This paper presents U Sco nebular spectra collected in the period March-May 2010 after the binary outburst on Jan 28, 2010. The spectra display strong [Ne V] and [Ne III] lines that can be used to compute the relative abundance of [Ne/O]. The value obtained ([Ne/O]=1.69) is higher than the typical [Ne/O] abundance found in classical novae from CO progenitors and suggests that U Sco has a ONeMg white-dwarf progenitor. It follows that U Sco will not explode as a SN Ia but rather collapse to become a neutron star or a millisecond pulsar.
We present near-IR observations of the 2010 outburst of U Sco. JHK photometry is presented on ten consecutive days starting from 0.59 days after outburst. Such photometry can gainfully be integrated into a larger database of other multi-wavelength data which aim to comprehensively study the evolution of U Sco. Early near-IR spectra, starting from 0.56 days after outburst, are presented and their general characteristics discussed. Early in the eruption, we see very broad wings in several spectral lines, with tails extending up to ~10000km/s along the line of sight; it is unexpected to have a no…
Aims. We present optical spectra of the fast recurrent nova U Sco during its recent outburst, obtained within 24 hr of maximum light. Methods. We use medium resolution (R~4000) spectra taken with the with the MagE spectrograph on the Magellan (Clay) 6.5m telescope of the Las Campanas Observatories. Results. The spectrum is notable for its lack of a low ionization transient heavy element absorption system that is visible in the large majority of novae near maximum light. We suggest that this may be due to the dominance of inner Lagrangian L1 mass transfer and the absence of a circumbinary gas r…
We present optical and NIR spectroscopic observations of U Sco 2010 outburst. From the analysis of lines profiles we identify a broad and a narrow component and show that the latter originates from the reforming accretion disk. We show that the accretion resumes shortly after the outburst, on day +8, roughly when the super-soft (SSS) X-ray phase starts. Consequently U Sco SSS phase is fueled (in part or fully) by accretion and should not be used to estimate $m_{\mathrm{rem}}$, the mass of accreted material which has not been ejected during the outburst. In addition, most of the He emission lin…
The orbital period of the recurrent nova U Sco has been observed to decrease during the 1999 outburst. In an outburst mass is ejected from the surface of the white dwarf. The separation of the binary system widens and the orbital period increases. We find that magnetic braking between outbursts, mass transfer to the companion, and frictional angular momentum losses during outbursts are all too small to account for this unexpected change. We find, however, that if the secondary has a sufficiently strong magnetic field, B=8x10^3 G, then the ejected material can couple to it and corrotate with th…
We present optical and infrared spectroscopy of V1309 Sco, an object that erupted in 2008 in a stellar-merger event. During the outburst, V1309 Sco displayed characteristics typical of red transients, a class of objects similar to V838 Mon. Our observations were obtained in 2009 and 2012, i.e. months and years after the eruption of V1309 Sco, and illustrate severe changes in the remnant, mainly in its circumstellar surroundings. In addition to atomic gas observed in earlier epochs, we identified molecular bands of TiO, VO, H$_2$O, ScO, AlO, and CrO. The infrared bands of CrO we analyse are the…
Synoptic spectroscopic observations of the U Sco 2010 outburst from maximum light to quiescence as well as a contemporaneous X-ray observation are presented and analyzed. The X-ray spectrum 52 days after outburst indicates a hot source (kTbb ~ 70 eV). . Narrow line components from the irradiated companion atmosphere were observed in hydrogen and helium optical recombination lines. The formation of a nebular spectrum is seen for the first time in this class of recurrent novae, allowing a detailed study of the ejecta using photoionization models. Unusual [OIII] auroral-to-nebular line ratios wer…
U Scorpii is a recurrent nova which has been observed in outburst on 10 occasions, most recently in 2010. We present near-infrared and optical spectroscopy of the 2010 outburst of U Sco. The reddening of U Sco is found to be $E(B-V) = 0.14\pm0.12$, consistent with previous determinations, from simultaneous optical and near-IR observations. The spectra show the evolution of the line widths and profiles to be consistent with previous outbursts. Velocities are found to be up to 14000\,kms$^{-1}$ in broad components and up to 1800\,kms$^{-1}$ in narrow line components, which become visible around …
The recurrent nova (RN) V745 Scorpii underwent its third known outburst on 2014 February 6. Infrared monitoring of the eruption on an almost daily basis, starting from 1.3d after discovery, shows the emergence of a powerful blast wave generated by the high velocity nova ejecta exceeding 4000 kms$^{-1}$ plowing into its surrounding environment. The temperature of the shocked gas is raised to a high value exceeding 10$^{8}$K immediately after outburst commencement. The energetics of the outburst clearly surpass those of similar symbiotic systems like RS Oph and V407 Cyg which have giant secondar…
CONTEXT: V1309 Sco is the only certain noncompact stellar merger, due to its indisputable preoutburst light curve matching that of a contact binary of almost equal mass stars. Therefore, anything that can be deduced from the existing observations serves as benchmark constraints for models. AIMS: We present some observational evidences to guide future hydrodynamical simulations and common envelope studies. METHODS: Using archive spectra taken at high and mid spectral resolution during the V1309 Sco outburst and late decline, together with the inferential methods we developed to study nova eject…
One of the two outcomes of a common envelope event is a merger of the two stars. To date, the best known case of a binary merger is the V1309 Sco outburst, where the orbital period was known and observed to decay up to the outburst. Using the hydrodynamical code StarSmasher, we study in detail which characteristics of the progenitor binary affect the outburst and produce the best match with observations. We have developed a set of tools in order to quantify any common envelope event. We consider binaries consisting of a 1.52$M_\odot$ giant and a 0.16$M_\odot$ companion with $P_{\rm orb}\sim1.4…
Stellar mergers are estimated to be common events in the Galaxy. The best studied stellar merger case to date is V1309 Sco (= Nova Scorpii 2008) which was originally misclassified as a Nova event. Later identified as the merger of the components of a cool overcontact binary system with 1.52 Msun and 0.16 Msun, V1309 Sco showed an initial period of P = 1.4 days before the merger. Post-outburst evolution demonstrated that V1309 Sco was unlike the typical Classical Novae and Symbiotic Recurrent Novae with significant dust production around it, and indicated that the system may become a post-AGB (…
We propose a new mechanism that produces an orbital period change during a nova outburst. When the ejected material carries away the specific angular momentum of the white dwarf, the orbital period increases. A magnetic field on the surface of the secondary star forces a fraction of the ejected material to corotate with the star, and hence the binary system. The ejected material thus takes angular momentum from the binary orbit and the orbital period decreases. We show that for sufficiently strong magnetic fields on the surface of the secondary star, the total change to the orbital period coul…
It has recently been discovered that some, if not all, classical novae emit GeV gamma-rays during outburst. Despite using an unreliable method to determine its distance, previous work showed that nova V1324 Sco was the most gamma-ray luminous of all gamma-ray-detected novae. We present here a different, more robust, method to determine the reddening and distance to V1324 Sco using high-resolution optical spectroscopy. Using two independent methods we derived a reddening of E(B-V) = 1.16 +/- 0.12 and a distance rD > 6.5 kpc. This distance is >40% greater than previously estimated, meaning that …
One very important object for understanding the nature of red novae is V1309 Sco. Its pre-outburst observations showed that, before its red-nova eruption in 2008, it was a contact binary quickly evolving to the merger of the components. It thus provided us with a direct evidence that the red novae result from stellar mergers. We analyse the spectral energy distribution (SED) of the object and its evolution with time. From various optical and infrared surveys and observing programmes carried out with OGLE, HST, VVV, Gemini South, WISE, Spitzer, and Herschel we constructed observed SED in 2010 a…
We present mid-IR photometry and spectra of the merged binary V1309 Sco taken between 18 and 23 months after outburst. Strong mid-IR emission and a solid state absorption feature indicate the presence of a significant amount of dust in the circumstellar environment. The absence of detectable mid-IR emission before the outburst suggests this dust was produced in the eruptive merger event. Model fits to the solid state absorption feature constrain the constituent species and column density of the dust around V1309 Sco. We find the absorption feature can be reproduced by large (3 micron) amorphou…
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）
Nova Sco 2008 (=V1309 Sco) is an example of a V838 Mon type eruption rather than a typical classical nova. This enigmatic object was recently shown to have resulted from the merger of two stars in a contact binary. It is the first stellar merger that was identified to be undergoing a common envelope transient. To understand the properties of its binary progenitor, the pre-outburst light curves were analyzed by using the W-D method. The photometric solution of the 2002 light curve shows that it is a deep contact binary (f = 89.5(+-40.5)%) with a mass ratio of 0.094. The asymmetry of the light c…
The old nova V728 Sco has been recently recovered via photometric and spectroscopic observations, 150 years after the nova eruption. The spectral properties pointed to a high-inclination system with a comparatively low mass-transfer rate. In this paper we show that the object is an eclipsing system with an orbital period of 3.32 h. It has enhanced long-term variability that can be interpreted as 'stunted' dwarf-nova-type outbursts. Using the ingress and egress times of the eclipsed components we calculate the radius of the central object. The latter turns out to be significantly larger than a …
Recurrent novae are binaries harboring a very massive white dwarf (WD), as massive as the Chandrasekhar mass, because of their short recurrence periods of nova outbursts of 10-100 years. Thus, recurrent novae are considered as candidates of progenitors of Type Ia supernovae (SNe Ia). In fact, the SN Ia PTF11kx showed evidence that its progenitor is a symbiotic recurrent nova. The binary parameters of recurrent novae have been well determined, especially for the ones with frequent outbursts, U Sco and RS Oph, which provide useful information on the elementary processes in binary evolution towar…
Nova V2491 Cyg is one of just two detected pre-outburst in X-rays. The light curve of this nova exhibited a rare "re-brightening" which has been attributed by some as the system being a polar, whilst others claim that a magnetic WD is unlikely. By virtue of the nature of X-ray and spectroscopic observations the system has been proposed as a recurrent nova, however the adoption of a 0.1 day orbital period is generally seen as incompatible with such a system. In this research note we address the nature of the progenitor system and the source of the 0.1 day periodicity. Through the combination of…
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）
We present the first identification of a candidate precursor for an imminent red nova. Our prediction is based on the example of the precursor to the red nova V1309 Sco, which was retrospectively found to be a contact binary with an exponentially decreasing period. We explore the use of this distinctive timing signature to identify precursors, developing the observational and analysis steps needed. We estimate that our Galaxy has roughly 1-10 observable precursors. Specifically, we lay out the observational case for KIC 9832227, which we identified as a tentative candidate two years ago (Molna…
V1309 Sco was proposed to be a stellar merger and a common envelope transient based on the pre-outburst light curve of a contact eclipsing binary with a rapidly decaying orbital period. Using published data, I show that the period decay timescale P/Pdot of V1309 Sco decreased from ~1000 to ~170 years in less than about 6 years, which implies a very high value of second period derivative. I argue that V1309 Sco experienced an onset of dynamical mass loss through the outer Lagrange point, which eventually obscured the binary. The photosphere of the resulting continuous optically-thick outflow ex…
The cataclysmic variable V893 Sco is an eclipsing dwarf nova which, apart from outbursts with comparatively low amplitudes, exhibits a particularly strong variability during quiescence on timescales of days to seconds.The present study aims to update the outdated orbital ephemerides published previously, to investigate deviations from linear ephemerides, and to characterize non-random brightness variations in a range of timescales. Light curves of V893 Sco were observed on 39 nights, spanning a total time base of about 14 years. They contain 114 eclipses which were used to significantly improv…
We inform on the progress of our on-going project to identify and classify old classical novae, using deep UBVR photometry and subsequent spectroscopy for a proper candidate confirmation, and time-resolved observations in order to find the orbital period and other physical properties of the identified old novae. This way, we have already increased the number of confirmed southern and equatorial post-novae from 33 to 50, and determined new orbital periods of eight objects. As an example, we summarise the results on V728 Sco (Nova Sco 1862) which we found to be an eclipsing system with a 3.32 h …
The Galactic transient V1309 Sco was the result of a merger in a low-mass star system, while V838 Mon was thought to be a similar merger event from a more massive B-type progenitor. In this paper we study an optical/IR transient discovered in the nearby galaxy NGC4490, which appeared similar to these merger events (unobscured progenitor, irregular multi-peaked light curve, increasingly red color, similar optical spectrum, IR excess at late times), but which had a higher peak luminosity and longer duration in outburst. NGC4490-OT has less in common with the class of SN~2008S-like transients. A …
It has recently been discovered that some, if not all, classical novae emit GeV gamma rays during outburst, but the mechanisms involved in the production of the gamma rays are still not well understood. We present here a comprehensive multi-wavelength dataset---from radio to X-rays---for the most gamma-ray luminous classical nova to-date, V1324 Sco. Using this dataset, we show that V1324 Sco is a canonical dusty Fe-II type nova, with a maximum ejecta velocity of 2600 km s$^{-1}$ and an ejecta mass of few $\times 10^{-5}$ M$_{\odot}$. There is also evidence for complex shock interactions, inclu…
We have examined the optical/X-ray light curves of seven well-observed recurrent novae, V745 Sco, M31N 2008-12a, LMC N 1968, U Sco, RS Oph, LMC N 2009a, T Pyx, and one recurrent nova candidate LMC N 2012a. Six novae out of the eight show a simple relation that the duration of supersoft X-ray source (SSS) phase is 0.70 times the total duration of the outburst ($=$ X-ray turnoff time), i.e., $t_{\rm SSS}=0.70 t_{\rm off}$, the total duration of which ranges from 10 days to 260 days. These six recurrent novae show a broad rectangular X-ray light curve shape, first half a period of which is highly…
