arXiv subjects

Patrick A. Woudt

Publications and source records attributed to Patrick A. Woudt.

At least 37 records · Page 2Linked to original sources

arXiv2012

SDSS J0349-0059 is a GW Virginis star

High speed photometric observations of the spectroscopically-discovered PG 1159 star SDSS J034917.41-005917.9 in 2007 and 2009 reveal a suite of pulsation frequencies in the range of 1038 - 3323 microHz with amplitudes between 3.5 and 18.6 mmag. SDSS J034917.41-005917.9 is therefore a member of the GW Vir class of pulsating pre-white dwarfs. We have identified 10 independent pulsation frequencies that can be fitted by an asymptotic model with a constant period spacing of 23.61 +/- 0.21 s, presumably associated with a sequence of l = 1 modes. The highest amplitude peak in the suite of frequencies shows evidence for a triplet structure, with a frequency separation of 14.4 microHz. Five of the identified frequencies do not fit the l = 1 sequence, but are, however, well-modeled by an independent asymptotic sequence with a constant period spacing of 11.66 +/- 0.13 s. It is unclear to which l mode these frequencies belong.

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arXiv2012

High speed photometry of faint Cataclysmic Variables - VII. Targets selected from the Sloan Digital Sky Survey and the Catalina Real-time Transient Survey

We present high speed photometric observations of 20 faint cataclysmic variables, selected from the Sloan Digital Sky Survey and Catalina catalogues. Measurements are given of 15 new directly measured orbital periods, including four eclipsing dwarf novae (SDSS0904+03, CSS0826-00, CSS1404-10 and CSS1626-12), two new polars (CSS0810+00 and CSS1503-22) and two dwarf novae with superhumps in quiescence (CSS0322+02 and CSS0826-00). Whilst most of the dwarf novae presented here have periods below 2 h, SDSS0805+07 and SSS0617-36 have relatively long orbital periods of 5.489 and 3.440 h, respectively. The double humped orbital modulations observed in SSS0221-26, CSS0345-01, CSS1300+11 and CSS1443-17 are typical of low mass transfer rate dwarf novae. The white dwarf primary of SDSS0919+08 is confirmed to have non-radial oscillations and quasi-periodic oscillations were observed in the short-period dwarf nova CSS1028-08 during outburst. We further report the detection of a new nova-like variable (SDSS1519+06). The frequency distribution of orbital periods of CVs in the Catalina survey has a high peak near ~80 min orbital period, independently confirming that found by Gaensicke et al (2009) from SDSS sources. We also observe a marked correlation between the median in the orbital period distribution and the outburst class, in the sense that dwarf novae with a single observed outburst (over the 5-year baseline of the CRTS coverage) occur predominantly at shortest orbital period.

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arXiv2011

Deep NIR Photometry of HI Galaxies Behind the Milky Way

Current studies of the peculiar velocity flow field in the Local Universe are limited by the lack of detection of galaxies behind the Milky Way. The contribution of the largely unknown mass distribution in this "Zone of Avoidance" (ZoA) to the dynamics of the Local group remains contraversial. We have undertaken a near infrared (NIR) survey of HI detected galaxies in the ZoA. The photomety derived here will be used in the NIR Tully-Fisher (TF) relation to derive the peculiar velocities of this sample of galaxies in the ZoA.

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arXiv2009

High speed photometry of faint cataclysmic variables - VI. Car2, V1040 Cen, Ha 075648, IL Nor (Nova Nor 1893), HS Pup (Nova Pup 1963), SDSS J2048-06, CSS 081419-005022 and CSS 112634-100210

We have observed 8 faint cataclysmic variable stars photometrically. The nova-like Car2 was extensively sampled but showed little variability. V1040 Cen was observed near the end of a dwarf nova outburst and possessed dwarf nova and quasi-periodic oscillations. Ha 075648 has strong large amplitude flickering and a possible orbital modulation at 3.49 h. The correct identification for the nova remnant IL Nor (Nova Nor 1893) has been established. HS Pup (Nova Pup 1963) has a possible orbital period of 3.244 h. SDSS J2048-06 is a low mass transfer dwarf nova that in quiescence shows slow variations at 7.67 h (though poorly sampled with our observations) and an orbital modulation at 87.26 min. The dwarf nova CSS 081419-005022 has an orbital period of 1.796 h and the eclipsing dwarf nova CSS 112634-100210 has an orbital period of 1.8581 h.

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arXiv2009

The Effect of Dust Extinction on the Observed Properties of Galaxies in the Near-Infrared

Galaxies behind the Milky Way suffer size reduction and dimming due to their obscuration by dust in the disk of our Galaxy. The degree of obscuration is wavelength dependent. It decreases towards longer wavelengths. Compared to the optical, the Near InfraRed (NIR) $K_s$ band extinction is only $\approx10%$ that of the $B$ band. This makes NIR surveys well suited for galaxy surveys close to the Galactic Plane where extinction is severe. While Galactic obscuration is less prominent in the NIR it is not negligible. In this paper we derive empirical relations to correct isophotal radii and magnitudes of galaxies observed in the NIR for foreground absorption. We simulate extinction in the $J$, $H$ and $K_s$ bands on 64 (unobscured) galaxies from the 2MASS Large Galaxy Atlas \citep{jarrett}. We propose two methods for the extinction correction, the first is optimized to provide the most accurate correction and the second provides a convenient statistical correction that works adequately in lower extinction regions. The optimized correction utilizes the galaxy surface brightness, either the disk central surface brightness, $μ_0$, or the combined disk plus bulge central surface brightness, elliptical and disk/spiral Hubble types. A detailed comparison between the different methods and their accuracy is provided.

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arXiv2009

Properties of the extremely HI-massive galaxy HIZOA J0836-43

Little is known about the properties of extremely massive HI-galaxies. They are extremely scarce and are - according to hierarchical structure formation - only forming now (z < 1). The forthcoming deep HI SKA Pathfinders surveys will uncover many more of them. This will lead to a better understanding of their evolution and frequency, and the shape of the bright end of the HI mass function. The recently discovered galaxy HIZOA J0836-43 is one of the most HI-rich galaxies (M(HI)=7.5 x 10^10Msun - and the nearest of its kind. As such it is an ideal local probe of these elusive galaxies. Results from a detailed investigation in the near- (IRSF) and far-infrared (Spitzer) of this local HI-massive galaxy are presented. Unlike other giant HI galaxies, it is not of low surface brightness. The galaxy is found to be a luminous starbursting galaxy at an unexpected early stage of stellar mass building, more typical of star-forming galaxies at higher redshift (z~0.7). With regard to its environment, hence possible clues to its formation, the near infrared imaging survey finds HIZOAJ0836-43 to lie in a region underdense in L* galaxies - consistent with the observation that HI-massive galaxies are preferentially found in low density regions - in the presence, however, of an uncommonly large number of low stellar mass galaxies.

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arXiv2009

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables - VII. OY Carinae and oscillations in dwarf novae in quiescence

We have observed dwarf nova oscillations (DNOs) in OY Car during outburst, down through decline and beyond; its behaviour is similar to what we have previously seen in VW Hyi, making it only the second dwarf nova to have DNOs late in outburst that continue well into quiescence. There are also occasional examples of DNOs in deep quiescence, well away from outburst - they have properties similar to those during outburst, indicating similar physical causes and structures. We discuss the occurrence of DNOs in other dwarf novae and conclude that DNOs during quiescence are more common than often supposed and exhibit properties similar to those seen in outburst.

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arXiv2009

The eclipsing Intermediate Polar V597 Pup (Nova Puppis 2007)

Photometric observations of V597 Pup made in 2008, 9.1 mag below maximum, 4 months after eruption, showed no certain orbital modulation but exhibited a quintuplet of oscillations centred on a period 261.9 s and uniform splitting at a frequency ~2.68 h^{-1}. One year later the system had fallen in brightness by a further 2.5 mag, showed deep eclipses with a period of 2.6687 h, and the 261.9 s modulation at a reduced amplitude. There is often power near the `subharmonic' at 524 s, showing that the shorter periods observed are actually first harmonics. V597 Pup is thus an intermediate polar and is in the `orbital period gap'. Furthermore it is the first to show a prominent secondary eclipse, caused by passage of the optically thick disc in front of the irradiated side of the secondary star.

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arXiv2008

QPOs in CVs: An executive summary

An overview is given of the properties of the various kinds of quasi-periodic luminosity modulations observed in cataclysmic variables (CVs). The two principal types, known in the CV literature as dwarf nova oscillations and quasi-periodic oscillations, have similarities to the high and low frequency quasi-periodic oscillations in X-Ray binaries. There is a further well observed class known as longer period dwarf nova oscillations. In CVs the observed interrelations between these oscillations suggests a model of magnetically controlled accretion onto a rapidly rotating equatorial belt of accreted gas. Non-radial oscillations of the central white dwarf are observed in some systems.

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arXiv2006

HST and Optical Observations of Three Pulsating Accreting White Dwarfs in Cataclysmic Variables

Ultraviolet observations using the Solar Blind Channel on the Hubble Space Telescope provide light curves and low resolution spectra of three pulsating white dwarfs in the cataclysmic variables SDSS013132.39-090122.3, SDSSJ161033.64-010223.3 and SDSSJ220553.98+115553.7. The UV light curves show enhanced pulsation amplitudes over those from simultaneous and previous optical photometry, while the UV-optical spectra are fit with white dwarf temperatures near 15,000K. These temperatures place the accreting white dwarfs outside the instability zone for non-interacting DAV white dwarfs and show that the instability strip is complex for accreting white dwarfs.

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arXiv2006

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables -- V. Results from an extensive survey

We present observations of dwarf nova oscillations (DNOs), longer period dwarf nova oscillations (lpDNOs), and quasi-periodic oscillations (QPOs) in 13 cataclysmic variable stars (CVs). In the six systems WW Cet, BP CrA, BR Lup, HP Nor, AG Hya, and V1193 Ori, rapid, quasi-coherent oscillations are detected for the first time. For the remainder of the systems discussed we have observed more classes of oscillations, in addition to the rapid oscillations they were already known to display, or previously unknown aspects of the behaviour of oscillations. The period of a QPO in RU Peg is seen to change by 84% over ten nights of the decline from outburst--the largest evolution of a QPO period observed to date. A period-luminosity relation similar to the relation that has long been known to apply to DNOs is found for lpDNOs in X Leo; this is the first clear case of lpDNO frequency scaling with accretion luminosity. WX Hyi and V893 Sco are added to the small list of dwarf novae that have shown oscillations in quiescence.

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arXiv2006

Dwarf Nova Oscillations and Quasi-Periodic Oscillations in Cataclysmic Variables, IV. Observations of Frequency Doubling and Tripling in VW Hyi

We present new observations of the rapid oscillations in the dwarf nova VW Hyi, made late in outburst. These dwarf nova oscillations (DNOs) increase in period until they reach 33 s, when a transition to a strong 1st harmonic and weak fundamental takes place. After further period increase the 2nd harmonic appears; often all three components are present simultaneously. This 1:2:3 frequency suite is similar to what has been seen in some neutron star and black hole X-Ray binaries, but has not previously been seen in a cataclysmic variable. When studied in detail the fundamental and 2nd harmonic vary similarly in phase, but the 1st harmonic behaves independently, though keeping close to twice the frequency of the fundamental. The fundamental period of the DNOs, as directly observed or inferred from the harmonics, increases to ~100 s before the oscillation disappears as the star reaches quiescence. Its maximum period is close to that of the `longer period' DNOs observed in VW Hyi. The quasi-periodic oscillations (QPOs), which have fundamental periods 400 -- 1000 s, behave in the same way, showing 1st and 2nd harmonics at approximately the same times as the DNOs. We explore some possible models. One in which the existence of the 1st harmonic is due to transition from viewing a single accretion region to viewing two regions, and the rate of accretion onto the primary is modulated at the frequency of the 1st harmonic, as in the `beat frequency model', can generate the suite of DNO frequencies observed. But the behaviour of the QPOs is not yet understood.

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arXiv2004

Spectroscopy and near-infrared photometry of the helium nova V445 Puppis

Nova Puppis 2000 (V445 Pup) has been proposed as the first example of a helium nova. Recent optical spectroscopy of V445 Pup at V=19.91 mag obtained with IMACS on the 6.5-m Magellan telescope, shows that the spectrum consists of HeI, [OI], [OII] and [OIII] emission lines and no hydrogen is present. The spectroscopy shows an expanding nova shell with blue- and redshifted velocity components around +/- 850 km/s and +/- 1600 km/s. Images taken with Magellan under very good seeing conditions (FWHM ~ 0.6") shows V445 Pup to be extended (full width at zero intensity ~ 1.9") and elongated (position angle ~ 150deg). We have followed the secular evolution of V445 Pup since the decline from (optical) maximum, at near-infrared wavelengths (J, H and Ks) using the Infrared Survey Facility (IRSF) at the Sutherland site of the South African Astronomical Observatory. We find that V445 Pup is still covered by a dense dust shell more than three years after its outburst.

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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

DENIS detections of highly obscured galaxies in the area around PKS1343-601

We present results of a search for galaxies around the highly obscured giant radio galaxy PKS1343-601 using the near-infrared DENIS survey. We compare our findings with surveys in the B-band, at the 21cm line emission, and with 2MASS. Recession velocities of galaxies in this area suggest a low-velocity-dispersion group or cluster of galaxies including an X-ray confirmed Seyfert 2. The colours of the galaxies have been used to examine the extinctions in this low-latitude area where IRAS/DIRBE estimates are unreliable. We find the true extinction to be roughly 15% lower than the IRAS/DIRBE extinctions.

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arXiv2004

A 2 x 2 Degree I-band Survey around PKS 1343-601

Motivated by the possibility that the highly obscured (A_B = 12 mag) radio galaxy PKS 1343-601 at (l,b,cz) = (309.7, +1.8, 3872km/s) might constitute the center of a heavily obscured cluster in the Great Attractor region, we have imaged about 2 x 2 degree of the core of this prospective cluster in the I-band using the WFI at the ESO 2.2m telescope at La Silla. We were able to identify 49 galaxies and 6 uncertain galaxy candidates. Although their distribution does not resemble a centrally condensed, massive cluster, its appearance -- severely influenced by the strong dust gradient across our surveyed region -- is entirely consistent with a cluster.

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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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