J/ApJ/459/278 Photometry of HD 3831 (Matthews+ 1996)
Opening a new window on Ap star atmospheres: a T-Tauri relation for HR 3831
from its limb-darkened pulsation amplitudes
Matthews J.M., Wehlau W.H., Rice J., Walker G.A.H.
<Astrophys. J. 459, 278 (1996)>
=1996ApJ...459..278M 1996ApJ...459..278M
ADC_Keywords: Stars, Ap ; Photometry ; Photometry, infrared
Keywords: stars: atmospheres - stars: individual (HR 3831) -
stars: oscillations - stars: peculiar
Abstract:
We demonstrate a new approach for probing the atmospheres of selected
chemically peculiar magnetic stars. Using the Cerro Tololo
Inter-American Observatory (CTIO) 1.0 and 1.5m telescopes
simultaneously on two nights in 1991, we obtained optical and infrared
high-speed photometry of the rapidly oscillating Ap (roAp) star HR
3831 (=HD 83368), which pulsates with a period of ∼11.8 minutes.
Oscillation amplitudes (or upper limits) in each of eight bandpasses
were measured by Fourier analysis, revealing the very steep decline in
amplitude with increasing wavelength characteristic of roAp stars.
Matthews and coworkers have shown that this can be explained by the
wavelength dependence of limb darkening and its filtering effect on
the integrated amplitude of an (l,m)=(1,0) nonradial pulsation mode.
Since the eigenfrequency spectrum of HR 3831 is dominated by just such
a dipole mode, it is possible to infer limb-darkening coefficients
beta(lambda) for its atmosphere from our amplitude measurements. These
coefficients are used to derive a source function through the
Eddington-Barber relation, which leads to a relation for temperature
versus optical depth in the stellar photosphere.
Our results show that the T-Tau(5000) curve is much steeper for HR
3831 than for the Sun (at least at the rotational phase when the
star's magnetic pole dominates the visible hemisphere). We also
calculate the gradient dT/dtau as a function of wavelength to compare
with the curve expected for H- continuous opacity. This type of
diagnostic may become a useful tool for checking the predictions of
diffusion theory.
Objects:
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RA (2000) DE Designation(s)
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09 36 25.3 -48 45 04 HR 3831 = HD 83368
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
hr3831b.dat 17 151 Differential photometry, b bandpass
hr3831v.dat 17 152 Differential photometry, v bandpass
hr3831y.dat 17 152 Differential photometry, y bandpass
hr3831r.dat 17 144 Differential photometry, R bandpass
hr3831i.dat 17 141 Differential photometry, I bandpass
hr3831j.dat 17 91 Differential photometry, J bandpass
hr3831h.dat 17 92 Differential photometry, H bandpass
hr3831k.dat 17 92 Differential photometry, K bandpass
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Byte-by-byte Description of file: hr3831?.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 d HJD-2448000 Heliocentric Julian Date - 2448000
11- 17 F7.4 mag dMag Differential magnitude normalized to the mean
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Origin: AAS CD-ROM series, Volume 6, 1996 Lee Brotzman [ADS] 22-Apr-96
(End) [CDS] 06-Sep-1996