A survey of extended matter around chromospherically active binary systems

Abstract

We present an analysis of colour excess (CE) observations for 13 chromospherically active binary systems, together with 27 inactive reference stars of similar spectral types and luminosity classes of the components of these 13 binaries. We used the observations which were made by Johnson-Cousins ${BVR}_{c}\mathrm{I}_{c}$ , 2MASS, and WISE photometric systems. Our new photometric ${BVR}_{c}\mathrm{I}_{c}$ observations were obtained by means of 1 m telescope at TÜBİTAK National Observatory and 40 cm telescope at Ankara University Kreiken Observatory. To check the existence of extended matter around an active binary component(s) of these 13 binary systems, we examined the CE values at around primary/secondary minima and outside eclipses. The comparison of these CEs, obtained relative to those of reference stars of the same ${(B-V)_\circ}$ colours, especially during primary minima with those of secondary minima and outside eclipses, showed that these systems have greater excess radiation in primary minima than in both secondary minima and outside eclipses. We observed that the colour excesses, in general, most likely arise from the extended matter around the cooler component of a binary system. The comparison of CE values also showed that the extended matter of some of these systems was most likely covered or affected both of their components. Since no observational data were obtained during primary minimum of RW UMa, by excluding this binary system, an examination of the locations of cool and active components of the remaining 12 systems of this study on Hertzsprung-Russell diagram, together with corresponding evolutionary tracks, showed that most of the active binary systems have an extended matter not only caused from stellar activity but also more likely caused from evolutionary processes.

1. Introduction

Chromospherically active binaries (CABs) are detached binary systems with cool components characterised by strong chromospheric, transition region, and coronal activity. Phenomena of the chromospheric activity are seen mostly in late-type stars, including RS CVn binaries and BY Dra variables. The current catalogue of CABs, as a third edition, was given by Eker et al. (2008). The RS CVn binaries have at least one cool evolved component, whereas both components of the BY Dra binaries are main sequence stars. Fekel, Moffet, & Henry (1986) indicate that chromospherically active stars have colour excesses (CEs) in ${(V-R)}$ and in ${(V-I)}$ by using their photometric observations of 52 late-type stars.

A survey for extended matter has been presented by Hall & Ramsey (1992) to determine the frequency and nature of circumstellar matter in these CABs. Hall & Ramsey (1992) have detected large regions of extended, prominence-like material, which has been shown to be a common feature in these systems. Extended material in the CABs is difficult to detect in emission, but if the same extended region occurs in an eclipsing star, it may obscure a large fraction of the eclipsed star’s disk at phases near the outer contact points of the light curve and may produce a significant absorption feature in the spectrum. When an extended region projected against the star disk appeared through the line of sight of an observer at a phase near the outer contact, some excess emission/absorption features may be discoverable. That is, such an extended region is more easily detected at a phase near the outer contact case (for well-illustrated figures, see Hall & Ramsey 1992, 1994). Although RS CVn- and BY Dra-type binaries were incorporated into a group after 1990s as CABs (see Strassmeier et al. 1988), which are a common group name for both RS CVn- and BY Dra-type stars, we also see that some BY Dra-type binaries exhibit similar IR excess, in infrared astronomical satellite (IRAS) bands, to those of RS CVn binaries (see Chugainov & Lovkaya 1989).

Busso et al. (1990) have studied the infrared (IR) emission of active binaries and they concluded that about 40% of RS CVn-type binary systems, studied up until then, exhibit IR excess. They also discussed the presence of thin circumstellar shells together with the evolutionary status of the binary components to give a possible explanation for this excess emission.

Montes et al. (1996) emphasised that ‘The high levels of activity observed in the chromospherically active stars are generally attributed to the presence of deep convection zones and the fast rotation that drives the dynamo mechanism’. As a component of CABs, the stars are usually forced to rotate relatively rapidly due to tidal interactions and typically the rotation period is synchronised with the orbital period of the binary system (Montes et al. 1996).

Scaltriti et al. (1993) have analysed the energy distributions of 12 RS CVn-type binaries and they also confirmed that the circumstellar matter around CABs is clearly present. They also evaluated the mass of absorbing material which is supposed to be in the form of silicate grains. They suggested that the circumstellar envelopes are built by the integrated mass loss, which is fed by stellar winds driven by magnetic activity. By comparing the IR excess of the sources in these 12 binary systems, they speculated that the circumstellar envelopes are related to stellar activity phenomena of the RS CVn-type binary systems. The stellar activity definition based on photospheric, chromospheric, and coronal phenomena was given in detail by Rodonó (1980).

Assessments of the roots of the disk structure around CAB stars began with the IRAS in 1983. IRAS was the first mission to put a telescope in space to survey the All-sky survey at 12, 25, 60, and 100 micron bands.

On the other hand, Busso et al. (1988) also found in their study of RS CVn-type binaries, which is based on IRAS observations, that the IR excess is definitely present in CF Tuc, while the spectral distributions of the $\lambda$ And, UX Ari, and AR Lac can be accounted for. They also concluded that the excess is not correlated with the activity level, nor with the evolutionary status, but may be correlated with the mass-loss phenomena (triggered by the binary nature?) near the Main Sequence (see Busso et al. 1988).

The aim of this study is to put forward the characteristics of the extended/circumstellar matter, that may be present in CAB systems, and then to search the relation between this matter and evolutionary status of the component stars, depending on stellar activity, by examining the locations of cooler components of CABs on the Hertzsprung-Russell (HR) diagram, with corresponding evolutionary tracks. Because the spectral types of the components of CABs are between (F2 IV-G V-IV) and M2 V (see Strassmeier et al. 1988; Eker et al. 2008). Therefore, the search of the activity level/IR excess (and therefore the investigation of extended/circumstellar matter), depending on the location of the components of CABs on the HR diagram, together with corresponding evolutionary tracks, may reveal an observational evidence that may be associated/correlated with evolution. Expectations of the presence of extended/circumstellar matter in CABs, as it can be seen from the summarisation of studies given above, can be based on the observational results that were previously found and listed below:

1. – presence of excess radiation at UV and IR spectral regions (e.g. Rhombs & Fix 1977; Busso et al. 1990; Scaltriti 1990; Scaltriti et al. 1993; Ekmekçi 2010),

2. – presence of flares (e.g. Simon, Linsky, & Schiffer 1980; Brown & Brown 2006),

3. – polarisation and radio observations (e.g. Mutel & Weisberg 1978; Mutel et al. 1987),

4. – IRAS observations (e.g. Busso et al. 1988; Mitrou et al. 1996).

That is, the detection of CEs, especially in IR spectral regions, clearly suggests that there is circumstellar material in the system (e.g. Scaltriti et al. 1993). The excess radiation at the UV spectral region provides observational evidence of stellar activity, while excess radiation at the IR spectral region provides observational evidence of extended/circumstellar matter. The other method to determine the existence of an extended/circumstellar matter in a binary system is to compare the spectral energy distribution (SED) of an active system with the SED of a reference star of the same ${(B-V)_\circ}$ (see Figures 2 and 3).

Table 1. List of programme stars selected for this study. CAB numbers were taken from the catalogue given by Eker et al. (2008)

In accordance with this purpose, 13 chromospherically active and total eclipsing binary systems, listed in Table 1, were selected and their photometric BVR $_{c}\textit{I}_{c}$ observations were made at TÜBİTAK National Observatory (TUG) and Ankara University Kreiken Observatory (AUKR) during the period 2012–2014. The Two Micron All-Sky Survey (2MASS) and Wide-field Infrared Survey Explorer (WISE) observations were also included in the photometric data obtained by using the TUG and AUKR telescopes. To search the CEs for these 13 eclipsing binaries, 27 single stars of the same spectral types and of the same luminosity classes with those of the components of these 13 binary systems were also included in the observation schedules. These 27 stars, used as reference stars in this study, are listed in Table 2. The observational results are presented below in Section 2.1.

2. Observations and data reductions

2.1. Photometric observations

We selected 13 chromospherically active and total eclipsing binary systems as programme stars. In addition, several inactive stars, as reference stars, of similar spectral types and luminosity classes with those of the components of these binary systems have also been observed. With the aim of investigation of photometric characteristics/effects of any extended matter around component(s) of these active binaries, we attempted to make BVR $_{c}\textit{I}_{c}$ observations during minima and outside eclipses.

Photometric observations of all stars, listed in Tables 1 and 2, in the Johnson-Cousins BVR $_{c}\textit{I}_{c}$ photometric system were obtained at TUGa 1 m (T100) telescope at Bakrltepe, Antalya, in Turkey and at AUKRb 40 cm (T40) telescope at Ankara, in Turkey from 2012 July to the end of 2014 August. Properties of photometric bands used in this study are given in Table 3. The log of observations is given in Tables 4 and 5. The reduction of the CCD frames has been performed with aperture photometry using standard packages of IRAFc.

Table 2. List of reference stars (inactive stars)

Table 3. Properties of photometric bands used in this study

The instrumental setup of the T100 telescope system of TUG contains an ACE RC 1.0, 1 m aperture Ritchey-Chretien telescope, SI 1100, 4K X 4K CCD camera, and Bessel BVRI filter set. The instrumental setup of the T40 telescope system of AUKR contains a MEADE LX200-GPS $16^{\prime\prime}$ aperture Schmidt-Cassegrain reflecting telescope, an APOGEE ALTA U47-MB 1024 X 1024 13 $\mu$ m pixels CCD camera, and Schüler Johnson-Cousins BVRI filter set.

Instrumental magnitudes were used to obtain the magnitudes outside of the atmosphere by using the first-order extinction coefficients for all observed nights. The average second-order extinction coefficients were derived from the calculations of the T100 telescope by Ak (2013) and of the T40 telescope by Karakuş & Ekmekçi (2017). Also, the instrumental magnitudes and colours were transformed to standard photometric systems by using the calibration coefficients of T100 and T40 telescopes given by Ak (2013) and Karakuş & Ekmekçi (2017), respectively. In order to estimate the nightly photometric zero points, Landolt’s standard stars (Landolt 2009) were used (see Karakuş & Ekmekçi 2017). First-order extinction coefficients, $k^{\prime}_B$ , $k^{\prime}_V$ , $k^{\prime}_R$ , and $k^{\prime}_I$ , have the average values of $0.337\pm0.119$ , $0.209\pm0.088$ , $0.152\pm0.069,$ and $0.101\pm0.053$ mag (obtained from 17 nights) for observations made at TUG and $0.413\pm0.110$ , $0.239\pm0.075$ , $0.174\pm0.066,$ and $0.107\pm0.057$ mag (obtained from 43 observation nights) for observations made at AUKR, respectively.

The light elements used in this study for each binary system were taken from the website of TIDAK (TIming DAtabase at Krakow) d. For all 13 active binary systems of this study, the zero phase corresponds to conjunction with the cooler component in front.

2.2. 2MASS and WISE observations

2MASSe has covered the whole sky observations (see Skrutskie et al. 2006) in the bands J(1.25 $\mu$ m), H(1.65 $\mu$ m), and Ks (2.17 $\mu$ m). The observational 2MASS data of all stars used in this study were taken from the All-Sky Point Source Catalog. The 2MASS data of 13 binaries and reference stars of this study, listed in Tables A.1 and A.2, have been obtained during the period 1997–2000. We were able to detect that only one scan was made for each of these stars during 2MASS observations.

The WISEf (see Wright et al. 2010) is a NASA mission that has mapped the sky which has four IR bands: W1 (3.4 $\mu$ m) , W2 (4.6 $\mu$ m), W3 (12 $\mu$ m), and W4 (22 $\mu$ m). Photometric data of reference stars and programme stars, obtained with these bands of WISE, were taken from All WISE Source Catalogue and All WISE Multiepoch Photometry Catalogue, respectively. WISE is achieving a sensitivity more than 100 times better than IRAS in the 12 $\mu$ m band. All WISE data used in this study were obtained between 2010 January 7 and 2010 July 16 with a cryogenically cooled telescope.

Our photometric CCD observations were also evaluated together with the observations of multiepoch IR photometry of WISE of these 13 programme stars by using all data depending on orbital phases. Thus, this study gave the first combination results with the multiepoch photometric data for these 13 chromospherically active and total eclipse binary stars.

Table 4. Log of CCD observations of chromospherically active binaries

Table 5. Log of CCD observations of reference (inactive) stars

2.3. De-reddening of magnitudes and the evaluation of colours

The interstellar medium has the effect of emission and absorption on the light of a star. This effect varies depending on the distances and galactic position of a star. The total interstellar absorption, $A_\infty(b)$ , depending on BVR $_{c}\textit{I}_{c}$ bands could be estimated by using NED serviceg (see Schlafly & Finkbeiner 2011). By using the equation given by Bahcall & Soneira (1980), as written below, the total absorption at an infinite distance [ $A_\infty(b)$ ] was reduced to the $A_d(b)$ absorption of the star at distance d:

(1) \begin{equation}A_d(b)= A_\infty(b)\left[1-exp\left(\frac{-\mid d \sin(b)\mid}{H}\right)\right].\end{equation}

Here, b and d are galactic latitude and distance of the star, respectively. H is the scale height for the interstellar dust. In this study, the value of H was adopted as 125 pc as considered in Marshall et al. (2006) and the distances of stars are obtained from Gaia hData Release 2 (GAIA DR2).

Figure 1. Three sample colour-colour graphs of linear correlation fits (straight lines) of reference stars, in $(V-R)$ (top panel), in $(V-I)$ (middle panel), and in $(R-I)$ (bottom panel). The colour-colour positions of programme star, SS Boo, at the primary minimum phases, were added to these diagrams as an explanation of the method we used for estimating their CE values. Reference stars of giant (III) are indicated as blue, of subgiants (IV) as green, and the main sequence stars (V) as red points, while programme star, SS Boo, is indicated black. Colours are in magnitudes.

Thus, the related $A_d(b)$ values for each star were calculated by using Equation (1), as given above. Also, in order to determine total absorptions ( $A_v$ values) in the bands of BVR $_{c}\textit{I}_{c}$ , 2MASS, and WISE photometric systems, we used the relations given by Cardelli, Clayton, & Mathis (1989).

After these reduction procedures, the colour-colour diagrams of programme stars at the primary minimum phases were obtained, and then the evaluations of these colours, together with the lines of linear correlation fits of reference stars, were obtained as shown in Figure 1. By applying the regression analysis to photometric CCD data of reference stars, we have the linear coefficients of colour-colour relations (as $y = a + b x$ ) as follows:

(2) \begin{equation}\begin{array}{lcl}(V-R)_\circ =0.034[\!\pm0.015] + 0.487[\!\pm0.018](B-V)_\circ\\[2pt] \quad \mathrm{with}\ r^2=0.967;\ \sigma_{CE(V-R)}=0.026,\end{array}\end{equation}

(3) \begin{equation}\begin{array}{lcl}(V-I)_\circ = 0.089[\!\pm0.027] + 0.888[\!\pm0.031](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.970;\ \sigma_{CE(V-I)}=0.045,\end{array}\end{equation}

(4) \begin{equation}\begin{array}{lcl}(R-I)_\circ = 0.053[\!\pm0.014] + 0.404[\!\pm0.016](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.961;\ \sigma_{CE(R-I)}=0.024,\end{array}\end{equation}

(5) \begin{equation}\begin{array}{lcl}(V-J)_\circ = 0.168[\!\pm0.033] + 1.599[\!\pm0.038](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.986;\ \sigma_{CE(V-J)}=0.055,\end{array}\end{equation}

(6) \begin{equation}\begin{array}{lcl}(V-H)_\circ = 0.134[\!\pm0.044] + 2.118[\!\pm0.049](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.986;\ \sigma_{CE(V-H)}=0.072,\end{array}\end{equation}

(7) \begin{equation}\begin{array}{lcl}(V-Ks)_\circ = 0.128[\!\pm0.044] + 2.244[\!\pm0.051](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.987;\ \sigma_{CE(V-Ks)}=0.073,\end{array}\end{equation}

(8) \begin{equation}\begin{array}{lcl}(V-W1)_\circ = 0.177[\!\pm0.049] + 2.256[\!\pm0.057](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.984;\ \sigma_{CE(V-W1)}=0.082,\end{array}\end{equation}

(9) \begin{equation}\begin{array}{lcl}(V-W2)_\circ = 0.108[\!\pm0.057] + 2.301[\!\pm0.066](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.979;\ \sigma_{CE(V-W2)}=0.095,\end{array}\end{equation}

(10) \begin{equation}\begin{array}{lcl}(V-W3)_\circ = 0.109[\!\pm0.047] + 2.290[\!\pm0.054](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.986;\ \sigma_{CE(V-W3)}=0.077,\end{array}\end{equation}

(11) \begin{equation}\begin{array}{lcl}(V-W4)_\circ = 0.109[\!\pm0.073] + 2.361[\!\pm0.085](B-V)_\circ\\[2pt] \quad\mathrm{with}\ r^2=0.969;\ \sigma_{CE(V-W4)}=0.122.\end{array}\end{equation}

The colour versus ${(B-V)_\circ}$ diagrams obtained by using corresponding reference stars are constructed to determine the CE of programme stars. To find CE values of 13 binary systems of this study, we use the differences between the colours of binary stars and the colours obtained from colour-colour relations (Equations 2–11) with corresponding ${(B-V)_\circ}$ values (see Figures 1 and A.1). The rms values of related regression analysis were taken into consideration in the estimation of each CE value. The errors of CE magnitudes, as a measure of precision, were obtained by considering all absolute errors (i.e. nightly rms errors of each band observations and errors of parallaxes of stars from updated Gaia observations) in the relative error estimations. The CE values of the programme stars, as a function of orbital phase, are shown in Figures A.2, A.3, A.4, A.5, A.6, A.7, A.8, A.9, A.10, A.11, A.12, A.13, and A.14. The final photometric data of all stars are listed in Tables A.1 and A.2.

The normalised SEDs from visual-, near-, and mid-IR photometric data obtained during primary minima of some active binary systems (e.g. SS Boo and UX Com) were compared with SEDs of reference stars of the same ${(B-V)_\circ}$ (by using the approximation of a black body radiation) to reveal the excess (or residual) radiations in these systems (see Figures 2 and 3).

We have also reviewed the spectral types and luminosity classes for all selected stars using our photometric ${(B-V)_\circ}$ results. The spectral types which correspond to our ${(B-V)_\circ}$ results were attained from Sung et al. (2013) (see also column 3 of Table 2). Luminosity classes of these stars were determined by using the equation of $M_v$ as

(12) \begin{equation}M_{v} =V_{o} - 5 log (d) +5 + A_{d}(b),\end{equation}

where d is Gaia 2 distance of the star in parsecs. By using these values of $M_v$ , the evolutionary status of all programme and reference stars is examined together with their positions on the HR diagram as shown in Figure A.17.

Figure 2. Comparison of SEDs of SS Boo and reference star HD 111094. The photometric values of HD 111094 [ ${(B-V)_\circ} = 0.98\pm 0.01$ ] are indicated as red points, while the values of SS Boo [ ${(B-V)_\circ} = 0.96 \pm 0.02$ ], during 0.0P, are indicated as blue points. The straight line shows the black body energy distribution of $T (K) = 4\,900$ .

Figure 3. Comparison of SEDs of UX Com and reference star BD+54 2777. The photometric values of BD+54 2777 [ ${(B-V)_\circ} =1.05 \pm 0.012$ ] are indicated as red points, while the values of UX Com [ ${(B-V)_\circ} = 1.04 \pm 0.04$ ], during 0.0P, are indicated as blue points. The straight line shows the black body energy distribution of $T (K) = 4\,700$ .

2.4. CE as a function of wavelength

We also try to present a search for distribution of CE values depending on wavelength (in optical and in 3.4, 4.6, 12, and 22 $\mu$ m bands) during minima and outside eclipses for 13 binary systems. Figure A.15 shows the CE of 13 programme stars of this study in all bands obtained during minima and outside eclipses. And, Figure A.16 shows the distributions of excesses as a function of ${(B-V)_{o}}$ for 13 programme stars together with related regression lines, during primary minima. During primary minima, these regression lines have slopes of

1. $0.09\pm0.04$ in ${CE(V-R)}$ versus ${(B-V)_{o}}$ ,

2. $0.19\pm0.15$ in ${CE(V-I)}$ versus ${(B-V)_{o}}$ ,

3. $0.92\pm0.53$ in ${CE(V-W1)}$ versus ${(B-V)_{o}}$ ,

4. $1.12\pm0.36$ in ${CE(V-W2)}$ versus ${(B-V)_{o}}$ ,

   and

5. $0.99\pm0.56$ in ${CE(V-W3)}$ versus ${(B-V)_{o}}$ .

The same trends were seen at secondary minima and at outside eclipses but with lower slopes. These slopes clearly show that the amount of excess radiation of 13 binary systems of this study has greater values towards longer wavelength (from optical to middle IR bands).

The characteristics of achievement results are given in Section 3 and discussed in Section 4.

3. Results

To test the confidence range of the CE values obtained from our observations, we used the rms values given in Equations (2)–(11) in Section 2.3. Also, to check the existence of extended/circumstellar matter of an active binary component(s) of 13 binary systems of this study (see Table 1), we examined the CE values of these systems (see Table A.2) at around 0.0P, 0.25P/0.75P, and 0.5P orbital phases by comparing their colours with those of the same ${(B - V)_{o}}$ reference stars which were used in the regression analysis of colour-colour diagrams (see Figure 1). These CE values were calculated by using the colour differences between the colours of systems and the colours of reference stars of the same ${(B-V)_{o}}$ colours. Corresponding colours of the same ${(B-V)_{o}}$ reference stars were estimated from the regression analysis of colour-colour diagrams. The characteristics of CE results obtained for 13 CAB systems of this study are summarised below (for the total observing nights of each binary system, see Table 4):

LX Per ( $F8V+G8IV-V$ ) was observed for a total of 12 nights between 2012 and 2014. By comparing the colours of the system at around 0.0P and 0.5P with the colours of the same spectral-type reference stars, we determined the CE values as listed in Table A.2. From this table, it can be seen that the CEs of LX Per, at around 0.0P, were increasing towards longer wavelengths. The similar trend was detected at around 0.5P with the increasing CE values towards longer wavelengths. At outside eclipses, around 0.25P or 0.75P, the LX Per binary system has some variations of CE values depending on wavelength.

SV Cam ( $F9V+K4V$ ) was observed for a total of 2 nights in 2012. From Table A.2, it is seen that SV Cam has sudden variations in CE values, at around 0.0P, depending on wavelength. But the CE values of the system, at around 0.5P and at outside eclipses, were increasing towards longer wavelengths.

VV Mon ( $K0IV+G2IV$ ) was observed for a total of 4 nights between 2013 and 2014. VV Mon had sudden variations in CE values, at around 0.0P and at outside eclipses, in optical V,R,I bands. But, in the mid-IR region, CE values of the VV Mon system, at outside eclipses, showed a gradual increase towards longer wavelengths.

GK Hya ( $F8V+G8IV$ ) was observed for a total of 2 nights in 2014. Unfortunately, the observations only included the data of the zero phase of the system. GK Hya had some fluctuations in CE values, at around 0.0P, in all bands (optical V,R,I and mid-IR bands).

RW UMa ( $F9V+K1IV$ ) was observed for a total of 4 nights between 2013 and 2014. Unfortunately, we could not have photometric data at around 0.0P, due to bad weather conditions during observing times. But we obtained the data around 0.5P and at outside eclipse phases of the system. From Table A.2, it can be seen that CE values of RW UMa, at around 0.5P, were increasing towards longer wavelengths. At outside eclipses, the system also had the same characteristics of increasing CE values depending on wavelength.

UX Com ( $G2V+K1III-IV$ ) was observed for a total of 4 nights between 2013 and 2014. UX Com had some remarkable CE values, at around 0.0P, in optical V,R,I bands, whereas the system showed small fluctuations around $\sim$ 0.5 mag in CE values, at around 0.0P, in mid-IR bands. At around 0.5P, the system had some increase in CE values towards longer wavelengths in optical V,R,I bands. No data at outside eclipses of UX Com system were obtained.

RS CVn ( $F4IV+G9IV$ ) was observed for a total of 9 nights between 2012 and 2013. RS CVn had some remarkable fluctuations in CE values, at around 0.0P, in optical V,R,I bands, while at around 0.5P, the system showed some lower fluctuation in CE values in optical V,R,I and mid-IR bands. At outside eclipses, the system also had the same characteristics of increasing CE values depending on wavelength.

SS Boo ( $G0V+K1IV$ ) was observed for a total of 8 nights between 2012 and 2013. The CE values of SS Boo, at around 0.0P, were increasing towards longer wavelengths, while at around 0.5P had some significant increases in CE values towards longer wavelengths in optical V,R,I bands. At outside eclipses, the system had the same characteristics of CE values in mid-IR bands.

PW Her ( $K0IV+F8-G2$ ) was observed for a total of 13 nights between 2012 and 2013. From Table A.2, it can also be seen that CE values of PW Her, at around 0.0P, were increasing towards longer wavelengths in optical V,R,I bands. The similar trend in CE values was detected at around 0.5P in optical V,R,I and mid-IR bands. At outside eclipses, the system also had the same characteristics of increasing CE values depending on wavelength.

AW Her ( $G2IV+K2IV$ ) was observed for a total of 15 nights between 2012 and 2013. AW Her had some detectable CE values, at around 0.0P and 0.5P, in optical V,R,I bands. At outside eclipses, the system also has the same characteristics of increasing CE values depending on wavelength.

RT Lac ( $G9IV+K1IV$ ) was observed for a total of 16 nights between 2012 and 2014. RT Lac had some increase in CE values towards longer wavelengths at around 0.0P, in optical V,R,I bands, while at around 0.5P, the system had some detectable CE values in optical V,R,I and mid-IR bands. At outside eclipses, the system had similar trends in CE variation in optical V,R,I and mid-IR bands. From these CE values (see Table A.2), it is seen that the CE values of the RT Lac system show the variations with the colours at outside eclipses, which are similar to those during both of the minima phases.

AR Lac ( $G2IV+K0IV$ ) was observed for a total of 11 nights between 2012 and 2013. AR Lac had some fluctuations in CE values, at around 0.0P, at all bands used in this study. But the system shows some characteristic variations in CE values towards longer wavelengths at both around 0.5P and outside eclipse phases, while at outside eclipses, AR Lac had lower and some detectable CE values in all bands used in this study.

RT And ( $G0V+K2V$ ) was observed for a total of 7 nights in 2012. RT And had some detectable CE values, at around 0.0P and 0.5P in all bands used in this study. At outside eclipses, the system had similar characteristics in CE values obtained from all bands used in this study.

4. Discussion and conclusions

For the purpose of this study, our BVR $_{c}\textit{I}_{c}$ photometric CCD observation data were obtained only during minima and outside eclipse phases of 13 chromospherically active total eclipsing binary systems we selected. Thus, it was attempted to evaluate both the contributions of the components of each binary system and CE measurements of a binary system that contribute to observed CE values, including total contributions of both components as a system. In order to investigate the existence and characteristics of possible extended/circumstellar matter in RS CVn-type binaries, we tried to evaluate our new Johnson-Cousins BVR $_{c}\textit{I}_{c}$ photometric CCD observations together with the near-IR JHK $_{s}$ (2MASS) and mid-IR W1, W2, W3, and W4 (WISE) broadband photometric data of 13 chromospherically active total eclipsing binary systems. By comparing the colour indexes of 13 binary systems with those of corresponding nonactive reference stars, it can be seen that the CEs of these active binary systems (with a constant offset of $\textit{CE} > 0$ mag; see Figures A.2, A.3, A.4, A.5, A.6, A.7, A.8, A.9, A.10, A.11, A.12, A.13, A.14, and A.15) could be attributed to existence and characteristics of possible extended/circumstellar materials located around one or both of the component(s). There are three phenomena that can cause this excess radiation in CAB systems:

1. (i) Existing cool spot(s) on the surface of an active star component,

2. (ii) Existing hot circumstellar gas in the system (e.g. Rhombs & Fix 1977), together with the effects of magnetic fields in the atmospheres of an active star component, and

3. (iii) Presence of a possible circumstellar disk/matter in the active binary system.

The best way to determine which of these phenomena may be in CABs is to find out whether these excess radiations are phase-dependent or not, and whether the excess radiation has variations depending on the phase or not. In addition, the excess radiation to be found by comparing the SED during primary/secondary minima of active binary system, with the SED of a reference star of the same ${(B-V)_{o}}$ , provides evidence of the presence of a circumstellar disk/matter in this active binary system.

For example, an observed CE value of 0.25 mag in ${(V-R)}$ corresponds to an increase in the radiation flux of R band by 20%. This increase in radiation flux at longer wavelengths gives us a larger contribution from a possible extended/circumstellar matter in a binary system (e.g. an observed CE value of about 0.8 mag in ${(V-W3)}$ corresponds to an increase in the radiation flux of W3 band by about 52%). The fact is that the larger CE values in the longer wavelengths of the spectral regions give us more precise observational evidence of the presence of extended/circumstellar matter in a binary system. For each binary system examined in this study, estimations about these flux contribution rates can be made by looking at the graphs given in Figure A.15.

Conclusions can be discussed as follows:

By examining the patterns of LX Per, given in Figure A.2, it can be seen that there may exist a small amount of CE independent of the orbital phase in the LX Per binary system. The comparison of CE levels of the system at about 0.0P with the levels of 0.5P and of the outside eclipses shows that there is some optical excess of about 0.04 mag and some near-IR excess of about 0.25 mag during secondary minimum in the LX Per binary system. Although there was a slight increase in CE values during the secondary minimum, there is almost no variation in CE values of the system, depending on orbital phases (see Figure A.2. Also, the comparison of CE levels in all bands during the minima and outside eclipses (see Figure A.15) shows that there is noticeable excess in the LX Per binary system. On the other hand, LX Per has CE values, at secondary minima phases, about $0.25\pm0.02$ in 2MASS bands and at outside eclipse phases, about $0.29\pm0.03$ in WISE bands (see Table A.2). Therefore, with these characteristics of CE levels, it can be concluded that the source of the excess in LX Per resulted mostly from the cooler component of the system. Hall & Ramsey (1992) denoted that excess emission of the LX Per binary system, obtained from their 1990 spectral observations, could probably have arisen from the chromospheres rather than the circumstellar environment. Our CE results of the LX Per binary system, obtained at all phases, are inconsistent with the results of Hall & Ramsey (1992). Based on the CE values of the LX Per active binary system in 2MASS and WISE bands obtained at all phases, it can be concluded that the extended/circumstellar matter could possibly be present in the system.

SV Cam is a short period, single-lined spectroscopic binary system ( $F9V+K4V$ , $P = 0^{d}.59$ ). The light curve shape of the system has variations as much as 0.1 mag during a month (Kjurkchieva, Marchev, & Ogłoza 2000). Busso et al. (1990) have not detected an IR excess in the SV Cam binary system. This result may correspond to J band data as we found a decrease in the CE value of 0.07 mag in ${(V-J)}$ . Aside from this result, the SV Cam binary system had some significant values of CE at other wavelength ranges. The SV Cam has noticeable CE values of about 0.09 mag in optical spectral ranges (see Figure A.3) and CE values of about 0.1 mag in near-IR spectral ranges (see Table A.2) at about 0.0P. There is also a variation in CE values of SV Cam, depending on orbital phases. From a review of CE values in all bands as shown in Figure A.15, it is also seen that the main contribution to IR excess comes mostly from the cooler component of the SV Cam binary system. Şenavcı et al. (2013) found that the SV Cam shows excess emissions in CaII IR triplet lines through all orbital phases and this excess emission resulted from chromospheric active regions associated with star-spots. When all these features are evaluated together with the graph of SV Cam given in Figure A.15, it is seen that this active binary system may have an extended/circumstellar matter with a small probability.

VV Mon has remarkable CE values of about 0.15 mag in optical spectral ranges at about 0.1P, 0.9P, and 1.0P orbital phases (see Figure A.4). No observation was made in the near- and middle-IR spectral ranges during primary minimum of the VV Mon binary system. Since we could not have observational V,R,I, 2MASS, and WISE data during 0.5P orbital phases, we do not have corresponding CE values of VV Mon taken during a secondary minimum. But we have 2MASS and WISE data taken during outside eclipses for the VV Mon binary system (see Figure A.15). From this 2MASS and WISE data, it can also be seen that there are significant CE values in these bands at the outside eclipses in the VV Mon binary system. Based on the observed characteristic trends of CE values seen in other binary systems of this study (see Figure A.15), it may be inferred that the IR excess comes mainly from the cooler component of the VV Mon binary system. Busso et al. (1990) denoted that there is an IR excess in VV Mon. Together with all these characteristics, it can be seen that there is some certain observational evidence of extended/circumstellar matter in the VV Mon active binary system.

GK Hya has CE values in a low level of about 0.05 mag in the optical spectral ranges between 0.9P and 1.0P orbital phases (see Figure A.5). Unfortunately, we do not have any IR data at other orbital phases from our observations, nor 2MASS/WISE observations. However, an evaluation together with WISE data taken during primary minima of this binary system (see Figure A.15 and Table A.2) shows that the GK Hya binary system may have an IR excess level as low as 0.06 mag in ${V-W3}$ and this excess emission may come mainly from the cooler component of the GK Hya binary system. As can be seen from Figure A.15, there is no observational evidence for the presence of extended/circumstellar matter in the GK Hya active binary system.

Unfortunately, we could not collect any CE data during primary minimum of RW UMa from our observations nor 2MASS/WISE observations. Fortunately, during secondary minimum and outside eclipses of this system, we could take some CE measurements from our observations and 2MASS/WISE observations (see Figure A.6 and Table A.2). From these CE data, obtained at secondary minimum and at outside eclipses, we see that there is some excess emission in the RW UMa binary system in optical spectral ranges with the level of about 0.08 mag. In the near- and middle-IR spectral ranges, the system also has some definite CE values during secondary minimum and outside eclipses, which can be taken into consideration as evidence for excess emission. This excess emission most probably comes from both components of RW UMa ( $F9V+K1IV$ ), which can be attributed to chromospheric activity phenomena. Busso et al. (1990) and Scaltriti et al. (1993) reported that they did not detect an IR excess in the RW UMa binary system based on their 1986 and 1987 IR observations. Although we have no observational CE data at primary minimum for the RW UMa binary system, our CE measurements at secondary minimum and at outside eclipse phases suggest that there may be an observational evidence of a possible presence of some extended/circumstellar matter with some definite CE levels in this active binary system (see Figures A.6 and A.15).

From Figures A.7 and A.15, it can be seen that UX Com has definite CE values at a level of about 0.1 mag during both minima in optical spectral regions. The similar trend was seen in 2MASS and WISE data but with large errors (as large as 0.42 mag) in ${(V-W4)}$ bandwidths. From the data with better level of errors, we see that UX Com has CE values of $\sim\!0.49$ mag in near-IR and of $\sim\! 0.46$ mag in middle-IR spectral regions during primary minimum. By excluding the WISE observation, which has an error as large as 0.42 mag (corresponds to CE levels of 0.29 mag in ${(V-W4)}$ bandwidths, see Table A.2), from observed CE levels, it can be concluded that the source of the excess in UX Com resulted mainly from the cooler component but with some contributions from its hotter companion of the system. Despite these high levels of uncertainty in CE measurements, these results suggest that there may be a structure in the UX Com binary system that provides some certain observational evidence of an extended/circumstellar matter (see Figures A.7 and A.15).

RS CVn has remarkable CE values of about $\geq 0.15$ mag in optical spectral ranges at about primary minimum (see Figure A.8). No observation was made in the near- and middle-IR spectral ranges during primary minimum of the RS CVn binary system. The system also has some remarkable CE values of about 0.09 mag in optical spectral ranges during both of the secondary minimum and outside eclipses. And fortunately, there are 2MASS and WISE observations of this system during the secondary minimum and outside eclipses (see Table A.2 and Figure A.15). From these 2MASS and WISE data, it can also be seen that there are remarkable CE values in the near- and middle-IR spectral regions during both of the secondary minimum and outside eclipses in the RS CVn binary system. Based on the observed characteristic trends of CE values seen in the RS CVn binary system, it may also be referred that these excess emissions come mainly from the cooler component of this system. However, Berriman et al. (1983) have not detected an IR excess in the RS CVn binary system. As can be seen from the graph of RS CVn given in Figure A.15, there is definite observational evidence of the presence of an extended/circumstellar matter in this active binary system.

SS Boo, similar to RS CVn, has remarkable CE values of about $\geq 0.15$ mag in optical spectral ranges at about primary minimum (see Figure A.9). This system has CE values of about $\sim\!0.63$ mag in both the near- and middle-IR spectral ranges at about primary minimum. Similarly with the RS CVn system, SS Boo also has some significant, but lower CE values in optical spectral ranges during secondary minimum (see Table A.2). There are only WISE observations during outside eclipses of SS Boo, but no 2MASS and WISE observations were made during secondary minimum of this system. Based on the observed characteristic trends of CE values seen in the SS Boo binary system, it may also be inferred that these excess emissions come mainly from the cooler component of this system. The results of CE measurements of the SS Boo binary system shown in Figures 2 and A.15 provide certain observational evidence of extended/circumstellar matter in this active binary system.

PW Her has definite CE values at a level of about 0.1 mag during both minima in optical spectral regions (see Figure A.10). No observation was made in the near- and middle-IR spectral ranges during primary minimum of the PW Her binary system. The system also had some CE values in the range of about $\sim 0.1$ mag in optical spectral ranges during both the secondary minimum and outside eclipses. Fortunately, there were 2MASS and WISE observations during secondary minimum of PW Her which gave us some definite CE values of about 0.2 mag in near-IR and of about 0.4 mag in middle-IR spectral ranges. With this characteristic level of CE values, it can be concluded that excess emissions come mainly from the cooler component of the PW Her binary system. From the graph of the PW Her binary system shown in Figure A.15, it is likely that this binary system, although not certain, seems to have observational evidence of an extended/circumstellar matter.

Similarly as in the LX Per system, AW Her has CE values as low as of $\sim\!0.04$ mag with high errors of $\sim\!0.03$ mag during primary minimum in optical spectral ranges (see Figure A.11). Our optical observations during secondary and outside eclipses of AW Her also gave CE values as low as of $\sim\!0.04$ mag with similar high errors as of primary minimum. No observation was made in the near- and middle-IR spectral ranges during primary and secondary minima of the AW Her binary system. The near-IR observations gave CE values of $\sim\!0.19\pm0.05$ mag, while middle-IR observations gave CE values of $\sim\!0.29\pm0.03$ mag during outside eclipses of the AW Her binary system. Based on these near-IR and middle-IR observations, which have higher accuracy than our optic observations, it can be concluded that there is some detectable excess emissions which probably come from the cooler component of the AW Her binary system. Based on their spectral observations taken in 1990 during primary eclipse of this system, Hall & Ramsey (1994) have concluded that AW Her shows evidence of an extended material. From the graph of the AW Her binary system shown in Figure A.15, we can see that our results support the results obtained by Hall & Ramsey (1994). It is also remarkable that it is similar to the LX Per binary system in terms of observational evidence of extended/circumstellar matter in this active binary system.

RT Lac has CE values of about 0.08 mag in optical spectral ranges at about primary minimum (see Figure A.12). No observation was made in the near- and middle-IR spectral ranges during primary minimum of the RT Lac binary system. The system also had some detectable CE values of about $\sim\!0.05$ and $\sim\!0.07$ mag in optical spectral ranges during secondary minimum and outside eclipses, respectively. No observation was made in the near-IR during secondary minimum of the RT Lac binary system. But there are 2MASS and WISE observations of this system during outside eclipses (see Table A.2 and Figure A.15). Based on all obtained CE values given in Table A.2, it can be concluded that the RT Lac binary system might have some excess emissions that mainly come from the cooler component of this system. This active binary system also has similarities with the LX Per system in terms of observational evidence of extended/circumstellar matter (see Figure A.15). That is, it can be concluded that the extended/circumstellar matter could possibly, but uncertainly, be present in the RT Lac active binary system.

The AR Lac binary system had CE values as low as of $\sim\!0.02$ mag with high errors of $\sim\!0.03$ mag during primary minimum in optical spectral ranges (see Figure A.13). Our optical observations during secondary minimum of AR Lac also gave CE values as low as of $\sim\!0.04\pm0.02$ mag while $\sim\!0.01\pm0.03$ mag during outside eclipses. No observation was made in the near-IR spectral ranges during outside eclipses of the AR Lac binary system. The middle-IR observations gave CE values of $\sim\!0.02$ mag during primary minimum of the AR Lac binary system. A comparison of CE levels in all bands during the minima and outside eclipses (see Figure A.15) shows that there is noticeable excess only in $(V-W3)$ bandwiths in the AR Lac binary system. Therefore, with these characteristics of CE levels, it can be concluded that the source of the excess in AR Lac resulted mostly from the cooler component of the system. Berriman et al. (1983) and Busso et al. (1990) have not detected an IR excess in the AR Lac binary system. By using the Spitzer Space Telescope data obtained between 2005 November and 2007 January, Matranga et al. (2010) have not detected a significant IR excess in the AR Lac binary system. But here, it should be noted that the WISE data have better sensitivity than of both IRAS and Spitzer data (see Wright et al. 2010). As can be seen from the graphs shown in Figures A.13 and A.15, there is no observational evidence that extended/circumstellar matter may exist in the AR Lac active binary system. In this system, the main source of excess radiation is stellar activity.

RT And had CE values of about 0.06 mag in optical spectral ranges at about primary minimum (see Figure A.14). No observation was made in the near- and middle-IR spectral ranges during primary minimum of the RT And binary system. But the observations made by WISE gave CE values of about $\sim\!0.22$ mag at about primary minimum. The system also had some detectable CE values of about $\sim\!0.03$ and $\sim\!0.04$ mag in optical spectral ranges during secondary minimum and outside eclipses, respectively. No observation was made in the near-IR during outside eclipses of the RT And binary system. A comparison of CE levels in all bands during the minima and outside eclipses (see Figure A.15) shows that there is noticeable excess in the RT And binary system. Therefore, with these characteristics of CE levels, it can be concluded that the source of the excess in RT And probably resulted from the cooler component of the system. There was no observational evidence for the presence of extended/circumstellar matter in the RT And active binary system either (see Figures A.14 and A.15). In this system, also, it is seen that excess radiations are caused by stellar activity.

Some characteristics of the evaluation of all CE measurements of 13 binary systems of this study can be summarised as follows:

1. – Our optical CCD observations of 13 CAB systems were obtained between 2012 and 2014. With the aim of investigating characteristics/effects of any extended matter around component(s) of a system, these observations of 13 binaries were attempted to be made during minima and outside eclipses. Fortunately, we were able to detect that only one scan made for each of the stars of this study during 2MASS observations was carried out between 1997 and 2000. We also found the WISE data of these stars obtained in 2010 with the full cooling systems of the satellite. The CE measurements from these 2MASS and WISE observations are consistent with those of our CCD observations (see Table A.2).

2. – The SV Cam, RS CVn, SS Boo, and PW Her binary systems showed CE variations in optical spectral ranges, depending on orbital phases, while the LX Per, VV Mon, RW UMa, UX Com, AW Her, and RT Lac binary systems did not show these types of CE variations as a function of orbital phases. However, the AR Lac and RT And binary systems were likely to have some CE variations depending on orbital phases. No enough photometric data were obtained to see this CE variation in GK Hya.

3. – Since the colour variations in optical filters are more sensitive to spot activity, the CE variations in these bands were attributed to stellar activity (Busso et al. 1987). Except for cases in SV Cam and RT And sytems, since the larger and cooler component is located in front of the hotter component and CE values at primary minimum are larger than that of the other orbital phases in the IR spectral ranges, the distributions shown in Figure A.16 provide some excess emission, which could be attributed to the presence of an extended/circumstellar matter around the cooler/primary component of the system.

4. – The active binary systems which show CE variations depending on orbital phases in optical spectral ranges may have some additional effects by about 0.03 mag in ${(V-R)}$ , due to star spots (with a large spot area of 30% of the visible hemisphere and $\Delta T = 1\,000$ K) as reported by Fekel et al. (1986).

5. – In general, the amount of excess radiation of these 13 binary systems had greater values towards longer wavelengths (from optical to IR bands, see Figures A.15 and A.16). The excess radiation was detected in all orbital phases (in the minima and at the outside of minima) of these systems. GK Hya had an excess emission during primary minimum in optical spectral regions, but this system showed an absorption feature in WISE spectral regions during primary minimum. GK Hya also had excess emissions in 2MASS and WISE spectral ranges during outside eclipses. It can be clearly seen from Figure A.15 that there are some increasing trends from relatively small CE values in optical V,R,I bands towards relatively larger CE values in middle-IR bands. This trend is to show that the excess in optical spectral ranges comes dominantly from the active component(s) of the system and towards the middle-IR spectral ranges, there are additional contributions due to heating the circumstellar matter around the active component(s). Therefore, the increase in CE values towards IR bands must be due to extended matter around active binary component(s) of an active binary system. Having clear excesses, at all phases and all bands, of some active binary stars of this study provided clear evidence of some hot and extended matter around cooler or both components of these systems.

6. – By comparing the excess radiation of these systems in primary minima with those of outside eclipses, we see that the systems have greater excess radiation in primary minimum than at outside eclipses. This trend may arise from the extended matter around the cooler component of a binary system.

7. – Amount of excess emission of a system may also provide information about the density of the gas around the system, showing the presence of a thin extended matter in the active binary system. The existence of a CE at W3 (12 $\mu$ m) could provide evidence for Silicate emission of an extended/circumstellar matter. From Table A.2, it can be seen that CE values, at ${(V-W3)}$ , for almost all 13 binaries of this study gave some evidence for Silicate emission (see Li, Zhao, & Li 2007; van Breemen et al. 2011) of an extended matter in these systems.

8. – Our results on measurements of excess emissions (obtained as CE values) in 13 binaries of this study were in agreement with the results of Busso et al. (1987) and Scaltriti (1990). They concluded that the IR spectral region proved to be a useful tool for study of IR emission, including VV Mon, from circumstellar matter which is formed in the expanding circumstellar envelopes as indicated by the case of W Hyd, which gave a large circumstellar dust shell around the red giant star (e.g. Hawkins 1990).

9. – According to our CE measurement results, the observational evidence regarding the extended/circumstellar matter is as follows:

1. (a) Active binary systems without observational evidence of the presence of extended/circumstellar matter are GK Hya, AR Lac, and RT And,

2. (b) Active binary systems with probable, but uncertain observational evidence of the presence of extended/circumstellar matter are LX Per, SV Cam, PW Her, AW Her, and RT Lac,

3. (c) Active binary systems with certain observational evidence of the presence of extended/circumstellar matter are VV Mon, RW UMa, UX Com, RS CVn, and SS Boo.

1. – An examination of the locations of cooler components of 12 systems, with the exception of RW UMa, on the HR diagram (see Figure A.17) with corresponding evolutionary tracks (with solar z value of 0.02; see Lejeune & Schaerer 2001) shows that the stars of greater ${(B-V)_\circ}$ have greater CE values. Therefore, it can be concluded that most of the active components of binary systems might have an extended matter, caused not only from stellar activity but also more likely from evolutionary processes (see De Loore & Doom 1992; Iben & Livio 1993). The zero-age main sequence data we used in Figure A.17 were taken from Sung et al. (2013). For the location of these cooler components of 12 programme stars on the HR diagram in Figure A.17, we used the related ${(B-V)_\circ}$ and $M_V$ as given in Tables A.2 and A.3, respectively.

2. – Based on our ${(B-V)_\circ}$ measurements (see Table A.1), the spectral types of reference stars which were used in this study have been updated as given in column 3 of Table 2.