arXiv subjects

Patricio Rojo

Publications and source records attributed to Patricio Rojo.

At least 19 recordsLinked to original sources

arXiv2026

Changes in Pluto's Atmosphere Based on Stellar Occultation Data from 2017 to 2023

Pluto's tenuous atmosphere has $\mu$bar-level pressure and is composed primarily of ${\text{N}}_2$, with a variable haze. Its eccentric orbit combined with high obliquity leads to significant changes in solar insolation throughout the Plutonian year. The atmosphere is supported by vapor-pressure equilibrium with the surface ices, thus surface changes are coupled with the atmospheric properties. Volatile-transport models have anticipated Pluto's atmospheric evolution: predictions range from collapse over the coming decades to an atmosphere that remains. Previous work claims that Pluto's atmospheric pressure monotonically increased from 1988 through 2016, that the atmosphere began freezing out in 2018-2019, and that there was a plateau as of 2020. Here, we report results from ten stellar occultations by Pluto between 2017 August and 2023 July. Four events were multi-chord, while six were from single sites. Our results indicate a pressure plateau between the New Horizons flyby in 2015 through roughly 2021 and suggest that the atmospheric pressure has started to drop. Between 2015-2021 and 2022, the clear-atmosphere pressure at 1275 km decreased $7\pm6\%$, and it dropped $16\pm2\%$ for pressure at 1215 km when including haze. From 2017-2023, the upper atmospheric structure is consistent, while there is a change in light-curve slope in the lower atmosphere. This change-of-slope is consistent with haze particles settling over yearly or shorter timescales. Spikes in one light curve are indicative of intermittent buoyancy waves. More data are needed to confirm a recent pressure change.

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arXiv2025

X-SHYNE: X-Shooter spectra of young exoplanet analogs II. Presentation and analysis of the full library

The X-SHYNE library is a homogeneous sample of 43 medium-resolution (R=8000) infrared (0.3-2.5um) spectra of young (<500Myr), low-mass (<20Mjup), and cold (Teff=600-2000K) isolated brown dwarfs and wide-separation companions observed with the VLT/X-Shooter instrument. To characterize our targets, we performed a global comparative analysis. We first applied a semi-empirical approach. By refining their age and bolometric luminosity, we derived key atmospheric and physical properties, such as Teff, mass, surface gravity (g), and radius, using the evolutionary model COND03. These results were then compared with the results from a synthetic analysis based on three self-consistent atmospheric models. To compare our spectra with these grids we used the Bayesian inference code ForMoSA. We found similar Lbol estimates between both approaches, but an underestimated Teff from the cloudy models, likely due to a lack of absorbers that could dominate the J and H bands of early L. We also observed a discrepancy in the log(g) estimates, which are dispersed between 3.5 and 5.5 dex for mid-L objects. We interpreted this as a bias caused by a range of rotational velocities leading to cloud migration toward equatorial latitudes, combined with a variety of viewing angles that result in different observed atmospheric properties (cloud column densities, atmospheric pressures, etc.). Finally, while providing robust estimates of [M/H] and C/O for individual objects remains challenging, the X-SHYNE library globally suggests solar values, which are consistent with a formation via stellar formation mechanisms. This study highlights the strength of homogeneous datasets in performing comparative analyses, reducing the impact of systematics, and ensuring robust conclusions while avoiding over-interpretation.

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arXiv2025

A closer look at LTT 9779b: The ESPRESSO endeavour to pierce the atmospheric veil

The proliferation of exoplanet discoveries in exotic environments like the Neptune desert challenges our understanding of planetary atmospheres under intense irradiation. The unexpected discovery of LTT9779 b, an ultra-hot Neptune within this desert, offers a prime opportunity for atmospheric studies. We build on prior observations of LTT9779 b from TESS, Spitzer, and CHEOPS, incorporating new VLT/ESPRESSO data to probe its atmospheric dynamics. Preliminary analyses suggest a metal-rich atmosphere and a high day-side geometric albedo, possibly indicating silicate clouds. Minimal atmospheric escape is observed, contrasting existing models of planetary evolution under extreme irradiation. We obtained the transmission spectrum of LTT9779 b between 0.4 and 0.78 microns with ESPRESSO, addressing systematics across three transits. Our analysis focused on the sodium doublet and H-alpha, using cross-correlation with models containing Na, K, FeH, TiO, and VO. No significant atmospheric signal was detected, with metallicity limits set at [Fe/H] $\geq$ 2.25 ($\geq$ 180 times solar). The non-detection aligns with a high-metallicity, cloud-free model, implying a high mean molecular weight and reduced atmospheric scale height. We interpret this as evidence for a metal-rich atmosphere with suppressed spectral features, possibly due to high-altitude clouds or hazes. These findings are consistent with JWST observations, supporting the hypothesis of metal-rich atmospheres obscured by aerosols in extreme environments.

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arXiv2024

The Terminator Region Atmosphere of the hot Jupiter WASP-77Ab with ESPRESSO/VLT observations

Atmospheric studies are essential for elucidating the formation history, evolutionary processes, and atmospheric dynamics of exoplanets. High-resolution transmission spectroscopy offers the advantage of detecting subtle variations in stellar spectral profiles, thereby enabling the identification of the sources of observed signals. In this study, we present the transmission spectra of the exoplanet WASP-77Ab, a hot Jupiter with a 1.36-day orbital period around a G8 host star with $V=11.29$ mag. These observations were conducted using the high-resolution spectrograph ESPRESSO at the Very Large Telescope over three transit events. We analyze the Rossiter-McLaughlin effect for WASP-77A and determine a projected spin-orbit angle of ${λ= 16.131^{\circ}}^{+2.106}_{-2.324}$, indicating that the planet's orbit is nearly aligned. Following the generation of transmission spectra for the three nights, we model and correct for center-to-limb variation and the Rossiter-McLaughlin effects. In the residual transmission spectra, we detect H$α$, H$β$ and CaII H with a significance exceeding 3.5$σ$. After applying 0.1-0.5 Å masks to the cores of these lines to mitigate stellar contamination, all them still shows visible absorptions although not significant, suggesting at least partial planet contribution to them. Therefore, we are yet unable to confirm or reject the planetary origin of these spectral signals based on the current data set. Further investigation of WASP-77Ab's atmosphere, particularly in areas beyond the terminator region, is essential to illuminate the planet's two-dimensional atmospheric structure.

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arXiv2023

Atmospheric composition of WASP-85Ab with ESPRESSO/VLT observations

Transit spectroscopy is the most frequently used technique to reveal the atmospheric properties of exoplanets, while that at high resolution has the advantage to resolve the small Doppler shift of spectral lines, and the trace signal of the exoplanet atmosphere can be separately extracted. We obtain the transmission spectra of the extrasolar planet WASP-85Ab, a hot Jupiter in a 2.655-day orbit around a G5, V=11.2 mag host star, observed by high-resolution spectrograph ESPRESSO at the Very Large Telescope array for three transits. We present an analysis of the Rossiter-McLaughlin effect on WASP-85A, and determine a spin-orbit angle ${λ= -16.155^{\circ}}^{+2.916}_{-2.879}$, suggesting that the planet is in an almost aligned orbit. Combining the transmission spectra of three nights, we tentatively detected H$α$ and Ca II absorption with $\gtrapprox 3σ$ via direct visual inspection of the transmission spectra with the Center-to-Limb variation and the Rossiter-McLaughlin effects removed, which still remain visible after excluding the cores of these strong lines with a 0.1 A mask. These spectral signals seems likely to origin from the planetary atmosphere, but we can not fully exclude their stellar origins. Via the cross-correlation analysis of a set of atoms and molecules, Li I is marginally detected at $\sim4σ$ level, suggesting that Li might be present in the atmosphere of WASP-85Ab.

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arXiv2023

Detection of TiO and VO in the atmosphere of WASP-121b and Evidence for its temporal variation

We report the transit observations of the ultra hot Jupiter WASP-121b using the Goodman High Throughput Spectrograph (GHTS) at the 4-meter ground-based telescope Southern Astrophysical Research Telescope (SOAR), covering the wavelength range $502-900$ nm. By dividing the target and reference star into 19 spectroscopic passbands and applying differential spectrophotometry, we derive spectroscopic transit light curves and fit them using Gaussian process framework to determine transit depths for every passbands. The obtained optical transmission spectrum shows a steep increased slope toward the blue wavelength, which seems to be too steep to be accounted for by the Rayleigh scattering alone. We note that the transmission spectrum from this work and other works differ obviously from each other, which was pointed out previously by \citet{Wilson2021} as evidence for temporal atmospheric variation. We perform a free chemistry retrieval analysis on the optical transmission spectra from this work and the literature HST/WFC3 NIR spectrum. We determine TiO, VO and H$_{2}$O with abundances of $-5.95_{-0.42}^{+0.47}$ dex, $-6.72_{-1.79}^{+0.51}$ dex, and $-4.13_{-0.46}^{+0.63}$ dex, respectively. We compare the abundances of all these three molecules derived from this work and previous works, and find that they are not consistent with each other, indicating the chemical compositions of the terminator region may change over long timescales. Future multi-epoch and high-precision transit observations are required to further confirm this phenomena. We note that when combining the transmission spectra in the optical and in NIR in retrieval analysis, the abundances of V and VO, the NIR-to-optical offset and the cloud deck pressure may be coupled with each other.

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arXiv2023

Tentative detection of titanium oxide in the atmosphere of WASP-69 b with a 4m ground-based telescope

Transiting planets provide unique opportunities for the atmospheric characterization of exoplanets as they can reveal composition and the temperature structures at the day-night terminator regions in planetary atmospheres, and help understand the atmospheric process and formation environments of exoplanets. Here, we present the optical transmission spectroscopic study of an inflated Saturn-mass planet WASP-69 b, obtained by the 4-meter ground-based telescope Southern Astrophysical Research Telescope (SOAR). We obtain spectroscopic transit light curves in 20 passbands from 502 to 890 nm, and fit them using Gaussian Processes and an analytical transit model to obtain independent transit depths for each. The derived transmission spectrum of WASP-69 b shows a slope with absorption depth increasing towards blue wavelengths, indicating a Rayleigh scattering in the atmosphere consistent with previous works. The retrieval analysis yields a tentative detection of TiO absorption feature in the transmission spectrum. We present the first results from the SOAR telescope to characterize exoplanetary atmospheres proving its capability and precision for hot Jupiters around bright stars in an area dominated by results from large ground-based telescopes or space telescopes.

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arXiv2021

An Open-source Bayesian Atmospheric Radiative Transfer (BART) Code: II. The Transit Radiative-transfer Module and Retrieval of HAT-P-11b

This and companion papers by Harrington et al. and Blecic et al. present the Bayesian Atmospheric Radiative Transfer (BART) code, an open-source, open-development package to characterize extrasolar-planet atmospheres. BART combines a thermochemical equilibrium abundances (TEA), a radiative-transfer (Transit), and a Bayesian statistical (MC3) module to constrain atmospheric temperatures and molecular abundances for given spectroscopic observations. Here, we describe the Transit radiative-transfer package, an efficient line-by-line radiative-transfer C code for one-dimensional atmospheres, developed by P. Rojo and further modified by the UCF exoplanet group. This code produces transmission and hemisphere-integrated emission spectra. Transit handles line-by-line opacities from HITRAN, Partridge \& Schwenke ({\water}), Schwenke (TiO), and Plez (VO); and collision-induced absorption from Borysow, HITRAN, and ExoMol. Transit emission-spectra models agree with models from C. Morley (priv. comm.) within a few percent. We applied BART to the {\Spitzer} and {\Hubble} transit observations of the Neptune-sized planet HAT-P-11b. Our results generally agree with those from previous studies, constraining the {\water} abundance and finding an atmosphere enhanced in heavy elements. Different conclusions start to emerge when we make different assumptions from other studies. The BART source code and documentation are available at https://github.com/exosports/BART.

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arXiv2021

An open-source Bayesian atmospheric radiative transfer (BART) code: III. Initialization, atmospheric profile generator, post-processing routines, and application to exoplanet WASP-43b

This and companion papers by Harrington et al. 2021, submitted and Cubillos et al. 2021, submitted describe an open-source retrieval framework, Bayesian Atmospheric Radiative Transfer (BART), available to the community under the reproducible-research license via https://github.com/exosports/BART . BART is a radiative-transfer code (transit, https://github.com/exosports/transit , Rojo 2009, 2009ASPC..420..321R), initialized by the Thermochemical Equilibrium Abundances (TEA, https://github.com/dzesmin/TEA , Blecic et al. 2016, arXiv:1505.06392) code, and driven through the parameter phase space by a differential-evolution Markov-chain Monte Carlo (MC3, https://github.com/pcubillos/mc3 , Cubillos et al. 2017, arXiv:1610.01336) sampler. In this paper we give a brief description of the framework, and its modules that can be used separately for other scientific purposes; outline the retrieval analysis flow; present the initialization routines, describing in detail the atmospheric profile generator and the temperature and species parameterizations; and specify the post-processing routines and outputs, concentrating on the spectrum band integrator, the best-fit model selection, and the contribution functions. We also present an atmospheric analysis of WASP-43b secondary eclipse data obtained from space- and ground-based observations. We compare our results with the results from the literature, and investigate how the inclusion of additional opacity sources influence the best-fit model.

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arXiv2020

Identification and Mitigation of a Vibrational Telescope Systematic with Application to Spitzer

We observed Proxima Centauri with the Spitzer Space Telescope InfraRed Array Camera (IRAC) five times in 2016 and 2017 to search for transits of Proxima Centauri b. Following standard analysis procedures, we found three asymmetric, transit-like events that are now understood to be vibrational systematics. This systematic is correlated with the width of the point-response function (PRF), which we measure with rotated and non-rotated Gaussian fits with respect to the detecor array. We show that the systematic can be removed with a novel application of an adaptive elliptical-aperture photometry technique, and compare the performance of this technique with fixed and variable circular-aperture photometry, using both BiLinearly Interpolated Subpixel Sensitivity (BLISS) maps and non-binned Pixel-Level Decorrelation (PLD). With BLISS maps, elliptical photometry results in a lower standard deviation of normalized residuals, and reduced or similar correlated noise when compared to circular apertures. PLD prefers variable, circular apertures, but generally results in more correlated noise than BLISS. This vibrational effect is likely present in other telescopes and Spitzer observations, where correction could improve results. Our elliptical apertures can be applied to any photometry observations, and may be even more effective when applied to more circular PRFs than Spitzer's.

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arXiv2020

Maintaining the Ephemeris of 20 CoRoT Planets: Transit Minimum Times and Potential Transit Timing Variations

We present 33 transit minimum times of 20 transiting planets discovered by the CoRoT mission, which have been obtained from ground-based observations since the mission's end in 2012, with the objective to maintain the ephemeris of these planets. Twelve of the observed planets are in the CoRoT fields near the galactic center and the remaining eight planets are in the fields near the anticenter. We detect indications for significant transit timing variations in the cases of CoRoT 3b, 11b, 13b, 27b. For two more planets (CoRoT 18b and 20b) we conclude that timing offsets in early follow-up observations led to ephemeris in discovery publications that are inconsistent with timings from follow-up observations in later epochs. In the case of CoRoT-20b, this might be due to the influence from a further non-transiting planet. We also note that a significant majority (23 of 33) of our reported minimum times have negative O-C values, albeit most of them are within the expected uncertainty of the ephemeris.

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arXiv2020

ALMA Observations of Io Going into and Coming out of Eclipse

We present 1-mm observations constructed from ALMA [Atacama Large (sub)Millimeter Array] data of SO$_2$, SO and KCl when Io went from sunlight into eclipse (20 March 2018), and vice versa (2 and 11 September 2018). There is clear evidence of volcanic plumes on 20 March and 2 September. The plumes distort the line profiles, causing high-velocity ($\gtrsim$500 m/s) wings, and red/blue-shifted shoulders in the line profiles. During eclipse ingress, the SO$_2$ flux density dropped exponentially, and the atmosphere reformed in a linear fashion when re-emerging in sunlight, with a "post-eclipse brightening" after $\sim$10 minutes. While both the in-eclipse decrease and in-sunlight increase in SO was more gradual than for SO$_2$, the fact that SO decreased at all is evidence that self-reactions at the surface are important and fast, and that in-sunlight photolysis of SO$_2$ is the dominant source of SO. Disk-integrated SO$_2$ in-sunlight flux densities are $\sim$2--3 times higher than in-eclipse, indicative of a roughly 30--50\% contribution from volcanic sources to the atmosphere. Typical column densities and temperatures are $N \approx (1.5 \pm 0.3) \times 10^{16}$ cm$^{-2}$ and $T \approx 220-320$ K both in-sunlight and in-eclipse, while the fractional coverage of the gas is 2--3 times lower in-eclipse than in-sunlight. The low level SO$_2$ emissions present during eclipse may be sourced by stealth volcanism or be evidence of a layer of non-condensible gases preventing complete collapse of the SO$_2$ atmosphere. The melt in magma chambers at different volcanoes must differ in composition to explain the absence of SO and SO$_2$, but simultaneous presence of KCl over Ulgen Patera.

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arXiv2020

TraMoS V. Updated ephemeris and multi-epoch monitoring of the hot Jupiters WASP-18Ab, WASP-19b, and WASP-77Ab

We present 22 new transit observations of the exoplanets WASP-18Ab, WASP-19b, and WASP-77Ab, from the Transit Monitoring in the South (TraMoS) project. We simultaneously model our newly collected transit light curves with archival photometry and radial velocity data, to obtain refined physical and orbital parameters. We include TESS light curves of the three exoplanets to perform an extended analysis of the variations in their transit mid-time (TTV) and to refine their planetary orbital ephemeris. We did not find significant $\rm TTV_{RMS}$ variations larger than 47, 65, and 86 seconds for WASP-18Ab, WASP-19b, and WASP-77Ab, respectively. Dynamical simulations were carried out to constrain the masses of a possible perturber. The observed RMS could be produced by a perturber body with an upper limit mass of 9, 2.5, 11 and $4~M_{\oplus}$ in 1:2, 1:3, 2:1, and 3:1 resonances in the WASP-18Ab system. In the case of WASP-19b, companions with masses up to 0.26, 0.65, 1 and $2.8~M_{\oplus}$, in 1:2, 2:1, 3:1, and 5:3 resonances, produce the RMS. And for the WASP-77Ab system, a planet with mass between $1.5-9~M_{\oplus}$ in 1:2, 1:3, 2:1, 2:3, 3:1, 3:5, 5:3 resonances. Comparing our results with RV variations, we discard massive companions with $350~M_{\oplus}$ in 17:5 resonance for WASP-18Ab, $95~M_{\oplus}$ in 4:1 resonance for WASP-19b and $105~M_{\oplus}$ in 5:2 resonance for WASP-77Ab. Finally, using a Lomb-Scargle period search we find no evidence of a periodic trend on our TTV data for the three exoplanets.

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arXiv2019

Proxima Centauri b is not a transiting exoplanet

We report Spitzer Space Telescope observations during predicted transits of the exoplanet Proxima Centauri b. As the nearest terrestrial habitable-zone planet we will ever discover, any potential transit of Proxima b would place strong constraints on its radius, bulk density, and atmosphere. Subsequent transmission spectroscopy and secondary-eclipse measurements could then probe the atmospheric chemistry, physical processes, and orbit, including a search for biosignatures. However, our photometric results rule out planetary transits at the 200~ppm level at 4.5$~μm$, yielding a 3$σ$ upper radius limit of 0.4~$R_\rm{\oplus}$ (Earth radii). Previous claims of possible transits from optical ground- and space-based photometry were likely correlated noise in the data from Proxima Centauri's frequent flaring. Follow-up observations should focus on planetary radio emission, phase curves, and direct imaging. Our study indicates dramatically reduced stellar activity at near-to-mid infrared wavelengths, compared to the optical. Proxima b is an ideal target for space-based infrared telescopes, if their instruments can be configured to handle Proxima's brightness.

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arXiv2017

Estimation of Exoplanetary Planet-to-Star Radius Ratio with Homomorphic Processing

In this paper a homomorphic filtering scheme is proposed to improve the estimation of the planet/star radius ratio in astronomical transit signals. The idea is to reduce the effect of the short-term earth atmosphere variations. A two-step method is presented to compute the parameters of the transit curve from both the unfiltered and filtered data. A Monte Carlo analysis is performed by using correlated and uncorrelated noise to determine the parameters of the proposed FFT filter. The method is tested with observations of WASP-19b and WASP-17b obtained with the FORS2 instrument at the Very Large Telescope (VLT). The multi parametric fitting and the associated errors are obtained with the JKTEBOP software. The results with the white light of the exo-planet data mentioned above suggest that the homomorphic filtering can lead to substantial relative reductions in the error bars as high as 45.5% and 76.9%, respectively. The achieved reductions in the averaged error bars per channel were 48.4% with WASP-19b and 63.6% with WASP-17b. Open source MATLAB code to run the method proposed here can be downloaded from http://www.cmrsp.cl. This code was used to obtain the results presented in this paper.

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arXiv2017

Unsupervised Method for Correlated Noise Removal for Multi-wavelength Exoplanet Transit Observations

Exoplanetary atmospheric observations require an exquisite precision in the measurement of the relative flux among wavelengths. In this paper, we aim to provide a new adaptive method to treat light curves before fitting transit parameters in order to minimize systematic effects that affect, for instance, ground-based observations of exo-atmospheres. We propose a neural-network-based method that uses a reference built from the data itself with parameters that are chosen in an unsupervised fashion. To improve the performance of proposed method, K-means clustering and Silhouette criteria are used for identifying similar wavelengths in each cluster. We also constrain under which circumstances our method improves the measurement of planetary-to-stellar radius ratio without producing significant systematic offset. We tested our method in high quality data from WASP-19b and low quality data from GJ-1214. We succeed in providing smaller error bars for the former when using JKTEBOP, but GJ-1214 light curve was beyond the capabilities of this method to improve as it was expected from our validation tests.

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arXiv2015

On non-coplanar Hohmann Transfer using angles as parameters

We study a more complex case of Hohmann orbital transfer of a satellite by considering non-coplanar and elliptical orbits, instead of planar and circular orbits. We use as parameter the angle between the initial and transference planes that minimizes the energy, and therefore the fuel of a satellite, through the application of two non-tangential impulses for all possible cases. We found an analytical expression that minimizes the energy for each configuration. Some reasonable physical constraints are used: we apply impulses at perigee or apogee of the orbit, we consider the duration of the impulse to be short compared to the duration of the trip, we take the nodal line of three orbits to be coincident and the three semimajor axes to lie in the same plane. We study the only four possible cases but assuming non-coplanar elliptic orbits. In addition, we validate our method through a numerical solution obtained by using some of the actual orbital elements of Sputnik I and Vanguard I satellites. For these orbits, we found that the most fuel-efficient transfer is obtained by applying the initial impulse at apocenter and keeping the transfer orbit aligned with the initial orbit.

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arXiv2014

Improved signal detection algorithms for unevenly sampled data. Six signals in the radial velocity data for GJ876

The hunt for Earth analogue planets orbiting Sun-like stars has forced the introduction of novel methods to detect signals at, or below, the level of the intrinsic noise of the observations. We present a new global periodogram method that returns more information than the classic Lomb-Scargle periodogram method for radial velocity signal detection. Our method uses the Minimum Mean Squared Error as a framework to determine the optimal number of genuine signals present in a radial velocity timeseries using a global search algorithm, meaning we can discard noise spikes from the data before follow-up analysis. This method also allows us to determine the phase and amplitude of the signals we detect, meaning we can track these quantities as a function of time to test if the signals are stationary or non-stationary. We apply our method to the radial velocity data for GJ876 as a test system to highlight how the phase information can be used to select against non-stationary sources of detected signals in radial velocity data, such as rotational modulation of star spots. Analysis of this system yields two new statistically significant signals in the combined Keck and HARPS velocities with periods of 10 and 15 days. Although a planet with a period of 15 days would relate to a Laplace resonant chain configuration with three of the other planets (8:4:2:1), we stress that follow-up dynamical analyses are needed to test the reliability of such a six planet system.

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