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Appendix A: Potential moving group members

In this appendix, we describe the properties of the planet-host stars with very wide companions that might belong to moving group as well as systems rejected as bona-fide pairs based on our spectroscopic follow-up (Sect. 3; Table 1).

Appendix A.1: BD 10–3166

Butler et al. (2000) announced a planet with almost circular orbit (e = 0.05) and a mass of 0.48 Jupiter masses (M_Jup) with a period of ~3.5 days around the G4V solar-type star BD 10−3166 (Hog et al. 1998; Høg et al. 2000). The star is located at 66 pc from the Sun, has an age of ~4.2 Gyr, is metal-rich ([Fe/H] = 0.5 dex), and has a proper motion of ~0.2 arcsec/yr. We confirm this estimated distance based on the absolute magnitude of a mid-G dwarf (e.g. Fig. 10 of Kirkpatrick et al. 2012).

We found a bright and wide common proper motion companion located at ~39 arcmin from BD 10−3166. We classify this potential companion as a M5–M5.5 dwarf based on the GTC optical spectrum. Using the J-band magnitudes of M5 and M5.5 dwarfs with their errors listed in Table 3 above, we derive a spectroscopic mean distance of 75–77 pc with a possible range of 63–90 pc. We conclude that these two objects are located at the same spectroscopic distance, with a projected physical separation of ~150 000–200 000 au.

Appendix A.2: HD 109749

Fischer et al. (2006) discovered a planet with a mass of 0.28 M_Jup with a period of ~5.2 days (e = 0.01) around the G3IV (or G3V C) star, HD 109749 (Houk 1978). The planet-host star is located at 56.3±4.3 pc with an age range of 7.4–13.2 Gyr and a metallicity estimated to [Fe/H] = 0.25±0.05 dex. The primary is part of a double system formed by CCDM J12373-4049A and CCDM J12373-4049B, which are separated by ~8.4–9.2 arcsec (Mason et al. 2001).

We detected two potential co-moving companions at 39.2 and 55.5 arcmin. We classify the closest wide companion as a K7 dwarf, comparing its spectrum with HD 157881 (Koen et al. 2010)⁹. Using Gl825 as a K7V reference at 3.946±0.012 pc (Hawley et al. 1996; van Leeuwen 2007), we determine a spectroscopic distance of approximately 140 pc. This distance estimate is 2.4 times greater than the distance of the planet-host star, implying that these two objects do not form a pair, even if we include the uncertainty on spectral classification and binary effects.

We classify the second companion as a M3.5±0.5 dwarf by direct comparison with Sloan templates. We derive a mean spectroscopic distance of 73.3 pc for the potential companion, with a range of 45–144 pc including the uncertainties on the spectral type and absolute magnitude vs. spectral type relations. Hence, we conclude that these two objects are located at the same spectroscopic distance.

Appendix A.3: HD 143361

Jenkins et al. (2009) detected an eccentric planet (e = 0.17 ± 0.15) with a mass of 3.12 M_Jup and a orbital period larger than 1000 days around HD 143361 (Houk 1978; Jenkins et al. 2011). The planet-host star is a G6V star (Houk 1978) at 65.66±5.51 pc from the Sun (van Leeuwen 2007) and a metallicity of Fe/H] = 0.29 dex (Nordström et al. 2004). We note that Minniti et al. (2009) quotes a spectral type of G0V (no reference is given though) and a distance of 59.35 pc for HD 143361 based on the early analysis of Hipparcos parallax (Perryman et al. 1997). Here we favour the new reduction of Hipparcos data performed by van Leeuwen (2007).

We found two wide companions at 33.7 and 45 arcmin from the planet-host star. We classify the closest candidate as a M6–M6.5 dwarf, suggesting a distance of 63–68 pc. Both components seem to be located at a very similar spectroscopic distance so we conclude that they might be physically associated. At the distance of 33.7 arcmin, we derive a projected physical separation of ~120 000–137 000 au for the pair.

We spotted a second potential co-moving companion at 45 arcmin from the planet-host star. We discarded that object photometrically. Nonetheless, we took an optical spectrum with NTT/EFOSC2 to confirm that it is an early-type star. Hence, this candidate companion is not associated with the planet-host star.

Appendix A.4: HD 159868

Wittenmyer et al. (2012) announced a second planet orbiting HD 159868 (Houk 1978) in addition to an eccentric planet candidate reported by O’Toole et al. (2007). After collecting more data and re-analysing the periodiograms of HD 159868, Wittenmyer et al. (2012) concluded that this subgiant star at 58.7±2.7 pc harbours two planets with masses of 2.1 and 0.73 M_Jup and periods of about 1180 and 353 days, respectively. The age of HD 159868 is estimated to be 8.1 Gyr with solar composition.

We uncovered two potential wide companion to the planet-host star, at about 40.7 and 42.3 arcmin. We classify the closest as a M3.0±0.5 dwarf and the furthest as a sdM0.5 subdwarf. For the former, we derive a mean spectroscopic distance of 130 (72–175) pc, twice larger than the distance of the planet-host star.

For the latter we infer a spectroscopic distance of 96±12 pc based on the parallax of LHS 536 (44.6±5.3 pc; van Altena et al. 1995) and its spectral type (sdM0.5; Gizis 1997). This distance is much larger than the distance of the planet-host star. Moreover, we observe a metallicity difference between this candidate and the planet-host star.

To summarise, we reject both potential companions as co-moving objects to the planet-host star HD 159868.

Appendix A.5: HD 207832

Haghighipour et al. (2012) discovered two jupiter mass planets orbiting the solar-metallicity (Fe/H = 0.06) G5V star HD 207832 (54.4±2.7 pc; van Leeuwen 2007; Jenkins et al. 2011) by radial velocity. Their minimum masses are estimated to 0.56 and 0.73 M_Jup, with orbital periods of about 162 and 1156 days, and eccentricities of 0.13 and 0.27, respectively.

We unearthed a wide common proper motion companion to HD 207832, located at 38.6 arcmin. We classify it as a M6.5 dwarf, implying a distance of 48 pc (42–50 pc).

We conclude that these two objects most likely form a pair with similar spectroscopic distances and a projected physical separation of ~97 000–132 000 au.

Appendix A.6: HD 216435

Butler et al. (2006) announced a new planet orbiting HD 216435, a G0V star at 32.62±0.42 pc (van Leeuwen 2007) with an age of 5.27 Gyr (Saffe et al. 2005) and a metallicity of [Fe/H] = 0.244. The planet, detected by radial velocity, has a minimum mass of 1.26 M_Jup, low eccentricity (e ~ 0.07), and a period of ~1300 days.

We discovered a potential wide companion with J = 12.631 mag at about 42 arcmin from HD 216435. We classify it as a M4–M4.5 dwarf. We derive a spectroscopic distance of 52–65 pc (41–82) for the companion, suggesting that these two objects are not physically associated.

Appendix A.7: 91 Aqr

Mitchell et al. (2013) published a 3.2 M_Jup planet orbiting the K0 giant, 91 Aqr. The planet-host star is located at 45.9±0.6 pc

(van Leeuwen 2007) with an age of 3.56±0.63 Gyr, and solar composition. This planet-host star has the largest proper motion of our sample (~0.37′′/yr). The planet has a low eccentricity (e = 0.027) and a orbital period of 181.4 days.

We found a wide companion located at 52.9 arcmin from 91 Aqr and a proper motion in good agreement with the planet-host star (van Leeuwen 2007). We infer a spectroscopic distance of 63 (39–125) pc. Hence, we can not discard the pair as wide co-moving system, which would have a projected separation of ~146 000 au. Radial velocity measurement are required to further assess the companionship.

© ESO, 2014