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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 74 50 Secondary standards
table3.dat 109 827 Cepheid variables
table4.dat 111 400 Rejected Cepheid Candidates
table6.dat 68 827 Cepheid Variables: Calculated Quantities
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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
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Bytes Format Units Label Explanations
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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 1993AJ....105.1813W) variability
index value IV (G1)
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Byte-by-byte Description of file: table[34].dat
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Bytes Format Units Label Explanations
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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 IV (G1)
111 A1 --- Rej [A-F] Reason for rejection (for table 4 only) (2)
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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)
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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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])
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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