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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: ftp://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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