Photometric and Spectroscopic Studies of the Intermediate -Polar Cataclysmic System DQ Her

The IUE low-resolution short wavelength spectra have been obtained from the INES (IUE Newly Extracted Spectra) site

http://ines.vilspa.esa.es.

Table 1

List of IUE observations for DQ Her.

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

http://archive.stsci.edu.

HJD=2434954.94423 + 0.193620873 × E$$\begin{array}{} \displaystyle HJD = 2434954.94423~+~0.193620873~\times~E \end{array}$$(1)

Table 2

List of HST observations for DQ Her.

Fig. 1

Fig. 2

Fig. 3

The CCD photometric observations of the target stars selected for the study are obtained using 2k × 2k CCD camera attached to Newtonian focus of the 74 inch reflecting Telescope at Kottamia Astronomical Observatory (KAO), Cairo, Egypt. The CCD camera has a set of photometric filters (UBVRI). For DQ Her we obtained photometry in VRI filters.

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).

Table 3

List of the comparison and the check of DQ Her.

Table 4

list of CCD Photometry of DQ Her in V filter.

Table 5

list of CCD Photometry of DQ Her in R filter.

Table 6

list of CCD Photometry of DQ Her in I filter.

Fig. 4

Fig. 5

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).

Fig. 6

Fig. 7

Fig. 8

Fig. 9

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].

LUV=2πFd2$$\begin{array}{} \displaystyle L_{UV} = 2\pi F d^2 \end{array}$$(2)

Table 7

Ultraviolet luminosities and accretion rate for the spectral line C IV (1550Å).

Table 8

Ultraviolet luminosities and accretion rate for the spectral line He II (1640Å).

For a white dwarf with M_wd = 0.6M_⊙ Horne et al. [12]. The radius of white dwarf R_WD = 8.6 × 10⁸cm is calculated by using the equation (3), while the mass accretion rates are calculated by using the equation (4).

RWD=0.78×109[(1.44M⊙MWD)2/3−(MWD1.44M⊙)2/3]1/2$$\begin{array}{} \displaystyle R_{WD} = 0.78 \times 10^9 [(\frac{1.44M_\odot}{M_{WD}})^{2/3}-(\frac{M_{WD}}{1.44M_\odot})^{2/3}]^{1/2} \end{array}$$(3)

M˙=LaccRaGMa$$\begin{array}{} \displaystyle \dot{M} = \frac{L_{acc}R_a}{GM_a} \end{array}$$(4)

Where M_a, R_a are the mass and radius of the accreting star, L_acc is the accretion luminosity, and G is the gravitational constant.