Notes on HETG View Graph Material, Ver.2.0 D. Dewey 5/29/92 HETG mechanical diagram Note that it shows six grating rings - we retain this design until the HRMA configuration is certain and mechanical issues force a redesign. "HETG Spectrometer Diagram" The lower CCD views show the grating readout array with and without the grating inserted to show the effect of adding the grating to the optical path. Normally we would not use the grating readout with out the grating inserted (except as a redundant imager of for focusing purposes). Note that this diagram shows five CCD chips. At this moment the ACIS baseline array is 6 chips, each 23x23 mm. The "diffracted beam"s shown are first-order: there are also beams at 2-theta, 3-theta etc. In reporting efficiencies, effective areas, etc I use only the first-order values. "Transmission Grating Spectrometer Diagram" As above but does not mention HETG or ACIS explicitly. I-DEAS Solid Model of HRMA cut-away (six shells shown) and HETG plate (Color VG) The HETG is shown to scale with the HRMA and a representative yoke. Note that passive components (CAPA, post-collimator, thermal closeouts etc) are not shown. I-DEAS is a solid modelling software package from SDRC (Structural Dynamics Research Corp.). Simulated HETG observation of SNR in M31 The parameters of the SNR N132D in the LMC (distance ~ 50 kpc) were used in this simulation of an SNR at the distance of M31 (700 kpc). The data include counts from both the HEG and MEG spectra. The x-ray diameter of N132D, ~25 pc, corresponds to 7.4 arc seconds at M31, other bright remnants in the LMC have sizes from 3 to 30 pc. Thus it is likely that some will be small enough for high-resolution spectroscopy. The resolution here of 455 can be achieved with the HEG gratings even for sources of 2 to 3 arc seconds size. Lines useful for plasma diagnostics are shown: the Ne IX He-like triplet at 900 to 920 eV (Forbidden, Intercombination, and Resonance, respectively) and the Ne X Lyman alpha line at 1020 eV. NOTE: All simulations here have no background included: because of the low background of the CCD combined with the background rejection that occurrs by requiring the CCD-measured energy of the x-ray event to be compatible with the dispersed location of the event (i.e., the grating-derrived energy) this is a realisitc assumption. The simulations use the correct Poisson distribution for low-count rate event simulation. Example of use of plasma diagnostics The measured ratio of intensity of the Ne IX He-like triplet to the intensity of the Ne X Lyman alpha line is a function of the plasma model parameters. Here the allowed region in "T,t" space is shown. The contours are for 11 and 12 sigma limits allowed by the measured ratio. The small square with error lines is the best-fit model parameters. T is the temperature of the plasma and t is called the "ionization age" and is the product of the plasma lifetime (i.e., time since the SNR shock occured) and the electron density (number per cm3). In order for the plasma to reach ionization equilibrium (that is a statistical equalibrium between the different ion species, e.g. the amount of Ne IX and Ne X) there has to have been enough interaction between the ions and the agents that excite them. Electron-ion collisions are a chief excitation mechanism, thus the product of electron density (ne) and time (t) is a measure of how much interaction the ions have had with their environment. If this interaction is low the ion species distribution will not be in equilibrium, if it is high then the expected thermal equilibrium distribution will hold. Simulated Observation of Capella This a simulation of an observation having as input our plasma code for a temperature of 0.51 keV, solar abundance of elements, equilibrium conditions, and normalization parameters for Capella at a distance of 13.2 parsecs. Simulated Observation of Cyg X-1 The spectrum of Cyg X-1 was modeled as a power law of index (-)1.75 , normalization of 1.55 counts/cm2 s keV (at 1 keV) and folded through the HETGS response. Except for the lines mentioned below, all the structure here reflects the effect of the HRMA, HETG, and ACIS efficiencies. In a recent paper (Vrtilek et al ApJ Supp 76 p1127) observations using the Einstein OGS are summarized and they suspect there is line emission from Cyg X-1. What I've done is to take the line emission they suspect at around 1.1 keV and distribute the 11 eV equivalent width of that emission among three lines: Fe XVII (1024 eV), FeXXIV(1125 eV) and another FeXXIV line (1164 eV). Thus each line has about 3.6 eV equivalent width. These lines are well separated and detected even with the low resolving power (152) of this simulation - this resolving power (or better) is available over the full bandwidth (0.4-8 keV) of the HETG. Tom Markert recommends you point out the lines on the view graph as they're not obvious to the untrained eye! Solid Model of the Aluminum Grating Frame We are designing our frames to be highly stable as well as light weight. HETG Geometry for Data Analysis This shows the process for extracting the spectral information from the spatial detection of x-rays. Diagram of Radiative Decays from 2 to 1 level This diagram shows the atomic levels that give rise to the resonance, intercombination, and forbidden lines and summarizes at the bottom the diagnostics that can be done with the line ratios. Note that these diagnostics are in addition to the ratio discussed above (which is the ratio of the He-like-ion emission to the Hydrogen-like-ion Lyman alpha emission) and shows the variety and power of diagnostics when the individual He-like lines can be resolved. This diagram is from a paper by Wargelin, Kahn and Beiersdorfer, a copy of which I've enclosed. Photograph(s) of HETG Gratings (Color VGs) The photograph shows both sides of the HEG (smaller frame) and MEG (larger frame) gratings. The gratings have periods of 2000 A and 6000 A respectively. Because the HEG will not diffract optical light longer than 4000 A no colors are visible on it. The MEG, on the other hand, can diffract light shortward of 12000 A so colors (depending on light and observer angle) are visible. Because of the polyimide support membrane the colors are most vibrant when viewed off of the grating-bar side as is the case of the grating not in the plastic container.