arXiv subjects

M. Bugatti

Publications and source records attributed to M. Bugatti.

4 recordsLinked to original sources

arXiv2026

Resolving protoplanetary H-alpha emission with the high-resolution spectrograph RISTRETTO

Thousands of exoplanets have been discovered to date, but only a handful of them are young planets in the latter stages of their formation. H-alpha emission is a strong tracer of this process, but it is difficult to isolate the planetary H-alpha signal from the stellar signal due to the small angular separation. RISTRETTO is a high-resolution (R~140,000) integral-field unit spectrograph with an attached coronagraph and extreme adaptive system that is currently under construction. Used in tandem with the VLT, its resolving power and seven-spaxel layout is designed to characterise the atmospheres of exoplanets in reflected light. It can also be leveraged to obtain spatially and spectrally resolved observations of planetary H-alpha emission lines. Using a combination of synthetic and real observations, we determined the detection limits for theoretical observations of protoplanets with on-sky separations of 37-600 mas (the equivalent of 4-70 AU at 113 pc). We used theoretical BT-Settl photospheric spectra, observed HARPS spectra of PDS70, and a model for the line emission at the planetary accretion shock to estimate the planetary H-alpha signal. Models with the PyEchelle simulator show that the H-alpha emission from theoretical objects similar to the four known protoplanet candidates (PDS70b, PDS70c, WISPIT2b, and 2MJ1612b) can be spectrally resolved with VLT/RISTRETTO down to a line flux between $F\sim(1.4-2.7)\times10^{-16} erg \;s^{-1} cm^{-2}$ with a 1 hour exposure. We show that the planetary H-alpha line can be spatially resolved from that of its stellar host and that the shape of the line can be used to constrain the pre-shock density (n0) and velocity (v0), thereby enabling new constraints on the accretion rate and flow geometry. This study and the instrument act as a pathfinder for the next generation of high-resolution spectrographs such as ELT/PCS and ELT/ANDES.

astro-ph.EP↗

arXiv2025

NuAncestor: an artificial satellite-borne star for accurate frequency calibration of ground-based EPRV spectrographs

The accuracy of state-of-the-art Extreme Precision Radial Velocity (EPRV) spectrographs depends on the access to extremely precise and stable wavelength calibration sources. There are several available calibration sources (e.g., emission lamps, laser frequency combs, reference cavities) that can be used to calibrate an astronomical spectrograph. However, the calibration as it is currently performed is always 'local'. In the proposed talk we will present the NuAncestor concept that proposes an accurate (absolute) and common wavelength calibration for astronomical high-resolution, high-precision spectrographs by embarking an optical frequency comb on-board a satellite equipped with an actively pointing telescope and precision orbitography. This calibration satellite shall be available and serve EPRV spectrographs in all major observatories around the world.

astro-ph.IM↗

arXiv2025

CORALIE radial-velocity search for companions around evolved stars (CASCADES) IV: New planetary systems around HD 87816, HD 94890, and HD 102888 and an update on HD 121056

With around 200 detections of exoplanets around giant stars to date, our knowledge of the population of exoplanets orbiting evolved hosts more massive than the Sun remains limited. The CORALIE radial-velocity search for companions around evolved stars (CASCADES) was launched in 2006 with the aim of improving our understanding of the demographics of exoplanets around intermediate-mass stars, by studying them once they have evolved off the main sequence. We intend to refine the current sample of known exoplanets orbiting intermediate-mass (1.5 - 5 M$_\odot$) giant stars of spectral types G and early K. We searched for exoplanets orbiting the four stars HD 87816, HD 94890, HD 102888, and HD 121056. We used data obtained with the CORALIE spectrograph, mounted on the Leonhard Euler Swiss telescope located at La Silla Observatory in Chile. We gathered high-precision radial-velocity measurements over more than ten years for each of the aforementioned targets. We started by performing a search for periodic signals in the radial-velocity time series of the four targets by using periodograms. Following this, we fit for a Keplerian model using the significant peak with the highest power of the periodogram as the starting guess for the period. We then subtracted this model and repeated the procedure iteratively on the residuals until no significant peaks were found. Finally, to explore the posterior distribution of our models, the final solution was determined using a Markov chain Monte Carlo approach. We report the discovery of five new massive planets around HD 87816, HD 94890, and HD 102888 as well as the presence of a distant, potentially substellar, companion around HD 102888. We confirm the presence of a previously announced exoplanet orbiting the HD 121056 multi-object system with a period of 89 days and propose an update to the period of the outer companion.

astro-ph.EP↗

arXiv2024

The RISTRETTO simulator: Exoplanet reflected spectra

The upcoming Ristretto spectrograph is dedicated to the detection and analysis of exoplanetary atmospheres, with a primary focus on the temperate rocky world Proxima b. This scientific endeavor relies on the interplay of a high-contrast adaptive optics (AO) system and a high-resolution echelle spectrograph. In this work, I present a comprehensive simulation of Ristretto's output spectra, employing the Python package Pyechelle. Starting from realistic spectra of both exoplanets and their host stars, I generate synthetic 2D spectra to closely resemble those that will be produced by Ristretto itself. These synthetic spectra are subsequently treated as authentic data and therefore analyzed. These simulations facilitate not only the investigation of potential exoplanetary atmospheres but also an in-depth assessment of the inherent capabilities and limitations of the Ristretto spectrograph.

astro-ph.IM↗