Hi, Welcome to my webpage!
My name is Johanna, I am a Chilean Astrophysicist living in Heidelberg, Germany since 2016.
I am currently a Postdoctoral researcher at the Max Planck Institute for Astronomy (MPIA).
Until July of 2020 I was a PhD student at MPIA and a fellow of the International Max Planck Research School
Astronomy and Cosmic Physics at the University of Heidelberg. (IMPRS-HD).
Here you can find my thesis: (THESIS)
A summary of My PhD thesis
I investigated the small-scale structure of the Milky Way's orbit distribution. Our Galaxy offers us the unique opportunity to be studied in detail, as we can obtain the positions, velocities and the chemical information on a star-by-star basis. Currently, the Gaia satellite is providing the full 6D stellar position-velocity phase-space measurements for millions of stars in our Galaxy. By combining Gaia with chemical information from spectroscopic surveys (e.g., LAMOST), we can obtain a detailed physical picture of our Galaxy. With both of these datasets I explored and quantified the orbit-space clustering of stars in the Galactic disc, as a function of their metallicity differences. Where I defined the orbit similarity between pairs of stars as the distance in action-angle space ∆(J, θ), and the abundance similarity as ∆[Fe/H]. I used these action-angle distances as an input for a friends-of-friends (FoF) algorithm where I recover a number of known clusters: e.g. M67, Praesepe and the Pleaides. I also recovered the Pisces Eridanus stream, an association with a very extended distribution in configuration space: extending hundreds of parsecs, and covering 120 degrees in the sky.
The orbit distribution of Galactic disc stars reveals distinct small-scale clustering, among stars with indistinguishable metallicities, extending across distances of hundreds of parsec. With these results we are in a great position to study the transition from clustered star formation to field stars in an unprecedented way.
The left figure shows the distribution in actions (orbit labels) for stars in Gaia DR2. The x-axis is the angular momentum and the y-axis the radial action that quantifies the oscillation of the orbit in the radial direction. This figure clearly illustrates the great amount of –and very extended– orbit structure present in Gaia DR2. The right-side figure illustrates the fraction of pairs in the Galaxy that are 'on the same orbits' or close in actions and angles (canonical conjugates of the actions) and also have indistinguishable metallicities, [Fe/H]. The majority of pairs in the closest log10 ∆(J, θ)-bin have indistinguishable [Fe/H], which then decline to ∼30% at log10 ∆(J, θ) ∼ 0, and then precipitously fall to nearly 0 at log10 ∆(J, θ) > 0.8 (presumed disc-halo pairs).
Orbits in action space with Gaia
During my PhD I combined Gaia's awesome astrometry with spectroscopic information to explore how chemical abundances
of stars in the Milky Way (reflecting a common birth place/time) are related to their present-day orbits, and what it can teach us
about the formation of the Galaxy. In the Galactic disc this will tells us directly how strong radial migration was, i.e. if the
present-day orbit of a normal disc-star is related with its birth-orbit and address the fundamental question of how much
"dynamical/orbit memory" disc galaxies retain.
The image above is a voronoi plot with 100 stars per cell showing the angular momentum in the horizontal axis and the radial action (amount of in and out motion) of stars in our
Milky Way color coded by their metallicity. This dataset is a combination of Gaia's second data release and the spectroscopic survey LAMOST. The black star indicates the position of the sun in this plot.
Halo Wide Binaries
My MSc. thesis consisted on assembling an extensive catalogue of wide binary stars. This program was aimed to probe the wide
binary population of the Galactic halo at significantly large distances, and
inform future searches that could improve the statistics by orders of magnitude. These systems are very important because they can be used to place constraints on dark matter in the form of Massive Compact Halo Objects (MACHOs).
The image above is a Reduced Proper Motion (RPM) diagram constructed with data from the 9th Data Release of SDSS. The stars in this
plot have proper motions larger than 30 mas/yr. This diagram allows us to discriminate between disc and halo populations that are located to the right and left side of the confidence lines, respectively.