We report the variability of 21 stars belonging to 17 systems considered to be Trapezium-type systems by Allenet al. (1977a). In order to avoid serious problems due to possible light contamination by neighbouring stars, we have only considered systems with angular separations between components equal or greater than five seconds of arc. Among the new variables here reported there are five having ΔV variations greater than 0m.3. For six systems we have spectrograms of the individual components. Three of the six systems are probably optical configurations and only two of the variables in the remaining three systems may be physical companions.Universidad Nacional de La Plat

Clariá, Juan J.

Lapasset, E.

Levato, Orlando Hugo

Malaroda, Stella Maris

Astrophysics and Space Science

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P H O T O M E T R I C  V A R I A B I L I T Y  OF S T A R S  B E L O N G I N G  TO THE T R A P E Z I U M - T Y P E  S Y S T E M S  J. J. C L A R I A  *t  and E. L A P A S S E T *  Observatorio Astronfimico, Universidad Nacional de Cdrdoba, Argentina H. L E V A T O *  and S. M A L A R O D A  Observatorio Astron6mico, Universidad Nacional de La Plata, Argentina (Received 21 June, 1984) Abstract. We report the variability of 21 stars belonging to 17 systems considered to be Trapezium-type systems by Allen et al. (1977a). In order to avoid serious problems due to possible light contamination by neighbouring stars, we have only considered systems with angular separations between components equal or greater than five seconds of arc. Among the new variables here reported there are five having A V variations greater than 0~3. For six systems we have spectrograms of the individual components. Three of the six systems are probably optical configurations and only two of the variables in the remaining three systems may be physical companions. 1. Introduction If among the components of a multiple system of three or more stars, three distances of the same order of magnitude (i.e., with ratios larger than 89 but less than 3) can be found, then the system is one of Trapezium-type; if no three distances of the same order of magnitude can be found, then the multiple system is of ordinary type (Ambartsumian, 1954). Our present knowledge of the nature of the Trapezium-type systems is still very poor. Moreover, some results obtained by different authors seem to be highly contradictory. In fact, while a number of dynamical considerations on Trapezium-type systems have led Allen and Poveda (1974, 1975) to the conclusion that these systems are young or even extremely young (ages between 105 and 106 yr), no evidence of youth seems to be present among a sample of 68 and 7 Trapezia photometrically studied by Echevarria etal.  (1979)and Roth et aL (1979), respectively. In particular, Echevarria et al. (1979) have found that the late-type Trapezia cannot be young. In general, however, the idea that Trapezia are young objects seems to be based on better grounds (Ambartsumian, 1954; Sharpless, 1954; Allen etal . ,  1977b; Warman and Echevarrla, 1977). * Visiting astronomer of Cerro Tololo Inter-American Observatory supported by the National Science Foundation under contract No. AST 74-04128. Visiting astronomer, University of Toronto (David Dunlap Observatory) 24-inch telescope at Las Campanas Observatory. Astrophysics and Space Science 108 (1985) 95-100. 0004-640X/85/1081-0095500.90. 9 1985 by D. Reidel Publishing Company. 96 J. J. CLARIA ET AL. 2. Preliminary Results Although Trapezia are considered very interesting objects as regards their kinematic and dynamical features (Allen and Poveda, 1974, 1975), very few observational data are available in the literature at present. The need for information on Trapezium-type systems of the southern hemisphere encouraged us to plan a straightforward obser- vational program to be carried out from Cerro Tololo (CTIO) and Las Camapanas (LCO) observatories. The project, initiated two years ago, consists in obtaining the UB V photometry and classification spectra as basic data to explore the nature of the stars which belong to the Trapezia. The Trapezium-type systems that we have observed have all been selected from the catalogue compiled by Allen et al. (1977a). This catalogue contains 915 Trapezium-type systems, spread out over the sky in a rather uniform way with respect to right ascension. With a few exceptions, the visual magnitudes of the individual components which have been photoelectrically measured range from 8.0 to about 14.0. Only those systems with weU-separated components have been observed. One of the main purposes of this project is to examine the physical reality of these unstudied group of stars. After the completition of the observing program we will discuss the colour-colour and HR-diagrams for each system and attempt to infer their evolu- tionary stages. A preliminary analysis of the spectrophotometric material collected from CTIO and LCO for 87 systems allowed us to obtain some preliminary results which can be succintly summarized as follows: (1) Most of the observed systems include late-type components, i.e., G and/or K-type stars. (2)No obvious sign of youth seems to be present throughout the sample. (3) The main physical characteristics of the observed systems differ considerably from those of the well-known Orion Trapezium. (4) Nearly 509/0 of the observed Trapezia are genuine physical systems. Therefore, the incidence of optical systems appears to be much higher than expected. 3. Observations and Results for the Variable Stars The photometric observations were carried out during various observing runs in 1982-1984 using the 1.0 m telescope of the CTIO and the 60 cm Canadian telescope of the David Dunlap Observatory located in LCO. Mean coefficients were employed in both observatories to correct for atmospheric extinction and nightly observations of about 12 E-region primary standards (Cousins, 1973, 1974) were used to transform to the U B V  system. The external (e) and internal (a) mean errors of the U B V  photometry are summarized in Table I. The mean internal error a v is about 0~. 02, a value being practically independent of the V-magnitude and the telescope used. On the other hand, there exists a small increase in the internal errors a B _ v and o" v_ B with the V-magnitude. As was already mentioned, spectroscopic observations for a few of the systems with stars that turned to be variables were obtained using the spectrograph of the 60 cm telescope of David Dunlap Observatory at Las Campanas. The VARO image tube was used during the observations. The dispersion of the spectrograms is 120 A mm- 1 VARIABILITY OF TRAPEZIUM-TYPE STARS TABLE I Mean errors of the UBV photometry 97 External mean errors ~v eB-v  ~u-n 60 cm (LCO) 0.010 0.009 0.009 100 cm (CTIO) 0.008 0.006 0.009 Internal mean errors Uv un- v uu-n 60 cm (LCO) 100 cm (CTIO) V -.< 8.0 0.018 0.013 0.014 8.0 < V < 9.0 0.021 0.012 0.019 9.0 < V < 10,0 0.015 0.014 0.019 10.0 < V< 11.0 0,019 0.017 0,022 11,0 < V < 12.0 0.020 0.021 0.021 12,0 < V 0.019 0.021 0.030 8.0< V_<9.0 0.014 0.005 0.012 9.0 < V < 10.0 0.012 0.006 0.014 10.0 < V < 11.0 0.022 0,010 0,015 11.0 < V< 12.0 0,018 0.011 0.021 12.0 < V < 13.0 0.018 0.016 0,021 13.0 < V 0.018 0,018 0,021 The purpo se of this paper is to report the variability of 21 stars belonging to 17 systems considered to be Trapezium-type systems by Allen et al. (1977a). We have considered a star to be a photometric variable when its individual V measures during different nights displayed variations greater than five times the mean internal error, i.e., AV > 0.'Yl. Several systems catalogued by Allen et al. have components whose angular separa- tions are very small. Consequently, the photoelectric measurements of such components are very difficult as they include generally a certain degree of light contamination. In the present work, however, we have only taken into account the individual variations of components belonging to systems whose angular separations are equal or greater than five seconds of arc. In this way, we have avoided the problems due to light contamination by neighbouring stars. Among the new variables detected there are five having V amplitudes greater than 0.'73 while the other 16 have AV variations in the interval 0.ml0 < V <  0.~30. The individual U B V  observations of the new variables are listed in Table II. Columns (1) and (2) give the star identification from Alien et al. (1977a). Column (3) lists the present MK classification. The spectral type given in parenthesis means that an MK type is not available and it has been estimated from the U B V  colours. The heliocentric Julian Date is listed in column (4), while columns (5-7) give the magnitudes and colours in the U B V  system. Identification charts of the 21 new variables will be published, in a short time, in a more extensive paper. 98 J. J, CLARIA ET AL. TABLE II Individual UB V data of new variable star System Corn- Sp. Hel. J.D. V B - V  U -  B Comments ponent type 2440000. + Allen 23 A (K4) 5293,5986 8.610 1.436 1.672 5287.6232 8.509 1.434 1.617 5291.6065 8.538 1,420 1.621 B (K1) 5292.6042 1 3 . 5 0 3  1,119 0.78t 5294.5960 14,144 1.025 - 5296.6110 1 3 . 8 6 9  0.905 0.558 Allen 30 A (K2) 5286,6921 7.736 0.949 0.691 5287,6362 7.718 0.965 0.715 5288,6370 7.698 0.970 0.716 5290,6662 7.798 0.988 0.679 Allen 38 C (F7) 5293.6089 1 2 . 6 6 6  0.527 0.013 5294.7708 1 2 . 7 8 6  0.537 0.004 Allen 61 C - 4927.7222 13.538 0.749 0.305 4928.5903 13.422 0.689 0.565 4933.5628 13.196 0.726 0.396 4933.5903 13.352 0.527 - Allen 108 B (GO) 4927.6319 1 2 . 8 2 8  0.483 0.108 4933.6125 12.940 0.423 0.162 4934.5806 12.688 0.657 0.290 Allen 108 B (GO) 4934.6001 1 2 . 6 8 6  0.665 0.267 5287.5556 1 2 , 6 0 1  0.674 0.106 52935903 12.704 0.635 0.081 Allen 108 C G8III 4927.6181 1 1 , 8 1 1  0.712 0.507 4933s 11.828 0.731 0.476 5287.5764 11.659 0.861 0.472 5293.5860 11.734 0.810 0.474 Allen 124 C (FT) 5292.6389 1 2 . 6 8 9  0.498 -0.023 5293.6319 1 2 . 5 8 8  0.555 0.020 Allen 147 D (F2) 4927.6597 1 1 . 6 4 8  0.400 0.086 4929.6391 1 1 . 6 2 9  0.425 0.130 4933.6743 11.587 0.444 0.176 5294.6252 11.534 0.415 0,059 Allen 163 (G5) 5294.6875 12 ,631  0,666 0.184 5295.6840 1 2 . 4 4 1  0.676 0.149 Allen 168 P (GS) 5287.7014 1 3 . 3 1 9  0,650 0.320 5295.6668 13.512 0,763 0.452 Allen 169 C (FS) 5292.7152 12.867 0.553 -0.049 5295.6806 1 2 . 7 5 1  0.568 - 0.066 Allen 205 B (B7) 5296.7639 9.290 -0.002 -0.380 5297.7847 9.154 - 0.007 - 0.367 C (B6) 5296,7800 9,519 0.016 -0.409 5297.7991 9.418 -0.019 - 0.423 Comp. A, F4V, V = 6.83 Comp. B, F5V, V = I 1.48 Probably an optical system Comp. A, M6III, V = 5.61 Comp. B may be a physical companion Comp. C may be optical Comp. AB, B8V, V = 6.44 Comp. C, A2V, V = 8.76 Comp. E, K5III, V = 7.83 Comp. F, F5IV-V, V = 8.25 VARIABILITY OF TRAPEZIUM-TYPE STARS 99 Table H (continued) System Compo- Sp. Hel. J.D. V B-V U - B Comments nent type 2440 000. + Allen 210 C (K3) 5291.7222 13.159 1.198 0.946 5292.7013 12.960 1.168 0.841 Allen 901 A (B5) 5287.6056 5.450 -0.054 -0.464 5291.6071 5.348 -0.032 -0.473 Allen 902 C (K0) 4927.5069 12,342 1.052 0.663 Comp. A, A1V, V = 7.98 4928.5139 12.281 1.007 - Comp. B, A2V, V = 8.43 4930.5301 12.169 0.887 0.400 Probably a physical 4933,5069 12.144 0.898 0.459 system Allen 920 A (F7) 5287.5572 11.747 0.629 0.122 5291.5727 11.525 0.580 0.098 5294.5547 11.414 0.653 - 0.039 Allen 937 B K31b 4929.5314 12.050 0.728 0.495 Comp. A, F3IV, V = 9.15 4930.5347 12.125 0,862 0.227 Comp. C, V = 13.10 4931.5382 11.147 0,722 0.372 Probably an optical 5294.5139 12.178 0.787 0.321 system Allen 937 D (F6) 4929.5501 13.458 0.370 0.012 4930.5548 13.532 0.410 - 4931.5600 13.670 0.404 - 0.059 5294.5361 13.580 0.518 - 0.010 5297.6089 13.406 0.538 0.070 Allen 948 B G5III 4933.5486 11.720 0.620 0.125 Comp. A, F8IV, V= 9.51 4934.5556 11.863 0.617 0.32l Probably an optical 5294.5417 11.795 0.585 0.071 system 5296.5556 11.906 0.756 0.242 In the comments  in the last co lumn of Table II  there are indications concerning with the probable physical nature  of the systems. In  those cases with available M K  types it is clear that several of the variables may be optical companions.  For  six systems we have spectra of the individual components  or at least of some of them. Three systems seem to be optical and in the remaining three there are two variables which may be physical companions .  However,  more observational work is needed to clarify the point. Acknowledgements We are very indebted to staff members,  night assistants and visitors' support  both of CTIO and LCO for the observing time and their kind hospitality. This work was partially supported by C O N I C E T  and CIC of Argentine. 100 J.J. CLARIA El" AL. References Allen, C. and Poveda, A.: 1974, in Y. Kozai (ed.), 'The Stability of the Solar System and of Small Stellar Systems', 1tt U Syrnp. 62, 239. Allen, C. and Poveda, A.: 1975, Publ. Astron. Soc. Pacific 87, 499. Allen, C., Parrao, L., Tapia, M., and Poveda, A.: 1977a, private communication. Allen, C., Tapia, M., and Parrao, L.: 1977b, Rev. Mexicana Astron. Astrophys. 3, 119. Ambartsumian, V. A.: 1954, Contr. Obs. Byurakan 15, 3. Cousins, A. W. J.: 1973, Mern. Roy. Astron. Soe. 77, 223. Cousins, A. W. J.: 1974, Monthly Notices Astron. Soc. South Africa 33, 149. Echevarria, J., Roth, M., and Warman, 3.: 1979, Rev. Mexicana Astron. Astrophys. 4, 287. Roth, M., Echevarria, J., Franco, J., and Warman, J.: 1979, Rev. Mexicana Astron. Astrophys. 4, 209. Sharpless, S.: 1954, Astrophys. J. 119, 334. Warman, J. and Echevarria, J.: 1977, Rev. Mexicana Astron. Astrophys. 3, 133. 

Photometric variability of stars belonging to the trapezium-type systems

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Photometric variability of stars belonging to the trapezium-type systems

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