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Optical Photometry of Dwarf Nova QZ Serpentis in Quiescence

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Optical Photometry of Dwarf Nova QZ Serpentis in Quiescence Optical Photometry of Dwarf Nova QZ Serpentis in Quiescence Erica D. Jones Center for Astrophysics, Space Physics and Engineering Research at Baylor University Dr. Dwight Russell Department of Physics at Baylor University Richard Campbell Department of Mechanical Engineering at Baylor University Abstract—We present quiescent photometry of dwarf nova QZ Serpentis. Given the limited amount of published information These binary systems are known to have periods of on this object, we present photometry at different wavelengths quiescence, outbursts, and superoutbursts. In quiescence, and comment on the spectral class. We collect data in four SS Cygni has an average magnitude of 11.2; however, in filters, BVRI, and calibrate data using bias subtraction, dark outburst, there is a reported magnitude of 9 [4]. Dwarf subtraction, and flat division. We also use multiple aperture photometry in the AstroImageJ software to obtain the novae also exhibit larger changes in magnitude during brightness of our target object and our comparator star. We outburst. An example of this is dwarf nova V725 Aquilae. calculate the average magnitude for QZ Serpentis in each With an outburst magnitude of 13.7 and a quiescent filter. We present light curves and folded light curves for each magnitude of 19.32, the object increases over 100 times in observing run. We use differential photometry to yield an brightness [5]. average R magnitude of 17.399 ± 0.007 and B-V = 0.747 ± 0.030. We report a secondary spectral class ranging from an The dwarf nova QZ Serpentis was discovered in 1998 by early G-type star to an early K-type star. Light curves exhibit Katsumi Haseda [6]. QZ Ser is located at right ascension sinusoidal features, which is typical of contact binaries. Our 15h56m54.47s and declination 21˚07’19.0”. QZ Ser has an findings are consistent with previously published data. orbital period, Porb, of 0.08316 days or 119.752 minutes [6]. Keywords—dwarf novae, accretion disk, cataclysmic variables, Thorstensen et. al (2002) report a the magnitude of the variable star photometry secondary star as V = 17.9 ± 0.4 [6]. I. INTRODUCTION In this paper, we present optical photometry of QZ Ser in the BVR and I filters. We discuss observing runs, data ATACLYSMIC variables (CVs) are close binary star calibration techniques, data analysis, and light curve C systems divided into subcategories based on features. The majority of the data were collected using the frequencies and amplitudes of luminosity variations [1]. R filter. We create folded light curves using the orbital These categories are novalike variables (NL), novae (N), period, Porb = 0.08316 days, and T0 = 2452328.044 HJD recurrent novae (RN), and dwarf novae. The CV of interest published in [6] in order to analyze the features of QZ Ser in this paper is the dwarf nova. based on the position, or phase, of the binary. II. METHODOLOGY Dwarf novae are close binaries with a “late-type main sequence” secondary star that fills its Roche lobe, transferring material through the Langrangian point L1, “the We collected data on 6 nights at the Paul and Jane Meyer inner Lagrangian point” [2]. This transfer of material forms Observatory using the 0.6 m Ritchey-Chretien telescope. an accretion disk around the white dwarf primary star [2]. Throughout the various observing runs, data were collected These objects exhibit interesting effects due to the presence in four filters: BVRI. On June 10, 2013, we collected 10 of an accretion disk, and various theories exists to explain exposures in the V filter with 60 s exposure time. Similar these effects observed in dwarf novae. Theories such as data were collected the next night in the I filter. change in mass-transfer rate and disk instability, offer explanations for effects observed when studying dwarf Data in the R filter were collected on both June 13, 2013 novae [3]. and June 14, 2013. On the second night, we were able to NSF CASPER RET 2013 – E. Jones observe QZ Ser over one complete orbital period. We collected data in three filters (BVR) on the night of June 19, To plot the data, we used an IDL program. The IDL 2013. One July 9, 2013, we observed two full orbital program uses the HJD to calculate the phase of an object. periods of QZ Ser in the R band filter using 60 second As mentioned in the introduction, we use an orbital period, exposures. More details of the observing runs are included Porb, of 0.08316 days and a T0 of 2452328.044 HJD. These in Table I. values were reported in [6]. The phase was calculated based on this initial time correlating to a phase of 0.0 and this orbital period. The HJD of each data point was user to TABLE I. calculate the phase of QZ Ser at that time, with phase OBSERVATION LOG FOR QZ SER ranging from 0.0 to 1.0. We used an IDL program to convert the Julian date (JD) to the heliocentric Julian date UT Start Time UT End Time # of Exposures UT Date (HJD). (first exposure) (last exposure) /Filter (exptime) 2013 June 10 07:09:33 07:35:14 10/V(60s) By converting to HJD, we take into account the motion of the Earth around the sun and its effect on the movement 2013 June 11 04:21:11 04:52:40 10/I(60 s) towards or away from the object, depending on the right 2013 June 13 03:57:45 04:08:22 11/R(60 s) ascension and declination of the object. “In order to determine the HJD, astronomers must consider the time it 2013 June 14 04:39:44 06:57:43 130/R(60 s) would take light to travel from a celestial object to the 6/V(90 s) 2013 June 19 03:24:41 03:51:15 center of the Sun rather than to the Earth” [7]. This 6/R(90 s) calculation provides a reference for the amount of time it 16/B(180 s) 2013 June 19 03:38:32 05:58:06 16/V(120 s) takes light to reach one point, regardless of the motion of 16/R(120 s) the Earth. 2013 July 9 03:48:08 08:01:59 240/R(60 s) We also use phased average binning to calculate the mean magnitude at a phase step of 0.05, and we calculated the error using the standard deviation of the mean. The data were calibrated using the AstroImageJ software. AstroImageJ software outputs a flux error for the flux Bias frames, darks frames, and flat fields were median measurement of both the target and the comparator star. combined to create masters using the software. The master The flux measurements are converted to magnitude and dark with the same exposure time as the flats was subtracted magnitude error. The average magnitude of QZ Ser in each from all flats before the master flat using the appropriate filter is calculated using the average of the magnitude filter was created. Images were bias subtracted, dark measurements and error of this average is calculated using subtracted, and flat divided. The CCD was kept at -35˚ C traditional error analysis on the sum of values in the for all exposures. numerator of the average and on the constant in the denominator. Multi-aperture photometry was completed using the AstroImageJ software. Photometry was measured for the target, QZ Ser, and various comparator stars in the field of III. LIGHT CURVES view. Comparator star 4, or C4 as shown in Figure 1, was used for differential photometry. In this section we present light curves from each observing run. Figures 2 through 11 contain a light curve with magnitude versus time in the upper panel and magnitude versus phase in the lower panel. The lower panel of Figures 2-11 shows the changes in the brightness of QZ Ser over two periods, with data from one period repeated for continuity. The light curve in Figure 10 contains data collected using the B filter. The brightness of QZ Ser in the B magnitude ranges from 19.2 to 18.0 within error bars. Figures 2, 6, and 8, represent the brightness of QZ Ser in the V filter. The V magnitude ranges from 18.2 to 17.4, including error bars. The R magnitude ranges from 17.6 to 17.1 in Figures 4, 7, 9, and 1l. Figure 5 shows the R magnitude ranging from 18.0 to 16.8. In the I filter, the magnitude of QZ Ser Figure 1. Finding chart of QZ Ser based on data taken in the R band Filter (60 s exposure) including the target and various ranges from 17.2 to 16.9 (Figure 3). The brightness of QZ comparator stars. The filter of view is with north at the Ser appears to increase at redder wavelengths. bottom and east to the left. NSF CASPER RET 2013 – E. Jones Figure 4. Upper panel – light curve of data set collect 2013 June 13. Figure 2. Upper panel – light curve of data set collect 2013 June 10. Data were collected using the R filter. Lower panel – Data were collected using the V filter. Lower panel – folded light curve of the same data plotted twice to view folded light curve of the same data plotted twice to view over two periods. over two periods. Figure 3. Upper panel – light curve of data set collect 2013 June 11. Figure 5. Upper panel – light curve of data set collect 2013 June 14. Data were collected using the I filter. Lower panel – Data were collected using the R filter.
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