Andersen, J.

Casey, B.W.

Clausen, J.V.

Cunha, N.C.S.

Garcia, J.M.

Gimenez, A.

Koff, S. de

Vaz, L.P.R.

NARCIS 

Four-colour photometry of eclipsing binaries. XXXVI. Light curves of the O7V+O9V system V 3903 Sagittarii

Leiden University Scholary Publications

ASTRONOMY & ASTROPHYSICS MARCH I 1998, PAGE 251SUPPLEMENT SERIESAstron. Astrophys. Suppl. Ser. 128, 251-254 (1998)Four-colour photometry of eclipsing binariesXXXVI. Light curves of the O7V+O9V system V 3903 Sagittarii?,??L.P.R. Vaz1,6, N.C.S. Cunha1,2, J. Andersen3, J.V. Clausen3, J.M. Garcia4,5, A. Giménez2,5,B.W. Casey6, and S. de Koff7,81 Departamento de F́ısica, ICEx, UFMG, C.P. 702, 30161–970 Belo Horizonte, MG, Brazil2 Laboratorio de Astrof́ısica Espacial y F́ısica Fundamental, INTA, Apdo. 50727, 28080 Madrid, Spain3 Astronomical Observatory, NBIfAFG, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark4 Departamento de F́ısica, E.U.I.T. Industriales, UPM, Ronda de Valencia 3, E-28012 Madrid, Spain5 Instituto de Astrof́ısica de Andalućıa, Apdo. 3004, E-18080 Granada, Spain6 Department of Astronomy, University of Wisconsin, wadison, Wisconsin 53706, U.S.A.7 Sterrewacht Leiden, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands8 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, U.S.A.Received May 22; accepted July 11, 1997Abstract. Complete uvby light curves of the youngdetached double-lined massive O-type eclipsing binaryV 3903 Sagittarii, obtained from 1989 to 1994, are pre-sented. The observations were obtained at two differentsites and a discussion of the characteristics of both datasets is included.Key words: binaries: eclipsing: spectroscopic — stars:individual: V 3903 Sgr — stars: early-type1. IntroductionThe southern, reasonably bright and massive early type(O7V + O9V, V = 7.m3, P = 1.d74, circular orbit)detached eclipsing binary V 3903 Sgr (see Table 1) wasdiscovered as eclipsing by Cunha et al. (1990), after re-ports of variations in the brightness of the system byCousins (1973) and Clariá (1976). The system is alsoa double lined spectroscopic binary (Conti & Alschuler1971; Niemela & Morisson 1988; Vaz et al. 1993, 1997).Therefore, V 3903 Sgr was included in our program forSend offprint requests to: L.P.P. Vaz at address 1? Based on observations done with the ZEISS 60 cm telescopeat the Pico dos Dias Observatory (PDO), National Laboratoryof Astrophysics, LNA–CNPq, Brasópolis, MG, Brazil, and withthe Danish 50 cm Telescope (SAT) at the European SouthernObservatory (ESO), La Silla, Chile.?? The Tables 2, 3 and 4, presented in this paper will be onlyavailable in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.htmlattainment of high precision differential photometry, asa good candidate for absolute dimension determinations.Strong proximity effects are present in the light curves,which show shallow but well defined and unequal min-ima, the primary minimum having a depth of 0.m18, 0.m02deeper than the secondary one in the y band.V 3903 Sgr is one of the rare massive systems with com-ponents still on the main sequence. Amongst these, onlyEM Car (Andersen & Clausen 1989) and Y Cyg (Simonet al. 1994; Hill & Holmgren 1995) have masses > 17 Mdetermined, together with the radii, to the accuracy de-sirable for tests of evolutionary models: 1− 2%. However,both EM Car and Y Cyg have nearly equal mass compo-nents, what makes difficult the control of theoretical evo-lutionary tracks. It turned out that V 3903 Sgr is the sys-tem with the most massive primary, with the largest massdifference between the components, and the one closestto the theoretical ZAMS (Vaz et al. 1997) amongst thosewith the highest reliable absolute dimensions known todate.In this paper we present the first accurate and com-plete light curves of V 3903 Sgr. Medium– (18 Å/mm)and high– (6 Å/mm) dispersion CCD coudé spectra havealso been obtained. A study based on these data, in-cluding times of minimum and a period analysis, (pub-lished separately, Vaz et al. 1997) yields precise absolutedimensions (MA = 27.27 ± 0.55, RA = 8.088 ± 0.088;MB = 19.01± 0.44, RB = 6.125± 0.060, solar units) andconcludes that the system is a member of the LagoonNebula complex, very close to the young open clusterNGC 6530, and with an age between 1.7 and 2.5 106 years.252 L.P.R. Vaz et al.: Four-colour photometry of eclipsing binaries. XXXVI.2. ObservationsThe photoelectric observations were collected at twosites, with different telescopes and equipment: the ZEISS60 cm telescope of PDO-LNA-CNPq with a single–channelTEXAS photometer and the Danish 50 cm telescope(SAT) at ESO with a 6-channel photometer. Although theuvby photometric system was used in all runs, it is naturalto expect differences between the two sets of data, causedby differences in the equipment (e.g. filter transmission)and in the site properties (altitude and humidity).2.1. The PDO measurementsDuring 35 nights (10 from Jun. 16 to Aug. 17, 1989, 9from Jul. 30 to Aug. 15, 1990, 16 from May 23 to Jun.18, 1991) V 3903 Sgr was observed at PDO (LNA–CNPq,Brasópolis, Brazil), with the 60 cm telescope and a single–channel photometer equipped with a photon counting sys-tem. A slightly elliptical diaphragm with 39.′′2 major axiswas used (Cunha 1990). No other star was detected insidethis diaphragm with an image intensifier placed at the eye-piece, despite the richness of the field close to V 3903 Sgr.Extinction corrections were based on the nightly co-efficients from the four comparison stars and other con-stant stars. When needed, linear or quadratic correctionswere applied for eventual instrumental drifts, since thetemperature of the cooled photomultiplier was kept 30◦Cbelow the (variable) ambient temperature and/or for vari-ations in the atmosphere transparency during the night.The dead time of the RCA 8850 tube (spectral response116, RCA Photomultiplier Tubes Catalogue, 1971) wasaccounted for in the reduction procedure.HD 165 999, HD 164 681, HD 164 584 (7 Sgr) andHD 167 666, all close (maximum projected distance inthe sky of 4.◦9) to V 3903 Sgr, were used as comparisonstars and observed alternately between the measurementsof V 3903 Sgr. All four stars were found to be constantwithin the observational accuracy throughout the observ-ing periods. The observations of C2, C3 and C4 were trans-formed to C1 by means of the constant difference of mag-nitude between them and C1 obtained from all nights.For completeness we repeat here Table 1 from Vaz et al.(1997), with information for V 3903 Sgr and the compar-ison stars.The light curves V 3903 Sgr − HD 165 999 in the in-strumental system u (478 points), v (532), b (544), y(537), are shown in Fig. 1 and are accessible in electronicform at the CDS as Table 2. Typical rms errors of one mag-nitude difference between the comparison stars were foundto be: 0.m009 (∆u), 0.m006 (∆v), 0.m005 (∆b, ∆y). Most ofthe phases were covered at least twice.2.2. The ESO measurementsV 3903 Sgr was also observed, during 32 nights (3 fromMay 04 to 17, 1990, 3 from Apr. 12 to 25, 1991, Jun. 06 andTable 1. Catalogue data and standard uvbyβ indicesfor V 3903 Sgr and the comparison stars. The indices forV 3903 Sgr are for phases 0.p75 (uvby) and 0.p22 (β)V 3903 Sgr C1 C2 C3 C4HR − − − 6 724 6 835HD 165 921 165 999 164 681 164 584 167 666SAO 186 366 186 375 186 160 186 163 186 594DM −24◦13 962 −23◦13 991 −26◦12 724 −24◦13 793 −28◦13 407Sp O7V+O9V A5III A4V F5II A4IIIα1950 18h06m14s 18h06m33s 18h00m17s 17h59m47s 18h14m13sδ1950 −23◦59′52′′ −23◦34′40′′ −26◦19′18′′ −24◦17′01′′ −28◦40′17′′l 6.◦9 7.◦3 4.◦3 6.◦0 3.◦7b −2.◦1 −2.◦0 −2.◦1 −1.◦0 −5.◦9V 7.306 7.683 7.340 5.408 6.198±6 ±8 ±10 ±9 ±6b−y 0.183 0.170 0.071 0.336 0.114±2 ±4 ±4 ±6 ±5m1 −0.009 0.142 0.122 0.140 0.162±5 ±2 ±7 ±4 ±9c1 −0.109 1.096 1.038 1.030 1.145±9 ±9 ±9 ±11 ±13β 2.584 2.869 2.879 2.709 2.852±2 ±4 ±6 ±6 ±318, 1993 and 24 from Jun. 06 to Aug. 09 1994), with the50 cm Strömgren Automatic Telescope at ESO, La Silla,Chile. The instrument was equipped with the six–channelspectrograph–photometer (four channels for simultaneousuvby photometry and two channels for simultaneous mea-surements of Hβ narrow and wide filters) and the pho-ton counting system described by Nielsen et al. (1987).In the measurements taken from 1990 to 1993 a circulardiaphragm of 13′′ diameter was used, but in 1994 obser-vations a 17′′ diameter diaphragm was used.The comparison stars used in the PDO observations,(Table 1), were adopted, and they were constant withinthe observational accuracy throughout the observing pe-riod. Each night several variables were observed, and thenightly extinction corrections were based on coefficientsdetermined from all the comparison stars. As happened inthe reduction of PDO measurements, linear or quadraticcorrections for instrumental drift and/or changes in skytransparency during the night were applied when needed.The dead times of the six EMI 9789QA uncooled pho-tomultipliers, which have S11 spectral response, were ac-counted for in the reduction procedure.Typical rms errors of one magnitude difference be-tween the comparison stars in the ESO measurementswere found to be: 0.m006 (∆u), 0.m003 (∆v, ∆b, ∆y). Mostof the phases were covered at least twice. The light curvesare shown in Fig. 3 of Vaz et al. (1997) and the obser-vations are available in electronic form at the CDS, asTables 3 and 4. Table 3 contains 180 magnitude differencesV 3903 Sgr − HD 165 999 in the instrumental system for1990, 1991 and 1993, obtained with the diaphragm of13′′ diameter, and Table 4 contains the 1994 observationsL.P.R. Vaz et al.: Four-colour photometry of eclipsing binaries. XXXVI. 253Fig. 1. uvby magnitude differences V 3903 Sgr−HD 165999 obtained at PDO, with the theoretical light curves (Vaz et al. 1997)(507 points, instrumental system), which were obtainedwith a diaphragm of 17′′ diameter.3. Comparison of observations obtained indifferent sites and using different diaphragmsEven though different sites, instruments, photometers anddiaphragms were used in these observations, these datamatch very well with each other, especially for the coloursy and b, for which no discrepancy is noticed between theobservations of Tables 2, 3 and 4. The v magnitude differ-ences obtained at PDO (instrumental system) lay system-atically fainter than those obtained at ESO by ≈0.m013,and the PDO u measurements are systematically fainterthan the ESO ones by ≈0.m025 (again in the instrumen-tal system). The PDO observations were obtained with asingle–channel photometer and each filter was measured ata time, while the SAT observations were obtained simulta-neously measuring the four colours each time. Despite thisdifference, the reduction procedures are essentially equaland could not account for the these discrepancies.One reason for such differences could be the fact thatthe photometers are essentially different: not only the setsof filters are different, but the PDO photometer is filterdefined, while the SAT one has, besides the filters, a grat-ing and a slit in the light path, defining the bandwidth ofthe measurements (a spectrograph-photometer).Fig. 2. Transmission curves for the uvby filters used at PDO(dashed line) and at ESO (continuous line). The slit limits ofthe SAT photometer are also shown as vertical dotted linesIn fact, the u filter transmission curve for the PDO in-strument is ≈ 15% broader in the “red” end than that for254 L.P.R. Vaz et al.: Four-colour photometry of eclipsing binaries. XXXVI.the filter used in SAT photometer. In Fig. 2 we show thetransmission functions for the filters of both the PDO andSAT photometers. The most striking difference happensfor the u filter. Considering that C1 (Table 1) is coolerthan V 3903 Sgr, there will be an excess of u light, pro-ceeding from the variable in the PDO measurements incomparison with the SAT ones. This could explain the ar-tificial third light (1.4%) found for the PDO u light curvein Vaz et al. (1997, no third light was found necessary forall the SAT light curves and the PDO vby ones). On theother hand, it is difficult to use the same argument toexplain the fact that the PDO u light curve be system-atically fainter then the SAT one. This happens in theinstrumental system only; the light curves transformed tothe standard system do agree in both sets for all fourcolours, showing that the transformations of Table 5 doeliminate the problem. However, in order to keep errors inthe geometrical parameters as small as possible, we avoidthe transformation to the standard system and analysethe light curves only in the instrumental system.A red leak in the PDO u filter could also be the rea-son for these problems, but we do not have any informa-tion about the existence of such a leak. Another possibleexplanation for such discrepancies might be the differentaltitudes of the 2 sites: while PDO is at 1 800 m in a veryhumid region, La Silla is located at 2 400 m above sea levelin a much drier climate. This would have stronger effectfor the shorter wavelengths.V 3903 Sgr illuminates the bright nebulae IC 4685(Hirshfeld & Sinnot 1982, 1985), and it is surprising thenegligible effect of using different diaphragms in ESO ob-servations (Tables 3 and 4) on the light curves. As theregion is rich of bright nebulae, measurements (especiallywith SAT, which has automatic pointing, but also manu-ally with the PDO telescope) of the sky background weretaken careful and consistently in the same relative posi-tions and after every observation of both variable and thefour comparison stars. This indicates that the backgroundcontributions, at the places selected for its measurements,are fairly constant in counts per unit area, the only ex-planation for the excellent agreement between the dataobtained with SAT using the different diaphragms.Coefficients for transformation to the standard uvbysystem are given in Table 5 for the data obtained in thetwo sites and in the different runs. The differences dis-cussed above are reflected in the coefficients of Table 5.Further discussion of these observations, includingtimes of minima, some observations in Hβ, and a spec-troscopic study will be published as part of a detailedphotometric analysis of V 3903 Sgr, based on these uvbylight curves and β index measurements (Vaz et al. 1997).Acknowledgements. We acknowledge grants from the DanishNatural Science Research Council, the Danish Board forAstronomical Research, the American National ScienceTable 5. Transformation coefficients; ∆ indicates the differ-ences in the instrumental system (Tables 2, 3 and 4) and δ thetransformed values in the standard systemδ(b− y)= D ∆(b− y)δm1 = F ∆m1 + J δ(b− y)δc1 = H ∆c1 + I δ(b− y)δV = ∆y + B δ(b− y)For data obtained at PDO–LNA–CNPq (Table 2):B = 0.026±0.010 H = 1.050±0.013D = 0.996±0.008 I = 0.016±0.037F = 1.047±0.072 J = 0.043±0.031For data obtained at SAT–ESO 1990 to 1993 (Table 3):B = 0.061±0.032 H = 1.015±0.008D = 1.022±0.008 I = 0.103±0.017F = 0.954±0.074 J = 0.019±0.015For data obtained at SAT–ESO 1994 (Table 4):B = 0.034±0.015 H = 1.014±0.010D = 1.022±0.010 I = 0.143±0.008F = 0.950±0.022 J = 0.000±0.008Foundation (AST94-1715), the Wisconsin Alumni ResearchFoundation, the Wisconsin Space Grant Consortium, theESO traveling fund, and from the Brazilian institutionsCNPq, FAPEMIG, FINEP, CAPES. Support was also receivedthrough the programme of cultural, educational, and scientificcooperation between Spain and Denmark. LPV gratefully ac-knowledges the hospitality received at the Dept. of Astronomy,Univ. of Wisconsin, Madison, from Aug. 93 to Oct. 94. Thisresearch has made use of the Simbad database, operated atCDS, Strasbourg, France.ReferencesAndersen J., Clausen J.V., 1989, A&A 213, 183Clariá J.J., 1976, IBVS 1106Cousins A.W.J., 1973, Mon. Notes Astron. Soc. S. Afr. 32, 11Conti P.S., Alschuler W.R., 1971, ApJ 170, 325Cunha N.C.S., 1990, M. Sci. Dissertation, Physics Dept.,Federal University of Minas Gerais, BrazilCunha N.C.S., Vaz L.P.R., Pôssa C.M.M., Helt B.E., ClausenJ.V., 1990, IBVS 3436Hill G., Holmgren D.E., 1995, A&A 297, 127Hirshfeld A., Sinnot R.W., 1982, Sky Catalogue 2000.0, Vol. 1.Cambridge Univ. Press and Sky Publishing Co.Hirshfeld A., Sinnot R.W., 1985, Sky Catalogue 2000.0, Vol. 2.Cambridge Univ. Press and Sky Publishing Co.Nielsen R.F., Nørregaard P., Olsen E.H., 1987, ESO Messenger50, 45Niemela V., Morrison N.D., 1988, PASP 100, 1436Simon K.P., Sturm E., Fiedler A., 1994, A&A 292, 507Vaz L.P.R., Cunha N.C.S., Vieira E.F., Myrrha M.L.M., 1993,ASP Conf. Ser. 40, 371Vaz L.P.R., Cunha N.C.S., Vieira E.F., Myrrha M.L.M., 1997,A&A 327, 1094

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Four-colour photometry of eclipsing binaries. XXXVI. Light curves of the O7V+O9V system V 3903 Sagittarii

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