Documents and Tools for Proposers

• Please see the Proposer's page for detailed information on how to submit a proposal.
• The Proposers' Observatory Guide (POG) is the primary LETG reference manual.
• ProVis is the Chandra target visibility tool. It gives target visibility, roll and pitch angle as a function of time. Pitch angle can be important for a time constrained observation (see notes on time constrained observations and POG chapter on visibility and constraints)
• PIMMS is the Chandra count rate simulator
• Response files (ARFs, RMFs) are available for spectral simulations and analyses.
• ObsVis allows Chandra instrument fields-of-view to be overlaid on sky images.
The Spectrum Visualization Tool shows the location of the spectral features on the ACIS-S detector as a function of Y-offset and redshift.

LETG Observing Strategies

Before submitting a proposal, LETG proposers need to be aware of the following properties:

• Choice of readout detector:

  HRC-S and ACIS-S are most frequently used to read out the LETG. The LETG/HRC-S combination is the instrument of choice for very high resolution spectroscopy of bright soft sources. It has significantly higher QE at wavelengths longer than 20 Å than ACIS-S. ACIS-S has the following advantages for wavelengths < 20 Å : the intrinsic resolution allows for order sorting, the effective area is larger and it is possible to obtain a low resolution spectrum of the zeroth order image. Please see the detailed discussion in the POG on which detector to choose.

• Background Rates:

  The HRC-S operated in spectroscopic mode has a background rate of approximately 80 counts/sec, compared to a HRC telemetry saturation limit of 184 counts/sec. Care should be taken that the combined source and background counts do not exceed the telemetry limit. See the discussion on HRC-S background in the POG.

• HRC-S Windowing

  The HRC-S has a default spectroscopic "window" for use in LETG observations. Only events which fall inside the window are telemetered to the ground. The purpose of the window is to decrease the number of background counts telemetered and hence avoid telemetry saturation. This window can be configured to a specific observation -- please see the discussion in the LETG chapter of the POG.

• Instrument Features and Gaps:

  Observers should ensure that spectral features of interest do not fall on instrument gaps or features. These are listed in Tables 9.3 and 9.4 of the POG and discussed in Section 9.4.2. See the Spectrum Visualization Tool for ACIS-S observations. Offset Pointing (see section 9.4.2) can be used to move source features away from instrument gaps or artifacts.

• ACIS Considerations

  Proposers need to specify optional chips and subarrays if ACIS is selected as the read-out instrument. Please see Checking your LETG/ACIS-S setup parameters for a detailed discussion.