Periodic Reporting for period 1 - MicroStars (Extreme time and angular resolution in the optical with Cherenkov telescopes)
Période du rapport: 2023-04-01 au 2025-09-30
The universe in the visible wavelength range remains largely unexplored at sub-second time scales and sub-milliarcsecond angular resolutions due to instrumental limitations. Overcoming these impediments would bring a breakthrough in our knowledge of stellar physics, evolution and modelling by imaging the stars and their surroundings and unravel the history of the Solar System.
Imaging Atmospheric Cherenkov Telescopes (IACTs), originally designed to detect very-high-energy gamma rays by observing Cherenkov light from air showers, possess unique capabilities that can be repurposed for optical astronomy. Their large apertures, fast time resolution (~1 ns), and sensitivity to UV/blue light make them ideal for high-time-resolution photometry and stellar intensity interferometry (SII). The revival of SII, a technique pioneered in the 1960s, offers a cost-effective way to achieve microarcsecond (μas) resolution by correlating photon arrival times across multiple telescopes, bypassing the need for optical path stability required by traditional amplitude interferometry.
The Cherenkov Telescope Array Observatory (CTAO), a next-generation IACT project, presents an unprecedented opportunity to leverage these capabilities. With its extensive array of telescopes and long baselines, CTAO could become the first observatory to achieve μas resolution in the visible regime. However, realizing this potential requires significant upgrades to existing and future IACTs, including advanced readout electronics, high-speed correlators, and innovative calibration and imaging techniques.
The MicroStars project, led by its Principal Investigator Tarek Hassan at CIEMAT, aims to transform current and next-generation IACTs into powerful tools for ultra-fast optical astronomy. The project has two primary scientific goals:
1) Unprecedented Imaging of Stars and Their Surroundings: By upgrading IACTs into SII arrays, MicroStars will demonstrate CTAO could achieve μas resolution, enabling direct imaging of stellar surfaces, limb darkening, and starspots. This would provide new insights into stellar physics, magnetic activity, and the properties of massive stars like OB and Wolf-Rayet stars. This will be only possible if we demonstrate the feasibility of a correlator capable of handling a large number of input signals as well as a high-level analysis capable of employing this information. MicroStars will develop a scalable GPU-based correlator to handle the high data rates of SII and validate imaging techniques to reconstruct model-independent images from interferometric data.
2) Unraveling the Collisional History of the Solar System: MicroStars will use IACTs as high-time-resolution photometers to detect occultations of stars by sub-kilometer Kuiper Belt Objects. These observations will constrain the size distribution of primordial planetesimals, shedding light on the formation processes of the Solar System. The project will implement fast readout electronics and template-matching algorithms to identify occultation events with millisecond precision, significantly improving sensitivity to small KBOs.
Imaging Atmospheric Cherenkov Telescopes (IACTs), originally designed to detect very-high-energy gamma rays by observing Cherenkov light from air showers, possess unique capabilities that can be repurposed for optical astronomy. Their large apertures, fast time resolution (~1 ns), and sensitivity to UV/blue light make them ideal for high-time-resolution photometry and stellar intensity interferometry (SII). The revival of SII, a technique pioneered in the 1960s, offers a cost-effective way to achieve microarcsecond (μas) resolution by correlating photon arrival times across multiple telescopes, bypassing the need for optical path stability required by traditional amplitude interferometry.
The Cherenkov Telescope Array Observatory (CTAO), a next-generation IACT project, presents an unprecedented opportunity to leverage these capabilities. With its extensive array of telescopes and long baselines, CTAO could become the first observatory to achieve μas resolution in the visible regime. However, realizing this potential requires significant upgrades to existing and future IACTs, including advanced readout electronics, high-speed correlators, and innovative calibration and imaging techniques.
The MicroStars project, led by its Principal Investigator Tarek Hassan at CIEMAT, aims to transform current and next-generation IACTs into powerful tools for ultra-fast optical astronomy. The project has two primary scientific goals:
1) Unprecedented Imaging of Stars and Their Surroundings: By upgrading IACTs into SII arrays, MicroStars will demonstrate CTAO could achieve μas resolution, enabling direct imaging of stellar surfaces, limb darkening, and starspots. This would provide new insights into stellar physics, magnetic activity, and the properties of massive stars like OB and Wolf-Rayet stars. This will be only possible if we demonstrate the feasibility of a correlator capable of handling a large number of input signals as well as a high-level analysis capable of employing this information. MicroStars will develop a scalable GPU-based correlator to handle the high data rates of SII and validate imaging techniques to reconstruct model-independent images from interferometric data.
2) Unraveling the Collisional History of the Solar System: MicroStars will use IACTs as high-time-resolution photometers to detect occultations of stars by sub-kilometer Kuiper Belt Objects. These observations will constrain the size distribution of primordial planetesimals, shedding light on the formation processes of the Solar System. The project will implement fast readout electronics and template-matching algorithms to identify occultation events with millisecond precision, significantly improving sensitivity to small KBOs.
Now approaching the mipoint of the project, the MicroStars team has achieved a significant number of milestones:
Upgrading the capabilities of LST1: Large Sized Telescopes (LSTs) are the largest telescopes that will be part of the future CTAO. LST1 is the first prototype of these telescopes, currently under commissioning. The capabilities of these enormous telescopes (apertures of 23 m in diameter) are ideal for the scientific objectives of MicroStars. The project has been able to manufacture, install and test the required modifications transforming these telescopes into intensity interferometers as well as fast optical photometers.
First MAGIC-LST1 correlation signals: by employing the modifications described in the previous point, and using the MAGIC Intensity Interferometry correlator, we were able to perform on-sky joint observations between MAGIC and LST1, detecting the first correlation signals from such telescopes. We also upgraded the interferometry analysis to handle these correlations, and stellar angular diameter measurements were performed. Even if nominal performance is not yet achieved, these results demonstrate a significant fraction of MicroStars objectives will likely be achieved. A total of 5 observing proposals have been granted to scientifically exploit the upgraded system within the MAGIC-LST1 Collaborations.
Acquisition of the GPU-based correlator hardware: one of the main objectives of MicroStars is to demonstrate a GPU-based correlator, using state of the art high-bandwidth hardware, will be able to handle up to 12 input signals. This solution is defined as a scalable solution, capable of correlating the full CTAO-N and CTAO-S arrays. The MicroStars team was able to perform the licitation of a 350 k€ computing cluster that will serve as infrastructure for the correlator, as well as the modification in the MAGIC Counting House building to allocate the new cluster. A new chiller to cool it down has been provisioned and comissioned, and the correlator will soon be ready to acquire data.
Upgrading the capabilities of LST1: Large Sized Telescopes (LSTs) are the largest telescopes that will be part of the future CTAO. LST1 is the first prototype of these telescopes, currently under commissioning. The capabilities of these enormous telescopes (apertures of 23 m in diameter) are ideal for the scientific objectives of MicroStars. The project has been able to manufacture, install and test the required modifications transforming these telescopes into intensity interferometers as well as fast optical photometers.
First MAGIC-LST1 correlation signals: by employing the modifications described in the previous point, and using the MAGIC Intensity Interferometry correlator, we were able to perform on-sky joint observations between MAGIC and LST1, detecting the first correlation signals from such telescopes. We also upgraded the interferometry analysis to handle these correlations, and stellar angular diameter measurements were performed. Even if nominal performance is not yet achieved, these results demonstrate a significant fraction of MicroStars objectives will likely be achieved. A total of 5 observing proposals have been granted to scientifically exploit the upgraded system within the MAGIC-LST1 Collaborations.
Acquisition of the GPU-based correlator hardware: one of the main objectives of MicroStars is to demonstrate a GPU-based correlator, using state of the art high-bandwidth hardware, will be able to handle up to 12 input signals. This solution is defined as a scalable solution, capable of correlating the full CTAO-N and CTAO-S arrays. The MicroStars team was able to perform the licitation of a 350 k€ computing cluster that will serve as infrastructure for the correlator, as well as the modification in the MAGIC Counting House building to allocate the new cluster. A new chiller to cool it down has been provisioned and comissioned, and the correlator will soon be ready to acquire data.
Over the first half of the MicroStars project we have built a team that has been able to ensure most of the technical objectives of the project are either achieved or well on track. The project now approaches a second stage in which we will start performing more on-sky observations and exploit the already available capabilities of the MAGIC-LST1 array to expand the state of the art of high angular resolution stellar astrophysics as well as evaluate the feasibility of constraining the collisional history of the Solar System via high temporal resolution measurements of serendipitous occultations of Kuiper Belt Objects.
By measuring the first MAGIC-LST1 correlation signals, we have demonstrated the proposed solution to upgrade LST telescope capabilities as an intensity interferometer is a success. This means upgrading the incoming LST2-4 telescopes will be straightforward. The other type of telescope planned to be part of the CTAO-N array, the Medium Sized Telescope, is performing modifications analogous to the ones proposed by the MicroStars project for the LSTs, and therefore first correlation signals also including these telescopes are planned well before the end of the MicroStars project. These results will allow MicroStars to deliver to the scientific community the highest angular resolution optical interferometer on Earth.
A joint MAGIC+LST1 observing proposal has been accepted to perform 20 hours of high-time resolution on-sky observations to evaluate the signal to noise achieved by these telescopes as millisecond-scale photometers. If the signal to noise ratio achieved is as high as predicted, KBO occultations should be easily detectable with the 4 LST array. The hardware that will be used to perform these measurements will be tested and carefully evaluated, as strong noise components could jeopardize the scientific potential of the observations.
In addition to these efforts, MicroStars was also able to explore alternative technologies to improve the sensitivity of these measurements. The team is exploring a feasible technical solution using Hybrid photo detectors (HPDs) in combination with alternative ways of using IACTs Active Mirror Control, we identified feasible technical solutions to upgrade in the foreseeable future the capabilities of these telescopes.
By measuring the first MAGIC-LST1 correlation signals, we have demonstrated the proposed solution to upgrade LST telescope capabilities as an intensity interferometer is a success. This means upgrading the incoming LST2-4 telescopes will be straightforward. The other type of telescope planned to be part of the CTAO-N array, the Medium Sized Telescope, is performing modifications analogous to the ones proposed by the MicroStars project for the LSTs, and therefore first correlation signals also including these telescopes are planned well before the end of the MicroStars project. These results will allow MicroStars to deliver to the scientific community the highest angular resolution optical interferometer on Earth.
A joint MAGIC+LST1 observing proposal has been accepted to perform 20 hours of high-time resolution on-sky observations to evaluate the signal to noise achieved by these telescopes as millisecond-scale photometers. If the signal to noise ratio achieved is as high as predicted, KBO occultations should be easily detectable with the 4 LST array. The hardware that will be used to perform these measurements will be tested and carefully evaluated, as strong noise components could jeopardize the scientific potential of the observations.
In addition to these efforts, MicroStars was also able to explore alternative technologies to improve the sensitivity of these measurements. The team is exploring a feasible technical solution using Hybrid photo detectors (HPDs) in combination with alternative ways of using IACTs Active Mirror Control, we identified feasible technical solutions to upgrade in the foreseeable future the capabilities of these telescopes.