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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 ApJdataFrames Hernandez2014
Title
Step1:  Table 4 -  Low Resolution Analysis
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Python Code:
%pylab inline
import seaborn as sns
sns.set_context("notebook", font_scale=1.5)
import warnings
warnings.filterwarnings("ignore")
from astropy.io import ascii
Explanation: ApJdataFrames Hernandez2014
Title: A SPECTROSCOPIC CENSUS IN YOUNG STELLAR REGIONS: THE σ ORIONIS CLUSTER
Authors: Jesus Hernandez, Nuria Calvet, Alice Perez, Cesar Briceno, Lorenzo Olguin, Maria E Contreras, Lee Hartmann, Lori E Allen, Catherine Espaillat, and Ramírez Hernan  
Data is from this paper:
http://iopscience.iop.org/0004-637X/794/1/36/article
End of explanation
tbl4 = ascii.read("http://iopscience.iop.org/0004-637X/794/1/36/suppdata/apj500669t4_mrt.txt")
tbl4[0:4]
Na_mask = ((tbl4["f_EWNaI"] == "Y") | (tbl4["f_EWNaI"] == "N"))
print "There are {} sources with Na I line detections out of {} sources in the catalog".format(Na_mask.sum(), len(tbl4))
tbl4_late = tbl4[['Name', '2MASS', 'SpType', 'e_SpType','EWHa', 'f_EWHa', 'EWNaI', 'e_EWNaI', 'f_EWNaI']][Na_mask]
tbl4_late.pprint(max_lines=100, )
Explanation: Table 4 -  Low Resolution Analysis
End of explanation
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