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Register a new userCool dwarfs in wide multiple systems. Paper 3: Two common-proper-motion, late-type stars separated by over 11 arcmin
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Added by
Jos\\'e A. Caballero
Publication date
2012
fields
Physics
and research's language is
English
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LP 209-28 and LP 209-27 have similar proper motions as tabulated by several catalogues. Using seven astrometric epochs spanning 59 years, we confirm a common tangential velocity by measuring a constant angular separation of rho = 666.62+/-0.09 arcsec. Accurate SDSS and 2MASS photometry indicates that they are normal dwarfs of approximate spectral types K7 V and M3 V. However, from their apparent magnitudes, both LP 209-28 and LP 209-27 are located at 200-250 pc, from where one can deduce an astonishing projected physical separation of 0.6-0.8 pc. The system Koenigstuhl 6 AB represents another world record among the least-bound systems with low-mass star components.
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This is the first of a series of works devoted to investigate cool dwarfs in wide multiple systems. Here, I present Koenigstuhl 4 A and B, two bright, intermediate M dwarfs with a common high proper-motion and separated by 299 arcsec. At the most probable distance of the system, 19 pc, the projected physical separation is 5700 AU, which makes Koenigstuhl 4 AB to be one of the least bound binary systems with late-type components found to date. I also associate the primary with a ROSAT X-ray source for the first time.
We have made a search for common proper motion (CPM) companions to the wide binaries in the solar vicinity. We found that the binary GJ 282AB has a very distant CPM companion (NLTT 18149) at a separation $s=1.09 arcdeg$. Improved spectral types and radial velocities are obtained, and ages determined for the three components. The Hipparcos trigonometric parallaxes and the new radial velocities and ages turn out to be very similar for the three stars, and provide strong evidence that they form a physical system. At a projected separation of 55733AU from GJ 282AB, NLTT 18149 ranks among the widest physical companions known.
The multiplicity of early-type stars is still not well established. The derived binary fraction is different for individual star forming regions, suggesting a connection with the age and the environment conditions. The few studies that have investigated this connection do not provide conclusive results. To fill in this gap, we started the first detailed adaptive-optic-assisted imaging survey of early-type field stars to derive their multiplicity in a homogeneous way. The sample has been extracted from the Hipparcos Catalog and consists of 341 BA-type stars within ~300 pc from the Sun. We report the current status of the survey and describe a Monte-Carlo simulation that estimates the completeness of our companion detection.
A common proper motion survey of M dwarf stars within 8 pc of the Sun reveals no new stellar or brown dwarf companions at wide separations (~100-1400 AU). This survey tests whether the brown dwarf ``desert extends to large separations around M dwarf stars and further explores the census of the solar neighborhood. The sample includes 66 stars north of -30 degrees and within 8 pc of the Sun. Existing first epoch images are compared to new J-band images of the same fields an average of 7 years later to reveal proper motion companions within a ~4 arcminute radius of the primary star. No new companions are detected to a J-band limiting magnitude of ~16.5, corresponding to a companion mass of ~40 Jupiter masses for an assumed age of 5 Gyr at the mean distance of the objects in the survey, 5.8 pc.
A set of 41 nearby stars (closer than 25 pc) is investigated which have very wide binary and common proper motion (CPM) companions at projected separations between 1000 and $200 000$ AU. These companions are identified by astrometric positions and proper motions from the NOMAD catalog. Based mainly on measures of chromospheric and X-ray activity, age estimation is obtained for most of 85 identified companions. Color -- absolute magnitude diagrams are constructed to test if CPM companions are physically related to the primary nearby stars and have the same age. Our carefully selected sample includes three remote white dwarf companions to main sequence stars and two systems (55 Cnc and GJ 777A) of multiple planets and distant stellar companions. Ten new CPM companions, including three of extreme separations, are found. Multiple hierarchical systems are abundant; more than 25% of CPM components are spectroscopic or astrometric binaries or multiples themselves. Two new astrometric binaries are discovered among nearby CPM companions, GJ 264 and HIP 59000 and preliminary orbital solutions are presented. The Hyades kinematic group (or stream) is presented broadly in the sample, but we find few possible thick disk objects and none halo stars. It follows from our investigation that moderately young (age $lesssim 1$ Gyr) thin disk dwarfs are the dominating species in the near CPM systems, in general agreement with the premises of the dynamical survival paradigm. Some of the multiple stellar systems with remote CPM companions probably undergo the dynamical evolution on non-coplanar orbits, known as the Kozai cycle.
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