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Astron. Astrophys. 343, 137-150 (1999)
Episodic accretion around the Herbig Ae star BF Orionis *
Evidence for the presence of extra-solar comets
D. de Winter ** 1,2,
C.A. Grady 3,
M.E. van den Ancker 4,
M.R. Pérez 5 and
C. Eiroa 1
1 Departemento Física Teórica, C-XI,
Facultad de Ciencias, Universidad Autónoma de Madrid,
Cantoblanco, E-28049 Madrid, Spain
2 Centro de Astrofísica de Universidade do
Porto, Rua Campo Alegre 823, 4150 Porto, Portugal
3 Eureka Scientific, 2452 Delmar St., Suite 100,
Oakland, CA 94602, USA
4 Astronomical Institute "Anton Pannekoek", University
of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
5 Space Applications Corp., 9315 Largo Drive West,
Suite 250, Largo MD 20774, USA
Received 5 June 1998 / Accepted 2 December 1998
Abstract
The results of a monitoring programme of high and intermediate
resolution spectra covering He I 5876 Å,
Na I ![[FORMULA]](img1.gif)
and
H![[FORMULA]](img2.gif)
of the isolated Herbig Ae star BF
Ori are presented. We detect the presence of blue and redshifted
emission and absorption components of these lines which vary from
day-to-day with correlated changes suggesting a similar origin.
The appearance, strength and variations of the redshifted
Na I D absorption component on a time scale of
days show variable accretion activity similar to that seen toward the
Herbig Ae star UX Ori and ![[FORMULA]](img3.gif)
Pic,
suggesting evaporation of star-grazing bodies. We estimate for one
event that such a body is kilometer sized, evaporates at a distance of
about 0.4 AU from the central star and has a mass comparable to comets
in the solar system.
A dependence was found of the H
line profile on the photometric brightness of BF Ori similar to that
observed for UX Ori. It is evidence for obscuration of a dense dusty
body located in the outer disk regions as no extra absorption
components from a gaseous content and no direct influences on the
cometary activity were observed. More complex variations of the
H profile could be explained in part
by absorption of star-grazer material, equal to the absorption at the
sodium lines, and in part by obscuration of its line forming region by
the cometesimal. More evidences for detections of revolving clumpy
material are: observed changes in the velocity direction of the very
strong Na I low
velocity absorption components and the observed flip over of the
relative strength of the blue and red peak of
H simultaneous with the change of blue
to redshifted absorption components in both the Na I
and He I lines. In
case of orbiting bodies, the estimated period lies between 60 and 100
days with a distance from 0.35 to 0.57 AU, respectively.
The detection of possible orbiting and comet-like objects in the
disk of BF Ori, a ![[FORMULA]](img4.gif)
Myr old pre-main
sequence A5-6 IIIe star, making it a possible progenitor of the
HR 4796 (protoplanetary) disk system, suggests the existence of
structures similar to those probably present in the solar system at a
time of formation of planetesimals. The estimated much higher than
cosmic abundances of refractory (Na) over volatile (H, He) gases for
the detected bodies supports this suggestion.
Key words: comets:
general 
stars:
emission-line
stars: individual:
Beta Pic
stars: individual:
BF Ori
stars: individual:
UX Ori
stars: pre-main sequence
* Based on observations made at the European Southern Observatory, La Silla, Chile.
** Current address: Instituto de Astrofísica de Canarias, C/ Via Láctea s/n, E-38200 La Laguna, Tenerife, Spain
Send offprint requests to: D. de Winter (dolf@astro1.ft.uam.es; dwinter@iac.es)
Contents
- 1. Introduction
- 2. BF Ori: background and astrophysical parameters
- 3. Observations
- 4. Analysis of the spectra
- 5. The spectral features discussed
- 6. Size of the October, 1993, comet-like body
- 7. Comparison with other Herbig Ae/Be stars
- 8. Model interpretations and results
- 9. Concluding remarks
- Acknowledgements
- References
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999
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