Sin t

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Stellar evolution in the post-AGB stage
Or... An optical catalogue of post-AGB
candidates
Olga Suárez Laboratorio de Astrofísica Espacial
y Física Fundamental Madrid (Spain)
Supervisors Minia Manteiga Outeiro Pedro
García Lario
In colaboration with Arturo Manchado, Ana Ulla,
S.R. Pottasch
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Objectives

• Study of stars in the transition phase from AGB
  to PN.
• Catalogue - large number of objects
• Multiwavelength study - SEDs
• Use of statistical tools

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Objectives

• Study of stars in the transition phase from AGB
  to PN.
• Catalogue - large number of objects
• Multiwavelength study - SEDs
• Use of statistical tools

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Stellar evolution
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Post-AGB evolution
(Blöcker, 1995)
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Nomenclature used in this work

• Post-AGB AGB mass loss has ceased.
• not ionized envelope
• Transition objects stellar continuum
• forbidden lines (no OIII)
• Planetary Nebula (PN) no stellar continuum
• forbidden
  lines

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The catalogue - Selection criteria

• IRAS colours
• 12 25 ?2.5 ? log (F12?m/F25?m)
• 25 60 ?2.5 ? log (F25?m /F60?m)
• Flux ratios
• F12?m /F25?m ? 0.50
• F25?m /F60?m ? 0.35
• F60?m /F100?m ? 0.60
• Low IRAS variability ? to avoid AGBs

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The catalogue in the IRAS c-c diagram
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The catalogue - spectroscopic observations
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The catalogue - imaging observations
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The catalogue - the search
Ha - cont
Ha
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The catalogue - the search
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The catalogue - the search
IRAS 17395-0841
Ha
NII
Riera et al., RevMexAA, 2003
Suárez et al., in preparation
Ha
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The catalogue - number of objects

• 255 observed objects
• 104 post-AGB stars (with optical spectra)
• 21 transition objects
• 36 Planetary Nebulae
• 3 AGB stars
• 38 young stellar objects or HII regions
• 2 Seyfert galaxies
• 5 peculiar stars
• 47 objects without optical counterpart (42
  believed to be obscured post-AGB stars)

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The catalogue - a sample
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The catalogue - a sample
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Analysis of the spectra

• Spectral classification of post-AGB stars and
  young stellar objects.
• Comparison with catalogues (Silva, 1992 Pickles,
  1998 Jacoby, 1984)

Relative flux
Wavelength
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Analysis of the spectra

• Excitation classes for PNe (Morgan, 1984 Dopita,
  1990 and Crowther, 1998)
• Based on strength line ratios.

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Analysis of the spectra
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Spectral Energy Distributions

• Data from optical spectra, 2MASS, MSX, IRAS.
• Classification according to van der Veen et al.
  (1989)

Class I
Class II
Class III
Class IVa
Class IVb
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IRAS colour-colour diagram

• Models by van Hoof et al. (1997), based on
  Blöcker (1995), show the evolution in this
  diagram.

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IRAS colour-colour diagram
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Conclusions

• Observations - selection criteria based on IRAS
  colours
• Catalogue - 255 sources 104 post-AGB stars, 21
  transition objects, 36 PNe.
• Spectra and SEDs classified - multiwavelength
  analysis using statistical tools

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Galactic latitude distribution

• Statistical indicator of the mass of a population
  of stars.
• High latitude (wide galactic latitude
  distribution) ? lower mean mass
• Low latitude (narrow galactic latitude
  distribution) ? higher mean mass

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Results

• Evolutionary status Galactic latitude
  statistics

Post-AGB stars and PNe have different galactic
latitude distributionfrom obscured post-AGB stars
Objects without optical counterpart are obscured
post-AGB stars similar to those not observed
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Conclusions

• Observations - selection criteria based on IRAS
  colours
• Catalogue - 255 sources 104 post-AGB stars, 21
  transition objects, 36 PNe.
• Spectra and SEDs classified - multiwavelength
  analysis using statistical tools