V445 Puppis – a unique helium nova Collaborators: Patrick Woudt (Univ. of Cape Town, RSA) Danny Steeghs (Univ. of Warwick, UK) Margaritha Karovska (Center for Astrophysics, USA) Brian Warner (Univ. of Cape Town, RSA) Derck Smits (Univ. of South Africa, RSA) Paul Groot (Radboud Univ. Nijmegen, NL) Gijs Nelemans (Radboud Univ. Nijmegen, NL) Gijs Roelofs (Radboud Univ. Nijmegen, NL) Tom Marsh (Warwick Univ., UK) Takahiro Nagayama (Kyoto Univ, Japan) Tim O’Brien (Univ. of Manchester, UK) Image: J (IRSF), H (IRSF), K s (IRSF) 3.4' x 3.4' colour-composite of V445 Puppis (taken on 22/03/05). The near infrared evolution of V445 Puppis A distance determination from the expansion parallax The nature of the binary

Last nova of the previous millenium Discovered by K. Kanatsu (8.6 mag on 28 November 2000) Outburst between September and 28 November 2000 (HJD ) Slow nova (outburst lasted ~7 months) Ashok & Banerjee (2003) Wagner et al. (2001) Carbon-rich ejecta, helium (He I), no hydrogen! More on the outburst of V445 Puppis in the subsequent talk by Mariko Kato V445 Puppis: the outburst in 2000

V445 Pup: outburst & model Proposed as the first observed helium nova ( Kato & Hachisu 2003 ; Ashok & Banerjee 2003 ). Various unique aspects: Hydrogen-deficient (Wagner et al. 2001) Enriched in carbon and helium (e.g. Ashok & Banerjee 2003) The initially formed optically thin dust shell has developed in an optically thick shell (Henden et al. 2001) Shell still obscures the nova (6 years later)… See our IRSF/SIRIUS photometry One of a kind! From modelling of the optical outburst light curve, Kato & Hachisu (2003) deduced the following (model-dependent) parameters: Helium shell flash on the surface of the white dwarf primary Mass-transferring binary with massive primary (recurrent nova models) Mass of the primary: M 1 > 1.33 M Sun Mass transfer rate (dM/dt) is several times M Sun /yr Nova recurrence time (t r ) is ~ 70 years M 1 and t r in their models depend sensitively on the assumed distance: d = 640 pc (1.33 M Sun and 61 year); d = 700 pc (1.35 M Sun and 84 year)

V445 Pup: nature of the binary In Kato & Hachisu’s models of a helium nova, the nature of the companion is ill-constrained. The companion can be: a white dwarf the binary would be an AM CVn cataclysmic variable (binary period can be as short as ~5 minutes) a helium star helium cataclysmic ( Iben & Tutukov 1991 ) a normal companion (accreting hydrogen-rich material) but with a very high accretion rate → hydrogen-burning on the surface of the white dwarf primary (hydrogen processed in to helium) Supersoft source (strong X-ray emission… not observed!) After many helium shell flashes, the helium nova with a massive primary (as the models suggest, but model-dependent) could end up as a supernova Ia, or an accretion-induced collapsed neutron star.

Near infrared photometry with the InfraRed Survey Facility (IRSF) Since 22 March 2002, continuous monitoring (~ once per 1-2 months) 22/03/0219/06/0228/08/0204/11/0214/05/0326/04/04 02/02/99 2MASS pre-outburst V445 Pup: (slow) near-infrared evolution 5-year light curve obtained thanks to many observers at IRSF in service mode.

HJD – HJD – HJD – HJD – Rapid change in (J – H) colour over the 610-day period (blue dots) due to the appearance of He I at micron as seen in the infrared spectra of Lynch et al. (2004). He I recombination lines require ionising photons with E > eV. A V = 1.8 mag

Optical imaging of V445 Puppis in the V-band using the 6.5-m Magellan telescope in excellent seeing conditions (FWHM ~ 0.6") Data obtained: 17 December 2003 (3 years after the outburst) V445 Puppis appears extended and elongated! V445 Pup: resolving the nova shell 5"

Expansion parallax: For an expanding nova shell, the distance to the nova can be determined from high-angular resolution imaging ( → expansion on the sky) and (preferably) integral field unit spectroscopy ( → measure the velocity of the expanding material). Complications: complex (non-spherically symmetric) geometry unknown inclination (convert radial into tangential velocities) Modelling of the shell geometry important. → distance error ~10% ddistance (kpc) Δttime since outburst (in days) v exp expansion velocity (km/s) αangular radius (in arcsec) The bipolar shell of the slow nova HR Del (Harman & O’Brien 2003)

Field of view: 1.6" x 1.6" VLT + NAOS/CONICA 4 epochs of K-band imaging - (E1) 25 March (E2) 06 December (E3) 06 October (E4) 03 March 2007 Good seeing (~0.6") Achieved FWHM ~ 0.11" Expanding bipolar nova shell Deconvolution: M. Karovska (CfA) V445 Pup: the nova shell at high resolution Knots at extremes of major axis Viewing dust disk/torus nearly edge-on

clear (uniform?) expansion along the knots (knot-to-knot): epoch 1 to epoch 2, 257 days:0.28" epoch 1 to epoch 3, 561 days: 0.66" epoch 1 to epoch 4, 709 days:0.83" → 0.215" per year along the major axis (from centre) 1.6" x 1.6" 3.5" x 3.5" March 2005 (E1) December 2005 (E2) March 2007 (E4) V445 Pup: angular expansion of the nova shell October 2006 (E3)

Magellan + IMACS: Dec 2003 V445 Pup: optical (long-slit) spectroscopy Dominant lines: [O II] 7320, 7330 Å [O III]4959, 5007 Å He I recombination lines No hydrogen lines! Multiple velocity components: -1600, -900, +800 km/s Presence of [O III] 4363 Å and [O II] 7320/7330 Å indicates a high temperature

He I ( 7065 Å) – 3000 km/s – 2000 km/s – 1000 km/s 0 km/s km/s km/s km/s Clear (radial) velocity structure in each line: NE lobe: km/s and km/s (–65 km/s) SW lobe: -760 km/s and km/s (+480 km/s) V445 Pup: optical (IFU) spectroscopy Magellan + IMACS: Jan 2006 and 2007

IFU line profile across the central column black: centred on He I at 7065 Å red: centred on Hα at 6563 Å Blue- and redshifted components on either side of the shell → bi-conical outflow? Opening angle? Inclination? No evidence for any hydrogen. V445 Pup: hydrogen deficient

Opening angle of the cone of 14° and an inclination of 3.5° w.r.t. plane of the sky, and an outflow velocity of ~5000 km/s gives a distance of 4.9 ± 0.5 kpc (from the expansion parallax). ↓ d ~ 4.9 ± 0.5 kpc V445 Pup: expansion parallax Estimate of the opening angle of the cone from imaging (~14°). Varying over time?

V445 Pup: continuous outflow Velocity profile relatively unchanged over 2 year period. → Continued post-nova outflow at similar velocities consistent with escape velocity of WD. Redshifted component heavily obscured by dust in the shell.

A distance of 4.9 kpc, would imply a distance modulus (m – M) = 13.4 mag. The pre-outburst magnitude of V445 Puppis is V = 14.5 mag and the galactic foreground extinction A V ~ 1.8 mag → M V ~ mag Note: pre-existing dust around V445 Puppis? Candidate helium nova progenitors:  white dwarf + white dwarf absolute magnitude (V-band): about +7 mag white dwarf + helium star absolute magnitude (V-band): about -1 mag  white dwarf + normal companion (accreting hydrogen-rich material at high accretion rates)… but no X-rays detected, nor any hydrogen. absolute magnitude (V-band): –2 to +3 mag V445 Pup: expansion parallax

Clearly detected an expanding, bipolar nova shell with an strongly obscuring dust disk/torus perpendicular to the ejecta. Distance from expansion parallax: 4.9 ± 0.5 kpc - strong limits on the nature of the companion; not a WD+WD binary - Model must be tested rigorously (allow for changing shell structure) No previous outburst observed in the CfA plate archives (1890 – 1960) - Recurrent nova? Time scale? Evolution of V445 Puppis is still ongoing - continued near-infrared (IRSF) monitoring Supernova Ia progenitor? - New distance estimate must be compared with Kato’s models to check for compatibility with the massive WD models White dwarf / helium star binary? When the dust clears, an orbital period must be obtained using high-speed photometry! Eclipsing? V445 Pup: conclusions (so far)