Post on 14-Jan-2016
description
FUSE spectroscopy of cool PG1159 Stars
Elke Reiff (IAAT)
Klaus Werner, Thomas Rauch (IAAT)Jeff Kruk (JHU Baltimore)
Lars Koesterke (University of Texas)
Hydrogen-Deficient Stars, Tübingen, September 18th 2007
Observations
Observations obtained with FUSE
• 905 – 1187 Å (R ≈ 10000 – 20000 ≈ 0.1Å)
• Rowland spectrograph: 4 gratings and 2 detectors, 2 coatings (Lithium-Fluoride, Silicon-Carbide)
Data reduction:
• standard Calfuse Pipeline, done by J.W. Kruk
• shifted to rest wavelength of photospheric lines
• corrections for interstellar reddening EB-V and NH
Static Models
Modelling of the stellar atmosphere
• NLTE model atmospheres, using TMAP
• basic assumptions:
plane-parallel geometry, homogeneous structure
hydrostatic equilibrium (matter is at rest)
radiative equilibrium (no convection)
statistical equilibrium / rate equations (NLTE)
particle and charge conservation
Static Models
Detailed analysis of 2 „cool“ PG1159 stars
• PG1424+535 (110 kK, log g = 7.0)• PG1707+427 (85 kK, log g = 7.5)
• literature values for Teff and log g
• literature values for abundances
• models comprise He, C, N, O, Ne
• analysis of light metals F, Si, S, P
• analysis of Fe and Ni upper abundance limits
Static Models
Beyond light metals: including iron and nickel
• too many levels and lines for numerical treatment
• concept: combine energy levels to few „superlevels“
• lines are combined to transitions between bands
• POS lines: observed; precisely known wavelengths LIN lines: observed + theoretically predicted
IrOnIc (Iron Opacity Interface)
Static Models
Iron group elements in PG1159 stars
• strong depletion of iron found, e.g. in the prototype PG 1159-035 (Jahn et al. 2007)
• iron depletion might be due to transformation into heavier elements by s-process neutron capture
• upper limit for nickel abundance still uncertain
POS lines for the final synthetic spectrum
upper limits for Fe and Ni abundance determined
Static Models
Fe VII in PG1424+535
• Teff = 110kK, log g 7.0
• POS lines of Fe VII used
• upper limit of the iron abundance is 0.1 x solar (compared to 0.01 x solar and solar abundance)
Fe ≲ 0.1 x solar abund.
Static Models
Fe VI in PG1707+427
• Teff = 85kK, log g 7.5
• POS lines of Fe VI used
• upper limit of the iron abundance is about solar (compared to 0.1 x solar and 10 x solar)
Fe ≲ solar abundance
Static Models
Ni VI in PG1707+427
• Teff = 85kK, log g 7.5
• POS lines of Ni VI used
• upper limit of the nickel abundance is about solar (compared to 0.1 x solar and 10 x solar)
Ni ≲ solar abundance
Summary
Analyses with static stellar atmospheres
• upper limits for Fe and Ni abundance determined
depletion for Fe observable but no enrichment of Ni detectable
origin of Fe-depletion not yet understood
Wind Models
Six objects in the sample of PG1159 stars showstrong P Cygni wind profiles in their spectra:
• RXJ 2117.1+3412 (170kK, log g 6.0)
• NGC 246 (150kK, log g 5.7)
• K 1-16 (140kK, log g 6.4)
• Abell 78 (110kK, log g 5.5)
• NGC 7094 / Abell 43 (110 kK, log g 5.7) Static models do not reproduce P Cygni profiles Analysis with wind models required
Wind Models
Modelling of expanding stellar atmospheres
• characteristic parameters
Teff, log g, L R, M
mass loss rate M
terminal velocity v∞ and velocity field v(r)
• using wind-code of Lars Koesterke
spherically expanding atmosphere (1D)
homogeneous and stationary wind
wind models include H, He, C, N, O, Ne, F
·
Wind Models
Previous analyses investigated…
but spectra show also P Cygni profiles of…
Wind Models
Ne VII
@ 973 Å
Wind Models
F VI
@ 1139 Å
Summary
Analyses with static stellar atmospheres
• upper limits for Fe and Ni abundance determined
depletion for Fe observable but no enrichment of Ni detectable
origin of Fe-depletion not yet understood
Analyses with expanding stellar atmospheres
• P Cygni wind profiles for trace elements Ne and F
determine and confirm abundances
see following talk by Marc Ziegler
Static Models
Modelling of the stellar atmosphere
• NLTE model atmospheres, using TMAP
• basic assumptions:
plane-parallel geometry, homogeneous structure
hydrostatic equilibrium (matter is at rest)
radiative equilibrium (no convection)
statistical equilibrium / rate equations (NLTE)
particle and charge conservation
• solve radiative transfer equation