sdss, iphas and galex photometry of post-agb and centrals...

SDSS, IPHAS and GALEX Photometry of post-AGB and Centrals Stars of

Planetary Nebulae

Simon Weston, Ralf Napiwotzki

University of Hertfordshire

Outline

• PN – formation, evolution and observational problems

• IPHAS (INT Photometric Hα Survey)‏

• Distance determination methods

• CSPN synthetic photometry in GALEX/SDSS/IPHAS

• Post-AGB halo stars using GALEX/SDSS

• Outcomes & Future work

Low and Intermediate Mass Stellar Evolution

• All single stars with M < 8.0Mּס

• Mass loss and envelope ejected in thermal pulse phase

• As central star contracts and heats up, the ejected nebula is illuminated.

Evolutionary tracks from Blöcker (1995)‏

PN Observational Problems

• Birthrates uncertain

• Local density difficulties

– Incompleteness and morphological bias

– Distances notoriously difficult to determine.

• Many PN non-spherical

– Difficult to explain with single star scenario

Formed by single or binary stellar systems?

IPHAS

• Galactic plane survey (b < |5|)‏

• Hα, r’ and i’ band down to r’≈20 (10σ)‏

• Found 233 unknown PN candidates in RA =18-20hr region alone (Zijlstra, priv. comm.)

PN Size Distribution

Figure taken from Zijlstra (Priv. comm.)‏

PN distance determination

IF central star is known:

• Reddening distance from 3D dust map

• UV and optical colours of central stars

Survey data often sufficient for these two methods

Locating the Central Star

There is one candidate CSPN

Distance Estimate

Prince’s‏Nebula‏in‏IPHAS‏- Figure from Sale (Priv. Comm.)‏

Synthetic Photometry

• Kurucz ‘Atlas9’ O and B stars and Koester white dwarfs model atmospheres.

• SEDs folded with GALEX/SDSS/IPHAS filters giving UV/optical and near-IR magnitudes.

• Calibrated with hot DA WDs

• Synthetic photometry for GALEX and IPHAS bands will be made public soon.

Synthetic Photometry may be extended to post-AGB stars

Post-AGB stars in Galactic halo

• Teff and logg can be estimated using UV and optical photometry alone.

• We will find post-AGB stars combining SDSS and GALEX photometry – if they exist.

Post-AGB stars in Galactic halo

• Standard evolution models expect all low and intermediate mass stars to go through a post-AGB phase.

• Simulation of the Galactic population predicts many in the halo (Napiwotzki 2009).

• Torun catalogue of post-AGB stars (Szczerba et al. 2007) finds very few in the halo.

Galactic Post-AGB Stars (V=16)‏

Galactic Post-AGB Population

Figures 2 and 3 from Szczerba et al (2007)‏

Possible Outcomes

1. Expected number of post-AGB stars found

• Standard scenario

• Systematic search for PN around them

• Check of predicted evolutionary timescales possible

2. Results confirm deficit of post-AGB stars

halo stars avoid the AGB and evolve directly from the horizontal branch to the white dwarf sequence

Summary & Future Work

• Locate and determine distances to CSPN in SDSS/GALEX

• Also IPHAS with UVEX – U, g’, r’ photometry in IPHAS field

• Start systematically look for halo post-AGB stars in SDSS with GALEX

• Spectra of CSPNe in MASH survey from ESO UT2 telescope.

• Look at revised PN space densities and birthrates

Questions?

NGC6781‏image‏taken‏from‏Nick‏Wright’s‏webpage‏

NGC 6781image‏taken‏from‏Nick‏Wright’s‏webpage‏

Sh2-188‏image‏taken‏from‏Nick‏Wright’s‏webpage‏

Sh2-188 image‏taken‏from‏Nick‏Wright’s‏webpage‏

Galactic Post-AGB Stars

Simulated post-AGB populations

• Monte Carlo simulation of thin disc, thick disc and halo stars (Napiwotzki 2009).

• Stars are created with initial masses drawn from a Salpeter IMF

• Stars distributed randomly based on standard model of Galactic structure (Robin et al. 2003)‏

• Detailed simulation of stars evolved to post-AGB phase and beyond.

• Calibrated with observed WDs from the ESO SN Ia Progenitor Survey (SPY)‏

M32 UV CMD

Figure taken from Brown (2005)‏

GALEX/SDSS Synthetic Photometry of post-AGB stars