The Secondary Star in Cataclysmic Variables and Low Mass X-ray Binaries

We critically re-examine the available data on the spectral types, masses and radii of the secondary stars in cataclysmic variables (CVs) and low-mass X-ray binaries (LMXBs), using the new catalogue of Ritter & Kolb (1998) as a starting point. We find there are 55 reliable spectral type determinations and only 14 reliable mass determinations of CV secondary stars (10 and 5, respectively, in the case of LMXBs). We derive new spectral type-period, mass-radius, mass-period and radius-period relations, and compare them with theoretical predictions. We find that CV secondary stars with orbital periods shorter than 7-8 hours are, as a group, indistinguishable from main sequence stars in detached binaries. We find it is not valid, however, to estimate the mass from the spectral type of the secondary star in CVs or LMXBs. We find that LMXB secondary stars show some evidence for evolution, with secondary stars which are slightly too large for their mass. We show how the masses and radii of the secondary stars in CVs can be used to test the validity of the disrupted magnetic braking model of CV evolution, but we find that the currently available data are not sufficiently accurate or numerous to allow such an analysis. As well as considering secondary star masses, we also discuss the masses of the white dwarfs in CVs, and find mean values of M_1 = 0.69+/-0.13 M_sun below the period gap, and M_1 = 0.80+/-0.22 M_sun above the period gap.Comment: 18 pages, 5 figure

Random Projections For Large-Scale Regression

Fitting linear regression models can be computationally very expensive in large-scale data analysis tasks if the sample size and the number of variables are very large. Random projections are extensively used as a dimension reduction tool in machine learning and statistics. We discuss the applications of random projections in linear regression problems, developed to decrease computational costs, and give an overview of the theoretical guarantees of the generalization error. It can be shown that the combination of random projections with least squares regression leads to similar recovery as ridge regression and principal component regression. We also discuss possible improvements when averaging over multiple random projections, an approach that lends itself easily to parallel implementation.Comment: 13 pages, 3 Figure

A Self-Occulting Accretion Disk in the SW Sex Star DW UMa

We present the ultraviolet spectrum of the SW Sex star and nova-like variable DW UMa in an optical low state, as observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope (HST). The data are well described by a synthetic white dwarf (WD) spectrum with T_eff = 46,000 +/- 1000 K, log g = 7.60 +/- 0.15, v*sin(i) = 370 +/- 100 km/s and Z/Z_solar = 0.47 +/- 0.15. For this combination of T_eff and log g, WD models predict M_WD = 0.48 +/- 0.06 M_solar and R_WD = (1.27 +/- 0.18) * 10^9 cm. Combining the radius estimate with the normalization of the spectral fit, we obtain a distance estimate of d = 830 +/-150 pc. During our observations, DW UMa was approximately 3 magnitudes fainter in V than in the high state. A comparison of our low-state HST spectrum to a high-state spectrum obtained with the International Ultraviolet Explorer shows that the former is much bluer and has a higher continuum level shortward of 1450 A. Since DW UMa is an eclipsing system, this suggests that an optically thick accretion disk rim blocks our view of the WD primary in the high state. If self-occulting accretion disks are common among the SW Sex stars, we can account for (i) the preference for high-inclination systems within the class and (ii) their V-shaped continuum eclipses. Moreover, even though the emission lines produced by a self-obscured disk are generally still double-peaked, they are weaker and narrower than those produced by an unobscured disk. This may allow a secondary line emission mechanism to dominate and produce the single-peaked, optical lines that are a distinguishing characteristic of the SW Sex stars.Comment: 9 pages, including 2 figures; accepted for publication in Astrophysical Journal Letters; New version matches version in press (footnote added to discussion section; figures now use color

Searching for nova shells around cataclysmic variables

We present the results of a search for nova shells around 101 cataclysmic variables (CVs), using Halpha images taken with the 4.2-m William Herschel Telescope (WHT) and the 2.5-m Isaac Newton Telescope Photometric Halpha Survey of the Northern Galactic Plane (IPHAS). Both telescopes are located on La Palma. We concentrated our WHT search on nova-like variables, whilst our IPHAS search covered all CVs in the IPHAS footprint. We found one shell out of the 24 nova-like variables we examined. The newly discovered shell is around V1315 Aql and has a radius of approx.2.5 arcmin, indicative of a nova eruption approximately 120 years ago. This result is consistent with the idea that the high mass-transfer rate exhibited by nova-like variables is due to enhanced irradiation of the secondary by the hot white dwarf following a recent nova eruption. The implications of our observations for the lifetime of the nova-like variable phase are discussed. We also examined 4 asynchronous polars, but found no new shells around any of them, so we are unable to confirm that a recent nova eruption is the cause of the asynchronicity in the white dwarf spin. We find tentative evidence of a faint shell around the dwarf nova V1363 Cyg. In addition, we find evidence for a light echo around the nova V2275 Cyg, which erupted in 2001, indicative of an earlier nova eruption approx.300 years ago, making V2275 Cyg a possible recurrent nova.Comment: 14 pages, 50 figures, 3 Table

Prevalence and correlates of achieving recommended physical activity levels among children living in rural South Asia—A multi-centre study

Background: We report the prevalence of recommended physical activity levels (RPALs) and examine the correlates of achieving RPALs in rural South Asian children and analyse its association with anthropometric outcomes. Methods: This analysis on rural South Asian children aged 5–14 years (n = 564) is a part of the Chronic Disease Risk Factor study conducted at three sites in India (Chennai n = 146; Goa n = 218) and Bangladesh (Matlab; n = 200). Data on socio-demographic and lifestyle factors (physical activity (PA); diet) were collected using an interviewer-administered questionnaires, along with objective anthropometric measurements. Multivariate logistic regression models were used to examine whether RPALs (active travel to school (yes/no); leisure-time PA ≥ 1 h/day; sedentary-activity ≤ 2 h/day) were associated with socio-demographic factors, diet and other forms of PA. Multivariate linear regression models were used to investigate associations between RPALs and anthropometrics (BMI- and waist z-scores). Results: The majority of children (71.8 %) belonged to households where a parent had at least a secondary education. Two-thirds (66.7 %) actively travelled to school; 74.6 % reported ≥1 h/day of leisure-time PA and 55.7 % had ≤2 h/day of sedentary-activity; 25.2 % of children reported RPALs in all three dimensions. Older (10–14 years, OR = 2.0; 95 % CI: 1.3, 3.0) and female (OR = 1.7; 95 % CI: 1.1, 2.5) children were more likely to travel actively to school. Leisure-time PA ≥ 1 h/day was more common among boys (OR = 2.5; 95 % CI: 1.5, 4.0), children in Matlab, Bangladesh (OR = 3.0; 95 % CI: 1.6, 5.5), and those with higher processed-food consumption (OR = 2.3; 95 % CI: 1.2, 4.1). Sedentary activity ≤ 2 h/day was associated with younger children (5–9 years, OR = 1.6; 95 % CI: 1.1, 2. 4), children of Goa (OR = 3.5; 95 % CI: 2.1, 6.1) and Chennai (OR = 2.5; 95 % CI: 1.5, 4.3) and low household education (OR = 2.1; 95 % CI: 1.1, 4.1). In multivariate analyses, sedentary activity ≤ 2 h/day was associated with lower BMI-z-scores (β = −0.3; 95 % CI: −0.5, −0.08) and lower waist-z-scores (β = −1.1; 95 % CI: −2.2, −0.07). Conclusion: Only one quarter of children in these rural areas achieved RPAL in active travel, leisure and sedentary activity. Improved understanding of RPAL in rural South Asian children is important due to rapid socio-economic transition

The component masses of the cataclysmic variable V347 Puppis

We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of KR= 198 ± 5 km s−1. The rotational velocity of the secondary star in V347 Pup is found to be v sin i= 131 ± 5 km s−1 and the system inclination is i= 840 ± 23. From these parameters we obtain masses of M1= 0.63 ± 0.04 M⊙ for the white dwarf primary and M2= 0.52 ± 0.06 M⊙ for the M0.5V secondary star, giving a mass ratio of q= 0.83 ± 0.05. On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc