J/ApJ/718/L97 Early asteroseismic results from Kepler (Van Grootel+, 2010)
Early asteroseismic results from Kepler: structural and core parameters of the
hot b subdwarf KPD 1943+4058 as inferred from g-mode oscillations.
Van Grootel V., Charpinet S., Fontaine G., Brassard P., Green E.M.,
Randall S.K., Silvotti R., Ostensen R.H., Kjeldsen H.,
Christensen-Dalsgaard J., Borucki W.J., Koch D.
<Astrophys. J., 718, L97-L101 (2010)>
=2010ApJ...718L..97V 2010ApJ...718L..97V
ADC_Keywords: Stars, B-type ; Stars, variable
Keywords: stars: individual (KPD 1943+4058) - stars: interiors -
stars: oscillations - subdwarfs
Abstract:
We present a seismic analysis of the pulsating hot B subdwarf
KPD 1943+4058 (KIC 005807616) on the basis of the long-period,
gravity-mode pulsations recently uncovered by Kepler. This is the
first time that g-mode seismology can be exploited quantitatively for
stars on the extreme horizontal branch, all previous successful
seismic analyses having been confined so far to short-period, p-mode
pulsators. We demonstrate that current models of hot B subdwarfs can
quite well explain the observed g-mode periods, while being consistent
with independent constraints provided by spectroscopy. We identify the
18 pulsations retained in our analysis as low-degree (l=1 and 2),
intermediate-order (k=-9 through -58) g-modes. The periods
(frequencies) are recovered, on average, at the 0.22% level, which is
comparable to the best results obtained for p-mode pulsators. We infer
the following structural and core parameters for KPD 1943+4058 (formal
fitting uncertainties only): Teff=28050±470K, logg=5.52±0.03,
M*=0.496±0.002M☉, log(Menv/M*)=-2.55±0.07,
log(1-Mcore/M*)=-0.3±0.01, and Xcore(C+O)=0.261±0.008. We
additionally derive the age of the star since the zero-age extended
horizontal branch 18.4±1.0Myr, the radius R=0.203±0.007R☉,
the luminosity L=22.9±3.13L☉, the absolute magnitude
MV=4.21±0.11, the reddening index E(B-V)=0.094±0.017, and the
distance d=1180±95pc.
Description:
In this Letter, we exploit the exceptional data obtained on
KPD 1943+4058 by Kepler. We also obtained a low-resolution (9Å),
moderately high S/N (∼112 in the blue) spectrum of KPD 1943+4058 with
the Steward Observatory 2.3m Bok Telescope on 2008 12 June.
Objects:
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RA (2000) DE Designation(s)
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19 45 25.48 +41 05 33.8 KIC 005807616 = KPD 1943+4058
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 50 35 List of frequencies fn (n is by order of
decreasing amplitude) detected in KPD 1943+4058
table2.dat 80 79 Mode identification and other properties
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See also:
J/A+A/525/A23 : Frequency analysis of HD 49434 (Mathias+, 2011)
J/A+A/506/471 : Frequency analysis of CoRoT B stars (Degroote+, 2009)
J/A+A/506/111 : Frequency analysis of HD 180642 (V1449 Aql) (Degroote+, 2009)
J/A+A/506/79 : Asteroseismic analysis of HD 174936 (Garcia Hernandez+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- ID Mode identification (f1-f27, u1-u14)
7 A1 --- f_ID [*] *: pulsation period safely assumed to be
independent (18 periods used in the analysis)
9- 15 F7.2 s Per Period
17- 23 F7.3 uHz Freq Frequency
25- 28 F4.1 --- S/N Signal to noise ratio
30- 50 A21 --- Comm Comments
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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 I1 --- l [1/4] Degree
3- 5 I3 --- k [-63/-3] Radial order
7- 13 F7.3 uHz nuObs ? Observed frequency
15- 22 F8.3 uHz nuTh Theoretical frequency
24- 30 F7.2 s PObs ? Observed period
32- 38 F7.2 s PTh Theoretical period
40- 45 F6.3 [10-7J] logE Log of the energy; in erg
47- 52 F6.4 --- Ckl Ledoux coefficient
54- 58 F5.2 % DelX/X ? Relative dispersion (on P or ν)
60- 65 F6.2 s DelP ? Period dispersion ΔP
67- 72 F6.3 uHz Delnu ? Frequency dispersion Δν
74- 78 A5 --- ID Mode identification (f1-f27, u1-u14)
80 A1 --- f_ID [1/2] Flag on ID (1)
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Note (1): Flag as follows:
1 = Additional frequencies (see Table 1; un).
2 = Left-aside frequencies (see section 3.2 and Table 1).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 08-Jun-2012