New perspectives on B star X-ray emission:

The high-resolution X-ray spectra of Spica and β Cen

• Collaborators on both projects: – Nathan Miller– Joe Cassinelli

• β Cen – Ton Raassen– Emre Tepedelenlioglu– Rolf Mewe

• Spica – Ron Reynolds– Joe MacFarlane– Nate Hall

Main Question: Where and how do B stars produce their

X-rays? Three approaches:

– Line profiles – broadened or not?– Line ratios from He-like ions– Is X-ray flux affected by β Cep-type pulsations

Stars’ Biographical Details

Beta Cen Spica

Spectral Type B1 III B1 IV

Vinf (km/s) 1640 1750

Mdot (Msun/yr) 2.7x10-8 1.0x10-8

β Cep Period (d) 0.157 d 0.1738 d

Satellite XMM Chandra

Instrument RGS/MOS/PN ACIS-S/LETG

β Cen XMM spectra

Spica LETG-ACIS-S spectrum

1. Emission Line Profiles

Profiles of CVI lineof β Cen

Spica Line Profiles(vs. scaled Capella in red)

(Capella Aa (the main X-ray source) had v ≈ +25 km/s during the observation shown here (Ishibashi & Dewey 2005)

2. f/i Ratios from He-like Ions

f/i ratios for β Cen (Kurucz model)

Spica’s Ne IX fir region

Spica’s O VII fir region

Density falloff in Spica’s windCritical Densities Marked:

Radiation will control f/i ratio

Interpreting Spica’s f/i ratios(Hubeny model)

Interpreting Spica’s f/i ratios

(Kurucz model – calc by MacFarlane)

-H II region is relatively isolated-Will use to measure ionizing flux and calibrate photospheric FUV/EUV flux which effects f/i ratios

Spica’s H II region (Wisconsin H-Alpha Mapper (WHAM) image)

3. X-ray Lightcurves

β Cen Lightcurves: 3 XMM instruments

β Cen – folded on β Cep period

Spica β-Cep-Type History• Seen as β Cep variable by Shobbrook et al.

(1969) with p=0.1738 d (pulsations evident in archived observations)

• Photometric variations died out by 1972 (Lomb 1978)

• May still be pulsing, but axis of NRP may have processed so that we are observing pole-on (Balona 1985) (precession period 130-140 yrs) (Dukes 1974)

Spica’s X-ray Lightcurve

Spica data folded on β Cep period

Conclusions:• X-ray emission lines are not strongly

Doppler-broadened in either case

• He-like ions indicate X-rays formed at a range of radii (at least for Spica)

• No evidence is found for either star to be variable in X-rays on their β Cep periods