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Guidelines For Echelle High Level Science Products

Spring 2013

In addition to the general spectroscopic HLSP guidelines, Echelle data have a few additional guidelines to account for the mulitple orders associated with such data products. These guidelines are specified to make it easier to interact with your data products, to ingest into database structures at MAST, to interact with other data products at MAST (increasing discoverability), and to ensure that associated products are kept bundled together.

File Names

The naming convention of HLSP's is described on the main HLSP Guidelines page. In brief, the file name consists of multiple text fields, separated by underscore characters ("_"). As a quick example, suppose you had a "MAMA" Echelle spectrum using the E230M grating from the STIS instrument on Hubble for the arbitrary star HD 12345, and that you have done some additional processing using the standard HST pipeline product. The filename would be:


Here, "myproj" would be the name of your project. Also note that the entire file name is in lowercase, e.g., the grating identifier in the "filter" text field is "ge230m", NOT "gE230M".

FITS Data Format

Primary Header Unit (HDU1)

The format of the provided files should be multi-extension FITS (MEF) files. The primary header should contain the majority of metadata associated with the observation, e.g., coordinates, timestamps, etc. The required and recommended header keywords for spectroscopic HLSP's can be found here. There are a few additional keywords that should be present in the primary header related to the Echelle origin of the data. These additional primary header keywords are summarized below:

Keyword Req./Rec. Description
NORDER Required The total number of extracted spectral orders in the file, this should equal the number of FITS extensions in the file.

Extension Headers (HDU2 - HDUn)

Each extracted spectral order should be provided in extensions. The wavelengths, fluxes, and flux uncertainties within a given order should be provided as binary FITS tables within this extension. Note the wavelength and flux arrays are required, while the flux uncertainties are strongly recommended to be provided as well. There are also order-specific keywords to be added in each order's extension header. We summarize the header keywords that should be included in each order's FITS extension below:

Keyword Req./Rec. Description
XTENSION Required This should be set to 'BINTABLE'
TFIELDS Required The number of columns in the table. Set TFIELDS=2 (min. requirement) or set TFIELDS=3 if flux uncertainties are also provided.
TTYPE1 Required Name of the first table column, set TTYPE1='WAVE'.
TTYPE2 Required Name of the second table column, set TTYPE2='FLUX'.
TTYPE3 Recommended Name of the third table column, set TTYPE3='ERROR' for flux uncertainties, which we strongly recommend be provided.
TFORM1 Required Data format in this column, specified as a string in <nn><format_code> style, where "nn" is the length of the array, and "format_code" is based on the FITS standard, e.g. TFORM1='2048E'.
TFORM2 Required Data type in this column.
TFORM3 Recommended Data type in this column, if flux uncertainties are provided (i.e. TTYPE3 is defined).
RELORDER Required Relative spectral order, starting at 1, from blue to red, e.g., RELORDER=1 is the bluest extracted order.
MINWL Required Minimum wavelength for this order.
MAXWL Required Maximum wavelength for this order.
ABSORDER Recommended Absolute (physical) spectral order, if known, e.g., ABSORDER=65.
SPECRES Recommended Spectral resolution (Δλ) at the wavelength specified by the WLRES keyword for this order.
WLRES Recommended The reference wavelength of SPECRES for this order.
BLAZEWL Recommended The blaze wavelength for this order, if known.

FITS Data Format Values For Use In "TFORMn" Keywords

TFORMn is the FITS header keyword that defines the data format for columns in a FITS binary table. For quick reference, we provide Table 18 from Pence et al. 2010, A&A, 524, 42 below. Note that the letters specifying the data format type (A, I, F, E, D) must be in uppercase.