arXiv subjects

N. Godoy

Publications and source records attributed to N. Godoy.

14 recordsLinked to original sources

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

A JWST/MIRI view of k Andromedae b: Refining its mass, age, and physical parameters

Context. kAndb is a substellar companion near the planet-brown dwarf boundary, orbiting a B9IV star at 50-100 au. Estimates of its age and mass vary, fueling a decade-long debate. Atmospheric parameters (Teff 1650-2050 K, log(g) 3.5-5.5) remain poorly constrained due to model differences and heterogeneous datasets. Aims. We refine the characterization of kAndb using mid-infrared data to capture its bolometric emission. Combined with NIR measurements, we constrain Teff, log(g), and radius to reduce uncertainties in age and mass. Methods. We obtained JWST/MIRI coronagraphic data (F1065C, F1140C, F1550C) and recalibrated NIR photometry with an updated ATLAS stellar model. MIRI color-magnitude diagrams (CMDs) probe the likelihood of species (CH4, NH3, silicates). We compared H and F1140C colors and magnitudes to isochrones to constrain age and mass. We modeled the spectral energy distribution with atmosphere models to refine Teff, radius, and log(g), and to constrain age and mass using evolutionary models. Results. Cloudy atmosphere models fit best, consistent with the L0/L2 spectral type and position near silicate-atmosphere field objects in the MIRI CMD. We derived an age of 47+-7 Myr and mass of 17.3+-1.8 MJup by weighted-mean model combination. Modeling yielded Teff = 1791+-68 K and radius = 1.42+-0.06 RJup, improving precision by 30%. Log(g) = 4.35+-0.07 dex represents a 70% improvement over the previous best value (4.75+-0.25). Conclusions. The new mass places kAndb just above the deuterium-burning limit. The age is 75% more precise and consistent with the Columba association (42 Myr). The Teff suggests silicate clouds, requiring spectroscopic confirmation. MIRI data were crucial to refining radius and temperature, which led to stronger constraints on age and mass and improving the overall characterization of kAndb.

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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

ESCAPE project: fundamental detection limits of JWST/NIRCam coronographic observations

In this study, we explored the fundamental contrast limit of NIRCam coronagraphy observations, representing the achievable performance with post-processing techniques. This limit is influenced by photon noise and readout noise, with complex noise propagation through post-processing methods like principal component analysis. We employed two approaches: developing a formula based on simplified scenarios and using Markov Chain Monte Carlo (MCMC) methods, assuming Gaussian noise properties and uncorrelated pixel noise. Tested on datasets HIP\,65426, AF\,Lep, and HD\,114174, the MCMC method provided accurate but computationally intensive estimates. The analytical approach offered quick, reliable estimates closely matching MCMC results in simpler scenarios. Our findings showed the fundamental contrast curve is significantly deeper than the current achievable contrast limit obtained with post-processing techniques at shorter separations, being 10 times deeper at $0.5''$ and 4 times deeper at $1''$. At greater separations, increased exposure time improves sensitivity, with the transition between photon and readout noise dominance occurring between $2''$ and $3''$. We conclude the analytical approach is a reliable estimate of the fundamental contrast limit, offering a faster alternative to MCMC. These results emphasize the potential for greater sensitivity at shorter separations, highlighting the need for improved or new post-processing techniques to enhance JWST NIRCam sensitivity or contrast curve.

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arXiv2023

Black Hole masses for 14 gravitational lensed quasars

We estimate black hole masses (M$_{\rm BH}$) for 14 gravitationally lensed quasars using the Balmer lines along with estimates based on MgII and CIV emission lines for four and two of them, respectively. We compare with results obtained for other lensed quasars. We use spectroscopic data from the Large Binocular Telescope (LBT), Magellan and the Very Large Telescope (VLT) to measure the FWHM of the broad emission lines. Combined with the bolometric luminosity measured from the spectra energy distribution, we estimate M$_{\rm BH}$ including uncertainties from microlensing and variability. We obtain MBH using the single-epoch method from the H$α$ and/or H$β$ broad emission lines for 14 lensed quasars, including the first estimates for QJ0158-4325, HE0512-3329 and WFI2026-4536. The masses are typical of non-lensed quasars of similar luminosity, and the implied Eddington ratios are typical. We have increased the sample of lenses with estimates of MBH by 60%.

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arXiv2021

ISPY -- NaCo Imaging Survey for Planets around Young stars. CenteR: the impact of centering and frame selection

Abridged: Direct imaging has made significant progress over the past decade leading to the detection of several giant planets. Observing strategies and data rates vary from instrument to instrument and wavelength, and can result in tens of thousands of images to be combined. We here present a new approach, tailored for VLT/NaCo observations performed with the Annular Groove Phase Mask (AGPM) coronagraph at $L'$ filter. Our pipeline aims at improving the post-processing of the observations on two fronts: identifying the location of the star behind the AGPM to better align the science frames and performing frame selection. Our method relies on finding the position of the AGPM in the sky frame observations, and correlate it with the circular aperture of the coronagraphic mask. This relationship allows us to retrieve the location of the AGPM in the science frames, in turn allowing us to estimate the position of the star. In the process we also gather additional information useful for our frame selection approach. We tested our pipeline on several targets, and find that we improve the S/N of companions around $β$ Pictoris and R CrA by $24\pm3$ \% and $117\pm11$ \% respectively, compared to other state-of-the-art reductions. The astrometry of the point sources is slightly different but remains compatible within $3σ$ compared to published values. Finally, we find that even for NaCo observations with tens of thousands of frames, frame selection yields just marginal improvement for point sources but may improve the final images for objects with extended emission such as disks. We proposed a novel approach to identify the location of the star behind a coronagraph even when it cannot easily be determined by other methods, leading to better S/N for nearby point sources, and led a thorough study on the importance of frame selection, concluding that the improvements are marginal in most case.

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arXiv2021

First black hole mass estimation for the quadruple lensed system WGD2038-4008

The quadruple lensed system WGD2038-4008 was recently discovered with the help of new techniques and observations. Even though black hole mass has been estimated for lensed quasars, it has been calculated mostly for one broad emission line of one image, but the images could be affected by microlensing, affecting the results. We present black hole mass (MBH) estimations for images A and B using the three most prominent broad emission lines (H$α$, H$β$ and MgII) obtained in one single-epoch spectra. This is the first time the mass is estimated in a lensed quasar in two images, allowing us to disentangle the effects of microlensing. We used the X-shooter instrument mounted in VLT, to observe this system taking advantage of its wide spectral range. Using the flux ratio between the continuum and the core of the emission lines we analyzed if microlensing was present in the continuum source. We obtained MBH using the single-epoch method with the H$α$ and H$β$ emission lines from the monochromatic luminosity and the velocity width. The luminosity at 3000 Å was obtained using the Spectral Energy Distribution (SED) of image A while the luminosity at 5100 Å was estimated directly from the spectra. The average MBH between the images obtained was $\rm log_{10}$(M$_{BH}/M_{\odot}$) = 8.27 $\pm$ 1.05, 8.25 $\pm$ 0.32 and 8.59 $\pm$ 0.35 for MgII, H$β$ and H$α$ respectively. We find Eddington ratios similar to those measured in the literature for unlensed low-luminosity quasars. Microlensing of -0.16 $\pm$ 0.06 mag. in the continuum was found but the induced error in the MBH is minor compared to the one associated to the macromodel magnification. We also obtained the accretion disk size using the MBH for the three emission lines, obtaining an average value of $\rm log_{10}(r_{s}/cm)$ = 15.3 +/- 0.63, which is in agreement with theoretical estimates.

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arXiv2020

Most EL CVn systems are inner binaries of hierarchical triples

In spite of their importance for modern astronomy, we do not fully understand how close binary stars containing at least one white dwarf form from main sequence binary stars. The discovery of EL CVn binaries, close pre-white dwarfs with A/F main sequence star companions, offers now the unique possibility to test models of close compact binary star formation. Binary evolution theories predict that these EL CVn stars descend from very close main sequence binaries with orbital periods shorter than 3 days. If this is correct, nearly all EL CVn stars should be inner binaries of hierarchical triples because more than 95 per cent of very close main sequence binaries (the alleged progenitor systems) are found to be hierarchical triples. We here present SPHERE/IRDIS observations of five EL CVn binaries, finding in all of them tertiary objects, as predicted. We conclude that EL CVn systems are inner binaries of hierarchical triples and indeed descend from very close main sequence binaries that experience stable mass transfer.

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arXiv2020

ISPY -- NACO Imaging Survey for Planets around Young stars: Survey description and results from the first 2.5 years of observations

The occurrence rate of long-period giant planets around young stars is highly uncertain since it is not only governed by the protoplanetary disc structure and planet formation process, but also reflects dynamical re-structuring processes after planet formation as well as possible capture of planets not formed in-situ. Direct imaging is currently the only feasible method to detect such wide-orbit planets and constrain their occurrence rate. We carry out a large L'-band high-contrast direct imaging survey for giant planets around young stars with protoplanetary or debris discs using the NACO instrument at the ESO Very Large Telescope on Cerro Paranal in Chile. We use very deep angular differential imaging observations with typically >60 deg field rotation, and employ a vector vortex coronagraph where feasible to achieve the best possible point source sensitivity down to an inner working angle of about 100mas. This paper introduces our NACO Imaging Survey for Planets around Young stars ("NACO-ISPY"), its goals and strategy, the target list, and data reduction scheme, and presents preliminary results from the first 2.5 survey years. We achieve a mean 5 sigma L' contrast of 6.4mag at 150mas and a background limit of 16.5mag at >1.5". Our detection probability is >50\% for companions with 8\,M$_{\rm Jup}$\ at semi-major axes 80-200au. It thus compares well to the detection space of other state-of-the-art high-contrast imaging surveys. We have contributed to the characterisation of two new planets originally discovered by VLT/SPHERE, but we have not yet independently discovered new planets around any of our target stars. We report the discovery of close-in low-mass stellar companions around four young stars and show L'-band scattered light images of the discs around eleven stars, six of which have never been imaged at L'-band before.

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arXiv2019

A dusty benchmark brown dwarf near the ice line of HD 72946

Context. HD72946 is a bright and nearby solar-type star hosting a low-mass companion at long period (P~16 yr) detected with the radial velocities (RV) method. The companion has a minimum mass of 60.4+/-2.2 MJ and might be a brown dwarf. Its expected semi-major axis of ~243 mas makes it a suitable target for further characterization with high-contrast imaging, in particular to measure its inclination, mass, and spectrum and thus definitely establish its substellar nature. Aims. We aim to further characterize the orbit, atmosphere, and physical nature of HD72946B. Methods. We present high-contrast imaging data in the near-infrared with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. We also use proper motion measurements of the star from Hipparcos and Gaia. Results. The SPHERE data reveal a point source with a contrast of ~9 mag at a projected separation of ~235 mas. No other point sources are detected in the field of view. By jointly fitting the RV, imaging, and proper motion data, we constrain all the orbital parameters of HD72946B and assess a dynamical mass of 72.4+/-1.6 MJ and a semi-major axis of 6.45$^{+0.08}_{-0.07}$ au. Empirical comparison of its IFS spectrum to template dwarfs indicates a spectral type of L5.0+/-1.5. The J-H3 color is close to the expectations of the DUSTY models and suggests a cloudy atmosphere. Comparison with atmospheric models of the spectrophotometry suggests an effective temperature of ~1700 K. The bolometric luminosity (log(L/LS)=-4.11+/-0.10 dex) and dynamical mass of HD72946B are more compatible with evolutionary models for an age range of ~0.9-3 Gyr. The formation mechanism of the companion is currently unclear as it appears slightly away from the bulk of model predictions. HD72946B is currently the closest benchmark brown dwarf companion to a solar-type star with imaging, RV, and proper motion measurements.

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arXiv2019

ISPY - the NaCo Imaging Survey for Planets around Young stars: A young companion candidate embedded in the R CrA cloud

Within the NaCo-ISPY exoplanet imaging program, we aim at detecting and characterizing the population of low-mass companions at wide separations ($\gtrsim$10AU), focusing in particular on young stars either hosting a known protoplanetary disk or a debris disk. R CrA is one of the youngest (1-3 Myr) and most promising objects in our sample because of two previous studies that suggested the presence of a close companion. Our aim is to directly image and characterize the companion for the first time. We observed R CrA twice with the NaCo instrument at VLT in the $L'$ filter with a one year time baseline in between. The high-contrast imaging data were reduced and analyzed, and in both datasets the companion candidate was detected. The companion is detected at a separation of $196.8\pm4.5$/$196.6\pm5.9$ mas ($18.7\pm1.3$/$18.7\pm1.4$ AU) and position angle of $134.7\pm0.5^\circ/133.7\pm0.7^\circ$ in the first/second epoch observation. We measure a contrast of $7.29\pm0.18$/$6.70\pm0.15$ mag with respect to the primary. Stellar proper motion study rejects the hypothesis of the signal being a background object. The companion candidate orbits in the clockwise direction and, if on a face-on circular orbit, its period is $\sim43-47$ yr. This value disagrees with the estimated orbital motion and therefore a face-on circular orbit may be excluded. Depending on the assumed age, extinction and brightness of the primary, the stellar companion has a mass between $0.10\pm0.02\, M_\odot$ and $1.03^{+0.20}_{-0.18}\,M_\odot$ range, if no contribution from circumsecondary material is taken into account. The presence of the companion needs to be taken into account when analyzing the complex circumstellar environment of R CrA.

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arXiv2018

Spectral and orbital characterisation of the directly imaged giant planet HIP 65426 b

HIP 65426 b is a recently discovered exoplanet imaged during the course of the SPHERE-SHINE survey. Here we present new $L'$ and $M'$ observations of the planet from the NACO instrument at the VLT from the NACO-ISPY survey, as well as a new $Y-H$ spectrum and $K$-band photometry from SPHERE-SHINE. Using these data, we confirm the nature of the companion as a warm, dusty planet with a mid-L spectral type. From comparison of its SED with the BT-Settl atmospheric models, we derive a best-fit effective temperature of $T_{\text{eff}}=1618\pm7$ K, surface gravity $\log g=3.78^{+0.04}_{-0.03}$ and radius $R=1.17\pm0.04$ $R_{\text{J}}$ (statistical uncertainties only). Using the DUSTY and COND isochrones we estimate a mass of $8\pm1$ $M_{\text{J}}$. Combining the astrometric measurements from our new datasets and from the literature, we show the first indications of orbital motion of the companion (2.6$σ$ significance) and derive preliminary orbital constraints. We find a highly inclined orbit ($i=107^{+13}_{-10}$ deg) with an orbital period of $800^{+1200}_{-400}$ yr. We also report SPHERE sparse aperture masking observations that investigate the possibility that HIP 65426 b was scattered onto its current orbit by an additional companion at a smaller orbital separation. From this data we rule out the presence of brown dwarf companions with masses greater than 16 $M_{\text{J}}$ at separations larger than 3 AU, significantly narrowing the parameter space for such a companion.

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arXiv2018

Resolving faint structures in the debris disk around TWA7

Debris disks are the intrinsic by-products of the star and planet formation processes. Most likely due to instrumental limitations and their natural faintness, little is known about debris disks around low-mass stars, especially when it comes to spatially resolved observations. We present new VLT/SPHERE IRDIS Dual-Polarization Imaging (DPI) observations in which we detect the dust ring around the M2 spectral type star TWA\,7. Combined with additional Angular Differential Imaging observations we aim at a fine characterization of the debris disk and setting constraints on the presence of low-mass planets. We model the SPHERE DPI observations and constrain the location of the small dust grains, as well as the spectral energy distribution of the debris disk, using the results inferred from the observations, and perform simple N-body simulations. We find that the dust density distribution peaks at 25 au, with a very shallow outer power-law slope, and that the disk has an inclination of 13 degrees with a position angle of 90 degrees East of North. We also report low signal-to-noise detections of an outer belt at a distance of ~52 au from the star, of a spiral arm in the Southern side of the star, and of a possible dusty clump at 3.9 au. These findings seem to persist over timescales of at least a year. Using the intensity images, we do not detect any planets in the close vicinity of the star, but the sensitivity reaches Jovian planet mass upper limits. We find that the SED is best reproduced with an inner disk at 7 au and another belt at 25 au. We report the detections of several unexpected features in the disk around TWA\,7. A yet undetected 100 M$_\oplus$ planet with a semi-major axis at 20-30 au could possibly explain the outer belt as well as the spiral arm. We conclude that stellar winds are unlikely to be responsible for the spiral arm.

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arXiv2016

The bimodal initial mass function in the Orion Nebula Cloud

Due to its youth, proximity and richness the Orion Nebula Cloud (ONC) is an ideal testbed to obtain a comprehensive view on the Initial Mass Function (IMF) down to the planetary mass regime. Using the HAWK-I camera at the VLT, we have obtained an unprecedented deep and wide near-infrared JHK mosaic of the ONC (90% completeness at K~19.0mag, 22'x28). Applying the most recent isochrones and accounting for the contamination of background stars and galaxies, we find that ONC's IMF is bimodal with distinct peaks at about 0.25 and 0.025 M_sun separated by a pronounced dip at the hydrogen burning limit (0.08 M_sun), with a depth of about a factor 2-3 below the log-normal distribution. Apart from ~920 low-mass stars (M < 1.4 M_sun) the IMF contains ~760 brown dwarf (BD) candidates and ~160 isolated planetary mass object (IPMO) candidates with M > 0.005 M_sun, hence about ten times more substellar candidates than known before. The substellar IMF peak at 0.025 M_sun could be caused by BDs and IPMOs which have been ejected from multiple systems during the early star-formation process or from circumstellar disks.

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