2000AJ....120..810M

Query : 2000AJ....120..810M

2000AJ....120..810M - Astron. J., 120, 810-820 (2000/August-0)

The DIRECT project: influence of blending on the cepheid distance scale. I. Cepheids in M31.

MOCHEJSKA B.J., MACRI L.M., SASSELOV D.D. and STANEK K.Z.

Abstract (from CDS):

We investigate the influence of blending on the Cepheid distance scale. Blending is the close association of a Cepheid with one or more intrinsically luminous stars. High-resolution HST images are compared with our ground-based data, obtained as part of the DIRECT project, for a sample of 22 Cepheids in the M31 galaxy. The average (median) V-band flux contribution from luminous companions that are not resolved on the ground-based images is about 19% (12%) of the flux of the Cepheid. This is a large effect–at the 10% level for distances. The current Cepheid distance estimates to M31 are all ground based and are thus affected (underestimated). We discuss indirect methods to find which Cepheids are blended, e.g., by the use of well-sampled light curves in at least two optical bands. More generally, our ground-based resolution in M31 corresponds to the HST resolution at about 10 Mpc. Blending leads to systematically low distances in the observed galaxies and therefore to systematically high estimates of H0; we discuss the issue and the implications.

Abstract Copyright: ∼

Journal keyword(s): Stars: Variables: Cepheids - Cosmology: Distance Scale - galaxies: individual (M31)

Simbad objects: 29

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Number of rows : 29
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 DIRECT V7074 M31F cC* 00 40 09.3883331064 +40 46 39.546427332     20.78   19.70 ~ 3 0
2 GAPO 20 cC* 00 40 26.6266676136 +40 43 59.464366212     20.46   19.63 ~ 7 0
3 GAPO 24 cC* 00 40 27.7092384624 +40 43 42.297876228     21.24   19.65 ~ 6 0
4 GAPO 72 cC* 00 40 28.5225290736 +40 45 38.146688964     20.55   19.85 ~ 8 0
5 GAPO 108 cC* 00 40 28.8798291504 +40 45 59.769893448     21.28   20.52 ~ 5 0
6 DIRECT V3289 M31F cC* 00 40 29.5715871525 +40 44 42.965557886     20.89   19.76 ~ 3 0
7 GAPO 109 cC* 00 40 32.2273603512 +40 45 55.815074640     20.27   19.54 ~ 7 0
8 DIRECT V2203 M31F cC* 00 40 32.8816259108 +40 43 52.673890314 19.6   17.94   17.17 F5I 7 0
9 NGC 206 As* 00 40 33.8 +40 44 22           ~ 128 0
10 GAPO 98 Ce* 00 40 33.9653467440 +40 44 29.956822728 19.963 19.961 18.79   17.47 M/KI+B 7 0
11 GAPO 107 cC* 00 40 35.1179589552 +40 46 33.378436164     21.30   19.85 ~ 6 0
12 GAPO 145 cC* 00 40 35.3413972680 +40 46 06.915326628     20.94   19.86 ~ 6 0
13 GAPO 54 cC* 00 40 35.7370411920 +40 45 24.787759140     20.72   19.68 ~ 7 0
14 M 31 AGN 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 13622 1
15 DIRECT V13705 M31C cC* 00 44 43.7541080112 +41 28 35.517232380   22.822 21.499   19.98 ~ 7 0
16 [MAP97] 94 cC* 00 44 48.1454167128 +41 26 57.393806532   22.729 21.303   20.136 ~ 9 0
17 [MAP97] 95 cC* 00 44 48.6990317976 +41 29 15.377286408   20.822 19.999   18.95 ~ 10 0
18 DIRECT V14661 M31C cC* 00 44 50.2343965968 +41 27 09.455782248   22.479 21.295   19.745 ~ 8 0
19 [MAP97] 97 cC* 00 44 54.0236889960 +41 31 45.319162368   21.695 20.913   19.61 ~ 6 0
20 DIRECT V5646 M31B Ce* 00 44 57.89478960 +41 30 33.4387440   22.204 20.811   19.656 ~ 7 0
21 [MAP97] 103 cC* 00 45 02.0598038856 +41 33 56.546417124   21.824 20.604   19.748 ~ 9 0
22 DIRECT V6872 M31B cC* 00 45 05.89751760 +41 30 44.5850280   22.294 21.500   20.62 ~ 5 0
23 [MAP97] 107 cC* 00 45 07.1369504928 +41 37 18.230823948   19.529 19.122   18.45 ~ 13 0
24 DIRECT V7209 M31B cC* 00 45 07.5431682095 +41 35 15.870012668   21.100 20.122   19.390 ~ 8 0
25 M 33 GiG 01 33 50.8965749232 +30 39 36.630403128 6.17 6.27 5.72     ~ 6226 1
26 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 19090 0
27 NGC 2541 GiG 08 14 40.1160678912 +49 03 42.021679932 12.03 12.26 11.80     ~ 333 1
28 NGC 4535 H2G 12 34 20.3443516704 +08 11 51.908488116   11.1       ~ 679 0
29 NGC 4639 Sy1 12 42 52.3785000336 +13 15 26.706153600   13.62 12.72     ~ 642 0

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