CONTEXT: The Nova V1405 Cas, which erupted on 18 March 2021, showed a pre-maximum phase of almost two months. After the main maximum, during several month the nova only weakened slightly and showed clear fluctuations in brightness. AIMS: The aim of this work is to investigate the relationship between brightness and half-width (FWHM) and equivalent width (EW) of the H-alpha emission line, and from this to infer possible causes for the abnormal behavior of the Nova. METHODS: Magnitudes and spectra from online databases were used, the H-alpha line of the spectra was measured and 2-day normal values were formed in order to establish a temporal comparison. RESULTS: After the main maximum, during the period investigated by JD 2459292 to 2459305 at intervals of 2-5 weeks secondary maxima with different characteristics. The maxima of the equivalent width were 6-14 days after the respective brightness maxima. The maxima are interpreted as subsequent outbreaks of the nova. Possibly these are subsequent weaker eruptions of the nova or other mechanisms that lead to an increase in density in the envelope.
The outburst of Nova Sgr 2011 N.2 (=V5588 Sgr) was followed with optical and near-IR photometric and spectroscopic observations for 3.5 years, beginning shortly before the maximum. V5588 Sgr is located close to Galactic center, suffering from E(B-V)=1.56 (+/-0.1) extinction. The primary maximum was reached at V=12.37 on UT 2011 April 2.5 (+/-0.2), and the underlying smooth decline was moderately fast with t(2,V)=38 and t(3,V)=77 days. On top of an otherwise normal decline, six self-similar, fast evolving and bright secondary maxima (SdM) appeared in succession. Only very few other novae have p…
We report on the spectral evolution of the enigmatic, very slow nova V5558 Sgr, based on the low-resolution spectra obtained at the Fujii-Bisei Observatory and the Bisei Astronomical Observatory, Japan during a period of 2007 April 6 to 2008 May 3. V5558 Sgr shows a pre-maximum halt and then several flare-like rebrightenings, which is similar to another very slow nova V723 Cas. In our observations, the spectral type of V5558 Sgr evolved from the He/N type toward the Fe II type during the pre-maximum halt, and then toward the He/N type again. This course of spectral transition was observed for …
Nova Cas 2021 erupted on 18 March 2021, reaching naked-eye brightness when passing through photometric maximum 53 days later. We describe our ~daily monitoring of its evolution, covering the first 660 days since discovery. In all we obtained 574 highly accurate photometric runs simultaneously in the BVRI bands, and 110 Echelle high-resolution spectra. The multi-band photometric evolution of Nova Cas 2021 has been mapped in detail, and the strict similarities to the proto-type very-slow novae HR Del and V723 Cas are discussed. All three novae displayed multiple and short-lasting maxima while fo…
We present a detailed study of the 2017 eruption of the classical nova ASASSN-17pf (LMCN 2017-11a), which is located in the Large Magellanic Cloud, including data from AAVSO, ASAS-SN, SALT, SMARTS, SOAR, and the Neil Gehrels \textit{Swift} Observatory. The optical light-curve is characterized by multiple maxima (flares) on top of a slowly evolving light-curve (with a decline time, $t_2>$ 100 d). The maxima correlate with the appearance of new absorption line systems in the optical spectra characterized by increasing radial velocities. We suggest that this is evidence of multiple episodes of ma…
We present results of a world-wide observing campaign of the eclipsing dwarf nova - HT Cas during its superoutburst in November 2010. Using collected data we were able to conduct analysis of the light curves and we calculated $O-C$ diagrams. The CCD photometric observations enabled us to derive the superhump period and with the timings of eclipses the orbital period was calculated. Based on superhump and orbital period estimations the period excess and mass ratio of the system were obtained.
We present light curves of three classical novae (KT Eridani, V598 Puppis, V1280 Scorpii) and one recurrent nova (RS Ophiuchi) derived from data obtained by the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite. SMEI provides near complete sky-map coverage with precision visible-light photometry at 102-minute cadence. The light curves derived from these sky maps offer unprecedented temporal resolution around, and especially before, maximum light, a phase of the nova eruption normally not covered by ground-based observations. They allow us to explore fundamental parameters of in…
We present modeling and analysis of the ejecta of nova V723 Cas based on spatially resolved IR spectroscopic data from Keck-OSIRIS, with LGSAO (adaptive optics module). The 3D photoionization models include the shell geometry taken from the observations and an anisotropic radiation field, composed by a spherical central source and an accretion disk. Our simulations indicate revised abundances $log(N_{Al}/N_{H})=-5.4$, $log(N_{Ca}/N_{H})=-6.4$ and $log(N_{Si}/N_{H})=-4.7$ in the shell. The total ejected mass was found as $M_{shell}=1.1\times 10^{-5}$ $M_{\odot}$ and the central source temperatu…
Evolution in the spectrum of very slow novae PU Vul and V723 Cas during their transition from the optical maximum to the nebular phase is investigated using the method of disentangling the composite UV/optical spectra. Model SEDs suggested that a transient decrease in the WD luminosity, during the decline from the maximum, was caused by a negative beaming effect, when a neutral disk around the WD was formed. When the disk disappeared, the luminosity increased again to values from the beginning of the outburst (in the case of V723 Cas, at/above the Eddington limit). This suggests the presence o…
A fraction of classical novae form dust during the early stages of their outbursts. The classical CO nova V5668 Sgr (Nova Sgr. 2015b) underwent a deep photometric minimum about 100 days after outburst that was covered across the spectrum. A similar event was observed for an earlier CO nova, V705 Cas (Nova Cas 1993) and a less optically significant event for the more recent CO nova V339 Del (Nova Del 2013). This study provides a "compare and contrast" of these events to better understand the very dynamical event of dust formation. We show the effect of dust formation on multiwavelength high res…
We report results of the eclipse mapping analysis of an ensemble of light curves of HT Cas. The fast response of the white dwarf to the increase in mass transfer rate, the expansion rate of the accretion disc at the same time, and the relative amplitude of the high-frequency flickering indicate that the quiescent disc of HT Has has high viscosity, alpha ~ 0.3-0.7. This is in marked disagreement with the disc-instability model and implies that the outbursts of HT Cas are caused by bursts of enhanced mass-transfer rate from its donor star.
We present multi-epoch near-infrared photo-spectroscopic observations of Nova Cephei 2014 and Nova Scorpii 2015, discovered in outburst on 2014 March 8.79 UT and 2015 February 11.84 UT respectively. Nova Cep 2014 shows the conventional NIR characteristics of a Fe II class nova characterized by strong CI, HI and O I lines, whereas Nova Sco 2015 is shown to belong to the He/N class with strong He I, HI and OI emission lines. The highlight of the results consists in demonstrating that Nova Sco 2015 is a symbiotic system containing a giant secondary. Leaving aside the T CrB class of recurrent nova…
Optical Spectroscopy and Temporal Evolution of the Nova V1405 Cas
Debre Berhan University（德布雷伯罕大学）；SN Bose National Centre for Basic Sciences（S.N.玻色基础科学国家中心）；Texas Tech University（德克萨斯理工大学）；Vihorlat Observatory in Humenne（胡梅内维霍拉特天文台）
I will explain why most novae show a sharp optical peak in the light curve, whereas a small number of novae, such as PU Vul, shows a long-lasted flat optical maximum. Re-examination of occurrence condition of optically thick winds clarifies that hydrostatic evolutions, in which optically thick winds are suppressed, are realized during nova outbursts on low mass white dwarfs (WDs) (less than about 0.7 Mo). In such a case, a nova outburst evolves very slowly, because of no strong mass-ejection, and stays at low temperature stage a long time, which results in a long-lasted flat optical peak. This…
V2491 Cygni (Nova Cygni 2008 No.2) was detected as a transient supersoft X-ray source with the Swift XRT as early as 40 days after the outburst, suggesting a very massive white dwarf (WD) close to the Chandrasekhar limit. We present a unified model of near infrared, optical, and X-ray light curves for V2491 Cyg, and have estimated, from our best-fit model, the WD mass to be 1.3 \pm 0.02 M_\sun with an assumed chemical composition of the envelope, X=0.20, Y= 0.48, X_{CNO} =0.20, X_{Ne} =0.10, and Z = 0.02 by mass weight. We strongly recommend detailed composition analysis of the ejecta because …
A TESS View of Post-Eruption Variability in the Novae V1405 Cas,V1716 Sco, and V1674 Her
Universidad Nacional de Hurlingham (UNAHUR)（乌尔希林国立大学）；Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)（国家科学研究委员会）；Advanced Technologies Research Institute, Faculty of Materials Science and Technology in Trnava, Slovak University of Technology in Bratislava（布拉迪斯拉发斯洛伐克技术大学特伦材料科学与技术学院先进技术研究所）；INAF-Osservatorio Astronomico di Padova（帕多瓦天文台）；Department of Astronomy, University of Wisconsin（威斯康星大学天文学系）
We present optical and near-infrared (NIR) photometry of a classical nova, V2362 Cyg (= Nova Cygni 2006). V2362 Cyg experienced a peculiar rebrightening with a long duration from 100 to 240 d after the maximum of the nova. Our multicolor observation indicates an emergence of a pseudophotosphere with an effective temperature of 9000 K at the rebrightening maximum. After the rebrightening maximum, the object showed a slow fading homogeneously in all of the used bands for one week. This implies that the fading just after the rebrightening maximum ( less or equal 1 week ) was caused by a slowly sh…
The First Multi-Messenger Nova: External Shocks, TeV Photons, and Neutrinos in the Next Eruption of T CrB
Texas Tech University（德克萨斯理工大学）；Michigan State University（密歇根州立大学）；Naval Research Laboratory（海军研究实验室）；INAF-Osservatorio Astronomico di Capodimonte（意大利国家天体物理研究所卡波迪蒙特天文台）；National Radio Astronomy Observatory（美国国家射电天文台）；Columbia University（哥伦比亚大学）；Flatiron Institute（平顶山研究所）；University of Virginia（弗吉尼亚大学）；NASA/GSFC（美国宇航局戈达德太空飞行中心）；University of Maryland, Baltimore County（马里兰大学巴尔的摩县分校）；University of California, Berkeley（加州大学伯克利分校）
