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WILLEM JACOB LUYTEN March 7, IS99-November2l, 1994 BY ARTHUR UPGREN Wl~EM LUMEN WAS the central figure in the determina- tion of the stellar luminosity function, the frequency function of stars by their luminosity. In this, his major re- search contribution, he follower! in the tradition of Dutch astronomers, mostly of the Leiclen Observatory, which be- gan before 1900 with I. C. Kapteyn en c! incluclec! P. I. van Rhijn, Ejnar Hertzsprung, Willem De Sitter, en c! {an H. Oort. Luyten was one of a number of clistinguishec! students of these scientists who emigratec! to the Uniter! States en c! hac! a memorable career. His contemporaries incluclec! Bart I. Bok, Dirk Brouwer, Gerarc! P. Kuiper, Jan SchiTt, Kaj Aa. Strand, en c! Peter van cle Kamp. Luyten spoke of his ancestry as part French, originating in Provence in the fourteenth century. The family name may have been Lutin en c! clerivec! from lute players en c! minstrels attending the popes who resiclec! in Avignon. In 1377 the popes mover! back to Rome en c! the progenitor lute player resettlec! at the Court of Burgundy. The flukes there uniter! the cities of HolIancI, en c! cluring clucal rule over the next century, the family may have fount! its way to the NetherIancis. His mother's family name of Francken reveals her origin there. 199

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200 BIOGRAPHICAL MEMOIRS Luyten, himself, was born of parents of North HollancI, who hac! settlec! in Indonesia, then a colony of the Nether- lancis. His birth on March 7, 1899, was in the city of Semarang in north-central Java, where his father taught French in the local high school. Luyten liver! there until 1912, when the family mover! back to the NetherIancis. At that time he spoke Dutch en c! French, he also became fluent in German en c! English before his high school graduation. Later in college he masterec! Latin en c! Greek, en c! still later, he picket! up some Spanish en c! Italian, en c! finally, in 1927, Russian. He was rightfully prouc! of his ability to learn to react en c! speak so many languages. Willem Luyten's interest in astronomy ciates from the 1910 appearance of Halley's comet over his home in Semarang. He macle his first astronomical observations on lava in 1912, en c! continues! them while a student at the University of Amsterdam, where he received a B.A. degree in 1918. His earliest research was publisher! at that time en c! he com- pleted his doctoral thesis four years later at the University of Leiden, where he was awarded his Ph.D. degree in 1921. He was Hertzsprung's first student there. Luyten's thesis was baser! on 13,500 visual observations of variable stars, some of which he macle in high school en c! others with the 6-inch refractor at the Leiclen Observatory. His contacts at Leiclen incluclec! Kapteyn, cle Sitter, en c! Paul Ehrenfest, at whose home he socializer! on occasion with Albert Einstein, Hencirik Lorentz, en c! A. S. Eciclington. Although he became interested in many lines of astro- nomical research, Luyten's lifelong interest centered on the properties of the common nearby stars en c! especially their proper motions. Near the end of his career, he participated in International Astronomical Union Colloquium No. 97 on wicle components in clouble en c! multiple stars hell! in 1987 in Brussels, which was cleclicatec! to him. There he

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WILLEM JACOB LUYTEN 201 gave a review of his lifetime of research on these objects. In it he remarkoc! that: We should remember that, . . . of the 6,000 stars [that] the average human eye could see in the entire sky, probably not more than thirty or one-half of one percent are less luminous than the Sun; that probably, of the 700- odd stars nearer than ten parsecs, at least 96% are less luminous than the Sun. There is not even ONE real yellow giant such as Capella, Pollux, or Arcturus nearer than ten parsecs and only about four Main-Sequence A stars. He was always aware of the havoc this great dichotomy be- tween the brightest en c! the nearest stars fraught as it is with bias conic! wreak upon anyone who clic! not take full account of it in their work. Perhaps no one explorer! the immensity of this dichotomy in more cletail than clic! Luyten. He turner! his early interest in proper motions into a better calibration of the HR clia- gram than hac! been known at the time. His early years at the Lick Observatory en c! as a guest investigator at the Royal Greenwich Observatory witnessed his clevelopment en c! ap- plication of techniques using proper motions to estimate the distances of stars in large numbers. Through the use of Hertzsprung's concept of the reclucec! proper motion to obtain statistical paralIaxes for common stars, he was the first to provicle a realistic census of stars in the solar neigh- borhooc! en c! an HR diagram more truly representative of the fainter stars that dominate the solar neighborhood. The reclucec! proper motion connects the apparent en c! absolute magnitudes (luminosities) with proper motion in much the same way as are the apparent en c! absolute mag- nitucles with trigonometric parallax. lust as the parallax fixes the absolute magnitude exactly, so do proper motions roughly determine it. Roughly, because proper motions of stars at a given distance differ consiclerably. But, if many stars are

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202 BIOGRAPHICAL MEMOIRS examiner! en c! the mean proper motion is caTibratec! on parallax, the methoc! works. It is worth noting that, not long ago, the only properties known about the majority of the nearest stellar neighbors were the apparent magnitude and the proper motion. In fact, the proper motion became the feature by which a faint nearby star conic! be recognizec! as such. In his autobiogra- phy published in 1987, Luyten cites his seventy years of work on this subject. His amazingly extensive en c! pioneer- ing efforts in this domain dwarf those of anyone else. Since 1925 he cleterminec! over 200,000 proper motions, itself a testimonial to his stamina en c! cleclication. In 1925 Luyten lost the sight of one eye in a tennis accident. Thus, he accomplishes! all of this with his remaining eye, it is prob- able that he has blinkocI, observed, en c! measurer! more stellar images than anyone else. The prececling feat alone wouIc! merit a permanent place in the annals of astronomy, but his insight into the worth of the collectec! ciata lies even more at the center of his achieve- ment. His Dutch predecessors especially Kapteyn, van Rhijn, and his Danish mentor at Leiden, Ejnar Hertzsprung picked up about where Sir William Herschel left off a century ear- lier in the study of the stellar makeup of the Milky Way. The luminosity function concept was well known by the time Luyten enterer! the scene, but it was he, working al- most alone, who first Filly! in its faint end. In 1923, after two years at the Lick Observatory, Luyten was offerer! a position at the Harvarc! College Observatory by HarIow Shapley. He spent the next seven years on its staff, the last two in Bloemfontein, South Africa. At both Lick en c! Harvard, Luyten was engages! in a number of other research subjects. While at Lick, he preclictec! en c! confirmed! that the sodium D lines cliffer wiclely in intensity among the cooler stars, between giants and normal dwarfs of the same

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WILLEM JACOB LUYTEN 203 surface temperature. But his Harvarc! years became clomi- natec! by the stucly of proper motions that former! the ma- jor focus of research for the rest of his professional life. At Harvarc! en c! Bloemfontein, he began his Tong associa- tion with the 0.6-meter Bruce refracting telescope. Between IS96 en c! 1910 at its former location at Arequipa, Peru, the telescope hac! been user! to photograph almost the entire southern celestial hemisphere in three-hour exposures that reacher! the seventeenth magnitude. Altogether, the collec- tion comprises! more than 1,000 plates. These plates conic! serve as first-epoch observations for a large proper motion survey, en c! in 1927, with the air! of a Guggenheim Fellow- ship, the Bruce Proper Motion Survey began. Luyten took over 300 of the 1,000 plates forming the seconcI-epoch ma- terial en c! blinker! all of the plate pairs. Altogether 94,263 stars with significant proper motions were founcI. Most of these stars were brighter than magnitude 14.5 en c! hac! proper motions in excess of one-tenth of an arc seconc! per year. The measurement of positions en c! proper motions for these stars took many years to acquire, en c! requires! a number of measurers, inclucling myself cluring my unclergracluate clays at Minnesota. The final catalog appearec! in 1963. In compiling this catalog, Luyten shower! much resource- fuIness. In ~ 923 he publisher! a paper in which he em- ployed a cumulative probability plot, or probit plot, de- cacles before its common use in astronomy. These plots outliner! a technique for determining whether specific sets of ciata follow a Gaussian distribution by rendering the cu- mulative normal distribution into linear form. The test is often more robust than the Kolmogorov-Smirnov en c! simi- lar goociness-of-fit tests for randomness. In funcling such a long-term project, he was creative en c! persistent, at different periods he acknowlecigec! not only the National Science Foundation en c! the Office of Naval

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204 BIOGRAPHICAL MEMOIRS Research but also other fecleral relief organizations, such as the fecleral student air! program en c! even the Works Progress Administration, along with a number of private philanthropic sources. The Bruce Proper Motion Survey lee! to improvements in stellar kinematics at the faint enc! of the luminosity func- tion, but it also proviclec! a rich harvest of degenerate stars, known also as white dwarfs. These are enc! products of stel- lar evolution with degenerate matter in their interiors after the fusion process has compacter! their atomic nuclei en c! compressed them into planet-size objects. One of the goals of the survey was to cliscover en c! identify many degenerate or white dwarf stars. Only three were known in 1921, when Luyten began his term at Lick, far too few to support the many theoretical studies macle of them then en c! since. Luyten collaborates! with E. F. Carpenter of the University of Ari- zona, E. Gaviola of the Corcloba Observatory, en c! G. Haro of the TonantzintIa Observatory to obtain colors of the faint proper motion stars fount! in the survey. From the colors, magnitudes, en c! assumer! distances, the degenerates were iclentifiec! as such and, by the time of its publication in 1963, Luyten hac! cliscoverec! the great majority of the sev- eral huncirec! then known. With the completion of the Bruce survey project, Luyten sought to extent! its achievements in the search for stellar neighbors, to fainter magnitudes, en c! to the northern ce- lestial hemisphere, which was not observable with the Bruce telescope in its southerly locations. For these reasons, he initiates! the immense project known as the National Geo- graphic/Palomar Observatory survey. The name honors the principal sponsor en c! the I.2-~.~-meter Palomar Schmidt telescope on which much of the plate material hac! aIreacly been obtained. This wicle-fielc! instrument hac! photographic!

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WILLEM JACOB LUYTEN 205 the entire sky north of clecTination -34 en c! to stars of magnitude ~ 8 en c! fainter. This is the plate material that former! the Palomar Ob- servatory Sky Survey of the 1950s en c! is still very useful tociay. It also proviclec! an icleal first epoch for the measure of proper motions. Luyten quickly realizer! that the oIc! blink machine at Minnesota, on which measures for the Bruce survey were macle by hancI, was much too slow for this project. He approaches! the Control Data Corporation with plans to built! a rapicI-scanning microclensitometer. The CDC ma- chine, clesignec! primarily by lames Newcomb en c! Anton LaBonte, became the fastest of the new generation of auto- matic machines capable of measuring en c! blinking stellar images with high precision. It finally became possible to determine the proper motions of huncirecis of thousands of stars in a short time, in a few years motions for 300,000 stars were founcI, cloubling the number with these ciata. The catalogues that emerges! from this effort are among the most wiclely user! in the fielcI. They inclucle the first rounc! of catalogues of 1955 to 1961, the LET (Luyten-Five- Tenths) catalogue of 1,849 stars, en c! the LTT (Luyten Two- Tenths) catalogue of 16,994 stars with proper motions ex- ceecling 0."5 en c! 0."2 arc seconds per year, respectively. Twenty years later, well after his retirement, he publisher! their successors, the LHS (Luyten Half SeconcI) en c! NLTT (New Luyten Two-Tenths) catalogues with the same limits, but with 3,583 en c! 58,700 stars. Honors accrues! to Luyten at about the time of his retire- ment in 1967, he was the Catherine Wolfe Bruce mecialist of the Astronomical Society of the Pacific in 1968, en c! was electec! to the National Academy of Sciences in 1970. Also in 1970 he receiver! an honorary doctorate degree from St. Ancirew's University, the oIclest eclucational institution in ScotiancI, only Benjamin Franklin en c! two others prececlec!

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206 . . BIOGRAPHICAL MEMOIRS him in the aware! of this honor. He organizer! en c! heaclec! the first conference hell! specifically on proper motions. The meeting was hell! at the Control Data Corporation in Minneapolis in April 1970, en c! the proceedings constitutes! the International Astronomical Union Colloquium No. 7. However one obtains a value for the stellar luminosity function, one must calibrate the ciata for the many thou- sancis of stars coverer! in the survey against a much smaller group of stars for which the incliviclual luminosities are cli- rectly determined from the parallax. Until the present de- cacle, these were few en c! were biases! in one way or an- other. For his calibration sample Luyten user! 610 stars with proper motions in excess of 0.5 arc seconds per year, en c! for which luminosities were available from trigonometric ?aralIaxes. In 1964 James Wanner completer! a cloctoral thesis at Harvarc! University on the same subject but with a different calibration group. Wanner user! a limit in distance insteac! of proper motion as his major criterion. He user! only stars within ten parsecs of the Sun Il7 altogether which also fulfilled secondary criteria in parallax and proper motion. Wanner's technique has the advantage of being far less sus- ceptible to a bias towards stars with a high velocity across the sky. Both Luyten and Wanner used Hertzsprung's ap- proach, but with proper motions being such a funciamental parameter in Luyten's work, a high-velocity bias is apparent in the result. Wanner's function comes closer to recent cle- terminations that can to a large extent bypass proper mo- tion en c! thus better represent all stars in this part of the galaxy. This controversy became a matter of great contention, until settled by access to very large stellar samples with distances cleterminec! for each star incliviclually. Luyten's function was vitiates! only among the very faintest of stars,

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WILLEM JACOB LUYTEN 207 unfortunately, these are the ones most critical to the stucly of certain aspects of stellar evolution en c! of other plan- etary systems. They are also among the hardest to moclel, to assign with confidence the interior domains of racliative en c! convective energy transfer by which the energy pro- clucec! at the stellar core rises to the surface en c! out into space. In any event, the merit of his work is beyonc! re- proach when we consider the ciata en c! methods available to him at the time. Willem Luyten joined the faculty of the University of Min- nesota in 1931, his appointment at Harvarc! having been terminatec! the previous autumn, apparently without cause. In his autobiography, Luyten contends that Henry Norris Russell, then the putative "clean of American astronomers," was instrumental in the termination. He describes their first encounter: Luyten hac! comparer! stellar luminosities from Mount Wilson spectral classifications en c! from paral- laxes en c! hac! concluclec! that, if all M giants were assignee! the same luminosity, the mean error in luminosity from parallax wouIc! be reclucecI. Upon seeing this work, Russell, according to Luyten, saicI, "Even if this were true, I conic! say it, but you can't." Young Luyten responclecI, "I thought that in science the only thing that matterec! was what was sail! not who sail! it." These en c! further encounters alleg- ecITy turner! the influential Russell against him. Over his career, Luyten publisher! some 500 research pa- pers en c! wrote numerous popular articles for the New York Times, Minneapolis Star and Tribune, en c! other perioclicals. His association with the Times began in 1925 with his report on the total solar eclipse of that year as seen from the air. He credits its editors with his success in obtaining the Min- nesota position after a long job search. At Minnesota, where a single astronomer was then in fash- ion, he succeeclec! the binary star astronomer en c! observer

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208 BIOGRAPHICAL MEMOIRS Francis P. Leavenworth, who retiree! en c! cliec! in 1928. At some time cluring the three-year interim, the observatory en c! its 0.25-meter refracting telescope were mover! to the top of the then new physics building, a questionable im- provement in location. Neither astronomer hac! a role in this decision. While a student there, I cliscoverec! that the coordinates of the oic! site hac! continues! to be propagates! in the literature. Luyten concurred, but he may not have correctec! the error in the American Ephemeris en c! else- where, where the oic! coordinates were listec! until at least 1 980. I knew his work habits well. He user! a blink machine to align two plates taken years apart to discover the stars that mover! noticeably, en c! were therefore likely to be nearby neighbors of the Sun. This was exhausting work, en c! none of the rest of us conic! stanc! to do it for Tong. With his one goof! eye, he conic! blink for hours at a time, his persever- ance seemec! limitless. The rest of us measurer! the loca- tions of each moving star en c! several of its neighbors for positions en c! enterer! them in notebooks. In that computer- less era, we neeclec! to combine the two motion compo- nents along each of the two orthogonal axes, into a total motion en c! direction. From repeater! use, I came to know the squares of all integers from ~ to 100 from memory. Luyten was a master in teaching students to make offl,anc! estimates, always a difficult point to get across. For example, he encouragec! the memorization of the logarithms of 2, 3, and 7. From these, one can quickly derive the logarithms of any integer up to ten en c! can interpolate larger ones closely. At the completion of the information on motions in each fielcI, he wouic! assign magnitudes to the stars that hac! moved. Having none of the photometric equipment of today, he would, with an eyepiece in hand, call out the magnitudes to be recorded. He claimed that a certain image size was set at

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WILLEM JACOB LUYTEN 209 magnitude 12.7, as I recall, en c! he went on from there. He was well aware that emulsion en c! other differences pro- clucec! a consiclerable magnitude error of as much as a full magnitude. On this he wouic! cite a rule common to as- tronomers of his generation en c! all but forgotten since, that the systematic errors conic! be assumer! to be about one-fifth of the acciclental errors from all sources. (I heart! this same remark from his contemporaries Bart Bok en c! Peter van cle Kamp as well.) Until his retirement in 1967, he regularly taught intro- cluctory astronomy, as well as some acivancec! courses, at the university. His enthusiasm extenclec! to every corner of as- tronomy, as was evident in lectures en c! in conversation, I for one learner! very much from him, insicle en c! outside the classroom. He was a superb teacher, en c! he regales! the students with stories that reveaTec! a clelightfuT sense of hu- mor. After getting off a bon mot, he retainer! his typical saturnine facial expression, but the twinkle in his eyes was notes! by many. His strainer! en c! sometimes hostile approach to some of his colleagues en c! the public in general never extenclec! to students, as I well know. Typical of his gruff public manner was an item appearing in a column by "Mr. Fixit" in the Minneapolis Tribune in 1956. A woman hac! written for the identity of a brilliant star appearing in the sky. She cited her neighbor as an authority on astronomy who hac! never behelc! such a spectacle before. "I referrer! your query to Prof. Willem l. Luyten, chairman of the University of Min- nesota Department of Astronomy," Mr. Fixit repliecI. "His comment: 'If you remover! the drama en c! hooky, the planet Venus is left."' Yet, it was clear that he knew the place en c! value of humor in his lectures en c! other remarks. In response to a student in my introductory course with him, who was hav

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210 BIOGRAPHICAL MEMOIRS ing trouble visualizing a galaxy, he remarkoc! that a galaxy looks like a cow pie. Typical of his humorous gruffness was his response to a persistent telephone. He finally interruptec! a lecture in my celestial mechanics class to answer it. After a minute, he returnee! en c! grumblecI, "Some SOB has a piece of shiny steel he thinks is a meteorite." Amidst riot- ous laughter, he resumes! his lecture. His fluency in English was assurer! if a bit florid. This is evident in his popular book on astronomy The Pageant of the Stars, first publisher! in 1929, with a seconc! eclition appearing five years later. Willem Luyten became a factor in my own enthusiasm for astronomy more than once. It was he who, in the spring of 1940, pointer! out to me the five nakocI-eye planets strung along the ecliptic in the western sky at clusk. Later that year he invites! me to see Jupiter en c! Saturn through the refrac- tor. Yet, ten years afterward, when I matriculates! at the university, I still hac! no thought of astronomy as a profes- sion, en c! I took up engineering instead. After three years of a mediocre recorc! baser! squarely on a lack of interest, I consiclerec! astronomy as a career. When I approaches! him about a change of careers, he promptly saicI, "You get the hell out of engineering en c! into astronomy, where you be- long." I have never regretted taking his advice. Later, after my graduate work was completecI, I fell afoul of his wrath more than once. At issue was a group of seven F-type stars near the North Galactic Pole that simple Pois- son statistics strongly suggester! must be physically associ- ated. From spectroscopic and photometric evidence they appearec! to form a small cluster of the oIc! clisk popula- tion, similar in age to the well-known clusters M 67 en c! . . ~ NGC 188. Later known as Upgren I, this is the fourth or fifth nearest cluster to the Solar System. The evidence for physical association from proper mo- tions was marginal, with 3 to 5 of the 7 stars showing paral

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WILLEM JACOB LUYTEN 211 le! motion. Luyten's complaint was that proper motion in- formation shouIc! be paramount in the recognition of a group of stars as a cluster. He publisher! a partial refutation centerec! on this point, en c! never again cliscussec! it, en c! soon turner! his attention to correct the perceived mistakes of others. Recent raclial velocities confirm five stars as mem- bers, though no longer gravitationally bound together. More than once in his writings, Luyten quoter! Lorc! Pe- ter Wimsey, Dorothy Sayers's fictional detective, who remarkoc! in Gaudy Night that "the point about it is that the only ethical principle which has macle science possible is that the truth shall be toIc! all the time. If we clo not penalize false statements macle in error, we open up the way for false statements macle by intention." This comment became his touchstone for professional behavior, en c! in his own way he applier! it relentlessly to himself en c! to his colleagues. Couplet! with an intransigent approach towards the propri- etary rights of one who first studies a star or group of stars, it lee! to repeater! admonishments on his part of a number of clistinguishec! colleagues in en c! out of astronomy. Such actions resultec! in embittered relations en c! even total alien- ation between him en c! some of them. Most took it in stricle or responclec! in kind. But the potential for harm to the career of a younger astronomer was not always negligible. Luyten hac! a talent for alliterative broacisicles in his pub- lications. Some of his feistiest papers bore such titles en c! references to colleagues as "The Messiahs of the Missing Mass," "More Bedtime Stories from Lick," en c! "The Weistrop Watergate." They macle for very amusing reacting, but they were too clisrespectful en c! too full of negative allusions to his colleagues en c! their work to be at all times in the best interest of science, even though much in them was factually correct. In his later years, he referrer! to himself as a cur- mucigeon, an epithet bestowoc! on him at times by others.

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212 BIOGRAPHICAL MEMOIRS In this, too, a certain modicum of humor crept into his otherwise stern bearing. Although we met on several occa- sions since then, he last spoke to me at the general assem- bly of the International Astronomical Union in Patras, Greece, in 1982. While living en c! working in South Africa, Willem Luyten met en c! marries! Willemina Mieclema, it was a close mar- riage en c! laster! over sixty years until his cleath on Novem- ber ill, 1994. The Luytens hac! three chilciren, all among my neighborhood! chiTc~hooc! acquaintances. Mona Coatzee is now on the faculty of the University of Pittsburgh, Ann Dieperink was a Fulbright scholar en c! is a practicing attor- ney, and James Luyten earned a Ph.D. degree in physics at Harvarc! en c! is now an oceanographer at the Woocis Hole Oceanographic Institution in Falmouth, Massachusetts. All three are marries! to professional people en c! have families of their own. In 1939, about when I first knew him, he and Mrs. Luyten built a house only a block from my own, not far from the university campus in Minneapolis. It was the only one of an art deco style ultramoclern for the time in a neighbor- hooc! of gables, dormers, en c! pitcher! roofs. Although it appears conventional tociay, it is almost as conspicuously different from its neighbors as is Frank Lloyc! Wright's Guggenheim Museum in New York City. In his home, as in so much of his life, he was a nonconformist among non- conformists. He liver! in that house for the remainder of his life en c! cliec! there over half a century later. In home en c! family life, he lee! a remarkably stable existence. He was a man of many interests in aciclition to astronomy. His well-known knowledge of wines, especially those of Burgundy, was occasional! by many annual visits to that region of France for tasting en c! other celebration. Willem Luyten maintainer! his research activity cluring

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WILLEM JACOB LUYTEN 213 the years after his retirement. He remainec! steadfast to his principles, but principle is best tempered at times with com- passion en c! forgiveness. This he too selclom realizer! in the course of his relations with other astronomers. Yet, however he may come to be jucigec! by those who knew him, he remains almost universally respected as the great imagina- tive en c! cleclicatec! scholar en c! scientist he was. They are likely to agree with Shakespeare that "he was a man, take him for all in all, I shall not look upon his like again." MY PRIMARY SOURCE for this memoir was Willem Luyten's own autobi- ography (1987~. Secondary sources were a paper by Helmut Abt in Publ. Astron. Soc. Pac. (80~19681:247-251) written upon Luyten's award of the Bruce Medal, and obituaries by Dorrit Hoffleit in 7. Am. Assoc. Variable Star Obs. (24~19961:43-49) end bymyselfinPubl.Astron. Soc. Pac. (107~19951:603-605) and Q. 7. Roy. Astron. Soc. (37~19961: 453-456~. In addition, I relied on many memories I have of Willem and his family over nearly five decades and some correspondence with him. I have included only the anecdotes that I witnessed or verified from independent evidence.

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214 BIOGRAPHICAL MEMOIRS SELECTED BIBLIOGRAPHY 1922 Observations of variable stars. Ann. Obs. Leiden 13: 1-64. On the relation of mean parallax to proper motion, apparent mag- nitude, and spectrum. Lick Obs. Bull. 336:135-40. 1923 On the form of the distribution law of stellar velocities. Proc. Natl. A cad. Sci. U.S.A. 9:181. A study of the nearby stars. Hare. Obs. Ann. 85:73-115. Note on the possible relation between the intensity of the sodium lines and absolute magnitude. Publ. Astron. Soc. Pac. 35:175. On the mean absolute magnitudes of the K and M giants and the synthetic errors in trogonometric parallaxes. Proc. Natl. A cad. Sci. U.S.A. 9:317-23. 1925 With E. B. Wilson. The population of New York City and its envi- rons. Proc. Natl. Acad. Sci. U.S.A. 11:137. 1926 The properties of stars in the solar neighborhood. Sci. Mon. 32:494. 1930 On the systematic and accidental errors of modern trigonometric parallaxes. Proc. Natl. Acad. Sci. U.S.A. 16:464. 1934 Report on the state of the Bruce Proper Motion Survey. Publ. Astron. Soc. Pac. 46:194. 1938 On the distribution of absolute magnitudes in the vicinity of the Sun. Mon. Not. Roy. Astron. Soc. 98:677. 1942 On the origin of the Solar System. Astrophys. f. 96:482.

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WILLEM JACOB LUYTEN 1945 215 A proposal for the classification of white dwarf spectra. Astrophys. I. 101:131. 1952 The spectra and luminosities of white dwarfs. Astrophys. I. 116:283. 1955 A Catalogue of 1849 Stars With Motions Exceeding 0".5 Annually. Min- neapolis: Lund Press. 1956 White dwarfs and degenerate stars. Vistas in Astronomy, p. 1048. 1957 A Catalogue of 9867 Stars in the Southern Hemisphere With Motions Larger Than 0".2. Minneapolis: Lund Press. 1958 The Hyades: A search for faint blue stars. Faint Blue Stars X. 1961 A Catalogue of 7127 Stars in the Northern Hemisphere With Motions Larger Than O ". 2. Minneapolis: Lund Press. 1963 Bruce Proper Motion Survey General Catalogue: The Motions of 94,000 Stars. Proper Motion Survey With the 48-Inch Schmidt Telescope. I. Or- ganization and Purpose. Proper Motion Survey I. 1965 The luminosities of faint blue stars. In Proceedings of the First Confer- ence on Faint Blue Stars, ed. pp. 66-72. Saint Paul: Hill Founda- tion. 1967 A comparison between the Bruce, Palomar Schmidt, and Lowell proper motions. Pub. Minn. 3:20.

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216 BIOGRAPHICAL MEMOIRS 1971 Performance of an automated computerized plate scanner. Proc. Natl. A cad. Sci. U.S.A. 68:513. 1974 The Weistrop Watergate. Proper Motion Survey XXXVIII. 1976 On the alleged plethora of nearby M dwarfs with little or no proper motion. Proper Motion Survey XLVI. LHS catalogue: Proper motions for 3583 stars larger than 0".5 an- nually. Univ. Minn. Publ. 1980 NLTT catalogue: Proper motions larger than 0".18 annually for 58,700 stars. 1981 More bedtime stories from Lick. Proper Motion Survey LVI. 1986 Data and proper motions for 250,000 faint stars on magnetic tape. 1987 My First 72 Years of Astronomical Research: Reminiscences of an Astro- nomical Curmudgeon, Revealing the Presence of Human Nature in Sci- ence. Minneapolis: W. J. Luyten.

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