A Prediction of Supersoft X-Ray Phase of Classical Nova V5583 Sagittarii
Izumi Hachisu, Mariko Kato, Seiichiro Kiyota, Hiroyuki Maehara
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Preprint typeset using L A TEX style emulateapj v. 08/22/09
A PREDICTION OF SUPERSOFT X-RAY PHASE OF CLASSICAL NOVA V5583 SAGITTARII I ZUMI H ACHISU
Department of Earth Science and Astronomy, College of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan M ARIKO K ATO
Department of Astronomy, Keio University, Hiyoshi 4-1-1, Kouhoku-ku, Yokohama 223-8521, Japan S EIICHIRO K IYOTA
VSOLJ, Matsushiro 4-405-1003, Tsukuba 305-0035, Japan
AND H IROYUKI M AEHARA
Kwasan Observatory, Graduate School of Science, Kyoto University, Ohmine-cho Kita Kazan 17, Yamashina-ku, Kyoto 607-8471, Japan submitted to the Astrophysical Journal, Letters
ABSTRACTWe have observed the fast nova V5583 Sagittarii with five B , V , y , R C , and I C bands, and found that thesemulti-band light curves are almost identical with those of V382 Vel 1999 until at least ∼
100 days after outburst.A supersoft X-ray phase of V382 Vel was detected with
BeppoSAX about six months after outburst. V5583Sgr outbursted a few days ago the discovery on 2009 August 6.5 UT near its optical peak. From a completeresemblance between these two nova light curves, we expect a supersoft X-ray phase of V5583 Sgr six monthsafter outburst. Detection of supersoft X-ray turn-on/turnoff dates strongly constrain the evolution of a novaand, as a result, mass range of the WD. For a timely observation of a supersoft X-ray phase of V5583 Sgr, wehave calculated nova outburst evolution based on the optically thick wind theory, which predicts the supersoftX-ray phase: it will most probably start between days 100 and 140 and continue until days 200 -
240 afteroutburst. We strongly recommend multiple observations during 2009 December, and 2010 January, February,and March to detect the turn-on and turnoff times of the supersoft X-ray phase of V5583 Sgr.
Subject headings: binaries: close — novae, cataclysmic variables — stars: individual (V382 Velorum, V5583Sagittarii) — white dwarfs — X-rays: stars INTRODUCTION
Classical novae are a thermonuclear runaway event on awhite dwarf (WD) in a binary system, in which the WD ac-cretes hydrogen-rich matter from the companion star. Whenthe accreted matter reaches a critical value, hydrogen at thebottom of the WD envelope ignites to trigger a shell flash.Just after the nova outburst, the envelope on the WD rapidlyexpands to a giant size and optically thick winds blow. Thenthe photosphere gradually shrinks whereas the total luminos-ity is almost constant during the outburst. Thus, the photo-spheric temperature T ph increases with time. The main emit-ting wavelength region moves from optical to ultraviolet andfinally to supersoft X-ray (e.g., Kato & Hachisu 1994).Thus, classical novae become a transient supersoft X-raysource in a later phase of the outburst, but their X-ray de-tections are rather rare mainly because of sparse observingtime of X-ray satellites (e.g., Krautter et al. 1996; Orio et al.2001a; Ness et al. 2007a). If the turn-on/turnoff dates of thesupersoft X-ray are detected, we are able to constrain the evo-lution of hydrogen shell-burning on the WD and, as a result,the mass range of the WD (e.g., Hachisu & Kato 2006, 2009,2010; Hachisu et al. 2007). Therefore detection of a super-soft X-ray phase of a nova provides us with rich informationon the WD. Electronic address: [email protected] address: [email protected] address: [email protected] address: [email protected]
V5583 Sgr is a fast classical nova, discovered on 2009 Au-gust 6.5 UT by K. Nishiyama and F. Kabashima at mag ∼ . V = 7 .
78 on August 6.2 UT(Nishiyama et al. 2009).We started multi-band photometric observation of V5583Sgr from one day after the discovery, i.e., from August 7.5UT. To our surprise, the observed multi-band light curves arealmost identical with those of V382 Vel, which is also a fastclassical nova outbursted in 1999. A supersoft X-ray phase ofV382 Vel was clearly detected with the X-ray satellite
Bep-poSAX about six months after the outburst. From the perfectresemblance between these two novae, we expect a supersoftX-ray phase of V5583 Sgr similar to that of V382 Vel. In thisLetter, we have calculated a supersoft X-ray phase for V5583Sgr, and predict turn-on/turnoff dates for timely detection.In the next section (Section 2), we briefly describe ourmulti-band photometric observation of V5583 Sgr. Section3 introduces our model of nova light curves based on the opti-cally thick wind theory and summarizes numerical results forprediction of a supersoft X-ray phase. Discussion follows inSection 4. OBSERVATION
Optical observation was started one day after the discovery(Nishiyama et al. 2009). Each observer and their observa-tional details are listed in Table 1. Maehara started observa- Hachisu et al.
TABLE 1O
BSERVATIONS name of location telescope observed No. of obs.observer aperture bands nightsKiyota Mayhill, USA 30cm B , V , R c , I c B , V , R c , I c B , V , y , R c , I c tion on August 7 and obtained 23 nights data for five bandsof B , V , y , R C , and I C (until 2009 November 3). Kiyota ob-tained four bands of B , V , R C , and I C for 14 nights startingfrom 2009 August 8 (until 2009 October 18). The magni-tudes of this object were measured by using the local stan-dard star, HD 321237 with V = 11 .
683 and B - V = + . V = 9 .
80 and B - V = + .
50 (Maehara) from Tycho catalog.Our observational results are plotted in Figure 1 for fourbands of B , V , R C , and I C of V5583 Sgr together with the B , V , R , and I light curves of V382 Vel. We have addedother observational points available in VSOLJ (the VariableStar Observing League of Japan) and AAVSO archives. It isvery clear that these two nova light curves are almost identi-cal with each other. Here we assume that the outburst day ofV5583 Sgr is t OB =JD 2455048.0 (2009 August 4.5 UT).From the almost complete resemblance between these twonovae, we can deduce various features of the classical novaV5583 Sgr. (1) V5583 Sgr is probably a neon nova becauseV382 Vel was identified as a neon nova (Woodward et al.1999). (2) The chemical composition of nova ejecta is sim-ilar to that of V382 Vel obtained by Shore et al. (2003) andAugusto & Diaz (2003). (3) A supersoft X-ray phase will bedetected about six months after the outburst similarly to theV382 Vel case (Orio et al. 2002). (4) The interstellar extinc-tion is calculated to be E ( B - V ) = 0 .
33 from[ E ( B - V )] V5583 Sgr - [ E ( B - V )] V382 Vel = [( B - V ) - ( B - V ) ] V5583 Sgr - [( B - V ) - ( B - V ) ] V382 Vel = ( B ) V5583 Sgr - ( B ) V382 Vel + ( V ) V5583 Sgr - ( V ) V382 Vel = 4 . - . .
13 (1)together with E ( B - V ) = 0 . B - V ) is thesame between V5583 Sgr and V382 Vel. (5) The distancemodulus of V5583 Sgr is estimated from the comparison be-tween the two nova brightnesses. Since the distance modulusof V382 Vel is already known to be ( m - M ) V = 11 . ± . ∆ V = 4 . m - M ) V = 16 . ± . d ∼ ± m - M ) V = 5 log( d / + A V and A V = 3 . E ( B - V ) = 1 .
0. Thesevalues are summarized in Table 2. MODEL LIGHT CURVES AND SUPERSOFT X-RAY PHASE
The decay phase of novae can be followed by a se-quence of steady-state solutions (e.g., Kato & Hachisu 1994).Using the same method and numerical techniques as inKato & Hachisu (1994), we have followed evolutions of no-vae by connecting steady state solutions along the decreasingenvelope-mass sequence. The mass of the hydrogen-rich en-velope is decreasing due to wind mass-loss and nuclear burn-ing. We solve a set of equations, consisting of the conti-
TABLE 2P
HYSICAL P ROPERTIES OF
V5583 S GR subject symbol present worknova type ... ... neon novaextinction E ( B - V ) ... 0.33absorption in V -band A V ... 1.0distance modulus ( m - M ) V ... 16 . ± . d ... 11 ± M WD ... 1 . ± . M ⊙ supersoft X-ray on t X - on ... 120 ±
20 dayssupersoft X-ray off t X - off ... 220 ±
20 days nuity, equation of motion, radiative diffusion, and conserva-tion of energy, from the bottom of the hydrogen-rich enve-lope through the photosphere assuming spherical symmetry.Winds are accelerated deep inside the photosphere so that theyare called “optically thick winds.”We have calculated nova light curves of V5583 Sgr in thesame way as for V382 Vel (Hachisu & Kato 2010). Super-soft X-ray light curves are calculated assuming blackbodyspectrum with the photospheric temperature, T ph , for the en-ergy range of 0.2–0.6 keV (see, e.g., Hachisu & Kato 2009).The UV 1455Å band is also useful to follow nova evolu-tions and to determine WD masses (e.g., Cassatella et al.2002; Hachisu & Kato 2006, 2010; Kato et al. 2009), al-though they are not available both for V382 Vel and V5583Sgr.For optical and near IR light curves, flux at the frequency ν is estimated from free-free emission spectrum, Equation (9)of Hachisu & Kato (2006), i.e., F ν ∝ ˙ M v R ph , (2)during the optically thick wind phase, where ˙ M wind is the windmass-loss rate, v ph the wind velocity at the photosphere, and R ph the photospheric radius, all of which are taken from ouroptically thick wind solutions. After the optically thick windstops, the total mass of the ejecta remains constant in time.The flux from such homologously expanding ejecta is esti-mated from Equation (19) of Hachisu & Kato (2006), i.e., F ν ∝ t - , (3)where t is the time after the outburst.We assume that the chemical composition of hydrogen-richenvelope is similar to that of V382 Vel and adopt a set of X =0 . Y = 0 . Z = 0 . X CNO = 0 . X Ne = 0 .
03, based on thecomposition analyses for V382 Vel by Shore et al. (2003) andby Augusto & Diaz (2003) (see Table 1 of Hachisu & Kato2006). We plot our model free-free and X-ray light curvesin Figure 2. Hachisu & Kato (2010) estimated the WD massof V382 Vel to be M WD = 1 . ± . M ⊙ and the supersoftX-ray turn-on/off times of t X - on ∼
120 days and t X - off ∼ DISCUSSION upersoft X-ray Phase of V5583 Sgr 3 F IG . 1.— Our four multi-band ( B , V , R C , and I C ) optical light curves for V5583 Sgr together with those of V382 Vel 1999. Observational V382 Vel data of B , V , R , and I are taken from IAU Circulars 7176, 7179, 7196, 7209, 7216, 7226, 7232, 7238, and 7277. Here we assume the outburst day of t OB =JD 2455048.0(2009 August 4.5 UT) for V5583 Sgr, and t OB =JD 2451319.0 (1999 May 20.5 UT) for V382 Vel (Hachisu & Kato 2010).TABLE 3D ISTANCE AND A BSORPTION OF N OVAE a object ... ( m - M ) V b A V distance discovery ref. c (kpc) satelliteV1281 Sco 2007 a supersoft X-ray on/off detected novae except V5583 Sgr b distance modulus taken from Table 8 of Hachisu & Kato (2010) c reference for A V or E ( B - V ), where we assume that A V = 3 . E ( B - V ): 1-Russell et al.(2007a), 2-Wesson et al. (2008), 3-Ness et al. (2008c), 4-Mazuk et al. (2007), 5-Burlak(2008), 6-present work, 7-Vanlandingham et al. (2007), 8-Iijima & Esenoglu (2003), 9-Chochol et al. (1993), 10-Read et al. (2008), 11-Shore et al. (2003), Hachisu et al. F IG . 2.— Optical and supersoft X-ray light curves for V5583 Sgr to-gether with V382 Vel. We plot free-free emission model light curves (labeled“Opt&IR”) and 0 . - . M WD = 1 . M ⊙ ( thick dash-dotted line ), 1 . M ⊙ ( thick solid line ), and 1 . M ⊙ ( thin solid line ), for the envelope chemical com-position of X = 0 . Y = 0 . Z = 0 . X CNO = 0 . X Ne = 0 .
03. We selectthe 1 . M ⊙ WD as a best model reproducing the supersoft X-ray data ofV382 Vel. The X-ray absorbed flux data ( large open diamonds ) of V382 Velare taken from Orio et al. (2002) and Burwitz et al. (2002). Large open cir-cles at the right edge of each free-free light curve correspond to the end epochof an optically thick wind phase, during which the free-free flux is calculatedby Equation (2).
The distance modulus of V5583 Sgr can also be estimatedfrom the comparison with the absolute magnitude of free-freeemission model light curves. Hachisu & Kato (2010) ob-tained the absolute magnitudes at the points denoted by open circles of model light curves, which correspond to the end ofan optically thick wind phase. For the model of 1 . M ⊙ WD,its absolute magnitude is M w = 0 . m w = 16 . m - M ) V = m w - M w = 16 . - . . . (4)This value is consistent with ( m - M ) V = 16 . ± . d ) but alsoon the absorption ( A V ). Table 3 lists 11 novae with a supersoftX-ray phase being detected in the order of decreasing distancemodulus. The position of V5583 Sgr is mid of the list, that is,neither the distance nor the absorption is too large to be de-tected. We expect detection of supersoft X-rays from V5583Sgr.We thank the Variable Star Observing League of Japan(VSOLJ) and the American Association of Variable Star Ob-servers (AAVSO) for the optical photometric data on V5583Sgr. This research has been supported in part by Grants-in-Aid for Scientific Research (20540227) of the Japan Societyfor the Promotion of Science.). Table 3 lists 11 novae with a supersoftX-ray phase being detected in the order of decreasing distancemodulus. The position of V5583 Sgr is mid of the list, that is,neither the distance nor the absorption is too large to be de-tected. We expect detection of supersoft X-rays from V5583Sgr.We thank the Variable Star Observing League of Japan(VSOLJ) and the American Association of Variable Star Ob-servers (AAVSO) for the optical photometric data on V5583Sgr. This research has been supported in part by Grants-in-Aid for Scientific Research (20540227) of the Japan Societyfor the Promotion of Science.