We report the discovery of rapid periodic signals in the light curves of two cataclysmic variables with prominent white dwarf components in their spectra, SDSS J1457+51 and BW Sculptoris. These stars ...therefore appear to be new members of the GW Librae class of variable stars, in which the fast periodic (and non-commensurate with the orbital period) signals are believed to arise from non-radial pulsations in the underlying white dwarf. The power spectra of both stars show complex signals with primary periods near 10 and 20 min, respectively. These signals change in frequency by a few per cent on a time-scale of weeks or less, and probably contain an internal fine structure unresolved by our observations. We also detect double-humped waves signifying the underlying orbital periods, near 78 min for both stars.
In addition, BW Sculptoris shows a transient but powerful signal with a period near 87 min, a quiescent superhump. The ∼11 per cent excess over the orbital period is difficult to understand, and may arise from an eccentric instability near the 2:1 resonance in the accretion disc.
We report the results of long observing campaigns on two novalike variables: V442 Ophiuchi and RX J1643.7+3402. These stars have high‐excitation spectra, complex line profiles signifying mass loss at ...particular orbital phases, and similar orbital periods (respectively, 0.12433 and 0.12056 days). They are well‐credentialed members of the SW Sex class of cataclysmic variables. Their light curves are also quite complex. V442 Oph shows periodic signals with periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar signals at 0.11696(8) and 4.05(12) days. We interpret these short and long periods, respectively, as a “negative superhump” and the wobble period of the accretion disk. The superhump could then possibly arise from the heating of the secondary (and structures fixed in the orbital frame) by inner‐disk radiation, which reaches the secondary relatively unimpeded since the disk is not coplanar. At higher frequencies, both stars show another type of variability: quasi‐periodic oscillations with a period near 1000 s. Underlying these strong signals of low stability may be weak signals of higher stability. Similar quasi‐periodic oscillations, and negative superhumps, are quite common features in SW Sex stars. Both can in principle be explained by ascribing strong magnetism to the white dwarf member of the binary; and we suggest that SW Sex stars are borderline AM Herculis binaries, usually drowned by a high accretion rate. This would provide an ancestor channel for AM Hers, whose origin is still mysterious.
The Spin-period History of Intermediate Polars Patterson, Joseph; de Miguel, Enrique; Kemp, Jonathan ...
Astrophysical journal/The Astrophysical journal,
07/2020, Letnik:
897, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report the detailed history of spin-period changes in five intermediate polars (DQ Herculis, AO Piscium, FO Aquarii, V1223 Sagittarii, and BG Canis Minoris) during the 30-60 yr since their ...original discovery. Most are slowly spinning up, although there are sometimes years-long episodes of spin-down. This is supportive of the idea that the underlying magnetic white dwarfs are near spin equilibrium. In addition to the ∼40 stars sharing many properties and defined by their strong, pulsed X-ray emission, there are a few rotating much faster (P < 80 s), whose membership in the class is still in doubt-and who are overdue for closer study.
T Pyxidis: death by a thousand novae Patterson, Joseph; Oksanen, Arto; Kemp, Jonathan ...
Monthly Notices of the Royal Astronomical Society,
04/2017, Letnik:
466, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We report a 20-yr campaign to track the 1.8 h photometric (and orbital) wave in the recurrent nova T Pyxidis. Before and after the 2011 eruption, the period increased on a time-scale P/
...$\dot{P}$
= 3 × 105 yr. This suggests a mass transfer rate in quiescence of ∼10–7 M⊙ yr−1, in substantial agreement with the accretion rate based on the star's luminosity. During the eruption itself, a rapid period increase of 0.0054(7) per cent occurred. This is probably a measure of the mass ejected in the outburst. For a plausible choice of binary parameters, that mass is at least 3 × 10–5 M⊙, and probably more. This represents >300 yr of accretion at the pre-outburst rate, but the time between outbursts was only 45 yr. Thus, the erupting white dwarf (WD) seems to have ejected at least six times more mass than it accreted. If this eruption is typical, the WD must be eroding, rather than growing, in mass. Unless the present series of eruptions is a short-lived episode, the binary dynamics will evaporate the secondary in ∼105 yr. This could be a major channel by which short-period cataclysmic variables are removed from the population.
Resynchronization of the Asynchronous Polar CD Ind Myers, Gordon; Patterson, Joseph; Miguel, Enrique de ...
Publications of the Astronomical Society of the Pacific,
04/2017, Letnik:
129, Številka:
974
Journal Article
Recenzirano
Odprti dostop
CD Ind is one of only four confirmed asynchronous polars (APs). APs are strongly magnetic cataclysmic variables of the AM Herculis subclass with the characteristic that their white dwarfs rotate a ...few percent out of synchronism with their binary orbit. Theory suggests that nova eruptions disrupt previously synchronized states. Following the eruption, the system is expected to rapidly resynchronize over a timescale of centuries. The other three asynchronous polars-V1432 Aql, BY Cam, and V1500 Cyg-have resynchronization time estimates ranging from 100 to more than 3500 years, with all but one being less than 1200 years. We report on the analysis of over 46,000 observations of CD Ind taken between 2007 and 2016, combined with previous observations from 1996, and estimate a CD Ind resynchronization time of 6400 800 years. We also estimate an orbital period of 110.820(1) minutes and a current (2016.4) white dwarf spin period of 109.6564(1) minutes.
The intermediate polar FO Aquarii (FO Aqr) experienced its first reported low-accretion states in 2016, 2017, and 2018, and, using newly available photographic plates, we identify prediscovery low ...states in 1965, 1966, and 1974. The primary focus of our analysis, however, is an extensive set of time-series photometry obtained between 2002 and 2018, with particularly intensive coverage of the 2016-2018 low states. After computing an updated spin ephemeris for the white dwarf (WD), we show that its spin period began to increase in 2014 after having spent 27 yr decreasing; no other intermediate polar has experienced a sign change of its period derivative, but FO Aqr has now done so twice. Our central finding is that the recent low states all occurred shortly after the WD began to spin down, even though no low states were reported in the preceding quarter-century, when it was spinning up. Additionally, the system's mode of accretion is extremely sensitive to the mass-transfer rate, with accretion being almost exclusively disk-fed when FO Aqr is brighter than V ∼ 14 and substantially stream-fed when it is not. Even in the low states, a grazing eclipse remains detectable, confirming the presence of a disklike structure (but not necessarily a Keplerian accretion disk). We relate these various observations to theoretical predictions that during the low state, the system's accretion disk dissipates into a non-Keplerian ring of diamagnetic blobs. Finally, a new XMM-Newton observation from a high state in 2017 reveals an anomalously soft X-ray spectrum and diminished X-ray luminosity compared to pre-2016 observations.
Resynchronization of the Asynchronous Polar CD Ind Myers, Gordon; Patterson, Joseph; de Miguel, Enrique ...
Publications of the Astronomical Society of the Pacific,
04/2017, Letnik:
129, Številka:
974
Journal Article
Recenzirano
CD Ind is one of only four confirmed asynchronous polars (APs). APs are strongly magnetic cataclysmic variables of the AM Herculis subclass with the characteristic that their white dwarfs rotate a ...few percent out of synchronism with their binary orbit. Theory suggests that nova eruptions disrupt previously synchronized states. Following the eruption, the system is expected to rapidly resynchronize over a timescale of centuries. The other three asynchronous polars—V1432 Aql, BY Cam, and V1500 Cyg—have resynchronization time estimates ranging from 100 to more than 3500 years, with all but one being less than 1200 years. We report on the analysis of over 46,000 observations of CD Ind taken between 2007 and 2016, combined with previous observations from 1996, and estimate a CD Ind resynchronization time of 6400 ± 800 years. We also estimate an orbital period of 110.820(1) minutes and a current (2016.4) white dwarf spin period of 109.6564 (1) minutes.
We observed the long-term behavior of the helium dwarf nova V803 Cen, and clarified the existence of at least two distinct states (a state with 77-d supercycles and a standstill-like state) that ...interchangeably appeared with a time-scale of 1–2 yr. We also conducted a time-resolved CCD photometry campaign during a bright outburst in 2003 June. The overall appearance of the outburst closely resembles that of the late stage of the 2001 outburst of WZ Sge, consisting of the initial peak stage (superoutburst plateau), the dip, and the oscillating (rebrightening) states. During the initial peak stage, we detected a large-amplitude superhump-type variation with a period of
$0.018686(4) \,\mathrm{d} = 1614.5(4) \,\mathrm{s}$
, and during the oscillation stage we detected variations with a period of
$0.018728(2) \,\mathrm{d} = 1618.1(2) \,\mathrm{s}$
. We consider that the former period better represents the superhump period of this system, and the latter periodicity may be better interpreted as arising from late superhumps. The overall picture of the V803 Cen outburst resembles that of a WZ Sge-type outburst, but apparently with a higher mass-transfer rate than that in hydrogen-rich WZ Sge-type stars. We suggest that this behavior may be either the result of difficulty in maintaining the hot state in a helium disk, or the effect of an extremely low tidal torque resulting from the extreme mass ratio.
We report on the results of our optical photometric observations of a black hole X-ray binary, V4641 Sgr during an outburst in 2003 August. During the outburst, we detected several properties having ...noteworthy similarities to those observed during an outburst in 2002 May; the outburst lasted about 6 days, during which it exhibited flares and rapid fluctuations, having timescales of
$10^{2\hbox{--}4} \,\mathrm{s}$
. In complicated profiles of light curves, we identified several recurring patterns, which were also observed during the 2002 outburst. First, the object frequently experienced sudden temporary fadings, which we call “dips”, appearing just after the states characterized by strong short-term fluctuations. Second, we detected optical flashes, which are characterized by a brightening by
$\sim 0.5 \,\mathrm{mag}$
within
$\sim 50 \,\mathrm{s}$
. Based on the similarity of the outbursts in 2002 and 2003, we conclude that they have the same nature. This is the first time that repetitive outburst phenomena have been confirmed in V4641 Sgr. The object probably has an outburst interval that can be as small as 1–2 years.
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