PRO rdybsc4,n,desig,rtasc,dec,mag, thresh=thresh

;program to read in the designation, right ascention, declination, and 
;magnitude of stars fron the ybsc4.dat file
; Added THRESH keyword 94/06/20 DPS
; Modified for DOS 96/03/22 DPS
@isitdos
n = 0
OPENR, unit, ybscdir+dd+'ybsc4s.dat', /GET_LUN
READF,unit,n ;n=number of stars - first line of the file
p1='' & desig=REPLICATE(p1,n)

;right ascention is in hours,mins,secs
p2=0  & rah=REPLICATE(p2,n)
p3=0  & ram=REPLICATE(p3,n)
p4=0. & ras=REPLICATE(p4,n)

;negative or positive declination
p5='' & sign=REPLICATE(p5,n)

;declination in degrees, min, sec
p6=0  & dec=REPLICATE(p6,n)
p7=0  & decmin=REPLICATE(p7,n)
p8=0  & decsec=REPLICATE(p8,n)

p9=0. & mag=REPLICATE(p9,n)

FOR i=0,n-1 DO BEGIN
    READF,unit,p1,p2,p3,p4,p5,p6,p7,p8,p9 $
         ,FORMAT='(A14,2I3,F5.1,1X,A1,I2,2I3,F6.2)'
    desig(i)=p1
    rah(i)=p2
    ram(i)=p3
    ras(i)=p3
    sign(i)=p5
    dec(i)=p6
    decmin(i)=p7
    decsec(i)=p8
    mag(i)=p9
ENDFOR
CLOSE,unit
;conversion to decimal degrees
rtasc = 15.*(rah + (ram + ras/60.)/60.)
dec=dec+(decmin+decsec/60.)/60.
ndec=WHERE(sign EQ '-')
dec(ndec)=-dec(ndec)
FREE_LUN,unit

; Restrict to stars less than a given magnitude
IF KEYWORD_SET(thresh) THEN BEGIN
    sel=WHERE(mag LT thresh,n)
    desig=desig(sel)
    rtasc=rtasc(sel)
    dec=dec(sel)
    mag=mag(sel)
    ENDIF

RETURN
END