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

Abstract

We present results of a high-resolution, near-infrared survey of 41 nearby, young (P300 Myr) M0YM5.0 dwarfs using the Altair natural guide star adaptive optics system at the Gemini North telescope. Twelve of the objects appear to be binaries, seven of which are reported here for the first time. One triple system was discovered. Statistical properties are studied and compared with earlier ( F to K ) and later (!M6 very low mass [VLM ]) populations. We find that the separation distribution of the binaries in this sample peaks at 13 þ14 À9 AU, which is consistent with previous measurements of early M binaries. Hence, early M binaries seem to occur in-on average-tighter systems than G binaries. At the same time they are significantly wider than field VLM binary stars. The distribution of mass ratios q of primary and secondary stars was found to show an intermediate distribution between the strongly q ! 1 peaked distribution of field VLM systems and the almost flat distribution of earlier type stars. Consequently, we show evidence for relatively young, early M binaries representing a transition between the well-known earlier star distributions and the recently examined field VLM population characteristics. Despite the fact that this survey was dedicated to the search for faint brown dwarf and planetary mass companions, all planetary mass candidates were background objects. We exclude the existence of physical companions with masses greater than 10 Jupiter masses (M J ) at separations of k40 AU and masses greater than 24M J for separations k10 AU around 37 of the 41 observed objects.

The magnetically-active, low-mass, triple system WDS 19312+3607

“…According to Chabrier et al (2007), the lower heat fluxes and, thus, larger radii and cooler effective temperatures of active low-mass stars and brown dwarfs compared to regular (inactive) stars are caused by the reduced convective efficiency, produced by the rapid rotation and high field strengths, and/or to magnetic spot coverage of the radiating surface. Previously, the activity scenario of G 125-15 AB was only consistent with the high relative X-ray flux (Daemgen et al 2007;Allen & Reid 2008). We now find that its is consistent with its Hα emission (Reid et al 2004; this work), stellar expansion (by about 30%; this work), and photometric variability (Hartman et al 2004).…”

“…Daemgen et al (2007) and Allen & Reid (2008) inferred from its location in a log (F X /F J ) versus V − J diagram that G 125-15 has X-ray activity levels that exceed those of Pleiades stars of a similar spectral type and conservatively assumed an age of 300-500 Ma, although the M dwarfs in their sample may be younger. Youth, closeness, and late spectral type are optimal properties when searching for faint companions to stars, ensuring that G 125-15 became the target of adaptive optics and IRAC/Spitzer searches by Daemgen et al (2007) and Allen & Reid (2008), respectively. They provided restrictive upper limits to the magnitudes and masses of hypothetical brown dwarf and planetary companions at close separations (up to a few arcseconds).…”

CARMENES input catalogue of M dwarfs

“…Although T Tauri stars are not natural targets for radial-velocity searches of low-mass exoplanets and none of the trio satisfies our criteria to be considered in the CARMENES sample (Table 1), a monitoring of bright, young, M dwarfs could shed light on the process of exoplanet formation (e.g., Crockett et al 2012). Furthermore, young, nearby, very late stars are also ideal targets for direct-imaging surveys for Jupiter-like planetary companions at wide separations (Masciadri et al 2005;Daemgen et al 2007;Chauvin et al 2010;Biller et al 2013;Delorme et al 2013, and references therein). Some of these targets are J13143+733 AB (NLTT 33370, M6.0 V in AB Doradus) and J09328+269 (DX Leo B, M5.5 V in Hercules-Lyra).…”

The discrepancy between dynamical and theoretical mass in the triplet-system 2MASS J10364483+1521394

“…We obtain one of the epochs in this study from Daemgen et al (2007) 2 , where the Gemini North/Altair natural guide star adaptive optics was used. A more detailed description of the individual astrometry measurements is presented in Table 1.…”

“…The system consists of one low-mass primary A with two companions B and C orbiting A at a distance of ≈ 1 , separated by roughly 0.16 − 0.18 themselves (see Figure 1). There are hints that the system is associated with the Ursa-Major Moving Group (UMa MG) (Klutsch et al 2014), but distance measurements to the system remain ambiguous, ranging from 7 to 20 pc depending on the technique employed (Riaz et al 2006;Daemgen et al 2007;Shkolnik et al 2012). Here, we adopt the trigonometric parallax distance estimate from Shkolnik et al (2012) as d = 20.1 ± 2.0 pc, as it should be the more reliable estimate compared to previous unresolved measurements.…”