White Dwarf Spin Period Research Articles

The formation of the magnetic symbiotic star FN Sgr

Context. There are several symbiotic stars (e.g., BF Cyg, Z And, and FN Sgr) in which periodic signals of tens of minutes have been detected. These periods have been interpreted as the spin period of magnetic white dwarfs that accrete through a magnetic stream originating from a truncated accretion disc. Aims. To shed light on the origin of magnetic symbiotic stars, we investigated the system FN Sgr in detail. We searched for a reasonable formation pathway to explain its stellar and binary parameters including the magnetic field of the accreting white dwarf. Methods. We used the MESA code to carry out pre-CE and post-CE binary evolution and determined the outcome of CE evolution assuming the energy formalism. For the origin and evolution of the white dwarf magnetic field, we adopted the crystallization scenario. Results. We found that FN Sgr can be explained as follows. First, a non-magnetic white dwarf is formed through CE evolution. Later, during post-CE evolution, the white dwarf starts to crystallize and a weak magnetic field is generated. After a few hundred million years, the magnetic field penetrates the white dwarf surface and becomes detectable. Meanwhile, its companion evolves and becomes an evolved red giant. Subsequently, the white dwarf accretes part of the angular momentum from the red giant stellar winds. As a result, the white dwarf spin period decreases and its magnetic field reaches super-equipartition, getting amplified due to a rotation- and crystallization-driven dynamo. The binary then evolves into a symbiotic star, with a magnetic white dwarf accreting from an evolved red giant through atmospheric Roche-lobe overflow. Conclusions. We conclude that the rotation- and crystallization-driven dynamo scenario, or any age-dependent scenario, can explain the origin of magnetic symbiotic stars reasonably well. This adds another piece to the pile of evidence supporting this scenario. If our formation channel is correct, our findings suggest that white dwarfs in most symbiotic stars formed through CE evolution might be magnetic, provided that the red giant has spent ≳3 Gyr as a main-sequence star.

Optical spectroscopic and photometric classification of the X-ray transient EP240309a (EP J115415.8−501810) as an intermediate polar

ABSTRACT We report on optical follow-up observations of an X-ray source initially detected by the Einstein Probe mission. Our investigations categorize the source as an intermediate polar, a class of magnetic cataclysmic variables, exhibiting an orbital period of 3.7614(4) h and a white dwarf spin period of 3.97 min. The orbital period was identified through TESS observations, while our high-speed photometric data, obtained using the 1.9m and Lesedi 1.0m telescopes at the South African Astronomical Observatory, revealed both the spin and beat periods. Additionally, we present orbitally phase-resolved spectroscopic observations using the 1.9m telescope, specifically centred on the H β emission line, which reveal two emission components that exhibit Doppler variations throughout the orbital cycle.

Optical identification and follow-up observations of SRGA J213151.5+491400

Context. The paper is comprised of optical identification and multiwavelength studies of a new X-ray source discovered by the Spectrum Roentgen-Gamma (SRG) observatory during the ART-XC survey and its follow-up optical and X-ray observations. Aims. We aim to identify SRGA J213151.5+491400 in the optical wavelengths. We determine spectra and light curves in the optical high and low states to find periodicities in the light curves and resolve emission lines in the system using optical ground-based data. We intend to study the spectral and temporal X-ray characteristics of the new source using the SRG surveys in the high and low states and NICER data in the low state. Methods. We present optical data from telescopes in Türkiye (RTT-150 and T100 at the TÜBİTAK National Observatory) and in Russia (6-m and 1-m at SAO RAS), together with the X-ray data obtained with ART-XC and eROSITA telescopes aboard SRG and the NICER observatory. Using the optical data, we performed astrometry, photometry, spectroscopy, and power spectral analysis of the optical time series. We present optical Doppler tomography along with X-ray data analysis producing light curves and spectra. Results. We detected SRGA J213151.5+491400 in a high state in 2020 (17.9 mag) that decreased by about 3 mag into a low state (21 mag) in 2021. We find only one significant period using optical photometric time series analysis, which reveals the white dwarf spin (orbital) period to be 0.059710(1) days (85.982 min). The long slit spectroscopy in the high state yields a power-law continuum increasing towards the blue with a prominent He II line along with the Balmer line emissions with no cyclotron humps, which is consistent with a magnetic cataclysmic variable (MCV) nature. Doppler Tomography confirms the polar nature revealing ballistic stream accretion along with magnetic stream during the high state. These characteristics show that the new source is a polar-type MCV source. ART-XC detections yield an X-ray flux of (4.0−7.0) × 10−12 erg s−1 cm−2 in the high state. eROSITA detects a dominating hot plasma component (kTmax > 21 keV in the high state) declining to (4.0−6.0) × 10−13 erg s−1 cm−2 in 2021 (low state). The NICER data obtained in the low state reveal a two-pole accretor showing a soft X-ray component at (6−7)σ significance with a blackbody temperature of 15−18 eV. A soft X-ray component has never been detected for a polar in the low state before.

X-ray measurement of a high-mass white dwarf and its spin for the intermediate polar IGR J18434−0508

ABSTRACT IGR J18434−0508 is a Galactic Intermediate Polar (IP) type Cataclysmic Variable (CV) previously classified through optical spectroscopy. The source is already known to have a hard Chandra spectrum. In this paper, we have used follow-up XMM–Newton and NuSTAR observations to measure the white dwarf (WD) mass and spin period. We measure a spin period of P = 304.4 ± 0.3 s based on the combined MOS1, MOS2, and pn light curve. Although this is twice the optical period found previously, we interpret this value to be the true spin period of the WD. The source has an $8\pm 2~{{\ \rm per\ cent}}$ pulsed fraction in the 0.5–10 keV XMM–Newton data and shows strong dips in the soft energy band (0.5–2 keV). The XMM–Newton and NuSTAR joint spectrum is consistent with a thermal bremsstrahlung continuum model with an additional partial covering factor, reflection, and Fe-line Gaussian components. Furthermore, we fit the joint spectrum with the post-shock region ‘ipolar’ model which indicates a high WD mass ≳1.36 M⊙, approaching the Chandrasekhar limit.

Unveiling the white dwarf in J191213.72 − 441045.1 through ultraviolet observations

ABSTRACT J191213.72 − 441045.1 is a binary system composed of a white dwarf and an M-dwarf in a 4.03-h orbit. It shows emission in radio, optical, and X-ray, all modulated at the white dwarf spin period of 5.3 min, as well as various orbital sideband frequencies. Like in the prototype of the class of radio-pulsing white dwarfs, AR Scorpii, the observed pulsed emission seems to be driven by the binary interaction. In this work, we present an analysis of far-ultraviolet spectra obtained with the Cosmic Origins Spectrograph at the Hubble Space Telescope, in which we directly detect the white dwarf in J191213.72 − 441045.1. We find that the white dwarf has a temperature of Teff = 11485 ± 90 K and mass of 0.59 ± 0.05 M⊙. We place a tentative upper limit on the magnetic field of ≈50 MG. If the white dwarf is in thermal equilibrium, its physical parameters would imply that crystallization has not started in the core of the white dwarf. Alternatively, the effective temperature could have been affected by compressional heating, indicating a past phase of accretion. The relatively low upper limit to the magnetic field and potential lack of crystallization that could generate a strong field pose challenges to pulsar-like models for the system and give preference to propeller models with a low magnetic field. We also develop a geometric model of the binary interaction which explains many salient features of the system.

Classifying IGR J15038−6021 as a magnetic CV with a massive white dwarf

ABSTRACT Cataclysmic variables (CVs) are binary systems consisting of a white dwarf (WD) accreting matter from a companion star. Observations of CVs provide an opportunity to learn about accretion discs, the physics of compact objects, classical novae, and the evolution of the binary and the WD that may ultimately end in a Type Ia supernova (SN). As Type Ia SNe involve a WD reaching the Chandrasekhar limit or merging WDs, WD mass measurements are particularly important for elucidating the path from CV to Type Ia SN. For intermediate polar (IP) type CVs, the WD mass is related to the bremsstrahlung temperature of material in the accretion column, which typically peaks at X-ray energies. Thus, the IPs with the strongest hard X-ray emission, such as those discovered by the INTEGRAL satellite, are expected to have the highest masses. Here, we report on XMM–Newton, Nuclear Spectroscopic Telescope Array (NuSTAR), and optical observations of IGR J15038−6021. We find an X-ray periodicity of 1678 ± 2 s, which we interpret as the WD spin period. From fitting the 0.3–79 keV spectrum with a model that uses the relationship between the WD mass and the post-shock temperature, we measure a WD mass of $1.36^{+0.04}_{-0.11}$ M⊙. This follows an earlier study of IGR J14091−6108, which also has a WD with a mass approaching the Chandrasekhar limit. We demonstrate that these are both outliers among IPs in having massive WDs and discuss the results in the context of WD mass studies as well as the implications for WD mass evolution.

Observations of Recent Novae Visible on the Northern Hemisphere

We are experiencing an increased rate of nova explosion observed from the northern hemisphere in the recent 2 years. Starting from July 2020 with the strongly reddened nova V1391 Cas, we are continuously observing some novae in outburst. Here, we report the observations of 5 classical novae: Nova Cas 2020 = V1391 Cas, Nova Per 2020 = V1112 Per, Nova Cas 2021 = V1405 Cas, Nova Her 2021 = V1674 Her and Nova Vul 2021 = V606 Vul. The best at the end - the recurrent symbiotic nova RS Oph. In this paper, we report our photometric and spectroscopic observations. Thorough analysis is to be done in the near future. At this moment we want to highlight two important facts. In the case of V1405 Cas, we know the orbital period of the progenitor. The progenitor of V1674 Her is an intermediate polar with known white dwarf spin period. In both cases, it will be very interesting to compare the values after the nova explosion. In the case of V1674 Her, we have already measured both the orbital and the spin period.

The Periodic Signals of Nova V1674 Herculis (2021)

We present time-series photometry during the early decline phase of the extremely fast nova V1674 Herculis. The 2021 light curve showed periodic signals at 0.152921(3) days and 501.486(5) s, which we interpret as respectively the orbital and white dwarf spin periods in the underlying binary. We also detected a sideband signal at the difference frequency between these two clocks. During the first 15 days of outburst, the spin period appears to have increased by 0.014(1)%. This increase probably arose from the sudden loss of high-angular-momentum gas (“the nova explosion”) from the rotating, magnetic white dwarf. Both periodic signals appeared remarkably early in the outburst, which we attribute to the extreme speed with which the nova evolved (and became transparent to radiation from the inner binary). After that very fast initial period increase of 71 ms, the period subsequently decreased—at 182(18) ms yr−1 in 2021, and 88(18) ms yr−1 in 2022. These rates are ∼100× faster than typically seen in intermediate polars. This could be due to high accretion torques from very high mass-transfer rates, which might be common when low-mass donor stars are strongly irradiated by a nova outburst.

A Magnetic Valve at L1 Revealed in TESS Photometry of the Asynchronous Polar BY Cam

We present TESS photometry of the asynchronous polar BY Cam, which undergoes a beat cycle between the 199.384 min white dwarf (WD) spin period and the 201.244 min orbital period. This results in changes in the flow of matter onto the WD. The TESS light curve covers 92% of the beat cycle once and 71% of the beat cycle twice. The strongest photometric signal, at 197.560 min, is ascribed to a side-band period. During times of light-curve stability, the photometry modulates at the spin frequency, supporting our WD spin-period identification. Both one-pole and two-pole accretion configurations repeat from one beat cycle to the next with clear and repeatable beat-phase-dependent intensity variations. To explain these, we propose the operation of a magnetic valve at L1. The magnetic valve modulates the mass-transfer rate, as evidenced by a factor of 5 variation in orbital-averaged intensity, over the course of the beat cycle in a repeatable manner. The accretion stream threading distance from the WD is also modulated at the beat period, because of the variation of the WD magnetic field with respect to the stream and because of changes in the mass transfer rate due to the operation of the magnetic valve. Changes in the threading distance result in significant shifts in the position of accreting spots around the beat cycle. As a consequence, only the faintest photometric minima allow for an accurate ephemeris determination. Three regions on the WD appear to receive most of the accretion flow, suggestive of a complex WD magnetic field.

V392 Persei: A γ-ray bright nova eruption from a known dwarf nova

ABSTRACT V392 Persei is a known dwarf nova (DN) that underwent a classical nova eruption in 2018. Here we report ground-based optical, Swift UV and X-ray, and Fermi-LAT γ-ray observations following the eruption for almost three years. V392 Per is one of the fastest evolving novae yet observed, with a t2 decline time of 2 d. Early spectra present evidence for multiple and interacting mass ejections, with the associated shocks driving both the γ-ray and early optical luminosity. V392 Per entered Sun-constraint within days of eruption. Upon exit, the nova had evolved to the nebular phase, and we saw the tail of the supersoft X-ray phase. Subsequent optical emission captured the fading ejecta alongside a persistent narrow line emission spectrum from the accretion disc. Ongoing hard X-ray emission is characteristic of a standing accretion shock in an intermediate polar. Analysis of the optical data reveals an orbital period of 3.230 ± 0.003 d, but we see no evidence for a white dwarf (WD) spin period. The optical and X-ray data suggest a high mass WD, the pre-nova spectral energy distribution (SED) indicates an evolved donor, and the post-nova SED points to a high mass accretion rate. Following eruption, the system has remained in a nova-like high mass transfer state, rather than returning to the pre-nova DN low mass transfer configuration. We suggest that this high state is driven by irradiation of the donor by the nova eruption. In many ways, V392 Per shows similarity to the well-studied nova and DN GK Persei.

TESS light curves of cataclysmic variables – I – Unknown periods in long-known stars

ABSTRACT Cataclysmic variables (CVs) exhibit a plethora of variable phenomena many of which require long, uninterrupted light curves to reveal themselves in detail. The month long data sets provided by TESS are well suited for this purpose. TESS has the additional advantage to have observed a huge number of stars, among them many CVs. Here, a search for periodic variations in a sample of CVs of the novalike and old novae subtypes is presented. In 10 of the 15 targets either previously unseen positive or negative superhumps or unusual features in known superhumps are identified. The TESS light curves demonstrate that the occurrence of superhumps in these types of CVs is not an exception but quite common. For 8 systems new or improved values for the orbital period are measured. In TV Col the long-sought optical manifestation of the white dwarf spin period is first seen in form of its orbital sideband. The mystery of multiple photometric periods observed in CP Pup in the past is explained by irregularly occurring anomalous states which are reflected in the light curve.

Slow convection and fast rotation in crystallization-driven white dwarf dynamos

ABSTRACT It has been recently suggested that white dwarfs generate magnetic fields in a process analogous to the Earth. The crystallization of the core creates a compositional inversion that drives convection, and combined with rotation, this can sustain a magnetic dynamo. We reanalyse the dynamo mechanism, arising from the slow crystallization of the core, and find convective turnover times tconv of weeks to months – longer by orders of magnitude than previously thought. With white dwarf spin periods P ≪ tconv, crystallization-driven dynamos are almost always in the fast-rotating regime, where the magnetic field B is at least in equipartition with the convective motion and is possibly further enhanced by a factor of B ∝ (tconv/P)1/2, depending on the assumed dynamo scaling law. We track the growth of the crystallized core using mesa and compute the magnetic field B(Teff) as a function of the white dwarf’s effective temperature Teff. We compare this prediction with observations and show that crystallization-driven dynamos can explain some – but not all – of the ∼MG magnetic fields measured for single white dwarfs, as well as the stronger fields measured for white dwarfs in cataclysmic variables, which were spun up by mass accretion to short P. Our B(Teff) curves might also explain the clustering of white dwarfs with Balmer emission lines around Teff ≈ 7500 K.

The First OGLE-discovered Ultracompact X-Ray Binary is an Intermediate Polar

Abstract The variable source OGLE-UCXB-01 is the first OGLE-discovered ultracompact X-ray binary (UCXB). The 12 yr long-term OGLE optical photometry of this source shows a period of P = 12.8 min and a fast period-decreasing rate P ̇ = − 9.2 × 10 − 11 s s−1. At a luminosity of L X ≈ 4 × 10 33 erg s−1, its X-ray emission is also variable and correlated with the optical variability. To determine the nature of this variable source, specifically the masses and types of its binary components, we first consider an attractive possibility that the optical variation is due to the secondary’s ellipsoidal variation and a strong gravitational wave emission drives the orbital decay. However, we cannot find an allowable solution to the secondary that simultaneously satisfies the three constraints: an ultratight orbit, the bright absolute magnitude, and the large-amplitude brightness variation. Moreover, the inferred mass-transfer rate is too high. This scenario is therefore ruled out. We then find the system is fully consistent with an “intermediate polar” model, in which the optical and X-ray emission comes from a magnetized white dwarf (WD) accreting from a low-mass (≲ 0.7 M ⊙ ) main-sequence secondary. The observed period decay is the accretion-driven spin-up of the WD. The WD spin period is 12.8 minutes and the orbital period is shorter than 10 hr. The method presented here can be applied to other UCXB candidates or impostors with only time-domain data available.

Discovery of 13 New Orbital Periods for Classical Novae

Abstract I report new orbital periods (P) for 13 classical novae, based on light curves from TESS, AAVSO, and other public archives. These new nova periods now constitute nearly one-seventh of all known nova periods. Five of my systems have P > 1 day, which doubles the number of such systems that must have evolved companion stars. (This is simply because ground-based time series have neither the coverage nor the stability required to discover these small-amplitude long periods.) V1016 Sgr has a rare P below the period gap, and suddenly becomes useful for current debates on evolution of novae. Five of the novae (FM Cir, V399 Del, V407 Lup, YZ Ret, and V549 Vel) have the orbital modulations in the tail of the eruption after the transition phase. Soon after the transition, YZ Ret shows a unique set of aperiodic diminishing oscillations, plus YZ Ret shows two highly significant transient periods, 1.1% and 4.5% longer than the orbital period, much like for the superhump phenomenon. I also report an optical 591.27465 s periodicity for V407 Lup, which is coherent and must be tied to the white dwarf spin period.

Chandra, NuSTAR, and Optical Observations of the Cataclysmic Variables IGR J17528-2022 and IGR J20063+3641

Abstract We report on Chandra, NuSTAR, and MDM observations of two International Gamma-ray Astrophysics Laboratory (INTEGRAL) sources, namely IGR J17528−2022 and IGR J20063+3641. IGR J17528−2022 is an unidentified INTEGRAL source, while IGR J20063+3641 was recently identified as a magnetic cataclysmic variable (mCV) by Halpern et al. The Chandra observation of IGR J17528−2022 has allowed us to locate the optical counterpart to the source and to obtain its optical spectrum, which shows a strong Hα emission line. The optical spectrum and flickering observed in the optical time-series photometry in combination with the X-ray spectrum, which is well fit by an absorbed partially covered thermal bremsstrahlung model, suggest that this source is a strong mCV candidate. The X-ray observations of IGR J20063+3641 reveal a clear modulation with a period of 172.46 ± 0.01 s, which we attribute to the white dwarf spin period. Additional MDM spectroscopy of the source has also allowed for a clear determination of the orbital period at 0.731 ± 0.015 days. The X-ray spectrum of this source is also well fit by an absorbed partially covered thermal bremsstrahlung model. The X-ray spectrum, spin periodicity, and orbital periodicity allow this source to be further classified as an intermediate polar.

Least-squares Spectral and Wavelet Analyses of V455 Andromedae Time Series: The Life After the Super-outburst

An extensive spectral analysis is performed on the light curve of dwarf nova V455 Andromedae (V455 And = HS 2331+3905) using the Least-squares WAVElet software (LSWAVE) to highlight its robustness for analyzing astronomical time series. The V455 And properties are briefly reviewed, and the recent results are compared with the results obtained herein. It is shown that the new analytical tools are superior to the traditional ones in that they consider observational uncertainties, do not require any interpolation and/or gap-filling, and can estimate the spectral peaks at a higher time–frequency resolution. First, the Anti-leakage Least-squares Spectral Analysis (ALLSSA) is applied to analyze a V455 And unequally spaced time series since 2008. ALLSSA has estimated spectral peaks at 80.40, 40.54, 1.12, and 0.56 minutes that correspond to the orbital period, its first harmonic, the white dwarf spin period, and its harmonic, respectively, confirming the earlier results. ALLSSA is then applied to all sufficiently large-size segments of the light curve to estimate the periodic components and demonstrate the double-humped orbital variations. Next, the Least-squares Wavelet Analysis (LSWA) is applied to four light curve segments each with a sufficient number of observations to study the periodic and aperiodic components. LSWA also detects the spectral peaks corresponding to the orbital period and non-radial white dwarf pulsations at a period of 4–5 minutes in 2010 October which gradually shifts toward 5–6 minutes in 2015 and 2018.

HP Cet and Swift J0820.6–2805: two candidate intermediate polars observed by XMM–Newton

ABSTRACT We report on the XMM–Newton observation of HP Cet and Swift J0820.6–2805, two X-ray photon sources that are candidates to be members of the intermediate polar class of cataclysmic variables. If the historical optical light curve of HP Cet shows a periodic feature at ≃96 min, a clear identification of such a signature in the high energy band (apart for a variability on a time-scale of ≃8 min as detected by the ROSAT satellite) is lacking. By using XMM–Newton archive data, we clearly identify a feature (at ≃88 min) which is marginally consistent with one of the binary system orbital periods reported in the literature. We also found a signature of a periodic features on the time-scale of ≃5.6 min. In the case of Swift J0820.6–2805, the intermediate polar nature was previously unclear and the orbital and the white dwarf spin periods were unknown. Here, the 0.3–10 keV data undoubtedly reveal an orbital period and a white dwarf spin of ≃87.5 and ≃27.9 min, respectively. The spectral analysis showed that both HP Cet and Swift J0820.6–280 are members of the underluminous IP subclass since their luminosity in the 0.3–10 keV band is estimated to be ≃5 × 1030 and ≃3.8 × 1029 erg s−1, respectively.

XMM-Newton observations of eleven intermediate polars and possible candidates

Aims. We aim to identify new intermediate polars (IPs) in XMM-Newton observations from a list of promising candidates. By selecting targets not previously known to be X-ray bright, we aim to uncover evidence for an X-ray underluminous IP subpopulation. Methods. We performed period searches on the XMM-Newton X-ray and optical data of our targets to seek both the spin and orbital periods, which differ in IPs. We also investigated the X-ray spectra to find the hot plasma emission shown by these objects. With archival Swift data we coarsely investigated the long-term X-ray variability, and with archival optical data from a variety of catalogues, we compared the optical to X-ray luminosity to identify X-ray faint objects. This paper presents the first XMM-Newton observation of the prototype IP, DQ Her. Results. We find firm evidence for HZ Pup, V349 Aqr, and IGR J18151-1052 being IPs, with likely white dwarf spin periods of 1552, 390, and 390 s, respectively. The former two have luminosities typical of IPs, and the latter is strongly absorbed and with unknown distance. GI Mon and V1084 Her are apparently non-magnetic CVs with interesting short-term variability unrelated to WD spin. V533 Her is probably a magnetic CV and remains a good IP candidate, while V1039 Cen is possibly a polar. The remaining candidates were too faint to allow for any firm conclusions.

TESS photometry of the asynchronous polar CD Ind: A short period analog of BY Cam

We present a time-series analysis of the asynchronous polar CD Ind, using fast cadence TESS photometry. A similar analysis is performed using ground based photometry of BY Cam. These asynchronous polars show remarkably similar light curves and enigmatic timing characteristics. A pair of competing models for the assignment of the white dwarf spin period have been presented for both binaries. TESS allows for the breaking of this degeneracy by providing continuous coverage over several beat-cycles. The CD Ind light curve displays a super-orbital period of 7.2 days due to beat-phased modulation of the accretion rate onto a permanently visible spot. This (main) accretion region is active for 3/4 of the beat-cycle. The dominant photometric signal is at 109.654(4) min and is identified as a side-band related to the white dwarf spin and the binary orbit, analogous to that found in BY Cam. We obtain the white dwarf spin period of CD Ind as 110.820(5) min and an orbital period of 111.952(8) min. The TESS light curve supports a pole-switching scenario for CD Ind, with a total of 4 alternating, and oppositely positioned accretion regions. This inclination of CD Ind is estimated as i = 65°±10°. One accretion region remains in view of the observer at all times. In addition, two pulsed accretion spots each accrete for just less than 1/2 of the beat-cycle. These alternating spots are orthogonal to the main accretion region (which is always in view), and are found to be roughly 180° apart in longitude. Finally, since the mean flux drops by a factor of 2 for about 1/4 of the beat-cycle and the dominant accretion region turns off during this time, we hypothesize the existence of a fourth (permanently hidden) accretion region opposite to the one permanently in view. Photometric models for the 2- and 4-pole accretion configurations are developed and only the 4-pole model is consistent with the observed periodogram for CD Ind. We conclude that complex magnetic fields affect accretion flow onto these white dwarf stars. In particular, the magnetic field of the white dwarf in both of these binaries is inconsistent with either a centered or an offset dipole configuration.

A NEW NON-ECLIPSING CV SDSSJ 122405.58+184102.7 - A PROBABLE MEMBER TO THE SW SEXTANTIS TYPE STARS

We present observational evidence that helps classify the non-eclipsing binary system SDSSJ 122405.58+184102.7 as a new member of the SW Sextantis (SW Sex) class. First, from the analysis of the optical light curve, we identify the presence of two periodic signals that develop on different time scales. The first one is the orbital period of 0.167811(1) days (= 4.027464 (3) h) and the second one is the white dwarf spin period of 28.6 minutes. This second period is probably the first evidence for the presence of a magnetic white dwarf in the system. The second evidence is the presence of the HeII λ4886 emission line in its optical spectrum. In this work we interpret the detected periodicities within the context of a magnetic accretion model for SW Sex stars.