V392 Per in outburst

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Re: V392 Per in outburst

Postby Francois Teyssier » Thu May 03, 2018 5:31 am

Nice results Paolo and and Robin!

Contribution of Steve Shore:

The V392 Per spectra now in the ARAS database are highly reddened examples of an Fe-curtain stage nova, with indicated expansion velocities (based on the absorption component of the P Cyg profiles on Halpha of about 1500 km/s. This is hardly unusual for a nova for which the mass is about 10E-4} Ms (Solar mass) and has a large covering factor. What seems most interesting is the eruptive nature of the pre-outburst binary. The variable was already known as a faint cataclysmic (hence the designation). The CBET lists it as a U Gem type, meaning it undergoes occasional eruptions of a few magnitudes. These are from a disk thermal instability, just like SS Cyg but not as regular, and is not typical of a nova system in long quiescence. While GK Per 1901 showed dwarf nova-like outbursts in the post-maximum decline, these less than years after the peak and still in the decline stage. V392 Per was, instead, a system apparently in quiescence (as least regarding its nuclear activity) . The recent study by Shara et al. (2017) of the quiescent cataclysmic that isnow identified as the originating system for the historical Nova Sco 1437 is a polar, identified by periodic variations in the emission lines and X-rays consistent with channeled accretion at the magnetic poles. This is, however, a very different kind of cataclysmic, one without the massive disk required to produce the dwarf nova outbursts. Assuming the identification of the progenitor is correct, and at this writing it seems to be, this is the first such progenitor found for a classical nova. There is nothing unusual (so far) about the nova. That it has been reported as a gamma-ray source from Fermi is also no longer an unusual feature of the early decline stage. One of the holy grails of nova research has been the search for a link between accretion powered single degenerate close binaries (otherwise known as cataclysmics) and classical novae and this may finally be one such case. The cataclysmic has not previously been asociated with an extended nebulosity, as was Nova Sco 1437 although if there is one it may show up in the photoionization pulse some time in the future. There is a parallax for the precursor system that places it at a distance for which neither the catacysmic nor the nova are unusual.

Francois has asked that I repeat a point from some time back about the so-called ``Fe II'' and ``He/N'' classes for novae in outburst. First, I'll be blunt: these are purely descriptive and have no other meaning. This is not like spectral types, although the CTIO classification by Williams subdivided these into different groups depending on specific lines. The scheme is just a shorthand for the appearance of the spectrum. Its physical content is {it only} hat the relative opacity of the ejecta is captured by the statement. If the Fe II (and low ionization metallic line) spectrum is in absorption, or eventually in emission (including [Fe II] and related species) then the eject are optiall thick both radially from the center of the ejection and along your line of sight through the expanding matter. If the Fe II spectrum is either very shortliveed (so-called ``hybrid'') systems, or goes immediately into emission displaying the He I and N II/III lines, then at least in {\it your} direction the ejecta are optically thin. Assuming a expanding sphere, the latter would mean a very low mass since the line of sight colun density would be everywhere low enough to allow for ionization an emission by excited state transitions. But you know he ejecta are not spherical, in general, and inclination effects are important. The ejecta can be completely opaque on the line connecting any point in the ejecta and the central radiation source but sufficiently aspherical that toward you the column density is low and you see the emission lines from below the optically thick Fe curtain. The curtain results from recombination of he fireball so at some point in the expansion, however brief it may be, there {\it must} be a stage of a strong Fe II optical spectrum. You may miss it, it may occur during the rising branch (e.g. pre-maximum halt). It may last only a day or even less, depending on geometry and ejecta mass. Not catching these systems in the ultraviolet means the onset of he curtain can only be inferred from changes in the optical spectrum. But the appearance of any Fe II lines (in absorption, emission, or P Cyg) and the [Fe II] lines, means the UV is so opaque that the only avenue for photon escape is through the upper state transitions of the Fe lines that connect to the ground states occurring in the UV spectral interval.

Just to be clear on this point: stellar spectral types -- no matter how arbitrary the subdivision -- are systematically linked to stellar properties such as T$_{eff}$ and mass and radius because stelar photospheres and atmospheres are hydrostatic structures. The temperature and pressure (hence ionization and column density) of the atmosphere adjust to accommodate mechanical equilibrium. This is not true for nova ejecta, for which the free expansion freezes out the conditions at different places in the expanding gas at different times. One part (the periphery) has a low density, and may have a low excitation temperature, while the inner part is highly ionized but absorbed by the overlying layers. {\it Only if the ejecta are spherical does every direction appear the same along your line of sight as within the ejecta so the appearance of high excitation an/or ionization lines early in the expansion i more likely due to aphericity (lobes, cones, whatever, just not space filling) than a necessarily low mass.
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Re: V392 Per in outburst

Postby Robin Leadbeater » Thu May 03, 2018 9:44 am

Hi Francois, Steve,

Gary Poyner on the BAA forum pulled out this article on V1213 Cen (Nova Cen 2009) Is this a similar system ?
https://www.space.com/33772-hibernating ... osion.html

Cheers
Robin
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Re: V392 Per in outburst

Postby Francois Teyssier » Thu May 03, 2018 11:01 am

Yes, Robin

See: http://www.astronomie-amateur.fr/Documents%20Spectro/Novae.pdf
in which I try to explain the mechanism of classical novae (from page 27)

François
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Re: V392 Per in outburst

Postby Robin Leadbeater » Thu May 03, 2018 11:47 am

Hi Francois,

OK but Steve said about V392 Per " Assuming the identification of the progenitor is correct, and at this writing it seems to be, this is the first such progenitor found for a classical nova." What is the difference between V392 Per and the progenitor of Nova Cen 2009 ?

Cheers
Robin
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Re: V392 Per in outburst

Postby Daniel Dejean » Thu May 03, 2018 1:24 pm

Hello all,

Still very cloudy here in Toulouse...many doubts for observations in the next coming days.

Thank to Robin for the latest news. Very interesting chart showing fast changes in continuum.
I did a quick check of AAVSO data (https://www.aavso.org/lcg) to compar V392Per with Nova Del 2013 used in reference on the excellent novae.pdf presentation from François (p'41-47).
Visual magnitude from AAVSO :
V392Per in black
Nova Del 2013 in gray

Image

As per definition of François presentation (p13 Classes de rapidité), V392 luminosity decline looks to be very fast (mag -2 in about 2 days...).
In the same point of view, V1213 Cen (about 10 days for mag-2) was also relatively slow compared to V392 Per.

Hope in clear sky to track that event.
Daniel
Last edited by Daniel Dejean on Sat May 05, 2018 3:03 pm, edited 3 times in total.
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Re: V392 Per in outburst

Postby etienne bertrand » Thu May 03, 2018 1:45 pm

Thanks to Steve Shore's paper.
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Re: V392 Per in outburst

Postby Daniel Dejean » Thu May 03, 2018 2:47 pm

Yes, many many thanks to Steve for the time he spent to help our understanding. A very difficult matter for my very limited knowledge...

In practice, I would be very interested to understand his following statement regarding measurement of expansion velocity :
"The V392 Per spectra now in the ARAS database are highly reddened examples of an Fe-curtain stage nova, with indicated expansion velocities (based on the absorption component of the P Cyg profiles on Halpha of about 1500 km/s" .

In our data I don't see evidence of this Halpha absorption component at 1500km/s… Analysis could be even more complex as the Ha pattern tend to split in 3 lines (cf Paolo data this morning) . How to compute that expansion velocity based on our data ??

Obviously, I still have many things to learn...That is part of that funny game !
Thank again.
Daniel
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Re: V392 Per in outburst

Postby Robin Leadbeater » Thu May 03, 2018 3:08 pm

Robin Leadbeater wrote:OK but Steve said about V392 Per " Assuming the identification of the progenitor is correct, and at this writing it seems to be, this is the first such progenitor found for a classical nova." What is the difference between V392 Per and the progenitor of Nova Cen 2009 ?


I've found the arXiv version of the V1213 Cen paper in Nature
https://arxiv.org/abs/1608.04753

There they say of the progenitor "Its outburst properties (pre nova event) are typical of a U
Geminorum-like dwarf nova"

To me it looks similar to the event we are seeing now in V392 Per. (Except as Daniel pointed out the Nova phase in V392 Per seems much faster)

Cheers
Robin
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Re: V392 Per in outburst

Postby Robin Leadbeater » Thu May 03, 2018 3:22 pm

There is also V1017 Sgr which also underwent dwarf nova-like outbursts before and after a classical nova event in 1919
https://arxiv.org/abs/1612.00405

Robin
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Re: V392 Per in outburst

Postby Olivier GARDE » Thu May 03, 2018 5:07 pm

Always bad weather, so no spectrum of this nova for me....
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