Data Central uses cookies to make your browsing experience better. By using Data Central you agree to its use of cookies. Learn more I agree


Find information, examples, FAQs and extensive descriptions of the data, curated by the survey teams.

Docs hc

Help Center

Browse FAQs, guides and tutorials on common use cases.
Feb. 10, 2021 by B. Miszalski
Feb. 17, 2021, 12:40 a.m. B. Miszalski

SSA: Accessing the Original Spectra

Example plots of g0340183-285657 using the specutils 6dFGS-combined loader

Typically users will only need to access the simplified spectra using the access_url links (see the FITS FORMAT section of the SSA page for full details).

In the following example we perform the same query as in SSA: Retrieving and Parsing a VOTable but instead use the 6dFGS-combined loader within the specutils package to access the original spectra.

from import parse_single_table
import requests
from io import BytesIO
from astropy.time import Time
from specutils import SpectrumList
import re
import matplotlib.pyplot as plt

#SSA query URL
#query 6dF final data release only around RA=55 deg, DEC=-29.1 deg in a circle of 0.4 deg diameter 
url = ",-29.1&SIZE=0.4&REQUEST=queryData&COLLECTION=6dfgs_fdr"

#perform the query via the above url and store contents in vot 
vot = requests.get(url).content
#optionally write table to file
#fptr = open("ssa_table.xml","wb")

#open the table with astropy's votable package
table = parse_single_table(BytesIO(vot))
data = table.array

#A dictionary to keep track of target_name and urls to original fits file
urls = {}

#Go through each row in the table
for i in range (0,len(data)):
    target_name = data['target_name'][i]
    #Note that the SSA service returns results on all spectra available
    #i.e. all spectra contained in original files are included in the results
    #so the full (original) spectrum they were extracted from appears multiple times
    #in the VOTable results under the full_data_url column
    if(target_name not in urls):
        #Add to our dictionary if not already added before
        #Note the addition of RESPONSEFORMAT=fits here to ensure 
        #the results are returned in fits format
        urls[target_name] = data['full_data_url'][i] + "&RESPONSEFORMAT=fits"

#width of line to use in matplotlib

#Go through each of the full (original) spectra
#and plot in a simple way the V, R and VR spectra
for target, u in urls.items():
    print (target,u)
    ofname = "%s.fits" % target
    print ("Downloading ",ofname)
    spec = requests.get(u).content
    #write out the spectrum to a file
    fptr = open(ofname,"wb")
    #Load in the spectra using specutils and the 6dFGS-combined loader
    slist =,format='6dFGS-combined')
    nspec = len(slist)
    for idx in range(0,nspec):
        hdr = slist[idx].meta['header']
        band = re.sub('SPECTRUM ','',hdr['EXTNAME'])
        wave = slist[idx].wavelength
        flux = slist[idx].flux
        titre = "%s: %s spectrum" % (target,band)
        plt.xlabel("Wavelength ($\mathrm{\AA}$)")
Feb. 10, 2021 by B. Miszalski
Feb. 17, 2021, 12:40 a.m. B. Miszalski