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Building a Comprehensive Picture of Stellar Evolution

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Building a Comprehensive Picture of Stellar Evolution 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 M67 NGC 6819 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 Jewel Box Cluster (NGC 4755) members of the cluster? APOD N. M. Gosnell September 28, 2018 Accurate cluster memberships are important for more detailed studies of stellar evolution 11 NGC 188: Bright -7 billion years old 12 -5500 light years away 13 1498 stars in the region of the cluster V 14 Magnitude 15 Group of hundreds to thousands of stars • born at the same time 16 Hot Cool • made from the same Faint 0.4 0.6 0.8 1.0 1.2 1.4 StellarB - Vcolor material • 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 11 NGC 188: Bright -7 billion years old 12 -5500 light years away 13 1498 stars in the region of the cluster V 14 Magnitude 15 Group of hundreds to thousands of stars • born at the same time 16 Hot Cool • made from the same Faint 0.4 0.6 0.8 1.0 1.2 1.4 StellarB - Vcolor material • all at the same distance Gosnell 2014, adapted from Geller et al. 2008 N. M. Gosnell September 28, 2018 The Astronomical Journal,148:38(20pp),2014August Milliman et al. 100 100 The Astronomical Journal,146:43(12pp),2013August 80 Platais et al. 80 Table 4 A Sample of the Catalog of Positions and Proper Motions in NGC 6819 a a a a a b c c d e ID R.A. (J2000) Decl. (J2000) g g r µx µy σµ σµ 60σest Pµ Xt Yt Plates ndel 60 ′ ′ − ′ x y 155298 294.890863 39.818837 14.272 0.510 10.61 9.19 0.75 0.75 0.75 0 19.908 22.605 00001 0 − − 159195 294.936317 39.821684 13.905 1.128 7.55 0.39 0.82 0.82 0.82 0 17.812 22.444 00001 0 − − 160120 295.124249 39.822393 16.125 1.336 10.94 0.75 0.70 0.7040 0.70 0 9.151 22.430 00001 0 40 − − − − Completeness (%) 162002 295.053344 39.823850 15.594 0.799 6.94 4.22 0.70 0.70 0.70 0 12.418 22.334 00001 0 Completeness (%) − − − 162175 294.948913 39.823970 15.238 0.425 6.30 1.14 0.70 0.70 0.70 0 17.231 22.309 00001 0 Kinematic information separates− cluster− members− 20 20 Notes. a 1 Unitsfrom in mas yr− the. field population b Proper-motion membership probability in percent. c Tangential coordinates in arcmin with zeropoint at the center of NGC 6819. 0 0 d Encoded number of plates, tuuvz,wheret is McDonald; uu is Yale; v is Hale; z is Mt. Wilson (see Table 10). 5 10 15 20 25 30 11 12 13 14 15 16 e Number of rejected datasets.Proper motions Radial velocitiesRadius (arcmin) V (This table is available in its entirety in machine-readable and Virtual Observatory (VO) forms in the online journal. A portion is shown here for guidance regarding Figure 4. Percentage of stars in our sample that have three or more RV observations and either no P information or a P 4% with respect to distance from the its formCompare and content.) modern images with photographic Requires at least 3 spectra of every star, and µ µ ! plates from 50–70 years ago clusteryears center of (left) coverage and V magnitude to obtain (right). binary memberships 140 Table 3 RV Distribution Gaussian Fit Parameters for Cluster and Field RV Distributions Cluster Member Distribution 120 Parameter Cluster Field Field Population Stars in cluster 100 Ampl. (number) 112.99 8.81 RV (km s 1)2.4514.59 − − σ (km s 1)1.0225.79 80 Stars in cluster − 60 Table 4 Number of Stars Within Each Classification Number of Objects 40 Classification N Stars Number of stars Stars in field of galaxy SM 566 Figure20 4. Distribution of Pµ as a function of magnitude. The decline of maximum Pµ toward fainter magnitudes is a consequence of steadily growing SN 1381 Proper motion movement (y) Proper luminosity function of field stars and an increase of proper motion errors. At 0 BM 93 g′ > 20.5theseparationbetweentheclusterandfieldstarsispoorandthatis BN 79 indicated by-60 a flat and unrealistically-40 -20 high distribution0 of Pµ.Thesecondary20 40 BLM 20 distribution peaking at g′ 16 (maxRVPµ (km/s)63%) is for the stars outside the Proper motion movement (x) radius r 10 . ∼Radial velocity= (km/s) BLN 172 = ′ Figure 3. Vector-point diagram in the area of NGC 6819. A tight clump FigureMilliman 5. Histogramet al. 2014 of the RV distribution of single stars, e/i < 4, with BU 22 1 at µPlataisx µy &0 Gosnell.0masyr− etindicates al. 2013 the location of cluster members, closely three or more RV observations. Also plotted are the Gaussian distributions U1562 surrounded= by= a slightly offset and slanted distribution of field stars. simultaneously fit to the cluster, the large peak at a mean velocity of 2.4 km s 1 30◦ to align the field distribution along the R.A. and decl. axes. − (blue− dotted line), and the field (orange dashed line). At g′ 16, the center of field-star distribution in the VPD is only (A color version= of1 this figure is available in the online journal.) stars, Φf ,whichadequatelyrepresentthechosenlocalsample. 0.8 mas yr− away from the center of the cluster distribution. 1 estimate from the cluster and field Gaussian functions a field star N.The M. parameters Gosnell of these distributions can be estimated in situ The corresponding Gaussian dispersions are September 2.5 mas yr− 28,for 2018 1 contamination of 13% at this membership threshold (Figure 5). and prior to calculating: becausefield stars they along require the better minor observing axis and 3.6 conditions mas yr− (cleareralong the skies, major axis, but only 0.4 mas yr 1 in either axis for cluster stars, Interestingly, using Pµ < 4% as a criterion for non-membership, dimmer moon, etc.) and longer− exposures to meet our signal-to- Φc illustrating how unlike the two distributions are. We note that we find a field-star contamination of 12% 2% among stars Pµ . (3) noise requirements. with P 50%. ± = Φc + Φf at fainter magnitudes (g′ 20) the distributions are separated RV ! 1 = by 2.5 mas yr− , but the cluster dispersion also grows up to 14.4. RV Membership Probabilities For technical details, we refer the reader to Kozhurina-Platais 1masyr− . 4.5. Membership Classification of Stars ∼ et al.
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