Cataclysmic variables with magnetic white dwarf whose magnetic field is not strong enough to synchronize the white dwarf spin with the orbit of the system are known as intermediate polars (IPs).
In the intermediate polars, the white dwarf star has a small magnetic field less than 10 MG, so a complete accretion disk cannot be formed. Intermediate polars reveal periodic variations that reflect the orbital period of the binary system and the spin period of the primary star. The asynchronous rotation of white dwarfs in IPs can be interpreted by the reaction between the magnetic field of the white dwarf and the disk matter near the magnetosphere. More details can be found in Warner [34], Patterson [24], Hellier [11], Warner [33], and Campbell [4].
DQ Her (Nova Herculis 1934) was first detected at its bright phase with a magnitude of ~ 3.3
The mass transfer in DQ Her was detected by Kraft [16]. Mumford [19] and Nather & Warner [20] suggested an increase in DQ Her orbital period. Later on (Patterson et al. [23]; Africano & Olson [1]; Zhang et al. [39]; Wood et al. [35]) indicated modulation of 14 yr period. However, an updated O-C analysis done by Wood et al. [35] found no evidence for a secular orbital period increase.
DQ Her is one of the most studied classical novae. Its maximum brightness recorded in 1934 with
The first radial velocity measurements of DQ Her suggested both high-mass solutions with
The IUE low-resolution short wavelength spectra have been obtained from the INES (IUE Newly Extracted Spectra) site
List of IUE observations for DQ Her.Data ID Exp Time(s) HJD 2440000+ Phase SWP06358 5400 4118.934 0.55 SWP06848 9900 4159.704 0.12 SWP07408 10800 4222.544 0.67 SWP09147 25200 4222.544 0.67 SWP09201 22200 4396.614 0.70 SWP17593 4800 5186.821 0.91 SWP17614 7200 5188.652 0.36 SWP17615 2400 5188.752 0.88 SWP25440 1440 6137.675 0.81 SWP25441 2400 6137.711 0.99 SWP25442 3600 6137.768 0.29 SWP27812 18300 6490.105 0.02
Due to lack of IUE spectra for DQ Her, Hubble Space Telescope (HST-FOS) observations of DQ Her have been collected from the Hubble Space Telescope center (MAST) at site
List of HST observations for DQ Her.Data ID Exp Time(s) Gratings HJD 2440000+ Phase Y1DZ0603T 2400 G190H 49275.3442 0.34 Y1DZ0602T 2169.361 G160L 49275.27584 0.28 Y1DZ0601T 2169.361 G160L 49275.21044 0.21 Y1DZ0501T 2169.361 G160L 49275.15263 0.15 Y2LU0604T 2400 G190H 49834.92946 0.93 Y2LU0603T 1737.476 G160L 49834.85829 0.86 Y2LU0602T 1737.476 G160L 49834.7912 0.79 Y2LU0601T 1737.476 G160L 49834.72603 0.73 Y2XPA103T 2418.216 G130H 50003.3599 0.36 Y2XPA102T 2418.216 G130H 50003.29308 0.29 Y2XPA104T 2243.053 G130H 50003.4261 0.43 Y2XPA101T 1717.566 G130H 50003.23115 0.23 Y2XPB203T 2418.216 G130H 50007.45564 0.46 Y2XPB202T 2418.216 G130H 50007.38878 0.39 Y2XPB201T 2340.365 G130H 50007.32284 0.32 Y2XPB204T 2262.516 G130H 50007.52198 0.52
The CCD photometric observations of the target stars selected for the study are obtained using 2
Data reduction, where CCD observed frames (for the variable the comparison and the check stars) are corrected for bias and flat field is mainly performed using different tasks of IRAF software packages. Then we used the packages of C-Munipack program to do the photometry and extract the magnitude variability for each system by means of differential photometry.
Differential photometry is performed for measuring the small variations in brightness of the target variable star in comparison with other two non-variable stars known as comparison (C) and check stars (Ck). This technique is widely used in variable stars, especially for short period variables and eclipsing binary systems. In differential photometry a comparison and a check stars together with the variable are exposed in the same CCD frame.
The photometric observations for DQ Her are obtained in V, R and I filters as shown in Tables (4), (5) and (6) respectively. Fig 4 displays the field chart of the system. The differential photometry was performed with respect to 000-BCB-330 and 000-BCB-348 as comparison and check stars respectively, Table 3 lists their coordinates. Fig 5 shows the phase diagrams for DQ Her in V, R and I filters folded with phase equation (1).
List of the comparison and the check of DQ Her.ID RA DEC Label 000-BCB-330 18:07:23.97 45:49:47.6 142 14.231 000-BCB-348 18:07:33.58 45:49:33.5 154 15.375
list of CCD Photometry of DQ Her in V filter.JD 2457624+ phase v-c 0.219 0.666 0.319 0.224 0.693 0.267 0.229 0.718 0.328 0.234 0.743 0.295 0.238 0.768 0.290 0.243 0.792 0.241 0.248 0.817 0.328 0.253 0.842 0.340 0.258 0.867 0.402 0.262 0.892 1.030 0.267 0.917 2.183 0.272 0.942 3.391 0.277 0.966 2.605 0.282 0.991 1.469 0.286 0.016 0.930 0.291 0.041 0.688 0.296 0.066 0.529 0.301 0.091 0.449 0.306 0.116 0.456 0.311 0.140 0.483 0.315 0.165 0.404 0.320 0.190 0.358 0.325 0.215 0.452 0.330 0.240 0.475 0.335 0.264 0.493 0.339 0.289 0.436 0.344 0.314 0.332 0.349 0.339 0.375 0.354 0.364 0.291 0.359 0.389 0.349 0.364 0.414 0.334 0.368 0.439 0.340 0.373 0.464 0.324 0.378 0.488 0.273 0.383 0.513 0.284 0.388 0.539 0.315 0.393 0.564 0.343 0.397 0.589 0.408 0.402 0.614 0.394 0.407 0.639 0.380 0.412 0.663 0.435 0.417 0.691 0.362 0.422 0.716 0.369 0.427 0.741 0.369
list of CCD Photometry of DQ Her in R filter.JD 2457624+ phase v-c 0.220 0.674 0.429 0.226 0.702 0.424 0.230 0.726 0.456 0.235 0.751 0.435 0.240 0.776 0.403 0.245 0.801 0.402 0.250 0.825 0.493 0.254 0.850 0.538 0.259 0.875 0.731 0.264 0.900 1.430 0.269 0.925 2.507 0.274 0.950 3.080 0.278 0.975 2.096 0.283 0.999 1.276 0.298 0.074 0.620 0.303 0.099 0.558 0.307 0.124 0.578 0.312 0.149 0.597 0.317 0.174 0.514 0.322 0.198 0.507 0.327 0.223 0.574 0.331 0.248 0.564 0.336 0.272 0.590 0.341 0.297 0.509 0.351 0.347 0.405 0.355 0.372 0.417 0.360 0.398 0.497 0.365 0.422 0.423 0.370 0.447 0.438 0.375 0.472 0.433 0.380 0.497 0.407 0.384 0.521 0.359 0.389 0.547 0.438 0.394 0.572 0.425 0.399 0.597 0.482 0.404 0.622 0.468 0.409 0.647 0.501 0.414 0.672 0.511 0.419 0.699 0.470 0.424 0.724 0.501 0.428 0.749 0.509
list of CCD Photometry of DQ Her in I filter.JD 2457624+ phase v-c 0.222 0.683 0.504 0.232 0.735 0.537 0.237 0.759 0.528 0.242 0.784 0.496 0.246 0.809 0.556 0.251 0.833 0.610 0.256 0.858 0.689 0.261 0.883 0.984 0.266 0.908 1.556 0.270 0.933 2.246 0.275 0.958 2.203 0.280 0.983 1.570 0.285 0.008 1.104 0.290 0.033 0.866 0.295 0.057 0.748 0.299 0.083 0.636 0.304 0.107 0.599 0.309 0.132 0.643 0.314 0.157 0.619 0.319 0.182 0.551 0.323 0.206 0.575 0.328 0.231 0.603 0.333 0.256 0.609 0.338 0.281 0.614 0.343 0.306 0.487 0.347 0.330 0.523 0.352 0.356 0.447 0.357 0.380 0.503 0.362 0.406 0.517 0.367 0.430 0.511 0.372 0.455 0.491 0.376 0.480 0.461 0.381 0.505 0.472 0.386 0.529 0.429 0.391 0.556 0.485 0.396 0.580 0.476 0.401 0.605 0.505 0.405 0.630 0.490 0.410 0.655 0.556 0.415 0.680 0.520 0.420 0.708 0.545 0.425 0.732 0.551 0.430 0.757 0.548
The most obvious spectral lines features are seen in the spectra of the system: The high ionized C IV emission line at 1550 Å is a resonance doublet emission line, while He II 1640 Å is a recombination line, previously discussed by (Howell et al. [13]). These spectral lines are produced in the accretion curtain region as suggested by Bloemen et al. [2].
Figs. 8 and 9 reveal the spectral behavior of line fluxes with orbital phase for the C IV and He II, emission lines for DQ Her. The fluxes of spectral lines vary with orbital phases between high, intermediate and low values on short time scale of some hours and long time scale of some years. The behavior of C IV and H II line fluxes with orbital phase for DQ Her. The behavior are noted for DQ Her, since the line fluxes of C IV are the more intense one over the whole phases. Highly ionized C IV is vary by a factor of 4, while the fluxes of He II vary by a factor of 2. The maximum line fluxes of C IV and He II for DQ Her obviously seen around phase (0.1,0.85) while reached its least values around the orbital phase (0.3,1.0).
In this paper, we can explain the spectral variations in IUE and HST observations as shown in the figures (8& 9) by the following physical mechanisms. The emission lines of the intermediate polars (DQ Her) originated in the accretion curtain region. The high energy photons in the emitting region produce the ultraviolet emission lines seen in this system. In this view, we can refer the luminosity of DQ Her to be correlated to the rate of its mass transfer and the origin of the ultraviolet spectral lines to the accretion curtain region. So as the rate of mass transfer increases, the gravitational potential energy increases, and this will lead to an increase in the temperature and consequently in the strength of ultraviolet spectral lines. The accretion curtain model for intermediate polars, Kim & Beuermann [15], Hellier et al. [10] and Buckley & Tuohy [3] support the results of current IUE & HST data as due an evidence of magnetically controlled accretion curtains near the white dwarf. The model described well the present spectral fluxes behavior of IUE and HST data for this system. In this model the emission lines seem to be originated in the region where the strength of the magnetic field prohibit the formation of the disk.
As shown from the fig our photometric observations almost covered the whole period of variations of DQ Her. The photometric variation of DQ Her revealed that the system is an eclipsing binary and the binary DQ Her shows variability with orbital period of ~4.6 hours caused by rotation of the white dwarf and the radiation emitted by the two magnetic poles. We see that light reprocessed through the accretion disk because we see the disk edge-on, and the white dwarf itself is obscured.
Fig. 6 represents all photometric observations collected through ~ 17 years at data base of the American Association of Variable Stars Observers (AAVSO). Different characteristic features of DQ Her variations, i.e., burst, super-burst, quiescent and narrow-burst can be detected well through Fig. 7 which shows the phase diagram of all observations for DQ Her. In both figures, the KAO photometry is in red.
For DQ Her, we used the integrated fluxes of emission lines C IV 1550 Å and He II 1640 Å, and equation (2), we obtained the variable ultraviolet luminosities for this spectral lines, it tabulated in Tables 7 and 8 using a mean distance value 400 pc, derived by Horne et al. [12].
Ultraviolet luminosities and accretion rate for the spectral line C IV (1550Å).State Flux High 4.09 × 10−12 (erg 3.95× 1031(erg 4.5× 1014(g 7.17× 10−12 Intermediate 1.3×10−12(erg 1.3×1031(erg 1.44×1014(g 2.29×10−12 Low 5.3×10−13(erg 5.13×1030(erg 5.85×1013(g 9.32×10−13
Ultraviolet luminosities and accretion rate for the spectral line He II (1640Å).State Flux High 4.32×10−13(erg 4.18×1030(erg 4.8×1013(g 7.65×10−13 Intermediate 2.8×10−13(erg 2.7×1030(erg 3.08×1013(g 4.91×10−13 Low 1.98×10−13(erg 1.9×1030(erg 2.18×1013(g 3.47×10−13
For a white dwarf with
Where
We report the results of the photometric and spectroscopic behavior of DQ Her. The photometric analysis of DQ Her is performed using the CCD photometry of KAO and that collected over long time through AAVSO data base. The main results for the system can be summarized as:
Photometry of DQ Her revealed that the system is an eclipsing binary with high inclination deg. KAO photometry and that collected from AAVSO are obviously comparable. The light variation reveal very deep primary minimum (where, main sequence component lie in front of the white dwarf) 17.7 mag., no secondary minima has been detected due to the dominant flux of the massive component. The intermediate Polar system DQ Herculis, in which the white dwarf is gravitationally stripped the matter from the main-sequence companion star and forms an accretion disk around the white dwarf and the inner disk region is truncated by the magnetic field of the white dwarf. In the region where the disk is truncated, the gas in the disk begins to transfer along the white dwarf’s magnetic field lines, forming curved sheets of luminous material called accretion curtains. Disk material passes through the curtains and then accretes onto the white dwarf near one of its magnetic poles. The study revealed the presence of periodic and/or semi-periodic changes in the brightness of this system. One periodicity is related to the orbital period of the binary star system. A second periodic signal originates from the rotation of the white dwarf spinning on its axis and it is shorter than the orbital period. The observational characteristic that clearly defines this system is the existence of more than one overlap period which appear in general as irregular variables. The physical cause of optical spin period oscillations may be attributed to the changing viewing aspect of the accretion curtain as it converges near the white dwarf. Identification of emission lines in the spectral region 1150 Å - 1950 Å with detailed description of continuum and profiles. There are variations in the ultraviolet luminosities and the mass accretion rates. There are modulations in line fluxes for all studied emission lines (C IV and He II), we attributed these variations to the variations of the rate of mass transfer from the secondary star to the white dwarf leading to variation in temperature and consequently to the variations in the intensities of emission lines. The variations in both ultraviolet luminosities and the mass accretion rates in this system can be interpreted in terms of the accretion curtain model.