arXiv subjects

Jorge Llop-Sayson

Publications and source records attributed to Jorge Llop-Sayson.

33 records · Page 2Linked to original sources

arXiv2024

JWST-TST High Contrast: Achieving direct spectroscopy of faint substellar companions next to bright stars with the NIRSpec IFU

The JWST NIRSpec integral field unit (IFU) presents a unique opportunity to observe directly imaged exoplanets from 3-5 um at moderate spectral resolution (R~2,700) and thereby better constrain the composition, disequilibrium chemistry, and cloud properties of their atmospheres. In this work, we present the first NIRSpec IFU high-contrast observations of a substellar companion that requires starlight suppression techniques. We develop specific data reduction strategies to study faint companions around bright stars, and assess the performance of NIRSpec at high contrast. First, we demonstrate an approach to forward model the companion signal and the starlight directly in the detector images, which mitigates the effects of NIRSpec's spatial undersampling. We demonstrate a sensitivity to planets that are 3e-6 fainter than their stars at 1'', or 3e-5 at 0.3''. Then, we implement a reference star point spread function (PSF) subtraction and a spectral extraction that does not require spatially and spectrally regularly sampled spectral cubes. This allows us to extract a moderate resolution (R~2,700) spectrum of the faint T-dwarf companion HD 19467 B from 2.9-5.2 um with signal-to-noise ratio (S/N)~10 per resolution element. Across this wavelength range, HD~19467~B has a flux ratio varying between 1e-5-1e-4 and a separation relative to its star of 1.6''. A companion paper by Hoch et al. more deeply analyzes the atmospheric properties of this companion based on the extracted spectrum. Using the methods developed here, NIRSpec's sensitivity may enable direct detection and spectral characterization of relatively old (~1 Gyr), cool (~250 K), and closely separated (~3-5 au) exoplanets that are less massive than Jupiter.

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arXiv2024

Implicit Electric Field Conjugation Through a Single-mode Fiber

Connecting a coronagraph instrument to a spectrograph via a single-mode optical fiber is a promising technique for characterizing the atmospheres of exoplanets with ground and space-based telescopes. However, due to the small separation and extreme flux ratio between planets and their host stars, instrument sensitivity will be limited by residual starlight leaking into the fiber. To minimize stellar leakage, we must control the electric field at the fiber input. Implicit electric field conjugation (iEFC) is a model-independent wavefront control technique in contrast with classical electric field conjugation (EFC) which requires a detailed optical model of the system. We present here the concept of an iEFC-based wavefront control algorithm to improve stellar rejection through a single-mode fiber. As opposed to image-based iEFC which relies on minimizing intensity in a dark hole region, our approach aims to minimize the amount of residual starlight coupling into a single-mode fiber. We present broadband simulation results demonstrating a normalized intensity greater than 10^{-10} for both fiber-based EFC and iEFC. We find that both control algorithms exhibit similar performance for the low wavefront error (WFE) case, however, iEFC outperforms EFC by approximately 100x in the high WFE regime. Having no need for an optical model, this fiber-based approach offers a promising alternative to EFC for ground and space-based telescope missions, particularly in the presence of residual WFE.

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arXiv2024

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems IV: NIRISS Aperture Masking Interferometry Performance and Lessons Learned

We present a performance analysis for the aperture masking interferometry (AMI) mode on board the James Webb Space Telescope Near Infrared Imager and Slitless Spectrograph (JWST/NIRISS). Thanks to self-calibrating observables, AMI accesses inner working angles down to and even within the classical diffraction limit. The scientific potential of this mode has recently been demonstrated by the Early Release Science (ERS) 1386 program with a deep search for close-in companions in the HIP 65426 exoplanetary system. As part of ERS 1386, we use the same data set to explore the random, static, and calibration errors of NIRISS AMI observables. We compare the observed noise properties and achievable contrast to theoretical predictions. We explore possible sources of calibration errors and show that differences in charge migration between the observations of HIP 65426 and point-spread function calibration stars can account for the achieved contrast curves. Lastly, we use self-calibration tests to demonstrate that with adequate calibration NIRISS F380M AMI can reach contrast levels of $\sim9-10$ mag at $\gtrsim λ/D$. These tests lead us to observation planning recommendations and strongly motivate future studies aimed at producing sophisticated calibration strategies taking these systematic effects into account. This will unlock the unprecedented capabilities of JWST/NIRISS AMI, with sensitivity to significantly colder, lower-mass exoplanets than lower-contrast ground-based AMI setups, at orbital separations inaccessible to JWST coronagraphy.

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arXiv2024

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems V: Do Self-Consistent Atmospheric Models Represent JWST Spectra? A Showcase With VHS 1256 b

The unprecedented medium-resolution (R~1500-3500) near- and mid-infrared (1-18um) spectrum provided by JWST for the young (140+/-20Myr) low-mass (12-20MJup) L-T transition (L7) companion VHS1256b gives access to a catalogue of molecular absorptions. In this study, we present a comprehensive analysis of this dataset utilizing a forward modelling approach, applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: Teff, log(g), [M/H], C/O, gamma, fsed, and R. Our findings reveal that each parameter's estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS1256b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a Teff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST's data for VHS1256b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.

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arXiv2023

Searching for Planets Orbiting Fomalhaut with JWST/NIRCam

We report observations with the JWST/NIRCam coronagraph of the Fomalhaut system. This nearby A star hosts a complex debris disk system discovered by the IRAS satellite. Observations in F444W and F356W filters using the round 430R mask achieve a contrast ratio of ~ 4 x 10-7 at 1'' and ~ 4 x 10-8 outside of 3''. These observations reach a sensitivity limit <1 MJup across most of the disk region. Consistent with the hypothesis that Fomalhaut b is not a massive planet but is a dust cloud from a planetesimal collision, we do not detect it in either F356W or F444W (the latter band where a Jovian-sized planet should be bright). We have reliably detected 10 sources in and around Fomalhaut and its debris disk, all but one of which are coincident with Keck or HST sources seen in earlier coronagraphic imaging; we show them to be background objects, including the "Great Dust Cloud" identified in MIRI data. However, one of the objects, located at the edge of the inner dust disk seen in the MIRI images, has no obvious counterpart in imaging at earlier epochs and has a relatively red [F356W]-[F444W]>0.7 mag (Vega) color. Whether this object is a background galaxy, brown dwarf, or a Jovian mass planet in the Fomalhaut system will be determined by an approved Cycle 2 follow-up program. Finally, we set upper limits to any scattered light from the outer ring, placing a weak limit on the dust albedo at F356W and F444W.

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arXiv2023

Spatially resolved imaging of the inner Fomalhaut disk using JWST/MIRI

Planetary debris disks around other stars are analogous to the Asteroid and Kuiper belts in the Solar System. Their structure reveals the configuration of small bodies and provides hints for the presence of planets. The nearby star Fomalhaut hosts one of the most prominent debris disks, resolved by HST, Spitzer, Herschel, and ALMA. Images of this system at mid-infrared wavelengths using JWST/MIRI not only show the narrow Kuiper-Belt-analog outer ring, but also that (1) what was thought from indirect evidence to be an asteroid-analog structure is instead broad, extending outward into the outer system; (2) there is an intermediate belt, probably shepherded by an unseen planet. The newly discovered belt is demarcated by an inner gap, located at ~ 78 au, and it is misaligned relative to the outer belt. The previously known collisionally generated dust cloud, Fomalhaut b, could have originated from this belt, suggesting increased dynamical stirring and collision rates there. We also discovered a large dust cloud within the outer ring, possible evidence of another dust-creating collision. Taken together with previous observations, Fomalhaut appears to be the site of a complex and possibly dynamically active planetary system.

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arXiv2023

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems I: High Contrast Imaging of the Exoplanet HIP 65426 b from 2-16 $μ$m

We present JWST Early Release Science (ERS) coronagraphic observations of the super-Jupiter exoplanet, HIP 65426 b, with the Near-Infrared Camera (NIRCam) from 2-5 $μ$m, and with the Mid-Infrared Instrument (MIRI) from 11-16 $μ$m. At a separation of $\sim$0.82" (86$^{+116}_{-31}$ au), HIP 65426 b is clearly detected in all seven of our observational filters, representing the first images of an exoplanet to be obtained by JWST, and the first ever direct detection of an exoplanet beyond 5 $μ$m. These observations demonstrate that JWST is exceeding its nominal predicted performance by up to a factor of 10, depending on separation and subtraction method, with measured 5$σ$ contrast limits of $\sim$1$\times10^{-5}$ and $\sim$2$\times10^{-4}$ at 1" for NIRCam at 4.4 $μ$m and MIRI at 11.3 $μ$m, respectively. These contrast limits provide sensitivity to sub-Jupiter companions with masses as low as 0.3$M_\mathrm{Jup}$ beyond separations of $\sim$100 au. Together with existing ground-based near-infrared data, the JWST photometry are well fit by a BT-SETTL atmospheric model from 1-16 $μ$m, and span $\sim$97% of HIP 65426 b's luminous range. Independent of the choice of model atmosphere we measure an empirical bolometric luminosity that is tightly constrained between $\mathrm{log}\!\left(L_\mathrm{bol}/L_{\odot}\right)$=-4.31 to $-$4.14, which in turn provides a robust mass constraint of 7.1$\pm$1.2 $M_\mathrm{Jup}$. In totality, these observations confirm that JWST presents a powerful and exciting opportunity to characterise the population of exoplanets amenable to high-contrast imaging in greater detail.

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arXiv2023

JWST Observations of the Enigmatic Y Dwarf WISE 1828+2650: I. Limits to a Binary Companion

The Y-dwarf WISE 1828+2650 is one of the coldest known Brown Dwarfs with an effective temperature of $\sim$300 K. Located at a distance of just 10 pc, previous model-based estimates suggest WISE1828+2650 has a mass of $\sim$5-10 Mj, making it a valuable laboratory for understanding the formation, evolution and physical characteristics of gas giant planets. However, previous photometry and spectroscopy have presented a puzzle with the near-impossibility of simultaneously fitting both the short (0.9-2.0 microns) and long wavelength (3-5 microns) data. A potential solution to this problem has been the suggestion that WISE 1828+2650 is a binary system whose composite spectrum might provide a better match to the data. Alternatively, new models being developed to fit JWST/NIRSpec and MIRI spectroscopy might provide new insights. This article describes JWST/NIRCam observations of WISE 1828+2650 in 6 filters to address the binarity question and to provide new photometry to be used in model fitting. We also report Adaptive Optics imaging with the Keck 10 m telescope. We find no evidence for multiplicity for a companion beyond 0.5 AU with either JWST or Keck. Companion articles will present low and high resolution spectra of WISE 1828+2650 obtained with both NIRSpec and MIRI.

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arXiv2023

First Observations of the Brown Dwarf HD 19467 B with JWST

We observed HD 19467 B with JWST's NIRCam in six filters spanning 2.5-4.6 $μm$ with the Long Wavelength Bar coronagraph. The brown dwarf HD 19467 B was initially identified through a long-period trend in the radial velocity of G3V star HD 19467. HD 19467 B was subsequently detected via coronagraphic imaging and spectroscopy, and characterized as a late-T type brown dwarf with approximate temperature $\sim1000$K. We observed HD 19467 B as a part of the NIRCam GTO science program, demonstrating the first use of the NIRCam Long Wavelength Bar coronagraphic mask. The object was detected in all 6 filters (contrast levels of $2\times10^{-4}$ to $2\times10^{-5}$) at a separation of 1.6 arcsec using Angular Differential Imaging (ADI) and Synthetic Reference Differential Imaging (SynRDI). Due to a guidestar failure during acquisition of a pre-selected reference star, no reference star data was available for post-processing. However, RDI was successfully applied using synthetic Point Spread Functions (PSFs) developed from contemporaneous maps of the telescope's optical configuration. Additional radial velocity data (from Keck/HIRES) are used to constrain the orbit of HD 19467 B. Photometric data from TESS are used to constrain the properties of the host star, particularly its age. NIRCam photometry, spectra and photometry from literature, and improved stellar parameters are used in conjunction with recent spectral and evolutionary substellar models to derive physical properties for HD 19467 B. Using an age of 9.4$\pm$0.9 Gyr inferred from spectroscopy, Gaia astrometry, and TESS asteroseismology, we obtain a model-derived mass of 62$\pm 1M_{J}$, which is consistent within 2-$σ$ with the dynamically derived mass of 81$^{+14}_{-12}M_{J}$.

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arXiv2023

Planet Search with the Keck/NIRC2 Vortex Coronagraph in Ms-band for Vega

Gaps in circumstellar disks can signal the existence of planetary perturbers, making such systems preferred targets for direct imaging observations of exoplanets. Being one of the brightest and closest stars to the Sun, the photometric standard star Vega hosts a two-belt debris disk structure. Together with the fact that its planetary system is being viewed nearly face-on, Vega has been one of the prime targets for planet imaging efforts. Using the vector vortex coronagraph on Keck/NIRC2 in Ms-band at 4.67 $μ$m, we report the planet detection limits from 1 au to 22 au for Vega with an on-target time of 1.8 h. We reach a 3 Jupiter mass limit exterior to 12 au, which is nearly an order of magnitude deeper than existing studies. Combining with existing radial velocity studies, we can confidently rule out the existence of companions more than ~8 Jupiter mass from 22 au down to 0.1 au for Vega. Interior and exterior to ~4 au, this combined approach reaches planet detection limits down to ~2-3 Jupiter mass using radial velocity and direct imaging, respectively. By reaching multi-Jupiter mass detection limits, our results are expected to be complemented by the planet imaging of Vega in the upcoming observations using the James Webb Space Telescope to obtain a more holistic understanding of the planetary system configuration around Vega.

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arXiv2022

Topological Designs for Scalar Vortex Coronagraphs

The detection and characterization of Earth-like exoplanets around Sun-like stars for future flagship missions requires coronagraphs to achieve contrasts on the order of 1e-10 at close angular separations and over large spectral bandwidths (>=20%). We present our progress thus far on exploring the potential for scalar vortex coronagraphs (SVCs) in direct exoplanet imaging. SVCs are an attractive alternative to vector vortex coronagraphs (VVCs), which have recently demonstrated 6e-9 raw contrast in 20% broadband light but are polarization dependent. SVCs imprint the same phase ramp on the incoming light and do not require polarization splitting, but are inherently limited by their chromatic behavior. Several SVC designs have been proposed in recent years to solve this issue by modulating or wrapping the azimuthal phase function according to specific patterns. For one such design, the staircase SVC, we present our best experimental SVC results demonstrating raw contrast of 2e-7 in 10% broadband light. Since SVC broadband performance and aberration sensitivities are highly dependent on topology, we conducted a comparative study of several SVC designs to optimize for high contrast across a range of bandwidths. Furthermore, we present a new coronagraph optimization tool to predict performance in order to find an achromatic solution.

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arXiv2022

High Contrast Demonstrations of Novel Scalar Vortex Coronagraph Designs at the High Contrast Spectroscopy Testbed

For direct imaging of exoplanets, Scalar Vortex Coronagraphs (SVCs) are an attractive alternative to the popularly used Vector Vortex Coronagraphs (VVCs). This is primarily because they are able to induce the same phase ramp regardless of the incoming light's polarization state. We tested a set of stepped SVC staircase masks in the Exoplanet Technology Laboratory (ET Lab) at Caltech on the High-Contrast Spectroscopy Testbed (HCST). Here we present some preliminary findings of their starlight suppression ability, achieving raw contrasts on the order of 1e-5 for 7 to 9 lambda/D. We also characterized their chromatic performance and performed wavefront control to achieve preliminary contrasts on the order of 1e-7 with EFC. These initial experimental results with SVCs have shown scalar vortex technology has a great potential for future exoplanet direct imaging missions.

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arXiv2021

Constraining the Orbit and Mass of epsilon Eridani b with Radial Velocities, Hipparcos IAD-Gaia DR2 Astrometry, and Multi-epoch Vortex Coronagraphy Upper Limits

$ε$~Eridani is a young planetary system hosting a complex multi-belt debris disk and a confirmed Jupiter-like planet orbiting at 3.48 AU from its host star. Its age and architecture are thus reminiscent of the early Solar System. The most recent study of Mawet et al. 2019, which combined radial velocity (RV) data and Ms-band direct imaging upper limits, started to constrain the planet's orbital parameters and mass, but are still affected by large error bars and degeneracies. Here we make use of the most recent data compilation from three different techniques to further refine $ε$~Eridani~b's properties: RVs, absolute astrometry measurements from the Hipparcos~and Gaia~missions, and new Keck/NIRC2 Ms-band vortex coronagraph images. We combine this data in a Bayesian framework. We find a new mass, $M_b$ = $0.66_{-0.09}^{+0.12}$~M$_{Jup}$, and inclination, $i$ = $77.95_{-21.06}^{\circ+28.50}$, with at least a factor 2 improvement over previous uncertainties. We also report updated constraints on the longitude of the ascending node, the argument of the periastron, and the time of periastron passage. With these updated parameters, we can better predict the position of the planet at any past and future epoch, which can greatly help define the strategy and planning of future observations and with subsequent data analysis. In particular, these results can assist the search for a direct detection with JWST and the Nancy Grace Roman Space Telescope's coronagraph instrument (CGI).

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arXiv2021

New method to achieve the proper polarization state for a vector vortex coronagraph

The vector vortex coronagraph (VVC) performance in the laboratory and in ground-based observatories has earned it a spot on the NASA mission concepts HabEx and LUVOIR. The VVC induces a phase ramp through the manipulation of the polarization state. Left- and right-circular polarizations get imprinted a phase ramp of opposite signs, which prevents model-based focal plane wavefront sensing and control strategies in natural light. We thus have to work with a polarization state than ensures circularly polarized light at the VVC mask. However, achieving this polarization state can be non trivial if there are optics that add phase retardance of any kind between the circular polarizer and the focal plane mask. Here we present the method currently used at the Caltech high contrast spectroscopy testbed (HCST) to achieve the proper circular polarization state for a VVC, which only uses the deformable mirror and appropriate rotation of the circular polarizer and analyzer optics. At HCST we achieve raw contrast levels of \tentoe~for broadband light with a VVC.

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arXiv2020

High-contrast Demonstration of an Apodized Vortex Coronagraph

High contrast imaging is the primary path to the direct detection and characterization of Earth-like planets around solar-type stars; a cleverly designed internal coronagraph suppresses the light from the star, revealing the elusive circumstellar companions. However, future large-aperture telescopes ($>$4~m in diameter) will likely have segmented primary mirrors, which causes additional diffraction of unwanted stellar light. Here we present the first high contrast laboratory demonstration of an apodized vortex coronagraph (AVC), in which an apodizer is placed upstream of a vortex focal plane mask to improve its performance with a segmented aperture. The gray-scale apodization is numerically optimized to yield a better sensitivity to faint companions assuming an aperture shape similar to the LUVOIR-B concept. Using wavefront sensing and control over a one-sided dark hole, we achieve a raw contrast of $2\times10^{-8}$ in monochromatic light at 775~nm, and a raw contrast of $4\times10^{-8}$ in a 10\% bandwidth. These results open the path to a new family of coronagraph designs, optimally suited for next-generation segmented space telescopes.

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