35 Eclipsing binaries presenting unambiguous total eclipses were selected
from a subsample of the list of Wyrzykowski et al. (2003). The photometric
elements are given for the I curve in DiA photometry, as well as approximate
Teff and masses of the components. The interest of these systems is stressed in
view of future spectroscopic observations.Comment: 4 pages, 1 figure; poster presented at the conference "Close binaries
  in the 21st Century: new opportunities and challenges", Syros, 27-30 June
  200

B. Hauck

D. Schaerer

G. Michalska

I. Ribas

J.F. Gonzáles

J.S.B. Wyithe

L. Wyrzykowski

P. North

Pierre North

R.L. Kurucz

S.J. Kenyon

English

arXiv

35 Eclipsing binaries presenting unambiguous total eclipses were selected from a subsample of the list of Wyrzykowski et al. (2003). The photometric elements are given for the I curve in DiA photometry, as well as approximate teff and masses of the components. The interest of these systems is stressed in view of future spectroscopic observations

North, Pierre

Archive ouverte UNIGE

Binaries with Total Eclipses in the LMC: Potential Targets for Spectroscopy

Crossref

Infoscience - École polytechnique fédérale de Lausanne

35 Eclipsing binaries presenting unambiguous total eclipses were selected from a subsample of the list of Wyrzykowski et al. (2003). The photometric elements are given for the I curve in DiA photometry, as well as approximate teff and masses of the components. The interest of these systems is stressed in view of future spectroscopic observation

RERO DOC Digital Library

Astrophys Space Sci (2006) 304:219–221DOI 10.1007/s10509-006-9116-xO R I G I NA L A RT I C L EBinaries with Total Eclipses in the LMC: Potential Targetsfor SpectroscopyPierre NorthReceived: 1 October 2005 / Accepted: 18 November 2005C© Springer Science + Business Media B.V. 2006Abstract 35 Eclipsing binaries presenting unambiguous to-tal eclipses were selected from a subsample of the list ofWyrzykowski et al. (2003). The photometric elements aregiven for the I curve in DiA photometry, as well as ap-proximate Teff and masses of the components. The interestof these systems is stressed in view of future spectroscopicobservations.Keywords LMC . Stars: fundamental parameters1. IntroductionAs recalled by Wyithe and Wilson (2001), “systems wherethe stars are completely eclipsed are particularly importantbecause they can provide robust measurements of the ratioof radii”, k. Accurate determination of k is indeed a wellknown problem in partially eclipsed systems. An impressivedemonstration of this is provided by Fig. 3 of Gonza´les et al.(2005). Here, I draw attention to a few tens of totally eclipsingsystems in the LMC, which would deserve spectroscopic ob-servations for an orbit determination, and possibly additionalphotometric ones for a more accurate determination of radiiand surface brightness ratio. Such systems will be useful, notonly for distance determination, but also for comparison withstellar structure models.2. Sample, lightcurve solutionand stellar parametersFrom the sample of Wyrzykowski et al. (2003) based onOGLE photometry, we have selected a subsample of 510P. NorthLaboratoire d’astrophysique, Ecole Polytechnique Fe´de´rale deLausanne (EPFL), Observatoire, CH–1290 Sauverny, Switzerlandbinaries with Imax ≤ 18.0, a depth of the secondary mini-mum ≥ 0.20 mag and an EA type. This is the same sampleas that used by North and Zahn (2004). All lightcurves weresolved interactively with the EBOP code, assuming a lin-ear limb-darkening coefficient u p = us = 0.18 except in thefew cases of clearly cool components. Out of this sample,we selected visually 35 systems with clearly total eclipses.The fundamental stellar parameters were determined throughinterpolation in the evolutionary tracks of Schaerer et al.(1993) computed for a metal-content Z = 0.008 typical ofthe LMC. This was done as in North and Zahn (2004),but without the hypothesis of identical components and as-suming (m − M)0 = 18.5. The relative radii, orbital periodand surface brightness ratio Js were used to constrain thesolution. Js was calibrated in terms of Teff ratio throughthe models of Kurucz (1979). In addition, E(B − V ) andAV = 3.1 E(B − V ) were determined simultaneously, us-ing the measured B − V index, following North (2004). Thecondition that both components lie on the same isochronewas not implemented, because of the presence of some post-mass exchange systems; for the latter, the masses givenare just those of single stars with same Teff and luminos-ity, and therefore may be wrong. For main sequence sys-tems lacking a B − V index, stellar parameters were deter-mined in a cruder way, assuming both components lie ona log t = 7.0 isochrone. The Teff of cool giants in a fewsystems were derived from the B − V or the V − I in-dex assuming E(B − V ) = 0.143, while the masses wereassumed identical to those of stars with same MV on theisochrone. Some parameters of the I DIA lightcurve as wellas Teff and mass of both components are given in Table 1,a more complete version of which is available at the sitehttp://obswww.unige.ch/~north/DEB/tot_param.The errors are the formal ones given by the EBOP codeand give an idea of the quality of the fit, though one has toSpringer220 Astrophys Space Sci (2006) 304:219–221Table 1 Totally eclipsing systems in the LMC. The er-rors on rp , k and e cos ω are given as the last digit(s) ofthe corresponding values. The null uncertainties stand forparameters which were fixed during the fit, though theywere generally adjusted in a previous iteration. Elevenstars in the list are common to Michalska and Pigulski(2005): W03 No 114, 362, 1148, 1291, 1520, 1551, 1748,1880, 1996, 2279 and 2462. The Teff of cool stars wereestimated from B − V with the calibration of Hauckand Ku¨nzli (1996) or from V − I with the calibrationof Kenyon and Hartmann (1995) (their Table A5)No Iquad Porb rp k e cos ω L p(I) Teff p Mp Teff s Ms114 15.125 2.98958 0.258 2 0.537 04 0.0704 00 0.842 34768 23.2 26930 11.1362 15.266 3.37025 0.306 1 0.733 03 −0.0093 03 0.682 21999 9.6 20959 7.8398 16.862 3.33782 0.176 4 1.666 47 0.0031 00 0.563 23133 7.6 8256 2.7406 18.037 13.16448 0.315 5 0.427 09 0.0000 00 0.965 6387 6.1? 4056 1.6?416 16.736 5.16691 0.175 3 0.473 05 −0.2392 09 0.829 19066 6.6 17758 4.6460 16.618 2.68062 0.278 4 0.423 04 0.0005 00 0.866 19924 7.2 18539 4.8670 16.604 4.14459 0.178 4 1.632 35 0.0058 00 0.561 21405 7.0 8226 2.9810 16.743 3.31516 0.342 4 0.357 04 0.0061 00 0.896 14032 4.9 13591 3.1841 17.861 5.40797 0.158 3 0.542 09 −0.0012 09 0.798 12686 3.5 11453 2.51148 17.224 2.16054 0.262 2 0.653 05 −0.0341 09 0.741 18293 5.7 16106 4.11208 17.602 2.58542 0.258 3 0.476 06 0.0192 18 0.867 16308 5.0 12647 2.81212 18.034 2.05110 0.245 7 0.497 09 0.0535 23 0.858 7348 5.9? 6440 2.7?1263 17.076 6.12966 0.175 2 0.556 05 0.1714 06 0.762 14506 4.6 14514 3.61278 17.567 7.42814 0.168 3 0.413 07 0.0011 00 0.852 11135 3.3 11313 2.41291 16.898 5.23194 0.184 3 0.504 05 0.1656 08 0.816 17385 5.9 15840 4.01344 17.710 4.14494 0.233 5 0.505 08 0.0009 17 0.812 11088 3.2 10558 2.31381 16.860 79.17160 0.126 2 0.526 07 −0.0016 10 0.819 5552 8.6? 5214 4.7?1450 15.439 2.72713 0.330 1 0.605 02 0.0001 05 0.765 31983? 14.6? 23557? 8.2?1469 17.334 1.56400 0.316 3 0.482 04 0.0006 00 0.889 19480 6.1 13044 2.81520 16.082 1.33832 0.354 1 0.694 04 0.0000 00 0.720 27348? 10.8? 21970? 7.2?1551 16.393 1.53805 0.349 2 0.778 05 0.0000 00 0.716 22260 7.9 17536 5.21566 17.566 3.23738 0.223 6 0.450 09 −0.0256 13 0.864 15696 4.7 13351 2.91675 17.574 3.39105 0.295 8 0.364 09 0.0088 00 0.886 11436 3.5 11451 2.41748 15.544 5.45728 0.248 2 0.535 03 0.0254 06 0.800 19860 8.4 18469 5.81880 17.202 1.34524 0.333 3 0.668 07 −0.0001 00 0.753 18153 5.4 15305 3.81996 17.045 1.82795 0.258 3 0.535 05 −0.0037 12 0.850 23050 8.1 16899 4.22009 17.570 3.22935 0.204 4 0.447 09 −0.1751 23 0.869 18001 5.5 13873 3.02073 17.007 2.89578 0.303 5 0.386 06 0.0159 16 0.883 14864 4.8 14108 3.12279 16.289 3.31752 0.257 2 0.691 07 −0.1347 09 0.680 18293 6.5 18112 5.52289 17.789 3.80450 0.196 4 0.568 10 0.0001 15 0.769 13681 3.9 13130 3.02380 17.374 2.83324 0.275 4 0.447 07 0.0939 20 0.852 14296 4.4 13320 3.02462 16.767 4.26120 0.189 2 0.617 06 0.0993 10 0.766 23378? 8.1? 17646? 4.9?2482 16.272 8.07316 0.177 4 1.547 39 0.0000 00 0.616 8800? 9.6? 7050? 8.0?2533 17.748 3.27882 0.269 6 0.640 11 −0.0394 19 0.736 10035 2.8 9311 2.22583 17.717 2.07166 0.266 4 0.567 09 −0.0346 20 0.788 14909 4.2 13389 3.0keep in mind that some parameters were kept fixed in the fit,so that the errors displayed are rather lower limits to the realuncertainties.The HR diagrams in Figure 1 show that all but four binarieshost main sequence components.3. DiscussionMany systems with total eclipses have also relatively shal-low minima. Although this might be due to 3rd light in somecases, this cannot explain all of them. Many such systemsare certainly pairs of main sequence stars with a relativelysmall ratio of masses and radii. Among them, those for whichJs ∼ 1 are especially interesting: they are composed of twostars close to the turn-off, with an evolved primary and anunevolved secondary. The ratio of radii is often near 0.5.Such systems allow to probe efficiently the global metal-licity and helium content of each component – as far asthe stellar structure models can be trusted – according tothe method of Ribas et al. (2000). Since the metallicity ofthe LMC is less than half that of the Sun, this can poten-tially improve the Y/Z relation obtained by Ribas et al.on the basis of Galactic systems. Adding totally eclipsingsystems of the SMC will further improve the determinationof this relation, even providing an independent estimate ofthe primordial He abundance through extrapolation to zerometallicity.SpringerAstrophys Space Sci (2006) 304:219–221 221Fig. 1 HR diagram of the totally eclipsing systems in the LMC. Noticethe three systems with giant components (a fourth one, in the I vs V-Idiagram, is an Algol-type system)However, the great interest of these systems has a price asregard to spectroscopic observations: the small k implies asmall luminosity ratio – especially in the blue (λ domainof choice because of the number of spectral lines) if thesecondary is cooler than the primary – so that high S/Nspectra will be needed. The UVES instrument on the VLT,used with a wide slit, may be appropriate. Another possi-bility would be the use of FLAMES-GIRAFFE in the IFU“low” resolution mode (R ∼ 10000), which would allow toobserve a few systems simultaneously.ReferencesGonza´les, J.F., Ostrov, P., Morrell, N., Minniti, D.: ApJ 624, 946 (2005)Hauck, B., Ku¨nzli, M.: Baltic Astronomy 5, 303 (1996)Kenyon, S.J., Hartmann, L.: ApJS 101, 117 (1995)Kurucz, R.L.: ApJS 40, 1 (1979)Michalska, G., Pigulski, A.: A&A 434, 89 (2005)North, P.: ASP Conf. Series 318, 273 (2004)North, P., Zahn, J.-P.: New Astron. Rev. 48, 741 (2004)Ribas, I., Jordi, C., Torra, J., Gime´nez, ´A.: MNRAS 313, 99 (2000)Schaerer, D., Meynet, G., Maeder, A., Schaller, G.: A&AS 98, 523(1993)Wyithe, J.S.B., Wilson, R.E.: ApJ 559, 260 (2001)Wyrzykowski, L., Udalski, A., Kubiak, M. et al.: AcA 53, 1 (W03)(2003)Springer

http://doc.rero.ch/record/317855/files/10509_2006_Article_9116.pdf

Binaries with total eclipses in the LMC: potential targets for
  spectroscopy

Binaries with total eclipses in the LMC: potential targets for spectroscopy

Abstract

Similar works

Full text

Available Versions

Archive ouverte UNIGE

Crossref

Infoscience - École polytechnique fédérale de Lausanne

RERO DOC Digital Library