arXiv subjects

Sagi Ben-Ami

Publications and source records attributed to Sagi Ben-Ami.

At least 37 records · Page 2Linked to original sources

arXiv2023

A search for Kuiper Belt occultations using the Weizmann Fast Astronomical Survey Telescope

Measuring the size distribution of small (km-scale) KBOs can help constrain models of Solar System formation and planetary migration. Such small, distant bodies are hard to detect with current or planned telescopes, but can be identified as sub-second occultations of background stars. We present the analysis of data from the Weizmann Fast Astronomical Survey Telescope (W-FAST), consisting of fast photometry of ~10^6 star hours at a frame rate of 10-25 Hz. Our pipeline utilizes a matched-filter approach with a large template bank, including red-noise treatment, and injection of simulated events for estimating the detection efficiency. The KBO radius at which our survey is 10% (50%) efficient is 1.1 (2.0) km. The data from 2020-2021 observing seasons were analyzed and no occultations were identified. We discuss a sample of sub-second false-positive events, both occultation-like and flare-like, which are still not fully understood but could be instructive for future surveys looking for short-duration events. We use our null-detection result to set limits on the km-scale KBO number density. Our individual radius bin limits are consistent with most previous works, with N(r>1km) <=10^6 deg^-2 (95% confidence limit). Our integrated (all size) limits, assuming a power law normalized to large (~45 km) KBOs gives a power law index q<3.93 (95% confidence limit). Finally, our results are in tension with a recently reported KBO detection from the ground, at the p=4x10^-4 level.

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arXiv2023

First on-sky results of a FIOS prototype, a Fabry Perot Based Instrument for Oxygen Searches

The upcoming Extremely Large Telescopes (ELTs) are expected to have the collecting area required to detect potential biosignature gases such as molecular oxygen, $\mathrm{O_2}$, in the atmosphere of terrestrial planets around nearby stars. One of the most promising detection methods is transmission spectroscopy. To maximize our capability to detect $\mathrm{O_2}$ using this method, spectral resolutions $\mathrm{R}\geq 300,000$ are required to fully resolve the absorption lines in an Earth-like exoplanet atmosphere and disentangle the signal from telluric lines. Current high-resolution spectrographs typically achieve a spectral resolution of $\mathrm{R}\sim100,000$. Increasing the resolution in seeing limited observations/instruments requires drastically larger optical components, making these instruments even more expensive and hard to fabricate and assemble. Instead, we demonstrate a new approach to high-resolution spectroscopy. We implemented an ultra-high spectral resolution booster to be coupled in front of a high-resolution spectrograph. The instrument is based on a chained Fabry Perot array which generates a hyperfine spectral profile. We present on-sky telluric observations with a lab demonstrator. Depending on the configuration, this two-arm prototype reaches a resolution of R=250,000-350,000. After carefully modeling the prototype's behavior, we propose a Fabry Perot Interferometer (FPI) design for an eight-arm array configuration aimed at ELTs capable of exceeding R=300,000. The novel FPI resolution booster can be plugged in at the front end of an existing R=100,000 spectrograph to overwrite the spectral profile with a higher resolution for exoplanet atmosphere studies.

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arXiv2023

The scientific payload of the Ultraviolet Transient Astronomy Satellite (ULTRASAT)

The Ultraviolet Transient Astronomy Satellite (ULTRASAT) is a space-borne near UV telescope with an unprecedented large field of view (200 sq. deg.). The mission, led by the Weizmann Institute of Science and the Israel Space Agency in collaboration with DESY (Helmholtz association, Germany) and NASA (USA), is fully funded and expected to be launched to a geostationary transfer orbit in Q2/3 of 2025. With a grasp 300 times larger than GALEX, the most sensitive UV satellite to date, ULTRASAT will revolutionize our understanding of the hot transient universe, as well as of flaring galactic sources. We describe the mission payload, the optical design and the choice of materials allowing us to achieve a point spread function of ~10arcsec across the FoV, and the detector assembly. We detail the mitigation techniques implemented to suppress out-of-band flux and reduce stray light, detector properties including measured quantum efficiency of scout (prototype) detectors, and expected performance (limiting magnitude) for various objects.

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arXiv2022

Laboratory test of the VIS detector system of SOXS for the ESO-NTT telescope

SOXS is the new spectrograph for the ESO NTT telescope able to cover the optical and NIR bands thanks to two different arms: the UV-VIS (350-850 nm), and the NIR (800-2000 nm). In this article, we describe the final design of the visible camera cryostats, the test facilities for the CCD characterization, and the first results with the scientific detector. The UV-VIS detector system is based on a e2v CCD 44-82, a custom detector head coupled with the ESO Continuous Flowing Cryostat (CFC) cooling system and the New General Detector Controller (NGC) developed by ESO. The laboratory facility is based on an optical bench equipped with a Xenon lamp, filter wheels to select the wavelength, an integrating sphere, and a calibrated diode to measure the flux. This paper outlines the visible camera cryostat, the test facilities for the CCD characterization and the first results with the scientific detector in the laboratory and after the integration to the instrument.

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arXiv2022

The Quality Check system architecture for Son-Of-X-Shooter SOXS

We report the implemented architecture for monitoring the health and the quality of the Son Of X-Shooter (SOXS) spectrograph for the New Technology Telescope in La Silla at the European Southern Observatory. Briefly, we report on the innovative no-SQL database approach used for storing time-series data that best suits for automatically triggering alarm, and report high-quality graphs on the dashboard to be used by the operation support team. The system is designed to constantly and actively monitor the Key Performance Indicators (KPI) metrics, as much automatically as possible, reducing the overhead on the support and operation teams. Moreover, we will also detail about the interface designed to inject quality checks metrics from the automated SOXS Pipeline (Young et al. 2022).

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arXiv2022

Progress on the SOXS NIR Spectrograph AIT

The Son Of X-Shooter (SOXS) is a single object spectrograph, built by an international consortium for the 3.58-m ESO New Technology Telescope at the La Silla Observatory, ranging from 350 to 2000 nm. In this paper, we present the progress in the AIT phase of the Near InfraRed (NIR) arm. We describe the different AIT phases of the cryo, vacuum, opto-mechanics and detector subsystems, that finally converged at the INAF-OAB premises in Merate (Italy), where the NIR spectrograph is currently being assembled and tested, before the final assembly on SOXS.

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arXiv2022

SOXS AIT: a paradigm for system engineering of a medium class telescope instrument

SOXS (SOn of X-Shooter) is a high-efficiency spectrograph with a mean Resolution-Slit product of 3500 over the entire band capable of simultaneously observing the complete spectral range 350-2000 nm. It consists of three scientific arms (the UV-VIS Spectrograph, the NIR Spectrograph and the Acquisition Camera) connected by the Common Path system to the NTT, and the Calibration Unit. We present an overview of the flow from the scientific to the technical requirements, and the realization of the sub-systems. Further, we give an overview of the methodologies used for planning and managing the assembly of the sub-systems, their integration and tests before the acceptance of the instrument in Europe (PAE) along with the plan for the integration of SOXS to the NTT. SOXS could be used as an example for the system engineering of an instrument of moderate complexity, with a large geographic spread of the team.

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arXiv2022

The Son-Of-X-shooter (SOXS) Data-Reduction Pipeline

The Son-Of-XShooter (SOXS) is a single object spectrograph (UV-VIS & NIR) and acquisition camera scheduled to be mounted on the ESO 3.58-m New Technology Telescope at the La Silla Observatory. Although the underlying data reduction processes to convert raw detector data to fully-reduced science ready data are complex and multi-stepped, we have designed the SOXS Data Reduction pipeline with the core aims of providing end-users with a simple-to-use, well-documented command-line interface while also allowing the pipeline to be run in a fully automated state; streaming reduced data into the ESO Science Archive Facility without need for human intervention. To keep up with the stream of data coming from the instrument, there is the requirement to optimise the software to reduce each observation block of data well within the typical observation exposure time. The pipeline is written in Python 3 and has been built with an agile development philosophy that includes CI and adaptive planning.

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arXiv2021

Sensor characterization for the ULTRASAT space telescope

The Ultraviolet Transient Astronomical Satellite is a scientific space mission carrying an astronomical telescope. The mission is led by the Weizmann Institute of Science in Israel and the Israel Space Agency, while the camera in the focal plane is designed and built by Deutsches Elektronen Synchrotron in Germany. Two key science goals of the mission are the detection of counterparts to gravitational wave sources and supernovae. The launch to geostationary orbit is planned for 2024. The telescope with a field-of-view of $\approx200$deg$^2$, is optimized to work in the near-ultraviolet band between $220$ and $280$nm. The focal plane array is composed of four $22.4$-megapixel, backside-illuminated CMOS sensors with a total active area of 90x90mm$^2$. Prior to sensor production, smaller test sensors have been tested to support critical design decisions for the final flight sensor. These test sensors share the design of epitaxial layer and anti-reflective coatings (ARC) with the flight sensors. Here, we present a characterization of these test sensors. Dark current and read noise are characterized as a function of the device temperature. A temperature-independent noise level is attributed to on-die infrared emission and the read-out electronics` self-heating. We utilize a high-precision photometric calibration setup to obtain the test sensors` quantum efficiency (QE) relative to PTB/NIST-calibrated transfer standards ($220$-$1100$nm), the quantum yield for $λ< 300$nm, the non-linearity of the system, and the conversion gain. The uncertainties are discussed in the context of the newest results on the setup`s performance parameters. From three ARC options, Tstd, T1 and T2, the latter optimizes out-of-band rejection and peaks in the mid of the ULTRASAT operational waveband (max. QE $\approx80\%$ at $245\mathrm{nm}$). We recommend ARC option T2 for the final ULTRASAT UV sensor.

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arXiv2021

Design of the ULTRASAT UV camera

The Ultraviolet Transient Astronomical Satellite (ULTRASAT) is a scientific UV space telescope that will operate in geostationary orbit. The mission, targeted to launch in 2024, is led by the Weizmann Institute of Science (WIS) in Israel and the Israel Space Agency (ISA). Deutsches Elektronen Synchrotron (DESY) in Germany is tasked with the development of the UV-sensitive camera at the heart of the telescope. The camera's total sensitive area of ~90mm x 90mm is built up by four back-side illuminated CMOS sensors, which image a field of view of ~200 deg2. Each sensor has 22.4 megapixels. The Schmidt design of the telescope locates the detector inside the optical path, limiting the overall size of the assembly. As a result, the readout electronics is located in a remote unit outside the telescope. The short focal length of the telescope requires an accurate positioning of the sensors within +-50 mu along the optical axis, with a flatness of +-10 mu. While the telescope will be at around 295K during operations, the sensors are required to be cooled to 200K for dark current reduction. At the same time, the ability to heat the sensors to 343K is required for decontamination. In this paper, we present the preliminary design of the UV sensitive ULTRASAT camera.

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arXiv2021

A high-rate foreground of sub-second flares from geosynchronous satellites

The Weizmann Fast Astronomical Survey Telescope (W-FAST) is a 55cm optical survey telescope with a high cadence (25Hz) monitoring of the sky over a wide field of view (~7deg^2). The high frame rate allows detection of sub-second transients over multiple images. We present a sample of ~0.1--0.3s duration flares detected in an un-targeted survey for such transients. We show that most, if not all of them, are glints of sunlight reflected off geosynchronous and graveyard orbit satellites. The flares we detect have a typical magnitude of 9--11, which translates to ~14--16th magnitude if diluted by a 30s exposure time. We estimate the rate of events brighter than ~11mag to be on the order of 30--40 events per day per deg^2, for declinations between -20 and +10^\circ, not including the declination corresponding to the geostationary belt directly above the equator, where the rate can be higher. We show that such glints are common in large area surveys (e.g., ZTF and LSST), and that some of them have a point-like appearance, confounding searches for fast transients such as Fast Radio Burst counterparts and Gamma-ray bursts. By observing in the direction of the Earth's shadow we are able to put an upper limit on the rate of fast astrophysical transients of 0.052deg^{-2}day^{-1} (95\% confidence limit) for events brighter than 11mag. We also suggest that the single image, high declination flare observed in coincidence with the GN-z11 galaxy and assumed to be a Gamma-ray burst, is also consistent with such a satellite glint.

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arXiv2021

The Weizmann Fast Astronomical Survey Telescope (W-FAST): System Overview

A relatively unexplored phase space of transients and stellar variability is that of second and sub-second time-scales. We describe a new optical observatory operating in the Negev desert in Israel, with a 55 cm aperture, a field of view of 2.6x2.6 deg (~7deg^2) equipped with a high frame rate, low read noise, CMOS camera. The system can observe at a frame rate of up to 90HZ (full frame), while nominally observations are conducted at 10-25Hz. The data, generated at a rate of over 6Gbits/s at a frame rate of 25Hz, are analyzed in real time. The observatory is fully robotic and capable of autonomously collecting data on a few thousand stars in each field each night. We present the system overview, performance metrics, science objectives, and some first results, e.g., the detection of a high rate of glints from geosynchronous satellites, reported in Nir et al. 2020.

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arXiv2020

The SOXS Data-Reduction Pipeline

The SOXS is a dual-arm spectrograph (UV-VIS & NIR) and AC due to mounted on the ESO 3.6m NTT in La Silla. Designed to simultaneously cover the optical and NIR wavelength range from 350-2050 nm, the instrument will be dedicated to the study of transient and variable events with many Target of Opportunity requests expected. The goal of the SOXS Data Reduction pipeline is to use calibration data to remove all instrument signatures from the SOXS scientific data frames for each of the supported instrument modes, convert this data into physical units and deliver them with their associated error bars to the ESO SAF as Phase 3 compliant science data products, all within 30 minutes. The primary reduced product will be a detrended, wavelength and flux calibrated, telluric corrected 1D spectrum with UV-VIS + NIR arms stitched together. The pipeline will also generate QC metrics to monitor telescope, instrument and detector health. The pipeline is written in Python 3 and has been built with an agile development philosophy that includes adaptive planning and evolutionary development. The pipeline is to be used by the SOXS consortium and the general user community that may want to perform tailored processing of SOXS data. Test driven development has been used throughout the build using `extreme' mock data. We aim for the pipeline to be easy to install and extensively and clearly documented.

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arXiv2020

The AIV strategy of the Common Path of Son of X-Shooter

Son Of X-Shooter (SOXS) is a double-armed (UV-VIS, NIR) spectrograph designed to be mounted at the ESO-NTT in La Silla, now in its Assembly Integration and Verification (AIV) phase. The instrument is designed following a modular approach so that each sub-system can be integrated in parallel before their assembly at system level. INAF-Osservatorio Astronomico di Padova will deliver the Common Path (CP) sub-system, which represents the backbone of the entire instrument. In this paper, we describe the foreseen operation for the CP alignment and we report some results already achieved, showing that we envisaged the suitable setup and the strategy to meet the opto-mechanical requirements.

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arXiv2020

SOXS: Effects on optical performances due to gravity flexures, temperature variations, and subsystems alignment

SOXS (Son Of X-Shooter) is the new medium resolution wide-band spectrograph to be installed at the 3.6m New Technology Telescope (NTT) in La Silla. SOXS will offer simultaneous wavelength coverage from 0.35 to 2.0 μm and will be dedicated to the study of transient and variable sources. While nominal optical performances of the system were presented in previous proceedings (arXiv:1809.01521), we here present a set of further analyses aimed to identify and quantify optical effects, due to changes in temperature and orientation of the instrument during alignment and operations.

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arXiv2020

Progress on the UV-VIS arm of SOXS

We present our progress on the UV-VIS arm of Son Of X-Shooter (SOXS), a new spectrograph for the NTT. Our design splits the spectral band into four sub-bands that are imaged onto a single detector. Each band uses an optimized high efficiency grating that operates in 1st order (m=1). In our previous paper we presented the concept and preliminary design. SOXS passed a Final Design Review in July 2018 and is well into the construction phase. Here we present the final design, performances of key manufactured elements, and the progress in the assembly. Based on the as-built elements, the expected throughput of the visual arm will be >55%. This paper is accompanied by a series of contributions describing the progress made on the SOXS instrument.

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arXiv2020

Development status of the SOXS instrument control software

SOXS (Son Of X-Shooter) is a forthcoming instrument for ESO-NTT, mainly dedicated to the spectroscopic study of transient events and is currently starting the AIT (Assembly, Integration, and Test) phase. It foresees a visible spectrograph, a near-Infrared (NIR) spectrograph, and an acquisition camera for light imaging and secondary guiding. The optimal setup and the monitoring of SOXS are carried out with a set of software-controlled motorized components and sensors. The instrument control software (INS) also manages the observation and calibration procedures, as well as maintenance and self-test operations. The architecture of INS, based on the latest release of the VLT Software (VLT2019), has been frozen; the code development is in an advanced state for what concerns supported components and observation procedures, which run in simulation. In this proceeding we present the INS current status, focusing in particular on the ongoing efforts in the support of two non-standard, "special" devices. The first special device is the piezoelectric slit exchanger for the NIR spectrograph; the second special device is the piezoelectric tip-tilt corrector used for active compensation of mechanical flexures of the instrument.

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arXiv2020

Design and development of the SOXS calibration unit

SOXS is a new spectrograph for the New Technology Telescope (NTT), optimized for transient and variable objects, covering a wide wavelength range from 350 to 2000 nm. SOXS is equipped with a calibration unit that will be used to remove the instrument signatures and to provide wavelength calibration to the data. The calibration unit will employ seven calibration lamps: a quartz-tungsten-halogen and a deuterium lamp for the flat-field correction, a ThAr lamp and four pencil-style rare-gas lamps for the wavelength calibration. The light from the calibration lamps is injected into the spectrograph mimicking the f/11 input beam of the NTT, by using an integrating sphere and a custom doublet. The oversized illumination patch covers the length of the spectrograph slit homogeneously, with $< 1\%$ variation. The optics also supports the second mode of the unit, the star-simulator mode that emulates a point source by utilizing a pinhole mask. Switching between the direct illumination and pinhole modes is performed by a linear stage. A safety interlock switches off the main power when the lamp box cover is removed, preventing accidental UV exposure to the service personnel. All power supplies and control modules are located in an electronic rack at a distance from the telescope platform. In this presentation we describe the optical, mechanical, and electrical designs of the SOXS calibration unit, and report the status of development in which the unit is currently in the test and verification stage.

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