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TW Hydrae and HD 98800A:
Chandra Adds to Story of the Way We Were
An artist's conception shows TW Hydrae (left) and HD 98800A (right), two young star systems that are both members of the TW Hydrae stellar association which formed about 10 million years ago. Chandra
observations of their X-ray spectra revealed that, although the stars
were both formed in the same region of space at the same time, they
produce X-rays by different mechanisms.
The insets show portions of the X-ray spectra for each system. Of
particular interest are the peaks labeled r, i, and f. These peaks, due
to X-rays from neon atoms that have lost all but two of their ten
orbital electrons, are sensitive indicators of the density and
temperature in the hot, X-ray emitting gas in the star systems.
The relative sizes of the peaks in TW Hydrae provide strong evidence
that the matter is accreting onto the star from a circumstellar disk as
shown in the illustration. X-rays are produced as matter is guided by
the star's magnetic field onto one or more hot spots on the surface of
the star.
In contrast, the spectrum of the binary star system HD 98800A revealed
that its brightest star is producing X-rays much as the Sun does, from a
hot upper atmosphere or corona. This indicates that any disk around
these stars has been greatly diminished or destroyed in ten million
years, perhaps by the ongoing formation of planets or by its companion stars.
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Fast Facts for
TW Hydrae:
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Credit
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Spectra: NASA/CXC/RIT/J.Kastner et al.; Illustration: NASA/CXC/M.Weiss
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Coordinates
(J2000)
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RA 11h 01m 52.00s | Dec -34º 42' 16.00"
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Constellation
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Cetus
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Observation
Date
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July 18, 2000
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Observation
Time
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13.4 hours
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Obs.
ID
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5
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Instrument
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ACIS/HETGS
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Distance
Estimate
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About 190 light years from Earth
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Release Date
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May 26, 2003
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Fast Facts for
HD 98800A:
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Credit
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Spectra: NASA/CXC/RIT/J.Kastner et al.; Illustration: NASA/CXC/M.Weiss
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Coordinates
(J2000)
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RA 11h 22m 05.30s | Dec -24º 46' 39.80"
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Constellation
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Crater
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Observation
Date
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March 07, 2003
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Observation
Time
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16.5 hours
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Obs.
ID
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3728
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Instrument
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ACIS/HETGS
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Distance
Estimate
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About 160 light years from Earth
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Release Date
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May 26, 2003
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