We report the discovery by the HATSouth survey of HATS-3b, a transiting extrasolar planet orbiting a V = 12.4 F dwarf star. HATS-3b has a period of P = 3.5479 days, mass of M p = 1.07 M J , and radius of R p = 1.38 R J . Given the radius of the planet, the brightness of the host star, and the stellar rotational velocity (v sin i = 9.0 km s −1 ), this system will make an interesting target for future observations to measure the Rossiter-McLaughlin effect and determine its spin-orbit alignment. We detail the low-/medium-resolution reconnaissance spectroscopy that we are now using to deal with large numbers of transiting planet candidates produced by the HATSouth survey. We show that this important step in discovering planets produces log g and T eff parameters at a precision suitable for efficient candidate vetting, as well as efficiently identifying stellar mass eclipsing binaries with radial velocity semi-amplitudes as low as 1 km s −1 .
We report the discovery by the HATSouth survey of HATS-4b, an extrasolar planet transiting a V=13.46 mag G star. HATS-4b has a period of P ≈ 2.5167 d, mass of M p ≈ 1.32 M Jup , radius of R p ≈ 1.02 R Jup and density of ρ p = 1.55 ± 0.16 g cm −3 ≈ 1.24ρ Jup . The host star has a mass of 1.00 M ⊙ , a radius of 0.92 R ⊙ and a very high metallicity [Fe/H]= 0.43 ± 0.08. HATS-4b is among the densest known planets with masses between 1-2 M J and is thus likely to have a significant content of heavy elements of the order of 75 M ⊕ . In this paper we present the data reduction, radial velocity measurement and stellar classification techniques adopted by the HATSouth survey for the CORALIE spectrograph. We also detail a technique to estimate simultaneously v sin i and macroturbulence using high resolution spectra.
We report the discovery of four transiting F-M binary systems with companions between 0.1 − 0.2 M ⊙ in mass by the HATSouth survey. These systems have been characterised via a global analysis of the HATSouth discovery data, combined with highresolution radial velocities and accurate transit photometry observations. We determined the masses and radii of the component stars using a combination of two methods: isochrone fitting of spectroscopic primary star parameters, and equating spectroscopic primary star rotation velocity with spin-orbit synchronisation. These new very low mass companions are HATS550-016B (0.110 +0.005 −0.006 M ⊙ , 0.147 +0.003 −0.004 R ⊙ ), HATS551-019B (0.17 +0.01 −0.01 M ⊙ , 0.18 +0.01 −0.01 R ⊙ ), HATS551-021B (0.132 +0.014 −0.005 M ⊙ , 0.154 +0.006 −0.008 R ⊙ ), HATS553-001B (0.20 +0.01 −0.02 M ⊙ , 0.22 +0.01 −0.01 R ⊙ ). We examine our sample in the context of the radius anomaly for fully-convective low mass stars. Combining our sample with the 13 other well-studied very low mass stars, we find a tentative 5% systematic deviation between the measured radii and theoretical isochrone models.
We report the discovery of HATS-2b, the second transiting extrasolar planet detected by the HATSouth survey. HATS-2b is moving on a circular orbit around a V = 13.6 mag, K-type dwarf star , at a separation of 0.0230 ± 0.0003 AU and with a period of 1.3541 days. The planetary parameters have been robustly determined using a simultaneous fit of the HATSouth, MPG/ESO 2.2 m/GROND, Faulkes Telescope South/Spectral transit photometry, and MPG/ESO 2.2 m/FEROS, Euler 1.2 m/CORALIE, AAT 3.9 m/CYCLOPS radial-velocity measurements. HATS-2b has a mass of 1.37 ± 0.16 M J , a radius of 1.14 ± 0.03 R J , and an equilibrium temperature of 1567 ± 30 K. The host star has a mass of 0.88 ± 0.04 M and a radius of 0.89 ± 0.02 R , and it shows starspot activity. We characterized the stellar activity by analyzing two photometric follow-up transit light curves taken with the GROND instrument, both obtained simultaneously in four optical bands (covering the wavelength range of 3860−9520 Å). The two light curves contain anomalies compatible with starspots on the photosphere of the host star along the same transit chord.
Context. EX Lup-type objects (EXors) are low-mass pre-main sequence objects characterized by optical and near-infrared outbursts attributed to highly enhanced accretion from the circumstellar disk onto the star. Aims. The trigger mechanism of EXor outbursts is still debated. One type of theory requires a close (sub)stellar companion that perturbs the inner part of the disk and triggers the onset of the enhanced accretion. Here, we study the radial velocity (RV) variations of EX Lup, the prototype of the EXor class, and test whether they can be related to a close companion. Methods. We conducted a five-year RV survey, collecting 54 observations with HARPS and FEROS. We analyzed the activity of EX Lup by checking the bisector, the equivalent width of the Ca 8662 Å line, the asymmetry of the Ca II K line, the activity indicator S FEROS , the asymmetry of the cross-correlation function, the line depth ratio of the VI/FeI lines, and the TiO, CaH 2, CaH 3, CaOH, and Hα indices. We complemented the RV measurements with a 14-day optical/infrared photometric monitoring to look for signatures of activity or varying accretion. Results. We found that the RV of EX Lup is periodic (P = 7.417 d), with stable period, semi-amplitude (2.2 km s −1 ), and phase over at least four years of observations. This period is not present in any of the above-mentioned activity indicators. However, the RVs of narrow metallic emission lines suggest the same period, but with an anti-correlating phase. The observed absorption line RVs can be fitted with a Keplerian solution around a 0.6 M central star with m sin i = (14.7 ± 0.7) M Jup and eccentricity of e = 0.24. Alternatively, we attempted to model the observations with a cold or hot stellar spot as well. We found that in our simple model, the spot parameters needed to reproduce the RV semi-amplitude are in contradiction with the photometric variability, making the spot scenario unlikely. Conclusions. We qualitatively discuss two possibilities to explain the RV data: a geometry with two accretion columns rotating with the star, and a single accretion flow synchronized with the orbital motion of the hypothetical companion; the second scenario is more consistent with the observed properties of EX Lup. In this scenario, the companion's mass would fall into the brown dwarf desert, which, together with the unusually small separation of 0.06 au would make EX Lup a unique binary system. The companion also has interesting implications on the physical mechanisms responsible for triggering the outburst.
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