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               |                                    | 
               |          Biuletyn PTA nr 7         | 
               |                                    | 
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  Biuletyn informacyjny Zarzadu Glownego Polskiego Towarzystwa Astro- 
  nomicznego (Adres kontaktowy: M. Ostrowski, pta@oa.uj.edu.pl ,
  a w bardzo pilnych sprawach: mio@oa.uj.edu.pl ) 
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Spis tresci: 
 
   I.   Strona WWW PTA znowu aktualna  
   II.  Ogloszenie: Stanowiska adiunkta w CA UMK  
   III. Nowinki astronomiczne  
 
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   I.   Strona WWW PTA znowu aktualna: http://phobos.camk.edu.pl/pta/  

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   II.  Ogloszenie  


Dziekan Wydzialu Fizyki I Astronomii Uniwersytetu M.Kopernika w Toruniu
                               oglasza 
                   KONKURS NA DWA STANOWISKA ADIUNKTA 
                       w Centrum Astronomii UMK.


W wypadku odpowiednio wysokich kwalifikacji kandydata, mozliwe bedzie
zatrudnienie na wyzszym stanowisku.

Centrum Astronomii oferuje szerokie mozliwosci prowadzenia badan
astrofizycznych z Katedrze Astronomii i Astrofizyki oraz Radioastronomii
zarowno przy pomocy posiadanych przez siebie instrumentow jak rowniez przez
istniejace i planowane programy wspolpracy miedzynarodowej. W posiadaniu
Centrum znajduje sie miedzy innymi niedawno oddany do uzytku, nowoczesnie
wyposazony 32-metrowy radioteleskop, oraz intensywnie modernizowany
90-centymetrowy teleskop Schmidta.

Centrum uczestniczy w miedzynarodowych programach interferometrii
wielkobazowej (VLBI, VSOP), chronometrazu pulsarow i jest w trakcie staran 
o wlaczenie sie wraz z innymi osrodkami w kraju do projektu budowy
10-metrowego teleskopu optycznego SALT w Afryce Poludniowej.

W Centrum prowadzone sa miedzy innymi badania poznych stadiow ewolucji
gwiazd, materii miedzygwiazdowej, pulsarow oraz radiozrodel
pozagalaktycznych.

Kandydaci powinni legitymowac sie doktoratem z astronomii lub fizyki oraz
udokumentowanymi osiagnieciami w dziedzinie astrofizyki.

Obok podania z zyciorysem oraz listow referencyjnych wymagane jest opisowe
przedstawienie planow dzialalnosci naukowej w Centrum.

Kandydatury beda rozpatrywane do czasu obsadzenia wszystkich stanowisk,
ktorymi dysponuje Centrum.


Termin zgloszen uplywa 15 czerwca 1998r.


From: Romuald Tylenda <tylenda@astri.uni.torun.pl>

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III. Nowinki astronomiczne  

THE STRONGEST GRAVITATIONAL FIELDS EVER
MEASURED, corresponding to a spacetime warping of 30%, have
been recorded by scientists using the Rossi X-Ray Timing Explorer
(RXTE) satellite.  By comparison, the proportional curvature of space
is 100% at a black hole, but only about one part in a million near the
sun's surface and one part per billion near the Earth's surface. RXTE
was designed to monitor (over microsecond time intervals) the x rays
coming from binary star systems in which matter from a conventional
star is siphoned off into an accretion disk surrounding a nearby
neutron star or black hole. In about 16 binary-star systems that
contain neutron stars, blobs of gas in the disk are thought to spiral in
toward the neutron star, picking up speed before they make a final
plunge onto the surface. The x rays produced in this process are
regularly dimmed when the hot gas is on the far side of the star.  This
leads to quasi-periodic oscillations (QPOs) in the x-ray brightness of
the star.  Also notable is the fact that the brightness variations only
occur at certain well-defined rates, "pure tones" corresponding to
special orbital periods for the gas going around the star. The
spacetime encountered by the gas is so highly warped because the gas
is able to skim within a few km of the neutron star, which itself is only
about 10 km in diameter.  At this week's meeting of the American
Physical Society in Columbus, Ohio, Frederick Lamb of the University
of Illinois (217-333-6363, f-lamb@uiuc.edu) described how the
observed variations in the x-ray brightness can be used to deduce
properties of the neutron star, such as its mass and size. At a press
conference, Lamb and William Zhang of NASA Goddard concentrated
on the binary-star system 4U1820-30, about 20,000 light years from
Earth.  The neutron star has a mass of 2.3 solar masses and orbits its
companion star in only 11 minutes. Close observations of this system
confirm a prediction made by Lamb and his colleagues Coleman Miller
and Dimitrios Psaltis that the gas blobs would continue to spiral
inward until they reached an "innermost stable orbit," where they
would orbit before making the dive for the surface.  This is a purely
general relativistic (GR) effect; in Newton's mechanics, by contrast,
the blob could have gotten arbitrarily close to the surface, providing
it were going fast enough. The observations by Zhang and his
collaborators now confirm Lamb's prediction, thus opening up a new
"strong-gravitational field" era in GR studies.  The measurements of
the gas motion even provide hints as to the nature of the strong
nuclear force sustaining the neutron star against further gravitational
collapse.  The new evidence indicates that the nuclear force is stiffer
and more repulsive than has generally been thought.

PLANETARY SYSTEMS IN THE MAKING have been discovered
in the form of tenuous dust disks surrounding several more stars. 
Astronomers believe that our own solar system evolved out of such
a disk of material left over after the formation of the sun.  Previously
a disk like this had been found around the star Beta Pictoris. Now a
report in Nature (23 April) reveals disks around two more stars,
Formalhut and Vega. Yet another, around the star HR4796A, was
announced at a NASA press conference on 21 April.  Formalhut's
disk even has a dust-free inner zone which one would have expected
if rocky planets formed there had swept all such material  for their
own use.  The observations are possible because of new infrared
detectors sensitive to the radiation emitted by the relatively cool dust.

THE MOST DISTANT GAMMA RAY BURST, at a red shift of 3.4, was
discovered in December and observed at several wavelengths.  Optical
measurements (yielding a red shift) of the object made with the Keck
Telescope and the Hubble Space Telescope were announced by Caltech
astronomer Shrinivas Kulkarni at last week's APS/AAPT meeting.   Optical
astronomers were led to the burst's spot in the sky by x-ray observations
made by the BeppoSax satellite.   (Science, 24 April 1998.)

THE BEST ARTIFICIAL VACUUM ever achieved is produced behind a
4-meter disk dragged through Earth orbit by the Space Shuttle. Called the
Wake Shield, the deflector pushes atoms out of the way, producing a small
region in which the typical distance between residual atoms is a millimeter.
Judging tenuousness by this some convention, the best pumped vacuum on
Earth attains a residual atom spacing ten times worse---a tenth of a mm. By
comparison, the atoms between stars are spaced a centimeter apart; in the
gaseous halo of our galaxy the spacing is about 10 cm; and for intergalactic
voids, it's up to 10 m, the lowest density (or highest vacuum) ever
measured. (New Scientist, 25 April.)

CORRECTION: The best artificial vacuum was reported above  
as corresponding to a spacing between residual atoms of about 1
mm. Several labs have done better:  Gerald Gabrielse, for example,
achieves a vacuum of 5 x 10^-17 torr, corresponding to about 2 atoms
per cm^3.

From: physnews@aip.org (AIP listserver)
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