arXiv subjects

Cyrielle Opitom

Publications and source records attributed to Cyrielle Opitom.

At least 19 recordsLinked to original sources

arXiv2026

The future of high-resolution UV spectroscopy: Science with a UV \'Echelle spectrograph on the Habitable Worlds Observatory, or a dedicated mission

High-resolution UV spectroscopy serves a diversity of science cases, from small bodies to planets, stars, and galaxies, but is currently limited to the Hubble Space Telescope and bright targets. Major advances require increasing sensitivity by at least one order of magnitude. Here we present the UV science cases for PEGASUS (Planets, Earths, Galaxies, And Stars UV Spectrograph), a UV \'Echelle high-resolution spectrograph concept, with $R = \lambda/\delta\lambda \sim 100\,000$ (full range 10 000-140 000) and covering 90--400 nm, with a foreseen extension to at least 800 nm. PEGASUS is ideally suited for the Habitable Worlds Observatory (HWO), enabling transformative science across the UV/optical wavelength ranges. PEGASUS will be unique in high sensitivity (effective area) and high spectral resolution -- an uncharted territory -- as well as robustness, thanks to the simplicity of its design. Its UV science cases include: I) Formation and evolution of planets and their habitability: properties of exoplanets and atmospheres, protoplanetary disks, Solar System bodies; II) Stellar lives and deaths at their extremes: the first stars and the origin of the elements, compact and massive stars, Supernovae; III) Gas and metals in the baryon cycle of galaxies: the interstellar, circumgalactic, and intergalactic medium and their roles in galaxy growth. These are essential for the Astro Decadal 2020 Survey, Voyage 2050, and HWO. While this paper focuses on high-impact science enabled by UV high-resolution spectroscopy, PEGASUS will extend into the optical regime and lower spectral resolution, making it a multi-purpose, widely used, workhorse spectrograph for HWO.

astro-ph.IM↗

arXiv2026

Ion abundances in the plasma tail of 3I/ATLAS show that it is N2-rich

Interstellar objects allow us to compare the early planetary formation process in the Solar System and around other stars. The second and third interstellar objects, 2I/Borisov and 3I/ATLAS, showed visible signs of activity, making it possible to assess their composition via spectroscopic analysis of their gas coma. While neutral volatiles surrounding comets are easily probed by common spectrographs, ion emissions emanate mostly from the tail, making them easier to detect with integral-field units. We present WHT/WEAVE-LIFU observations of 3I/ATLAS, performed post-perihelion on 2025 November 30 and 2025 December 02. We simultaneously detect the ions N2+, CO+, CO2+, H2O+ and CH+ located in an anti-solar tail. Using common fluorescence factors, we determine abundance ratios of these species in the tail. In particular, the N2+/CO+ ratio allows us to constrain the lower-limit N2/CO>0.023+/-0.001, indicating that 3I/ATLAS is N2-rich compared to Solar System comets, a property which can be linked to cold formation conditions. Abundance ratios between other ions cannot directly be used to constrain abundances of neutrals but seem consistent with the fact that 3I/ATLAS is enriched in hypervolatiles. We also investigate whether these ratios vary along the tail, and only detect a marginal decrease of CH+ with cometocentric distance.

astro-ph.EP↗

arXiv2026

Origin and evolution of NiI and FeI in the coma of the interstellar comet 3I/ATLAS throughout its trajectory

We present high-resolution UVES+VLT observations of neutral nickel and iron atoms in the coma of the interstellar comet 3I/ATLAS taken after perihelion. Metal emission was strong shortly after perihelion and persisted at large heliocentric distances. At $r_h \sim 2$ au the total metal production rate was found to be at least an order of magnitude larger than that of typical solar-system comets. Post-perihelion production rates exhibit pronounced asymmetry compared to the pre-perihelion behavior: production rates are higher after perihelion and decline more gradually with $r_h$, the difference being stronger for FeI. The NiI/FeI abundance ratio, initially anomalously large before perihelion, evolved toward values comparable to solar-system comets near 2 au, and shows a weaker $r_h$ dependence after perihelion. To interpret these results, we revisited and extended the carbonyl hypothesis in which FeI and NiI are produced by the rapid photodissociation of Fe(CO)$_5$ and Ni(CO)$_4$ vaporized from the nucleus. Fits that include direct sublimation of carbonyls reproduce the observed rates and the high NiI/FeI line ratio, which is determined by the higher volatility of Ni(CO)$_4$. Desorption of carbonyls from sublimating CO$_2$ and H$_2$O ices is found to be negligible. The temperature profiles needed to reproduce the observations were found to be shallower than the equilibrium $T \propto r_h^{-1/2}$ relation, suggesting that the sublimation could occur below the surface of the nucleus. Fits using temperature profiles from thermal models require sublimation from depths of several cm, especially post-perihelion. An additional transient heat source ($T \simeq$ 100-140~K), possibly linked to the amorphous-crystalline ice transition, is proposed to explain the early NiI excess before perihelion.

astro-ph.EP↗

arXiv2026

An Enriched Methane D/H Ratio in the Interstellar Object 3I/ATLAS

Interstellar objects are interlopers from other planetary systems, and their volatile compositions provide a glimpse into planet formation around their host star. We present near-infrared spectra of the coma of interstellar object 3I/ATLAS measured with the James Webb Space Telescope. Our results demonstrate an unexpectedly high D/H = $(3.33\pm0.31)\%$ for methane and represent an exceedingly rare detection of deuterated organic molecules in an interstellar object. This D/H ratio exceeds any other value for methane measured in the solar system, and is a factor of $14\pm2$ higher than that measured in comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft, the only other comet for which CH$_3$D has been detected. Both 3I/ATLAS and 67P/Churyumov-Gerasimenko show a higher degree of methane dueteration compared to water, consistent with trends seen in other solar system bodies and the nearby interstellar medium, where deuteration in organics exceeds that of water by up to an order of magnitude. The D/H ratio in methane itself is observationally unconstrained in extrasolar sources to date, but the enriched ratio in 3I/ATLAS is similar to those measured in methanol and formaldehyde toward primitive environments. The elevated D/H ratio for methane in 3I/ATLAS is consistent with the hypothesis that its ices formed in a cold, low metallicity interstellar or protostellar environment under a high cosmic ray irradiation rate (Cordiner et al. 2026).

astro-ph.EP↗

arXiv2026

Coma Physics of an Interstellar Object: JWST Spatial-Spectral Mapping of 3I/ATLAS

We report a survey of molecular emission from cometary volatiles using the James Webb Space Telescope (JWST) toward interstellar object 3I/ATLAS carried out on UT 2025 December 22 and 23 at a heliocentric distance ($r_H$) of $2.37-2.41$ au. These measurements of CO, CO$_2$, H$_2$O, CH$_3$OH, and CH$_4$ sampled molecular chemistry in 3I/ATLAS as it receded from its encounter with our Sun and entered the vicinity of the H$_2$O ice line -- the region between $r_H$ = $2-3$ au where the temperature becomes too low for H$_2$O to vigorously sublime and CO and CO$_2$ begin to control the overall activity. CO was the most abundant molecule, followed by H$_2$O and CO$_2$, whose molecular abundances with respect to CO were $(40.5\pm3.1)\%$ and ($41.6\pm0.3)\%$, respectively. This work presents spatial-spectral maps of column density and rotational temperature as a function of distance from the nucleus for all detected species. The spatial distributions of both quantities were highly anisotropic for the apolar species in the coma of 3I/ATLAS, yet were more nearly symmetric for the polar molecules. These results demonstrate how volatiles were segregated in the nucleus ices of 3I/ATLAS and reveal heating and cooling mechanisms in its coma. Derived maps of the ortho-to-para ratio (OPR) for H$_2$O were flat with increasing distance from the nucleus and consistent with a coma-averaged value $\mathrm{OPR}=2.7\pm0.2$, slightly less than the expected equilibrium value of three.

astro-ph.EP↗

arXiv2026

Isotopic Evidence for a Cold and Distant Origin of the Interstellar Object 3I/ATLAS

Interstellar objects provide the only directly observable samples of icy planetesimals formed around other stars, and can therefore provide insight into the diversity of physical and chemical conditions occurring during exoplanet formation. Here we report isotopic measurements of the interstellar comet 3I/ATLAS, which reveal an elemental composition unlike any Solar System body. The water in 3I/ATLAS is enriched in deuterium, at a level of D/H = (0.95 +- 0.06)%, which is more than an order of magnitude higher than in known comets, while its range of 12C/13C ratios (141-191 for CO2 and 123-172 for CO) exceeds typical values found in the Solar System, as well as nearby interstellar clouds and protoplanetary disks. Such extreme isotopic signatures indicate formation at temperatures $\lesssim30$ K in a relatively metal-poor environment, early in the history of the Galaxy. When interpreted with respect to models for Galactic chemical evolution, the carbon isotopic composition implies that 3I/ATLAS accreted roughly 10-12 billion years ago, following an early period of intense star formation. 3I/ATLAS thus represents a preserved fragment of an ancient planetary system, and provides direct evidence for active ice chemistry and volatile-rich planetesimal formation in the young Milky Way.

astro-ph.EP↗

arXiv2026

Rotation Period of C/2006 P1 (McNaught) Through Morphological Analysis with Narrowband Imaging

This study presents findings from narrowband imaging of comet C/2006 P1 (McNaught) using the 3.6-metre New Technology Telescope (NTT) at La Silla, Chile. Observations commenced on January 27, 2007, 15 days after perihelion, and continued until February 4, with additional sessions from February 25 to 28. Imaging was conducted using the ESO Multi-Mode Instrument (EMMI) in both broadband (B, V, R) and six comet-specific narrowband filters (CN, C3, C2, NH2, blue and red continuum). Various image processing techniques were employed to enhance structural features, including azimuthal mean/median division and subtraction, azimuthal renormalisation, and division by inverse profile, as well as the Larson-Sekanina technique. These enhancements revealed dynamic coma structures, with jets transitioning from spiral patterns to linear or fan-like shapes over time. The consistency of morphological patterns across different processing methods validated their authenticity. The periodic recurrence and temporal evolution of CN coma features in narrowband images indicate a nucleus rotation period of 11.8 h, consistent with stable active regions and rotationally modulated outgassing near perihelion.

astro-ph.EP↗

arXiv2025

Intercepting Interstellar Objects

We describe how the ESA Comet Interceptor mission, which is due to launch in 2028/29 to a yet-to-be-discovered target, can provide a conceptual basis for a future mission to visit an Interstellar Object. Comet Interceptor will wait in space until a suitable long period comet is discovered, allowing rapid response to perform a fast flyby of an object that will be in the inner Solar System for only a few years; an enhanced version of this concept could realistically provide the first in situ investigation of a visitor from another star system.

astro-ph.IM↗

arXiv2025

Pre-perihelion evolution of the NiI/FeI abundance ratio in the coma of the interstellar comet 3I/ATLAS. From extreme to normal

Emission lines of FeI and NiI are commonly found in the coma of Solar System comets, even at large heliocentric distances. These atoms are most likely released from the surface of the comet's nucleus or from a short-lived parent. These lines were also found in the interstellar comet 2I/Borisov, which has a NiI/FeI abundance ratio similar to that observed in Solar System comets. Here, we report observations of the interstellar comet 3I/ATLAS, which were carried out with the ESO Very Large Telescope equipped with the UVES and X-shooter spectrographs. Spectra were obtained at heliocentric distances ranging from 3.14 to 1.85 au. NiI was detected at all epochs. FeI was only detected at heliocentric distances smaller than 2.64 au. We estimated the NiI and FeI production rates by comparing the observed line intensities with those produced by a dedicated fluorescence model. Comet 3I first exhibited extreme and unusual NiI/FeI abundance ratios during the initial stages of its activity. However, as its heliocentric distance decreased, this ratio became indistinguishable from those observed in Solar System comets and in comet 2I/Borisov. Comet 3I was found to be C$_2$-depleted, with a NiI/FeI abundance ratio finally consistent with other C$_2$-depleted comets. Nevertheless, comet 3I remains exceptional due to its high, total production rate of NiI and FeI, which is at least one order of magnitude larger than that of other comets. We interpreted these observations assuming that the NiI and FeI atoms were released through the sublimation of Ni(CO)$_4$ and Fe(CO)$_5$ carbonyls. This scenario provides a straightforward explanation for the asymmetric release of NiI and FeI atoms in the cometary coma and how it depends on the heliocentric distance. It also supports the presence of carbonyls in the cometary material.

astro-ph.EP↗

arXiv2025

JWST detection of a carbon dioxide dominated gas coma surrounding interstellar object 3I/ATLAS

3I/ATLAS is the third confirmed interstellar object to visit our Solar System, and only the second to display a clear coma. Infrared spectroscopy with the James Webb Space Telescope (JWST) provides the opportunity to measure its coma composition and determine the primary activity drivers. We report the first results from our JWST NIRSpec campaign for 3I/ATLAS, at an inbound heliocentric distance of $r_H=3.32$ au. The spectral images (spanning 0.6-5.3 $\mu$m) reveal a CO2 dominated coma, with enhanced outgassing in the sunward direction, and the presence of H2O, CO, OCS, water ice and dust. The coma CO2/H2O mixing ratio of $7.6\pm0.3$ is among the highest ever observed in a comet, and is 4.5-sigma above the trend as a function of heliocentric distance for long-period and Jupiter-family comets (excluding the outlier C/2016 R2). Our observations are compatible with an intrinsically CO2-rich nucleus, which may indicate that 3I/ATLAS contains ices exposed to higher levels of radiation than Solar System comets, or that it formed close to the CO2 ice line in its parent protoplanetary disk. A low coma H2O gas abundance may also be implied, for example, due to inhibited heat penetration into the nucleus, which could suppress the H2O sublimation rate relative to CO2 and CO.

astro-ph.EP↗

arXiv2025

Very Large Telescope Observations of Interstellar Comet 3I/ATLAS. II. From Quiescence to Glow: Dramatic Rise of Ni i Emission and Incipient CN Outgassing at Large Heliocentric Distances*

We report VLT spectroscopy of the interstellar comet 3I/ATLAS (C/2025~N1) from $r_{\rm h}\!\simeq\!4.4$ to $2.85$~au using X-shooter (300--550\,nm, $R\!\simeq\!3000$) and UVES (optical, $R\!\simeq\!35k-80k$). The coma is dust-dominated with a fairly constant red optical continuum slope ($\sim$21--22\%/1000\AA). We report detection of CN emission and also detect numerous Ni\,\textsc{ii}~lines while Fe\,\textsc{i}~remains undetected, potentially implying efficiently released gas-phase Ni. At $r_{\rm h}\!\simeq\!3.14$~au we derive $3\sigma$ limits of $Q({\rm OH})<{1.48\times10^{26}}\ {\rm s^{-1}}$, but find no indications for [O\,\textsc{i}], C$_2$, C$_3$ or NH$_2$. From our latest X-shooter measurements conducted on 2025-08-21 ($r_{\rm h} = 2.85$\,au) we measure production rates of $\log~Q(\mathrm{CN}) = {24.81\pm 0.01}$ molecules s$^{-1}$ and $\log~Q$(Ni) $= {23.30\pm0.07}$ atoms s$^{-1}$, and characterize their evolution as the comet approaches perihelion.~We observe a steep heliocentric-distance scaling for the production rates $Q(\mathrm{Ni}) \propto r_h^{{-7.7 \pm 1.0}}$ and for $Q(\mathrm{CN}) \propto r_h^{{-6.7 \pm 0.2}}$, and predict a Ni--CO$_{(2)}$ correlation if the Ni\,\textsc{ii}\ emission is driven by the carbonyl formation channel.~Energetic considerations of activation barriers show that this behavior is inconsistent with direct sublimation of canonical metal/sulfide phases and instead favors low--activation--energy release from dust, e.g.~photon-stimulated desorption or mild thermolysis of metalated organics or Ni-rich nanophases, possibly including Ni--carbonyl-like complexes.~These hypotheses are testable with future coordinated ground-based and space-based monitoring as 3I becomes more active during its continued passage through the solar system.

astro-ph.SR↗

arXiv2025

Recent Chemo-morphological Coma Evolution of Comet 67P/Churyumov-Gerasimenko

We present VLT/MUSE observations of comet 67P/Churyumov-Gerasimenko during its 2021 perihelion passage, from which we generated simultaneous maps of dust, [OI], C$_2$, NH$_2$, and CN comae across 12 pre- and post-perihelion epochs. These maps reveal the evolutionary and compositional trends of 67P's coma and further enrich the context and findings of ESA's Rosetta mission. Dust and gas species displayed distinct structures, where NH$_2$ and CN signals were uniquely associated with known dust fans, raising the question of possible correlation to the dust and contributions of extended sources. Localised fitted NH$_2$ scale lengths were 1.5-1.9$\times$ larger than those fitted for the rest of the coma, which is consistent with an extended source component for northern pre-perihelion emissions. In the southern hemisphere, CN was correlated with a prominent and sharp dust structure, potentially revealing an extended source origin via larger dust particles that preserve the CN parent species, as evidenced by higher spectral slopes in the region. Gas maps depicted two distinct evolutionary regimes: (1) evolving H$_2$O ([OI]$^{1}$D) and C$_2$ emissions driven by nucleus sublimation and subsolar insolation, and (2) stable NH$_2$ and CN emissions associated with seasonal dynamics and possible distributed sources. Dust spectral slope maps revealed spectral slope trends consistent with Rosetta findings, while green/red [OI] ratios generally indicate a coma dominated by H$_2$O.

astro-ph.EP↗

arXiv2025

A portrait throughout perihelion of the NH$_2$-rich interstellar comet 2I/Borisov

The interstellar comet 2I/Borisov is the first interstellar object where compositional characterisation was possible throughout its entire perihelion passage. We report all 16 epochs of a comprehensive optical observation campaign with ESO VLT's integral field spectrograph MUSE, spanning 126 days from 2019 November 14 to 2020 March 19. The spatial dust emission of 2I/Borisov was predominantly smooth, with no seasonal effect. A jet-like feature was consistently visible. The gas production morphology of its coma was also smooth and similar for C$_2$, NH$_2$, and CN: symmetric around the photocentre. The production rates of these species gently declined into and beyond perihelion, until 2I's outburst and splitting event in early 2020 March. C$_2$, NH$_2$, and CN production rates all increased, with NH$_2$ being the most significant; the dust emission also slightly reddened. 2I/Borisov is a carbon-depleted, relatively NH$_2$-rich comet when compared to those comets yet measured in the Solar System.

astro-ph.EP↗

arXiv2025

Snapshot of a new interstellar comet: 3I/ATLAS has a red and featureless spectrum

The interstellar comet 3I/ATLAS is only the third interstellar object to be discovered. Pre-perihelion measurements provide a unique opportunity to study its activity and composition, which may alter as it is heated in the coming months. We provide an initial baseline from optical spectroscopic observations obtained only two days after discovery, using the MUSE instrument on the VLT on 2025 July 3, while 3I was at 4.47 au from the Sun and 3.46 au from the Earth. These observations confirm the cometary nature of 3I, and reveal a red coma with a spectral slope of $(18\pm4)\%/1000$~\AA, redder than most Solar System comets but similar to the surface colour of some Solar System Trans-Neptunian Objects or Centaurs. We searched for but did not detect gas emission from C$_2$, NH$_2$, CN, and [OI], which is consistent with volatile non-detections for Solar System comets at this heliocentric distance. At present, the coma appears entirely dusty. Future observations of 3I as it comes closer to the Sun will provide an invaluable opportunity to witness the evolution of its activity, study its composition, test predictions of interstellar object population models, and compare 3I to Solar System comets.

astro-ph.EP↗

arXiv2025

A Swarm of WASP Planets: Nine giant planets identified by the WASP survey

The Wide Angle Search for Planets (WASP) survey provided some of the first transiting hot Jupiter candidates. With the addition of the Transiting Exoplanet Survey Satellite (TESS), many WASP planet candidates have now been revisited and given updated transit parameters. Here we present 9 transiting planets orbiting FGK stars that were identified as candidates by the WASP survey and measured to have planetary masses by radial velocity measurements. Subsequent space-based photometry taken by TESS as well as ground-based photometric and spectroscopic measurements have been used to jointly analyze the planetary properties of WASP-102 b, WASP-116 b, WASP-149 b WASP-154 b, WASP-155 b, WASP-188 b, WASP-194 b/HAT-P-71 b, WASP-195 b, and WASP-197 b. These planets have radii between 0.9 R_Jup and 1.4 R_Jup, masses between 0.1 M_Jup and 1.5 M_Jup, and periods between 1.3 and 6.6 days.

astro-ph.EP↗

arXiv2025

First JWST spectrum of distant activity in Long Period Comet C/2024 E1 (Wierzchos)

We observed the new Long Period Comet C/2024 E1 (Wierzchos), inbound at 7 au from the Sun, using the NIRSpec integral field unit on JWST. The spectrum shows absorption features due to water ice in the coma and evidence for CO$_2$ driven activity, with a production rate of $Q(CO_2) = 2.546 \pm 0.019 \times 10^{25}$ molecules s$^{-1}$, and no emission features of water or CO. The latter is surprising, given that CO is more volatile than CO$_2$, and suggests that this comet may have lost its near-surface CO during its early evolution, before implantation in the Oort cloud.

astro-ph.EP↗

arXiv2024

CUBES, the Cassegrain U-Band Efficient Spectrograph: towards final design review

In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high instrumental efficiency ( $>$ 37\%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R $>$ 20, 000 (with a lower-resolution, sky-limited mode of R $\sim$ 7, 000). With the design focusing on maximizing the instrument throughput (ensuring a Signal to Noise Ratio -SNR- $\sim$ 20 per spectral resolution element at 313 nm for U $\sim$ 17.5 mag objects in 1h of observations), it will offer new possibilities in many fields of astrophysics: i) access to key lines of stellar spectra (e.g. lighter elements, in particular Beryllium), extragalactic studies (e.g. circumgalactic medium of distant galaxies, cosmic UV background) and follow-up of explosive transients. We present the CUBES instrument design, currently in Phase-C and approaching the final design review, summarizing the hardware architecture and interfaces between the different subsystems as well as the relevant technical requirements. We describe the optical, mechanical, electrical design of the different subsystems (from the telescope adapter and support structure, through the main opto-mechanical path, including calibration unit, detector devices and cryostat control, main control electronics), detailing peculiar instrument functions like the Active Flexure Compensation (AFC). Furthermore, we outline the AITV concept and the main instrument operations giving an overview of its software ecosystem. Installation at the VLT is planned for 2028-2029 and first science operations in late 2029.

astro-ph.IM↗

arXiv2024

Tuning the Legacy Survey of Space and Time (LSST) Observing Strategy for Solar System Science: Incremental Templates in Year 1

The Vera C. Rubin Observatory is due to commence the 10-year Legacy Survey of Space and Time (LSST) at the end of 2025. To detect transient/variable sources and identify solar system objects (SSOs), the processing pipelines require templates of the static sky to perform difference imaging. During the first year of the LSST, templates must be generated as the survey progresses, otherwise SSOs cannot be discovered nightly. The incremental template generation strategy has not been finalized; therefore, we use the Metric Analysis Framework (MAF) and a simulation of the survey cadence (one_snap_v4.0_10yrs}) to explore template generation in Year 1. We have assessed the effects of generating templates over timescales of days-weeks, when at least four images of sufficient quality are available for $\geq90\%$ of the visit. We predict that SSO discoveries will begin $\sim$2-3 months after the start of the survey. We find that the ability of the LSST to discover SSOs in real-time is reduced in Year 1. This is especially true for detections in areas of the sky that receive fewer visits, such as the North Ecliptic Spur (NES), and in less commonly used filters, such as the $u$ and $g$-bands. The lack of templates in the NES dominates the loss of real-time SSO discoveries; across the whole sky the MAF Main-Belt asteroid (MBA) discovery metric decreases by up to $63\%$ compared to the baseline observing strategy, whereas the metric decreases by up to $79\%$ for MBAs in the NES alone.

astro-ph.EP↗