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We present results from {\it XMM-Newton/RGS} observations of prominent knotsin the southest portion of Tycho's supernova remnant, known to be the remnantof a Type Ia SN in 1572 C.E. By dispersing the photons from these knots out ofthe remnant with very little emission in front of or behind them, we obtainedthe nearly uncontaminated spectra of the knots. In the southernmost knot, theRGS successfully resolved numerous emission lines from Si, Ne, O He$\alpha$ andLy$\alpha$, and Fe L-shell. This is the first clear detection of O lines inTycho's SNR. Line broadening was measured to be $\sim 3$ eV for the OHe$\alpha$ and $\sim 4.5$ eV for Fe L lines. If we attribute the broadening topure thermal Doppler effects, then we obtain kT$_{O}$ and kT$_{Fe}$ to be $\sim400$ keV and 1.5 MeV, respectively. These temperatures can be explained byheating in a reverse shock with a shock velocity of $\sim 3500$ km s$^{-1}$.The abundances obtained from fitting the RGS and MOS data together implysubstantially elevated amounts of these materials, confirming previous studiesthat the knots are heated by a reverse shock, and thus contain ejecta materialfrom the supernova. We are unable to find a Type Ia explosion model thatreproduces these abundances, but this is likely the result of this knot beingtoo small to extrapolate to the entire remnant.

RGS Observations of Ejecta Knots in Tycho's Supernova Remnant