PoS(GOLDEN2019)043 https://pos.sissa.it/ ∗ [email protected] [email protected] [email protected] [email protected] Speaker. Symbiotic stars are strongly interactingmainly of binaries, spectral consisting type M. of AG Draconis a belongssystems, to white a as dwarf less numerous the and group cool a of the componentafter cool yellow seven symbiotic in giant, years this of quiescence, binary this is symbioticfour star of minor exhibited outbursts a a observed. spectral very Thanks unusual type to activeprofessional the earlier stage observatories, excellent with we than can involvement the of K4. study amateur the activity astronomersthe Recently, of and present AG Draconis work, in we unprecedented details. discussentire In the group activity of symbiotic and stars peculiarities whose of propertiesDatabase have of this recently Symbiotic interacting been Variables. system presented in within our the New Online ∗ Copyright owned by the author(s) under the terms of the Creative Commons c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). The Golden Age of Cataclysmic Variables2-7 and September Related 2019 Objects V (GOLDEN2019) Palermo, Italy Laurits Leedjärv Tartu Observatory, University of Tartu, Observatooriumi 1,E-mail: Tõravere, 61602 Tartumaa, Estonia Marek Wolf Faculty of Mathematics and Physics, CharlesRepublic University, Ke Karlovu 3, 121 16E-mail: Prague 2, Czech Rudolf Gális Faculty of Science, P. J. Šafárik University,E-mail: Park Angelinum 9, 040 01 Košice, Slovak Republic Jaroslav Merc Yellow symbiotic star AG Draconis inthe the New scope Online of Database of Symbiotic Variables Faculty of Mathematics and Physics, CharlesRepublic University, Ke Karlovu 3, 121 16Faculty of Prague 2, Science, Czech P. J. Šafárik University,E-mail: Park Angelinum 9, 040 01 Košice, Slovak Republic PoS(GOLDEN2019)043 Jaroslav Merc character (Merc hot type (Leedjärv et al., 2016). Zanstra temperature drops as II hot Zanstra temperature increases or remains II outbursts, the He 1 cool and smaller-scale outbursts are of the cool K), as the accretor of transferred matter (Mikołajewska, 2007). 5 10 ). We have observed series of four outbursts during the ongoing active stage (Gális outbursts, the brightness of AG Dra is more or less linearly correlated with variations 1 ≈ hot ones which makes the ongoing active stage very unusual. A detailed discussion of the features AG Dra is a variable star whose symbiotic character has been known for years (e.g. Kenyon, According to the brightness of AG Dra, all four recent outbursts can be classified as minor Symbiotic variables are the widest interacting binaries consisting of a cool giant (or a super- AG Dra is one of the best studied symbiotic systems, but as discussed below, there are some The system undergoes characteristic symbiotic activity with alternating quiescent and active As previously indicated by UV observations (González-Riestra et al., 1999), the characteristics Prodigious amount of observations of the symbiotic system have revealed that AG Dra under- 1986). It was discovered accidentallyever, like systematic most search symbiotic for binaries in suchbrought the a objects previous lot has century. of begun How- newof in results. candidates recent Surveys in decades have the and led Milky this to Way effort the (e.g. has discovery already of Miszalski many et new al., objects and 2013; dozens Miszalski & Mikołajewska, 2014) et al., 2018). However, outburstscool in the beginning ofof active this phases activity of will AG be Dra the subject are of usually the major, forthcoming article. 2. New Online Database of Symbiotic Variables et al., 2019). ones. The increase of EWs observed during these outbursts is indicating their unchanged. On the other hand, during the giant) of a spectral typewhite K dwarf or ( M (rarely G) as a donor andunique a features of compact this star, star. most AG- commonly Dra the a belongs cool to hot component a is less aa common red higher group luminosity giant of than of the that an yellow of early symbioticwhite a stars spectral dwarf standard type (WD) class (K0 III sustaining – (giant). a K4), Itset high with hot al., luminosity a component 2012). and low is The temperature metallicity considered orbital (Mikołajewska to and period et be of al., a this 1995; binary Sion system isstages. 551 The days active (Hric stages et occur al., in 2014). intervalsat of about 9 - one-year 15 years interval andmajor, (Gális consist prominent of et outburst several followed al., outbursts by repeating several 2017). minor ones. The activity ofof AG the optical Dra emission lines usually clearly begins confirmedmajor the with presence ones of the are two usually types of the outbursts of AG Dra: went at least six active stages1993 since and continued 1889. until Previous, 2008 particularly (Hricquiescence et long (Q6) al., active and 2014). stage AG This (E+F) Dra active started begun stage rising in panel was again of followed in by Fig. brightness seven in years the of late spring of 2015 (see the top AG Dra in the New Online Database of Symbiotic Variables 1. AG Draconis During the the pseudo-atmosphere of the WD expands. 1.1 Recent outburst activity of AG Dra of emission lines characteristics (e.g. EWs) and the He PoS(GOLDEN2019)043 58500 58500 58500 58500 2018 2018 2018 2018 58000 58000 58000 58000 Jaroslav Merc 57500 57500 57500 2016 2016 2016 57500 2016 57000 57000 57000 57000 2014 2014 2014 2014 56500 56500 56500 56500 56000 56000 56000 2012 2012 2012 56000 2012 55500 55500 55500 55500 2010 2010 2010 2010 55000 55000 55000 55000 2 54500 54500 2008 2008 54500 2008 54500 2008 JD - 2 400 000 [days] JD - 2 400 000 [days] JD - 2 400 000 [days] JD - 2 400 000 [days] 54000 54000 54000 54000 2006 2006 2006 2006 53500 53500 53500 53500 filter over the period 1997 - 2019 of four galactic symbiotic stars B 2004 2004 2004 53000 53000 53000 2004 53000 52500 52500 52500 52500 2002 2002 2002 2002 52000 52000 52000 52000 2000 2000 2000 2000 51500 51500 51500 51500 Z And AX Per AG Dra AG Peg 51000 51000 51000 51000 1998 1998 1998 1998

8 9 8 9 9 7 8

12 10 11 10 11 12 10 11 13 14 10 11 12 B [mag] B B [mag] B B [mag] B B [mag] B Figure 1: The light curveswhich in experienced outbursts in2019), recent Skopal years. et al. Data (2002, 2004, are 2007, obtained 2012) and from Sekeráš AAVSO et database al. (Kafka, (2019). AG Dra in the New Online Database of Symbiotic Variables PoS(GOLDEN2019)043 83%) ≈ Jaroslav Merc (Ogley et al., (Skopal, 2005)

). For the objects ◦ 15 ´ nski et al. (2000) be- 11R < ± | b | ). The metallicity of the giant 3 ). 10%) of so-called yellow symbiotic 4c ≈ and 4b ), these suggest that AG Dra belongs to the old 4a 3 ). The radius of the giant was estimated to be 33 3; Smith et al., 1996). Together with the radial velocity of the system 2 . 1 ≈ − and its position on the sky (Fig. 1 − On the other hand, AG Dra belongs to a small group ( The database is divided into two main parts according to the location of symbiotic variables. With the increasing number of known symbiotic stars, the vast amount of observations ob- Several symbiotic stars have been studied very extensively during previous decades. Among AG Dra is a classical symbiotic star of the infrared type S (Friedjung et al., 1998). Majority is very low (Fe/H in the current version of theare database, located 89 % in of this the sky confirmed region and (Merc 83 et % al., of 2020; candidate Fig. symbiotic stars of -147 km s population of the galactic halo. Although theterm location observations, of at AG Dra the on same theall sky time favors galactic it convenient long- symbiotic is stars not are common located for around variable the stars Milky from Way this equator group, ( as nearly belongs to this type (Fig. and if we assume the2002), volume the giant radius is of under-filling its it, corresponding which is Roche typical lobe for to most be symbioticstars binaries. 170R characterized by anmore early typical spectral spectral type type of M.not the While known, giant the it exact is (K spectral definitely or of type even an of G) early the which spectral giant type is in (K0 different the - from AG K4; Dra Fig. system is The first part consistsare of located 74 in confirmed 14 andNGC 88 galaxies 185, suspected (LMC, NGC 205, extragalactic SMC, NGC 300, symbiotic Dracoof NGC systems 2403, Dwarf, more NGC which IC 6822). than 10, 480 The M31, second galactictables, M33, part objects. which of M81, can the The M87, database be data NGC consists and 55, explored of used symbiotic directly offline variables through in are theries different presented dedicated formats included in web-portal (csv, in the or xlsx, form themation, can txt of database, be and references, we downloaded pdf). notes, have prepared andhttp://astronomy.science.upjs.sk/symbiotics/. Moreover, their useful for object all links. pages symbiotic bina- covering The all database available2.1 is infor- accessible AG Dra through in the the New web-page: Online Database tained particularly thanks to amateur observersSymbiotic and Variables, the symbiotic availability binaries of the can Newable be Online stars. studied Database as In of a addition, whole individualpopulation, stars population allowing can comparison of of be interesting parameters studied vari- and in behavior. relation to other objectsthem, from AG the Dra known is an exceptionalSystem case mentioning with this hundreds object. of articlesponents However, there of available on this are interacting the still system Astrophysics many or Data number open the of questions outburst observations regarding mechanisms and as the studies, well. which com- is Moreover, it unique is about not the only star. the of the objects in the present version of the New Online Database of Symbiotic Variables ( AG Dra in the New Online Database of Symbiotic Variables and the Local Group (e.g. Gonçalveset et al., al., 2014, 2008, 2017; 2012, 2015; Sharasystems Kniazev grew, et et the al., al., catalog 2009; 2016; of Mikołajewska Roth symbioticcame stars et rapidly outdated. which al. was For this published 2018). reason, byextragalactic we Subsequently, Belczy symbiotic have as systems prepared (Merc a the et new number online al., of database 2019a). of known the galactic and PoS(GOLDEN2019)043 , I II , He I ˙ e (2009), Jaroslav Merc types (Akras et sources, 18 have β α and outbursts. The Raman- α cool type in the scheme introduced by type. α δ / β type in which X-ray emission originates from the 4 δ lines vanishing during the VI are observed almost all the time, with the emission lines of Fe VI type in which the X-ray emission is interpreted as due to the shock-heated β types and are therefore classified as the δ and β and Raman-scattered O The hot component of AG Dra is a WD. Although some symbiotic binaries with a neutron star Very prominent emission lines are observed in optical spectra of the II type), and twelve have been classified as the al., 2019; Fig. 2He in Merc et al.,appearing 2019c). during the outbursts In and the the O case of AG Dra, the emission lines of H as an accretor have beenWDs. discovered (e.g. Quasi-steady shell Enoto burning et ofalso al., the the hydrogen-rich 2014), source material majority of on of super-soft the X-ray themhave surface emission contain been of of accreting WD detected AG is Dra. in probably Therethe X-rays are super-soft 58 (Merc other emission et symbiotic which al., stars which have 2019c). been classified Nine as sources, the AG Dra among them, show Figure 2: The positionas of other symbiotic objects stars of insequence various the (MS) infrared near and types IR Red (S, giant color-colorBe S+IR, branch diagram stars D (RGB) from based and loci Zhang D’) on are etT as 2MASS taken Tauri al. well stars from observations. from Straižys (2005), Dahm & & The planetary Simon Lazauskait nebulae Main (2005). from Ramos-Larios & Phillips (2005) and been classified as the plasma emerging in the collision of windsγ from the components, nine are neutron star accretors (the boundary layer between the accretion disk andof the both WD. Eleven systems are showing characteristics AG Dra in the New Online Database of Symbiotic Variables Muerset et al. (1997) and extended by Luna et al. (2013). In addition to nine PoS(GOLDEN2019)043 ). 3 Jaroslav Merc filters are dominated by V or ), because the giant dominates 1 B filters. In symbiotic stars comprising M V filter (Fig. B or B 5 3mag at optical wavelengths that are repeating at intervals of about one 55% of symbiotic stars (Akras et al., 2019). − ≈ 1 ). ≈ 1 filter, and are not so pronounced in lines, which are typically considered as an evidence of the symbiotic nature of an U VI In addition, several other mechanisms contribute to the complexity of the AG Dra light curve. The spectral characteristics of symbiotic systems are changing dramatically throughout their Comparing of the light curves of outbursting symbiotic stars is interesting for several reasons. or several years.of The activity shape differ and not duration onlyactivity of from stages. the object to outbursts The object of AGdemonstrates but Dra symbiotic (Fig. also is stars for an showing one excellent this symbiotic example type binary of during this various variability as its light curve clearly The AG Dra binarywith star amplitudes manifests of the Z And-type activity, characterized by recurrent outbursts giants, these variations are easily observable at least in Although this symbiotic systemand is its not changing visibility an during eclipsing theof orbital one, revolution the are the light responsible photometrically curve for recognizable the asymmetricof sinusoidal mainly nebula variations during the the giant, quiescent the stages.particularly photometric in Due variations to of the early AG spectral Dra type are most significant at shorter wavelengths, object are observed in outbursts (comparison of the quiescent and active optical spectra of AG Dra is shown in Fig. scattered O at longer wavelengths. In case of AG Dra, the light curves in the Figure 3: Optical spectra ofspectral type AG M3) Dra during (the their giant’s quiescencethe spectral (blue) ARAS type and database K0 outburst (Teyssier, 2019). (red) - stages. K4) Data and are AG obtained Peg from (the giant’s The similarities may indicateobserved the activity. For same example, Sokoloski nature et al. of (2006) the proposed the outburst combination mechanisms nova model responsible as an for their AG Dra in the New Online Database of Symbiotic Variables modulations with a period of around 355by days, Gális explained et by the al. pulsations (1999). of the giant as suggested PoS(GOLDEN2019)043 Jaroslav Merc (c) Histogram showing theotic stars distribution over of the galactic symbi- AG latitude. Dra is The shown position by of the green line. 6 Figure 4: The position of AG Dra on the sky. (b) Histogram showing the distributionotic of stars symbi- over the galactic longitude.of The AG position Dra is shown by the green line. (a) The distribution ofgalactic galactic coordinates). symbiotic stars Confirmed overlaid andrespectively. on suspected The symbiotic position the of stars 2MASS AG are Dra infrared denoted is image shown by of by blue the the dots green sky and cross. (in red squares, the AG Dra in the New Online Database of Symbiotic Variables PoS(GOLDEN2019)043 outbursts . Jaroslav Merc 1 cool -1.1; Pereira et al., 1998) outbursts are explained by ≈ hot SS YesYes No No 551 476 -1.3 -1.1 -147 -107 4300 4400 Z And Z And AG Dra LT Del H I, He I, He II H I, He I, He II 7 During some outbursts No K. The symbiotic system LT Del, similarly to AG Dra, 5 10 ≈ Table 1: Comparison of the parameters of AG Dra and LT Del. ). Comparison of the parameters of AG Dra and LT Del is listed in Tab. 1 Activity Orbital period [d] Dominant spectral lines X-rays Temperature of the giant [K] Metallicity [Fe/H] Radial velocity [km/s] IR type Fe II lines O VI lines − During the observation period, LT Del experienced two outbursts (in 1994 and 2017). The On the other hand, it was very exciting to observe the symbiotic system AG Peg to show the As already mentioned, the cool component of AG Dra is the giant of a spectral type K. Most of One of the relatively appropriate candidates is the yellow, infrared type S symbiotic star latter one has been studied by Ikonnikova et al. (2019). They reported that the outburst was explanation of the outburst activity of Z And, in which smaller-scale AG Dra in the New Online Database of Symbiotic Variables the accretion disc instability model, as in the dwarf novae (Warner 1995) and major Z And-type outburst in 2015 (Skopalflare-up. et al., In 2017, the Merc case et ofbeginning al., AG of 2019b), Dra, 165 observations very years in long after 1889 its periodAG until nova-like of Dra 1927 (and quiescence (or other had maybe classical also even symbioticand been 1932). stars then observed as started since It well) to the is experienced show therefore thesystems Z possible, can symbiotic And-type that help nova activity. to stage Comparing solve in this the past issue. current behavior of these symbiotic 3. Comparison of AG Dra and LT Del the symbiotic stars mentioned inants. the previous When section looking for (e.g. an AG objectgiant Peg, markedly (a Z similar yellow And) to symbiotic AG are star), Dra, comprising it besidestype M should an S, gi- meet early Z several spectral And-type other type activity, criteria: of andson the it low of giant should metallicity, both be infrared regularly objects. observed The tosuch New some a Online extent, search. Database allowing compari- of Symbiotic Variables can be used effectively for LT Del. The binarysisting system of with a an giant orbital of a period spectral of type 476 K3 days with (Arkhipova a et low al., metallicity 2011) (Fe/H is con- are due to the thermonuclearapplicable runaway in as the in case the of AG classical Dra nova (Leedjärv outbursts. et al., This 2016) model and may other also symbiotic be stars. and a hot WD with a temperature of belongs to the halo population(-107 which km is s suggested by the low metallicity and high radial velocity PoS(GOLDEN2019)043 VI Jaroslav Merc 8 ´ nski, K., Mikołajewska, J., Munari, U., et al. 2000, A&AS, 146, 407 type, in contrast with the one observed in 1994 during which the temperature did not hot Symbiotic stars are important astrophysical laboratories in studying a great variety of interest- The purpose of this work was not only to present the New Online Database of Symbiotic This research was supported by the Slovak Research and Development Agency grant No. The main difference of the two symbiotic stars is in the presence of Raman-scattered O [4] Dahm, S. E., & Simon, T. 2005, AJ, 129, 829 [1] Akras, S., Guzman-Ramirez, L., Leal-Ferreira, M.[2] L., et al.Arkhipova, V. 2019, P., Esipov, ApJS, V. 240, F., Ikonnikova, 21 N. P.,[3] et al.Belczy 2011, Astronomy Letters, 37, 343 ing phenomena. Yellow symbiotic starsare are not of influenced particular by interest TiO because moleculeof their absorption atomic absorption features lines. spectra which The allowsRecent more symbiotic precise efforts system measurements have AG resulted Dra in isthe the several symbiotic new prototype population. discoveries of that this allow small for but more growing group. systematic studiesVariables but of also to show howcase it can of be AG utilized Dra. for thestage The study and of binary therefore specific aroused symbiotic it the system, issymbiotic in interest stars, more our e.g. recently than those when showing ever Z it interestingsuper-soft And-type X-ray showed activity, to those emission. very containing compare As K unusual we the giants have activity or demonstrated, behaviorcomparison those there of based with are several on the AG options similarities Dra to or select to samples differenceson for other of this example, AG Dra the New to Online otherinteresting Database known symbiotic of symbiotic systems. Symbiotic stars. Variables can Based be used for studies of other Acknowledgements APVV-15-0458, by the Faculty ofgrant Science, VVGS-PF-2019-1047, P. by J. the Šafárik CharlesEstonian University Ministry University, project in of Education GA Košice and UK under Research No. the institutional research internal 890120, funding IUT and 40-1. byReferences the emission lines, which have not been detecteddetected in in spectra the of X-rays LT Del. as This wellor symbiotic which in star points geometry has to and not a optical been difference thickness in of the the hot symbiotic components nebulae. of these systems 4. Conclusions AG Dra in the New Online Database of Symbiotic Variables of the change compared to its quiescentsymbiotic system values. AG Dra. As Similarly to mentioned AGby Dra, before, the sinusoidal quiescent such variations light behavior curves caused of isrevolution LT by Del typical of are the the for dominated binary changing the system. visibility Ikonnikovain et of the al. emitting case (2019) of regions reported the similar during EWs variability the of observed low also orbital excitation emission lines. PoS(GOLDEN2019)043 Jaroslav Merc https://www.aavso.org 9 Pleso, 49, 197 2, 142 Pleso, 49, 228 50, 426 [5] Enoto, T., Sasano, M., Yamada, S., et[6] al. 2014,Friedjung, ApJ, M., 786, Hric, 127 L., Petrik, K.,[7] et al.González-Riestra, 1998, R., A&A, Viotti, 335, R., 545 Iijima, T., et[8] al. 1999,Gonçalves, A&A, D. 347, R., 478 Magrini, L., Munari,[9] U., etGonçalves, al. D. 2008, R., MNRAS, Magrini, 391, L., L84 Martins, L. P., et al. 2012, MNRAS, 419, 854 AG Dra in the New Online Database of Symbiotic Variables [10] Gonçalves, D. R., Magrini, L., de[11] la Rosa,Gális, I. R., G., Hric, et L., al. 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DISCUSSION ALESSANDRO EDEROCLITE: [42] Skopal, A. 2005, A&A, 440, 995 [43] Skopal, A., Va [45] Skopal, A., Shugarov, S. Y., Sekeráš, M.,[46] et al.Smith, 2017, V. A&A, V., Cunha, 604, K., A48 Jorissen, A.,[47] et al.Sokoloski, 1996, J. A&A, L., 315, Kenyon, 179 S. J.,[48] Espey, B. R.,Straižys, et V., & al. Lazauskait 2006, ApJ, 636,[49] 1002 Teyssier, F. 2019, Contributions of the Astronomical[50] Observatory SkalnateWarner, Pleso, B. 49, 1995, 217 Cataclysmic Variables, Cambridge Astrophysics[51] Series, 28 Zhang, P., Chen, P. S., & Yang, H. T. 2005, New Astronomy, 10, 325 AG Dra in the New Online Database of Symbiotic Variables [36] Roth, M. M., Sandin, C., Kamann,[37] S., etSekeráš, al. M., 2018, Skopal, A&A, A., 618, Shugarov, A3 S., et al. 2019, Contributions of the[38] Astronomical Observatory Shara, M. M., Doyle, T. F., Lauer,[39] T. R.,Sion, et E. al. M., 2016, Moreno, ApJS, J., 227, Godon, 1 [40] P., et al.Skopal, 2012, A., AJ, Vanko, M., 144, Pribulla, 171 T., et al. 2002, Contributions of the[41] Astronomical Observatory Skopal, A., Pribulla, T., Va [44] Skopal, A., Shugarov, S., Va