Classical Nova Persei 2018 outburst from the dwarf nova V392 Per
Drahomír Chochol, Sergey Shugarov, Ľubomír Hambálek, Augustin Skopal, Štefan Parimucha, Pavol Dubovský
aa r X i v : . [ a s t r o - ph . S R ] J u l Classical Nova Persei 2018 outburst from the dwarfnova V392 Per
Drahomír Chochol ∗ , Sergey Shugarov , , L’ubomír Hambálek , Augustin Skopal ,Štefan Parimucha and Pavol Dubovský Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica, Slovakia P.K. Sternberg Astronomical Institute, M.V. Lomonosov Moscow State University, Russia Institute of Physics, Faculty of Natural Sciences, Šafárik University, Jesenná 5, 040 01 Košice,Slovakia Vihorlat Astronomical Observatory, Mierová 4, 066 01 Humenné, SlovakiaE-mail: [email protected] , [email protected] , [email protected] , [email protected] , [email protected] , [email protected] On 2018, April 29, a bright classical nova (CN) Per 2018 was discovered. Its progenitor is well-known dwarf nova V392 Per. In this contribution we analyse
UBV R C I C photometry and opticalspectroscopy of the CN V392 Per. From the V light curve (LC) we found the brightness declinetimes t , V = 3 d, t , V = 10 d and calculated absolute magnitude of the nova at maximum MV max = -9.30 ± MV max - t "universal" decline law and MV relations, adopting theGaia data for CNe. We determined the colour excess E B − V = 0.90 ± d = 3.55 ± M wd = 1.21 M ⊙ . The CN Per 2018 canbe classified as a fast super-Eddington nova with an outburst LC of plateau type. Nova displayedHe/N spectrum classification, large expansion velocities, and triple-peaked emission-line profilesduring the decline, explained by equatorial ring seen nearly face on and a bipolar flow alignedalmost with the line of sight. The post maximum spectra of CN Per 2018 and available radio datawere used to estimate the inclination angle of the system as i ∼ ◦ . The difference in intensity ofredward and blueward emission bumps is possible to explain by about 1.5 times higher density ofthe receding outtflow. The rapid increase of the bipolar outflow radial velocities by ∼
300 km/saround day 5 after the maximum was caused by the fast bipolar winds from the burning whitedwarf after shrinking of its pseudophotosphere.
The Golden Age of Cataclysmic Variables and Related Objects V (GOLDEN2019)2-7 September 2019Palermo, Italy ∗ Speaker. c (cid:13) Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/ lassical nova outburst from the dwarf nova V392 Per
Drahomír Chochol
1. Introduction
CNe are cataclysmic variables (CVs) with 6 to 19 mag brightness increase, caused by ther-monuclear runaway (TNR) event on the surface of a white dwarf (WD). They arise in close bina-ries with orbital periods of a few hours up to ∼ ⊙ , during the outburst can reach a few times 10 L ⊙ . After the TNR, the photosphere of the WDcomponent of the CN expands to supergiant dimensions and engulfs the binary. Due to a strongwind, a large part of the envelope is ejected and the photospheric radius shrinks.Classical novae can be divided according to their photometric appearance to the fast and slow.Classification is usually based on a time interval in which nova fades by 2 or 3 magnitudes ( t , t ) from its maximum brightness. The fast super-Eddington novae ( t < t <
30 days) havesmooth LCs with well-defined maxima. The slow Eddington novae ( t > t >
30 days) havestructured LCs and many of them have standstills at maximum and dust formation at later stages[9]. According to the properties of the LCs during nova declines, [28] proposed seven types ofLCs: S (smooth), P (plateau), D (dust dip), C (cusp), O (oscillations), F (flat-topped), and J (jitter).The spectra display either He+N or Fe II emission lines as the most prominent non-Balmerlines at maximum light. Fe II spectra are formed in a large circumbinary envelope of gas, whoseorigin is the secondary star, while He/N spectra are formed in WD ejecta. In hybrid objects, bothclasses of spectra appear sequentially due to changing parameters in the two emitting regions [32].Dwarf novae (DNe) are CVs with 1-6 mag brightness increases and durations of days-to-weeks. Osaki [23] proposed a unification model for DN outbursts within the framework of the diskinstability model, in which two different intrinsic instabilities (the thermal and the tidal instability)within accretion disks play an essential role.The donor in CNe, recurrent novae (RNe) and DNe can be either a red dwarf (for orbitalperiods of the order of hours) or a cool subgiant (for orbital periods in the range 10 hrs to 6 days).
2. Discovery of the CN Per 2018 and its progenitor DN V392 Per
Classical Nova Persei 2018 was discovered as a new transient TCP J04432130+4721280 byNakamura [22] on 2018 April 29.474 UT at mag 6.2. He noted that the transient is spatially coinci-dent with U Gem type dwarf nova (DN) V392 Persei [10]. According to our data, the nova reachedthe brightness maximum V max = 6.24 mag, B max = 7.12 mag on 2018 April 29.83 (JD 2458238.33),taken as a zero point (0.0 d AM ) for counting the times of photometric and spectroscopic observa-tions through our paper.Darnley & Starfield [8] discussed the available data of Nova progenitor V392 Per. The 2004-2018 AAVSO LC indicates the quiescent system with V ∼ ± + . − . kpc. The 3D dust maps of Green et al. [13][14] yield a reddening of E B − V =0.9 ± + − pc and 3416 + − pc, respectively. Darnley and1 lassical nova outburst from the dwarf nova V392 Per Drahomír Chochol
Starfield [8] found that the SED of V392 Per in quiescence is similar to the CN GK Per or RNe USco and M31N 2008-12a, that contain evolved donors (subgiant or red-clump giant).
3. ATels spectroscopy and multifrequency observations of the CN Per 2018
Classical nova outburst was confirmed spectroscopically [31] on April 30.116 UT (0.286 d AM )with the 2.4-m Hiltner telescope on Kitt Peak MDM Observatory. The spectrum exhibits broad H α emission, with FWHM 5200 km s − and absorption displaced by - 2680 km s − with respect tothe fitted center of emission, and Fe II P Cygni-type line profiles. The spectrum is similar to thespectrum taken by R. Leadbeater (ARAS) at April 29.898 UT (0.068 d AM ).Li et al. [15] detected nova as a strong gamma-ray source using the data collected on April 30(00:00:00 - 23:25:53) by Fermi Large Area Telescope, covering the energy range from 20 MeV tomore than 300 GeV.The high-resolution spectra (R ∼
30 000) of the nova, obtained by Tomov et al. [29] on May1.78 (1.95 d AM ) and May 2.78 (2.95 d AM ) with the 2-m telescope at Rozhen observatory exhibitedbroad emission lines with complex shape. The strongest emissions are H α , H β , Fe II 42 multiplet,Ca II IR triplet and O I lines. The FWHM for H α , H β emissions are 5600 ±
200 km/s. Threeemission peaks at about -2000 km/s, -250 km/s and 1900 km/s, and weak P Cyg absorptions at-4000 km/s in H α , while -3700 and -4100 km/s in H β are detected. The extinction derived from5780 Å, 5797 Å, 6614 Å diffuse interstellar bands and KI line is E B − V = 1.18 ± ∼ ∼ AM ) [6].Linford et al. [16] reported radio observations with Karl G. Jansky Very Large Array (VLA) inSoccoro and Arcminute Microkelvin Imager Large Array (AMI-LA) in Cambridge. The nova wasclearly detected with VLA at 5.0 and 7.0 GHz on 2018, May 8.7 (8.87 d AM ) and May 12.6 (12.77d AM ) and with AMI-LA at 15.5 GHz on 2018, May 11.5 (11.67 d AM ) and May 13.6 (13.77). Thenova is increasing in flux density at all frequencies. A brightness temperature of the order of 10 K,estimated from radio data, the ejecta expansion velocity of 4000 km/s [29] and a distance of 3.9 kpc[8] is higher, than expected for nova ejecta emitting via thermal bremsstrahlung. Therefore, theysuspected a significant contribution from synchrotron emission, related to the shocks that producedthe population of accelerated particles necessary for the detected gamma-ray emission [15]. During2018, May 17 - 21 compact knots (with brightness temperature in excess of 10 K) moved awayfrom each other with a projected velocity of 1350 km/s [17].The LT spectra of the nova taken after the sun constrain on 2018, July 13.21 UT (74.38 d AM )showed that the object entered the post-nova eruption nebular phase [4],[5]. The spectra exhibitedH α , H β , H γ , H δ , He I and He II (4686 Å) triple-peaked emission lines and extremely strongdouble-peaked [O III] lines at 4363, 4959 and 5007 Å. The width of the [O III] lines are consistentwith those of H I lines. The central narrow ( ∼
50 km/s) and bright emission peak of H α line isaccompanied by fainter and broad blueward and redward emission bumps with FWHM of ∼ ∼ ± AM ), when itcould be pointed by the Swift Observatory after the sun constrains. The Swift UVOT photometry2 lassical nova outburst from the dwarf nova V392 Per Drahomír Chochol in v,b,u,w1,m2,w2 filters was obtained on 2018, July 20, 26, 27. The large flux deficit through them2 filter suggests a high extinction toward the system.The spectra with the resolution R ∼ AM ) using the Asiago 1.22-m telescope, show the transition to advanced nebularconditions with [OIII] 4959+5007 flux 3.6 times the integrated flux of H α + [NII]. All emissionlines were composed of two broad and well-separated components (both with a FWHM 1800km/s). The bluer component was generally the strongest. The velocity separation of these broadcomponents ranges from 3400 km/s for H α up to 4500 km/s for [NeV] 3426 Å. In most of theemission lines, except [NeV], the central narrow and low-velocity component is detected. The peakintensity of this central, narrow component (Nw) varies greatly from line to line compared to theintensity of the broad components (Bc), ranging from Nw >> Bc for HeII 4686, to Nw > Bc forHeI lines, Nw ∼ Bc for Balmer lines and Nw << Bc for [NeIII], [OIII], [NII] nebular lines. Suchprofiles for the emission lines are closely similar to those observed at late stages in the extremelyfast and He/N V2672 Nova Oph 2009, modelled by Munari et al. [20] as a bipolar flow alignedwith the line of sight plus an equatorial torus seen face-on. The large intensity of the [NeV] 3426line, comparable in intensity to H α + [NII], suggests that V392 Per is a Neon Nova.The outburst of CN Per 2018 has begun to wane during the sun constraint between April 26,2019 and July 18, 2019, when optical spectra dominated by broad nebular forbidden lines of [OIII] at 4959 and 5007 decreased in intensity [21].
4. Our photometry and basic parameters of the CN Per 2018
Our U , B , V , R C , I C CCD observations of the nova were obtained at the Stará Lesná Observatoryof the Astronomical Institute of the Slovak Academy of Sciences (AISAS) (Zeiss 60-cm telescope,Maksutov 18-cm telescope, 6-cm telephoto lens) and the Kolonica Observatory (100-cm VihorlatNational Telescope (VNT) and 3 other small telescopes of the Vihorlat Astronomical Observatory,Humenné, Schmidt-Cassegrain 50.8-cm telescope of the Šafárik University, Košice). The datawere processed by a standard way using the nearby comparison stars and reduced to the standardJohnson-Cousins system. Our data were complemented with those available from AAVSO, VSNETand other sources. The B and V data around the brightness maximum and during 16 days aftermaximum are presented in Fig. 1. The nova displays a photometric plateau phase between day5 and 8 after maximum, so the LC is of a type P (Plateau) according to classification [28]. Theavailable U , B , V , R C , I C data and corresponding colour indices during 38 days after maximum arepresented in Fig. 5.From the V LC we found the brightness decline after maximum V max = 6.24 mag characterizedby the times t , V = 3 d, t , V = 10 d, and the V magnitude at day 15, V = 10.3 mag ( V max - V = - 4.06 mag). Selvelli and Gilmozzi [25] published new "universal" decline law relation MV max = ( − . ± . ) + ( . ± . ) log t and MV = − . ± .
41 empirical relation, basedon which we estimated the absolute magnitude of the CN Per 2018 in maximum as MV , max = -8.96 ± MV , max = -9.64 ± MV max = -9.30 ± M wd = . − . logt allows to find the mass of the WD in thebinary as M wd = 1.21 M ⊙ . 3 lassical nova outburst from the dwarf nova V392 Per Drahomír Chochol
Figure 1: V and B LCs of the CN Per 2018 in the first 16 days after maximum brightness
The interstellar extinction towards the CN Per 2018 can be found using our photometric B , V data and methods described in [30]: i) from the comparison of the observed CN Per 2018 colourindex ( B − V ) max = 0.88, affected by extinction, with the intrinsic colour index for novae ( B − V ) = 0.23 ± E B − V = 0.65 ± B − V = − . ± .
04, so the value B − V = 0.83 found for CN Per 2018 yields E B − V = 0.85, iii) Tomov et al. [29] determined the reddening E B − V = 1.18 ± + − found by [1] to determine E B − V = 0.91 + . − . . The mean value of the reddeningfound from the data mentioned above is E B − V = 0.90 ± ± V max − MV max = 15.54 ± ± V max = 5.6 mag, t = 2 d, t = 4 d, V = 10.2 mag, A V = 1.6 mag, M max = - 9.0 mag.The distance determined from these data is 3981 pc, close to the distance 4161 + − pc found bySchaefer [24] from Gaia data. The source of discrepancy between the Schaefer’s and our resultsis the fact, that he used the value of brightness maximum 5.6 mag from an unfiltered image takenby D. Buczynski [2] at JD 2458238.4 (see also https://britastro.org/node/13057). As seen from ourdata, the V magnitude of the nova in maximum was only 6.24 mag.Basic parameters of CN Per 2018, we derived from photometric observations, are indepen-dently supported by modelling the optical spectrum obtained at the maximum brightness of thenova. Fig. 2 shows the low-resolution spectrum (R ∼ AM ) near the optical maximum. The spectrum is dereddenedwith E B − V = . BV R C I C photometric fluxes. The continuum4 lassical nova outburst from the dwarf nova V392 Per Drahomír Chochol
V392 Per
April 29, 2018 E B-V = 0.9 F l ux [ - e r g c m - s - A - ] Wavelength [A] spectrumBVR C I C T eff = 7000 KT BB = 9000 K Figure 2:
The spectrum of V392 Per (in magenta) taken at the optical maximum of the nova on April 29.89,2018, scaled to
BV R C I C fluxes (squares). The continuum can be matched by the atmospheric model (gray)and/or by the blackbody radiation (blue). Observations are dereddened with E B − V = . spectrum resembles that produced by a star of spectral type F2. Using the grid of atmosphericmodels [18] we matched the continuum by a synthetic spectrum characterized with the effectivetemperature T eff = θ WD = R effWD / d ∼ . × − , which is the an-gular radius of the WD pseudophotosphere given by its effective radius R effWD (= the radius of asphere which has the same luminosity as the observed stellar photosphere) and the distance d .These fitting parameters correspond to R effWD ∼ ( d / . ) R ⊙ and the luminosity of the WD L WD ∼ . × ( d / . ) erg s − . The continuum spectrum is also well comparable to that ofa blackbody radiating at the temperature T BB ∼ θ WD ∼ . × − , which cor-respond to R effWD ∼ ( d / . ) R ⊙ and L WD ∼ . × ( d / . ) erg s − . When we acceptthe distance 3.55 kpc, the bolometric magnitudes of the outbursted WD for the atmospheric andblackbody models are M abol = -9.0 mag and M bbol = -9.33 mag, respectively. Their absolute visualmagnitudes MV a = -8.85 mag and MV b = -9.18 mag, are close to the values, which we derivedfrom photometry.
5. Our spectroscopy of the CN Per 2018 and its expanding shell
Our optical echelle spectra of the CN Per 2018 were obtained on 2018, May 2-6 (3 to 7 days af-ter maximum) with the 60-cm telescope in the G1 pavilion of the AISAS observatory at Stará Lesná(three spectra with the resolution R ∼
12 000) and 1.3-m telescope of the AISAS observatory atSkalnaté Pleso (three spectra with the resolution R ∼
24 000). Our data were completed by the As-tronomical Ring for Access to Spectroscopy (ARAS) data obtained by small telescopes and spectro-5 lassical nova outburst from the dwarf nova V392 Per
Drahomír Chochol R ∼
500 - 800 and 8spectra with the resolution R ∼ α region. Wavelength (A)
Figure 3:
The spectrum of the CN Persei 2018 with identified features. Continuum is normalized to theintensity 1
The spectrum taken by our 1.3-m telescope 6 days after the maximum is presented in Fig. 3. Itclearly shows the structured Balmer H α - H γ and He I (5876 Å ) line profiles with three individualpeaks, HeI, [OI] and NII lines and strong interstellar NaI lines and DIBs. The sequence of theH α and H β line profiles of the CN Per from day 3 to day 7 after the brightness maximum in theradial-velocity scale is presented in Fig. 4. It is clearly seen, that the intensity of the redward broademission bump is higher than the intensity of the blueward one.For fitting of H α line profile and continuum, we used the code fityk [33]. It is a general-purpose peak fitting software with a graphical interface. It offers many non-linear functions, sub-traction of continuum, and can fit an arbitrary number of peaks simultaneously by the Levenberg-Marquardt least square method. We selected the region of spectrum around the H α line and fittedcontinuum by the second-order polynomial. We added a few Gaussian peaks based on the shapeof the line, emission, and absorption features. The main emission peak was selected to cover theshape of the wings and the intensity at the central wavelength. We have calculated 3 σ distancefrom λ C and computed corresponding radial velocity to λ C -3 σ while using the laboratory wave-length for H α . Then the full width at zero intensity (FWZI) of the H α profile, half-width at halfmaximum (HWHM) of the central emission and differences in RVs between the central emissionand emission bumps were found and expressed in the radial-velocity scale. They are presented inFig. 5.An increase of the B , V magnitudes at 5-6 d AM was accompanied by the increase of FWZI ofthe H α profile with a maximum at 7-8 d AM . Due to the fact, that the HWHM of the central emission6 lassical nova outburst from the dwarf nova V392 Per Drahomír Chochol
Figure 4:
The sequence of the CN Per 2018 H α (a) and H β (b) line profiles on high dispersion spectraobtained at Skalnaté Pleso and Stará Lesná Observatory lassical nova outburst from the dwarf nova V392 Per Drahomír Chochol peak during this period continuously decreases, the increase of FWZI was caused by broadeningof emission bumps of the H α profile. The absolute values of radial velocity differences betweenthe central peak and emission bump rapidly increased for about 300 km/s at 5 d AM and lasted till12 d AM . At the same time, we detected the decrease in intensity of the H α emission. Figure 5:
The comparison of the U , B , V , R C , I C photometry, colour indices, FWZI of the H α profile, HWHMof the central emission peak, differences in RVs between the central emission peak and emission bumps andintensities of the H α profile of the CN Per 2018 during the first 38 days after maximum Chochol et al. [3] derived a kinematic model of an expanding shell of the fast CN V1974Cygni using the optical and UV spectra, HST and radio images. The shell consists of two majorcomponents: an outer fast tenuous low-mass envelope and an inner slow main high-mass envelope,accelerated by slower spherical and faster polar winds. The outer envelope (detected spectroscop-ically and on radio images) is spherical except for the polar region, where an outflow with largervelocity is observed. The most pronounced features of the inner envelope (detected spectroscopi-cally and on HST images) are an expanding equatorial ring and polar blobs.The similar structure of the shell of CN V392 Per is possible to reveal by disentangling of theH α line profile in the early stages of the outburst using the low dispersion spectra presented in Fig.6. They were obtained by members of the ARAS group R. Leadbeater, Three hills Observatory,8 lassical nova outburst from the dwarf nova V392 Per Drahomír Chochol
Figure 6:
Disentangling of the H α profiles of the CN Persei 2018 in the first two days after maximum. Thetotal profile (TP), ellipsoidal nebula (EN) and components of the outer envelope (OE) and inner envelope (IE)are distinguished by different colours: TP (orange), EN (green), approaching spherical OE (blue), approach-ing polar outflow OE (magenta), receding polar outflow OE (pink), equatorial ring IE (grey), approachingpolar outflow IE (cyan), receding polar outflow IE(red) lassical nova outburst from the dwarf nova V392 Per Drahomír Chochol
UK (0.068 d AM , 1.059 d AM ) and E. Bertrand, St. Sordelin, France (2.006 d AM ). The spectrum at0.607 d AM was obtained by M. Fujii (Fujii Kurosaki Observatory, Japan). We detected the outerenvelope, shaped by spherical wind during the brightness maximum (day 0.068) as an H α P-Cygabsorption at ∼ α P-Cyg absorption andan emission bump. Their radial velocities show about ± AM ) as two compact knots with brightness temperatures in excess of10 K, which move away from each other with a projected velocity of 1350 km/s using a distanceof 3.9 kpc [8]. The radial velocity of the outflow 4200 km/s and its tangential velocity 675 km/sallows estimating the inclination angle of the object as i ∼ ◦ . Figure 7:
The SHAPE model with equatorial ring (o) and polar blobs (B,R)
The structure of the ejecta consisted of equatorial ring and polar blobs was find by Munariet al. [20] in the extremely fast nova V2672 Oph (Nova Oph 2009). Their morpho-kinematicalmodelling of the triple-peaked H α profile of the nova using the code SHAPE2 [26],[27] showedthat the system is seen pole-on, with an inclination of 0 ◦ ± ◦ and an expansion velocity of thepolar blobs 4800 + − km/s. A bipolar flow is aligned with the line of sight and an equatorial torusseen face-on.We applied the morpho-kinematical code SHAPE2 [26], [27] for analysis and disentanglingthe three-dimensional geometry and kinematic structure of the outburst H α spectra of V392 Per.The SHAPE model is presented in Fig. 7. The equatorial ring was detected on triple-peaked H α profiles as a central emission and polar blobs as blueward and redward bumps. The line profilesmodelling presented in Fig. 8, confirm a small inclination angle of the object ( i ∼ ◦ ). The asym-metric outflow can be caused by ∼
6. Conclusions
CN Per 2018 (DN V392 Per) is the fast super-Eddington nova with outburst LC of P-type(smooth decline interrupted by a plateau) according to the classification [28]. The behaviour of thenova is similar to RN U Sco and extremely fast nova V2672 Oph (suspected RN). All three objectsdisplayed He/N spectrum classification, large expansion velocities, and triple-peaked emission-lineprofiles during the decline. The structure of the expanding shell of CN Per 2018 is similar to theCN V1974 Cygni [3], consisting of an outer fast tenuous low-mass envelope and an inner slow10 lassical nova outburst from the dwarf nova V392 Per
Drahomír Chochol
Figure 8:
The SHAPE model fits. The total profile (TP), ellipsoidal nebula (EN) and components of theinner envelope (IE) are distinguished by different colours: TP (orange), EN (green), equatorial ring IE (grey),approaching polar outflow IE (cyan), receding polar outflow IE(red) high-mass envelope. The expanding spherical outer envelope and its polar outflows were detectedaround the maximum. The inner envelope consisting of an equatorial ring and polar blobs wasclearly detected 3 days after maximum. The rapid increase of absolute values of radial velocitiesof polar blobs from ∼ ∼ ∼ ◦ . Acknowledgments
We thank to observers R. Leadbeater, E. Bertrand, C. Boussin, J. Edlin, P. Berardi, D. Dejean,J. Montier, O. Garde, M. Verlinden and M. Buchet for the spectra of CN Per 2018 available at theARAS (Astronomical Ring for Access to Spectroscopy) database. ARAS is an initiative promotingcooperation between professional and amateur astronomers in the field of spectroscopy, coordi-nated by Francois Teyssier. Our thanks belongs also to R. Komžík for 3 spectra obtained at theSkalnaté Pleso Observatory. We acknowledge the variable star observations from the AAVSO In-ternational Database contributed by observers worldwide and used in this research. This work wassupported by the Slovak Research and Development Agency under contract No. APVV-15-0458and by the Slovak Academy of Sciences grant VEGA No. 2/0008/17.
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