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J/ApJ/459/278            Photometry of HD 3831 (Matthews+ 1996)
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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
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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:
    ----------------------------------------------------------
       RA   (2000)   DE    Designation(s)
    ----------------------------------------------------------
    09 36 25.3 -48 45 04   HR 3831 = HD 83368
    ----------------------------------------------------------

File Summary:
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 FileName    Lrecl    Records   Explanations
--------------------------------------------------------------------------------
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: hr3831b.dat, hr3831v.dat, hr3831y.dat
Byte-by-byte Description of file: hr3831r.dat, hr3831i.dat, hr3831j.dat
Byte-by-byte Description of file: hr3831h.dat, hr3831k.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
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(End)                                                         [CDS]  06-Sep-1996