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Brian Warner

Publications and source records attributed to Brian Warner.

At least 37 records · Page 2Linked to original sources
arXiv2004

The Helium-Rich Cataclysmic Variable ES Ceti

We report photometry of the helium-rich cataclysmic variable ES Ceti during 2001-2004. The star is roughly stable at V ~ 17.0 and has a light curve dominated by a single period of 620 s, which remains measurably constant over the 3 year baseline. The weight of evidence suggests that this is the true orbital period of the underlying binary, not a "superhump" as initially assumed. We report GALEX ultraviolet magnitudes, which establish a very blue flux distribution (F_nu ~ nu^1.3), and therefore a large bolometric correction. Other evidence (the very strong He II 4686 emission, and a ROSAT detection in soft X-rays) also indicates a strong EUV source, and comparison to helium-atmosphere models suggests a temperature of 130+-10 kK. For a distance of 350 pc, we estimate a luminosity of (0.8-1.7)x10^34 erg/s, yielding a mass accretion rate of (2-4)x10^-9 M_sol/yr onto an assumed 0.7 M_sol white dwarf. This appears to be about as expected for white dwarfs orbiting each other in a 10 minute binary, assuming that mass transfer is powered by gravitational radiation losses. We estimate mean accretion rates for other helium-rich cataclysmic variables, and find that they also follow the expected M-dot ~ P_o^-5 relation. There is some evidence (the lack of superhumps, and the small apparent size of the luminous region) that the mass transfer stream in ES Cet directly strikes the white dwarf, rather than circularizing to form an accretion disk.

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arXiv2004

DNOs and QPOs in Cataclysmic Variables

We describe some of the recent observations of Dwarf Nova Oscillations and Quasi-Periodic Oscillations in cataclysmic variable stars. The similarities to high frequency QPOs seen in X-Ray binaries make this an increasingly useful field to explore. Our principal new result is the discovery of 1:2:3 harmonic structure in the DNOs of VW Hyi late in outburst. Similar structure is seen in the QPOs of some black hole and neutron star X-Ray binaries. In VW Hyi there is a sudden frequency-doubling when the DNO period reaches ~39 s. This first harmonic increases in period to ~28 s at which point the second harmonic appears. Both harmonics continue with increasing period, together or separately, with an occasional appearance of the fundamental, until the latter reaches ~105 s, by which time VW Hyi has fallen to its quiescent magnitude. We also report the first extensive observations of DNOs in a dwarf nova (OY Car) in quiescence. These are lpDNOs (longer period DNOs) and show similar short time scale properties to the DNOs and lpDNOs seen in outburst.

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arXiv2004

Rapid Oscillations in Cataclysmic Variables, and a Comparison with X-Ray Binaries

We compare some of the properties of rapid oscillations in cataclysmic variables and X-Ray binaries. In addition to the earlier recognition that both types possess the same correlation between high and low frequency quasi-periodic oscillations, we have now found that the dwarf nova VW Hyi in its late stages of outburst shows the 1:2:3 oscillations harmonics that are seen in some neutron star and black hole X-Ray binaries. We point out that the behaviour of the dwarf nova WZ Sge has some similarities to those of accreting millisecond pulsars.

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arXiv2004

Cataclysmic Variables from SDSS III. The Third Year

This paper continues the series that identifies new cataclysmic variables found in the Sloan Digital Sky Survey. We present 36 cataclysmic variables and one possible symbiotic star from Sloan spectra obtained during 2002, of which 34 are new discoveries, 2 are known dwarf novae (BC UMa, KS UMa) and one is a known CV identified from the 2dF survey. The positions, colors and spectra of all 37 systems are presented, along with follow-up spectroscopic/photometric observations of 10 systems. As in the past 2 years of data, the new SDSS systems show a large variety of characteristics based on their inclination and magnetic fields, including 3 eclipsing systems, 4 with prominent He II emission, and 15 systems showing features of the underlying stars.

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arXiv2004

High speed photometry of faint Cataclysmic Variables: IV. V356 Aql, Aqr1, FIRST J1023+0038, Ha 0242-2802, GI Mon, AO Oct, V972 Oph, SDSS 0155+00, SDSS 0233+00, SDSS 1240-01, SDSS 1556-00, SDSS 2050-05, FH Ser

We present results from high speed photometry of a further thirteen faint cataclysmic variables. V356 Aql (Nova Aql 1936) shows flare-like outbursts with recurrence time scales ~ 3000 s, but no coherent periodicities. Aqr1 is an intermediate polar with a spin period of 6.7284 min and a probable orbital period P(orb) = 3.226 h derived from orbital sidebands. Its orbital sideband frequencies show very variable amplitudes. The published spectroscopic period of 2.0 h suggests that Aqr1 is similar to GW Lib and FS Aur in having an additional periodicity of unknown origin. FIRST J1023+0038 has P(orb) = 4.7548 h with an orbital modulation of range 0.45 mag, probably caused by reflection effect from a hot white dwarf primary; as such it may have been a nova sometime in the past few decades. Ha 0242 is a deeply eclipsing very low mass-transfer rate system, probably a dwarf nova of very long outburst interval, with P(orb) = 1.792 h. GI Mon, an old nova, has optical modulations at 4.325 h and possibly also at 48.6 min and is thus a candidate intermediate polar. AO Oct, an SU UMa type dwarf nova, shows orbital modulation at quiescence with P(orb) = 94.097 min. V972 Oph (Nova Ophiuchi 1957) showed no flickering activity during one set of observations, but did so at a later time, confirming the correctness of the identification of this object, but it shows no orbital modulation. SDSS 0155 is a deeply eclipsing polar with an orbital period of 87.13 min. SDSS 0233 shows flaring activity but no discernible periodicity. No periodicity was found in the new AM CVn candidate SDSS 1240. SDSS 1556 shows a periodic modulation at 1.778 h which is possibly due to orbital motion. SDSS 2050 is an eclipsing polar with P(orb) = 1.5702 h. FH Ser (Nova Serpentis 1970) has strong flickering activity but no detectable orbital modulation.

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arXiv2003

Rapid Oscillations in Cataclysmic Variables

I give an overview of the rich phenomenology of dwarf nova oscillations (DNOs) and Quasi-periodic Oscillations (QPOs) observed in cataclysmic variable stars (CVs). The favoured interpretation of these rapid brightness modulations (3 - >1000 s time scales) is that they are magnetic in nature - magnetically channelled accretion from the inner accretion disc for DNOs and possible magnetically excited travelling waves in the disc for QPOs. There is increasing evidence for the magnetic aspects, which extend to lower field the well known properties of strong field (polars) and intermediate strength field (intermediate polars) CVs. The result is that almost all CVs show the presence of magnetic fields on their white dwarf primaries - though for many the intrinsic field may be locally enhanced by the accretion process itself. There are many parallel behaviours with the QPOs seen in X-Ray binaries, with high and low frequency X-Ray QPOs resembling respectively the DNOs and QPOs in CVs.

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arXiv2003

SDSS J161033.64-010223.3: A second Cataclysmic Variable with a Non-radially Pulsating Primary

We find from high speed photometry of the Sloan Digital Survey cataclysmic variable candidate SDSS J161033.64-010223.3 that it has a double humped modulation, which is probably orbital, with a period of 80.52 minutes, and shows strong ZZ Cet type pulsations. The largest amplitude oscillations have periods near 607, 345, 304 and 221 s. The amplitudes of some of the oscillations are seen to vary on time scales of hours, indicating modes with unresolved multiplets in which the splittings are ~1 d^-1. This is only the second dwarf nova found to have non-radial pulsations of its white dwarf primary.

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arXiv2003

AM CVn stars in the UCT CCD CV survey

High speed photometry of the helium-transferring binary ES Cet - taken over a two-year period (2001 October - 2003 October) - shows a very stable photometric period of 620.211437 +/- 0.000038 s, with a tentative indication of curvature in the O-C diagram suggesting a change in period at a rate of dP/dt ~ 1.6x10^-11. Phase-resolved spectroscopy of ES Cet obtained with the Hobby-Eberly Telescope shows a clear modulation on the photometric period. We have followed a newly identified AM CVn star (`2003aw') photometrically through its 2003 February/March outburst during which it varied in brightness over a range of V = 16.5 - 20.3; we find a superhump period of 2041.5 +/- 0.3 s. Questions are raised about the reality of the detected spin-up in RX J0806 (Hakala et al. 2003; Strohmayer 2003).

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arXiv2003

Intermediate polars in low states

Although no intermediate polar (IP) has been observed in recent years to descend into a state of low rate of mass transfer, there are candidate stars that appear to be already in intermediate and low states. V709 Cas is probably an intermediate state IP; NSV 2872 appears to be a low state IP, and will probably resemble the long orbital period IP V1072 Tau if it returns to a high state. The enigmatic V407 Vul, which has had many interpretations as an ultra-short period binary, has many resemblances to the pre-cataclysmic variable V471 Tau, and may therefore be an IP precursor of quite long orbital period, and not yet a fully fledged cataclysmic variable.

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arXiv2003

Accretion in Cataclysmic Variable stars

We consider accretion onto the white dwarfs in cataclysmic variables in relation to nova eruptions, dwarf nova outbursts, hibernation and non-radial oscillations.

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arXiv2003

X-rays from Cataclysmic Variables

Cataclysmic Variables are a distinct class of interacting binaries, transferring mass from a donor star to a degenerate accretor, a white dwarf. We here review X-ray observations of these systems, with some emphasis on what has been achieved in the last decade.

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arXiv2003

The new AM CVn star in Hydra

High speed photometry of the new AM CVn star in Hya (previously known as SN2003aw), spectroscopically identified by Chornock & Filippenko, shows it to have a superhump period of 2041.5 +/- 0.3 s. We find a range of brightness from V ~ 16.5 to 20.3, presumably caused by variations in the rate of mass transfer. In the intermediate state the system cycles in brightness with a period of ~ 16 h and range >= 0.4 mag. There are sidebands to the principal frequencies in the Fourier transform which have constant frequency difference from the superhump harmonics.

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arXiv2003

Dwarf Nova Oscillations and Quasi-Periodic Oscillations in Cataclysmic Variables: III. A New Kind of Dwarf Nova Oscillation, and Further Examples of the Similarities to X-Ray Binaries

We present measurements of the periods of Dwarf Nova Oscillations (DNOs) and Quasi-Periodic Oscillations (QPOs) in Cataclysmic Variable stars (CVs), many culled from published literature, but also others newly observed (in VZ Pyx, CR Boo, OY Car, Z Cha, AQ Eri, TU Men, HX Peg, CN Ori, V893 Sco, WX Hyi and EC2117-54). These provide data for 26 systems. We show that in general P_QPO ~ 15 P_DNO and that the correlation for CVs extends by three orders of magnitude lower in frequency the similar relationship found for X-Ray binaries. In addition, we have found that there is a second type of DNO, previously overlooked, which have periods ~ 4 times those of the regular DNOs (As well as those mined from publications, we have observed them in VW Hyi, OY Car, AQ Eri, V803 Cen, CR Boo, VZ Pyx, HX Peg and EC2117-54). Often both types of DNO coexist. Unlike the standard DNOs, the periods of the new type, which we refer to as longer period DNOs (lpDNOs), are relatively insensitive to accretion luminosity and can even appear in quiescence of dwarf novae. We interpret them as magnetically channelled accretion onto the differentially rotating main body of the white dwarf primary, rather than onto a rapidly slipping equatorial belt as in the case of the standard DNOs. This is supported by published measurements of v sin(i) for some of the primaries. Some similarities of the DNOs, lpDNOs and QPOs in CVs to the three types of QPO in X-Ray binaries (burst pulsation, high and low frequency QPOs) are noted.

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arXiv2003

High-speed photometry of the Recurrent Nova IM Normae

The recurrent nova IM Nor is found to have an orbital period of 2.462 h, shown by periodic dips in brightness. This is only the second recurrent nova known to have such a short period. We interpret the light curve as largely produced by a reflection effect from the heated face of the secondary star, probably with addition of a partial eclipse of the accretion disc.

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arXiv2003

Magnetic CVs in the UCT CCD CV Survey

An overview is given of all the magnetic CVs found in the UCT CCD CV Survey (Woudt & Warner 2001, 2002, 2003a). We have identified eight new candidate Intermediate Polars (IP), of which six are classical novae (RR Cha, DD Cir, AP Cru, V697 Sco, V373 Sct, and RX J1039.7-0507). The two other candidate IPs are Aqr1 (2236+0052) and RX J0944.5+0357. In addition, there are two probable Polars, namely V351 Pup (= Nova Puppis 1991) and FIRST J102347.6+003841.

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arXiv2003

RX J0944.5+0357: A Probable Intermediate Polar

From optical photometry the cataclysmic variable RX J0944.5+0357 is shown to have a double-peaked pulse profile with a period of ~2160 s. The two peaks vary rapidly in relative amplitude. Often most of the optical power is concentrated in the first harmonic of the 2160s modulation: RX J0944.5+0357 therefore probably belongs to the relatively rare class of two-pole accreting intermediate polars exemplified by YY Dra and V405 Aur.

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arXiv2003

High speed photometry of faint Cataclysmic Variables: III. V842 Cen, BY Cir, DD Cir, TV Crv, V655 CrA, CP Cru, V794 Oph, V992 Sco, EU Sct and V373 Sct

We present further results from a high speed photometric survey of faint cataclysmic variables. We find that V842 Cen (Nova Cen 1986 No. 2) is highly active, but with no evident orbital modulation. BY Cir (Nova Cir 1995) is an eclipsing system with an orbital period P(orb) of 6.76 h. TV Crv, an SU UMa type dwarf nova, is found to have P(orb) = 1.509 h from photometry at quiescence. DD Cir (Nova Cir 1999) is an eclipsing system with P(orb) = 2.339 h, a possible secondary eclipse, and a ~670 s photometric modulation. V655 CrA is highly active but shows no orbital modulation. The identification of V794 Oph is probably incorrect as we find no photometric variability. CP Cru (Nova Cru 1996) is an eclipsing system with P(orb) = 22.7 h. V992 Sco has P(orb) = 3.686 h from its periodic modulation. The supposed identification of EU Sct is probably incorrect. And finally, during one run V373 Sct (Nova Sct 1975) had a 258.3 s coherent periodicity, making it a candidate DQ Herculis star.

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