A direct imaging search for wide (sub)stellar companions around rad-vel planet host stars

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**TITLE**ASP Conference Series,Vol.**VOLUME***,**YEAR OF PUBLICATION****NAMES OF EDITORS**A direct imaging search for wide (sub)stellar companions around rad-vel planet host stars M.Mugrauer,R.Neuh¨a user,T.Mazeh,M.Fernandez,E.Guenther and C.Broeg AIU,Schillerg¨a sschen 2-3,07745Jena Abstract.We present an overview of our ongoing systematic search for wide (sub)stellar companions around the stars known to host rad-vel planets.By using a relatively large ?eld of view and going very deep our survey can ?nd all directly detectable stellar and brown dwarf companions (m >40M Jup )within a 1000AU orbit.As of may 2003more than one hundreds extra-solar were found.Some of those planets are found in binary stellar systems.Those cases are intriguing,and might even exhibit some statistical di?erent features than the planets around single stars (Zucker &Mazeh 2002).It is therefore that we started a systematic deep imaging of the stars known to have planets to look for faint companions in wide orbits.Several groups have already searched for very close stellar compan-ions using adaptive optics,but these searched could not ?nd wide companions due to their too small ?eld of view.By using a relatively large ?eld of view and going very deep our survey will ?nd all stellar and even brown dwarf companions (m >40M Jup )within a 1000AU orbit.We use the ESO 3.58-m NTT,the 3.8-m UKIRT and the 2.2-m Calar Alto telescopes to image all stars known to host planets.These stars are relatively close and therefore their proper motion is large.Consequently,their 1st epoch observations can be compared with images from 2MASS to reveal objects that co-move with the rad-vel planet host stars.Objects brighter than H ～15mag (2MASS limit)can be studied using this method (see Figure 1).To reach the

detection limit of the NTT,which is at H >19mag,we need 2nd epoch NTT observations.By this approach we can ?nd faint and therefore low-mass com-panions even with planetary masses.Due to a pixelscale which is more than 10times better than 2MASS,an epoch di?erence of almost one year is su?cient to ?nd co-moving companions around nearly all rad-vel planet host stars (see Figure 2).

References

Zucker.,S.&Mazeh,T.2002,A&A,568,113-116

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M H [mag]

mass [M ⊙]5.5

0.57..0.604.8

0.60..0.707.40.20..0.30

Figure 1.H band images obtained with MAGIC at the CA 2.2m.The rad-vel planet host stars HD 46375,BD-103166and 55CnC are shown with their co-moving stellar companions (see white markers)which were detected by comparing the MAGIC images with 2MASS images.The absolute H magnitude,the projected distance to the pri-mary and the estimated mass of the stellar companions are shown in the table

below.

Figure 2.Left:NTT H band image of the rad-vel planet host star HD 37124.Objects in black circles are not detected in 2MASS.By comparing two NTT images taken with an epoch di?erence of one year we could measure the spatial motion of all detected faint companion-candidates.Right:Derived proper motion of objects detected on the left image.The white square is the expected motion of HD 37124for the given epoch di?erence,based on Hipparcos data.All faint objects are clearly not co-moving,hence they are all background stars.