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

[nightskyDeltager Neutron star]

Atel 5434 bekræfter støv.

L-Bånd målinger af novaen passer med tilstedeværelsen af støv.

This flux level is consistent with a small amount of dust having formed recentlynsistent with Presence of Dust

[nightskyDeltager Neutron star]

Fik en observation kassen i aften igen, men det holdt p.g.a. af en del skyer.

Ikke nogen ændringer udover at kontinuum stadig falder som forventet.

Data er ikke dark, bias, flat behandlet.

[nightskyDeltager Neutron star]

Artikel 14

About luminosity curve and dust formation

Our friend continues a steady decline, with some bumps, despite the recent flurry of reports
of dust formation. First, let me explain what the observations may be saying and then,
to illustrate what you’re seeing in the data, add a few points about the ejecta structure.

Dust, being the solid state, behaves like bricks. Radiation is absorbed with efficiency
depending on the grain composition and re-emitted locally with whatever temperature the
grain has to reach to balance the rate of absorption. This is referred to as “radiative
equilibrium”: if the temperature reaches a steady state while the irradiation is steady,
it will get as hot as it “needs to be”. The incident photons are energetic, optical and
UV. But they are diluted by distance from the emitter. So the energy density is lower
than near the central White Dwarf or even the inner ejecta. Thus the rate of absorption
is lower with increasing distance. A solid doesn’t behave like a blackbody in its spectrum,
but the emission rate depends only on temperature so the farther the grain is from the
central source the lower its temperature will be in equilibrium. This is almost independent
of the size of the grain so it could be a peanut or a planet, the energy per unit area
(flux) is all that has to balance (the book-keeping is: what comes in, goes out). Some
critical temperature must be crossed for the solid to be stable, otherwise it will evaporate
by heating (loss of atoms), that is the so-called “Debye temperature” below which the
solid (or atomic cluster) remains structurally intact.

This, for silicates and various forms of carbon (usually called “astronomical graphite”
because of laboratory analogies) is about 1500 K. It means, in a kinetic (particle) sense
that collisions with this relative velocity (the sound — or gas — speed corresponding to
this temperature is about 1 km/s) can bind (stick) and nuclear clusters remain stable.
As the cross section increases the quantity of energy absorbed increases so while the
temperature doesn’t change the luminosity does. Since the grains reach a low temperature,
they radiate in the infrared and that’s the tell-tale signature of their presence. It
isn’t only a drop in the light of the ejecta photosphere and White Dwarf. That depends
on viewing angle, how you see through this growing smog. But the infrared is transparent
so you see the cumulative radiation from the grains as an increase in the part of the spectrum
where a solid would radiate. The controversy now is whether L and M band photometry
(longward of a few microns) has increased sufficiently to signal the presence of this
absorber. Two groups seem to agree on this now but as a recent event, around Sept. 29
but this require further data. If we’re in that stage, it’s just preliminary and recall
that neither CN nor CO were detected in the nova when the NaI lines were strong.

The cross section, if dominated by direct absorption, also has certain characteristics.
Silicates (SiO complexes) are rather opaque at 10 and 12 microns (there’s a peak in the
broadband emissivity there) and rather inefficient absorbers in the UV. In contrast, the
carbon complexes are very good absorbers at around 0.20 – 0.22 microns (2000-2200A) in
the UV so they absorb where the irradiation is maximal and radiate less efficiently in
the IR because they lack the bands of the silicates. Thus, graphite (carbon) grains will
be systematically higher temperature in equilibrium than silicates. It’s likely that the
grains will be carbonaceous so they’ll be hotter than silicate grains (that are inefficient
absorbers, efficient radiators in the peak emitting range).

This all relates to where the dust will form. To date, the NOT profiles are the same as
they were, no obscuration by the grains. This may change, we’ll have to wait a bit. The
main interest now will be the process itself, if grains are there. But there’s another,
albeit slower, physical effect that we can now see.

Lines profiles

Data fra Nordic Optical Telescope, 30 sep. 2013

Since the ejecta are ionizing now, the profiles of different ions will trace out different
parts of the ejecta at the same time. In the figure above, you see this. The top is
neutral oxygen, ionized nitrogen, and twice ionized oxygen (the 5007 is a doublet with
4959, that is just barely present) and has the greatest velocity width and a unique
profiles that resembles what was seen at the start on the Balmer lines. Yes, the [O III]
lines do seem to be there. Since these are forbidden transitions, they trace low density
ionized gas and the wings suggest these are in the outer portions of the ejecta. The [N II]
is intermediate. And now the He I line profiles share the Balmer line structure, these
require a very a high excitation energy so suggest that recombination formed these. The
C II 8335 line is also now present, but there’s nothing yet at the [Fe VV] or [Fe X}
optical lines.

There’s a flight scheduled for SOFIA and we’ll keep monitoring the spectrum. Please don’t
give up now, remember that if we’re ever going to understand such a simple thing as a
nova, a lot of hard work will be preceding. The XR/Swift data to date requires about a
factor of 10 higher column density than derived from the UV Lyman alpha line, have in the
whole ISM toward the nova.

The XR turn-on was fast as far as can be known from the descriptions.

SOFIA Teleskopet (Stratospheric Observatory for Infrared Astronomy)

Nightsky2013-10-02 21:29:25

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Artikle 15 fra Steve Shore

Røngtenstrålingen stiger
Densitet af ejecta
Fordelingen og mængderne af stof

Why this last stage is so important

If it weren’t a possible offense to French patriotism, I’d cite Henry V (Shakespeare) about
“we happy few” to explain how important it is to continue observations of V339 Del for as
long as possible. But instead, poetry notwithstanding, I should explain why this last stage
is so important.

The X-ray emission from the nova is continuing to increase, we have hardly yet seen the
maximum, and it is still “hard” (meaning it is stronger in the higher energy bands, around
10 keV, that indicate a temperature of > 10 MK). This is still likely from internal shocks
in the expanding ejecta but this should decrease and a soft source (< 1 MK) should appear
shortly. When it does, it will be the brightest XR nova ever observed by Swift during its
mission lifetime.

When the soft source becomes visible, the optical proxies (like the coronal lines) will
indicate the low density structure of the ejecta and allow the determination of the abundances.
That’s the other important reason for continuing low resolution observations, they are the
thermometers of the ejecta. While the individual structures in the line profiles matter,
those can be obtained from the high resolution observations (e.g. NOT, Ondrejov, etc) and
from HST. The low resolution data, instead, shows the morphology of the continuum and the
total emissivity changes — this gives the mean properties of the ejecta. We don’t have
a record of a CO nova with this precision and coverage, as I’ve said before, but it is now
at a stage where the data will be comparable in resolution to some for extragalactic
novae (for instance, in the LMC and M 31).

As an example, the main electron density diagnostic is the ratio [O III] 4959+5007 / [O III]
4363. This relates directly to the electron density and, in turn, gives an estimate of the
mass. But it requires a temperature for that number, usually chosen on energetic arguments
about cooling of the gas. BUT if you also have [N II] 6548+6583 / [N II] 5755, then you
have two independent estimates of the temperature and density that give a unique solution.
It will be important to follow the developments of [Ar III] 7135, the He I lines (especially He I 6678)
and the Balmer lines (especially H-beta since the normalization of the uncalibrated spectra
for plasma diagnostics is based on the emissivity of that line).

The other, more essential result that requires low resolution data over a broad spectral
coverage is the determination of the abundances. I think the mass problem has been solved
(personal prejudice only) but the abundances will drastically differ from one event to
another. This is the detritus of the nuclear processing so it is the fundamental, virtually
unique signature of the TNR. Only when the gas is completely transparent can standard methods
be applied, those developed for H II regions. Until one knows that there is no pumping from
the UV any flux is suspect and these density diagnostic ratios can’t be converted into
abundances for, as an example, O and N. Those two, along with C, are the overabundant
species that record the temperature and density conditions at the moment of the explosion.

There’s another reason to keep observing, although not with an extraordinary cadence.
There are so few continued programs into this stage that we don’t know if something MIGHT
happen in the later stages.

To see, for instance, if an accretion disk re-appears (as it must) requires certain lines
(e.g., He II 4686) to remain invariant while the others decline. This line is a very
good indicator of the high density, high temperature environment within the disks. And
even at a resolution of 500 you should be able to distinguish the lines from the ejecta
and disk (by the appearance of the line profile and it’s stability).

Steve roser de amatører som har meldt sig til at bidrage med data.
… de har allerede produceret en stor arv……
En af fordelene ved denne type arbejde er, at det har en begyndelse, en fornuftig afslutning,
og produktet er en permanent mine af oplysninger.

[nightskyDeltager Neutron star]

Vejret har ikke været med mig, så det er kun blevet til et forsøg på noget fotometri og lidt RGB.

En V og I optagelse gav en v-mag. på 10,9 for V339, med en usikkerhed omkring +-0,07 – Har ingen
anelse om hvorfor jeg ikke kan gøre det bedre, men mon ikke det skyldes et ringe S/N.

Hvordan hulen jeg beregner i-mag. står hen i det uvisse. Hjælp modtages gerne.

På den store frame ses den planetariske tåge NGC 6905, fin i v men næsten usynlig i I

Et enkelt forsøg med noget RGB blev det også til, men resultatet blev ikke helt som forventet.

100% crop

33% size

En skam jeg ikke har fået lavet noget spektroskopi på den i nogle dage. Kontinuum er
droppet yderligt og nu står der kun klare emissionslinjer tilbage. Bl.a. Balmer linjerne
og noget OIII.

Desuden viser det nyeste spektre også blåforskydning af bl.a. Ha og Hb. Er lidt spændt på hvordan
dette skal tolkes.

[nightskyDeltager Neutron star]

Artikel #16
Steve Shore

Supersoft Røgnten

It’s been a long silence, and my apologies, but it doesn’t mean there’s nothing to write
about.

As you may know from the ATels, V339 Del was detected as a supersoft source (SSS for short)
last week. To explain, this is when the ejecta are finally transparent in the high energy
range of about 100 eV to 1 keV. Even though this would usually be thought optically thin
because you’re talking about X-rays after all (Superman notwithstanding), hydrogen has an
enormous cross section at these wavelengths despite their distance in energy from the
ionization edge (13.6 eV, 912 A) since the absorption cross section changes relatively
slowly, by the inverse cube of the energy (so at 500 eV the cross section is lower by a
factor of about 50000 than at 14 eV but there is so much hydrogen that this can still be
opaque — the column densities are high). This doesn’t mean the source isn’t there, on
the contrary. As with the Fe curtain phase, this is when the effects of the XRs within
the ejecta are observable even though there is no direct detection of the white dwarf.
The SSS is, as you recall, the signature of continuing nuclear burning on the central
object after the explosion, when residual not ejected continues to process below the
photosphere. The high luminosities, this can be several thousand L_sun (hence enormous
fluxes), and low envelope mass (hence not an enormous in situ absorption) leads to a
photospheric temperature of a few 1^5K to 1E6 K for the duration of the event. The larger
the residual mass, the longer the source is active. Its turn-on is at the same time as
the explosion, but it remains like a covered “hot pile” until the ejecta finally thin out
sufficiently to see the WD directly. The rise observed by us, as external observers,
depends on the line of sight absorption, not the intrinsic absorption along a radial line
to the WD within the ejecta, so it’s possible to see the central star before the ejecta
are completely thin if the ejecta aren’t spherical (as is the case here). The slower rise
we see is just the unveiling of the source along out sightline.

This is why I’d recommended noting if certain lines, formed in the ejecta at the periphery
— low density — are detected: [Fe VII] 6086 and [-Fe X] 6378. The latter is hard in low
resolution spectra since it’s blended with the O I 6364 line but it can show up. The former,
and [Ca V] 5307, are ideal optical indicators of the hot source but they have to be emitting
in those lines and, it seems from your latest set of spectra, that this in nova it isn’t. Yet.
They must be there eventually.

The nova was behaving very well, for a degenerate, until a week ago when it went through
a massive (factor of 10) increase in XR brightness for a few days before returning to its
originally smooth rise. The spectrum also was temporarily very soft, meaning the range
around 500 eV. The source, according to the Swift data we’re collecting along with your
spectra, confirms the soft nature but the column density indicated in neutral hydrogen is
still an order of magnitude above the interstellar value. A minor mystery that, but the
flare is much more intriguing. When the nuclear source is active, it seems to be decidedly
unsteady, showing factor of 2 or so variability over hours to days.

V339 Del is doing that. But such a singular brightening isn’t normal.

Whether it’s from the ejecta or the source depends on the radiative transfer. At this
point, I can’t give you an explanation other than a suggestion based on your spectra.
There’s been a dramatic shift in the structure of the line on the blueward side. This
significantly affects interpretation of the XR data since it’s the side of the ejecta
that shield the source. The rapid rise is likely the change in opacity in the UV of the
Lyman lines that have now allowed an increasing emptying of the lower level of H-alpha so
that side is completely optically thin. The red side of the profile hasn’t changed much
if you scale to flux (you can take the ratios of the profiles to see this in velocity).
If the change in the XRs is a transparency effect it occurred very quickly, in a few
days, and that indicates an electron density of about (3-4)E7/cm^3 for that portion of
the ejecta. This should have been seen in other lines and indeed it is — the He II 4686
shows the same (!) profile as H-beta and H-alpha (comparing data from Graham, Potter,
Buil, and Guarro). The low resolution data is ideal for showing the growth of the high
ionization species.

If it’s an ionization event, a spurt of emission from the WD, this would produce an ionization
in the same timescale. So it will take a bit more work to give you a definitive answer
but the observations you’ve all accumulated are a goldmine, this is — yet again — a
stage not previously seen in this detail. And one more, important finding in your collective
spectra: He II 4686 IS there, despite the statement in the recent report, ATel #5493, that
it isn’t there. You see, those in the business can make some pretty egregious mistakes.
We are getting grating spectra with the UVOT on Swift that compare well with your low
dispersion data, in quality and time coverage, but in the IV (2000-4000A) so we will have
complete continua for this entire stage of the nova.

The XR monitoring is continuing, there should be more very high resolution data when the
weather permits at La Palma from the NOT (they’ve had some bizarre humidity and wind in
the last few days, an observation on Friday failed) but as soon as it comes I’ll write
about it. There is an HST/STIS spectrum in the works for mid-November, this should be the
observation in the transition stage of the nova when the ejecta are free of the Fe curtain
and we will get the velocities and abundances for the ejecta for the first time. There
will also be an XMM/Newton XR spectrum at almost the same time (around 15 Nov). We are
now planning how to organize the first papers on this, I’ll keep you all informed; for
the first — including you all — we’ll use the spectra from the fireball and Fe-curtain,
possibly to the date of solar obscuration.

Links:
ATEL
http://www.astronomerstelegram.org/?read=5505

Om Cross Section
http://en.wikipedia.org/wiki/Absorption_cross_section

Illustration fra Mariko KATO (Keio Univ., Japan)
Online Presentations of the 2009 XMM-Newton Workshop, ‘Supersoft X-ray Sources – New Developments’,
ESAC, Madrid, Spain, 18th – 20th May 2009
http://xmm.esac.esa.int/external/xmm_science/workshops/2009_science/#presentations

Lidt ekstra info:
Der kommer mere information I løbet af meget kort tid, skriver Steve.

I går den 28. okt. fik de endelig gang i NOT’en spektra igen og de foreløbige data viser
definitivt ændringer i emissionen. Lige arbejdes der med data.

Super spændende at amatører er med helt i front. Spektroskopi og amatører er det næste
store.

Nova Del 2013 = V339
Novaen er pt. på et plateau hvor der ikke sker større ændringer i magnituden.

[nightskyDeltager Neutron star]

Data fra NOT 28. oktober

Steve Shore skriver:

The Hbeta profile is the key for the Balmer sequence and you see there are substantial
differences with Halpha. This is an ionization effect but I haven’t sorted out the details.
The Hgamma looks weird, and that’s another important indicator. It’s blended with the
[O III] 4363 line, the upper transition of the nebular triplet that gives a measure of
the electron density. The profiles for the [N II] and [O III] and He I lines are almost
the same, but the [O I] 6300, 6364 are showing a completely different, narrower, more
symmetric form so the ionization is clearly highly structures. Some of the features agree
but it’s formed in a more limited velocity range.

So more will be coming but these are the first pass results. The photometric calibration
needs to be applied for secure scaling, the fluxes used a standard (BD+28d4211).

The Balmer lines form NOT, note H gamma is blended with [O III] 4363

He II 4686 on the red edge of NIII and comparison with H beta profile (dashed line)

[nightskyDeltager Neutron star]

The Astronomer’s Telegram
Continuing spectroscopic observations (3600-8800A) of V339 Del = Nova Del 2013 in the early
nebular stage with the Nordic Optical Telescope, Ondrejov Observatory and the ARAS group

ATel #5546; S. N. Shore (Univ. of Pisa, INFN-Pisa); J. Cechura, D. Korcakova,
J. Kubat, P. Skoda, M. Slechta, V. Votruba (Charles Univ. and Astronomical Institute,
Academy of Sciences of the Czech Republic- Ondrejov, Czech Republic); K. Alton, D. Antao,
E. Barbotin, P. Berardi, T. Blank, P. Bohlsen, F. Boubault, D. Boyd, J. Briol, Y. Buchet,
C. Buil, S. Charbonnel, P. Dubreuil, M. Dubs, J. Edlin, T. de France, A. Favaro, P. Gerlach,
O. Garde, K. Graham, D. Greenan, J. Guarro, T. Hansen, D. Hyde, T. Lemoult, R. Leadbeater,
G. Martineau, J. P. Masviel, B. Mauclaire, J. Montier, E. Pollmann, M. Potter, J. Ribeiro,
B. Schramm, O. Thizy, J.-N. Terry, F. Teyssier (contributing participants, ARAS)

on 5 Nov 2013; 01:12 UT

Credential Certification: S. N. Shore

Subjects: Nova, Star
We have been continuing almost nightly spectroscopic observations of V339 Del (see ATel#5378)
with the 2.6 m Nordic Optical Telecope (NOT) FIbre-fed Echelle Spectrograph (FIES) (R ~ 67000),
the Ondrejov Observatory 2m Zeiss coude spectrograph (R = 18000), and a variety of grating
and echelle spectrographs of the ARAS group in the wavelength range 3684 – 7431A with
resolutions ranging from 580 – 12000. As noted by Munari et al. (ATel#5533), the ejecta
have now turned optically thin and entered the nebula phase but there are intriguing details.
The strong lines include: [O I] 6300,6364,8446A, [O II] 7320/7330A, [O III] 4363, 4959,
5007A, C II 7235A and [N II] 5755A (the 6548,6583A lines are still strongly blended with
Halpha), N II 4639, He I (especially 4471, 5876, and 7065), and He II 4686A (peak flux
5.9E-13 erg/s/cm^2/A on Oct. 28). He II was clearly present as early as Oct. 10 (but see
Woodward et al. ATel#5493). There is no further indication of either Na I D or any Fe II
(or related) emission in the spectrum. The line profiles remained nearly symmetrical and
identical to the [O I] 6300A, 6364A lines until Oct. 11. A drastic change in the Balmer
line profiles occurred between Oct. 12 (Day 59) and Oct. 14 (Day 61) — the interval from
-500 to -800 km/s increased by a factor of about 3 relative to the red wing (in the velocity
interval 500 to 800 km/s). This transition occurred around the time of the supersoft X-ray
detection (Osborne et al. ATel#5505). This same profile change was reproduced in all ionized
species lines, only the [O I] lines have remained unchanged.

On the Oct. 28 NOT spectrum (Day 76), comparisons of Hbeta and Hdelta reveals narrow
emission features with halfwidths of ~100 km/s throughout the profile, suggesting that
the broad emission is composed of individual knots with possibly low filling factor, the
same narrow features appear on [N II] 5755A. The [O III] 5007A line blue and red peaks
are at more negative (positive, respectively) velocities than Hbeta by ~150 km/s while
the FWZI is the same for both profiles; the same contrast is seen with respect to [N II]
5755A, which shows a weaker red peak (500-800 km/s) than Hbeta. The He I triplets show a
similar profile to Hbeta, the singlets (e.g., 5016A, 6678A) are either weak (showing only
the -500 to -800 km/s peak) or absent. To date (Nov. 5), there is no evidence of [Ar III]
7135A, [Fe VII] 6086A or any higher ionization emission lines. A weak continuum is
present, ~ 6E-14 erg/s/cm^2/A at 4000-7000A. At this point, the publicly available ARAS
archive contains more than 1000 spectra, many flux calibrated. Based, in part, on
observations made with the Nordic Optical Telescope, operated on the island of La Palma
jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del
Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

ARAS database for Nova Del 2013
http://www.astrosurf.com/aras/Aras_DataBase/Novae/Nova-Del-2013.htm

Comparison of H beta and [OIII] 5007 with NOT

Nightsky2013-11-05 09:17:59

[nightskyDeltager Neutron star]

Artikel #17 (2013-11-23)
Steve Shore

Modelling the ejecta

…. I ran a model for the [O I] and used it to see if the asymmetry in the profile could
be quantified. That’s the enclosed figure. Using the usual maximum velocity, 2500 km/s
(from the UV) and comparing with the observation from the NOT on 28/10, something interesting
comes out.

There wasn’t an attempt to fit things precisely. This time I used the raw data from the
model (no sum, no smooth, so this is one statistical realization). If you normalize and
subtract the profiles then the lowest density region is on the red side; this is opposite
the Hbeta and Balmer profiles (and others too). So it seems to be a clue to the
asymmetries in the ejecta. Again the inclination is moderate, I haven’t yet done the full
radiative transfer solution but that will come after we have the STIS spectrum. As usual,
I’m sort of shocked when the models work so well, they really shouldn’t be so precise!

The plateau phase
For the plateau phase, there can be several reasons, all of which are connected with the
interplay of the illumination from the WD and the expansion. The density is dropping but
the ionization is increasing so there is a point where the emission lines (depending on
which) can remain constant. The higher ionization stages will be like this, your plot of
the [O III] is a good example. We don’t yet have access to the He II cleanly from the
ARAS data, that’s one of the hopes for the NOT and Ondrejov spectra (to separate the
profiles). If the [N II] is constant, the N III 1751 and N V 1240 should be increasing.
The anomaly is always O I but the change in the 8446 line is important. An interesting
feature of the XRs is that they’re now very stable, nothing like the coronary we saw
earlier in the month.

About novae ligh curves :
http://iopscience.iop.org/1538-3881/140/1/34/pdf/aj_140_1_34.pdf

Soft X rays light curve from SWIFT

Observing: reformation of the accretion disk
There are two things that will be important to see now, and you all are in the position
to see it.

The Halpha is so broad that he [N II] 6548, 6583 doublet is masked. That leaves only [O III]
as a density indicator. But in the next weeks, before the nova is inaccessible, there
could be evidence for the reformation of an accretion disk.

Even low resolution data will be important here. The He II line is important, but the
continuum is too. If the weather ever clears this is worth calibrating, a signature is a
rise toward the blue. We haven’t seen this with certainty in any nova to date but it has
to happen sometime!

[nightskyDeltager Neutron star]

Atel #5573 – Variation af super-soft røntgen stråling.

Large amplitude super-soft X-ray intensity variations and a 54 sec QPO in Nova Del 2013 (V339 Del)

ATel #5573; A. P. Beardmore, J. P. Osborne and K. L. Page (U. Leicester) on 12 Nov 2013; 15:53 UT

In ATEL #5505 we reported the rise of the super-soft X-ray source in Nova Del 2013 (V339 Del)
seen by the Swift XRT. Since the last observation reported there, at 1.5 c/s on day 70.8
after outburst, the soft X-ray count rate has risen to a peak count rate of ~100 c/s on
day 87.9 (10 Nov). All count rates are from grade 0 events only. The rising count rate
was interspersed by a few large dips, one of which reached down to <1% of the count rate
one day earlier. Since day 84.6 (7 Nov) the interval of large amplitude variations appears
to have ended, with no variations larger than a factor of two up to the most recent observation
on day 89.7 (12 Nov).

We have searched XRT WT light curves for variability on shorter timescales. An FFT analysis
of the data from day 77.5 to 88.6, in which power spectra of 40 intervals of data of
duration 409.6s at 0.1s binning were averaged, has revealed the presence of a quasi-
periodic oscillation (QPO) and low frequency noise (LFN). Fitting the averaged power
spectrum with a power-law for the LFN, a Gaussian for the QPO and a constant for the
statistical (i.e. Poisson) noise gives a best fit QPO period of 53.2 +/- 1.2 sec, a QPO
FWHM of (3.5 +/- 1.7)e-3 Hz and a LFN power law index of -1.44 +/- 0.16 (where the errors
are 1-sigma). The strongest detection was on day 88.0; the QPO is seen in the remaining
data at a level 4 sigma above the LFN. The coherence as measured from the average power
spectrum is ~12 cycles. The average power in the Gaussian corresponds to a fractional
r.m.s. of 2.5%. Although not detected in all observations, individual sections of data in
which the QPO is clearly visible (e.g. day 84.4 and 88.0) show a sinusoidal-like
modulation with fractional amplitudes up to 6%.

The large amplitude variation in the super-soft flux is very similar to that seen from
the recurrent/classical novae RS Oph, KT Eri, and V458 Vul (Osborne et al. 2011 ApJ 727,
124, Schwarz et al. 2011 ApJS 197, 31). Its origin is not certain, but may be due to
clumps in the ejecta causing variable and possibly ionised absorption (Ness et al. 2007
ApJ 665 1334) or white dwarf photospheric temperature variations (S11). The QPO detected
here is also similar to one seen in RS Oph at 35 sec by the XRT (O11) and XMM (N07), and
in KT Eri also by the XRT at 35 sec (ATEL #2423). The origin of this short-period QPO is
also not certain, possibly being related to either the spin of the white dwarf or an
oscillation in the nuclear burning rate.Nightsky2013-11-30 18:19:23

[nightskyDeltager Neutron star]

ATel # 5593

Chandra observations reveal a rich absorption line system in the supersoft X-ray spectrum
of V339 Del (Nova Del 2013)

ATel #5593; T. Nelson (Minnesota), K. Mukai (NASA/UMBC), L. Chomiuk (MSU) and J. Sokoloski (Columbia)
on 22 Nov 2013; 23:22 UT

Following the report of the emergence of a bright supersoft X-ray source in V339 Del (see
ATEL #5505), we obtained a high resolution X-ray spectrum of the nova with the LETG/HRC-S
instrument on board the Chandra observatory starting on 2013 November 09.75 (88 days
after discovery). The observation had a net exposure time of 46 ks, during which the source
was detected in the 22–44 Angstrom range with a mean count rate of 21 (24) cts/s in the
+1 (-1) order light. The nova did not exhibit the large scale variations in count rate
previously detected by Swift (ATEL #5573), and a preliminary timing analysis did not find
the 54 s QPO in the power spectrum.

The high signal-to-noise Chandra spectrum reveals a rich system of absorption lines
superimposed on a supersoft continuum source – no emission lines are present. We identify
the deepest absorption features in the spectrum as lines of hydrogen- and helium-like
carbon and nitrogen, and the strongest lines appear to be blue shifted by ~1200 km/s.
Other weaker absorption lines are also present. We detect no X-ray flux at wavelengths
shorter than 22 Angstroms—the total observed flux in the energy range 0.1 – 1 keV is
2.8e-9 erg/s/cm^2. Modeling the data as a simple absorbed blackbody, we find an
interstellar absorbing column of 1.8 x 10^21 cm^-2, and a photospheric temperature of 27 eV
(~310000 K).
However, we caution that the model fit is statistically poor and that blackbody fits to
supersoft spectra in novae are known to substantially underestimate the temperature.

[nightskyDeltager Neutron star]

Støv målt i det infrarøde område

Atel 5604
2.3-11.6 Micron Measurements of Nova Del 2013 Consistent with Presence of Dust

ATel #5604; A. C. Cass, R. L. Carlon, D. T. Corgan, D. A. Dykhoff, R. D. Gehrz, R. D. and
D. P. Shenoy (Minnesota Institute for Astrophysics, Minneapolis, MN, USA)

on 27 Nov 2013; 00:32 UT

Our 2.3-11.6 micron measurements of Nova Del 2013 on 24.04 November 2013 UT using an As:Si
bolometer mounted on the 0.76-m infrared telescope of the University of Minnesota’s
O’Brien Observatory (Marine on St. Croix, Minnesota, USA) yielded the following magnitudes:
K = +5.24 +/- 0.15, L = +3.25 +/- 0.38, M = +2.00 +/- 0.26, [10.3] = -0.17 +/- 0.38, and
[11.6] = -0.19 +/- 0.21. An additional measurement on 19.08 November 2013 yielded [10.3]
= -0.10 +/- 0.36. Co-addition of the data from the two nights gives [10.3] = -0.13 =/-
0.26. The measurements are consistent with the presence of a dust shell with a temperature
of ~720K emitting about 10% of the outburst luminosity. Our observations were made possible
by a generous gift from Edward Glickman and technical support by A. Knutson and J.
Marchetti.

Nightsky2013-11-30 20:22:06

[nightskyDeltager Neutron star]

Artikel #18
Steve Shore

Hubble, XMM/Newton, NOT og ARAS data.
Ser vi en gendannet tilvækstsskive? Støvet er måske ikke observeret alligevel..

—–

It’s been too long since I last wrote, and there have been significant developments to
explain. As ever, the collective contributions (ARAS gruppen) are wonderful, it is especially
important to see the move to also obtain spectra longward of Halpha.

We are now well into the nebular phase. The emission lines of all species show ionization-
dependent structures but within a single ion the profiles are the same. This maps the ejecta
structure and leads to a three dimensional view that is especially important (for instance,
in comparison with HR Del 1967 for which the ejecta are superbly resolved). A STIS/HST
spectral sequence (1150 – 3050A) with a resolution of > 30000 was obtained simultaneously
with a NOT observation (3700-7400A), an XMM/Newton XR pointing, and a number of your spectra.
What’s emerged from the UV is that the emission lines are all asymmetric, with profiles
similar to that seen in the optical (with the -1000 km/s peak stronger or dominant relative
to +1000 km/s; for [O II] only the blue is seen) and that all of the ions with ionization
potentials above He I (about 25 eV) have the same profile. There are no absorption lines
other than interstellar, but those are a key to setting the continuum level since they’re
purely absorption and entirely foreground (not in the ejecta).

This shows that a continuum, seen in the optical, is present and strong in the UV. At this
stage, it’s likely a mix from the white dwarf and the thermal emission from transparent
gas in the ejecta. If it’s due to the WD, which is now a strong (but as of today slowly
declining) supersoft source (SSS), then it indicates an intermediate temperature since
the slope in the UV band is quite visible. As a side note, the hotter the central source
the more uniform the continuum in longer wavelengths will be singe the strongest change
is near the maximum (1) . While for now this seems just a technical point, but it’s much more.
The UV+optical luminosity, if a distance of 4+/-0.2 kpc is assumed (which we have from
the comparison with OS And 1986) and a reddening of E(B-V)=0.2, then the luminosity is the
entire spectrum at lower energy than about 13 eV (i.e. roughly the ionization of neutral
hydrogen) is only about 2000 L_sun or less. The X-Rays are very bright; the reported
uncorrected integrated flux from Chandra is about equal to the UV/optical corrected value,
so it must be much stronger. A hopelessly naive assumption, that the emission behaves
like a blackbody, provides a clue (but one to take — as for any comparison with a Planck
function — with much caution) is that only about 5% of the flux has been measured in the
longer spectral interval so the luminosity could really be quite high. In the absence of
any spectral indicators of the WD temperature (or even presence other than the X-Rays) it’s
still a “to be seen eventually”. Some lines might be masked by ejecta emission, for instance,
but that could remain true for months to years.

You might be wondering if an accretion disk has reappeared yet. The 0.1-10 keV range
(reported for Chandra observations by Nelson and collaborators) shows nothing in emission!
OK, there’s a reported continuum but there are no P Cygni type lines (indicative of a
stellar wind). On the contrary, strong absorption was seen (this about a week before the
STIS observations). That’s not so remarkable if it is photospheric, but all lines are blue
shifted (!) by 1000 km/s or so.

Strangely, this is the same velocity at which we see the asymmetric emission peaks. So
think of what would happen if the outer ejecta, which have lower number density and higher
expansion velocity, are nebular (transparent) but the inner, hotter parts of the ejecta
are still marginally optically thick in the lines. Then what you should see are lines shifted,
uniformly and completely, to the velocity of the inner ejecta. In this case, it’s reasonable
to take 1000 km/s. Thus, and this seems to very lovely part of the future work, as these
features turn from absorption (by absorption I also include optically thick resonance
line scattering) to optically thin emission, we will get a new, independent estimate of
the mass and abundances in the ejecta. To encourage you, the Chandra and XMM/Newton data
have about the same resolution in X-Rays that you are getting in the optical. I may have
mentioned that in T Pyx this was detected only very late, after 300 days, and here we have
nothing in the intermediate ions (e.g. N IV]1487, N IV]1718) that we saw in detached
absorption features, but it’s a new and essential probe of the ejecta (2). If this works, it
will allow precise information to be obtained about heavy element abundances, the yields
from the explosions, the correctness of the nuclear reaction modelling (nucleosynthesis
is the sort of radioactive waste from a reactor gone bad, as you all know). There’s been
one claim that dust formed (when have you heard that one before?) but it’s likely a red
herring (we’ll know once there’s a SOFIA flight, the aircraft is grounded now for engine
problems).

So what we have is: excited state transitions: O V] 1371, N IV] 1718, He II 1640; some of
the strongest UV transitions detected: N V 1240, O I 1302, C II 1335, N IV] 1486, C IV 1550,
He II 1640/2733, O II] 1667, N II 2143, C III 2297, O II 2470, O IV 2510/2517, Mg II 2800,
C II 2837, F III 2932. The complex blend at 1400 is primarily O IV 1401 but likely has a
contribution from S IV; the Si IV doublet is absent.

There’s nothing particularly remarkable about the nova properties, the electron density
is now about 1E7/cm^3 (so still marginally high), there’s an indication that the filling
factor (the knottiness of the ejecta, as seen on your profiles of Halpha, for instance),
is about 0.1-0.5 (in other words, not large, not small, intermediate), and the ejecta
mass is about a few 10^-5 M_sun, consistent with other classical novae but that will become
more precise soon. Once this is all over, the next step is the detailed abundance analysis,
he line profile modelling, and the write-up of the first paper.

Your spectral sequences will be the check against which all detailed modelling will be
done since the density, quality, dispersion, and coverage make then precious. There are
now Hamburg Remote Telescope observations (between 15000 and 20000 resolution with 3700 to
9000 A coverage in two groups of echelle spectra), about 20 days in the sequence from
30/8 to 7/11, but without your data, well enough said.

I’ll stop now, and some spectral plots will be coming soon.

Steve

Links
Hubble Space Telescope Space Telescope Imaging Spectrograph
http://www.stsci.edu/hst/stis/
XMM-Newton satellit
http://xmm.esac.esa.int/

SOFIA NASA
http://www.nasa.gov/mission_pages/SOFI
A/#.UppuDCdFYyU

Nightsky2014-01-01 15:40:26

[nightskyDeltager Neutron star]

En lille jule hilsen fra Nova Del 2013 (V339) og den nye nova Nova Centauri 2013 (V1369)

Nova Cen 2013 er vist den 11 klareste som er observeret.

Nova Del 2013 (V339) er stadig på plateau fasen ~mag. 11.25 og der sker ikke mange ændringer i spektret lige nu.

Nedenfor en sammenligning mellem V339, V1369 og V705 (Nova Cas 1993) på samme udviklingstrin ved Na I så man kan se hvor ens forskellige træk er.
Alle CO (kulstof-ilt) WD (hvide dværge), som V705 Cas udvikler store mængder støv omkring 90 dage henne i forløbet.)

Jeg har nogle flere spændende noter på vej fra Steve Shore, så hold øje med denne tråd de næste dage.

Nedenfor en sammenligning mellem Nova Del 2013 (V339) NOT data og Nova Cen 2013 (V1369) Chiron data,
på samme udviklingstrin over en stor del af det visuelle område.

PS:
Chiron er en echelle spektrograf på SMART 1,5 meter teleskopet. Lyset sendes til via fiber.

Lidt data:
Spectral resolution R~ 80000 (with image slicer: normal or Iodine mode) / 25000 (fiber mode)
Spectral range 410-870 nm, fixed
Total efficiency ~6%

Placering:
Cerro Tololo Inter-American Observatory, 500km nord for Santiago, Chile, elevation 2200 meter.

Nightsky2013-12-21 18:31:16

[nightskyDeltager Neutron star]

Nogle bemærkninger til sidste artikel #18

I artiklen ovenfor har jeg markedet stederne med fed

(1)
A clarification here, 30/11/13: the slope changes near the peak of the function so it you have a
steep variation it means you’re closer to the peak (OK, better said, the long wavelength limit
depends on the temperature, that is B(T) T so at a fixed wavelength the slope of the function
depends on the temperature. It’s better to leave it out, just enough to mention that the slope
at any frequency depends on the ratio of the frequency of observation to that of the maximum
(in that sense at max T so you can use this to indicate if the peak is near or far from the observation.

(2)
A clarification after a question by Francois: In the T Pyx spectra, after day 170, there were
detached (high velocity) discrete (narrow in velocity, dV/V 0.1) absorption lines on the profiles.
These remained at the same velocity when seen in absorption, much later, in ultraviolet spectra
at C IV and N V. The thing I’m talking about here is that in V339 Del we have not (yet) seen
this, but it may be what the XR is showing (so we’re seeing the structure probed by a different
set of ions now, perhaps in the next HST spectra we’ll see this on the other lines). In the last
T Pyx paper (the one called paper III in the series in A&A) the pumping is due to EUV and XR
absorptions, at energies of 50-100 eV. The lines, in other words, that are in absorption (which
are reported as He-like and H-like, i.e. C+5) are the transitions that should show this without
an optical or nearer UV counterpart (they’re too ionized) but could be showing up in the FUV
(e.g. O VI instead of O V).

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