J/AJ/144/113 Cepheids and companions in M33 from HST images (Chavez+, 2012)
Blending of Cepheids in M33.
Chavez J.M., Macri L.M., Pellerin A.
<Astron. J., 144, 113 (2012)>
=2012AJ....144..113C 2012AJ....144..113C
ADC_Keywords: Galaxies, nearby ; Stars, variable ; Photometry, HST ;
Photometry, VRI
Keywords: galaxies: individual (M33) - stars: variables: Cepheids
Abstract:
A precise and accurate determination of the Hubble constant based on
Cepheid variables requires proper characterization of many sources of
systematic error. One of these is stellar blending, which biases the
measured fluxes of Cepheids and the resulting distance estimates. We
study the blending of 149 Cepheid variables in M33 by matching
archival Hubble Space Telescope data with images obtained at the
Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5m telescope, which differ by a
factor of 10 in angular resolution. We find that 55%±4% of the
Cepheids have no detectable nearby companions that could bias the WIYN
V-band photometry, while the fraction of Cepheids affected below the
10% level is 73%±4%. The corresponding values for the I band are
60%±4% and 72%±4%, respectively. We find no statistically
significant difference in blending statistics as a function of period
or surface brightness. Additionally, we report all the detected
companions within 2" of the Cepheids (equivalent to 9pc at the
distance of M33) which may be used to derive empirical blending
corrections for Cepheids at larger distances.
Description:
We used the Cepheid sample listed in Table 3 of the M33 Synoptic
Stellar Survey (Pellerin & Macri, 2011, cat. J/ApJS/193/26). Data from
the DIRECT survey of M33 (Macri et al. 2001, cat. J/AJ/121/870) were
combined with new images obtained at the Wisconsin-Indiana-Yale-NOAO
(WIYN) 3.5m telescope with the Mini-Mosaic (MiniMo) camera to detect
563 Cepheids ranging in period from 2 to 110days. The typical FWHM of
the WIYN images was 0.75", sampled at a plate scale of 0.28"/pixel.
The photometry and astrometry were calibrated using the catalogs of
Massey et al. (2006, cat. J/AJ/131/2478).
We queried the Hubble Legacy Archive (HLA) and the Mikulski Archive
for Space Telescopes (MAST) for HST images of M33 obtained with either
WFPC2 or ACS which had overlap with the WIYN images of Pellerin &
Macri (2011, cat. J/ApJS/193/26). We restricted our study to fields
that were imaged in V (HST filters F555W or F606W) and I (HST filter
F814W).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 96 150 Cepheid properties
table3.dat 70 13748 Stars found within 2" of Cepheid variables
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See also:
J/ApJS/193/26 : The M33 synoptic stellar survey. I. (Pellerin+, 2011)
J/ApJ/730/119 : HST/WFC3 observations of Cepheids in SN Ia hosts
(Riess+, 2011)
J/ApJ/699/839 : Newly identified M33 star clusters. II. (San Roman+, 2009)
J/AJ/134/2168 : BVI photometry of M33 star clusters (Park+, 2007)
J/ApJ/652/1133 : BVI photometry of NGC 4258 Cepheids (Macri+, 2006)
J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)
J/MNRAS/371/1405 : Variables in M33 (Hartman+, 2006)
J/ApJ/652/313 : BV phot. of a detached EB in M33 (Bonanos+, 2006)
J/AJ/132/1361 : RR Lyrae variables in M33 (Sarajedini+, 2006)
J/AJ/121/870 : BVI photometry of Variables in M33 (Macri+, 2001)
J/AJ/121/861 : BVI photometry of central part of M33 (Macri+, 2001)
J/AJ/122/2477 : DIRECT variables in M33B field (Mochejska+, 2001)
J/AJ/121/2032 : Direct variables in M33A field (Mochejska+, 2001)
J/A+A/366/498 : VI photometry of M33 star clusters (Chandar+, 2001)
J/ApJS/122/431 : Star Clusters in M33 (Chandar+, 1999)
J/AJ/110/1649 : HST VI photometry near the M33 nucleus (Mighell+ 1995)
J/AJ/110/2715 : UBV photometry in NGC 6822, M31 and M33 (Massey+ 1995)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- [M33SSS] Cepheid identifier (G1)
21- 26 F6.3 d Per Period of Cepheid
28- 33 F6.3 mag Vmag V-band (HST F555W or F606W) magnitude of
Cepheid
35- 39 F5.3 mag e_Vmag Uncertainty in Vmag
41- 45 F5.3 --- SV [0/1.2] V-band blending level (G2)
47- 51 F5.3 --- e_SV Uncertainty in SV
53- 58 F6.3 mag Imag I-band (HST F814W) magnitude of Cepheid
60- 64 F5.3 mag e_Imag Uncertainty in Imag
66- 70 F5.3 --- SI [0/0.9] I-band blending level (G2)
72- 76 F5.3 --- e_SI Uncertainty in SI
78- 82 F5.2 mag/arcsec2 muV V-band background surface brightness
84- 88 F5.2 mag/arcsec2 muI I-band background surface brightness
90- 92 A3 --- HST Field designation (for HST image) where
Cepheid is located
94- 96 A3 --- WIYN Field designation (for WIYN image) where
Cepheid is located (G1)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- [M33SSS] Cepheid identifier (G1)
20- 21 A2 --- --- [-c]
22- 24 I03 --- cID [1/428] Companion ID
26- 31 F6.3 arcsec Sepx x-axis separation from Cepheid
33- 38 F6.3 arcsec Sepy y-axis separation from Cepheid
40- 44 F5.3 arcsec Sepr [0.04/2.08] radial separation from Cepheid
46- 51 F6.3 mag Vmag ? V-band (HST F555W or HST F606W) magnitude
of star
53- 57 F5.3 mag e_Vmag ? Uncertainty in Vmag
59- 64 F6.3 mag Imag ? I-band (HST F814W) magnitude of star
66- 70 F5.3 mag e_Imag ? Uncertainty in Imag
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Global Notes:
Note (G1): From the M33 Synoptic Stellar Survey (M33SSS, Pellerin & Macri,
2011, Cat. J/ApJS/193/26).
Note (G2): the blending level in filter F is defined as
SF = Σfi/fC, where fC is the flux of the Cepeheid,
and fi the flux of an individual companion tar located within the
critical radius.
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 25-Oct-2013