Bostonia. Volume 5

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Assessing the Effect of Stellar Companions from High-Resolution Imaging of Kepler Objects of Interest

We report on 176 close (<2") stellar companions detected with high-resolution imaging near 170 hosts of Kepler Objects of Interest. These Kepler targets were prioritized for imaging follow-up based on the presence of small planets, so most of the KOIs in these systems (176 out of 204) have nominal radii <6 R_E . Each KOI in our sample was observed in at least 2 filters with adaptive optics, speckle imaging, lucky imaging, or HST. Multi-filter photometry provides color information on the companions, allowing us to constrain their stellar properties and assess the probability that the companions are physically bound. We find that 60 -- 80% of companions within 1" are bound, and the bound fraction is >90% for companions within 0.5"; the bound fraction decreases with increasing angular separation. This picture is consistent with simulations of the binary and background stellar populations in the Kepler field. We also reassess the planet radii in these systems, converting the observed differential magnitudes to a contamination in the Kepler bandpass and calculating the planet radius correction factor, $X_R = R_p (true) / R_p (single)$. Under the assumption that planets in bound binaries are equally likely to orbit the primary or secondary, we find a mean radius correction factor for planets in stellar multiples of $X_R = 1.65$. If stellar multiplicity in the Kepler field is similar to the solar neighborhood, then nearly half of all Kepler planets may have radii underestimated by an average of 65%, unless vetted using high resolution imaging or spectroscopy.Comment: 23 pages, 12 figures. Accepted for publication in The Astronomical Journa

A dark energy multiverse

We present cosmic solutions corresponding to universes filled with dark and phantom energy, all having a negative cosmological constant. All such solutions contain infinite singularities, successively and equally distributed along time, which can be either big bang/crunchs or big rips singularities. Classicaly these solutions can be regarded as associated with multiverse scenarios, being those corresponding to phantom energy that may describe the current accelerating universe

Effect of adherend thickness and mixed mode loading on debond growth in adhesively bonded composite joints

Symmetric and unsymmetric double cantilever beam (DCB) specimens were tested and analyzed to assess the effect of: (1) adherend thickness, and (2) a predominantly mode I mixed mode loading on cyclic debond growth and static fracture toughness. The specimens were made of unidirectional composite (T300/5208) adherends bonded together with EC3445 structural adhesive. The thickness was 8, 16, or 24 plies. The experimental results indicated that the static fracture toughness increases and the cyclic debond growth rate decreases with increasing adherend thickness. This behavior was related to the length of the plastic zone ahead of the debond tip. For the symmetric DCB specimens, it was further found that displacement control tests resulted in higher debond growth rates than did load control tests. While the symmetric DCB tests always resulted in cohesive failures in the bondline, the unsymmetric DCB tests resulted in the debond growing into the thinner adherend and the damage progressing as delamination in that adherend. This behavior resulted in much lower fracture toughness and damage growth rates than found in the symmetric DCB tests

Limits on Stellar Companions to Exoplanet Host Stars With Eccentric Planets

Though there are now many hundreds of confirmed exoplanets known, the binarity of exoplanet host stars is not well understood. This is particularly true of host stars which harbor a giant planet in a highly eccentric orbit since these are more likely to have had a dramatic dynamical history which transferred angular momentum to the planet. Here we present observations of four exoplanet host stars which utilize the excellent resolving power of the Differential Speckle Survey Instrument (DSSI) on the Gemini North telescope. Two of the stars are giants and two are dwarfs. Each star is host to a giant planet with an orbital eccentricity > 0.5 and whose radial velocity data contain a trend in the residuals to the Keplerian orbit fit. These observations rule out stellar companions 4-8 magnitudes fainter than the host star at passbands of 692nm and 880nm. The resolution and field-of-view of the instrument result in exclusion radii of 0.05-1.4 arcsecs which excludes stellar companions within several AU of the host star in most cases. We further provide new radial velocities for the HD 4203 system which confirm that the linear trend previously observed in the residuals is due to an additional planet. These results place dynamical constraints on the source of the planet's eccentricities, constraints on additional planetary companions, and informs the known distribution of multiplicity amongst exoplanet host stars.Comment: 10 pages, 7 figures, 2 tables, accepted to Ap

The medical student

The Medical Student was published from 1888-1921 by the students of Boston University School of Medicine