My name is Marina Kounkel, I am an assistant professor in the Physics and Astronomy Department at the University of North Florida. Much of my research involves observing dynamics of the young stars. Star formation is a clumpy process, and this clustering happens across all scale, from the size of individual stellar systems, to the subtructure within star forming regions, to the distribution of these star forming regions across the Galaxy. The history of how these structures has formed, and how it is going to evolve over time, as well as the fundamental properties of these structures are imprinted in the stellar kinematics.
Measuring these kinematics is only possible thanks to several large astronomical surveys. Gaia space telescope is meticulously measuring accurate positions of stars, from which it is possible to derive distances and motions in the plane of the sky for over 1.6 billion stars across the entire sky, singlehandedly revolutionizing Galactic astronomy overnight with the first major release of these data. Radial velocities - the last remaining component of motion - is accessable through high resolution spectroscopic surveys, such as SDSS-V APOGEE. Combining these parameters together, it is possible to identify kinematically coherent groups of stars that have most likely formed together from the same molecular cloud at the same time. In populations that are young enough, it is still possible to reconstruct the initial conditions that have influenced the formation of these stars, such as supernovae, cloud-cloud collisions, gravitational feedback, and many others. Through careful analysis of stellar ages, we can see how and when different events were triggered, and how they propagate throughout a population. And, as our ability to measure ages of increasingly larger number of stars improves, we can reconstruct the history of our Galaxy.
For this, it is crucial to better understand stellar properties, including but not limited to their masses, their radii, their temperature, their rotation rate, their magnetic activity, as the combination of these parameters allows us to better probe stellar ages. These measurements are non-trivial to perform, and unfortunately they often depend on comparisons to theoretical models of stellar evolution, which may not always be sufficiently precise. Because of this, it is also necessary to carefully isolate the sample of stars for which it is possible to perform all of these measurements, as it will help improving the calibration for all the other stars as well.
Examining the census of members of >1800 Theia moving groups within 1 kpc of the Sun. These populations are separated into compact cluster-like "groups", and the more extended and diffuse "strings". Each population is color coded by its age. Different panels show their location as a projection on the sky, relative to their distance, and relative to their motions. Selectable and searchable. Published in Kounkel, M., & Covey, K. 2019, AJ, 158, 122
Extinction-corrected HR diagram of the Theia groups within 1 kpc. All of the populations are color-coded based on their age. Can be generated with different bandpasses. Selectable and searchable. Published in Kounkel, M., & Covey, K. 2019, AJ, 158, 122
3d view of the moving groups in our Solar neighborhood within 1 kpc. Dots show the location of all of the cluster-like groups, thicker lines trace all the stellar strings by their spine. Thinner lines show the velocities of the structures over the next 5 Myr, ignoring the galactic potential, can be turned on and of with V+ button. Published in Kounkel, M., & Covey, K. 2019, AJ, 158, 122. Featured as a cover of “Sound of Interstellar Space” music album by TRIFID.
An updated version of the above plot, including more than 8000 Theia groups within 3 kpc. Solid dots are the average position of the stars in the populations; their sizes correlate to a log of the number of sources with MG<4 mag. Thick lines on the top panel show the trace of the strings along their spine. Thinner lines show the typical kinematics of the groups over next 5 Myr, in the local standard of rest, corrected for the circular velocity of 220 km/s. Transparent dots on the face-on view show the areas where the clustering is incomplete due to extinction. Black lines in the top panel show the location of the Perseus, Sagittarius, and Scutum Arms from Reid et al. (2019); the olive line shows the Radcliffe Wave (Alves et al. 2020), which is similar to the position of the Local Arm. Published in Kounkel, M., Covey, K., & Stassun, K. G. 2020, AJ, 160, 279.
Three-dimensional distribution of the sub-groups in Orion from Kounkel et al. 2018. The groups are color coded by the average age of the stars within them, with red being the youngest; the size of the dot corresponds to the number of stars inside each group. Figure can be adjusted to show the traceback and the trace forward look over the −12 and +12 Myr, with 0 Myr corresponding to the present day. Positions of these groups linearly evolved through time, assuming the current velocity. The observer is positioned to the right of the image. Published in Kounkel, M. 2020, ApJ, 902, 122.
Three-dimensional distribution of the sub-groups in Per OB2 association. The dots refer to the current position of all the groups, color-coded by their age. Lines emitting from them show the traceback path over last 10 Myr. The solid portion of each line shows the path after the group has already formed. The dashed lines predate the bulk of star formation, when a population could have existed primarily as gas in a molecular cloud, and they should be treated with caution. Includes groups in Taurus from Krolikowski et al. (2021; smaller symbols with blue lines). Note that IC 348 is originating from the same point as Per OB2a, but it is moving toward Per OB2b. Black line shows the trace of the Perseus molecular cloud from Zucker et al. (2021), and is only shown for the current epoch). Note the bend in the cloud relative to Per OB2a. Interactive plot allows rotation of the plot in 3D using dragging of the plot, zooming in using the scrolling wheel, and evolution of the position of the groups back in time using the slider on the bottom of the plot. Dots become small once the time step is older than the age of that group. The preset buttons allow changing the reference frame for the velocities (reference velocity is displayed in the corner), as well as orientation of the plot in the plane of the sky. Clicking on the legend allows certain traces to be hidden. Published in Kounkel, M., Deng, T., & Stassun, K. G. 2022, AJ, 164, 57.
marina.kounkel (at) unf.edu
Department of Physics and Astronomy
1 UNF Dr., Building 50, Office 2808
Jacksonville, FL 32224