Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993ycat..61050036s&link_type=abstract
VizieR On-line Data Catalog: J/PASP/105/36. Originally published in: 1993PASP..105...36S
Astronomy and Astrophysics
Astronomy
Stars: Double And Multiple, Photometry: Uvby
Scientific paper
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) = epsilony [(b-y)(std)] + zetay + (y - kappa'_y X) (1) (b-y)(std) = epsilonb-y [ (b-y) - kappa' b-y X ] + zeta_b-y (2) m1(std) = epsilonm1 [ m1 - kappa' m1 X ] + zetam1 (3) c1(std) = epsilonc1 [ c1 - 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 m1 and c1 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. (2 data files).
Sowell James R.
Wilson William J.
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