V407 Cygni and RS Ophiuchi are two similar but unique objects. It can be said that they each belong to an individual type of stars. During their quiet state they seem to be symbiotic stars. However, both stars have previously displayed nova-like outbursts. We would like to take a closer look at these two unique objects, and to compare them. We presented spectroscopic and photometric observations of V407 Cyg and RS Oph obtained throughout the period from 2006 until 2013. Our data show the di erent activity stages connected with the two components of these binary systems. Multicolour photometry and spectra obtained in a wide frequency range are utilized to understand the behaviour of such extremely binaries

Buil, C.

Drozd, K.

Ragan, E.

Swierczynski, E.

Advances in Astronomy and Space Physics

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

V407 Cyg and RS Oph  comparison of two exotic variablesK.Drozd1, E. Swierczynski1, E.Ragan1, C. Buil2Advances in Astronomy and Space Physics, 3, 75-78 (2013)© K.Drozd, E. Swierczynski, E.Ragan, C.Buil, 20131Centre for Astronomy, Nicolaus Copernicus University, Poland 87100 Torun, ul. Gagarina 112Castanet Tolosan Observatory, Toulouse, FranceV407 Cygni and RS Ophiuchi are two similar but unique objects. It can be said that they each belong toan individual type of stars. During their quiet state they seem to be symbiotic stars. However, both stars havepreviously displayed nova-like outbursts. We would like to take a closer look at these two unique objects, andto compare them. We presented spectroscopic and photometric observations of V407Cyg and RSOph obtainedthroughout the period from 2006 until 2013. Our data show the dierent activity stages connected with the twocomponents of these binary systems. Multicolour photometry and spectra obtained in a wide frequency range areutilized to understand the behaviour of such extremely binaries.Key words: stars, binaries, observationsintroductionV407 Cygni was discovered by Homeister [8] in1936 as a possible classical nova. However, extensiveobservations of the object showed that it exhibitedsymbiotic star attributes, rather than those of clas-sical nova: a dense nebula and the presence of a redgiant [9]. Some features are characteristic of a D-type(dust) system, similar to that of the CHCyg star [20].With such peculiar objects it is rather challenging tounderstand their true nature.The same problem occurs with RSOph, whichwas rstly recognized as probably a new star byCannon [4] on Draper Memorial photographs. Now,following outbursts in 1933 [11], 1958 [27], 1967 [26],1985 [1] and 2006 [22], it is considered to be a recur-rent nova [11].Identication of the type of variability stronglydepends on the activity stage during which our obser-vations are carried out. In the case of the V407Cygsystem, we nd the red giant which pulsates like aMira variable, with a period of about 745d and am-plitude of mpg > 3m [16]. The second componentis the white dwarf, which is the source of long-lastingactive phases observed during recent decades by sev-eral authors [13, 14, 17]. Active stages of V407 Cygniare connected by occasionally increasing of the masstransfer rate from the red giant to hot componentvia stellar wind [23]. Simultaneously, in 2010 V407Cygni revealed the classical nova outburst and unex-pectedly become a good candidate for the recurrentsymbiotic nova.RSOph system contains a red giant and a whitedwarf inside a massive envelope, which formed fol-lowing several outbursts [2]. This conguration, along orbital period (Porb = 455:72  0:83 days [5]),and the presence of both TiO bands and emissionlines, make this binary appear similar to many sym-biotic stars.symbiotic stars surveyFor the past three decades many symbiotic starsand related objects were observed at Piwnice Obser-vatory near Toru« in Poland. We monitored practi-cally all symbiotic stars brighter than 15m, locatedin the Northern hemisphere. Simultaneously, theTargets of Opportunity project enabled us to col-lect many useful data on classical novae. Our ob-servations are collected using a Schmidt Cassegrain60/90 cm telescope to obtain spectra in low and highresolution, and a Cassegrain 60 cm telescope to ob-tain UBVRI photometry. Our experience with erupt-ing events aids us in observations and analysis ofsymbiotic novae. For example, we observed the out-burst of RSOph and AGDra in 2006 and CICygin 2008. One of the recent nova-like outbursts in asymbiotic star was observed in Piwnice in 2010 andaected the V407 Cygni system.photometric observationsOutburst of V407 Cygni in 2010 was rst reportedin [18]. Several features suggest that it was classicalnova outburst, unlike the symbiotic outburst mostoften observed in symbiotic stars: (i) strong windwas observed shortly after maximum outburst, whatin our colour light curves is seen as fast changes inV-R and R-I indices (Fig. 1); (ii) in the short pe-riod of time prior to the appearance of the strongwind, ejecta from the white dwarf surface formed athick envelope, observed in the B-V index as reddrozd@astri.umk.pl75Advances in Astronomy and Space Physics K.Drozd, E. Swierczynski, E.Ragan, C.Buildip, at a time very close to the outburst maximum(JD2455266). The mean measurement errors are0:07m in the U band, 0:04m in B, 0:03m in V, 0:03min R, and 0:02m in the I band. 8 9 10 11 12 13 14 15 1200  1400  1600  1800  2000  2200∆  mag ni t ud eHJD-2454000 B-V +9  V  V-R +9  R-I +11 Fig. 1: The light and colour evolution after V407Cygoutburst maximum.It is interesting how a classical nova outburst andstrong wind from the white dwarf have inuencedthe Mira structure and pulsations. Swift satellite de-tected strong X-ray radiation following the outburstmaximum [21]. This was a sign that strong shockswere formed in a very hot environment between com-ponents, caused by the interactions of the winds em-anating from Mira and that of the white dwarf. Onthe other hand, we plotted ephemeris for giant pul-sations from [12, 19] together with our Infrared data,and presented the results in Fig. 2  prior to the out-burst maximum (JD2455266) the pulsations were ingood agreement with predictions for this Mira, how-ever following the outburst maximum the characterof variability changed. In frequency it is evident,but hard to determine due to a long pulsation pe-riod. However, the change in amplitude is not clear,because a deep minimum in the light curve is notnecessarily caused by changes in cool giant; it canalso be caused by the opaque envelope. 4 5 6 7 8 9 10 11 0  500  1000  1500  2000Ma gn it ud eHJD-2454000InfraredKiziloglu and Kiziloglu (2010)Munari et al. 1990Fig. 2: Brightness changes connected with pulsations ofMira component in V407Cyg binary observed after andbefore outburst maximum. Plotted ephemeris containsperiods from [12, 19] (thick and thin line, respectively),amplitude and oset are adjusted to the selected lter (Iband). The moment of the outburst maximum is indi-cated by an arrow.A similar minimum can be seen in the RSOphlight curve (Fig. 3). However, what is of interest inFig. 3, is that there are several changes long afterthe outburst (indicated by arrows). There was noevidence prior to 2006 of pulsations in the system,however we could not be sure that the brighteningswere not connected with some kind of pulses. Nev-ertheless, there might be other explanations (arrowsin Fig. 3 are also pointing to the conjunctions): it ispossible that changes are caused by dust destroyedby high-energetic radiation at this moment [25]. 2 4 6 8 10 12 200  400  600  800  1000  1200  1400  1600  1800  2000  2200[ ma g]HJD-2453000B-V+5B-I+2VV-R+3.5Fig. 3: The light and colour evolution after RSOph out-burst maximum. Conjunctions in the system are pointedwith arrows.In both stars the plateau was observed in lightcurves shortly after the rapid early decline phase(Fig. 4). These attributes are common to USco sub-class of the recurrent novae, and indicate that fol-lowing the outburst maximum, an extended super-soft source illuminated the accretion disc [15]. Mo-ments of nearby constant magnitudes occurred ap-proximately 40 days and 65 days following the out-burst maximum for V407 Cygni and RSOph, respec-tively. This indicates the presence of a more massivewhite dwarf in V407 Cygni than in RSOph [7]. How-ever, it is unusual for the disc to form so shortlyafter such an energetic outburst, and even more un-usual for the disc to survive such a destructive event.Nevertheless, the presence of a disc may explain theplateau stages. 7 8 9 10 11 12 13 14 0  20  40  60  80  100  120  140V  [ ma g]days after outburstRS OphV407 CygFig. 4: Optical light curves of RSOph and V407 Cygni,plateau mid-phases pointed with arrows.76Advances in Astronomy and Space Physics K.Drozd, E. Swierczynski, E.Ragan, C.BuilThe presence of discs prior to outbursts in bothsystems may explain the well-observed ickering[3, 6]. But for RSOph, ickering can be seen for sev-eral months, not days, following the outburst [28],while for V407Cyg, the ickering is not clearly vis-ible. Therefore, if the rapid changes in the lightcurves are caused by changes in disc, then the pe-culiar events discussed above can not be explainedby the presence of the disc.spectroscopic observationsMost of the spectroscopic data of the V407Cygwere taken by Schmidt-Cassagrain Telescope with anobjective prism, during the outburst of 2010. Fig. 6shows some of the most representative data. Even insuch low-resolution spectra (12Å in H), one can seechanges in several emission lines. The changes areespecially pronounced in the end of April H , anddecline towards early June. What is noteworthy, 85days following the outburst, the ux in H prole islower than the ux in forbidden [Oiii] 5007 prole([Oiii]/H = 1:83). This is potentially an indica-tion of the beginning of the nebular stage [10] andshows that the envelope started to be optically thin.Spectra also show the dual nature of system. At thesame time, features of a nova star and symbiotic starcan be seen. For example, the number of lines of Feis characteristic for Fe-nova (e. g. [24]), but in thered part TiO bands can be found, which indicates alate spectral type object; this is a characteristic ofsymbiotic system. 0 20 40 60 80 100 120 6480  6500  6520  6540  6560  6580  6600  6620Re la ti ve  i nt en si t yWavelengh [Å]RS Oph × 5V407 CygFig. 5: Comparison of H prole in V407Cyg andRSOph, four and two days following the outburst, respec-tively. Spectrum of RSOph was multiplied by a factor ofve.Spectra for the investigation of RSOph were col-lected by a 28 cm diameter telescope with a grat-ing spectrograph. Fig. 5 shows the shape of H pro-les shortly after outbursts in both discussed stars.For this comparison we used echelle spectrum forV407Cyg and 2400 g/mm grating for RSOph, so theresolution is comparable. As we can see, proles aredierent in the wings, but the core of this compli-cated line looks exactly the same: an asymmetricemission with central absorption.More than ve years after the outburst in RSOphsystem, one can still see that the nebular stage isnot over: many emission lines can be seen, includ-ing Fe lines (Fig. 7). However, this feature can notbe mistaken with Fe-nova properties, for example, inV407Cyg, those lines disappeared shortly after theenvelope became transparent. There are no leads topresume, that 5 years after the outburst in RSOphwe still have to deal with an optically-thick environ-ment, so emission in Fe lines must be generated byanother source.conclusionsV407 Cygni and RSOph exhibit several featuresthat make them one of the most interesting starsobserved at Piwnice Observatory. Their unique be-haviour may show us a new class of binaries; it maybe passage stage between nova systems and sym-biotic stars, as they exhibit characteristics of bothtypes of stars. New observations could bring moreinsight, however, both objects are faint in their quietstates, so there are diculties with regular data col-lecting, especially with V407Cyg, which tends toblend with another object in the blue part of spec-trum. Simultaneously, observations during quies-cence can shed some light on the nature of secondarycomponents, because the pulsations that might besources of brightness changes in late type stars, areattenuated during outburst.acknowledgementWe are greatful to former students of Nico-laus Copernicus University, Cezary Galan and PiotrWychudzki, for conducting part of the photometricobservations, and Agnieszka Fidos, Jedrzej Osiwala,Grzegorz Rycyk, and Malgorzata Wozniak, for con-ducting part of the spectroscopic observations.references[1] BodeM.F. & KahnF.D. 1985, in Cosmical gas dynam-ics, Proc. of the Conference, Utrecht, VNU SciencePress, 111[2] Bohigas J., Echevarria J., DiegoF. & Sarmiento J.A.1989, MNRAS, 238, 1395[3] BruchA. 1986, A&A, 167, 91[4] CannonA. J. & PickeringE.C. 1905, Harvard CollegeObservatory Circular, 99, 1[5] Fekel F.C., JoyceR.R., HinkleK.H. & SkrutskieM.F.2000, AJ, 119, 1375[6] GromadzkiM., MikolajewskiM., TomovT. et al. 2006,Acta Astronomica, 56, 97[7] Hachisu I. & KatoM. 2012, Baltic Astronomy, 21, 68[8] HomeisterC. 1949,`Verzeichnis von 1440 neuen ve-randerlichen Sternen MIT Angaben uber die Art ihresLichtwechsels', Berlin, Akademie-Verlag[9] IijimaT. 1989, A&A, 215, 5777Advances in Astronomy and Space Physics K.Drozd, E. Swierczynski, E.Ragan, C.Buil0.51.01.52.0 4000  4500  5000  5500  6000  6500  7000  7500  8000  8500F lu x + of f se t [ er g /c m2 / s/ Å] * 10−1 2Wavelegth [Å]Hαoffset 0.0+0.2+0.3HβHγO IHδHe  I IF e I I[ N I I ][ F e X]F e I IO I IIMax 7.94He  I[O III]He  I[O III]N I IIF e I IF e I IF e I I2010.06.032010.05.252010.04.24Fig. 6: Evolution of optical spectrum of the V407Cyg during the 2010outburst. Only some emission lines are identied [18]. 0.5 1 1.5 2 2.5 4000  4500  5000  5500  6000  6500  7000Re la ti ve  i nt en si t yWavelengh [Å]HαHβHγHδF e I IMax 9.2He  IHe  IN I IIF e I IF e I IFig. 7: Optical spectrum of the RSOph during the 2006 outburst. Onlysome emission lines are identied [18].[10] IijimaT. 2006, A&A, 451, 563[11] JoyA.H. & SwingsP. 1945, AJ, 102, 353[12] KizilogluU. & KizilogluN. 2010, Information Bull. onVariable Stars, 5947, 1[13] KolotilovE.A., MunariU., PopovaA.A. et al. 1998, As-tron. Lett., 24, 451[14] KolotilovE.A., ShenavrinV. I., Shugarov S.Yu. &YudinB. F. 2003, Astron. Rep., 47, 777[15] KozaiY., KuwanoY., Mattei J. & AnnalR. 1979, IAUCirc., 3344, 1[16] Meinunger L. 1966, Mitt. Veränderl. Sterne, 3, 111[17] MunariU., BragagliaA., GuarnieriM.D. et al. 1994,IAU Circ., 6049, 2[18] MunariU., JoshiV.H., AshokN.M. et al. 2011, MN-RAS, 410, L52[19] MunariU., MargoniR. & StagniR. 1990, MNRAS, 242,653[20] MunariU., YudinB. F., TaranovaO.G. et al. 1992,A&AS, 93, 383[21] NelsonT., DonatoD., MukaiK., Sokoloski J. &ChomiukL. 2012, ApJ, 748, 43[22] O'BrienT., BodeM.F., PorcasR.W. et al. 2006, inProc. of the 8th European VLBI Network Symp., eds.:BaanW., BachillerR., BoothR. et al., 52[23] Paczynski B. & RudakB. 1980, A&A, 82, 349[24] RaganE., MikolajewskiM., TomovT. et al. 2010,[arXiv:1004.0420R][25] RushtonM.T., KaminskyB., LynchD.K. et al. 2010,MNRAS, 401, 99[26] SawD.R.B. 1967, The Astronomer, 4, 129[27] WeberR. 1958, Monthly Notes of the Astron. Soc. South-ern Africa, 17, 71[28] WortersH. L., Eyres S. P. S., BromageG.E. & Os-borne J. P. 2008, ASP Conf. Series, 401, 22378

V407 Cyg and RS Oph - comparison of two exotic variables

http://dspace.nbuv.gov.ua/bitstream/handle/123456789/119623/01-Drozd.pdf?sequence=1

V407 Cyg and RS Oph - comparison of two exotic variables

Abstract

Similar works

Full text

Available Versions

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)