Infrared Line Emission from Planetary Nebulae. I - General Theory

General theory of infrared line emission from planetary nebul

Peering Forward, 10 Years After: International Policy and Consumer Credit Regulation

A key change since the financial crisis of 2008 is the internationalization of interest in consumer finance. International institutions monitor household credit because of its impact on financial stability and market expansion. Macroprudential concerns drove this interest, resulting in a sea change in approaches to consumer credit regulation in many jurisdictions. This article critically analyses the emerging international policy paradigm, contrasting pre-and post-crisis regulatory approaches and highlighting continuing tensions about key policy choices. It then uses two recent sites of contestation, debt adjustment and the regulation of high-cost credit to demostrate the persistence of conflict over the positioning of consumers within an emergent stability focused paradigm of financial consumer protection

The Turn-On of Mass Transfer in AM CVn Binaries: Implications for RX J0806+1527 and RX J1914+2456

We report on evolutionary calculations of the onset of mass transfer in AM CVn binaries, treating the donor's evolution in detail. We show that during the early contact phase, while the mass transfer rate, \Mdot, is increasing, gravity wave (GW) emission continues to drive the binary to shorter orbital period, \Porb. We argue that the phase where \Mdot > 0 and \nudot > 0 (\nu = 1/\Porb) can last between $10^3$ and $10^6$ yrs, significantly longer than previously estimated. These results are applied to RX J0806+1527 (\Porb = 321 s) and RX J914+2456 (\Porb=569 s), both of which have measured \nudot > 0. \emph{Thus, a \nudot > 0 does not select between the unipolar inductor and accretion driven models proposed as the source of X-rays in these systems}. For the accretion model, we predict for RX J0806 that \ddot{\nu} \approx \ee{1.0-1.5}{-28} Hz s$^{-2}$ and argue that timing observations can probe $\ddot{\nu}$ at this level with a total $\approx 20$ yr baseline. We also place constraints on each system's initial parameters given current observational data.Comment: 5 pages, 3 figures, accepted to ApJ

A burst from the direction of UZ Fornacis with XMM-Newton

The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For finds the source to be a factor > 10^3 fainter than previous EXOSAT and ROSAT observations. The source was not detected for the majority of a 22 ksec exposure with the EPIC cameras, suggesting that the accretion rate either decreased, or stopped altogether. However a 1.1 ksec burst was detected from UZ For during the observation. Spectral fits favour optically thin, kT = 4.4 keV thermal emission. Detection of the burst by the on-board Optical Monitor indicates that this was most probably an accretion event. The 0.1-10 keV luminosity of 2.1 x 10^30 erg/s is typical for accretion shock emission from high state polars and would result from the potential energy release of ~ 10^16 g of gas. There is no significant soft excess due to reprocessing in the white dwarf atmosphere.Comment: 7 pages, 2 postscript figures, ApJL, in pres

KIC 10449976: discovery of an extreme-helium subdwarf in the Kepler field

Optical spectroscopy of the blue star KIC 10449976 shows that it is an extremely helium-rich subdwarf with effective temperature T=40000+/-300 K and surface gravity log g=5.3+/-0.1. Radial-velocity measurements over a five-day timescale show an upper variability limit of ~50+/-20 km/s. Kepler photometry of KIC 10449976 in both long and short cadence modes shows evidence for a periodic modulation on a timescale of ~3.9 days. We have examined the possibility that this modulation is not astrophysical but conclude it is most likely real. We discuss whether the modulation could be caused by a low-mass companion, by stellar pulsations, or by spots. The identification of any one of these as cause has important consequences for understanding the origin of helium-rich subdwarfs.Comment: Accepted by MNRA

FUSE and HST/STIS far-ultraviolet observations of AM Herculis in an extended low state

We have obtained FUSE and HST/STIS time-resolved spectroscopy of the polar AM Herculis during a deep low state. The spectra are entirely dominated by the emission of the white dwarf. Both the far-ultraviolet (FUV) flux as well as the spectral shape vary substantially over the orbital period, with maximum flux occurring at the same phase as during the high state. The variations are due to the presence of a hot spot on the white dwarf, which we model quantitatively. The white dwarf parameters can be determined from a spectral fit to the faint phase data, when the hot spot is self-eclipsed. Adopting the distance of 79+8-6pc determined by Thorstensen, we find an effective temperature of 19800+-700K and a mass of Mwd=0.78+0.12-0.17Msun. The hot spot has a lower temperature than during the high state, ~34000-40000K, but covers a similar area, ~10% of the white dwarf surface. Low state FUSE and STIS spectra taken during four different epochs in 2002/3 show no variation of the FUV flux level or spectral shape, implying that the white dwarf temperature and the hot spot temperature, size, and location do not depend on the amount of time the system has spent in the low state. Possible explanations are ongoing accretion at a low level, or deep heating, both alternatives have some weaknesses that we discuss. No photospheric metal absorption lines are detected in the FUSE and STIS spectra, suggesting that the average metal abundances in the white dwarf atmosphere are lower than 1e-3 times their solar values.Comment: ApJ in press, 12 pages, 11 figure