Hobby-Eberly Telescope Witnesses Vaporizing of a Cometlike Body by a Very Young Hot Star

http://www.science.psu.edu/alert/Ge4-2004.htm

Hobby-Eberly Telescope Witnesses Vaporizing of a Cometlike Body by a Very Young Ho
t Star
Steve Miller
Pennsylvania State University
April 16, 2004

Evidence that a cometlike body with a diameter of at least 100
kilometers fell into a massive, very young star has been obtained by a team of
astronomers at Penn State using the 9.2-meter Hobby-Eberly Telescope at the
McDonald Observatory in Texas. "This discovery is significant because this is the
youngest star ever found with this kind of infall of a cometlike body," says Jian
Ge,
assistant professor of astronomy and astrophysics and the leader of the team. The
other scientists involved in the work are Abhijit Chakraborty, a postdoctoral
researcher in astronomy, and Suvrath Mahadevan, a graduate student, both at Penn
State.

The star, which astronomers identify as LkHalpha 234, is classified as a Herbig Be
star, which has a mass about six times the mass of the sun and an estimated very
young age of about 100,000 years. "This detection indicates that solid bodies of 1
00
km in size can form this early around a star," Ge explains. A report of the work w
ill
appear in the 1 May 2004 issue of Astrophysical Journal Letters.

The evidence of the infall comes from spectral analysis of the young star's
light, which has traveled about 3200 years to reach Earth. Five sets of
observations taken at intervals of 5 to 10 days during October and November
2003 indicated that the stellar light was absorbed by clouds of hydrogen
and helium surrounding the star as well as by emissions from these
clouds. "The spectacular appearances and disappearances of the
neutral-sodium-absorption lines on one particular observation and the
absence of its correlation with the hydrogen and helium lines suggests a
cometlike body," says Chakraborty. "We know how hot the star is and how
close to the star the neutral sodium atoms can survive. From that, and from
the motion of the cometlike body during infall onto the star, we calculated
how large the body would have to be to get this close to the star--one-tenth
of the distance between the Sun and the Earth--before vaporizing."

"This is a quite extraordinary event," said Eric Feigelson, Penn State
professor of astronomy and astrophysics, who specializes in the study of
young stars. "Something happened on a time scale of days or less that
created an enormous change in the spectrum of this star while the
astronomers were looking." According to Feigelson, evidence for cometary
infall has been seen in the spectrum of the nearby star beta Pictoris, which
is older and less massive than LkHalpha 234, but not with the dramatic
spectral variations seen here.

The infall provides new data for understanding planetary formation and
the timescale involved in the evolution of a massive star system. "The
main reason we see comets in our solar system is that large snowballs in
the outer parts of the solar system are disturbed by Jupiter's gravity,"
says Ge. "Eventually, some of the snowballs fall towards the inner solar
system and we see then as comets." The observed infall of a cometlike body
around LkH_234 may also point to disturbances produced by giant planets in
this young star system. The team is now monitoring a number of similar stars
and also LkH_234 in order to understand how common and how often this type
of cometlike body occurs around these young massive stars.

This research was funded by the National Aeronautics and Space Administration
and the National Science Foundation.

CONTACTS:
Jian Ge: , (+1)814-863-9553
Abhijit Chakraborty: (+1)814-863-6091
Barbara Kennedy (PIO): , (+1)814-863-4682