Diego Godoy-Rivera

Diego Godoy-Rivera

Research

Gyrochronology, Rotation and Activity
Rotation is one of the fundamental properties of stars and has been proposed as a proxy to obtain (the elusive) ages of stars, an idea known as gyrochronology. The rotation of stars also drives magnetic activity, which in turn influences their high-energy radiation. My research focuses on exploring the dependences of stellar rotation and activity with age, mass, binarity, evolutionary stage, and others.

Some of my research projects are summarized below.

Representation of stellar rotation (Credits: mps)

Enhanced magnetic activity after the intermediate period gap traced by the chromospheric Ca II IRT
During their rotational evolution, cool stars experience an epoch of apparent stalling on their surface rotation rates. After this, it has been observed that stars display enhanced magnetic activity on the stellar photosphere as probed by the photometric Sph index (obtained from light curves).

In this work, I tested the above using the chromospheric magnetic activity index Ca II infrated triplet (IRT) from Gaia DR3 spectroscopy. The rotation-activity relation illustrated on the figure demonstrates that a similar magnetic activity enhancement is shown at the stellar chromosphere, pointing to a universal behavior across the stellar atmosphere. For more details, please check out our paper: Godoy-Rivera, et al. (2026b).

Rotation-magnetic activity relation, as probed by the Ca II IRT index, for G-dwarf stars. The upper envelope of the distribution (dashed line) shows a peak after the intermediate period-gap (white points), coinciding with the Sph features (vertical green lines).

Kepler Field Atmospheric Parameters, Bolometric Corrections, and Luminosities
The ~ 200,000 stars observed by Kepler have yielded unprecedented constraints across astrophysics. With the advent of modern surveys (8 of them shown on the right), new limits in stellar characterizations are possible.

In this work, I compiled atmospheric parameters (Teff, logg, [M/H]) for the Kepler stars, and used them to calculate bolometric corrections. With this, in combination with Gaia color-magnitude diagram (CMD) positions, I derived luminosities, a crucial astrophysical parameter, in a self-consistent, survey-by-survey base. For more details, please check out our paper: Godoy-Rivera, et al. (2026a).

Hertzsprung-Russell (HR) diagram for the Kepler stars in common with each of the spectroscopic or spectro-photometric surveys (one per panel). Some heterogeneities appear across panels, due to the inherited atmospheric parameters from different surveys.

Kepler meets Gaia DR3: Color-Magnitude Diagram (CMD) and Binary Classification
The stars observed by the Kepler mission are of paramount importance for multiple research fields (seismology, rotation, exoplanets, and Galactic archaeology). Characterizing them is essential.

In this work, I have used the data from Gaia DR3 to perform a homogeneous (and extinction-corrected!) CMD classification based on empirical and theoretical comparisons. I also flag binary candidates according to several criteria: RUWE, RV-variable, Gaia non-single stars (NSS), eclipsing from Kepler and Gaia, among others. For more details, please check out our paper: Godoy-Rivera, Mathur, García, et al. (2025).

Absolute and de-reddened Gaia CMD for the 200,000 Kepler targets. Each CMD category is represented by a color and a region.

The Impact of the Spin-Down Stalling on the Photometric Magnetic Activity Proxy (Sph)
Sun-like stars show periodic variations in their light curves as magnetic features appear on their surface. From these, rotation periods and magnetic activity indices (Sph) can be derived.

In this work, led by Angela Santos, we studied the impact of a discontinuity in the rotational evolution of stars (a.k.a. the spin-down stalling) on the magnetic activity of Kepler-field stars as traced by Sph. The stalling does cause enhanced magnetic activity on the Sph distribution, as indicated by the blue arrow. For more details, please check out our paper: Santos, Godoy-Rivera, et al. (2025).

Magnetic activity proxy (Sph) vs. rotation period for the Kepler stars. The location of the stalling (in this Teff range) is indicated by the arrow, which coincides with enhanced magnetic activity.

Red Giant Activity: Singles vs. Binaries
The magnetic activity of red giant stars, in terms of photometric and chromospheric CaII indices, has been shown to depend on their architecture (singles vs. binaries) and tidal configuration.

In this work, lead by Charlotte Gehan, we have tested these results with the Near-UV (NUV) excess as well as other chromospheric lines. Our findings support the picture of red-giant binaries in spin-orbit resonance displaying larger chromospheric emission. For more details, please check out our paper: Gehan, Godoy-Rivera & Gaulme (2024).

Rotation period vs. orbital period for red-giants in binary systems. The binaries in spin-orbit resonances showed enhanced NUV activity (color-bar).

The Rotation of Kepler-field Solar-like Stars
Over the past decade, the Kepler mission has revolutionized our knowledge of stellar rotation by providing unprecedented photometry that allow for period determination. More recently, the photometric monitoring of Gaia has allowed novel period determinations that probe the regime of more rapid rotation.

In this review, lead by Angela Santos, we contextualize the Kepler sample and compare it with known features in terms of activity and rotation. For more details, please check out our paper: Santos, Godoy-Rivera, et al. (2024).

Rotation period vs. Teff diagram for the Kepler mission (percentiles in black lines) and Gaia mission (color map).

Testing Gyrochronology with Co-eval Stars
The components of wide binary systems are thought to have formed together (thus sharing the same age) and to have evolved independently. Therefore, wide binaries with rotation period measurements for both component can be used to test age-rotation relations.

In this work, led by student Joaquín Silva-Beyer, we examined the state-of-the-art gyrochronology relations with Kepler-field wide binaries and clusters. Our researched showed that existing calibrations degrade towards older ages. For more details, please check out our paper: Silva-Beyer, Godoy-Rivera & Chanamé (2023).

Fraction of co-eval pairs in clusters and binaries that agree with gyrochronology relations at the 1, 2, and 3-sigma levels. The breakdown of gyrochronology is illustrated by the worsening of the agreement for older samples.

Revised Memberships of Clusters for Rotation
To first order, open clusters are group of stars that were born together and that share the same chemical composition. Therefore, they offer snapshots of the evolution of stellar rotation at specific ages and metallicities.

My research uses the exquisite photometric monitoring of several open clusters (from both the ground and space, e.g., Kepler and K2), in combination with astrometric data from the Gaia mission, in order to clean their memberships and remove the non-member contamination. With this, we have obtain an updated view of stellar rotation, which can be used to place stringent constraints on the physical processes that regulate its evolution. For more details, please check out our paper: Godoy-Rivera, Pinsonneault & Rebull (2021b).

Rotation period vs. Teff for the M50 open cluster, where the stars are color- and symbol-coded by their membership classification. The non-member contamination (red squares) can be significant and needs to be removed.

Subgiant Characterization and Activity
Once the hydrogen-burning stops in their core, stars leave the main-sequence and go through the subgiant phase before ascending onto the red giant branch. Given their intermediate stage of evolution, subgiant stars can place interesting constraints on several open questions in astrophysics (e.g., the existence of a common dynamo mechanism across different evolutionary stages, mixing processes in stellar interiors, the occurrence rates of exoplanets as a function of stellar mass).

My research has focused on a thorough and systematic characterization of subgiants that have been observed by the TESS mission. I have used uniform and precise photometric, astrometric, and spectroscopic data from Gaia and APOGEE to effectively test the limits of how precisely we can characterize subgiant stars. Among the results, I have found a correlation that supports the rotation-activity connection in post-MS stars. For more details, please check out our paper: Godoy-Rivera, Tayar, Pinsonneault, et al. (2021a).

NUV Excess vs log(vsini) for a sample of subgiants stars. We find a statistically significant (anti-) correlation in these post-MS stars.

Wide Binaries as Constraints for Rotation
Unlike our Sun, most stars in the universe have companions, and we classify those with semi-major axes greater than ~ 100 AU as "wide" binaries. A helpful way of thinking about them is as the tiniest versions of open clusters.

I have used astrometric information to identify a sample of bona-fide wide binaries in the Kepler field, a field with ~ 200,00 stars photometrically monitored for ~ 4 years by the Kepler mission, and that could therefore have rotation period measurements. I have used these binary stars to explore the behavior of stellar rotation in co-eval systems, finding that their rotation rates often show discrepancies compared with the expectations. For more details, please check out our paper: Godoy-Rivera & Chanamé (2018).

Rotation period vs. color for the wide binary sample we identify. The binary components are connected by lines, showing that the relation of their rotation rates are often at odds with the expectations (dotted lines).