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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