CCD SPECKLE OBSERVATIONS OF BINARY STARS FROM THE SOUTHERN HEMISPHERE. IV. MEASURES DURING 2001

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1 The Astronomical Journal, 131: , 2006 June # The American Astronomical Society. All rights reserved. Printed in U.S.A. A CCD SPECKLE OBSERVATIONS OF BINARY STARS FROM THE SOUTHERN HEMISPHERE. IV. MEASURES DURING 2001 Elliott P. Horch, 1 Brian J. Baptista, and Daniel R. Veillette 2 Department of Physics, University of Massachusetts, Dartmouth, 285 Old Westport Road, North Dartmouth, MA ; ehorch@umassd.edu, u_bbaptista@umassd.edu, u_dveillette@umassd.edu and Otto G. Franz 1 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001; otto.franz@lowell.edu Received 2005 December 27; accepted 2006 February 10 ABSTRACT We present 549 observations of 181 primarily southern binary stars. Of these, 32 are high-quality nondetections, meaning that, if binary, the system had a separation below the diffraction limit at the time of the observation, and relative astrometry is presented for the remaining 517 observations. In addition, a magnitude difference measure is reported in 312 cases in which the observation was judged to be of sufficient quality to have little decorrelation of the speckle pattern of the secondary relative to the primary star. These data were obtained from speckle observations taken at the Lowell-Tololo 0.6 m telescope at Cerro Tololo Inter-American Observatory using a fast-readout CCD detector during 2001 November. Results from an astrometric measurement precision study indicate that the measures have typical uncertainties of 12:2 1:4 mas in separation and 1N28 0N21 in position angle with little systematic error. The magnitude differences presented show good agreement with values in the Hipparcos catalog where comparisons can be made. Their uncertainties are also characterized; they show a typical value of 0.18 mag per 2 minute observation. Four systems of particular interest are discussed. Key words: astrometry binaries: visual techniques: high angular resolution techniques: interferometric techniques: photometric Online material: machine-readable table 1 Visiting Astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory. 2 Current address: 115 Heritage Drive, Waterbury, CT 06708; danielv@ freeshell.org INTRODUCTION Since the mid-1970s speckle observations have dramatically improved our knowledge of the orbital motion of many binary stars. There are now well over 100 orbits that have been determined or refined with the inclusion of speckle data spanning a significant amount of time compared with the orbital period, many of which are due to the series of papers by W. I. Hartkopf, H. A. McAlister, B. D. Mason, and their collaborators (e.g., Mason et al and references therein). Still, these systems are generally north of the celestial equator, even though there is an excellent tradition of double star observing programs in the Southern Hemisphere, including the work of W. S. Finsen, W. H. van den Bos, and others. Of course, some investigators have done speckle work in the Southern Hemisphere, such as H. A. McAlister, W. I. Hartkopf, and their collaborators (McAlister et al. 1990; Hartkopf et al. 1996b) and the Yale San Juan collaboration (Horch et al and references therein), but the number of measures still lags well behind that obtained from the observatories in the Northern Hemisphere. The results from Hipparcos have also made a significant impact on binary star astronomy. In particular, the satellite determined position angles and separations to high precision for many wellknown systems and also discovered some 3400 previously unknown components whose orbital status remains unclear in all but a few cases. As one would expect, approximately half of these systems lie in the Southern Hemisphere, and roughly onethirdaresouthof ¼ 30 and therefore virtually inaccessible to northern speckle observers. The Hipparcos catalog (Perryman et al. 1997) has already provided parallaxes to these, as well as well-known southern systems, meaning that mass information is at hand if sustained, high-precision differential astrometry can be obtained to determine the orbital elements in each case. When making mass determinations, care should be taken in the interpretation of the parallax measurements for close binaries, as they can be substantially affected by both color and orbital motion in blended images. Nonetheless, the Hipparcos results represent a significant opportunity for the binary star observer. Furthermore, comparisons with stellar structure and evolution calculations could be made if, in addition to the astrometry, reliable differential photometry were obtained. With these things in mind, one of us (E. P. H.) first used a 2033 ; 2048 pixel fast-readout CCD to collect speckle images from the Las Campanas Observatory in Chile using the University of Toronto 0.6 m telescope in 1997 (Horch et al. 1997, hereafter Paper I). (That telescope has since been moved to the Complejo Astronómico El Leoncito, the site of the Argentine National Observatory, near Barreal, Argentina.) That work showed that high-quality speckle observing could be done with the instrument-telescope combination. In 1999 two of us (E. P. H. and O. G. F.) observed with the same instrumentation on the Lowell-Tololo 0.6 m telescope at Cerro Tololo Inter-American Observatory (CTIO), producing 280 position angle and separation measures (Horch et al. 2000, hereafter Paper II). We have also studied the differential photometry obtained from both the Las Campanas and the 1999 CTIO runs (Horch et al. 2001, hereafter Paper III) and in many cases found this reliable enough to publish based on comparisons with Hipparcos data

2 SOUTHERN BINARY STARS. IV Fig. 1. Histograms of the seeing measured from point-source calibration objects used to analyze the objects presented in Table 1. The lighter histogram is that of all observations taken, while the darker histogram contains only observations listed in Table 1. We adopt the same seeing cutoff for inclusion in the table as in Paper II, 2B3. Only observations with seeing values below this value and fulfilling the criteria for high-quality astrometry mentioned in the text appear in Table 1. and studies using adaptive optics. In the present work we present observational results of over 500 binary star observations and characterize the measurement precision in separation, position angle, and magnitude difference. 2. OBSERVATIONS AND DATA REDUCTION Observations were taken during the period 2001 October 9 22 at the Lowell-Tololo 0.6 m telescope. The instrumentation was identical to that described in Paper II, namely, a Kodak KAF-4200 CCD camera with 500 kpixel s 1 readout. The device is front-illuminated with a peak quantum efficiency of approximately 40% and a read noise of 10 electrons. A filter wheel was placed between the detector and the telescope with three filter options, Bessel B, V, andr (Bessel 1990). The seeing was reasonably consistent throughout the run, and only half of one night was lost due to clouds. Figure 1 shows two histograms of the seeing measures obtained from point-source observations throughout the run, one for all observations obtained during the run and one for only those observations surviving the standard quality criteria we impose in the data analysis phase for highquality astrometry discussed in Paper II. (Based on signal-tonoise ratio, final reduced 2 of the fit, and other factors, some observations are judged to be of insufficient quality to publish relative astrometry. In a number of other cases, no fringes were detected in the analysis.) The mean value in both cases is 1B7. There are two secondary mirrors that can be mounted on the Lowell-Tololo Telescope; for all observations during our run, we used the higher magnification secondary, which gives a focal ratio of f /75. Pixels on the CCD were then binned 4 ; 4 prior to readout so that a full-frame image of the detector consisted of 512 ; 512 pixels, including a small overscan region. Speckle observing consisted of obtaining a data file using the speckle strip method described in Paper I. In this technique a subarray strip is defined prior to the observation that is perpendicular to the CCD s serial register. The strip contains the star image at the end of the strip farthest from the serial register. A sequence of speckle data frames is then obtained by opening the shutter, waiting for an exposure time (typically ms for all the observations here), and then shifting the accumulated charge toward the serial register by 32 rows. More charge is then accumulated for a second exposure time, and then the row shift is executed again. In this way the strip is used as a memory cache of speckle data frames prior to readout of the strip. When the first image has been row-shifted enough times to be adjacent to the serial register, the frame sequence is read out together. The observation sequence is repeated as many times as desired to obtain the required number of data frames. We typically acquired 1000 or more speckle frames of data on a target, which took approximately 2 minutes, including readout time. This technique does leave a low-level streak between speckle images on the strip because the shutter does not close during the row shifts toward the serial register, but because of the relatively fast electronics on this CCD system, the level is at most 1% 2% of the light in the speckle images per pixel, as estimated in Paper I Pixel Scale and Orientation We measured the scale on the detector with the help of a Michelson mask already made for the telescope and used in collimation. That mask had multiple holes drilled within it, and all but two of these would be covered prior to mounting it to the top of the telescope. As a result, when pointed at a single star, the mask would create a fringe pattern on the detector in which the separation between fringes and their orientation can be related TABLE 1 Double Star Speckle Measures, 2001 November, Lowell-Tololo 61 cm HR, ADS, DM, etc. (1) Discoverer Designation (2) HD (3) HIP (4) WDS (, J2000.0) (5) Date (6) (deg) (7) (arcsec) (8) m (9) k (nm) (10) k (nm) (11) CD I a CD I CP HJ CP HJ CP HJ CP HJ CP GLI CP GLI HR HDO b HR HDO b Note. Table 1 is published in its entirety in the electronic edition of the Astronomical Journal. A portion is shown here for guidance regarding its form and content. a Quadrant ambiguous. b Quadrant is inconsistent with previous measures in Hartkopf et al. (2001b).

3 3010 HORCH ET AL. Vol. 131 TABLE 2 Orbits Used for the Measurement Precision Study Discoverer Designation HIP WDS Reference I Mason et al. (1999) BU Hartkopf et al. (1996a) KUI Hartkopf et al. (1996a) KUI Hartkopf et al. (1996a) BU 151AB W. I. Hartkopf (2001, private communication) STT 535AB Hartkopf et al. (1996a) BU 163AB Fekel et al. (1997) A Mason (1997) to the spacing and orientation of the two holes and the wavelength of the light reaching the detector. Mask calibration files were taken every four to five nights throughout the run. In each case the telescope was pointed to the horizontal with the telescope tracking turned off. The mask was mounted in place so that a line on the mask bisecting each hole (and containing both centers) was aligned with a plumb bob hung from near the mask. In this way the hole spacing on the sky was in the north-south direction. Then the telescope was pointed to a bright single star, and speckle data files were taken in the desired filters using the method described above. Because the filters used were broad, the derived fringe spacing was affected slightly by the color of the target. We have determined the final pixel scale measures by incorporating information about the spectral type of the target into our calculation. Specifically, a spectrum from the spectral catalog of Pickles (1998) that most nearly matched the cataloged spectrum of our calibration single star was multiplied by the filter transmission, a typical atmospheric transmission curve, and the measured detector quantum efficiency curve. From these, a centroid wavelength for the observation was obtained, and this value was used to compare with the fringe spacing to determine the pixel scale. Single stars of various spectral types were observed over the course of the run in multiple filters to ensure a complete understanding of this effect. The final pixel scale value obtained was within 1 of our last run at CTIO for the f /75 secondary (see Paper II), namely, 164:5 1:1 maspixel 1 (whereas we obtained 163:6 0:6 maspixel 1 in 1999), and the orientation angle was small, 0N23 0N13, but in the opposite direction from the 1999 run (with 0N35 0N17 obtained in 1999). One reason for this difference may be that the method of placing the plumb bob next to the mask was improved over the earlier experience. The values obtained from the current calibration observations are applied to all results described in x Reduction Method The reduction of the speckle frame sequences continues to be a weighted least-squares fit to the average spatial frequency power spectrum of the frame sequence, as described more fully in Papers I and II. Briefly, the images contained on the speckle strips are separated, and the streak between images is estimated and subtracted. Images are bias-subtracted and flat-fielded, and the power spectrum of the frame is formed directly from the frame image by taking the Fourier transform of the image and computing the modulus square of that result. Once all frames in the observation are processed in this way, the average power spectrum is formed. If this function is divided by the average power spectrum of a single (unresolved) star, then the result is in theory a pure fringe pattern of the form f (u) ¼ A 2 þ B 2 þ 2AB cos ½2(x A x B ) = uš; ð1þ Fig. 2. (a) Residuals in position angle when comparing measures in Table 1 with the predicted position angle in the case of high-quality orbits. Open circles represent orbits with larger predicted uncertainties (>0N6), and filled circles represent those with smaller predicted uncertainties (0N6). The dotted curves indicate the expected uncertainty in given a linear measurement uncertainty of 8.6 mas. (b) Residuals in separation when comparing measures in Table 1 with the predicted separation in the case of high-quality orbits. Open circles represent orbits with larger predicted uncertainties (>6.0 mas), and filled circles represent those with smaller predicted uncertainties (6.0 mas). The solid lines indicate offsets in the separation residuals that would be generated from 1 errors in the pixel scale, given the values mentioned in x 2.1. In both plots the gray band at the left marks the region below the diffraction limit at V, and the error bars indicate the predicted uncertainties derived from the uncertainties of the published orbital elements.

4 No. 6, 2006 SOUTHERN BINARY STARS. IV TABLE 3 Astrometric Measurement Precision Object Type Parameter Average Residual RMS Deviation from Average Residual Number of Measures All speckle orbits mas mas 54 Speckle orbits with 6:0 mas mas mas 26 Multiple measures mas 26 All speckle orbits... 1N18 0N35 2N57 0N25 54 Speckle orbits with 0N6... 0N34 0N51 1N91 0N37 15 Multiple measures N28 0N21 26 where A is the brightness of the primary, B is the brightness of the secondary, x A and x B are the locations of the primary and secondary on the image plane, respectively, and u is the Fourier variable conjugate to x, which is the spatial variable on the image plane. We obtain single-star speckle observations in addition to the binary observations in which the single stars are chosen from the Bright Star Catalogue (Hoffleit & Jaschek 1982). Stars of suspected or known duplicity are excluded. We observed enough single stars so that we had at least one observation near in time and sky position to, as well as in the same filter as, each binary we observed. Whenever we observed two or more binaries within a few degrees of one another on the sky, we would typically observe only one single star and use that observation as the calibration observation for all binaries in the group, in order to make the science observations as productive as possible. At a small telescope, atmospheric dispersion does not elongate speckles as dramatically as at a larger telescope (where the speckle size is significantly smaller), but the point sources also serve the purpose of monitoring and compensating for the dispersion, especially at high zenith angles. Because the nominal diffraction limit is, e.g., 0B23 at V, the final pixel scale undersamples speckles. This is advantageous in the sense that when the light is spread over fewer pixels, a speckle can be fainter and still be seen clearly above the read noise. On the other hand, it is disadvantageous, because the power spectra formed will have some high spatial frequencies aliased to lower frequencies, and this complicates the analysis. The detection limit in CCD-based speckle imaging may be seen as determined by the middle ground between these two extremes. We compute a weighted least-squares binary fit to the undersampled data as described fully in Paper I. 3. RESULTS Table 1 contains the speckle results obtained during our 2001 run at CTIO. The column headings give (1) the Bright Star Catalogue (HR) number or, if none, the Aitken Double Star Catalogue (ADS) number or, if none, the Durchmusterung number; (2) the discoverer designation from the Washington Double Star Catalog (WDS; Mason et al. 2001); 3 (3) the Henry Draper Catalogue (HD) number; (4) the Hipparcos catalog number; (5) the WDS catalog number, which also gives the celestial coordinates of the object in J coordinates; (6) the observation date, in Besselian year; (7) the position angle, in degrees east of north; (8) the separation, in arcseconds; (9) the magnitude difference obtained, if the observation was judged to be of sufficient quality, as described in x 3.2; (10) the center wavelength of the filter used in the observation, in nanometers; and (11) the full width at half-maximum of the filter passband, also in nanometers. The astrometric results shown have not been precessed and are therefore appropriate for the observation epoch shown. The center wavelength of 440 nm corresponds to the Bessel B filter, 541 nm to V, and 644 nm to R. 3 See /wds/wds.html. Fig. 3. (a) Standard deviation of the position angle determination for objects observed five or more times. The dashed line indicates 0.49/, where is in arcseconds, which is the function expected for a linear measurement precision of 8.6 mas, the figure obtained in the speckle orbit study. The dotted curve indicates 0.70/, which is the function expected for a linear measurement precision of 12.2 mas, the value obtained from multiple observations of the same targets. (b) Standard deviation of the separation determination for objects observed five or more times. The dashed line is drawn at 8.6 mas, the value obtained from the speckle orbit study, and the dotted line is drawn at 12.2 mas, the value from the study of multiple measures of the same targets. The solid line indicates the systematic separation error caused by a 1 offset in the pixel scale. In both plots the gray band at the left marks the region below the diffraction limit at V, and the shades of the plot symbols indicate the H p value for the system appearing in the Hipparcos catalog, with white circles being the smallest magnitude difference and black circles being the largest. Systems that were also used in the speckle orbit study are circled.

5 3012 HORCH ET AL. Vol. 131 Fig. 4. (a) Standard deviation of the separation determination for objects observed five or more times as a function of the total (system) V magnitude as it appears in the Hipparcos catalog. The shade of the plot symbol indicates the H p value for the system appearing in the Hipparcos catalog, with white circles being the smallest magnitude difference and black circles being the largest. (b) Standard deviation of the separation determination for objects observed five or more times as a function of magnitude difference. The shade of the plot symbol indicates the system V magnitude for the pair, with white circles being the brightest objects and black circles being the faintest. In both plots the dashed line is drawn at 8.6 mas, the value obtained from the speckle orbit study; the dotted line is drawn at 12.2 mas, the value obtained from repeat observations of the same targets; and objects in common with the speckle orbit study are circled Astrometric Accuracy and Precision In order to determine the astrometric measurement accuracy and precision, we have completed a comparison of our results with ephemeris predictions in cases in which the binary system already had a very high-quality orbit. Objects and orbits used for this purpose are shown in Table 2. In all cases the orbits are published with uncertainty estimates for the orbital parameters, and we have used a Monte Carlo approach to propagate these uncertainties through the standard visual orbit formulae to estimate uncertainties in the ephemeris predictions. The residuals obtained when comparing to our measures in Table 1 are shown in Figure 2 for both position angle and separation. Table 3 gives the average residual for all orbits and for a subset having the smallest ephemeris uncertainties; in all cases except the position angle residual, when all speckle orbits are considered, the average values of the residuals are not statistically different from zero. In the case of all speckle orbits, the position angle result is affected by two orbits, where our values are slightly smaller in position angle than predicted by the orbit, leading to a systematically negative residual. These objects are BU 1163 (HIP 6564) and A2100 (HIP ). In the former case there is a trend in the contemporaneous speckle observations shown in the Fourth Catalogue of Interferometric Measures of Binary Stars (Hartkopf et al. 2001b) 4 toward a negative residual, so perhaps the orbit will need refinement in the future. In the latter case the uncertainty of the position angle as determined by the error propagation from the orbital elements can account for nearly all of the residual. The position angle residuals have an rms deviation from the average residual of 1N91 0N37, while the result for separation is 8:6 1:2 mas for the highest quality orbits. As the ephemeris uncertainties are much smaller than these values, we take them to be good estimates of our own measurement precision in these cases, although it should be noted that the objects used in this study are bright and generally have small separations. In fact, for the position angle, the average separation for the objects used 4 See Fig. 5. Observed magnitude difference minus H p as a function of seeing times separation. Open circles represent measures taken in the V filter,and filled circles represent measures taken in the B filter. Observations in the R filter were not plotted because the H p filter is significantly different from R in terms of the center wavelength and filter width. Fig. 6. Observed magnitude vs. H p for observations with seeing times separation less than 2.0 arcsec 2. Open circles represent measures taken in the V filter, and filled circles represent measures taken in the B filter. The dashed line marks y ¼ x.

6 No. 6, 2006 SOUTHERN BINARY STARS. IV TABLE 4 m H p Results H p Range (mag) Average Residual rms Deviation from Average Residual Filter Number of Measures B B :35 þ0:52 0:23 B 2 All B V V V 20 All V 104 is approximately 0B3, meaning that one expects a larger scatter in position angle. The position angle uncertainties should follow the function ¼ arctan (=); where is the linear measurement uncertainty (i.e., that of the separation coordinate). Thus, for a linear measurement uncertainty of 8.6 mas, we expect a position angle uncertainty of 1N64 at a separation of 0B3. This value falls within the 1 error estimate of the position angle rms deviation. There are a number of objects in Table 1 with more than five measures of position angle and separation. These can also be used to estimate the measurement precision by calculating the standard deviation of the values listed in Table 1. These standard deviations must be corrected for small sample statistics according to the standard formulae, but they can then be compared with the values obtained in the speckle orbit study. Figure 3 shows the () and () values obtained in these cases as a function of observed average separation. Some objects are common to both the speckle orbit study and the multiple-observation study, and these points are circled. The same data are plotted in Figure 4 as a function of both total V magnitude for the pair and magnitude difference as it appears in the Hipparcos catalog (Perryman et al. 1997). The average value of the position angle uncertainties is lower than the speckle orbit study ( probably because the collection of objects includes separations out to 2B4, where the position angle can be more precisely measured), and the average ( ) valueis12:2 1:4 mas, somewhat higher than the speckle orbit study. This may be due to the fact that the objects span a larger range in both V magnitude and in magnitude difference. Indeed, Figure 4b does show a slight trend toward larger () valuesasthemagnitude difference increases. This is consistent with the results in Paper III. Based on the astrometric precision results of both studies (summarized in Table 3), we suggest that our linear measurement precision is no worse than 12:2 1:4 mas on average, meaning that the position angle measurement precision is given by 0.70/, where is the observed separation. These values compare favorably with, e.g., Douglass et al. (2000) and Horch et al. (2006) for similar-sized telescopes and more standard intensified imaging systems for speckle imaging. The speckle orbit study indicates that systematic error, if present, is at a very low level. For position angle and separation values appearing in Table 1, one may estimate the uncertainty of a measure by combining these values in quadrature with the pixel scale uncertainty stated earlier using the standard error propagation formula Photometric Accuracy and Precision In addition to astrometry, we also present magnitude differences for 312 observations in Table 1. For many of these objects, ð2þ magnitude differences also exist in the Hipparcos catalog in the H p filter. This filter has a transmission curve that is significantly broader than any of the Bessel filters used in our observations, and it has a peak wavelength between the B and V filters. In Figure 5 the difference between our magnitude difference measures in B and Vand those in the Hipparcos catalog is shown as a function of the q 0 parameter discussed in Paper III, defined to be seeing times observed separation. This parameter is related to the degree of correlation between the primary and secondary speckle patterns and hence the ability to measure the magnitude difference without systematic error with the speckle technique. As in Paper III we find that the difference between the space-based measures and our observations is small and nearly constant for q 0 < 2:0arcsec 2, and so only observations with q 0 values below this value in Table 1 contain a reported magnitude difference value. With the values remaining, we plot in Figure 6 the observed speckle magnitude difference versus the H p value with the line y ¼ x. These show a very good linear correlation between the two types of measurement. Table 4 shows the average residual value for three ranges in H p, as well as the rms deviation from the average residual for the same ranges. The lowest values of the latter occur in the range 1 < H p < 2, similar to what was found in Paper III. This is expected due to the measurement method (since the magnitude difference value is obtained from the depth of the fringe minima in the Fourier domain) and was also discussed in Horch et al. (2004) for speckle data taken at the WIYN telescope. Fig. 7. Standard deviation in m as a function of average m for objects observed four or more times in one filter. Open circles represent observations taken in the V filter, and filled circles represent observations taken in the R filter. Thedashedlineisdrawnat(m) ¼ 0:22, the average value of the nine values shown for the V filter, and the dotted line is drawn at (m) ¼ 0:13, the average value of the nine values shown for the R filter.

7 3014 HORCH ET AL. Vol. 131 Fig. 8. Orbits and interferometric data for the four binaries discussed in the text: (a) HDS 154 (HIP 5514), (b) HDS644(HIP 23116),(c)BU 1003 (HIP 17544), and (d ) I7 (HIP 35296). In all plots, north is down and east is to the right. Open circles indicate measures appearing in Hartkopf et al. (2001b), and filled circles indicate measures from Table 1. A line segment is drawn from these points to the predicted position from the orbital elements for the same epoch for (c)and(d ). Small crosses mark visual observations appearing in the WDS in these two cases, and the large plus sign indicates the origin in all four plots. There are a number of objects in Table 1 that have four or more observations in one filter. The standard deviation of these observations, corrected for small sample bias, has been plotted as a function of the average magnitude difference obtained in Figure 7. The average value of the standard deviation obtained in nine cases for the V filter is 0.22 mag and that of nine objects fulfilling the same criteria in the R filter is 0.13 mag. These values are indicated on the plot. If one assumes that overall these numbers are a fair indication of our measurement precision and uncorrelated with Hipparcos measurement precision, then the numbers in Table 4 should be consistent with adding our measurement precision in quadrature with the Hipparcos measurement precision, stated in Mignard et al. (1995) as mag. For the V filter, which is the only filter in common for the two studies, this predicts that the rms deviation from the average residual is mag, consistent with the value obtained (for all magnitude differences) of 0:27 0:02. Therefore, it would appear that if systematic error exists in our magnitude differences, the level is at most a few hundredths of a magnitude. The placement of components of the systems in Table 1 on the H-R diagram will be taken up in a future paper Discussion In Figure 8 we show four examples of objects of interest within the data set. We observed a number of double stars discovered by Hipparcos; unfortunately, all but three of these objects were not resolved. Of these, two have shown substantial motion since the discovery observation. These are HDS 154 and HDS 644,

8 No. 6, 2006 SOUTHERN BINARY STARS. IV displayed in Figures 8a and 8b. HDS 154 has a distance of 91:7 7:3 pc and a spectral type of F5 V, while HDS 644 has a distance of only 49:68 2:66 pc and also has spectral type F5. The two other objects in Figure 8 are examples of orbits that can benefit from further refinement after more interferometric data are obtained. In both cases the most recent orbit appearing in the Sixth Orbit Catalog of Hartkopf et al. (2001a) 5 is plotted in addition to data from the Fourth Catalog of Interferometric Measurements (Hartkopf et al. 2001b). In Figure 8c we show the orbit of Hopmann (1960) for BU In this case only the Hipparcos relative astrometry exists in Hartkopf et al. (2001b). Our observation shows significant motion in the last 2 yr, but both are substantially off of the orbit. With a declination of 27, the system is marginally observable from northern observatories. It has a distance of only 21:76 0:67 pc and a spectral type of K2 Vand should therefore be of interest for the mass-luminosity relation. Using Kepler s third law, one may then obtain from the Hopmann orbit a total mass of 1.2 M. With a magnitude difference from our results of nearly 3 at R, we may roughly estimate that the primary is near K2 V and the secondary is perhaps an M2 V. This would then give a total mass of 1.15 M, according to Schmidt-Kaler (1982). A smaller value of the semimajor axis,asindicatedbythedata,wouldofcoursedecreasethe1.2m value of the Hopmann orbit. In Figure 8d we see the example of I7, which has observations in Hartkopf et al. (2001b) that cover a substantial portion of the orbit, starting with several observations of W. S. Finsen with his eyepiece interferometer (e.g., Finsen 1951, 1961), but the most recent points at the largest apparent separations (including those from Table 1) are all systematically smaller than the orbit prediction. The orbit plotted is that of Heintz (1995), where, given the distance in the Hipparcos catalog of 14:77 0:19 pc, the total mass should be approximately 0.16 M, seemingly in contradiction to the K2 V spectral type for the pair appearing in the Hipparcos catalog. A smaller semimajor axis, as indicated by the data, would only worsen the discrepancy. Looking at individual visual observations appearing in the WDS prior to 1930, most show separations larger than 0B9 at position angles of 5 See /wds/orb6.html ThesystemV magnitude for the pair is 6.70, so that the absolute magnitude is approximately 5.85, favoring a spectral type near K0. The B V color of is also consistent with an early-k spectral type. We suggest that further interferometric observations are urgently needed for this target. 4. CONCLUSIONS We have presented 517 position angle and separation measures and 312 magnitude difference measures of primarily southern binary stars. The results obtained are consistent with ephemeris predictions in cases in which a very high quality orbit already exists and show an uncertainty of approximately 8:6 1:2mas in separation and 1N91 0N37 in position angle. A study of repeat observations leads to a measurement precision of 12:2 1:4 mas in separation and 1N28 0N21 in position angle. The true measurement precision is probably closer to the latter numbers, as these span a larger range in system magnitudes, magnitude differences, and separations. Magnitude difference measurements are consistent with results from the Hipparcos catalog and have a mean uncertainty (averaging results from the V and R filters) of approximately 0.18 mag per 2 minute observation, as judged from repeat observations of targets. These measures highlight the need for continued southern speckle observing. We are very grateful to Oscar Saa at CTIO and Clark Enterline at NOAO in Tucson for their help with the logistics of transporting the equipment and setting it up for use on the telescope. Special thanks go to Zoran Ninkov of Rochester Institute of Technology for the use of the CCD camera and filter wheel and to Robert Millis of Lowell Observatory for his support of this project. Finally, we thank the referee, William Hartkopf, for his very helpful comments. This work was funded by a small research grant from the American Astronomical Society. It also made use of the Washington Double Star Catalog, maintained at the US Naval Observatory, and the SIMBAD database, operated at CDS, Strasbourg, France. Funds for publication of this paper were provided by the University of Massachusetts, Dartmouth. Bessel, M. S. 1990, PASP, 102, 1181 Douglass, G. G., Mason, B. D., Rafferty, T. J., Holdenried, E. R., & Germain, M. E. 2000, AJ, 119, 3071 Fekel, F. C., Scarfe, C. D., Barlow, D. 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