Dr. Carl Melis is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at the University of California, San Diego (UCSD). Multiple stellar systems are ubiquitous in our Galaxy and likely in other galaxies as well. Understanding how these systems evolve over time, especially when individual components begin the giant phase of stellar evolution, are critical in determining the final states of these groups of stars and how they will affect the evolution of their host galaxies. Dr. Melis will characterize a new class of first-ascent giant stars discovered in the PI's thesis research and will connect them to the final stages of multiple-star evolution for a special class of short orbital-period binary systems. Dubbed "Phoenix Giants," these first-ascent giant stars are nearing the end of their lives, yet are surrounded by dusty and gaseous disks similar to those found around young, planet forming stars.
The research program will include a comprehensive observational campaign extending from the near-infrared to the microwave, model fitting of these data sets to derive the structures of Phoenix Giant disks, and the development of analytical and numerical models describing the interaction between tightly bound pairs when the primary enters into the first-ascent giant phase of evolution. Comparison of the observational results for Phoenix Giant disk structure to the analytical and numerical modeling results will aid in connecting the Phoenix Giant phenomenon and the fate of short orbital-period binaries. The data obtained will also be extended to probe whether Phoenix Giant disks are hospitable environments for forming protoplanets and hence to begin to answer the question of whether these stars can undergo a second epoch of planet formation billions of years after their first.
Dr. Melis will also conduct a program of education and outreach aimed at the recruitment, retention, and advancement of students in science, technology, engineering, and mathematics (STEM). Dr. Melis will develop and teach a laboratory course for UCSD advanced undergraduate physics and engineering majors that will incorporate best practices from recent educational research and lessons learned from astronomy laboratory courses successfully implemented at other institutions. This laboratory course will focus on preparing students for advanced academic studies or industry work within STEM through the development of relevant technical skills, but will also introduce students to the basics of observational astronomy research. Dr. Melis will also volunteer with Project ASTRO to bring astronomy to the earliest levels of pre collegiate education where young minds can be turned on to science. These two educational programs will plant the seeds of a science career in young students' minds and provide them the tools in a collegiate setting to succeed in a STEM career path.
Pairs or groups of stars orbiting each other are ubiquitous in our Galaxy and thus understanding their evolution is critical in developing a comprehensive Galactic evolution model. The research portion of this project aimed to characterize dust and gas orbiting a previously unknown class of old stars. Old stars should not have easily detectable gas and dust orbiting them as such material is removed early in the star's life and we hypothesize that this matter originated when two stars merged near the end of their lives. Testing this hypothesis was a major objective of this award. The circumstellar characteristics of these newly discovered old stars are quite similar to those of young, planet forming stars, and as such earned them the name of "Phoenix Giants". Most of the major research objectives for this project were realized. Observations for a sample of 20 Phoenix Giant stars were obtained allowing initial descriptions of their orbiting material and tests to see if it could have originated in the merging of two stars. The discovery and characterization of a bona-fide stellar merger event in the inner Milky Way Galaxy lent itself as a rosetta stone for the progenitors of the Phoenix Giant stellar class. The initial study of the dusty aftermath of this merger event has brought unique insight into the stars being studied herein and is a major success of this award. Beyond Phoenix Giant stars, important research contributions were made to the study of the process of forming planets like the Earth and understanding the fate of asteroids, dwarf planets, and rocky planets similar in size to Earth when their host star dies. I have also contributed to the characterization of failed stars called brown dwarfs and radio astronomy. In the course of this award 24 publications were produced with the PI as a first or co-author, 22 of which were published in reputable, peer-reviewed journals. The outreach portion of this project aimed to connect with local youth to excite them to the possibility of a career in science, technology, engineering, or mathematics. Educational activities sought to develop an undergraduate/graduate level astrophysics laboratory course for the University of California, San Diego Physics Department. The successful development of the astrophysics laboratory class at UC San Diego fulfills the major education objective of this award. Additionally, I was able to reach out to the San Diego community to allow students a taste of real research and aided in the training of researchers and undergraduates. Mentoring activities for several individuals led to their advancement in science, technology, engineering, or mathematics career paths. With the help of a colleague, I was also able to create the astronomy fund at MiraCosta Community College which will provide support in developing targeted approaches to the problems faced by community college students.
