New white dwarfs for the stellar initial mass-final mass relation (…preliminary results!)

Paul D DobbieAustralian Astronomical Observatory

16th August 2010

Martin Barstow, Matt Burleigh, Ralf Napiwotzki, Sarah Casewell, Kurtis Williams, Ivan Hubeny, Gilles Fontaine, David Boyce,Quentin Parker, Richard Baxter

The stellar initial mass final mass relation

16th August 2010

Predicted correlation between MS mass and remnant

mass of low/intermediate mass star.

Prescription for mass of metal enriched gas returned

to ISM.

Chemical evolution of galaxies (e.g. C,N, s-process

elements)

IFMR remains a challenge to calculate from first

principles.

The stellar initial mass final mass relation

16th August 2010

Usually constrained using WD members of star

clusters

Associate WD mass and cooling time with stellar

lifetime (e.g. numerous papers of Weidemann,

Koester, Reimers in 70s/80s/90s).

End of talk at last meeting drew together data from

11 open clusters with near solar metallicity + WD in

Sirius system:

The stellar initial mass final mass relation

16th August 2010

What’s new ?

16th August 2010

Target rich (nearby) cluster(s) τ~250-300Myr to

further study purported change in gradient of IFMR at

Minit ~ 4M

NGC2516: 4 known WD members (M>0.9M),

~150Myr, Mtot~1000M (MNRAS, 333, 547).

NGC3532: ~300Myr, Mtot~1200M (A&AS, 104, 379),

4 known WD members……expect ~84 WDs

(NGC2287: ~240Myr, Mtot~720M (A&A, 437, 483), 2

known WD members….expect ~63 WDs)

CCD surveys of NGC3532 and NGC2287

16th August 2010

Plan B → obtained imaging data from ESO archive.

NGC3532, NGC2287 observed with 2.2m + WFI in

B, V + I bands, down to B~V~21.5 although only 1

pointing per cluster.

Approximate zeropoints / default extinction

coefficients → ~10% photometry

CCD surveys of NGC3532 and NGC2287

16th August 2010

VLT spectroscopy: temperatures and gravities

16th August 2010

Two nights of VLT + FORS time earlier this year to

obtain good S/N low resolution optical spectroscopy.

Observed 3 objects in NGC2287 and 4 in NGC3532,

poor weather first night prevented additional follow-

up.

Compared observed H-Balmer lines to synthetic

profiles from TLUSTY + SYNSPEC in XSPEC → Teff and

log g

NB. These models use original Lemke profiles, not

more recent and physically realistic Montreal

calculations.

New imaging: robust photometry and distances

16th August 2010

Obtained new V band photometry with Magellan +

IMACS.

Absolute magnitudes using grids of synthetic

photometry (Montreal group) and spectroscopic

temperatures and surface gravities.

…and proper motions

16th August 2010

Preliminary thoughts in context of the IFMR

16th August 2010

WDJ0646-203 potentially heaviest cluster WD to

date, M~1.120.04M (CO models) or 1.08M (ONe

models).

On ‘classical’ CO core ignition limit (~1.1M) and

above more recent estimates (~1.05M). Likely to be

of ONe core composition (ie. an ultra-massive WD).

cool (~150-200Myr) consistent with SF from large

intermediate mass star (M≥4.5M). Further

observational evidence that SSE can produce UMWD

(at solar metalicity).

Preliminary thoughts in the context of the IFMR

16th August 2010

New NGC3532 WDs fainter but not substantially

more massive (M~0.9-1.0M) than previously known

WD-10 (M~0.97M).

Formation of 4 WDs with M>0.9M spans ~100Myr for

little change in their mass so consistent with flatter

IFMR at Minit>4M

Performed 2 fits 1) simple line and 2) model

allowing gradient change @ Minit~4M. Latter provides

improved description - mildly significant. Conclusion

not very sensitive to age of cluster between plausible

limits.

The white dwarf mass distribution.

16th August 2010

New NGC3532 WDs lend further support to earlier

suggestion that O/C WD data IFMR less steep at

Minit>4M than immediately below.

Adds to evidence that no need to invoke more

complex channel to produce bulk of WDs with

M~0.8-1.0M

Results maybe bolstered with spectral follow-up of 3

remaining candidate WD members and more

spatially extensive CCD search / spectral follow-up of

cluster.

Summary

16th August 2010

Performed preliminary CCD search of NGC2287 and

NGC3532 for fainter WD members and unearthed

four new massive cluster WDs.

Revealed potentially most massive cluster WD to

date and further evidence that single star evolution

can produce ultra-massive WDs.

New NGC3532 WDs lend support to our earlier

suggestion that we are seeing change in slope of

IFMR at Minit~4M as predicted by theory.