IBIS: IRSKY Batch Inquiry SystemIBIS: IRSKY Batch Inquiry System* The COBE datasets were developed by the NASA Goddard Space Flight Center under the guidance of the COBE Science Working Group and were provided by the NSSDC. As a user of IBIS, your comments and suggestions will be appreciated. Comments and problem reports should be made to the IRSKY team. < irsky-help@ipac.caltech.edu >
When submitting to the processor via e-mail, it is recommended that the number of target positions be limited to 30-35 to avoid problems with overloading mail queues on some systems. Output for each source takes about a page.
ibis@ipac.caltech.edu
Responses will be mailed back to the sender of the request - make sure
your e-mail is sent with a correct and interpretable return address!
flux_units MJy/Srwould tell IBIS to use MJy/Sr for the output flux units.
Here is the list of keywords to be specified:
aperture 1.7e-7
aperture_units arcmin^2
reference_offset 3
flux_units Jy/aperture
do_galaxy yes
search_gsc yes
gsc_radius 15
gsc_mag 10
input_coordinates Ecliptic
input_equinox J2000
wavelength 22 8 100
16.3678 16 hr 22 min 04.08 sec (if in "longitude"
field with equatorial RA set)
or
16.3678 degrees (otherwise)
16 16 hr (if in "longitude" field
with equatorial RA set)
or
16.0 degrees (otherwise)
6h3m23s 06 hr 03 min 23 sec
26h7m23s 02 hr 07 min 23 sec (where 02 hr = 26 - 24)
79d23m90s +79 deg 24 min 30 sec (with warning message)
20d9'50" +20 deg 09 min 50 sec
20:9:50 20 hr 09 min 50 sec (if in "longitude"
field with equatorial RA set)
or
20.16388 (otherwise, with warning message)
20:9 20 hr 09 min of time (if in "longitude"
field with equatorial RA set)
or
20.15 deg (if in "longitude" field,
with warning message)
or
20 deg 09 min (if in "latitude" field)
After all the keyword values have been defined, the longitude and latitude positions are specified for all the targets to be processed with those parameters.
Input lines are processed in order so it is possible to change parameters between sources. In the sample files, the first source position is given in galactic coordinates, then the input_coordinates are changed to equatorial and the second source position is given in the new coordinate system, like so:
input_coordinates Galactic 36.62706d 53.02687d input_coordinates Equatorial 5h32m20.11s -5d02m59.2sAny of the input parameters may be changed. They effect the IBIS execution when they are encountered in the file, for all subsequent target positions.
Comments can be included in the input file -- just begin the comment with a pound sign (#). Blank lines are treated as comments.
do_bkgnd yescommand was given. The background flux at the wavelength of interest is estimated by decomposing the ISSA 4 point spectrum at the selected location into the best-fitting combination of two far-infrared emission models taken from the literature. The models were drawn from the emission models representing different physical regions (cirrus, dark clouds, reflection nebula, stars and HII regions), given by Desert, Boulanger and Puget, A&A 237, 215 (1990). The flux density shown is the sum of the two contributing models' values at the selected wavelength. With this method, the continuum background within the range 12 to 100 microns can generally be estimated to within 0.5 MJy/sr at a given wavelength. Outside this range, background estimates may not be as robust.
The Zodiacal Background column lists a model value computed from the smooth model prepared by J. Good. Details of the model are found in the ISSA Explanatory Supplement, Wheelock et al. 1994, Appendix G. The value was computed at a fixed solar elongation angle of 90 degrees and at the point in the Earth's orbit where the orbit crosses the ecliptic plane. When the actual solar elongation angle is between 60 and 120 degrees and/or the Earth is slightly out of the ecliptic plane (inclination is 1.5 degrees), the true zodiacal contribution may be different from the values listed by a factor of as much as two.
For details on the algorithms and processing for each of the IRSKY estimators, and information on the zodiacal background, click here
do_galaxy yescommand was given. To estimate the confusion noise contributed by the background of faint galaxies we use a set of modeled galaxy source counts to estimate the statistical distribution of sources within an aperture. Then we use the variance of the total flux expected from such a sample as an estimate of the confusion noise. The method is detailed in Helou and Beichman 1990, Proc. 29, Liege Intn. Astr. Coll., ESA SP 314.
In this method, source counts are taken from the analytic fits to infrared galaxy counts (Soifer et al. 1987) and are extrapolated to two sets of functions of source counts vs. limiting flux. Each set contains functions computed for two wavelengths. The two sets of functions differ in that each set is computed under the a different cosmological model, to bracketing the results of the calculation. The program finds the smallest flux at which the flux variance of the faint source background will contribute an uncertainty of less than 20%, and equates this variance to the confusion noise. The two bracketing cosmological models are: Model 1 (q0=0.5, H0=100, source density~(1+z)^5) and Model 2 (Euclidean).
do_cirrus yescommand was given. Computation of the confusion noise is based on Gautier, T. N. et al. 1992, AJ, 103 1313; and Helou and Beichman 1990, Proc. 29, Liege Intn. Astr. Coll., ESA SP 314.
The calculation works as follows: An estimate of the brightness of the cirrus emission is made at the wavelength of interest. To get the brightness of the cirrus, the mean values in each of the four bands and the 30' square aperture are used and an interpolation is performed. If the background cannot be determined due to insufficient flux, or a pathological 4-band spectrum, an attempt is made to extrapolate the background flux from 100 um to the wavelength lambda by scaling the 100 um flux by F(lambda)/F(100), where F(.) is the model dust spectrum taken from Desert, F. -X. Desert, Boulanger, F. and Puget, J.L. 1990, AA 237, 215. If the flux found in the 100 um ISSA image is insignificant (below the noise level), the program will not calculate the confusion.
Next the parameters necessary for estimating the factor E0 required by the Gautier et al. formulation are prepared. The confusion is calculated twice, once at 100 um, the wavelength for which the model is most appropriate, and once at the wavelength of interest. To bracket the confusion, we chose two specific cases from the Gautier work. We chose alpha = -2.6 and alpha= -3.2, which bracket the exponent of the spatial power spectrum falloff of cirrus structure. The reference subtraction method assumed is the double aperture chopping method. The beam separations (between source and reference beams) are preselected to be two beam diameters, but the user is allowed to reset this.
Output lines that begin with # are commentary;
Output lines that begin with a space, contain source specific information or derived information;
Output lines that begin with ! are warnings.
Output for each source begins with the lines:
#********************************************************* Source Number: 1and ends with
Done Number: 1 #*********************************************************Warning messages appear with exclamation marks in the first column.
Last updated 19-February-1999