[vsnet-sequence 190] Re: SN 2002hc field

["Berto Monard" <LAGMonar@csir.co.za>]

Dear Hitoshi and readers,

for unfiltered CCD measurements of Southern star fields (Decl <-15), I
would suggest to use the USNO-A2.0 B and R mags only to get an
indication of the star colours. 

To derive a sequence for CVs and SNe, it suffices to select a handful
non-red reference stars and to use their UCAC1 mags as approximate R
values. 
The UCAC1 mags are close to R, but apply to a slightly shorter
effective wavelength. Therefore the term 'orange magnitude' (O) is
sometimes used. 

For blue stars (B-V<0.3) I assume O=R. If the stars are not 'blue'
enough, I modify those values slightly.

Regards,

Berto
 


>>> Hitoshi YAMAOKA <yamaoka@rc.kyushu-u.ac.jp> 11/15/02 05:39PM >>>
Dear SN watchers,

  I have examined the field of SN 2002hc (NGC 2559), and found that
the r magnitude of USNO-A2.0 in this field is very incredible for most
stars.  For example, two stars about 1' SW-WSW of the SN (star A and
star B):  
                       USNO-A2.0      GSC-2.2.1
  RA          Dec       r     b   F(~r)  J(~b)    V
08:17:02:5 -27:27:57  17.1  15.5  15.22   --    15.42  star A
08:17:01.8 -27:27:41  16.9  16.5  15.35  15.78  15.45  star B

  The UCAC1 magnitude (Berto's reference magnitudes) is comparable to
the GSC-2.2.1 red magnitude, especially in non-red stars.  For
example,

                       USNO-A2.0      GSC-2.2.1        UCAC1
  RA          Dec       r     b   F(~r)  J(~b)    V    UCmag
08:16:52.7 -27:27:20  14.1  13.3  12.45  13.33  12.93  12.60
08:17:19.6 -27:30:33  15.8  15.1  13.80  15.19  14.43  14.13
08:17:11.3 -27:28:00  15.6  15.8  13.45   --    13.95  13.53

  The KAIT discovery image shows that the SN was as bright as star A
or B (http://astron.berkeley.edu/~bait/2002/sn2002hc.html).  So, the
discovery magnitude reported in IAUC 7999 (mag about 17) seems to be
underestimated, when we rely on the GSC 2.2 magnitudes or UCAC1
magnitudes.  

  Note that there is bright H II region in the neighbour of SN 2002hc,
so the magnitude estimate of this object requires background
subtraction.  B. Monard has kindly supply the image taken on Nov 4.927
and the reference image taken on Sept. 9.  I performed the
subtraction, and measured the magnitude of SN was mag about 15.4CR,
based on GSC2.2 Fmag and UCAC1 magnitude.

  For southern objects, it is considerable to verify the cataloged
magnitudes between USNO-A2.0, GSC 2.2.1 and UCAC1, I guess.

Sincerely Yours,
Hitoshi Yamaoka, Kyushu Univ., Japan
yamaoka@rc.kyushu-u.ac.jp

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