Apsidal advance in SS 433?

Context. The Galactic microquasar SS 433 launches oppositely directed jets at speeds approximately a quarter of the speed of light. Both the speed and direction of the jets exhibit small fluctuations. A component of the speed variation has 13 day periodicity and the orbital phase at which its maximum speed occurs has advanced approximately 90 degrees in 25 years. Aims. To examine the possibility that these variations are associated with a mildly eccentric orbit and conditions necessary to achieve this apsidal advance. Methods. The advance of the orbital phase for maximum speed is taken to be advance of the apses of the putative elliptical orbit. It is compared with calculations of the effects of tides induced in the companion and also with gravitational perturbations from the circumbinary disc. These calculations are made in the light of recent results on the SS 433 system. Results. The 13 day periodicity in the speed of the jets of SS 433 might be attributed to a mildly elliptical orbit, through periodic approaches of the donor and the compact object. Advance of the apses of such an elliptical orbit due to tidal effects induced in a normal companion looks to be to small; if caused by the circumbinary disc the mass of the inner regions of that disc is ~ 0.15 solar masses.Comment: 2 pages, no figures To appear in A & A. No significant changes from original version poste

Job changes and hours changes: understanding the path of labor supply adjustment

We use British panel data to investigate single women’s labor supply changes in response to three reforms that affected individuals’ work incentives. We use these reforms to identify changes in labor supply. There is evidence of small hours of work effects for two of such reforms. A third reform in 1999 instead led to a significant increase in single mothers’ hours of work. The mechanism by which the labor supply adjustments were made occurred largely through job changes rather than hours changes with the same employer. This is little overall effect of the reforms on wages

SS433's circumbinary ring and accretion disc viewed through its attenuating disc wind

We present optical spectroscopy of the microquasar SS433 covering a significant fraction of a precessional cycle of its jet axis. The components of the prominent stationary H-alpha and H-beta lines are mainly identified as arising from three emitting regions: (i) a super-Eddington accretion disc wind, in the form of a broad component accounting for most of the mass loss from the system, (ii) a circumbinary disc of material that we presume is being excreted through the binary's L2 point, and (iii) the accretion disc itself as two remarkably persistent components. The accretion disc components move with a Keplerian velocity of ~600 km/s in the outer region of the disc. A direct result of this decomposition is the determination of the accretion disc size, whose outer radius attains ~8 R_sun in the case of Keplerian orbits around a black hole mass of 10 M_sun. We determine an upper limit for the accretion disc inner to outer radius ratio in SS433, R_in/R_out ~ 0.2, independent of the mass of the compact object. The Balmer decrements, H-alpha/H-beta, are extracted from the appropriate stationary emission lines for each component of the system. The physical parameters of the gaseous components are derived. The circumbinary ring decrement seems to be quite constant throughout precessional phase, implying a constant electron density of log N_e(cm^-3) ~ 11.5 for the circumbinary disc. The accretion disc wind shows a larger change in its decrements exhibiting a clear dependence on precessional phase, implying a sinusoid variation in its electron density log N_e(cm^-3) along our line-of-sight between 10 and 13. This dependence of density on direction suggests that the accretion disc wind is polloidal in nature.Comment: 7 pages, 5 figures. Accepted for publication in MNRAS Main Journal

Spectral ageing: a new age perspective

We present an up-to-date critique of the physical basis for the spectral ageing method. We find that the number of cases where this method may be meaningfully applied to deduce the ages of classical double radio sources is small indeed. This critique is much more than merely a re-expression of anxieties about the calibration of spectral ageing (which have been articulated by others in the past).Comment: 9 pages, 3 figures, published in `Particles & Fields in Radio Galaxies', PASP, eds RA Laing & KM Blundel

Job changes, hours changes, and the path of labour supply adjustment

This paper uses the first twelve waves of the British Household Panel Survey covering the period 1991-2002 to investigate single women’s labour supply changes in response to three tax and benefit policy reforms that occurred in the 1990s. We find evidence of small labour supply effects for two of such reforms. A third reform in 1999 instead led to a significant increase in single mothers’ hours of work. This increase was primarily driven by women who changed job, suggesting that labour supply adjustments within a job are harder than across jobs. The presence of hours inflexibility within jobs and labour supply adjustments through job mobility are strongly confirmed when we look at hours changes by stated labour supply preferences. Finally, we find little overall effect on wages

The importance of incentives in influencing private retirement saving: known knowns and known unknowns

We summarise what economic theory predicts about how retirement savings decisions are affected by marginal withdrawal rates created by the tax, tax credit and benefit system, and by the information individuals are provided with. All these predictions vary across individuals with their circumstances. In documenting the incentives to save in a private pension provided by the tax, tax credit and benefit system we show that some individuals face a very strong incentive to place funds in a private pension at particular times during their working lives. Those who are basic rate taxpayers who expect to become higher rate taxpayers or move onto the taper of the Working Tax Credit have an incentive to delay making any private pension contributions until that time, while those expecting to move off that taper have an incentive to bring forward future pension contributions. When examining retirement saving it is important to consider both saving decisions and also the choice of retirement age. We cite previous evidence that both of these margins have been adjusted by individuals in the light of changed financial incentives. In particular there is evidence that spending by working age individuals was increased in the light of the introduction of the State Earnings-Related Pension Scheme. In addition evidence from West Germany and the United States shows that individuals' retirement ages can be affected substantially by changing financial incentives. There is less evidence of reduced spending by working age individuals in the light of the decision to index the Basic State Pension in line with prices rather than the greater of prices or earnings. New evidence from the English Longitudinal Study of Ageing shows that it is low and high wealth individuals who are most likely to be out of the labour market prior to the State Pension Age, though often for very different stated reasons. This suggests that if retirement incomes of those with low wealth are to be increased then increased labour market participation is perhaps a margin for them to adjust. Incentives to work and save are potentially affected by two recent UK reforms: the introduction of the two new tax credits (Working Tax Credit and Child Tax Credit) and the introduction of the Pension Credit. We present some preliminary evidence on whether the strong incentive to contribute to a private pension provided by the two new tax credits has boosted private pension participation, the results of which are somewhat inconclusive and are worthy of further research. Examining the distribution of current pensioner incomes with respect to the incentives induced by the Pension Credit reform we find that many single pensioners will see an unambiguous increase in the incentive to increase their private retirement income -- for example through increased saving or later retirement. There are still large numbers of single pensioners who see a reduction in the incentive to increase their retirement income, the majority of whom have private income which they might decide to reduce. Fewer individuals in pensioner couples are eligible for the Pension Credit. Despite this we find that a similar proportion faces a reduced incentive to acquire greater income as we did for single pensioners. If the expectations of individuals do not reflect the current rules of the system, then we cannot expect to observe responses fully in line with economic theory that is predicated on full information. Recent evidence from the English Longitudinal Study of Ageing suggests that on average individuals underestimate their longevity and overestimate the private pension income that they can expect to receive. On the other hand, expectations of being in paid employment at older ages are, on average, similar to the current proportions of older individuals who are in paid work and individuals' expectations of remaining in the labour market at older ages appear to square up with the marginal financial incentives to remain in work that are created by different types of pension scheme

The central engines of radio-quiet quasars

Two rival hypotheses have been proposed for the origin of the compact radio flux observed in radio-quiet quasars (RQQs). It has been suggested that the radio emission in these objects, typically some two or three orders of magnitude less powerful than in radio-loud quasars (RLQs), represents either emission from a circumnuclear starburst or is produced by radio jets with bulk kinetic powers 10^3 times lower than those of RLQs with similar luminosity ratios in other wavebands. We describe the results of high resolution (parsec-scale) radio-imaging observations of a sample of 12 RQQs using the Very Long Baseline Array (VLBA). We find strong evidence for jet-producing central engines in 8 members of our sample.Comment: 7 pages, 8 figures. Accepted for publication in MNRA

The impact of tax and benefit changes between April 2000 and April 2003 on parents' labour supply

This Briefing Note provides the first published estimates of the labour market impact of the new tax credits, and the tax and benefit reforms that preceded them, on families with children. Specifically, this note examines all personal tax and benefit reforms introduced between April 2000 and April 2003. We use a structural model of labour supply to examine how these changes affect both the participation rate (the proportion of parents who would like to work at a given hourly wage) and the average weekly hours of work. We examine how the impact varies between lone mothers and adults in couples with children, and how it varies with both the number of children and the age of the youngest child in the family

Evaluating the labour market impact of Working Families' Tax Credit using difference-in-differences

A difference-in-differences methodology cannot identify the labour market impact of WFTC alone because other taxes and benefits changed at the same time as its introduction. However, a comparison of the change in employment rates for parents against adults without children should underestimate any positive labour supply impact of WFTC for lone parents. Using two different household surveys, we find WFTC and associated reforms increased lone parents' employment by around 3.6 percentage points (ppt). For couples with children, we find that WFTC and associated reforms had no significant effect on mothers' employment, and was associated with a -0.5ppt change in fathers' employment, with the reforms encouraging households to have one earner rather than two. Overall, these changes correspond to between 25,000 and 59,000 extra workers depending upon the data source used. Robustness analysis of our identifying assumptions is generally favourable to our conclusions for lone parents