J/ApJ/652/1133 BVI photometry of NGC 4258 Cepheids (Macri+, 2006)
A new Cepheid distance to the maser-host galaxy NGC 4258 and its implications
for the Hubble constant.
Macri L.M., Stanek K.Z., Bersier D., Greenhill L.J., Reid M.J.
<Astrophys. J., 652, 1133-1149 (2006)>
=2006ApJ...652.1133M 2006ApJ...652.1133M
ADC_Keywords: Galaxies, nearby ; Stars, variable ; Photometry, UBVRI
Keywords: Cepheids - distance scale - galaxies: individual (NGC 4258)
Abstract:
We present initial results from a time series BVI survey of two fields
in NGC 4258 using the HST ACS. This galaxy was selected because of its
accurate maser-based distance, which is anticipated to have a total
uncertainty of 3%. The goal of the HST observations is to provide an
absolute calibration of the Cepheid distance scale and to measure its
dependence on chemical abundance (the so-called metallicity effect).
We carried out observations of two fields at different galactocentric
distances with a mean abundance difference of 0.5dex. We discovered a
total of 281 Cepheids with periods ranging from 4 to 45 days (the
duration of our observing window).
Description:
We used the HST (GO program 9810) to observe two fields located at
widely different galactocentric radii within the disk of NGC 4258
(M106). The fields were observed on 12 separate epochs between 2003
December 5 and 2004 January 19.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 62 47 Log of Observations
table2.dat 78 137 Secondary standards
table4.dat 105 281 Cepheid variables - Basic data
table5.dat 107 332 Rejected Cepheid candidates
table6.dat 61 281 Cepheid variables - Derived properties
table7.dat 55 6704 Cepheid photometry
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Obs Observation number
6- 9 A4 --- NVis Visit Number (A-NN) (G1)
10 A1 --- n_NVis [b] Note for For Visit No 7 (1)
12 I1 --- Norb [1/2] First or second orbit during
the visit
14- 23 A10 "YYYY/MM/DD" Date UT Date
25- 36 F12.4 d JD(B) B-band JD at midexposure
38- 49 F12.4 d JD(I) I-band JD at midexposure
51- 62 F12.4 d JD(V) V-band JD at midexposure
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Note (1): "b" (for Visit No 7) indicates no second orbit data because of
Guide star problems; limited usefulness
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- [MSB2006] Star identification, A-NNNNN (G1)
10- 11 I2 h RAh Hour of Right Ascension (J2000)
13- 14 I2 min RAm Minute of Right Ascension (J2000)
16- 21 F6.3 s RAs Second of Right Ascension (J2000)
23 A1 --- DE- Sign of Declination (J2000)
24- 25 I2 deg DEd Degree of Declination (J2000)
27- 28 I2 arcmin DEm Arcminute of Declination (J2000)
30- 34 F5.2 arcsec DEs Arcsecond of Declination (J2000)
36- 41 F6.1 pix Xpix The X pixel coordinate
43- 48 F6.1 pix Ypix The Y pixel coordinate
50- 55 F6.3 mag Vmag The V band magnitude
57- 58 I2 mmag e_Vmag Uncertainty in Vmag in millimagnitudes
60- 65 F6.3 mag Imag The I band magnitude
67- 68 I2 mmag e_Imag Uncertainty in Imag in millimagnitudes
70- 75 F6.3 mag Bmag The B band magnitude
77- 78 I2 mmag e_Bmag Uncertainty in Bmag in millimagnitudes
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Byte-by-byte Description of file: table[45].dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- [MSB2006] Cepheid identification (G1)
10- 14 F5.2 d Per Period
16- 17 I2 h RAh Hour of Right Ascension (J2000)
19- 20 I2 min RAm Minute of Right Ascension (J2000)
22- 27 F6.3 s RAs Second of Right Ascension (J2000)
29 A1 --- DE- Sign of Declination (J2000)
30- 31 I2 deg DEd Degree of Declination (J2000)
33- 34 I2 arcmin DEm Arcminute of Declination (J2000)
36- 40 F5.2 arcsec DEs Arcsecond of Declination (J2000)
42- 47 F6.1 pix Xpix The X pixel coordinate
49- 54 F6.1 pix Ypix The Y pixel coordinate
56- 61 F6.3 mag Vmag The V band magnitude
63- 65 I3 mmag e_Vmag Uncertainty in Vmag in millimagnitudes
67- 72 F6.3 mag Imag ? The I band magnitude
74- 76 I3 mmag e_Imag ? Uncertainty in Imag in millimagnitudes
78- 83 F6.3 mag Bmag ? The B band magnitude
85- 87 I3 mmag e_Bmag ? Uncertainty in Bmag in millimagnitudes
89- 91 I3 mmag Vamp The V band semi-amplitude
93- 95 I3 mmag Iamp ? The I band semi-amplitude
97-100 I4 mmag Bamp ? The B band semi-amplitude
102-105 F4.2 --- LV Modified Welch-Stetson V-band variability
index value
107 A1 --- Rej [A-F] Reason for Cepheid candidate
rejection (2)
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Note (2): Reason for Cepheid candidate rejection flag as follows:
A = NV<18 or NI<18 or NB<18
B = V/I amp outside 0.5±0.25
C = B/V amp outside 1.5±0.50
D = E(B-V)< foreground (2σ or greater)
E = E(B-V)>0.5mag
F = Δµ0>12 or iterative sigma clipping
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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- 8 A8 --- [MSB2006] Cepheid identification (g1)
10- 14 F5.2 d Per Period
16- 21 F6.3 mag DM.VI Extinction corrected distance modulus
determined from V and I data only
23- 25 I3 mmag e_DM.VI Uncertainty in muVI in millimagnitudes
27- 31 F5.3 mag E(V-I) The (V-I) color excess
33- 35 I3 mmag e_E(V-I) Uncertainty in E(V-I) in millimagnitudes
37- 42 F6.3 mag DM.avg Average extinction corrected distance
modulus from B, V and I data (2)
44- 46 I3 mmag e_DM.avg Uncertainty in DM.avg in millimagnitudes
48- 52 F5.3 mag E(B-V) Average (B-V) color excess from B, V
and I data (2)
54- 56 I3 mmag e_E(B-V) Uncertainty in E(B-V) in millimagnitudes
58- 61 F4.2 --- RGal Deprojected galactocentric radius in units of
the isophotal radius (3)
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Note (2): Average value of extinction corrected distance modulus and (B-V)
color excesses were derived from BVI data using Equations 7-9.
Note (3): Derived using Equations 11-13.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- [MSB2006] Cepheid identification (G1)
10- 14 F5.2 d Per Period
16- 19 A4 --- Obs Observation number (2)
21- 26 F6.3 mag Vmag ?=99.999 V band magnitude (3)
28- 30 I3 mmag e_Vmag ?=999 Uncertainty in Vmag in millimagnitudes
31 A1 --- u_Vmag [*] Rejected measurement (4)
33- 38 F6.3 mag Imag ?=99.999 I band magnitude (3)
40- 42 I3 mmag e_Imag ?=999 Uncertainty in Imag in millimagnitudes
43 A1 --- u_Imag [*] Rejected measurement (4)
45- 50 F6.3 mag Bmag ?=99.999 B band magnitude (3)
52- 54 I3 mmag e_Bmag ?=999 Uncertainty in Bmag in millimagnitudes
55 A1 --- u_Bmag [*] Rejected measurement (4)
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Note (2): The Julian Date for each visit can be found in table1.dat file.
Note (3): Magnitudes of 99.999 and errors of 999 indicate NULL values.
Note (4): "*" indicates that the measurement deviated by more than 3σ
from best-fit template light curve and was rejected
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Global notes:
Note (G1): O-NNNN = outer field; I-NNNNN = inner field.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 29-Jul-2008