of magnitude better than the resolution of any other Earth-based method. S. Cikota: Stellar occultation observations by MAGIC 3 / 18 Determination of precise diameter of dwarf planet Eris Ortiz Scientific et ERIS ± . • R = 1163 6 km al Importance: IAA,2010 ., TNOs • RPLUTO = 1153 ± 10 km • Almost same diameter • Mass of Eris is 27% larger than Mass of Pluton. • AlbedoPLUTON = ~0.58 AlbedoERIS = ~0.96 S. Cikota: Stellar occultation observations by MAGIC 4 / 18 Recently used to probe ring systems and atmospheres outer solar system 4 very high impact publications published in the Journal Nature: • Sicardy et al. (2011): A Pluto-like radius and a high albedo for the dwarf planet Eris Scientific from an occultation • Ortiz, J.L. et al. (2012): Albedo and atmospheric constraints of dwarf planet Importance: Makemake from a stellar occultation • Braga-Ribas, F. et al. (2014): A ring system detected around the Centaur (10199) TNOs Chariklo • Ortiz, J.L. et al. (2017): The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation Braga - Ribas , F. et (201 et al. F. , 4) S. Cikota: Stellar occultation observations by MAGIC 5 / 18 Eris • Stellar occultations by TNOs are extremely rare events from which plenty of scientific information can be gathered Occultation • They are very difficult to predict predictions and observe because the ephemeris of all the TNOs are far more uncertain than their angular diameters. • Angular size of Eris: like a tennis ball on a distance of 411 km • Seen from the Earth, the stars are always point-like sources S. Cikota: Stellar occultation observations by MAGIC 6 / 18 Optical telescopes vs. MAGIC Why Optical telescopes with CCD cameras MAGIC? Sampling rate: 1-10 Hz sampling frequency Best case resolution on TNO occultations: ~ 5 - 10 km Telescope mirror diameters: 0.4 – 10.4 m MAGIC II Central Pixel MAGIC is sensitive to millisecond-duration optical pulses (periodic signals from the Crab pulsar are regularly monitored) Sampling rate: 10000 Hz Best case resolution on TNO resolution: 0.5 - 1 m MAGIC mirror diameter: 17 m S. Cikota: Stellar occultation observations by MAGIC 7 / 18 MAGIC is capable of detecting the Crab pulsation in very short observation time (Hassan, T. et al., 2017, Proceedings of the 35th Central pixel International Cosmic Ray Conference: MAGIC sensitivity to millisecond-duration optical pulses) performance SAMPLING PERIOD: 0.000100 SEC VOLTAGE RANGE: 2000 MILLIVOLTS Hassan , T. et al. et , 2017 Left: Crab light-curve after 5 minutes Upper: Raw Central Pixel data of Crab of observation with the MAGIC II CPix pulsar – individual pulses detectable S. Cikota: Stellar occultation observations by MAGIC 8 / 18 Hassan, T. et al., 2017: Sensitivity test to isolated optical pulses Central pixel • experimental determination of the sensitivity of the central pixel to isolated 1-10 ms long optical pulses performance • Central pixel’s data was collected during MAGIC’s slewing • optical pulses of ∼20 ms were produced by the stars of known brightness and length passing through the central pixels’ FOV (∼0.1 deg) were used to determine the correlation between the maximum voltage of a pulse with the known magnitude of the stars S. Cikota: Stellar occultation observations by MAGIC 9 / 18 Direct measurement of voltage vs. magnitude dependence • The central pixel’s sensitivity to isolated optical pulses is Central pixel determined by extrapolating the fitted curve to the voltage performance corresponding to a 5-σ excess over the background noise level Hassan , T. • The limiting al. et , magnitude 2017 to detect a 1 ms optical flash is m = 13.5 ± 0.6 S. Cikota: Stellar occultation observations by MAGIC 10 / 18 • Hardware limitations: CPix is designed to detect very fast brightness changes (RC-circuit, normalizing the signal within ~3 ms) Expectation • We know we can detect such fast pulses down to magnitude B~14, on observation so an equivalent drop of ~14 m would be detectable. Occultation LC A drop in flux lasting for ~1 ms will turn into a Cpix signal spike of ~3 ms width and the same amplitude S. Cikota: Stellar occultation observations by MAGIC 11 / 18 Central pixel sensitivity test for Stellar Occultation observations • General goal: use the central pixel detector for specific occultations, Our goals like those of TNOs with rings • Because such occultation events are very rare (in average less than once per year for a specific location): find an appropriate Main Belt Asteroid occultation candidate to test the method • For the sensitivity test, we propose to follow up some well known, high-probability occultation events • The required observation time is generally very short • Predictions usually come with a relatively short notice, therefore observations should be scheduled as targets of opportunity (or similar) • Interesting side-results: stelar radii S. Cikota: Stellar occultation observations by MAGIC 12 / 18 (50) Virginia (746) Marlu (13) Egeria 21 Dec 2017 , 04:22 UT 10 Apr 2018 , 03:40 UT 12 May 2018, 22:21 UT Combined brightness: Target star: 11.2 mag. Combined brightness: 11.2 mag. Brightness drop: 3.3 mag. 9.6 mag. Missed Brightness drop: 0.6 mag. Brightness drop: 0.7 m Additional astrometry from opportunities Scheduled, but no San Pedro de Atacama DDT, scheduled, later observations due to strong confirmed shadow removed from schedule due wind to misunderstanding No observations due to humidity, wind and later ice S. Cikota: Stellar occultation observations by MAGIC 13 / 18 • Less discussions, more action: VERITAS is more effective than MAGIC in immplementing new ideas Nature Astronomy S. Cikota: Stellar occultation observations by MAGIC 14 / 18 Nature Astronomy „The authors want to acknowledge discussions with S. Cikota and J. Cortina.” S. Cikota: Stellar occultation observations by MAGIC 15 / 18 • Proposal approved (PI) for Cycle 14: Central pixel observations of stellar occultations by asteroids Cycle 14 • 10 x 10 minutes of telescope time approved • Focusing tests performed during observation shift P199 S. Cikota: Stellar occultation observations by MAGIC 16 / 18 One promising candidate until now: Asteroid: (751) Faina (mag 12.9) Target star: UCAC4-465-51138 Cycle 14 (mag 10.1) Date: 27 April 2019 , 00:57 UT -> fluid leakage in the MAGIC II server racks S. Cikota: Stellar occultation observations by MAGIC 16 / 18 • MAGIC is a world-class optical telescope to detect brief optical signals in millisecond scale • Star occultations are a field in which MAGIC, because of his Conclusions large aperture and high sensitivity, might have a significant scientific impact • There is no Project Working Groups for non-high energy physics projects like this, although it deserves special attention Future plan: • Keep searching for appropriate MBA candidates to test the method, and looking for good TNO candidates S. Cikota: Stellar occultation observations by MAGIC 17 / 18 Croatian group MAGIC & CTA meeting Thank you for your attention! September 25, 2019 University of Zagreb - FER Questions? Contact: Stefan Cikota, [email protected].