Radiation Pattern of Radio and Optical Components of Extended Radio Sources
aa r X i v : . [ a s t r o - ph . GA ] D ec Radiation Pattern of Radio and Optical Components of Extended RadioSources
V.R. Amirkhanyan
1, 2 Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnij Arkhyz, 369167, Russia Sternberg Astronomical Institute, M.V.Lomonosov Moscow State University, Moscow, 119992 Russia * The relation between parameters the D/ √ I and I C /I SUM and radiation patterns of the opticaland radio components of an extended radio source is analyzed, where D and I are the apparentsize and observed radiation intensity of the source or its components respectively. The parametersof the pattern in the optical and radio (1.4 GHz) ranges are estimated. The radiation pattern ofextended radio-emitting regions is close to spherical and the radiation of the central component isconcentrated in a ◦ wide beam. Its luminosity is a factor of 4.58 higher than that of the extendedcomponent of the radio source. The radiation pattern of the optical component of the radio sourceturned out to be unexpectedly non-spherical: the main lobe of the pattern is about ◦ wide. The g -band luminosity is 6.4–12.3 times higher than the luminosity of the spherical fraction of the “optical”radiation pattern. A list of 116 new giant radio sources is presented.
1. INTRODUCTIONCurrently, the radiation pattern (RP) of a classicalextended source is represented by the sum of twomodels of the radio sources.(1) The Shklovsky–van der Laan model [1],[2]con-siders the motion of relativistic electrons in irregu-lar magnetic fields. The radiation pattern of sucha radio source is close to spherical.(2) The model of the radiation of relativistic elec-trons moving in regular magnetic fields [3–6]. Theradiation pattern of this structure has the form ofa narrow beam, which in the simplest case of uni-form magnetic field can described by the followingequation [7] A ( ϕ ) = [ γ (1 − β ) cos ϕ ] − (2 − α ) , where ϕ is the angle between the observer’sline of sight and the direction of the relativisticjet; γ = (1 − β ) − / and α is the spectral index( S ν ∼ ν + α ). The model yields a simple formula forestimating the of the radiation pattern ∆ φ = 1 / γ ,which is independent of frequency. The γ valuesinferred from observations of superluminal motionsin radio-source jets lie in the 3–40 interval, whichcorresponds to ∆ φ values from ◦ to . ◦ . May bethat the resulting RP of the central component isequal to the sum of the patterns of different por-tions of the jet with different generation conditions.This conclusion is suggested by the study of thecentral region of Centaurus A radio source by Ho-riuchi et al. [8], which demonstrates the variation ofthe jet opening angle from 12 to ◦ at the distanceof 1000 to 20 000 Schwartzschield radii from the * Electronic address: [email protected] central engine. This result suggests that electronsejected by the central engine into a wide openingangle “converge” as they move away from the cen-ter. Hence the “hedgehog” model with radial mag-netic field whose RP was analyzed by Kovalev [9]applies near the central engine. In this article au-thor performs computations over a wide frequencyrange, which imply that the width the RP increaseswith increasing frequency. For example, 1.4 GHzand 5 GHz ∆ φ = 13 . ◦ and . ◦ at 1.4 and 5 GHz,respectively. Possibly , the truth is in a combina-tion of models [7] and [9] as that is demanded bydialectic.There are very few experimental estimates of theRP of extended radio sources. This include, first,the paper by Orr and Browne [10]. The above au-thors combined the RP from [7] with the flux densityratio of the compact and extended components (pa-rameter R = S C /S E ) and used it as the indicator ofthe orientation of the radio source with respect tothe observer’s line of sight. They further assumedequiprobable distribution of the space orientation toconstruct the computed distribution of parameter R and compare it with the histogram of observed R values for quasars. As a result, they estimated at5 GHz the Lorentz factor γ ∼ and found the ra-diation level of the spherical component to be equalSuch parameters imply a RP width of ∆ φ = 14 ◦ .Amirkhanyan [11] used a similar method for esti-mating the RP, but unlike Orr and Browne [10] heinvestigated the statistics of the ratios of the com-pact component flux density to the total radio sourceflux density, R S = S C /S SUM . In addition, an upperredshift of the objects list was limited to preventselection of the radio sources orientation with re-spect to the observer. As a result, the RP widthwas estimated to be ∆ φ = 42 ◦ and ∆ φ = 54 ◦ at 1.4and 5 Ghz, respectively. Yet another estimate wasobtained in [12] by constructing the “angular size–redshift” dependence, which yielded ∆ φ = 24 ◦ at1.4 GHz. Complete disorder and reel.2. OBSERVED PARAMETERS AND SPATIALORIENTATION OF RADIO SOURCESTo study the RP of an antenna, we change its ori-entation and measure its radiation. We cannot sim-ilarly manipulate with radio sources. However, wecan assume that the distribution of their orientationsis close to equiprobable and try to find a relationbetween several parameters that depend on the ori-entation of the radio source. Such bonds should in-evitably show up if the structure of the radio sourceand its RP are interconnected. We assume that thiscondition is fulfilled.Our conviction that R S = S C /S SUM can be usedas an orientation indicator is based on the assump-tion that RP is not spherical. The statistics of R S from whose behavior we conclude about the form ofthe radiation pattern depends very strongly on thesample of radio sources, radio-telescope parameters,and eye of the observer. We therefore need yet an-other indicator, which inevitably depends on the pa-rameters of the RP and orientation of the object andwhich can be inferred from observational data. Wecan then compare the behavior of these parameterswith our theoretical studies ,try to find their connec-tion and understand to which extent our assump-tions are consistent with reality. To approach thetruth as close as possible, we must try to “tear off”connection of our indicators from the space model.As the first orientation indicator we use the ratioof the emission of the compact component to the to-tal radiation intensity of the source R L = I C /I SUM .Note that by radiation intensity we mean the inten-sity in the direction of the observer. In the generalcase of non-spherical RP R L is not equal to the ratioof the luminosities of the objects.Transition to R L allows us to eliminate the red-shift dependence of the supposed orientation indi-cator, whereas such dependence is inevitable for R S = S C /S SUM : spectral indices S C and S SUM , andhence their K corrections differ from each other.Let us derive the formula for R L in terms of theobserved parameters of extended radio sources. Letthe flux density depend on frequency as S ∝ ν α .Given that I = Sl b ( z )(1 + z ) − (1+ α ) , where l b is thebolometric distance, we write R L = I C I SUM == S C l b ( z )(1+ z ) − (1+ αC ) S C l b ( z )(1 + z ) − (1+ α C ) + S E l b ( z )(1 + z ) − (1+ α E ) .Here α E and S E are the spectral index and fluxdensity of the extended component, respectively,and α C and S C are the spectral index and flux den-sity of the compact component, respectively. Given that S E = S SUM − S C , we derive, after simple trans-formations, the following formula R L = S C S C + S SUM − S C (1+ z ) αC − αE = (1+ z ) αE − αC (1 + z ) α E − α C + 1 R S − . (1)The second parameter T = D √ I , (2)where D = D sin ϕ is the visible size of the radiosource and I = I A ( ϕ ) , the visible radiation of theradio source or its component. The word “visible”is used to indicate that both D and I depend onthe orientation of the radio source relative to theobserver; ϕ is the angle between the line of sightand the direction toward the maximum of emissionof the radio source; D is the true size of the radiosource and I is the radiation in the direction ofthe maximum of the radiation pattern A ( ϕ ) . The T value can be easily computed from the observedparameters T = Θ √ S (1 + z ) − (3 − α )2 (3)and does not depend on the model of space. Θ isthe angular size of the radio source and S , the fluxdensity of the radio source or of its component.The author assumes that substituting the fluxdensity of the entire radio source or some of its com-ponents (compact, extended, optical) into the de-nominator in formula (3) will make it possible to es-timate the parameters of the RP of both the entireradio source and its corresponding fractions.Let us relate R L and T via RP A ( ϕ ) . Considerthe canonical model of a radio source with symmet-ric two-sided components [7, 10]. Let the ideal RPof such object be axisymmetric with respect to thejet axis and have two symmetric maxima in oppo-site directions. Let us adopt the description of theradiation pattern from [11] A ( ϕ ) = II = a + (1 − a ) cos n ϕ. (4)Here a is the level of the spherical component of theRP and n , a parameter that determines the widthof the main lobe of the RP. If n = 0 then the RPdegenerates into a spherical pattern ( A ( ϕ ) = 1 ).Let us now determine the relation between R L and the orientation of the radio source relative tothe observer R L = I C I SUM = (1 − a ) cos n ϕa + (1 − a ) cos n ϕ . (5)It is evident from this equation that R L < − a .Let us now extract the following relation from for-mula (5) cos ϕ = (cid:20) aR L (1 − a )(1 − R L ) (cid:21) n and, given that D = D sin ϕ , substitute it into for-mula (2). As a result, we obtain the following com-puted dependence of T on R L for different compo-nents of the radio source:(1) The total radiation of the radio source T SUM = D √ I SUM = D sin ϕ √ I [ a +(1 − a ) cos n ϕ ] = D vuuut − aR L (1 − a )(1 − R L ) n vuut aI − R L ; (6)(2) The compact component of the radio source T C = D √ I C = D sin ϕ √ I (1 − a ) cos n ϕ = D vuuut − aR L (1 − a )(1 − R L ) n vuut I aR L − R L ; (7)(3) the extended component of the radio source T E = D √ I E = D sin ϕ √ aI = D vuuut − aR L (1 − a )(1 − R L ) n √ aI . (8)Formulas (6)–(8) include parameters of the RPand therefore there is hope that these parameterscan be estimated by comparing the model with ex-periment. Note that all the three equations mustdemonstrate the agreement with the experiment forthe same parameters of RP.The optical object is a component of the radiosource and we can extend the above reasoning to itin order to estimate the RP in the optical range. Wenow consider the general case allowing non-sphericalradiation of the optical component. We further as-sume that the optical radiation is associated withthe structure of the radio source: the symmetryaxis of the optical radiation coincides with the jetaxis. It follows from the canonical model of the radiosource, which assume the synchrotron mechanism ofjet radiation over a wide range of wavelengths andthe closeness of the spatial orientation of the rota-tion axes of the host galaxy and the jet. Here we can draw upon the works by Condon et al. [13] andBrowne and Battye [14], who showed based on ex-perimental data that the the distribution functionof the difference of the position angles radio sourcesand of elliptical galaxies identified with them is hasmaximum near ◦ . Hence the position angle of theminor axis, which is close to the position angle of thenormal to the galaxy, coincides with the orientationof the radio jet. Let the form of the optical RP bedescribed by formula (4), but with its proper valuesof n opt and a opt : A opt ( ϕ ) = I opt I , opt = a opt +(1 − a opt ) cos n opt ϕ (4 ′ ) Currently, we cannot separate the radiation intothe extended and compact fractions of the opticalobject. We therefore use formula (6) for the totalradiation, where we leave parameter R L determinedfrom radio data as the orientation indicator, but re-place RP (4) by formula ( ′ ). We then have T opt = D √ I opt = D sin ϕ p I , opt [ a opt +(1 − a opt ) cos n opt ϕ ]= D vuuut − aR L (1 − a )(1 − R L ) n vuuuut I , opt a opt +(1 − a opt ) aR L (1 − a )(1 − R L ) n opt n . (9)3. SAMPLES OF RADIO SOURCESTo compare formulas (6)–(9) with real mea-surements, we used two lists of extended radiosources:(1) Sample of objects whose apparent size doesnot exceed 0.7 Mpc in the Λ CDM model. Thislist includes 2947 identified radio sources fromAmirkhanyan [15]. For each of these objects its an-gular size, total flux density, component flux densi-ties, redshift, and g -band magnitude of the opticalcounterpart are known.(2) Objects whose apparent sizes exceed 0.7 Mpc.This sample contains 254 giant radio sources fromcatalogs [15 ? –25].The list does not include objects with photometricredshifts. To ensure uniformity of parameterdetermination, we found all objects in the NVSS( )or SUMSS ( ) cata-logs. We thereby determined the flux densities andcoordinates of the radio-source components, andalso their angular sizes measured as the separationbetween the most spaced components.If there was a radio component within – ′′ ofthe optical component then this radio componentwas considered to be the central one and S C wasset equal to its flux density. If no central com-ponent was present then its flux density was as-signed as S C = 0.1 mJy, which is below the detec-tion threshold for NVSS. The data of the FIRSTsurvey ( http://sundog.stsci.edu/cgi-bin/ searchfirst ) were used to refine the coordinatesof the central components if the radio source waslocated in the area covered by this survey.We further added to the list 92 radio sources foundin the NVSS catalog using the software developed bythe author [25] (see Table below). This table alsoincludes the “giants” from [15]. The author brokeselection criteria for the radio source 2057 + 0012,because its extent exceeds the formal 0.63 Mpc be-cause of its complex shape. List of giants α δ Angular Total Flux density g-band z Apparent Objectsize, flux of the central magnitude size, typearcsec density, component, of the optical MpcmJy mJy component(1) (2) (3) (4) (5) (6) (7) (8) (9)NVSS00 03 31.50 +03 51 11 . −
22 23 20 . −
20 16 13 . +26 13 12 . +31 37 20 . −
17 01 55 . +06 24 38 . −
26 54 04 . −
20 30 11 . +15 50 13 . −
31 30 01 . −
06 31 58 . +15 10 59 . +17 08 10 . +34 30 32 . +24 47 36 . +04 24 36 . −
25 38 18 . +52 29 15 . +05 55 23 . +01 31 30 . +08 12 31 . +68 34 25 . +10 06 41 . +16 11 57 . +51 04 22 . +27 15 59 . −
01 46 12 . +39 31 21 . +38 31 31 . +74 19 40 . −
02 34 37 . +21 03 17 . +27 54 49 . −
12 53 10 . −
04 04 10 . +03 38 05 . +26 32 32 . +21 06 56 . −
12 51 40 . +08 32 02 . +36 24 24 . +58 18 42 . +64 25 55 . −
33 03 56 . +27 37 41 . +45 51 23 . −
01 29 18 . −
03 07 45 . +54 03 17 . −
16 34 50 . +26 31 47 . +45 09 05 . −
27 27 56 . +14 50 38 . (Cont.) α δ Angular Total Flux density g -band z Apparent Objectsize, flux of the central magnitude size, typearcsec density, component, of the optical MpcmJy mJy component(1) (2) (3) (4) (5) (6) (7) (8) (9)14 31 51.10 +10 29 59 . +30 14 35 . −
34 56 46 . +22 10 07 . +14 06 11 . +53 33 54 . −
10 12 00 . +48 32 14 . +19 59 57 . +32 48 42 . +02 25 15 . −
01 27 10 . +69 49 35 . +22 47 39 . +22 33 12 . +36 59 52 . +43 34 11 . +24 49 16 . +25 21 47 . +30 46 52 . +17 34 20 . +48 06 19 . +00 12 07 . −
06 59 08 . −
16 19 04 . −
39 42 52 . −
02 24 18 . +27 32 59 . −
34 55 31 . −
28 23 53 . −
24 25 52 . +00 5658 . −
23 43 40 . −
04 48 54 . +26 24 14 . +13 58 10 . +12 45 03 . +47 05 29 . −
02 47 18 . +13 46 57 . +27 43 43 . +51 04 02 . +11 29 19 . +22 19 58 . +18 28 15 . +40 54 29 . +04 50 48 . +19 04 20 . +49 09 21 . +07 48 56 . +45 50 28 . +41 33 18 . +45 49 54 . +11 41 08 . +22 17 07 . +11 04 03 . +06 58 01 . +00 47 32 . +17 54 10 . +27 35 13 . −
01 31 51 .
4. DETERMINATION OF THE PARAMETERSOF THE RADIATION PATTERN
D < . Mpc
For all radio sources we determine parameter R L by formula (1). Figure 1 shows the relation between R L and R S . The dashed line shows the identity rela-tion R L = R S . The lower boundary of the plot (thesolid line) was computed by formula (1) for z = 3 . (the maximum redshift in the sample). We adoptedthe same spectral indices for all radio sources be- Figure 1.
Relation between R L and R S for theradio sources of the first list. The dashed line showsthe R L = R S relation. The lower boundary of theplot (the solid line) was computed by formula (1) for z = 3 . (maximum redshift in this sample). z Figure 2.
Dependence of z on R L for radio sourceswith apparent sizes D < . Mpc. We subdividedthe entire range of R L values into ten equal bins. Ineach bin we computed the mean redshift byaveraging the z values of the objects and thecorresponding standard deviation. cause these data are unavailable for most of the radiosources. We set α E = − . and α C = − . for ex-tended and compact components, respectively. Theeventual selection by redshift appears to be small be-cause the average z of radio sources weakly dependson R L (Fig. 2).We now determine parameter T for different radio-source components by substituting into formula (3)the total flux densities S SUM , flux densities S C ofthe central fraction, or flux densities S E of exter-nal components. Figs. 3a, 3b, and 3c show the plots T SUM , T C , and T E as functions of R L for objects ofthe first sample.The distribution functions of the true sizes andtrue luminosities of extended radio sources do notdepend on their spatial orientation and therefore the upper boundary of parameter T as a function of R L is determined by the RP of radio sources (formu-las (6)–(8)). When computing the upper limit (thesolid line in Figs. 3a–3c) we set the maximum truesized of radio sources equal to D = 0 . Mpc.We then varied a , n , and I to determine the pa-rameter values that allow achieving the best agree-ment between the computed and visible boundariessimultaneously in three plots: a = 0 . , n = 15 , I = 10 W Hz − sr − .The normalization of RP (4) differs from tradi-tional π : N = 4 π (cid:18) a + 1 − a n + 1 (cid:19) , (10)and is equal to 0.49 for the inferred RP parameters.Hence the minima, luminosity of the radio sourcesof the sample is N × I = 4 . × W Hz − .The dashed line in Figs. 3a and 3c demonstrate thesensitivity of the computed upper boundaries for pa-rameter values from a = 0 . to a = 0 . . For thesame purpose we show by the dashed line in Fig. 3bthe boundary for n = 12 and n = 18 . Figures 3a,3b and 3c clearly demonstrate that the RP of theextended source is evidently non-spherical. Its mainlobe whose maximum coincides with the major axisof the radio source has the width of about ◦ . Thedistribution of the radiation of outer components isclose to spherical and its level is 140 times lower thanthe intensity at the maximum and the luminosity ofthe compact component is a factor of 5.48 higherthan that of outer components.Before computing parameter T of the opticalcomponent we must decide how to compute the K -correction for the AGN. The K -correction is usu-ally viewed as a magnitude correction. Here we de-fine it as the g -band flux density correction for theoptical component of the radio source. To determinethe K -correction, we used the most complete andhomogeneous photometric measurements in the u -, g -, r -, i -, and z -filters from the SDSS-survey . For540 objects with redshifts greater than 1 we supple-mented these data with infrared photometry fromthe 2MASS ( J -, H -, and K -filters) [26] and WISEAll-sky ( W -filter) survey [27]. We then constructedthe spectrum of the optical component based on theentire set of photometric data and determined the K -correction.To compute T opt we rewrite equation (3) takinginto account the inferred K -correction : T opt = Θ p S g K COR (1 + z ) − . (11) http://skyserver.sdss.org/dr12/en/tools/crossid/crossid.aspx. Figure 3.
Radio sources with apparent sizes smaller than 0.7 Mpc. Dependence on R L : (a) T SUM , (b) T C , (c) T E ,(d) T opt . The solid line in Figs. (a), (b), and (c) shows the upper limit computed by formulas (6)–(8) for the optimumparameters of the RP of the radio source: a = 0 . , n = 15 . The upper limit in Fig. (d) is computed by formula (9)for the parameters of the RP of the optical component a opt = 0 . , n opt = 15 . The dashed line shows the boundaryof spherical RP. Here S g is the observed flux density of the object inthe g -band filter. We show the results of computa-tions in Fig. 3d. Unexpectedly, the plot showed thatthe RP of the optical component of the radio sourceis far from spherical. The solid line shows the opti-mum upper boundary for a opt = 0 . , n opt = 15 , I , opt = 2 × W Hz − sr − . The dashed lineshows where the boundary should be in the caseof spherical RP in the optical range with intensity I , opt . D > . Mpc
The computations performed for objects of thefirst sample were repeated for the giant radio sourcesof the second sample. Figures 4a, 4b, 4c, and 4dshow the results of computations for T SUM , T C , T E ,and T opt (the open circles). The boundary of thedistribution was computed for a = 0 . , n = 15 , I = 1 . × W Hz − sr − , D = 2 . Mpc. It isevident that because of the limited statistics theagreement with experimental data is not so goodas in the case of the first sample. It is, however, evident that the RP of giant radio sources is alsonon-spherical and its parameters are close to thoseinferred for the first list. To demonstrate the latterstatement, we added to Fig. 4b objects from Fig. 3b(the filled circles). To cover the wide range of T C and R L values, the figure is plotted in logarithmicscale. The relative shift of the boundaries of thefirst and second samples along the vertical axis (thedashed and solid lines, respectively) is primarilydetermined by the change of the true maximumsize of radio sources and not the parameters ofthe RP. We could find photometry in the SDSScatalog for computing T opt (Fig. 4d) only for 146giant radio sources. We compiled the BV RIJHK photometry from VizieR database . This allowedus to determine the g -band flux density and thecorresponding K -correction reduced to this band for254 objects. The boundary was computed for thefollowing parameter values: a opt = 0 . , n opt = 13 , I , opt = 3 × W Hz − sr − , D = 2 . Mpc http://vizier.u-strasbg.fr/viz-bin/VizieR. Figure 4.
Radio sources with apparent sizes greater than 0.7 Mpc. Dependence on R L : (a) T SUM , (b) T C , (c) T E ,(d) and T opt . The solid line in Figs. a, b, c shows the upper limit computed by formulas (6)–(8) for parameters of theradio-source RP a = 0 . , n = 15 . The dashed line in (b) shows, for comparison, the boundary of objects of the firstlist (the filled circles). The upper boundary in (d) was computed by formula (9) for parameters of the RP of theoptical component a opt = 0 . , n opt = 13 . The dashed line shows the boundary of the spherical RP. (Fig. 4d).The dashed line in the same figure shows wherethe boundary should be if the RP in the optical isspherical and I , opt = 3 × W Hz − sr − . It fol-lows from these parameters that the FWHM of themain lobe of the optical RP is . ◦ .5. CONCLUSIONSIt can be concluded from the above that:(1) The ratio of the radiation of the compact com-ponent to total radiation of the extendet radiosource is indeed connects with its spatial orienta-tion.(2) The form of the RP does not depend on thesize or luminosity of the radio source. This mayalso be true for objects with luminosities higherthan L = 4 . × W Hz − . (3) The central component emits within a narrowbeam whose width at 1.4 GHz is of about ◦ . Thisvalue corresponds to γ = 2 . .(4) The RP of the extended component is closeto spherical, its level is about 0.005–0.01 of theintensity at the maximum, and its luminosity isequal to 0.13–0.24 that of the entire radio source.(5) The RP of the optical component of the radiosource is also non-spherical, its radiation is concen-trated within a beam of width – ◦ , and the levelof the spherical component is of about 0.003–0.005of the intensity at the maximum.ACKNOWLEDGMENTSThis research has made use of the VizieR cata-logue access tool, CDS, Strasbourg, France.
1. I. S. Shklovskii, Astronom. Zh. , 30 (1965). 2. H. van der Laan, Nature (London) , 1131 (1966).
3. M. J. Rees, Nature (London) , 468 (1966).4. L. M. Ozernoy and V. N. Sazonov, Astrophys. andSpace Sci. , 365 (1969).5. V. N. Kuril’chik, Astronom. Zh. , 684 (1971).6. Y. A. Kovalev and V. P. Mikhailutsa, Sov. As-tronom. , 400 (1980).7. P. A. G. Scheuer and A. C. S. Readhead, Nature(London) , 182 (1979).8. Y. Y. Kovalev, Astronom. Zh. , 846 (1994).9. S. Horiuchi, D. L. Meier, R. A. Preston, andS. J. Tingay, Publ. Astronom. Soc. Japan , 211(2006).10. M. J. L. Orr and I. W. A. Browne, Monthly NoticesRoy. Astronom. Soc. , 1067 (1982).11. V. R. Amirkhanyan, Astronom. Zh. , 16 (1993).12. V. R. Amirkhanyan, Astrophysical Bulletin , 383(2014).13. J. J. Condon, D. T. Frayer, and J. J. Broderick, As-tronom. J. , 362 (1991).14. I. W. A. Browne and R. A. Battye, ASP Conf. Ser. , 365 (2010).15. V. R. Amirkhanyan, Astrophysical Bulletin , 333(2009).16. K. Nilsson, M. J. Valtonen, J. Kotilainen, andT. Jaakkola, Astrophys. J. , 453 (1993).17. L. Lara, W. D. Cotton, L. Feretti, et al., Astron. Astrophys., , 409 (2001).17. L. Lara, I. M´arquez, W. D. Cotton,et al.,Astronom.and Astrophys. , 826(2001).18. C. H. Ishwara-Chandra and D. J. Saikia, MonthlyNotices Roy. Astronom. Soc. , 100 (1999).19. A. P. Schoenmakers, A. G. de Bruyn,H. J. A. R¨ottgering, and H. van der Laan, As-tronom. and Astrophys. , 861 (2001).20. J. Machalski, M. Jamrozy, and S. Zola, Astronom.and Astrophys. , 445 (2001).21. J. Machalski, M. Jamrozy, S. Zola, and D. Koziel,Astronom. and Astrophys. , 85 (2006).22. K. Chy˙zy, M. Jamrozy, S. J. Kleinman, et al., BalticAstronomy , 358 (2005).23. A. Buchalter, D. J. Helfand, R. H. Becker, andR. L. White, Astrophys. J. , 503 (1998).24. L. Saripalli, R. W. Hunstead, R. Subrahmanyan, andE. Boyce, Astronom. J. , 896 (2005).25. V. R. Amirkhanyan, V. L. Afanasiev, and A. V. Moi-seev, Astrophysical Bulletin , 45 (2015).26. R. M. Cutri, M. F. Skrutskie, S. van Dyk, et al.,VizieR Online Data Catalog (2003).27. R. M. Cutri, et al., VizieR Online Data Catalog2328