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