Received xx xxxxx xxxx; Revised xx xxxxx xxxx; Accepted xx xxxxx xxxx DOI: xxx/xxxx ORIGINAL ARTICLE Review of light curves of novae in the modified scales. II. Classical novae. Rosenbush A.* 1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, 27 Akademika Zabolotnoho St., 03143 The presentation of the light curves of the novae on the logarithmic scale of the Kyiv, Ukraine radius of the shell ejected during the outburst and in the scale of the amplitude of Correspondence the outburst simplified the review of the light curves of all the known, about 500, *Email: [email protected] classical novae of our Galaxy and the Large and Small Magellanic Clouds. As a result, the modified light curves about of 250 classical novae were grouped into 7 typical groups with subgroups defined by the light curves of prototypes. The largest group is the DQ Her group with V1280 Sco as the main prototype and the key to grouping. Novae of this group have three or four variants of a dust con- densation. Novae of the small GQ Mus group may be a bright X-ray source during an outburst. CP Pup, CP Lac, V1974 Cyg, and V1493 Aql are prototypes for 4 groups with close tilts of the initial brightness decline phase of the light curves. The group with the prototype RR Pic, including the HR Del subgroup,has a prolonged state of maximal brightness with the presence of several brightness variations before the final decline phase. The relationship of groups of novae, or form of the light curve, with processes in the circumstellar and circum-binary system environment is discussed. The material ejected during an outburst forms expanding shells of a generally ellipsoidal shape. In the Lac, Pup, and Cyg groups,the shells do not show a pronounced regular structure, except for their ellipsoidal shape. Shells of novae with a dust condensation (the DQ Her group) have an ellipsoidal shape with an equatorial belt. The uniqueshell of CK Vul, Nova Vul 1670, gives an idea about the possible shape of the shells of other members in the V1493 Sql group. The prototypes RR Pic and HR Del have a very bright belt. arXiv:2007.11025v1 [astro-ph.SR] 21 Jul 2020 Each of groups has own position along the well-known "absolute maximal magni- tude, rate of brightness decline" relation. KEYWORDS: stars: novae âĂŞ- stars: individual – methods: data analysis 1 INTRODUCTION In certain binary systems, in specific conditions, a short- term surface source of thermonuclear energy may arise 2 (Starrfield, Iliadis, & Hix, 2016). As a result, the phenomenon a schematic light curve (Payne-Gaposchkin, 1957). Spectrum of âĂIJnewâĂİ stars or a nova is observed. With the outburst development went through 9 general phases (McLaughlin, amplitude of more than 9-11m, the nova is classified as a clas- 1942). The presence of common details of light curves in sical nova (CN). The energy of such an outburst is enough to different combinations served as the basis for novae classifi- eject a large mass of a matter that can form a expanding shell cation schemes. An increase in the sample size of novae and existing for a long time. The duration of outburst is several or a more detailed idea of the light curves revealed shortcom- tens years, unlike recurrent novae outbursts with the duration ings in the existing classifications of novae, starting with the of 70-700 days. classical scheme based on the rate of brightness decline after m m The ejected shell becomes second radiation source, but due a maximum of 2 or 3 : t2 or t3 (Payne-Gaposchkin, 1957). to the re-radiation of flux from a central high-temperature A lot of efforts were aimed at creating classification schemes source. We fix the interaction of these two variable sources, in for light curves of novae based on the grouping of parts on particular, in the form of a visual light curve. The spectrum of light curves: by the presence of a plateau, temporary decline of an expanding source transforms over time from an absorption brightness, or the absence of details on light curves (Duerbeck, spectrum to purely an emission one. If the energy distribution 1981, 1987a; Strope, Schaefer, & Henden, 2010). in the spectrum of a nova at outburst maximum has a maximum But Strope et al. (2010) concluded that "the primary reason in the optical spectral region and the absolute visual bright- why none of these classification schemes has been usefully ness is almost equal to the absolute bolometric magnitude of adopted is that the classes are so broad that greatly different the nova, then as the shell expands, the maximum of the energy physical settings are lumped together and they have not been distribution in the spectrum of a nova shifts to the ultraviolet. found to correlate with anything else". The reason for this It is believed that sometimes the bolometric luminosity of a state of affairs may also be the wrong approach to solving the nova can a constant for a long time (Gallagher & Code, 1974; problem. Existing schemes rely mainly on the shape of the first Wu & Kester, 1977). By the end of a outburst, the contribution half of the light curve and pay less attention to the comple- of the central source radiation to the observed brightness in the tion of the outburst. Our review of the light curves of recurrent optical region of the spectrum is greatly reduced in compar- novae ((Rosenbush, 2020), hereafter Paper I) showed that for ison with the line spectra of the shell radiation (Kaler, 1986; a recurrent nova by any part of an incomplete light curve in Vorontsov-Velyaminov, 1953). any outburst, we can be restored the complete light curve in a One of the results of such set of radiation sources is a given outburst if there is a template. This is the classification prolonged light curve. And if at the beginning of the out- of light curves of classical novae should also strive for such a burst a light curve shows clearly noticeable fast and large state. Then the combination of some physical characteristics changes, then as you move away from the outburst maximum, of the novae in the same group will most likely be the same. all changes slow down in time, decrease in amplitude and are It is possible that in the other group a slight difference in one harder to notice. Therefore, sometimes a logarithmic time scale characteristic can lead to a striking difference in the shape of is used to represent the light curve (Vorontsov-Velyaminov, the light curve. Such a scheme is proposed in this study. 1953), since in this case the initial and some other parts of the We have changed the basic provisions. The basis of the new light curve of the nova are displayed by straight lines, and the approach was the transition to the construction of light curves prolonged second half of the light curve is compressed and the in modified scales: the logarithmic scale of time, or radius light curve becomes compact, convenient for her full review. of the shell ejected during an outburst (Rozenbush, 1996a), Each year, the list of novae stars is replenished with new and the amplitude of outburst (Rosenbush, 1999a). The impe- objects. To date, the number of known classical novae in our tus for using the shell radius as an argument was the work Galaxy reaches 400. of (Clayton & Wickramasinghe, 1976) on the study of dust The most extensive and accessible information on novae is condensation in expanding shells of novae, one of the results provided by photometry, which has a 150-year history, and in of which can be interpreted as follows: when the luminosity some cases centuries-old. A great amount of photometric infor- and temperature of two novae are equal, dust condensation mation has always served as the basis for the systematization occurs at equal distances. Such novae, with a dust conden- of objects. Spectral observations mainly served for the confir- sation, have always been combined into a novae group of mation of the identification of the star as nova. It has long been the DQ Her types, in which the transition phase of the out- noticed that both the photometric and spectral behaviour of the burst, a temporary decline in brightness, is identified with novae have common features. This consistency in behaviour dust condensation, which did not violate the general trend found itself expression in the definition of phases in the devel- of the light curve. Rozenbush (1996a) showed that the same opment of brightness and spectrum of a nova during an out- phases of the light curve and the phases of spectra develop- burst. For light curves, the result is expressed in the phases of ment in the shell radius scale for different novae, including 3 DQ Her, occur at a smaller relative radius range than the 2014)1, in particular, in the region of the galactic bulge ratio of the corresponding time intervals after the maximum (Mroz, Udalski, Poleski, & et al., 2015) and the LMC brightness when the shell is reset. As a consequence of this and the SMC (Mroz, Udalski, Poleski, & et al., 2016b); circumstance, the studies of Rosenbush (1999a, 1999b, 1999c, ASAS-SN (Kochanek, Shappee, Stanek, & et al., 2017; 1999e) showed the possibility of grouping novae according to Shappee, Prieto, Grupe, & et al., 2014); SMARTS specialized a form of light curves in the scale of the radius of the ejected review (F. M. Walter, Battisti, Towers, Bond, & Stringfellow, shell. Applying the results to specific objects made it pos- 2012), data of mission Gaia and others.