J/AJ/125/1261 VI photometry of Sextans A Cepheids (Dolphin+, 2003)
Deep Hubble Space Telescope imaging of Sextans A. II. Cepheids and distance.
Dolphin A.E., Saha A., Skillman E.D., Dohm-Palmer R.C., Tolstoy E.,
Cole A.A., Gallagher J.S., Hoessel J.G., Mateo M.
<Astron. J. 125, 1261 (2003)>
=2003AJ....125.1261D 2003AJ....125.1261D
ADC_Keywords: Stars, variable ; Photometry
Keywords: Cepheids - galaxies: distances and redshifts -
galaxies: individual (Sextans A) - Local Group
Abstract:
We have identified 82 short-period variable stars in Sextans A from
deep Wide Field Planetary Camera 2 observations. All the periodic
variables appear to be short-period Cepheids, with periods as small as
0.8 days for fundamental mode Cepheids and 0.5 days for first-overtone
Cepheids. These objects have been used, along with measurements of the
red giant branch (RGB) tip and red clump, to measure a true distance
modulus to Sextans A of µ0=25.61±0.07, corresponding to a
distance of d=1.32±0.04Mpc. Comparing distances calculated by these
techniques, we find that short-period Cepheids (P<2-days) are accurate
distance indicators for objects at or below the metallicity of the
Small Magellanic Cloud. As these objects are quite numerous in
low-metallicity star-forming galaxies, they have the potential for
providing extremely precise distances throughout the Local Group. We
have also compared the relative distances produced by other distance
indicators. We conclude that calibrations of RR Lyrae stars, the RGB
tip, and the red clump are self-consistent, but that there appears to
be a small dependence of long-period Cepheid distances on metallicity.
Finally, we present relative distances of Sextans A, Leo A, IC 1613,
and the Magellanic Clouds.
Description:
The observations were described in detail in Paper I (Dohm-Palmer et
al., 2002AJ....123..813D 2002AJ....123..813D). Summarizing briefly, the data consist of 24
pairs of 1200s images. Sixteen of the pairs were taken through the
F814W filter; eight, through F555W. Data were taken with four
dithering positions, with one quarter of the observations (four pair
of F814W images and two pair of F555W images) made at each. A pair of
F656N images was also taken but was not used for our variable star
work and thus will not be referenced again in this paper. The total
baseline of observations was slightly over 3 days.
Objects:
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RA (2000) DE Designation(s)
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10 11 00.5 -04 41 29 Sextans A = UGCA 205
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 41 1968 Photometry of Variable Stars
table2.dat 70 82 Sextans A Variable Stars
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See also:
J/AJ/116/2341 : UBVRI photometry in Sextans A (Van Dyk+ 1998)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- [DSS2003] Object identification (G1)
8- 12 A5 --- Filt [F555W F814W] Filter name (2)
14- 25 F12.4 d HJD Heliocentric Julian Date
27- 31 F5.2 mag mag ? WFPC filter band magnitude
33- 36 F4.2 mag e_mag ? Error in mag
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Note (2): F555W∼Vmag ; F814W∼Imag
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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- 6 A6 --- [DSS2003] Identification number (G1)
8 I1 --- Chip WFPC chip number
10- 15 F6.2 pix Xpos The X pixel coordinate
17- 22 F6.2 pix Ypos The Y pixel coordinate
24- 28 F5.2 mag Vmag Mean phase-averaged V-band magnitude
30- 33 F4.2 mag e_Vmag Error in Vmag (2)
35- 39 F5.2 mag Imag Mean phase-averaged I-band magnitude
41- 44 F4.2 mag e_Imag Error in Imag (2)
46- 49 F4.2 mag V-I Mean phase-averaged (V-I) color
51- 54 F4.2 mag e_V-I Error in V-I (2)
56- 59 F4.2 d Per Period
61- 64 F4.2 d e_Per Error in Per
66- 67 A2 --- Mode Cepheid mode (3)
69 I1 --- Q Star quality (4)
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Note (2): Formal error only and does not account for uncertainties
caused by limited phase coverage.
Note (3): Cepheid mode:
FM = Fundamental
FO = First overtone
Note (4): Based on the cleanness of the light curves, uniqueness of
the period, and coherence between F555W and F814W light curves,
where 4 is the maximum.
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Global notes:
Note (G1): In chip number-variable number format, CN-VNN
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History:
From electronic version of the journal
References:
Dohm-Palmer et al., Paper I 2002AJ....123..813D 2002AJ....123..813D
(End) Greg Schwarz [AAS], Patricia Bauer [CDS] 29-Apr-2003