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J/ApJ/733/124    Cepheids in M101 observed with HST          (Shappee+, 2011)

A new Cepheid distance to the giant spiral M101 based on image subtraction of Hubble Space Telescope/Advanced Camera for Surveys observations. Shappee B.J., Stanek K.Z. <Astrophys. J., 733, 124 (2011)> =2011ApJ...733..124S
ADC_Keywords: Photometry, HST ; Stars, variable ; Galaxies, nearby ; Stars, distances Keywords: distance scale - galaxies: distances and redshifts - galaxies: individual (M101) - stars: variables: Cepheids - stars: variables: general - techniques: image processing Abstract: We accurately determine a new Cepheid distance to M101 (NGC 5457) using archival Hubble Space Telescope (HST)/Advanced Camera for Surveys V and I time series photometry of two fields within the galaxy. We make a slight modification to the ISIS image subtraction package to obtain optimal differential light curves from HST data. We discovered 827 Cepheids with periods between 3 and 80 days, the largest extragalactic sample of Cepheids observed with HST by a factor of two. With this large Cepheid sample, we find that the relative distance of M101 from the Large Magellanic Cloud is ΔµLMC=10.63±0.04 (random) ±0.06 (systematic) mag. If we use the geometrically determined maser distance to NGC 4258 as our distance anchor, the distance modulus of M101 is µ0=29.04±0.05 (random) ±0.18 (systematic) mag or D=6.4±0.2 (random) ±0.5 (systematic) Mpc. The uncertainty is dominated by the maser distance estimate (±0.15mag), which should improve over the next few years. Description: For this work, we used archival ACS/WFC data (GO program 10918; PI: Wendy Freedman) of M101 (NGC 5457). The program observed two fields in M101 with Field 1 centered at J140328.8+542135.0 (F1) and Field 2 centered at 140251.0+542022.0 (F2); in both F555W (V band) and F814W (I-band) for 12 epochs. The observations have a baseline of ∼30 days and were completed between 2006 December 23 and 2007 January 21 (Field 1) and between 2006 December 25 and 2007 January 23 (Field 2). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 74 50 Secondary standards table3.dat 111 827 Cepheid variables table4.dat 111 400 Rejected Cepheid Candidates table6.dat 68 827 Cepheid Variables: Calculated Quantities
See also: B/hst : HST Archived Exposures Catalog (STScI, 2007) J/ApJ/715/277 : Insights into the Cepheid distance scale (Bono+, 2010) J/other/A+ARV/15.289 : Distances of local galaxies (Tammann+, 2008) J/ApJ/508/491 : M101 Cepheids (Stetson+, 1998) J/ApJ/463/26 : VI photometry of 29 Cepheids in M101. (Kelson+ 1996) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 8 A8 --- ID Cepheid identification (F[12]-NNNNN) 10- 21 F12.8 deg RAdeg Right Ascension in decimal degrees (J2000) 23- 33 F11.8 deg DEdeg Declination in decimal degrees (J2000) 35- 40 F6.1 pix Xpix X pixel location 42- 47 F6.1 pix Ypix Y pixel location 49- 54 F6.3 mag Vmag Mean HST V band magnitude 56- 58 I3 mmag e_Vmag Uncertainty in Vmag 60- 65 F6.3 mag Imag Mean HST I band magnitude 67- 69 I3 mmag e_Imag Uncertainty Imag 71- 74 F4.1 --- Var Welch-Stetson (1993AJ....105.1813W) variability index value IV (G1)
Byte-by-byte Description of file: table[34].dat
Bytes Format Units Label Explanations
1- 9 A9 --- ID Cepheid identification (F[12]-NNNNNN) 11- 20 F10.6 d Per Period 22- 30 F9.6 d e_Per Uncertainty in Per 32- 43 F12.8 deg RAdeg Right Ascension in decimal degrees (J2000) (1) 45- 55 F11.8 deg DEdeg Declination in decimal degrees (J2000) (1) 57- 62 F6.1 pix Xpix X pixel location 64- 69 F6.1 pix Ypix Y pixel location 71- 76 F6.3 mag Vmag Mean HST V band magnitude 78- 80 I3 mmag e_Vmag Uncertainty in Vmag 82- 87 F6.3 mag Imag Mean HST I band magnitude 89- 91 I3 mmag e_Imag Uncertainty Imag 93- 97 F5.3 mag Vamp Semi-amplitude of V band 99-103 F5.3 mag Iamp Semi-amplitude of I band 105-109 F5.1 --- Var Welch-Stetson variability index value I_V_ (G1) 111 A1 --- Rej [A-F] Reason for rejection (for table 4 only) (2)
Note (1): Astrometry presented is referenced to the HST headers of j9o401010_drz.fits for Field 1 and j9o413010_drz.fits for Field 2 (drizzled images (_drz.fits) from the STScI HST archive). Note (2): Rejection flag as follows: A = amplitude ratio Iamp/Vamp>0.75 or Iamp/Vamp<0.25; B = blue blend: E(V-I)<2σ below foreground extinction C = red blend: E(V-I)>0.68mag (equivalent to E(B-V)>0.5mag) D = population II Cepheid: Distance modulus>12; E = period cut: P<3days; F = iterative sigma clipping (removes outliers)
Byte-by-byte Description of file: table6.dat
Bytes Format Units Label Explanations
1- 9 A9 --- ID Cepheid identification (F[12]-NNNNNN) 11- 16 F6.3 d Per Period 18- 23 F6.3 --- F-Test F-Test ratio of reduced χ2 25- 30 F6.3 mag DM Relative distance modulus 32- 34 I3 mmag e_DM Uncertainty in DM 36- 41 F6.3 mag E(V-I) E(V-I) color excess 43- 45 I3 mmag e_E(V-I) Uncertainty in E(V-I) 47- 52 F6.3 mag E(B-V) E(B-V) color excess 54- 56 I3 mmag e_E(B-V) Uncertainty in E(B-V) 58- 63 F6.4 --- rho Deprojected galactoradius as fraction of isophotal radius 65- 68 F4.2 [-] [O/H] Oxygen abundance at location (12+log[O/H])
Global Notes: Note (G1): the variability index IV is defined by Eq.(1): IV=ΣδVδI/sqrt(n(n-1)) from the residuals normalized to their ubcertainties.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 16-Nov-2012
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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