Building a Comprehensive Picture of Stellar Evolution Natalie M. Gosnell Assistant Professor, Colorado College September 28, 2018 St. Olaf College Physics Colloquium AIDA: R. Chromik
What am I going to talk about today? A large fraction of stars don’t evolve as they “should” Current understanding of stellar evolution is incomplete, so we need observations to improve our models Blue straggler stars provide the largest handle on this population of stars My work on mass transfer formation of blue straggler stars with the Hubble Space Telescope is helping fill in the gaps N. M. Gosnell September 28, 2018
Open clusters are the ideal laboratory for studying stellar evolution Group of hundreds to thousands of stars • born at the same time • made from the same material • all at the same distance Jewel Box Cluster (NGC 4755) APOD N. M. Gosnell September 28, 2018
Open clusters exist in the disk of our galaxy VLT Telescopes, ESO/Y. Beletsky N. M. Gosnell September 28, 2018
Open clusters exist in the disk of our galaxy NGC 6819 M67 Xanadu Observatory DSS NGC 188 NGC 290 www.robgendlerastropics.com APOD VLT Telescopes, ESO/Y. Beletsky N. M. Gosnell September 28, 2018
Created by A. Geller, Northwestern University N. M. Gosnell September 28, 2018
Hertzsprung-Russell (H-R) diagrams organize stars by temperature (color) and luminosity (brightness) Hot (blue) Cool (red) Movie credit: NASA, ESA, J. Anderson, & R. van der Marel (annotations mine) N. M. Gosnell September 28, 2018
Hertzsprung-Russell (H-R) diagrams organize stars by temperature (color) and luminosity (brightness) Bright (large) Hot (blue) Cool (red) faint (small) Movie credit: NASA, ESA, J. Anderson, & R. van der Marel (annotations mine) N. M. Gosnell September 28, 2018
H-R diagrams reveal different stages of typical stellar evolution Bright (large) Horizontal Branch Giant Branch Subgiants White Dwarf Sequence Main Sequence Hot (blue) Cool (red) faint (small) Movie credit: NASA, ESA, J. Anderson, & R. van der Marel (annotations mine) N. M. Gosnell September 28, 2018
H-R diagrams reveal different stages of typical stellar evolution Bright (large) Over time Main Sequence Hot (blue) Cool (red) faint (small) Movie credit: NASA, ESA, J. Anderson, & R. van der Marel (annotations mine) N. M. Gosnell September 28, 2018
H-R diagrams reveal different stages of typical stellar evolution Bright (large) Horizontal Branch Giant Branch Subgiants White Dwarf Sequence Main Sequence Hot (blue) Cool (red) faint (small) Movie credit: NASA, ESA, J. Anderson, & R. van der Marel (annotations mine) N. M. Gosnell September 28, 2018
H-R diagrams reveal different stages of typical stellar evolution Bright (large) Horizontal Branch Giant Branch Subgiants White Dwarf Sequence Main Sequence Hot (blue) Cool (red) We have reliable models for how a single star will evolve faint (small) Movie credit: NASA, ESA, J. Anderson, & R. van der Marel (annotations mine) N. M. Gosnell September 28, 2018
Open clusters are the ideal laboratory for studying stellar evolution Group of hundreds to thousands of stars • born at the same time • made from the same material • all at the same distance But which stars are members of the cluster? Jewel Box Cluster (NGC 4755) APOD N. M. Gosnell September 28, 2018
Accurate cluster memberships are important for more detailed studies of stellar evolution NGC 188: 11 11 Bright -7 billion years old -5500 light years away 12 12 1498 stars in the region of Magnitude 13 13 the cluster V 14 14 Group of hundreds to 15 15 thousands of stars • born at the same time • made from the same 16 16 Cool Hot Faint material Stellar color 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0 1.2 1.2 1.4 1.4 B - V • all at the same distance Gosnell 2014, adapted from Geller et al. 2008 N. M. Gosnell September 28, 2018
Accurate cluster memberships are important for more detailed studies of stellar evolution NGC 188: 11 11 Bright -7 billion years old -5500 light years away 12 12 1498 stars in the region of Magnitude 13 13 the cluster V 14 14 Group of hundreds to 15 15 thousands of stars • born at the same time • made from the same 16 16 Cool Hot Faint material Stellar color 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0 1.2 1.2 1.4 1.4 B - V • all at the same distance Gosnell 2014, adapted from Geller et al. 2008 N. M. Gosnell September 28, 2018
Kinematic information separates cluster members from the field population Proper motions Radial velocities Compare modern images with photographic Requires at least 3 spectra of every star, and plates from 50 – 70 years ago years of coverage to obtain binary memberships 140 RV Distribution Cluster Member Distribution Proper motion movement (y) 120 Field Population Stars in cluster Number of Objects 100 Number of stars Stars in cluster 80 60 40 Stars in field of galaxy 20 0 -60 -40 -20 0 20 40 Radial velocity (km/s) RV (km/s) Proper motion movement (x) Milliman et al. 2014 Figure 5. Histogram of the RV distribution of single stars, 4, with Platais & Gosnell et al. 2013 N. M. Gosnell September 28, 2018
Accurate cluster memberships are important for more detailed studies of stellar evolution NGC 188: 11 11 Bright -7 billion years old -5500 light years away 12 12 1498 stars in the region of Magnitude 13 13 the cluster V 14 14 Group of hundreds to 15 15 thousands of stars • born at the same time • made from the same 16 16 Cool Hot Faint material Stellar color 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0 1.2 1.2 1.4 1.4 B - V • all at the same distance Gosnell 2014, adapted from Geller et al. 2008 N. M. Gosnell September 28, 2018
Accurate cluster memberships are important for more detailed studies of stellar evolution NGC 188: 11 11 Bright -7 billion years old -5500 light years away 12 12 1498 stars in the region of 13 13 Magnitude the cluster ➔ 473 members V 14 14 Group of hundreds to 15 15 thousands of stars • born at the same time ✔ • made from the same 16 16 Cool Hot ✔ Faint material Stellar color 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0 1.2 1.2 1.4 1.4 B - V • all at the same distance ✔ Gosnell 2014, adapted from Geller et al. 2008 N. M. Gosnell September 28, 2018
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