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Started by Larry Klaes
Tue, 07 Apr 1992 23:25
Electronic Journal of the ASA - April 1992
Author: Larry Klaes
Date: Tue, 07 Apr 1992 23:25
Date: Tue, 07 Apr 1992 23:25
438 lines
22815 bytes
22815 bytes
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Moderator's Note:
I'm posting this issue of the EJASA since it was sent to sci.astro.hubble as
a test posting. Does the readership think this is appropriate, since it is
carried by sci.astro too? Please email me your opinions.
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THE ELECTRONIC JOURNAL OF
THE ASTRONOMICAL SOCIETY OF THE ATLANTIC
Volume 3, Number 9 - April 1992
###########################
TABLE OF CONTENTS
###########################
* ASA Membership and Article Submission Information
* The 179th Meeting of the American Astronomical Society (AAS):
A Volunteer's View - Ingrid Siegert-Tanghe
* The Partial Eclipse of March 22, 1992 - Tom Polakis
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ASA MEMBERSHIP INFORMATION
The Electronic Journal of the Astronomical Society of the Atlantic
(EJASA) is published monthly by the Astronomical Society of the
Atlantic, Incorporated. The ASA is a non-profit organization dedicated
to the advancement of amateur and professional astronomy and space
exploration, as well as the social and educational needs of its members.
ASA membership application is open to all with an interest in
astronomy and space exploration. Members receive the Journal of the
ASA (hardcopy sent through United States Mail - Not a duplicate of this
Electronic Journal) and the Astronomical League's REFLECTOR magazine.
Members may also purchase discount subscriptions to ASTRONOMY and
SKY & TELESCOPE magazines.
For information on membership, you may contact the Society at any
of the following addresses:
Astronomical Society of the Atlantic (ASA)
c/o Center for High Angular Resolution Astronomy (CHARA)
Georgia State University (GSU)
Atlanta, Georgia 30303
U.S.A.
asa@chara.gsu.edu
ASA BBS: (404) 985-0408, 300/1200/2400 Baud.
or telephone the Society Recording at (404) 264-0451 to leave your
address and/or receive the latest Society news.
ASA Officers and Council -
President - Don Barry
Vice President - Nils Turner
Secretary - Ingrid Siegert-Tanghe
Treasurer - Mike Burkhead
Directors - Bill Bagnuolo, Eric Greene, Tano Scigliano
Council - Bill Bagnuolo, Bill Black, Mike Burkhead, Frank Guyton,
Larry Klaes, Ken Poshedly, Jim Rouse, Tano Scigliano,
John Stauter, Wess Stuckey, Harry Taylor, Gary Thompson,
Cindy Weaver, Bob Vickers
ARTICLE SUBMISSIONS -
Article submissions to the EJASA on astronomy and space exploration
are most welcome. Please send your on-line articles in ASCII format to
Larry Klaes, EJASA Editor, at the following net addresses or the above
Society addresses:
klaes@verga.enet.dec.com
or - ...!decwrl!verga.enet.dec.com!klaes
or - klaes%verga.dec@decwrl.enet.dec.com
or - klaes%verga.enet.dec.com@uunet.uu.net
You may also use the above addresses for EJASA back issue requests,
letters to the editor, and ASA membership information.
When sending your article submissions, please be certain to include
either a network or regular mail address where you can be reached, a
telephone number, and a brief biographical sketch.
DISCLAIMER -
Submissions are welcome for consideration. Articles submitted,
unless otherwise stated, become the property of the Astronomical
Society of the Atlantic, Inc. Though the articles will not be used for
profit, they are subject to editing, abridgment, and other changes.
Copying or reprinting of the EJASA, in part or in whole, is encouraged,
provided clear attribution is made to the Astronomical Society of
the Atlantic, the Electronic Journal, and the author(s). Opinions
expressed in the EJASA are those of the authors' and not necessarily
those of the ASA. This Journal is Copyright (c) 1992 by the
Astronomical Society of the Atlantic, Inc.
THE 179TH MEETING OF THE AMERICAN ASTRONOMICAL SOCIETY (AAS):
A VOLUNTEER'S VIEW
by Ingrid Siegert-Tanghe
The 179th meeting of the American Astronomical Society (AAS)
was held in Atlanta, Georgia on January 12-15, 1992 at the Marriot
Marquis hotel. For the 1,247 astronomers who attended, the meeting
was an opportunity to present their latest discoveries and research
to their colleagues and the world. For the ASA members and students
who volunteered their help during the meeting, it was an opportunity
to hear about the astronomers' exciting work first hand and rub
shoulders with some of the great astronomers of our time. Over
thirty-five Society members took part, either as Georgia State
University (GSU) organizers or as amateur volunteers.
The news briefs which follow are a combination of press releases
and the notes I took at the press conference. In some cases I will
directly quote the press releases and identify the sources. There
is much information to pass on. In this article I will report on
the major AAS announcements. In a later article I will cover other
celestial discoveries and some interesting research that is currently
being conducted.
Pulsars, Planets, and Neutron Stars -
The announcement in July of 1991 by Dr. Andrew Lyne and his
colleagues of the Jodrell Bank radio observatory in England of
their discovery of planets around the pulsar PSR 1829-10 rocked the
astronomical world. At the AAS meeting, Dr. Lyne announced that their
findings were in error. They had failed to compensate for slight
variations in Earth's orbital motion around the Sun. When this was
taken into account, Dr. Lyne said the "planet just evaporated."
In a letter to the British journal NATURE, Dr. Lyne said,
"Although there is no planet orbiting PSR 1829-10, pulsar timing
remains the most sensitive technique for detecting planets outside
the solar system."
Another discovery of planets beyond our solar system was announced
on January 9 in the journal NATURE. By timing the arrival of radio
signals from a rapidly spinning pulsar to the Arecibo Observatory's
radio/radar telescope in Puerto Rico, Alexander Wolszczan and Dale
Frail have found the strongest evidence so far for a planetary system
outside our own: Two or possibly three planets that orbit the neutron
star PSR1257+12.
Dr. Wolszczan discussed their findings in further detail at the
AAS meeting, noting that they had double-checked the pulsar's position
and the timing of radio fluctuations, ruling out the mistakes made by
Dr. Lyne.
A long series of observations that Wolszczan made between July of
1990 and November of 1991 revealed the following information about the
pulsar and its apparent planetary system:
"PSR1257+12 is an old pulsar, with more than one billion years
having elapsed since it and a binary companion were formed as ordinary
stars, out of a gravitationally contracting interstellar cloud. Some
10 million years after the binary formation, the more massive of the
pair underwent a supernova explosion and its collapsed core became a
neutron star."
Further evolution of the remaining stellar companion caused
accretion of some of its expanding envelope onto the neutron star.
This process helped to spin the pulsar up to a 6.2 millisecond
rotation period observed today. The companion itself probably had
been vaporized by the pulsar's high energy radiation and supplied
material for a formation of planets that are now seen orbiting
PSR1257+12.
Two planets are orbiting PSR1257+12 about 53.6 million and 69.92
million kilometers (33.5 million and 43.7 million miles) from the
pulsar, about the same distance that Mercury is from the Sun. Both
are moving in nearly circular orbits, taking 66.6 and 98.2 Earth days
to complete each revolution.
A detailed analysis of the observations made to date suggest
the existence of one more planet circling the pulsar about 1.1
Astronomical Units (AU) away and with an orbital period close to
one Earth year.
The newly discovered planets' masses are greater than that of
Earth, at about 2.8 and 3.4 masses. "In principle, they are massive
enough to retain atmospheres. But it is likely that any atmosphere
would be blown away by the pulsar wind," Wolszczan said. In density,
composition, and size, these planets may be not unlike Earth or Venus.
Responding to the gravitational pull of its planets, PSR1257+12
is wobbling in space. It is that wobble which affected the precisely
measured arrival times of pulsar signals at the Arecibo telescope and
allowed the detection of the planets.
Dr. Wolszczan said that a few more years of observation will be
required for absolute proof. Dr. Frederic Rasio and his colleagues
from Cornell University believe they can supply the proof fairly soon.
The Cornell astronomers point out that, if the interpretation of the
observations in terms of orbiting planets is correct, then additional
perturbations corresponding to the mutual gravitational interactions
between the planets themselves should be present in the data of
Wolszczan and Frail.
Dr. Marco Tavani of the Institute of Geophysics and Planetary
Physics at Lawrence Livermore National Laboratory presented a theory
to the AAS on the formation of planets orbiting millisecond pulsars.
The new theory explains that the newly discovered planets may be
the final remnants of a companion star completely vaporized by the
pulsar's energetic radiation. Planetary formation can occur in two
different ways. According to the first scenario, the planets form
after the pulsar has been created and has begun to vaporize its
companion by irradiation. According to the second scenario, there is
a binary star system evolving into an isolated millisecond pulsar, and
the planets form when the neutron star is receiving matter from and
being "spun-up" by its companion. In both cases, the vaporized
material can produce a gravitationally-bound disk of matter from
which planets can form.
Cornell University News Service, NATURE, THE NEW YORK TIMES,
Dr. Marco Tavani
Wisconsin Scientists Discover a Hot Spot on a Pulsar -
Scientists from the University of Wisconsin-Madison reported the
discovery of a pulsar with a "hot spot" on its surface, a finding that
seems to pinpoint the source of the distinctive pulsations of energy
that give pulsars their name.
Using the X-ray satellite ROSAT to measure the surface temperature
of a nearby pulsar, astrophysicists John P. Finley, Hakki Ogelman, and
Umit Kiziloglu found a hot patch on the star that swept through the
satellite's line of sight once every rotation.
The pulsar in question, according to Finley, is an unnamed pulsar
situated just 1,500 light years from Earth. Smaller that Manhattan
Island, the pulsar has a hot spot on its surface which is about four
percent hotter than the rest of the surface of the star.
The X-rays emitted by the star are higher in energy at precisely
the same time the pulsed X-ray emission is greatest.
"The whole star is glowing with X-rays and when you see this hot
spot, your counts go up," Finley said. "We can't say for certain that
the radio beacon is coincident with the hot spot, but it's certainly a
reasonable assumption to make."
University of Wisconsin-Madison News and Information Service
First Supernova of 1992 -
Supernova 1992A was discovered on January 10 by William Liller
of Vina del Mar in Chile. Scientists at NASA's Goddard Space Flight
Center (GSFC) confirmed the observation on January 13 with the
International Ultraviolet Explorer (IUE) satellite. Astrophysicist
George Sonneborn directed the pointing of IUE from Atlanta while
attending the AAS meeting.
The Type Ia supernova had a visual brightness of 12.8 magnitude
when it was discovered. It is located in the spiral galaxy NGC 1380
in the constellation Fornax.
Cosmic Dark Matter Mapped -
Dr. J. Anthony Tyson et al announced that they have been able to
map the invisible cosmic "dark matter" in many giant clusters of
galaxies.
The Universe is thought to contain much more dark matter than
stars and gas. The significance of this latest research is that it
is now possible to directly map the dark matter concentrations. The
image warping of background galaxy images due to the gravitational
pull of the foreground dark matter is used to reconstruct a fuzzy
picture of the dark matter.
Hubble Space Telescope (HST) Investigations -
Black Hole in M87: Astronomers report that they have found
evidence that a black hole weighing over 2.6 billion times the mass
of the Sun exists at the center of the giant elliptical galaxy M87.
Images from HST show that stars become strongly concentrated towards
the center of the galaxy, as if drawn into the center and held there
by the gravitational field of a massive black hole. The results were
reported by Dr. Tod R. Lauer of the National Optical Astronomy
Observatories to the AAS meeting.
Early in the Twentieth Century astronomers discovered a gigantic
jet of plasma being ejected out of the M87 nucleus. The jet and
nucleus were found to emit strong radio and X-ray radiation. The
cause of this activity remained a mystery until the HST observations.
HST has revealed the density of stars in M87 increases abruptly
toward the core. It is, in fact, five hundred times denser than
thought from ground observations. Stars once freely orbiting in and
out of the M87 core are being gradually pulled toward the center and
then into orbits closely bound to the black hole. The whole core of
the galaxy thus smoothly collapses inward, and the density of stars
near the very center becomes extreme.
High resolution spectra from HST will confirm with certainty the
existence of the black hole. This will unfortunately have to wait
until HST is repaired. Dr. Lauer is convinced that this is a black
hole, but is reluctant to state with certainty its existence until all
the tests have been performed. "It looks like a duck but we haven't
heard it quack yet," he observed.
Planetary Nebula in the Large Magellanic Cloud: HST has imaged
N66, a planetary nebula in the Large Magellanic Cloud. The image
was obtained at 10:41 EDT on June 26, 1991, using the European Space
Agency's (ESA) Faint Object Camera (FOC). This is the first time a
planetary nebula has ever been seen so clearly in a galaxy beyond our
own Milky Way. N66 is located 169,000 light-years from Earth. The
FOC image reveals complex details as small as 0.1 arcseconds. The
nebula was ejected by a luminous red giant star, which subsequently
contracted to form a blue remnant star.
NGC 1275 Star Clusters: Dr. Jon Holtzman of Lowell Observatory
announced the discovery of fifty bright, young massive globular
clusters at the center of NGC 1275. Holtzman and his colleagues were
observing this galaxy in Perseus because of its peculiarities observed
from the ground. What they discovered was another strange feature.
Globular clusters are among the oldest objects in the Universe. To
find the blue, young clusters in the center was a surprise.
NGC has such a peculiar shape, some astronomers previously have
suspected that it may actually be two galaxies - a giant elliptical
galaxy and a smaller spiral galaxy - passing through one another.
Holtzman suggests that the clusters may have formed as a result of
just such a merger or collision.
NGC 1275 lies at the heart of the Perseus cluster of galaxies, a
rich collection of more than five hundred galaxies. The galaxy is
surrounded by a luminous halo of hot gas, which glows in X-rays.
Gravity pulls this superheated gas into the galaxy as a "cooling
flow", which produces filaments. This cooling, condensing gas might
also produce newborn stars.
Space Telescope Science Institute
Coming soon: More AAS reports containing exciting investigations
of gamma-ray bursts, supernovae, binary pulsars, the Pleiades star
cluster, and the origin of the Universe.
About the Author -
Ingrid Siegert-Tanghe is Secretary to the Astronomical Society of
the Atlantic and past (as well as present) member of the Louisville
Astronomical Society, where she served in several officer positions.
Her interests are computer-controlled telescopes and learning more
about the science of astronomy.
THE PARTIAL ECLIPSE OF MARCH 22, 1992
by Tom Polakis
There was only one message on my telephone answering machine
when I got home at eleven p.m. on Saturday, March 21. It was Pierre
Schwaar's voice from three hours earlier, inviting me over to watch
a partial eclipse of a moon. Not Earth's moon, but Ganymede, the
largest of Jupiter's four Galilean satellites.
The circumstances were such that the relatively tiny shadow of
the smallest Galilean moon, Europa, was to be cast onto the surface of
Ganymede at 1:00 the next morning. Having seen another in a series of
weekend downpours earlier that day, and knowing that I was going to be
viewing with Mr. Pierre Schwaar - that magnetic attractor of clouds -
it took a lot of contemplation before deciding that it was worth the
trip to his house in Phoenix, Arizona.
Sure enough, when I arrived, hanging overhead was what seemed to
be an endless stream of mid-level clouds which Pierre claimed were
forming over his backyard. We had intermittent views of the giant
Jovian planet before the event began through Jim Stevens' binocular
viewer on Pierre's fifty-centimeter (twenty-inch) telescope. After
tweaking the collimation on his viewer, Jim was able to convince me
in no time how much better the planet looked when viewed through both
eyes. The seeing conditions were decent enough to easily show the
difference in size between the disks of Europa (one arcsecond) and
Ganymede (1.7 arcseconds). Ganymede shone almost a magnitude brighter
than Europa, about ten arcseconds further out from Jupiter.
For the first one-half hour of the eighty-minute event, the clouds
got the better of us. What appeared to be a clearing line never
materialized - Pierre was going to miss yet another eclipse! Finally,
however, the cloud show finally abated and we were treated to an
unforgettable sight. The atmosphere was now steady enough to show
that something was definitely 'wrong' with Ganymede's disk. It was
no longer round but appeared to show an oval form. Looking closer
still at over 300x with his fifty-centimeter stopped down to forty
centimeters (sixteen inches), Pierre claimed to be seeing the actual
"bite" out of the satellite's disk. Jim verified this claim and even
identified that the bite was taken out of the northern hemisphere of
the moon.
After a prolonged look, I finally saw the 'kidney bean' shape of
Ganymede. This became clearer as the seeing improved, and for the
next twenty minutes we watched as the shadow receded from the disk
of Ganymede. Viewing at a similar magnification with the conventual
monocular view, the spectacle was not nearly as obvious. The only
apparent feature at mid-eclipse was the brightness of Ganymede, which
had dropped to approximately that of Europa.
This event showed us what can be seen by pushing high resolution
observing to its limit. There will not be many more of these satel-
lite phenomena left in this series for several years, as the orbital
plane geometry of the moons becomes unfavorable. Probably the high-
light of the event was that, after a daunting string of cloudouts,
Pierre finally did get to see an eclipse. It was of a two-arcsecond
Galilean moon, but at least it was an eclipse.
Related EJASA articles -
"The Ice Moons of the Jovian Worlds", by Craig M. Levin - March 1990
"Viewing Jupiter's Galilean Moons with the Unaided Eye", by Alan
William Paeth - July 1990
About the Author -
Tom Polakis is member of the Saguaro Astronomy Club (SAC). Tom
is an avid amateur astronomer currently residing in Mesa, Arizona.
He has had articles and photographs published in such magazines as
SKY & TELESCOPE, ASTRONOMY, and DEEP SKY.
Tom's E-mail address is: 70413.1543@compuserve.com
THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC
April 1992 - Vol. 3, No. 9
Copyright (c) 1992 - ASA
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