arXiv subjects

T. Lépine

Publications and source records attributed to T. Lépine.

6 recordsLinked to original sources

arXiv2026

Guiding Design Choices for Wide-Field IFS: Trade-Offs Between Replication and Complexity for WST

The Wide-field Spectroscopic Telescope (WST) is a proposed 12-meter segmented facility optimized for seeing- and Ground Layer Adaptive Optics-limited observations in the visible and designed to operate both a high-multiplex multi-object spectrograph and a panoramic integral field spectrograph (IFS). The WST IFS concept builds on instruments such as MUSE at the VLT (Very Large Telescope), using field splitters and image slicers to reformat a large field into pseudo-slits feeding spectrographs with two optimized spectral channels. This paper presents the integrated design approach adopted for the IFS, focusing on a trade study of spectrograph architectures. We explore design choices such as pixel pitch, detector format, and camera optical design against throughput, image quality, error budgets, volume, cost. The study adds one ecological metric: the carbon footprint of building each spectrograph, to inform design sustainability. The study also explores the potential of curved detectors. Early results suggest that many simpler spectrographs outperform fewer complex units technically and economically.

astro-ph.IM↗

arXiv2025

Very High Precision Astrometry for Exoplanets and Dark Matter with the Habitable Worlds Observatory

Astrometry, one of the oldest branches of astronomy, has been revolutionized by missions like Hipparcos and especially Gaia, which mapped billions of stars with extraordinary precision. However, challenges such as detecting Earth-like exoplanets in nearby habitable zones and probing the influence of dark matter in galactic environments require sub-microarcsecond accuracy. With a 6--8 meter large-aperture telescope operating across at visible wavelengths, the Habitable Worlds Observatory by NASA can combine astrometry and direct imaging to detect rocky exoplanets within 10 parsecs and study their atmospheres. We consider here the scientific requirements and present a concept for a dedicated astrometric instrument on HWO. It is capable to produce diffraction-limited images of large fields, achieving a point-spread function (PSF) precision of 20 milliarcseconds. Equipped with a detector calibration system, HWO can perform high precision astrometry, and, detect and measure the orbit of Earth-mass planets in the habitable zone of Nearby Solar-type stars. HWO can dramatically improve current constraints on the self- interaction cross-section of heavy dark matter particles (WIMPs) and on the masses of ultra-high dark matter particles, through the study of stellar motions in galactic environments. The visible channel of the instrument features a large CMOS-based focal plane with stitched pixel arrays, enabling a large field of view. The ``Detector Calibration Unit'' system uses interferometric laser fringes to calibrate pixel positions. Using differential astrometry and pointed observations with a stable telescope design enables extended integration times, enhancing sensitivity to sub-microarcsecond precision for detecting exoplanets and studying dark matter through stellar motion.

astro-ph.IM↗

arXiv2024

Challenges in focal plane and telescope calibration for High-Precision Space Astrometry

With sub-microarcsecond angular accuracy, the \theia telescope will be capable of revealing the architectures of nearby exoplanetary systems down to the mass of Earth. This research addresses the challenges inherent in space astrometry missions, focusing on focal plane calibration and telescope optical distortion. We propose to assess the future feasibility of large-format detectors (50 to 200 megapixels) in a controlled laboratory environment. The aim is to improve the architecture of the focal plane while ensuring that specifications are met. The use of field stars as metrological sources for calibrating the optical distortion of the field may help to constrain telescope stability. The paper concludes with an attempt to confirm in the laboratory the performance predicted by simulations. We will also address the possibility of using such techniques with a dedicated instrument for the Habitable World Observatory.

astro-ph.IM↗

arXiv2024

WST -- Widefield Spectroscopic Telescope: design of a new 12m class telescope dedicated to widefield Multi-object and Integral Field Spectroscopy

The Wide-Field Spectroscopic Telescope (WST) is a concept for a 12-m class seeing-limited telescope providing two concentric fields of view for simultaneous Multi-Object Spectroscopy and Integral Field Spectroscopy. The specified wavelength range is 0.35-1.6 microns. The baseline optical design relies on a corrected Cassegrain solution feeding Multi-Object spectrographs through fibres, while the central area of the field is propagated down to a gravity-stable Integral Field Station housing 144 spectrographs. The Cassegrain corrector also provides for atmospheric dispersion compensation. All optical components are within commercially available dimensions. With a view to minimizing risks and costs, to the maximum possible extent the telescope relies on proven subsystem solutions. An exception is the tip-tilt secondary mirror, which would likely have to provide some rejection of wind shake. An iteration of the optical design is ongoing, with a view to mitigating the weaknesses of the first baseline design. The telescope would be wavefront-controlled on-sky at the common-path MOS focus. Controls in the IFS path will need to compensate for the effect of subsequent differentials - wavefront and line of sight. There is no shortage of degrees of freedom and metrology solution to do so. The size of the dome is driven by the Nasmyth footprint and the height of the pier, which houses the IFS station. The baseline assumption is that a VLT-like enclosure would provide suitable shielding and ventilation.

astro-ph.IM↗

arXiv2021

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

In this study, all unpublished time series photometric data of BM UMa ($q \sim$ 2.0, P = 0.2712\,d) from available archives were re-investigated together with new data taken from the TNT-2.4m of the Thai National Observatory (TNO). 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 $\mathrm{d}P/\mathrm{d}t = -3.36(\pm 0.02)\times10^{-8}$ d $\textrm{yr}^{-1}$. This long-term period decrease can be explained by mass transfer from the more massive component ($M_2 \sim 0.79 M_{\odot}$) to the less massive one ($M_1 \sim 0.39 M_{\odot}$), combination with AML. For photometric study, we found that the binary consists of K0\,V stars and at the middle shallow contact phase with evolution of fill-out factor from 8.8\,\% (in 2007) to 23.2\,\% (in 2020). Those results suggest that the binary is at pre-transition stage of evolution from W-type to A-type, agreeing to the results of statistical study of W-type contact binaries. The mass of $M_2$ will be decreased close to or below $M_1$ and the mass ratio will be decreased ($q < 1.0$). By this way, the binary will evolve into A-type as a deeper normal over-contact system with period increase. Finally the binary will end as a merger or a rapid-rotating single star when the mass ratio meet the critical value ($q < 0.094$), as well as produce a red nova.

astro-ph.SR↗

arXiv2021

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

The 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 ($λ_c =$ $800$ $nm$, $Δλ/λ \approx 20\%$) and equal to 4 $λ/D$ over the full R-band ($λ_c =$ $650$ $nm$, $Δλ/λ \approx 23\%$) 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.

astro-ph.IM↗