Volume 562, February 2014
|Number of page(s)||20|
|Section||Planets and planetary systems|
|Published online||14 February 2014|
We describe here each of the empirical subsamples that were used to construct Fig. 3:
Scorpious-Centaurus – for this sample, we used the list ofChen et al. (2012). We re-moved known spectroscopic, eclipsing, and subarcsec-ond resolved binaries and Herbig AeBe stars to minimizephotometric scatter in the CMD. Photometry and distanceswere collected from the Hipparcos catalog (Perrymanet al. 1997; van Leeuwen 2007).Photometry was corrected using the individual extinctions listedin Chen et al. (2012).
IC 2391 – this sample is comprised of early-type stars selected from the membership list of Perry & Bond (1969). Distances and photometry are from Hipparcos. The photometry was corrected using an average cluster reddening of 0.01 (Patten & Simon 1996)
The Pleiades – we drew early-type members from the list of Stauffer et al. (2007) and used individual distances and photometry from Hipparcos. Individual reddening values from Breger (1986) were used to correct the photometry.
Ursa Majoris moving group – we chose A-type stars proposed as members of the group nucleus by King et al. (2003). Photometry calculated in this reference was also adopted. We applied no correction for reddening.
Young Moving Groups – we compiled proposed A and B-type members of the AB Doradus, Tucana/Horologium, Columba, and β Pictoris young kinematics groups from Malo et al. (2013, and references therein). For these stars, when available, we compiled the mean photometry from the catalogs of Mermilliod (Mermilliod & Mermilliod 1994, including κ And A). When photometry was not available in these catalogs it was taken from Hipparcos. In the construction of the CMD, we used Hipparcos distances (van Leeuwen 2007) and applied no reddening correction.
Our APO-ARCES spectrum of κ And A resembles those of other luminosity class IV and V B-type stars. Our spectral analysis followed the procedure developed by Marsh Boyer et al. (2012) which uses model spectral template fitting to estimate the atmospheric parameters of the star. Their method uses four lines, Hγλ4340 Å, He I λ4387 Å, λ4471 Å, λ4713 Å, and Mg II λ4481 Å, to determine vsini, Teff, and log g (see Fig. B.1). Since the lines that are sensitive to vsini (He I and Mg II) were weak in our spectrum, we maintained a fixed vsini (vsini = 190 km s-1, Glebocki et al. 2000; Fitzpatrick & Massa 2005) with a conservative uncertainty (20 km s-1) during the analysis of the Hγ line, which is sensitive to temperature and gravity. This analysis found two solutions: one where the model spectrum was a better fit to the line wings and core, but was slightly off in the line width, and another where the best-fit model reproduces the line width better but gave a poorer fit to the wings. We combined the results from these two solutions to
estimate Teff = 10900 ± 300K, log g = 3.50 ± 0.08dex, where the larger uncertainties reflect the combined results. As described in Sect. 3, we applied a correction to the measured surface gravity for the rapid rotation of the star using the method of Huang & Gies (2006). This method uses models to estimate the surface gravity at the pole of the star, which should remain relatively unaffected by rapid rotation an give a better indication of the stars true evolutionary state. We find log gpol = 3.78 ± 0.08dex for κ And A. Our estimated Teff generally agrees with those determined using other methods in the literature (e.g., Wu et al. 2011). However, the surface gravity is lower than previous estimates, which have not been corrected for the star’s rotation (see Table 6). The spread in estimated surface gravities illustrates the inherent challenges in accurate atmospheric parameter determination for early-type stars.
Hydrogen Hγ line of κ And A (solid lines) fitted by atmospheric models (dotted lines). Residuals from the fit are shown in the upper part of the figures. Top: solution where the line wings and the core are well fitted, but where the fit degrades in the line breadth. Bottom: solution for which the line breadth is better fitted. These solutions were combined to derive the new estimate of the temperature and the surface gravity of the star.
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We applied the disk-instability models of H. Klahr to the rare brown dwarfs companions identified around young (age ≤ 100 Myr) early-A/late-B type stars. The models require the metallicity and initial luminosity of the star as input (the latter roughly scales with the stellar mass). We retrieved the zero-age main sequence luminosity of the stars by inputing the present effective temperature or mass estimates of the stars and the known age of the system as inputs of evolutionary tracks Ekström et al. (2012). The properties of the systems are summarized in Table C.1. We considered a solar metallicity for HR 7329B as the present measurements are roughly solar (a variation of +0.17 dex does not affect the cooling timescale significantly; Saffe et al. 2008). We also find low sensitivity of the model predictions to the choice of the metallicity for HD 1160 (Fe/H = 0.0 and –0.3 considered here; see Sect. 3.4 of Nielsen et al. 2012). Finally, we assumed HIP 78530B has a roughly solar metallicity. This is likely to be the case given recent measurements for lower mass stars of the associations (Viana Almeida et al. 2009).
We deprojected the observed separation of HIP 78530B, HD 1160B, and C following the values from the Monte Carlo simulation of Allers et al. (2009). We used the values reported in Neuhäuser et al. (2011) for HR 7329B. The properties of the three companions are compared to models predictions in Fig. C.1.
Young 2.2–2.5 M⊙ stars with brown-dwarf (or low-mass) companions on wide orbits.
Same as Fig. 14, but for the brown-dwarf companions HR 7329B (left, red cross), HD 1160B (middle, green triangle), and HIP 78530B (right, pink hourglass). We added the NaCo detection limit obtained by Rameau et al. (2013b) for HR 7329B. Model predictions do not extend beyond 1000 AU.
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© ESO, 2014
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