30 years studying of galaxies at Rozhen NAOGeorgi PetrovInstitute of Astronomy and NAO, Bulgarian A ademy of S ien es, BG-1784 So�apetrov�astro.bas.bg(Conferen e talk. Submitted on 8.12.2011; A epted on 14.02.2012)Abstra t. This survey is devoted to the 30-year anniversary of the Rozhen NAO. The ontributions of the Bulgarian astronomers in the observational extragala ti studies arereviewed. The �ve main proje ts of the investigations in lude individual galaxies, nearbygalaxies, a tive gala ti nu lei, voids and large s ale stru tures, and Bulgarian virtual ob-servatory. More than 80 Bulgarian authors and 340 s ienti� papers have been reviewed.All the results are grouped in 17 dire tions and a lot of spe ial tasks. The greatest part ofthe results are based on the observations at Rozhen NAO and Belograd hik AO.Key words: galaxies-observation; system of galaxiesIntrodu tionObservational study of galaxies and systems of galaxies is traditional for Bul-garian astronomers. Extragala ti astronomy is the �eld that deals with ob-je ts beyond the Milky Way, espe ially galaxies and quasars. Su h investi-gations before the regular exploitation of the National astronomi al observa-tory Rozhen have been made in the former Soviet Union observatories. Sin e1980 the main dire tions of our extragala ti investigation have be ome as-trophysi s of galaxies and systems of galaxies and AGN. These investigationsin lude physi al pro esses and hemi al abundan e in galaxies, systems ofgalaxies, photometry and surfa e photometry of normal and a tive galaxiesand galaxies in voids, disk pro�les and star formation, stru tures of galax-ies and lusters of galaxies, et . Parallel investigations of nebulae, stars andstellar asso iations in the nearby galaxies have been arried out. The pro-gram looking for novae in M 31 and M 33 galaxies and the investigations andsear hes for star lusters in nearby galaxies ontinue.The investigations mentioned above were organized in several proje ts �Individual galaxies, Nearby galaxies, A tive gala ti nu lei, Large s ale stru -ture of the Universe and �nally � Bulgarian virtual observatory.This review draws our attention to the ontributions of the Bulgarianastronomers in the �eld of observational extragala ti studies. Theoreti alworks on erning lusters of galaxies and the physi al pro esses in the earlyUniverse are not in luded here.1 Basi dire tions of investigations � proje ts and tasksSome details on erning subproje ts of our investigations are following:� Proje t Individual galaxies: Box/Peanut galaxies, Open lusters, Gala-xy Spe tra, Gravitational Lenses, Surfa e photometry, Star Formation,Chemi al abundan e, Masses of galaxies, Gaseous Nebulae, Pairs of galax-ies, High Surfa e Brightness Galaxies, Ele tro-photometry of galaxies, et .� Proje t Nearby galaxies: Dwarf Galaxies, Pro�le de omposition, S al-ing relations, Novae in M 31 and M 33, Spiral stru ture, OB asso iationsin galaxies, et .Bulgarian Astronomi al Journal 18(1), 2012

72 G. Petrov� Proje t A tive Gala ti Nu lei: Variability monitoring of quasars andblazars, Surfa e photometry of AGN, Eigenve tors determination, Bla khole masses, AGN environment, et .� Proje t Voids and Large S ale Stru ture: Galaxies in Voids, Clusteranalysis, et .� Bulgarian Virtual observatory: Galaxian Virtual Observatory, Bul-garian GRID.Details for all proje ts and tasks an be found in the WEB pages of the author- http://www.astro.bas.bg/�petrov/, Department of astronomy of the So�aUniversity - http://phys.uni-so�a.bg/�astro/ and Department Galaxies of theIA and NAO - http://www.astro.bas.bg/galaxies/.The astronomers from the Institute of Astronomy with Rozhen NAO andfrom the Department of Astronomy of the So�a University work in lose ol-laboration. Tens of s ientists from Germany, Russia, Austria, Norway, Swe-den, Turkey, Armenia, Italy, Fran e, England, Poland and many other oun-tries visited our observatory and took part in a lot of ooperative works too.2 S ienti� potential for extragala ti investigationsDuring the last 30 years a s hool of Bulgarian extragala ti astronomy was reated. Ba helor and master of s ien e degrees have been adjudi ated to18 students, 15 PhD students ompleted their edu ation at So�a Universityand Institute of Astronomy with NAO and 15 PhD dissertations have beendefended. In Fig.1 the above mentioned people are listed.Our investigations were arried out at the two Bulgarian observatories �Rozhen NAO and Belograd hik AO with di�erent teles opes and equip-ment :2.1 Rozhen NAO50/70 m S hmidt teles ope - 16x16 sq. m, 4x4 sq.deg.� ST-6 CCD, BVRIHa �lters, 375x242 sq.px ; 8.6 x 6.5 sqr.mm� ST-8 CCD amera with higher B_sensibility; 1530x1020 sq.px, 9x9 sq.mkmpixel size� SBIG CCD amera STL-11000M, 4008x2672 sqr.px., 9x9 sqr.mkm pixelsize� CCD amera FLI PL 16803, 4096x4096 sqr.px., 9x9 sqr.mkm pixel size60 m Cassegrain teles ope� UBV- and dual hannel photometer� CCD amera FLI PL 9000, 3056x3056 sqr.px, 12x12 sqr.mkm pixel size2m RCC teles ope� dire t plates 30x30 sq. m, UBVRI �lters, 1x1 sq.deg.� Photometri s CE200A CCD_ amera, 1024 x 1024 sqr.px., 24x24 sqr.mkmpixel size� VersArray CCD amera, 1340 x 1300 sqr.px., 20x20 sqr.mm pixel size� Image Tube Systems XX-1050, XX-1063 (Phillips) and UM-92� GRISM

30 years galaxies at Rozhen NAO 73

Fig. 1. Students, PhD students and PhDs in extragala ti astronomy2.2 Belograd hik AO60 m Cassegrain teles ope� UBV photometer� ST-8 CCD, BVRIHa �lters, 1530x1020 sq.px, 9x9 sq.mkm; 13.8x9.2 sq.mm� CCD amera FLI PL 9000, 3056x3056 sqr.px, 12x12 sqr.mkm pixel size,BVR I Johnson-Cousins standard �lters40 m Celestron teles ope� 'STAR-1' CCD, 512x376 sq.px, fo al redu er and spe trograph

74 G. Petrov2.3 SoftwareIRAF, MIDAS, IDL and a lot of di�erent spe ial programs and pa kages.The basi operational system for s ienti� investigations is LINUX and theS ienti� Linux is the basement of the Bulgarian GRID.3 Basi ontributions of the Bulgarian astronomersDuring these 30 su essful years more than 70 Bulgarian authors are authorsor/and oauthors of 340 s ienti� papers. The full list of publi ations withat least one author/ oauthor whose a�liation is So�a University or/and theInstitute of Astronomy and NAO ould be found in the WEB page of theauthor - http://www.astro.bas.bg/petrov/.Figure 2 presents the ontribution of the Bulgarian authors with morethan 15 publi ations in the �eld of observational extragala ti astronomy. 1

Fig. 2. Distribution of extragala ti investigations publi ations1 All pi tures below are omposed for illustration purposes only � if interested one ouldtake the pi tures from the original papers.

30 years galaxies at Rozhen NAO 75Following are the main ontributions of our investigations, grouped in 17dire tions:3.1 Astrophysi s of gaseous nebulaeAbundan es of some ions (He +; O +; N +; S +, et .) for 50 di�use nebulaein our galaxy and 45 di�use nebulae in nearby galaxies have been determined(Golev et al., 1980; Yankulova et al., 1981).Physi al onditions and hemi al omposition were determined for 114nu lear HII regions, in luding in 14 Arakelian, 31 Markarian and 40 nearbygalaxies (Petrov et al., 1984).3.2 Kinemati s and dynami s of stellar systemsThe rotation urves were examined and the parameters of the gas omponentand the masses of the galaxies NGC 1084, 5879, 6503, 7339, 7537 were deter-mined. All galaxies ontain a lot of neutral gas in the disk, while the gas inthe nu leus is not so mu h (Petrov et al., 1989).The masses and the rotational momenta for 47 Seyfert X-ray galaxies, 84Markarian, 21 Arakelian and 13 normal galaxies were determined (Mineva &Petrov, 1990; Petrov & Mineva, 1988, 1991).3.3 Ele trophotometry of double and triple galaxiesU, B, V photometry for about 200 double and triple galaxies has been arriedout. Evaluation of their behavior on the two- olor diagram was made (Tomov& Tomov, 1989; Tomov & Tomova, 1990).The surfa e brightnesses and the diameters of 75 double and 15 triplesystems were de�ned (Tomov, 1979, 1983).3.4 Study of stellar omplexes and asso iations in nearby galaxiesM 31 � Andromeda galaxy� The brightest blue and red stars in the galaxy M 31 - Andromeda, were atalogued. The brightest blue star in M31 has M(v) = -9. The survey on�rms that the brightest red star has M(v) = -8 (Nedialkov et al, 1989).� The existen e of a gradient in the surfa e brightness of the spiral arm S4was found and many OB-asso iations were lo ated. The distribution inspiral arms is expe ted to des ribe a spiral density wave. The parametersof the spiral density wave estimated, showing that the angular velo ity ofthe spiral stru ture ranges from 7 to 15 km/s/kps (Ivanov, 1985; Georgievet al., 1989).� Two hundred and ten groups were dete ted as real O-asso iations themean diameter of whi h is 80 p . Many of Hodge�s open lusters were alsore lassi�ed as O-asso iations. Almost all O-asso iations are lo ated insidethe star omplexes (Efremov et al., 1987).

76 G. Petrov� UBV photometry of 521 stars in the spiral arm S5 of the Andromedagalaxy was obtained. The olor-magnitude and olor- olor diagrams havebeen onstru ted (Kourtev et al, 1986).� BVR - photometry was arried out for 100 bright obje t in the nu learregion of M 31.� The properties of the dis were determined - namely: opa ity, extin tionlaw and gas-to-dust ratio are studied by means of opti al and near-infraredphotometry (Velt hev et al., 2004; Nedialkov et al., 2005, 2009)� Investigation of sour es of soft X-ray radiation in M 31 was performed(Nedialkov et al., 2002).� The distribution of bright stars and HII regions was examined. The gas/ dust ratio wass determined and the opti al density of the disk of thegalaxy M 31 in Andromeda was obtained (Nedialkov et al., 2000).� Coordinates and R-band magnitudes (plus BV-bands if available) for 14newly dis overed nova andidates were reported (Val heva et al., 2010).M 33 � Triangulum galaxy� Asso iations and star omplexes in the galaxy M 33 have been studiedin luding the distribution of red supergiants in the galaxy (Velt hev etal., 2009).� B- and V- photometry for about 3500 and U- photometry for about 2500young stars have been arried out. The age of the di�erent stellar popu-lations has been determined.� Using the data for 65,000 stars, a atalogue of blue and red supergiants was ompiled. A list of magnitudes and positions for 2112 blue stars, de�nedby (U-V)<0.0 mag, and V<19.5 mag, and 389 red stars de�ned by (B-V)>1.8 mag and V<19.5 mag was reated. Of these, 1156 are andidateO stars on the basis of (U-V)<-0.9 mag (Ivanov et al., 1993).� A atalog of 481 OB asso iations with over 3,500 blue high luminositystars was pro essed (Georgiev & Ivanov, 1991).� It was shown that about 200 HII regions with hara teristi length ofabout 80 p oexist with OB asso iations in M33. U-band photometryfor 36 of them and UBV-photometry of 105 bright stars were performed(Ivanov, 1991).In Fig.3, ompiled from the publi ations of G.Ivanov and oauthors, thedistribution of some stellar omplexes and asso iations in M 33 and M 81is presented.� Some a tivity in the nu leus of the galaxy has been established due toenhan ed star formation (Ivanov et al., 1986).M 81 galaxy� A omposite atalog of 180 star asso iations in the galaxy M 81 has been ompiled. The atalogue gives the positions of asso iations, their meanangular sizes, and H II identi� ations (Ivanov, 1992).� A narrow-band photometry of galaxies in the M 81 group was performedto look for supernovae remnants with negative result, but many obje tswere atalogued as HII like regions.

30 years galaxies at Rozhen NAO 77

Fig. 3. Distribution of some stellar omplexes and asso iations in M 33 and M 81� Surveys of the stellar populations in the galaxy M 81 and around it wereperformed by plates of 6 m (SAO, Russia) and 2 m (Rozhen) teles opes(Georgiev et al., 1992ab)� The existen e of an extensive extra-nu lear emission gas stru ture withan irregular morphology in the [OIII℄ line was on�rmed in the galaxy M81 (Georgiev et al., 2005).Dwarf galaxies and LMC� U-band photometry of 2500 young stars and BV-band photometry of 3540stars in the �eld entred on the HII regions in the north-east se tor ofthe dwarf irregular galaxy IC 1613, a member of the Lo al Group, wasperformed and the age of the di�erent stellar populations has been deter-mined. The slope of the initial mass fun tion and the extin tion urve forthe Large Magellani Cloud were obtined (Borissova et al., 1999).� The stallar populations of the dwarf galaxy Ho IX, whi h is very inpor-tant for the extragala ti distan e s ale, was investigated by plates of 6m (SAO, Russia) and 2 m (Rozhen) teles opes in the beginning of a ol-laboration between Russian and Bulgarian astronomers (Georgiev et al.,1991)� CCD - photometry of bright stars in 10 nearby late type galaxies has been arried out (Georgiev & Bomans, 2001). Figure4 presents the �eld of thegalaxy M 81 and its lose satellite Ho IX, resolved into stars by the 2mRozhen teles ope (Georgiev & Bomans, 2004).� A detailed kinemati analysis of the ionized gas in the nearby irregulargalaxy NGC 4449 was presented (Valdez-Gutierrez et al., 2002).

78 G. Petrov

Fig. 4. Dwarf galaxy Ho IX in the periphery of giant galaxy M 81 and Ho IX, resolved intostars by the 2m Rozhen teled ope� Opti al spe tros opy of H II regions in the Lo al Group galaxy IC 10 andUBVR photometry of foreground stars in three �elds towards this galaxywas held (Ri her et al., 2001).� The presen e of a ri h population of arbon stars in the dwarf galaxyWLM (Wolf-Lundmark-Melotte) was found, based on Js, Ks- photometryof over 550 stars in the galaxy. The number of arbon ri h stars omparedto oxygen ri h ones, s ale length, gas/dust ratio and the 'real' distan emodulus of the galaxy WLM was determined (Val heva t al., 2007).3.5 Surfa e photometry of nearby galaxiesUsing UBVR photographi photometry from the Tautenbourg S hmidt tele-s ope and the 2 m teles ope of NAO the mean values of the olor indi es andtheir large s ale gradients were estimated. The dependen e of the axial ratioand the position angle on the semi-major axis were investigated. The resultsgive indire t eviden e of existen e of a two-armed trailing spiral stru ture anda bar in M 31. A ertain asymmetry of the brightness pro�les of the spiralarms of the galaxy M 31 was presented (Georgiev, 1988ab ).By a digital pro essing of Rozhen plates extended low brightness forma-tions in luding the bright galaxies of the M 81 group were found and inter-preted as intergala ti star omplexes(Getov & Georgiev, 1988, 1990).The morphology of the bright part of the galaxy M 81 was investigated inplates of 3 teles opes and an inner ring and a mini bar were revealed (Georgiev& Getov, 1991).The luminosity fun tion, the andidates for star asso iations, and thedistan e modulus of the galaxy M 51 was determined (Georgiev et al., 1990).For the 2/3 of the pro�les of 'edge on' spiral galaxies the major axes ofgalaxies are strongly onvex. It was found that the radial brightness pro�le has

30 years galaxies at Rozhen NAO 79

Fig. 5. Tully-Fisher relation for di�erent type of galaxiesan approximately exponential de rease only in the late spiral and irregulardis systems. At the earlier spirals the disk pro�le be omes more onvex(Georgiev et al., 2004).

80 G. Petrov3.6 S aling relations and distan es to galaxiesIt was shown that the luminosity and size of large spiral galaxies visible 'fa e-o�' lie on the Tully-Fisher diagrams with a relatively small dispersion andreassure an independent assessment of the Hubble parameter. About 150 fa e-o� galaxies, and about 110 galaxies with di�erent slopes to the line of sightwere examined using data from the literature (Stan hev et al., 2002, 2004a).In Fig.5, ompiled from the publi ations of O. Stan hev and oauthors, theTully-Fisher relations for di�erent types of galaxies is presented.The fundamental plane in the spa e of fundamental parameters (mass,luminosity, size) in spiral galaxies has also been determined (Stan hev et al.,2004b, 2006).3.7 Stru ture and evolution of normal and a tive galaxiesA detailed morphologi al hara terization of a sample of 35 galaxies Seyfertand a orresponding sample of normal galaxies was arried out. A numberof photometri and geometri parameters hara terizing the galaxies and theparameters of the bars in barred galaxies hawe been determined. New mor-phologi al stru tures in the galaxies were found, thus the morphology lassi-� ation wass pre ised. The nearby region to the galaxies was studied for thepresen e of ompanions. The results showed that the gas fueling from Seyfertnu lei is not dire tly related to the large s ale morphology of galaxies and thepresen e of ompanions (Slav heva-Mihova & Mihov, 2011a, 2011b).Using a suitable original software one-dimensional stru tural de omposi-tion of 5 Seyfert galaxies was arried out and the parameters hara terizingthe surfa e brightness distribution of galaxies were de�ned (e.g. Mihov &Slav heva-Mihova, 2006).3.8 A tive gala ti nu leiMost of the investigations of the Bulgarian astronomers are on entrated onthe physi s of quasars, the nature of the blazars and the entral bla k hole ofthe a tive galaxies.� Ions abundan es and hemi al omposition in the nu lei of 36 SyG 1 type,5 radio galaxies with broad lines, 23 SyG 2 type and 16 radio galaxies withnarrow lines were determined (Petrov,1979, 1980).� The physi al onditions and hemi al omposition in the nu lei of thea tive galaxies Mark 313, 531, 534, 609, III Zw 103, NGC 7469 and othershave been studied in details.(Golev et al., 1984; Mihov et al., 2006).� Photometry and surfa e photometry of the galaxies Akn 564, Mark 335,506, 509, NGC 1275, 6764, 7469, III Zw 2 were arried out and for someof them de omposition of the pro�les of the emission lines was made.� More than 100 HII regions in the galaxy NGC 6764 were dis overed(Petrov et al., 2006).� 98 Seyfert and X-ray galaxies were studied. It is shown that for 50% ofthem the most likely energy sour e is the a retion of gas on the en-tral bla k hole. A epting a uni�ed model estimation of the bla k holemass and a retion rates was made (Petrov & Veli hkova, 1991; Ba hev& Petrov, 1996).

30 years galaxies at Rozhen NAO 81

Fig. 6. Surfa e photometry of the galaxies Mark 279 and Mark 506� An observational program of extragala ti X-ray sour es was proposed(Petrov, 1988).� In order to build a satisfa tory pi ture of Seyferts in relation to normalgalaxies a series of papers established some of their basi environmentalproperties, espe ially the di�eren e in the number of lose ompanionsbetween Seyfert 1 and Seyfert 2 galaxies. A sample of 104 Seyfert galaxiesand 138 ontrol �eld galaxies was built (Laurikainen et al., 1994).� Opti al variability of sele ted a tive gala ti nu lei (quasars) were exam-ined for more than 10 years, mainly on the 60 m teles ope AO Belo-grad hik. While all obje ts show a variability on long-term s ale, on shorts ales (within a few hours) as a rule, su h hanges do not o ur for theso- alled radio-weak obje ts (Ba hev et al., 2005 ).� The opti al variability of Mkn 279, where the possible existen e of di�erentmodes of a retion disk required to explain the olor hanges of this obje t,was studied in details. (Ba hev & Striga hev, 2004; Mihov & Slav heva-Mihova, 2006).� In Fig.6, ompiled from the publi ations of L. Slav heva-Mihova and oau-thors, some results from the surfa e photometry of Mark 279 and Mark506 are presented.� Photometri monitoring of sele ted quasars and blazars, during the in-ternational monitoring blazar program - WEBT, has been systemati ally arried out. The aim was obtaining light urves of blazars with good ov-erage at the time (B�ott her et al., 2007; Raiteri et al., 2007). In Fig.7,

82 G. Petrov ompiled from the publi ations of Mihov and oauthors, the results fromthe monitoring of the blasar 3C345 are presented.� The hara teristi s of the variability of radio quiet a tive gala ti nu lei atdi�erent time s ales - from within one night to within years, are explored(Ba hev,2009).� Based on ar hival spe tra from the Hubble Spa e Teles ope, the pro�le ofthe ultraviolet CIV 1549 line for about 150 obje ts has been analyzed. Itwas shown that the pro�le hanges (mainly shifted to the blue) are largelydetermined by the hange of a retion rate (Sulenti et al., 2007).� Eigenve tors for over 200 obje ts were determined. It was shown that themajor eigenve tor probably is mainly related to the rate of a retion, i.e.the a retion rate mainly determines the di�eren es in quasars hara ter-isti s (Ba hev & Striga hev, 2004; Ba hev et al., 2004).� Spe tra of bright, but not well studied quasars, were taken at the ob-servatories Rozhen and Skinakas � Gree e. Their entral bla k holes anda retion rates were determined (Ba hev et al., 2008).� The presen e of extranu lear emission region in the galaxy Mark 620 was on�rmed (Yankulova, 1999).� A narrow-band photometry of the galaxy NGC 3516 was held, whi h on-�rmed the Z-shaped stru ture of the emitting gas in extended emissionlines region (EELR) (Golev et al., 1995 ).� A Fabry-Perot interferometri study of the galaxy NGC 2273- SyG type2 was arried out (Golev et al., 1995a)� A spe trophotometri study of the galaxy Mark 817 was ondu ted (Ili et al., 2007).� The presen e of a weak bridge between the galaxy Mark 1040 and its ompanion LEDA 212995 was not on�rmed (Popovi et al., 2005).� There is a progress on the proje t on measuring the bla k hole masses ofthe SDSS quasar sample from their broad emission lines and the ontin-uum luminosity (Ov harov et al., 2005).3.9 HSBG � spe trophotometry and Luminosity fun tionA full spe trophotometri study of the galaxies Akn 144 and 583 was made(Mineva et al., 1982; Petrov et al., 1982; Petrov et al., 2011).The spatial density was de�ned and the Hubble diagram was built for 247Arakelian galaxies and 156 Seyfert galaxies. The two distributions are almostidenti al. (Golev et al., 1983).The luminosity fun tion of 284 Arakelian galaxies with known radial ve-lo ity was built (Golev et al., 1984).Spe tros opi study for 22 Arakelian galaxies (Golev et al., 1985) andmorphologi al study of Akn 26, 27, 28, 31, 32, 79 and 144 were ondu ted(Markov et al. 1985).A list of additional 47 high surfa e brightness galaxies in the Nilson systemwas proposed (Petrov, 1986).3.10 Chemi al abundan e of nebulae and emission-line galaxiesAbundan es of some ions and the hemi al omposition of 49 galaxies withemission lines have been determined (Petrov, 1979).

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Fig. 7. Monitoring of the Blazar 3 345 in V and R bandsDetailed analysis of the galaxies NGC 3690 + IC 694 (Mark 171 a, b),NGC 5929, 5879, Mark 558, and others has been made (Yankulova et al.,1980; Petrov et al., 1981;).Physi al onditions and hemi al omposition of 31 galaxies from theKara hentsev's list of double galaxies have been determined (Petrov et al.,1985).

84 G. Petrov3.11 Star formation and IR propertiesStudies of the star formation rate in 182 High Surfa e Brightness Galaxies(HSBG) were held. It was found to be 10-30 times higher than that of normalgalaxies (Petrov, 1989; Yankulova, 1993).The star formation for 640 Markarian galaxies from IRAS data was stud-ied. The temperature of the dust of about 50 degrees was de�ned. A ordingto their IR hara teristi s (star formation rate, et .) Markarian and HSBgalaxies are loser to the a tive ones than to the normal galaxies. The pres-en e of a bar in 'nona tive' Markarian galaxies does not lead to higher a tivityin the infrared region (Petrov, 1991, 1993).The star formation rate of Kara hentsev double galaxies is lower and is omparable to that of bright spiral galaxies of the Virgo luster (Petrov &Mineva, 1992).In Fig.8 the star formation regions in the galaxy NGC 7479 are marked.

Fig. 8. Star formation regions in the galaxy NGC 74793.12 Globular and open lustersObservational data for 30 open lusters - 7 bright lusters, 7 lusters towardsthe anti enter and 16 probable double lusters (8 pairs) were obtained tofollow the spiral stru ture of the Galaxy. The sequen e of standard stars inNGC 7790 luster was extended in U and I bands (Petrov et al., 2001).The age of the lusters King 14, NGC 146, NGC 2383, NGC 2384, Pismis6 and Pismis 8 was determined (Kop hev et al., 2005; 2006).BV photometry was arried out and a probable age for the double lus-ter NGC 7031/NGC 7086 was determined (Kop hev & Petrov, 2006, 2008).UBVRI photometry was performed and a probable age of the double lusterNGC 6755/NGC 6756 was determined. Based on these data, the suspe t-ing �being luster pairs� is not on�rmed (Kop hev et al., 2007). In Fig.9,

30 years galaxies at Rozhen NAO 85 ompiled from the publi ations of V. Kop hev and oauthors, the age deter-mination and two- olor diagrams for probable double luster NGC 6755 /NGC 6766 is presented.

Fig. 9. Age determination for the members of the 'double luster' NGC 6755/NGC 6756Studies of ellipti ity and morphology of globular star lusters in the An-dromeda Galaxy was arried out (Golev et al., 1995; Staneva et al., 1996).An observational program for studying of open lusters in nearby galaxiesand sear hing for ertain types of stars in them was started. The programin ludes a sear h for variable stars in lusters too. Twenty eight star luster andidates were sele ted, using various methods (Kourtev et al., 2002).3.13 VOIDS and Large s ale stru ture of the UniverseNineteen plates with exposures 2.5-3 hours were taken with th 2 m Rozhenteles ope for studying of about 10 sele ted voids were obtained. For ompar-ison under the same onditions the �eld of the galaxy luster A 1376 was

86 G. Petrovimaged too. Limiting magnitude of B = 23 was rea hed. About 8300 galaxieswere lassi�ed ob the base of their morphologi al features as spiral, ellipti al,et ., and their diameters were measured (Petrov & Kova hev, 1992; Petrov,2006).In the initial treatment 550 galaxies in the �eld of void entred at 1042-00and totally 2745 galaxies in the �eld of void 1306+34, +35, +36 were mea-sured and atalogued (Kova hev & Petrov, 1992; Striga hev & Petrov, 1995).The same was performed for 444 galaxies for 1213+35 (Petrov & Strigat hev,1993), 2297 galaxies in the void 0049+05 (Petrov et al., 2007). More detailedstudy were performed for about 1800 galaxies from over 2250 dete ted galax-ies in the Her ules 1600 +18 void (photometry, e�e tive diameters, surfa ebrightness, distribution of the brightness of the galaxy disk et .(Petrov, 2005).A luster analysis of the galaxies in voids 0049 +05 and 1600 +18 wasmade. The options for sele ting low surfa e brightness galaxies were demon-strated (Petrov et al., 2006; 2007).3.14 Gravitational lensingThe distribution of mass in galaxies in the lens system 2237 +0305 was ex-amined. Parameters hara terizing the mass distribution in the galaxy-lens( entral dispersion velo ities, mass and mass-luminosity relation for its en-tral parts et .) were derived. The in�uen e of a probable se ond lens has beenstudied determining the parameters hara terizing the distribution of its mass(Mihov, 2001a). In Fig.10, ompiled from Mihov (2005a), the lens model ofthe Einstein Cross is presented.The time delay for the system 0957 +561 was estimated (Slav heva-Mihova, 2001; Petrov & Strigat hev, 2006). Observations of the Double Quasar0957+561 at NAO Rozhen following the MEGAPHOT ollaboration weremade. The possible enhan ement of the quasar HS 1946 +7658 brightening, aused by gravitational lensing, was investigated (Mihov et al., 1999; Mihov,2001b).A model of Einstein Cross - quasar 2237 +0305 was built (Petrov et al.,1996; Mihov, 2005a).3.15 BOX / PEANUT galaxies(U), (B), V, R, I � CCD frames for 30 galaxies - with BOX / PEANUT har-a teristi s and a ontrol sample have been taken and the surfa e brightnessand the brightness distribution over the galaxy disks have been determined(Petrov & Dettmar, 2011).A detailed study of the galaxy NGC 5610 was arried out (Petrov et al.,2005). In Fig.11, ompiled from the publi ations of G. Petrov and oauthors,some results from analysis of the box/peanut galaxy NGC 5610 are presented.3.16 GRID and Virtual ObservatoryThe ideology of the Bulgarian virtual observatory was des ribed. A brief de-s ription of over 900 CCD frames for 30 open lusters in our galaxy, hundreds

30 years galaxies at Rozhen NAO 87

Fig. 10. Lens modeling of the Einstein Cross

Fig. 11. Study of unusual Box/Peanut galaxy NGC 5610of CCD frames of quasars - gravitational lenses, over 500 (U, B), V, R, I CCDimages of BOX / PEANUT galaxies, over 1800 FITS-�les for more than 6000galaxies in sele ted voids, about 700 spe tra, in luding 27 spe tra of 9 plane-tary nebulae, 100 spe tra of a tive galaxies and more than 300 spe tra of highsurfa e brightness galaxies was presented. All the data are in preparation forunlimited a ess on the servers of the Institute of Astronomy (Petrov et al.,2009).

88 G. PetrovThe �rst steps towards the use of GRID for astrophysi al models andevaluations were made. (Petrov et al., 2010; Petrov & De hev, 2010).Two book- referen e materials for GRID and BGVO and Linux operatingsystem for astronomers are in preparation.3.17 Astronomi al maintenan e and others� The onstru tion and alibration of the photographi amera for the 60- m teles opes, able to image stellar lusters and galaxies, were des ribed(Roussev et al., 2006).� Observational equipment of an ele tro-photometer for the Belograd hi k60- m teles ope, able to measure light �ows from stars and galaxiess, aswell a s its alibration in the UBV system, is onstru ted and des ribed(Tomov, 1985).� Astrophysi al methods were implemented for the ontrol of the tempera-ture regime during an ele tron-beam welding (Petrov et al., 1998).� The alibration of the CCD ST-8 ameras to the Belograd hik 60- mteles ope (noise, temperature dependen e, linearity, et .) and the BV RcIcphotometri system is des ribed using a photometry of standard stars(Ba hev et al., 1999).� Spe ialized software was developed to solve di�erent spe ial tasks - pri-marily designed for di�erent types of statisti al analysis of the light urveset ., some of whi h is available for free use (Georgiev, 1991).� An aperture photometry program of images - FITS Imager, in ludingpatrol observations, was prepared and the program itself lo ates the starsof interest (Ba hev, unpublished).� Adaptive �lter for surfa e photometry of galaxies was tested and optimized(Slav heva - Mihova et al., 2006).� The possibility of spe tral observations of galaxies with 2 -m teles opeof NAO with a CCD amera and the spe trograph UAGS was studied(Mihov et al., 2006).� A methodology for pro essing observations obtained with Fabry - Perotinterferometer, was developed and utilized (Golev et al., 1995).Con lusionMany years of fruitful ollaboration between Bulgarian and foreign astronomersand institutions gave signi� ant results. Extragala ti investigations from theobservational point of view ontinue to be one of the interesting �elds to-ward understanding the Universe. Rozhen NAO gives and will ontinue togive an important ontribution in studying the physi al pro esses in galaxiesand their systems.The author is thankful to all the olleagues for the support and un-derstanding. All the data �les on erning galaxies in voids are available athttp://www.astro.bas.bg/�petrov/ and soon via the WEB page of the Bul-garian Virtual Observatory.

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