arXiv subjects

E. Muslimov

Publications and source records attributed to E. Muslimov.

11 recordsLinked to original sources

arXiv2026

On-sky demonstration of a vector Zernike wavefront sensor in a cascaded adaptive optics system

To directly image and characterise Earth-like exoplanets, future high-contrast instruments will require adaptive-optics systems operating at increasingly high loop frequencies to reduce temporal errors. Increasing the loop frequency reduces the signal-to-noise ratio per wavefront-sensor frame, making highly sensitive wavefront sensors, such as the Zernike wavefront sensor (ZWFS), attractive candidates. However, the limited dynamic range of the classical ZWFS makes on-sky operation challenging. We therefore investigate whether a ZWFS can be used as a second-stage sensor in an on-sky cascaded adaptive-optics system. To this end, we added a second AO stage, called OZIRIIS, to the PAPYRUS platform at the Observatoire de Haute-Provence. OZIRIIS combines a vector Zernike wavefront sensor (v-ZWFS) with a 97-actuator deformable mirror operating at 400 Hz downstream of the pyramid-based first AO stage. Real-time control relied on a single ZWFS signal, while the full v-ZWFS was used a posteriori for non-linear reconstruction and telemetry analysis. The second-stage correction increased the measured Strehl ratio by up to 16 percentage points. Analysis of the telemetry using the full v-ZWFS to reconstruct residuals revealed optical-gain effects affecting the ZWFS at low Strehl ratio. The good agreement between on-sky measurements and numerical simulations further supports the calibration strategy based on synthetic reference signals and interaction matrices. These results demonstrate that Zernike wavefront sensing can be operated in closed loop on sky and support its use in future cascaded extreme adaptive-optics systems.

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arXiv2026

Cold and eccentric: a high-spectral resolution view of 51 Eri b with VLT/HiRISE

Discovered almost 10 years ago, the giant planet 51 Eridani b is one of the least separated (0.2 arcsec) and faintest (J = 19.74 mag) directly imaged exoplanets known to date. Its atmospheric properties have been thoroughly investigated through low- and medium-resolution spectroscopic observations, enabling robust characterization of the planet's bulk parameters. However, the planet's intrinsically high contrast renders high-resolution spectroscopic observations difficult, despite their potential to yield key measurements essential for a more comprehensive characterization. This study seeks to constrain the planet's radial velocity, enabling a full 3D orbital solution when integrated with previous measurements. We have obtained 4 high-contrast high-resolution (R = 140000) spectroscopic datasets of the planet, collected over a two-year interval with the HiRISE visitor instrument at the VLT to derive the planet's radial velocity. Using self-consistent models of atmosphere, we were able to derive the radial velocity of the planet at each of the 4 epochs. These radial velocity measurements were then used in combination with all existing relative astrometry in order to constrain the orbit of the planet. Our radial velocity measurements allow us to break the degeneracy along the line of sight, making it now possible the unambiguous interpretation of the phase curve of the companion. We further constrain the orbital parameters, particularly the eccentricity, for which we derive e = 0.55 (-0.07, +0.03). The relatively high eccentricity indicates that the system has experienced dynamical interactions induced by an external perturber. We place constraints on the mass and semi-major axis of a hypothetical, unseen outer planet capable of producing the observed high eccentricities.

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arXiv2025

Characterization of AF Lep b at high spectral resolution with VLT/HiRISE

Since the recent discovery of the directly imaged super-Jovian planet AF Lep b, several studies have been conducted to characterize its atmosphere and constrain its orbital parameters. AF Lep b has a measured dynamical mass of $3.68 \pm 0.48$ MJup, a radius of $1.3 \pm 0.15$ RJup, a nearly circular orbit in spin-orbit alignment with the host star, a relatively high metallicity, and a near-solar to super-solar C/O ratio. However, key parameters such as the rotational velocity and radial velocity could not be estimated as they require high-resolution spectroscopic data that is impossible to obtain with classical spectrographs. AF Lep b was recently observed with the new HiRISE visitor instrument at the VLT, with the goal of obtaining high-resolution (R~140,000) spectroscopic observations to better constrain the orbital and atmospheric parameters of the young giant exoplanet. We compare the extracted spectrum of AF Lep b to self-consistent atmospheric models using ForMoSA. We then use our measurements of the radial velocity of the planet to provide new constraints on the orbit of the planet. From the forward modeling, we find a C/O ratio that aligns with previous low-resolution analyses, and we confirm the super-solar metallicity. We also confirm unambiguously the presence of methane in the atmosphere of the companion. Based on all available relative astrometry and radial velocity measurements of the host star, we show that two distinct orbital populations are possible for the companion. We derive the radial velocity of AF Lep b to be $10.51 \pm 1.03$ km/s, and show that this value agrees well with one of the two orbital solutions, allowing us to rule out an entire family of orbits. Additionally, assuming that the rotation and orbit are coplanar, the derived planet's rotation rate is consistent with the observed trend of increasing spin velocity with higher planet mass.

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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.

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arXiv2024

Multi-purpose InSTRument for Astronomy at Low-resolution: MISTRAL@OHP

MISTRAL is the new Faint Object Spectroscopic Camera mounted at the folded Cassegrain focus of the 1.93m telescope of Haute-Provence Observatory. We describe the design and components of the instrument and give some details about its operation. We emphasise in particular the various observing modes and the performances of the detector. A short description is also given about the working environment. Various types of objects, including stars, nebulae, comets, novae, galaxies have been observed during various test phases to evaluate the performances of the instrument. The instrument covers the range of 4000 to 8000A with the blue setting, or from 6000 to 10000A with the red setting, at an average spectral resolution of 700. Its peak efficiency is about 22% at 6000A. In spectroscopy, a limiting magnitude of 19.5 can be achieved for a point source in one hour with a signal to noise of 3 in the continuum (and better if emission lines are present). In imaging mode, limiting magnitudes of 20-21 can be obtained in 10-20mn (with average seing conditions of 2.5 arcsec at OHP). The instrument is very users-friendly and can be put into operations in less than 15mn (rapid change-over from the other instrument in use) if required by the science (like for Gamma-Rays Bursts). Some first scientific results are described for various types of objects, and in particular for the follow-up of GRBs. While some further improvements are still under way, in particular to ease the switch from blue to red setting and add more grisms or filters, MISTRAL is ready for the follow-up of transients and other variable objects, in the soon-to-come era of e.g. the SVOM satellite and of the Rubin telescope.

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arXiv2023

First light of VLT/HiRISE: High-resolution spectroscopy of young giant exoplanets

A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT), which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The goal of HiRISE is to enable the characterization of known companions in the $H$ band, at a spectral resolution of the order of $R = λ/Δλ= 100\,000$, in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak value of $\sim$3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to illustrate its potential.

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arXiv2022

Connecting SPHERE and CRIRES+ for the characterisation of young exoplanets at high spectral resolution: status update of VLT/HiRISE

New generation exoplanet imagers on large ground-based telescopes are highly optimised for the detection of young giant exoplanets in the near-infrared, but they are intrinsically limited for their characterisation by the low spectral resolution of their integral field spectrographs ($R<100$). High-dispersion spectroscopy at $R \gg 10^4$ would be a powerful tool for the characterisation of these planets, but there is currently no high-resolution spectrograph with extreme adaptive optics and coronagraphy that would enable such characterisation. With project HiRISE we propose to use fiber coupling to combine the capabilities of two flagship instruments at the Very Large Telescope in Chile: the exoplanet imager SPHERE and the high-resolution spectrograph CRIRES+. The coupling will be implemented at the telescope in early 2023. We provide a general overview of the implementation of HiRISE, of its assembly, integration and testing (AIT) phase in Europe, and a brief assessment of its expected performance based on the final hardware.

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arXiv2022

Validation of strategies for coupling exoplanet PSFs into single-mode fibres for high-dispersion coronagraphy

On large ground-based telescopes, the combination of extreme adaptive optics (ExAO) and coronagraphy with high-dispersion spectroscopy (HDS), sometimes referred to as high-dispersion coronagraphy (HDC), is starting to emerge as a powerful technique for the direct characterisation of giant exoplanets. The high spectral resolution not only brings a major gain in terms of accessible spectral features but also enables a better separation of the stellar and planetary signals. Ongoing projects such as Keck/KPIC, Subaru/REACH, and VLT/HiRISE base their observing strategy on the use of a few science fibres, one of which is dedicated to sampling the planet's signal, while the others sample the residual starlight in the speckle field. The main challenge in this approach is to blindly centre the planet's point spread function (PSF) accurately on the science fibre, with an accuracy of less than 0.1 $λ/D$ to maximise the coupling efficiency. In the context of the HiRISE project, three possible centring strategies are foreseen, either based on retro-injecting calibration fibres to localise the position of the science fibre or based on a dedicated centring fibre. We implemented these three approaches, and we compared their centring accuracy using an upgraded setup of the MITHiC high-contrast imaging testbed, which is similar to the setup that will be adopted in HiRISE. Our results demonstrate that reaching a specification accuracy of 0.1 $λ/D$ is extremely challenging regardless of the chosen centring strategy. It requires a high level of accuracy at every step of the centring procedure, which can be reached with very stable instruments. We studied the contributors to the centring error in the case of MITHiC and we propose a quantification for some of the most impacting terms.

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arXiv2020

Direct characterization of young giant exoplanets at high spectral resolution by coupling SPHERE and CRIRES+

Studies of atmospheres of directly imaged exoplanets with high-resolution spectrographs have shown that their characterization is predominantly limited by noise on the stellar halo at the location of the studied exoplanet. An instrumental combination of high-contrast imaging and high spectral resolution that suppresses this noise and resolves the spectral lines can therefore yield higher quality spectra. We study the performance of the proposed HiRISE fiber coupling between the SPHERE and CRIRES+ at the VLT for spectral characterization of directly imaged planets. Using end-to-end simulations of HiRISE we determine the S/N of the detection of molecular species for known exoplanets in $H$ and $K$ bands, and compare them to CRIRES+. We investigate the ultimate detection limits of HiRISE as a function of stellar magnitude, and we quantify the impact of different coronagraphs and of the system transmission. We find that HiRISE largely outperforms CRIRES+ for companions around bright hosts like $β$ Pic or 51 Eri. For an $H=3.5$ host, we observe a gain of a factor of up to 16 in observing time with HiRISE to reach the same S/N on a companion at 200 mas. More generally, HiRISE provides better performance than CRIRES+ in two-hour integration times between 50-350 mas for hosts with $H<8.5$ and between 50-700 mas for $H<7$. For fainter hosts like PDS 70 and HIP 65426, no significant improvements are observed. We find that using no coronagraph yields the best S/N when characterizing known exoplanets due to higher transmission and fiber-based starlight suppression. We demonstrate that the overall transmission of the system is in fact the main driver of performance. Finally, we show that HiRISE outperforms the best detection limits of SPHERE for bright stars, opening major possibilities for the characterization of future planetary companions detected by other techniques.

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arXiv2020

CASTLE: performances and science cases

We present here the Calar Alto Schmidt-Lemaitre Telescope (CASTLE) concept, a technology demonstrator for curved detectors, that will be installed at the Calar Alto Observatory (Spain). This telescope has a wide field of view (2.36x1.56 deg^2) and a design, optimised to generate a Point Spread Function with very low level wings and reduced ghost features, which makes it considerably less susceptible to several systematic effects usually affecting similar systems. These characteristics are particularly suited to study the low surface brightness Universe. CASTLE will be able to reach surface brightness orders of magnitude fainter than the sky background level and observe the extremely extended and faint features around galaxies such as tidal features, stellar halos, intra-cluster light, etc. CASTLE will also be used to search and detect astrophysical transients such as gamma ray bursts (GRB), gravitational wave optical counterparts, neutrino counterparts, etc. This will increase the number of precisely localized GRBs from 20% to 60% (in the case of Fermi/GMB GRBs).

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arXiv2018

Bringing high-spectral resolution to VLT/SPHERE with a fibre coupling to VLT/CRIRES+

Atmospheric composition provides essential markers of the most fundamental properties of giant exoplanets, such as their formation mechanism or internal structure. New-generation exoplanet imagers, like VLT/SPHERE or Gemini/GPI, have been designed to achieve very high contrast (>15 mag) at small angular separations ($<$0.5\as) for the detection of young giant planets in the near-infrared, but they only provide very low spectral resolutions ($R<100$) for their characterization. High-dispersion spectroscopy at resolutions up to $10^5$ is one of the most promising pathways for the detailed characterization of exoplanets, but it is currently out of reach for most directly imaged exoplanets because current high-dispersion spectrographs in the near-infrared lack coronagraphs to attenuate the stellar signal and the spatial resolution necessary to resolve the planet. Project HiRISE (High-Resolution Imaging and Spectroscopy of Exoplanets) ambitions to develop a demonstrator that will combine the capabilities of two flagship instruments installed on the ESO Very Large Telescope, the high-contrast exoplanet imager SPHERE and the high-resolution spectrograph CRIRES+, with the goal of answering fundamental questions on the formation, composition and evolution of young planets. In this work, we will present the project, the first set of realistic simulations and the preliminary design of the fiber injection unit that will be implemented in SPHERE.

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