Getting SEGUE file data

How do I get SEGUE file data?

The data are distributed from the Science Archive Server (SAS), using two main commands, rsync and wget. To browse the available data, you might want to start at the top level of the DR17 tree.

rsync

First, a disclaimer: the full data volume of the DR17 sample is tens of terabytes (see the Data Volume for exact sizes). rsync (and http) are not designed for such large data transfers. If you really do need the full data set, please contact the Help Desk to talk to a data transfer expert who can arrange a custom transfer. This will be faster for you and easier on our servers.

The rsync command below will download FITS files of all spectra taken on MJD 55008 (June 26, 2009), and save them into a local directory:

rsync -av rsync://dtn.sdss.org/dr17/sdss/spectro/data/55008

To get spectra for a different MJD, just replace the "55008" with the date you are interested in.

Getting the data: SEGUE-2

General Description

The data in the SAS is a "clean" sample of SEGUE-2 data. This definition of "clean" specifically covers two things:

  • All the plates in the list are SEGUE-2 plates, so no need to separate from MARVELS or BOSS plates.
  • A plate is not available until after it is finished. That https://data.sdss.org/sas/dr17/means that once you download a plate directory, all you have to do is sort to get the version of the data files that have the latest MJD in the filename and you will get all the S/N there is to get for that plate.

There are a few exceptions to the latest-MJD-is-best rule. See "Notes on individual plates" below.

NOTE that there are "rerun" numbers, 104 for the spectra and 122 for the stellar parameters. Those rerun numbers are used to designate different versions of the pipeline software. If those get changed you will get many obtrusive announcements to tell you about it, but PLEASE do keep track. The rerun number for the spectra hasn't changed since March 2010 (rerun 104), and is the same pipeline that was run for DR7. Rerun 122 for the SSPP is new for DR10, and has been run on all the SEGUE-1, SEGUE-2 and SDSS legacy plates. This rerun of the SSPP has several improvements over the version used for SSPP rerun 116 (from DR8) and rerun 104 (which was used for DR7).

The data model tells you what's what in each file. Easiest is probably to use the file index link at the data model top page.

From the plate subdirectories, the most useful files are the spZbest files (containing parameters measured from the spectra, e.g. redshift, etc) and spPlate files (containing the spectra themselves). For the SSPP outputs, the ssppOut files contain all the stellar parameters, the ssppOut-*-lineindex.fit files contain the measured line indices, and the ssppOut-*.ps.gz files have the condensed plots for the SSPP diagnostic outputs. There are also SSPP diagnostic plots for each object, with instructions for getting them below.

You can get data from the Science Archive Mirror by substituting mirror.sdss3.org for data.sdss3.org in all the commands below.

Spectra

To get the spectra you can use the wget commands. For example, the command below will get the spPlate file (containing all spectra observed on a given plate) for plate 3131 on MJD 54731 (September 22, 2008).

wget https://data.sdss.org/sas/dr17/sdss/spectro/redux/104/3131/spPlate-3131-54731.fits

Note that wget cannot download an entire directory at once, so if you want multiple spectra, you will need to loop through the directory using a script.

You can also use rsync to get files. For example, this command gets the same file as the wget command above:

rsync -lv rsync://dtn.sdss.org/dr17/sdss/spectro/redux/104/3131/spPlate-3131-54731.fits

Note that you will need to include the period at the end of the command, or else specify a local filename, so that rsync knows what to call this file locally.

The data are stored in subdirectories by plate number in various places on the SAS, so that the plate 3131 reduction 104 directory has the spectroscopic parameter data (as .par files), and the plate 3131 SSPP 122 directory has the stellar parameters (SSPP) data for plate 3131.

Target and Field (all objects)

Photometry, astrometry, proper motion, and target selection information

You can also get the photometry, proper motions and other target selection information from the seguetsObj directory on the SAS. See the data model link again for what is in these files.

To get all the photometric information for the spectroscopic targets on plate 3131:

wget https://data.sdss.org/sas/dr17/sdss/segue2/target/seguetsObj/seguetsObjPlate-3131-54715-02.fits

or

rsync -av rsync://dtn.sdss.org/dr17/sdss/segue2/target/seguetsObj/seguetsObjPlate-3131-54715-02.fits .
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