An Effective Combination of Two Medium- Band Photometric Systems

Home , 4 Aquilae, 69 Aquilae, R Aquilae, W Aquilae

Baltic Astronomy, vol. 5, 83-101, 1996.

THE STROMVIL SYSTEM: AN EFFECTIVE COMBINATION OF TWO MEDIUM- BAND PHOTOMETRIC SYSTEMS

V. Straizys1-3, D. L. Crawford2 and A. G. Davis Philip3-4 1 Institute of Theoretical Physics and Astronomy, Gostauto 12, Vilnius 2600, Lithuania 2 Kitt Peak National Observatory, P.O. Box 26732, Tucson, AZ 85726, U.S.A. * 3 Union College, Schenectady, NY 12308, U.S.A. 4 Institute for Space Observations, 1125 Oxford Place, Schenectady, NY 12308, U.S.A.

Received September 15, 1995.

Abstract. It is shown that the addition to the Stromgren four-color photometric system of three passbands at 374, 516 and 656 nm from the Vilnius photometric system makes the combined system more universal. This new system, called the Strômvil system, makes it possible to classify stars of all spectral types, even in the presence of interstellar reddening. This property of the system is especially important in CCD photometry, allowing the photometric classification of very faint stars. A preliminary calibration of the system in terms of spectral and luminosity classes, temperatures and surface gravities is available. A list of preliminary standards for the Strômvil system in the regions of Cygnus, Aquila and near the North Celestial Pole is given. Key words: methods: observational - techniques: photometric - stars: fundamental parameters

* Operated by AURA, Inc., under cooperative arrangement with the National Science Foundation, Washington, DC 84 V. Straizys, D. L. Crawford and A. G. Davis Philip

1. INTRODUCTION

In the nineteen sixties, a number of medium-band photometric systems were proposed for two- and three-dimensional classification of stars. One of the first was the Stromgren uvby system for the determination of temperatures and luminosities of B-A-F and early G-type stars and metallicities for A-F-G type stars (Stromgren 1963, 1966). Later on, the system was supplemented by two additional narrow passbands, measuring the intensity of the H(3 line (Crawford & Mander 1966). In other attempts to improve the uvby system, Jones (1971, 1973) and Anthony-Twarog et al. (1991) have supplemented the system with a narrow band filter, measuring the intensity of the Ca II H and K lines to improve determination of the metallicity for A-F-G type stars. At about the same time, the first version of the Vilnius photometric system for photometric classification of stars of all spectral types and in the presence of interstellar reddening was described (Straizys 1963, 1965; Straizys Sz Zdanavicius 1965). The selection of optimum passbands of this system was based on photoelectric energy distributions in stars of different spectral and luminosity classes and on the interstellar reddening law. Both systems and their possibilities were described recently by one of us (Straizys 1992a, 1993). The parameters of the passbands of these systems are listed in Tables 1 and 2 and the passbands themselves are plotted in Fig. 1. One can see that four passbands of the uvby system have close analogs in the Vilnius system. Let us describe the main purposes of the passbands in each system (Figs. 2 and 3). The ultraviolet magnitudes of both systems (u and U) measure the radiation intensity to the ultraviolet side of the Balmer jump. The violet magnitudes of both systems (v and X) measure the radiation intensity to the red side of the Balmer jump. For B-A-F type stars the color indices u — v and U — X give the Balmer jump height, which depends both on temperature and luminosity. Addi- tionally, for A-F-G type stars the violet magnitudes of both systems measure the blanketing by metallic lines, and thus are important for the photometric determination of the [Fe/H] ratio. The blue magnitudes b and Y, in combination with the green magnitudes y and V, give the color indices b — y and Y — V which are almost blanketing-free for A, F and early G stars. Additionally, the blue magnitudes of both systems are close to the break-point of the interstellar reddening law. For this reason all color indices, which The Stròmvil system 85

Table 1. Mean wavelengths and half-widths of passbands of the Stromgren uvby, ¡3 photometric system

Passband U V b y wp nfl

Ao (nm) 350 411 467 ' 547 485-489 486-487 AA (nm) 30 19 18 23 14-21 3

Table 2. Mean wavelengths and half-widths of passbands of the Vilnius photometric system

Passband U P X Y z V s

Ao (nm) 345 374 405 466 516 544 656 AA (nm) 40 26 22 26 21 26 20

Fig. 1. Response functions of the Stromgren and the Vilnius systems, normal to 100 at maximum. Continuous lines indicate the Vilnius system and dots connected by broken line indicate the Stromgren system passbands. 86 V. Straizys, D. L. Crawford and A. G. Davis Philip

Fig. 2. Passbands of both systems plotted on the energy distribution function of Vega. The width of each box corresponds to the width of a response function at 0.5 transmission.

X run Fig. 3. Passbands of both systems plotted on the energy distribution function of a star of spectral type K3 V. The Strómvil system 87 include b and Y magnitudes, show the maximum possible effect of temperature reddening and interstellar reddening differences. This means that on two-color diagrams containing either b or Y magnitude, the angle between intrinsic sequences of stars and interstellar reddening lines is close to maximum. The green magnitudes, y and V, have their mean wavelengths close to the mean wavelength of the V passband of the UBV photometric system. This makes possible the transfer of the broad-band V magnitudes into the medium-band system and vice versa. In addition to the four passbands which are close to similar passbands in the uvby system, the Vilnius system contains three more passbands, P, Z and S. These passbands are important in the classification of late-type stars as well as for detection of the Ha line in emission. (1) The passband P at Ao = 374 nm is placed on the crowding of the higher members of the Balmer series near its limit. As a result, P magnitudes are very sensitive to luminosity for early-type stars. (2) The passband Z at A0 = 516 nm is placed on a wide and deep absorption feature in the spectra of G-K-M stars made by a crowding of metallic lines, of which the Mg I triplet is the strongest. Additionally, in late K-type dwarfs and M-type dwarfs the Z passband contains strong MgH molecular bands. Both the Mg I lines and MgH bands show a strong negative luminosity effect, making the color indices, containing the Z magnitude, to be luminosity dis- criminants for G, K and M-type stars. (3) The passband S is placed on the Ha line and for all types of stars it indicates the presence of emission in this line. In the case of normal absorption spectra the S magnitude can be combined into temperature-sensitive color indices, such as Y — S or V — S with a small blanketing effect. The aim of this study is to examine the usefulness of supple- menting the Stromgren system with three additional passbands from the Vilnius system to achieve better classification possibilities over a larger range of spectral types, especially in the presence of interstellar reddening. Synthetic color indices are used to analyze the combined system. Magnitude differences are calculated by the formula

where F(A) are the energy fluxes of stars of different spectral and luminosity classes from Straizys & Sviderskiene (1972) and Svider- 88 V. Straizys, D. L. Crawford and A. G. Davis Philip skiene (1988), 5i(A) and 62(A) are the response functions of two passbands, r(A) is the standard transmittance function of the unit quantity of interstellar dust from Straizys (1992a) and x is the number of dust units. A value of x has been varied in calculations from 0.0 to 1.0. This last value of x gives EB-V = 1 for an early-type star. Color excesses were calculated as the differences between color indices of reddened and unreddened stars. The constant in Eq. (1) was always selected so as to make color indices equal to zero for an unreddened O-type star. This condition makes the color indices of all normal stars positive. The response functions of the u, v and y passbands were taken from Olson (1974), v from Crawford & Barnes (1970) and the Vilnius system passbands were taken from Straizys (1992a). The integration step was 5 nm. This step value is defined by the character of the flux distribution functions which give fluxes at every 5 nm interval, averaged within ±25 around the given wavelength. The response functions S(A) before integration were also weighted within every 5 nm interval.

2. INTERRELATIONS BETWEEN SIMILAR MAGNITUDES

Fig. 4 shows the differences of analog magnitudes of both systems plotted against the B — V color index. One can see that the ultraviolet, blue and green magnitudes are very close and simple linear equations can be used for their mutual transformation with an accuracy of the order of 0.01 mag:

(U - U) = 0.05(B - V - 0.33),

(Y - b) = 0.02 (B -V- 0.33), (2)

(V - y) = 0.02(5 - V - 0.33). The same equations are good both for unreddened and reddened stars. Transformation equations of color indices can be obtained as differences between corresponding equations for magnitudes. The interrelation between the X and v magnitudes is more com- plicated and the sequences of points representing stars of different luminosities are curves. The interstellar reddening effect causes additional transformation difficulties: interstellar reddening lines in the The Stròmvil system 89

i 1

+0.1 - • 0 • »0 • • GM • 9 • X X 0* 0.0 ... o»*«o*o0°» •

-0.1 - -

X-V o - X • 8 <* * 0 • %• +0.1 • • • • . _ »Moo O 0.0

-0.1 - -

Y-b - -

+0.1 - • • «.. o* • e«»c*> • • • 0 • • 9. . 9 éXQix« X

V-y

+0.1 • • xc»x« x x> \ tx 0 0.0 • *. o. • jMoeo, . • • o • • » • • t>

-0.1 i 1 i 0.0 0.5 1.0 1.5 B-V

Fig. 4. Differences of close magnitudes of the Stromgren and Vilnius systems. An arrow in the X-v, 5-Fplot indicates the reddening line.

X—v, B — V plot do not coincide with the intrinsic temperature reddening lines. Consequently, for the exact transformation of X to v magnitudes and vice versa, one must know at least the luminosity class and the interstellar reddening of every star.

3. DIAGRAMS FOR THE CLASSIFICATION OF NORMAL STARS AFFECTED BY INTERSTELLAR REDDENING

The proximity of four magnitudes in the Stromgren and Vil- nius systems means that the combined photometric system, includ- ing magnitudes of both systems, will preserve most of the classification properties of the original systems. Thus, we decided to investi- gate the classification properties of the combined seven-color system u,P,v,b,Z,y,S which further will be designated as the system 55, 90 V. Straizys, D. L. Crawford and A. G. Davis Philip

37, 41i 52, 55, 66 where the numerals indicate the rounded mean wavelengths. We have named the new system the Stromvil system. Reddening-free Q-parameters, suitable for classification of stars in two dimensions, were calculated from the synthetic color indices for the Straizys & Sviderskiene (1972) and Sviderskiene (1988) energy distributions of real stars by the equation

Q1234 = (mi - m2) - (E12/E34)(m3 - m4) (3) where magnitudes 2 and 3 in most cases coincide. Color excess ratios E12/E34 were calculated for every star individually, to make the Q parameters really independent of interstellar reddening. The following Q-parameters were calculated: Q{35,37,47), Q{37,47,55), Q(41,47,55), Q{35,41,47), Q{35,37,47,55), Q(41, 52, 66) and Q(41, ^7, 52). The Q-parameters of these types are used for determining spectral classes (or temperatures) and ab- solute magnitudes (or surface gravities) of stars of solar chemical composition in the Vilnius system. The <5,Q-diagrams of the Stromvil system for classification of solar chemical composition stars are plotted in Figs. 5-8. Each of these diagrams (after calibration in terms of physical parameters) is usable for the classification of stars in different intervals of spectral classes; only stars within these spectral intervals are plotted. The diagram Q(35, 37,47), Q(37,47,55) (Fig. 5) is useful for the classification of B-type stars of all luminosities and A-F supergiants. The diagram Q{35,37,47), Q(41,47,55) (Fig. 6) is useful for the classification of B8-G stars of all luminosities (except A5-F2 main-sequence stars), the diagram Q(35, 41, 47), Q(35, 37, 47, 55) (not shown) is useful for A5-F2 stars near the main sequence, the diagram Q{35,37,47), Q(41,52,66) (Fig. 7) is useful for G- and K-type stars of all luminosities, and the diagram Q(41, 52, 66), Q(41,47,52) (Fig. 8) is useful for K-type stars of all luminosities. With different calibration, the same diagram shown in Fig. 8 can be used for classification of M-type stars. The Stromvil system 91

Q(35,37,47)

0.0

0.2

0.4

0.6

0.0 0.2 0.4 0.6 0.8 1.0 Q(37,47,55)

Fig. 5. The diagram Q(35,37,47), Q(37,47,55) for classification of B-type stars of all luminosities and A-F supergiants. Dots indicate main- sequence stars, crosses indicate giants and circles indicate supergiants. Q(35,37,47) -0.4

-0.2 G5 • OS

0 0.0 TO- •85 » • AO « *«

0.2

AO • 0.4 A2 •

0.6

0.0 0.2 0.4 0.6 Q(41.47,55)

Fig. 6. The diagram Q(35,37,47), Q(41,4%55) for classification of B8-G stars of all luminosities (except of A5-F2 stars near the main sequence). 92 V. Straizys, D. L. Crawford and A. G. Davis Philip Q(35,37,47) 1 1 1 -0.6 1 • 1 • 1 1 1 "T ' " T 1 T 1 K7. M - U • • K4 M" M0 • X3 • , KZ • -0.4 K2 x M2 • U • W K2 K < « K0 M2 • _ -0.2 K0 • G5...a «C5 e °C5 _ • _ . CO

0.0 - F5 • • • GO «rs

M 0.2 i 1 , . 0 1 1 1 1 0.0 0.2 0.4 0.6 0.8 Q(41,52,66)

Fig. .7. The diagram Q(35,37,47), Q(41,52,66) for classification of G and K stars of all luminosities. Q(41.52,66 )

-0.2 K3 • "J . ' 1" 0.0 M0

0.2

0.4 - G« » « K1

0.6 M2 * K0 08 • K4 0.8

0.6 0.8 1.0 1.2 1.4 Q(41,47.52)

Fig. 8. The diagram Q(41,52,66), Q(41,47,52) for classification of K-type stars of all luminosities. The Stròmvil system 93

4. OBSERVATIONAL TEST OF THE STROMVIL SYSTEM

The Q, Q-diagrams for the two-dimensional quantification of stars can be constructed using the stars observed in both of the original systems. Such common stars were selected from the general photometric catalog of stars observed in the Vilnius system by Straizys & Kazlauskas (1993) and the uvby,/3 photometric catalog by Hauck & Mermilliod (1985). There are about 2000 such stars, the majority of them are brighter than 9th magnitude and of B, A, F or G spectral classes. More common supergiants were added from Arellano Ferro et al. (1990). The color indices of the stars in the combined system were obtained in the following way:

35 - 55 = (u - y) + 0.45,

31-55 =(P- V),

41 - 55 = (v - y) + 0.23,

47 — 55 = (b — y) + 0.15,

52 - 55 = (Z - V),

55 - 66 = (V - S). The constants -0.45, -0.23 and -0.15 are the color indices u — y, v — y and b — y of an unreddened O-type star (Straizys 1977). This normalizes all color indices to zero for unreddened O-type stars. The combined color indices have been used to calculate the four Q, Q-diagrams plotted in Figs. 9 - 12. To decrease the number of overlapping symbols, instead of luminosity V class stars we have plotted only the ZAMS stars from several associations and open clusters. Late K dwarfs have been taken from the field. All recognized peculiar and binary stars, as well as stars of luminosities other than V, III and I, were excluded. The numbers of stars of different luminosity classes (as well as the ranges of their spectral classes) are listed in Table 3. 94 V. Straizys, D. L. Crawford and A. G. Davis Philip

Table 3. Spectral types and number of stars plotted in Figs. 9-12

Luminosity Class Diagram V III I Sp n Sp n Sp n

Q(35,37,47), Q(37,47,55) O -A5 69 B1-A5 77 B0-F0 25 Q(35,37,47), Q(41,47,55) B8-K2 115 B8-A5 195 B9-G5 60 Q(35,37,47), Q(41,52,66) F5-K7 77 F5-M0 114 F5-K2 50 QUI,52,66), Q(41,47,5S) G5-K7 45 G5-M0 89 G5-K2 14

The observational Q, Q diagrams are completely similar to the corresponding synthetic diagrams shown in Figs. 5-8. Consequently we confirm their suitability for two-dimensional classification of normal stars of all spectral types. M-type stars can be classified with the same Q(41 > 52, 66), Q(41, 4^•> 52) diagram but with different calibration than for G-K stars.

5. THE STROMVIL SYSTEM STANDARDS

Standards of high accuracy in the combined system are to be established later by special seven-color measurements. These standards should include the set of isolated stars in different right ascen- sions and declinations for future use as local standards for differential photometry, as well as some areas containing stars of different spectral classes and luminosities for determination of the color equations between the standard and instrumental systems. However, for now we propose three areas which are in use by observers in the Vilnius system, as temporary standard areas. Two of them, the Cygnus Standard Region (CygSR) and the Aquila Stan- dard Region (AqlSR) each contain 32 stars of different spectral types and of magnitudes between 5 and 7 (Zdanavicius et al. 1969 and Zdanavicius & Cerniene 1985). The CygSR is very comfortable for observers in the northern hemisphere while the AqlSR is also accessible at the southern latitudes. The third area near the North Celestial Pole (NCP) is north of +70 deg and contains 115 stars of different spectral types in the same range of magnitudes (Cernis et al. 1989). This area is accessible for observations in the northern hemisphere all year round. The Strómvil system 95 Q(35,37,47) -0.2

* ° • -r -J i .•. . • »••'•• % ; 0.0 - . •T• p

" ".I* „1 « , 0.2

0.4 o 0

0.6

0.0 0.2 0.4 0.6 0.8 1.0 Q(37,47,55)

Fig. 9. The Q(35,37,47), Q(35,47,55) diagram using the combined observations in the uvby and Vilnius systems. Dots are main-sequence stars, crosses are giants and circles are supergiants. Q(35,37,47) -0.4 V '«•«* * o» . -0.2 5 o W 6 /*8o it '. & » o** 0.0

02 o o 0.4 o

0.6

_1 L_1 L_J 1 1 1_ 0.0 0.2 0.4 0.6 Q(41,47,55)

Fig. 10. The Q(35,37,47), Q(41,47,55) diagram using the combined observations in the uvby and Vilnius systems. Symbols are the same as in Fig. 9. 96 V. Straizys, D. L. Crawford and A. G. Davis Philip

Q(35,37,47) -0.6 -1—i—i—i—f-

-0.4 -

• . * * * w6>°o -0.2 -

0.0 - *« s *x x O x

0.2 - 0 0.4 -

0.0 0.2 0.4 0.6 0.8 Q(41,52,66)

Fig. 11. The Q(35,37,47), Q(41,52,66) diagram using the combined observations in the uvby and Vilnius systems. Symbols are the same as in Fig. 9.

Q(4i,52,66) —j—i 1—i 1—i—i—i—|—i—i—r-

0.0

0.2

* 0.4 "o. si " " " W X « ° "(3 A * 0.6

0.8 -

0.4 0.6 0.8 1.0 1.2 Q(41.47,52)

Fig. 12. The Q(41,52,66), Q(41,47,52) diagram using the combined observations in the uvby and Vilnius systems. Symbols are the same as in Fig. 9. The Stromvil system 97

We find that 20 stars in the CygSR, 15 stars in the AqlSR and 46 stars in the NCP Region have been measured in the uvby system and it is possible to form their combined color indices in the Stromvil system. The variable, close binary and Ap stars have been excluded from the list of standards of the NCP region: Table 4 contains only 38 stars in this area. Among them is the O-type subdwarf BD+75°325. This star is very important in the observational determination of color equations between the instrumental and standard Stromvil systems, being the bluest among all standard stars. The magnitudes and color indices of these stars are given in Table 4 together with their MK spectral types collected from different sources. It is expected that the accuracy of these indices is of the order of ±0.01 mag. These stars may be used as preliminary standards for the new system.

6. CONCLUSIONS

It is shown that addition to the Stromgren photometric system of three passbands from the Vilnius photometric system makes the system more universal, capable of classifying stars in spectral types and luminosities (or determining their temperatures and surface gravities) everywhere in the HR diagram. This property of the Stromvil system is especially important in CCD photometry, making possible photometric classification of stars as faint as 20th mag and even fainter (Straizys 1992b). We recommend using the combined system in the photometric classification of faint stars where it is difficult or even impossible to obtain narrow-band Hf3 photometry and where the classification of G-K-M stars is needed in the presence of interstellar reddening. The Stromvil system is as good for determination of metallicities and peculiarities of stars as the original systems. The Stromvil system has been discussed at the meeting "Photo- metric Systems and Standard Stars" which took place at the Moletai Observatory in Lithuania in August 1995. Proceedings of the Con- ference will be published as a separate issue of the Baltic Astronomy journal (Straizys & Philip 1996). The application of this system with CCD image photometry will allow studies to be made of the distributions of stars by stellar type out to greater distances than have been possible up to now. We plan to observe standards of the system in several galactic fields and clusters both photoelectrically and with CCD cameras (Philip, Boyle & Straizys 1996). The system 98 V. Straizys, D. L. Crawford and A. G. Davis Philip

Table 4. Preliminary standards of the Stromvil system

Cygnus SR

HD MK V 35-55 37-55 41-55 47-55 52-55 55-66

184960 F7 V 5.73 2.12 1.71 1.02 0.47 0.18 0.48 186177 A5 lb 7.05 2.69 1.64 0.68 0.32 0.12 0.31 186408 G2 V 5.96 2.48 2.10 1.26 0.56 0.23 0.56 186427 G2.5 V 6.20 2.50 2.13 1.29 0.57 0.23 0.57 186440 Al V 6.05 1.79 1.29 0.38 0.15 0.06 0.12 187013 F7 V 4.99 2.14 1.69 1.02 0.47 0.19 0.46 187235 B8 V 5.77 1.29 0.90 0.29 0.13 0.05 0.11 188074 F2 V 6.20 2.09 1.63 0.89 0.40 0.15 0.39 188209 09.5 lb 5.62 0.43 0.41 0.28 0.16 0.07 0.17 188665 B5 V 5.14 0.92 0.71 0.21 0.09 0.05 0.10 189687 B3 IV-Ve 5.19v 0.72 0.56 0.20 0.09 0.06 0.16 191243 B5 lb 6.11 1.38 1.00 0.56 0.31 0.12 0.29 193370 F5 lb 5.17 3.14 2.22 1.28 0.59 0.23 0.57 194951 FI II 6.39 3.07 2.02 1.05 0.51 0.20 0.48 195050 A3 V 5.62 1.95 1.46 0.47 0.18 0.08 0.16 195324 Al lb 5.88 2.69 1.71 0.94 0.53 0.20 0.45 195593d F5 lab 6.19 3.85 2.75 1.73 0.86 0.33 0.77 196379 A9 II 6.11 2.82 1.77 0.79 0.39 0.15 0.38 199478 B8 Iae 5.67 1.80 1.35 0.97 0.56 0.20 0.51 199579 06 Ve 5.96 0.70 0.61 0.45 0.26 0.09 0.25

Aquila SR

HD MK V 35-55 37-55 41-55 47-55 52-55 55-66

169111 A2 V 5.95 2.00 1.38 0.45 0.19 0.08 0.18 177082 G2 V 6.92 2.36 1.99 1.23 0.54 0.23 0.57 178125 B8 III-V 5.09v 1.23 0.87 0.32 0.14 0.05 0.17 179406 B3 V 5.34 1.33 0.99 0.54 0.29 0.09 0.30 180028 F6 lb 6.97 3.34 2.48 1.50 0.73 0.28 0.68 181383 A2 V 6.02 2.03 1.47 0.51 0.19 0.08 0.18 182101 F6 V 6.35 2.07 1.65 0.98 0.46 0.16 0.46 183936 F2 III 7.20 2.13 1.69 0.98 0.45 0.17 0.48 187203 F8 Ib-II 6.44 3.45 2.71 1.71 0.77 0.29 0.74 187691 F8 V 5.11 2.30 1.86 1.13 0.51 0.19 0.52 187811 B2.5 Ve 4.95 0.71 0.55 0.18 0.08 0.04 0.18 187923 GO V 6.13 2.43 2.02 1.27 0.57 0.22 0.58 189090 B9 III 5.53 1.60 1.09 0.32 0.14 0.06 0.14 190323 GO la 6.83 3.54 2.63 1.62 0.69 0.27 0.68 190405 F2 lb 6.86 2.62 1.91 1.06 0.48 0.19 0.51 The Strömvil system 99

Table 4 (continued) North Celestial Pole SR

HD MK V 35-55 37-55 41-55 47-55 52-55 55-66

BD+75°325 sd05 9.55 -0.16 -0.02 -0.04 -0.01 0.00 0.02 6798 A3 V 5.64 1.86 1.36 0.40 0.14 0.07 0.14 12230 F0 V 5.27 2.10 1.63 0.82 0.36 0.14 0.37 12467 Al V 6.05 1.97 1.48 0.53 0.21 0.07 0.20 22701 F5 IV 5.86 2.08 1.68 0.91 0.41 0.19 0.42 26356 B5 V 5.57 0.96 0.72 0.22 0.09 0.04 0.12 33541 AO V 5.77 1.60 Í.19 0.34 0.12 0.07 0.09 33564 F6 V 5.05 2.17 1.77 1.03 0.47 0.18 0.46 45947 F5 IV 6.24 2.03 1.64 0.91 0.41 0.20 0.42 46588 F8 V 5.45 2.13 1.76 1.07 0.49 0.20 0.48 55075 AO III 6.31 1.67 1.15 0.34 0.13 0.06 0.12 82189 F7 V 5.72v 2.29 1.86 1.07 0.48 0.22 0.49 82210 G4 III-IV 4.56 2.77 2.36 1.46 0.64 0.29 0.65 83727 F0 V: 6.17 2.23 1.65 0.76 0.33 0.14 0.32 90089 F2 V 5.26 1.99 1.59 0.90 0.41 0.17 0.41 99945 A2m 6.12 2.16 1.61 0.75 0.30 0.12 0.30 106112 A5m 5.14 2.19 1.68 0.85 0.35 0.16 0.34 131873 K4 III 2.08 5.01 4.34 2.76 1.03 0.41 1.02 133002 F9 V 5.64 2.51 2.08 1.31 0.59 0.23 0.59 146926 B8 V 5.48 1.24 0.86 0.25 0.11 0.06 0.11 148048 F5 V 4.95 2.11 1.64 0.88 0.40 0.16 0.40 162003 F5 IV-V 4.58 2.12 1.68 0.96 0.44 0.18 0.43 162004 GO V 5.79 2.19 1.77 1.08 0.49 0.19 0.48 163989 F6 IV-V 5.04 2.23 1.79 1.06 0.49 0.19 0.48 164613 F2 II-III 5.45 2.41 1.71 0.82 0.36 0.15 0.37 166205 Al V 4.36 1.89 1.34 0.40 0.16 0.08 0.15 175286 Al V 5.35 1.90 1.37 0.47 0.18 0.07 0.16 180777 A9 V 5.13 2.03 1.56 0.81 0.35 0.13 0.36 197508 A4m 6.19 2.15 1.54 0.62 0.24 0.10 0.22 199095 AO V 5.75 1.77 1.25 0.36 0.14 0.06 0.14 201908 B8 V 5.91 1.41 0.99 0.29 0.11 0.05 0.10 209369 F5 V 5.03 2.14 1.68 0.99 0.46 0.17 0.46 210807 G7 II-III 4.79 3.23 2.72 1.71 0.71 0.28 0.68 212710 B9 .5 V 5.27 1.68 1.19 0.34 0.13 0.06 0.12 213403 A2m 5.83 2.12 1.55 0.62 0.22 0.10 0.21 214035 A2 V 5.68 1.96 1.31 0.39 0.16 0.07 0.16 214470 F3 III-IV 5.08 2.30 1.77 0.91 0.39 0.16 0.39 219485 AO V 5.86 1.80 1.27 0.36 0.14 0.07 0.11 221525 A7 IV 5.58 2.24 1.62 0.70 0.29 0.11 0.29 100 V. Straizys, D. L. Crawford and A. G. Davis Philip

Table 4 (continued) Normalizing O-type stars

HD MK V 35-55 37-55 41-55 47-55 52-55 55-66

24912 07.5 Illf 4.04v 0.59 0.50 0.40 0.22 0.08 0.22 47839d 07 Ve 4.66 0.16 0.15 0.09 0.05 0.03 0.06 203064 08e 5.00 0.53 0.43 0.36 0.21 0.08 0.23 214680 09 V 4.88 0.21 0.20 0.13 0.08 0.04 0.06

is proposed for the ESA astrometric and photometric GAIA satellite (Straizys & H0g 1995).

ACKNOWLEDGMENTS. We are grateful to G. Valiauga (In- stitute of Theoretical Physics and Astronomy, Vilnius) for the soft- ware for the calculation of the Q-parameters and to A. Kazlauskas (the same institute) for the selection of common stars between the Vilnius and Strömgren systems. One of us (V.S.) thanks Union Col- lege Physics Department for the financial support.

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