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COS data utilizes a modified naming convention from other HST instruments. In, particular COS FUV files can have TWO suffixes. The first suffix identifies the filetype and the second suffix if present identifies the FUV detector segment. For the remainder of this document the use of "suffix" will refer to the first suffix which identifies the filetype and will always include filetypes with the additional FUV segment suffix if they exist.

Please look at the original COS data handbook for more info.

Any files could be retrieved using the direct proxy method

http://www.cadc.hia.nrc.gc.ca/getData?archive=HSTCA&file_id=

Long Suffix	Data Format	Spectroscopic				Imaging		Contents
		FUV		NUV		NUV
		TIME-TAG	ACCUM	TIME_TAG	ACCUM	TIME_TAG	ACCUM
	Uncalibrated Science Data
rawtag	table			·		·		Raw NUV TIME-TAG events list
rawtag_a, rawtag_b	table	·						Raw FUV TIME-TAG events list
rawaccum	image				·		·	Raw NUV ACCUM image
rawaccum_a, rawaccum_b	image		·					Raw FUV ACCUM image
rawacq	table or image	·		·		·	·	Raw acquisition file
pha_a, pha_b	image		··					Pulse height distribution
	Uncalibrated Support Data
asn	table	·	·	·	·	·	·	Association file
jit	table	·	·	·	·	·	·	Spacecraft pointing data averaged over 3 s intervals
jif	image	·	·	·	·	·	·	2-D histogram of the _jit file
spt	image	·	·	·	·	·	·	Support, planning and telemetry information
trl	table	·	·	·	·	·	·	Trailer file with a historical record of generic conversion processing
	Intermediate Data Products
trl	table	·	·	·	·	·	·	The raw trailer file is updated with a historical record and errors log of calibration pipeline processing
corrtag	table			·				NUV TIME-TAG events list with calibrated values
corrtag_a, corrtag_b	table	·						FUV TIME-TAG events list with calibrated values
flt	image			·	·	·	·	NUV flat-fielded science image
flt_a, flt_b	image	·	·					FUV flat-fielded science image
counts	image			·	·	·	·	NUV not flat-fielded science image
counts_a, counts_b	image	·	·					FUV not flat-fielded science image
lampflash	table	·		·				1-D extracted TAGFLASH (FLASH=yes) spectra
x1d	table	·	·	·	·			1-D extracted spectra for a single exposure
x1dsum<n>	table	·	·	·	·			Averaged 1-D extracted spectra for multiple exposures with the same grating, central wavelength, aperture and FP-POS=<n>
	Final Data Products
fltsum	image					·	·	Summed flat-fielded image (imaging only). Final calibrated association product for all COS imaging datasets
x1dsum	table	·	·	·	·			Final combined 1-D extracted spectra for multiple exposures with the same grating, central wavelength and aperture combining all FP-POS. Final calibrated association product for all COS spectroscopic datasets.

Raw Accum images ( rawaccum)

For ACCUM data, the raw files contain a set of images which have filenames with the suffix rawaccum for NUV data, or rawaccum_a and rawaccum_b for the two segments of the FUV detector. The SCI extension contains an image of the total accumulated counts during an exposure. For NUV data the ERR and DQ extensions have only a header with no data. For FUV data the ERR extension has only a header with no data, and the DQ extension is populated with data quality information only for pixels that are outside the subarray boundary. These extensions will be populated with data in the flt files after calibration pipeline processing. Even though FUV rawaccum_a[b] data are 16384 x 1024 images, only a portion of them contain actual data. These portions are called sub-arrays. Typically, three subarrays are used for each segment of an FUV ACCUM image. Two of these are centered on the STIM positions and the third is a stripe 128 pixels wide which is centered on the spectrum of the object.

Raw TIME-TAG Events Lists (rawtag)

Raw events tables contain the locations and arrival times of individual photon events collected in TIME-TAG mode. These files have the suffix rawtag for NUV or rawtag_a[b] for the two FUV segments. The first extension contains the events list, in which each row of the table corresponds to a single event in the data stream and the columns of the table contain scalar quantities that describe the event. The second extension contains the good time intervals (GTI) table, where an uninterrupted period of time is considered as one good time interval. Interruptions in the data taking due to memory overflow could result in more than one GTI.

Pulse Height Amplitude Files (pha):

For FUV ACCUM data only, a 7 bit pulse height amplitude histogram is accumulated in the detector electronics on-board. This information is placed in a file with the suffix pha. The pulse-height histogram files contain a primary header with no data and a single FITS image SCI extension containing a histogram of the pulse-height distribution during the exposure. The pulse height amplitude files do not contain an ERR or DQ extension. The pulse height distribution is an image array of length 128, corresponding to the number of photons with values from 0 to 127, corresponding to the pulse heights of 0-31 available in TIME-TAG data.

Corrected Events Lists (corrtag):

The COS pipeline produces corrected TIME-TAG events lists and stores them in binary tables with suffix corrtag. These files have the same file format as the rawtag files, with a corrected events list and a good time interval extensions. The corrected events table includes X and Y event locations that have been corrected for distortion, doppler shift, and offsets due to OSM motions in both the dispersion and cross-dispersion directions.

Lampflash Files (lampflash):

For TAGFLASH data, calcos produces an events list with suffix lampflash, that contains the extracted wavecal lamp flashes with one row for each unique segment or stripe and flash number. Columns TIME, LAMP_ON, and LAMP_OFF are in seconds since the exposure start time; they are therefore in the same units and have the same zero point as the values in the TIME column of the rawtag or corrtag tables.

Flat-Fielded Image Files (flt):

For spectroscopic data a flat-fielded image is an intermediate calibrated data file. The files has suffix flt, and contains three extensions (SCI, ERR, and DQ). The data are in units of the count rate. For FUV data the images are 16384 x 1024, and, like the counts images, the NUV images are 1274 x 1024 for spectroscopic data and 1024 x 1024 for data obtained in imaging mode. The flt images are corrected for flat field and deadtime effects, and this is what distinguishes them from the counts images.

The association name (asn)

The initial input files to calcos are the association tables with suffix asn. These files provide the calibration pipeline with information about how the data files are associated. In general, only exposures taken in sequence with the same spectral element, central wavelength (if applicable), and aperture at any FP-POS will be associated.

Processing of each individual exposure in the association produces a final calibrated result named with exposure rootname and suffix x1d (spectroscopy) or flt (imaging).

Next, for each FP-POS position (where =1,2,3, or 4), if there are multiple spectroscopic exposures in the association that use the same FP-POS position, calcos will combine them into a file named with the association rootname and suffix x1dsum, where is the integer FP-POS value.

Lastly, a final association product file is produced with association rootname and suffix x1dsum (spectroscopy) or fltsum (imaging) by combining all science exposures in the association. [Note: in the special case of associations with only one science exposure, the resultant exposure rootname x1d file and the association rootname product x1dsum file contain identical information.

One-Dimensional Extracted Spectra (x1d, x1dsum(1-4))

The COS pipeline produces extracted one-dimensional spectra and stores them in binary tables with suffix x1d, x1dsum or x1dsum. These COS extracted spectra tables are 3-Dimensional, with one row for each unique segment or stripe. For FUV data there are two rows labeled 1 and 2 which correspond to segments A and B respectively. For NUV data there are three rows labeled 1,2, and 3 which corresponding to stripes A,B, and C respectively. Each table column can contain either a scalar value or an array of values, such as WAVELENGTH or FLUX. For example, NELEM will contain a scalar number, while the WAVELENGTH column will contain an array of wavelengths.

Flat-Fielded Image Files (flt, fltsum)

For NUV imaging observations, the flt and fltsum images are the final data products, with the latter being a simple sum of the individuals when several exposures are processed together. They are fully linearized and flat field corrected images. Unlike the flt files produced for the spectroscopic data (which are intermediate data products with a format of 1274 x 1024), the formats of the flt and fltsum files for imaging data is 1024 x 1024, since Doppler and OSM motions are not applied.

Trailer File (trl)

When COS data are processed through OTFR in the HDA, the output messages from generic conversion and the different calibration steps are stored in a FITS ASCII table known as the trailer file, with suffix trl. Each time the archive processes data before retrieval, the old trailer file is erased and a new one created using the results of the most recent processing performed. The archive will produce a trailer file for each individual exposure and association product. Association product trailer files contain the appended information from all the exposures in the association, in order of processing. The order of processing is the same as the order of exposures in the association table, with the exception of auto or GO wavecals which are always processed first.

In the trailer files from the HDA, the output messages from generic conversion appear first in the file. This section contains information relevant to the selection of the best reference files and the population of some of the header keywords. The second part of this file contains information from calcos processing. Each task in the calcos pipeline creates messages during processing which describe the progress of the calibration, and appear in the order in which each step was performed. These messages are quite relevant to understanding how the data were calibrated, and in some of the cases, to determining the accuracy of the products.

Preview files

The preview files generated by the cache software. One fits file and its correxponding jpg file for each COS end product.

Acquisition Files (RAWACQ)

All COS acquisition exposures will produce a single raw data file with suffix rawacq. Almost all COS spectroscopic science exposures are preceded by an acquisition sequence or exposure to center the target in the aperture. Keywords in the header of COS science data identify the exposure names of relevant acquisition exposures in each visit. In addition, there are several other useful keywords in the COS acquisition exposures that describe the acquisition parameters used, as well as the calculated centroid positions and slew offsets.

Support Files (SPT)

The support files contain information about the observation and engineering data from the instrument and spacecraft that was recorded at the time of the observation. A COS support file contains a primary header and at least three FITS image extensions. The first extension contains a header with the proposal information and an (16-bit) image array containing the data which populate the spt header keyword values. The image array element values are used by conversion software to populate the header keywords. Following the support extension, the COS spt files contain two engineering snapshot extensions. These extensions contain a readout of several instrument and telescope parameters from telemetry data at different times during the course of an exposure. The very first snapshot extension will always contain telemetry information from the beginning of an exposure. Depending on the length of the exposure, the support file may also contain one or several "imsets" which include a support extension and two snap extensions. These intermediate imsets will have only their second snapshot extension populated with telemetry data taken during the course of an exposure, while the first snapshot will be populated with default values. The very last imset of an spt file will have all three extensions (1 support and 2 snaps) populated with telemetry values at the completion of the exposure.