New Observations and Analysis of the Bright Semi-Detached Eclipsing Binary mu1 Sco

Using new and published photometric observations of mu1 Sco (HR 6247), spanning 70 years, a period of 1.4462700(5) days was determined. It was found that the epoch of primary minimum suggested by Shobbrook at HJD 2449534.178 requires an adjustment to HJD 2449534.17700(9) to align all the available photometric datasets. Using the resulting combined-data light-curve, radial velocities derived from IUE data and the modelling software PHOEBE, a new system solution for this binary was obtained. It appears that the secondary is close to, or just filling, its Roche-lobe.Comment: 4 figures, 6 tables, 9 pages, uses mn2e.sty, to be published in MNRA

Protostellar disk formation and transport of angular momentum during magnetized core collapse

Theoretical studies of collapsing clouds have found that even a relatively weak magnetic field (B) may prevent the formation of disks and their fragmentation. However, most previous studies have been limited to cases where B and the rotation axis of the cloud are aligned. We study the transport of angular momentum, and its effects on disk formation, for non-aligned initial configurations and a range magnetic intensities. We perform 3D AMR MHD simulations of magnetically supercritical collapsing dense cores using the code Ramses. We compute the contributions of the processes transporting angular momentum (J), in the envelope and the region of the disk. We clearly define what could be defined as centrifugally supported disks and study their properties. At variance with earlier analyses, we show that the transport of J acts less efficiently in collapsing cores with non-aligned rotation axis and B. Analytically, this result can be understood by taking into account the bending of field lines occurring during the gravitational collapse. For the transport of J, we conclude that magnetic braking in the mean direction of B tends to dominate over both the gravitational and outflow transport of J. We find that massive disks, containing at least 10% of the initial core mass, can form during the earliest stages of star formation even for mass-to-flux ratios as small as 3 to 5 times the critical value. At higher field intensities, the early formation of massive disks is prevented. Given the ubiquity of Class I disks, and because the early formation of massive disks can take place at moderate magnetic intensities, we speculate that for stronger fields, disks will form later, when most of the envelope will have been accreted. In addition, we speculate that some observed early massive disks may actually be outflow cavities, mistaken for disks by projection effects. (Abridged version of the abstract.)Comment: 23 pages, 23 figures, to be published in A&

Multiple large shareholders, excess leverage and tunneling: evidence from an emerging market

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Manuscript Type: Empirical Research Question/Issue: Past empirical efforts in corporate governance have examined the effects of large shareholders with the excess control rights on tunneling activities. However, no study has systematically investigated the effects of multiple large shareholders on excess leverage policies and tunneling in an emerging country environment where minority rights protection is weak. In this study, we examine the role of multiple large shareholders and the effects of control contestability of multiple large shareholders on firm excess leverage decision and tunneling by controlling shareholders. Research Findings/Insights: Using a sample of 2,341 Chinese firms for the years 2001 to 2013, we document that the contestability of multiple non-controlling large shareholders relative to controlling shareholders reduces the adoption of excess leverage policies, tunneling and enhances capital investment. Another intriguing finding is that the government as a controlling shareholder exerts significant influence and reduces the monitoring effectiveness of multiple larger shareholders. Theoretical/Academic Implications: By addressing the role of multiple large shareholders on excess leverage decisions, this study makes an important contribution to the corporate governance literature. We extend the recent developments in agency theory regarding the role of multiple large shareholders in constraining expropriation of controlling shareholders with excess control rights and their effect on firm leverage decisions. Our results support the theoretical models which indicate that the presence of multiple large shareholders is an important and efficient internal governance mechanism that mitigates a firm’s agency costs, particularly, in an emerging market environment where corporate governance is weak and inadequate to curb tunneling problem. JEL classification: G15; G34; G3

The structure of molecular gas associated with NGC2264: wide-field 12CO and H2 imaging

We present wide-field, high-resolution imaging observations in 12CO 3-2 and H2 1-0 S(1) towards a ~1 square degree region of NGC2264. We identify 46 H2 emission objects, of which 35 are new discoveries. We characterize several cores as protostellar, reducing the previously observed ratio of prestellar/protostellar cores in the NGC2264 clusters. The length of H2 jets increases the previously reported spatial extent of the clusters. In each cluster, <0.5% of cloud material has been perturbed by outflow activity. A principal component analysis of the 12CO data suggests that turbulence is driven on scales >2.6 pc, which is larger than the extent of the outflows. We obtain an exponent alpha=0.74 for the size-linewidth relation, possibly due to the high surface density of NGC2264. In this very active, mixed-mass star forming region, our observations suggest that protostellar outflow activity is not injecting energy and momentum on a large enough scale to be the dominant source of turbulence.Comment: MNRAS accepte

Formation of low-mass stars and brown dwarfs

These lectures attempt to expose the most important ideas, which have been proposed to explain the formation of stars with particular emphasis on the formation of brown dwarfs and low-mass stars. We first describe the important physical processes which trigger the collapse of a self-gravitating piece of fluid and regulate the star formation rate in molecular clouds. Then we review the various theories which have been proposed along the years to explain the origin of the stellar initial mass function paying particular attention to four models, namely the competitive accretion and the theories based respectively on stopped accretion, MHD shocks and turbulent dispersion. As it is yet unsettled whether the brown dwarfs form as low-mass stars, we present the theory of brown dwarfs based on disk fragmentation stressing all the uncertainties due to the radiative feedback and magnetic field. Finally, we describe the results of large scale simulations performed to explain the collapse and fragmentation of molecular clouds.Comment: proceedings of the Evry Schatzman School on "Low-mass stars and the transition between stars and brown dwarfs" (Roscoff 2011), to appear in EAS Publication Series (Eds C.Reyl\'e, C.Charbonnel, & M.Schultheis

Infant mortality in the hierarchical merging scenario: dependence on gas expulsion time-scales

We examine the effects of gas expulsion on initially substructured and out-of-equilibrium star clusters. We perform N-body simulations of the evolution of star clusters in a static background potential before adjusting that potential to model gas expulsion. We investigate the impact of varying the rate at which the gas is removed, and the instant at which gas removal begins. Reducing the rate at which the gas is expelled results in an increase in cluster survival. Quantitatively, this dependence is approximately in agreement with previous studies, despite their use of smooth and virialized initial stellar distributions. However, the instant at which gas expulsion occurs is found to have a strong effect on cluster response to gas removal. We find if gas expulsion occurs prior to one crossing time, cluster response is poorly described by any global parameters. Furthermore, in real clusters the instant of gas expulsion is poorly constrained. Therefore, our results emphasize the highly stochastic and variable response of star clusters to gas expulsion

Extreme Magnification Microlensing Event OGLE-2008-BLG-279: Strong Limits on Planetary Companions to the Lens Star

We analyze the extreme high-magnification microlensing event OGLE-2008-BLG-279, which peaked at a maximum magnification of A ~ 1600 on 30 May 2008. The peak of this event exhibits both finite-source effects and terrestrial parallax, from which we determine the mass of the lens, M_l=0.64 +/- 0.10 M_Sun, and its distance, D_l = 4.0 +/- 0.6. We rule out Jupiter-mass planetary companions to the lens star for projected separations in the range 0.5-20 AU. More generally, we find that this event was sensitive to planets with masses as small as 0.2 M_Earth ~= 2 M_Mars with projected separations near the Einstein ring (~3 AU).Comment: 25 pages, 7 figures, submitted to Ap

MOA-2009-BLG-387Lb: A massive planet orbiting an M dwarf

We report the discovery of a planet with a high planet-to-star mass ratio in the microlensing event MOA-2009-BLG-387, which exhibited pronounced deviations over a 12-day interval, one of the longest for any planetary event. The host is an M dwarf, with a mass in the range 0.07 M_sun < M_host < 0.49M_sun at 90% confidence. The planet-star mass ratio q = 0.0132 +- 0.003 has been measured extremely well, so at the best-estimated host mass, the planet mass is m_p = 2.6 Jupiter masses for the median host mass, M = 0.19 M_sun. The host mass is determined from two "higher order" microlensing parameters. One of these, the angular Einstein radius \theta_E = 0.31 +- 0.03 mas, is very well measured, but the other (the microlens parallax \pi_E, which is due to the Earth's orbital motion) is highly degenate with the orbital motion of the planet. We statistically resolve the degeneracy between Earth and planet orbital effects by imposing priors from a Galactic model that specifies the positions and velocities of lenses and sources and a Kepler model of orbits. The 90% confidence intervals for the distance, semi-major axis, and period of the planet are 3.5 kpc < D_L < 7.9 kpc, 1.1 AU < a < 2.7AU, and 3.8 yr < P < 7.6 yr, respectively.Comment: 20 pages including 8 figures. A&A 529 102 (2011

Bridging the gap: disk formation in the Class 0 phase with ambipolar diffusion and Ohmic dissipation

Context: Ideal MHD simulations have revealed catastrophic magnetic braking (MB) in the protostellar phase, which prevents the formation of a centrifugal disk around a nascent protostar. Aims: We determine if non-ideal MHD, including the effects of ambipolar diffusion and Ohmic dissipation determined from a detailed chemical network model, allows for disk formation at the earliest stages of star formation (SF). Methods: We employ the axisymmetric thin-disk approximation in order to resolve a dynamic range of 9 orders of magnitude in length and 16 in density, while also calculating partial ionization using up to 19 species in a detailed chemical equilibrium model. MB is applied using a steady-state approximation, and a barotropic relation is used to capture the thermal evolution. Results: We resolve the formation of the first and second cores, with expansion waves at the periphery of each, a magnetic diffusion shock, and prestellar infall profiles at larger radii. Power-law profiles in each region can be understood analytically. After the formation of the second core, centrifugal support rises rapidly and a low-mass disk of radius ~10 R_Sun is formed, when the second core has mass ~0.001 M_Sun. The mass-to-flux ratio is ~10,000 times the critical value in the central region. Conclusions: A small centrifugal disk can form in the earliest stage of SF, due to a shut-off of MB caused by magnetic field dissipation in the first core region. There is enough angular momentum loss to allow the second collapse to occur directly, and a low-mass stellar core to form with a surrounding disk. The disk mass and size will depend upon how the angular momentum transport mechanisms within the disk can keep up with mass infall onto the disk. We estimate that the disk will remain <~10 AU, undetectable even by ALMA, in the early Class 0 phase.Comment: 19 pages, 17 figures. Accepted for publication at Astronomy & Astrophysic