Abstract. The University of New South Wales is undertaking a search for transiting extrasolar planets using the Automated Patrol Telescope (APT) at.
Transiting Extrasolar Planets Workshop ASP Conference Series, Vol. 366, 2007 C. Afonso, D. Weldrake and Th. Henning
Byproducts of the University of New South Wales Extrasolar Planet Search J. L. Christiansen, M. G. Hidas, M. C. B. Ashley, J. K. Webb, and D. Hamacher School of Physics, University of New South Wales, Sydney, Australia T. Young Institute of Astrophysics, Cambridge University, Cambridge, UK M. Lopez-Morales Carnegie Institute of Washington, Washington DC, USA Abstract. The University of New South Wales is undertaking a search for transiting extrasolar planets using the Automated Patrol Telescope (APT) at Siding Spring Observatory (SSO), Australia (Hidas et al. 2005). Many varieties of variable stellar phenomena will be found among the high precision lightcurves generated, including eclipsing and contact binaries, and numerous classes of variable stars (Christiansen et al. 2006). Eclipsing low-mass binary stars are extremely valuable for constraining theoretical models of star formation due to the precise constraints on the masses and radii of the components. We present here lightcurves of three eclipsing binary systems with low mass components — a K-K star system, a G-M star system, and a potential G-brown dwarf system which has now been re-classified as a probable blended system.
Introduction Testing of theoretical models of low-mass stars has been hindered by the lack of well-constrained data. For the small number of low-mass stars where good data have been obtained, there is a clear trend for theory to underestimate the radii of these stars at a given mass by ∼10% (Ribas 2006), as demonstrated in Figure. 1. Although it is difficult to precisely constrain the masses and radii of low-mass stars, detecting low-mass eclipsing binary systems makes this task much easier, due to the geometrical information derived from the lightcurves. UNSW-TR-2 The planet candidate UNSW-TR-2 was detected in a field centred on the open cluster NGC6633. The original APT lightcurve was comprised of 79 nights of data, compiled over three observing seasons from 2002–2004. The top panel of Figure. 1 shows a phase-folded lightcurve of 8 high-quality nights of data. The period is 2.11674 ± 0.00002 days, with the high precision a result of the observations spanning three years. As the depths of the primary and secondary transits are very similar, the initial period was determined as half this duration, 102
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Figure 1. Theoretical main-sequence isochrone (300Myr) compared to experimentally derived masses and radii of low-mass stars. The two K7 Ve components that comprise the UNSW-TR-2 system are plotted as triangles.
and the system was flagged as possibly containing a transiting planet. Spectroscopic followup with the Double-Beam Spectrograph on the 2.3m telescope at SSO was performed, indicating the presence of two K7 Ve dwarfs (Young et al. 2006) with masses of 0.529 ± 0.035 M⊙ and 0.512 ± 0.035 M⊙ (Fig. 1). UNSW-TR-13 The original APT lightcurve comprised of 32 nights of data taken in early 2005. The middle panel of Figure. 1 shows a phase-folded lightcurve with a period of 2.2838 ± 0.0001 days. Followup with the echelle spectrograph on the 2.5m du Pont telescope at Las Campanas Observatory yielded radial velocity variations of 56.4 ± 2.5 km/s. The host star was classified as a G5V star by comparison with UVILIB template spectra (Pickles 1998), indicating a early-type M-dwarf companion with a minimum (m sin i) mass of 0.43 ± 0.05 M⊙ . UNSW-TR-14 UNSW-TR-14 was discovered in the same dataset as UNSW-TR-13, in early 2005. The bottom panel of Figure. 1 shows the phase-folded APT lightcurve with a period of 1.2797 ± 0.0001 days. As for UNSW-TR-13, echelle spectra were obtained, and radial velocity variations of 3.58 ± 0.18 km/s were derived. Comparison with the UVILIB template spectra indicated a G2V host star. Combined with the radial velocity variations, this suggests a low-mass brown dwarf companion with a minimum (m sin i) mass of 0.018 ± 0.005 M⊙ . However this
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Figure 2. Phase-folded lightcurves of the three candidates. Top panel — UNSW-TR-2; middle panel — UNSW-TR-13; bottom panel — UNSW-TR14.
result is clearly in contradiction with the deep secondary eclipse in the original APT lightcurve, since the eclipse of a brown dwarf by a solar-type star would be significantly shallower than this. Although further analysis of this object is required, we have reclassified the system as a probable blended system, with a foreground G2V star dominating the spectra, and a diluted background eclipsing binary providing the primary and secondary eclipses of comparable depths. Conclusion Due to the nature of transiting extrasolar planet surveys, a variety of objects besides transiting planets will be monitored. Although survey byproducts can distract from the main science goals, it is important to note that some are interesting in their own right. This paper has outlined several recent examples discovered in the APT dataset. References Christiansen, J. L. et al. in preparation Hidas, M. G. et al. 2005, MNRAS, 360, 703 Pickles, A. J. 1998, PASP, 110, 863 Ribas, I. 2006, Ap&SS, 304, 89 Young, T. W. et al. 2006, MNRAS, 370, 1529
