Mechanisms for eclipsing in exotic eclipsing systems
ABSTRACT The stars ε Aur, KH 15D, and H 187 are utterly different in their fundamental characteristics. However, they share two important
features: (1) prolonged eclipses are observed in all three and (2) there are no spectroscopic signs of a second component.
The light curves of these objects are substantially similar, which may indicate a uniform mechanism for the eclipses. This
article analyzes models for eclipsing in these objects proposed by different authors and discusses the problems associated
with their application.
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Article: KH 15D: A Spectroscopic Binary[show abstract] [hide abstract]
ABSTRACT: We present the results of a high-resolution spectroscopic monitoring program of the eclipsing pre–main-sequence star KH 15D that reveal it to be a single-lined spectroscopic binary. We find that the best-fit Keplerian model has a period P = 48.38 days, which is nearly identical to the photometric period. Thus, we find the best explanation for the periodic dimming of KH 15D is that the binary motion carries the currently visible star alternately above and behind the edge of an obscuring cloud. The data are consistent with the models involving an inclined circumstellar disk, as recently proposed by Winn et al. and Chiang & Murray-Clay. We show that the mass ratio expected from models of pre–main-sequence evolution, together with the mass constraints for the visible star, restrict the orbital eccentricity to 0.68 ≤ e ≤ 0.80 and the mass function to 0.125 M ≤ FM/ i ≤ 0.5 M.The Astronomical Journal 12/2007; 128(3):1265. · 4.97 Impact Factor
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ABSTRACT: We present moderate-resolution optical spectra of the highly variable Herbig Ae star RR Tauri over 12 epochs spanning ~2.5 mag in V. Combining normalized spectra with contemporaneous photometry from two databases, we analyze both equivalent width and flux behavior as a function of system brightness for lines from the Ca II K line in the blue to the Paschen lines in the far red. The wings (Δv > 400 km s-1) of the Balmer lines and the equivalent widths of several weak metal lines are essentially constant, indicating very little change in the underlying photosphere over a factor of 10 change in brightness. We detect no measurable change in spectral type. Variability is apparent in the cores of Hα and Hβ, but the total flux in these lines is not correlated with photometric variability. Forbidden oxygen ([O I] λ6300) has essentially constant flux, indicating a stable low-density wind component. The low-ionization permitted lines of Fe II, Ca II, O I, and Na I are seen strongly in absorption for V ≤ 12.2 in these normalized spectra but change dramatically from absorption to emission during deep minima (V 12.6). Analysis of the Fe II (42) triplet indicates that these lines originate in circumstellar gas that is partially affected by the photometric minima, in that the absorbing gas changes with the stellar continuum (conserving equivalent width), while a weak emitting region is unaffected (roughly constant flux). Our results are consistent with a model in which the stellar minima are caused by an occulting screen of size such that it obscures the stellar surface and the innermost region of circumstellar gas producing permitted metal absorption lines but not the outer parts or the wind. The circumstellar hydrogen, while variable, is not strongly affected by the occultations.The Astrophysical Journal 12/2008; 564(1):405. · 6.73 Impact Factor
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ABSTRACT: Model calculations of the sodium ionization and excitation conditions in winds from T Tauri stars are reported. Line profiles for the sodium D doublet resonance lines are computed and compared to the observations. It is found that, in order to reproduce the observed features, the line optical depth, which is proportional to the neutral sodium column density in the wind, must be restricted to a narrow range (0.3 less than tau less than 3 for the blue component of the doublet). Tau is a strong function of the mass-loss rate M, but it is rather insensitive to the wind temperature Tg. By using both the values of tau inferred from the observed Na line profiles for a given object and the observed luminosity of hydrogen recombination lines, it is possible to obtain with good accuracy both Tg and M. The possible influence of different wind acceleration laws, of fast turbulent motions, of different stellar radiation fields (including photospheric lines), and of circumstellar disks are discussed. The method proposed to measure Tg and M turns out to be rather robust and insensitive to a variety of effects. The application to a restricted sample of T Tauri stars indicates Tg between 6000 K and 6500 K and mass-loss rates between 3 x 10 to the -8th and 3 x 10 to the -7th solar mass/yr. The winds are mostly neutral, and the mass-loss rates are in excellent agreement with those required to drive the associated CO outflows with a momentum-conserving shock.The Astrophysical Journal 05/1990; 356:646-661. · 6.73 Impact Factor