arXiv subjects

Guillermo Gonzalez

Publications and source records attributed to Guillermo Gonzalez.

At least 19 recordsLinked to original sources

arXiv2026

The Roman Coronagraph Community Participation Program: early calibration plan and pilot observation of a companion

Roman is set to launch in weeks! The Coronagraph Instrument - technology pathfinder for future direct imaging missions - is ready to fly too. According to predictions, laboratory tests and high fidelity simulations, it will open a new contrast regime enabling the imaging of mature, giant planets in visible reflected light. The Community Participation Program is responsible for preparing a comprehensive observing program with associated data processing software and calibrations. We give a brief update about the on-going "baseline" calibration plan for the first months. Additionally, we describe a pilot program aiming for the stellar companion HD 29992 B at moderate ~1e-5 to ~1e-6 Band 1 (575 nm) contrast, to be carried out as soon as the instrument is operational. The idea is to generate a canonical data set with a self luminous companion that is easily recoverable. This functional checkout will be precious to best prepare our community, exercise our calibration plan and suite of tools.

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arXiv2026

The Roman Coronagraph Community Participation Program: calibration strategy for the Mueller matrix using on-sky sources

The Nancy Grace Roman Space Telescope Coronagraph Instrument will provide space-based polarimetric observations of circumstellar disks and exoplanetary systems. Accurate reconstruction of the linear polarization fraction requires calibration of the instrumental Mueller matrix using polarized and weakly polarized standard stars. We constructed a candidate catalog by combining published optical polarimetry with Gaia DR3 astrometry and photometry and selected separate samples for coronagraphic calibration observations and observations using a neutral-density filter. Precursor $VRI$-band polarimetry of 18 faint candidates was obtained with HONIR on the 1.5-m Kanata telescope. The wavelength dependence of their normalized Stokes parameters was modeled using the Serkowski law to predict their polarization properties in \cgi\ Bands~1 and 4, and 2 sets of 3 calibrators were selected for the 2 calibration scenarios. We then estimated the achievable LPF reconstruction accuracy using Monte Carlo simulations that include uncertainties in the calibrator polarization properties, photometric noise, and residual detector-response errors. A dithered observing configuration was also simulated to reduce differential detector-response errors among the calibrators. The current estimates indicate LPF reconstruction errors at the few-percentage-point level, with a small bias arising from treating a weakly polarized calibrator as unpolarized. Finally, we present progress toward an end-to-end test using \texttt{corgisim} and \texttt{corgiDRP}, including successful processing of simulated datasets from Level~1 through Level~2b.

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arXiv2026

The Roman Coronagraph Community Participation Program: data reduction pipeline design and implementation

The Roman Space Telescope Coronagraph Instrument will demonstrate a series of technologies and techniques to enable the direct detection of reflected-light planets with space-based observatories. To characterize and validate the performance of the Coronagraph Instrument, the Community Participation Program is developing corgidrp, an open-source Python-based data reduction pipeline. The pipeline can process data from the required and best-effort observing modes and their associated calibration sequences into calibrated science-ready data products. We present the software design and implementation of corgidrp and the motivation behind specific design decisions. We describe the software architecture, data flow, processing steps, automation tools, testing framework, and development philosophy. We also outline future development plans in preparation for on-sky data.

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arXiv2026

The Roman Coronagraph Community Participation Program: Observation planning and data reduction for polarimetric mode

Reflected-light polarimetry of exoplanets constrains and resolves degeneracies in atmospheric properties, while polarized light observations of debris disks enable the characterization of dust-grain properties. The best-effort polarimetric mode of the Roman Coronagraph Instrument will be able to perform multi-wavelength observations of planetary systems using both the Hybrid Lyot Coronagraph (HLC) and the Shaped Pupil Coronagraph (SPC). This paper presents an overview of observation planning, simulations, and data reduction procedures for the polarimetric mode of the Roman Coronagraph. As an initial test of simulation and data reduction, a dataset of polarimetric observing sequences for the debris disk HD 172555 in HLC mode was generated using corgisim with estimated observation parameters, and data reduction was performed using corgidrp, incorporating all relevant noise factors and calibration products. Currently, mock calibration products are used in corgidrp; these will be replaced with simulated calibration products in future updates

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arXiv2025

Placing the Solar System in its Astrophysical Context

We examine recent astronomical data to assess whether the sun and Solar System possess anomalous properties compared to other stars and exoplanetary systems, providing context for astrobiology research. Utilising data primarily from large surveys like {\it Gaia}, {\it Kepler}, {\it TESS}, and ground-based spectroscopy (e.g., GALAH, LAMOST, HARPS), we construct comparison samples (e.g., nearby stars, solar analogues and twins within 20-200 pc) and employ statistical methods, including regression analysis, to account for parameter dependencies. We find that the sun is modestly metal-rich compared to nearby solar-age stars. More anomalous solar properties include its mass (top $\sim$8 percent locally), low photometric variability on short timescales ($\sim$0.2 percent), specific light and heavy element abundance patterns (high beryllium, low lithium, low carbon/oxygen and nitrogen/oxygen ratios, and low heavy neutron capture and refractory elements), slow rotation, and low superflare rate. The sun has average $\alpha$/iron, phosphorus/iron, and Ytterbium/iron abundance ratios. It also has average chromospheric activity as measured by R$^{\rm '}_{\rm HK}$(T$_{\rm eff}$), R$^{\rm +}_{\rm HK}$, and H$\alpha$ indices. The Solar System is unusual in its lack of super-Earths despite hosting a cold Jupiter ($\sim$3 percent), the low eccentricities of its planets (especially considering detectability, $<2$ percent), its large size scale for a multi-planet system ($\sim$6 percent), and potentially the sun's obliquity. The sun's galactic orbit is less eccentric and has lower vertical excursions than $\sim$95 percent of nearby solar analogues. Its current position is near perigalacticon and minimum distance from the Galactic plane, resulting in a higher local star density than 98.8 percent of randomly chosen times from $-0.5$ to $+0.5$ Gyrs.

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arXiv2022

Nancy Grace Roman Space Telescope Coronagraph Instrument Observation Calibration Plan

NASA's next flagship mission, the Nancy Grace Roman Space Telescope, is a 2.4-meter observatory set to launch no later than May 2027. Roman features two instruments: the Wide Field Imager and the Coronagraph Instrument. Roman's Coronagraph is a Technology Demonstration that will push the current capabilities of direct imaging to smaller contrast ratios ($\sim$10$^{-9}$) and inner-working angles (3~$λ$/D). In order to achieve this high precision, Roman Coronagraph data must be calibrated to remove as many potential sources of error as possible. Here we present a detailed overview of the Nancy Grace Roman Space Telescope Coronagraph Instrument Observation Calibration Plan including identifying potential sources of error and how they will be mitigated via on-sky calibrations.

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arXiv2017

Constraining Delta-T from Babylonian Lunar Appulse and Occultation Observations

We examine in detail 15 Babylonian observations of lunar appulses and occultations made between 80 and 419 BC for the purpose of setting useful limits on Earth's clock error, as quantified by $Δ$T, the difference between Terrestrial Time and Universal time. Our results are generally in agreement with reconstructions of $Δ$T using untimed solar eclipse observations from the same period. We suggest a revised version of the simple quadratic fit to $Δ$T in light of the new results.

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arXiv2016

A Revised Gyro-Age for M 67 from Kepler/K2-Campaign-5 Light Curves

We revisit the photometric variability of stars in the M 67 field using Kepler/K2-Campaign-5 light curves. In our previous work, we limited the search area around M\,67 to that of a recent ground-based study. In the present work, we expand the search area and apply a more rigorous period-finding algorithm to determine the rotation periods of 98 main sequence cluster members from the same data. In addition, we derive periods of 40 stars from the K2SC detrended light curves. We determine the mean period of single sun-like main sequence cluster members to be $29.6 \pm 0.6$ d. Assuming the periods correspond to stellar rotation, the corresponding mean gyro-age is $5.4 \pm 0.2$ Gyr.

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arXiv2016

Variability Among Stars in the M 67 Field from Kepler/K2-Campaign-5 Light Curves

We examine the photometric variability of stars in the M 67 field using Kepler/K2-Campaign-5 light curves. Variabilities and periods were determined for 639 stars. The mean photometric period of 28 single Sun-like members stars in M 67 is 23.4 +/- 1.2 d. This corresponds to a gyro-age of 3.7 +/- 0.3 Gyr, assuming the periods can be associated with rotation. The intrinsic variabilities of the solar analogs are greater than the Sun's variability, as measure from VIRGO fluxes. We also find evidence that the single cluster members have a different distribution of variability than the binary members.

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arXiv2015

Parent Stars of Extrasolar Planets. XV. Host Star Rotation Revisited with {\it Kepler} Data

We employed published rotation periods of {\it Kepler} field stars to test whether stars hosting planets tend to rotate more slowly than stars without known planets. Spectroscopic vsini observations of nearby stars with planets have indicated that they tend to have smaller visni values. We employ data for {\it Kepler} Objects of Interest (KOIs) from the first 16 quarters of its original mission; stellar parameters are based on the analysis of the first 17 quarters. We confirm that KOI stars rotate more slowly with much greater confidence than we had previously found for nearby stars with planets. Furthermore, we find that stars with planets of all types rotate more slowly, not just stars with giant planets.

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arXiv2014

Parent Stars of Extrasolar Planets - XIV. Strong Evidence of Li Abundance Deficit

We report the results of our analysis of new high resolution spectra of 30 late-F to early-G dwarf field stars for the purpose of deriving their Li abundances. They were selected from the subsample of stars in the Valenti and Fischer compilation that are lacking detected planets. These new data serve to expand our comparison sample used to test whether stars with Doppler-detected giant planets display Li abundance anomalies. Our results continue to show that Li is deficient among stars with planets when compared to very similar stars that lack such planets. This conclusion is strengthened when we add literature data to ours in a consistent way. We present a table of stars with planets paired with very similar stars lacking planets, extending the recent similar results of Delgado Mena et al.

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arXiv2014

The Metallicity Dependence of Giant Planet Incidence

We describe three corrections that should be applied to the observed relative incidence of nearby stars hosting giant planets. These are diffusion in the stellar atmosphere, use of the [Ref] index in place of [Fe/H] for metallicity, and correction for local sampling with the W velocity. We have applied these corrections to a subset of the SPOCS exoplanet survey with uniform giant planet detectability. Fitting the binned data to a power law of the form, $α10^{β[Fe/H]}$, we derived $α= 0.022 \pm 0.007$ and $β= 3.0 \pm 0.5$; this value of $β$ is 50\% larger than the value determined by \citet{fv05}. While the statistical significance of this difference is marginal, given the small number statistics, these corrections should be included in future analyses that include larger samples.

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arXiv2014

Solar System chemical abundances corrected for systematics

The relative chemical abundances between CI meteorites and the solar photosphere exhibit a significant trend with condensation temperature. A trend with condensation temperature is also seen when the solar photospheric abundances are compared to those of nearby solar twins. We use both these trends to determine the alteration of the elemental abundances of the meteorties and the photosphere by fractionation and calculate a new set of primordial Solar System abundances.

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arXiv2014

Parent Stars of Extrasolar Planets - XIII. Additional Evidence for Li Abundance Anomalies

We report the results of our analysis of new high resolution spectra of 37 late-F to early-G dwarf stars for the purpose of deriving their Li abundances. Most of the stars were selected from the large Valenti and Fischer compilation and had unknown Li abundances prior to the present study. When the new data are combined with data from our previous studies on this topic and analyzed in a similar way, we find, again, that stars with planets near the solar temperature are deficient in Li relative to a comparison set of stars. A similar result is obtained when we combine our data with a large database of stellar Li abundances from the literature.

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arXiv2014

Setting the Stage for Habitable Planets

Our understanding of the processes that are relevant to the formation and maintenance of habitable planetary systems is advancing at a rapid pace, both from observation and theory. The present review focuses on recent research that bears on this topic and includes discussions of processes occurring in astrophysical, geophysical and climatic contexts, as well as the temporal evolution of planetary habitability. Special attention is given to recent observations of exoplanets and their host stars and the theories proposed to explain the observed trends. Recent theories about the early evolution of the Solar System and how they relate to its habitability are also summarized. Unresolved issues requiring additional research are pointed out, and a framework is provided for estimating the number of habitable planets in the Universe.

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arXiv2013

Abundances in Stars with Debris Disks

We present preliminary results of a detailed chemical abundance analysis for a sample of solar-type stars known to exhibit excess infrared emission associated with dusty debris disks. Our sample of 28 stars was selected based on results from the Formation and Evolution of Planetary Systems (FEPS) Spitzer Legacy Program, for the purpose of investigating whether the stellar atmospheres have been polluted with planetary material, which could indicate that the metallicity enhancement in stars with planets is due to metal-rich infall in the later stages of star and planet formation. The preliminary results presented here consist of precise abundances for 15 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Fe, Co, and Ni) for half of the stars in our sample. We find that none of the stars investigated so far exhibit the expected trend of increasing elemental abundance with increasing condensation temperature, which would result from the stars having accreted planetary debris. Rather, the slopes of linear least-squares fits to the abundance data are either negative or consistent with zero. In both cases, our results may indicate that, like the Sun, the debris disk host stars are deficient in refractory elements, a possible signature of terrestrial and/or gas giant planet formation.

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arXiv2011

Parent Stars of Extrasolar Planets. XII. Additional evidence for trends with vsini, condensation temperature, and chromospheric activity

Several recent studies have reported differences in vsini, abundance-condensation temperature trends, and chromospheric activity between samples of stars with and without Doppler-detected planets. These findings have been disputed, and the status of these results remains uncertain. We evaluate these claims using additional published data and find support for all three.

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arXiv2010

Parent Stars of Extrasolar Planets. XI. Trends with Condensation Temperature Revisited

We report the results of abundance analyses of new samples of stars with planets and stars without detected planets. We employ these data to compare abundance-condensation temperature trends in both samples. We find that stars with planets have more negative trends. In addition, the more metal-rich stars with planets display the most negative trends. These results confirm and extend the findings of Ramirez et al. (2009) and Melendez et al. (2009), who restricted their studies to solar analogs. We also show that the differences between the solar photospheric and CI meteoritic abundances correlate with condensation temperature.

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