From regnault@lal.in2p3.fr Wed Jul 26 11:59 PDT 2000 Date: Wed, 26 Jul 2000 20:59:44 +0200 (MET DST) From: Nicolas Regnault To: penugent@lbl.gov, aldering@vics.lbl.gov cc: saul@lbl.gov, AGKim@lbl.gov Subject: Spring 1999 SNIa MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Content-Length: 6325 Hi Greg and Peter, Here is a small description of the SN 1999 light curve analysis I put in my thesis. I recently produced a first draft describing the LC production and analysis (part III). You can retrieve it at the following address : ftp://ftp.lal.in2p3.fr/pub/Eros/nicolas/these.ps.gz unfortunately, it is written in french, and may be hard to understand. In this email, I try to outline the most important points of the analysis. I) Photometry ------------- The photometry has been performed using 3 different procedures depending on the angular size of the host galaxy and the position of the SN with respect to the center of its host. (1) if the SN lies well outside its host, and the host's luminosity profile is smooth, the flux of the SN has been measured just by fitting PSF modeled with a moffat function. At the same time, the flux of the field stars, used for the images intercalibration were measured the same way. 1999aa, 1999ac, have been processed this way. (2) if the angular size of the host is small, but the SN can still be distinguished, the photometry has been done by fitting simultaneously a model of the host's luminosity profile and a PSF modeled with a Moffat function. The flux flux of the field stars were measured by fitting a moffat. This method have been used to process 1999af, 1999ao, 1999bk, 1999bm (3) if the SN cannot be distinguished from its host, we used a subtraction photometry a la Alard&Lupton (1999). The other SNe have been processed using this method. The study of the performances of these 3 methods is not yet finished (the priority for my thesis was to produce calibrated LC's and a Hubble plot). But the largest part of the simulation code has been written. The goal is to study each photometry using a simulation, and intercompare the 3 methods. II) Calibration --------------- (1) Reference images of our SNe have been taken in february and march 2000 on the 1.54m danish (La Silla) for all SNe excepted for 1999by and 1999bh located in the northern hemisphere, and 1999bq (lack of time). Standard stars have been taken at the same time, allowing us to calibrate the danish. (2) The 1.54 m danish has been calibrated. Unfortunately, we had access to the telescope only 3 hours per night. Therefore, we have not been able to take enough standard stars to be able to measure the absorption each night. We therefore determined a mean absorption in each passband. I think this is the largest contribution to our photometric uncertainty. Mean zero points have been determined for this period, as well as the color terms. The calibration equations I derived are (pp. 150 --154) : B = b + 23.70 + 0.14 (B-V) V = v + 24.07 + 0.00 (B-V) R = r + 23.98 + 0.04 (V-R) I = i + 22.82 + 0.07 (R-I) with b = m_{instr_B} -0.13 airmass v = m_{instr_V} -0.06 airmass r = m_{instr_R} -0.03 airmass i = m_{instr_I} -0.01 airmass and m_{inst} = -2.5 * log10(\phi^{ADU} / tpose) The color terms I determined agree well with those given by the danish manual. The absorption values are compatible with those given by ESO. The dispersion of the calibration residuals for standard stars of magnitude 15 -- 19 is about 4% (see figure 6.14 p. 155). (3) Using the danish observations, we derived the magnitudes of the field stars in BVRI. These calibrated field stars have then been used as secondary standards, to intercalibrate the follow-up images. We used a two-step precedure for the intercalibration process : (*) for each image, the instrumental star fluxes are compared with the calibrated fied stars fluxes derived from the danish observations. A calibration equation of the form : \phi_{cal} = \alpha \times \phi_{instr} is then adjusted for each image. At this stage, no color terms are taken into account. (*) The color terms of each telescope are then measured by comparing observed and <> magnitudes of the field stars. Table 6.5 p. 160 shows the color terms we obtained. Plots pp 156 -- 161 illustrate our method. (4) The apply these color corrections on each SN mag, we first fit a template, extract a color from this fit, which were used to correct the magnitudes. Figures 7.2 to 7.16 pp. 171 to 199 present the calibrated light curves we obtained. No K-corrections have been applied at this stage. III) LC-analysis ----------------- These light curves have been fitted using nine templates. From the best fit we extract estimations of M_{max}, colors and \Delta m_{15}. We standardized our sample using a simulateous 4 parameters fit (M_{max}, H_0, Dm_{15} slope, (B-V)_{slope}). (pp. 218 -- 219). The 2 parm standardization equation we obtained is : M_{max}^{corr} = -19.23(0.14) - 0.52(0.07) (\Delta m_{15} -1.1) - 1.78(0.13) (B-V)_{max} At the moment, using the calibrators given in he thesis, it leads to H_0 = 69 km s^{-1} Mpc^{-1}. The Hubble plot we obtained is shown page 221. The 1999 SNe are outlined by green crosses. Please note that this version of the thesis is not yet completelty finalized. In the following weeks, I would like to work on the following points : (*) integration of the CTIO1.5m and 0.90m follow-up images recently available on hpss. It may improve the sampling of the SNe discovered by L. Strolger et al. (*) comparison of the 2 photometries we use (subtraction a la Alard&Lupton or simultaneous fit of a PSF and a model of the galaxy luminosity profile). (*) extension of the LC analysis (standardization studies and constrution of a Hubble diagram) to other passbands (at least, the V passband). (*) if possible, improve the K-corrections. If you have comments (always welcome) or if some points remain obscure to you, please let me know. If you think that additionnal studies not mentionned above have to be performed, please tell me. Regards, Nicolas. Nicolas Regnault - LAL ORSAY BAT.200 - 91405 Orsay CEDEX FRANCE Email : regnault@lal.in2p3.fr - Tel : + 33 01 64 46 89 40