Optical spectroscopy of V4334 Sgr

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Optical spectroscopy of V4334 Sgr

• Simon Jeffery (Armagh Observatory)
• Don Pollacco (Queens Belfast)

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• what you want to know and why
• optical spectroscopy
• the ING record
• an AAT echelle spectrum
• the future

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what you want to know and why

• classification
• comparative analysis
• photosphere
• effective temperature
• surface gravity (L/M ratio)
• chemical composition
• circumstellar
• dust shell
• planetary nebula
• stellar wind

• fundamental questions
• what track has V4334 Sgr followed through the HR
  diagram?
• how has its surface composition changed during
  that evolution?
• is V4334 Sgr similar to any other stars?
• what are the evolutionary origin and fate of
  V4334 Sgr?

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first published spectrum

• outburst discovered on 1996 February 20
• low res spectrum obtained 1996 Mar 8.4
• spectrum early F supergiant
• weak Balmer lines
• strong C I, C II, O I, Si II
• NB characteristics of R CrB stars
• comparison with FF stars FG Sge, V605 Aql

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the once and future faint blue star

• Shetrone Keane 1996 10 FBSIII
• echelle spectrum 96 04 20
• comparison with RCrBs

T7750 K, log g1.0 slightly deficient H
(nH0.7) normal Fe, Cr slightly enhanced He,
Mg, Si, S, Ti, Ba, more enhancedLi, O, Na, Al,
Zn hugely enhancedC,N,Y,Zr H-burning (CNO
cycle) He-burning p-capture, n-capture (s-process)
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Asplund et al. 1997 AA 321, L17
Echelle spectra taken in May and October 1996 H
abundance decreased by 0.7 dex increase in Li,
Sr, Y and Zr similarity to RCrB stars
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Kipper Klochkova 1997, AA 324, L65
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Asplund et al. 1999, AA 343, 507
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V4334 Sgr as a carbon star
Pavlenko, Yakovina Duerbeck, 2000, AA 354,
229 by April 1997, spectrum had evolved to show
strong molecular bands, principally C2 (Swan),
CNv, CNr
simulations ? Teff5500 K, 0ltlog glt1,
EB-V0.70 -4 lt log nHlt -1.7 (not sensitive), log
nN -2.5
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evolution of optical spectrum
Isaac Newton TelescopeLa Palma
Observatory various resolutionsup to
5000mostly optical red, some blue from 1996
March 1(NB discovery on Feb 20) to deep decline
in 1999 ? one / month
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preliminary models of V4334 Sgr

• Asplund model atmospheres with RCrB mixture
• synthe (Kurucz/Lester)
• grid of high-resolution model spectra
  withTeff5000 to 8000 Klog g 0.0 to 1.5 (cgs)
  nH0.0001 to 0.4
• binned to match spectral resolution of INT data
• note evolution of spectrum with expansion
• problem with CII lines

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the hydrogen abundance?

• models effect of H opacity
• maximum in H? line strength at nH0.01-0.1
• metals get stronger with decreasing nH
• CII apparent at nHlt0.1 but other lines too strong
• 96 03 01
• CI and other metals suggest nH0.4
• H? too weak for any model
• need more CII in model
• another opacity source ?

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how H-deficient is V4334 Sgr?

• Asplund et al. 1999 nH,Te
• 96 04 20 0.04, 7750
• 96 05 05 0.02, 7500
• 96 10 07 0.004, 6900

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checking the opacity
Illustration normalized echelle spectrum.
Renormalize to BB continuum, eg 7500K. BB fit to
deepest lines 6500 K.
continuum of the spectrum reflects the
temperature in the photosphere where continuum
photons are formed. deepest lines in spectrum
reflect temperature of line-forming
region scattering in cooler layers places
fundamental limit on line depth good way to check
model has sufficient opacity less opacity, deeper
linesmore opacity, weaker lines
IS Ca HK
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checking the models
AATUCLES spectrum 1996 May 153880-5050
A STERNE model atmospheres LTE, plane parallel,
Kurucz-type continuous opacity Peach tables for
C and N, optimized for H-deficient mixtures, no
molecules or convection. SPECTRUM model spectra
complementary physics. New model gridTeff
10000,9000,8000,7500,7000,6500,6000 Klog g
0.0,0.5,1.0, nH0.1,0.5, nC0.00,0.03,0.10 Lines
H,He,C,N,O,FeI,II,III - verified atomic data
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preliminary conclusions
From red INT H?carbon abundance gt solar
ORhydrogen abundance gt 10 From blue echelle
H?carbon abundance 0.30 - 0.10log g
0.5hydrogen abundance lt 10 Future extend
synthesis calculations toa) entire blue echelle
spectrumb) sequence of INT red spectra
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the future of Sakurai?
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