Herculis System Research Articles

ENIGMAS FROM THE SLOAN DIGITAL SKY SURVEY DR7 KLEINMAN WHITE DWARF CATALOG

We report results from a continuation of our searches for high field magnetic white dwarfs paired in a detached binary with non degenerate companions. We made use of the Sloan Digital Sky Survey DR7 catalog of Kleinman et al. (2013) with 19,712 spectroscopically-identified white dwarfs. These include 1,735 white dwarf plus M dwarf detached pairs (almost 10\% of the Kleinman at al.'s list). No new pairs were found, although we did recover the polar (AM~Herculis system) ST\,LMi in a low state of accretion. With the larger sample the original situation reported ten years ago remains intact now at a much higher level of statistical significance: in the selected SDSS sample, high field magnetic white dwarfs are not found in an apparently-detached pairing with an M dwarf, unless they are a magnetic CV in a low state of accretion. This finding strengthens the case that the fields in the isolated high field magnetic white dwarfs are generated by stellar mergers but also raises questions on the nature of the progenitors of the magnetic CVs.

Analytical theories for near coplanar and polar circumbinary orbits

The recently discovered Kepler circumbinary systems and the circumbinary polar-ring debris disc in the 99 Herculis system call for the study of circumbinary orbits. As an approximation, it is advisable to investigate the problem with the assumption that the outer body is massless. In such a scheme, we briefly summarize the main characteristics of the evolution of the orbits and give the general solutions to some secular orbital elements under the quadrupole formalism and then, using the solution, explore the octupole Hamiltonian, which allows us to reveal the evolution of the eccentricity of the outer orbit. By doing so, we have discovered that the evolution of slightly inclined orbits does not deviate much from coplanar ones. For the near polar configurations, the inner binary can significantly excite the eccentricity of such orbits (in some cases to about 0.3); this may influence the stability of orbits near the binary.

99 Herculis: host to a circumbinary polar-ring debris disc

We present resolved Herschel images of a circumbinary debris disc in the 99 Herculis system. The primary is a late F-type star. The binary orbit is well characterized and we conclude that the disc is misaligned with the binary plane. Two different models can explain the observed structure. The first model is a ring of polar orbits that move in a plane perpendicular to the binary pericentre direction. We favour this interpretation because it includes the effect of secular perturbations and the disc can survive for Gyr time-scales. The second model is a misaligned ring. Because there is an ambiguity in the orientation of the ring, which could be reflected in the sky plane, this ring either has near-polar orbits similar to the first model or has a 30° misalignment. The misaligned ring, interpreted as the result of a recent collision, is shown to be implausible from constraints on the collisional and dynamical evolution. Because disc+star systems with separations similar to 99 Herculis should form coplanar, possible formation scenarios involve either a close stellar encounter or binary exchange in the presence of circumstellar and/or circumbinary discs. Discovery and characterization of systems like 99 Herculis will help understand processes that result in planetary system misalignment around both single and multiple stars.

The BANANA Survey: Spin-Orbit Alignment in Binary Stars

AbstractBinaries are not always neatly aligned. Previous observations of the DI Herculis system showed that the spin axes of both stars are highly inclined with respect to one another and the orbital axis. Here, we report on our ongoing survey to measure relative orientations of spin-axes in a number of eclipsing binary systems.These observations will hopefully lead to new insights into star and planet formation, as different formation scenarios predict different degrees of alignment and different dependencies on the system parameters. Measurements of spin-orbit angles in close binary systems will also create a basis for comparison for similar measurements involving close-in planets.

Photometric and polarimetric observations of the eclipsing polar SDSS J205017.84-053626.8

Photometric and polarimetric observations of the eclipsing polar (AM Herculis system) Sloan Digital Sky Survey 2050-05 are reported, in which both sets of data are found to be modulated on a period of ∼94.2 min. This is the first detection of polarization in this system, unambiguously confirming its identification. Circular polarization variations are seen from ∼− 10 to +4 per cent, consistent with a ‘two-pole’ accretor. Both accreting poles are self-occulted by the white dwarf during parts of the orbit. The photopolarimetry from different epochs shows the system to be in different states. During the epochs showing a higher state the polarimetry suggests accretion occurs preferentially near the pole displaying positive circular polarization, and vice versa during the epoch showing a lower state. From the eclipses we estimate some of the system’s parameters.

A Three Body Solution for the DI Her System

The DI Herculis system has been extensively studied over the past few decades because its observed rate of apsidal advance is less than a quarter of that which is expected from its physical and orbital properties. Work by Khaliullin et al. (1991) proposed that this slow rate of apsidal advance is a result of the presence of a third (stellar mass) body orbiting the system, however, observations by Guinan et al. (1994) severely restrict the orbital properties of such a solution. We show that a planetary mass object in a highly inclined orbit relative to the binary is capable of producing the observed apsidal motion, while remaining within the bounds of the most recent set of observations. A wide range of stable solutions are possible.

Photopolarimetric observations of the new eclipsing polar CTCV J1928 — 5001

We report photopolarimetric observations of a new eclipsing polar (AM Herculis system) discovered in the Calan-Tololo survey. The photometry and polarimetry are modulated on a period of � 101 minutes. Circular polarization variations are seen from � 8 to +12 per cent and from � 0 to 5 per cent in the red and blue parts of the optical spectrum, respectively. Two linearly polarized pulses are detected at orbital phases coinciding with the reversals in the circular polarization. This is consistent with a magnetic field strength of � 20 MG for the white dwarf primary, where accretion takes place at two regions. Both accretion regions are self-occulted by the white dwarf during parts of the orbit. We estimate some of the system's parameters from its eclipses, which we further refine by modelling the polarimetric observations.

Photometric and polarimetric observations of the eclipsing polar SDSS J015543.40+002807.2

We present photometric and polarimetric follow-up observations of the eclipsing Sloan Digital Sky Survey cataclysmic variable SDSS J015543.40+002807.2. Linear and circular polarizations were detected, confirming that it is a new polar (AM Herculis system). An accurate eclipse ephemeris yields an orbital period of 87.1435 ± 0.0002 min. Assuming a range of mass ratios 0.11 > M 2 /M 1 > 0.07, the inclination lies in the range 85° < i < 90°. The circular polarization shows a change in sign, implying that SDSS J015543.40+002807.2 is a two-pole accretor, although the possibility that it could be a single-pole accretor cannot yet be ruled out.

Stokes imaging, Doppler mapping and Roche tomography of the AM Herculis system V834 Cen

We report on new simultaneous phase-resolved spectroscopic and polarimetric observations of the polar (AM Herculis star) V834 Cen during a high state of accretion. Strong emission lines and high levels of variable circular and linear polarization are observed over the orbital period. The polarization data are modelled using the Stokes imaging technique of Potter et al. The spectroscopic emission lines are investigated using the Doppler tomography technique of Marsh and Horne and the Roche tomography technique of Dhillon and Watson. Up to now, all three techniques have been used separately to investigate the geometry and accretion dynamics in cataclysmic variables. For the first time, we apply all three techniques to simultaneous data for a single system. This allows us to compare and test each of the techniques against each other and hence to derive a better understanding of the geometry, dynamics and system parameters of V834 Cen. All three techniques are consistent with an interpretation in which a ballistic stream extends to a minimum of ∼40 degrees in azimuth around the white dwarf before becoming threaded by the magnetic field lines. Interestingly, the observed ballistic Doppler velocities do not show a reduced vy component, as found in Doppler imaging of other AM Her systems. Furthermore, the secondary star in V834 Cen shows more He ii (4686 Å) emission on its leading inner face, as opposed to the trailing face like in other AM Her systems. We propose that the accretion shock preferentially illuminates the leading face of the secondary star. In addition, the ballistic stream does not obscure the leading face of the secondary from the accretion shock, and, in fact, our Doppler maps show that the ballistic stream is a strong He ii (4686 Å) emission source in itself and thus adds to the illumination of the leading face of the secondary.

Analysis of new spectropolarimetric data of AR UMa

Optical spectropolarimetric observations of the high field AM Herculis system AR UMa during a low state of activity reveal a strongly structured circular polarization spectrum with a peak polarization of about 6 per cent. The strongest features can be identified with Zeeman split components of Hα and Hβ in an average magnetic field of 140‐170 MG. Attempts at modelling the data using centred and off-centred dipolar fields have only been partially successful. Mildly off-centred dipoles appear to be in better overall agreement with observations, but only marginally. Our favoured models belonging to this class have a dipolar field strength Bd ∼ 200‐235 MG displaced from the centre of the star by ∼5‐15 per cent of the stellar radius. These models also present a reasonable fit to the photospheric Ly απ and σ + components in the ultraviolet spectral region which are less sensitive to field structure. Our failure to obtain detailed agreement with the optical spectropolarimetry suggests that AR UMa, in common with some other well studied magnetic dwarfs, may have a field structure which differs from that of a dipole. Our study supports a previous suggestion that the variable emission feature near 1730 ˚ A and the feature near 2220 ˚ A, which are seen superimposed on the photospheric spectrum, are caused by cyclotron emission from a weakly accreting shock. We identify these features with cyclotron harmonics 4 and 3 respectively, in a field of 154 MG, which is the field strength expected near the weaker pole of our dipole model with Bd = 235 and an offset of 15 per cent of the stellar radius along the dipolar axis. A field of 154 MG can also explain the bump near 4450 ˚ A present in the high state circular polarization data of AR UMa, as harmonic number 2.

Photoelectric UBV observations and period study of AK Herculis system

New photoelectric UBV observations of the W Ursae Majoris-type eclipsing binary AK Her are presented. The system exhibits many phenomena such as O'Connell effect, unequal depth, phase shift and different duration in secondary eclipse due to its totality, which have been studied. O'Connell effect-duration relation may be exist. The (O-C) curve has been obtained and the new light elements have been calculated. The analysis of the minima-times data of the system reveals possible sinusoidal orbital period variation (LITE). The study of the (O-C)curve, the light curves, O'Connell effect and the duration effect have led to that the system is likely a case which undergoes cyclic around the marginal contact state conservatively with mass transfers between its components, i.e.in TRO mode.

Spectroscopy and polarimetry of the AM Herculis system RX J1313.32−3259

We present polarimetric and spectroscopic observations of the ROSAT source RX J1313.32−3259, recently identified as a polar. Circular polarization is modulated over the orbital period with an amplitude of ∼10 per cent. A brief reversal in circular polarization is detected at phase ∼0.0, when the main accretion region is seen face on to the observer. We deduce that the main cyclotron emission is absorbed by the accretion shock and/or stream at this phase, allowing a second accretion shock, located at the opposite ends of the field lines that feed the main pole, to be seen. Linear polarization is also detected with possible linear pulses at orbital phases where the accretion region is expected to be on the limb of the white dwarf. The general morphology of the photopolarimetry arises as a result of a combination of the absorption of cyclotron radiation by the accretion shock/stream and projection/cyclotron beaming effects of a main cyclotron emission region as the white dwarf rotates. The main cyclotron emission region remains on the visible hemisphere of the white dwarf throughout the orbit. Doppler maps of the emission lines show emission at or near the expected location of the secondary star and an extended arc-like feature coincident with the ballistic and possibly the magnetically confined accretion stream.

The short period supersoft source in M31

We show that the recently discovered short period supersoft source in M31 is probably a progenitor of a magnetic cataclysmic variable (CV). The white dwarf spins asynchronously because of the current high accretion rate. However its fieldstrength is typical of an AM Herculis system, which is what it will ultimately become. We discuss the relevance of this system to CV evolution, and its relation to some particular CVs with special characteristics.

UBVRI-polarimetry of the AM Herculis star RX J0203.8+2959

We present results of the rst simultaneous UBVRI-photopolarimetric observations of the long period (4.6 hrs) AM Herculis system RX J0203.8+2959. The observed circular polarization shows both negative and positive polarization, from +7% to 5% in the B-band. A rise of the positive circular polarization is observed near the same orbital phase as a change in HR1 hardness ratio from soft to hard in the earlier ROSAT X-ray observations. The negative circular polarization is observed near orbital phases where a soft X-ray component was seen in ROSAT observations. Linear polarization pulses coincide with the sign reversal of the circular polarization, and coincide also with changes in the X-ray hardness ratio in earlier ROSAT data. The observed polarization variations favour two-pole accretion. Least square ts to the position angle curves during linear pulses suggest high orbital inclination, estimates fromi =6 7 +21 24 to i =7 3 +13 15 .T heUBVRI-lightcurves show smooth variations with a broad maximum and minimum. RX J0203.8+2959 was in intermediate accretion state during observations in November 1998 (V =1 5:7 16:7). The observed flux and circular polarization variations are reproduced by using constant temperature cyclotron emission models having two accretion regions and with parameters: kT =1 0 keV, =1 0 5 and colatitude = 120 140 for the negative pole, and kT =2 0 keV, =1 0 4 and =2 0 30 for

X‐Ray and Optical Observations of BL Hydri

We acquired hard X-ray and unfiltered optical photometric data of the AM Herculis system BL Hydri. The X-ray data were obtained using the Proportional Counter Array detector of the Rossi X-Ray Timing Explorer satellite on 1997 October 17. The optical data were obtained using the 1.5 m telescope of the Cerro Tololo Inter-American Observatory on 1997 September 24. At the time of our observations, BL Hyi was in an unusual high-luminosity state with average visual magnitude mV ≈ 14.4 and orbital phase-averaged 2-10 keV X-ray flux ≈1.5 × 10-11 ergs cm-2 s-1, roughly 50% larger than had been seen previously. The X-ray light curves suggested that two accretion poles were active. The primary X-ray emission region was extended, covering ~45° in longitude on the white dwarf, while the secondary X-ray emission region was consistent with a point source with flux ~33% that of the primary region. The X-ray spectra were well fitted by absorbed bremsstrahlung with Gaussian emission-line models; and absorbed power law with Gaussian emission-line models. For the thermal models, the X-ray spectra were consistent with kTX ≈ 11 keV and an emission line at E ≈ 6.7-6.8 keV with equivalent width EW = 0.86-1.2 keV. The absorbed power-law models had slope α ≈ 2.1 and an emission line at E = 6.7-6.8 keV with EW = 1.1-1.5 keV. The optical data showed, 2.7% ± 0.2% rms quasi-periodic oscillations (QPOs) over the frequency range 0.2-0.8 Hz modulated strongly on the orbital period suggesting that the QPOs were connected with the dominant accretion hot spot. We did not find corresponding QPOs in the X-ray emission for an upper limit of 20% rms. There were no detections of other short-period QPOs or coherent features in either the optical or the X-ray data. The X-ray and optical data were consistent with a radiative shock model. Based primarily on the X-ray continuum and line spectrum, we infer that the mass of the white dwarf in the BL Hyi system is 0.3-0.7 M☉, depending on the relative cyclotron and hard X-ray luminosities.

Polarimetry of the eclipsing polar RX J0929.1 -- 2404

We report polarimetric, spectropolarimetric and photometric observations of the eclipsing ROSAT cataclysmic variable RX J0929.1−2404, which confirm that the system is a new polar (AM Herculis system). This brings the number of eclipsing polars to nine, with RX J0929.1−2404 being only the third such system above the period gap. Circular polarization variations from ∼−20 to 10 per cent are seen over the 3.39-h orbital period, with a minimum around the time of eclipse. The photopolarimetric data were modelled using arc-shaped cyclotron emission regions in a centred dipole geometry. Results imply that RX J0929.1−2404 is a ‘two-pole’ system, with one emission region partially visible at all orbital phases. Spectropolarimetry observations show some evidence for the presence of cyclotron humps in the continuum, with spacings consistent with a magnetic field strength of ∼20 MG. Photometry of the eclipses provides information on the size of the emission region, which is consistent with a hotspot on the surface of the white dwarf. The eclipse duration implies an inclination in the range 70°≲i≲78°.

EUVE J1429−38.0: A New Magnetic Cataclysmic Variable

The source EUVE J1429-38.0 was discovered serendipitously by the Extreme Ultraviolet Explorer (EUVE) satellite on 1993 March 5. Optical spectroscopy confirms a cataclysmic variable-type optical counterpart for the source, showing Balmer, He I, and Ca emission, as well as strong He II emission. The optical spectrum, the apparent high/low state behavior, and possible weak cyclotron humps visible in the spectrum indicate that this star is likely to be an AM Herculis system, but the possibility of being a DQ Her, or an unlocked AM Her system, cannot be excluded. Analysis of the highly modulated EUVE photometry yields a period of 2 hr 22 minutes, which we conclude is the binary orbital period. In addition, a 57 minute period is also present. An orbital period of 2.5 hr would make EUVE J1429-38.0 only the third known AM Her system within the cataclysmic variable period gap, all three of which were discovered through EUV observations.

Properties of the Exceptionally Long-Period AM Herculis System RX J0515.41+0104.6

view Abstract Citations (8) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Properties of the Exceptionally Long-Period AM Herculis System RX J0515.41+0104.6 Frank, J. ; Lasota, J. -P. ; Chanmugam, G. Abstract We show that the properties of the recently discovered AM Her type cataclysmic variable RX J0515.41+0104.6 can be understood in terms of the standard evolutionary model, which accounts for both the near-synchronism at the observed period and the size of the mass-donor star. We find that either the system is in a low state long enough to bring the white dwarf to synchronism or that the magnetic field of the secondary is strong enough, but not unusually so (≳1 kG), to maintain synchronism at this period and the system may exhibit radio flares. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176405 Bibcode: 1995ApJ...453..446F Keywords: STARS: BINARIES: CLOSE; STARS: EVOLUTION; STARS: INDIVIDUAL ALPHANUMERIC: RX J0515.41+0104.6; STARS: NOVAE; CATACLYSMIC VARIABLES full text sources ADS | data products SIMBAD (1)

The Magnetic Field of 1H1752+08

AbstractWe present spectropolarimetric observations of the eclipsing cataclysmic variable 1H1752+08. Modelling of the line intensity and polarisation spectra of 1H1752+08 shows that the magnetic field structure of the white dwarf is off-centre and the mean photospheric field strength is about 7 MG, the lowest measured in a cataclysmic variable (CV). We argue that 1H1752+08 is most probably a low-field AM Herculis system.

Detection of Cyclotron Lines in BL Hyi

AbstractWe present near-infrared spectroscopic observations over the wavelength range 0·9 to 2·5 μm of the AM Herculis system BL Hyi. During these observations, broad and resolvable cyclotron emission harmonics were visible near 1·25, 1·60 and 2·20 μm. We have interpreted these features as arising from a cyclotron emission region located near the white dwarf’s polar cap of magnetic field strength Bp = 23 MG.