J/A+A/453/155 Extended envelopes around Galactic Cepheids II. (Merand+, 2006)
Extended envelopes around Galactic Cepheids.
II. Polaris and delta Cep from near-infrared interferometry with CHARA/FLUOR
Merand A., Kervella P., Coude du Foresto V., Perrin G., Ridgway S.T.,
Aufdenberg J.P., ten Brummelaar T.A., McAlister H.A., Sturmann L.,
Sturmann2 J., Turner N.H., Berger D.H.
<Astron. Astrophys. 453, 155 (2006)>
=2006A&A...453..155M 2006A&A...453..155M
ADC_Keywords: Stars, variable ; Interferometry
Keywords: stars: variables: Cepheid - stars: circumstellar matter -
stars: individual: Polaris (alpha UMi) -
stars: individual: delta Cep - techniques: interferometric -
techniques: high angular resolution
Abstract:
We present the results of long-baseline interferometric observations
of the classical Cepheids Polaris and delta Cep in the near infrared
K' band (1.9-2.3 microns), using the FLUOR instrument of the CHARA
Array. Following our previous detection of a circumstellar envelope
(CSE) around L Car (Kervella et al., 2006A&A...448..623K 2006A&A...448..623K), we report
similar detections around Polaris and delta Cep. Owing to the large
data set acquired on Polaris, in both the first and second lobes of
visibility function, we have detected the presence of a circum-stellar
envelope (CSE), located at 2.4±0.1 stellar radii, accounting for
1.5±0.4% of the stellar flux in the K' band. A similar model is
applied to the delta Cep data, which shows improved agreement compared
to a model without CSE. Finally, we find that the bias in estimating
the angular diameter of delta Cep in the framework of the
Baade-Wesselink method (Merand et al., 2005A&A...438L...9M 2005A&A...438L...9M) is of the
order of 1% or less in the K' band. A complete study of the influence
of the CSE is proposed in this context, showing that at the optimum
baseline for angular diameter variation detection, the bias is of the
order of the formal precision in the determination of the delta Cep
pulsation amplitude (1.6%). Description: Individual interferometric
squared visibility measurements. Data were acquired in the wide
infrared K' band. We also provide informations about calibrator stars.
Objects:
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RA (2000) DE Designation(s)
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02 31 49.1 +89 15 51 HR 424 = * alpha UMi = Polaris
22 29 10.3 +58 24 55 HR 8571 = * del Cep
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 106 77 Individuals interferometric V2 measurements
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See also:
J/A+A/428/587 : Cepheids BVRIJHK dereddened magnitudes (Kervella+, 2004)
J/A+A/281/465 : Chemical Composition of alf UMi and V473 Lyr (Andrievsky+ 1994)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- HR HR number (424 for Polaris, 8571 for delta Cep)
6- 13 F8.4 d jd-jd0 Julian date - jd0 (1)
16- 20 F5.3 --- phase pulsating phase
23- 29 F7.2 m u baseline projection toward East
32- 38 F7.2 m v baseline projection toward North
42- 47 F6.3 % V2 Wide band squared visibility in 1/100
50- 54 F5.3 % e_V2 Absolute error in V2
58- 63 I6 --- HDa HD of calibrator star A, (0 means no cal. A)
67- 71 F5.3 --- alpha Correlated errors matrix coef. (2)
75- 80 F6.4 % e_V2a Absolute error in V2 for cal. A (2)
84- 89 I6 --- HDb HD of calibrator star B, (0 means no cal. B)
93- 97 F5.3 --- beta Correlated errors matrix coef. (2)
101-106 F6.4 % e_V2b Absolute error in V2 for cal. B (2)
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Note (1): Julian date jd0 as follows:
jd0 = 2452700.5 for HR 424 (Polaris)
jd0 = 2453200.5 for HR 8571 (delta Cep)
Note (2): Quantities for computing the correlated errors matrix
(see Perrin, 2003A&A...400.1173P 2003A&A...400.1173P)
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Acknowledgements: Antoine Merand, antoine(at)chara-array.org
References:
Kervella et al., Paper I 2006A&A...448..623K 2006A&A...448..623K
(End) Antoine Merand [CHARA - Mt Wilson Observatory, USA] 20-Mar-2006