Marcy & Butler - 1

From: Dan Werthimer <danw@ssl.Berkeley.EDU>
To:
Cc:
Subject: Transit of Planet
Date: Friday, November 12, 1999 11:55 PM

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Hi Dan,

Please forward this exciting news.

Geoff

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Transit of HD209458 
     G.Henry, Tennessee State Univ, G.Marcy, U.C. Berkeley,
R.P.Butler, Dept. of Terrestrial Magnetism, and S.S.Vogt, UCO Lick
Observatory report that HD 209458 (G0V) exhibits sinusoidal velocity
variations with semi-amplitude of 81 m/s, indicating presence of a
companion with Msini = 0.63 Jupiter masses and an orbital period of
3.523 d.

     Photometry reveals a transit ingress at JD 2451490.70 
with depth of 0.017 mag, consistent with the transit time predicted
from the velocities.  Further measurements of transits and velocities
would be valuable.  The next three predicted times of ingress
occur at UT times: 15 Nov 6:19, 18 Nov 18:53, 22 Nov 7:28, all
times uncertain by 1 hour.

     If correct, the inferred mass is 0.63 Mjup and radius is 1.6
Rjup, implying a density of 0.21 g/cc .  The enlarged radius is
consistent with models of Jovian planets thermally expanded by stellar
radiation (Saumon et al. 1996; Burrows et al.  1998).  HD 209458 resides
at a distance of 47 pc, with rotational Vsini = 3 km/s, and is 
chromospherically inactive, with an estimated age of 4.5 Gyr.  
Coordinates: RA = 22 03 10.7, DEC = +18 53 04 (2000), Vmag=7.65.

11/15/99 - File #
Contact: Robert Sanders, (510) 643-6998, rls@pa.urel.berkeley.edu

Astronomrs see silhouette of planet
cross distant star, proving
that extrasolar planets are real

FOR IMMEDIATE RELEASE

	Berkeley - Astronomers have witnessed for the first time a 
distant planet passing in front of its star, providing direct and 
independent confirmation of the existence of extrasolar planets that 
to date have been inferred only from the wobble of their star.
	"This is the first independent confirmation of a planet, and 
it also gives us the first-ever measure of the size of one of these 
planets," said Geoffrey Marcy, a professor of astronomy at the 
University of California, Berkeley.
	Marcy and his colleagues, Paul Butler of the Dept. of 
Terrestrial Magnetism at the Carnegie Inst. of Washington
and Steve Vogt of UC Santa Cruz and 
Lick Observatory, first detected a wobble in the star called HD 
209458 on Nov. 5. Ascribing the wobble to a nearby planet, they were 
able to estimate its orbit and approximate mass.
	As with all new planets they detect, the team immediately 
brought it to the attention of a collaborator at Tennessee State 
University, astronomer Greg Henry, who works at the Center of 
Excellence in Information Systems. He operates several telescopes at 
the privately funded Fairborn Observatory in the Patagonia Mts. of 
southern Arizona.
	Henry turned his automated telescope on the star at the time 
Marcy and Butler predicted the planet would cross the face of the star IF the 
planet's orbital plane were lucky enough to carry it between Earth 
and the star. Until now, none of the 18 other extrasolar planets 
Marcy and Butler have discovered has had its orbital plane oriented 
edge-on to Earth so that the planet could be seen to transit the 
star, nor have any of the other planets discovered by other 
researchers.
	This time, however, on Nov. 7, Henry observed a 1.7 percent 
dip in the star's brightness. Because the planet orbits its star once 
every 3.523 days, he was able to repeat the measurement on Nov. 14.
	"This planetary transit occurred at exactly the time 
predicted from Marcy's observations, confirming absolutely the 
presence of a companion," Henry said. "This says that our indirect 
evidence for planets, the change in radial velocity of the star, 
really is due to planets. We've essentially seen the shadow of the 
planet."
	The star HD 209458 is 47 parsecs (153 light years or 1.4 
million billion kilometers or 859,000 billion miles) away in the 
constellation of Pegasus, and is about the same age, color and size 
as our own Sun. It is very near the star, 51 Pegasi, around which the 
first extrasolar planet was discovered in 1995.
	With the orbital plane of the planet known, the astronomers 
for the first time could determine precisely the mass of the planet 
and its density.
	Interestingly, while the planet's mass is only about 
two-thirds (63 percent) of Jupiter's mass, its radius is 60 percent 
bigger than that of Jupiter. This fits with theories that predict a 
bloated planet when, as here, the planet is very close to the star.
	The density, about 0.2 grams per cubic centimeter, means it is 
a gas giant like Jupiter. However, such gas giants could not have 
formed at the distance this planet is from its star, Henry said.
	Various groups around the world have been searching for 
planets by looking for dimming of stars., or as Marcy says, "staring 
at the sky and seeing if any star blinks." To date, none of these 
searches has turned up a new planet.
	"With this one, everything hangs together," Marcy said. "This 
is what we've been waiting for."
					###

To be published in the Astrophysical Journal, Univ. Chicago Press.

The research was supported by NASA, the National Science Foundation, and
Sun Microsystems.
Geoff Marcy can be reached at gmarcy@etoile.Berkeley.EDU; Greg Henry 
is at henry@schwab.tsuniv.edu; Paul Butler is at paul@dtm.ciw.edu; 
and Steve Vogt is at vogt@ucolick.org

--Bob Sanders, Senior Science Writer
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