J/ApJ/507/655 J/ApJ/507/655 VI photometry of new Cepheids in NGC 2541 L Ferrarese F Bresolin R C Kennicutt Jr. A Saha P B Stetson W L Freedman J R Mould B F Madore S Sakai H C Ford B K Gibson J A Graham M Han J G Hoessel J Huchra S M Hughes G D Illingworth R Phelps C F Prosser N A Silbermann Astrophys. J. 507 655 1998 1998ApJ...507..655F Photometry Stars, variable Cepheids galaxies: distances and redshifts galaxies: individual (NGC 2541) We report the detection of Cepheids and a new distance to the spiral galaxy NGC 2541, based on data obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). A total of 25 exposures (divided into 13 epochs) were obtained using the F555W filter (transformed to Johnson V), and nine exposures were obtained (divided into five epochs) using the F814W filter (transformed to Cousins I). Photometric reduction of the data is performed using two independent packages, DoPHOT and DAOPHOT II/ALLFRAME, which give very good agreement in the measured magnitudes. A total of 34 bona fide Cepheids, with periods ranging from 12 to over 60 days, are identified based on both sets of photometry. By fitting V and I period-luminosity relations, apparent distance moduli are derived assuming a Large Magellanic Cloud distance modulus and mean color excess of {mu}_LMC_=18.50+/-0.10mag and E(B-V)=0.10mag, respectively. Adopting A(V)/E(V-I)=2.45, we obtain a true distance modulus to NGC 2541 of {mu}_0_=30.47+/-0.11 (random) +/-0.12 (systematic) mag (D=12.4+/-0.6 [random] +/-0.7 [systematic] Mpc), and a total (Galactic plus internal) mean color excess E(B-V)=0.08+/-0.05 (internal error) mag.

HST

[FBK98] Identification (CNN or VNN) number=1 CNN for Cepheids stars, VNN for other variable stars --- Xpos X position number=2 The X- and Y-coordinates are relative to the 1995 October 30 epoch. For each 800 x 800 pixels chip, pixel [1, 1] is located at the edge of the pyramid. pix Ypos Y position number=2 The X- and Y-coordinates are relative to the 1995 October 30 epoch. For each 800 x 800 pixels chip, pixel [1, 1] is located at the edge of the pyramid. pix RAh Right ascension (J2000) number=3 RA and DE are calculated using the IRAF task STSDAS.HST CALIB.WFPC.METRIC, version 1.3.5 (1996 July). h RAm Right ascension (J2000) number=3 RA and DE are calculated using the IRAF task STSDAS.HST CALIB.WFPC.METRIC, version 1.3.5 (1996 July). min RAs Right ascension (J2000) number=3 RA and DE are calculated using the IRAF task STSDAS.HST CALIB.WFPC.METRIC, version 1.3.5 (1996 July). s DE- Declination sign (J2000) --- DEd Declination (J2000) number=3 RA and DE are calculated using the IRAF task STSDAS.HST CALIB.WFPC.METRIC, version 1.3.5 (1996 July). deg DEm Declination (J2000) number=3 RA and DE are calculated using the IRAF task STSDAS.HST CALIB.WFPC.METRIC, version 1.3.5 (1996 July). arcmin DEs Declination (J2000) number=3 RA and DE are calculated using the IRAF task STSDAS.HST CALIB.WFPC.METRIC, version 1.3.5 (1996 July). arcsec Chip Chip (PC, WF 2, WF 3, WF 4) --- [FBK98] Identification (CNN or VNN) --- HJD Heliocentric Julian date d mag V or I magnitude mag e_mag rms uncertainty on mag mag [FBK98] Identification (CNN or VNN) --- l_Per Limit flag on Per --- Per Period d l_Per2 Limit flag on Per2 --- Per2 Upper limit for period interval d F555Wph Phase-weighted mean F555W magnitude mag F555Wav Intensity-averaged mean F555W magnitude mag F814Wph Phase-weighted mean F814W magnitude mag F814WphCor Correction adopted for F814Wph number=1 Value of the magnitude correction applied to the F814W magnitudes, defined as in section 4.4 of the paper. mag F814Wav Intensity-average mean F814W magnitude mag F814WavCor Correction adopted for F814Wav number=1 Value of the magnitude correction applied to the F814W magnitudes, defined as in section 4.4 of the paper. mag Vmagph Phase-weighted mean V magnitude mag Vmagav Intensity-averaged mean V magnitude mag Imagph Phase-weighted mean I magnitude mag Imagav Intensity-averaged mean I magnitude mag chi2/sigma Reduced {xi}^2^_r_ value for DoPHOT or {sigma} for ALLFRAME --- Xpos X position number=1 The X and Y coordinate are relative to the 1995 October 30 epoch. For each 800x800 pixels chip, pixel [1,1] is located at the edge of the WFPC2 pyramid pix Ypos Y position number=1 The X and Y coordinate are relative to the 1995 October 30 epoch. For each 800x800 pixels chip, pixel [1,1] is located at the edge of the WFPC2 pyramid pix RAh Right ascension (J2000) number=2 RA and DE are calculated using the IRAF task STSDAS.HST_CALIB.WFPC.METRIC, version 1.3.5 (July 1996) h RAm Right ascension (J2000) number=2 RA and DE are calculated using the IRAF task STSDAS.HST_CALIB.WFPC.METRIC, version 1.3.5 (July 1996) min RAs Right ascension (J2000) number=2 RA and DE are calculated using the IRAF task STSDAS.HST_CALIB.WFPC.METRIC, version 1.3.5 (July 1996) s DE- Declination sign (J2000) number=2 RA and DE are calculated using the IRAF task STSDAS.HST_CALIB.WFPC.METRIC, version 1.3.5 (July 1996) --- DEd Declination (J2000) number=2 RA and DE are calculated using the IRAF task STSDAS.HST_CALIB.WFPC.METRIC, version 1.3.5 (July 1996) deg DEm Declination (J2000) number=2 RA and DE are calculated using the IRAF task STSDAS.HST_CALIB.WFPC.METRIC, version 1.3.5 (July 1996) arcmin DEs Declination (J2000) number=2 RA and DE are calculated using the IRAF task STSDAS.HST_CALIB.WFPC.METRIC, version 1.3.5 (July 1996) arcsec F555W F555W magnitude(3) mag e_F555W rms uncertainty on F555W mag F814W F814W magnitude number=3 F555W and F814W instrumental magnitudes are intensity averaged over 13 and 5 epochs respectively. mag e_F814W rms uncertainty on F814W mag Vmag V magnitude number=4 V and I magnitudes are calculated from the instrumental F555W and F814W magnitudes as described in section 3 of the paper. mag Imag I magnitude number=4 V and I magnitudes are calculated from the instrumental F555W and F814W magnitudes as described in section 3 of the paper. mag [FBK98] Identification (CNN or VNN) --- Note Text of the note number=1 The term "isolated" is use d for stars for which no companions are identified within a 3 pixel radius. --- Patricia Bauer CDS 1999Mar09From ApJ electronic version J_ApJ_507_655.xml