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  • Kompedal Starparty
    Deltager
      • Main Sequence

      Kompedal Star Party Zoomer ind
      D. 7. april kl. 19:30

      Novaer, de klareste og mest hyppige stjerners udbrud i galaksen
      ved Astrofysiker Steve Shore


      Image credit: Nasa

      Vi får næsten dagligt besked om at der nu er observeret en ny nova I en eller anden galakse, og nogle gange er vi så heldige at en nova viser sig I vores egen galakse, Mælkevejen. Lige nu har vi en meget klar nova i stjernebilledet Cassiopeia som kan ses selv med en ganske lille håndkikkert, så emnet nova’er er ganske aktuelt. Steve Shores foredrag vil give os et indblik i hvad der sker når disse voldsomme udbrud sker, så man får viden om hvad det er man observerer og følger.

      Et foredrag om nova’er ved Steve har været højt på ønskelisten siden 2013, hvor han skrev en lang række artikler til os amatør astronomer omkring Nova Del 2013. Disse artikler kan findes Astronomisk Selskabs fora https://forum.astronomisk.dk/forums/search/V339/ søg efter “V339” hvis du ikke bruger linket.

      Steve Shore har studeret klassiske og tilbagevendende novaer, gennem mange år, for at forstå deres eksplosive og støvdannede processer, stjernevinde og stråling. Han udgivet mange videnskabelige artikler og skrevet bøger, bla. The Tapestry of modern astrophysics.

      Bemærk: Foredraget er på engelsk.

      Zoom møde detaljer
      Emne: Novaer ved Astrofysiker Steve Shore
      Bemærk: Foredraget er på engelsk.
      Tid: April 7, 2021 19:30 C

      Deltag i Zoom Meeting
      https://zoom.us/j/94288847666?pwd=RXZaakp1Q0UvMGYzR1prMzg1TjlwZz09

      Meeting ID: 942 8884 7666
      Passcode: 402035

      Youtube video Nova: https://youtu.be/a4smDVvECaQ

      Kompedal Starparty

      #123616
      nightsky
      Deltager
        • 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

        #112376
        nightsky
        Deltager
          • 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 < br>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

          #112370
          nightsky
          Deltager
            • 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).

            #111975
            nightsky
            Deltager
              • 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

              #110886
              nightsky
              Deltager
                • 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

                #110880
                nightsky
                Deltager
                  • 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

                  #110877
                  nightsky
                  Deltager
                    • 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.

                    #110865
                    nightsky
                    Deltager
                      • 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

                      #110864
                      nightsky
                      Deltager
                        • 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!

                        #110031
                        nightsky
                        Deltager
                          • Neutron star

                          Jo selvfølgelig er det hygge/sjovt Thomas. Men det svinger tit mellem at være ganske berigende og voldsomt frustrerende.

                          Jeg tror aldrig jeg har læst, regnet, søgt og tænkt så meget astrofysik som i i dette efterår. Nova Del 2013 og Steve Shore satte virkelig gang i noget og sidenhen kom Jacob’s objekt oveni.Tongue Heldigvis er der meget der gælder for begge.

                          Støv, støv og atter støv vil jeg mene er temaet for mit efterår. V339, Jacobs boble, mine meteoritter – det hele hænger nøje sammen som om der er en stor rød tråd bag det hele. Jeg mangler bare lige at finde og forstå det sidste… det er lige om hjørnet, eller om det næste hjørne eller det næste…..??????????

                          Og her skulle dette efterår være tilegnet studier af meteoritter, noget astrobiologi samt færdiggørelse af NGNT teleskopet.Cry

                          #109651
                          nightsky
                          Deltager
                            • 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

                            #109433
                            nightsky
                            Deltager
                              • 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)

                              #109391
                              nightsky
                              Deltager
                                • 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.

                                #109000
                                nightsky
                                Deltager
                                  • 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.

                                Viser 15 resultater - 1 til 15 (af 78 totalt)