Curious Variables Experiment (CURVE). IX Draconis - a Clue for Understanding Evolution of Cataclysmic Variable Stars (original) (raw)
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Acta Astronomica, 2004
We report extensive photometry of frequently outbursting dwarf nova IX Draconis. During five months of observations the star went into three superoutbursts and seven ordinary outbursts. This allowed us to determine its supercycle and cycle lengths as equal to 54 +/- 1 and 3.1 +/- 0.1 days, respectively. During the Sep 2003 superoutburst, which had the best observational coverage, IX Dra displayed clear superhumps with a period of Psh=0.066968(17) days. This period was constant during the whole superoutburst. Another period, which was clearly present in the light curve of IX Dra in superoutburst, had a value of 0.06646(6) days and we interpret it as the orbital period of the binary. Thus IX Dra is the first SU UMa star showing orbital modulation during the entire superoutburst. The beat between these two periods is the main cause of an unusual phase reversal of superhumps - a phenomenon which was previously observed in ER UMa. If our interpretation of the second periodicity is correct, IX Dra has an extremely low period excess epsilon\epsilonepsilon equal to only 0.76% +/- 0.03%. This implies very low mass ratio q=0.035 +/- 0.003, which strongly suggests that the system contains a brown dwarf-like degenerate secondary of mass ~0.03 Mo and that IX Dra is the most evolved dwarf nova known. Such a very low mass ratio results in the outer edge of the accretion disk reaching 80% of the distance between the components of the system. In turn, this allows the disk particles to enter a 2:1 resonance and leads to the appearance of the orbital period in the light curve of the entire superoutburst.The high level of activity and brightness of IX Dra indicate that very old cataclysmic variables go through episodes of increased activity leading to loss of angular momentum through mass loss from the system.
Superhumps in Cataclysmic Binaries. XIX. DV Ursae Majoris
Publications of the Astronomical Society of the Pacific, 2000
DV Ursae Majoris is a deeply eclipsing dwarf nova which shows very powerful superhumps when it attains superoutburst. We report detailed observations of the 1997 and 1999 eruptions. Some of the results reproduce what has been learned from other eclipsing dwarf novae: that the disk becomes very large in outburst; that superhumps develop in a few days; that superhumps remain strong even after the disk has shrunk by >30%. The mean superhump period was 0.08870(8) d, but in both eruptions the period decreased with P ! ≈-6×10-5. Globally distributed coverage of the 1997 eruption revealed two other interesting features: a transient strong modulation at the orbital period at the peak of eruption, and intricate fine structure in the harmonics of the main superhump signal. In particular, we found that the second harmonic occurred not at 3ω-3Ω as expected (where ω and Ω are respectively the orbital and "precession" frequencies), but at 3ω-2Ω and 3ω-Ω. The strong orbital modulation may have arisen from enhanced mass transfer from the secondary. We also report photometry at quiescence, which separates the luminous contributions of the white dwarf, accretion disk, and secondary star. We estimate a distance of 350±120 pc. Analysis of the eclipses suggests i=84.0±0.8°, q=0.155±0.015, M 2 =0.14±0.
Orbital, superhump and superorbital periods in the cataclysmic variables AQ Mensae and IM Eridani
Monthly Notices of the Royal Astronomical Society, 2013
We report photometric detections of orbital and superorbital signals, and negative orbital sidebands, in the light curves of the nova-like cataclysmic variables AQ Mensae and IM Eridani. The frequencies of the orbital, superorbital, and sideband signals are 7.0686 (3), 0.263 (3), and 7.332 (3) cycles per day (c d -1 ) in AQ Mensae, and 6.870 (1), 0.354 (7), and 7.226 (1) c d -1 in IM Eridani. We also find a spectroscopic orbital frequency in IM Eridani of 6.86649 (2) c d -1 . These observations can be reproduced by invoking an accretion disc that is tilted with respect to the orbital plane. This model works well for X-ray binaries, in which irradiation by a primary neutron star can account for the disc's tilt. A likely tilt mechanism has yet to be identified in CVs, yet the growing collection of observational evidence indicates that the phenomenon of tilt is indeed at work in this class of object. The results presented in this paper bring the number of CVs known to display signals associated with retrograde disc precession to twelve.
Superhumps in Cataclysmic Binaries. XII. CR Bootis, a Helium Dwarf Nova
Publications of the Astronomical Society of the Pacific, 1997
CR Bootis is an enigmatic blue variable star with rapid photometric variations and a spectrum dominated by helium. It consists of two white dwarfs in close orbit, with a probable underlying binary period of 1471 s. For years we have marveled at the star's large nightly variations-ramping up or down at a rate of-0.1 mag/hr. An intensive photometry campaign in 1996 showed that this variability is cyclic with a quasiperiod of about 19 hr, and demonstrated the association of 1490-s photometric variations ("superhumps") with extended bright states ("superoutbursts"). During the superoutburst, the 1490-s signal initially decreased with P =-2X10~5, but then stabilized at 1487.29±0.02 s after-300-600 binary orbits. Spectroscopy reveals variably asymmetric absorption lines, with the asymmetry migrating on a probable period of 36 hr; this may be the period of accretion disk precession. Neither the helium composition, nor the degeneracy of the mass-losing component, nor the shortness of the period (all of the periods) seem to present any barrier to the star in being fully certifiable as a bona fide dwarf nova. Stabilization of the superhump period at such a low value (1487.29 s) favors a model in which period changes arise from eccentricity changes rather than mean radius changes in the disk. This naturally explains why decreasing period and decreasing amplitude are strongly linked in the superhumps of dwarf novae.
Superhumps in Cataclysmic Binaries. VIII. V1159 Orionis
Publications of the Astronomical Society of the Pacific, 1995
We report photometry of the cataclysmic variable VI159 Orionis for-400 hours over 168 nights during 1992-4. The long-term light curves show that this is a dwarf nova of the SU UMa class, with normal outbursts recurring on a mean period of 4.0 days, and superoutbursts recurring on a period of 47.6 days. These periods wander slightly, as is typical of the class. High-speed photometry at minimum light, far from superoutbursts, reveals a weak photometric signal at 89.83 ±0.10 min, which is presumably the underlying orbital period of the binary. During superoutburst, large-amplitude superhumps are observed with P=92.4 min. The superhumps appear very suddenly on the rising branch. In a few days they fade to a full amplitude of-0.1 mag and become more complex in wave form. However, they can be traced throughout the decline phase to quiescence, and even apparently succeed in enduring to the next normal eruption. In fact, we note the occasional existence of superhumps at essentially all phases of the eruption cycle-not merely in supermaxima, where they are very common and downright famous. The "positive" (.P>P orb) superhumps resemble in detail the common superhumps seen in the best-known SU UMa stars, and can be reasonably interpreted as arising from an eccentric accretion disk with an advancing line of apsides. But additional subtle details are detected in VI159 Ori. In one superoutburst the frequencies of the high harmonics are slightly higher than expected, and in another they are far lower than expected. And on two occasions there appeared "negative" superhumps (P<P orb) with a period of 82.7±0.2 min. We discuss these features in terms of the disk-precession model, but without any convincing resolution. Two other periodic signals, of unknown origin, were detected: rapid oscillations ("DNOs") with a period increasing from 29 to 34 s over 7 days in mid-decline from a superoutburst; and a probable signal near 8 c/day, appearing mainly in quiescence.
2011
), the long-period system GX Cas showed an exceptionally large positive period derivative. An analysis of public Kepler data of V344 Lyr and V1504 Cyg yielded less striking stage transitions. In V344 Lyr, there was prominent secondary component growing during the late stage of superoutbursts, and the component persisted at least for two more cycles of successive normal outbursts. We also investigated the superoutbursts of two conspicuous eclipsing objects: HT Cas and the WZ Sge-type object SDSS J080434.20+510349.2. Strong beat phenomena were detected in both objects, and late-stage superhumps in the latter object had an almost constant luminosity during the repeated rebrightenings. The WZ Sge-type object SDSS J133941.11+484727.5 showed a phase reversal around the rapid fading from the superoutburst. The object showed a prominent beat phenomenon even after the end of the superoutburst. A pilot study of superhump amplitudes indicated that the amplitudes of superhumps are strongly correlated with orbital periods, and the dependence on the inclination is weak in systems with inclinations smaller than 80 deg.
Superhumps in Cataclysmic Binaries. XXIII. V442 Ophiuchi and RX J1643.7+3402
Publications of the Astronomical Society of the Pacific, 2002
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 d). 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) d and 4.05(12) d. 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.
Publications of the Astronomical Society of Japan, 2015
Continuing the project described by Kato et al. (2009), we collected times of superhump maxima for 102 SU UMa-type dwarf novae observed mainly during the 2014-2015 season and characterized these objects. Our project has greatly improved the statistics of the distribution of orbital periods, which is a good approximation of the distribution of cataclysmic variables at the terminal evolutionary stage, and confirmed the presence of a period minimum at a period of 0.053 d and a period spike just above this period. The number density monotonically decreased toward the longer period and there was no strong indication of a period gap. We detected possible negative superhumps in Z Cha. It is possible that normal outbursts are also suppressed by the presence of a disk tilt in this system. There was no indication of enhanced orbital humps just preceding the superoutburst, and this result favors the thermal-tidal disk instability as the origin of superoutbursts. We detected superhumpsin three AM CVn-type dwarf novae. Our observations and No. ] Period Variations in SU UMa-Type Dwarf Novae VII 3 recent other detections suggest that 8% of objects showing dwarf nova-type outbursts are AM CVn-type objects. AM CVn-type objects and EI Psc-type object may be more abundant than previously recognized. OT J213806, a WZ Sge-type object, exhibited a remarkably different feature between the 2010 and 2014 superoutbursts. Although the 2014 superoutburst was much fainter the plateau phase was shorter than the 2010 one, the course of the rebrightening phase was similar. This object indicates that the O − C diagrams of superhumps can be indeed variable at least in WZ Sge-type objects. Four deeply eclipsing SU UMatype dwarf novae (ASASSN-13cx, ASASSN-14ag, ASASSN-15bu, NSV 4618) were identified. We studied long-term trends in supercycles in MM Hya and CY UMa and found systematic variations of supercycles of ∼20%.
A Photometric Study of the Newly Discovered Eclipsing Cataclysmic Variable SDSS J040714.78–064425.1
Publications of the Astronomical Society of Australia, 2005
We present the results obtained from unfiltered photometric CCD observations of the newly discovered cataclysmic variable SDSS J040714.78-064425.1 made during 7 nights in November 2003. We establish the dwarf nova nature of the object as it was in outburst during our observations. We also confirm the presence of deep eclipses with a period of 0.17017 d ±0.00003 in the optical light curve of the star. In addition, we found periods of 0.166 d ±0.001 and possibly also 5.3 d ±0.7 in the data. The 0.17017 d periodicity is consistent within the errors with the proposed orbital period of 0.165 d ) and 0.1700 d (Monard 2004). Using the known relation between the orbital and superhump periods, we interpret the 0.166 d and 5.3 d periods as the negative superhump and the nodal precession period respectively. SDSS J040714.78-064425.1 is then classified as a negative superhump system with one of the largest orbital periods.