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Post Info TOPIC: Nova Sco 2008
Blobrana


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Posts: 131433
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RE: Nova Sco 2008
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Title: V1309 SCO - Understanding a merger
Author: Jose L.A. Nandez, Natalia Ivanova, James Lombardi Jr

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 solar masses giant and a 0.16 solar masses companion with Porb~1.4 days, varying the nature of the companion and its synchronisation. We show that all considered progenitor binaries evolve towards the merger primarily due to the Darwin instability. The merger is accompanied by mass ejection that proceeds in several separate mass outbursts and takes away a few percent of the donor mass. This very small mass, nonetheless, is important as it is not only sufficient to explain the observed light-curve, but it also carries away up to 1/3 of the both initial total angular momentum and initial orbital energy. We find that all synchronized systems experience L2 mass loss that operates during just a few days prior to merger and produces ring-shaped ejecta. The formed star is always a strongly heated radiative star that differentially rotates. We conclude that the case of a synchronised binary with a main-sequence companion gives the best match with observations of V1309 Sco.

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Blobrana


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Posts: 131433
Date:
V1309 Scorpii
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Title: The Dusty Aftermath of the V1309 Sco Binary Merger
Authors: C. P. Nicholls, C. Melis, I. Soszyski, A. Udalski, M. K. Szymaski, M. Kubiak, G. Pietrzyski, R. Poleski, K. Ulaczyk, . Wyrzykowski, S. Kozowski, P. Pietrukowicz

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 {\mu}m) amorphous pyroxene grains at a temperature of 800 K. This grain size, if confirmed with longer wavelength spectroscopy and modelling, would be suggestive of dust processing in the circumstellar environment. The data in hand do not allow us to discriminate between disk or shell configurations for the dusty material.

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Blobrana


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Posts: 131433
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Title: Evolution of the progenitor binary of V1309 Scorpii before merger
Authors: K. Stepien (Warsaw University Observatory, Warszawa, Poland)

It was recently demonstrated that the eruption of V1309 Sco was a result of a merger of the components of a cool contact binary. We computed a set of evolutionary models of the detached binaries with different initial parameters to compare it with pre-burst observations of V1309 Sco. The models are based on our recently developed evolutionary model of the formation of cool contact binaries. The best agreement with observations was obtained for binaries with initial masses of 1.8-2.0 solar masses and initial periods of 2.5-3.1 d. The evolution of these binaries consists of three phases: at first the binary is detached and both components lose mass and angular momentum through a magnetized wind. This takes almost two thirds of the total evolutionary lifetime. The remaining third is spent in a semi-detached configuration of the Algol-type, following the Roche-lobe overflow by the initially more massive component. When the other component leaves the main sequence and moves toward the giant branch, a contact configuration is formed for a short time, followed by the coalescence of both components.

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Blobrana


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Title: V1309 Scorpii: merger of a contact binary
Authors: R. Tylenda, M. Hajduk, T. Kamiski, A. Udalski, I. Soszyski, M. K. Szymaski, M. Kubiak, G. Pietrzyski, R. Poleski, . Wyrzykowski, K. Ulaczyk

Stellar mergers are expected to take place in numerous circumstances in the evolution of stellar systems. In particular, they are considered as a plausible origin of stellar eruptions of the V838 Mon type. V1309 Sco is the most recent eruption of this type in our Galaxy. The object was discovered in September 2008. Our aim is to investigate the nature of V1309 Sco. V1309 Sco has been photometrically observed in course of the OGLE project since August 2001. We analyse these observations in different ways. In particular, periodogram analyses were done to investigate the nature of the observed short term variability of the progenitor. We find out that the progenitor of V1309 Sco was a contact binary with an orbital period of ~1.4 day. This period was decreasing with time. Similarly the light curve of the binary was also evolving, indicating that the system evolved toward its merger. The violent phase of the merger, marked by the systematic brightening of the object, started in March 2008, i.e. half a year before the outburst discovery. We also investigate the observations of V1309 Sco during the outburst and the decline and show that they can be fully accounted for within the merger hypothesis. For the first time in the literature we show, from direct observations, that contact binaries indeed end up by merging into a single object, as it was suggested in numerous theoretical studies of these systems. Our study also shows that stellar mergers indeed result in eruptions of the V838 Mon type.

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Blobrana


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Posts: 131433
Date:
Nova V1309 Scorpii
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Two stars become one, and trigger a rare type of nova.

For the first time, astronomers have watched the spiralling dance performed by two stars merging into a single star. The observations, taken between 2001 and 2008, suggest a solution to the vexed problem of how rare 'red novae' form.
Most novae are blue and occur when material on a white dwarf star explodes. But what causes red novae has been a mystery.
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Blobrana


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Posts: 131433
Date:
Nova Scorpii 2008
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Title: The peculiar nova V1309 Sco/Nova Sco 2008: A candidate twin of V838 Mon
Authors: Elena Mason, Marcos Diaz, Robert E. Williams, George Preston, Thomas Bensby

Nova Scorpii 2008 was the target of our Directory Discretionary Time proposal at VLT+UVES in order to study the evolution, origin and abundances of the heavy-element absorption system recently discovered in 80% of classical novae in outburst. The early decline of Nova Scorpii 2008 was monitored with high resolution echelle spectroscopy at 5 different epochs. The analysis of the absorption and the emission lines show many unusual characteristics. Nova Scorpii 2008 is confirmed to differ from a common Classical Nova as well as a Symbiotic Recurrent Nova, and it shows characteristics which are common to the so called, yet debated, red-novae. The origin of this new nova remains uncertain.

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Blobrana


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Posts: 131433
Date:
Nova Sco 2008
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A nova (V1309 Sco) was discovered by K. Nishiyama  and F. Kabashima (Japan) and on CCD images obtained on the 3rd September by the Kazan State University Astrotel observatory (Russia).

Magnitude: V9.5

MAP (78kb, 1654 x 2339)

Position(2000): RA=17h 57m 32.91s, Dec=-30d 43 10.3

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