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New Wide Common Proper Motion Binaries Vol. 6 No. 1 January 1, 2010 Journal of Double Star Observations Page 30 New Wide Common Proper Motion Binaries Rafael Benavides1,2, Francisco Rica2,3, Esteban Reina4, Julio Castellanos5, Ramón Naves6, Luis Lahuerta7, Salvador Lahuerta7 1. Astronomical Society of Córdoba, Observatory of Posadas, MPC-IAU Code J53, C/.Gaitán nº 20, 1º, 14730 Posadas (Spain) 2. Double Star Section of Liga Iberoamericana de Astronomía (LIADA), Avda. Almirante Guillermo Brown No. 4998, 3000 Santa Fe (Argentina) 3. Astronomical Society of Mérida, C/José Ruíz Azorín, 14, 4º D, 06800 Mérida (Spain) 4. Plza. Mare de Dèu de Montserrat, 1 Etlo 2ªB, 08901 L'Hospitalet de Llobregat (Spain) 5. 0bservatory with MPC-IAU Code 939, Av. Primado Reig 183, 46020 Valencia (Spain) 6. Observatory of Montcabrer, MPC-IAU Code 213, C/Jaume Balmes, 24, 08348 Cabrils (Spain) 7. G.E.O.D.A., Observatorio Manises, MPC-IAU Code J98, C/ Mayor, 111-4, 46940 Manises (Spain) Abstract: In this work we report the discovery of 150 new double stars of which 142 are wide common proper motion stellar systems. In addition to this, we report the study of 23 recently catalogued wide common proper motion binaries discovered by other observers. Spectral types, photometric distances, kinematics and ages were determined from data ob- tained consulting the literature. Several criteria were used to determine the nature of each double star. Orbital periods and the semimajor axes were calculated. they are good sensors to detect unknown mass concen- 1. Introduction trations that they may encounter along their galactic For several years double-star amateurs have con- trajectories. So, wide binary star systems have became tributed to the astronomical community with interest- objects of considerable theoretical and observational ing works (see Introduction section in Rica (2008)). interest. They are relevant to the understanding of Recently Rafael Caballero (2009), a spanish amateur, the processes of formation and dynamical evolution of has published in the JDSO an article reporting about the Galaxy. Thus, the present-day distribution of wide 110 new uncataloged and wide common proper motion binaries can provide information about the disruption binaries. process as well as binary formation. Study of wide bi- One more example is the work that we present. In naries have largely concentrated on the calculation of this work we report the study of 173 wide, common dissolution times since the main effect of encounters is proper motion stellar systems of which 150 are new to cause such weakly bound pairs to break up. Profes- double stars. The remaining 23 were discovered by sionals have published many papers studying suc ob- other observers and recently cataloged. The new dou- jects: (Retterer & King (1982), Dommanget (1984), ble stars were discovered by Rafael Benavides inspect- Lathan, Tonry, Bahcall & Soniera (1984), Halbwachs ing visually the Guide 8.0 software and using the (1988), Close & Richer (1990), Lathan, Abt et al. proper motion line showed by this software to detect (1991), Poveda & Allen (2004), Sesar, Ivezić & Jurić common proper motion pairs. It was a great surprise (2008)) to see that many binaries are discovered by this We finally would like cite to Dommanget (1984): method. Wide binaries of common proper motion are com- "Wide pairs and wide multiple systems have been too posed of stars with large separation that results in much neglected during many years by visual double star orbital periods ranging from a few thousand to mil- astronomers with the argument that only close visual pairs lions of years. Because of their small binding energies, (short periods) may lead to mass-determination in a rela- tively short time interval. But mass-determination should Vol. 6 No. 1 January 1, 2010 Journal of Double Star Observations Page 31 New Wide Common Proper Motion Binaries not be considered as the only interest of double star astron- Photometry in B, V and I bands came from Hippar- omy, even if it is of a fundamental nature. cos (ESA 1997) and Tycho-2 (Hog et al. 2000) catalogs. Today, it appears that researches on the origin and the Infrared J, H and K photometry came from Two Mi- evolution of the wide systems are urgently wanted, not only cron All Sky Catalogue (Cutri 2000), hereafter 2MASS. for the understanding of the evolution of the stellar medium, Proper motion came from Tycho-2, UCAC-2 (Zacharias but also for a better knowledge of galactic dynamics". et al. 2004) and USNO-B1.0 (Monet et al. 2003) cata- logs. Tycho-2 was chosen because the Hipparcos proper In section 2, we explain how the binaries were motions could be affected by Keplerian motion due to found; sections 3-8 describe the astrophysical study its smaller baseline. Historical relative astrometric (consulting astronomical literature, spectral type esti- data were kindly supplied by Brian Mason from The mate, distance estimation, tangential velocity, stellar United States Naval Observatory (hereafter USNO). masses, age and stellar population). In section 9 we Spectral types, radial velocity and other astrophysical comment in detail on the criteria used to classify the data were taken from several sources from CDS web double stars as optical or physical. In section 10 we page. explain how we obtained the semimajor axis and or- bital periods; 11 the astrometric measures are ana- 4. Spectral Types and Luminosity Class lysed. The study for same binaries stars are in section Estimates 12. Spectral types and luminosity classes were ob- 2. Searching for New Binaries tained from photometric and kinematical data. Several The search for new wide common proper motion tables which relate photometric colours with spectral binaries was carried out by Rafael Benavides in 2005, types were used (Allen 1973, Bessell & Brett 1988). inspecting visually the sky using the Guide 8.0 soft- A computer program was designed to transform -23 -1 ware of project Pluto. This software allows display the BVIJHK photometric data to Jy (1 Jy = 10 erg * sec 2 -1 Tycho-2 (Hog et al. 2000) and Hipparcos (ESA 1997) * cm * Hz ) which were plotted against wavelength proper motion vector and so the identification of com- (in Angstroms). This plot shows the spectral energy mon proper motion binaries is straightforward. distribution which is compared automatically with the Benavides found 141 uncataloged binaries. Literature empirical spectral energy distribution deduced from was consulted carefully to confirm that the binaries are Bessell & Brett (1988) and Zombeck (1990). The com- not cataloged. Since the time that these binaries were puter program gives the spectral type for the best fit. found to the publish date of this article, some binaries The luminosity classes are determined by means of were reported by others double star observers and infrared two color diagram (Bessell & Brett 1988) and listed in the Washington Double Star Catalog (Mason, mainly by means of reduced proper motion diagrams Wycoff & Hartkopf 2003), hereafter WDS. (Jones 1972; Salim 2002; Nelson 2003). Reduced proper So finally we report the discoveries of 148 new bi- motion diagrams were very useful to distinguish dwarf naries. stars from giants, subdwarfs or white dwarfs. Photometric data, spectral types, photometric dis- In a preliminary study (Rica 2005) we compared tances, kinematical data and ages were determined our spectral types and luminosity classes for 19 compo- from data obtained consulting the literature. Several nents (13 dwarf stars and 6 normal giants) with spec- criteria were used to determine the nature of each dou- tral types and luminosity classes obtained by profes- ble star. Values for the orbital periods and the semi- sionals and published in the astronomical literature. axis major were calculated. These components are listed in Hipparcos, Tycho-2 and 2MASS catalogues so the BVIJHK photometric data 3. Consulting the Astronomical Litera- and proper motions are known. The mean difference ture was 0.5 spectral subclasses and the luminosity classes The astronomical literature was consulted in order were estimated correctly for the 19 components. to obtain photometric, astrometric and kinematical 5. Distance Estimation data. Aladin, VizieR, Simbad (Wenger et al. 2003) and The absolute magnitudes were calculated using the the “services abstract” tools were used from the web- tables published by Zombeck (1990) and Henry et al. site of Centre de Dones Astronomiques de Strasburg (1997) who cite a RMS of 0.43 magnitudes for their ab- (CDS), maintained by the Strasburg Observatory, and solute magnitudes. the Astrophysical Data Services (ADS) maintained by When the object is located on or near the galactic the NASA. Vol. 6 No. 1 January 1, 2010 Journal of Double Star Observations Page 32 New Wide Common Proper Motion Binaries plane, it is important to determine the interstellar ab- was of 20 % (in excellent agreement with the 18 % er- sorption and correct the astrophysical data. Maps of ror estimate of Herny et al. (1997)). For BVD 148 we Burtein & Heiles (1982) and Schlegel, Finkbeiner & obtained the larger error. See discussion for BVD 148 Davis (1998) were used. The obtained values were in section 13. scaled to the initial distance using the cosecant law of van Herk (1965). 6. Tangential Velocities If the star is located near the galactic plane (|b| < From the proper motion and the distance of a star, 10 - 15º) then the interstellar map of Paresce (1984) the calculation of the tangential velocity is straightfor- was used if the star is located nearer than 250 pc. If ward. This is the projected motion of the star over the the star is located at a distance greater than 250 pc plane of the sky in km*s-1 and was calculated using the then the catalog of Neckel & Klare (1980) is used plot- followed expression: ting the stars in a reddening-distance graphic and us- ing a logarithmic fit.
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