explanation blue bibcodes open ADS page with paths to full text
Author name code: johansson
ADS astronomy entries on 2022-09-14
author:"Johansson, Sven-Eric"
---------------------------------------------------------
Title: VizieR Online Data Catalog: {eta} Car emission spectrum
(1700-10400Å) (Zethson+, 2012)
Authors: Zethson, T.; Johansson, S.; Hartman, H.; Gull, T. R.
2012yCat..35400133Z Altcode: 2012yCat..35409133Z
The spectra were recorded in a low state (March 1998) and an early
high state (February 1999) with the Hubble Space Telescope/Space
Telescope Imaging Spectrograph (HST/STIS) from 1640 to 10400Å using
the 52"x0.1" aperture centered on Eta Carinae at position angle, PA=332
degrees. Extractions of the reduced spectrum including both Weigelt B
and D, 0.28" in length along the slit, were used to identify the narrow,
nebular emission lines, measure their wavelengths and estimate their
fluxes. <P />A linelist of 2500 lines is presented for the high and
low states of the combined Weigelt blobs B and D. <P />(1 data file).
---------------------------------------------------------
Title: η Carinae: linelist for the emission spectrum of the Weigelt
blobs in the 1700 to 10 400 Å wavelength region
Authors: Zethson, T.; Johansson, S.; Hartman, H.; Gull, T. R.
2012A&A...540A.133Z Altcode:
<BR /> Aims: We present line identifications in the 1700 to 10 400 Å
region for the Weigelt blobs B and D, located 0″.1 to 0″.3 NNW of
<ASTROBJ>Eta Carinae</ASTROBJ>. The aim of this work is to characterize
the behavior of these luminous, dense gas blobs in response to the broad
high-state and the short low-state of η Carinae during its 5.54-year
spectroscopic period. <BR /> Methods: The spectra were recorded in a
low state (March 1998) and an early high state (February 1999) with the
Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS)
from 1640 to 10 400 Å using the 52″ × 0″.1 aperture centered on
Eta Carinae at position angle, PA = 332 degrees. Extractions of the
reduced spectrum including both Weigelt B and D, 0″.28 in length along
the slit, were used to identify the narrow, nebular emission lines,
measure their wavelengths and estimate their fluxes. <BR /> Results:
A linelist of 2500 lines is presented for the high and low states
of the combined Weigelt blobs B and D. The spectra are dominated by
emission lines from the iron-group elements, but include lines from
lighter elements including parity-permitted and forbidden lines. A
number of lines are fluorescent lines pumped by H Lyα. Other lines
show anomalous excitation. <P />Table C.1 is also available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/540/A133">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/540/A133</A>
---------------------------------------------------------
Title: VUV oscillator strengths for iron lines of astrophysical
importance
Authors: Hartman, H.; Nilsson, H.; Huldt, S.; Johansson, S.; Sörensen,
S.; Johnson, M. S.; von Hessberg, P.
2008JPhCS.130a2010H Altcode:
FeII lines are of great importance in analyses of stars and nebulae,
not only for abundance studies, but also for diagnostics of the plasma
conditions and derivation of physical properties such as temperature,
electron density and radiation field. <P />We present a project where
the ultimate goal is to derive transition rates for specific Fe II 4s
— 5p transitions at VUV wavelengths. These are important for many
astrophysical applications, e.g. in objects where line fluorescence is
prominent as well as stars observed in the ultraviolet FUSE and HST/STIS
region. In this wavelength region many other iron-group element ions
have important transitions, which also will be measured. This work
is performed as absorption measurements using a FeII hollow-cathode
discharge, illuminated by synchrotron radiation at the MAX-lab facility
(Lund, Sweden). The intensity ratio between absorption lines from a
specific lower level can be determined, and transformed to an absolute
scale using previously known f-values for a few lines. <P />We present
results from low spectral resolution test runs on MAX-I, and outline the
next step with its requirements for a high-resolution setup at MAX-III.
---------------------------------------------------------
Title: Unidentified lines in the spectra of two iron overabundant
CP stars: are they FeII lines?
Authors: Castelli, F.; Johansson, S.; Hubrig, S.
2008JPhCS.130a2003C Altcode:
The analysis of the high-resolution UVES spectra of the chemically
peculiar stars HR6000 and 46 Aql has revealed the presence of an
impressive number of unidentified lines, mostly concentrated in the
regions 4404-4411 Å and 5100-5300 Å. Almost all of the unidentified
lines are the same in both stars, which both have an iron abundance
enhancement of the order of +0.7 dex over the solar value. The
parameters adopted for HR 6000 and 46 Aql are T<SUB>eff</SUB>=12850 K,
log g=4.1 and T<SUB>eff</SUB>=12750 K, log g=3.8, respectively. We show
that some of the unknown lines can be identified as high-excitation
(lower EP13eV) FeII and that most of them appear as unclassified lines
in laboratory iron spectra.
---------------------------------------------------------
Title: Precision Laboratory UV and IR Wavelengths for Cosmological
and Astrophysical Applications
Authors: Aldenius, M.; Johansson, S.
2008psa..conf..257A Altcode: 2007astro.ph..3356A
The quality of astronomical spectra is now so high that the accuracy
of the laboratory data is getting more and more important. Both
in astrophysics and in cosmology the needs for accurate laboratory
wavelengths have increased with the development of new ground-based
and air-borne telescopes and spectrographs. The high-resolution UV
Fourier Transform (FT) spectrometer at Lund Observatory is being used
for studying laboratory spectra of astrophysically important elements.
---------------------------------------------------------
Title: Possibility of Heterodyne Correlation Interferometry with a
Tunable Laser and Absolute Frequency Measurements
Authors: Johansson, S.; Letokhov, V.
2008psa..conf..243J Altcode:
We consider the possibility of measuring the true width of the narrow
optical spectral lines of astrophysical lasers. The lines should
have a subDoppler spectral with of 30-100 MHz or even less. To make
measurements with spectral resolution better than 10<SUP>7</SUP>
and angular resolution better than 0.1 arcsec we suggest to use
the ground-based Brown-Twiss-Townes optical heterodyne intensity
correlation interferometry with the possibility of absolute frequency
measurement. The estimates made of the S/N ratio for optical heterodyne
astrophysical laser experiments imply that it should be feasible.
---------------------------------------------------------
Title: Astrophysical lasers and nonlinear optical effects in space
Authors: Johansson, S.; Letokhov, V. S.
2007NewAR..51..443J Altcode:
The present state of the art concerning astrophysical lasers (APL)
and nonlinear optical effects under astrophysical conditions is
reviewed. The operational conditions of an APL (amplification
under non-LTE conditions) and astrophysical predecessors of
the laboratory lasers are considered in the introduction of the
review. The rareness of observed APL action in the visible range in
comparison with astrophysical masers (APM) in the microwave range
is explained. Early proposals of APLs with collisional and optical
pumping are discussed. APL/M in the mid-IR and submillimeter ranges
linking APL and APM are also discussed. APLs in the Weigelt blobs of
Eta Carinae operating in FeII and OI with a Bowen type optical pumping
are considered in detail. General questions (narrowing of APL spectral
lines, the possibility of scattering feedback and ways of measuring
the true spectral width of an APL) are considered. Nonlinear optical
effects in astrophysical conditions and resonance-enhanced two-photon
conditions, in particular, are discussed in the conclusion.
---------------------------------------------------------
Title: Accurate Ritz wavelengths of parity-forbidden [Fe II],
[Ti II], and [Cr II] infrared lines of astrophysical interest
Authors: Aldenius, M.; Johansson, S.
2007A&A...467..753A Altcode: 2007astro.ph..3145A
Context: With new astronomical infrared spectrographs the demands of
accurate atomic data in the infrared have increased. In this region
there is a large amount of parity-forbidden lines, which are of
importance in diagnostics of low-density astrophysical plasmas. <BR
/>Aims: We present improved, experimentally determined, energy levels
for the lowest even LS terms of Fe II, Ti II and Cr II, along with
accurate Ritz wavelengths for parity-forbidden transitions between and
within these terms. <BR />Methods: Spectra of Fe II, Ti II and Cr II
have been produced in a hollow cathode discharge lamp and acquired using
high-resolution Fourier Transform (FT) spectrometry. The energy levels
have been determined by using observed allowed ultraviolet transitions
connecting the even terms with upper odd terms. Ritz wavelengths of
parity-forbidden lines have then been determined. <BR />Results: Energy
levels of the four lowest Fe II terms (a<SUP>6</SUP>D, a<SUP>4</SUP>F,
a<SUP>4</SUP>D and a<SUP>4</SUP>P) have been determined, resulting
in 97 different parity-forbidden transitions with wavelengths between
0.74 and 87 μm. For Ti II the energy levels of the two lowest terms
(a<SUP>4</SUP>F and b<SUP>4</SUP>F) have been determined, resulting
in 24 different parity-forbidden transitions with wavelengths between
8.9 and 130 μm. Also for Cr II the energy levels of the two lowest
terms (a<SUP>6</SUP>S and a<SUP>6</SUP>D) have been determined,
in this case resulting in 12 different parity-forbidden transitions
with wavelengths between 0.80 and 140 μm. <P />Tables 6-8 are only
available in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Experimental Mg I oscillator strengths and radiative lifetimes
for astrophysical applications on metal-poor stars. New data for
the Mg I b triplet
Authors: Aldenius, M.; Tanner, J. D.; Johansson, S.; Lundberg, H.;
Ryan, S. G.
2007A&A...461..767A Altcode: 2006astro.ph.10033A
Context: The stellar abundance ratio of Mg/Fe is an important
tool in diagnostics of galaxy evolution. In order to make reliable
measurements of the Mg abundance of stars, it is necessary to have
accurate values for the oscillator strength (f-value) of each of the
observable transitions. In metal-poor stars the Mg I 3p-4s triplet
around 5175 Å (Fraunhofer's so-called b lines) are the most prominent
magnesium lines. The lines also appear as strong features in the
solar spectrum. <BR />Aims: We present new and improved experimental
oscillator strengths for the optical Mg I 3p-4s triplet, along with
experimental radiative lifetimes for six terms in Mg I. With these data
we discuss the implications on previous and future abundance analyses
of metal-poor stars. <BR />Methods: The oscillator strengths have been
determined by combining radiative lifetimes with branching fractions,
where the radiative lifetimes are measured using the laser induced
fluorescence technique and the branching fractions are determined using
intensity calibrated Fourier Transform (FT) spectra. The FT spectra
are also used for determining new accurate laboratory wavelengths
for the 3p-4s transitions. <BR />Results: The f-values of the Mg I
3p-4s lines have been determined with an absolute uncertainty of 9%,
giving an uncertainty of ± 0.04 dex in the log gf values. Compared
to values previously used in abundance analyses of metal-poor stars,
rescaling to the new values implies an increase of typically 0.04 dex
in the magnesium abundance.
---------------------------------------------------------
Title: New and improved experimental oscillator strengths in Zr II
and the solar abundance of zirconium
Authors: Ljung, G.; Nilsson, H.; Asplund, M.; Johansson, S.
2006A&A...456.1181L Altcode:
Using the Fourier Transform Spectrometer at Lund Observatory, intensity
calibrated spectra of singly ionized zirconium have been recorded and
analyzed. Oscillator strengths for 263 Zr II spectral lines in the
region 2500-5400 Å have been derived by combining new experimental
branching fractions with previously measured radiative lifetimes. The
transitions combine 34 odd parity levels with 29 low metastable levels
between 0 and 2.4 eV. The experimental branching fractions have been
compared with theoretical values and the oscillator strengths with
previously published data when available. The oscillator strengths
have been employed to derive the solar photospheric Zr abundance
based on both 1D and 3D model atmospheres. Based on the seven best
and least perturbed Zr II lines in the solar disk-center spectrum, we
determine the solar Zr abundance to log ɛ_Zr=2.58±0.02 when using a
3D hydrodynamical solar model atmosphere. The new value is in excellent
agreement with the meteoritic Zr abundance.
---------------------------------------------------------
Title: Accurate laboratory ultraviolet wavelengths for quasar
absorption-line constraints on varying fundamental constants
Authors: Aldenius, M.; Johansson, S.; Murphy, M. T.
2006MNRAS.370..444A Altcode: 2006MNRAS.tmp..601A; 2006astro.ph..5053A
The most precise method of investigating possible
space-time variations of the fine-structure constant, α ≡
(1/ħc)(e<SUP>2</SUP>/4πɛ<SUB>0</SUB>), using high-redshift quasar
absorption lines is the many-multiplet (MM) method. For reliable
results this method requires very accurate relative laboratory
wavelengths for a number of UV resonance transitions from several
different ionic species. For this purpose laboratory wavelengths and
wavenumbers of 23 UV lines from MgI, MgII, TiII, CrII, MnII, FeII and
ZnII have been measured using high-resolution Fourier transform (FT)
spectrometry. The spectra of the different ions (except for one FeII
line, one MgI line and the TiII lines) are all measured simultaneously
in the same FT spectrometry recording by using a composite hollow
cathode as a light source. This decreases the relative uncertainties
of all the wavelengths. In addition to any measurement uncertainty,
the wavelength uncertainty is determined by that of the ArII
calibration lines, by possible pressure shifts and by illumination
effects. The absolute wavenumbers have uncertainties of typically
+/-0.001-+/-0.002cm<SUP>-1</SUP> (Δ λ ~ 0.06-0.1mÅ at 2500Å),
while the relative wavenumbers for strong, symmetric lines in the same
spectral recording have uncertainties of +/- 0.0005 cm<SUP>-1</SUP>
(Δλ ~ 0.03mÅ at 2500Å) or better, depending mostly on uncertainties
in the line-fitting procedure. This high relative precision greatly
reduces the potential for systematic effects in the MM method, while
the new TiII measurements now allow these transitions to be used in
MM analyses.
---------------------------------------------------------
Title: Resonance-enhanced two-photon ionization (RETPI) of Si II
and an anomalous, variable intensity of the λ1892 Si III] line in
the Weigelt blobs of η Carinae
Authors: Johansson, S.; Hartman, H.; Letokhov, V. S.
2006A&A...452..253J Altcode: 2006astro.ph..2365J
Context: .The Si III] 1892 Å intercombination line shows an anomalously
high intensity in spectra of the radiation-rich Weigelt blobs in the
vicinity of Eta Carinae. The line disappears during the 100 days long
spectral events occurring every 5.5 years.<BR /> Aims: .The aim is to
investigate whether resonance-enhanced two-photon ionization (RETPI)
is a plausible excitation mechanism for the Si III] λ1892 line.<BR />
Methods: .The possible intensity enhancement of the λ1892 line is
investigated as regards quasi-resonant intermediate energy levels of
Si II.<BR /> Results: .The RETPI mechanism is effective on Si II in
the radiation-rich Weigelt blobs where the two excitation steps are
provided by the two intense hydrogen lines Lyα and Lyγ.<BR />
---------------------------------------------------------
Title: The nature of ultraviolet spectra of AG Pegasi and other
symbiotic stars: locations, origins, and excitation mechanisms of
emission lines
Authors: Eriksson, M.; Johansson, S.; Wahlgren, G. M.
2006A&A...451..157E Altcode:
A detailed study of ultraviolet spectra of the symbiotic star AG Peg has
been undertaken to derive the atomic excitation mechanisms and origin
of formation for the lines common in symbiotic systems. More than 600
emission lines are observed in spectra from {IUE}, {HST} and {FUSE} of
which 585 are identified. Population mechanisms and origin of formation
are given for a majority of those lines. Based on the understanding
of the AG Peg spectra {IUE} data of 19 additional symbiotic stars are
investigated and differences and similarities of their spectra are
discussed. Fe II fluorescence lines pumped by strong emission lines
between 1000 and 2000 Å are observed in 13 of these systems. Some of
the symbiotic systems belonging to the subclass symbiotic novae have
more than 100 Fe II fluorescence lines in the ultraviolet wavelength
region. Forbidden lines are detected for 13 of the stars, mostly
from highly-ionized spectra such as Ar V, Ne V and Mg V. Further,
[Mg VI] and [Mg VII] lines are observed in a symbiotic star (AG Dra)
for the first time. Five of the symbiotic stars have broad white-dwarf
wind profiles ({FWHM} > 400 km s<SUP>-1</SUP>) for a few lines in
their spectra. The stars with no such broad lines can be divided into
two similarly sized groups, one where all lines have FWHM less than 70
km s<SUP>-1</SUP> and the other where one, a few or all of the broad
({FWHM} > 400 km s<SUP>-1</SUP>) lines of AG Peg have an enhanced
broad wing (110-140 km s<SUP>-1</SUP>).
---------------------------------------------------------
Title: Astrophysical laser operating in the OI 8446-Åline in the
Weigelt blobs of η Carinae
Authors: Johansson, S.; Letokhov, V. S.
2005MNRAS.364..731J Altcode: 2005MNRAS.tmp..964J
Within the framework of a simple model of photophysical processes in
the Weigelt blobs in the vicinity of the luminous blue variable (LBV)
star η Carinae, we explain the presence of the fluorescent <OI>
8446-Åand forbidden [OI] 6300-Ålines as well as the absence of
the allowed OI 7774-Åline in spectra recorded with the Hubble Space
Telescope (HST)/STIS instrument (Gull et al.). From atomic data and
estimated stellar parameters we demonstrate that there is a population
inversion and stimulated emission in the 3p<SUP>3</SUP>P-3s<SUP>3</SUP>S
transition λ8446 due to photoexcitation by accidental resonance (PAR)
by H Lyβ radiation.
---------------------------------------------------------
Title: Bowen excitation of O III and N III in symbiotic stars
Authors: Eriksson, M.; Wahlgren, G. M.; Johansson, S.
2005AAS...207.1302E Altcode: 2005BAAS...37.1173E
When ions in a plasma are subjected to emission lines very close in
photon energy to the energy difference between two levels in the ions,
the photons can pump the ions through the corresponding channel. This
is called photoexcitation by accidental resonance (PAR). The most
famous example of PAR is the Bowen mechanism, where the He II Lyα
line at 303.783 Å pumps two 2p<SUP>2</SUP> - 2p3d channels in O III,
at 303.800 and 303.695 Å, resulting in the so called O III Bowen
lines between 2800 and 4000 Å. In IUE spectra of 20 symbiotic stars
we observe the O III Bowen lines in 16. The O III Bowen lines are
analyzed and the pumping efficiencies are discussed. In spectra of
four of the symbiotic stars, AG Peg, RR Tel, HM Sge and V1016 Cyg, we
observethe N III 3s-3p lines at 4000 Å and the 3p-3d lines at 4640 Å
are observed. It was proposed already by Bowen (1935) that one of the
O III lines, λ 374.432 could photoexcite N III through the channels
at 374.434 and 374.442 Å, which would actually lead to the N III
lines we observe in the symbiotic stars. We have modeled intensity
ratios between the N III lines to test pumping by O III emission as
the explanation for the N III 3s-3p and 3p-3d emission. This is valid
for AG Peg but can be excluded for HM Sge. For RR Tel and V1016 Cyg
the Bowen mechanism seems to be involved in the formation of the N
III lines, but additional processes such as radiative recombination
or charge-exchange with neutral hydrogen are needed to explain the
observed intensity ratios.
---------------------------------------------------------
Title: The FERRUM project: experimentally determined metastable
lifetimes and transition probabilities for forbidden [TiII] lines
observed in η Carinae
Authors: Hartman, H.; Schef, P.; Lundin, P.; Ellmann, A.; Johansson,
S.; Lundberg, H.; Mannervik, S.; Norlin, L. -O.; Rostohar, D.;
Royen, P.
2005MNRAS.361..206H Altcode: 2005MNRAS.tmp..563H
In the spectrum of an emission-line region ejected from the massive star
Eta Carinae, called the strontium filament (SrF), forbidden lines from
many elements, in particular [SrII] and [TiII], are observed. These
lines are strong in this specific region and valuable for plasma
diagnostics. Forbidden lines are not easily produced in laboratory
light sources and the atomic parameters for these lines can thus not
be measured in a straightforward way. <P />We use a combination of
laboratory and astrophysical measurements to determine transition
probabilities for the [TiII] lines. Lifetimes for metastable levels
in TiII are measured using a laser probing technique on a stored
ion beam at CRYRING, MSL, Stockholm. Branching fractions from
some of these levels are derived from Hubble Space Telescope/STIS
spectra of the SrF. The astrophysical branching fractions are
combined with the experimental lifetimes to determine absolute
transition probabilities. <P />We report lifetimes for the TiII
levels b<SUP>4</SUP>P<SUB>3/2</SUB>, b<SUP>2</SUP>P<SUB>1/2</SUB>,
c<SUP>2</SUP>D<SUB>3/2</SUB> and c<SUP>2</SUP>D<SUB>5/2</SUB>,
in the range 0.29-17 s, and transition probabilities for eight
parity-forbidden lines from the levels c<SUP>2</SUP>D<SUB>3/2</SUB>
and c<SUP>2</SUP>D<SUB>5/2</SUB>, along with uncertainty estimates.
---------------------------------------------------------
Title: Time variations of the narrow Fe II and H I spectral emission
lines from the close vicinity of η Carinae during the spectral
event of 2003
Authors: Hartman, H.; Damineli, A.; Johansson, S.; Letokhov, V. S.
2005A&A...436..945H Altcode: 2005astro.ph..3410H
The spectrum of <ASTROBJ>Eta Carinae</ASTROBJ> and its ejecta shows
slow variations over a period of 5.5 years. However, the spectrum
changes drastically on a time scale of days once every period called the
"spectral event". We report on variations in the narrow emission line
spectrum of gas condensations (the Weigelt blobs) close to the central
star during a spectral event. The rapid changes in the stellar radiation
field illuminating the blobs make the blobs a natural astrophysical
laboratory to study atomic photoprocesses. The different responses of
the HI Paschen lines, fluorescent <Fe II> lines and forbidden
[Fe II] lines allow us to identify the processes and estimate physical
conditions in the blobs. This paper is based on observations from the
Pico dos Dias Observatory (LNA/Brazil) during the previous event in
June 2003.
---------------------------------------------------------
Title: Astrophysical Lasers in Optical Fe II Lines in Gas
Condensations near η Carinae
Authors: Johansson, S.; Letokhov, V. S.
2005AIPC..770..399J Altcode:
We report here on the discovery of laser action in the range 0.9-2
μm in several spectral lines of Fe II, which are associated with
transitions from “pseudo-metastable” states populated by spontaneous
transitions from Lyα pumped Fe II levels. The intense Lyα radiation
is formed in the HII region of gas condensations close to the star η
Car. The laser transitions form together with spontaneous transitions
closed radiative cycles, one of which includes the extremely bright
2507/09 Å lines. This fact, together with an accidental mixing of
energy levels, may provide an explanation of the abnormal intensities of
these UV non-lasing lines. Using the complicated energy level diagram of
Fe II we present those peculiar features, which are essential for the
inverted population and laser effect: the pumping, the level mixing,
and the “bottle neck” for spontaneous decay. The laser action is a
new indicator of non-equilibrium and spatially non-homogeneous physical
conditions as well as a high brightness temperature of Lyα in ejecta
from eruptive stars. Such conditions are very difficult to probe by
existing methods.
---------------------------------------------------------
Title: Metastable hydrogen absorption in ejecta close to η Carinae
Authors: Johansson, S.; Gull, T. R.; Hartman, H.; Letokhov, V. S.
2005A&A...435..183J Altcode:
Spectroscopy with the high spatial resolution of the Hubble Space
Telescope (HST) reveals narrow absorption in the hydrogen Balmer
lines in spectra of Eta Carinae and the nearby nebular-scattered
starlight. While hydrogen Balmer absorption lines are seen in stellar
photospheres and winds, we are not aware of such being seen in
galactic nebulae. This exceptional case is caused by intense stellar
UV radiation acting on high-density neutral clumps of gas in the close
vicinity of the central source. The interaction of the UV radiation
with hydrogen results in photo-ionization and photo-excitation leading
to a non-equilibrium population of the metastable 2s <SUP>2</SUP>S
level. This occurs throughout the equatorial region surrounding η
Carinae in sufficient quantity to produce strong narrow absorption
on top of the broad P Cygni emission profile. This absorption can be
considered to be a probe of the very non-uniform ejecta in the disk
region surrounding η Carinae.
---------------------------------------------------------
Title: Bowen excitation of N III lines in symbiotic stars
Authors: Eriksson, M.; Johansson, S.; Wahlgren, G. M.; Veenhuizen,
H.; Munari, U.; Siviero, A.
2005A&A...434..397E Altcode:
We present a semi-empirical equation for prediction of the strengths
of those N III lines that are generated by the Bowen mechanism and
observed in spectra of symbiotic stars. The equation assumes that the
Bowen mechanism is the only source populating the 3d state in N III,
and comparisons with observations of the 3s-3p and 3p-3d transitions
serve as a test of this assumption. In an ongoing study of symbiotic
stars the equation has been applied to two symbiotic novae, RR Tel and
AG Peg, by comparing the predicted N III line strengths to observed
line intensities. It is clear that besides the Bowen mechanism there is
another process, most likely radiative recombination, that contributes
to the N III 3d population in AG Peg and is the main population process
of this state in RR Tel. It is also clear that a second, not previously
considered, N III channel, 2p <SUP>2</SUP>P{1/2}-3d <SUP>2</SUP>D{3/2}
at 374.198 Å, is pumped by O III in both RR Tel and AG Peg.
---------------------------------------------------------
Title: Possibility of measuring the width of narrow Fe II
astrophysical laser lines in the vicinity of η Carinae by means of
Brown-Twiss-Townes heterodyne correlation interferometry
Authors: Johansson, S.; Letokhov, V. S.
2005NewA...10..361J Altcode: 2005astro.ph..1246J
We consider the possibility of measuring the true width of the
narrow Fe II optical lines observed in spectra of the Weigelt blobs
in the vicinity of η Carinae. The lines originate as a result of
stimulated amplification of spontaneous emission of radiation in
quantum transitions between energy levels showing inverted population
[Johansson, S., Letokhov, V., 2002. JETP Lett. 75 (10) 495; Johansson,
S., Letokhov, V., 2003. Phys. Rev. Lett. 90 (1) 01110-1; Johansson,
S., Letokhov, V., 2004. A&A 428,497]. The lines should have a
subDoppler spectral width of 30-100 MHz, depending on the geometry of
the lasing volume. To make measurements with a spectral resolution of
R > 10<SUP>7</SUP> and an angular resolution better than 0.1″, we
suggest the use of the Brown-Twiss-Townes optical heterodyne intensity
correlation interferometry. The estimates made of the S/N ratio for
the optical heterodyne astrophysical laser experiment imply that it
is feasible.
---------------------------------------------------------
Title: Experimental Oscillator Strengths for Forbidden Lines in
Complex Spectra
Authors: Hartman, H.; Johansson, S.; Lundberg, H.; Lundin, P.;
Mannervik, S.; Schef, P.
2005PhST..119...40H Altcode:
In dilute astrophysical plasmas, such as planetary nebulae and H II
regions, strong lines appear that only have weak, if any, correspondence
to the spectrum of laboratory light sources. Some of these are parity
forbidden lines, i.e. emission from long-lived metastable states that
cannot decay via normal electric dipole (E1) routes but only via the
slower M1 and E2 transitions. The long lifetime of the upper levels
and their sensitivity to collisions make the lines good diagnostics
of the emitting plasma, but then the transition probability, or
A-value, of these lines must be known. <P />We report on a technique
to experimentally determine A-values for forbidden lines using
the method of combining the lifetime of the upper level with the
branching fractions for the different decay channels. The lifetime
is measured using the laser probing technique (LPT) on a stored ion
beam. Since these lines are rarely produced in laboratory plasmas,
we use astrophysical spectra to determine the branching fractions
(BF). The lifetime and the BF then give the A-value, which is one
quantity needed for modeling the spectrum of the plasma emitting the
forbidden lines. <P />The present measurements are performed within the
FERRUM project, an international collaboration producing and evaluating
transition probabilities for iron group element lines of astrophysical
importance (Johansson P I S et al 2002 Physica Scripta T100 71)
---------------------------------------------------------
Title: Stimulated Amplification under Spatially Nonhomogeneous
Conditions: An Astrophysical Fe II Laser in the Vicinity of Eta
Carinae
Authors: Johansson, S.; Letokhov, V.
2005PhST..120...99J Altcode:
We consider the conditions necessary for the development of an inverted
population among the energy levels of free atoms in a medium exposed
to radiation in spectral non-equilibrium. In particular, we focus
on monochromatic radiation occurring as a result of an accidental
wavelength coincidence between a pumping emission line and a pumped
absorption line in two different elements. We examine especially
the influence of `pseudo-metastable' states (at medium excitation)
in the complex spectrum of Fe II, which cause a `bottleneck' in the
radiative decay leading to an inverted level population. We also
discuss the effect of `spectral compression' of the Lyman continuum
into HLyα radiation at a high effective temperature. In conclusion
we describe those differences between microwave astrophysical masers
(APM) and optical astrophysical lasers (APL) that make the latter a
more rare phenomenon in Nature.
---------------------------------------------------------
Title: Astrophysical lasers operating in optical Fe II lines in
stellar ejecta of η Carinae
Authors: Johansson, S.; Letokhov, V. S.
2004A&A...428..497J Altcode: 2004astro.ph..9069J
After the discovery of space masers based on OH radicals (Weaver et
al. \cite{Wea65}) and H<SUB>2</SUB>O (Cheung et al. \cite{Che69}) such
microwave lasers have been found to work in more than 100 molecular
species (Elitzur \cite{Eli92}; Townes \cite{Tow97}), as well as in
highly excited H atoms (Strelnitski et al. \cite{Str96}). In the IR
region (10 \mum), the effect of stimulated emission of radiation in the
CO<SUB>2</SUB> molecule has been discovered in the Martian and Venus'
atmospheres (Betz et al. \cite{Bet76}; Mumma et al. \cite{Mum81}). We
report here on the discovery of laser action in the range 0.9-2 μm in
several spectral lines of Fe II, which are associated with transitions
from “pseudo-metastable” states populated by spontaneous transitions
from Lyα pumped Fe II levels. The intense Lyα radiation is formed
in the HII region of gas condensations close to the star η Car. The
laser transitions form together with spontaneous transitions closed
radiative cycles, one of which includes the extremely bright 2507/09 Å
lines. Closed radiative cycles, together with an accidental mixing of
energy levels, may provide an explanation of the abnormal intensities of
these UV non-lasing lines. Using the complicated energy level diagram of
Fe II we present those peculiar features, which are essential for the
inverted population and laser effect: the pumping, the level mixing,
and the “bottle neck” for spontaneous decay. The laser action is a
new indicator of non-equilibrium and spatially non-homogeneous physical
conditions as well as a high brightness temperature of Lyα in ejecta
from eruptive stars. Such conditions are very difficult to probe by
existing methods, and we propose some future experiments. The fact,
that the lasing near-IR lines appear in the spectrum with about the
same intensity as non-lasing lines is discussed and compared with the
situation in masers.
---------------------------------------------------------
Title: Fe II Diagnostic Tools for Quasars
Authors: Verner, E.; Bruhweiler, F.; Verner, D.; Johansson, S.;
Kallman, T.; Gull, T.
2004ApJ...611..780V Altcode: 2004astro.ph..4593V
The enrichment of Fe relative to α-elements such as O and Mg represents
a potential means to determine the age of quasars and probe the galaxy
formation epoch. To explore how Fe II emission in quasars is linked to
physical conditions and abundance, we have constructed an 830 level Fe
II model atom and investigated through photoionization calculations
how Fe II emission strengths depend on nonabundance factors. We have
split Fe II emission into three major wavelength bands, Fe II (UV),
Fe II (Opt1), and Fe II (Opt2), and explore how the Fe II (UV)/Mg
II, Fe II (UV)/Fe II (Opt1), and Fe II (UV)/Fe II (Opt2) emission
ratios depend on hydrogen density and ionizing flux in the broad-line
regions (BLRs) of quasars. Our calculations show that (1) similar Fe II
(UV)/Mg II ratios can exist over a wide range of physical conditions,
(2) the Fe II (UV)/Fe II (Opt1) and Fe II (UV)/Fe II (Opt2) ratios
serve to constrain ionizing luminosity and hydrogen density, and (3)
flux measurements of Fe II bands and knowledge of the ionizing flux
provide tools to derive distances to BLRs in quasars. To derive all
BLR physical parameters with uncertainties, comparisons of our model
with observations of a large quasar sample at low redshift (z<1)
are desirable. The STIS and NICMOS instruments aboard the Hubble Space
Telescope offer the best means to provide such observations.
---------------------------------------------------------
Title: Fe II fluorescence in symbiotic stars
Authors: Eriksson, M.; Veenhuizen, H.; Wahlgren, G. M.; Johansson, S.
2004RMxAC..21..132E Altcode: 2004IAUCo.191..132E
Fe 0 fluorescence by PAR has been investigated in eight symbiotic
stars having a wide range in temperature of the hot component and
orbital period. The data used are spectra obtained from the IUE
archive. All pumping lines investigated in this work are in the
short wavelength region of IUE (1200-2000 Å), except for He 0 λ
1084.942 and O 0 λ 1032.041. The resulting Fe 0 fluorescence lines
are mainly in the long wavelength region (2000-3300 Å), but a few fall
in the same region as the pumping lines. The aim is to understand the
optimal conditions for formation of Fe 0 fluorescence lines caused by
PAR. Three of the selected systems, RR Tel, AG Peg and V1016 Cyg, have
10-30 active Fe 0 channels. Two conditions connect those systems to
each other: The hot component is a white dwarf of extreme temperature
(80 . 10<SUP>3</SUP>-150 . 10<SUP>3</SUP> K) and all three systems
are so called symbiotic novae and have had outbursts during the last
150 years. Three systems, AG Dra, RW Hya and R Aqr, have only 2-3
active Fe 0 channels. In the two remaining systems, CI Cyg and T CrB,
Fe 0 fluorescence lines were totally absent. These two systems have two
features in common: The emission strength of highly ionized elements is
less than in most symbiotic systems, and the hot component is suspected
to be an accreting main sequence star rather than a white dwarf.
---------------------------------------------------------
Title: Modeling the wind structure of AG Peg by fitting of C IV and
N V resonance doublets
Authors: Eriksson, M.; Johansson, S.; Wahlgren, G. M.
2004A&A...422..987E Altcode:
The latest outburst of AG Peg has lasted for 150 years, which makes
it the slowest nova eruption ever recorded. During the time of IUE
observations (1978-1995) line profiles and intensity ratios of the N V
and C IV doublet components changed remarkably, and we discuss plausible
reasons. One of them is radiative pumping of Fe II which is investigated
by studying the fluorescence lines from pumped levels. Three Fe II
channels are pumped by C IV and one by N V. The pumping rates of those
Fe II channels as derived by the modeling agree well with the strengths
of the Fe II fluorescence lines seen in the spectra. We model the C
IV and N V resonance doublets in IUE spectra recorded between 1978
and 1995 in order to derive optical depths, expansion velocities,
and the emissivities of the red giant wind, the white dwarf wind and
their collision region. The derived expansion velocities are ∼60 km
s<SUP>-1</SUP> for the red giant wind and ∼700 km s<SUP>-1</SUP> for
the white dwarf wind. We also suggest a fast outflow from the system
at ∼150 km s<SUP>-1</SUP>. The expansion velocity is slightly higher
for N V than for C IV. Emission from the collision region strongly
affects the profile of the N V and C IV resonance doublets indicating
its existence.
---------------------------------------------------------
Title: Erratum: "Anomalous Fe II Spectral Effects and High H I Lyα
Temperature in Gas Blobs Near η Carinae" [Astron. Lett. 30, 58
(2004)]
Authors: Johansson, S.; Letokhov, V. S.
2004AstL...30..433J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Possibility of Resonance-Enhanced Two-Photon Ionization
of Ne and Ar Atoms in Astrophysical Plasmas
Authors: Johansson, S.; Letokhov, V. S.
2004ARep...48..399J Altcode:
We consider possible schemes for the resonance-enhanced two-photon
ionization (RETPI) of Ne and Ar atoms under the action of bichromatic
radiation of intense resonance lines of HI, HeI, and HeII in a
radiation-rich astrophysical plasma. The ionization rate is comparable
to or exceeds the recombination rate in rarified astrophysical plasma,
which leads to the accumulation of singly ionized ions with a subsequent
transition to the higher ionization state via RETPI. We consider the
RETPI reaction chains NeI → ... → NeV and ArI → ... → ArVI.
---------------------------------------------------------
Title: Identification of emission lines in the low-ionization
strontium filament near Eta Carinae
Authors: Hartman, H.; Gull, T.; Johansson, S.; Smith, N.; HST Eta
Carinae Treasury Project Team
2004A&A...419..215H Altcode: 2004astro.ph..2489H
We have obtained deep spectra from 1640 to 10 100 Å with the Space
Telescope Imaging Spectrograph (STIS) of the strontium filament, a
largely neutral emission nebulosity lying close to the very luminous
star Eta Carinae and showing an uncommon spectrum. Over 600 emission
lines, both permitted and forbidden, have been identified. The majority
originates from neutral or singly-ionized iron group elements (Sc,
Ti, V, Cr, Mn, Fe, Co, Ni). Sr is the only neutron capture element
detected. The presence of Sr II, numerous strong Ti II and V II lines
and the dominance of Fe I over Fe II are notable discoveries. While
emission lines of hydrogen, helium, and nitrogen are associable with
other spatial structures at other velocities within the Homunculus,
no emission lines from these elements correspond to the spatial
structure or velocity of the \ion{Sr} filament. Moreover, no
identified \ion{Sr} filament emission line requires an ionization
or excitation energy above approximately 8 eV. Ionized gas extends
spatially along the aperture, oriented along the polar axis of the
Homunculus, and in velocity around the strontium filament. We suggest
that the strontium filament is shielded from ultraviolet radiation
at energies above 8 eV, but is intensely irradiated by the central
star at wavelengths longward of 1500 Å. <P />Based on observations
made with the NASA/ESA Hubble Space Telescope, obtained at the Space
Telescope Science Institute, which is operated by the Association
of Universities for Research in Astronomy, Inc., under NASA contract
NAS5-26555. <P />Tables 2 and 3 are only available in electronic form
at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/419/215
---------------------------------------------------------
Title: VizieR Online Data Catalog: Emission lines of Sr filament
near {eta} Car (Hartman+, 2004)
Authors: Hartman, H.; Gull, T.; Johansson, S.; Smith, N.; HST Eta
Carinae Treasury Project Team
2004yCat..34190215H Altcode:
Spectral lines observed in the Sr-filament of {eta} Car in the
wavelength region 2480-10140Å. The lines are sorted by wavelength in
table 2 and sorted according to the periodic table in table 3. Both
tables are available in postscript format as the file tables23.ps where
the sub and superscripts for the atomic transitions are kept. <P />(3
data files).
---------------------------------------------------------
Title: Anomalous Fe II Spectral Effects and High H I Lyα Temperature
in Gas Blobs Near η Carinae
Authors: Johansson, S.; Letokhov, V. S.
2004AstL...30...58J Altcode:
We consider the origin of the anomalously high intensity of the
ultraviolet Fe II lambda 2507/2509 A lines observed with high spatial
and spectral resolutions from gas blobs (GBs) near Carinae. This rare
effect in stellar spectra is attributable to a combination of several
factors: (1) the high hydrogen density (>10^{8} cm^{-3}) that
ensures the blocking of the Lyman continuum by GBs and, accordingly,
the formation of a cold H I region with completely ionized Fe atoms;
(2) the small distance between the GBs and the central star that
ensures a high (>8000-10 000 K) Ly_alpha H spectral temperature,
which photoexcites Fe II selectively; and (3) the population of Fe II
levels and, accordingly, the opening of a stimulated emission channel,
which together with spontaneous transitions creates a radiative cycle
where a single Fe II ion can multiply absorb Ly_alpha emission.
---------------------------------------------------------
Title: Anomalously bright UV lines of Fe II as a probe of gas
condensations in the vicinity of hot stars
Authors: Johansson, S.; Letokhov, V. S.
2003A&A...412..771J Altcode:
Two UV lines of Fe II at 2507/2509 Å are extremely bright in spatially
resolved HST/STIS spectra of dense gas condensations (the so called
Weigelt blobs) close to the central star of η Carinae. The lines
also appear unresolved in HST/FOS spectra of the star AE And. Under
normal conditions the lines should hardly be observable. Based on
recent studies of the formation of the łambdałambda2507/2509 lines
as part of a radiative cycle driven by HLyα pumping and including
stimulated emission we propose the possibility of using them as a
probe of non-homogeneities in gas condensations located outside hot,
massive stars.
---------------------------------------------------------
Title: Line absorption in the FUSE spectrum of the CP star 17 Com A
Authors: Wahlgren, G. M.; Ivarsson, S.; Johansson, S.; Proffitt, C. R.;
Adelman, S. J.; Rice, J.; Gulliver, A. F.; Hill, G.; Leckrone, D. S.;
Smith, D. P.
2003AAS...203.9303W Altcode: 2003BAAS...35.1358W
We report on progress made in our Far Ultraviolet Spectroscopic Explorer
(FUSE) program (ID A130; PI J.Rice) that pertains to understanding the
absorption line spectrum of the magnetic chemically peculiar B star
17 Com A (HD108662). Spectral observations were made on ten occasions
with the FUSE observatory over a five day interval in April 2001 for
the purpose of studying temporal flux variations over the stellar
rotational period of 5.07 days. These data will allow us to correlate
the far-UV flux variations with elemental abundance variations over
the stellar surface as mapped out by optical Doppler image mapping
techniques. Complementing the FUSE data are high-resolution optical
spectra obtained at the Nordic Optical Telescope and the McDonald
Observatory. From the optical spectra we have determined the rotational
velocity (v sin i = 17 km s<SUP>-1</SUP>) and chemical abundances. The
iron-group elements are generally enriched by a factor of 10 relative
to the solar values and as such, are responsible for a large part
of the line absorption in the FUSE spectral region. Using synthetic
spectrum techniques with the abundances derived from the optical region
data and FUSE archival spectra of normal and non-magnetic CP stars,
we can identify approximately two-thirds of the absorption features
in the FUSE spectrum of 17 Com A. In particular, we have concentrated
on contributions from the Cr II/III and Fe II/III spectra. Aspects
of atomic spectroscopy are also being carried out with the FUSE
spectra. New experimental oscillator strengths for 4d-4f transitions of
Fe II observed at optical wavelengths are used in conjunction with the
FUSE spectra of chemically normal B type stars to determine oscillator
strengths for important Fe II 3d-4f transitions.
---------------------------------------------------------
Title: Astrophysical Lasers with Radiation Pumping by Accidental
Resonance
Authors: Johansson, S.; Letokhov, V. S.
2003PASP..115.1375J Altcode:
In this paper we consider a general problem of astrophysical lasers
operating with optical pumping by accidental resonance (PAR) with
strong spontaneous emission lines of other elements. The origin of
population inversion and the coefficient of amplification due to the
optical excitation of atoms (ions) by a four-level scheme with PAR are
analyzed. We elucidate conclusively the question of the manifestation of
astrophysical lasers in the optical region of the spectrum, which in
principle differs from that of astrophysical masers in the microwave
range.
---------------------------------------------------------
Title: The HST Treasury Project on Eta Carinae
Authors: Davidson, K.; Ishibashi, K.; Gull, T. R.; Martin, J. C.;
Humphreys, R. M.; Damineli, A.; Weis, K.; Stahl, O.; Hillier, D. J.;
Corcoran, M.; Hamann, F.; Walborn, N.; Johansson, S.; Hartman, H.;
Bautista, M.
2003AAS...203.5805D Altcode: 2003BAAS...35.1302D
This program is valuable for a broad range of stellar and nebular
astrophysics, as well as data processing techniques and instrument
characteristics. While observing this object's mysterious 5.5-year
cycle, we obtained data on several distinct, complex, unfamiliar
classes of spectra which cannot be observed well elsewhere. The
stellar wind parameters lie outside normal experience, the Weigelt
ejecta produce narrow-line spectra unlike any other known object, and
the other spectra are also unusual. Altogether our results pertain to
stellar instabilities close to the Eddington limit, extreme stellar
winds, unexplored nebular/atomic excitation processes, nebular gas
dynamics, and instrument performance. <P />The project also represents
an extreme application of HST spectroscopy. Since η Car and its ejecta
are spatially, spectrally, and temporally complex, they require the best
available performance of HST/STIS across its full wavelength range. Such
observations will probably not be attainable again within the next 15
years. They also require improved data processing techniques which we
have developed, useful for HST/STIS programs on other objects. The
Eta Car Treasury data archive will be pertinent to a variety of
significant problems mentioned above -- not just η Carinae. (See
a related poster concerning the Archive.) <P />Here we report that
(1) the predicted event did indeed occur during May--July 2003; (2)
we obtained the planned data; (3) they show numerous fascinating and
difficult-to-explain phenomena; and (4) we sketch improved reduction
routines to achieve maximum resolution with STIS/CCD data in general. We
also show examples of the spectral structure and variations in Eta
Carinae. <P />This project is supported by STScI grant GO-9420.
---------------------------------------------------------
Title: Improved oscillator strengths and wavelengths for Os I and
Ir I, and new results on early r-process nucleosynthesis
Authors: Ivarsson, S.; Andersen, J.; Nordström, B.; Dai, X.;
Johansson, S.; Lundberg, H.; Nilsson, H.; Hill, V.; Lundqvist, M.;
Wyart, J. F.
2003A&A...409.1141I Altcode:
The radioactive decay of <SUP>238</SUP>U and <SUP>232</SUP>Th has
recently been used to determine ages for some of the oldest stars in
the Universe. This has highlighted the need for accurate observational
constraints on production models for the heaviest r-process elements
which might serve as stable references, notably osmium and iridium. In
order to provide a firmer basis for the observed abundances, we have
performed laser-induced fluorescence measurements and Fourier Transform
Spectroscopy to determine new radiative lifetimes and branching
fractions for selected levels in Os I and Ir I. From these data, we
determine new absolute oscillator strengths and improved wavelengths for
18 Os I and 4 Ir I lines. A reanalysis of VLT spectra of CS 31082-001
and new results for other stars with Os and Ir detections show that (i):
the lines in the UV and lambda 4260 Å yield reliable Os abundances,
while those at lambda lambda 4135, 4420 Å are heavily affected by
blending; (ii): the Os and Ir abundances are identical in all the stars;
(iii): the heavy-element abundances in very metal-poor stars conform
closely to the scaled solar r-process pattern throughout the range 56
<= Z <= 77; and (iv): neither Os or Ir nor any lighter species
are suitable as reference elements for the radioactive decay of Th
and U. <P />Based in part on observations obtained with the Very Large
Telescope of the European Southern Observatory at Paranal, Chile.
---------------------------------------------------------
Title: Revisited Abundance Diagnostics in Quasars: Fe II/Mg II Ratios
Authors: Verner, E.; Bruhweiler, F.; Verner, D.; Johansson, S.;
Gull, T.
2003ApJ...592L..59V Altcode: 2003astro.ph..6533V
Both the Fe II UV emission in the 2000-3000 Å region [Fe II(UV)]
and resonance emission line complex of Mg II at 2800 Å are prominent
features in quasar spectra. The observed Fe II(UV)/Mg II emission ratios
have been proposed as means to measure the buildup of the Fe abundance
relative to that of the α-elements C, N, O, Ne, and Mg as a function
of redshift. The current observed ratios show large scatter and no
obvious dependence on redshift. Thus, it remains unresolved whether a
dependence on redshift exists and whether the observed Fe II(UV)/Mg
II ratios represent a real nucleosynthesis diagnostic. We have used
our new 830 level model atom for Fe<SUP>+</SUP> in photoionization
calculations, reproducing the physical conditions in the broad-line
regions of quasars. This modeling reveals that interpretations of
high values of Fe II(UV)/Mg II are sensitive not only to Fe and Mg
abundance, but also to other factors such as microturbulence, density,
and properties of the radiation field. We find that the Fe II(UV)/Mg
II ratio combined with Fe II(UV)/Fe II(optical) emission ratio, where
Fe II(optical) denotes Fe II emission in 4000-6000 Å band, can be
used as a reliable nucleosynthesis diagnostic for the Fe/Mg abundance
ratios for the physical conditions relevant to the broad-line regions
of quasars. This has extreme importance for quasar observations with
the Hubble Space Telescope and also with the future James Webb Space
Telescope.
---------------------------------------------------------
Title: Experimental f-Value and Isotopic Structure for the Ni I Line
Blended with [O I] at 6300 Å
Authors: Johansson, S.; Litzén, U.; Lundberg, H.; Zhang, Z.
2003ApJ...584L.107J Altcode: 2003astro.ph..1382J
We have measured the oscillator strength of the Ni I line at 6300.34
Å, which is known to be blended with the forbidden line [O I]
λ6300 used for the determination of the oxygen abundance in cool
stars. We also give wavelengths of the two isotopic line components
of <SUP>58</SUP>Ni and <SUP>60</SUP>Ni derived from the asymmetric
laboratory line profile. These two line components of Ni I have to
be considered when calculating a line profile of the 6300 Å feature
observed in stellar and solar spectra. We also discuss the labeling of
the energy levels involved in the Ni I line since level mixing makes
the theoretical predictions uncertain.
---------------------------------------------------------
Title: The FERRUM Project: Experimental transition probabilities of
[Fe II] and astrophysical applications
Authors: Hartman, H.; Derkatch, A.; Donnelly, M. P.; Gull, T.;
Hibbert, A.; Johansson, S.; Lundberg, H.; Mannervik, S.; Norlin,
L. -O.; Rostohar, D.; Royen, P.; Schef, P.
2003A&A...397.1143H Altcode:
We report on experimental transition probabilities for thirteen
forbidden [Fe II] lines originating from three different metastable Fe
Ii levels. Radiative lifetimes have been measured of two metastable
states by applying a laser probing technique on a stored ion
beam. Branching ratios for the radiative decay channels, i.e. M1
and E2 transitions, are derived from observed intensity ratios
of forbidden lines in astrophysical spectra and compared with
theoretical data. The lifetimes and branching ratios are combined to
derive absolute transition probabilities, A-values. <P />We present
the first experimental lifetime values for the two Fe II levels
a<SUP>4</SUP>G<SUB>9/2</SUB> and b<SUP>2</SUP>H<SUB>11/2</SUB> and
A-values for 13 forbidden transitions from a<SUP>6</SUP>S<SUB>5/2</SUB>,
a<SUP>4</SUP>G<SUB>9/2</SUB> and b<SUP>4</SUP>D<SUB>7/2</SUB> in the
optical region. A discrepancy between the measured and calculated
values of the lifetime for the b<SUP>2</SUP>H<SUB>11/2</SUB> level
is discussed in terms of level mixing.\ We have used the code CIV3 to
calculate transition probabilities of the a<SUP>6</SUP>D-a<SUP>6</SUP>S
transitions. <P />We have also studied observational branching ratios
for lines from 5 other metastable Fe II levels and compared them to
calculated values. A consistency in the deviation between calibrated
observational intensity ratios and theoretical branching ratios for
lines in a wider wavelength region supports the use of [Fe II] lines
for determination of reddening.
---------------------------------------------------------
Title: Temporal Variations of Fe II Fluorescence Lines in the
Symbiotic Star AG Peg
Authors: Eriksson, M.; Johansson, S.; Wahlgren, G. M.
2003ASPC..303..109E Altcode: 2003ssps.conf..109E
No abstract at ADS
---------------------------------------------------------
Title: Radiative Cycle with Stimulated Emission from Atoms and Ions
in an Astrophysical Plasma
Authors: Johansson, S.; Letokhov, V. S.
2003PhRvL..90a1101J Altcode: 2002astro.ph.12382J
We propose that a radiative cycle operates in atoms and ions located
in a rarefied gas in the vicinity of a hot star. Besides spontaneous
transitions the cycle includes a stimulated transition in one very
weak intermediate channel. This radiative “bottleneck” creates a
population inversion, which for an appropriate column density results
in amplification and stimulated radiation in the weak transition. The
stimulated emission opens a fast decay channel leading to a fast
radiative cycle in the atom (or ion). We apply this model by explaining
two unusually bright FeII lines at 250.7 and 250.9nm in the UV spectrum
of gas blobs close to η Carinae, one of the most massive and luminous
stars in the Galaxy.
---------------------------------------------------------
Title: Comments on atomic data for the GAIA spectral region
Authors: Wahlgren, G. M.; Johansson, S.
2003ASPC..298..481W Altcode: 2003gsst.conf..481W
No abstract at ADS
---------------------------------------------------------
Title: The -145 km/s Absorption System of Eta Carinae
Authors: Vieira, G. L.; Gull, T. R.; Danks, A. C.; Johansson, S.
2002AAS...201.4904V Altcode: 2002BAAS...34.1184V
With the STIS E230H mode (R 118,000), we have identified about twenty
absorption components in line of sight from Eta Carinae. Two components,
one at -513 km/s and another at -145 km/s, are quite different in
character from the others, mostly at intermediate velocities (See
adjacent posters by T. Gull and A. Danks). The -145 km/s component
is significantly wider in fwhm, is seen in many more species, and
the lower level can be above 20,000 cm-1, well above the 2000 cm-1
noted in the -513 km/s component. In the spectral region from 2400 to
3160A, approximately 500 absorption lines have been identified. In this
poster, we will present line identifications and atomic parameters of
the measured lines, hopefully providing insight as to what levels are
being excited and by what processes. Observations were accomplished
through STScI under proposal 9242 (Danks, P.I.). Funding is through
the STIS GTO resources.
---------------------------------------------------------
Title: Properties of the -513 km/s Ejecta in the Spectrum of Eta
Carinae
Authors: Danks, A. C.; Gull, T. R.; Vieira, G. L.; Johansson, S.
2002AAS...201.4905D Altcode: 2002BAAS...34.1184D
In the spectral region 2400-3160A of Eta Carinae, we have identified
approximately 500 absorption lines each with up to twenty velocity
components.The -512 km/s component is truely unique as 1) the typical
line width is <3 km/s, 2) the identified lines are in Fe I, Fe II,
V II and Ti II, and 3) the lines originate from lower levels up to 2000
cm-1 above the ground level. We have measured the velocity centers,
full width at half maximum and equivalent widths for approximately
100 absorption lines. Initial results were very confusing as we
found more variation in central velocities than would be expected
from known STIS echelle wavelength standards. Upon further review, we
found that the reporteded wavelengths in the NIST and Kurucz databases
were not sufficiently accurate. S. Johansson searched FTS laboratory
measurements performed at Lund for V II and Ti II and provided much
improved wavelength measures. Likewise, we find more variation in
column density than expected statistically from the accuracy of the
equivalent widths for lines originating from the same energy level. We
are reviewing the published gf values and our measurements to improve
the measured column densities. Some spectroscopy of the ejecta
has already been accomplished at two different epochs. Preliminary
measures of equivalent widths indicate there may be some variation
with time, but we await measurements planned for July 2003 during the
upcoming spectroscopic minimum of Eta Carinae. These observations were
accomplished through STScI and funding was from STIS GTO resources.
---------------------------------------------------------
Title: The FERRUM Project: Experimental oscillator strengths of
the UV 8 multiplet and other UV transitions from the y<SUP>6</SUP>P
levels of Fe II
Authors: Pickering, J. C.; Donnelly, M. P.; Nilsson, H.; Hibbert,
A.; Johansson, S.
2002A&A...396..715P Altcode:
We report on experimental branching fractions (BFs) for 19 transitions
from the three 3d<SUP>5</SUP>(<SUP>6</SUP>S)4s4p(<SUP>3</SUP>P)
y<SUP>6</SUP>P levels in Fe II, measured in Fourier transform spectra
of a Penning discharge lamp and a hollow cathode lamp. The transition
wavelengths span the interval between 1600 and 2850 Å. Absolute
oscillator strengths (f-values) have been derived by combining
the BFs with experimental radiative lifetimes recently reported
in the literature. Theoretical f-values have been calculated using
configuration interaction wavefunctions. The new experimental and
theoretical f-values are compared with data available in the literature
and in databases. The strongest lines measured belong to the UV 8
multiplet of Fe II, which has one ground state transition appearing
as a prominent feature at 1608 Å in interstellar spectra. The line
is accompanied by a satellite at 1611 Å due to a level mixing, which
is discussed in the paper.
---------------------------------------------------------
Title: The Origin of Fe II and [Fe II] Emission Lines in the
4000-10000 Å Range in the BD Weigelt Blobs of η Carinae
Authors: Verner, E. M.; Gull, T. R.; Bruhweiler, F.; Johansson, S.;
Ishibashi, K.; Davidson, K.
2002ApJ...581.1154V Altcode:
We present numerical simulations that reproduce the salient features of
the amazingly strong [Fe II] and Fe II emission spectra in the B and
D Weigelt blobs of η Carinae. For our studies we have used spectra
obtained during the 1998 epoch observations with the Hubble Space
Telescope (HST). The spectrum of the B and D Weigelt blobs dominates in
[Fe II] and Fe II emission lines. The same observations show no Fe I or
Fe III. We have compared our measurements of the strongest (>=200)
[Fe II] and Fe II lines and blends in the spectrum with theoretical
predictions. Our predictions are based on non-LTE modeling of the Fe II
atom, which includes the lowest 371 energy levels (all levels up to 11.6
eV). We have investigated the dependence of the spectrum on electron
density, pumping by the blackbody-like stellar continuum, and intense
Lyα emission. We find that radiative pumping is essential in explaining
the observed spectrum. We have identified the main pumping routes
responsible for the observed Fe II emission. Comparison between the
model and observations reveals details of the radiation field. Pumping
by the blackbody-like stellar radiation field from η Carinae explains
the numerous strong [Fe II] and Fe II lines in the range of 4000-6500
Å. The strongest Fe II lines in a range of 8000-10000 Å are pumped by
intense Lyα radiation. Based on observations made with the NASA/ESA
Hubble Space Telescope, obtained at the Space Telescope Science
Institute, which is operated by the Association of Universities for
Research in Astronomy, Inc., under NASA contract NAS 5-26555.
---------------------------------------------------------
Title: Erratum: Successsive resonance-enhanced two-photon ionization
of elements abundant in nebulae. I. Atoms and ions of C, N, and O
Authors: Johansson, S.; Letokhov, V. S.
2002A&A...395..345J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The origin of the anomalous intensity ratio between very
bright UV FeII lines and their satellites in gaseous condensations
close to the star eta Carinae
Authors: Klimov, V.; Johansson, S.; Letokhov, V. S.
2002A&A...385..313K Altcode:
We present a model that explains the anomalous intensity ratios
between each of two very bright UV lines of Fe II at 2507 Å and 2509
Å and its corresponding satellite line, observed in HST spectra
of a compact gaseous condensation (blob B) in the vicinity of the
star protect eta Car.The model is based on the assumption that the
FeII transitions have a substantial optical thickness, which varies
as a result of the photodepletion of the long-lived lower states,
c<SUP>4</SUP>F<SUB>7/2,9/2</SUB>, by the intense Lyalpha radiation. In
conditions where the photodepletion rates of these two states differ,
the resonance scattering lengths of the spectral lines become different
as well. In the presence of a weak, nonresonant (continuous) absorption,
this gives rise to a difference in attenuation between the spectral
lines (the Hummer effect (Hummer 1968)). It is the combination of
these two effects that explains the anomalous (as compared with
laboratory data) intensity ratios observed in the two pairs of UV
FeII lines. Ionization channels of stimulated photodepletion by the
Lyalpha radiation, including the possible role of autoionization levels,
are considered.
---------------------------------------------------------
Title: Experimental oscillator strengths in U II of cosmological
interest
Authors: Nilsson, H.; Ivarsson, S.; Johansson, S.; Lundberg, H.
2002A&A...381.1090N Altcode:
Oscillator strengths for 57 U II lines in the region 3500-6700 Å have
been derived by combining new branching fraction measurements with
recently measured lifetimes. The lines combine six upper levels with
numerous low levels having excitation energies of 0-1.5 eV. The data
include the U II line at 3859 Å, which is used for cosmochronology.
---------------------------------------------------------
Title: The FERRUM Project: New f-value Data for Fe II and
Astrophysical Applications
Authors: Johansson, S.; Derkatch, A.; Donnelly, M. P.; Hartman, H.;
Hibbert, A.; Karlsson, H.; Kock, M.; Li, Z. S.; Leckrone, D. S.;
Litzén, U.; Lundberg, H.; Mannervik, S.; Norlin, L. -O.; Nilsson,
H.; Pickering, J.; Raassen, T.; Rostohar, D.; Royen, P.; Schmitt,
A.; Johanning, M.; Sikström, C. M.; Smith, P. L.; Svanberg, S.;
Wahlgren, G. M.
2002PhST..100...71J Altcode:
We present the FERRUM Project, an international collaboration aiming
at a production and evaluation of oscillator strengths (transition
probabilities) of selected spectral lines of singly ionized iron group
elements, that are of astrophysical relevance. The results obtained
include measurements and calculations of permitted and forbidden
lines of Fe II. The data have been applied to both emission and
absorption lines in astrophysical spectra. We make comparisons between
experimental, theoretical and astrophysical f-values. We give a general
review of the various measurements, and discuss the UV8 multiplet of
Fe II around 1610 Å in detail.
---------------------------------------------------------
Title: Experimental oscillator strengths in Th II
Authors: Nilsson, H.; Zhang, Z. G.; Lundberg, H.; Johansson, S.;
Nordström, B.
2002A&A...382..368N Altcode:
We have measured radiative lifetimes of ten Th II levels by using
the laser-induced fluorescence technique and branching fractions
with Fourier transform spectroscopy. By combining the new branching
fractions with a total of 23 lifetimes, from the present work and from
measurements by Simonsen et al. (\cite{Simonsen}), absolute oscillator
strengths for 180 lines have been derived. Some of these new f-values
reported are relevant for radioactive dating of stars.
---------------------------------------------------------
Title: The Strontium Filament within the Homunculus of Eta Carinae
Authors: Gull, T. R.; Hartman, H.; Zethson, T.; Johansson, S.;
Ishibashi, K.; Davidson, K.
2001AAS...19913501G Altcode: 2001BAAS...33R1505G
During a series of HST/STIS observations of Eta Carinae and associated
ejecta, we noticed a peculiar emission filament located a few arcseconds
north of the central source. While bright in nebular standards, it
is submerged in a sea of scattered starlight until moderately high
dispersion, long-slit spectroscopy with the STIS (R 8000) brings
the emission lines out. The initial spectrum, centered on 6768A with
the STIS G750M grating, led to identification of twenty lines from
singly-ionized species including [Sr II], [Fe II], [Ti II], [Ni II],
[Mn II], and [Co II] (Zethson, etal., 2001, AJ 122, 322). No Balmer
emission is detected from this filament and the Fe II 2507,9 lines,
known to be pumped by Lyman alpha radiation in other regions near the
central source, are not detected. Followup observations have led to
detection of hundreds more emission lines from iron group elements in
neutral and singly-ionized states. Thus far all are excited by less
than 10 eV. This peculiar nebular emission is thought to be due to
very intense stellar radiation, stripped of uv flux shortward of Lyman
alpha, bathing a neutral structure. We are systematically identifying
the many lines (over 90% identified) and measuring line intensities
that will then be modeled to determine excitation mechanisms,
temperature and density. Two [Sr II] and two Sr II lines have now been
measured. Bautista, etal. (in preparation) have modeled the strontium
flux ratios and find that large radiation fluxes and/or high strontium
abundances may account for the detected emission. These observations
were supported by STIS GTO funding and GO funding through the STScI.
---------------------------------------------------------
Title: A model for the origin of the anomalous and very bright UV
lines of Fe II in gaseous condensations of the star η Carinae
Authors: Johansson, S.; Letokhov, V. S.
2001A&A...378..266J Altcode:
We present a qualitative physical model of the origin of two very
bright UV lines of Fe II at 2507-2509 Å, present in high-resolution
spectra of gaseous condensations (blobs) close to the central star
of eta Carinae. The spectra have been obtained with the Hubble Space
Telescope (HST). The model is based on a type of Bowen mechanism
with selective photoexcitation of Fe II by a broad HLyalpha profile,
generated in the HII region and diffusely transferred to the optically
thick HI region. The frequency distribution by large Doppler diffusion
into the HI region provides a substantial broadening of HLyalpha ,
which makes it possible to selectively photo-excite short-lived
(~1 ns) states at 11.2 eV in Fe II. Within the frame of the present
model the intense HLyalpha radiation induces a depletion of the lower,
long-lived (~1 ms) level of the strong UV lines by photoionization. The
subsequent recombination of Fe III explains the appearance of the
“forest” of narrow Fe II lines. The possibility of a cyclic process
is also discussed, where HLyalpha induces depletion to bound states,
which have fast decays in the far-UV to the lower state of the Bowen
pumping channel.
---------------------------------------------------------
Title: The FERRUM project: Branching ratios and atomic transition
probabilities of Fe II transitions from the 3d<SUP>6</SUP>(a
<SUP>3</SUP>F)4p subconfiguration in the visible to VUV spectral
region
Authors: Pickering, J. C.; Johansson, S.; Smith, P. L.
2001A&A...377..361P Altcode:
We report measurements of the relative intensities of 81 emission
lines of Fe II between 160 nm and 350 nm (62 168 cm<SUP>-1</SUP>
to 28 564 cm<SUP>-1</SUP>) from 4 levels by high resolution Fourier
transform spectrometry, using a Penning discharge lamp as light
source. These relative intensities have been used to determine
the line branching fractions, which have then been combined with
accurate experimental radiative lifetime measurements reported
recently to give absolute transition probabilities and oscillator
strengths for 81 lines. The accuracy of these f-values is compared
with other previous experimental measurements, and with theoretical
values. The new transition probabilities will allow accurate
determinations of Fe II abundances in a wide variety of astrophysical
objects. Tables 2 and 3 are only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/377/361
---------------------------------------------------------
Title: Successsive resonance-enhanced two-photon ionization of
elements abundant in nebulae. I. Atoms and ions of C, N, and O
Authors: Johansson, S.; Letokhov, V. S.
2001A&A...375..319J Altcode:
We discuss resonance-enhanced two-photon ionization (RETPI) and
present schemes of successive RETPI of the elements C, N, and O in
nebulae. RETPI is activated by intrinsic radiation stored in the form
of trapped spectral lines of HI, HeI, and HeII in the optically thick
nebula. The rate of this two-step photoionization is comparable with
or exceeds the low recombination rate of the photoions formed in the
process. This leads to an accumulation of photoions and subsequent
RETPI until such highly charged ions are formed that they cannot
further be ionized in this way by the intrinsic radiation from the
strong spectral lines of HI, HeI, and HeII.
---------------------------------------------------------
Title: New laboratory lifetime measurements of U II for the uranium
cosmochronometer
Authors: Lundberg, H.; Johansson, S.; Nilsson, H.; Zhang, Z.
2001A&A...372L..50L Altcode:
We present new measurements of radiative lifetimes for
six energy levels of singly ionized uranium, U II, using
laser-induced fluorescence technique. One of the levels,
5f<SUP>3</SUP>6d7p<SUP>6</SUP>M<SUB>13/2</SUB> at 26191 cm<SUP>-1</SUP>,
decays by a transition at 3859.6 Å. This line has recently been
observed in the spectrum of the metal-poor star CS1082-001, the
first detection of uranium outside the solar system. The lambda 3859
line can be used as the presently most accurate cosmochronometer
(Cayrel et al. \cite{Cayrel}). Our value of the lifetime of the
<SUP>6</SUP>M<SUB>13/2</SUB> level is 18.6+/-0.7 ns, and it confirms the
f-value used in the Nature article by Cayrel et al. (\cite{Cayrel}),
which is based on an experimental lifetime of 20+/-5 ns (Chen &
Borzileri \cite{Chen}). The new measurement also removes the doubt about
the choice between that value and other f-values in the literature,
differing by a factor of 3. Adopting the same branching fraction as
Chen & Borzileri (\cite{Chen}) for the 3859.6 Å line, we derive
a gf-value of 0.68, which is 8% higher than the value used by Cayrel
et al. (\cite{Cayrel}). Of significance for the chronometer is also
the reduced uncertainty of the radiative lifetime, 4% compared to 25%,
and consequently of the f-value, which should decrease the uncertainty
in the determination of the stellar age considerably.
---------------------------------------------------------
Title: The FERRUM project: Experimental f-values for 4p-5s transitions
in Fe II
Authors: Karlsson, H.; Sikstrom, C. M.; Johansson, S.; Li, Z. S.;
Lundberg, H.
2001A&A...371..360K Altcode:
New measurements of radiative lifetimes of four 3d<SUP>6</SUP>5s levels
in Fe II at about 10 eV are presented along with absolute oscillator
strengths for twenty 4p-5s transitions involving the four levels. The
experimental measurements are compared with two different sets of
theoretical calculations. The lines are of particular interest in the
modeling of HLyalpha pumped fluorescence of Fe II in astrophysical
plasmas.
---------------------------------------------------------
Title: The Bismuth Abundance in the HGMN Stars χ Lupi and HR 7775
and Improved Atomic Data for Selected Transitions of BI I, BI II,
and BI III
Authors: Wahlgren, G. M.; Brage, T.; Brandt, J. C.; Fleming,
J.; Johansson, S.; Leckrone, D. S.; Proffitt, C. R.; Reader, J.;
Sansonetti, C. J.
2001ApJ...551..520W Altcode:
High-resolution spectra of the chemically peculiar HgMn stars χ Lupi
and HR 7775, obtained with the Hubble Space Telescope/Goddard High
Resolution Spectrograph, are investigated for their abundance of bismuth
by comparison with LTE synthetic spectrum modeling. HR 7775, previously
known from International Ultraviolet Explorer spectra to display strong
lines of Bi II, is determined to have bismuth present at an enhancement
level of nearly 5 orders of magnitude from the lines Bi II λλ1436,
1902 and Bi III λ1423. The bismuth enhancement for χ Lupi is found
to be near a level of 1.5 dex, and an ionization anomaly between
Bi<SUP>+</SUP> and Bi<SUP>++</SUP> is apparent. HR 7775 abundance
enhancements of the heavy elements platinum, [Pt/H]=4.7 dex, and gold,
[Au/H]=3.8 dex, have also been determined. New laboratory measurements
for wavelengths and hyperfine structure patterns of Bi I/Bi II/Bi
III lines are presented, as well as the results of calculations for
hyperfine structure constants and oscillator strengths for selected
lines of Bi II and Bi III. Based on observations with the NASA/ESA
Hubble Space Telescope, obtained at the Space Telescope Science
Institute, which is operated by the Association of Universities for
Research in Astronomy, Inc., under NASA contract NAS5-26555.
---------------------------------------------------------
Title: Intensity anomalies in the C IV doublet caused by Fe II
fluorescence
Authors: Eriksson, M.; Johansson, S.; Wahlgren, G.
2001ASPC..242..325E Altcode: 2001ecom.conf..325E
No abstract at ADS
---------------------------------------------------------
Title: Identification of Lines in the Strontium Region of Eta Carinae
Authors: Hartman, H.; Zethson, T.; Johansson, S.; Gull, T.; Ishibashi,
K.; Davidson, K.; Smith, N.
2001ASPC..242..107H Altcode: 2001ecom.conf..107H
No abstract at ADS
---------------------------------------------------------
Title: Mysterious UV Lines of Fe II in the Blob Spectrum of Eta
Carinae
Authors: Johansson, S.; Letokhov, V.
2001ASPC..242..309J Altcode: 2001ecom.conf..309J
No abstract at ADS
---------------------------------------------------------
Title: Fluorescence Lines in Eta Carinae and Other Objects
Authors: Johansson, S.; Zethson, T.; Hartman, H.; Letokhov, V.
2001ASPC..242..297J Altcode: 2001ecom.conf..297J
No abstract at ADS
---------------------------------------------------------
Title: Cr II Fluorescence in Eta Carinae due to H Lyman Alpha Pumping
Authors: Zethson, T.; Hartman, H.; Johansson, S.; Gull, T.; Ishibashi,
K.; Davidson, K.
2001ASPC..242...97Z Altcode: 2001ecom.conf...97Z
No abstract at ADS
---------------------------------------------------------
Title: Fluorescence Observed in the Ultraviolet Spectrum of RR
Telescopii
Authors: Hartman, H.; Johansson, S.
2001ASPC..242..361H Altcode: 2001ecom.conf..361H
No abstract at ADS
---------------------------------------------------------
Title: Accurate laboratory wavelengths of some ultraviolet lines
of Cr, Zn and Ni relevant to time variations of the fine structure
constant
Authors: Pickering, J. C.; Thorne, A. P.; Murray, J. E.; Litzén,
U.; Johansson, S.; Zilio, V.; Webb, J. K.
2000MNRAS.319..163P Altcode:
The quality of astronomical spectroscopic data now available is
so high that interpretation and analysis are often limited by the
uncertainties of the laboratory data base. In particular, the limit
with which space-time variations in the fine structure constant α
can be constrained using quasar spectra depends on the availability
of more accurate laboratory rest wavelengths. We recently measured
some transitions in magnesium by high-resolution Fourier transform
spectroscopy for this purpose, and we now report measurements on some
ultraviolet resonance lines of Znii (2062 and 2026Å), Crii (2066,
2062 and 2056Å) and Niii (1751, 1741, 1709 and 1703Å). Apart from the
last line, which is very weak, the uncertainty of these measurements
is 0.002cm<SUP>-1</SUP> (0.08må) for the lines around 2000Å and
0.004cm<SUP>-1</SUP> (0.12må) for the lines around 1700Å.
---------------------------------------------------------
Title: The FERRUM project: new experimental and theoretical f-values
for 4p-4d transitions in Fe II applied to HST spectra of chi Lupi
Authors: Nilsson, H.; Sikström, C. M.; Li, Z. S.; Lundberg, H.;
Raassen, A. J. J.; Johansson, S.; Leckrone, D. S.; Svanberg, S.
2000A&A...362..410N Altcode:
Radiative lifetimes for six highly excited levels in Fe II have been
measured at Lund Laser Centre applying the laser induced fluorescence
technique and two-step excitation. The energy levels belong to the
even-parity 3d<SUP>6</SUP>(<SUP>5</SUP>D)4d subconfiguration at about
10 eV. Branching fractions (BF:s) of 29 transitions from these levels
to the 3d<SUP>6</SUP>(<SUP>5</SUP>D)4p subconfiguration at about 5
eV have been measured in the wavelength region 2000-3000 Å with the
Lund Fourier Transform Spectrometer. By normalizing the BF:s with the
lifetimes we get experimental oscillator strengths for these 29 4p-4d
lines. The oscillator strengths are compared with new theoretical
calculations using the orthogonal operator technique and applied to
high-resolution spectra of the star chi Lupi, recorded with the Hubble
Space Telescope.
---------------------------------------------------------
Title: New forbidden and fluorescent Fe III lines identified in HST
spectra of eta Carinae
Authors: Johansson, S.; Zethson, T.; Hartman, H.; Ekberg, J. O.;
Ishibashi, K.; Davidson, K.; Gull, T.
2000A&A...361..977J Altcode:
We discuss the origin of eight emission lines in the spectra of
gas blobs close to the central star of eta Carinae. The spectra
have been obtained with the Goddard High Resolution Spectrograph
(GHRS) and the Space Telescope Imaging Spectrograph (STIS) onboard
the Hubble Space Telescope. Between 2400 and 2500 Å five narrow
lines are identified as new forbidden lines of doubly ionized iron,
[Fe III]. We present gA-value data for the corresponding transitions,
which combine two different metastable configurations of Fe III. An
anomalous intensity of the narrow Fe III line (UV 34) at 1914 Å is
explained as fluorescence due to HLyalpha pumping. A level mixing of
about 1% increases the f-value of the pumped excitation channel by
more than two orders of magnitude, which makes the pumping efficient
and the fluorescence significant. We introduce a new designation for
fluorescence lines photoexcited by an accidental resonance, eg. < Fe
III> in the case of doubly ionized iron. Based on observations with
the NASA/ESA Hubble Space Telescope, and supported by grant numbers
GO-6501 and GO-7302 from the Space Telescope Science Institute. The
STScI is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS5-26555.
---------------------------------------------------------
Title: Ultraviolet fluorescence lines of Fe II observed in satellite
spectra of the symbiotic star RR Telescopii
Authors: Hartman, H.; Johansson, S.
2000A&A...359..627H Altcode:
By examining all emission lines of Fe II in high resolution satellite
spectra of the symbiotic star RR Tel we have made a systematic study
of fluorescence lines in the ultraviolet wavelength region 1200-3000
Ä. We list 33 energy levels of Fe II that are selectively excited
in the stellar system by photons from strong lines of H, He II, Si
III, O III, C IV, O V, Ne V, and O VI. All energy levels listed are
accompanied by the most probable pumping line. The subsequent decay
from the pumped levels results in about 120 fluorescence lines observed
in spectra recorded with the International Ultraviolet Explorer and
the Hubble Space Telescope. The tables include 9 energy levels and 17
emission lines of Fe II, which are for the first time attributed to
fluorescence. In a finding list we also include potential fluorescence
lines, which means additional transitions from the pumped energy levels
observed in laboratory spectra but not in the stellar spectra. Based on
observations by the International Ultraviolet Explorer (IUE) and the
Goddard High Resolution Spectrograph (GHRS) onboard the Hubble Space
Telescope (HST). Tables 1-5 are only available electronically with
the On-Line publication at http://link.springer.de/link/service/00230/
---------------------------------------------------------
Title: [Sr II] Detected in a Nebular Filament Near Eta Carinae
Authors: Gull, T.; Zethson, T.; Hartman, H.; Johansson, S.; Davidson,
K.; Ishibashi, K.
2000AAS...196.0508G Altcode: 2000BAAS...32..682G
Observations with the Space Telescope Imaging Spectrograph on the Hubble
Space Telescope reveal a peculiar emission line region in the close
vicinity to Eta Carinae. The lines of [SrII], [MnII], [CoII], [TiII],
[NiII] and [FeI] are detected in the 6400-7000A spectral interval at
a blue-shifted velocity of 95 km/sec and seem to be associated with a
long, narrow filament with dimensions of <0.5" by 1.1". The filament
is notable as it is separate both in velocity and structure from the
bright emission of the Integral Nebula. This filament is buried within
the Homunculus and is not visible in direct images which are dominated
by reflection nebulosities. In our literature searches we have found
no evidence of strontium emission lines in nebulae. We are aware of
permitted transitions of strontium seen in AGB stars. S-processed
elements like strontium are not expected in the ejecta of a massive
star like Eta Carinae. Detection of [SrII] and the fact that the [NiII],
[MnII] and [CoII] lines are unusually strong compared to [FeI] are quite
a surprise. It has long been known that nitrogen is overabundant in
the ejecta of Eta Carinae. Is this processed material from the present
star(s)? Has there been processed material ejected from a more evolved
companion? The situation is decidedly mysterious. This research has
been supported by NASA through STScI grants and the STIS GTO funding.
---------------------------------------------------------
Title: The FERRUM Project
Authors: Johansson, S.; Lundberg, H.; Li, Z.; Nilsson, H.; Sikström,
C. M.; Zethson, T.; Hartman, H.; Karlsson, H.; Dolk, L.; Mannervik,
S.; Raassen, T.; Leckrone, D.
2000IAUJD...1E..20J Altcode:
The FERRUM project aims at improving the database for oscillator
strengths in iron group elements with an emphasis on astrophysically
important ions. The international collaboration includes experts on
experimental, theoretical and observational data. The first results
concern Fe II. Experimental radiative lifetimes (LIF technique) for
some particular levels of Fe II are combined with experimental (FT
spectroscopy) and theoretical branching fractions to obtain absolute
oscillator strengths, which are then compared with new theoretical
data (orthogonal operator technique). Depending on the agreement
complementary theoretical data are included. The new data are tested
in stellar spectra (HST, NOT). We have obtained f-values for Fe II
lines in the UV and optical regions originating from lower levels
with excitation energies in the range 3-10 eV. The lines belong to
four different transition arrays. The difference between experimental
and theoretical data is of the order of 10%. The new data provide
independent and new lines for abundance analysis and a test of LTE
conditions in stellar atmospheres. Lifetimes of metastable states are
measured at a storage ring, providing the first experimental data for
forbidden lines, [Fe II].
---------------------------------------------------------
Title: Commission 14: Atomic and Molecular Data: (Donnees Atomiques
et Moleculaires)
Authors: Rostas, F.; Smith, P. L.; Berrington, K. A.; Feautrier, N.;
Grevesse, N.; Johansson, S.; Jørgensen, U. G.; Martin, W. C.; Mason,
H.; Parkinson, W.; Tchang-Brillet, W. -Ü. L.
2000IAUTA..24..380R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New Zr II oscillator strengths and the zirconium conflict in
the HgMn star chi LUPI
Authors: Sikström, C. M.; Lundberg, H.; Wahlgren, G. M.; Li, Z. S.;
Lynga, C.; Johansson, S.; Leckrone, D. S.
1999A&A...343..297S Altcode:
Lifetimes on the sub-nanosecond scale for the levels v(2) D_{3/2}, v(2)
F_{3/2} and v(2) F_{5/2} in the 4d5s5p configuration in Zr II have been
measured, using the method of laser-induced fluorescence. Combined with
branching fractions obtained with the Lund Ultraviolet (UV) Fourier
Transform Spectrometer (FTS), experimental oscillator strengths have
been derived. From Hubble Space Telescope/Goddard High-Resolution
Spectrograph spectra, the zirconium abundance in the HgMn star chi
Lupi has been determined from Zr II and Zr III lines. More than an
order of magnitude difference in the Zr II abundance has been derived
from these ionization stages. The difference is much too large to
be explained by uncertainties in the oscillator strengths. Possible
explanations of this difference have to be found in the stellar models,
such as the influence of non-LTE or diffusion.
---------------------------------------------------------
Title: Strange Velocities in the Equatorial Ejecta of η Carinae
Authors: Zethson, T.; Johansson, S.; Davidson, K.; Humphreys, R. M.;
Ishibashi, K.; Ebbets, D.
1999ASPC..179..123Z Altcode: 1999ecm..conf..123Z
No abstract at ADS
---------------------------------------------------------
Title: Atomic Physics Aspects on Previously and Newly Identified
Iron Lines in the HST Spectrum of η Carinae
Authors: Johansson, S.; Zethson, T.
1999ASPC..179..171J Altcode: 1999ecm..conf..171J
No abstract at ADS
---------------------------------------------------------
Title: Emission line profiles in the spectrum of υ Sgr (poster)
Authors: Strid, K.; Kalus, G.; Johansson, S.; Wahlgren, G. M.;
Zapadlik, I.; Ardeberg, A.; Lundström, I.
1999anot.conf..252S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Spectrum and Term Analysis of Co II
Authors: Pickering, Juliet C.; Raassen, A. J. J.; Uylings, P. H. M.;
Johansson, S.
1998ApJS..117..261P Altcode:
High-resolution spectra of singly ionized cobalt have been recorded by
Fourier transform spectrometry in the region 1420-33333 Å (70422-3000
cm<SUP>-1</SUP>) with cobalt-neon and cobalt-argon hollow cathode
lamps as sources. Most of the Co II lines exhibit broadening due to
hyperfine structure, but the wavenumber uncertainty for the center of
gravity of the strongest lines is less than 0.002 cm<SUP>-1</SUP>. Of
the previously listed energy levels of Co II, 215 have been revised
and six have been discarded. In addition, 171 new levels have been
found of which 125 are reported here for the first time. The number of
classified lines has doubled with wavenumbers and classifications being
presented for 2373 Co II lines, of which 1242 involve the new levels.
---------------------------------------------------------
Title: The Impact of GHRS on Atomic Physics - A Fruitful Collaboration
Between Laboratory and Stellar Spectroscopy
Authors: Johansson, S.; Leckrone, D. S.; Davidson, K.
1998ASPC..143..155J Altcode: 1998sigh.conf..155J
No abstract at ADS
---------------------------------------------------------
Title: Abundances and Isotopic Compositions of Singly Ionized Platinum
in Chi LUPI and HR 7775
Authors: Kalus, G.; Johansson, S.; Wahlgren, G. M.; Leckrone, D. S.;
Brandt, J. C.; Thorne, A. P.
1998ASPC..143..326K Altcode: 1998sigh.conf..326K
No abstract at ADS
---------------------------------------------------------
Title: High-Resolution Observation of B II A1362 in Chi LUPI
Authors: Zethson, T.; Johansson, S.; Wahlgren, G. M.; Leckrone, D. S.
1998ASPC..143..339Z Altcode: 1998sigh.conf..339Z
No abstract at ADS
---------------------------------------------------------
Title: Atomic Calculations Inspired by the GHRS - gf-Values, Hyperfine
Structure Constants, and Isotope Shifts for Heavy Elements
Authors: Brage, T.; Proffitt, C. R.; Wahlgren, G. M.; Leckrone, D. S.;
Johansson, S.
1998ASPC..143..378B Altcode: 1998sigh.conf..378B
No abstract at ADS
---------------------------------------------------------
Title: Very Heavy Elements in the HgMn Star Chi LUPI
Authors: Wahlgren, G. M.; Leckrone, D. S.; Brage, T.; Proffitt, C. R.;
Johansson, S.
1998ASPC..143..330W Altcode: 1998sigh.conf..330W
No abstract at ADS
---------------------------------------------------------
Title: The Abundance of CO in the HgMn Star Chi LUPI
Authors: Zethson, T.; Johansson, S.; Wahlgren, C. M.; Pickering, J.;
Leckrone, D. S.
1998ASPC..143..334Z Altcode: 1998sigh.conf..334Z
No abstract at ADS
---------------------------------------------------------
Title: Oscillator Strengths and the Rhodium Abundance in the HgMn
Type Star Chi LUPI
Authors: Lundberg, H.; Johansson, S.; Litzen, U.; Wahlgren, C. M.;
Leckrone, D. S.
1998ASPC..143..343L Altcode: 1998sigh.conf..343L
No abstract at ADS
---------------------------------------------------------
Title: Strange velocities in the equatorial ejecta of Eta Carinae
Authors: Davidson, K.; Zethson, T.; Johansson, S.; Ishibashi, K.;
Ebbets, D.
1997AAS...191.3406D Altcode: 1997BAAS...29R1261D
In 1996--1997 we obtained HST/GHRS and HST/FOS data on locations thought
be be in the equatorial ejecta of Eta Carinae. One motivation was a
desire to test the age of the equatorial debris-disk, which, according
to some evidence, may be younger than the bipolar lobes. In fact,
however, the velocities are inconsistent with both of the obvious
models. The observed values may indicate the presence of old, slow
material, or that the geometrical situation has been misinterpreted,
or something else even more bizarre. This is one more instance
of an important detail concerning Eta Car that should have been
straightforward but which turns out instead to be, essentially,
not understood.
---------------------------------------------------------
Title: The Boron Isotope Ratio in HD 76932
Authors: Rebull, L.; Duncan, D.; Johansson, S.; Thorburn, J.; Fields,
B.; Schramm, D.
1997AAS...191.1305R Altcode: 1997BAAS...29.1230R
Data in the lambda 2090 B region of HD 76932 were obtained using the
HST GHRS echelle at a resolution of 90,000. This wavelength region has
been previously identified as a likely candidate for observing the (11)
B/(10) B isotopic splitting (Johansson et al. 1993). Data presented
here provides some constraints on the isotopic ratio, but it is not
certain whether or not the line in question is blended with unknown
stellar absorption feature(s), making an unambiguous detection of the
isotopic ratio impossible. The constraints that can be placed on the
isotopic ratio based on these data are discussed.
---------------------------------------------------------
Title: Status of the AMANDA and BAIKAL Neutrino Telescopes
Authors: Askebjer, P.; Barwick, S. W.; Bay, R.; Bergström, L.;
Bouchta, A.; Carius, S.; Dahlberg, E.; Engel, K.; Erlandsson, B.;
Goobar, A.; Gray, L.; Hallgren, A.; Halzen, F.; Heukenkamp, H.; Hulth,
P. O.; Hundertmark, S.; Jacobsen, J.; Johansson, S.; Kandhadai, V.;
Karle, A.; Liubarsky, I.; Lowder, D.; Mikolajski, T.; Miller, T. C.;
Mock, P.; Morse, R.; Nygren, D.; Porrata, R.; Price, P. B.; Richards,
A.; Rubinstein, H.; Schneider, E.; Spiering, C.; Streicher, O.; Sun,
Q.; Thon, T.; Tilav, S.; Walck, C.; Wiebusch, C.; Wischnewski, R.;
Yodh, G.; Belolaptikov, I. A.; Bezrukov, L. B.; Borisovets, B. A.;
Budnev, N. M.; Chensky, A. G.; Danilchenko, I. A.; Djilkibaev,
Zh. -A. M.; Dobrynin, V. I.; Domogatsky, G. V.; Doroshenko,
A. A.; Fialkovsky, S. V.; Gaponenko, O. N.; Garus, A. A.; Gress,
T. A.; Ignat'ev, S. B.; Karle, A.; Klabukov, A. M.; Klimov, A. I.;
Klimushin, S. I.; Koshechkin, A. P.; Kulepov, V. F.; Kuzmichev, L. A.;
Lubsandorzhiev, B. K.; Mikolajski, T.; Milenin, M. B.; Mirgazov,
R. R.; Moroz, A. V.; Moseiko, N. I.; Nikiforov, S. A.; Osipova,
E. A.; Pandel, D.; Panfilov, A. I.; Parfenov, Yu. V.; Pavlov, A. A.;
Petukhov, D. P.; Pocheikin, K. A.; Pokhil, P. G.; Pokolev, P. A.;
Rosanov, M. I.; Rubzov, V. Yu.; Sinegovsky, S. I.; Sokalski, I. A.;
Spiering, Ch.; Streicher, O.; Tarashansky, B. A.; Thon, T.; Wiebusch,
C.; Wischnewski, R.
1997NuPhS..52..256A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Defining the chi LUPI Abundance Peak Among the 5d and 6p
Elements
Authors: Wahlgren, G. M.; Leckrone, D. S.; Brage, T.; Johansson, S.;
Proffitt, C. R.
1996AAS...189.7811W Altcode: 1996BAAS...28.1378W
Using the echelle mode of the Hubble Space Telescope/Goddard High
Resolution Spectrograph, observations of the extremely sharp-lined HgMn
star chi Lupi have provided new insights into the ultraviolet spectrum,
both for the purposes of astrophysics and atomic spectroscopy. Testing
the diffusion paradigm, generally believed to be the dominant influence
in creating the plethora of spectral line strength anomalies in HgMn
stars, requires knowledge of the isotope mixture at several ionization
stages. Our exciting data for the element mercury provided the impetus
to expand our study to include other heavy elements. The high quality
GHRS spectra have placed stringent requirements upon the accuracy of the
atomic data utilized in our synthetic spectrum analyses. Therefore,
we have undertaken a concerted effort to employ both laboratory
techniques and theoretical calculations in order to provide such
needed data. As a result of this effort we are now able to nearly
fully define quantitatively the abundance distribution in this star
over the element range defined by the 5d elements tungsten (Z = 74)
through mercury (Z = 80) and the 6p elements thallium (Z = 81) through
bismuth (Z = 83). We present new abundance determinations for several
of these elements, the result of which is to emphasize the presence of
a peak in the abundance distribution, defined by the elements platinum
(Z = 78) through thallium (Z = 81). This peak, with abundances four
to five orders of magnitude greater than the solar system values, is
present for the three lowest stages of ionization and is broader than
either the r- or s-process peaks that are found in this vicinity of
the periodic table in the solar system elemental abundance distribution.
---------------------------------------------------------
Title: Branching Fractions and Oscillator Strengths for Fe II
Transitions from the 3d 6( 5D)4p Subconfiguration
Authors: Bergeson, S. D.; Mullman, K. L.; Wickliffe, W. E.; Lawler,
J. E.; Litzen, U.; Johansson, S.
1996ApJ...464.1044B Altcode:
New experimental branching fractions and transition probabilities
are reported for 56 transitions in Fe II. The branching fractions
are measured with a Fourier transform spectrometer and also with a
high-resolution grating spectrometer on an optically thin hollow cathode
discharge. Highly accurate experimental radiative lifetimes from the
recent literature provide the normalization required to convert our
branching fractions into absolute transition probabilities. Results are
compared with experimental and theoretical values in the literature. Our
new transition probabilities will establish the absolute scale for
relative absorption oscillator strengths of vacuum ultraviolet lines
measured using a new high-sensitivity absorption experiment at the
University of Wisconsin.
---------------------------------------------------------
Title: Is there a Dichromatic UV Laser in Eta Carinae?
Authors: Johansson, S.; Davidson, K.; Ebbets, D.; Weigelt, G.; Balick,
B.; Frank, A.; Hamann, F.; Humphreys, R. M.; Morse, J.; White, R. L.
1996swhs.conf..361J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Investigating fluorescence mechanisms in the atmosphere of
the cool, supergiant star alpha ORI
Authors: Wahlgren, G. M.; Johansson, S.
1996ASPC..109..551W Altcode: 1996csss....9..551W
No abstract at ADS
---------------------------------------------------------
Title: Term analysis of a complex spectrum.
Authors: Johansson, S.
1996PhST...65....7J Altcode:
A term analysis of a complex spectrum is like a giant jigsaw puzzle
with pieces of different sizes, shapes, colours, etc., and the result
is a picture of the atomic structure of an atom or ion having several
valence electrons. This knowledge of the atomic structure tests the
theoretical model of complex atoms and theoretical calculations of
various atomic parameters. These atomic parameters are fundamental
ingredients in, e.g. abundance analyses of astrophysical spectra. The
author discusses the atomic structure of transition group elements
based on term analyses of their spectra. He gives examples from Fe II
and Zr II. The strong coupling to high-resolution stellar spectroscopy,
in particular in the satellite ultraviolet and near-infrared wavelength
regions, is emphasized. Missing atomic data for transition elements
is still the main reason for missing opacity in stellar spectra,
calculated from stellar model atmospheres.
---------------------------------------------------------
Title: Atomic Data for High Resolution Stellar Spectroscopy: A Review
Authors: Johansson, S.; Leckrone, D. S.
1996ASPC..108..113J Altcode: 1996mass.conf..113J
No abstract at ADS
---------------------------------------------------------
Title: Stellar chemical abundances with the GHRS.
Authors: Leckrone, D. S.; Johansson, S.; Wahlgren, G. M.; Proffitt,
C. R.; Brage, T.
1996PhST...65..110L Altcode:
The accurate quantitative analysis of high resolution ultraviolet
spectra of ultra-sharp-lined, early-type, chemically peculiar
stars, obtained with the Goddard High Resolution Spectrograph on
the Hubble Space Telescope, has been made possible by the synergism
between state-of-the-art astrophysics and state-of-the-art atomic
spectroscopy. The authors illustrate this with several examples,
including the discovery of spin-forbidden "parasite" transitions of Fe
II, the first observations of hyperfine components and isotopic shifts
of stellar lines of thallium, and measurements of the photospheric
abundances of a large number of normally trace elements.
---------------------------------------------------------
Title: High excitation Rydberg levels of Fe I from the ATMOS solar
spectrum at 2.5 and 7 μm.
Authors: Schoenfeld, W. G.; Chang, E. S.; Geller, M.; Johansson, S.;
Nave, G.; Sauval, A. J.; Grevesse, N.
1995A&A...301..593S Altcode:
The quadrupole-polarization theory has been applied to the
3d^6^4s(^6^D)4f and 5g subconfigurations of Fe I by a parametric fit,
and the fitted parameters are used to predict levels in the 6g and
6h subconfigurations. Using the predicted values, we have computed
the 4f-6g and 5g-6h transition arrays and made identifications in the
ATMOS infrared solar spectrum. The newly identified 6g and 6h levels,
based on ATMOS wavenumbers, are combined with the 5g levels and found to
agree with the theoretical values with a root mean-squared-deviation of
0.042cm^-1^. Our approach yields a polarizability of 28.07 a_o_^3^and
a quadrupole moment of 0.4360+/-0.0010ea_o_^2^for Fe II, as well as
an improved ionization potential of 63737.700+/-0.010cm^-1^ for Fe I.
---------------------------------------------------------
Title: Fluorescence lines of MnII in the red spectrum of η Carinae.
Authors: Johansson, S.; Wallerstein, G.; Gilroy, K. K.; Joueizadeh, A.
1995A&A...300..521J Altcode:
Five emission lines in the wavelength region 6122-6132 A in the
spectrum of η Carinae are identified as the 4d ^5^D-4f ^5^F multiplet
of Mn^44^Sc II. These are the only high-excitation lines of Mn^44^Sc
II present in the spectrum. The upper levels of the multiplet are most
likely populated through photoexcitation by an accidental coincidence
in wavelength between the ultraviolet multiplets UV 15 of Mn^44^Sc
II and UV 5 of Si^44^Sc II. Improved laboratory wavelengths for the
Mn^44^Sc II lines are presented.
---------------------------------------------------------
Title: Initial Analysis of Coincident Events Between the SPASE and
AMANDA Detectors
Authors: Miller, T.; Beaman, J.; Evenson, P. A.; Gaisser, T. K.; Hart,
S.; Lloyd-Evans, J.; Martello, D.; Ogden, P.; Petrakis, J.; Stanev,
Todor; Watson, A. A.; Askebjer, P.; Barwick, S. W.; Bergström,
L.; Bouchta, A.; Carius, S.; Erlandsson, B.; Goobar, A.; Gray, L.;
Hallgren, L. A.; Halzen, F.; Hulth, P. O.; Jacobsen, J.; Johansson,
S.; Kandhadai, V.; Liubarsky, I.; Lowder, D. M.; Miller, T.; Mock,
P.; Morse, R.; Porrata, R.; Price, P. B.; Richards, A.; Rubinstein,
H.; Sun, Q.; Tilav, S.; Walck, C.; Yodh, G.
1995NuPhS..43..245M Altcode:
We report on the status of the SPASE-AMANDA coincidence experiment.
---------------------------------------------------------
Title: VizieR Online Data Catalog: New multiplet table for FeI
(Nave+, 1994)
Authors: Nave, G.; Johansson, S.; Learner, R. C. M.; Thorne, A. P.;
Brault, J. W.
1995yCat..20940221N Altcode:
We have recorded spectra of iron-neon and iron-argon hollow cathode
lamps in the region 1700A-5um (59,000-2000cm<SUP>-1</SUP>), with Fourier
transform (FT) spectrometers at the National Solar Observatory, Tucson,
Arizona, and Imperial College, London, UK, and with a high-resolution
grating spectrograph at the National Institute of Standards and
Technology, Gaithersburg, Maryland. The uncertainty of the strongest
lines in the FT spectra is less than 0.002cm<SUP>-1</SUP> (0.2mA at
3000A; 8mA at 2um). Pressure- and current-dependent shifts are less
than 0.001cm<SUP>-1</SUP> for transitions between low-lying levels,
increasing to 0.006cm<SUP>-1</SUP> for transitions between the most
highly excited levels. We report 28 new energy levels of Fe I and
revised values of another 818 levels. We have identified 9501 lines as
due to 9759 transitions in Fe I, and these are presented in the form
of a new multiplet table and finding list. This compares with the ~5500
lines due to 467 energy levels in the multiplet tables of Moore (1950,
NBS Circ., No.488 and 1959, NBS Tech. note 30). The biggest increase is
in the near-ultraviolet and near infrared, and many of the new lines
are present in the solar spectrum. Experimental log (gf) values are
included where they are available. A further 125 unidentified lines
due to Fe I are given. (4 data files).
---------------------------------------------------------
Title: Optical Properties of the South Pole Ice at Depths Between
0.8 and 1 Kilometer
Authors: Askebjer, P.; Barwick, S. W.; Bergstrom, L.; Bouchta, A.;
Carius, S.; Coulthard, A.; Engel, K.; Erlandsson, B.; Goobar, A.; Gray,
L.; Hallgren, A.; Halzen, F.; Hulth, P. O.; Jacobsen, J.; Johansson,
S.; Kandhadai, V.; Liubarsky, I.; Lowder, D.; Miller, T.; Mock, P. C.;
Morse, R.; Porrata, R.; Price, P. B.; Richards, A.; Rubinstein, H.;
Schneider, E.; Sun, Q.; Tilav, S.; Walck, C.; Yodh, G.
1995Sci...267.1147A Altcode:
The optical properties of the ice at the geographical South Pole
have been investigated at depths between 0.8 and 1 kilometer. The
absorption and scattering lengths of visible light (~515 nanometers)
have been measured in situ with the use of the laser calibration setup
of the Antarctic Muon and Neutrino Detector Array (AMANDA) neutrino
detector. The ice is intrinsically extremely transparent. The measured
absorption length is 59 ± 3 meters, comparable with the quality
of the ultrapure water used in the Irvine-Michigan-Brookhaven and
Kamiokande proton-decay and neutrino experiments and more than twice
as long as the best value reported for laboratory ice. Because of a
residual density of air bubbles at these depths, the trajectories of
photons in the medium are randomized. If the bubbles are assumed to
be smooth and spherical, the average distance between collisions at
a depth of 1 kilometer is about 25 centimeters. The measured inverse
scattering length on bubbles decreases linearly with increasing depth
in the volume of ice investigated.
---------------------------------------------------------
Title: Measurements of the Absorption Length of the Ice at the South
Pole in the Wavelength Interval 410 nm to 610 nm
Authors: Erlandsson, B.; Askebjer, P.; Barwick, S. W.; Bergström,
L.; Bouchta, A.; Carius, S.; Goobar, A.; Gray, L.; Hallgren, A.;
Halzen, F.; Heukenkamp, H.; Hulth, P. O.; Jacobsen, J.; Johansson,
S.; Kandhadai, V.; Karle, A.; Liubarsky, I.; Lowder, D.; Miller,
T. C.; Mock, P. C.; Morse, R.; Porrata, R.; Price, P. B.; Richards,
A.; Rubinstein, H.; Spiering, C.; Sun, Q.; Thon, T.; Tilav, S.; Walck,
C.; Wishnewski, R.; Yodh, G.
1995ICRC....1.1039E Altcode: 1995ICRC...24a1039E
No abstract at ADS
---------------------------------------------------------
Title: Status and Capabilities of AMANDA-94
Authors: Mock, P. C.; Askebjer, P.; Barwick, S. W.; Bergström,
L.; Bouchta, A.; Carius, S.; Erlandsson, B.; Goobar, A.; Gray, L.;
Hallgren, A.; Halzen, F.; Heukenkamp, H.; Hulth, P. O.; Jacobsen, J.;
Johansson, S.; Kandhadai, V.; Karle, A.; Liubarsky, I.; Lowder, D.;
Miller, T. C.; Morse, R.; Porrata, R.; Price, P. B.; Richards, A.;
Rubenstein, H.; Spiering, C.; Sun, Q.; Thon, T.; Tilav, S.; Walck,
C.; Wischnewski, R.; Yodh, G.
1995ICRC....1..758M Altcode: 1995ICRC...24a.758M
No abstract at ADS
---------------------------------------------------------
Title: Analysis of High-Resolution Laboratory Spectra of Iron and
Identification of Fe I Lines in the Solar Spectrum
Authors: Nave, G.; Johansson, S.
1995ASPC...81..197N Altcode: 1995lahr.conf..197N
No abstract at ADS
---------------------------------------------------------
Title: SPASE -- AMANDA Coincidences At The South Pole
Authors: Miller, T. C.; Gaisser, T. K.; Hart, S.; Lloyd-Evans, J.;
Martello, D.; Petrakis, J.; Stanev, T.; Watson, A. A.; Askebjer, P.;
Barwick, S. W.; Bergstrom, L.; Bouchta, A.; Carius, S.; Erlandsson,
B.; Goobar, A.; Gray, L.; Hallgren, A.; Halzen, F.; Heukenkamp, H.;
Hulth, P. O.; Jacobsen, J.; Johansson, S.; Kandhadai, V.; Karle, A.;
Liubarksky, I.; Lowder, D.; Miller, T. C.; Mock, P.; Porrata, R.;
Price, P. B.; Richards, A.; Rubinstein, H; Schneider, E.; Spiering,
C.; Sun, Q.; Tilav, S.; Walck, C.; Wischnewski, R.; Yodh, G.
1995ICRC....2..768M Altcode: 1995ICRC...24b.768M
No abstract at ADS
---------------------------------------------------------
Title: Indirect Evidence for Long Absorption Lengths in Antarctic Ice
Authors: Tilav, S.; Askebjer, P.; Barwick, S. W.; Bergström, L.;
Bouchta, A.; Carius, S.; Erlandsson, B.; Goobar, A.; Gray, L.;
Hallgren, A.; Halzen, F.; Heukenkamp, H.; Hulth, P. O.; Jacobsen,
J.; Johansson, S.; Kandhadai, V.; Karle, A.; Liubarsky, I.; Lowder,
D. M.; Martello, D.; Miller, T. C.; Mock, P. C.; Morse, R.; Porrata,
R.; Price, P. B.; Richards, A.; Rubenstein, H.; Spiering, C.; Sun,
Q.; Thon, T.; Walck, C.; Wishnewski, R.; Yodh, G.
1995ICRC....1.1011T Altcode: 1995ICRC...24a1011T
No abstract at ADS
---------------------------------------------------------
Title: Isotope Shift in Pt II Observed in Laboratory FTS Spectra
Authors: Kalus, G. M.; Johansson, S.; Thorne, A. P.; Leckrone, D. S.;
Wahlgren, G. M.
1995ASPC...81..239K Altcode: 1995lahr.conf..239K
No abstract at ADS
---------------------------------------------------------
Title: Improved Wavelengths and Extended Analysis of TI II
Authors: Zapadlik, I.; Johansson, S.; Litzen, U.
1995ASPC...81..237Z Altcode: 1995lahr.conf..237Z
No abstract at ADS
---------------------------------------------------------
Title: The Design of a Neutrino Telescope Using Natural Deep Ice as
a Particle Detector
Authors: Gray, L.; Askebjer, P.; Barwick, S. W.; Bergström, L.;
Bouchta, A.; Carius, S.; Erlandsson, B.; Goobar, A.; Hallgren, A.;
Halzen, F.; Heukenkamp, H.; Hulth, P. O.; Jacobsen, J.; Johansson,
S.; Kandhadai, V.; Karle, A.; Liubarsky, I.; Lowder, D. M.; Miller,
T. C.; Mock, P. C.; Morse, R.; Porrata, R.; Price, P. B.; Richards,
A.; Rubenstein, H.; Spiering, C.; Sun, Q.; Tilav, S.; Thon, T.; Walck,
C.; Wishnewski, R.; Yodh, G.
1995ICRC....1..816G Altcode: 1995ICRC...24a.816G
No abstract at ADS
---------------------------------------------------------
Title: Optical Properties of South Pole Ice for Neutrino Astrophysics
Authors: Price, P. B.; Askebjer, P.; Barwick, S. W.; Bergstrom,
L.; Bouchta, A.; Carius, S.; Erlandsson, B.; Goobar, A.; Gray, L.;
Hallgreen, A.; Halzen, F.; Heukenkamp, H.; Hulth, P. O.; Jacobsen,
J.; Johansson, S.; Kandhadai, V.; Karle, A.; Liubarsky, I.; Lowder,
D. M.; Miller, T. C.; Mock, P. C.; Morse, R.; Porrata, R.; Richards,
A.; Rubenstein, H.; Spiering, C.; Sun, Q.; Tilav, S.; Walck, C.;
Westphal, A. J.; Wischnewski, R.; Yodh, G.
1995ICRC....1..777P Altcode: 1995ICRC...24a.777P
No abstract at ADS
---------------------------------------------------------
Title: Remote Surveys of AMANDA
Authors: Askebjer, P.; Barwick, S. W.; Bergström, L.; Bouchta, A.;
Carius, S.; Engel, K.; Erlandsson, B.; Gaisser, T. K.; Goobar, A.;
Gray, L.; Hallgren, A.; Halzen, F.; Heukenkamp, H.; Hulth, P. O.;
Jacobsen, J.; Johansson, S.; Kandhadai, V.; Karle, A.; Liubarsky, I.;
Lowder, D. M.; Martello, D.; Miller, T. C.; Mock, P. C.; Morse, R.;
Porrata, R.; Price, P. B.; Richards, A.; Rubenstein, H.; Spiering,
C.; Sun, Q.; Thon, T.; Tilav, S.; Walck, C.; Wishnewski, R.; Yodh, G.
1995ICRC....1.1009A Altcode: 1995ICRC...24a1009A
No abstract at ADS
---------------------------------------------------------
Title: High Resolution Spectroscopy of Singly Ionized Transition
Elements
Authors: Johansson, S.
1995ASPC...81..151J Altcode: 1995lahr.conf..151J
No abstract at ADS
---------------------------------------------------------
Title: A New Multiplet Table for Fe i
Authors: Nave, G.; Johansson, S.; Learner, R. C. M.; Thorne, A. P.;
Brault, J. W.
1994ApJS...94..221N Altcode:
We have recorded spectra of iron-neon and iron-argon hollow cathode
lamps in the region 1700 A-5 micrometers (59,000-2000/cm), with Fourier
transform (FT) spectrometers at the National Solar Observatory, Tucson,
Arizona, and Imperial College, London, UK, and with a high-resolution
grating spectrograph at the National Institute of Standards and
Technology, Gaithersburg, Maryland. The uncertainty of the strongest
lines in the FT spectra is less than 0.002/cm (0.2 mA at 3000 A; 8 mA
at 2 micrometers). Pressure- and current-dependent shifts are less
than 0.001/cm for transitions between low-lying levels, increasing
to 0.006 cm<SUP>-1</SUP> for transitions between the most highly
excited levels. We report 28 new energy levels of Fe I and revised
values of another 818 levels. We have identified 9501 lines as due to
9759 transitions in Fe I, and these are presented in the form of a new
multiplet table and finding list. This compares with the approximately
5500 lines due to 467 energy levels in the multiplet tables of Moore
(1950, 1959). The biggest increase is in the near-ultraviolet and
near infrared, and many of the new lines are present in the solar
spectrum. Experimental log (gf) values are included where they are
available. A further 125 unidentified lines due to Fe I are given. The
tables are also available in computer-readable form.
---------------------------------------------------------
Title: UV-spektra från Hubble-teleskopet avslöjar en stjärna i
Vargen som lagrar tunga isotoper av mycket tunga grundämnen.
Authors: Johansson, S. E.; Leckrone, D. S.; Wahlgren, G. M.
1994ATi....27..113J Altcode:
UV spectra from the Hubble Space Telescope reveal a star that stores
heavy isotopes of very heavy elements. Atomic and plasma physics
arguments for UV spectroscopy from space borne observatories are
given. As an example, the authors discuss the analysis of high
resolution spectra of the chemically peculiar star χ Lupi, obtained
with the Hubble Space Telescope, in terms of identification of spectral
lines of very heavy elements.
---------------------------------------------------------
Title: Analysis of the 3d 64 s( 6D)4f--5g Supermultiplet of Fe i in
Laboratory and Solar Infrared Spectra
Authors: Johansson, S.; Nave, G.; Geller, M.; Sauval, A. J.; Grevesse,
N.; Schoenfeld, W. G.; Change, E. S.; Farmer, C. B.
1994ApJ...429..419J Altcode: 1994astro.ph..4050J
The combined laboratory and solar analysis of the highly-excited
subconfigurations 4f and 5g of Fe I has allowed us to classify 87
lines of the 4f-5g supermultiplet in the spectral region 2545-2585
cm-1. The level structure of these JK-coupled configurations
is predicted by semiempirical calculations and the quadrupolic
approximation. Semiempirical gf-values have been calculated and
are compared to gf values derived from the solar spectrum. The solar
analysis has shown that these lines, which should be much less sensitive
than lower excitation lines to departures from LTE and to temperature
uncertainties, lead to a solar abundance of iron which is consistent
with the meteoritic value (A_Fe = 7.51).
---------------------------------------------------------
Title: A glimpse into the post-COSTAR GHRS: detections of As II and
Bi II in the UV spectrum of the HgMn star χ Lupi.
Authors: Wahlgren, G. M.; Brage, T.; Gilliland, R. L.; Johansson,
S.; Leckrone, D. S.; Lindler, D. J.
1994BAAS...26..869W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A New Multiplet Table for Fe
Authors: Nave, I. G.; Johansson, S.; Learner, R. C. M.; Thorne, A. P.;
Brault, J. W.
1994astro.ph..4049N Altcode:
We have recorded spectra of iron-neon and iron-argon hollow cathode
lamps in the region 1700A -- 5um (59000 -- 2000cm-1), with Fourier
transform (FT) spectrometers at the National Solar Observatory,
Tucson, Arizona, U.S.A. and Imperial College, London, U.K., and with
a high resolution grating spectrograph at the National Institute of
Standards and Technology, Gaithersburg, U.S.A. The uncertainty of the
strongest lines in the FT spectra is <0.002cm-1 (0.2mA at 3000A;
8mA at 2um). Pressure and current-dependent shifts are <0.001cm-1
for transitions between low lying levels, increasing to 0.006 cm-1 for
transitions between the most highly excited levels. We report 28 new
energy levels of Fe I and revised values of another 818 levels. We
have identified 9501 lines as due to 9759 transitions in Fe I, and
these are presented in the form of a new multiplet table and finding
list. This compares with the 5500 lines due to 467 energy levels in
the multiplet tables of Moore (1950, 1959). The biggest increase is in
the near ultraviolet and near infra-red, and many of the new lines are
present in the solar spectrum. Experimental log(gf) values are included
where available. A further 125 unidentified lines due to Fe I are given.
---------------------------------------------------------
Title: Analysis of Very High Excitation Fe I Lines (4f - 5g) in the
Solar Infrared Spectrum
Authors: Johansson, S.; Nave, G.; Geller, M.; Sauval, A. J.;
Grevesse, N.
1994IAUS..154..543J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Highly-excited levels of Fe I obtained from laboratory and
solar Fourier transform and grating spectra. II. Laboratory and
solar identifications
Authors: Nave, G.; Johansson, S.
1993A&AS..102..269N Altcode:
New identifications of ∼2200 Fe I lines between 1700 Å and 5 μm
(59 000 cm<SUP>-1</SUP> -2000 cm<SUP>-1</SUP>) due to highly-excited
configurations are presented. These have been observed in hollow cathode
lamps using Fourier transform and grating spectroscopy. About 1700 of
the lines have been observed in the solar spectrum. A companion paper
presents the experimental energy levels.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Lab. and solar highly-excited
levels of Fe I (Nave+ 1993)
Authors: Nave, G.; Johansson, S.
1993yCat..41020269N Altcode:
New identifications of about 2200 FeI lines between 170nm and 5μm
(59000 to 2000 cm<SUP>-1</SUP>) due to highly-excited configurations
are presented. These have been observed in hollow cathode lamps using
Fourier transform and grating spectroscopy. About 1700 if the lines
have been observed in the solar spectrum. A companion paper presents
the experimental energy levels. (1 data file).
---------------------------------------------------------
Title: Highly-excited levels of Fe i obtained from laboratory and
solar Fourier transform and grating spectra. 1. Energy levels
Authors: Nave, G.; Johansson, S.
1993A&A...274..961N Altcode:
86 new levels due to the highly-excited configurations 3d64s(6D)nl,
3d<SUP>6</SUP>4s(<SUP>6</SUP>D)nl, 3d<SUP>6</SUP>4s(<SUP>4</SUP>D)nl,
and 3d<SUP>7</SUP>(<SUP>4</SUP>F)nl of Fe I have been established
using visible and infra-red Fourier transform spectra of iron-neon and
iron-argon hollow cathodes. 110 previously reported levels have also
been revised to an accuracy of 0.003-0.005 cm<SUP>-1</SUP>. The levels
were confirmed by comparison with ultraviolet spectra measured with a
1O.7m grating spectrograph. A companion paper presents the identified
lines in both laboratory and solar spectra.
---------------------------------------------------------
Title: High resolution UV stellar spectroscopy with the HST/GHRS,
challenges and opportunities for atomic physics.
Authors: Leckrone, D. S.; Johansson, S.; Wahlgren, G. M.; Adelman,
S. J.
1993PhST...47..149L Altcode:
The Goddard High Resolution Spectrograph (GHRS) on the Hubble Space
Telescope (HST) is producing ultraviolet spectra of unprecedented
resolution and photometric quality. The authors illustrate this with
observations of the ultra-sharp-lined, chemically peculiar B-type star,
χ Lupi. The photosphere of this star is rich in heavy elements, and
its UV spectrum is replete with transitions of species not commonly
observed in astrophysical spectra. It is an excellent "laboratory"
for atomic spectroscopy. Kurucz's comprehensive calculations of
transition probabilities for the iron-group and other elements provides
a reasonable starting point for theoretical spectrum synthesis. However,
evidence is found of large systematic errors in his data base for
transitions from particular energy levels in Fe II, Cr II, Co II,
and other ions.
---------------------------------------------------------
Title: Fluorescence lines in ultraviolet spectra of stars
Authors: Johansson, S.; Hamann, F. W.
1993PhST...47..157J Altcode:
We discuss the presence of fluorescence lines that appear in stellar
spectra in the satellite ultraviolet region between 1200 and 3200
Å. Strong lines in partial multiplets result from a selective
excitation, which in most cases is due to accidental wavelength
coincidences. The prototype of photoexcitation by accidental resonance
(PAR) is the classical Bowen mechanism. Photoexcitation by continuum
radiation (PCR) is another source of selective population. <P />Besides
a brief review of ultraviolet fluorescence lines identified in spectra
of symbiotic stars and cool stars we discuss in detail two emission
peaks at 2506-2508 Å. We give three different explanations for the
appearance of this feature in IUE spectra of three different objects:
RR Tel, η Car and KQ Pup. In connection to these lines we also
discuss primary and secondary cascades in the near-infrared observed
in high-resolution spectra. Comments are made on the strong Fe II line
at 9997 Å.
---------------------------------------------------------
Title: Using HST / GHRS Echelle Spectra as Templates for IUE Data
Analysis
Authors: Wahlgren, G. M.; Leckrone, D. S.; Johansson, S.; Rosberg, M.
1993ASPC...44..121W Altcode: 1993pvnp.conf..121W; 1993IAUCo.138..121W
No abstract at ADS
---------------------------------------------------------
Title: Ly Alpha Pumping of Fe II in Quasars and AGN
Authors: Hamann, F.; Ferland, G.; Johansson, S.
1992AAS...181.3512H Altcode: 1992BAAS...24Q1174H
No abstract at ADS
---------------------------------------------------------
Title: Lyα pumping of Fe II in quasars and AGN.
Authors: Hamann, F.; Ferland, G.; Johansson, S.
1992BAAS...24R1174H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fe II Emission from Qussars and AGN
Authors: Hamann, F.; Ferland, G.; Pradhan, A.; Johansson, S.
1992AAS...179.6315H Altcode: 1992BAAS...24R.682H
No abstract at ADS
---------------------------------------------------------
Title: Detection of high energy neutrinos in PAN
Authors: Bergström, L.; Johansson, S.
1992hena.conf..309B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fe II emission from quasars and AGN.
Authors: Hamann, F.; Ferland, G.; Pradhan, A.; Johansson, S.
1991BAAS...23R1424H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measuring the Energy of Multi-TeV Muons with a Water Cerenkov
Detector
Authors: Johansson, S.
1991ICRC....4..552J Altcode: 1991ICRC...22d.552J
No abstract at ADS
---------------------------------------------------------
Title: New Identifications of Highly-Excited Fe I Lines Around 4μm
in Cool Stars
Authors: Johansson, S.; Nave, G.; Learner, R. C. M.; Thorne, A. P.
1991isrs.conf..189J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High Resolution Atomic Spectroscopy in the Infrared and its
Application to Astrophysics
Authors: Johansson, S.
1991isrs.conf...87J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New Identifications of Highly-Excited Fe I Lines Around 4
μm in Cool Stars
Authors: Johansson, S.; Rosberg, M.; Hamann, F.
1991isrs.conf..107J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Fe II Fluorescence Emission in UV Spectra of Symbiotics
and Nuclei of Planetary Nebulae
Authors: Bruhweiler, F.; Feibelman, W. A.; Johansson, S.
1990BAAS...22R1205B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Gas dynamics, accretion and evolution of Algols: initial
results for three representative systems
Authors: Gimenez, A.; Gonzalez-Riestra, R.; Guinan, E. F.; Kondo, Y.;
McCluskey, G. E.; Bradstreet, D. H.; McCook, G. P.; Dorren, J. D.;
Johansson, S.; Sahade, J.
1990ESASP.310..383G Altcode: 1990eaia.conf..383G
No abstract at ADS
---------------------------------------------------------
Title: Fe II lines from laboratory and astrophysical sources.
Authors: Baschek, B.; Johansson, S.
1990JQSRT..44..215B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High Resolution Ultraviolet Stellar Spectroscopy From Space
Observatories - Atomic Physics and Astrophysics
Authors: Leckrone, D. S.; Johansson, S.; Kurucz, R. L.; Adelman, S. J.
1989BAAS...21.1198L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Complex atoms in astrophysical spectra.
Authors: Johansson, S.; Cowley, C. R.
1988JOSAB...5.2264J Altcode: 1988OSAJB...5.2264J
The paper reviews the spectroscopic work on atomic lines and energy
levels in neutral and singly and doubly ionized iron-group elements
during the past 35 years. The completeness of the analysis of these
spectra was graded and they were compared with the data included in
the multiplet tables of Moore (1962, 1972). Specific comments are
given on each spectrum. New demands for atomic data resulting from
high-resolution spectroscopy of peculiar stars and observations from
above the earth's atmosphere are discussed. The atomic data that have
become available since Moore's compilations are referred to here as
second-generation spectra.
---------------------------------------------------------
Title: Absorption spectra of Fe I in the 1550 - 3215-Å region.
Authors: Brown, C. M.; Ginter, M. L.; Johansson, S.; Tilford, S. G.
1988JOSAB...5.2125B Altcode: 1988OSAJB...5.2125B
The high-dispersion absorption spectrum of Fe I is reported in the
1550-3215-A region. Included are wavelengths of about 3000 observed
spectral features, improved spectral assignments, 248 new energy
levels, and a value for the ionization potential of 63 737/cm obtained
from extrapolation of Rydberg series. Improved wavelengths for several
hundred V I and Ti I spectral lines determined on the same spectrograms
as the iron data also are presented.
---------------------------------------------------------
Title: Doubly Excited Feii Lines in the A-Star 21-PEGASI
Authors: Adam, J.; Baschek, B.; Brage, T.; Nilsson, A. E.; Johansson,
S.
1988ASSL..138..243A Altcode: 1988IAUCo..94..243A; 1988pffl.proc..243A
The majority of about 120 ultraviolet iron lines, among them strong
lines around 1850 Å, which have recently been identified as transitions
from doubly excited levels in Fe II during a new investigation of the
hollow-cathode spectrum of iron, coincide with absorption lines in the
high-resolution IUE spectrum of the sharp-lined A star 21 Pegasi. Model
atmosphere calculations of the line strengths confirm the identification
for about one third of the lines.
---------------------------------------------------------
Title: Accidental Degeneracy Between Doubly Excited States in Feii
Authors: Brage, T.; Nilsson, A. E.; Johansson, S.; Baschek, B.;
Adams, J.
1988ASSL..138...63B Altcode: 1988IAUCo..94...63B; 1988pffl.proc...63B
No abstract at ADS
---------------------------------------------------------
Title: Future Laboratory Work in Feii
Authors: Johansson, S.
1988ASSL..138..313J Altcode: 1988pffl.proc..313J; 1988IAUCo..94..313J
No abstract at ADS
---------------------------------------------------------
Title: On regularities in complex spectra of iron group elements
and their dominance in stellar spectra
Authors: Johansson, S.
1987PhyS...36...99J Altcode:
Regularities in complex spectra of iron group elements are
illustrated as regards iso-electronic and iso-ionic sequences as
well as iso-elemental comparisons. Determination of series limits and
ionization potentials in spectra of doubly ionized iron-group elements
from iso-ionic plots and Ritz diagrams is discussed. New data for
doubly-excited states in Fe I are deduced from iso-ionic regularities
in the binding energy of two-electron configurations nl<SUP>2</SUP>
relative to a core of d-electrons. New spectroscopic data for Fe I
are presented together with a discussion of the dominance of the Fe
I spectrum in the sun.
---------------------------------------------------------
Title: Ultraviolet Doubly Excited Fe II Lines in the Laboratory and
in the A-Type Star 21 Pegasi
Authors: Adam, J.; Baschek, B.; Johansson, S.; Nilsson, A. E.;
Brage, T.
1987ApJ...312..337A Altcode:
During a new investigation of the UV hollow-cathode spectrum of iron,
some 120 lines were identified, among them strong lines around 1850 A,
as transitions from doubly excited levels in Fe II. A combination of
selective population by charge-transfer processes in the laboratory
source and of a strong configuration interaction is probably the cause
of unexpectedly large intensities of a great number of lines. The
new energy levels and calculated oscillator strengths for the newly
identified transitions are presented. Most of the new lines coincide
with absorption lines in the high-resolution IUE spectrum of the
sharp-lined A star 21 Pegasi. For about one-third of them, located
mostly in the region 1750-1900 A, the identifications are confirmed
by modal atmosphere calculations. For the remaining coincidences the
stellar line is probably blended with another contributor.
---------------------------------------------------------
Title: The absorption spectrum of titanium between 1900 Å and 2315 Å
Authors: Forsberg, P.; Johansson, S.; Smith, P. L.
1986PhyS...34..759F Altcode:
The absorption spectrum of Ti I has been analyzed in the region
1900-2315 A. The list contains 219 lines, of which 64 have been
identified as transitions between the ground term and terms of the odd
configurations (3d + 4s)3 np (n = 4, 5). Sixteen new energy levels
have been found, and three odd level values have been revised. Most
of the identified Ti I lines are present in the solar spectrum.
---------------------------------------------------------
Title: The identification of high-level transitions of Fe II in
stellar spectra.
Authors: Johansson, S.; Cowley, C. R.
1984A&A...139..243J Altcode:
Positive identifications are made in four
B and A-type stellar spectra of lines from
3d<SUP>6</SUP>(<SUP>5</SUP>D)4d-3d<SUP>6</SUP>(<SUP>5</SUP>D)4f
transitions in Fe II. The lowest levels of the 4d terms have
excitation energies of 10.3 eV, while those of the 4f terms are at
12.8 eV. Numerous features that were previously unidentified in B and
A stars may now be explained. The obvious presence of such transitions
makes it probable that many other high-level transitions are present in
stellar spectra. Some of these transitions have not yet been identified
in laboratory studies analyses, but they could be of considerable
importance in the chemical analyses of stellar atmospheres.
---------------------------------------------------------
Title: Selective excitation of Fe II in the laboratory and late-type
stellaratmospheres.
Authors: Johansson, S.; Jordan, C.
1984MNRAS.210..239J Altcode:
Low resolution spectra of cool giants and supergiants observed with the
International Ultraviolet Explorer (IUE) satellite contain emission
features for which it has been difficult to establish unambiguous
identifications. High resolution spectra of RR Tel and Beta Gru
(M 3 II) show lines which can be definitely attributed to Fe II. The
presence of particular transitions and absence of others suggests that
the source of excitation for levels with excitation energy around 10
eV is emission in the H Ly alpha line which is strong and broad in
the cool giants and supergiants. New laboratory spectra confirm the
excitation route for Ly alpha pumping to a further 4G0 level at about
13 eV, which decays to give the strong feature at 1870 A observed at
low spectral resolution in several cool stars.
---------------------------------------------------------
Title: New Fe II lines in IUE spectra of stars.
Authors: Johansson, S.
1984ESASP.218..307J Altcode: 1984iue..conf..307J
The never-ceasing need for more atomic data of Fe II for astrophysical
purposes is discussed in terms of present state and future work
on the term analysis of this spectrum. More data already exist and
an extended analysis of laboratory data has just started. Special
excitation conditions in stars allow highly excited states to be
populated for which data is needed. Some new presumptive interstellar
lines are reported.
---------------------------------------------------------
Title: Ultraviolet Spectroscopy of Cool Stars from IUE (invited Paper)
Authors: Jordan, C.; Judge, P.; Johansson, S.
1984uxsa.coll...51J Altcode: 1984IAUCo..86...51J; 1984uxsa.conf...51J
No abstract at ADS
---------------------------------------------------------
Title: A comparison between the observed and predicted Fe II spectrum
in different plasmas.
Authors: Johansson, S.
1984PhST....8...63J Altcode: 1984PhyS....8...63J
This paper gives a survey of the spectral distribution of emission
lines of Fe II, predicted from a single atomic model. The observed
differences between the recorded and the predicted spectrum are
discussed in terms of deficiencies of the model and interactions within
the emitting plasma. The author gives a number of illustrative examples
of unexpected features with applications to astrophysics.
---------------------------------------------------------
Title: Strong Fe II fluorescence lines in RR Tel and V1016 Cyg
excited by C IV in a Bowen mechanism.
Authors: Johansson, S.
1983MNRAS.205P..71J Altcode:
Ten strong lines in the IUE spectrum of RR Tel have been
identified as transitions from a common upper level of Fe
II, y<SUP>4</SUP>H<SUP>0</SUP><SUB>11/2</SUB>. The level is
selectively populated through resonant photoexcitation from
a<SUP>4</SUP>F<SUB>9/2</SUB> by one of the resonance lines of C IV,
λ1548.2 Å. Five of these lines appear also in the spectrum of
V1016 Cyg.
---------------------------------------------------------
Title: Two CR II multiplets around 1430 A appearing in absorption
in the spectrum of a solar active region
Authors: Johansson, S.
1982MNRAS.201P..63J Altcode:
In a current analysis of Cr II two new multiplets have been identified
around 1430 Å. The identification of 27 lines establishes the new
terms y <SUP>6</SUP>F<SUP>0</SUP> and y <SUP>6</SUP>D<SUP>0</SUP>
of the 3d<SUP>3</SUP> 4s 4p configuration by their combinations
with 3d<SUP>4</SUP> 4s a <SUP>6</SUP>D. Most of the lines appear in
absorption in the spectrum of a solar active region.
---------------------------------------------------------
Title: Atomic Spectroscopy for Astrophysical Applications
Authors: Johansson, S.
1981SSRv...29..387J Altcode:
The recent work in atomic spectroscopy at the Department of Physics,
University of Lund, is briefly reviewed and some examples of application
to astrophysics are presented.
---------------------------------------------------------
Title: Beam-foil lifetime measurements of some Fe II energy levels
Authors: Johansson, S.; Litzen, U.; Lundin, L.; Mannervik, S.
1981PhyS...24...30J Altcode:
The decay of 11 Fe II spectral lines in the region 2500-3200 A has been
recorded with the beam-foil technique. The line-blending problem has
been carefully studied, and the measurements have yielded lifetimes
for 5 levels believed to be unaffected by blends. No previous lifetime
measurements were reported for these levels.
---------------------------------------------------------
Title: New Spectroscopic Data for the Iron Group Elements
Authors: Johansson, S.
1981LIACo..23..229J Altcode: 1981cpsu.conf..229J
No abstract at ADS
---------------------------------------------------------
Title: Absorption lines in upsilon Sgr identified as high-level
transitions of Fe II.
Authors: Johansson, S.
1978MNRAS.184..593J Altcode:
Summary. An analysis of the high configurations of Fe ii has led to
the identification of some 100 absorption lines in the photographic
infrared spectrum of V Sagittarii. Almost all these lines belong to
the transition arrays 3d6 5s-3d6 5p, 3d6 5p-3d6 Sd, 3d6 Sp-3d6 6s
and 3d64d-3d64f of Fe ii, where the lower levels have an excitation
potential between 9.6 and 11.3 eV. Some of these high-level transitions
are enhanced in the laboratory source because of accidental resonance
charge-transfer.
---------------------------------------------------------
Title: The spectrum and term system of Fe II.
Authors: Johansson, S.
1978PhyS...18..217J Altcode:
The spectrum of singly ionized iron, Fe II, has been recorded in
the wavelength regions 900-2200 Å and 4800-11200 Å by means of a
pulsed hollow-cathode discharge. In the vacuum-ultraviolet region
identifications are given for 1358 lines. The list for the region
above 4800 Å contains 1564 observed lines, 1341 of which are
identified. In the 2200-4800 Å range about 350 lines in the line
list published by Dobbie in 1938 have been newly identified. On
the basis of interferometric measurements made by G. Norlén
of 350 lines a recalculation of the whole term system has been
performed. Altogether 576 energy levels are now known in Fe II,
some 250 of which are the results of the present analysis. The
levels belong to the configurations (3d<SUP>6</SUP>)4s, 5s, 6s,
4p, 5p, 3d, 4d, 5d, 4f and (3d<SUP>5</SUP>4s)4s, 5s, 4p, 4d and
3d<SUP>5</SUP>4p<SUP>2</SUP>. Theoretical predictions of the structure
of the (3d<SUP>6</SUP>4p + 3d<SUP>6</SUP>5p + 3d<SUP>5</SUP>4s4p)
complex by J. Sinzelle and J. F. Wyart are in good agreement with the
observations. The ionization energy has been determined to 130 563 ±
10 cm<SUP>-1</SUP>.
---------------------------------------------------------
Title: New Fe II identifications in the infrared spectrum of Eta
Carinae.
Authors: Johansson, S.
1977MNRAS.178P..17J Altcode:
Summary. An extended analysis of the Fe ii spectrum, based on new
observations in the infrared, has led to the identification of about
50 lines in the infrared spectrum of Eta Carinae. More than half of
the lines belong to the 3d6 5s-3d6 Sp transition array.
---------------------------------------------------------
Title: The Finnish-Swedish laser project
Authors: Johansson, S.; Paunonen, M.; Sharma, A.
1975lti..proc..120J Altcode:
The design and operation of a laser satellite rangefinder are
described. The design parameters of the system are outlined, and
directional calibration is discussed. The transmitter is based on a
Pockels-cell Q-switched ruby-laser configuration with pulse slicing
and amplification stages. The receiver consists of an astronomical
telescope with a parabolic mirror and a photomultiplier installed at
the prime focus. Timing is accomplished using a quartz clock system
synchronized with the Universal Time Scale by a LORAN phase-locked
frequency-comparison receiver.
---------------------------------------------------------
Title: Analysis of 4d-4f transitions in Fe II.
Authors: Johansson, S.; Litzen, U.
1974PhyS...10..121J Altcode:
The Fe II-spectrum emitted from a pulsed hollow cathode has been
investigated in the region 4 800-11 500 Å. As a first result of
the analysis 481 lines have been identified as belonging to the
3d<SUP>6</SUP>(<SUP>5</SUP>D)4d-3d<SUP>6</SUP> (<SUP>5</SUP>D)4f
transition array. The term structure shows good agreement with
predictions by R. D. Cowan.
