125-day Spectral Record of the Classical Nova Delphini 2013 (V339 Del) William Wiethoff, SOLO Observatory, P.O. Box 88, Port Wing, WI 54865 Howard Mooers, Department of Geological Sciences, University of Minnesota Duluth, 230 Heller Hall, 1114 Kirby Dr., Duluth, MN 55812 Alec Habig, Department of Physics, University of Minnesota Duluth, 371 Marshall W. Alworth Hall, 1023 University Drive Duluth, MN 55812

Abstract The August 14, 2013 eruption of Nova Delphini 2013 presented a unique opportunity for amateur astronomers to study the evolution of a classical nova. We present a 125-day spectral record of the evolution of this nova acquired with a low-resolution 100 line per millimeter grating and a commercially available CCD camera mounted on an 14” Schmidt Cassegrain telescope. Records were acquired beginning one day after discovery. At the time of writing this abstract 44 spectra were acquired and analyzed. Raw data were calibrated against star 29vul a type A0V with clear H-Balmer lines. Spectra were then corrected for instrument response and analyzed with commercially available software from Field Tested Systems (R-Spec®). Earliest spectra characterize the fireball phase with a bright continuum and clear H-Balmer emission lines. The transition to the Iron Curtain phase is uncertain in our spectra because of lack of sensitivity in the UV. By +6 days the expanding gas shell has cooled to the point where various emission lines appear prominently; particularly H, H , and Fe II. Elemental oxygen (O I) at 7773 and 8446 Å also emerges from the continuum and by +10 day dominate the near-IR. Further progression shows the C III and N III complex at 4640 Å and He I at 7065 Å. Further evolution of the phases of Nova Delphini 2013 is clearly defined in the emission spectra. Lyman-b pumping of O I at 8446 Å is clearly evident by +17 days and drops precipitously between days 48 and 49. The nebular phase becomes apparent when O III at 5007 Å becomes obvious.

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Figure 9. Illustration of the appearance of O III and the beginning of the Nebular Phase.

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Figure 8. Evolution of the appearance of iron (Fe II) emission and Lyman-Beta pumping of oxygen (O I) at 8446 Å.

Figure 7. Spectra from days +3 through +5 showing the transition from the fireball phase to recombination.

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Observatory Spectra were acquired at SOLO (Studying Old Light Observatory) Observatory located near Port Wing, Wisconsin. The observatory is a roll-off-roof type featuring a 14” Celestron® Schmidt Cassegrain telescope on an equatorial mount (Figures 2 and 3). The system uses a Meade DSI Pro II monochrome CCD camera for image and spectra acquisition.

Spectra were analyzed with the RSpec®, a user-friendly software package from Field Tested Systems, LLC (www.rspec-astro.com), which when coupled with the Star Analyzer 100 is an easy, very-low-cost way for beginners to learn spectroscopy. The 70 mm spacing of the grating gave a resolution of approximately 13.7 Å/pixel. However, each spectrum was calibrated individually by determining the image Å/pixel from the calibration star 29 Vul using the H absorption line; image scale varied slightly from 13.72 to 13.77 Å/pixel. All spectra were corrected for instrument response and normalized for graphing (Figure 5). The RSpec interface makes calibration and processing of spectra straightforward. Spectra can be imported in a variety of formats including .fits. Figure 6 shows the RSpec interface with a spectrum profile of 2013 Del loaded (red curve) along with the instrument response reference (green curve). A utility allows calculations on the two series and the resultant corrected profile is shown in the “Math” window (Figure 6).

Results and Discussion The 44 normalized spectra are shown in Figure 5 and labeled in Universal Time and Day relative to peak magnitude of nova 2013 Del. Major phases of the nova evolution that are readily identified with the low-resolution system are identified on the right vertical axis of Figure 5. These include the a) fireball and optically thick phase, b) recombination, c) the appearance of Fe II (5187 and 5316 Å), d) the O I emissions at 7773 and 8446 Å; the latter results from Lyman-Beta pumping, and e) the appearance of O III (5007 Å) that signals the transition to the nebular phase (Shore, 2012; 2013). Despite the low resolution of the spectra using the 100 line per millimeter grating, the details of the nova evolution can be easily followed. Spectra from days +3 to +5 clearly illustrate the transition from the fireball and optically thick phase to the beginning of recombination (Figure 7). H and H lines become prominent and Fe II emission lines appear (Figure 7).

Conclusions Low resolution spectra obtainable by nearly any amateur astronomer with relatively modest equipment can be used to study the evolution novae or investigate a host of other astronomical phenomena. Resolution of spectra is greatly improved by using larger imaging sensors but requiring longer exposures because of decreased photon flux per pixel.

References: American Association of Variable Star Observers (AAVSO), http://www.aavso.org/. Astronomical Ring for Access to Spectroscopy (ARAS), www.astrosurf.com/aras/. IAU Central Bureau for Astronomical Telegrams, 8/14/2013, http://www.cbat.eps.harvard.edu/unconf/followups/J20233073+2046041.html. Shore, Steven N., 2012, Spectroscopy of Novae--A User's Manual. arXiv preprint arXiv:1211.3176. Shore, Steven N., 2013, Notes on novae, spectroscopy, and astrophysics for the ARAS group, http://www.astrosurf.com/aras/novae/Images_NovaDel2013/SteveNotes.pdf. Williams, Robert, 2012, Origin of the "He/N" and "Fe II" spectral classes of novae, The Astronomical Journal, v. 144, no. 4, 8pp.

Introduction The August 14 eruption of the classical nova 2013 Delphini gave amateur astronomers a rare opportunity to study first-had the evolution of novae. This poster presents the results of 44 spectra gathered over 125 days with a 100 line per millimeter grating and an inexpensive commercially-available CCD camera. The nova was discovered August 14.5 UT by Koichi Itagaki (IAU CBAT, 8-14-2013) and peaked on August 16.25 UT at an apparent visual magnitude of 4.3 (ATEL #5304) (Figure 1). Our first spectrum was acquired August 15.3 UT (-1 day relative to peak) and nightly thereafter through August 24 UT (+8 days). Additional spectra were acquired every clear night through December 19 UT (+125 days).

Figure 1. Nova 2013 Del on Aug. 18 UT (+2 days).

Figure 2. SOLO Observatory. Figure 3. Telescope and mount.

Methods Spectroscopy was done with a Star Analyzer® 100 mounted 70 mm from the sensor (Figure 4). Spectra were recorded by stacking 20, one-second exposures during the early phases of the nova evolution and as the magnitude faded exposure time was increased to 5.7 sec. The Meade DSI Pro II has a sensitivity range from 3900 – 9500 Å. All exposures were dark-frame subtracted but no bias or flat-field correction was done. After acquiring each spectrum the star 29 Vul, a type A0V, was imaged to be used for later calibration.

Figure 4. CCD camera and grating configuration.

Figure 5. Normalized spectra of Nova 2013 Del (V339 Del) Figure 6. Layout of the RSpec® graphical interface.

The transition to the nebular phase is observed in the appearance of the forbidden O III (5007 Å) emission line, which becomes apparent by day +40. By Day +62 the amplitude of the emission of O III (5007 Å) equals and begins to exceed that of H; the forbidden transitions accompany the thinning of outer ejecta. Between day +62 and +100 the prominent O I line at 8446 Å disappears.

By day +8 the permitted O I emission is increasing rapidly and Fe II becomes prominent (Figure 8). By +31 days, O I (7773), which is supported by collisional and recombination energy, is dropping but O I (8446) supported by Lyman-Beta pumping is still increasing (Williams, 2012). Fe II emissions are no longer discernable by day +47.

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Figure 10. Spectrum of Nova 2013 Del on day -1 compared to reference spectrum of an A7V star. Figure from RSpec® software.

Swenson College of Science and Engineering

Department of Geological Sciences

Department of Physics