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From: DWest61506@aol.com Date: Sat, 16 Mar 2002 13:04:53 EST MAR 15.4786 Ic = 14.4 +/- 0.5 SNR = 6 MAR 15.4900 V = 13.11 +/- 0.15 SNR = 22 The measurements were taken with a 0.2m SCT + SBIG ST-8 CCD camera and V and Ic band filters. I stacked five 45 second exposures for the V band estimate and eight Ic images for the Ic magnitude estimate. The comparison stars were TYC 7392 3001 1 (V=10.53, Ic = 9.31), TYC 7392 3006 1 (V=9.96, Ic = 8.78), and HIP 89124 (V=9.91, Ic= 8.71). See the explanation below on how the comparison star magnitudes were determined. High thin clouds were present at the time of observation. The position of V4740 was measured using 38 (V band) and 21 (Ic band) GSC 1.1 stars in the plate solutions. V band image: 18 11 45.99 -30 30 50.8 Ic band image: 18 11 46.07 -30 30 50.7 I continued my literature search and didn't find any cases where nova had V-Ic < 0. 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 and 2MASS catalogs. The V magnitudes are taken directly from the Tycho 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. Table 1 - Comparison Star Magnitude Estimates Star Tycho B-V Est V-Ic 2MASS J-K Est V-Ic TYC 7392 3006 1 1.20 1.24 0.683 1.12 TYC 7392 3001 1 1.27 1.33 0.671 1.11 TYC 7392 2484 1 1.233 1.28 0.683 1.12 TYC 7392 2650 1 1.58 1.84 1.121 1.63 HIP 89124 1.23 1.28 0.683 1.12 Table 2 - Comparison Star V and Ic Magnitudes Star Tycho V Avg V-Ic TYC 7392 3006 1 9.96 1.18 TYC 7392 3001 1 10.53 1.22 TYC 7392 2484 1 10.11 1.20 TYC 7392 2650 1 10.30 1.73 HIP 89124 9.91 1.20 Previous e-mail: Subj: Nova V4740 Sgr Photometry Date: 3/14/02 2:40:53 PM Central Standard Time From: mailto:DWest61506DWest61506 To: brian.skiff@lowell.edu, tkato@kusastro.kyoto-u.ac.jp, aavso@aavso.org, dgreen@cfa.harvard.edu, aah@nofs.navy.mil Seiichiro Kiyota's recent submission to VSNET caught my attention and I followed up with additional observations. The part that perplexed me was that usually for novae, V-Ic>0, in this case V-Ic = -0.7 mag. I had not seen a nova with this color in the past. 20020220.837 13.00Ic (Seiichiro Kiyota) 20020220.842 12.30V (Seiichiro Kiyota) My follow up measurements were taken with a 0.2m SCT + SBIG ST-8 CCD camera and V and Ic band filters. I stacked three 45 second exposures. The comparison stars were TYC 7392 3001 1 (V=10.53, Ic = 9.46) and TYC 7392 3006 1 (V=9.96, Ic = 8.72). The check star was HIP 89124 (V=9.91, Ic = 8.72). For the Tycho stars, the Ic magnitudes were inferred from the B-V color of the stars. My observations: 20020314.478 V = 12.8 +/- 0.1 and Ic = 15.9 +/- ~1.0 mag. The error bar of 1.0 mag on Ic may not be conservative enough, I only had a SNR of 2. The point is, V-Ic << 0. I used astrometry and images from previous observations during the outburst (IAUC 7708) for comparison. The V band image astrometry was within error limits of the published position and my previous observations. Due to the low SNR for the Ic band observation, I could not use the centroid feature of my software to verify the correct position. The Ic band observation position was determined based on the position from previous images during outburst. There were no stars within the immediate vicinity of V4740 Sgr's position with Ic < 12.9. I did a quick search of the literature on novae photometry in ADS and couldn't find any examples where V-Ic<0. A possible progenitor star is GSC 2.2 S301213252784 which has position end figures of 45.302 s and 49.28" (J2000). The GSC 2.2 magnitudes for this star are V(green) = 16.09 and Red = 15.30. The color of this possible progenitor star is not consistent with my observations. I am confused, any comments, suggestions, and/or corrections would be welcomed. Thanks, Doug West
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