Research

My research focusses on the disks of gas and dust that surround newborn stars. Planets form in these disks, and their characteristics are crucial to understand the huge diversity of planets that we are just starting to unveil. By studying these disks at different wavelengths and comparing them with physical models, we can learn about their structure, evolution, and their connection with planetary formation. You can find a summary of some of my research below.

My research interests include protoplanetary and debris disks, exoplanets, and planet formation. I am also a huge fan of Python, and am also interested in Bayesian statistics, data mining and visualization, and machine learning.


The evolution of protoplanetary disks in the solar neighborhood

The evolution of protoplanetary disks determines the properties and fates of future planetary systems. However, these disks live for millions of years, and waiting that long is not practical. Instead, we look at different young star-forming regions across the sky with different ages. By looking at the fraction of disks as a function of age, we can infer how they evolve.

Disk dispersal as a function of time. Each dot is the disk fraction in a given star-forming region. The red line shows the overall evolution (Ribas et al. 2014).

Disk evolution is usually studied by combining results from previous, but samples compiled in this way are very heterogeneous, which can produce some biases. To overcome this issue, we compiled the largest sample of nearby young stars in 22 star-forming regions and gathered data from different surveys and catalogs covering from optical to mid-infrared wavelengths. After several homogenizing steps, we derived accurate disk fractions for all these regions by analyzing infrared excesses produced by disk around stars. We confirmed that protoplanetary disks disperse in less than 10 million years, and found evidence of the disk clearing occurring from inside out. These results were presented in Ribas et al. 2014.

The evolution of protoplanetary disks may also depend on factors other than simply time. A good example is the host star of the disk: the strong radiation fields and stellar winds around high-mass stars could disperse circumstellar disks faster than in the case of the low-mass stars. If this is the case, then the planets around high-mass and low-mass stars may have different properties. Using the large sample of young stars mentioned before, we found statistically evidence for a faster dispersal of protoplanetary disks around massive stars (Ribas et al. 2015).

Evolution of protoplanetary disks as a function of stellar mass and age (Ribas et al. 2015).

More recently, we expanded the wavelength coverage of our dataset up to millimeter wavelengths for three of the most studied star-forming regions in our sample: Taurus, Chamaeleon I, and Ophiuchus. Long wavelengths can be used to study the size and properties of dust particles in protoplanetary disks (the initial stages of planet formation), and we found that most sources in the sample showed some signatures of dust grain growth even at just 1 million years (Ribas et al. 2017). We are currently working to apply detailed physical models of protoplanetary disks to this sample using machine learning techniques, which will give us a unique look at some of their properties.


Transitional disks in Chamaeleon as seen by Herschel

Transitional disks are protoplanetary disks with gaps and cavities in them. They are extremely interesting because these gaps could be carved by newborn planets, and hence may be the perfect scenario to study in-situ planet formation or even detect planetary embryos.

The Chamaeleon-I star-forming region, as seen in the far infrared by the Herschel Space Observatory (Ribas et al. 2013). Click on the image to enlarge.

Part of my research has focused on studying transitional disks with the Herschel Space Observatory. Herschel covered the far-infrared part of the spectrum (from 70 to 500 microns) and probed the emission from the cold, outer regions of disks. In Ribas et al. 2013, we analyzed Herschel observations of transitional disks in the Chamaeleon-I star-forming region and showed the potential of these data to identify transitional sources. We also found hints of the transitional disks in this regions being brighter in the far-infrared than protoplanetary sources, which could point to more exposed disk walls because of cavities, or even some piling-up of mass caused by the gravitational influence of planets.

To further investigate what these new data can tell us about transitional disks, we studied them using disk models and statistics tools. We found that Herschel data can improve our knowledge of the structure and mass of these disks (Ribas et al. 2016).

Modeling observations of a transitional disk. The Herschel data (orange squares) can better constrain the disk inner radius and dust mass (Ribas et al. 2016).


Searching for warm debris disks around transiting planets systems

Debris disks are the remnant of planet formation, and can be found around older stars. They are similar to our Kuiper belt, consisting mainly of asteroids, planetesimals, and cold dust located far from their host star (several tens of astronomical units). Because they are that cold, they emit in the far infrared regime. However, a small fraction of these disks are detected in the mid infrared, meaning that their components are hotter (and hence closer to their star) than typical debris disks. These “warm” debris disks are exciting, because they could be produced by collisions of bodies in the inner regions of the system. Even more interesting, these collisions could be the result of the dynamical excitation of an asteroid belt analog by planets in these systems.

In Ribas et al. 2012 we searched for warm debris disks around all the known stars with transiting planets, plus the planetary systems candidates from the Kepler mission. By including mid infrared data from the WISE survey, we identified 13 stars with promising mid infrared excess at 12 and/or 22 microns and compared the estimated location of the dust with the orbits of the planets/planetary candidates in these systems.

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