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Rochester Institute of Technology RIT Scholar Works Articles 6-2002 Speckle observations of binary stars with the WIYN Telescope. II. Relative astrometry measures during 1998-2000 Elliott .P Horch Rochester Institute of Technology Sarah Robinson Rochester Institute of Technology Reed D. Meyer Yale University William F. van Altena Yale University Zoran Ninkov Rochester Institute of Technology See next page for additional authors Follow this and additional works at: http://scholarworks.rit.edu/article Recommended Citation Elliott .P Horch et al 2002 AJ 123 3442 https://doi.org/10.1086/340360 This Article is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Articles by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. Authors Elliott .P Horch, Sarah Robinson, Reed D. Meyer, William F. van Altena, Zoran Ninkov, and Albert Piterman This article is available at RIT Scholar Works: http://scholarworks.rit.edu/article/802 The Astronomical Journal, 123:3442–3459, 2002 June # 2002. The American Astronomical Society. All rights reserved. Printed in U.S.A. SPECKLE OBSERVATIONS OF BINARY STARS WITH THE WIYN TELESCOPE. II. RELATIVE ASTROMETRY MEASURES DURING 1998–20001 Elliott P. Horch2 and Sarah E. Robinson2 Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623-5604; [email protected], [email protected] Reed D. Meyer2 and William F. van Altena2 Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101; [email protected], [email protected] and Zoran Ninkov and Albert Piterman2 Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623-5604; [email protected], [email protected] Received 2002 January 4; accepted 2002 February 19 ABSTRACT Five hundred twelve relative astrometry measures are presented for 253 double stars, including 53 double stars discovered by Hipparcos. In 15 cases, relative astrometry is reported for the first time for newly con- firmed pairs. In addition, 20 high-quality nondetections of companions are reported for stars suspected of being nonsingle by Hipparcos. Observations were taken using a fast-readout CCD camera system at the WIYN 3.5 m telescope at Kitt Peak, Arizona. In comparing these measures with ephemeris predictions for binary stars with very well known orbits, we find that the measurement precision is better than 3 mas in sepa- ration and 1 in position angle per individual observation. Measurement precision and detection capabilities are fully discussed, and confirmed orbital motion is reported in four cases of the Hipparcos double star discoveries. Key words: astrometry — binaries: visual — techniques: interferometric 1. INTRODUCTION Hipparcos distances (Martin et al. 1998; So¨derhjelm 1999), the leading source of uncertainty in most cases remains the Binary stars continue to be an important tool in stellar parallax. Looking toward the future, three major space as- astronomy because of the fact that they represent the only trometry missions have been planned for the next decade: way currently accepted for determinations of stellar masses the Space Interferometry Mission, the European Galactic other than that of the Sun. Up to the present time, however, Census Project (GAIA), and the Full-Sky Astrometric Map- few masses precise enough to provide detailed comparisons ping Explorer. (As of this writing, the future of FAME with stellar structure and evolution models have been forth- appears uncertain.) Because of the improved sensitivities of coming. Indeed, even the basic empirical relationship these systems, it is likely that parallax uncertainties of most between mass and luminosity remains poorly determined, nearby stars will be no more than 50 las after the comple- particularly in the important mass range of 1.0 to 0.2 M (Henry & McCarthy 1993; Henry et al. 1999). Most of the tion of these projects. This is, finally, small enough that the distance measure will not overwhelm other sources of uncer- stars contributing to this portion of the empirical mass- tainty in the overall error budget for the masses of many luminosity relation (MLR) are classic visual and speckle important stars on the lower MLR. binaries. Often, the main limiting factor in the determina- Because of the expected improvements in the distances to tion of masses is not the orbital information but rather the stars within a few hundred parsecs of the Sun over the next system parallax, which sets the absolute scale of the visual decade, reducing uncertainties in orbital parameters and orbit. magnitude differences in order to take the highest possible The publication of the Hipparcos Catalogue (ESA 1997) benefit from improved distances is of substantial impor- has been a major step forward in the determination of the tance. In addition, Hipparcos discovered over 3400 previ- distances to nearby stars. With parallax uncertainties in the range of 1 to 2 mas, these values are more precise than ously undetected double stars and flagged thousands of others as ‘‘ suspected nonsingle ’’ stars (i.e., those with an ground-based parallax results by a factor of 2 to 5 in most ‘‘ S ’’ flag in column H61 of the Hipparcos Catalogue entry). cases. Nonetheless, even after revising the MLR with post- The nearest of these objects are potentially important as future MLR stars, if gravitational motion can be confirmed and the orbital parameters determined with sufficient preci- 1 The WIYN Observatory is a joint facility of the University of sion. We therefore began a long-term program of speckle Wisconsin–Madison, Indiana University, Yale University, and the observations from the WIYN 3.5 m telescope in 1997. One National Optical Astronomy Observatory. of the main goals of the program is to provide high-quality 2 Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of relative astrometry measures of stars of potential impor- Universities for Research in Astronomy, Inc., under cooperative agreement tance to the MLR, both of previously known binaries and with the National Science Foundation. of the Hipparcos discoveries. In addition, we seek to observe 3442 SPECKLE OBSERVATIONS OF BINARY STARS. II. 3443 the Hipparcos suspected nonsingle stars, in order to resolve sis is resolved with a basic reconstructed image computed any potential pairs lying just below the detection threshold using two orthogonal near-axis subplanes of the object of the satellite. bispectrum. The first paper in this series (Horch et al. 1999, hereafter The speckle optics package developed at Stanford Uni- Paper I) presented measures obtained at WIYN with both a versity by J. Morgan and J. G. Timothy has been used for multianode microchannel array (MAMA) detector system all observations here. This system magnifies the image to the and a fast-readout CCD during 1997. In this paper, we appropriate scale for speckle observations, contains narrow present results obtained during the period 1998 to 2000. In bandpass filters necessary for good speckle contrast, and this time interval, only the CCD system was used. Only rela- uses Risley prisms for atmospheric dispersion compensa- tive astrometry is presented here; an analysis of the relative tion. As noted in Paper I, the lenses within the system gener- photometry of these speckle measures is underway and will ate a measurable amount of optical field angle distortion be reported in a future publication in this series. Recent (OFAD; a change in the pixel scale as a function of position work at two small telescopes has indicated that photometric relative to the optical axis), which in turn affects the astrom- information is retained in the CCD-based speckle technique etry if not properly corrected. By mounting a slit mask to (Horch, Ninkov, & Franz 2001), and if confirmed in WIYN the tertiary baffle support structure of the telescope, we data, this would provide a basis for determining luminosi- measure the pixel scale using the standard technique of ties and colors of the components of binary star systems in observing the fringe spacing that results when one observes the course of normal speckle observations. Also, in this a bright unresolved star through the mask. We also account paper we focus only on known binaries and the Hipparcos for the color of the target star in the calculation of the suspected and discovered doubles. WIYN results of a survey expected fringe spacing, as described in Paper I. However, project of F and G dwarfs carried out over the same time in order to characterize the OFAD, we place the fringe pat- period in collaboration with the US Naval Observatory tern at various locations in the field of view, thereby taking (USNO) will be discussed elsewhere. several measures of the local pixel scale over the entire field once per run. In addition, we have also monitored the posi- tion of the optical axis on each run, as judged from flat-field 2. OBSERVATIONS AND DATA REDUCTION images. On the large CCD chip that we use, there is consid- The observational technique is described fully in Paper I. erable vignetting, and we consider the center of that pattern With the CCD, we typically take 700 to 1000, 50 ms frames to be coincident with the optical axis. By accounting for of a target object, where for all observations discussed here these slight shifts in the location of the optical center and the speckle-strip method of Horch, Ninkov, & Slawson then measuring the pixel scale from mask observations as a (1997) is employed. The CCD chip has been the same since function of distance from the optical center, we obtain the the inception of the program; it is a front-illuminated plot shown in Figure 1. The curve drawn is the average best- Kodak device with 2038 Â 2048 pixel format and read noise fit quadratic to the pixel scale as a function of distance from of approximately 10 eÀ.

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