HD 174884: a strongly eccentric, short-period early-type binary system discovered by CoRoT

Abstract

Accurate photometric CoRoT space observations of a secondary seismological target, HD 174884, led to the discovery that this star is an astrophysically important double-lined eclipsing spectroscopic binary in an eccentric orbit (e ∼ 0.3), unusual for its short 3. d 65705 orbital period. The high eccentricity, coupled with the orientation of the binary orbit in space, explains the very unusual observed light curve with strongly unequal primary and secondary eclipses having the depth ratio of 1-to-100 in the CoRoT "seismo" passband. Without the high accuracy of the CoRoT photometry, the secondary eclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-up program provided 45 high dispersion spectra. The analysis of the CoRoT light curve was performed with an adapted version of PHOEBE that supports CoRoT passbands. The final solution was obtained by a simultaneous fitting of the light and the radial velocity curves. Individual star spectra were obtained by spectrum disentangling. The uncertainties of the fit were achieved by bootstrap resampling and the solution uniqueness was tested by heuristic scanning. The results provide a consistent picture of the system composed of two late B stars. The Fourier analysis of the light curve fit residuals yields two components, with orbital frequency multiples and an amplitude of ∼0.1 mmag, which are tentatively interpreted as tidally induced pulsations. An extensive comparison with theoretical models is carried out by means of the Levenberg-Marquardt minimization technique, and the discrepancy between the models and the derived parameters is discussed. The best fitting models yield a young system age of 125 million years which is consistent with the eccentric orbit and synchronous component rotation at periastron.

Light Curve Solutions of Ten Eccentric Kepler Binaries, Three of them with Tidally Induced Humps

“…(10) The ratios T 2 /T 1 of our targets fall in the range 0.8-1.0 with one exception, KIC 6220470, which value is 0.56 (Figure 14, middle). Opposite discrepancy has been found for HD 174884 (Maceroni et al 2009), which components are with equal temperatures irrespective of the negligible secondary eclipse. (11) The values q st of the mass ratios, obtained by the empirical relation temperature-mass of MS stars (Table 4), differed from those determined by our phoebe models q ≡ q PH (Figure 14, right).…”

Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue

“…There is an additional difficulty in finding low-q binaries, which is the low brightness ratio of the binary components. The identification of the faint lines of the secondary or the shallow secondary eclipse is then challenging and requires high SNR data (for an extreme case of eclipse depths see Maceroni et al 2009). Considering that, any new object with q < ∼ 0.85 is valuable.…”

The variability behaviour of CoRoT M-giant stars

“…Full Tables 2-4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/583/A122 of surface differential rotation (Lanza et al 2014), and the detection of eclipsing binary systems (e.g., Maceroni et al 2009;Slawson et al 2011;Maciel et al 2011). The aforementioned science cases represent only a few of the major topics among the many aspects of time-domain, high-precision photometry.…”