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We present analysis of HST Planetary Camera images of twenty L dwarfs identified in the course of the Two Micron All-Sky Survey. Four of the targets have faint, red companions at separations between 0.07 and 0.29 arcseconds (1.6 to 7.6 AU). In three cases, the bolometric magnitudes of the components differ by less than 0.3 magnitudes. Since the cooling rate for brown dwarfs is a strong function of mass, similarity in luminosities implies comparable masses. The faint component in the 2M0850 system, however, is over 1.3 magnitudes fainter than the primary in the I-band, and ~0.8 magnitudes fainter in M(bol). Indeed, 2M0850B is ~0.8 magnitudes fainter in I than the lowest luminosity L dwarf currently known, while the absolute magnitude we deduce at J is almost identical with M_J for Gl 229B. Theoretical models indicate a mass ratio of ~0.75. The mean separation of the L dwarf binaries in the current sample is smaller by a factor of two than amongst M dwarfs. We discuss the implications of these results for the temperature scale in the L/T transition region and for the binary frequency amongst L dwarfs.
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We report discovery of a young 0.32 L dwarf binary, SDSS J2249+0044AB, found as the result of a Keck LGSAO imaging survey of young field brown dwarfs. Weak K, Na, and FeH features as well as strong VO absorption in the integrated-light J-band spectrum indicate a young age for the system. From spatially resolved K-band spectra we determine spectral types of L3 and L5 for components A and B, respectively. SDSS J2249+0044A is spectrally very similar to G196-3B, an L3 companion to a young M2.5 field dwarf. Thus, we adopt 100 Myr (the age estimate of the G196-3 system) as the age of SDSS J2249+0044AB, but ages of 12-790 Myr are possible. By comparison to G196-3B, we estimate a distance to SDSS J2249+0044AB of 54 +- 16 pc and infer a projected separation of 17 +- 5 AU for the binary. Comparison of the luminosities to evolutionary models at an age of 100 Myr yields masses of 0.029 and 0.022 Msun for SDSS J2249+0044A and B, respectively. Over the possible ages of the system (12-790 Myr), the mass of SDSS J2249+0044A could range from 0.011 to 0.070 Msun and the mass of SDSS J2249+0044B could range from 0.009 to 0.065 Msun. Evolutionary models predict that either component could be burning deuterium, which could result in a mass ratio as low as 0.4, or alternatively, a reversal in the luminosities of the binary. We find a likely proper motion companion, GSC 00568-01752, which lies 48.9 away (2600 AU) and has SDSS+2MASS colors consistent with an early M dwarf. The photometric distance to GSC 00568-01752 is 53 +- 15 pc, in agreement with our distance estimate for SDSS J2249+0044AB. The space motion of SDSS J2249+0044AB shows no obvious coincidence with known young moving groups. The unusually red near-IR colors, young age, and low masses of the binary make it an important template for studying planetary-mass objects found by direct imaging surveys.
[abridged] We report four years of radial velocity monitoring observations of SDSS J080531.84+481233.0 that reveal significant and periodic variability, confirming the binary nature of the source. We infer an orbital period of 2.02$pm$0.03 yr, a semi-major axis of 0.76$^{+0.05}_{-0.06}$ AU, and an eccentricity of 0.46$pm$0.05, consistent with the amplitude of astrometric variability and prior attempts to resolve the system. Folding in constraints based on the spectral types of the components (L4$pm$0.7 and T5.5$pm$1.1), corresponding effective temperatures, and brown dwarf evolutionary models, we further constrain the orbital inclination of this system to be nearly edge-on (90$^opm$19$^o$), and deduce a large system mass ratio (M$_2$/M$_1$ = 0.86$^{+0.10}_{-0.12}$), substellar components (M$_1$ = 0.057$^{+0.016}_{-0.014}$ M$_{odot}$, M$_2$ = 0.048$^{+0.008}_{-0.010}$ M$_{odot}$), and a relatively old system age (minimum age = 4.0$^{+1.9}_{-1.2}$ Gyr). The measured projected rotational velocity of the primary ($vsin{i}$ = 34.1$pm$0.7 km/s) implies that this inactive source is a rapid rotator (period $lesssim$ 3 hr) and a viable system for testing spin-orbit alignment in very-low-mass multiples. The combination of well-determined component atmospheric properties and masses near and/or below the hydrogen minimum mass make SDSS J0805+4812AB an important system for future tests of brown dwarf evolutionary models.
The Latitude Density Search utilized Hyper Suprime-Cam on Subaru Telescope to discover 60 moving objects in the outer Solar System, 54 of which have semi-major axes beyond 30 AU. The images were acquired in exceptional seeing (0.4) and reached a detection limit of m_r~=25.2. The two night arcs were used to calculate orbits which are poorly constrained, however, the distance and inclination are the parameters best constrained by short arcs and a reasonable determination can be made of which objects are cold classical TNOs and which are dynamically excited. We identify 10 objects as likely cold classical objects. We searched all of the detections for binary sources using a trailed Point Spread Function subtraction method, and identified one binary object with a separation of 0.34 and a secondary with 17% the brightness of the primary (2.0 magnitudes fainter). This is the brightest TNO in the sample, the previously known object 471165 (2010 HE79), which has a dynamically excited orbit. Because of the excellent seeing, this search was sensitive to binaries with 0.34 separation and a brightness of >=50% the primary brightness for 7 objects, including one cold classical. This gives an intrinsic binary fraction of ~17% (1 of 6) for the dynamically excited objects within our detection limits. The trailed point spread function subtraction method to identify binaries, fit the two components, and determine the sensitivity limits, used in the Latitude Density Search is a useful tool that could be more broadly applied to identify binary TNOs and track known binary TNO orbits.
The Laser Interferometer Space Antenna (LISA) will provide the largest observational sample of (interacting) double white dwarf binaries, whose evolution is driven by radiation reaction and other effects, such as tides and mass transfer. We show that, depending on the actual physical parameters of a source, LISA will be able to provide very different quality of information: for some systems LISA can test unambiguously the physical processes driving the binary evolution, for others it can simply detect a binary without allowing us to untangle the source parameters and therefore shed light on the physics at work. We also highlight that simultaneous surveys with GAIA and/or optical telescopes that are and will become available can radically improve the quality of the information that can be obtained.
M dwarfs are ideal targets for the search of Earth-size planets in the habitable zone using the radial velocity method, attracting the attention of many ongoing surveys. As a by-product of these surveys, new multiple stellar systems are also found. This is the case also for the CARMENES survey, from which nine new SB2 systems have already been announced. Throughout the five years of the survey, the accumulation of new observations has resulted in the detection of several new multiple stellar systems with long periods and low radial-velocity amplitudes. Here, we newly characterise the spectroscopic orbits and constrain the masses of eight systems and update the properties of a system that we reported earlier. We derive the radial velocities of the stars using two-dimensional cross correlation techniques and template matching. The measurements are modelled to determine the orbital parameters of the systems. We combine CARMENES spectroscopic observations with archival high-resolution spectra from other instruments to increase the time-span of the observations and improve our analysis. When available, we also added archival photometric, astrometric, and adaptive optics imaging data to constrain the rotation periods and absolute masses of the components. We determine the spectroscopic orbits of nine multiple systems, eight of which are presented for the first time. The sample is composed of five SB1s, two SB2s, and two ST3s. The companions of two of the single-line binaries, GJ 3626 and GJ 912, have minimum masses below the stellar boundary and, thus, could be brown dwarfs. We find a new white dwarf in a close binary orbit around the M star GJ 207.1. From a global fit to radial velocities and astrometric measurements, we are able to determine the absolute masses of the components of GJ 282C, which is one of the youngest systems with measured dynamical masses.
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