High-resolution X-ray spectroscopy of CTTS and WTTS reveals an anomaly among CTTS: The observed OVII r /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"). OVII r /OVIII Ly  flux ratio as a function of N H. 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. 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", N H = few cm -2 ) component and a hot, very strongly absorbed ("hard", N H > 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! Active Brown Dwarfs 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 (L X  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: ProtostarsCTTSWTTSBDsotherstotal Surveyed Detected10 (48%)60 (86%)50 (96%) 9 (53%)7 (78%)136 (80%) 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 Jets: Double Absorbers Accretion: Soft Excess r i f absorbed OVIII OVII OVII triplet of T Tau: forbidden line (f) strong  low density (  cm -3 ) active: low OVII/OVIII inactive: high OVII/OVIII continuum CTTS WTTS T Tau log N H 4" time cts/s/kev Energy dust destruction at 10 R * Photoelectric absorption no excess visual extinction constant soft X flaring hard X, absorbed x jet shocks hard soft DG Tau Counter jet (blue) harder than forward jet (red/yellow): absorption by disk [OI] optical forward jet (Dougados et al. 2002) DG Tau (Chandra ACIS-S, keV) hardness (red to blue for keV): counter jet constant soft X, absorbed x counter jet forward jet non-accreting accreting detected XEST detects of 9 out of 17 surveyed BDs, typically at L X of a few x10 28 erg s -1. It is mostly the earlier spectral types/higher L bol BDs that are X- ray detected. They fit the stellar L X vs mass and L X vs L bol relations quite well, i.e., young BDs behave like lowest-mass stars. 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. XEST observed a long, gradual U-band event in one of the observed BDs (2M J ). 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. Gradual optical event in a BD near V773 Tau: undetected Photoelectric absorption by disk 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 A&A 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 (N H -A V ), IRAS Güdel et al.: Soft excess in CTTS Scelsi et al.: Coronal abundances Acknowledgments: We acknowledge financial support from the International Space Science Institute (ISSI) in Bern, the Swiss NSF (grants and /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. New TMC Member Candidates 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-L X relation valid for TMC members. mass-L X relation common range for TMC candidates known members candidates known members field around V410 Tau (L1495E) known members For every detected object, the X-ray spectrum has been used to determine the hydrogen column density N H from the absorption measured predominantly in the soft part ofthe spectrum. Together with extinction measurements (e.g., A V orA J ), we test whether the stellar environment (disk, envelope, cloud gas) agrees with a standard gas-to-dust (G/D) mix (as in the ISM). This is, overall, the case, although more detailed investigations using 2MASS and Spitzer are in progress. Gas-to-Dust Ratios We also model 3-D dust disks around highly extincted TTS and combine the modeled dust column density toward the star with our gas column densities. IRAS shows a mass ratio G/D  220 +/- 160, excluding strong depletion of dust. XEST sample range of ISM IR SED and spectral modeling Spitzer IRS IRAS H-band observation (left) and model IRAS