trends in the chandra x-ray spectra of o and early b stars june 24, 2008
Post on 22-Dec-2015
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Spectra of Stars
• We know that spectra result from physical processes within stars.
• They often reflect physical properties of the stars that created them.
ex. Optical Spectra
X-Ray Spectra of O and Early B Stars
• The spectra on the left are a representative sampling of O and early B star spectra, with earlier spectral types at top.
• The spectra were taken on the Chandra X-Ray telescope using the high energy transmission grating (HETG) on the advanced camera for imaging spectroscopy (ACIS).
• Nolan Walborn suggested in a 2006 paper that these spectra may reveal a temperature trend similar to that observed for optical spectra.
• I will be looking for evidence that tends to confirm or disprove this hypothesis.
X-Ray Production in Hot Stars
• X-Ray emission arises in the stellar winds of these stars.
• The stellar winds are radiatively driven.
• The line-driven stellar winds are inherently unstable.
• Shocks in the wind arise from the instability and produce x-rays.
X-Ray Spectra and Temperature
• Line strength ratios• Differential Emission Measure
dEM= nenH dV
In a plasma with a single well-defined temperature, or
D(T)= ne(T)nH(T)(dV/d logT)
in a plasma with a temperature distribution.
Stars and ParametersHD93129AB
O2 If* + (2x) O3.5 V((f+))Teff = 50000 K
R= 20 Rsun
M=120 Msun
vinf = 3200 km/sdM/dt = 1.8 * 10-5 Msun/yr
Xi Persei
O7.5 III(n)((f))Teff = 36000 K
R= 12 Rsun
M=34 Msun
vinf = 2450 km/sdM/dt = 2.0 * 10-6 Msun/yr
Delta Orionis
O9.5 II + B0.5 IIITeff = 33000 K
R= 17 Rsun
M=23 Msun
vinf = 2000 km/sdM/dt = 1.07 * 10-6 Msun/yr
Silicon XIV/Silicon XIII Ratios
HD93129AB
0.05 ± 0.02
Xi Persei
0.05 ± 0.02
Delta Orionis
0.21 ± 0.06
Magnesium XIV/Magnesium XIII Ratios
Xi Persei
0.12 ± 0.02
HD93129AB
0.27 ± 0.04
Delta Orionis
0.24 ± 0.03
Conclusions (for now)
• Line ratios of stars in our sample seem to have little to do with effective temperature.
• This tends to disprove Walborn’s suggestion that the trend in the spectrum is temperature-related.
• However, there does appear to be some slight tendency for individual lines to become broader and more blueshifted in the hotter stars.
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