DW UMa Research Articles

The Potential of The Cataclysmic Variable DW UMa to Host Planets

Evrimleşmiş bir altcüce ya da beyaz cüce ile bir M cücesinden oluşan örten çiftler kısa yörünge dönemleri, hızlı geçilen, simetrik, V-şeklindeki minimum profilleri nedeniyle hassas tutulma zamanlarının belirlenmesi için ideal sistemlerdir. Tutulma zamanlarındaki değişimin incelenmesi sonucu sisteme kütle çekimle bağlı birinci nesil ya da sistemin evrimi sırasında bileşenlerden birinin kaybettiği materyalden kaynaklı birikim disklerinde oluşabilecek ikinci nesil ötegezegenlerin neden olabileceği ışık-zaman etkisi tespit edilebilir. Bugüne kadar bu yöntemle yapılan ötegezegen keşiflerinin çok büyük bir çoğunluğu evriminin ileri aşamalarındaki bu tür sistemlerde gerçekleştirilmiştir. Bu çalışmada nova benzeri kataklizmik çift sistem DW UMa’nın tutulma zamanları analiz edilerek sonuçlar kütle transferi, eksen dönmesi ve ışık zaman etkisi bağlamında yorumlanmış ve tartışılmıştır.

White Dwarf Photospheric Abundances in Cataclysmic Variables. IV. Deriving the [N/C] Ratio* *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of University for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

We present results from our ongoing far-ultraviolet archival analysis of cataclysmic variable white dwarf (WD) abundances for six more systems: four SU UMa dwarf novae (BW Scl, SW UMa, BC UMa, and VW Hyi) together with the dwarf nova RX And, and the novalike DW UMa. To derive a reliable nitrogen abundance, for the four SU UMa systems (with a WD temperature T wd ∼ 14,000 to ∼22,000 K), we use the dominant N i (1492 Å) absorption line; for DW UMa (with T wd possibly as high as 60,000 K), we use the N v (∼1240 Å) doublet; and for RX And (with T wd = 33,800 K), we use the N iii (1183.0 and 1184.6 Å) absorption lines. We find a [N/C] ratio of the order of 1–100 (in solar units). Oxygen, silicon, phosphorus are mostly underabundant while aluminum is mostly overabundant. We also derive magnesium, sulfur, calcium, and iron for a few systems. VW Hyi has a solar composition secondary implying the suprasolar [N/C] ratio very likely originates in the WD itself, e.g., accretion-driven dredge-up, mixing, and convection bringing material from deeper regions to the WD surface. If the donor star in the other five systems is nonevolved, the WD is the origin for the [N/C] ratio in these systems, either directly as in VW Hyi or due to contamination of the donor and accretion disk by the repetitive explosive CNO burning during the common envelope stage of the nova explosions.

A 16-yr photometric campaign on the eclipsing novalike variable DW Ursae Majoris

We present an analysis of photometric observations of the eclipsing novalike variable DW UMa made by the CBA consortium between 1999 and 2015. Analysis of 372 new and 260 previously published eclipse timings reveals a 13.6 year period or quasi-period in the times of minimum light. The seasonal light curves show a complex spectrum of periodic signals: both positive and negative superhumps, likely arising from a prograde apsidal precession and a retrograde nodal precession of the accretion disc. These signals appear most prominently and famously as sidebands of the orbital frequency but the precession frequencies themselves, at 0.40 and 0.22 cycles per day, are also seen directly in the power spectrum. The superhumps are sometimes seen together and sometimes separately. The depth, width and skew of eclipses are all modulated in phase with both nodal and apsidal precession of the tilted and eccentric accretion disc. The superhumps, or more correctly the precessional motions which produce them, may be essential to understanding the mysterious SW Sextantis syndrome. Disc wobble and eccentricity can both produce Doppler signatures inconsistent with the true dynamical motions in the binary, and disc wobble might boost the mass-transfer rate by enabling the hot white dwarf to directly irradiate the secondary star.

Ultraviolet spectral behavior of IP Peg and DW UMa in high, intermediate and low states from the HST and IUE satellites

Ultraviolet spectra of IP Peg and DW UMa observed with Hubble Space Telescope Space Telescope Imaging Spectrograph & Faint Object Spectrograph (HST STIS FOS) and International Ultraviolet Explorer (IUE) satellites were analyzed during the period between 1989–1994 and 1985–2004. Different profiles of two systems showing variations of line fluxes at different orbital phases are presented. Both IP Peg and DW UMa are characterized by emission lines in high, intermediate and low states. DW UMa is characterized by absorption lines in an unusual low state. This paper focuses on the C IV emission line at 1550Å produced in an accretion disk for two systems (Saito et al., 2005; Knigge et al., 2000), by calculating spectral line fluxes. Our results show that there are significant variations of line fluxes with time for two systems. The variations of line fluxes are attributed to the variations of both density and temperature as a result of a changing rate of mass transfer from the secondary star to the white dwarf (Saito et al., 2005; Knigge et al., 2000). These results from the IUE and HST observations support a white dwarf model atmospheres of IP Peg and DW UMa producing sufficient UV flux for orbital modulations.

The SW Sex enigma

The SW Sex stars are a class of cataclysmic variables, originally identified because they shared a number of enigmatic properties - most notably, single-peaked emission lines instead of the double-peaked lines one would expect from their high-inclination accretion discs. We present high time-resolution spectrophotometry of the eclipsing nova-like variables SW Sex and DW UMa, two of the founding members of the SW Sex class. Both systems show single-peaked Balmer and HeII 4686A emission lines that appear to originate from a region in the disc that lies close to, but downstream of, the bright spot. The emission-line light curves are consistent with the finding from X-ray and ultraviolet observations that we predominantly see the flared disc rim and the unobscured back portion of the disc in these systems. In DW UMa, the HeII 4686A emission line originates from close to the white dwarf and exhibits flaring. Such flares have been used to argue for magnetically-channelled accretion, as in the intermediate polars, but the lack of a clear periodicity in the flares argues for a simpler model in which we are viewing the central regions of the disc through the non-uniform upper edge of a flared disc rim. We also observe narrow, blue-shifted, transient absorption features in the Balmer lines of DW UMa, which we attribute to blobs of material ejected from the system, possibly by a magnetic propeller, that happen to be passing between us and the binary. Our results suggest that the solution to the SW Sex enigma is a combination of dominant bright-spot emission and a self-occulting disc. We also propose a simplified classification scheme for nova-like variables.

SIMULTANEOUS X-RAY AND ULTRAVIOLET OBSERVATIONS OF THE SW SEXTANTIS STAR DW URSAE MAJORIS

We present the first pointed X-ray observation of DW Ursae Majoris, a novalike cataclysmic variable (CV) and one of the archetype members of the SW Sextantis class, obtained with the XMM-Newton satellite. These data provide the first detailed look at an SW Sex star in the X-ray regime (with previous X-ray knowledge of the SW Sex stars limited primarily to weak or non-detections in the ROSAT All Sky Survey). It is also one of only a few XMM-Newton observations (to date) of any high mass transfer rate novalike CV, and the only one in the evolutionarily important 3–4 hr orbital period range. The observed X-ray spectrum of DW UMa is very soft, with ∼95% of the detected X-ray photons at energies <2 keV. The spectrum can be fit equally well by a one-component cooling flow model, with a temperature range of 0.2–3.5 keV, or a two-component, two-temperature thermal plasma model, containing hard (∼5–6 keV) and soft (∼0.8 keV) components. The X-ray light curve of DW UMa shows a likely partial eclipse, implying X-ray reprocessing in a vertically extended region, and an orbital modulation, implying a structural asymmetry in the X-ray reprocessing site (e.g., it cannot be a uniform corona). We also obtained a simultaneous near-ultraviolet light curve of DW UMa using the Optical Monitor on XMM-Newton. This light curve is similar in appearance to published optical–UV light curves of DW UMa and shows a prominent deep eclipse. Regardless of the exact nature of the X-ray reprocessing site in DW UMa, the lack of a prominent hard X-ray total eclipse and very low fraction of high energy X-rays point to the presence of an optically and geometrically thick accretion disk that obscures the boundary layer and modifies the X-ray spectrum emitted near the white dwarf.

Time-resolved Ultraviolet Spectroscopy of the SW Sex Star DW UMa: Confirmation of a Hidden White Dwarf and the Ultraviolet Counterpart to Phase 0.5 Absorption Events

We present time-resolved ultraviolet (UV) spectroscopy of the SW Sex star DW UMa in the high state. We confirm that shortward of 1500 A, the high-state UV continuum level is lower than the white dwarf (WD) dominated low-state level. We also do not see the WD contact phases in the high-state eclipse light curves. These results confirm our earlier finding that the WD in this system is hidden from view in the high state. On the basis of this, we caution that eclipse mapping of high-inclination SW Sex stars in the high state may yield incorrect or misleading results. In the context of DW UMa, we demonstrate explicitly that distance estimates obtained by recent eclipse-mapping studies cannot be reconciled with the WD-dominated low-state spectrum. We also show that the fluxes of the UV emission lines in the high state drop near orbital phase 0.5. This is the first detection of a UV counterpart to the class-defining phase 0.5 absorption seen in the optical emission lines of SW Sex stars.

Accretion disc evolution in DW Ursae Majoris: A photometric study

We present an analysis of CCD photometric observations of the eclipsing novalike cataclysmic variable DW UMa obtained in two different luminosity states: high and intermediate. The star presents eclipses with very different depth: ~1.2 mag in the high and ~3.4 mag in the intermediate state. Eclipse mapping reveals that this difference is almost entirely due to the changes in the accretion disc radius: from ~ in the intermediate state to ~ in the high state ( is the distance from the white dwarf to the first Lagrangian point). In the intermediate state, the entire disc is eclipsed while in the high state, its outer part remains visible. We also find that the central intensity of the disc is nearly the same in the two luminosity states and that it is the increase of the disc radius that is responsible for the final rise from the 1999/2000 low state. We find that the intensity profile of the disc is rather flat and suggest a possible explanation. We also discuss the effect of using a more realistic limb-darkening law on the disc temperatures inferred from eclipse mapping experiments. Periodogram analysis of the high state data reveals “positive superhumps" with a period of in 2002 and in 2003, in accord with the results of Patterson et al. However, we cannot confirm the quasi-periodic oscillations reported by these authors. We obtain an updated orbital ephemeris of DW UMa: .

FUSE Results on Magnetic CVs: VV Pup, YY Dra, LS Peg and DW UMa

AbstractIn Cycles 2 and 3, we obtained FUSE observations of the Polar VV Pup, and the IP/SW Sex stars YY Dra, LS Peg and DW UMa. The spectra show a wide range of line intensities and structure. The phase-resolved spectra in each case reveal interesting properties about the hot accretion zones.

Observations of the SW Sextantis Star DW Ursae Majoris with theFar Ultraviolet Spectroscopic Explorer

We present an analysis of the first far-ultraviolet observations of the SW Sextantis type cataclysmic variable DW Ursae Majoris, obtained in 2001 November with the Far Ultraviolet Spectroscopic Explorer. The time-averaged spectrum of DW UMa shows a rich assortment of emission lines (plus some contamination from interstellar absorption lines including molecular hydrogen). Accretion disk model spectra do not provide an adequate fit to the far-ultraviolet spectrum of DW UMa. We constructed a light curve by summing far-ultraviolet spectra extracted in 60 s bins; this shows a modulation on the orbital period, with a maximum near photometric phase 0.93 and a minimum half an orbit later. No other periodic variability was found in the light-curve data. We also extracted spectra in bins spanning Δ = 0.1 in orbital phase; these show substantial variation in the profile shapes and velocity shifts of the emission lines during an orbital cycle of DW UMa. Finally, we discuss possible physical models that can qualitatively account for the observed far-ultraviolet behavior of DW UMa, in the context of recent observational evidence for the presence of a self-occulting disk in DW UMa and the possibility that the SW Sextantis stars may be the intermediate polars with the highest mass transfer rates and/or weakest magnetic fields.

The System Parameters of DW Ursae Majoris

We present new constraints on the system parameters of the SW Sextantis star DW Ursae Majoris, based on ultraviolet (UV) eclipse observations with the Hubble Space Telescope. Our data were obtained during a low state of the system, in which the UV light was dominated by the hot white dwarf (WD) primary. Eclipse analysis, using the full Roche lobe geometry, allows us to set firm limits on the masses and radii of the system components and the distance between them: 0.67 \leq M_1/M_sun \leq 1.06, 0.008 \leq R_1/R_sun \leq 0.014, M_2/M_sun > 0.16, R_2/R_sun > 0.28 and a/R_sun > 1.05. For q = M_2/M_1 71 degrees. Using Smith & Dhillon's mass-period relation for CV secondaries, our estimates for the system parameters become M_1/M_sun = 0.77 \pm 0.07, R_1/R_sun = 0.012 \pm 0.001, M_2/M_sun = 0.30 \pm 0.10, R_2/R_sun = 0.34 \pm 0.04, q =0.39 \pm 0.12, i = 82 \pm 4 degrees and a/R_sun = 1.14 \pm 0.06. We have also estimated the spectral type of the secondary, M3.5 \pm 1.0, and distance to the system, d =930 \pm 160 pc, from time-resolved I- and K-band photometry. Finally, we have repeated Knigge et al.'s WD model atmosphere fit to the low-state UV spectrum of DW UMa in order to account for the higher surface gravity indicated by our eclipse analysis. In this way we obtained a second estimate for the distance, d = 590 \pm 100 pc, which allows us to obtain a second estimate for the spectral type of the secondary, M7 \pm 2.0. We conclude that the true value for the distance and spectral type will probably be in between the values obtained by the two methods.

V533 Herculis: the second SW Sex old nova displaying emission-line flaring

We present high-time-resolution spectroscopy of the non-eclipsing old nova V533 Herculis (N Her 1963). It is the second nova remnant affected by the ‘SW Sex syndrome’. A modulation of the equivalent width of the emission lines with a period of 23.33 min has been detected. This, together with the strong He II λ4686 emission characteristic of magnetic systems, leads us to link this period to the spin of a magnetic white dwarf. Similar flaring activity has been recorded in other SW Sex stars, namely, the old nova BT Mon, LS Peg and DW UMa, supporting the idea of these systems being magnetic accretors. Stationary emission features are also observed in the Balmer lines, which we attribute to the ejected nova shell.

A Self-occulting Accretion Disk in the SW Sextantis Star DW Ursae Majoris

We present the ultraviolet spectrum of the SW Sextantis star and nova-like variable DW Ursae Majoris in an optical low state, as observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope (HST). The data are well described by a synthetic white dwarf (WD) spectrum with Teff = 46,000 ± 1000 K, log g = 7.60 ± 0.15, v sin i = 370 ± 100 km s-1, and Z/Z☉ = 0.47 ± 0.15. For this combination of Teff and log g, WD models predict MWD = 0.48 ± 0.06 M☉ and RWD = (1.27 ± 0.18) × 109 cm. Combining the radius estimate with the normalization of the spectral fit, we obtain a distance estimate of d = 830 ± 150 pc. During our observations, DW UMa was approximately 3 mag fainter in V than in the high state. A comparison of our low-state HST spectrum with a high-state spectrum obtained with the International Ultraviolet Explorer shows that the former is much bluer and has a higher continuum level shortward of 1450 A. Since DW UMa is an eclipsing system, this suggests that an optically thick accretion disk rim blocks our view of the WD primary in the high state. If self-occulting accretion disks are common among the SW Sex stars, we can account for (1) the preference for high-inclination systems within the class and (2) their V-shaped continuum eclipses. Moreover, even though the emission lines produced by a self-obscured disk are generally still double-peaked, they are weaker and narrower than those produced by an unobscured disk. This may allow a secondary line emission mechanism to dominate and produce the single-peaked, optical lines that are a distinguishing characteristic of the SW Sex stars.

Infrared spectroscopy of cataclysmic variables -- III. Dwarf novae below the period gap and nova-like variables

We present K-band spectra of the short-period dwarf novae YZ Cnc, LY Hya, BK Lyn, T Leo, SW UMa and WZ Sge, the nova-like variables DW UMa, V1315 Aql, RW Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral types ranging from K2 to M6. The spectra of the dwarf novae are dominated by emission lines of H i and He i. The large velocity and equivalent widths of these lines, in conjunction with the fact that the lines are double-peaked in the highest inclination systems, indicate an accretion disc origin. In the case of YZ Cnc and T Leo, for which we obtained time-resolved data covering a complete orbital cycle, the emission lines show modulations in their equivalent widths that are most probably associated with the bright spot (the region where the gas stream collides with the accretion disc). There are no clear detections of the secondary star in any of the dwarf novae below the period gap, yielding upper limits of 10–30 per cent for the contribution of the secondary star to the observed K-band flux. In conjunction with the K-band magnitudes of the dwarf novae, we use the derived secondary star contributions to calculate lower limits to the distances to these systems. The spectra of the nova-like variables are dominated by broad, single-peaked emission lines of H i and He i– even the eclipsing systems we observed do not show the double-peaked profiles predicted by standard accretion disc theory. With the exception of RW Tri, which exhibits Na i, Ca i and 12CO absorption features consistent with a M0V secondary contributing 65 per cent of the observed K-band flux, we find no evidence for the secondary star in any of the nova-like variables. The implications of this result are discussed.

Observations of the eclipsing nova-like variable Dw Ursae Majoris in a low state

We present observations of the eclipsing nova-like variable DW UMa during a previously unseen low state. The continuum is deeply eclipsed and, from measurements of the eclipse width, we deduce that the accretion disc is smaller than during the normal state. In contrast to the normal state, there are no high-excitation emission lines present. The Balmer lines are dominated by strong, narrow emission spikes superposed upon faint wings. The emission spikes originate from the inner face of the secondary star, and the line wings show evidence of an accretion disc origin. We attribute the low state to a decrease in the mass-accretion rate and discuss possible causes of the phenomenon

THE LONG-TERM LIGHT CURVE OF THE CATACLYSMIC VARIABLE DW URSAE MAJORIS

ABSTRACT A 2.5 year sequence of CCD photometry on DW UMa has shown an unusaul 4 magnitude fall and rise in the light curve. The rise appears relatively smooth and regular, unlike the transitions of other high state/low state systems. The effect could be due to solar-type magnetic variations on the secondary of the cataclysmic variable. Some observational as well as theoretical work suggests that a nova prior to outburst may show photometric behavior similar to that displayed by DW UMa.

A spectroscopic study of the eclipsing cataclysmic binary star PG0818 + 513 - A puzzling novalike variable

Spectroscopic observations of a novalike variable are reported. The emission-line radial velocities yield an orbital period of 0.156 d (= 3.74 hr), in agreement with the eclipse timings of Andronov et al. (1989). The H-alpha emission shows abrupt increases in equivalent width around the eclipse phase; it is not eclipsed as strongly as the continuum. The radial velocities have a pronounced (about 57 deg) phase lag compared to the eclipse. This object may be a somewhat fainter example of a common, but very puzzling, class of luminous novalike variables, which includes SW Sex, DW UMa, V1315 Aql, and PG0027 + 260. 27 refs.

PG0027 + 260 - an example of a class of cataclysmic binaries with mysterious, but consistent, behavior

view Abstract Citations (184) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS PG 0027+260: an Example of a Class of Cataclysmic Binaries With Mysterious, But Consistent, Behavior Thorstensen, John R. ; Ringwald, F. A. ; Wade, Richard A. ; Schmidt, Gary D. ; Norsworthy, Jane E. Abstract This paper reports extensive optical observations on the PG0027 + 260 binary, carried out on August 1984 with the 1.3 McGraw-Hill telescope and Mark II spectrometer at Michigan-Dartmouth-MIT Observatory on Kitt Peak. It is shown that this object is an eclipsing novalike variable with an orbital period of 3.51 hr. The PG0027 + 260 displays several unexplained phenomena which are remarkably similar to those of the SW Sex, DW UMa, and V1315 Aql, which are eclipsing novalike stars with periods between 3 and 4 hrs. The eclipse of the PG0027 + 260 is modeled, and it is shown that, while the mean eclipse light curve is easy to match, there is no simple explanation for the variable depth. Publication: The Astronomical Journal Pub Date: July 1991 DOI: 10.1086/115874 Bibcode: 1991AJ....102..272T Keywords: Cataclysmic Variables; Eclipsing Binary Stars; Novae; Stellar Spectra; Emission Spectra; Light Curve; Ultraviolet Spectra; Visible Spectrum; Astrophysics; STARS: ECLIPSING BINARIES; STARS: NOVAE full text sources ADS | data products SIMBAD (7) MAST (1) INES (1)

A study of the eclipsing cataclysmic variable Lanning 90

Photometric and spectroscopic observations of Lanning 90 (V1776 Cyg) show that it is an eclipsing cataclysmic variable with an orbital period of 3h57m. The shape of the eclipse is variable, and the brightness out of eclipse can change by over a magnitude in less than a day. The broad-band light curves do not show a hump before eclipse, but time-resolved spectroscopy of one orbit suggests that the H-alpha emission-line strength peaks near phase 0.75. Observations of a number of orbits, however, are needed to confirm that the line strength depends on phase. The velocity amplitude of the primary is 144 + or - 20 km/s as measured from the wings of the H-alpha line. The masses of the components, the orbital inclination, and semimajor axis are estimated from the observations, but the derived system parameters are suspect since the spectroscopic phase lags the photometric phase by 70 deg. A similar shift has been observed in DW UMa and is attributed to a disturbance on the disk which contaminates the Balmer line wings. 20 refs.

The phase 0.5 absorption in V1315 Aquilae, SW Sextantis, and DW Ursae Majoris

Medium-resolution (1.5-2.5-A) spectra of three eclipsing novalike cataclysmic variables (V1315 Aql, SW Sex, and DW UMa) have been obtained on several nights throughout the 0.4-0.7 phase interval. These spectra are used to study the time scale and velocity of the absorption feature which appears near phase 0.5 in these three systems. The results show that the absorption feature appears at slightly changing times from night to night within the phase interval of 0.39-0.42, and disappears in the interval 0.57-0.67. The time scale for the feature to emerge and disappear is within 0.025 phase. All the absorption velocities are displaced to the red with respect to the emission wings, while the best data (for DW UMa) show a systematic excursion of the absorption velocities with respect to the emission. While the general results are consistent with absorbing gas associated with the outer disk, at least two components are necessary to explain the velocity behavior of the lines in DW UMa.