Simultaneous Doppler maps of IP Peg in outburst

IP Pegasi is an eclipsing dwarf nova lying above the period gap with an orbital period of 3.8h. It is the first cataclysmic variable to show evidence of spiral arms in its accretion disc. We present new time-resolved echelle spectroscopic observations of IP Peg, covering the 3900-7700 Angstrom range. This allows us to produce simultaneous Doppler Maps in 9 emission lines

Eclipse maps of spiral shocks in the accretion disc of IP Pegasi in outburst

Eclipse lightcurves of the dwarf nova IP Peg during the November 1996 outburst are analysed with eclipse mapping techniques to constrain the location and investigate the spatial structure of the spiral shocks observed in the Doppler tomograms (Harlaftis et al. 1999). Eclipse maps in the blue continuum and in the CIII+NIII 4650 emission line show two asymmetric arcs of \sim 90 degrees in azimuth and extending from intermediate to the outer disc regions (R \simeq 0.2 - 0.6 R_{L1}, where R_{L1} is the distance from disc centre to the inner Lagrangian point) which are interpreted as being the spiral shocks seen in the Doppler tomograms. The HeII 4686 eclipse map also shows two asymmetric arcs diluted by a central brightness source. The central source probably corresponds to the low-velocity component seen in the Doppler tomogram and is understood in terms of gas outflow in a wind emanating from the inner parts of the disc. We estimate that the spirals contribute about 16 and 30 per cent of the total line flux, respectively, for the HeII and CIII+NIII lines. Comparison between the Doppler and eclipse maps reveal that the Keplerian velocities derived from the radial position of the shocks are systematically larger than those inferred from the Doppler tomography indicating that the gas in the spiral shocks has sub-Keplerian velocities. We undertake simulations with the aim to investigate the effect of artifacts on the image reconstruction of the spiral structures.Comment: MNRAS, in press. 6 pages, 1 embedded PS and 3 JPEG figures; typed with MNRAS latex styl

The orbital period and system parameters of the recurrent nova T Pyx

T Pyx is a luminous recurrent nova that accretes at a much higher rate than is expected for its photometrically determined orbital period of about 1.8 h. We here provide the first spectroscopic confirmation of the orbital period, P = 1.8295 h (f = 13.118368 +/- 1.1 x 10(-5) c d(-1)), based on time-resolved optical spectroscopy obtained at the Very Large Telescope and the Magellan telescope. We also derive an upper limit of the velocity semi-amplitude of the white dwarf, K 1 = 17.9 +/- 1.6 kms(-1), and estimate amass ratio of q = 0.20 +/- 0.03. If the mass of the donor star is estimated using the period-density relation and theoretical main-sequence mass-radius relation for a slightly inflated donor star, we find M-2 = 0.14 +/- 0.03 M-circle dot. This implies a mass of the primary white dwarf of M-1 = 0.7 +/- 0.2 M-circle dot. If the white-dwarf mass is > 1 M-circle dot, as classical nova models imply, the donor mass must be even higher. We therefore rule out the possibility that T Pyx has evolved beyond the period minimum for cataclysmic variables. We find that the system inclination is constrained to be i approximate to 10 degrees, confirming the expectation that T Pyx is a low-inclination system. We also discuss some of the evolutionary implications of the emerging physical picture of T Pyx. In particular, we show that epochs of enhanced mass transfer (like the present) may accelerate or even dominate the overall evolution of the system, even if they are relatively short-lived. We also point out that such phases may be relevant to the evolution of cataclysmic variables more generally

Doppler tomography of accretion in binaries

Since its conception, Doppler tomography has matured into a versatile and widely used tool. It exploits the information contained in the highly-structured spectral line-profiles typically observed in mass-transferring binaries. Using inversion techniques akin to medical imaging, it permits the reconstruction of Doppler maps that image the accretion flow on micro-arcsecond scales. I summarise the basic concepts behind the technique and highlight two recent results; the use of donor star emission as a means to system parameter determination, and the real-time movies of the evolving accretion flow in the cataclysmic variable WZ Sge during its 2001 outburst. I conclude with future opportunities in Doppler tomography by exploiting the combination of superior data sets, second generation reconstruction codes and simulated theoretical tomograms to delve deeper into the physics of accretion flows.Comment: 4 pages, two color figures, to appear in the proceedings of IAU JD9, "Astro-tomography", eds. A.Cameron, A.Schwope and S.Vrielmann, movies available at http://hea-www.harvard.edu/~dsteeghs/wzsge/movies.htm

Optical spectroscopy of (candidate) ultra-compact X-ray binaries: constraints on the composition of the donor stars

We present optical spectroscopy of several (candidate) ultra-compact X-ray binaries (UCXBs) obtained with the ESO VLT and Gemini-North telescopes. In only one of five observed UCXB candidates did we find evidence for H in its spectrum (4U 1556-60). For XB 1905+00 the optical counterpart is not detected. For the known UCXBs 4U 1626-67 and XB 1916-05 we find spectra consistent with a C/O and a He/N accretion disc respectively, the latter is the first optical spectrum of a He-rich donor in an UCXB. Interestingly, the C/O spectrum of 4U 1626-67 shows both similarities as well as marked differences from the optical C/O spectrum of 4U 0614+09. We obtained phase resolved spectroscopy of 4U 0614+09 and the 44 min transient XTE J0929-314. In neither object were we able to detect clear orbital periodicities, highlighting the difficulties of period determinations in UCXBs. We reanalysed the spectra of XTE J0929-314 that were taken close to the peak of its 2003 X-ray outburst and do not confirm the detection of Halpha emission as was claimed in the literature. The peak spectra do show strong C or N emission around 4640A, as has also been detected in other UCXBs. We discuss the implications of our findings for our understanding of the formation of UCXBs and the Galactic population of UCXBs. At the moment all studied systems are consistent with having white dwarf donors, the majority being C/O rich.Comment: Accepted for publication in MNRA

Extending emission line Doppler tomography ; mapping modulated line flux

Emission line Doppler tomography is a powerful tool that resolves the accretion flow in binaries on micro-arcsecond scales using time-resolved spectroscopy. I present an extension to Doppler tomography that relaxes one of its fundamental axioms and permits the mapping of time-dependent emission sources. Significant variability on the orbital period is a common characteristic of the emission sources that are observed in the accretion flows of cataclysmic variables and X-ray binaries. Modulation Doppler tomography maps sources varying harmonically as a function of the orbital period through the simultaneous reconstruction of three Doppler tomograms. One image describes the average flux distribution like in standard tomography, while the two additional images describe the variable component in terms of its sine and cosine amplitudes. I describe the implementation of such an extension in the form of the maximum entropy based fitting code MODMAP. Test reconstructions of synthetic data illustrate that the technique is robust and well constrained. Artifact free reconstructions of complex emission distributions can be achieved under a wide range of signal to noise levels. An application of the technique is illustrated by mapping the orbital modulations of the asymmetric accretion disc emission in the dwarf nova IP Pegasi.Comment: 8 pages, 4 figures; accepted for publication in MNRA

IP Pegasi in outburst: Echelle spectroscopy & Modulation Doppler Tomography

We analyse a unique set of time-resolved echelle spectra of the dwarf nova IP Peg, obtained at ESO's NTT with EMMI. The dataset covers the wavelength range of 4000-7500A and shows Balmer, HeI, HeII and heavier elements in emission. IP Peg was observed one day after the peak of an outburst. The trailed spectra, spectrograms and Doppler maps show characteristics typical of IP Pegasi during the early stages of its outburst. The high-ionisation line of HeII 4686A is the most centrally located line and has the greatest radial extension compared to the HeI lines. The Balmer lines extend from close to the white dwarf up to approximately 0.45 times R_L, with the outer radius gradually increasing when moving from H delta to H alpha. The application, for the first time, of the modulation Doppler tomography technique, maps any harmonically varying components present in the system configuration. We find, as expected, that part of the strong secondary star emission in Balmer and HeI lines is modulated predominantly with the cosine term, consistent with the emission originating from the irradiated front side of the mass-donor star, facing the accreting white dwarf. For the Balmer lines the level of the modulation, compared to the average emission, decreases when moving to higher series. Emission from the extended accretion disk appears to be only weakly modulated, with amplitudes of at most a few percent of the non-varying disk emission. We find no evidence of modulated emission in the spiral arms, which if present, is relatively weak at that our signal-to-noise ratio was good enough to put a lower detection limit of any modulated emission at 5--6%. Only in one arm of the HeII 4686A line, is there a possibility of modulated emission, but again, we cannot be sure this is not caused by blending with the nearby Bowen complex of lines.Comment: 20 pages, 8 figures, submitted to Journal of Astronomical Dat

Spiral shocks in the accretion disc of IP Peg during outburst maximum

In response to our recent discovery of spiral arms in the accretion disc of IP Peg during rise to outburst, we have obtained time-resolved spectrophotometry of IP Peg during outburst maximum. In particular, indirect imaging of HeII 4686, using Doppler tomography, shows a two-arm spiral pattern on the disc image, which confirms repeatability over different outbursts. The jump in HeII intensity (a factor of more than two) and in velocity (~200--300 km/s) clarifies the shock nature of the spiral structure. The HeII shocks show an azimuthal extent of ~90 degrees, a shallow power-law emissivity ~V^{-1}, an upper limit of 30 degrees in opening angle, and a flux contribution of 15 per cent of the total disc emission. We discuss the results in view of recent simulations of accretion discs which show that spiral shocks can be raised in the accretion disc by the secondary star.Comment: 5 pages, 4 figures, MNRAS journal paper. in pres