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X-RAY DIAGNOSTICS of GRAIN DEPLETION in
MATTER ACCRETING onto T TAURI STARS
Paola Testa (MIT)
Jeremy Drake (SAO)
Lee Hartmann (SAO)
http://chandra.harvard.edu/photo/2003/twhy/index.html
Chandra Workshop – July 13 2005
OUTLINE
•
X-ray SPECTROSCOPY of CLASSICAL T TAURI STARS:
signatures of accretion – TW Hya et al.
• SURVEY of CORONAL ABUNDANCES in ACTIVE STARS:
Ne/O
• Ne/O as DIAGNOSTICS for the ACCRETING MATERIAL
X-ray EMISSION from YOUNG STARS
X-ray HIGH RESOLUTION SPECTROSCOPY
of CLASSICAL T TAURI STARS
 TW Hydrae
MEG
HEG
X-ray HIGH RESOLUTION SPECTROSCOPY
of CLASSICAL T TAURI STARS
 TW Hydrae
• cool He-like triplets (Ne, O) indicate unusually
high plasma density
• thermal distribution extremely peaked
• anomalous abundances: extremely abundant
(~ factor 10) Ne, underabundant Fe
X-ray HIGH RESOLUTION SPECTROSCOPY
of CLASSICAL T TAURI STARS
is TW Hya the only young object with these peculiar characteristics?

OTHER TTS in TWA do not show signature of accretion:
HD 98800 (Kastner et al. 2004), TWA 5 (Argiroffi et
al. 2005)
 BP TAU: XMM-RGS spectra show high density for OVII
 HD 163296 (HERBIG Ae STAR): remarkably isothermal
plasma (BUT only low energy resolution spectra,
ACIS-I, Swartz et al. 2005)
CORONAL ABUNDANCES from CHANDRA
HETG SPECTRA
large sample of HETG spectra: 22 active stars, within ~140 pc from the
Sun, at different activity levels

ABUNDANCES DIAGNOSTICS: Ne, the Sun, Star
Formation and Planets
CHANDRA
HETG
SPECTRA:
Single
Stars
CHANDRA
HETG
SPECTRA:
Binary
Stars
ELEMENT ABUNDANCES
Chandra HETG spectral resolution allows line-based abundances analysis
(based on strong X-ray emission lines of H-like and He-like abundant
ions)
e.g. for Ne/O diagnostics,
line ratio of NeIX, NeX,
OVII
ELEMENT ABUNDANCES
 Ne/O
(Drake & Testa, 2005)
ELEMENT ABUNDANCES
 Ne/O
• Ne/O extremely constant on a wide
range of activity levels
• Ne/O in coronae of nearby stars ~2.7
times higher than the assumed
solar photospheric value
(Drake & Testa, Nature, 2005)
Ne and the SOLAR MODEL PROBLEM
• Models calculated with latest solar
abundances (Asplund et al 2004)
fail to predict sound speed, He
abundance and depth of
convection zone inferred from
helioseismology (Bahcall et al
2005; Antia & Basu 2005)
• Ne higher by a factor > 2.6 can solve
the solar model problem
(Bahcall et al 2005 ; Antia & Basu
2005; Antia & Basu 2004)
Bahcall et al (2005)
STAR FORMATION and PLANETS
• Constancy of Ne/O in coronae
use for
exploring O depletion in accreting systems
– Measure of disk/planetary evolution
• Two known T Tauri stars with X-ray accretion
shock signatures: BP Tau (~1Myr, Schmitt et al 2005);
TW Hya (~10Myr, Kastner et al. 2002, Stelzer & Schmitt
2004)
cool He-like triplets of
OVII and NeIX indicate
unusually high ne
http://chandra.harvard.edu/photo/2003/twhy/index.html
STAR FORMATION and PLANETS
• Constancy of Ne/O in coronae
use for
exploring O depletion in accreting systems
– Measure of disk/planetary evolution
• Two known T Tauri stars with X-ray accretion
shock signatures: BP Tau (~1Myr, Schmitt et al
2005); TW Hya (~10Myr, Kastner et al. 2002,Stelzer
& Schmitt 2004)
• TW Hya shows O depletion by a factor ~2
indicative of evolved disk with large grains
Drake, Testa & Hartmann (2005)