Kinematics of the ultracompact helium accretor AM canum venaticorum

We report on the results from a five-night campaign of high-speed spectroscopy of the 17-min binary AM Canum Venaticorum (AM CVn), obtained with the 4.2-m William Herschel Telescope on La Palma. We detect a kinematic feature that appears to be entirely analogous to the 'central spike' known from the long-period, emission-line AM CVn stars GP Com, V396 Hya and SDSS J124058.03-015919.2, which has been attributed to the accreting white dwarf. Assuming that the feature indeed represents the projected velocity amplitude and phase of the accreting white dwarf, we derive a mass ratio q = 0.18 +/- 0.01 for AM CVn. This is significantly higher than the value found in previous, less direct measurements. We discuss the implications for AM CVn's evolutionary history and show that a helium star progenitor scenario is strongly favoured. We further discuss the implications for the interpretation of AM CVn's superhump behaviour, and for the detectability of its gravitational-wave signal with the Laser Interferometer Space Antenna (LISA). In addition, we demonstrate a method for measuring the circularity or eccentricity of AM CVn's accretion disc, using stroboscopic Doppler tomography. We test the predictions of an eccentric, precessing disc that are based on AM CVn's observed superhump behaviour. We limit the effective eccentricity in the outermost part of the disc, where the resonances that drive the eccentricity are thought to occur, to e = 0.04 +/- 0.01, which is smaller than previous models indicated

Phase-resolved spectroscopy of the helium dwarf nova 'SN 2003aw' in quiescence

High time resolution spectroscopic observations of the ultracompact helium dwarf nova 'SN 2003aw' in its quiescent state at V similar to 20.5 reveal its orbital period at 2027.8 +/- 0.5 s or 33.80 min. Together with the photometric 'superhump' period of 2041.5 +/- 0.5 s, this implies a mass ratio q approximate to 0.036. We compare both the average and time-resolved spectra of 'SN 2003aw' and Sloan Digital Sky Survey (SDSS) J124058.03-015919.2. Both show a DB white dwarf spectrum plus an optically thin, helium-dominated accretion disc. 'SN 2003aw' distinguishes itself from the SDSS source by its strong calcium H & K emission lines, suggesting higher abundances of heavy metals than the SDSS source. The silicon and iron emission lines observed in the SDSS source are about twice as strong in 'SN 2003aw'. The peculiar 'double bright spot' accretion disc feature seen in the SDSS source is also present in time-resolved spectra of 'SN 2003aw', albeit much weaker

The expanding bipolar shell of the helium nova V445 Puppis

From multi-epoch adaptive optics imaging and integral field unit spectroscopy, we report the discovery of an expanding and narrowly confined bipolar shell surrounding the helium nova V445 Puppis (Nova Puppis 2000). An equatorial dust disc obscures the nova remnant, and the outflow is characterized by a large polar outflow velocity of 6720 +/- 650 km s(-1) and knots moving at even larger velocities of 8450 +/- 570 km s(-1). We derive an expansion parallax distance of 8.2 +/- 0.5 kpc and deduce a pre-outburst luminosity of the underlying binary of log L/L-circle dot = 4.34 +/- 0.36. The derived luminosity suggests that V445 Puppis probably contains a massive white dwarf accreting at high rate from a helium star companion making it part of a population of binary stars that potentially lead to supernova Ia explosions due to accumulation of helium-rich material on the surface of a massive white dwarf

Binaries discovered by the SPY project. IV, Five single-lined DA double white dwarfs

We present results from our ongoing follow-up observations of double white dwarf binaries detected in the ESO SN Ia Progenitor SurveY (SPY). We discuss our observing strategy and data analysis and present the orbital solutions of five close double white dwarf binaries: HE0320−1917, HE1511−0448, WD0326−273, WD1013−010 and WD1210+140. Their periods range from 0.44 to 3.22 days. In none of these systems we find any spectral lines originating from the companion. This rules out main sequence companions and indicates that the companion white dwarfs are significantly older and cooler than the bright component. Infrared photometry suggests the presence of a cool, helium-rich white dwarf companion in the binary WD 0326−273. We briefly discuss the consequences of our findings for our understanding of the formation and evolution of double white dwarfs

A Solve-RD ClinVar-based reanalysis of 1522 index cases from ERN-ITHACA reveals common pitfalls and misinterpretations in exome sequencing

Purpose Within the Solve-RD project (https://solve-rd.eu/), the European Reference Network for Intellectual disability, TeleHealth, Autism and Congenital Anomalies aimed to investigate whether a reanalysis of exomes from unsolved cases based on ClinVar annotations could establish additional diagnoses. We present the results of the “ClinVar low-hanging fruit” reanalysis, reasons for the failure of previous analyses, and lessons learned. Methods Data from the first 3576 exomes (1522 probands and 2054 relatives) collected from European Reference Network for Intellectual disability, TeleHealth, Autism and Congenital Anomalies was reanalyzed by the Solve-RD consortium by evaluating for the presence of single-nucleotide variant, and small insertions and deletions already reported as (likely) pathogenic in ClinVar. Variants were filtered according to frequency, genotype, and mode of inheritance and reinterpreted. Results We identified causal variants in 59 cases (3.9%), 50 of them also raised by other approaches and 9 leading to new diagnoses, highlighting interpretation challenges: variants in genes not known to be involved in human disease at the time of the first analysis, misleading genotypes, or variants undetected by local pipelines (variants in off-target regions, low quality filters, low allelic balance, or high frequency). Conclusion The “ClinVar low-hanging fruit” analysis represents an effective, fast, and easy approach to recover causal variants from exome sequencing data, herewith contributing to the reduction of the diagnostic deadlock

ULTRACAM photometry of the ultracompact binaries V407 Vul and HM Cnc

V407 Vul (RXJ1914.4+2456) and HM Cnc (RXJ0806.3+1527) are X-ray emitting stars with X-ray light curves that are 100 per cent modulated on periods of 569 and 321 s, respectively. These periods are thought possibly to represent the orbital periods of close pairs of white dwarfs. In this paper we present optical light curves taken with the high-speed CCD camera ULTRACAM on the 4.2-m William Hershel Telescope in 2003 May and 2005 August and with the VLT in 2005 November. The optical and X-ray light curves of HM Cnc have been reported as being in antiphase, but we find that in fact the X-rays peak around 0.2 cycles after the maximum of the optical light, as seen also in V407 Vul. The X-ray/optical phase shifts are well explained under the accreting models of the systems if most of the optical modulation comes from the heated faces of the mass donors and if the X-ray emitting spots are positioned in advance of the mass donors, as is expected given the angular momentum of the accreting material. Some optical emission may also come from the vicinity of the X-ray spot, and we further show that this can explain the non-sinusoidal light curves of HM Cnc. On the basis of this model we constrain the temperature of the heated face of the companion star finding a bolometric luminosity > 10(33) erg s(-1) and a distance, d > 1.1 kpc. We can identify no explanation for the X-ray/optical phase shifts under the intermediate polar and unipolar inductor models of the systems. The only significant difference between the two stars is that V407 Vul is observed to have the spectrum of a G star. The variation in position on the sky of a blend of a variable and a constant star can be used as a measure of their separation, and is sensitive to values well below the limit set by seeing. We apply this 'pulsation astrometry' to deduce that the G star is separated from the variable by about 0.027 arcsec and hence plays no role in the variability of V407 Vul. We show that light traveltime variations could influence the period change in V407 Vul if it forms a triple system with the G star

The long-period AM CVn star SDSS J155252.48+320150.9

The Sloan Digital Sky Survey has been instrumental in obtaining a homogeneous sample of the rare AM CVn stars: mass-transferring binary white dwarfs. As part of a campaign of spectroscopic follow-up on candidate AM CVn stars from the Sloan Digital Sky Survey, we have obtained time-resolved spectra of the g = 20.2 candidate SDSS J155252.48+320150.9 on the Very Large Telescope of the European Southern Observatory. We report an orbital period P-orb = 3376.3 +/- 0.3 s, or 56.272 +/- 0.005 min, based on an observed 'S-wave' in the helium emission lines of the spectra. This confirms the ultracompact nature of the binary. Despite its relative closeness to the orbital period minimum for hydrogen-rich donors, there is no evidence for hydrogen in the spectra. We thus classify SDSS J1552 as a new bona fide AM CVn star, with the second-longest orbital period after V396 Hya (P = 65.5 min). The continuum of SDSS J1552 is compatible with either a blackbody or helium atmosphere of T-eff = 12 000-15 000 K. If this represents the photosphere of the accreting white dwarf, as is expected, it puts the accretor at the upper end of the temperature range predicted by thermal evolution models. This suggests that SDSS J1552 consists of (or formerly consisted of) relatively high-mass components

The Thermal State of the Accreting White Dwarf in AM Canum Venaticorum Binaries

Contains fulltext : 35202_1.pdf (preprint version ) (Open Access) Contains fulltext : 35202._2.pdf (publisher's version ) (Open Access)We calculate the heating and cooling of the accreting white dwarf (WD) in the ultracompact AM Canum Venaticorum (AM CVn) binaries and show that the WD can contribute significantly to their optical and ultraviolet emission. We estimate the WD's effective temperature, Teff, using the optical continuum for a number of observed binaries, and we show that it agrees well with our theoretical calculations. Driven by gravitational radiation losses, the time-averaged accretion rate, , decreases monotonically with increasing Porb, covering 6 orders of magnitude. If the short-period (Porbeff>50,000 K accreting WD. At longer Porb we calculate the Teff and absolute visual magnitude, MV, that the accreting WD will have during low accretion states, and we find that th

SDSS J0926+3624, the first eclipsing AM CVn star, as seen with ULTRACAM

We present light curves of SDSS J0926+3624, the first eclipsing AM CVn star, observed with the high-speed CCD camera ULTRACAM on the WHT. We find, unusually, that the accreting white dwarf is only partially eclipsed by its companion. Apart from this, the system shows the classic eclipse morphology displayed by eclipsing dwarf novae, namely the eclipse of a white dwarf and accretion disc followed by that of the bright spot where the mass transfer stream hits the disc. We are able to fit this well to find masses of the accretor and donor to be M-1 = 0.84 +/- 0.05 M-circle dot and M-2 = 0.029 +/- 0.02 M-circle dot respectively. The mass of the donor is significantly above its zero temperature value and it must possess significant thermal content

Photometry of V407 Vul and RXJ0806.3+1527 : twin systems?

We present new photometry of V407 Vul and RXJ0806.3+1527. These stars are thought to be ultra-compact pairs of white dwarfs and the shortest period binaries known. They have periods of 569 and 321 sec respectively. We found that the X-ray and optical light curves of RXJ0806.3+1527 are not anti-pbased as was previously thought. Instead, the X-ray lags the optical by 0.2 of cycle, indistinguishable from the phase offset seen in V407 Vul. Although very similar to RXJ0806.3+1527, V407 Vul surprisingly is observed to have the spectrum of a G star. We test whether this could be a line-of-sight coincidence by searching for variations in the V407 Vul's position on the sky on the 569 second period. We find that the G star is separated from the variable by 0.03 arcsec, and has no direct connection with the 569 second source. This supports a common nature for V407 Vul and RXJ0806.3+1527