A Coronagraphic Survey for Companions of Stars within 8 Parsecs

Abstract

We present the technique and results of a survey of stars within 8 pc of the Sun with declinations d [ [35¡ (J2000.00). The survey, designed to Ðnd without color bias faint companions, consists of optical coronagraphic images of the 1@ Ðeld of view centered on each star and infrared direct images with a 32A Ðeld of view. The images were obtained through the optical Gunn r and z Ðlters and the infrared J and K Ðlters. The survey achieves sensitivities up to 4 absolute magnitudes fainter than the prototype brown dwarf, Gliese 229B. However, this sensitivity varies with the seeing conditions, the intrinsic brightness of the star observed, and the angular distance from the star. As a result, we tabulate sensitivity limits for each star in the survey. We used the criterion of common proper motion to distinguish companions and to determine their luminosities. In addition to the brown dwarf Gl 229B, we have identiÐed six new stellar companions of the sample stars. Since the survey began, accurate trigonometric parallax measurements for most of the stars have become available. As a result, some of the stars we originally included should no longer be included in the 8 pc sample. In addition, the 8 pc sample is incomplete at the faint end of the main sequence, complicating our calculation of the binary fraction of brown dwarfs. We assess the sensitivity of the survey to stellar companions and to brown dwarf companions of di †erent masses and ages.

New Hipparcos ‐based Parallaxes for 424 Faint Stars

“…The columns in Table 4 are the same as those in Table 3. Five of these 29 stars have previously recorded parallaxes, of which three (NLTT 923, 26247, 47621) were determined by Oppenheimer et al (2001) based on their being CPM companions to Hipparcos stars, and the other two (NLTT 18218, 42494) were determined by van Altena et al (1995) based on their being CPM companions to brighter stars with parallaxes. Only 12 of the 29 have spectral types listed in SIMBAD, and many are not listed at all (and hence have no identifier in Table 4).…”

“…The Yale Parallax Catalog (van Altena, Lee, & Hoffleit 1995) lists the proper motions of CPM pairs together with the parallax of the primary, clearly intending the same distance estimate to be applied to the fainter star as well. Oppenheimer et al (2001) applied this technique to CPM companions of Hipparcos stars to establish distances to some stars in their 8 pc sample. However, no one has attempted to systematically search for CPM companions of Hipparcos stars.…”

The Late‐T Dwarf Companion to the Exoplanet Host Star HD 3651: A New Benchmark for Gravity and Metallicity Effects in Ultracool Spectra

“…These brown dwarf companions serve as ''benchmarks'' for studying substellar atmospheres and evolution. Such objects are rare, as numerous published (and unpublished) imaging surveys have searched for brown dwarf companions to nearby mainsequence stars with very limited success (e.g., Lloyd et al 2004;Oppenheimer et al 2001;McCarthy & Zuckerman 2004;Carson et al 2006). Mugrauer et al (2006) have recently identified a low-luminosity companion to the nearby K0 V star HD 3651 (GJ 27,54 Psc,HR 166,HIP 3093,SAO 74175).…”

Discovery of Nine New Companions to Nearby Young M Stars with the Altair AO System

“…The efficiency of this search process is well illustrated by its success in identifying the archetypical ultracool M dwarf, VB 10 (van Biesbroeck 1944), the first L dwarf, GD 165B ( Becklin & Zuckerman 1988), and the first T dwarf, Gl 229B ( Nakajima et al 1995). Subsequent studies have built on this foundation, using a variety of methods, including coronagraphy (e.g., Oppenheimer et al 2001), wide-field ground-based imaging (e.g., Simons et al 1996), and high-resolution imaging with both the Hubble Space Telescope (HST ; e.g., Golimowski et al 2004) and ground-based adaptive optics (AO) systems (e.g., Close et al 2003;Siegler et al 2005;Burgasser et al 2006, and references within).…”