Seismology of the Accreting White Dwarf in GW Lib

We present a first analysis of the g-mode oscillation spectrum for the white dwarf (WD) primary of GW Lib, a faint cataclysmic variable (CV). Stable periodicities have been observed from this WD for a number of years, but their interpretation as stellar pulsations has been hampered by a lack of theoretical models appropriate to an accreting WD. Using the results of Townsley and Bildsten, we construct accreting models for the observed effective temperature and approximate mass of the WD in GW Lib. We compute g-mode frequencies for a range of accreted layer masses, Macc, and long term accretion rates, . If we assume that the observed oscillations are from l=1 g-modes, then the observed periods are matched when M ~= 1.02 Msun, Macc ~= 0.31 x 10^-4 Msun and ~= 7.3 x 10^-11 Msun/yr. Much more sensitive observations are needed to discover more modes, after which we will be able to more accurately measure these parameters and constrain or measure the WD's rotation rate.Comment: 4 pages, 3 figures; uses emulateapj; Accepted by the Astrophysical Journal Letter

Discovery of a Second Nova Eruption of V2487 Ophiuchi

A directed search for previously-undiscovered nova eruptions was conducted in the astronomical plate archives at Harvard College Observatory and Sonneberg Observatory. We found that an eruption of V2487 Oph (Nova Oph 1998) occurred on 1900 June 20. V2487 Oph was previously classified as a classical nova, which we identified as a probable recurrent nova based on its large expansion velocities and the presence of high excitation lines in the outburst spectrum. The event was recorded on Harvard plate AM 505, at a B magnitude of 10.27 +/- 0.11, which is near peak. The outburst can only be seen on one plate, but the image has a characteristic dumbbell shape (caused by a double exposure) that is identical to the other star images on the plate, and thus is not a plate defect. We conclude that this is in fact a previously-undiscovered nova outburst of V2487 Oph, confirming our prediction that it is a recurrent nova. We also examine the discovery efficiency for eruptions of the system and conclude that a randomly-timed outburst has, on average, a 30% chance of being discovered in the past century. Using this, we deduce a recurrence time for V2487 Oph of approximately 18 years, which implies that the next eruption is expected around 2016.Comment: 18 pages, 2 figures, to be published in the Astronomical Journa

Novae With Long-Lasting Supersoft Emission That Drive a High Accretion Rate

We identify a new class of novae characterized by the post-eruption quiescent light curve being more than roughly a factor of ten brighter than the pre-eruption light curve. Eight novae (V723 Cas, V1500 Cyg, V1974 Cyg, GQ Mus, CP Pup, T Pyx, V4633 Sgr, and RW UMi) are separated out as being significantly distinct from other novae. This group shares a suite of uncommon properties, characterized by the post-eruption magnitude being much brighter than before eruption, short orbital periods, long-lasting supersoft emission following the eruption, a highly magnetized white dwarf, and secular declines during the post-eruption quiescence. We present a basic physical picture which shows why all five uncommon properties are causally connected. Most novae do not have adequate accretion for continuous hydrogen burning, but some can achieve this if the companion star is nearby (with short orbital period) and a magnetic field channels the matter onto a small area on the white dwarf so as to produce a locally high accretion rate. The resultant supersoft flux irradiates the companion star and drives a higher accretion rate (with a brighter post-eruption phase), which serves to keep the hydrogen burning and the supersoft flux going. The feedback loop cannot be perfectly self-sustaining, so the supersoft flux will decline over time, forcing a decline in the accretion rate and the system brightness. We name this new group after the prototype, V1500 Cyg. V1500 Cyg stars are definitely not progenitors of Type Ia supernovae. The V1500 Cyg stars have similar physical mechanisms and appearances as predicted for nova by the hibernation model, but with this group accounting for only 14% of novae.Comment: Astronomical Journal, in press, 39 pages, 10 figure

The Nova Shell and Evolution of the Recurrent Nova T Pyxidis

T Pyxidis is the prototypical recurrent nova (RN) with a mysterious nova shell. We report new observations of the shell with HST. The knots in the shell are expanding with velocities 500-715 km/s, for a distance of 3500 pc. The fractional expansion of the knots is constant, and this implies no significant deceleration. Hence, the knots were ejected by an eruption close to the year 1866. Knots have turned on after 1995, and this demonstrates that the knots are powered by shocks from the collision of the 1866 ejecta with fast ejecta from later RN eruptions. The 1866 ejecta has a total mass of 10^-4.5 Msun, which with the low ejection velocity shows that the 1866 event was an ordinary nova eruption, not a RN eruption. The accretion rate before the ordinary nova event must have been low (around the 4x10^-11 Msun/yr expected for gravitational radiation alone) and the matter accumulated on the surface of the white dwarf for ~750,000 years. The current accretion rate (>10^-8 Msun/yr) is 1000X higher than expected for a system below the period gap, with the plausible reason being that the 1866 event started a continuing supersoft source that drives the accretion. A key fact about T Pyx is that its accretion rate has been secularly declining since before the 1890 eruption, with the current rate being only 3% of its earlier rate. The decline in the observed accretion rate shows that the supersoft source is not self-sustaining, and we calculate that the accretion in T Pyx will effectively stop in upcoming decades. With this, T Pyx will enter a state of hibernation, lasting for an estimated 2,600,000 years, before gravitational radiation brings the system into contact again. Thus, T Pyx has an evolutionary cycle going from an ordinary CV state, to its current RN state, to a future hibernation state, and then repeating this cycle.Comment: Astrophysical Journal in press, 62 pages, 11 figures (accepted version; minor changes and shortening

Changing practice in dementia care in the community: developing and testing evidence-based interventions, from timely diagnosis to end of life (EVIDEM)

Background Dementia has an enormous impact on the lives of individuals and families, and on health and social services, and this will increase as the population ages. The needs of people with dementia and their carers for information and support are inadequately addressed at all key points in the illness trajectory. Methods The Unit is working specifically on an evaluation of the impact of the Mental Capacity Act 2005, and will develop practice guidance to enhance concordance with the Act. Phase One of the study has involved baseline interviews with practitioners across a wide range of services to establish knowledge and expectations of the Act, and to consider change processes when new policy and legislation are implemented. Findings Phase 1, involving baseline interviews with 115 practitioners, identified variable knowledge and understanding about the principles of the Act. Phase 2 is exploring everyday decision-making by people with memory problems and their carers

Catching Element Formation In The Act

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous gamma-ray instruments. This transformative capability permits: (a) the accurate identification of the gamma-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new gamma-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new gamma-ray instruments to address a wide set of astrophysical questions.Comment: 14 pages including 3 figure

ULTRACAM observations of two accreting white dwarf pulsators

In this paper, we present high time-resolution observations of GW Librae (GW Lib) and SDSS J161033.64-010223.3 (SDSS 1610) - two cataclysmic variables which have shown periodic variations attributed to non-radial pulsations of the white dwarf (WD). We observed both these systems in their quiescent states with ULTRACAM on the Very Large Telescope (VLT) and the University of Cape Town Photometer on the SAAO 1.9m telescope, and detect the strong pulsations modes reported by previous authors. The identification of further periodicities in GW Lib is limited by the accretion-driven flickering of the source, but in the case of SDSS 1610 we identify several additional low-amplitude periodicities. In both the sources, we find the pulsation modes to be stronger in amplitude at bluer wavelengths. In the case of SDSS 1610, there is evidence to suggest that the two primary signals have a different colour dependence, suggesting that they may be different spherical harmonic modes. We additionally observed GW Lib during several epochs following its 2007 dwarf nova outburst, using ULTRACAM on the VLT and the Auxiliary Port Imager on the William Herschel Telescope. This is the first time a dwarf nova containing a pulsating WD has been observed in such a state. We do not observe any periodicities, suggesting that the heating of the WD had either switched-off the pulsations entirely, or reduced their relative amplitude in flux to the point where they are undetectable. Further observations 11 months after the outburst taken with RATCam on the Liverpool Telescope still do not show the pulsation modes previously observed, but do show the emergence of two new periodic signals, one with a frequency of 74.86 +/- 0.68 cycles d(-1) (P = 1154 s) and a g '-band amplitude of 2.20 per cent +/- 0.18 and the other with a frequency of 292.05 +/- 1.11 cycles d(-1) (P = 296 s) and a g ' amplitude of 1.25 per cent +/- 0.18. In addition to the WD pulsations, our observations of GW Lib in quiescence show a larger amplitude modulation in luminosity with a period of approximately 2.1 h. This has previously been observed, and its origin is unclear: it is unrelated to the orbital period. We find this modulation to vary over the course of our observations in phase and/or period. Our data support the conclusion that this is an accretion-related phenomenon, which originates in the accretion disc