Hallo ,
ist uns diese Gruppe bekannt ?
Grüße
Wolfgang
------ Start of attached email. Subject: [RSpec_Real_Time_Spectroscopy] Nova Del 2013 02-09-2013 ------
*ARAS
Nova Del 2013
02-09-2013*
*Abstract**
**
**New notes of Steve Shore about the spectroscopic developpement of the
nova. Enjoy and thanks again to Steve.*
Zitat:
*New observer : Jose Ribeiro (Portugal)*
ARAS Forum :
http://www.spectro-aras.com/forum/viewt ... &start=120
ARAS Aras :
http://www.astrosurf.com/aras/novae/Nova2013Del.html
*
Luminosity curve from AAVSO data base*
Mag ~ 7.0
2.6 mags under max luminosity
*Spectroscopic **evolution*
Franck Boubault
IR from Joan Guaro : up to 10 000 A !
*Absolute flux calibration : two methods*
Web pages
Basic photometric method avec V mag :
http://www.astronomie-amateur.fr/feuill ... ement.html
Spectrophotometric method with spectrophotometric standart :
http://www.astrosurf.com/buil/calibrati ... ration.htm
There's been interest in some explanation of what developments are yet
to come so here are a few notes for the next week or so.
First, a word of advice. In thinking about what your spectra are
telling you, it's best to "think like a photon". By that I mean think
about what a photon traversing a medium, in this case the ejecta, will
encounter and what will happen. In fact, this is the origin of the
Monte Carlo method, a technique for simulating the passage of a
particle through a very complex environment, subject to a wide range of
processes and a wide range of densities and states. You couldn't find
a better description for the ejecta. Recall that the inner and outer
parts, even were this a wind, have different outward velocities. So a
photon emitted in one place sees the rest of the surrounding gas moving
-- on macroscopic scales -- at different velocities and therefore
differently Doppler shifted. So if a photon is emitted in the outer
parts, where the density is low, it most probably escapes. If,
instead, it's emitted in the inner part, where the density is higher,
it will quite literally bounce around in both space and frequency
(absorbed in a line center, emitted in a line wing, encountering
another atom in the line core, perhaps, and being re-emitted there,
etc). So in the initial stages, where the photons are actually from
the hot gas itself, the thinning of the outer regions is like the
expansion of a wind and the photosphere (an intrinsic one) moves
inward. You see this in some of the film version of the spectral
sequences some of you have produced (especially for H-alpha). At first
the P Cyg absorption seems to move inward as the outer layers become
optically thin, and then the absorption disappears on that line
(leaving a sort of dent) as even the approaching material becomes
transparent. The higher Balmer lines, on the other hand, have a
smaller emission/absorption ratio (the emission is formed further in)
and the absorption is progressively stronger. At the same time, you
see with increasing clarity and strength the structure of the whole
ejecta, the various emission peaks, that signal the thinning of the
material at the highest distances and velocities.
But don't forget the poor remaining white dwarf. It's now in the
supersoft phase, although we don't yet see that, burning the residual
material from the explosion in a source that reaches several 100,000's
K (of order 0.05-0.1 keV). The nuclear source is deep, not at the
surface, and has a photosphere of its own that depends on the newly
established structure of the envelope of the WD. This is inside the
ejecta, at this stage (as of 1 Sept) we don't yet see that directly.
But we see another, important effect: the ionization produced by this
source is gradually advancing outward in the ejecta from its base as
the ejecta thin and the photosphere moves inward. This is the
so-called "lifting of the Iron curtain" that's happening in the UV and
the cause of the decline in the optical. Progressively more of the
photons can escape in the UV without being degraded through optical or
IR transitions and the continuum temperature increases as the two
oppositely directed "fronts" approach. The individual transitions from
the ground state of neutral and low ions are in the UV and some of them
remain opaque although the continuum is increasing sufficiently to
power emission lines in the optical. Oxygen, in the form of O I, is
the best example. The [O I]6364 and 6300 lines are connected to the O
I 1302, 1304 resonance lines. The latter are still thick, so the
photons knock around and finally emerge through "open channels", e.g.
8446 and the two forbidden lines. Their presence indicates the density
is finally low enough at the photospheric depth that the emission from
forbidden line sis no longer collisionally suppressed. The transition
is abrupt in the optical, hence the term "flash" used by the early
observers, because when the right optical depth is hit, the transition
is almost instantaneous since the emission becomes local. The [O I]
line widths, you will have noticed, are lower than the wings of the
Balmer lines so this is from the inner parts. The O I 8446 was visible
for a longer time. In the UV, we would see absorption at O I
1302,1304 but that will gradually give way to P Cyg and then emission.
Something else to remember is that different elements ionize at
different energies. Oxygen, for instance, is slightly more bound than
H, so the Balmer lines will be strong when the O is still completely
neutral. Once the O (and N) start ionizing, they also contribute
recombination lines that can't decay to the ground state directly
because of the blockage of the UV channels so they emerge where they
can, at the exits marked "6300" and "6364" and so on. The same for the
C I and C II, and the N II lines. We are not yet at the point where
the N III 4640 lines appear but they will in due course.
The Fe II lines are now turning completely into emission as the peak
moves toward Fe III and higher and the UV lines turn transparent. The
Fe-curtain will, once the ionization reaches Fe^+3, disappear since
that ion (Fe IV) has very few transitions in the part of the spectrum
where the UV is strongest. All of this is powering the decline of the
light curve and is what "the founders" didn't suspect: the changes in
the UV from the light curve are timed to appearances of specific ions
and transitions because the continuum temperature continually changes,
moving toward stronger UV and even XR, while the optical is a passive
responding medium. When the Lyman series turns transparent, and
becomes recombination dominated, the P Cyg profile disappears. The
same for the He I lines, they will reappear along with He II and other
higher ions as the opacity in the UV drops. Once the two fronts meet,
that's the nebular stage: the moment when the spectrum turns to
emission, we see completely through it, and the line profiles all look
basically the same. I say "basically" because density and structural
differences leave their signature on individual lines depending on
their transition probabilities (forbidden or permitted, as discussed a
while back).
The nebular stage is a complicated period and very sensitive to the
specifics of the explosion. If the ejecta are spherical and smooth,
all profiles will be basically the same but differ in width because of
their "weighted depth of line formation" (in other words, recombination
line strengths depend on on density so the inner part always
contributes more, but it also depends on where in the ejecta a specific
ion appears). All of this changes quantitatively for nonspherical
explosions, but not qualitatively. The strength and velocities are
those we see projected along a line of sight through the expanding
medium.
I apologize if this is staring to get heavy, it's not intended. You
have here a problem of photons (motorcycles) weaving their way through
traffic (cars, trucks) whose speeds depend on where they are in the
lane of traffic. If the ejecta are spherical the only escape is along
the direction of the flow. If aspherical, there's a way out and free
escape by swerving to the side. This is something we're just starting
to deal with in detail, and it's your work that will illuminate it even
more clearly for this prototypical nova.
And as a last comment, one on the intensities/fluxes. In the next
weeks, as the ejecta change ionization and approach the sate of
freeze-out (when the recombinations are independent of the WD
illumination and depend only on the rate of expansion), we will see how
structured the ejecta really are, the density and ionization
stratification, and the abundance inhomogenities. The absolute fluxes
are the key, they tell you how much energy is in each transition and
therefore the number of radiating atoms. It seems, for instance, that
a few days ago H-alpha alone accounted for almost 8000 L_sun if the
distance is 5 kpc (less as1/D^2 depending on the distance). From this
we'll have a first estimate of the ejecta mass, one of the key unknowns
in any explosion and the pointer to the conditions at the outburst. Th
eother is that there is structure here in the ejecta, you've already
seen that in emission and absorption, and as different ions appear that
will link to the central engine.
So more notes coming, and as always thank you for the interest.
*Next steps*
*The priority is , at least, one eShel spectrum a day as long as possible.*
Continuous coverage with low resolution (Alpy and Lisa) in order to
continue when luminosity will be too low for eShel
*Important note for LHIRES III 2400/1200/600 l/mm*
Range of interest : H alpha, Na I D, H béta, *4200 and 3800 region*
*List of ARAS observers :**
O. Garde **
**O. Thizy **
**T. de France **
**D. Antao **
**J. Edlin **
**K. Graham **
**J. Guarro **
**F. Teyssier **
**P. Berardi**
**T. Bohlsen**
E. Pollmann
**T. Lemoult**
**A. Favaro**
**J.-N. Terry*
*E. Barbotin**
**F. Boubault*
*J.P. Masviel**
**R. Leadbeater*
*J. Montier*
*C. Buil*
*M. Dubbs*
*B. Mauclaire**
**T. Hensen*
*D.Grennan *
*D. Hyde**
**S. Charbonnel*
*How to submit your spectra :**
**
**Please : **
**- respect the procedure**
**- check your spectra BEFORE sending them*
Zitat:
1/ reduce your data into BeSS file format
2/ name your file with: _novadel2013_yyyymmdd_hhh_Observer
novadel2013: name of the nova, fixed forthis object
yyyy: year
mm: month
dd: day
hhh: fraction of the day, beginning of the observation
Observer: your pseudo/name
Exemple: _chcyg_20130802_886_toto.fit
3/ send you spectra to François Teyssier to be included in the ARAS
database visible here:
*
http://www.astrosurf.com/aras/Aras_Data ... l-2013.htm
*
François Teyssier
--
François Teyssier
www.astronomie-amateur.fr
--
François Teyssier
www.astronomie-amateur.fr
------ End of attached email ------
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