23 was was discovered. This was visual visual 1 Argentina RESUMEN ABSTRACT Virpi S. Niemela 1. 1. A SHORT HISTORY Ori by Huygens 11, 23-26 (2001) 6 STARS: BINARIES — STARS: EARLY TYPE

Se Se presenta una corta historia de estrellas binarias desde los primeros des­ A short history of binary stars from the first discoveries is presented. Exam- Cen by Farther Richaud Cru by Farther Fontenay Vir by Bradley & Pound Ari by Hooke a a 7 7 Key Words: ples ples of currently known binary Systems with and mass components are discussed. of highest temperature cubrimientos. Se discuten ejemplos actualmente conocidos de nentes sistemas conde temperaturacompo­ y masas mas altas. A SHORT HISTORY AND OTHER STORIES OF BINARY STARS [email protected]. ar • • in 1719, Castor by Bradley & Pound These discoveries were considered as mere curiosities of accidental fine of sight coincidences. Until Isaac Thecatalogue first of bybinary C. published containing stars, in Mayer, who1781 systems, was speculated80 However, in the opinión ofthe owner ofthe then largest telescope in the world, Wilhelm Herschel, evidence It seems that W. Herschel in principie did not believe that binary stars may be physical systems. He • • in 1664, • in 1685, • in 1689, • in 1718, • • in 1656, three components of Soon after the construction of the first telescopes, also the first Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentinaand CIC, 1 structure of the Universe, a passion still driving much of the astronomical research with the currently largest revolving round larger ones” . He decided to examine “every star in the heavens” . wanted to observe binary stars to determine differential parallaxes W. in order Herchel’s to astronomical find the passion, distanees to and the obsession, stars. was to discover with his largest telescope of telescopesthe world of thethe world today. Newton grew older and began publishing theories. was completely lacking for this speculation, since nobody had ever observed such motions of “small suns that “these stars could be small suns revolving around larger suns” (as predicted by I. Newton). Mizar (£ U Ma) discovered by the oíd). Italian astronomer During the J. 70 years B. following the Ricciolidiscovery of ~the namely: first visual binary star, 1650 only (when a Isaac few more Newton were resolved, was 7 years RevMexAA (Serie de Conferencias),

K£Z'' ' II ''DVXWHIOOS Finally he published the mean from the periodic light variations when one , , then he measured the relative positions of Mensurae Micrometricae. Catalogus Catalogus Novus eclipsing eclipsing binaries from the periodic movements of their spectral lines; or iftheir Positiones Mediae. spectroscopic binaries http: //ar ies. usno. navy. mil/ad_home/wds/wds. ht lm ht mil/ad_home/wds/wds. navy. usno. ies. //ar http: A catalogue of orbital elements of spectroscopic binaries is presently mantained by astronomers at the The first catalogue ofspectroscopic binaries was published only years after the 15 discovery ofthe first such The first eclipsing binary, Algol, had been discovered by Goodericke in 1782. In November, 1889, H. C. The first spectroscopic binary system was discovered by E. C. Pickering in August, 1889, and remarkably Catalogues of the orbital elements of visual binaries can now be found at the website: When the components of a binary star are very cióse, they cannot be observed as visual binaries. These At the end of 1800 and beginning of 1900, the astronomers worldwide were competing with each other in In In 1839 Wilhelm Struve was invited to build the new Russian Imperial Observatory at Pulkovo, where he W. Struve’s aim towas examine binary stars as physical systems. He set to work with systematic efficiency. The first equatorial telescope with a driving dock used in observations of binary stars was the Fraunhofer With the coming in Europe of new telescope technologies incorporating equatorial mountings and driving Wilhelm Herschel’s son, John, continued his farther’s work after 1816. John Herschel first worked in In In 1803 W. Herschel published a demonstration, based on his measurements of binary stars, that some In In W. 1797 published Herschel a revisión of all his work with binary stars, revealing that changes had taken W. presented Herschel his first catalogue of binary269 in stars 1782. Two later, years he presented a second Dominion Astrophysical Observatory, Victoria, Cañada (cf. Batten et al. 1989). system, system, and it contained already 140 stars. it it was one of the components of the first visual binary, namely Mizar. Vogel found that Algol was also a spectroscopic binary. orbital plañe is sufficiently cióse to the visual, as component hides the other. binaries binaries can be detected as discovered the with the largest redshift. acquired the then largest refractor of the world, a telescope with equatorial mounting and a lens of 15 inches who had discovered more binary stars. Much in the same manner as today the competing involves who has of aperture. The study of binary systems with this instrument was performed by Wilhelm’s son, Otto Struve. positions of the stars in 1852 as fact he observed stars 120000 in 129 nights. First First he made a catalogue, published in 1827 as the components, and published the results in 1837 as refractor acquired by Wilhelm telescope, Struve for and Tartu four Observatory. days observations. after Struve receiving Struve said was that the very the telescope telescope enthusiastic about was so in easy to his 1824, use new that he he could had examine already 400 stars per mounted hour! it In and begun his his his telescope again. astronomy in his private observatory. Together, John Herschel and James South produced a catalogue of 380 mechanisms, John Herschel decided to observe the largely father’s unknown telescopes sky. Southern and tosailed In South Africa. 1833 he packed He dedicated 3 of the next his four in years observing sky, measuring the clusters, whole nebulae Southern and over 2100 binary stars. In he 1838 returned to England and never opened cooperation with his friend, James South, who having binary married stars. a rich woman, could dedicate his time to systems systems should be physical of Systems mutual attraction. the universality of This Newton’s is probably law of the gravitational first observational attraccion. evidenceof ofthe And components it is quite in remarkable visual how the binary tinywithout motions systems a driving could mechanism. be observed with an alt-azimuth mounted huge telescope catalogue with 434 additional binary stars. He continued observing with the skillfull aid of his sister Caroline. changes changes could not be due to differential parallaxes. 24 24 place in the relative positions of the components observed during many years. He admitted that the observed BINARY STARS

K£Z'' ' II ''DVXWHIOOS However, we should keep in mind that HD 92740 HD 93205 NIEMELA 25 2.2. 2.2. 2.1. 2.1. Binaries in the Magellanic Clouds 2.3. 2.3. 2. 2. OTHER STORIES OF BINARY STARS ' Empirical Stellar Mass-Luminosity Relation. The first O type spectroscopic binary discovered in the LMC, was Sk—67°105 (Niemela & Morrell 1986). The spectroscopic binary with the most massive component known today, is HD 92740, a neighbour of It It tointeresting is note, that the most luminous observed stars the in core of Dor30 nébula in our neighbour A new of HD 93205 based on high resolution digital spectra obtained at Complejo Astronómico El In In our Galaxy the spectroscopic binary system which harbours the component of earliest spectral type is One of the most important results of the many years spent by so many astronomers securing observations What do we know about the ofmasses highest temperature early type stars? The binary stars, both visual and spectroscopic, our are fundamental source ofinformación about the stellar 2operated under agreement between CONICET, SeCyT, and the Universities of La Plata, Córdoba and San Juan, Argentina. (Massey & Hunter 1998). 1979). 1979). A new orbital study recently published by Rauw et al. (1996), finds a mass of 72 M0 for the WN type This system, as 04f-b06V,classified perioda has of 3.3 days. Therefore, strong interaction oneffeets the binary Corti et al. 1999). A somewhat different mass ratio than in previous studies is found for the components, Such and valué is less than predicted by the stellar evolutionary models for stars as hot as spectral type 03, but components are expected, 105 probably thus Sk—67° is unreliable for comparisonsingle stars. with evolutionary models of assuming assuming that the 08 V star has a normal mass of 25 M0 , results in a mass of 60 M0 for the 0 3 V component. component. The emission line spectrum ofcomponent HD 92740 was ineludes born strong H near the lines, and stellar high-mass may limit. indicate that the WN HD HD 93205, discovered and classified as 03VH-08V by Conti & Walborn Unfortunately, light (1976). variations have not This been binary found undetermined. belongs for this to binary, thus the the inclination of the orbit remains galaxy, galaxy, the Large Magellanic Cloud (LMC), have spectra to similar that of HD 92740. stars, The when luminosities ofthese compared with the stellar evolutionary models, correspond to stars more massive than 100 M0 Leoncito (CASLEO2), in San Juan, Argentina, has been recently determined (cf. Morrell & Niemela 1998; would be compatible with the main sequence models uncertainties of for spectraljust stars classification one for spectral components class later. of double This lined is spectroscopic within the binaries. HD 93205 in the Car OBItype spectrum assotiation. and a period HD of about 92740 is 80 days, a double the WN7 lined component spectroscopic being the binary more with massive one WN7 (cf. + Niemela OB very young open cluster Tr 16 in the Car OBI association, and has an elliptical orbit with a period of 6 days. about dozens of stars more massive than dozens of stars which have 100 luminosities as high M0thoseas predicted by in some evolutionarystellar e.g., models the for more stars Magellanic massive than Clouds, 100 this M0 means that . there Different mass-luminosity are relations may Their opérate high in the luminosity domain of could high-mass metallicities. stars, and be in environs of as different well due to multiplicity, as often happens. despite of two hundred years of observations, this relation is only known for stars up to about 25 M0 in our own Galaxy (e.g., Andersen 1991), and extrapolated to higher masses, and to other . When you read masses. masses. In particular those spectroscopic binaries which also mass are eclipsing estimates to systems, are bethe principalcompared source withof numerical models of . of binary systems, is the

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REFERENCES ..and the culprits are ... 2.4. 2.4. Car, HD 5980) r¡ Hunter, D. 1998, ApJ, 493, 180 S¿ ...it must be a binary... • • etc. And when the observations disagree with models • • showing strange atmospheres (Am stars) • • pouring non thermal radiation by their colliding winds (cf. Niemela et al. 1998) • • explosive manners (e.g., Novae) • polluting the space with X-rays • producing eruptions (e.g., But much work is ahead. The evolution of binary stars is more complex than that of single stars. When a component of a binary Baptista R. &; Did Fernandes, Santa Catarina: Univ. Fed. Santa Catarina, Brazil, 66 The microlensing searches in the Magellanic Clouds have detected large amounts of eclipsing binaries. Rauw, G., Vreux, J.-M., Gosset, E., Hutsemekers, D., Magain, P., Rochowicz, K. 1996, A& A, 306, 771 Conti, R S., & Walborn, N. R. 1976, ApJ, 207, 502 Niemela, V. S., Shara, M. M., Wallace, D. J., Zurek, D. R., Moffat, A. F. J. 1998, AJ, 115, 2047 Corti, M ., Albacete, F., Morrell, N., Niemela, V. 1999, Morrell, RevMexAA N., & Niemela, Conf. V. Series 8, 1998, 137 in Science with Gemini, a South American Niemela, Perspective, V. ed. B. S. Barbuy, 1979, E. in Mass Lapsset, Loss Niemela, and R. Evolution V. of O S., type Stars, Morrell, ed. N. P. S. I. Conti C. 1986, &; de Loore, ApJ, Dordrecht: 310, Reidel, 715 291 Massey, R , Andersen, J. 1991, A& AR, Batten, 3, 91 A. H., Fletcher, J. M ., MacCarthy, D. G. 1989, Publ. DAO Victoria, 17, 1 Therefore, whenever a star has been observed to Among behave other oddly, things, it binary is suspect stars are blamed of for belonging to a binary system. System System begins to evolve, complicated massive end of interactions the early betweentype stars, the their powerful components stellar winds whirl around take and collide place. with the neighbours. In addition, at the 26 26 BINARY STARS The coming into operation of larger telescopes in the Southern hemisphere in the near future, e.g., Gemini, will will hopefully allow the determination of empiricalspectroscopic Mass-Luminosity relation for our for nearest these neighbour eclipsing galaxies. binaries, and finally find an

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