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Adriaan Blaauw, Stellar Populations and the Milky Adriaan Blaauw, Stellar Populations and the Milky Way Steven Majewski (University of Virginia) University of Chicago, Yerkes Observatory Blaauw @ 1947-8, ‘52, ‘53-57 (photo: November 1947) University of Chicago, Yerkes Observatory Blaauw @ 1947-8, ‘52, ‘53-57 (photo: November 1947) (back row, standing, from left) Daniel E. Harris, Guido Münch, Henry Chun, Su-Shu Huang, Douglas Duke, Mrs. Marshall H. Wrubel, Marshall H. Wrubel, Mr. Clearman, Arne Slettebak, William Bidelman, Roy Wickham, Irene Hansen, Frances H. Breen, Marjorie Hall Harrison, Gertrude Peterson, Robert H. Hardie, Arthur D. Code, K. N. Rao, Henry G. Horak, Marvin L. White, Frank N. Edmonds, Anne B. Underhill, Nancy G. Roman, Mr. Robinson, John Vosatka, Margaret Phillips, John G. Phillips, Mr. Sinha; (front row) Thornton L. Page, William W. Morgan, Charles Ridell, Yu-Che Chang, Adriaan Blaauw, Luise Oettinger Herzberg, Gerard P. Kuiper, Jan H. Oort, George Van Biesbroeck, William A. Hiltner, Otto Struve, Gerhard Herzberg, Marguerite Van Biesbroeck, Fred Pearson, Subrahmanyan Chandrasekhar. McCormick Observatory, University of Virginia • appointment with UVa Dept. of Astronomy from 1967-1969+ • visited about twice a year for about a month at a time • advised UVa Ph.D. thesis (Katy Garmany :“A Spectroscopic Study of the OB Association III Cepheus “) • responsible for bringing in one new faculty member (Tolbert) Early Stellar Populations Work (distinct from young stars, magnitude calibrations) • Blaauw (1939, BAN, VIII, 305; No. 315): “A determination of the longitude of the vertex and the ratio of the axes of the velocity-ellipsoid from the dispersions of the proper motions of faint stars measured at the Radcliffe Observatory” • Blaauw (1944, BAN, X, 19; No. 363): “On systematic errors in the proper motions of the General Catalogue and on the preference to be given either to this catalogue or the Dritter Fundamentalkatalog” • Hins & Blaauw* (1948, BAN, X, 365; No. 391): “Star-streaming among faint low-latitude stars investigated according to the dispersion method” (*A.B. completing work suggested by him to Dr. Hins but unfinished by Hins due to army service.) 1957 Vatican Conference • In 1957, invited to the Pontifical Academy of Sciences’ Semaine d’Etude on the Problem of Stellar Populations • “The Academy invites … illustrious scholars – comprising those who have especially studied a given question and have arrived at different conclusions -- to meet in Rome at its headquarters … so as to make a joint examination, free from all other preoccupations, of all data concerning the problem.” • “…the number of participants is strictly limited, in order to ensure freer and more intimate discussions.” 1957 Vatican Conference • In 1957, invited to the Pontifical Academy of Sciences’ Semaine d’Etude on the Problem of Stellar Populations Baade's 1944 definition of two primary stellar populations based on CMD type. Semaine d’Etude on the Problem of Stellar Populations of the Vatican Academy, May 1957 Semaine d’Etude on the Problem of Stellar Populations, May 1957 The 1957 Vatican Conference § A seminal event in the history of stellar populations studies. § Set modern context by defining principal Galactic populations. Blaauw at 1957 Vatican Conference § At age 42, Blaauw was among the younger participants (youngest of the “mid-career”). Blaauw at 1957 Vatican Conference § But as active a participant as other (more senior) participants. Blaauw at 1957 Vatican Conference § Among the participants who gave multiple presentations: • Session III: Young Population I Stars in the Spiral Arms of Our Galaxy: – “Stellar Associations” • Session VI: Stellar Populations in our Own Galaxy – “Kinematic Properties of the Strong and Weak-Line Stars” – A detailed analysis of “Miss Roman’s” data, focusing on planar kinematics Hins & Blaauw (1948, BAN, X, 365; No. 391): “Star-streaming among faint low-latitude stars investigated according to the dispersion method” • “The galactic longitude of the vertex direction is found to be 323°.5 ± 1°.8 (m.e.). This confirms the coincidence with the direction of the galactic center found in an earlier application of the method, • and indicates that the vertex deviation exhibited by bright stars is but a local phenomenon.” Revising Galactic Coordinates Blaauw et al. (1960, MNRAS, 121, 123) Blaauw et al. (1959, ApJ, 130, 702) Revising Galactic Coordinates Blaauw (1960, MNRAS, 121, 164) Revising Galactic Coordinates Blaauw (1960, MNRAS, 121, 164) Large variations by longitude due to local groupings like h and χ Persei. Negative values due to solar height above Galactic plane. Revising Galactic Coordinates Blaauw (1960, MNRAS, 121, 164) Farther objects more consistent, but still an overall tilt with respect to HI defined plane. Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • Began with recap of Baade’s work, stressing primary focus on physical properties, spectral class and luminosity with location. Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • Began with recap of Baade’s work, stressing primary focus on physical properties, spectral class and luminosity with location. • Pointed out the subsequent emphasis on adding kinematical trends (building on work of Jeans, Lindlbad, Oort, etc. previously showing MW = superposed “star streams” of different densities). Lindblad (1936) Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • Began with recap of Baade’s work, stressing primary focus on physical properties, spectral class and luminosity with location. • Pointed out the subsequent emphasis on adding kinematical trends (building on work of Jeans, Lindlbad, Oort, etc. previously showing MW = superposed “star streams” of different densities • But that investigation of differences in chemical composition was in infancy (indeed, chemical uniformity seemed most impressive in work to date). Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • Recalls Vatican Conference subdivision into additional, “intermediate” populations. • See also Blaauw’s retrospective on the Vatican Conference published in IAU Symp. 164 (1995) and reprinted in (1999, A&SS 267, 45). Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • Recalls Vatican Conference subdivision into additional, “intermediate” populations. • Summarizes a top-down formation scenario resembling that described in Eggen, Lynden-Bell & Sandage (1962). • Early-formed stars metal-poor from outer halo on radial, plunging orbits. – Today have orbits to large radii and any orientation. – Metal poor, since formed before much of the ISM had cycled through generations of stars. • Late formed stars are metal-rich stars of disk and on circular orbits. – Formed from highly enriched gas after many generations of stars enriched ISM. Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • Laments that 70% of mass is in “disk populations”, but their properties least well known, studies hampered by “prohibitively large interstellar absorption” and lack of high luminosity objects (like supergiants and Cepheids). • “The most promising objects for determining the large scale density distribution are the red giants, through the spectral classification in the near infrared.” Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • Laments that 70% of mass is in “disk populations”, but their properties least well known, studies hampered by “prohibitively large interstellar absorption” and lack of high luminosity objects (like supergiants and Cepheids). • “The most promising objects for determining the large scale density distribution are the red giants, through the spectral classification in the near infrared.” • “These difficulties are also the reasons why the question of subdividing the disk population into categories with different degrees of central concen- tration formed a controversial subject at the Vatican Conference. We do not know how much larger the concentration toward the galactic center of the bright red giants is as compared to that of the weak-line stars.” • Anticipating the eventuality of a comprehensive, near infrared spectroscopic study like that just now being undertaken as the APOGEE project. The Concept of Galactic Chemical Enrichment Heavy elements created by nuclear fusion of lighter elements in stars. Burbidge et al. 1957 (B2FH) Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • Section 4: “Modern work on the relation between the kinematical and distributional properties and chemical parameters.” • Summarizes new emphasis to incorporate chemistry: • Spectral classification of globular clusters (Morgan, Mayall, Kinman) • Nancy Roman: kinematics of weak versus strong line stars • Photometric/spectrophotometric means: UVX, Stromgren m, ΔS ELS 1962 Wildey et al. 1962, Sandage 1969 Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • “Of great significance for the study of stellar populations is Wallerstein’s U,V velocity diagram…with discrimination according to … [Fe/H].” • “another significant way of discriminating stars with different kinematics… marking the stars…according to…the ratio of α-elements with respect to iron.” Wallerstein 1962 Stars and Stellar (1965) Chapter: “The Concept of Stellar Populations” • “Of great significance for the study of stellar populations is Wallerstein’s U,V velocity diagram…with discrimination according to … [Fe/H].” • “another significant way of discriminating stars with different kinematics… marking
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