To investigate the evolution of our Galaxy, we plan to measure the distances and motions of stars in the Galactic center region. Additionally, our goal is to detect planets within the habitable zone around mid-M-type stars using transit phenomena. To achieve these objectives, we initiated the Japan Astrometry Satellite Mission for Infrared Exploration (JASMINE) project, targeting a 40 microarcsecond annual parallax measurement and aiming photometric accuracy of less than 0.3% for mid-M-type stars. A conceptual study of the observation instrument was conducted. As a result, the telescope is designed with high stability in orbit through carefully chosen materials and a special thermal design. A three-year operation is planned to collect sufficient data for annual parallax measurements. The telescope, with a diameter of 36 cm, covers wavelengths from 1.0 to 1.6 microns using InGaAs detectors. This paper will detail how instrument parameters were selected based on scientific objectives.
JASMINE is a Japanese planned space mission that aims to reveal the formation history of our Galaxy and discover habitable exoEarths. For these objectives, the JASMINE satellite performs high-precision astrometric observations of the Galactic bulge and high-precision transit monitoring of M-dwarfs in the near-infrared (1.0—1.6 µm in wavelength). For feasibility studies, we develop an image simulation software named JASMINE-imagesim, which produces realistic observation images. This software takes into account various factors such as the optical point spread function (PSF), telescope jitter caused by the satellite’s attitude control error (ACE), detector flat patterns, exposure timing differences between detector pixels, and various noise factors. As an example, we report a simulation for the feasibility study of astrometric observations using JASMINE-imagesim. The simulation confirms that the required position measurement accuracy of 4 milliarcseconds for a single exposure of 12.5-mag objects is achievable if the telescope pointing jitter uniformly dilutes the PSF across all stars in the field of view. On the other hand, the simulation also demonstrates that the combination of realistic pointing jitter and exposure timing differences in the detector can significantly degrade accuracy and prevent achieving the requirement. This means that certain countermeasures against this issue must be developed. This result implies that this kind of simulation is important for mission planning and advanced developments to realize more realistic simulations help us to identify critical issues and also devise effective solutions.
The Japan Astrometry Satellite Mission for Infrared Exploration (JASMINE) aims at high-precision astrometry in the near-infrared wavelengths (1.0–1.6 μm). This mission focuses on the Galactic center region, obscured by interstellar dust in optical wavelengths. JASMINE’s observation strategy differs from other missions and must be verified via dedicated simulations. To verify the mission concept, we designed a simplified simulation, the JASMINE mini survey, covering three years with 100 orbits. As a simple case, the data obtained in a single satellite orbit are analyzed simultaneously (Plate Analysis). The observation model was made differentiable and implemented as a probabilistic model to make the best use of Stochastic Variational Inference. Model parameters converged to a certain solution, while the observation model contained more than 30,000 parameters. The estimated coordinates well represented the stellar motions expected from the ground truth. A typical positional error was estimated to be about 70 µas, consistent with the measurement error and the number of measurements. The present results validate parts of JASMINE’s mission concepts, leading to significant advancements in understanding the Galactic center.
There is currently a strong push towards infrared astronomy, like the ground-breaking JWST and the upcoming ROMAN and Gaia NIR missions. The Japanese JASMINE telescope will be the first Near Infrared (NIR) astro-photometric mission to focus on the Galactic central region and, in many senses, it will be pioneering the field of NIR high-precision astrometry for Milky Way (MW) dynamics. In order to test our data processing pipelines, we require a robust and reliable way to generate mock images. In this contribution, we present the JASMINE input catalogue: the most complete census of point-like sources in the NIR towards the Galactic centre. We used this catalogue as a blueprint from which to generate mock sources that resemble real stars as much as possible, while offering also the possibility of generating entirely new sources to compensate for the observational incompleteness. The method, while conceptually simple, requires treating each star of the input catalogue as new evidence that updates our prior knowledge, which in this case is represented by the underlying model of the MW used. The result is a custom probability distribution function for each star from which to draw mock sources. This represents the biggest and most realistic mock catalogue of the MW centre to date. In the future, we will improve it by adding more proper motions and parallaxes to the input catalogue, and by modelling the dependence of the distance on the kinematics.
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