DIRBE Data Products
* A => full intensity; B and C => polarimetry Note: the quoted bandwidths assume a source spectrum nu*I (nu) = constant.
Time-ordered Data (TOD)Consider using the Calibrated Individual Observations instead. The TOD product includes calibrated sky brightness values and is the most complete public record of the DIRBE observations. It is necessary to understand the operating modes of the instrument and to recognize various mission events in order to select and interpret the data of interest; thorough familiarity with information contained in the DIRBE Explanatory Supplement is recommended. The contents and format of the TOD product are given in an ASCII file called dirbe_tod_record_structure.asc. The TOD product is not intended for heavy use by the research community, although there may be some applications, such as correlative studies of transient events, for which this product is necessary. The DIRBE TOD - in 41 files each covering one week - are available by request. Calibrated Individual Observations (CIO)The CIO files contain calibrated 1/8th second sampled sky survey data, in pixel number order, for each day of the cryogenic mission. In nearly all applications, the CIO can be thought of as a user-friendly version of the TOD. There are 285 CIO data files. Corresponding to each data file is a CIO Pixel Index file, which is designed to facilitate data retrieval (e.g., selection of time strings). All CIO files are FITS binary tables. The CIO files are on line. A typical data file is about 60 MB in size. Weekly Sky MapsThese maps provide weekly-averaged intensity values for each pixel and photometric band, plus Stokes Q and U parameters at 1.25, 2.2, and 3.5 microns. Each map covers approximately half of the sky. As a set, the 41 Weekly Sky Maps offer an unprecedented view of the interplanetary dust (IPD) cloud as each celestial direction was observed by DIRBE at a variety of angles through the IPD. The Weekly Sky Maps are on line. DIRBE Calibrated Annual File (DCAF)Consider using the DIRBE Sky and Zodi Atlas instead. The DCAF files contain the same data as the Weekly Sky Maps but are organized differently. This product gives a pixel-by-pixel view of the intensity variations seen as a function of time, collecting all the weekly-averaged intensities measured at a given pixel into a single file. Those who wish to study or model time-variable signals, such as the zodiacal light, will find this organization convenient. There are 6 DCAF data files, one for each face of the COBE Sky Cube, and each data file is accompanied by a DCAF Pixel Index file, which is designed to facilitate data retrieval. The files are FITS binary tables. A typical DCAF data file is ~200 MB in size. The DCAF files are on line. Annual Average MapsThese maps provide a single, mission-averaged intensity value per pixel for each of the 10 DIRBE bands. The effect of coaddition is to improve sensitivity to faint emission. Since these maps average over the variable zodiacal light signal, they are useful primarily at wavelengths at which the IPD signature is weak, especially 140 and 240 microns. The Annual Average Maps also provide information on the depth of sky coverage over the whole cryogenic mission. These maps (1 FITS file per wavelength band, each 10.6 MB) are on line network-accessible. Solar Elongation = 90 deg Sky MapsThese maps provide an estimate of the infrared intensity at each pixel and wavelength band based on an interpolation of the observations made at various times at solar elongations close to 90 degrees. To first order, this product depicts the sky as if it were observed through a temporally constant IPD foreground, thus enabling straightforward modeling and subtraction of the zodiacal light to a level adequate for many Galactic studies, the obvious drawback being that only a small portion of the available DIRBE data is represented. The Solar Elongation = 90 deg Sky Maps (1 FITS file per wavelength band, each 12.9 MB), are on line network-accessible. Galactic Plane MapsThese maps are subsets of the Solar Elongation = 90 deg Sky Maps designed to facilitate studies of the Galaxy. The maps cover Galactic latitudes |b| < 10 deg at longitudes 30 deg < l < 330 deg and cover |b| < 15 deg elsewhere. The Galactic Plane Maps (all 10 DIRBE bands) are in a single 5.9 MB FITS file. The file is on line network-accessible. DIRBE Sky and Zodi Atlas (DSZA)In many applications, the DSZA can be used instead of the DCAF; most of the information in the DCAF is repeated in the DSZA. However, the DSZA also includes estimates of the zodiacal light (thermal emission and scattered light from the interplanetary dust) intensity which can be compared directly with, or subtracted from, the DIRBE measurements. For example, using the DSZA, one can readily compare the apparent time variability of the sky, as observed by the DIRBE, with that of the DIRBE interplanetary dust model (Kelsall et al. 1998, ApJ, submitted), or construct sky maps like the ZSMA maps using different data selection criteria (e.g., maps based on data obtained during different weeks in the cryogenic mission). The DSZA is accompanied by a pixel index and organized in the same fashion as the DCAF. Data and model intensities from all 10 full-intensity wavelength bands appear in the DSZA. The DSZA files are on line. Zodi-Subtracted Mission Average (ZSMA) MapsThe ZL intensities recorded in the DSZA were subtracted week by week and the residual intensity values were averaged to create the ZSMA Maps, which give the best available picture of the Galactic and extragalactic diffuse infrared emission on degree or coarser angular scales. In many applications, the ZSMA Maps will supersede the Annual Average Sky Maps. Like the Annual Average Maps, the ZSMA Maps are provided in ten FITS binary tables, one each at 1.25, 2.2, 3.5, 4.9, 12, 25, 60, 100, 140 and 240 microns. Each row of the FITS table corresponds to a DIRBE pixel. One zodiacal light-subtracted intensity value, representing an average over the cryogenic mission, is given per pixel. The ZSMA files are on line. Photometric Standard Values TableThis FITS binary table contains photometric data obtained on 92 standard objects which were judged not to vary in brightness at a particular wavelength over the course of the cold mission and were used to stabilize the DIRBE photometric system. The Table is on line. An explanation of table can be found in the DIRBE Explanatory Supplement). Solar System Objects DataThe Solar System Object Dataset provides flux densities and other data pertaining to individual passages of solar system objects through the DIRBE field of view during the period of cryogenic operation, from 11 December 1989 to 21 September 1990. The data are given in FITS tables, one for each of the following objects: Mars, Jupiter, Saturn, Uranus, Ceres, Pallas, and Vesta. The Solar System Object data are on line. Faint Source ModelThe Faint Source Model gives the predicted contribution to the diffuse sky brightness at 1.25, 2.2, 3.5, 4.9, 12 and 25 microns due to (faint) stars and other discrete Galactic sources. It was used in the search for the cosmic infrared background to subtract an important component of the observed near-infrared sky brightness. The model is described by Arendt et al. (1998, ApJ, submitted) and in Appendix F of the DIRBE Explanatory Supplement. The Faint Source Model files are on line. Beam Profile MapsThe DIRBE beam profiles are provided in a set of 16 FITS (image) files, one file for each of the 10 full intensity bands, plus `B' and `C' polarization channels for the three short-wavelength bands. As explained in the DIRBE Explanatory Supplement, the beam profile in bands 1 - 4 changed slightly with time during the mission; the FITS files for these bands each contain three beam maps corresponding to three time intervals. The Beam Profile Maps are on line. Beam offsets and solid angles are given in Table 4.2-1 of the DIRBE Explanatory Supplement, and also, for convenience, in an ASCII table. System Spectral Response FunctionsNormalized system (filter + detector) response functions for each of the 10 DIRBE bands are given in an ASCII table. The table also appears in Appendix A of the DIRBE Explanatory Supplement. Color Correction TablesFollowing the IRAS convention, DIRBE flux densities are derived assuming a nu*I(nu) = constant source spectrum. Color corrections must be applied to the quoted flux densities to derive true flux densities when the spectrum differs in shape from that assumed. The set of Color Correction Tables given in Appendix B of the DIRBE Explanatory Supplement take into account the system spectral response and pertain to a variety of source spectra (power laws and modified Planck functions). The same data are provided in an ASCII table. The COBE datasets were developed by the NASA Goddard Space Flight Center under the guidance of the COBE Science Working Group .
|