We present the discoveries of two of AM CVn systems, Gaia14aae and SDSS~J080449.49+161624.8, which show X-ray pulsations at their orbital periods, indicative of magnetically collimated accretion. ...Both also show indications of higher rates of mass transfer relative to the expectations from binary evolution driven purely by gravitational radiation, based on existing optical data for Gaia14aae, which show a hotter white dwarf temperature than expected from standard evolutionary models, and X-ray data for SDSS~J080449.49+161624.8 which show a luminosity 10-100 times higher than those for other AM~CVn at similar orbital periods. The higher mass transfer rates could be driven by magnetic braking from the disk wind interacting with the magnetosphere of the tidally locked accretor. We discuss implications of this additional angular momentum transport mechanism for evolution and gravitational wave detectability of AM CVn objects.
Using the ACS on HST, we have surveyed the FUV and NUV populations in the core region of M80. The CMD reveals large numbers of blue and extreme horizontal branch stars and blue stragglers, as well as ...approx. 60 objects lying in the region of the CMD where accreting and detached white dwarf binaries are expected. Overall, the blue straggler stars are the most centrally concentrated population, with their radial distribution suggesting a typical blue straggler mass of about 1.2 Msun. However, counterintuitively, the faint blue stragglers are significantly more centrally concentrated than the bright ones and a Kolmogorov-Smirnov test suggest only a 3.5% probability that both faint and bright blue stragglers are drawn from the same distribution. This may suggest that (some) blue stragglers get a kick during their formation. We have also been able to identify the majority of the known X-ray sources in the core with FUV bright stars. One of these FUV sources is a likely dwarf nova that was in eruption at the time of the FUV observations. This object is located at a position consistent with Nova 1860 AD, or T Scorpii. Based on its position, X-ray and UV characteristics, this system is almost certainly the source of the nova explosion. The radial distribution of the X-ray sources and of the cataclysmic variable candidates in our sample suggest masses > 1 Msun.
Ultrafast time-resolved velocity map ion imaging (TR-VMI) and time-resolved ion-yield (TR-IY) methods are utilised to reveal a comprehensive picture of the electronic state relaxation dynamics in ...photoexcited catechol (1,2-dihydroxybenzene). After excitation to the S1 ((1)ππ*) state between 280.5 (the S1 origin band, S1(v = 0)) to 243 nm, the population in this state is observed to decay through coupling onto the S2 ((1)πσ*) state, which is dissociative with respect to the non-hydrogen bonded 'free' O-H bond (labelled O(1)-H). This process occurs via tunnelling under an S1/S2 conical intersection (CI) on a timeframe of 5-11 ps, resulting in O(1)-H bond fission along S2. Concomitant formation of ground state catechoxyl radicals (C6H5O2(X)), in coincidence with translationally excited H-atoms, occurs over the same timescale as the S1 state population decays. Between 254-237 nm, direct excitation to the S2 state is also observed, manifesting in the ultrafast (~100 fs) formation of H-atoms with high kinetic energy release. From these measurements we determine that the S1/S2 CI lies ~3700-5500 cm(-1) above the S1(v = 0) level, indicating that the barrier height to tunnelling from S1(v = 0) → S2 is comparable to that observed in the related 'benchmark' species phenol (hydroxybenzene). We discuss how a highly 'vibrationally-enhanced' tunnelling mechanism is responsible for the two orders of magnitude enhancement to the tunnelling rate in catechol, relative to that previously determined in phenol (>1.2 ns), despite similar barrier heights. This phenomenon is a direct consequence of the non-planar S1 excited state minimum structure (C1 symmetry) in catechol, which in turn yields relaxed symmetry constraints for vibronic coupling from S1(v = 0) → S2- a scenario which does not exist for phenol. These findings offer an elegant example of how even simple chemical modifications (ortho-hydroxy substitution) to a fundamental, biologically relevant, UV chromophore, such as phenol, can have profound effects on the ensuing excited state dynamics.
