Ssiss is sse titel

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An X-Ray Survey of the Taurus Star Formation
Region Manuel Güdel (PSI/Switzerland) the XEST
Team (PSI/Switz. K. Arzner, K. Briggs, A.
Glauser, A. Telleschi LAOG Grenoble/Fr J.
Bouvier, C. Dougados, N. Grosso, S. Guieu, F.
Ménard, J.-L. Monin, T. Montmerle Palermo/It E.
Franciosini, G. Micela, I. Pillitteri, L. Scelsi,
B. Stelzer Colorado Univ./Boulder S. L.
Skinner Columbia Univ/Geneva Univ/Switz. M.
Audard Firenze/It F. Palla MPIfR
Bonn/Germany T. Preibisch PennState/USA E. D.
Feigelson Caltech/USA D. Padgett, L. Rebull
Porto/Pt B. Silva
The XMM-Newton Extended Survey of the Taurus
Molecular Cloud (XEST) is a large X-ray (and U
band) survey of the Taurus star-forming region
designed to study the generation of high-energy
radiation in young stars, its interaction with
the surrounding molecular gas, and its potential
impact on disks and forming planets. Stars in TMC
form in relative isolation, high-mass stars being
entirely absent. Strong mutual influence due to
outflows, jets, winds, or UV radiation is
therefore minimized. XEST thus ideally
complements X-ray studies of clustered star
formation regions such as Orion. It
systematically surveys, for the first time, TMC
protostars and substellar objects in X-rays. TMC
surveys about 5 sq. degrees of the TMC cloud
containing the most crowded stellar fields
typically located in the densest molecular
regions. The entire survey so far comprises 27
XMM-Newton EPIC fields of view, each being
roughly circular with a diameter of 30 arcmin.
The sensitivity is such (LX ? 1028 erg/s for
average absorption) that almost every classical
and weak-lined T Tauri star (CTTS/WTTS) has been
detected, and so were about50 of the surveyed
Class-I protostars and brown dwarfs (BDs). The
detection statistics are as follows Protostars
CTTS WTTS BDs others total Surveyed 21 70 52 17
9 169 Detected 10 (48) 60 (86) 50 (96) 9
(53) 7 (78) 136 (80)
Active Brown Dwarfs
Accretion Soft Excess
Jets Double Absorbers
XEST detects of 9 out of 17 surveyed BDs,
typically at LX of a few x1028 erg s-1. It is
mostly the earlier spectral types/higher Lbol BDs
that are X-ray detected. They fit the stellar LX
vs mass and LX vs Lbol relations quite well,
i.e., young BDs behave like lowest-mass stars.
DG Tau
active low OVII/OVIII
OVII triplet of T Tau forbidden line (f) strong
? low density (? 1010 cm-3)
continuum
soft
OVIII OVII
cts/s/kev
absorbed
hard
continuum
r
f
inactive high OVII/OVIII
Energy
time
i
New spectral phenomenology was found in a few
jet-driving CTTS (e.g. DG Tau). The X-ray
spectrum requires two unrelated components a
cool, very little absorbed ("soft", NH few
1021 cm-2) component and a hot, very strongly
absorbed ("hard", NH gt 1022 cm-2) component. The
hard component shows flares and is therefore
coronal. But its absorption by gas is much higher
than expected from the stellar visual extinction
This points to absorption by dust-depleted
accreting gas streams evidence for dust
sublimation. The soft component must
therefore be emitted further out We hypothesize
that it is formed in shocks at the jet base.
Chandra indeed sees faint jets with a spectrum
similar to the soft component. The counter jet is
harder'' its X-rays are absorbed by the gas
disk!
High-resolution X-ray spectroscopy of CTTS and
WTTS reveals an anomaly among CTTS The observed
OVIIr/OVIII Ly? is large in CTTS (of order unity)
whereas OVII is hardly detected in WTTS, similar
to active ZAMS stars. In T Tau, the OVIIr line is
intrinsically the most luminous X-ray line! In
that respect, CTTS resemble inactive, old and
cool coronae like Procyon's. On the other hand, a
very prominent continuum and "hot" lines are
seen in CTTS, as in extremely active field
stars. The soft excess in CTTS may be due to
accretion shocks, but in T Tau, the predicted
high densities are not seen in the O VII line
triplet. Alternatively, the cool accreting gas
may stream into some of the coronal active
regions, mixing with the hot plasma and thus
adding large amounts of cool plasma ("coronal
cooling"). OVIIr/OVIII Ly? flux
ratio as a function of NH. CTTS are in the upper
part of the figure, WTTS (and ZAMS stars) in the
lower. Curves indicate flux ratios for isothermal
plasma as labeled.
detected
There is no significant difference in the
de-tection rates of accre-ting vs non-accreting
BDs. Accretion does not si-gnificantly alter the
X-ray properties of BDs.
accreting
non-accreting
constant soft X
jet shocks
Photoelectric absorption no excess visual
extinction
undetected
flaring hard X, absorbed
x
dust destruction at 10 R
XEST observed a long, gradual U-band event in one
of the observed BDs (2M J041411882811535). No
simultaneous X-rays were detected (the star
remained entirely undetected in X-rays). Although
rotational modulation remains a possibility, the
time scales also suggest an explanation in terms
of an accretion event that increased the
hot-spot luminosity a temporary accretion rate
increase by a factor of ?6 is required.
constant soft X, absorbed
x
counter jet
Photoelectric absorption by disk
CTTS
T Tau
Gradual optical event in a BD near V773 Tau
Counter jet (blue) harder than forward jet
(red/yellow) absorption by disk
DG Tau (Chandra ACIS-S, 0.5-1.7keV)
counter jet
forward jet
hardness (red to blue for
0.5-1.7 keV)
WTTS
log NH
OI optical forward jet (Dougados et al. 2002)
New TMC Member Candidates
NOTE This poster shows selected results from a
larger body of studies related to XEST. A first
series of refereed papers will be published
shortly in a special issue of AA containing 15
papers on various topics. First authors and
topics Güdel et al. Introduction, Overview
Tables Arzner et al. Low-count spectra Arzner
et al. Stochastic flaring (light curves) Audard
et al. U-band/UV survey (XMM-OM) Briggs et
al. Activity-rotation relations Franciosini et
al. Flare geometric modeling Grosso et al. BD
X-ray survey Grosso et al. BD U-band accretion
event Güdel et al. X-rays from jet-driving
CTTS Güdel et al. Case study of T Tau Scelsi et
al. New TMC member candidates Stelzer et al.
Flare variability statistics Telleschi et al.
High-res X-ray spectroscopy Telleschi et al.
Case study of AB Aur (Herbig) Telleschi et al.
Accretion X-rays, C/WTTS and in
preparation Glauser et al. Gas/dust (NH-AV),
IRAS 04158 Güdel et al. Soft excess in
CTTS Scelsi et al. Coronal abundances Acknowledg
ments We acknowledge financial support from the
International Space Science Institute (ISSI) in
Bern, the Swiss NSF (grants 20-66875.01 and
20-109255/1), NASA (grant NNG05GF92G), and
ASI/INAF (grant I/023/05/0). XMM-Newton is an ESA
mission funded by ESA member states and the USA.
field around V410 Tau (L1495E)
known members
Typically, 90 of 100 detections per FoV are not
known TMC members. IR color-color and
color-magnitude diagrams find 60 new potential
stellar members of TMC. About one dozen show high
probability given their thermal spectra and
flares. They may be low-extinction WTTS, mostly
following the mass-LX relation valid for TMC
members.
common range for TMC
mass-LX relation
candidates
known members
known members
candidates