August 28, 2014 PTF Summer School

Novae in Local Group Galaxies, Novae in Local Group Galaxies, but really just Andromedabut really just Andromeda

Novae in Local Group Galaxies, Novae in Local Group Galaxies, but really just Andromedabut really just Andromeda

A. W. Shafter San Diego State University

Modified and delivered by Lars Bildsten

Kavli Institute for Theoretical Physics

Anatomy of a Cataclysmic VariableAnatomy of a Cataclysmic Variable

Secondary star

White dwarf

Accretion disk

Bright spot

Basic Nova PropertiesBasic Nova Properties• WD cannot burn the material at

the rate accreted, and so piles up to ignition, then starts to burn and runs away.

• Runaway expands the WD radius, either overflowing the Roche Lobe or driving a wind.

• Luminous! MV ~ -6 to -10

• All novae are recurrent at intervals of ~100 - ~105 yr.

Hydrogen Burning is Usually UnstableFujimoto ‘76; Nomoto et al ‘07; Townsley & Bildsten 2005

Supersoft Sources: Burn H Stably (van den Heuvel et al 1992), or weakly unstable

Cataclysmic Variables (CVs): undergo unstable burning, leading to Classical Novae. Most accumulated mass appears to leave.

Accumulated mass

Trajectory in HR Diagram

The Role of Extragalactic Nova StudiesThe Role of Extragalactic Nova Studies

M31: Principal Historical TargetM31: Principal Historical Target

Major Studies: Novae• Hubble (1929) 85• Arp (1956) 30• Rosino (1964;1973) 142• Ciardullo et al. (1987) 40• Shafter & Irby (2001) 82• Darnley et al. (2006) 20• Others (inc. amateurs) >500 Total: ~1000 Principal Conclusions:• Nova Rate ~ 65 +/- 15 yr-1

• Appear consistent with a mainly bulge population!

964 Novae Discovered in M31 1909-2014964 Novae Discovered in M31 1909-2014

Estimating the RNe population in M31

• W. Pietsch et al. have compiled the positions of >900 M31 novae since 1909.

• From these there are a total of ~102 eruptions with reported separations < 5” from 45 potential RN systems.

• Of these 12 are almost certainly RNe, 4 are possible RNe, with the rest chance positional coincidences.

PTF/iPTF Monitoring of M31

PTF Results on Novae in M31• The MMRD

relation was already in question. .

• Though justified ‘after the fact’, in my view there never was a solid argument for it.

Cao et al. 2012

PTF found a novae with a recurrence time of 1 year, ten times more rapid than any in our galaxy. The short recurrence time and the rapid and hot supersoft phase imply a rapidly accreting M>1.3M white dwarf, one of the most massive yet. It’s fate as accretion continues is unclear!

White Dwarf Masses in Open Clusters

1.21.0 1.40.80.6

WD Mass Distributions from SDSS

Only 5 WD with M>1.3. Very rare, origin often speculated to be WD mergers

MESA is open source: anyone (over 800 users!) can download the source code, compile it, and run it for their own research or education purposes.

Bill Paxton, Father of MESA

Second “Instrument Paper” Published in 2013

http://mesa.sourceforge.net

Fourth MESA Summer School at UCSB August 10-14, 2015

Classical Novae from Unstable Thermonuclear Burning of Accumulated Matter

• Accretion of H/He at low rates leads to a limit cycle of accumulation followed by thermonuclear instability

• Recurrence times depend on WD mass and accretion rate

• Stable burning can occur at high rates due to shell thickening

Wolf et al. 2013

Accumulated Masses and Stable Burning

Wolf et al. 2013

• Higher mass WDs have higher gravity and, hence, smaller accumulated masses.

• Always an amount of Hydrogen left to burn stably over a prolonged time

• Seen as a supersoft phase after the novae that is studied in M31 (Heinze et al.) in excellent agreement with theory.

Relation to other Classical NovaeTang et al. 2014

Implications from the Short Recurrence Time

• MESA Calculations (Wolf et al. ) showed that M>1.3M and accretion rates of 1-3x10-7 M /yr

• The Super-Soft Phase should be short and hot. Triggered SWIFT follow-up with a rather high cadence. . .

SWIFT Observations

• Only 15 day duration.

• Spectra imply a temperature of nearly 0.1 keV

Tang et al. 2014

Theory and Observations place WD mass in the 1.32-1.36 range

Tan

g et

al.

2014

Conclusions• Goes off again in Nov-Dec 2014 !• Excellent system for testing our theories of classical

novae• We don’t know whether the WD mass is increasing

is decreasing, many would like to say that this is a Type Ia progenitor, but we honestly have no idea. . . IF it keeps most, then the core will either unstably ignite (if C/O) or undergo catastrophic electron captures (if O/Ne) in one million years.