J/AJ/149/66 VI photometry of 8 Cepheid candidates in M31 (Ngeow+, 2015)
VI-band follow-up observations of Ultra-Long-Period Cepheid candidates in M31.
Ngeow C.-C., Lee C.-H., Yang M.T.-C., Lin C.-S., Hsiao H.-Y., Cheng Y.-C.,
Lin Z.-Y., Lin I.-L., Kanbur S.M., Ip W.-H.
<Astron. J., 149, 66 (2015)>
=2015AJ....149...66N 2015AJ....149...66N
ADC_Keywords: Galaxies, nearby ; Stars, variable ; Photometry, VRI
Keywords: distance scale - galaxies: individual: M31 - stars: distances -
stars: variables: Cepheids
Abstract:
The ultra-long-period Cepheids (ULPCs) are classical Cepheids with
pulsation periods exceeding ∼80days. The intrinsic brightness of ULPCs
are ∼1 to ∼3mag brighter than their shorter period counterparts. This
makes them attractive in future distance scale work to derive
distances beyond the limit set by the shorter period Cepheids. We have
initiated a program to search for ULPCs in M31, using the single-band
data taken from the Palomar Transient Factory, and identified eight
possible candidates. In this work, we presented the VI-band follow-up
observations of these eight candidates. Based on our VI-band light
curves of these candidates and their locations in the color-magnitude
diagram and the Period-Wesenheit diagram, we verify two candidates as
being truly ULPCs. The six other candidates are most likely other
kinds of long-period variables. With the two confirmed M31 ULPCs, we
tested the applicability of ULPCs in distance scale work by deriving
the distance modulus of M31. It was found to be
µM31,ULPC=24.30±0.76mag. The large error in the derived
distance modulus, together with the large intrinsic dispersion of the
Period-Wesenheit (PW) relation and the small number of ULPCs in a
given host galaxy, means that the question of the suitability of ULPCs
as standard candles is still open. Further work is needed to enlarge
the sample of calibrating ULPCs and reduce the intrinsic dispersion of
the PW relation before re-considering ULPCs as suitable distance
indicators.
Description:
The VI-band follow-up observations were carried out with the automated
Palomar 60inch telescope (P60) at the Palomar Observatory and the
Lulin 1m Telescope (LOT) at the Lulin Observatory. These observations
began in 2012 October and ended in 2013 November. P60 is equipped with
a 2k*2k CCD with a pixel scale of 0.379'' per pixel, while LOT used a
CCD with a pixel scale of 0.512'' per pixel.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 37 954 VI-band light curves for the candidates
table3.dat 96 8 Revised periods and mean magnitudes for the
candidates
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See also:
B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013)
J/ApJ/799/144 : M31 Cepheids in near-IR (Kodric+, 2015)
J/AJ/145/106 : M31 Cepheid disk sample of 1st year of PS1 (Kodric+, 2013)
J/ApJ/745/156 : M31 Cepheids with HST/WFC3 (Riess+, 2012)
J/ApJ/743/19 : M31 variable star candidates photometry (Clementini+, 2011)
J/AcA/59/239 : Light curves of LMC long-period variables (Soszynski+, 2009)
J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)
J/A+A/459/321 : BV photometry of M31 eclipsing binaries (Vilardell+, 2006)
J/A+A/445/423 : WeCAPP Survey. M31 variables (Fliri+, 2006)
J/MNRAS/351/1071 : POINT-AGAPE Survey. M31 variables (An+, 2004)
J/A+A/421/509 : AGAPE catalogue of M31 variables (Ansari+, 2004)
J/A+A/402/113 : (RI)c photometry of variables in M31 (Joshi+, 2003)
J/AJ/126/175 : M31Y eclipsing binaries and Cepheids (Bonanos+, 2003)
J/AJ/118/2211 : M31F eclipsing binaries and Cepheids (Mochejska+ 1999)
J/AJ/118/346 : M31D eclipsing binaries and Cepheids (Kaluzny+ 1999)
J/AJ/117/2810 : Eclipsing binaries and Cepheids in M31C (Stanek+, 1999)
J/AJ/115/1894 : Eclipsing binaries and Cepheids in M31A field (Stanek+ 1998)
J/AJ/115/1016 : M31B eclipsing binaries and Cepheids (Kaluzny+ 1998)
J/A+AS/126/401 : M31 Cepheids periods (Magnier+ 1997)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- ULPC Internal identifier for the Ultra-Long-Period
Cepheid candidate (G1)
8- 10 A3 --- Tel Telescope used in the observation (LOT or P60) (1)
12 A1 --- Band [VI] Bandpass used in the observation
14- 24 F11.5 d MJD Modified Julian Date of the observation
26- 31 F6.3 mag mag [17.0/21.2] Observed magnitude in Band
33- 37 F5.3 mag e_mag Error in mag
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Note (1): The two telescope codes are defined as follows:
LOT = The Lulin 1m Telescope (LOT) at the Lulin Observatory;
P60 = The automated Palomar 60inch telescope at the Palomar Observatory.
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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- 2 A2 --- f_ULPC Class of ULPC: C=M31 ULPC candidate,
NC=M31 non-ULPC candidate)
4- 9 A6 --- ULPC Internal identifier for the Ultra-Long-Period
Cepheid candidate (G1)
11- 17 F7.3 d Per Period
19- 24 F6.3 d e_Per Uncertainty in Per
26- 31 F6.3 mag <Vmag> Mean V band magnitude
33- 38 F6.3 mag <Imag> Mean I band magnitude
40- 45 F6.3 mag Wmag Extinction-free Wesenheit magnitude,
defined as W=I-1.55(V-I) (1)
47- 48 I2 h RAh Hour of Right Ascension (J2000) (2)
50- 51 I2 min RAm Minute of Right Ascension (J2000) (2)
53- 58 F6.3 s RAs Second of Right Ascension (J2000) (2)
60 A1 --- DE- Sign of the Declination (J2000) (2)
61- 62 I2 deg DEd Degree of Declination (J2000) (2)
64- 65 I2 arcmin DEm Arcminute of Declination (J2000) (2)
67- 71 F5.2 arcsec DEs Arcsecond of Declination (J2000) (2)
73- 96 A24 --- Simbad Simbad name (2)
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Note (1): In order to be consistent with previous works (Bird et al.,
2009ApJ...695..874B 2009ApJ...695..874B; Fiorentino et al., 2012Ap&SS.341..143F 2012Ap&SS.341..143F), we adopted
the same Wesenheit function in the form of W=I-1.55(V-I) from
Udalski et al. (1999AcA....49..201U 1999AcA....49..201U). The coefficient of 1.55 in the
Wesenheit function is based on the extinction law from
Schlegel et al. (1998ApJ...500..525S 1998ApJ...500..525S).
Note (2): Positions and Simbad names are from Paper I
(Lee et al., 2013arXiv1309.5127L 2013arXiv1309.5127L).
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Global notes:
Note (G1): The first digit in this identifier corresponds to the chip number as
given in Table I of Paper I (2013arXiv1309.5127L 2013arXiv1309.5127L), followed by 4 digits
numbering from the difference imaging analysis (DIA) catalogs
(Alard & Lupton, 1998ApJ...503..325A 1998ApJ...503..325A).
History:
From electronic version of the journal
References:
Lee et al., Paper I, 2013arXiv1309.5127L 2013arXiv1309.5127L
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 26-Feb-2015