BM UMa: A middle shallow contact binary at pre-transition stage of evolution from W-type to A-type

International audienceAbstract In this study, all unpublished time series photometric data of BM UMa (q ∼ 2.0, P = 0.2712 d) from available archives were re-investigated together with new data taken from the 2.4-m Thai National Telescope of the Thai National Observatory. Based on period analysis, there is a short-term variation superimposed on the long-term period decrease. The trend of period change can be fitted with a downward parabolic curve indicating a period decrease at a rate of dP/dt = −3.36(±0.02) × 10−8 d yr−1. This long-term period decrease can be explained by mass transfer from the more massive component (M2 ∼ 0.79M⊙) to the less-massive one (M1 ∼ 0.39M⊙), in combination with angular momentum loss. For photometric study, we found that the binary consists of K0 V stars and at the intermediate shallow of contact configuration with evolution of fill-out factor from 8.8% (in 2007) to 23.2% (in 2020). Those results suggest that the binary is at the pre-transition stage of evolution from W-type to A-type, agreeing with the results of statistical study of W-type contact binaries. The mass of M2 will be decreased close to or below M1 and the mass ratio will be decreased (q < 1.0). In this way, the binary will evolve into an A-type as a deeper normal over-contact system with period increase. Finally, the binary will become a merger or a rapid-rotating single star when the mass ratio meets the critical value (q < 0.094), and produce a red nova

TSC-1 Optical Payload Hyperspectral Imager Preliminary Design and Performance Estimation

The Thai Space Consortium aims at building capacities in space technologies and industries with the objective to develop satellites in Thailand. In this framework, the first Earth Observation satellite that will be developed by this consortium is called TSC-1. This satellite comprises a hyperspectral imager orbiting in a Sun-Synchronous Low-Earth Orbit at the altitude equal to 630 km. The optical payload is specified to provide data cubes with a Ground Sample Distance equal to 30 m, a swath equal to 30 km, a spectral resolution equal to 10 nm over the spectral domain from 400 nm to 1000 nm with a Signal-to-Noise Ratio (SNR) higher than 100. Firstly, we present the trade-off performed to select the design of the Front Telescope and the Spectrometer. Secondly, we describe the payload design and present the image quality, Modulation Transfer Function and distortion. Next, we establish the tolerance budget to estimate the performance of the optical system including manufacturing errors, assembly errors and stability of the mechanical structure. After that, we calculate the instrument’s spatial and spectral response functions and the contamination of the adjacent pixels due to the straylight. Finally, we estimate radiometric performance in both nadir pointing mode and forward motion compensation mode

Design, performance, and potential scientific applications of the evanescent wave coronagraph with an adjustable inner working angle

International audienceThe Center for Optics and Photonics of the National Astronomical Research Institute of Thailand, together with the Institut d'Optique Graduate School and the Centre de Recherche Astrohpysique de Lyon (CRAL), is currently developing the Evanescent Wave Coronagraph (EvWaCo). The coronagraph relies on the tunneling effect to produce a fully achromatic focal plane mask (FPM) with an adjustable size. The full instrument comprises a coronagraph and adaptive optics system that will be mounted on the Thai National Telescope and is specified to reach a raw contrast of 10−4 at an inner working angle of 3 Airy radii. The coronagraph will be used to perform high contrast observations of stellar systems during on-sky observations over the spectral domain [600 nm, 900 nm]. In this paper, we present the opto-mechanical design of the EvWaCo prototype and the performance measured in laboratory conditions. We also discuss the potential applications for space-based observations and the development plan under this project in the next five years

Deep Contrast and Companion Detection Using the EvWaCo Test Bed Equipped with an Achromatic Focal Plane Mask and an Adjustable Inner Working Angle

International audienceThe evanescent wave coronagraph uses the principle of frustrated total internal reflection (FTIR) to suppress the light coming from the star and study its close environment. Its focal plane mask is composed of a lens and a prism placed in contact with each other to produce the coronagraphic effect. In this paper, we present the experimental results obtained using an upgraded focal plane mask of the Evanescent Wave Coronagraph (EvWaCo). These experimental results are also compared to the theoretical performance of the coronagraph obtained through simulations. Experimentally, we reach a raw contrast equal to a few 10-4 at a distance equal to 3 λ/D over the full I band (λc = 800 nm, Δλ/λ ≍ 20%) and equal to 4 λ/D over the full R band (λc = 650 nm, Δλ/λ ≍ 23%) in unpolarized light. However, our simulations show a raw contrast close to 10-4 over the full I band and R band at the same distance, thus confirming the theoretical achromatic advantage of the coronagraph. We also verify the stability of the mask through a series of contrast measurements over a period of 8 months. Furthermore, we measure the sensitivity of the coronagraph to the lateral and longitudinal misalignment of the focal plane mask and to the lateral misalignment of the Lyot stop