V339 Del, NYT 29/10 – billeder af novaens ildkugle

[nightskyDeltager Neutron star]

Afsluttende bemærkning for 2013.

Det har været meget spændende at følge og lære om Nova Del 2013 i dette efterår. Vi har alle kunnet følge
novaen, visuelt, fotografisk, med fotometri, med spektroskopi eller bare ved at læse på forum. Og nogen
har gjort det i en eller anden udstrækning. Antallet af visninger for artiklerne har rundet 11.000 – 7.500
på astro-forum og 3.500 på Astro’s forum. Jeg kan hilse fra Steve Shore og sige at det gør indtryk. Ganske
imponerende for et lille land som Danmark.

I det kommende år vil der ind imellem komme nye artikler om V339, om Nova Cen 2013 og kommende novaer.
Jeg har bedt Steve om forsætte med at sende opdateringer, så vi også i dette nye år kan lære en masse.

Desuden håber jeg personligt at flere kommer i gang med spektroskopi. Selv opgrader jeg voldsomt og jeg
tror der er par stykker mere som vil gære det samme. Høj frekvent spektroskopi blev i 2013 beviseligt en
disciplin som kun amatør astronomers kan mestre – godt gået af ARAS gruppen.

I 2014 arbejdes der på at foredrag omkring Nova Del 2013 med Steve Shore (via Internet) – Jeg håber det
lykkes at få sat dette op snarest.

Hvis man vil sende en hilsen til Steve kan man blot skrive det her, så skal jeg samle dem sammen og sende
videre.

Hermed også et godt nytår fra Tvis.
Lars Zielke

Artikel #19 28 dec. 2013
Steve Shore

Hvad har vi sammen set og lært af V339 (Nova Del 2013)

So we arrive at the end of the year and of the visibility of V339 Del for this year. It should come
out from solar avoidance again in March. In the interim, as you all know, in this past month it’s
been surpassed – in brightness – by V1369 Cen, discovered about four weeks ago. Before continuing,
there is one important thing to note here: without this campaign, V1369 Cen would be studied in a
vacuum.

In the past month, during the last stages of fading of v339 Del, we’ve seen – finally – the higher
ionization stages of the ejecta. From your spectra and from the NOT, there are indications of the
[Fe VII] 6087Å line as early as mid-No. but this is now clearly present and will be the “line to watch”
in the months after emergence from solar obscuration. The He II 4686Å line is strong and of a
similar profile, indications that the ionization and emission are still powered by the continuum
of the central engine (the WD). Now, depending on the development of the X-ray emission – whether
the source is still “on” when we see the nova again in the early spring or has shut down and is in
the cooling phase – the ionization of the ejecta will display changes dominated by the interplay of
expansion and photo-processes.

Perhaps now we can reflect on what we don’t know from all we’ve collectively seen and learned from
this nova because it prepares us collectively for all those to come.

Figure 1: Further comparison of [O III] 5007 and N V 1240Å profiles from 2013 Nov. 21.
Note that the N V is a doublet and that the individual components more likely have the
He II-like profile than these forbidden transitions. The absorption features are Mg II
interstellar lines.

For V959 Mon 2012 we had the disadvantage of not having seen the peak of the outburst, the mirror image
of what’s happening now for V339 Del. Having missed the Fe-curtain phase, we did not see the earlier
optically thick stages of the ejecta that probed the recombination following the fireball. Instead,
for V339 Del, we have an exquisite picture, in minute detail, of every moment of that period. It
shows that many of the phenomena seen in the earlier outburst of the recurrent nova T Pyx, in 2011,
are not peculiar to that system but actually generic. The structure that you observed in the absorption
troughs of the P Cyg lines, the disappearance and then re-appearance of the detached absorptions on
the He I profiles, the Na I doublet complexity, are all standard features. Now, for V1369 Cen, we’re
seeing the same thing, albeit with more complex structure and higher velocities. But why? What imposes
this feature of the ejecta? The narrow lines are well known from other novae but the optical depth
changes show that what starts out as a broad (hundreds of km s−1) feature decomposes on a drop in
column density into an ensemble of individual components. It appears that the filamentary character
of the ejecta is far more complex than it seemed. But there is larger scale structure, otherwise we
wouldn’t see these distinguished features. The same lines appear on the Ca II H and K lines, ion
resonance lines, as Na I, despite these being different ionization states they are both from high
column density, low temperature gas. Again, why? There has to be something pointing back to the
explosion.

Figure 2: How to probe the ionization stratification of the ejecta using lines of
nitrogen (there’s a good sampling from the UV) from 2013 Nov. 21.

In V1369 Cen we’re seeing a very complicate light curve, one that is reminiscent of T Pyx in its
excursions in V. The gamma-ray emission we saw in V339 Del, and V959 Mon (remember, this character
was first seen in very high energy emission months before it as detected optically, was confined
to a brief interval near peak. For V1369 Cen that’s not so clear. But perhaps the difference in
the photometric development – along with the line profile changes – will allow an eventual resolu-
tion of the structure question.

The second is for the future. V339 Del was spatially resolved very early, within a week of outburst,
at optical and near infrared wavelengths. That data has yet to be digested thoroughly but for now it
seems consistent with different interferometers (CHARA in the north, VLTI in the south) found different
expansionrates that could indicate an axisymmetric (bipolar) sort of structure. When the nova emerges
again, it will be after almost as long an absence as its presence, so it should be considerably more
extended and maybe accessible to direct imaging from ground based telescopes like the Keck, VLT, or
Gemini. The same is true for V1369 Cen, although there is no northern partner to provide that infor-
mation. It isn’t unthinkable that a direct comparison will be possible with HR Del 1967, for which
HST/WFPC2 images were obtained in the ’90s (nearly 30 years after outburst). Remember, once the central
source ceases to control the ionization the gas continues to radiate by recombination, although
always more weakly, so the line emission traces electron density. The advantage of brightness, of
nearness of the nova, is purely geometric – the closer it is, the easier the resolution of the ejecta.
The same holds for the radio, interferometric observations of V339 del are the basis for interpretation
of the more sparsely sampled V139 Cen cm-wavelength data.

HST/WFPC2 billede af HR Del (Nova 1967) i H-alpha (venstre) og [O III] (højre) – Tilføjet af mig.

The third is sill open: there is now accumulating evidence that V339 Del really did for dust although
it isn’t yet clear how much. The latest observations, by Fred Walter using near infrared spectra, is
in strong support of that contention from earlier bolometer photometry in the IR by the Minnesota
group. How much and where, and when isn’t known – yet – but you all worked like daemons to cover the CN lines during the optically thick stages and nothing emerged. Neither was CO observed in the IR as
it was for V705 Cas. So there is a crack in the edifice, perhaps molecular precursors are not necessary
– or are not visible – if the ejecta have the right geometry. The dust didn’t produce a DQ Her-type
event, but the ejecta aren’t spherical, so now to see what happens in V1369 Cen. I wish I could give
you all a neat summary of this but its new territory, as we’ve seen so often in this nova.

The line profile changes in the last month for V339 Del trace the electron densities. There is a hint
of the [N II] 6583Å line (the analog of [O III] 5007Å) on the wing of H_ and a first trial in getting
the electron density by using the ratio [N II] (6548+6583)/5755, along with the tracer [O III]
(4959+5007)/4363, gives a limit on the density in the range between -1000 and 1000 km s−1 of (6 −10)×106 cm−3
but the temperature is uncertain. the mass is a few times 10−5M⊙ and a large filling factor seems to
be emerging, but these statements are still very preliminary. The filaments that you’ve all noted are
not only still there but now more evident and on lines of different ion stages and elements – so it’s
now possible to study the homogeneity of the abundances in the ejecta at the level of a few percent of
the volume. OK, this is a technical point but by combining the emission from lines whose de-excitation
is from collisions with electrons in the ambient gas and otherwise only radiative de-excitation, the
branching ratio (ratio of the different “exit channels” for the photons) shows the competition between
the rates of collisional de-excitation and radiative decays for the excited states. The advantage of
these two indicators, even if they arise from different ions, hence from different parts of the ejecta,
is that they’re similar enough that the differences can be understood by using the line profiles.

You see, that’s why spectra are so important – in such rapid expansion, with so large a velocity
difference between the inner and outer parts of the ejecta – every piece of the volume leaves its
radiative imprint projected along the line of sight. So if two profiles are similar in structure,
they come from the same places in the ejecta and the differences are because of the peculiar sensiti-
vities to the ambient conditions of the transition in question. None of this is hand waving – we
have now the necessary plasma diagnostics to proceed systematically with the time dependent analysis
of the ejecta.

Here we turn again to the homogeneity problem: is the gas well mixed or not? What happened during the
explosion?? If V1369 Cen is showing multiple ejection events, the comparison with V339 Del will be an
incredible chance to see if individual events are similar in the nuclear waste produced and expelled.
We can, irrespective of whether V1369 Cen is a CO or ONe nova, to do a quantitative compare-and-contrast
analysis with any of the subtypes based on the last three years of novae. Here I really mean we,
you’re all part of this! Those observing (ARAS gruppen) V1369 Cen now, those who have followed with such
zeal V339 Del.

Figure 3: The spectra from V339 del (NOT) and V1369 Cen (ESO, FEROS from Luca Izzo) on
about the same day (about three weeks) into outburst. The fluxes are absolute, the scaling
is 3x for V339 Del, no extinction corrections (but you’ll notice that the spectra are so
close that it’s likely the reddening is similar).

This has gotten very long and it’s really only the beginning. The pair will remain visible for years
at a level accessible even with small telescopes, albeit at low resolution. It will be worthwhile
trying to restart observations when V339 Del re-emerges, we don’t know what it will be in V at that
time. And now it’s time to reflect on all that’s been accrued in this spectacular archive and begin
the detailed analysis. You’re all part of that now (ARAS gruppen). For those who have had the stamina
to reach this point in the notes, for a whole community that has reaped the rich rewards of your
collective effort, sincere thanks from the heart for all you have done. The first paper is now being
outlined, that will be sent around to you, and summaries of the analysis will be coming in the next
month. The new year begins with a new era in the study of this elusive phenomenon.

You are all the ones (ARAS gruppen) who have made that possible, turning voyeurism into a fine art
through spectroscopy and thought.

Best wishes for the holiday and very best wishes for the New Year.

—–
Steve Shore

[nightskyDeltager Neutron star]

Sådan – det er bare så smukt at der bliver ved med at komme nyt om den Nova Del 2013.
Det er ganske simpelt utroligt at man kan gøre dette på en afstand af 14.800 lysår.

For første gang har man taget billeder af en nova i den tidlige ildkugle fase og afsløret hvordan
strukturen af det udkastede materiale udvikler sig som gassen ekspanderer og afkøles.

CHARA Arrayet brugte optisk interferometri til at kombinere lyset fra 6 teleskoperfor at opnå
den høje opløsning, svarende til et teleskopet med en diameter på 300 meter, en opløsning
som er langt bedre end almindelige eller rumteleskoper.

http://www.newswise.com/articles/georgia-state-astronomers-image-the-exploding-fireball-stage-of-a-nova

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13834.html#figures
Hvis nogen har adgang vil det være super med en kopi….

Nu skal jeg selv i gang med at plotte mine egne data op model disse nye billeder. Super…

Georgia State Astronomers Image the Exploding Fireball Stage of a Nova

Astronomers
at Georgia State University’s Center for High Angular Resolution
Astronomy
(CHARA) have observed the expanding thermonuclear fireball
from a nova that erupted last
year in the constellation Delphinus with
unprecedented clarity.

The observations produced the first images
of a nova during the early fireball stage and
revealed how the
structure of the ejected material evolves as the gas expands and cools.

It appears the expansion is more complicated than simple models
previously predicted,
scientists said…………………

Animation af ildkuglens udvikling.

Nightsky2014-10-29 21:10:40

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