MAST has put together the following information because it is essential for data deliveries. If the archive cannot extract the information they need from dataset headers, MAST will attempt to calculate it based on original exposures when possible. If MAST is not able to extract or calculate what it needs based on the delivered dataset headers, then some of the data will not be searchable and will not be displayed across multi-mission search results.

The FITS BINARY file (rows and columns of data in binary representation) should abide by the material in FITS Standard v3.0 (Pence et al. 2010) paper. The required keywords for a FITS BINARY table can be viewed here: FITS Binary Table Extension.

Though strongly discouraged, we will accept some time series data as ASCII text tables in extenuating circumstances. This format equates to the FITS Binary format, but in straight ASCII files. More information is provided below.

Lastly, we will also accept CSV format, where the first line is always the list of column names, or otherwise listed in documentation.

For full details, visit the Filenames section in the HLSP main page, and expand for full details of how each field in the file name should be defined.

We suggest using the following commonly used column names:

For any other data, we encourage users to email the MAST team early in the process to determine the best labels to use in the binary table.

Note that undefined (NaN) or blank values within the "time" array are not allowed; all rows must be filled for the primary x-axis. See examples below for FITS extension header of a flux time-series HLSP dataset.

The data format (columns) must be documented within the file itself and/or the supporting README file. For tabular, time series data in either FITS or ASCII format, please follow the Data Columns guidelines provided above. All columns and rows must contain data values; blanks are not allowed. For blank values, please use value 'NaN' for numeric blanks or 'NULL' for string blanks, in the ASCII file. Note that undefined (NaN) values within the "time" array are not allowed; all rows must be filled with valid values for the primary x-axis.

Within a data line, fields are separated by one or more whitespace characters (space or tab). A field is either a sequence of non-whitespace characters or a sequence of characters between two matching quote characters (single (') or double (") quotes) - spaces are therefore allowed in quoted fields.

Column names should only contain a letter, digit and underscore; punctuation and special characters are not allowed; names must start with a letter. We also advise against using dash ("-") within a column name which results in a FITS warning message during FITS validation.

Specification of keywords and description of the column names in the ASCII file should be done as follows:

• Use the '#' symbol to precede all keyword text lines (non-data text lines)
• The next 8 characters are used for FITS keyword name; buffer the 8-chars name with spaces (see "NAXIS" keyword in example below)
• Keyword names can contain letters, digits, underscores or dashes, and must start with a letter
• The 9th character is an equal sign '=' followed by a at least a single space
• The keyword value can be a number or string; strings must be in single quotes
• Keyword comments are written after a "/" symbol
• The FITS 80-character line length limit applies here: no more than 79 characters in total can be used on any given line of text; the 80^th char is the end of line/return char
• The FITS "COMMENT = " keyword should be used to describe any additional information
• The "COMMENT = " keyword value is always a string within single quotes

The following is an ASCII header example of keyword, value pairs, including the 3 data column descriptions for time, flux and flux error. Note that these map directly onto FITS header keywords so that MAST can build FITS files from ASCII tabular time-series deliveries.

                                                           
#TELESCOP= 'GALEX'              / telescope used to acquire data                 
#INSTRUME= 'FUV'                / instrument used to acquire data                              
#RA_TARG =            82.586460 / right ascension of target (deg) (J2000)        
#DEC_TARG=            -7.434805 / declination of target (deg) (J2000)               
#DATE-OBS= '2006-04-28'         / UT date of start of first exposure             
#TIME-OBS= '09:20:38'           / UT start time of first exposure                
#TIMESYS = 'UTC'                / Coordinated Universal Time; defined since 1972.                                     
#
#XTENSION= 'BINTABLE'           /Written by IDL:  Mon May 25 12:26:32 2009       
#BITPIX  =                    8 /                                                
#NAXIS   =                    2 /Binary table                                    
#NAXIS1  =              1152000 /Number of bytes per row                         
#NAXIS2  =                    1 /Number of rows                                  
#PCOUNT  =                    0 /Random parameter count                          
#GCOUNT  =                    1 /Group count                                     
#TFIELDS =                    3 /Number of columns                               
#EXTNAME = 'LIGHTCURVE'         /Extension name                           
#EXTNO   =                    1 /Extension number                                
#TFORM1  = '64000D  '           /Real*8 (double precision)                       
#TTYPE1  = 'TIME    '           /Column 1: Time                            
#TUNIT1  = 'Seconds'            /Units of column 1                               
#TFORM2  = '64000E  '           /Real*4 (floating point)                         
#TTYPE2  = 'FLUX    '           /Column 2: Flux                           
#TUNIT2  = 'erg/s/cm^2'         /Units of column 2                               
#TFORM3  = '64000E  '           /Real*4 (floating point)                         
#TTYPE3  = 'FLUX_ERR   '        /Column 3: Flux Error                     
#TUNIT3  = 'erg/s/cm^2'         /Units of column 3                               
#
#END                                                                             

More information on TIMESYS can be found here. The convention suggested in Appendix B of the FITS Standard v3.0 is part of the mission-specific FITS conventions adopted for, and used in, the RXTE absolute timing accuracy, building on existing High Energy Astrophysics FITS conventions.

Please be sure to specify the precision level of your timestamps; number of significant digits in your data files must reflect this.

Time-related software suggestions:

• Jason Eastman's IDL Time Utilities contains routines to convert a UTC to BJD in TDB, convert a BJD in TDB to UTC, convert an HJD in TT or TDB to BJD in TDB, convert a JD in UTC to JD in TDB, as well as other time-conversions in IDL.
• The IDL Astronomy User's Library is available from Goddard. A listing of other Astronomy and IDL related sites is also useful.
• Russell Owen's Python RO utility package includes RO.Astro for Astronomical coordinates and time conversions, and RO.DS9 for displaying images in the ds9 image viewer.
• Additional Astronomical Python tools are listed on the AstroPy website.

For example, a catalog can be built from a single observation with FITS keyword 'INSTRUME' = "COS". For a composite catalog made extracting fluxes from several images, say STIS and COS data, the keys would be as follows:

• INSTRUME = "MULTI"
• INSTRU01 = "COS"
• INSTRU02 = "STIS"

To designate multiple keywords, we denote this as [nn].

1. KEYWORD + KEYWORD_UNIT pair

You can specify the keyword units using a second, similar keyword where the keyword name contains the string "_UNIT" or "UNIT". Please remember to stay within the FITS 8-character keyword name limit. E.g.:

WAVECENT = 1688 / central wavelength
WAVEUNIT = angstrom / central wavelength units

2. KEYWORD = value / [unit] in brackets within the FITS comment

Comments can contain the keyword unit within brackets; this should be the first text following the standard fits comment delimiter "/", the single slash. Please remember to stay within the FITS 80-character line length limit, which includes the comments. E.g.:

RA_TARG = 2.0952854139 / [deg] right ascension of target

In ASCII tables, you cannot mix numbers and string types in the same column (this is fundamentally not allowed in FITS tables). For example, a column called "FLUX" should not contain the float values 1.5, 56.98, 324.987 in some rows and the strings "None", "Bad" in other rows. We would encourage you to create a separate column called "FLUX_COMMENTS" with a string description of the data quality. Or, you can use a flag column ("FLUX_FLAG"); the mapping of the flag values can be described in the README file.

In order to denote an upper or lower limit within an ASCII or FITS table, you need to use two columns. There are two options available to implement upper/lower limits:

• One column should contain numeric values and the other a string of the limit (e.g. FLUX=1.0, FLUX_LIMIT=">1").
• One column should contain numeric values and the other a flag indicating the limit (e.g. FLUX=1.0, FLUX_FLAG=2, where the flag values are described in the README).

MAST has been ingesting and distributing HLSP data products for over 10 years. During this period, the requirements for HLSP data deliveries have expanded in order to help unify all datasets housed at MAST for ease of multi-mission searching. The example HLSP headers may not abide by all the requirements listed above because they were delivered prior to some requirements being written. We encourage the data delivery teams to provide data sample so that all header and data issues can be worked out prior to the actual delivery for ingestion into the archive.

The following projects contain many examples of time-series, lightcurve and event-list file headers, which can be used as a guideline for your datasets:

• FITS BINARY Table, Time-Series Lightcurve Examples with TIME, FLUX, ERROR (and additional columns)
  From the Kepler HLSP Project:
• Kepler Lightcurve Header (plain text kepler_lightcurve_header.txt header; primary header (HDU0), lightcurve BINARY table (HDU1), image extension (HDU2))
• Kepler Lightcurve FITS File (kepler_lightcurve_ex.fits BINARY table example in HDU1)


• ASCII Table, Time-Series Lightcurve Example
  From the Kepler HLSP Project:
• Kepler Lightcurve in ASCII format (plain text kepler_ASCII_lightcurve_ex.txt with three columns: TIME, SAP_FLUX, SAP_FLUX_ERR)