There have been no substantial changes to the HETGS calibration products in the past year. One small item is the value listed for the ACIS physical pixel size and a corresponding change in the HETG Rowland spacing back to the expected preflight value; wavelengths have been and should continue to be accurate to 100 km/s for energies below 1.5 keV. Effective area corrections derived from front-illuminated to back-illuminated CCD QE ratios are still being worked, see the HETG user web page for up-to-date information .
A development of note in the HETGS data analysis domain is the recent availability of software which can help analyze moderately piled-up grating spectra. ACIS pileup (POG section 6.16, ) in imaging (or zeroth-order) observations can be estimated and analyzed using ``pileup'' models implemented in ISIS V0.9.77, XSPEC V11.1, and Sherpa V2.2. The extension of these methods to grating dispersed data is now available as the ``gpileup'' model in ISIS. Pileup in the dispersed images happens for bright sources, e.g., lines in sources like Capella (see POG Figure 8.14) or continuum from Galactic binaries, see Figure 7. As in the imaging case, the effect of pileup is to reduce/distort the observed count rate in high-flux regions. The ``gpileup'' model can estimate and recover the underlying spectrum for moderately piled-up dispersed sources.
Eta Carina may be the most massive and luminous star in the Galaxy and is suspected to be a massive, colliding wind binary system. Corcoran et al.  used the Chandra HETGS to obtain a high-resolution X-ray spectrum of the star uncontaminated by the nearby extended soft X-ray emisssion, Figure 9. This HETGS spectrum of eta Carina is unlike recently published X-ray grating spectra of single massive stars in significant ways and is generally consistent with colliding wind emission in a massive binary.
- Dan Dewey
 CXC's HETG user web page:
 ``Event Pileup in Charge-coupled Devices'', J.E. Davis, ApJ, 562, pp. 575-582 (2001).
 ``ISIS: An Interactive Spectral Interpretation System for High Resolution X-Ray Spectroscopy'', Houck, J. C. and Denicola, L. A., ADASS IX, ASP Conf. Proc., Vol. 216, p.591 (2000). Web page: http://space.mit.edu/CXC/ISIS
XSPEC web page:
 ``High Resolution Chandra HETG and RXTE Observations of GRS 1915+105: A Hot Disk Atmosphere & Cold Gas Enriched in Iron and Silicon'', J.C. Lee et al., astro-ph/0111132 and ApJ, 567, in press (2002).
 ``On the Absorption of X-Rays in the Interstellar Medium'', Wilms, J., Allen, A., and McCray, R., ApJ, 542, 914 (2000).
 ``The Chandra HETGS X-ray Grating Spectrum of Eta Car'', M.F. Corcoran et al., ApJ, 562, 1031 (2001).