WD0837+185:the formation and evolution of an extreme mass ratio white dwarf-brown dwarf binary in Praesepe

There is a striking and unexplained dearth of brown dwarf companions in close orbits (< 3AU) around stars more massive than the Sun, in stark contrast to the frequency of stellar and planetary companions. Although rare and relatively short-lived, these systems leave detectable evolutionary end points in the form of white dwarf - brown dwarf binaries and these remnants can offer unique insights into the births and deaths of their parent systems. We present the discovery of a close (orbital separation ~ 0.006 AU) substellar companion to a massive white dwarf member of the Praesepe star cluster. Using the cluster age and the mass of the white dwarf we constrain the mass of the white dwarf progenitor star to lie in the range 3.5 - 3.7 Msun (B9). The high mass of the white dwarf means the substellar companion must have been engulfed by the B star's envelope while it was on the late asymptotic giant branch (AGB). Hence, the initial separation of the system was ~2 AU, with common envelope evolution reducing the separation to its current value. The initial and final orbital separations allow us to constrain the combination of the common envelope efficiency (alpha) and binding energy parameters (lambda) for the AGB star to alpha lambda ~3. We examine the various formation scenarios and conclude that the substellar object was most likely to have been captured by the white dwarf progenitor early in the life of the cluster, rather than forming in situ.Comment: Accepted for publication in ApJ

CO(2-1) Survey at 9 parsec resolution in the SMC

The Small Magellanic Cloud (SMC) is the closest low-metallicity galaxy to the Milky Way where the dynamical state of molecular clouds can be analyzed. We present a CO(2-1) survey at 9 pc resolution obtained with the APEX telescope in an extensive region of the SMC and characterize the properties of the molecular clouds. We study the dynamical state and stability of these clouds uniformly. We identify 177 molecular clouds within the SMC by using CPROPS, of which 124 clouds are fully resolved with signal-to-noise ratio $>$ 5. The scaling relationships show that the SMC clouds are (on average) less turbulent and less luminous than their inner Milky Way counterparts of similar size by a factor of 2 and 3, respectively, while for a fixed linewidth, the SMC clouds are over-luminous by a factor of 3.5. Using the virial masses, we derive a CO-to-H2 conversion factor for the SMC CO clouds of 10.5 M$_{\odot}(K km s^{-1} pc^{2})^{-1}$, measured at 9 pc resolution. We also determine a dust-based conversion factor of 28 M$_{\odot}(K km s^{-1} pc^{2})^{-1}$, obtained at 12 pc resolution. We find that the SMC clouds appear to be in approximate gravitational virial equilibrium. We find that the cumulative mass functions based on both the luminous mass and the virial mass are steeper than $\frac{dN}{dM} \propto M^{-2}$, suggesting that most of the molecular mass of the SMC is contained in low-mass clouds.Comment: 22 pages, 18 figures. Submitted to the Astronomy & Astrophysics (A&A) journa

Dust emission at 8-mic and 24-mic as Diagnostics of HII Region Radiative Transfer

We use the Spitzer SAGE survey of the Magellanic Clouds to evaluate the relationship between the 8-mic PAH emission, 24-mic hot dust emission, and HII region radiative transfer. We confirm that in the higher-metallicity Large Magellanic Cloud, PAH destruction is sensitive to optically thin conditions in the nebular Lyman continuum: objects identified as optically thin candidates based on nebular ionization structure show 6 times lower median 8-mic surface brightness (0.18 mJy arcsec^-2) than their optically thick counterparts (1.2 mJy arcsec^-2). The 24-mic surface brightness also shows a factor of 3 offset between the two classes of objects (0.13 vs 0.44 mJy arcsec^-2, respectively), which is driven by the association between the very small dust grains and higher density gas found at higher nebular optical depths. In contrast, PAH and dust formation in the low-metallicity Small Magellanic Cloud is strongly inhibited such that we find no variation in either 8-mic or 24-mic emission between our optically thick and thin samples. This is attributable to extremely low PAH and dust production together with high, corrosive UV photon fluxes in this low-metallicity environment. The dust mass surface densities and gas-to-dust ratios determined from dust maps using Herschel HERITAGE survey data support this interpretation.Comment: Accepted to ApJ, May 15, 2017. 10 pages, 9 figure

Basic Psychological Needs, Suicidal Ideation, and Risk for Suicidal Behavior in Young Adults

Associations between the satisfaction of basic psychological needs of autonomy, competence, and relatedness with current suicidal ideation and risk for suicidal behavior were examined. Two logistic regressions were conducted with a cross-sectional database of 440 university students to examine the association of need satisfaction with suicidal ideation and risk for suicidal behavior, while controlling for demographics and depressive symptoms. Suicidal ideation was reported by 15% of participants and 18% were found to be at risk for suicidal behavior. A one standard deviation increase in need satisfaction reduced the odds of suicidal ideation by 53%, OR (95% CI) = 0.47 (0.33–0.67), and the odds of being at risk for suicidal behavior by 50%, OR (95% CI) = 0.50 (0.37–0.69). Young adults whose basic psychological needs are met may be less likely to consider suicide and engage in suicidal behavior. Prospective research is needed to confirm these associations

Putting into Question the Imaginary of Recovery: A Dialectical Reading of the Global Financial Crisis and its Aftermath

In this article we put into question the discourses that emerged during the Global Financial Crisis (GFC) and that coalesced around a particular socio-economic imaginary of ?recovery? over the period 2009-2012. Our reading of these discourses is very much guided by the notion of the dialectic as developed by Fredric Jameson, and as such this paper can be read as attempt to put his theoretical ideas to work. Through our dialectical reading we aim to create a certain estrangement effect that makes the imaginary of recovery seem very odd and unnatural. In order to achieve such an effect we postulate four theses which are deliberately antagonistic: first, that there has been no ?crisis of capitalism?; second, that we must change the valence of the GFC from negative to positive; third, that the relationship between finance capitalism and ?free markets? is deeply contradictory; and fourth, that we must resist the regulation discourse

P324 RADIOGRAPHIC KNEE OSTEOARTHRITIS IS ASSOCIATED WITH AN INCREASE IN TRABECULAR BUT NOT CORTICAL BONE MINERAL DENSITY USING PERIPHERAL QUANTITATIVE CT

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