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), Ks (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 2451876)

• 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: M1 > 1.33 MSun

• Mass transfer rate (dM/dt) is several times 10-7 MSun/yr• Nova recurrence time (tr) is ~ 70 years• M1 and tr in their models depend sensitively on the assumed distance:

d = 640 pc (1.33 MSun and 61 year); d = 700 pc (1.35 MSun 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 starhelium 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 upas 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)

22/03/02 19/06/02 28/08/02 04/11/02 14/05/03 26/04/04

02/02/992MASS pre-outburst

V445 Pup: (slow) near-infrared evolution

5-year light curve obtainedthanks to many observersat IRSF in service mode.

• HJD 245 2515 – 245 2665• HJD 245 2712 – 245 3324• HJD 245 3365 – 245 3644• HJD 245 3669 – 245 4172

Rapid change in (J – H) colour overthe 610-day period (blue dots) due to the appearance of He I at 1.0830 micron as seen in the infrared spectra of Lynch et al. (2004).

He I recombination lines requireionising photons with E > 24.59 eV.

AV = 1.8 mag

Optical imaging of V445 Puppis in the V-band using the 6.5-m Magellantelescope 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 fromhigh-angular resolution imaging (→ expansion on the sky) and (preferably) integralfield 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%

d distance (kpc)Δt time since outburst (in days)vexp expansion velocity (km/s)α angular radius (in arcsec)

The bipolar shell of the slow nova HR Del(Harman & O’Brien 2003)

1exp

7 1077.5 vtd

Field of view: 1.6" x 1.6"

VLT + NAOS/CONICA

• 4 epochs of K-band imaging- (E1) 25 March 2005- (E2) 06 December 2005- (E3) 06 October 2006- (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/torusnearly 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

+ 1000 km/s

+ 2000 km/s

+ 3000 km/s

Clear (radial) velocity structure in each line:NE lobe: -1270 km/s and +1140 km/s (–65 km/s)SW lobe: -760 km/s and +1720 km/s (+480 km/s)

V445 Pup: optical (IFU) spectroscopyMagellan + 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 eitherside of the shell → bi-conical outflow?

Opening angle? Inclination?

No evidence for any hydrogen.

V445 Pup: hydrogen deficient

1

50

)Hβ(EW

)HeI(EW 5876

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 theexpansion parallax).

↓d ~ 4.9 ± 0.5 kpc

V445 Pup: expansion parallax

Estimate of the opening angle of thecone 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 heavilyobscured 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 thegalactic foreground extinction AV ~ 1.8 mag → MV ~ -0.7 mag Note: pre-existing dust around V445 Puppis?

Candidate helium nova progenitors:

white dwarf + white dwarfabsolute magnitude (V-band): about +7 mag

white dwarf + helium starabsolute magnitude (V-band): about -1 mag

white dwarf + normal companion (accreting hydrogen-rich material athigh 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 obscuringdust 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)