257 Acta Polytechnica CTU Proceedings 2(1): 257–260, 2015 257 doi: 10.14311/APP.2015.02.0257 Optical Low Resolution Spectroscopic Observations of T Pyx during the Early Phase of 2011 Outburst A. Arai1,2, M. Isogai2,3, M. Yamanaka4, H. Akitaya5, M. Uemura5 1Center for Astronomy, University of Hyogo 2Koyama Astronomical Observatory, Kyoto Sangyo University 3National Astronomical Observatory of Japan 4Kwasan Observatory, Kyoto University 5Higashi-Hiroshima Astronomical Observatory, Hiroshima University Corresponding author: arai@nhao.jp Abstract We report on the results of our low resolution spectroscopic observations during the 2011 outburst of the recurrent nova T Pyx. Our observations were performed from 0.19 days to 34 days after the eruption discovered by M. Linnolt. We found Wolf-Rayet like features in our spectrum during the initial rising phase on t = 0.19 d. Following spectral developments are consistent with previous works. We discuss that the early phase of T Pyx is divided into three stages, a short lived WR-like stage, He/N stage and Fe II stage. Keywords: cataclysmic variables - optical - spectroscopy - individual: T Pyx. 1 Introduction The initial rising phase of novae is a very intriguing phase in the point of view of thermonuclear runaway and development of spectral features. Generally, obser- vations are very poor in the initial rising phase, because it is very rare that novae are discovered during their ini- tial rising phase. Especially, spectroscopic observations lack at these very early epochs. T Pyx is one of the recurrent novae. Its previous outbursts were observed in 1890, 1902, 1920, 1944, and 1967 (Schaefer et al. 2010). Low resolution spectro- scopic observations in past outbursts were performed around their visual maximum (e.g., Adams and Joy 1920, Joy 1945, and Catchpole et al. 1969). Recurrent novae (RNe) are semi-detached binary systems consist- ing of a massive white dwarf with accretion material from a companion star (at typical mass transfer rate ' 10−7 M� yr−1). They are the prime candidates for being type Ia supernovae (SNe) progenitor. Recurrent novae are classified into three types, the U Sco-, the RS Oph- and the T Pyx-types, based on the light curves and spectroscopic features (Anupama et al. 2008). But, the light curve of T Pyx in the early phase is more simi- lar to slow rising classical novae, than the U Sco- or the RS Oph-type RNe. In past outbursts, T Pyx showed a rapid rising to V ∼ 8, followed by a pre-maximum halt and a further slow rising to the maximum light (V ∼ 6.5) for ∼ 20 days with variations of ∆V ∼ 0.2. The sixth outburst of T Pyx was discovered at vi- sual magnitude 13.0 on UT 2011 April 14.2931 (= JD 2455665.7931, t = 0 d) by M. Linnolt (Waagan et al. 2011). After the discovery, many observers carried out follow up observations. The study in the early spec- troscopic observations and photometry revealed that T Pyx showed rare hybrid spectral classification types (Williams 1992), He/N - Fe II - He/N transition (e.g. Izzo et al. 2012, Imamura and Tanabe 2012, Surina et al. 2014). Following prompt Target of Opportunity observations were also performed in X-ray and Radio just after the discovery of the outburst (e.g., Kuulk- ers et al. 2011, Nordsieck and Shara 2011, Chomiuk et al. 2011). Here, we report our spectroscopic results of T Pyx from the very early phase. In this paper, we focused on the Wolf-Rayet feature in the initial rising phase on t = 0.19 d (2011 April 14.48) and following de- velopments of spectral features from t = 2 d to t = 34 d. 2 Observations Our low dispersion optical spectroscopic observations of T Pyx were performed during 13 nights from 2011 April 14 to May 18 at two sites. One site is Koyama Astronomical Observatory (Kyoto Sangyo University). We used the Araki telescope with LOSA/F2 spectro- graph (Shinnaka et al. 2013). The wavelength coverage 257 http://dx.doi.org/10.14311/APP.2015.02.0257 A. Arai et al. is 4000–8000 Å and the spectral resolution is R ∼ 580 at 6563 Å. Another one is Higashi-Hiroshima Astro- nomical Observatory (Hiroshima University). We use the Kanata telescope with HOWPol (Kawabata et al. 2008). The wavelength coverage is 4200–9000 Å and the spectral resolution of R ∼ 400 at 6563 Å. The V-band light curve and epochs of our spectroscopic observations are shown in the panel (a) of Figure 1. -800 -700 -600 -500 -400 -300 -200 -100 0 0 5 10 15 20 25 30 35 40 E .W . [A n g st ro m s] Day from the discovery (c) 400 600 800 1000 1200 1400 1600 1800 F W H M [ km s -1 ] (b) Hα Hβ OI 7774 FeII 5169 HeI 5876 5 6 7 8 9 10 11 12 V -b a n d M a g n itu d e s (a) Figure 1: (a) The V-band light curve of the early phase of T Pyx 2011 quoted from AAVSO database. Short tics denote epochs of our observations. (b) The FWHMs of prominent emission lines. (c) The equiva- lent widths for the same lines in the panel (b). 3 Results and Discussion 3.1 Wolf-Rayet like features in the initial rising phase on t = 0.19 d Figure 2 shows our first spectrum on UT 2011 April 14.48 (t = 0.19 d), just 4.4 hours after the discovery by M. Linnolt. The spectrum exhibits many highly excited emission lines, He II, C IV, N III, N IV, on this spec- trum. The spectral features are reminiscent of WN type Wolf-Rayet (WR) stars (Crowther 2007 and references therein). We identified these emission lines with ref- erence to spectral atlases of Wolf-Rayet stars (Hamann 1995, Conti 1990). The strong emission at C VI (λ5802) is, however, observed in WC type rather than WN type. In Wolf-Rayet stars, emission lines of highly excita- tion levels for C, N or O are often observed as strong broaded emission lines (FWHM = 800 - 2000 km s−1). In generally, the stellar temperature for WR stars is around 5 × 104 – 105 K, and WR winds are accelerated by line driven pressure (Crowther 2007). In the ordinary picture of novae, during the initial rising phase, shells / a photosphere is expanding. Ab- sorption components are expected to be detected for the Balmer and Fe II, O I, or He I transition. T Pyx showed, however, no significant P-Cygni profiles at the expand- ing velocities of highly excited emission lines (FWHM ∼ 1100 km s −1) on t = 0.19 d. This implies that the envelope of WD would be optically thin on the moment, that is, the optically thick wind (Kato 1994) would be still weak on that time. The T Pyx binary system has an orbital period of 1.83 h and a mass ratio of 0.2±0.03 (Uthas et al. 2010). Such compact binary system has a dwarf companion, suggesting that the amount of surrounding gas supplied by the companion star of T Pyx is much less than the RS Oph-type RNe, which show highly excited emission by shock (e.g., [Fe VII]). Hence, the Wolf-Rayet like spectral features of T Pyx would be originated in the nova envelope, not by shocks with the circumbinary gas. At this time, Wolf-Rayet like spectral features are reported for a few novae. In the PU Vul (1979), WN type features are discovered in optical and UV dur- ing its decline phase (Tomov et al. 1991, Sion et al. 1993). In the spectra of AG Peg, RR Tel and RT Ser, WR-like emission lines appeared after the visual maxi- mum (Kenyon 1986, Tomov et al. 1991 and references therein). Our result is the first case of WR-like spectral features in the rising phase of novae. 3.2 Developments after t = 2 d Such WR-like spectral features disappeared in our spec- tra from t = 2 d as shown in Figure 3. No WR-like lines were reported after t = 0.8 – 1 d (Shore et al. 2011, Izzo et al., 2012, Surina et al. 2014). The brightness of T Pyx on t = 2 d was V = 8, in the pre-maximum halt as shown in the panel (a) of Figure 1. On t = 2 d, Hα, Hβ, O I, He I and N II have been strengthen, while emission lines of He II, C IV and N IV disappeared. This result indicates that the spectral type of T Pyx had changed from WR-like type to He/N type. The expanding ve- locity estimated from blue-shifted absorption minimum of P-Cygni profiles of Hβ is about 1400 km s−1. 258 Optical Low Resolution Spectroscopic Observations of T Pyx during the Early Phase of 2011 Outburst 1.0 2.0 3.0 4.0 5.0 6.0 4000 4500 5000 5500 6000 6500 7000 7500 N o rm a liz e d f lu x Wavelength (Å) H δ/ H e I I + N I V H e I I 4 1 9 9 H γ N I II 4 5 1 5 H e I I 4 5 4 1 + C I V N V 4 6 0 3 + 4 6 1 8 N I II 4 6 5 0 H e I I 4 6 8 6 H β O V 4 9 4 0 o r H e I 4 9 2 2 , F e I I 4 9 2 4 , F e V II 4 9 4 0 F e I I 5 5 8 1 + 5 5 8 2 + 5 5 9 0 C I V 5 8 0 2 H α H e I I 6 6 8 3 N I V 7 1 0 9 − 7 1 2 3 H e I I 7 1 7 7 ⊕ ⊕ Figure 2: First spectrum of T Pyx on t = 0.19 d. The highly excited emissions were detected likely to Wolf-Rayet stars. Cross circles denote positions of telluric absorption bands. 0 5 10 15 20 25 4000 4500 5000 5500 6000 6500 7000 7500 8000 N o rm a liz e d f lu x Wavelength (Å) H α H β H γ H δ F eI I H eI H eI /N II H eI H eI H eI O I t=0.19 KAO t=2 HHAO t=3 KAO, HHAO t=5 KAO t=6 KAO t=7 KAO t=9 HHAO t=11 KAO t=12 HHAO t=18 KAO t=29 KAO, HHAO t=33 KAO t=34 KAO Figure 3: Low resolution spectra of T Pyx from t = 0.19 – 34 d. Observations were carried out at Koyama Astronomical Observatory (KAO) and Higashi-Hiroshima Astronomical Observatory (HHAO). We identified the Balmer, He I, N II, Fe II multiplets, O I, Na I lines. The developments of FWHMs and equiv- alent widths of emission components of these lines are shown in the panel (b) and (c) of Figure 1, respectively. The FWHM of Hα (and also Hβ) measured in our spectra (the panel (b) of Figure 1) present a rapid in- crease from 1100 km s−1 to 1600 km s−1 during t = 0.19 – 2 d. Surina et al. (2014) reported faster velocity (Vej = 4000 km s −1) on t = 0.8 d. After this event, the FWHM of Hα decreased gradually to ∼ 1000 km s−1 until t = 12 d in parallel with the increasing of their equivalent widths from -70 Å to -320 Å, as shown in the panel(c) of Figure 1. FWHMs of other emission lines also showed similar trend, and their equivalent widths decreased to the minimum around t = 20 d (E.W. of Hα = -200 Å). From t = 12 d to t = 34 d, FWHMs of all lines increased again, from ∼ 1000 km s−1 to ∼ 1300 km s−1 for Hα, Hβ and O I (λ7774). Hβ, N II (λ5679), O I (λ7774) are accompanied with P-Cygni profiles clearly. T Pyx showed a He/N-type spectra from t = 2 d to t = 6 d, during pre-maximum halt. Decrease rates of equivalent widths of He I and N II are similar to the one observed in the Balmer lines at the same epoch. On the other hand, Fe II emission lines emerged aound t = 7 d as seen in the panel (c) in Figure 1. The equivalent widths of Fe II multiplets(42, 49) were growing gradu- ally from t = 7 d to t = 34 d. In this epoch, increasing trend of FWHM in Fe II and O I were also observed as seen in Hα and Hβ. On t = 34 d, the equivalent width of Fe II and O I were slightly decreased due to the growth of contin- uum light in this epoch. These results indicate that the strong optically thick wind were gradually developing and Fe II type features replace a He/N features around t = 7 d, consisting with Surina et al. (2014). After the entering into the Fe II type, Hβ, N II (λ5679), O 259 A. Arai et al. I (λ7774) are accompanied with clear P-Cygni profiles. These spectral developments are also reported and dis- cussed in detail in Shore et al. (2011), Izzo et al. (2012), Imamura and Tanabe (2012), and Surina et al. (2014). As pointed out by Imamura and Tanabe (2012), a similar hybrid behavior during the pre-maximum halt phase was also observed in only a slow developing nova, V5558 Sgr (Tanaka et al. 2011). T Pyx reveals intrigu- ing spectral transition of spectral type of nova at more earlier stage than that observed in V5558 Sgr. The hybrid (He/N - Fe II) transition would be a common behavior in slow rising novae. Very likely, the early observed WR-like features may be also a common evo- lution just after the explosion for slow rising novae. Based on our results and combination with previous studies, we summarize that the development during the very early phase of the 2011 outburst of T Pyx is com- posed of three stages: (1) the WR-like stage, which shows short lived (duration < 1 d) WR-like spectral line features, (2) the He/N stage (several days), and (3) the Fe II-type stage. Acknowledgement We thank Taichi Kato (Kyoto University) for valu- able comments on our observational data. 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E. 1992, AJ, 104, 725 260 http://dx.doi.org/10.1093/mnras/142.1.119 http://dx.doi.org/10.1086/168694 http://dx.doi.org/10.1146/annurev.astro.45.051806.110615 http://dx.doi.org/10.1086/125711 http://dx.doi.org/10.1086/175041 http://dx.doi.org/10.1088/0004-637X/708/1/381 http://dx.doi.org/10.1016/j.icarus.2012.08.001 http://dx.doi.org/10.1093/mnras/252.1.31P http://dx.doi.org/10.1111/j.1365-2966.2010.17046.x Introduction Observations Results and Discussion Wolf-Rayet like features in the initial rising phase on t = 0.19d Developments after t = 2d