Atomic absorption lines in the interstellar medium

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Atomic absorption lines in the interstellar medium

• Jacek Krelowski
• Centrum Astronomii UMK
• Gagarina 11, 87-100 Torun
• www.astri.uni.torun.pl/jacek

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Stationary spectral line in the spectroscopic
binary oPer discovered by Hartmann in 1904
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The second member of the same dublet
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Sodium dublet D1 and D2 discovered by Heger in
1919
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Two exposures of the HD 23180 star interstellar
lines are Doppler shifted in relation to telluric
features
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Neutral kalium dublet the second member of the
dublet (the green one) is usually intertwinned
with a strong telluric feature
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Neutral iron lines seen in ultraviolet
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Weak line of neutral calcium
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Very weak triplet of neutral lithium
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The Universe contains a lot of hydrogen atoms,
but we observe...
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A total lack of any sign of interstellar
absorption in HB
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Far-UV interstellar lines originated in MgII,
observed towards Xper with the aid of GHRS
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Oxygen, sulphur and phosphorus in HST spectra
taken with high resolution
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Carbon lines of interstellar origin observed in
far-UV with the aid of GHRS fed with HST
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Analysing interstellar atomic lines we arrive at
some conclusions...

• A vast majority of IS atomic lines (resonant
  ones) can be observed only if using space-born
  instruments this follows the extremely low
  density of ISM
• Many of the elements are heavily depleted only
  no more than 0.001 of their cosmic abundance is
  observed in interstellar gas (Fe, Ni, Mg etc.)
• Young stars do not show the above depletions the
  lost elements must be present in IS dust grains

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Doppler splitting observed in interstellar kalium
line the medium is not homogeneous
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Hole in the sky similar to that observed by
Herschel in XVIIIth century
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Various Doppler splittings in different
absorption lines towards the same target
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Various Doppler shifts of different interstellar
lines
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What can we learn analyzing Doppler shifts?

• In most of cases sightlines towards reddened
  stars intersect several clouds
• Doppler components of different lines originating
  in the same clouds are not necessarily closely
  correlated
• Radial velocities derived from wavelengths of
  different lines may be different

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Different profiles of interstellar lines seen
towards the same target
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The above is true also in the lack of any Doppler
splitting...
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Profiles of interstellar lines tell that...

• All interstellar lines, seen along one sightline
  may originate in different places
• Interstellar clouds may resemble large volumes
  filled with ionized gas with denser inclusions in
  which neutral elements are groupped

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Varying ratio of the column density of neutral
and ionized calcium
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Varying ratio of the kalium line intensity
relative to EB-V
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What measures the amount of interstellar matter
along any sightline?

• EB-V?
• AV ?
• EWs of some spectral lines?
• Total amount of hydrogen?
• Something else?