Study of Eclipsing Binary and Multiple Systems in OB Associations. I. Orion OB1a- IM Monocerotis

Abstract

All available photometric and spectroscopic observations were collected and used as the basis of a detailed analysis of the close binary IM Mon. The orbital period of the binary was refined to 1. d 19024249(0.00000014). The Roche equipotentials, fractional luminosities (in B, V and H p -bands) and fractional radii for the component stars in addition to mass ratio q, inclination i of the orbit and the effective temperature T eff of the secondary cooler less massive component were obtained by the analysis of light curves. IM Mon is classified to be a detached binary system in contrast to the contact configuration estimations in the literature. The absolute parameters of IM Mon were derived by the simultaneous solutions of light and radial velocity curves as M 1,2 = 5.50(0.24) M ⊙ and 3.32(0.16) M ⊙ , R 1,2 = 3.15(0.04) R ⊙ and 2.36(0.03) R ⊙ , T eff1,2 = 17500(350) K and 14500(550) K implying spectral types of B4 and B6.5 ZAMS stars for the primary and secondary components respectively. The modelling of the high resolution spectrum revealed the rotational velocities of the component stars as V rot1 = 147(15) km s −1 and V rot2 = 90(25) km s −1 . The photometric distance 1 of 353(59) pc was found more precise and reliable than Hipparcos distance of 341 (85) pc. An evolutionary age of 11.5(1.5) Myr was obtained for IM Mon. Kinematical and dynamical analysis support the membership of the young thin-disk population system IM Mon to the Ori OB1a association dynamically. Finally, we derived the distance, age and metallicity information of Ori OB1a sub-group using the information of IM Mon parameters.

Age Determination of Galactic B-type Stars in Double-lined Eclipsing Binaries

“…A comparison of the observed high-resolution spectrum with Kurucz atmosphere models gave atmospheric parameters and metallicity [Fe/H]= +0.2. The age of IM Mon determined by Bakis et al (2011) is in agreement with earlier determinations for Ori OB1a association by Blaauw (1991) and Brown et al (1999).…”

“…9. We found that metallicity of at least Z = 0.025 is needed to find a common age of the components which is in line with the values of [Fe/H] obtained by Bakis et al (2011). Then, the age of the system is about 9.7(2.9) Myr, which is in agreement with the previous determinations.…”

“…Till now, IM Mon was studied in details only in two papers, i.e., by Bakiş et al (2010) and Bakis et al (2011). In Bakis et al (2011), the analysis of all available photometric and spectroscopic observations allowed to determine the absolute values of masses: M A = 5.35(24) M and M B = 3.32(16) M , and radii: R A = 3.15(4) R and R B = 2.36(3) R . Moreover, it has been shown that IM Mon is a member of Ori OB1a association and the age of the system is about 11.5 Myr.…”

“…The inclination angle of the orbital axis is larger than i = 75 • for 31 binaries. Two systems have the value of i below 65 • , these are IM Mon (Bakis et al 2011) and V497 Cep (Yakut et al 2007).…”