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 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:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1 87 26 Reduction Coefficients
table2 114 303 Observations
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Byte-per-byte Description of file: table1
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Bytes Format Units Label Explanations
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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)
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Note (1): The night of 89 Nov 14 was divided into two halves due to
intervening clouds.
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Byte-per-byte Description of file: table2
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Bytes Format Units Label Explanations
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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
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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
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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