Possible Masters Projects

Project 1: 

The Dynamical Structure and Population of the Extremely Metal-Rich "Knot" at the center of the Milky Way 

Background

The Milky Way's formation history is encoded in the distribution of stellar orbits -- ages -- and chemical abundances. They are the key to: how many stars formed when from what material? Gaia and spectroscopic surveys such as SDSS/APOGEE make it now possible to draw up such map for the full galaxy. 

Given that the element abundances are permanent 'birth tags' it makes sense to ask what the spatial (or orbit) distribution of 'mono-abundance' populations is. In recent work, we have found/discovered that the extremely metal rich stars in our Galaxy mostly form an extremely metal-rich (EMR) knot at the center of the Milky Way.

All-sky maps of the stellar density for very metal-rich stars in the inner Galaxy (from Rix+2024). Note that the extremely metal-rich stars (EMR; bottom panel) are largely confined to a central "knot".

In light of this finding, some questions are:

• did the stars form there?
• on what orbits are they? radial, rotating, etc..
• how old are they? (did they form in several episodes)

We have initial kinematics, that point to radial, centrally confined orbits.

The current analyses are limited by a) dust (when considering radial velocities from Gaia), and b) by modest sample size, when considering SDSS IV/APOGEE spectra.

Goal

In the context of SDSS-V we are getting (and have gotten) many more spectra towards the central 1.5 kpc. The central goal of the masters project is to take these, potentially do some post-processing on them, and build a kinematic/dynamical model for the extremely metal-rich central knot.

(possible) steps

• collect all data (velocities, metallicities) of existing and new SDSS/APOGEE spectra in the inner 1.5 kpc of the Milky Way
• find the very metal rich ones
• get the best possible distances of these stars (Gaia and spectroscopic information)
• combine SDSS/APOGEE information with Gaia to determine orbits
• determine orbit distribution, mostly the distribution in binding energy (or apocenter) and eccentricity.
• build a simple dynamical model.
• determine the spatial and orbit distribution, and (optional) compare it to TNG50 Milky Way formation simulations.

Tools

• working with the sloan data base
• working with python dynamics packages such as galpy
• writing a set of jupyter notebooks (or other forms of python code) to do further analysis and make plots.

Hoped-For Outcome

Leading a refereed population on this analysis

Project 2: 

Mapping the Metallicity of Young Stars across the Milky Way Disk

or: how homogeneous is the birth material of stars at a given time and radius?

Background

We have reason to believe that the interstellar medium -- from which stars form -- is nearly homogeneous in azimuth, at a given radius and time in the life of a galaxy: at any given epoch, a star's chemical abundances only depend on the radius at which it was born. It would be important to test this hypothesis, as it is a starting point for understanding many evolutionary mechanisms in disk galaxies (e.g. radial migration). The way one could do this is to find young stars (say, less than an orbital period, or 250Mio yrs) luminous to be seen across the disk) and measure their abundances, to see whether this important assumption about "chemical homogeneity" is true.

What to take for young luminous stars: the easiest would be to take hot young stars (OB stars); but they have few metal lines, so it is hard to measure [Fe/H]. But all stars (>Mio years) have a red giant phase, where they are cool enough to yield metallicities. 

Goal

The goal is to find (among the 10 Mio) the red giants with [M/H] from Gaia the ones that are <200Mio old, and map their metallicities: are there azimuthal variations?

How: the two plots below show that the temperatures and luminosities of giants depend on age, and metallicity. If one know the metallicity, one gets the age:

CMD positions of red giants with solar metallicity, but different ages

CMD positions of stars of 10^9 years age, but of different
metallicities. Age and metallicity are covariant.

We have developed a piece of code (for application in the LMC) that takes the distances, magnitudes, metallicities and temperatures of giants and determines their ages.How: the two plots below show that the temperatures and luminosities of giants depend on age, and metallicity. If one know the metallicity, one gets the ages.

Goal (possible) steps

• take intellectual ownership of the age fitting code (with some possible tweaks/checks)
• collect the data (from Gaia; catalogs exist) of the stellar parameters for all "Gaia giants with spectroscopy". find the subset with good distances, and apply age-fitting code.
• find the young giants
• make metallicity maps
• take it from there..

Tools

• working with Gaia and zenodo data base
• learn and adopt a piece of existing code
• writing a set of jupyter notebooks (or other forms of python code) to do further analysis and make plots.

Hoped-For Outcome

Leading a refereed population on this analysis