Circumstellar Disks Around Binary Stars in Taurus

We have conducted a survey of 17 wide (> 100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and ten secondaries, with disk masses as low as $10^{-4} M_{\odot}$. We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of $F_{mm} \propto M_{\ast}^{1.5-2.0}$ to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.Comment: To appear in the Astrophysical Journal, 12 page

Protoplanetary Disk Mass Distribution in Young Binaries

We present millimeter-wave continuum images of four wide (separations 210-800 AU) young stellar binary systems in the Taurus-Auriga star-forming region. For all four sources, the resolution of our observations is sufficient to determine the mm emission from each of the components. In all four systems, the primary star's disk has stronger millimeter emission than the secondary and in three of the four, the secondary is undetected; this is consistent with predictions of recent models of binary formation by fragmentation. The primaries' circumstellar disk masses inferred from these observations are comparable to those found for young single stars, confirming that the presence of a wide binary companion does not prevent the formation of a protoplanetary disk. Some of the secondaries show signatures of accretion (H-alpha emission and K - L excesses), yet their mm fluxes suggest that very little disk mass is present.Comment: Accepted by ApJ, to appear Feb. 2003; 9 pages, 5 postscript figures, uses aastex, emulateapj5, and apjfonts style files. Also available at http://astro.swarthmore.edu/~jensen/publications.htm

Noise driven translocation of short polymers in crowded solutions

In this work we study the noise induced effects on the dynamics of short polymers crossing a potential barrier, in the presence of a metastable state. An improved version of the Rouse model for a flexible polymer has been adopted to mimic the molecular dynamics by taking into account both the interactions between adjacent monomers and introducing a Lennard-Jones potential between all beads. A bending recoil torque has also been included in our model. The polymer dynamics is simulated in a two-dimensional domain by numerically solving the Langevin equations of motion with a Gaussian uncorrelated noise. We find a nonmonotonic behaviour of the mean first passage time and the most probable translocation time, of the polymer centre of inertia, as a function of the polymer length at low noise intensity. We show how thermal fluctuations influence the motion of short polymers, by inducing two different regimes of translocation in the molecule transport dynamics. In this context, the role played by the length of the molecule in the translocation time is investigated.Comment: 11 pages, 3 figures, to appear in J. Stat. Mechanics: Theory and Experiment, 200

Resolved Young Binary Systems And Their Disks

We have conducted a survey of young single and multiple systems in the Taurus–Auriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25–30 au and have an average 3σ detection level of 0.35 mJy, equivalent to a disk mass of 4 × 10−5 M ⊙ for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30–4200 au have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass

Resolved Young Binary Systems And Their Disks

We have conducted a survey of young single and multiple systems in the Taurus–Auriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25–30 au and have an average 3σ detection level of 0.35 mJy, equivalent to a disk mass of 4 × 10−5 M ⊙ for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30–4200 au have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass

Misaligned protoplanetary disks in a young binary star system

Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our Solar System; their orbits may be eccentric or inclined with respect to the host star’s equator, and the population of giant planets orbiting close to their host stars suggests appreciable orbital migration. There is at present no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star in an orbit that is inclined relative to the planet’s orbital plane. Such mechanisms require significant mutual inclinations between the planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but often the measurements of these misalignments are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tauri are misaligned by 60 to 68 degrees, such that one or both of the disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently because of the binary formation process

Radial Structure in the TW Hya Circumstellar Disk

We present new near-infrared interferometric data from the CHARA array and the Keck Interferometer on the circumstellar disk of the young star, TW Hya, a proposed "transition disk." We use these data, as well as previously published, spatially resolved data at 10 μm and 7 mm, to constrain disk models based on a standard flared disk structure. We find that we can match the interferometry data sets and the overall spectral energy distribution with a three-component model, which combines elements at spatial scales proposed by previous studies: optically thin, emission nearest the star, an inner optically thick ring of emission at roughly 0.5 AU followed by an opacity gap and, finally, an outer optically thick disk starting at ~4 AU. The model demonstrates that the constraints imposed by the spatially resolved data can be met with a physically plausible disk but this requires a disk containing not only an inner gap in the optically thick disk as previously suggested, but also a gap between the inner and outer optically thick disks. Our model is consistent with the suggestion by Calvet et al. of a planet with an orbital radius of a few AU. We discuss the implications of an opacity gap within the optically thick disk

Multi-mission operations with the Interferometry Science Center

The Interferometry Science Center (ISC) at the California Institute of Technology (Caltech) is chartered with providing science operations, data analysis support, and data archiving support for the suite of interferometry projects within the NASA Origins theme. Beginning with the Science Operations System (SOS) for the Keck Interferometer (KI), the ISC will design, implement, and operate a multi-mission facility to provide operations and support functions for NASA Origins interferometers and the scientists and engineers that use them. Future Origins interferometry projects such as the Space Interferometry Mission (SIM) will further use and extend the functionality of the ISC’s multi-mission base. In this talk I will introduce the functional elements in the KI SOS; describe the common SOS core elements that KI and SIM will share; and provide prospective users of these facilities an introduction to user support model that the ISC is implementing

Proton Wires in an Electric Field: the Impact of Grotthuss Mechanism on Charge Translocation

We present the results of the modeling of proton translocation in finite H-bonded chains in the framework of two-stage proton transport model. We explore the influence of reorientation motion of protons, as well as the effect of electric field and proton correlations on system dynamics. An increase of the reorientation energy results in the transition of proton charge from the surrounding to the inner water molecules in the chain. Proton migration along the chain in an external electric field has a step-like character, proceeding with the occurrence of electric field threshold-type effects and drastic redistribution of proton charge. Electric field applied to correlated chains induces first a formation of ordered dipole structures for lower field strength, and than, with a further field strength increase, a stabilization of states with Bjerrum D-defects. We analyze the main factors responsible for the formation/annihilation of Bjerrum defects showing the strong influence of the complex interplay between reorientation energy, electric field and temperature in the dynamics of proton wire.Comment: 28 pages, 9 figure

Resolved young binary systems and their disks

We have conducted a survey of young single and multiple systems in the Taurus-Auriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25--30 AU and have an average 3$\sigma$ detection level of 0.35 mJy, equivalent to a disk mass of $4 \times 10^{-5}$ M$_{\odot}$ for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher order multiple systems observed, we detect $\lambda = 1.3$ mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30 to 4200 AU have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass.Comment: 30 pages, 12 figures, to be published in the Astrophysical Journa