Australia Telescope National Facility

UBV Photometry of the Massive Eclipsing Binary TT Aur
S. Oezdemir, H. Ak, M. Tanriver, H. Guelsecen, \\
S. Guelsecen,
A. T. Saygac, E. Budding, O. Demircan.
, PASA, 18 (2), in press.

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Period Variation

The adopted period of TT Aur P_d is 1.332735d. From our observations we have obtained the following new times of minima: HJD min I = 2450486.4438 $\pm$ 0.0003 HJD min I = 2451083.5091 $\pm$ 0.0003 HJD min I = 2451587.2873 $\pm$ 0.0004 HJD min II = 2450488.4431 $\pm$ 0.0004 HJD min II = 2451081.5089 $\pm$ 0.0003 HJD min II = 2451517.3183 $\pm$ 0.0003. These results were derived using the well-known method of Kwee and van Woerden (1956). A list of published times of minima of TT Aur was given by Agerer (1998). By combining all timing data we formed the O - C diagram of Figure 1, where the calculated estimates were obtained using Simon's (1999) elements. The photometric times of minima show a sinusoidal variation superimposed on a parabolic variation of longer term. The sinusoidal variation, realized by Simon (1999), is probably due to an unseen third companion in the system. Orbital elements of this hypothetical third body have been determined and compared with Simon's results in Table 1. Here A^d is the semi-amplitude of the O - C changes in days; $V_{\rm rad}$ is the deduced third body's radial velocity amplitude. Table 2 gives mass estimates for the third body for different inclinations. If we assume a coplanar orbit to that of TT Aur and adopt i = 88 $^\circ$ , the mass and luminosity of the third body should be about 1.18

$M_{\hbox{$\odot$}}$ and 1.7

$L_{\hbox{$\odot$}}$ . The fractional contribution to the overall light of such a body would be negligible ( $L_3 \sim$ 0.00025

$L_{\rm TT Aur}$ ). On this basis, the third body's light should not noticeably affect the light curves of TT Aur.

**Table 1:** Orbital Elements of the hypothetical third body in TT Aur
	This work	Simon (1999)

Period	4465d	4465d (12.2 years)
e	0	0.296
$\omega$ $^\circ$	...	346.9
A^d	0.0058	0.00545
$V_{\rm rad}$ (km s^-1)	27.8	...
$\Delta$ (AU)	12.5	...
L₃ (L $\odot$ )	1.7	...

**Table 2:** Masses of third body for different orbital inclinations
Inclination ( $^\circ$ )	Mass ( $M_{\hbox{$\odot$}}$ )

30	2.5
60	1.4
90	1.2

Next Section: The light curves
Title/Abstract Page: UBV Photometry of the
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Contents Page: Volume 18, Number 2

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