[vsnet-campaign-nova 883] (fwd) Revised Observation Report for Nova V4740 Sgr

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

From: DWest61506@aol.com
Date: Mon, 18 Mar 2002 06:22:49 EST
Subject: Revised Observation Report for Nova V4740 Sgr

I followed up with Brian's suggestion and when back and calculated the 
comparison star magnitudes using Tycho-2 photometry.  The comparison star 
magnitudes and color indices are given in Table 3.  The revised photometry is 
summarized below.  Based on these observations, it appears that V-Ic <= 0.  
This is still very "blue" for a nova (at least compared to the papers I 
read).  I will continue to observe this object, unfortunately, my 
observations will  be plagued with a low signal-to-noise ratio.

Thanks again,
Doug West

Summary of V and Ic Band Photometry

20020220.837 13.00Ic (Seiichiro Kiyota)
20020220.842 12.30V (Seiichiro Kiyota)
MAR 13.4780 V = 12.81  +/- 0.1
MAR 14.4777 V = 12.75  +/- 0.1
MAR 15.4786 Ic = 12.98 +/-  0.1
MAR 15.4900 V = 12.99  +/- 0.1
MAR 16.4829 V = 12.92 +/- 0.1
MAR 16.4862 Ic = 13.4   +/- 0.3

Calibration Stars in the Field of V4740 Sgr

Due to the high airmass of the V4740 Sgr field from my location in Mulvane, 
KS I am not able to perform all-sky photometry to calibrate the field.  
Therefore, I have determined the V and Ic magnitudes using the Tycho-2 and 
2MASS catalogs.  The V magnitudes are derived from the Tycho-2 catalog and 
the Ic magnitudes are estimated from B-V and J-K colors.  The polynomials 
that relate B-V and J-K to V-Ic are:

(V-Ic) = 0.3948*(B-V)^3 - 0.7279*(B-V)^2+1.3*(B-V)+0.0472
(V-Ic) = -0.4863*(J-K)^2 + 1.889*(J-K) + 0.0565

The third order polynomial for the V-Ic based on B-V is based on 43 standard 
stars.  The second polynomial for the V-Ic based on J-K is on 15 standard 
stars for V and Ic and the J and K magnitudes from the 2MASS catalog.

The V magnitude and B-V colors for the comparison stars is derived from the 
Tycho-2 Bt and Vt magnitudes.  These magnitudes are transformed using the 
relationships (Bessell, PASP, 112, 2000) found at this web page:
http://ftp.lowell.edu/pub/bas/starcats/bessell.tyc

Table 1 - Tycho-2 Magnitudes Converted to Johnson B-V and V
Star                       Bt   Vt        Bt-Vt V         B-V
TYC 7392 3001 1 11.969  10.621  1.348   10.493  1.15
TYC 7392 3006 1 11.465  9.974   1.491   9.832   1.259
HIP89124                11.403  10.077  1.326   9.893   1.142


Table 2 - Comparison Star Magnitude Estimates

Star                      Tycho-2 B-V   Est V-Ic    2MASS J-K    Est V-Ic
TYC 7392 3006 1 1.259               1.32          0.683        1.12
TYC 7392 3001 1 1.15                1.18          0.671        1.11
HIP 89124               1.142               1.17            0.683          
1.12


Table 3 - Comparison Star V and Ic Magnitudes

Star                      Tycho-2 V Avg V-Ic
TYC 7392 3006 1 9.832         1.22
TYC 7392 3001 1 10.493        1.145
HIP 89124                9.893      1.145

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