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J/PASP/105/36     All-sky uvby photometry of speckle binaries     (Sowell+ 1993)

All-sky Stroemgren photometry of speckle binary stars Sowell J.R., Wilson J.W. <Publ. Astron. Soc. Pac. 105, 36 (1993)> =1993PASP..105...36S
ADC_Keywords: Stars, double and multiple ; Photometry, uvby Authors' addresses: Electro-Optics Laboratory, Georgia Tech Research Institute Georgia Institute of Technology, Atlanta, GA 30332 Electronic Mail: Department of Physics and Astronomy Georgia State University, Atlanta, GA 30303 Electronic Mail: Abstract: All-sky Stroemgren photometric observations were obtained for 303 speckle binaries. Most stars were in the range of V = 5 to 8.These data, when combined with ratios of intensities from the CHARA speckle photometry program, will allow the determination of photometric indices for the individual components of binary stars with separations as small as 0.05 arcsec. These photometric indices will complement the stellar masses from the speckle interferometry observations to provide a much improved mass-luminosity relationship. Introduction: Binary stars play an important role in determining several key stellar physical parameters. The most fundamental quantity is stellar mass, which in order to be determined, requires knowledge of the orbital period and semi-major axis of the system. Unfortunately, the majority of visual binaries have orbital periods on the order of many decades, making complete cycles difficult to obtain during the lifetime of a single observer. The application of speckle interferometry has greatly improved the situation, for now hundreds of binary systems with periods on the order of ten years or less, are routinely observed, especially by astronomers at the Center for High Angular Resolution Astronomy (CHARA) at Georgia State University (McAlister & Hartkopf 1988). In conjunction with the appropriate spectroscopic data, precise ``visual'' orbits for these speckle binaries (Hartkopf et al 1989) will provide accurate masses for a wide range of spectral types.A second vital characteristic is intrinsic luminosity. This boundary condition is necessary for both stellar interior and evolutionary models. The CHARA speckle program recognized the need for luminosity information to complement astrometry observations. Accurate photometry, unlike astrometry, requires only a few observations of the system, unless a member is variable. Algorithms to extract luminosity ratios from the speckle data have been developed. Although the techniques are still limited (e.g., non-calibrated), previous ``speckle photometry'' results have been reported by Bagnuolo & Sowell (1988) and Bagnuolo & Hartkopf (1989) for Capella and by Dombrowski (1990) for several Hyades stars.The purpose of this observing program was to obtain accurate uvby photometry of a large set of speckle binaries discovered or frequently observed by CHARA. Knowing the integrated magnitude and the ratio of the luminosities at selected wavelengths provides sufficient information to solve for the intrinsic brightness and color of each component. When combined with the masses from the ongoing speckle astrometry program, these stars will be important calibrators of the mass--luminosity relationship. Visually unresolved binaries have usually been omitted from photometric programs. Most of the program stars are bright, and one would have expected them to be well observed. However, many were known to be visually unresolved or marginally resolved binaries; hence, these systems were often deleted from previous photometric programs. OBSERVATIONS The photoelectric observations were obtained during 1989 November 11 to 17 (by J.W.W.) and during 1991 April 24 to 30 (by J.R.S.). In both cases the Automated Filter Photometer was used on a 36-inch telescope at KPNO. The same 1P21 phototube and uvby filter set were used on the two runs, as was a 15 arcsec diaphragm. Standard deadtime corrections and sky subtraction procedures were applied (Henden & Kaitchuck 1982). The transformation equations are listed below: V(std) = epsilon_y [(b-y)(std)] + zeta_y + (y - kappa'_y X) (1) (b-y)(std) = epsilon_b-y [ (b-y) - kappa' _b-y X ] + zeta_b-y (2) m_1(std) = epsilonm1 [ m_1 - kappa' m1 X ] + zetam1 (3) c_1(std) = epsilonc1 [ c_1 - kappa' c1 X ] + zetac1 (4) The extinction, transformation, and zero point coefficients were determined nightly; these coefficients are listed in Table 1. The extinction, transformation, and zero point coefficients were determined nightly; these coefficients are listed in Table 1. Standard stars were taken from Perry et al (1987). Gronbech et al (1976) divided their standard stars (i.e., transformation equations) into two groups, with the division at b-y = 0.410. Olsen (1983) used three groups, for he subdivided the cooler standards into evolved and unevolved sets. We used only one set of standard stars and transformation equations for the following reason. The majority of our program speckle binaries were believed a priori to be unevolved B, A, F, or G stars. This assumption was due to the observational constraint that, in order to be resolved by speckle interferometry, the magnitude difference between the components cannot be too great. Figure 5 of McAlister & Hartkopf (1988) demonstrates that this difference is less than 2 mag for most of the speckle binaries. With the low number of either evolved or of cool stars expected to be in our sample, it was not felt that the time required for observations of multiple sets of standards was justified, especially since only the m_1 and c_1 indices would be affected. The current state of the CHARA speckle program dictated the faint limit to be on the order of V = 8. The bright limit was set by the photometer, which could not accurately measure brightnesses greater than V = 5. Consequently, the majority of the program binaries were of 5 and 6 mag. The highest priority stars were the ``McA'' binaries, discovered by H.A. McAlister using the KPNO photographic speckle camera during the late 1970's, and the ``CHARA'' binaries, discovered using the GSU/CHARA ICCD speckle camera, in operation since 1982. All binaries were discovered using the KPNO 4-m reflector (see McAlister & Hartkopf 1988). The stars have short periods of a few years and are being used to obtain complete orbital elements. Stroemgren filters were chosen for this photometric program, since these narrow bandpasses are routinely used for the CHARA speckle observations. The apparent Stroemgren magnitudes and indices obtained for 303 binary systems are presented in Table 2. Column 1 lists the HD number, column 2 gives either the HR, DM, or ADS number, and column 3 supplies the binary discoverer designation. Columns 4 and 5 give the right ascension and declination, respectively. Column 6 refers the reader to notes at the end of the table. Columns 7 through 15 give the magnitudes and the errors of the mean for the four Stroemgren indices, followed by the number of observations. The entries are in order of HD number. It should be noted that many of the program stars were known to be binary systems (e.g., spectroscopic) before the astrometric speckle observations were acquired. Consequently, many of the speckle binaries are actually in multiple systems. Unless the stellar system was a visual double separated by at least 10 arcsec, then the photometric observations presented here are for the entire multiple system. These cases can usually be determined from the binary designation given in column 3 of Table 2, whereas the inclusion or exclusion of wide components is referenced in column 6. Individual magnitudes can still be derived if the luminosity ratios (from speckle photometry) are obtained between all of the components. Analysis: The observations presented here were compared with the Stroemgren photometry by Olsen (1983). His program stars ranged from A5 to G0 in spectral type and were brighter than 8.3 mag. A total of 80 stars were common to both programs, and Figures 1 through 5 show the comparison of the four Stroemgren indices. Although a few stars have discrepant magnitudes in only one index, there were three stars, HD 173654, HD 168701, and HD 25555, that were consistently dissimilar in several of the indices. Although HD 173654 (HR 7059) has nearly a 0.3 mag difference in V, the cause is easily explained: Olsen's program excluded a nearby companion, whereas this program included it. However, the resolution of the differences (as much as 0.1 mag in V) for HD 168701 and HD 25555 (McA 13 Aa) are not apparent. These two stars are among the reddest ones observed by this program, so the lack of many red standard stars may be a factor in these two cases. Further observations of these two systems should provide the answer as to the cause for the differences. Individual magnitudes: As an example for deriving the magnitudes of individual components of an unresolved binary, we consider two Hyades stars whose orbital motions have been used by Dombrowski (1990) to find the cluster distance modulus. These stars, 51 Tau (HR 1331 = HD 27176 = McA 14 Aa) and Fin 342 Aa (HR 1391 = HD 27991), were assigned instrumental Deltay values of 0.72 and 0.29 mag, respectively (each having an assumed error of approximately ±0.1 mag). >From Table 2, the composite V value for 51 Tau is 5.64 mag, and for Fin 342 Aa it is 6.46 mag. Magnitudes for the components are found as follows. In the equation below, one uses the difference of the magnitudes to solve for the flux ratio. Deltay = y_b - y_a = +2.5 log (F_a / F_b) (5) The subscripts ``a'' and ``b'' represent the brighter and fainter components, respectively. The contribution of the fainter component (in magnitudes) to the system's magnitude is described by equation 6. yepsilon_= +2.5 log (1.000 + F_b F_a) (6) The magnitude of the brighter component is equal to the numerical sum of yepsilon_ and the system's magnitude. The magnitude of the fainter star is then easily computed with the Delta mag. Likewise, for brighter speckle systems, which could be observed in multiple bandpasses, photometric indices for each component can be derived. Table 3 lists the magnitudes and fluxes for 51 Tau and Fin 342 Aa. Ideally, one should use multiple bandpass data to derive photometric indices. But these two systems are members of the Hyades, an extensively studied cluster. Using the CM diagram from Hagen (1970) and making the assumption that all of the components are on the main sequence, one can derive (B-V)_o and then infer a spectral type. The brighter component of 51 Tau has (B-V)_o approximately equal to +0.4 mag, whereas the fainter component and the two stars of Fin 342 Aa are about +0.5 mag. Tables from Schmidt-Kaler (1982) suggest that the warmest star is F2-5; the others are roughly F8. J.R. Sowell wishes to thank R.S. Hyde (GTRI/EOL) for providing internal research funds. Likewise, J.W. Wilson acknowledges the support provided by H.A. McAlister through NSF Grant AST 8915324. The authors wish to thank H.A. McAlister, W.I. Hartkopf, and W.G. Bagnuolo for their help with the CHARA databases and for their comments on the manuscript. Also, the authors appreciate the improvements to the paper suggested by the anonymous referee. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1 87 26 Reduction Coefficients table2 114 303 Observations
Byte-by-byte Description of file: table1
Bytes Format Units Label Explanations
3- 10 A8 "YY.MM.DD" Date (UT) (1) 11 A1 --- DatePart [ab] See Note (1) 13- 17 F5.3 --- kappa_y' (mean error on second line) 19- 23 F5.3 --- kappa_b-y' (mean error on second line) 25- 29 F5.3 --- kappam1' (mean error on second line) 31- 35 F5.3 --- kappac1' (mean error on second line) 38- 42 F5.3 --- eps_y (mean error on second line) 44- 48 F5.3 --- eps_b-y (mean error on second line) 50- 54 F5.3 --- epsm1 (mean error on second line) 56- 60 F5.3 --- epsc1 (mean error on second line) 63- 68 F6.3 --- zeta_y (mean error on second line) 70- 74 F5.3 --- zeta_b-y (mean error on second line) 76- 81 F6.3 --- zetam1 (mean error on second line) 83- 87 F5.3 --- zetac1 (mean error on second line)
Note (1): The night of 89 Nov 14 was divided into two halves due to intervening clouds.
Byte-by-byte Description of file: table2
Bytes Format Units Label Explanations
2- 7 A6 --- HD HD designation 9- 18 A10 --- Ident Other designation 21- 32 A12 --- Desig Binary Discoverer Designation 36- 37 I2 h RAh Right Ascension J2000 (hours) 39- 40 I2 min RAm Right Ascension J2000 (minutes) 42- 45 F4.1 s RAs Right Ascension J2000 (seconds) 48 A1 --- DE- Declination J2000 (sign) 49- 50 I2 deg DEd Declination J2000 (degrees) 52- 53 I2 arcmin DEm Declination J2000 (minutes) 55- 56 I2 arcsec DEs Declination J2000 (seconds) 59 I1 --- Notes *[1/4]? Note number: 61- 66 F6.3 mag Vmag V magnitude 68- 72 F5.3 mag e_Vmag mean error on Vmag 74- 79 F6.3 mag (b-y) color index 81- 85 F5.3 mag e_(b-y) mean error on b-y 87- 92 F6.3 mag m1 color index 94- 98 F5.3 mag e_m1 mean error on m1 100-105 F6.3 mag c1 color index 107-111 F5.3 mag e_c1 mean error on c1 113-114 I2 --- N Number of observations
Note on Notes: the Note number takes the values 1: companion star excluded 2: companion star included 3: possibly variable 4: one component is a BaII star
Individual magnitudes (table 3): ------------------------------------------ Star V Dy Fa/Fb ya yb ------------------------------------------ 51 Tau 5.64 0.72 1.94 6.09 6.81 Fin∼342∼Aa 6.46 0.29 1.31 7.08 7.37 ------------------------------------------ References: Bagnuolo, W.G., Jr., & Hartkopf, W.I. 1989, AJ, 98, 2275 Bagnuolo, W.G., Jr., & Sowell, J.R. 1988, AJ, 96, 1056 Dombrowski, E. 1990, PhD Thesis, Georgia State University Gronbech, B., Olsen, E.H., and Stroemgren, B. 1976, AASS, 26, 155 Hagen, G.L., 1970, Pub David Dunlap Obs, 4, 1 Hartkopf, W.I., McAlister, H.A., & Franz, O.G. 1989, AJ, 98, 1014 Henden, A.A, & Kaitchuck, R.H. 1982, Astronomical Photometry (Van Nostrand Reinhold, New York) McAlister, H.A., & Hartkopf, W.I. 1988, Second Catalog of Interferometric Measurements of Binary Stars, CHARA Contribution No. 2 Olsen, E.H., 1983, AASS, 54, 55 Perry, C.L., Olsen, E.H., & Crawford, D.L. 1987, PASP, 99, 1184 Schmidt-Kaler, T., 1982, in Landolt-Boernstein, New Series, Group 6, Vol 2B, Stars and Star Clusters, 15
(End) [CDS] 28-Apr-1993
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