Spitzer Documentation & Tools
MIPS Instrument Handbook

Chapter 1              Introduction

1.1  Document Purpose and Scope

The MIPS Instrument Handbook is one in a series of documents that explain the operations of the Spitzer Space Telescope and its three instruments, the data received from the instruments, and the processing carried out on the data. Spitzer Space Telescope Handbook gives an overview of the entire Spitzer mission and explains the operations of the observatory, while the other three handbooks document the operation of, and the data produced by, the individual instruments (IRAC, IRS and MIPS).

 

The MIPS Instrument Handbook is intended to provide all the information necessary to understand the MIPS standard data products, as processed by Version S18.12 of the online pipeline system, and which are retrievable from the Spitzer Heritage Archive (SHA). Besides the detailed pipeline processing steps and data product details, background information is provided about the MIPS instrument itself, its observational modes and all aspects of MIPS data calibration. It also includes a description of the data acquisition sequences and planning procedures, as an understanding of how and why MIPS data was acquired can be crucial to understanding what to do now that you have data. 

 

In this document we present information on the:  

·         MIPS instrument and its observing modes,  

·         processing steps carried out on the Level 0 (raw) data,  

·         calibration of the instrument,

·         uncertainties in the data,

·         final MIPS archival data products.

An overview of the MIPS instrument is given in Chapter 2. In Chapter 3 we discuss the different operating modes which MIPS used to take data. The calibration is described in Chapter 4. Online pipeline processing is described in Chapter 5. The data products themselves are described in Chapter 6. Data features and artifacts are presented in Chapter 7. A brief introduction into MIPS data analysis is given in Chapter 8.

1.2  Basic Definitions

Below are descriptions of the most commonly used terms in this handbook.  A complete list of acronyms can be found in Appendix A.

 

Astronomical Observing Template (AOT): The list of parameters for a distinct Spitzer observing mode.  There are 4 possible MIPS AOTs. The Scan Mapping AOT is used to image large areas of the sky in one or more bands nearly simultaneously.  The Photometry AOT is used to image sources smaller than about 2 arcminute diameter, including point sources.  The Spectral Energy Distribution (SED) AOT is used to obtain low-resolution (R~20) spectra in the 70 µm band.  The Total Power (TP) AOT is used to measure the absolute brightness of highly extended emission, e.g., zodiacal light. Each AOT may have a number of modes (for instance, Photometry has 9 and Scan Map has 3) depending on the parameter selection.

 

Astronomical Observation Request (AOR): The fundamental unit of Spitzer observing. This is an AOT with all of the relevant parameters fully specified.

 

Data Collection Events (DCEs): Single-frame exposures, also referred to as the ''raw'' or Level 0 Data.

 

Basic Calibrated Data (BCD): Also known as Level 1 Data, BCDs are the data products derived from DCEs produced by the processing pipelines.  BCDs are designed to be the most reliable product achievable by automated processing. 

 

Post-BCD (PBCD):  Also known as Level 2 Data or even sometimes Browse Quality Data (BQD), these are data products derived from a full AOR, e.g., a combination of several BCDs.  Post-BCD products include (but are not limited to) mosaics, which are produced for both MIPS photometry and scan observations.  Automated post-BCD products do not combine data from more than one AOR; observers must do this task themselves (see below). 

 

MIPS BCDs and post-BCD products are 2-dimensional FITS images with a full set of header keywords, calibrated in MegaJanskys per steradian (MJy/sr).  To convert from MJy/sr to microJy/arcsecond2, multiply by 23.5045.

 

The MIPS pipelines handle the MIPS 24 micron data completely separately from the MIPS 70 and 160 micron data.  For this reason, frequently in this manual, the MIPS-24 data, also referred to as ''silicon'' data since the detectors are Si-based (Si:As), are discussed separately from the MIPS 70 and 160 micron data, commonly referred to as ''germanium'' since the detectors are Ge-based (Ge:Ga).

1.3  MIPS Essentials

Please be aware - there are some things you must understand prior to working with MIPS long-wavelength data.  The physical nature of the detectors makes fully automated data processing for all types of observations very difficult.  Even with the best planning and data pipeline, some detector artifacts will be present in the final processed data.

 

The MIPS 70 and 160 micron channels have Ge:Ga detectors.  This material is known to have multiple time constant behaviors when detecting infrared photons, including the MIPS internal calibration stimulators.  Please see 2.3.3 for further discussion. In addition, Ge:Ga detectors have response behavior that is different for point source than for extended emission. The pipeline in general cannot deal with these effects.  The automated pipelines are very effective in reducing the instrument signatures to a minimum.  But, some of the corrections are observation-dependent and, as such, are very difficult to automate.

 

The 70 and 160 micron mosaics provided are intended for quick look analysis only.  In general, we do not recommend these be used for detailed science analysis for Ge data.  The 24 micron mosaics can, in most cases, be used for detailed analysis, although some care should still be taken.  The best automated product produced by the pipelines is the Basic Calibrated Data (BCD) frames.  It is critical to understand artifacts (see Chapter 7) that can impact your data and how you might be able to further the processing of the pipelines to improve your data.  Most often you will want to apply some additional corrections to these data that depend on the characteristics of the observation.  This Handbook is intended to provide a starting point for such additional reductions.

 

The most relevant software for MIPS data reduction is MOPEX (mosaicking and point source extraction). For the germanium data (70 + 160 µm) one may also find the GeRT (Germanium Reprocessing Tools) valuable for reprocessing the raw data. Documentation for both can be found in the data analysis section of the documentation website. See Chapter 8 for a brief introduction into MIPS data analysis. The separate Data Analysis section of the documentation website provides access to tools, users guides and data analysis recipes.

1.4  Standard Acknowledgements for MIPS Publications

Any paper published based on Spitzer data should contain the following text: ''This work is based [in part] on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. ''

 

If you received NASA data analysis funding for the research, you should use one of the templates listed under http://irsa.ipac.caltech.edu/data/SPITZER/docs/spitzermission/publications/ackn/. We also ask that you cite at least the seminal MIPS paper (Rieke et al., 2004, ApJS, 154, 25) in your research paper, as well as any other MIPS-related papers where appropriate.

1.5  How to Contact Us

A broad collection of information about the MIPS and MIPS Data Analysis is available on the Spitzer Documentation website:  http://irsa.ipac.caltech.edu/data/SPITZER/docs/mips. In addition you may contact us at the helpdesk at http://irsa.ipac.caltech.edu/data/SPITZER/docs/spitzerhelpdesk.