explanation      blue bibcodes open ADS page with paths to full text
Author name code: vitense
ADS astronomy entries on 2022-09-14
author:"Vitense, Erika"  OR author:"Boehm-Vitense, Erika"

---------------------------------------------------------
Title: The Number of Rotations per Stellar Activity Cycle in G and
    K Main Sequence Stars
Authors: Böhm-Vitense, E.; Davenport, J. R. A.
2011ASPC..448.1077B    Altcode: 2011csss...16.1077B
  We find that for G and K main sequence stars, the number of rotations
  per stellar activity cycle n<SUB>c</SUB> increases inversely as the
  rotation period rm p<SUB>rot</SUB> decreases. The scaling constant C may
  vary by a factor of 10 for different types of stars, while n<SUB>c</SUB>
  may change by as much as 3 orders of magnitude. We show that we can
  understand this relation when we consider how the rotation period
  varies between the top and the bottom of the convection zone and with
  depth of the convection zone in stars of different mass. In general,
  faster rotating stars have thinner convection zones. We also show that
  the observed sequences in the relation between the rotation period
  and the activity cycle period for G and K stars are obtained if the
  rotation periods in the dynamo layer and at the surface are correlated,
  as is the case if both are due to convective angular momentum transport.

---------------------------------------------------------
Title: Hyades Morphology and Star Formation
Authors: Böhm-Vitense, Erika
2007AJ....133.1903B    Altcode:
  Perryman and collaborators found that for the Hyades cluster the
  fraction of multiple stars increases from G stars to early-A stars. We
  discuss here whether this may be a general property of star formation
  or whether collisions in the cluster environment change the fractions
  of binary stars. A star ring of mainly F and G stars is seen around
  the Hyades cluster core, supposedly created by a shock wave due to a
  supernova explosion. These ring stars show the same fraction of binary
  stars as observed for the F and G stars in the core of the cluster. This
  suggests that collisions in the high stellar density cluster center
  did not measurably change the multiple-star fractions. There is so
  far only evidence of this one supernova explosion in the Hyades. If
  this is indeed the only one, then only one massive star was born in
  the cluster. There are also fewer than 10 white dwarf descendants of
  B stars found in the cluster. Unless many white dwarfs and neutron
  stars evaporated from the cluster, the initial mass function for
  stellar masses &gt;2 M<SUB>solar</SUB> must have been very steep,
  corresponding to a Salpeter function with an exponent of less than -3.3.

---------------------------------------------------------
Title: Chromospheric Activity in G and K Main-Sequence Stars, and
    What It Tells Us about Stellar Dynamos
Authors: Böhm-Vitense, Erika
2007ApJ...657..486B    Altcode:
  For main-sequence G and K stars we study again the empirical relations
  between the periods of the activity cycles, P<SUB>cyc</SUB>, and the
  rotational periods, p<SUB>rot</SUB>. We use the high-quality data
  selected by Brandenburg, Saar, and Turpin. As found by those authors
  “the P<SUB>cyc</SUB> increase proportional to the p<SUB>rot</SUB>,
  along two distinctly different sequences,” the active “A” sequence,
  and the inactive “'I” sequence with cooler and more slowly rotating
  stars. It is found here that along each sequence the number of
  rotation periods per activity cycle is nearly the same, but the
  numbers are different for the different sequences, indicating that
  probably different kinds of dynamos are working for the stars on the
  different sequences. The transition from one sequence to the other
  occurs at a rotation period of 21 days. The rotation periods then
  increase abruptly by about a factor of 2 for the cooler stars. We
  suggest that this indicates abruptly increased deep mixing. Along the
  I sequence the overall dependence of the Ca II emission line fluxes,
  F(Ca II), on rotation and T<SUB>eff</SUB> is consistent with F(Ca
  II)~T<SUP>4</SUP><SUB>eff</SUB>p<SUP>-4/3</SUP><SUB>rot</SUB>. For
  the A-sequence stars the dependence of F(Ca II) on rotation seems to
  be stronger than for the I-sequence stars.

---------------------------------------------------------
Title: The Puzzle of the Metallic Line Stars
Authors: Böhm-Vitense, Erika
2006PASP..118..419B    Altcode:
  In the puzzle of the metallic line (Am) stars, there still seem to be
  missing pieces. While the “normal” A stars have elemental abundances
  close to solar, the classical Am stars show stronger absorption lines
  for most heavy elements in their spectra. Elements with ionization
  potentials that nearly agree with those of hydrogen or helium have
  reduced abundances. The Ca II and Sc II lines are especially weak. The
  Am stars have no ultraviolet emission lines. They are binaries that,
  with very few exceptions, have rotational velocities vsini lower
  than 100 km s<SUP>-1</SUP>. Of the main-sequence A stars, 20% to
  30% are Am stars. Here we rediscuss previous suggestions that tried
  to explain the peculiar line strengths in the Am star spectra. In
  particular, we compare the well-studied properties of Hyades A and
  Am stars in order to identify reasons that can or cannot explain
  the differences. We find that accretion of interstellar material by
  A stars with distorted magnetic fields, which are weaker than those
  in peculiar A (Ap) stars, has the best chance of explaining the main
  characteristics of the peculiar heavy-element abundances in Am star
  photospheres. Charge-exchange reactions also seem to be important.

---------------------------------------------------------
Title: Rotation and Lithium Surface Abundances, Revisited
Authors: Böhm-Vitense, Erika
2004AJ....128.2435B    Altcode:
  For giants in the Hertzsprung gap, the relations between
  T<SUB>eff</SUB>, vsini, and lithium surface abundances are
  reinvestigated and compared with the relations found for Hyades
  main-sequence F stars. For the Hyades main-sequence F stars, the vsini
  decrease steeply around T<SUB>eff</SUB>~6450 K. At the same temperature
  the lithium surface abundances show a narrow, deep dip. For most giants
  there is also a steep decrease of vsini for T<SUB>eff</SUB> around 6450
  K. At this temperature the lithium surface abundances of the giants
  also decrease steeply and remain low for T<SUB>eff</SUB>&lt;6400
  K. The changes in rotation and Li surface abundances occur over a
  temperature interval of less than 300 K, which for a 2 M<SUB>solar</SUB>
  giant corresponds to an age interval of about 10<SUP>6</SUP> yr. The
  simultaneous steep decreases of rotation velocities and Li surface
  abundances indicate that for the giants these changes are due to the
  same cause, which we suggest to be deep mixing. It then seems rather
  likely that for the Hyades main-sequence F5 V stars the decrease of
  rotation and Li surface abundance is also caused by deep mixing. We
  suggest that in both cases the changes are related to the merging of
  the hydrogen and helium convection zones.

---------------------------------------------------------
Title: The O VI and C III Lines at 1032 and 977 Å in Hyades F Stars
Authors: Böhm-Vitense, Erika; Robinson, Richard D.; Carpenter,
   Kenneth G.
2004ApJ...606.1174B    Altcode:
  We continue our investigations into the mechanisms heating the outer
  layers of cool dwarf stars. In this study we specifically seek to
  determine whether in the layers with temperatures around 250,000-300,000
  K, in which the O VI lines are emitted, the temperatures are determined
  by heat conduction from the coronae or by the same processes that
  heat the lower temperature regions. To study this we discuss here 22
  spectra of Hyades F stars taken by the Far Ultraviolet Spectroscopic
  Explorer (FUSE) satellite to study the O VI lines at 1032 Å and the C
  III lines at 977 Å and compare them with other lower transition layer
  lines, observed with HST and IUE, and with existing X-ray data. For our
  targets with B-V&gt;0.4, the X-ray fluxes of single F stars increase,
  on average, slowly with increasing B-V, while the O VI line fluxes show
  the same steep decrease around B-V=0.43 as previously found for the
  lower temperature transition layer lines. For single stars the X-ray
  fluxes decrease with increasing vsini, except for the stars with B-V
  between 0.418 and 0.455, while for the O VI lines, as for the other
  transition layer lines, fluxes increase with increasing vsini, if vsini
  is larger than 30 km s<SUP>-1</SUP>. For smaller vsini, line fluxes are
  independent of vsini. The B-V and vsini dependences of the O VI line
  fluxes are then very different from those of the X-ray fluxes. We thus
  conclude that for electron temperature T<SUB>e</SUB> below 300,000 K,
  the transition layers for Hyades F stars are not mainly heated by
  heat conduction from their coronae. <P />Based on observations made
  with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE)
  telescope, which is operated for NASA by Johns Hopkins University,
  under contract NAS5-32985.

---------------------------------------------------------
Title: Karl Schwarzschild Lecture: What Hyades F Stars tell us about
    Heating Mechanisms in the outer Stellar Atmospheres (With 15 Figures)
Authors: Boehm-Vitense, Erika
2004RvMA...17....1B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: What Is Happening at Spectral Type F5 in Hyades F Stars?
Authors: Böhm-Vitense, Erika; Robinson, Richard; Carpenter, Kenneth;
   Mena-Werth, Jose
2002ApJ...569..941B    Altcode:
  Aiming at a better understanding of the mechanisms heating the
  chromospheres, transition regions, and coronae of cool stars, we study
  ultraviolet, low-resolution Hubble Space Telescope/Space Telescope
  Imaging Spectrograph spectra of Hyades main-sequence F stars. We
  study the B-V dependence(s) of the chromospheric and transition layer
  emission line fluxes and their dependences on rotational velocities. We
  find that the transition layer emission line fluxes and also those of
  strong chromospheric lines decrease steeply between B-V=0.42 and 0.45,
  i.e., at spectral type F5, for which the rotational velocities also
  decrease steeply. The magnitude of the line-flux decrease increases
  for lines of ions with increasing degree of ionization. This shows
  that the line-flux decrease is not due to a change in the surface
  filling factor but rather due to a change of the relative importance
  of different heating mechanisms. For early F stars with B-V&lt;0.42
  we find for the transition layer emission lines increasing fluxes
  for increasing vsini, indicating magnetohydrodynamic heating. The
  vsini dependence is strongest for the high-ionization lines. On
  the other hand, the low chromospheric lines show no dependence on
  vsini, indicating acoustic shock heating for these layers. This also
  contributes to the heating of the transition layers. The Mg II and Ca
  II lines show decreasing fluxes for increasing vsini, as long as vsini
  is less than ~40 km s<SUP>-1</SUP>. The coronal X-ray emission also
  decreases for increasing vsini, except for vsini larger than ~100 km
  s<SUP>-1</SUP>. We have at present no explanation for this behavior. For
  late F stars the chromospheric lines show vsini dependences similar to
  those observed for early F stars, again indicating acoustic heating
  for these layers. We were unable to determine the vsini dependence
  of the transition layer lines because of too few single star
  targets. The decrease of emission line fluxes at the spectral type
  F5, with steeply decreasing vsini, indicates, however, a decreasing
  contribution of magnetohydrodynamic heating for the late F stars. The
  X-ray emission for the late F stars increases for increasing vsini,
  indicating magnetohydrodynamic heating for the coronae of the late F
  stars, different from the early F stars. 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, Incorporated, under NASA contract NAS5-26555.

---------------------------------------------------------
Title: Mg II Emission Lines of Hyades F Stars
Authors: Böhm-Vitense, Erika; Mena-Werth, Jose; Carpenter, Kenneth
   G.; Robinson, Richard D.
2001ApJ...550..457B    Altcode:
  With the Hubble Space Telescope (HST) we have observed Hyades
  F stars, using the Space Telescope Imaging Spectrograph (STIS),
  in order to get more information about the heating mechanism(s)
  for the chromospheres and transition layers and their dependence
  on rotation and age. In this paper we study the Mg II lines at 2800
  Å. We include earlier observations with the International Ultraviolet
  Explorer (IUE) satellite. The Mg II emission lines become observable
  for B-V&gt;0.3. The emission line fluxes increase steeply until
  B-V~0.40. For single stars there is a steep decrease in flux between
  B-V=0.41 and B-V=0.44, similar to the behavior of the Ca II emission
  line cores. For larger B-V the Mg II emission line fluxes again
  increase, but much more slowly than for the Ca II lines. Generally,
  the low point of the emission is reached between B-V=0.43 and B-V=0.45,
  i.e., similar to the Ca II emission cores. For the Hyades F stars there
  appears to be a difference between the emissions for single stars and
  those for binaries. We find that for Hyades stars with surface line
  fluxes larger than 10<SUP>6</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>
  the emission line fluxes decrease with increasing vsini. For smaller
  fluxes they may increase with increasing vsini. We have only three
  stars that perhaps show this. We study the flux ratios of the Mg II
  k and h lines at 2795.7 and 2802.5 Å in order to determine where
  the lines fall on the curve of growth. For the earliest F stars
  studied here the ratio is close to 2, as expected for optically thin
  lines. Generally, it seems that the optical depths in the line centers
  are less than 10. There remain problems in understanding the size of
  the line widths. We discuss the interpretation of the Wilson-Bappu
  effect. For the Hyades F stars there is a strong dependence of the
  line width on the effective temperature. 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. Incorporated, under NASA contract NAS5-26555.

---------------------------------------------------------
Title: Ultraviolet Emission Lines in BA and Non-BA Giants
Authors: Böhm-Vitense, Erika; Carpenter, Kenneth G.; Robinson,
   Richard D.
2000ApJ...545..992B    Altcode:
  With the Hubble Space Telescope (HST) and the Goddard High Resolution
  Spectrograph we have observed four barium and three weak barium stars
  in the ultraviolet spectral region, together with two nonpeculiar giant
  standard stars. An additional suspected Ba star was observed with HST
  and the Space Telescope Imaging Spectrograph. In the H-R diagram,
  three of the observed Ba stars lie on the same evolutionary tracks
  as the Hyades giants. Using International Ultraviolet Explorer (IUE)
  spectra of previously studied giants together with our HST spectra,
  we investigate whether the chromospheric and transition layer
  emission-line spectra of the Ba stars are different from those of
  nonpeculiar giants and from those of giants with peculiar carbon and/or
  nitrogen abundances. Except for the Ba star HD 46407 and the suspected
  Ba star HD 65699, the Ba star and mild Ba star emission-line fluxes are,
  for a given effective temperature and for a given luminosity, lower
  than those for the nonpeculiar giants observed with IUE. In comparison
  with the HST-observed standard stars, the C IV λ1550-to-C II λ1335
  line flux ratios are smaller, but not necessarily so in comparison
  with all IUE-observed nonpeculiar giants. However, the C IV-to-C II
  line flux ratios for the Ba stars decrease with increasing carbon
  abundances. This shows that the energy balance in the lower transition
  layer is influenced by the carbon abundance. The temperature gradient
  appears to be smaller in the C II line-emitting region. There does not
  seem to be a difference in chromospheric electron densities for the
  Ba and non-Ba stars, though this result is rather uncertain. 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
  NAS 5-26555.

---------------------------------------------------------
Title: Masses for Galactic Beat Cepheids
Authors: D'Cruz, Noella L.; Morgan, Siobahn M.; Böhm-Vitense, Erika
2000AJ....120..990D    Altcode:
  Accurate mass determinations for Cepheids may be used to determine
  the degree of excess mixing in the interiors of their main-sequence
  progenitors: the larger the excess mixing, the larger the luminosity
  of the Cepheid of a given mass, or the smaller the mass of a Cepheid
  with given luminosity. Dynamical masses determined recently for a
  few Cepheid binaries indicate excess mixing somewhat stronger than
  that corresponding to the convective overshoot models by Schaller et
  al. Beat Cepheids can be used similarly to test main-sequence mixing
  in stellar interiors. The period ratios for beat Cepheids depend on
  luminosity, T<SUB>eff</SUB>, heavy element abundance, and mass. By
  comparing pulsational models and the observationally derived luminosity,
  T<SUB>eff</SUB>, metallicities, and period ratios it is possible
  to obtain masses for these stars, the so-called beat masses. With
  the old opacities masses much smaller than the evolutionary masses
  were obtained. With the new OPAL opacities a beat mass close to the
  dynamical mass was obtained for the binary beat Cepheid Y Carinae,
  showing that it is now possible to obtain reliable beat masses. In
  this paper, we determine beat masses for seven Galactic beat Cepheids
  for which photometric and spectroscopic data are available. We find
  an average mass around 4.2+/-0.3 M<SUB>solar</SUB> for these stars,
  though the actual error limits for each star may be larger mainly
  because of uncertainties in E(B-V) and the heavy element abundances. (As
  derived spectroscopically, beat Cepheids are in general metal-poor,
  with -0.4&lt;~[Fe/H]&lt;~0.0). The relation between the derived beat
  masses and the luminosities again indicates excess mixing that is
  somewhat larger than that corresponding to the models by Schaller et al.

---------------------------------------------------------
Title: Do All BA II Stars Have White Dwarf Companions?
Authors: Böhm-Vitense, Erika; Carpenter, Kenneth; Robinson, Richard;
   Ake, Tom; Brown, Jeffery
2000ApJ...533..969B    Altcode:
  With the Hubble Space Telescope (HST) and the Goddard High Resolution
  Spectrograph (GHRS) we have observed four barium stars, three mild
  barium stars, and one weak G-band star in the ultraviolet spectral
  region. One barium star was observed with HST and the Space Telescope
  Imaging Spectrograph (STIS). The aim was to check the hypothesis
  that all these peculiar stars have white dwarf (WD) companions,
  which at their asymptotic giant branch phase transferred mass with
  peculiar element abundances to the present barium and CH peculiar
  stars. Assuming that the ultraviolet continua of the cool giants,
  including the barium stars, are generated in their chromospheres and
  that the relations between the continua and the emission lines created
  in the chromospheres and transition layers are similar in field giants
  and barium stars, we found that, indeed, most of our target barium and
  weak barium stars appear to have excess flux in the UV when compared
  to standard giant stars. For most of the stars the excess flux can
  be attributed to WD companions with temperatures between 10,000 and
  12,000 K, if the WD mass is about 0.6 M<SUB>solar</SUB>. Cooling times
  for the WDs were derived from their effective temperatures and model
  calculations by M. Wood. The calculated cooling times are longer than
  the lifetimes of the barium stars on the giant branch. For our target
  stars the mass transfer therefore happened while they were still on
  the main sequence. For two of the mild barium stars and one or perhaps
  two barium stars the derived cooling times for the WD companions come
  out to be longer than the total evolutionary times of the barium stars
  as calculated by Schaller et al. If our derivations are correct (the
  error bars are rather large) then either evolutionary models with larger
  convective overshoot have to be used for the barium stars or the cooling
  times of the white dwarfs have to be revised downward. Possibly an
  additional (as yet unknown) cooling mechanism has to be considered? The
  weak G-band star HD 165634, which has a carbon underabundance of about
  a factor of 10, also appears to have a WD companion. We discuss the
  implications of this very low carbon abundance. 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. Incorporated, under NASA contract NAS5-26555.

---------------------------------------------------------
Title: On VI emission lines in Hyades F stars
Authors: Bohm-Vitense, Erika
2000fuse.prop.A106B    Altcode:
  We propose to obtain additional empirical constraints on the atmospheric
  heating mechanisms operating in stellar transition regions (TR)
  and coronae. In particular, we will address the question of whether
  different heating mechanisms may be working in different layers of a
  given star and whether the relative importance of the mechanisms changes
  from star to star. The heating mechanisms may depend on T<SUB>eff</SUB>,
  gravity, rotation, magnetic fields, age, chemical composition, and,
  possibly, binarity. In order to identify the heating mechanisms, we need
  to disentangle the dependences on all these parameters. We propose to
  do this by observing the 1032 &amp; 1038 Å O VI emission lines in a
  large sample of main sequence Hyades F stars. These stars are chosen
  since they are the brightest cluster stars with strong TR-emission
  and because marked changes in the heating mechanisms apparently occur
  around spectral type F5, leading to easily-observable effects on our
  spectral diagnostics. In addition, the age, chemical composition,
  and surface gravity of these stars are essentially the same, removing
  dependences on 3 of the stellar parameters. Relations between the
  lower-TR and upper-TR emissions, together with their relationships
  to the coronal X-ray emission will tell us the relationship between
  heating mechanisms in the different layers. We already have reliable
  lower-TR emission line (e.g. C IV) measurements for 15 Hyades F stars
  observed by IUE and will be obtaining such for 17 additional Hyades
  F stars in an approved Cycle 7 HST program. FUSE will provide the
  critically needed flux measurements of upper-TR lines (O VI), as well
  as of an additional lower-TR line, C III.

---------------------------------------------------------
Title: The Mass of the Cepheid Binary V636 Scorpii
Authors: Böhm-Vitense, E.; Evans, N. R.; Carpenter, K.; Albrow,
   Michael D.; Cottrell, P. L.; Robinson, R.; Beck-Winchatz, B.
1998ApJ...505..903B    Altcode:
  The mass-luminosity relation for Cepheids depends on the degree of
  mixing in their main-sequence progenitors. Masses of Cepheids can be
  inferred by using different aspects of pulsation theory. These methods
  have in the past led to diverging results, showing that something was
  wrong in either evolution theory or pulsation theory or both. For some
  binary Cepheids dynamical masses, which are independent of pulsation and
  evolution theories, can be determined. V636 Sco is one of a handful of
  Cepheid binaries whose companions are bright enough in the ultraviolet
  that orbital radial velocities can be measured. We have here attempted
  to determine the radial velocity of the companion V636 Sco B to the
  Cepheid V636 Sco A by means of two Hubble Space Telescope (HST) spectra
  taken at phases of minimum and maximum Cepheid orbital velocities. The
  ratio of the orbital velocity of the companion and the Cepheid (which
  is the inverse of their mass ratio) came out to be 1.25 +/- 0.17. V636
  Sco B has a spectral type B9.5 V, for which we expect a stellar mass
  of 2.5 M<SUB>⊙</SUB>. For the Cepheid we thus determine a mass
  of 3.1 +/- 0.4 M<SUB>⊙</SUB>, which is surprisingly low. If true,
  such a low mass would indicate an extremely large amount of excess
  mixing, which is very unlikely. <P />We discuss the likely possibility
  that V636 Sco B may itself be a binary with an unseen secondary,
  in which case the mass derived from the two measurements discussed
  above is not correct. Although the error limits for the mass of each
  Cepheid are rather large, the combined mass-luminosity relation for
  all Cepheids studied by us so far by means of HST spectra indicates
  excess mixing corresponding to core convective overshoot by 0.25 to
  about 0.5 pressure scale height in the main-sequence progenitors of
  the Cepheids. <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 NASS-26555.

---------------------------------------------------------
Title: Classical Cepheid Masses: U Aquilae
Authors: Evans, Nancy Remage; Böhm-Vitense, Erika; Carpenter, Kenneth;
   Beck-Winchatz, Bernhard; Robinson, Richard
1998ApJ...494..768E    Altcode:
  We have obtained medium-resolution spectra (λ/Δλ ~ 20,000) of the hot
  binary companion to the classical Cepheid U Aql with the Goddard High
  Resolution Spectrograph on the Hubble Space Telescope (HST). These have
  been used to determine the orbital velocity amplitude. Combining this
  with the orbital velocity amplitude of the Cepheid from the ground-based
  orbit and the mass of the companion inferred from its spectral type, we
  measure a mass of the Cepheid of 5.1 +/- 0.7 M<SUB>⊙</SUB>. We discuss
  the full sample of Cepheids for which we have determined masses with HST
  (S Mus, V350 Sgr, Y Car, and U Aql) and also SU Cyg (mass from IUE). The
  HST masses are in agreement with the luminosities predicted by recent
  evolutionary tracks with moderate overshoot. This comparison, however,
  may be altered by reassessment of Cepheid distances based on Hipparcos
  parallaxes. <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 NASA-26555.

---------------------------------------------------------
Title: The Mass of the Classical Cepheid V350 SGR
Authors: Evans, N. R.; Bohm-Vitense, E.; Beck-Winchatz, B.; Carpenter,
   K.; Robinson, R.
1998ASPC..143..313E    Altcode: 1998sigh.conf..313E
  No abstract at ADS

---------------------------------------------------------
Title: The Mass of the Beat Cepheid Y Carinae
Authors: Bohm-Vitense, E.; Beck-Winchatz, B.; Evans, N. R.; Carpenter,
   K. G.; Robinson, R.
1998ASPC..143..317B    Altcode: 1998sigh.conf..317B
  No abstract at ADS

---------------------------------------------------------
Title: The Mass of the Classical Cepheid S MUSCAE
Authors: Evans, N. R.; Bohm-Vitense, E.; Beck-Winchatz, B.; Carpenter,
   K.; Robinson, R.
1998ASPC..143..309E    Altcode: 1998sigh.conf..309E
  No abstract at ADS

---------------------------------------------------------
Title: The Dynamical and Beat Masses of the Beat Cepheid Y Carinae
Authors: Bohm-Vitense, E.; Evans, N. R.; Carpenter, K.; Winchatz,
   B. Beck-; Morgan, S.; Robinson, R.
1998ASPC..135..280B    Altcode: 1998hcsp.conf..280B
  The mass-luminosity relation for Cepheids depends on the degree
  of excess mixing in their main sequence progenitors. The mass
  determination for Cepheids with their known luminosities therefore
  determines the degree of excess mixing in massive main sequence
  stars. We have determined the dynamical mass of several Cepheids with
  blue companions. Here we discuss the beat Cepheid Y Carinae. By means
  of HST, GHRS spectra we measured the radial velocity of the B9.5 V
  companion Y Car B at phases near minimum and maximum orbital radial
  velocities. The orbital velocity amplitude ratio between the Cepheid
  and the hot companion and thereby the mass ratio comes out to be 1.51
  0.5, leading to a mass of 3.8 1 1.2 solar masses. Taking the 3.8 solar
  masses at face value this indicates excess mixing corresponding to
  convective overshoot by about 1 pressure scale height, (see Bertelli et
  al.1986), but the error limits are too large for a firm conclusion. The
  beat masses, determined from the period ratios for the beat Cepheids,
  have puzzled astronomers for a long time (see Cox 1980) because they
  came out around 1 to 2 solar masses, when the Cox-Tabor opacities
  were used for the model calculations. Moskalik et al.(1992) showed
  that beat masses around 4 to 5 solar masses can now be derived, if
  the new OPAL opacities are used instead. With the determination of
  the dynamical mass for Y Car A we can now check the validity of the
  OPAL opacities more quantitatively than was possible before. Using the
  model calculations incorporating the OPAL opacities, and the observed
  effective temperature of Y Carinae we determine for its beat mass a
  possible range of 3.75 &lt; M/Ms &lt; 4.0, in very good agreement with
  the dynamical mass. This supports the validity of the OPAL opacities,
  and also supports the conclusion about the high degree of excess mixing
  in the main sequence progenitor of Y Carinae A.

---------------------------------------------------------
Title: The dynamical mass of the beat cepheid Y carinae and stellar
    opacities.
Authors: Bohm-Vitense, E.; Evans, N. R.; Carpenter, K.; Morgan, S.;
   Beck-Winchatz, B.; Robinson, R.
1997AJ....114.1176B    Altcode:
  The beat Cepheid, Y Carinae A, has a B9 V companion, Y Car
  B. The primary period P<SUB>0</SUB> of the Cepheid is 3.64 days
  and the secondary, P<SUB>1</SUB>, is 2.56 days. Its period ratio
  P<SUB>1</SUB>/P<SUB>0</SUB> is thus 0.703. Y Car is the only beat
  Cepheid known to be a binary and thus offers us the unique opportunity
  to determine the dynamical mass for a beat Cepheid. We have determined
  its mass by measuring the orbital velocity amplitude of the hot
  companion Y Car B using the Goddard High-Resolution Spectrograph (GHRS)
  with the G200M grating on the Hubble Space Telescope. When combined
  with the ground-based orbital velocity amplitude of the Cepheid
  and the mass of the companion, the implied mass of the Cephieid
  is M=3.8±1.2M<SUB>sun</SUB>. With the Cepheid luminosity given
  by the period-luminosity relation, this mass, taken at face value,
  indicates excess mixing in the main sequence progenitor corresponding
  to convective overshoot by about 0.9 pressure scale height, however,
  the large error bars prevent a firm conclusion. As shown by Simon the
  period ratio for beat Cepheids depends sensitively on the opacities. For
  models calculated with Cox-Tabor opacities the period ratios for beat
  Cepheids indicate masses between one and two M<SUB>sun</SUB>. Models
  calculated with the new Livermore OPAL opacities on the other hand
  indicate masses around 4 solar masses. The good agreement of the beat
  mass with the dynamical mass, determined here for Y Car, provides a
  confirmation that the OPAL opacities are a significant improvement
  over the Cox-Tabor (1976) opacities.

---------------------------------------------------------
Title: Chromospheres and transition layers in Hyades and Pleiades
    F stars
Authors: Boehm-Vitense, Erika
1997hst..prop.7389B    Altcode:
  This proposal seeks to obtain additional empirical constraints on the
  heating mechanisms for stellar chromospheres, transition layers and
  coronae. These mechanisms may depend on effective temperature, gravity,
  rotation, magnetic fields, age, chemical abundances, and possibly
  binarity. Thus, we need to disentangle the dependences on all these
  parameters if we want to identify the heating mechanisms. We propose to
  study main sequence F stars in the Hyades and Pleiades. For each cluster
  two parameters are constant: age and chemical abundances. Gravity
  is also essentially constant. We still have to deal with at least 3
  remaining parameters. This means we need to observe as many stars as
  feasible. The comparison of the Hyades and Pleiades stars will tell
  us the age dependence for the young stars. The verification of any age
  dependence, separately from the one on rotation, will show the influence
  of parameters other than rotation and those related to convection,
  which is not expected to depend on age. Main sequence F stars are the
  brightest cluster stars with strong chromospheric and transition layer
  emission. Changes in the heating mechanism occur around spectral type
  F5. The related changes in chromospheric and transition layer emission,
  and the steeply decreasing rotational velocities may hold the clue to
  the identification of the heating mechanisms.

---------------------------------------------------------
Title: The Mass of the Classical Cepheid V350 SGR
Authors: Evans, N. R.; Bohm-Vitense, E.; Carpenter, K.; Beck-Winchatz,
   B.; Robinson, R.
1997PASP..109..789E    Altcode:
  Two medium resolution spectra of the hot companion of the Cepheid V350
  Sgr have been obtained with the Goddard High Resolution Spectrograph
  aboard the Hubble Space Telescope. Comparison of these spectra (in the
  wavelength range 1840 to 1880 \AA) with the spectrum of $\alpha$ Lyr
  shows that V350 Sgr B has a projected rotation velocity which may be as
  high as 150 km sec$^{-1}$. The velocity difference between the spectra
  of V350 Sgr B at two orbital phases is measured to be -23.1 $\pm$ 3.8
  km sec$^{-1}$. The error is dominated by the aperture centering. When
  combined with the orbital velocity variation of the Cepheid derived
  from the ground-based orbit and the mass of the companion deduced
  from IUE spectra, the mass of the Cepheid is found to be 5.2 $\pm$
  0.9 M$\sun$. The observed mass--luminosity combination of V350 Sgr A
  is a good match to recent evolutionary calculations which use moderate
  convective overshoot near the main sequence, however, the blue loops
  do not extend to temperatures as hot as the Cepheid. (SECTION: Stars)

---------------------------------------------------------
Title: White dwarf companions of Barium and CH peculiar Stars
Authors: Boehm-Vitense, Erika
1997hst..prop.7753B    Altcode: 1997hst..prop.4085B
  In 1980 McClure et al.{ApJ 238, L35} discovered that all Ba stars show
  radial velocity variations indicative of their binary nature. These
  authors already suspected that the companions are white dwarfs. White
  dwarf companions were indeed detected for the Ba star zeta Cap and the
  mild Ba star zeta Cyg {Boehm-Vitense 1980, ApJ 239, L79} by means of
  IUE observations. Evidence for a high temperature radiation field was
  seen in the spectra of the mild Ba stars HR1016, 16Ser and 56UMa. If
  present, the white dwarf companions are too faint to be seen with
  IUE. We would like to look for them now with HST. It seems to us to be
  very important to check whether indeed all Ba stars have white dwarf
  companions. If so this makes it highly probable that the peculiar
  abundances are due to mass transfer from a very luminous companion to
  the present Ba star. After losing its envelope the luminous companion
  was left as the present white dwarf. This opens up the possibility
  that other peculiar abundances seen in other peculiar stars like the
  CH stars or perhaps also the weak G band stars might also be due to
  mass transfer. On the other hand if the white dwarfs are not found for
  all Ba stars we may have to look for other processes, that could bring
  to the surface of these stars material which has experienced the slow
  neutron capture process.

---------------------------------------------------------
Title: The Mass of the Classical Cepheid S Muscae
Authors: Böhm-Vitense, Erika; Remage Evans, Nancy; Carpenter, Kenneth;
   Beck-Winchatz, Bernhard; Robinson, Richard
1997ApJ...477..916B    Altcode:
  A good determination of the mass-luminosity relation for evolved stars
  on blue loops can determine the degree of excess mixing in the interiors
  of their main-sequence companions. In this study we determine the
  dynamical mass of the Cepheid binary S Muscae. This can be combined
  with its known luminosity and be fitted on evolutionary tracks to
  determine the amount of mixing in the main-sequence progenitor. <P
  />Using the Goddard High Resolution Spectrograph on the Hubble Space
  Telescope we have measured the orbital radial velocity changes for the
  companion of the Cepheid S Mus. Spectra taken at minimum and maximum
  orbital velocities were cross-correlated. The velocity difference was
  measured to be 30.6 +/- 0.4 km s<SUP>-1</SUP>. The difference for the
  orbital velocities of the Cepheid for the same phases was determined
  to be 26.9 km s<SUP>-1</SUP> +/- 0.4 km s<SUP>-1</SUP>. This gives
  a velocity ratio of 1.14 +/- 0.02, which gives us the mass ratio for
  the companions. Adding possible centering errors of the target in the
  entrance apertures the error limit would be increased to +/-0.06. <P
  />The derived spectral types of the companion S Mus B range from B3
  V to B5 V depending on the criterion used to determine it, with an
  average spectral type B3.8 V. Using the average spectral type and the
  main-sequence mass-spectral type relation from Andersen &amp; Harmanec
  we find for S Mus B a mass of 5.2 +/- 0.2 M<SUB>⊙</SUB>. With the
  newly determined mass ratio the mass for the Cepheid S Mus A comes out
  to be 5.9<SUP>+0.7</SUP><SUB>-0.6</SUB> M<SUB>⊙</SUB>. <P />Taking
  the mass of 5.9 M<SUB>⊙</SUB> at face value and adopting the absolute
  visual magnitude of M<SUB>v</SUB> = -4.29 (log L/L<SUB>⊙</SUB> =
  3.62) for the Cepheid S Mus this indicates mixing in its main-sequence
  progenitor slightly in excess of the one assumed for the Maeder and
  Meynet evolutionary tracks. The present uncertainties in mass and
  luminosity prevent, however, a firm conclusion about the exact degree
  of mixing. <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 No. NASS-26555.

---------------------------------------------------------
Title: The First Steps of the Extragalactic Distance Ladder
Authors: Bohm-Vitense, Erika
1997AJ....113...13B    Altcode:
  Recent distance determinations by means of the Cepheid period-magnitude
  relations are based on a true distance modulus of m-M=18.5 to the
  Large Magellanic Cloud. It has further been assumed that for the LMC
  Cepheids the average E(B-V)=0.10 and that the ratio of interstellar
  extinction A<SUB>v</SUB> in the visual to E(B-V), i.e., R<SUB>v</SUB>,
  is 3.1. In order to determine the distance to the LMC with its lower
  than solar metallicity, it is also assumed that the period-magnitude
  relation is independent of metallicity. Here we reexamine the different
  assumptions, i.e., the reddening and distance to the LMC and to the
  Galactic Cepheids. We also study the dependence of the period-magnitude
  relations for different heavy element abundances. In that process we
  rediscuss the distances to the LMC, to M31 and the Small Magellanic
  Cloud. Adopting the theoretical result, that the period-luminosity
  relation is independent of metallicity, we derive for the V and B bands
  the dependence of the period-magnitude relations on Z. The use of these
  relations changes the determination of the interstellar extinction
  for the three M3 1 fields, studied by Freedman and Madore, and yields
  very good agreement for the distance moduli of the three fields, namely
  m-M=24.59±0.02, or (m-M)<SUB>M31</SUB>-(m-M)<SUB>LMC</SUB>=6.09± 0.02,
  where the error limits refer only to the internal agreement for the
  three fields. We adopt a foreground reddening of E(B-V)=0.08 for M31 and
  estimate an average E(B-V)=0.18 for the LMC Cepheids. With a distance
  modulus to the Pleiades, m-M=5.57, we derive a distance modulus to the
  LMC of m-M=18. 11 andm-M=18.84±0.1 for the SMC. These error limits are
  only estimates. We also point out a way to get a rough estimate about
  large metallicity differences of Cepheids observed in external galaxies.

---------------------------------------------------------
Title: New Results on Cepheid Masses
Authors: Evans, N. R.; Bohm-Vitense, E.; Carpenter, K.; Robinson,
   R.; Beck-Winchatz, B.
1996AAS...189.9608E    Altcode: 1996BAAS...28.1399E
  Masses for Cepheid variable stars can be measured by combining the
  orbital velocity amplitude for the Cepheid (from a ground-based orbit)
  with the orbital velocity amplitude of a hot main sequence companion
  (observed in the ultraviolet from satellites such as IUE and HST) and
  the mass of the companion (inferred from from the ultraviolet energy
  distribution). Observations of 5 binary systems are now completed
  or in progress with the Goddard High Resolution Spectrograph on the
  Hubble Space Telescope. Recently completed observations of U Aql lead
  to a mass of 5.1 +/- 1.1 Msun . We will discuss the results for S Mus,
  V350 Sgr, U Aql, and Y Car, and the constraints they place on stellar
  evolution calculations. As would be expected, some of the B companions
  have high rotational velocities, decreasing the accuracy with which
  their orbital velocities can be measured. The preliminary conclusion
  from the 4 HST targets and SU Cyg (mass from IUE observations) is that
  a weighted mean indicates no convective overshoot but the mode (which
  reflects the HST results better) agrees with the modest overshoot
  used in the Geneva evolutionary calculations. Financial Support was
  provided by a NASA grant GO-4541-01 to EB--V and GO-4541.02 to KGC,
  a grant from the Natural Sciences and Engineering Council, Canada to
  NRE, from the AXAF Science Center NASA Contract NAS8-39073.

---------------------------------------------------------
Title: Cepheid Masses
Authors: Boehm-Vitense, Erika
1996hst..prop.6504B    Altcode: 1996hst..prop.2915B
  This is a proposal for the fourth year of an originally threeyear
  proposal which was accepted for cycles 3, 4, 5 and 6.The aim is to
  determine Cepheid masses for binaries withCepheids. For 2 decades
  the Cepheid “mass problem" haspersisted: Mass determinations from
  standard evolutionarytracks and those from pulsation theory gave
  conflictingresults. The luminosity of a Cepheid with a given mass
  dependssensitively on the amount of excess mixing above the core ofthe
  main sequence progenitor. Hence a good mass determinationfor a Cepheid
  with known luminosity measures the amount ofconvective overshoot. This
  knowledge is important for theinterpretation of HR diagrams of populous
  clusters in the LMC,especially for age determinations, and also for
  theunderstanding of mixing processes in stars. IUE observationshave
  revealed a number of Cepheids with blue companions,whose orbits have
  now been determined by groundbasedobservations. We propose to measure
  the orbital radialvelocities of altogether 5 companions for wavelengths
  shorterthan 2000A. The ratio of the orbital velocity amplitudes forthe
  binary provides the mass ratio for the stars. Theeffective temperature
  of the main sequence companion andthereby its mass is determined from
  its ultraviolet spectrumand energy distribution. With good GHRS spectra
  the velocityratio and thereby the mass ratio can be determined with
  anaccuracy of +/-10%.

---------------------------------------------------------
Title: White Dwarf Companions of Barium and CH Peculiar Stars
Authors: Boehm-Vitense, Erika
1996hst..prop.6594B    Altcode: 1996hst..prop.3005B
  In 1980 McClure et al.(ApJ 238, L35) discovered that all Bastars show
  radial velocity variations indicative of theirbinary nature. These
  authors already suspected that thecompanions are white dwarfs. White
  dwarf companions wereindeed detected for the Ba star zeta Cap and the
  mild Ba starzeta Cyg (Boehm-Vitense 1980, ApJ 239, L79) by means of
  IUEobservations. Evidence for a high temperature radiation fieldwas seen
  in the spectra of the mild Ba stars HR1016, 16Ser and56UMa. If present,
  the white dwarf companions are too faint tobe seen with IUE. We would
  like to look for them now with HST.It seems to us to be very important
  to check whether indeedall Ba stars have white dwarf companions. If so
  this makes ithighly probable that the peculiar abundances are due to
  masstransfer from a very luminous companion to the present Bastar. After
  losing its envelope the luminous companion wasleft as the present white
  dwarf. This opens up the possibilitythat other peculiar abundances
  seen in other peculiar starslike the CH stars or perhaps also the weak
  G band stars mightalso be due to mass transfer. On the other hand if
  the whitedwarfs are not found for all Ba stars we may have to look
  forother processes, that could bring to the surface of thesestars
  material which has experienced the slow neutron captureprocess.

---------------------------------------------------------
Title: The Mass of the Cepheid S Muscae.
Authors: Bohm-Vitense, E.; Evans, N. R.; Beck-Winchatz, B.; Carpenter,
   K.; Robinson, R.
1995AAS...18710205B    Altcode: 1995BAAS...27.1428B
  Using the Goddard High Resolution Spectrograph on the Hubble Space
  Telescope we have measured the orbital radial velocity changes for
  the companion of the Cepheid S Muscae. The observations were done
  at minimum and maximum orbital velocities. The two spectra were
  cross-correlated. The velocity difference was measured to be 30.6 +/-
  0.4 km/s. The difference for the orbital velocities of the Cepheid
  for the same phases was determined to be 26.9 +/-0.4 km/s. This gives
  a mass ratio of 1.14 +/-0.06. For a spectral type between B3.5 V and
  B5 V for the companion S Mus B its mass is 5.0 +/- 0.3 M(sun). With
  the mass ratio of 1.14 the mass of the Cepheid, with a period of 9.6
  days, comes out to be 5.7 +/- 0.4 solar masses. This compares with a
  pulsational mass of 5.5 solar masses. Taking the 5.7 solar masses for
  the Cepheid at face value its absolute visual magnitude of M(V)=-4.29
  indicates a high degree of excess interior mixing in its main sequence
  progenitor corresponding to convective overshoot by one pressure
  scale height. Even for the upper mass limit the excess mixing has to
  correspond to convective overshoot by 1/2 pressure scale height.

---------------------------------------------------------
Title: White Dwarf Companions to Hyades F Stars
Authors: Bohm-Vitense, Erika
1995AJ....110..228B    Altcode:
  We have studied archival, short-wavelength, low resolution IUE spectra
  of Hyades F stars in an effort to detect white dwarf companions, which
  can give us information about the IMF for the Hyades duster Weidemann
  et al. pointed out that we have not detected the expected number of
  white dwarfs in the Hyades. They suspected that the missing white dwarfs
  have evaporated from the cluster This cannot have happened with white
  dwarf companions to A and F stars. We estimate that for the 27 observed
  Hyades F stars we should have seen 3 white dwarfs while we found none.

---------------------------------------------------------
Title: Cepheid Masses
Authors: Boehm-Vitense, Erika
1995hst..prop.5854B    Altcode: 1995hst..prop.2327B
  This is a proposal for the third {and fourth} year of a three year
  proposal which was accepted for the last two years. The aim is to
  determine Cepheid masses for binaries with Cepheids. For 2 decades
  the Cepheid “mass problem" has persisted: Mass determinations from
  standard evolutionary tracks and those from pulsation theory gave
  conflicting results. The luminosity of a Cepheid with given mass
  depends sensitively on the amount of convective overshoot above the
  core of the main sequence progenitor. Hence a good mass determination
  for a Cepheid with known luminosity measures the amount of convective
  overshoot. This knowledge is important for the interpretation of
  HR diagrams of populous clusters in the LMC and especially for age
  determinations. It is also necessary for the understanding of mixing
  processes in stars. IUE observations have revealed a number of Cepheid
  binaries with blue companions whose orbits have now been determined
  by groundbased observations. We propose to measure the orbital radial
  velocities of altogether 5 blue Cepheid companions for wavelengths
  shorter than 2000 A. The ratio of the orbital velocity amplitudes
  for the binary provides the mass ratio for the stars. The effective
  temperature for the companion is determined from its ultraviolet
  energy distribution. For main sequence stars this also determines its
  mass. With good GHRS spectra the velocity ratio and thereby the mass
  ratio can be determined with an accuracy of +/- 10%

---------------------------------------------------------
Title: A dip in the CaII H and K emission line fluxes for Hyades
    F stars.
Authors: Bohm-Vitense, E.
1995A&A...297L..25B    Altcode:
  The Hyades chromospheric emission line fluxes for the Ca H and K
  lines show a minimum at B-V=0.45, very close to the minimum for the
  Li surface abundances. No anomalies have been reported for Ca surface
  abundances in Hyades F stars, though published abundance analyses may
  have missed stars at this B-V. We do, therefore not think that the dip
  in the CaII emission is due to diffusion (as believed to be the case
  for Li) but rather suspect that it is a chromospheric effect. Only on
  the branch of the dip with declining fluxes for increasing B-V (which
  means for B-V=0.43 and 0.44) a correlation of the CaII emission with
  v sini is seen.

---------------------------------------------------------
Title: Studies with IUE spectra: Stellar chromospheres and transition
    layers, and Cepheid Binaries
Authors: Bohm-Vitense, Erika
1995wub..rept.....B    Altcode:
  During the last years the work under this grant (NSG 5398) on IUE
  spectra was mainly concerned with two topics: the study of stellar
  chromospheres and transition layers; and the study of Cepheid companions
  in order to derive the masses of the Cepheids. Both are reported here.

---------------------------------------------------------
Title: The Lithium Content and Other Properties of F2-G5 Giants in
    the Hertzsprung Gap
Authors: Wallerstein, George; Bohm-Vitense, Erika; Vanture, Andrew D.;
   Gonzalez, Guillermo
1994AJ....107.2211W    Altcode:
  As stars of 2-5 solar mass evolve across the Hertzsprung Gap they
  should first deplete their surface lithium by convective dilution
  and then, when convection penetrates deeper, begin to bring CN
  processed material to their surfaces. To investigate this process
  we have observed 52 giants, 25 of which have known C/N ratios, for
  their Li abundances. After eliminating four stars that may actually
  be dwarfs and including the two components of Capella analyzed by
  Pilachowski and Sowell we have compared our (Li/Fe) ratios with
  models of Swenson. For stars showing v sin i greater than 50 km/s
  we find (Li/Fe) to be unaffected by mixing for B - V less than 0.7
  as predicted. For stars cooler than B - V = 0.7 both v sin i and
  (Li/Fe) drop to smaller values. For the sharp lined stars (v sin i
  less than 50 km/s) we find a drop in Li between B - V = 0.45 and 0.60
  which cannot be understood in terms of dilution by convection. Various
  possible causes of such an early depletion or dilution of surface Li
  are discussed including diffusion at the base of the convection zone,
  mass loss possibly enhanced by pulsation, and magnetic activity as in
  the magnetic A and B type stars. The models of Richer &amp; Michaud
  (1993) with diffusion point toward a satisfactory solution. A few
  giants with low v sin i values stand out with much higher than expected
  (Li/Fe) values despite their cool effective temperatures. We do not
  understand why those stars have not depleted their lithium as have
  most giants of similar color. The correlation of (N/C) with (Li/Fe)
  follows expectations in so far as almost all stars with enhanced (N/C)
  have depleted their Li as well.

---------------------------------------------------------
Title: The Two period-Luminosity Relations for Population I Cepheids
Authors: Bohm-Vitense, E.
1994AJ....107..673B    Altcode:
  We summarize the evidence that most Population I Cepheids with periods
  less than ~8 days pulsate in the first overtone mode. Fundamental mode
  and first overtone pulsators must follow different period-luminosity (P-
  L) relations. We demonstrate these different relations for different
  stellar systems, especially for the calibrating Cepheids in clusters
  and for Cepheids in the LMC, the SMC, M31, and IC 4182.

---------------------------------------------------------
Title: Cepheid Masses - Cyc 4 High - Part 2
Authors: Boehm-Vitense, Erika
1994hst..prop.5673B    Altcode: 1994hst..prop.2114B
  For 2 decades the "Cepheid mass problem" has persisted: Mass
  determinations from standard evolutionary tracks and those from
  pulsation theory gave conflicting values. The luminosity of a Cepheid of
  given mass depends sensitively on the amount of convective overshoot
  above the core of the main sequence progenitor. Hence a good mass
  determination for the Cepheid with known luminosity will measure the
  amount of convective core overshoot. This knowledge is important
  for interpretation of HR diagrams of populous clusters in the LMC
  and especially for age determinations. It is also necessary for the
  understanding of the mixing processes in stars. Program 5357 obtained
  the GHRS spectra for this program. This is a follow-on part 2 to obtain
  the calibration spectra to measure the radial velocity of the 2 primary
  targets observed in 5357.

---------------------------------------------------------
Title: Emission Lines in the Long-Period Cepheid L Carinae
Authors: Bohm-Vitense, Erika; Love, Stanley G.
1994ApJ...420..401B    Altcode:
  For the Cepheid l Carinae, with a pulsation period of 35.5 days, we
  have studied the emission-line fluxes as a function of pulsational phase
  in order to find out whether we see chromospheric and transition-layer
  emission due to an outward-moving shock. All emission lines show a steep
  increase in flux shortly before maximum light, suggestive of a shock
  moving through the surface layers. The large ratio of C IV to C II line
  fluxes shows that these are not transition-layer lines. During maximum
  light the large ratio of the large ratio of the C IV to C II line
  fluxes also suggests that we see emission from a shock with velocities
  greater than 100 km/s such that C IV emission can be excited. With such
  velocities mass outflow appears possible. The variations seen in the
  MG II line profiles show that there is an external absorption over a
  broad velocity band independent of the pulsation phase. We attribute
  this absorption to a circumstellar 'shell.' This 'shell' appears to
  be seen also as spatially extended emission in the O I line at 1300 A,
  which is probably excited by resonance with Ly beta.

---------------------------------------------------------
Title: Cepheid Masses -CYC4-HIGH
Authors: Boehm-Vitense, Erika
1994hst..prop.5357B    Altcode: 1994hst..prop.1803B
  For 2 decades the "Cepheid mass problem" has persisted: Mass
  determinations from standard evolutionary tracks and those from
  pulsation theory gave conflicting values. The luminosity of a Cepheid of
  given mass depends sensitively on the amount of convective overshoot
  above the core of the main sequence progenitor. Hence a good mass
  determination for the Cepheid with known luminosity will measure the
  amount of convective core overshoot. This knowledge is important
  for interpretation of HR diagrams of populous clusters in the LMC
  and especially for age determinations. It is also necessary for the
  understanding of the mixing processes in stars. IUE observations have
  revealed a number of Cepheid binaries with blue companions, whose orbits
  have now been determined by groundbased observations. We propose to
  measure the orbital radial velocities of 5 blue Cepheid companions on
  GHRS spectra for wavelengths shorter than 2000 A. The ratios of the
  orbital velocities for the binaries provide the mass ratios for the
  stars. The effective temperature of the companion can be determined from
  its energy distribution. For main sequence stars this also determines
  its mass. With GHRS spectra the orbital velocity ratio and thereby
  the mass ratio can be determined with an accuracLy of +/- 10 %.

---------------------------------------------------------
Title: Silicon Abundances in Population I Giants
Authors: Bohm-Vitense, Erika
1993AJ....106.2510B    Altcode:
  Silion to carbon abundance ratios for Population I giants were
  determined from emission lines originating in the transition layers
  between stellar chromospheres and coronae. For effective temperatures
  larger than 6200 K we find a group of stars for which the silicon
  to carbon abundance ratio appears to be increased. These stars
  are presumably descendents from AP stars on Am stars with increased
  surface silicon to carbon abundance ratios. Around B-V approximately
  equal to 0.45 this anomaly disappears as is to be expected due to the
  increased depth of the convection zone and therefore deeper mixing
  which dilutes the surface overabundances. Unexplained is the apparent
  increased silicon to carbon abundance ratio observed for several stars
  cooler than 5100 K. RS CVn and related stars do not show this increased
  abundance ratio.

---------------------------------------------------------
Title: Detection of a White Dwarf Compensation to the Hyades Stars
    HD 27483
Authors: Boehm-Vitense, Erika
1993AJ....106.1113B    Altcode:
  We observed with IUE a white dwarf (WD) companion to the Hyades F6 V
  binary stars HD 27483. This system is known to be a close binary of
  two nearly equal stars with an orbital period of 3.05 days. Our IUE
  observations revealed the presence of a third star, a white dwarf
  with an effective temperature of 23,000 +/- 1000 K and a mass of
  approximately 0.6 solar mass. Its presence in the Hyades cluster with
  a known age permits me to derive the mass of its progenitor, which must
  have been about 2.3 solar masses. The presence of the white dwarf in a
  binary system opens the possibility that some of the envelope material,
  which was expelled by the WD progenitor, may have been collected by
  the F6 stars. We may thus be able to study abundance anomalies of the
  WD progenitor with known mass on the surface of the F6 companions.

---------------------------------------------------------
Title: Cepheids, Distance Indicators and Tests of Stellar Evolution
    Theory
Authors: Bohm-Vitense, E.
1993AAS...182.5801B    Altcode: 1993BAAS...25..896B
  No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics
Authors: Bohm-Vitense, E.; De Greve, J. P.
1993SSRv...64..172B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet Studies of Cepheids
Authors: Bohm-Vitense, Erika
1993npsp.conf..387B    Altcode: 1993IAUCo.139..387B
  No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics - V.2 -
    Stellar Atmospheres
Authors: Bohm-Vitense, E.; Trimble, V.
1993ComAp..16..278B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Transition Layers of Hyades F Stars
Authors: Bohm-Vitense, Erika H.
1993iue..prop.4487B    Altcode:
  We would like to observe most Hyades F main sequence stars in order to
  determine the dependence of transition layer emission on temperature,
  rotation, binarity and Li abundances. In order to study the dependence
  on any one parameter one has to keep all other parameters constant. For
  the Hyades cluster age and metal abundance are constant. The Hyades
  cluster is the nearest one for which the F stars are bright enough to be
  observed with IUE in the SWP wavelength region. At the same time there
  are enough F stars to study the dependence on one parameter with all
  other parameters being nearly the same. In the F star region rotation
  decreases when going from early to late F stars. Simon and Drake
  suggest that the heating mechanism changes for B-V around 0.45. The
  chromospheric emission appears not to vary with time for stars earlier
  than F7 while it is variable for stars later than F8. Michaud suggests
  depletion of He for early F stars but not for late F stars. Boesgaard
  and Tripicco find a minimum in the Li abundances for stars with Teff
  around 6700 K. We want to study the changes (or not) in the transition
  layer emission related to all these events. This is last year's proposal
  which was accepted for two years, but the committee failed to assign
  shifts for the second year.

---------------------------------------------------------
Title: Absorption-Line Profiles in a Companion Spectrum of a
    Mass-losing Cool Supergiant
Authors: Rodrigues, Liliya L.; Boehm-Vitense, Erika
1992ApJ...401..695R    Altcode:
  Cool star winds can best be observed in resonance absorption lines seen
  in the spectrum of a hot companion, due to the wind passing in front
  of the blue star. We calculated absorption line profiles that would
  be seen in the ultraviolet part of the blue companion spectrum. Line
  profiles are derived for different radial dependences of the cool
  star wind and for different orbital phases of the binary. Bowen and
  Wilson find theoretically that stellar pulsations drive mass loss. We
  therefore apply our calculations to the Cepheid binary S Muscae which
  has a B5V companion. We find an upper limit for the Cepheid mass loss
  of M less than or equal to 7 x 10 <SUP>-10</SUP> solar mass per year
  provided that the stellar wind of the companion does not influence
  the Cepheid wind at large distances.

---------------------------------------------------------
Title: Detection of a White Dwarf in a Visual Binary System
Authors: Boehm-Vitense, Erika
1992AJ....104.1539B    Altcode:
  The F6 giant HD 160365 was detected to have a white dwarf companion
  about 8 arcsec south of the star. The UV energy distribution observed
  with IUE shows that the white dwarf has an effective temperature of
  23,000 +/- 2000 K. If log g = 8 the Lya profile indicates an effective
  temperature around 24,500 K. Using the theoretical models by Wesemael et
  al. (1980) one finds a visual magnitude of m(V) about 16.5. For T(eff)
  = 24,500 K one expects for a white dwarf a luminosity of log L/L(solar)
  about 1.3 and M(V) about 10.67. This gives a distance modulus for the
  system of m(V) - M(V) = 5.83 and an absolute magnitude M(V)= 0.3 for
  the giant.

---------------------------------------------------------
Title: Determination of nitrogen to carbon abundance ratios from
    transition layer emission lines
Authors: Boehm-Vitense, Erika
1992uwse.reptQ....B    Altcode:
  We have finished studying the nitrogen to carbon abundance ratios
  for stars with different effective temperatures T<SUB>eff</SUB>
  and luminosities using transition layer emission lines and using
  spectra available in the IUE archives. The N/C abundance ratio
  determinations using transition layer emission lines are as accurate
  as the photospheric abundance determinations as found by comparison of
  results obtained by both methods for the same stars. Our measurements
  confirm photospheric abundance determinations in regions of the HR
  diagram where they can be obtained. Our studies have extended the
  temperature range to higher temperatures. They have shown the exact
  positions in the HR diagram where the mixing due to the outer convection
  zones reaches deep enough to bring nuclear processed material to
  the surface. This occurs at effective temperatures which are higher
  by delta log T<SUB>eff</SUB> approximately 0.04 or roughly 400 K
  than expected theoretically. Since the depth of the convection zone
  increases rapidly with decreasing T<SUB>eff</SUB> this may indicate
  considerable overshoot beyond the lower boundary of the convection
  zone. Our N/C abundance ratio determinations from transition layer
  emission lines have confirmed that the actual enrichment observed
  for some cool giants is larger than expected theoretically, again
  indicating a larger degree of mixing in several stars either from below
  or from above. For the supergiants it probably indicates overshoot
  above the convective core in the progenitor main sequence stars. For
  the more massive giants this may also be the case, though we did not
  find a correlation between delta log N/C and the absolute magnitudes,
  but these are rather uncertain. As byproducts of these studies we also
  found anomalies in Si/C and N/C abundance ratios for F giants which
  can be understood as the relict of surface abundance changes for their
  main sequence progenitors due to diffusion. This anomaly disappears for
  G giants, for which the depths of the convection zones are apparently
  deep enough to wipe out these element separations (Bohm-Vitense 1992).

---------------------------------------------------------
Title: Cepheid Masses -CYC3-HIGH
Authors: Boehm-Vitense, Erika
1992hst..prop.4541B    Altcode:
  For 2 decades the "Cepheid mass problem" has persisted: Mass
  determinations from standard evolutionary tracks and those from
  pulsation theory gave conflicting values. The luminosity of a Cepheid of
  given mass depends sensitively on the amount of convective overshoot
  above the core of the main sequence progenitor. Hence a good mass
  determination for the Cepheid with known luminosity will measure the
  amount of convective core overshoot. This knowledge is important
  for interpretation of HR diagrams of populous clusters in the LMC
  and especially for age determinations. It is also necessary for the
  understanding of the mixing processes in stars. IUE observations have
  revealed a number of Cepheid binaries with blue companions, whose orbits
  have now been determined by groundbased observations. We propose to
  measure the orbital radial velocities of 5 blue Cepheid companions on
  GHRS spectra for wavelengths shorter than 2000 A. The ratios of the
  orbital velocities for the binaries provide the mass ratios for the
  stars. The effective temperature of the companion can be determined from
  its energy distribution. For main sequence stars this also determines
  its mass. With GHRS spectra the orbital velocity ratio and thereby
  the mass ratio can be determined with an accuracLy of +/- 10 %.

---------------------------------------------------------
Title: Carbon and Nitrogen Abundances Determined from Transition
    Layer Lines
Authors: Boehm-Vitense, Erika; Mena-Werth, Jose
1992ApJ...390..253B    Altcode:
  The possibility of determining relative carbon, nitrogen, and silicon
  abundances from the emission-line fluxes in the lower transition layers
  between stellar chromospheres and coronae is explored. Observations
  for main-sequence and luminosity class IV stars with presumably
  solar element abundances show that for the lower transition layers
  Em = BT<SUP>-gamma.</SUP> For a given carbon abundance the constants
  gamma and B in this relation can be determined from the C II and C IV
  emission-line fluxes. From the N V and S IV lines, the abundances of
  these elements relative to carbon can be determined from their surface
  emission-line fluxes. Ratios of N/C abundances determined in this way
  for some giants and supergiants agree within the limits of errors with
  those determined from molecular bands. For giants, an increase in the
  ratio of N/C at B-V of about 0.8 is found, as expected theoretically.

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics - V.3 -
    Stellar Structure and Evolution
Authors: Bohm-Vitense, E.
1992JBAA..102Q.109B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Rotation and Transition Layer Emission in Cool Giants
Authors: Boehm-Vitense, Erika
1992AJ....103..608B    Altcode:
  Gray (1981, 1982) found that field giants with T(eff) less than about
  5500 K experience a steep decrease in rotational velocities coupled
  with a decrease in transition layer emission. This decrease may be
  attributable to fast magnetic braking or to redistribution of angular
  momentum for rapidly increasing depths of the convection zones if these
  rotate with depth independent specific angular momentum. Additional
  arguments in favor of the latter interpretation are presented. The
  increase of N/C abundances due to deep mixing occurs at the same point
  as the decrease in v sin i. On the other hand, the ratios of the C
  IV to C II emission line fluxes decrease at this point indicating
  smaller contributions of MHD wave heating. The X-ray fluxes decrease
  at nearly the same T(eff). Thus, no observations are found which would
  indicate larger magnetic activity which could lead to fast magnetic
  braking. Theory predicts a rapid increase in the convection zone
  depth at the T(eff) where the decrease in v sin i is observed. This
  can explain the observed phenomena.

---------------------------------------------------------
Title: Introduction to Stellar Astrophysics. Vol.3: Stellar structure
    and evolution
Authors: Boehm-Vitense, Erika
1992itsa.book.....B    Altcode:
  The present volume on current physical understanding of the
  internal structure of stars gives attention to basic principles while
  stressing comparisons with observations capable of elucidating stellar
  evolution. Treatments are conducted of the hydrostatic and thermal
  equilibriums, opacities, convective instability and energy transport,
  the depths of the outer convection zones, stellar energy-generation
  processes, the basic stellar-structure equations, the influence of
  convection zones on stellar structure, main-sequence star models, the
  evolutionary paths of low mass and massive stars, the late stages of
  stellar evolution, pulsating stars, and the Cepheid mass problem.

---------------------------------------------------------
Title: Introduction to stellar astrophysics. Volume 3. Stellar
    structure and evolution.
Authors: Böhm-Vitense, Erika
1992isa..book.....B    Altcode:
  Introduction; Hydrostatic equilibrium; Thermal equilibrium;
  The opacities; Convective instability; Theory of convective energy
  transport; Depths of outer convection zones; Energy generation in stars;
  Basic stellar structure equations; Homologous stars in radiative
  equilibrium; Influence of convection zones on stellar structure;
  Calculation of stellar models; Models for main sequence stars;
  Evolution of low mass stars; Evolution of massive stars; Late stages
  of stellar evolution; Observational tests of stellar evolution theory;
  Pulsating stars; The cepheid mass problem; Star formation; Problems;
  Bibliography; Index.

---------------------------------------------------------
Title: Introduction to Stellar Astrophysics
Authors: Böhm-Vitense, Erika
1992isa3.book.....B    Altcode:
  This book is the final one in a series of three texts which together
  provide a modern, complete and authoritative account of our present
  knowledge of the stars. It discusses the internal structure and
  the evolution of stars, and is completely self-contained. There is
  an emphasis on the basic physics governing stellar structure and
  the basic ideas on which our understanding of stellar structure is
  based. The book also provides a comprehensive discussion of stellar
  evolution. Careful comparison is made between theory and observation,
  and the author has thus provided a lucid and balanced introductory text
  for the student. As for volumes 1 and 2, volume 3 is self-contained
  and can be used as an independent textbook. The author has not only
  taught but has also published many original papers in this subject. Her
  clear and readable style should make this text a first choice for
  undergraduate and beginning graduate students taking courses in
  astronomy and particularly in stellar astrophysics.

---------------------------------------------------------
Title: Transition Layers of Hyades F Stars
Authors: Bohm-Vitense, Erika H.
1992iue..prop.4205B    Altcode:
  We would like to observe most Hyades F main sequence stars in order to
  determine the dependence of transition layer emission on temperature,
  rotation, binarity and Li abundances. In order to study the dependence
  on any one parameter one has to keep all other parameters constant. For
  the Hyades cluster age and metal abundance are constant. The Hyades
  cluster is the nearest one for which the F stars are bright enough to be
  observed with IUE in the SWP wavelength region. At the same time there
  are enough F stars to study the dependence on one parameter with all
  other parameters being nearly the same. In the F star region rotation
  decreases when going from early to late F stars. Simon and Drake
  suggest that the heating mechanism changes for B-V around 0.45. The
  chromospheric emission appears not to vary with time for stars earlier
  than F7 while it is variable for stars later than F8. Michaud suggests
  depletion of He for early F stars but not for late F stars. Boesgaard
  and Tripicco find a minimum in the Li abundances for stars with Teff
  around 6700 K. We want to study the changes (or not) in the transition
  layer emission related to all these events.

---------------------------------------------------------
Title: Silicon abundances in population I giants
Authors: Boehm-Vitense, Erika
1992STIN...9233658B    Altcode:
  Silicon to carbon abundance ratios for population I giants were
  determined from emission lines originating in the transition layers
  between stellar chromospheres and coronae. For effective temperatures
  larger than 6200 K we find a group of stars with increased silicon to
  carbon but normal nitrogen to carbon abundance ratios. These stars are
  presumably descendents from Ap stars with increased surface silicon
  to carbon abundance ratios. For G stars this anomaly disappears as is
  to be expected due to the increased depth of the convection zone and
  therefore deeper mixing which dilutes the surface overabundances. The
  disappearance of the abundance anomalies proves that the anomalous
  abundances observed for the F giants are indeed only a surface
  phenomenon. It also proves that the same holds for their progenitors,
  the Ap and Am stars, as has been generally believed. Unexplained is
  the increased silicon to carbon abundance ratio observed for several
  stars cooler than 5100 L. RS CVn and related stars do not show this
  increased abundance ratio. There are also some giants which appear to
  be enriched in carbon, perhaps due to a helium flash with some mixing
  if the star is a clump star.

---------------------------------------------------------
Title: Ultraviolet studies of Cepheids
Authors: Boehm-Vitense, Erika
1992STIN...9311073B    Altcode:
  We discuss whether with new evolutionary tracks we still have a problem
  fitting the Cepheids and their evolved companions on the appropriate
  evolutionary tracks. We find that with the Bertelli et al. tracks
  with convective overshoot by one pressure scale height the problem is
  essentially removed, though somewhat more mixing would give a better
  fit. By using the results of recent nonlinear hydrodynamic calculations,
  we find that we also have no problem matching the observed pulsation
  periods of the Cepheids with those expected from their new evolutionary
  masses, provided that Cepheids with periods less than 9 days are
  overtone pulsators. We investigate possible mass loss of Cepheids from
  UV studies of the companion spectrum of S Mus and from the ultraviolet
  spectra of the long period Cepheid l Carinae. For S Mus with a period
  of 9.6 days we derive an upper limit for the mass loss of M less than
  10<SUP>-9</SUP> solar mass, if a standard velocity law is assumed for
  the wind. For l Carinae with a period of 35.5 days we find a probable
  mass loss of M is approximately 10<SUP>-5+/-2</SUP> solar mass.

---------------------------------------------------------
Title: Heating Mechanism(s) for Transition Layers in Giants
Authors: Bohm-Vitense, Erika; Mena-Werth, Jose
1991ApJ...378..718B    Altcode:
  The emission-line fluxes of lines originating in the lower parts of
  the transition layers between stellar chromospheres and coronas are
  studied. Simon and Drake (1989) suspect different heating mechanisms
  for 'hot' and cool stars. Changes in the flux ratios for the C IV to
  C II emission lines support this suspicion. Large C IV/C II line flux
  ratios appear to be indicative of magnetically controlled heating. A
  correlation between excess continuum flux around 1950 A and C II
  emission-line fluxes are confirmed for the cooler giants (late F and
  cooler). Excess continuum flux correlates positively with large C
  IV/C II line flux ratio. The excess continuum flux corresponds to an
  increase in temperature by several hundred degrees in layers with a
  mean optical depth of about 0.03. For chromospherically active stars
  these layers experience a mechanical flux deposition of the order
  of 1 percent of the total radiative flux. This flux is tentatively
  identified as an MHD wave flux similar to Alfven waves.

---------------------------------------------------------
Title: Report on carbon and nitrogen abundance studies
Authors: Boehm-Vitense, Erika
1991STIN...9211934B    Altcode:
  The aim of the proposal was to determine the nitrogen to carbon
  abundance ratios from transition layer lines in stars with different
  T<SUB>eff</SUB> and luminosities. The equations which give the
  surface emission line fluxes and the measured ratio of the NV to
  CIV emission line fluxes are presented and explained. The abundance
  results are compared with those of photospheric abundance studies
  for stars in common with the photospheric investigations. The results
  show that the analyses are at least as accurate as the photospheric
  determinations. These studies can be extended to F and early G
  stars for which photospheric abundance determinations for giants
  are hard to do because molecular bands become too weak. The abundance
  determination in the context of stellar evolution is addressed. The N/C
  abundance ratio increases steeply at the point of evolution for which
  the convection zone reaches deepest. Looking at the evolution of the
  rotation velocities v sin i, a steep decrease in v sin i is related to
  the increasing depth of the convection zone. It is concluded that the
  decrease in v sin i for T<SUB>eff</SUB> less than or approximately
  = 5800 K is most probably due to the rearrangement of the angular
  momentum in the stars due to deep convective mixing. It appears that
  the convection zone is rotating with nearly depth independent angular
  momentum. Other research results and ongoing projects are discussed.

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics - V.1 -
    Basic Stellar Observations and Data - Vol. - Stellar Atmospheres
Authors: Bohm-Vitense, E.; Stoll, D.; Stahlberg, J.
1991AN....312..276B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics - VOL.1 -
    Basic Stellar Observations and Data
Authors: Bohm-Vitense, E.; Doyle, J. G.
1991IrAJ...20...50B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Absorption Line Profiles in a Companion Spectrum of a Mass
    Losing Cool Supergiant
Authors: Rodrigues, L. L.; Böhm-Vitense, E.
1991BAAS...23..910R    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Transition Layers of F and Early G Giants
Authors: Bohm-Vitense, Erika H.
1991iue..prop.3932B    Altcode:
  Giants are especially well suited to study the dependence of transition
  layer stratifications on v sini and log Teff because they are a group
  of stars of nearly the same mass, age and chemical composition. We
  want to observe additional F and early G giants in order to better
  understand which heating mechanism(s) are responsible for the heating
  of the transition layers. We also want to determine N/C and Si/C
  abundance ratios which appear to be abnormal for several F giants in
  contradiction to theoretical expectations.

---------------------------------------------------------
Title: Emission lines in the long period Cepheid L Carinae
Authors: Boehm-Vitense, Erika; Love, Stanley G.
1991STIN...9234060B    Altcode:
  For the Cepheid (l) Carinae with a pulsation period of 35.5 days we have
  studied the emission line fluxes as a function of pulsational phase
  in order to find out whether we see chromosphere and transition layer
  emission or whether we see emission due to an outward moving shock. All
  emission lines show a steep increase in flux shortly before maximum
  light suggestive of a shock moving through the surface layers. The
  large ratio of the C IV to C II line fluxes shows that these are not
  transition layer lines. During maximum light the large ratio of the C
  IV to C II line fluxes also suggests that we see emission from a shock
  with velocities greater than 100 km/sec such that C IV emission can
  be excited. With such velocities mass outflow appears possible. The
  variations seen in the Mg II line profiles show that there is an
  internal absorption over a broad velocity band independent of the
  pulsational phase. We attribute this absorption to a circumstellar
  'shell'. This 'shell' appears to be seen also as spatially extended
  emission in the O I line at 1300 angstrom, which is probably excited
  by resonance with Ly beta.

---------------------------------------------------------
Title: Mass Loss of B3 to B6 Main Sequence Stars
Authors: Bohm-Vitense, Erika H.
1991iue..prop.3937B    Altcode:
  Mass Loss for early type stars down to B2 has been observed in CIV,
  SiIV and Si III lines. In these lines nothing has been seen for stars
  later than B2. This does not exclude the possibility that winds may
  he observed in lower ionization resonance lines like those of Fe II,
  Mn II or Si II. We want to study whether such cool stellar winds can
  be detected for single, slowly rotating B3 to B6 main sequence, non
  Be stars.

---------------------------------------------------------
Title: Ultraviolet Gas Absorption and Dust Extinction toward M8
Authors: Boggs, Don; Bohm-Vitense, Erika
1990ApJ...358..441B    Altcode:
  Interstellar absorption lines are analyzed using high-resolution IUE
  spectra of 11 stars in the young cluster NGC 6530 located in the M8
  region. High-velocity clouds at -35 km/s and -60 km/s are seen toward
  all cluster stars. The components arise in gases that are part of large
  interstellar bubbles centered on the cluster and driven by stellar
  winds of the most luminous members. Absorption lines of species of
  different ionization states are separated in velocity. The velocity
  stratification is best explained as a 'champagne' flow of ionized
  gas away from the cluster. The C IV/Si IV ratios toward the hotter
  cluster members are consistent with simple photoionization models if
  the gas-phase C/Si ratio is increased by preferential accretion onto
  dust grains. High ion column densities in the central cluster decline
  with distance from W93, suggesting that radiation from a hot source
  near W93 has photoionized gas in the central cluster.

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics VOL.2
    Stellar Atmospheres
Authors: Bohm-Vitense, E.
1990Sci...249...24B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Introduction to Stellar Astrophysics
Authors: Böhm-Vitense, Erika
1990isa2.book.....B    Altcode:
  Volume 2 contains the basic physical ideas and laws used in the study
  of the outer layers of a star including stellar magnitudes, spectra
  and temperatures, radiative transfer in a stellar atmosphere, line
  formation, the spectrum of hydrogen, spectral analysis, and available
  structural components.

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics - V.1 -
    Basic Stellar Observations and Data
Authors: Bohm-Vitense, E.
1990Sci...247..584B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Transition Layer Emission in Giants
Authors: Bohm-Vitense, E.; Mena-Werth, J.
1990ASPC....9..128B    Altcode: 1990csss....6..128B
  No abstract at ADS

---------------------------------------------------------
Title: UV Extinction Law and CIV, SIIV Column Densities in NGC 6530
Authors: Bohm-Vitense, Erika
1990iue..prop.3657B    Altcode:
  We discovered that in the central part of the young galactic cluster
  NGC 6530 there is a strong correlation between the C IV and Si IV
  column densities and the strength of the interstellar extinction bump
  at 2175 A. Both depend on the distance from the star W 93, which is
  close to the center of the high stellar density part of the cluster. In
  the absence of any evidence for high velocity gas we conclude that a
  strong UV radiation field is responsible for the ionization to CIV and
  for the changes in the UV extinction law. The BIV star W93 is too cool
  to photoionize CIII, however. An unseen neighbor or companion to W 93
  must be the source of the UV radiation. While the correlation between
  extinction bump and distance from W 93 is based on about 10 stars,
  the correlation between extinction bump and C IV, Si IV column density
  is based on four stars only. The data refer mainly to the southeast
  part of the cluster and to stars southeast of W 93. We would like to
  extend our studies to more stars and to different directions from W 93.

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics - Basic
    Stellar Observations and Data
Authors: Bohm-Vitense, E.
1990AstQ....7..188B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics - Volume
    2 - Stellar Atmospheres
Authors: Bohm-Vitense, E.
1990AstQ....7..251B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Absorption line profiles in a companion spectrum of a mass
    losing cool supergiant
Authors: Rodrigues, Liliya L.; Boehm-Vitense, Erika
1990STIN...9234230R    Altcode:
  Cool star winds can best be observed in resonance absorption lines seen
  in the spectrum of a hot companion, due to the wind passing in front
  of the blue star. We calculated absorption line profiles that would
  be seen in the ultraviolet part of the blue companion spectrum. Line
  profiles are derived for different radial dependences of the cool
  star wind and for different orbital phases of the binary. Bowen and
  Wilson find theoretically that stellar pulsations drive mass loss. We
  therefore apply our calculations to the Cepheid binary S Muscae which
  has a B5V companion. We find an upper limit for the Cepheid mass loss
  of M less than or equal to 7 x 10<SUP>-10</SUP> solar mass per year
  provided that the stellar wind of the companion does not influence
  the Cepheid wind at large distances.

---------------------------------------------------------
Title: The Dynamical Mass of S MUSCAE
Authors: Bohm-Vitense, Erika; Clark, M.; Cottrell, P. L.; Wallerstein,
   George
1990AJ.....99..353B    Altcode:
  The amplitudes and phase relations of pulsational velocities of
  the Cepheid S Muscae, measured for lines originating at different
  atmospheric depths, are investigated. A mass M(A) = 4.4 + or - 0.5 solar
  masses is found for the Cepheid; however, the Cepheid is the evolved
  star and should have a mass larger than that of its companion. If the
  measured velocity differences are too low by 2.5 km/s on the average,
  then the mass ratio M(B)/M(A) may be decreased to 0.94, giving
  an estimated upper limit to the Cepheid mass of 6.1 solar masses,
  consistent with the Cepheid being the more evolved star. Considering
  all the uncertainties, it is concluded that the mass of the Cepheid
  is between 4.6 and 6.1 solar masses.

---------------------------------------------------------
Title: UV observations of NGC 205
Authors: Wilcots, Eric M.; Hodge, Paul W.; Eskridge, Paul B.;
   Boehm-Vitense, Erika; Bertola, Francesco
1989uwsa.rept.....W    Altcode:
  Low resolution IUE observations of the dwarf elliptical galaxy NGC
  205 show that the UV spectral energy distribution (SED) of the galaxy
  is relatively flat. Spectra centered on the nucleus and on a region
  north of the nucleus show evidence of recent bursts of star formation
  which contribute strongly to the UV spectral energy distribution. The
  UV spectra was fit with a composite spectrum based on a Miller-Scalo
  initial mass function, an underlying older population (modelled using
  the UV spectrum of 47 Tuc), and an extinction based on a SMC-like
  extinction cure. This fit implies that the total mass of young stars
  (with M equal to or greater than 1 solar mass) in the galaxy is
  approx. 7x10(5) solar mass, which can be compared to the total mass of
  globular cluster like stars in the galaxy of approx. 8x10(7) solar mass.

---------------------------------------------------------
Title: Introduction to Stellar Astrophysics
Authors: Böhm-Vitense, Erika
1989isa1.book.....B    Altcode:
  This textbook introduction to the basic elements of fundamental
  astronomy and astrophysics serves as a foundation for understanding
  the structure, evolution, and observed properties of stars. The first
  half of the book explains how stellar motions, distances, luminosities,
  colors, radii, masses and temperatures are measured or derived. The
  author then shows how data of these sorts can be arranged to classify
  stars through their spectra. Stellar rotation and stellar magnetic
  fields are introduced. Stars with peculiar spectra and pulsating stars
  also merit special attention. The endpoints of stellar evolutions are
  briefly described. There is a separate chapter on the Sun and a final
  one on interstellar absorption. The usefulness of this text is enhanced
  by the inclusion of problems for students, tables of astronomical
  constants, and a selective bibliography. This is an excellent textbook
  for undergraduate and beginning graduate students studying astronomy
  and astrophysics.

---------------------------------------------------------
Title: Problems with the Baade-Wesselink Method
Authors: Boehm-Vitense, E.; Garnavich, P.; Lawler, M.; Mena-Werth,
   J.; Morgan, S.; Peterson, E.; Temple, S.
1989ApJ...343..343B    Altcode:
  The discrepancy noted in radii obtained by the Baade-Wesselink method
  when different colors are used to determine the effective temperatures
  is explored. The discrepancy is found to be due to an inconsistency
  in the applied temperature-color calibrations. The assumption of the
  maximum likelihood method that beta (the effective temperature + 0.1
  times the bolometric correction) is a linear function of the color
  is valid for the B-V and V-I colors, but not for the V-R colors. It
  is suggested that the errors introduced by the nonlinearity in the
  relation between beta and the V-R colors will produce radii which are
  too large. The radii derived from the V-B colors appear to be too small.

---------------------------------------------------------
Title: Ultraviolet Extinction Differences within NGC 6530
Authors: Boggs, Don; Bohm-Vitense, Erika
1989ApJ...339..209B    Altcode:
  Ultraviolet extinction curves are presented for 14 stars in the
  very young cluster NGC 6530. The variation of the short-wavelength
  extinction is consistent with that expected based on random errors
  alone, although the weakest extinction is found only toward the cluster
  center. Variations significantly larger than the measurement uncertainty
  are found in the area, width, and central peak position of the 2200 A
  extinction bump. These parameters are largest in the cluster center
  and decrease systematically outwards. Physical processes capable of
  modifying the grains in the H II region containing the cluster are
  discussed.

---------------------------------------------------------
Title: Problems with the Baade-Wesselink Method
Authors: Böhm-Vitense, E.; Garnavich, P.; Lawler, M.; Mena-Werth,
   J.; Morgan, S.; Peterson, E.; Temple, S.
1989upsf.conf..250B    Altcode: 1989IAUCo.111..250B
  No abstract at ADS

---------------------------------------------------------
Title: Introduction to Stellar Astrophysics. Vol.1: Basic stellar
observations and data; Vol.2: Stellar atmospheres
Authors: Boehm-Vitense, Erika
1989itsa.book.....B    Altcode:
  Volume 1: The global properties of stars and the observational
  techniques used to determine them are examined in an introduction for
  undergraduate students. Chapters are devoted to stellar positions,
  proper motions, brightness, color-magnitude diagrams, luminosities,
  angular radii, and effective temperatures. Also considered are stellar
  masses and radii, spectral classification, population II stars,
  stellar rotation, magnetic fields, peculiar spectra, pulsating stars,
  explosive stars, the sun, and interstellar absorption. Diagrams, graphs,
  sample images and spectra, tables of numerical constants, and a set of
  problems are provided. Volume 2: The basic principles used in the study
  of the outer layers of a star are discussed. The subjects addressed
  include stellar magnitudes, colors, and spectra; temperature estimates
  for stars; radiative transfer; depth dependence of the source function;
  the continuous absorption coefficient; the influence of the nongreyness
  of the absorption coefficient; pressure stratification; theory of line
  formation; hydrogen lines; spectrum analysis; nonlocal thermodynamic
  equilibrium; the hydrogen convection zone; stellar chromospheres,
  transition layers, and coronae; and stellar winds.

---------------------------------------------------------
Title: Introduction to Stellar Astrophysics
Authors: Böhm-Vitense, Erika
1989ESASP.290.....B    Altcode: 1989isa..book.....B
  No abstract at ADS

---------------------------------------------------------
Title: The Companion of the RR Lyrae Star TV Boo
Authors: Bohm-Vitense, Erika
1989iue..prop.3380B    Altcode:
  In her study of the RR Lyrae star TV Boo, Claudia Oliveira at the
  University of British Columbia, measured over a period of 3 days a mean
  radial velocity of Vr = -110 km/sec, while measurements made a few
  years earlier had shown V, - -30 km/sec. These measurements indicate
  orbital motions of a binary. Combining all available measurements an
  orbital period around 60 days is suggested. The color-color plot of
  V-I versus B-V is abnormal and indicates a blue companion. This must
  then be either a white dwarf or a horizontal branch star on the very
  blue end with decreasing Mv. This then is an extremely interesting
  binary which for the first time can give direct information about the
  masses of such stars. We want to observe the blue companion of this RR
  Lyrae star in order to determine its properties and possibly measure
  its orbital velocity.

---------------------------------------------------------
Title: UV Continua of Cluster OB Stars in the Wing of the SMC
Authors: Bohm-Vitense, Erika
1989iue..prop.3377B    Altcode:
  Many investigators have found that the UV color temperatures of galactic
  O stars are generally well below the effective temperatures of the
  stars as inferred from optical line spectra and Zanstra colors. The
  difference is so severe that even the earliest O stars have UV continua,
  normalized at V, no brighter than early B main sequence stars. The
  effects of two possible explanations for the relatively cool continua,
  wind blanketing and non-LTE line blanketing, should be dependent on
  the stellar metal content. In particular, the winds of early-type
  stars with lower metallicity should be weaker and less effective at
  scattering radiation back onto the photosphere. The net effect should
  be reduced surface heating and consequently steeper UV continua than
  stars of galactic abundance. We propose to measure the UV continua of
  main sequence O and B stars in two lightly reddened clusters in the
  extreme wing of the SMC. Our observations will allow a precise test
  of these theories. With a much lower metallicity in the SMC compared
  to the Galaxy, line- and wind blanketing effects should be greatly
  reduced. If neither of these mechanisms are shaping the UV continua,
  the color temperatures of the O stars should be as cool as the B
  stars. Restricting our target stars to a single lightly reddened
  association will limit the uncertainties in dereddening the spectra.

---------------------------------------------------------
Title: Variable Bump Extinction in NGC6530
Authors: Bohm-Vitense, Erika
1989iue..prop.3372B    Altcode:
  We have found that the area and width of the 2200 A ultraviolet
  extinction bump varies dramatically from star to star within the young
  cluster NGC 6530. The bump is strongest toward stars in the center
  of the cluster and systematically weakens with distance from center
  appearing to reach an asymptotic state. Because the highest temperature
  stars in our sample are generally farther from the center this may also
  mean that the extinction bump is dependent on stellar temperature. It is
  very unfortunate that five stars whose positions and/or temperatures
  make them well suited for separating the effects of distance and
  temperature have only low quality long wavelength spectra. We want to
  reobserve those stars and obtain spectra of new targets advantageously
  located within the cluster to study whether the extinction is dependent
  on distance from the center or on stellar temperature.

---------------------------------------------------------
Title: Ultraviolet Extinction in the Outer Galaxy
Authors: Bohm-Vitense, Erika
1989iue..prop.3373B    Altcode:
  We propose to test whether the empirical trend of increasing
  far-ultraviolet extinction and decreasing 2200 A bump strength with
  decreasing metallicity seen among the solar neighborhood, LMC, and
  SMC is also valid within the Milky Way. Recent re-examinations of the
  average extinction curve in the LMC suggest that the dependence may
  not be as strong as originally thought; stars outside of the atypical
  30 Doradus region exhibit extinction remarkably similar to that of
  diffuse regions in the Milky Way. To test the validity of the trend
  requires observations of the extinction in other systems of different
  metallicities. Long exposure IUE spectra of luminous stars in M31 and
  M33 have been used to estimate the extinction in these galaxies but the
  low flux levels and uncertainties of the true stellar intrinsic colors
  make the results susceptible to large errors. To study extinction
  in systems of low metal content does not require observations of
  extragalactic stars, however. With the galactic abundance gradient,
  a metallicity comparable to that in the LMC is reached in only three
  or four kiloparsecs from the solar circle. We intend to measure the
  extinction curves toward several stars at this distance or beyond. The
  low nearby extinction toward much of the outer Galaxy ensures that
  the extinction of the stars is dominated by distant dust. The use
  of relatively bright and nearby stars will allow us to measure the
  extinction in an unexplored metal poor environment with unusually
  high precision.

---------------------------------------------------------
Title: Dynamical Masses for V636 SCO
Authors: Bohm-Vitense, Erika
1989iue..prop.3368B    Altcode:
  For the Cepheid V636 Scorpii we want to determine the pulsational radial
  velocities for the spectral lines seen in the LWR region of the IUE
  Observatory. These measurements are essential for the determination
  of the dynamical masses for this binary. On LWR IUE high resolution
  images of V636 Sco the spectrum of the Cepheid can be studied for
  lambda &gt; 2400 A while the one for the companion can be studied
  for lambda &lt; 2400 A for minimum light of the Cepheid. This fact
  permits the measurement of the difference in radial velocity for the two
  components of the binary system. After subtraction of the pulsational
  velocity of the Cepheid the difference of the orbital velocities is
  obtained. With the orbital velocity of the Cepheid known from optical
  studies the velocity ratio and thereby the mass ratio of the binary
  components can be determined. So far the pulsational velocities for
  the Cepheid measured in the optical region have been used in this
  procedure. Observations show, however, that pulsational velocities
  are different for different layers of the atmosphere. Subtraction of
  the pulsational velocities determined for the absorption lines in the
  optical region, when we should subtract the pulsational velocities
  for the UV region, may cause large errors in the difference of the
  orbital velocities and their ratios. We therefore have during the lIth
  period redetermined for S Mus the pulsational velocities for those high
  layers in which the lines in the LWR region are formed. This requires
  measurements for many phases of the pulsational cycle. We want to do
  the same for V636 Sco.

---------------------------------------------------------
Title: Introduction to stellar astrophysics. Vol. 2. Stellar
    atmospheres.
Authors: Böhm-Vitense, E.
1989isa2.book.....B    Altcode:
  This comprehensive textbook conveys the basic physical ideas and laws
  in the study of the outer layers of a star. This complete account
  first introduces stellar magnitudes, spectra and temperatures. This
  is followed by a full discussion of radiative transfer in a stellar
  atmosphere, which leads to descriptions of line formation, the spectrum
  of hydrogen, and spectral analysis. Finally the structural components
  that are accessible, such as the convection zone, chromosphere,
  corona, and mass outflow are described. Contents: 1. Stellar
  magnitudes and stellar colors. 2. Stellar spectra. 3. Temperature
  estimates for stars. 4. Basics about radiative transfer. 5. Radiative
  transfer in stellar atmospheres. 6. The depth dependence of the
  source function. 7. The continuous absorption coefficient. 8. The
  influence of the non-greyness of the absorption coefficient. 9. The
  pressure stratification. 10. Theory of line formation. 11. The
  hydrogen lines. 12. Spectrum analysis. 13. Basics about non-local
  thermodynamic equilibrium. 14. The hydrogen convection zone. 15. Stellar
  chromospheres, transition layers, and coronae. 16. Stellar winds.

---------------------------------------------------------
Title: Effects of SN 1987A on the Interstellar Medium around it
Authors: Bohm-Vitense, Erika; Boggs, Don; Morgan, Siobahn
1989AJ.....97..131B    Altcode:
  It is shown that the interstellar spectrum from SN 1987A in the LMC
  shows a rather strong component in C IV and Si IV, and possibly a weak
  component in N V, at a velocity of about 300 + or - 10 Km/s. In the
  spectra of the neighboring stars HD38268 and R123, a component at this
  velocity is only seen in low-ionization lines, not in the C IV, or N V
  lines. The possibility is studied that SN 1987A ionized a measurable
  fraction of this 300 Km/s cloud within less than one day since the
  Si IV, C IV, and possibly, N V interstellar lines are seen only
  about one day after the first light from the supernova explosion was
  detected. This may be the case, but only if the supernova temperature at
  outburst was larger than 50,000 K, depending on the density assumed for
  the interstellar cloud. Also, H and He must have been preionized once.

---------------------------------------------------------
Title: ISM Chemical Abundances in Two Intermediate-Velocity Clouds
    in the Line of Sight to SN 1987A
Authors: Morgan, Siobahn; Bohm-Vitense, Erika
1988AJ.....96.1373M    Altcode:
  The earliest IUE high-resolution spectra of SN 1987A have been studied
  and reveal the presence of several clouds in the line of sight to the
  LMC. In particular, there are two clouds with radial velocities of ~
  130 km s^-1^ and ~ 180 km s^-1^. These clouds' velocities are between
  those of Galactic clouds at 0-80 km s^-1^ and those of LMC gas at ~270
  km s^-1^. Chemical-abundance determinations may help to determine the
  origin and location of these clouds. Curve-of-growth analysis and 21
  cm observations show that they may be underabundant in heavy elements
  by about a factor of 2 as compared to solar abundances. No depletion
  indicative of grain formation can be seen.

---------------------------------------------------------
Title: UV Observations of NGC 205
Authors: Wilcots, E. M.; Bohm-Vitense, E.; Hodge, P. W.; Eskridge, P.
1988BAAS...20.1039W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: ISM chemical abundances along the line-of-sight to SN 1987A
Authors: Morgan, Siobahn; Boehm-Vitense, Erika
1988ESASP.281b.207M    Altcode: 1988IUES....1..207M; 1988uvai....2..207M; 1988IUE88...2..207M
  The IUE high resolution spectra of SN 1987A were studied. Absorption
  lines of 2 clouds with velocities of 130 km/sec and 180 km/sec
  (heliocentric) are seen in addition to the local galactic gas and the
  Large Magellanic Cloud (LMC) gas. Curve of growth analysis shows that
  these clouds may be depleted in heavy elements when compared to the
  local ISM and the LMC ISM. There is no indication of depletion due
  to grain formation. There seems to be no way to determine whether the
  clouds are part of the galactic halo or part of the LMC's halo.

---------------------------------------------------------
Title: Carbon and nitrogen abundance determinations from transition
    layer lines and mixing in stars
Authors: Boehm-Vitense, Erika; Mena-Werth, Jose
1988ESASP.281a.381B    Altcode: 1988duvb.conf..381B; 1988uvai....1..381B
  For red giants a smooth increase in the nitrogen to carbon abundance
  ratio for increasing B-V as is expected for the first dredge up phase
  when the outer convection zone deepens is found. An average increase
  in the nitrogen to silicon ratio for B-V = 0.6 which goes back to
  almost solar values for cool giants with B - V approximately 1.0
  is reported. It looks as if Si would be enriched for deeper mixing
  contrary to expectations from standard evolution theory.

---------------------------------------------------------
Title: The energy input mechanism into the lower transition regions
    between stellar chromospheres and coronae
Authors: Boehm-Vitense, Erika
1988ESASP.281a.315B    Altcode: 1988uvai....1..315B
  The ratio of the emission line fluxes for the C II and C IV lines in
  the lower transition regions (T = 30,000 to 100,000 K) between stellar
  chromospheres and transition layers is shown to depend mainly on the
  temperature gradient in the line emitting regions which can therefore
  be determined from this line ratio. From the observed constant (within
  the limits of observational error) ratio of the emission line fluxes
  of the C II (1335 A) and C IV (1550 A) lines it is concluded that
  the temperature gradients in the lower transition layers are similar
  for the large majority of stars independently of T<SUB>eff,</SUB> L,
  and degree of activity. This means that the temperature dependence
  of the damping length for the mechanical flux must be the same for
  all these stars. Since for different kinds of mechanical fluxes the
  dependence of the damping length on gas pressure and temperature is
  quite different, it is concluded that the same heating mechanism must
  be responsible for the heating of all the lower transition layers
  of these stars, regardless of their chromospheric activity. Only the
  amount of mechanical flux changes. The T Tauri stars are exceptions:
  their emission lines are probably mainly due to circumstellar material.

---------------------------------------------------------
Title: Are Most Short-Period Cepheids Overtone Pulsators?
Authors: Bohm-Vitense, Erika
1988ApJ...324L..27B    Altcode:
  Data given and analyzed recently by Coulson et al. (1986) and Gieren
  (1982) provide a consistent set of Wesselink radii and Wesselink
  masses, for which the internal error bars appear to be small enough
  that a quantitative discussion appears to be warranted. When it is
  assumed that all Cepheids pulsate in the fundamental mode, a steep
  discontinuity in mass is found for periods around 6.5 days. When
  short-period Cepheids are interpreted as first-overtone pulsators as
  required theoretically (Christy, 1966; Stobie, 1969), the discontinuity
  disappears and the mass-period relation passes through the bump and
  beat masses for Cepheids.

---------------------------------------------------------
Title: Long Term Variations of AM Stars
Authors: Bohm-Vitense, Erika
1988iue..prop.3045B    Altcode:
  We would like to reobserve some selected Am stars which we originally
  observed in 1979 and 1980 in order to study long term time variations
  in the UV. Such variations have been observed earlier to occur
  in the optical spectral region for some of them (15 Vul, tau UMa)
  If temperature changes are responsible for the optical variations
  than larger variations in the energy distribution are expected in the
  ultraviolet. Our original observations were proposed because we wanted
  to study such variations. We would now like 10 reobserve some of the
  stars observed earlier in order to check whether any changes in the
  uv energy distribution or in the details of the spectra have occurred
  during the time span of 6-8 years. If we do not make the observations
  now we mail never get a chance to actually do the investigation which
  we set out to do 10 years ago.

---------------------------------------------------------
Title: Blue Companions of Supergiants
Authors: Bohm-Vitense, Erika
1988iue..prop.3054B    Altcode:
  We would like to observe blue companions of supergiants in star
  clusters. For binaries in clusters we know the distance with some
  accuracy. IUE observations of blue companions of supergiants therefore
  tell their absolute magnitudes, so we can decide whether we are dealing
  with giants or main sequence stars. Because of the short evolution
  times along the giant branch the supergiants and evolved companions
  must have essentially the same mass. They then outline two points
  on an evolutionary track. For other apparently giant stars in the
  cluster we can never be sure about their membership. The luminosity
  difference between a supergiant and a giant of the same mass depends on
  the degree of mixing in the interior of the main sequence progenitor
  star, which can therefore be determined empirically by studying the
  luminosity difference between the supergiant and a giant companion. As
  all supergiants in a cluster must have essentially the same mass
  a dynamical mass determination for a supergiant in a cluster with
  Cepheids also determines the mass of the Cepheid.

---------------------------------------------------------
Title: Masses for Four Cepheids
Authors: Bohm-Vitense, Erika
1988iue..prop.3049B    Altcode:
  Velocities from IUE high dispersion spectra have provided mass ratios
  between a Cepheid and a blue companion for the systems SIT Cyg,
  S Mus, and V636 Sco. The proposed IUE high dispersion observations
  will produce a mass ratio for a new system, U Aql, with a percentage
  error as low as 14%, depending on the orbital velocity amplitude of
  the companion. They will also provide a second optimal spectrum for
  both S Mus and V636 Sco which will confirm the previous results at the
  second velocity extremum, reduce the uncertainty in the mass ratio
  by sqrt2 to 14%, and also provide an error estimate from comparison
  with the previous spectrum. For AW Per a spectrum will provide a
  preliminary mass function. confirmation that it is not a triple system,
  and information about the rotational velocity for a system which can
  be resolved by Hubble Space Telescope. These results, together with
  the SU Cyg results, are the only mass determinations for Cepheids to
  decide between the discordant evolutionary and pulsational masses.

---------------------------------------------------------
Title: Emission Lines of the Long Period Copheid L Carinae
Authors: Bohm-Vitense, Erika
1988iue..prop.3051B    Altcode:
  We propose to observe the time dependence of the ultraviolet emission
  line fluxes in the Cepheid l Carinae. Previous observations by Schmidt
  and Parsons have shown that l Carinae appears to be the only Cepheid
  observed so far to show the high ionization lines up to C IV. This
  Cepheid therefore appears to be the best star to study the rise and
  decay of emission lines of different stages of ionization. During
  the phases of increasing emission we should be able to see the phase
  delay for the emission of high ionization line, as compared to low
  ionization lines, corresponding to the increasing amount of heating
  and the propagation of the ionization front through the surface layers
  when the transition region is built up. The amount of heating measures
  the amount of energy being deposited. If the emission is related
  to the onset of convection during the cool phases of the pulsation,
  as seems to be the case. then the rise and decay of the ultraviolet
  emission lines will be able to teach us a lot about the timescales
  for the generation of the mechanical flux heating the chromosphere and
  transition laver. This in turn will tell us something about the nature
  of this flux and about the time dependence of the developing convection.

---------------------------------------------------------
Title: High Resolution Studies of F and G Star Transition Layer Lines
Authors: Bohm-Vitense, Erika
1988iue..prop.3048B    Altcode:
  The question, which heating mechanism is responsible for the heating
  of the transition layers and stellar coronae. is still an open one. We
  have now developed a theory for stellar transition layers which are
  homogeneous. at least in sectors. which does permit to determine from
  the observed emission measures the amount of mechanical energy input in
  the lower transition layer and determine the boundary condition Pe(T)
  for the upper transition layer. The mechanical flux and the damping
  length for this flux for the upper part of the transition layer can be
  determined from the emission measures in the upper transition zone and
  from the coronal temperature. or, if no emission measures for the upper
  transition zone are available the emission measure determined from the
  coronal X-ray emission can be used instead. though less reliably. Using
  this method we found that the lower transition layers of the sun and
  Procyon are probably heated by shock wave heating. The upper transition
  layer of Procyon also seems to be heated by shock waves. while in the
  sun in the upper part of the transition layer the damping length is
  too long to be consistent with shock wave heating. We want to study
  whether and where in the late F star region a transition from shock
  wave heating to MHD wave heating of the upper transition layer occurs.

---------------------------------------------------------
Title: Dynamical Masses for the Two Cepheids S Mus and V636 Sco
Authors: Bohm-Vitense, Erika
1988iue..prop.3065B    Altcode:
  For the Cepheids S Muscae and V636 Scorpii we want to determine the
  pulsational radial velocities for the spectral lines seen in the LWR
  region of the IUE Observatory. These measurements are essential for
  the determination of the dynamical masses for these binaries. On LWR
  IUE high resolution images of S Mus and V636 Sco the spectrum of the
  Cepheid can be studied for lambda &gt; 2500 A while the one for the
  companion can be studied for lambda &lt; 2500 A. This fact permits
  the measurement of the difference in radial velocity for the two
  components of the binary system. After subtraction of the pulsational
  velocity of the Cepheid the difference of the orbital velocities is
  obtained. With the orbital velocity of the Cepheid known from optical
  studies the velocity ratio and thereby the mass ratio of the binary
  components can be determined. So far the pulsational velocities for
  the Cepheid measured in the optical region have been used in this
  procedure. Observations show, however, that pulsational velocities
  are different for different layers of the atmosphere. Subtraction of
  the pulsational velocities determined for the absorption lines in the
  optical region, when we should subtract the pulsational velocities
  for the uv region, may cause large errors in the difference of the
  orbital velocities and their ratios. We therefore want to determine
  the pulsational velocities for those high layers in which the lines in
  the LWR region are formed. This requires measurements for many phases
  of the pulsational cycle.

---------------------------------------------------------
Title: A Nonspherically Symmetric Model for the Peculiar A Star
    Alpha 2 CVn
Authors: Bohm-Vitense, Erika; van Dyk, Schuyler D.
1987AJ.....93.1527B    Altcode:
  Observations show that in the optical region the peculiar A star
  α<SUP>2</SUP>CVn has a flatter energy distribution during maximum light
  than during minimum light. This indicates that during maximum light we
  see a lower-temperature region, but necessarily larger surface area,
  than during minimum light. This suggests a nonspherically symmetric
  star, which is oblate with respect to the magnetic axis and which is
  cooler at the magnetic poles than at the magnetic equator. The authors
  have studied the light variations of such nonspherically symmetric
  oblique rotator models. They find for an oblate ellipsoid with an axial
  ratio of 0.92 and a temperature difference of about 1000K between the
  poles and the equator that the overall variations of the optical and
  the ultraviolet energy distributions can be well understood.

---------------------------------------------------------
Title: Theory of Transition-Layer Emission Measures and Coronae
Authors: Bohm-Vitense, Erika
1987ApJ...317..750B    Altcode:
  The basic equations describing the energy equilibria, the conductive
  heat flux, and the temperature stratifications for stellar transition
  layers and coronae with 'open' field lines are summarized. The
  temperature dependence of the emission measures for lines originating in
  different temperature regions of the transition zone is determined. It
  is found that the stellar transition regions consist of two basically
  different parts: the lower part where mechnical energy input is balanced
  by the radiative losses, and the upper part where the mechanical energy
  input is balanced by the divergence of the conductive flux and radiative
  losses. In the lower part, the temperature stratification is determined
  by an equilibrium between mechanical flux input and radiative energy
  losses. The coronal temperatures increase with increasing mechanical
  flux and damping length in the upper transition zone.

---------------------------------------------------------
Title: MG II Line Profiles in W VIR
Authors: Bohm-Vitense, Erika
1987iue..prop.2731B    Altcode:
  On low resolution spectra the Mg II emission lines at 2800 A of W
  Vir nearly always show the same central intensities, regardless of
  the pulsational cycle. This suggests that the Mg II emission lines do
  not originate in the stellar photosphere or chromosphere but rather in
  detached circumstellar material possibly indicating mass loss for this
  prototype population no. II Cepheid. During minimum light, however,
  the emission lines at 2800 A appears much weakened, an additional
  emission line appears at 2828 A. We would like to take high resolution
  IUE spectra with the long wavelength camera in order to study the Mg II
  line profiles and to see whether they share the photospheric velocities
  or at least the pulsational velocity cycle or whether they originate in
  detached circumstellar material. If so this would be a definite sign
  of mass loss by at least one population II Cepheid. If all population
  II Cepheids turn out to lose mass during their pulsationally unstable
  phases of stellar evolution this may possibly be a way to transform
  red giants into horizontal branch stars.

---------------------------------------------------------
Title: Mass Loss in Population I Cepheids
Authors: Bohm-Vitense, Erika
1987iue..prop.2742B    Altcode:
  It has been proposed by several authors that Cepheids lose mass during
  their pulsational cycle. due to outwards propagating shockwaves. The
  S Mus system offers a unique opportunity to check this hypothesis
  directly. The Cepheid has a main sequence companion with a temperature
  of about 17,700K. which means a spectral type of B4 V. This star is
  hot enough that the ultraviolet circumstellar and stellar wind lines
  can be observed, if present, with high resolution SWP images. On the
  other hand, it is cool enough that it is not a stellar wind source
  itself. The apparent visual magnitude of the companion is inferred
  to be mv ~ 7. The Cepheid has E(B-V) = 0.27. The orbital period
  is 506 days. so the companion is close enough that circumstellar
  material and stellar wind material still has high enough densities
  to be observable in the spectrum of the companion. There is no other
  known system with such favorable properties. Stellar wind lines can be
  recognized by their velocities and widths and variations during the
  orbital cycle. Circurnstellar lines, resting in the binary system,
  can be distinguished from interstellar lines by means of their
  velocity difference. We want to search for evidence of mass loss
  of the Cepheid by studying the companion spectrum during different
  orbital and pulsational phases, and see whether lines, normally seen
  in interstellar gas, can be seen to vary, which would show that they
  are circumstellar. The equivalent widths of the lines will show the
  amount of circumstellar material. The width or wavelength shift of
  the lines determines the velocity field.

---------------------------------------------------------
Title: A possible solution to the cepheid mass problem?
Authors: Bohm-Vitense, Erika
1987LNP...274..159B    Altcode: 1987stpu.conf..159B
  With new, smaller distances of the Cepheids, as determined recently by
  Schmidt (1984) and by Böhm-Vitense (1985), smaller pulsational masses
  are obtained than previously. Giant companions of Cepheids show that the
  luminosities of the Cepheids are too large in comparison with those of
  the giants. If increased mixing, for instance by convective overshoot
  at the boundary of the convective core during the main sequence stage,
  is responsible for this, then we expect an increase in the luminosity
  of the Cepheids of a given mass by approximately a factor of 4 as
  compared to conventional evolution calculations. Taking into account
  both of these effects we find good agreement between the corrected
  evolutionary masses, the pulsational masses, the dynamical masses,
  the giant companion masses and the Wesselink masses. The bump masses
  are only slightly smaller than the other masses.

---------------------------------------------------------
Title: Blue Companions of Long Period Cepheids
Authors: Bohm-Vitense, Erika
1987iue..prop.2730B    Altcode:
  We want to search for giant companions of very short and very long
  period Cepheids. These permit a check on the relative luminosities
  of giants and their Cepheid companions. which should fit on the same
  evolutionary tracks. For Cepheids with periods around 9 days we found
  a discrepancy between the observed relative luminosities and the
  theoretically expected values. This discrepancy might be explained by
  additional, probably convective overshoot, mixing at the boundaries
  of the convective cores of main sequence massive stars. If this is
  indeed the explanation we might probably expect that the mixing is
  mass dependent and that therefore the discrepancy between giant and
  Cepheid luminosities will be different for longer and shorter period
  Cepheids. We want to check this suspicion. If such an effect is seen
  it tells us about the importance of convective overshoot mixing for
  stars with different masses. In order to find Cepheids with giant
  companions we want to look at Cepheids whose Wesselink masses are
  especially low. Generally, blue giant companions contribute more
  light in the visual spectral region than do blue main sequence
  companions. "Wesselink" masses determined for Cepheids with blue
  companions give masses which are too low because of the influence of
  the companion on the optical colors. For giants this effect should be
  quite noticeable.

---------------------------------------------------------
Title: Masses for Four Cepheids
Authors: Bohm-Vitense, Erika
1987iue..prop.2732B    Altcode:
  Velocities from IUE high dispersion spectra have provided mass
  ratios between a Cepheid and a blue companion for the systems SU Cyg,
  S Mus, and V636 Sco. The proposed IUE high dispersion observations
  will produce a mass ratio for a new system, U Aql. with a percentage
  error as low as 14%. depending on the orbital velocity amplitude of
  the companion. They will also provide a second optimal spectrum for
  both S Mus and V636 Sco which will confirm the previous results at
  the second velocity extremum, reduce the uncertainty in the mass ratio
  by sqrt 2 to 14%. and also provide an error estimate from comparison
  with the previous spectrum. For AW Per a spectrum will provide a
  preliminary mass function. confirmation that it is not a triple system,
  and information about the rotational velocity for a system which can
  be resolved by Hubble Space Telescope. These results, together with
  the SU Cyg results, are the only mass determinations for Cepheids to
  decide between the discordant evolutionary and pulsational masses.

---------------------------------------------------------
Title: Intrinsically Variable Stars
Authors: Bohm-Vitense, Erika; Querci, Monique
1987ASSL..129..223B    Altcode: 1987euwi.book..223B
  The characteristics of intrinsically variable stars are examined,
  reviewing the results of observations obtained with the IUE satellite
  since its launch in 1978. Selected data on both medium-spectral-class
  pulsating stars (Delta Cep stars, W Vir stars, and related groups) and
  late-type variables (M, S, and C giants and supergiants) are presented
  in spectra, graphs, and tables and described in detail. Topics addressed
  include the calibration of the the period-luminosity relation, Cepheid
  distance determination, checking stellar evolution theory by the giant
  companions of Cepheids, Cepheid masses, the importance of the hydrogen
  convection zone in Cepheids, temperature and abundance estimates for
  Population II pulsating stars, mass loss in Population II Cepheids,
  SWP and LWP images of cold giants and supergiants, temporal variations
  in the UV lines of cold stars, C-rich cold stars, and cold stars with
  highly ionized emission lines.

---------------------------------------------------------
Title: Emission Measures and Heating Mechanisms for Stellar Transition
    Regions and Coronae
Authors: Bohm-Vitense, E.
1987IAUS..122..359B    Altcode:
  In order to determine the heating mechanisms for stellar transition
  regions and coronae the author tries to determine the damping lengths
  for the mechanical flux(es) responsible for the heating. For the
  lower part of the transition regions (30,000 &lt; T ≤ 100,000K) the
  damping lengths are consistent with shockwave damping. This appears to
  be also true for the upper part of the transition region in Procyon,
  while for the upper part of the solar transition region the damping
  length is much larger.

---------------------------------------------------------
Title: The Cepheid Mass Problem and Cepheid Binaries
Authors: Bohm-Vitense, E.
1986ApJ...303..262B    Altcode:
  Existing mass determinations for Cepheids with different periods are
  examined. Wesselink masses are independent of the adopted distance
  scale. For short periods (less than 6 days) they follow the sequence
  of evolutionary masses. For periods longer than 10 days they are lower
  by up to a factor of 2. The lower mass branch joins up with the bump
  masses. The new pulsational masses agree with the Wesselink masses
  for periods longer than 6 days. Cepheid masses determined by means of
  their giant companions also agree with the Wesselink masses and the
  new pulsational masses. While the error bars are large, the derived
  dynamical masses determined for S Mus and V636 Sco also agree with
  the low Wesselink and giant companion masses.

---------------------------------------------------------
Title: A Simple Explanation for the Linksy-Haisch Boundary Line for
    Transition Layers
Authors: Bohm-Vitense, E.
1986ApJ...301..297B    Altcode:
  It is found that, for stars with low gravitational acceleration,
  transition layers between chromosphere and corona cannot form, because
  the chromospheres are so extended that the mechanical energy flux
  decreases faster than the square of the electron density. There is
  not enough flux left to lead to a steep temperature increase in the
  transition layer and corona. If the disipation length lambda for the
  mechanical energy flux is the same for all stars, the boundary line
  for transition layers would be expected to coincide with a line of g
  = const in the H-R diagram. The numerial value for this g depends on
  the dissipation length. A comparison with the observed boundary line
  shows that the dissipation length is not the same for all stars but
  increases roughly as (Teff/g) exp 0.93.

---------------------------------------------------------
Title: The Effects of Metallicity on Stellar Winds
Authors: Bohm-Vitense, Erika
1986iue..prop.2417B    Altcode:
  A fundamental prediction of line driven wind theory is that the mass
  loss rate of hot stars should scale with the metallicity. Initial
  studies with the IUE, however, have found that the mass loss
  rates in the metal deficient Magellanic Clouds are similar to
  the galactic rates. We propose to test this prediction with low
  resolution observations of galactic O and B stars with different
  abundances. The target stars are associated with high and low abundance
  H II regions. The metallicity range is quite large and the stars are
  all expected to show unsaturated P Cygni profiles. A mass loss rate
  difference as predicted by radiatively driven wind theory will be
  readily detectable if present. If we find no dependence on z then
  a serious difficulty with radiatively wind theory will have to be
  addressed.

---------------------------------------------------------
Title: Periodic Light Variations of Alpha-Squared CVN
Authors: Bohm-Vitense, Erika
1986iue..prop.2405B    Altcode:
  Visual observations of the Ap star alpha^2 CVn show a steeper energy
  distribution during minimum light than at maximum. A steeper energy
  distribution means a higher temperature. The star must therefore show a
  region of higher temperature during minimum light, which is possible
  only if we see a smaller area at this phase than during maximum
  light. We have made model calculations for the light variations of a
  nonspherically symmetric star, which shows qualitative agreement with
  the observations in the uv and in the visual. We would like to check
  and improve our model calculations by detailed comparison with high
  and low resolution IUE spectra which will supplement existing optical
  spectra. We want to supplement existing IUE spectra to get complete
  phase coverage.

---------------------------------------------------------
Title: Age Dependence of the Boundary Line for Chromospheric Emission
    in the HR Diagram
Authors: Bohm-Vitense, Erika
1986iue..prop.2403B    Altcode:
  We want to observe late A stars in the Hyades and Pleiades in order
  to see whether the boundary line for the onset of convection changes
  for younger stars. This is suggested by the changing appearance of the
  B-V gap for different clusters. The extrapolation of observed emission
  line fluxes for early F stars shows that the C IV and perhaps the C
  II lines are expected to be strong enough to be observable in spite
  of the increasing photospheric radiation if indeed the young late A
  stars have chromospheres and transition layers like the early F stars.

---------------------------------------------------------
Title: Blue companions of cepheids.
Authors: Bohm-Vitense, E.; Proffitt, C.
1985ApJ...296..175B    Altcode:
  Twenty-one Cepheids, known or suspected to have blue companions, were
  studied with the International Ultraviolet Explorer satellite. For
  13 of them, companions were indeed seen, though they were generally
  fainter in the UV than expected. For four Population I Cepheids,
  the suspected companions were not seen. For none of the Population II
  Cepheids could a companion be detected. The effective temperatures and
  luminosities of the companions which could be observed are discussed,
  and the positions of Cepheids and companions in the T(eff) luminosity
  diagrams are compared with positions expected from stellar evolution
  calculations.

---------------------------------------------------------
Title: Theory of the Transition Layer Emission Measures
Authors: Böhm-Vitense, E.
1985BAAS...17..847B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Cepheid distances from blue main-sequence companions.
Authors: Bohm-Vitense, E.
1985ApJ...296..169B    Altcode:
  The author determines the absolute visual magnitudes of main-sequence
  Cepheid companions from their effective temperatures. These are
  obtained by comparing the measured relative energy distributions with
  model atmosphere energy distributions. Assuming an average galactic
  extinction law, it is found that the distance moduli for the Cepheids
  should be smaller by Δ(m<SUB>v</SUB>-M<SUB>v</SUB>) = -0.5 as compared
  to the Sandage-Tammann relation.

---------------------------------------------------------
Title: Detection of a compact companion of the mild barium star
    ksi1 Ceti.
Authors: Bohm-Vitense, E.; Johnson, H. R.
1985ApJ...293..288B    Altcode:
  In the present paper, the observation of a white dwarf companion of the
  mild Ba star Xi-1 Ceti (= 65 Ceti = HR 649 = HD 13611) is reported,
  taking into account also the properties of the mild Ba star and of
  its companion. The UV spectrum of Xi-1 Ceti is discussed along with an
  interpretation of this spectrum. Attention is given to the effective
  temperature of the companion, the absorption bands in the spectrum,
  the radius and mass of the Xi-1 Ceti companion, and questions regarding
  the obscuration of the companion by the atmosphere of the Ba star. It is
  found that the overall energy distribution of the Xi-1 Ceti companion
  can best be matched with a 14,000 K DA white dwarf of log g = 8 or
  less. However, the absolute intensity is too small and would require
  a radius too small and a mass too large for such a gravity.

---------------------------------------------------------
Title: The unexpected ultraviolet variability of Herbig-Haro object 1.
Authors: Brugel, E. W.; Bohm, K. H.; Shull, J. M.; Bohm-Vitense, E.
1985ApJ...292L..75B    Altcode:
  The line fluxes of the C IV 1550 A and semiforbidden C III 1909 A
  emission lines in HH 1 are noted to have monotonically decreased by
  factors of 4-6 between 1979 and 1983, despite a lack of indications
  of optical range changes. The thickness of the shocked layers and
  preshock density can be estimated on the basis of these rapid changes,
  with results suggesting a clumpy medium that leads to truncated shock
  waves with column densities insufficient for the development of complete
  recombination zones.

---------------------------------------------------------
Title: Ultraviolet studies of stars in the populous cluster NGC 2100
    in the Large Magellanic Cloud.
Authors: Bohm-Vitense, E.; Hodge, P.; Proffitt, C.
1985ApJ...292..130B    Altcode:
  The authors have studied the ultraviolet energy distributions of the B
  stars in the LMC cluster NGC 2100. The ultraviolet extinction law was
  studied for the LMC cluster. The T<SUB>eff</SUB>-luminosity diagrams
  were determined. The brightest stars in the clusters are evolved stars
  on the "horizontal" supergiant branch. No P Cygni profiles indicating
  mass loss were recognized for these supergiants.

---------------------------------------------------------
Title: Cepheid masses and cepheid binaries.
Authors: Böhm-Vitense, E.
1985BAAS...17..559B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Cepheid Masses and Cepheid Binaries
Authors: Böhm-Vitense, E.
1985BAAS...17Q.559B    Altcode: 1985BAAS...17Z.559B
  No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet Observations of the System Containing the Cepheid
    SU Cyg
Authors: Evans, N. R.; Bohm-Vitense, E.; Bolton, C. T.
1985BAAS...17..559E    Altcode: 1985BAAS...17R.559R
  No abstract at ADS

---------------------------------------------------------
Title: W Vir
Authors: Bohm-Vitense, Erika
1985iue..prop.2295B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The UV extinction laws in two very young clusters, NGC 6530
    in the Galaxy and NGC 2100 in the LMC.
Authors: Bohm-Vitense, E.; Hodge, P.; Boggs, D.
1984NASCP2349..187B    Altcode: 1984IUE84......187B; 1984fiue.rept..187B
  The UV extinction for a number of O and B stars in the galactic
  cluster NGC 6530 was studied along with the extinction law for several
  stars in the LMC cluster NGC 2100. Distinct differences were found
  for different stars in the same cluster. In NGC 6530 a correlation
  of the extinction law with T<SUB>EFF</SUB> or with position in the
  cluster was observed. In NGC 2100 the 2200 A absorption appears to be
  much stronger in the center of the cluster. The interstellar gas line
  absorption for the stars in NGC 6530 was also studied. No correlation
  with the variations in the UV extinction law was found so far.

---------------------------------------------------------
Title: Blue companions of Cepheids.
Authors: Bohm-Vitense, E.; Proffitt, C.
1984NASCP2349..344B    Altcode: 1984fiue.rept..344B; 1984IUE84......344B
  Nineteen Cepheids, known or suspected to have blue companions, have
  been observed. For 11 of them, blue companions were indeed seen,
  though many of them were fainter in the UV than suspected. For four
  Population I Cepheids the suspected companions were not seen. For
  none of the Population II Cepheids could a companion be detected. For
  the observed companions the authors have determined T<SUB>eff</SUB>,
  luminosities and masses from their position in the HR diagram.

---------------------------------------------------------
Title: The ultraviolet spectra of the O and B stars in the young
    galactic cluster NGC 6530.
Authors: Boehm-Vitense, E.; Hodge, P.; Boggs, D.
1984ApJ...287..825B    Altcode:
  The UV spectra between 1200 and 3000 A of stars in the young galactic
  cluster NGC 6530 and the surrounding association are studied. From
  the UBV colors and empirical as well as theoretical calibrations,
  the T(eff) and L for those stars which follow a sequence in the H-R
  diagram corresponding to the main sequence are determined. From a
  comparison with theoretical evolutionary tracks, the age of the cluster
  is estimated to be 5 + or - 2 x 10 to the 6th yr, with a very small
  scatter for the different stars. The UV extinction is determined for
  the stars from a comparison of theoretical model energy distributions
  for the stellar T(eff)s and the observed energy distributions. The
  stellar wind lines are studied, and strong stellar winds are found
  for bolometric magnetidues less than -8.

---------------------------------------------------------
Title: Ultraviolet observations of Population II Cepheids.
Authors: Bohm-Vitense, E.; Proffitt, C.; Wallerstein, G.
1984NASCP2349..348B    Altcode: 1984IUE84......348B; 1984fiue.rept..348B
  The two Population II Cepheids, ST Pup and W Vir, have nearly the same
  length of period and B-V colors, yet spectral types are very different,
  indicating large differences in metal abundances. The authors have
  determined metal abundances, T<SUB>eff</SUB> and the color excess from
  the observed discontinuities at 1700 Å, at 2600 Å, the ultraviolet to
  visual colors, and the 2400 Å absorption band. The observations for
  ST Pup were made shortly after maximum light. For ST Pup the authors
  found E(B-V) = 0.2, T<SUB>eff</SUB> = 6600±100K at 0.5 days after
  maximum. A metal abundance of [A/H] = -1.7±0.2 was determined. For
  W Vir a metal abundance of [A/H] ≡ -0.9 is suggested.

---------------------------------------------------------
Title: The white dwarf companion of the mild Ba star
    ξ<SUP>1</SUP>Cet.
Authors: Bohm-Vitense, E.; Proffitt, C.; Johnson, H.
1984NASCP2349..293B    Altcode: 1984IUE84......293B; 1984fiue.rept..293B
  The mild Ba star ξ<SUP>1</SUP>Cet was found to have a hot
  companion. The absolute intensities and the relative energy distribution
  shows that it is a DA white dwarf with broad absorption bands around
  1400 and 1650 Å. The temperature is determined to be T<SUB>eff</SUB>
  = 13000±1000K.

---------------------------------------------------------
Title: Ultraviolet analysis of the peculiar F supergiant HD 112374.
Authors: Bohm-Vitense, E.; Proffitt, C.
1984NASCP2349..352B    Altcode: 1984IUE84......352B; 1984fiue.rept..352B
  The authors have studied the ultraviolet energy distribution of the
  metal-poor supergiant HD 112347. They need a temperature T<SUB>eff</SUB>
  = 5500±100K, log g = -0.3±0.3 and a metal deficiency of log Z/Z_sun;
  = -0.7 in order to find agreement between theoretical and observed
  ultraviolet energy distributions with a reddening of E(B-V) ≤ 0.1
  consistent with its galactic latitude of +36°.

---------------------------------------------------------
Title: Ultraviolet studies of the young populous cluster NGC 2100
    in the LMC.
Authors: Bohm-Vitense, E.; Hodge, P.; Proffitt, C.
1984NASCP2349..191B    Altcode: 1984IUE84......191B; 1984fiue.rept..191B
  Stars in the populous young cluster NGC 2100 were observed with IUE
  in the low resolution mode. Color excesses, effective temperatures
  and luminosities were determined for eight stars in the cluster. A
  comparison of observed and model atmosphere energy distributions
  shows that the Nandy et al. (1981) average LMC extinction curve does
  not give good matches for the cluster stars. For most of the cluster
  stars no hump in the extinction at 2200 A is observed and too little
  flux is observed between 1400 and 2000 A. Masses between 15 and 30
  solar masses were found for the stars and an age of about 6 million
  years. Two stars, b27 and C1, may have an age of up to 12 million years.

---------------------------------------------------------
Title: The changing ultraviolet spectrum of Herbig-Haro object No. 1.
Authors: Bohm, K. H.; Bohm-Vitense, E.; Brugel, E. W.
1984NASCP2349..167B    Altcode: 1984IUE84......167B; 1984fiue.rept..167B
  IUE spectra of H-H1 taken in March 1982 and December 1983 show
  steady qualitative changes of the short wavelength emission line
  spectrum. Earlier IUE studies (in 1979 and 1980) had shown the typical
  "high excitation object" ultraviolet spectrum with the C IV 1550
  and the C III] 1909 lines being very strong. These line fluxes have
  steadily decreased and are presently not detectable on a 4-1/2 hour
  exposure. While the spectrum looked very similar to that of H-H2
  in 1980, it now gives more the impression of the spectrum of a low
  excitation H-H object with a possible presence of fluorescent lines
  from the H<SUB>2</SUB> Lyman bands.

---------------------------------------------------------
Title: Stellar winds in the young galactic cluster NGC 6530.
Authors: Bohm-Vitense, E.; Hodge, P.
1984NASCP2349..223B    Altcode: 1984fiue.rept..223B; 1984IUE84......223B
  The authors have studied line profiles for O stars on or close to
  the main sequence in the young galactic cluster NGC 6530. P Cygni
  profiles are seen for T<SUB>eff</SUB> &gt; 36000K. Different stars show,
  however, different lines and different outflow velocities. The degree
  of ionization in the wind appears to depend on T<SUB>eff</SUB>.

---------------------------------------------------------
Title: Ultraviolet analysis of the peculiar supergiant HD 112374 =
    HR 4912.
Authors: Bohm-Vitense, E.; Proffitt, C.
1984PASP...96..897B    Altcode:
  The ultraviolet energy distribution of the metal-poor supergiant
  HD 112374 is analyzed based on observations from the International
  Ultraviolet Explorer (IUE) satellite for the region between 1200
  and 2000 A. A discontinuity was found in the UV spectra at 2600 A
  which confirmed the low-abundance of heavy elements found by Luck et
  al. (1983). Values for effective temperature and log g in HD112374
  were consistent with the star being a very luminous Population II
  semi-regular variable. The full observational results are presented
  in a table.

---------------------------------------------------------
Title: Ultraviolet studies of O and B stars in the LMC cluster NGC
    2100, the SMC cluster NGC 330 and the Galactic cluster NGC 6530
Authors: Boehm-Vitense, E.; Hodge, P.
1984IAUS..108...59B    Altcode:
  High-resolution and low-resolution IUE spectra of O and B stars in the
  LMC cluster NGC 2100, the SMC cluster NGC 330, and the young Galactic
  cluster NGC 6530 are investigated. Temperatures and luminosities are
  determined. In the LMC and SMC clusters, the most luminous stars are
  evolved stars on the horizontal supergiant branch, while in NGC 6530
  the stars are all still on the main sequence. Extinction laws were
  determined. They confirm the known differences between LMC and Galactic
  extinctions. No mass loss was detected for the evolved B stars in the
  LMC and SMC clusters, while the high-luminosity stars in NGC 6530 show
  P Cygni profiles.

---------------------------------------------------------
Title: G and Early K Giant UV Continua and Early Emission Line
    Intensities
Authors: Bohm-Vitense, Erika
1984iue..prop.1766B    Altcode:
  The continuum flux around 1950A for cool giants is different for
  otherwise apparently similar stars. For the Hyades this flux is
  correlated with the chromospheric emission line intensities. We want to
  study this correlation for other giants. We want to study the systematic
  changes in emission line and continuum flux along the G to K giant
  sequence in order to understand the abrupt changes in continuum flux,
  CIV emission and v(r) sin i observed to occur at spectral types G5III.

---------------------------------------------------------
Title: Ultraviolet Spectra of Gamma Boo Stars
Authors: Bohm-Vitense, Erika
1984iue..prop.1761B    Altcode:
  Lambda Boo stars show abnormally weak metallic lines for their spectral
  type, if this is determined from the ratio of the CaII K to hydrogen
  line strength, yet they are no population II stars as shown by their low
  space velocities and by their apparently large rotational velocities
  which are around 100 km/sec. (Baschek and Searle,.1969). Spectrum
  analysis shows a metal deficiency except that OI has normal abundances
  and CI seems to be actually overabundant (Saschek et al 1983). The
  UV spectra suggest that another light source is contributing to the
  continuous light. It appears that the strong CI lines seen in the Lambda
  Boo uv spectrum may be formed in a shell of carbon rich material. We
  want to observe additional lambda Boo stars in order to see whether this
  interpretation fits all lambda Boo stars. We would like to re-observe
  lambda Boo in order to see whether time variations in the CI lines
  can be observed, which would support the interpretation as envelope
  lines. We want to study in detail the binary ADS 3910 which contains
  one A Boo star and one apparently normal B8V star (Sargent, 1966).

---------------------------------------------------------
Title: Interstellar Gas and Dust Absorptions Near NGC 6530
Authors: Bohm-Vitense, Erika
1984iue..prop.1772B    Altcode:
  In our study of the extinction law for 0 and early B stars in the
  young galactic clusters NGC 6530 we found a rather strong dependence of
  extinction on T(eff) (see Fig. 1). Since the highest temperature stars
  are also farthest away from the center of the cluster (see Fig. 2)
  this may also mean that the extinction law changes with distance from
  the cluster center. We want to study which is the true correlation
  by studying stars with the same T(eff) but at different distances
  from the Cluster center. We also want to study the interstellar gas,
  which is concentrated near the Cluster in order to see whether the gas
  properties change in a systematic way in accordance with the observed
  changes in the extinction law.

---------------------------------------------------------
Title: Variations of POP. II Cepheid UV Energy Distributions
Authors: Bohm-Vitense, Erika
1984iue..prop.1768B    Altcode:
  We want to observe the changes of the ultraviolet energy distribution
  of the population II Cepheid kappa Pav and the suspected population II
  Cepheid SZ Tau. The observations of the continuum energy distributions
  will give us log Z/Z(sun) and the change in Teff as a function of
  pulsational phase. We would also like to follow the properties of
  the outward moving shock by observing the changes in the emission
  lines. For the previously observed population II Cepheids ST Pup and
  W Vir, we saw emission lines develop shortly after maximum light. No
  more observing time was available to follow the changes. For the
  bright Cepheids kappa Pav and SZ Tau we will be able to follow the
  evolution of these emission lines. The ratio of the SiIII] to CIII]
  lines at 1892 and 1909A (both observed in ST Pup and W Vir) will give
  us the change in densities for the outward moving shock. Perhaps we
  will be able to determine rough values for the velocities and in that
  way probe the outer atmospheres of the Cepheids.

---------------------------------------------------------
Title: Ap Stars with Short-Period Optical Variability
Authors: Bohm-Vitense, Erika
1984iue..prop.1935B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Search for White Dwarf Companions of BA Stars Evolving up
    the Giant Branch
Authors: Bohm-Vitense, Erika
1984iue..prop.1775B    Altcode:
  We want to look for a correlation between temperatures of white dwarf
  companions of Ba stars and evolutionary state of the Ba stars. We expect
  to find generally cooler white dwarfs for cooler (i.e., further evolved)
  Ba stars. Only for the brightest (i.e., generally closest) Ba stars do
  we have a chance to see those cool white dwarf companions. Only mild Ba
  stars can be found bright enough. We therefore want to look for white
  dwarf companions in bright mild Ba stars of advancing spectral types.

---------------------------------------------------------
Title: Dynamical Masses for Population I and Population II Cepheids
Authors: Bohm-Vitense, Erika
1984iue..prop.1764B    Altcode:
  We would like to obtain additional LWR 1) high resolution spectra of
  Pop I Cepheid binaries in order to determine the orbital velocities of
  the companions. (Actually, the velocity difference between Cepheid and
  companion). The velocities of the Cepheids are known from ground-based
  observation. The ratio of the velocities and thereby the mass ratio of
  the stars can then be determined. The spectral type of the companion
  is determined from the measured SWP spectrum energy distribution and
  yields the mass of the companion. The mass of the Cepheid can thereby
  be found. We can thereby check pulsational and evolutionary masses. We
  would like to extend our observations to the peculiar Pop II binary
  Cepheid AU Peg, whose orbital elements have recently been determined.

---------------------------------------------------------
Title: The problem of the barium stars.
Authors: Bohm-Vitense, E.; Nemec, J.; Proffitt, C.
1984ApJ...278..726B    Altcode:
  The authors report on ultraviolet observations of barium stars
  and other cool stars with peculiar element abundances. Those
  observations attempted to find hot white dwarf companions. Among
  six real barium stars studied, only ζ Cap was found to have a white
  dwarf companion. Among seven mild, or marginal, barium stars studied,
  at least three were found to have hot subluminous companions. It is
  likely that all of them have white dwarf companions.

---------------------------------------------------------
Title: The ultraviolet spectrum of a strongly reddened,
    high-excitation Herbig-Haro object.
Authors: Bohm, K. H.; Bohm-Vitense, E.
1984ApJ...277..216B    Altcode:
  Short- and long-wavelength IUE spectra of the rather strongly reddened,
  high radial velocity Herbig-Haro object HH 32A have been obtained. The
  object is well known for its large positive radial velocity and for
  its unusually large velocity dispersion. In consequence of the large
  ultraviolet extinction, the spectra are faint. The semiforbidden C III
  1909 and Mg II 2800 emission lines are, however, clearly detected, and
  their fluxes can be measured with reasonable accuracy. C IV 1550 and
  Si III 1892 are very probably present. The continuum can be detected
  convincingly in the wavelength range 1500-1900 A. In other regions it
  is just barely detectable. The continuum has an energy distribution
  which is probably very similar to that of HH 1 and HH 2H. If an average
  galactic extinction curve is used, the line fluxes for semiforbidden C
  III 1909 and C IV 1550 indicate a shock velocity of at least 140 km/s
  which is higher than for HH 1 or HH 2. If a Theta Ori-type extinction
  curve is used instead, ultraviolet line ratios are obtained which are
  rather similar to those in HH 1 and HH 2.

---------------------------------------------------------
Title: Chromospheres, Transition Regions, and Coronas
Authors: Boehm-Vitense, E.
1984Sci...223..777B    Altcode:
  The increase in temperature outward from the surface of a stellar
  photosphere can be understood by looking at the local energy
  balance. The relatively high-density stellar photosphere is cooled
  effectively by radiative energy loss penetrating the optically thin
  corona. For the low-density chromosphere and corona, if the energy
  input cannot be balanced by radiative energy losses, the temperature
  will rise steeply, possibly up to 1 million degrees or more. Coronal
  heating and emission appear to be strongly influenced by magnetic
  fields, leading to large differences in x-ray emission for otherwise
  similar stars. Comparatively small variations are seen in the overall
  chromospheric emission of stars. Chromospheres are probably mainly
  heated by shock-wave energy dissipation, modified by magnetic fields.

---------------------------------------------------------
Title: On the Origin of the Barium Stars
Authors: Bohm-Vitense, E.
1984IAUS..105..191B    Altcode:
  The author shows that Ba stars cannot originate from single stars, they
  can only be formed in binaries by mass transfer. The companion must then
  have been an evolved star with log L/L_sun; ≥ 3.2, requiring a radius
  larger than 0.5 AU, explaining the long periods of the observed Ba star
  binaries. White dwarf companions with T<SUB>eff</SUB> ≈ 12000K have
  been seen for the nearest Ba stars. For Ba stars at larger distances
  companions can only be detected if they have T<SUB>eff</SUB> ≥ 20000K.

---------------------------------------------------------
Title: IUE observations of weak G-band stars.
Authors: Parthasarathy, M.; Sneden, C.; Bohm-Vitense, E.
1984PASP...96...44P    Altcode:
  High- and low-resolution ultraviolet spectra of several weak G-band
  giants have been obtained with the IUE satellite, to derive Be
  abundances and to search for degenerate companions. The abundances of
  Be in these stars are about log epsilon (Be) approximately -0.5. These
  values are in good agreement with the Be abundances of Hyades giants,
  and are consistent with standard theories of post-main-sequence Be
  depletion in stars. However, the Be abundances do not fit with the large
  Li abundances in weak G-band stars. Post-main-sequence production of
  Li or element segregation in main-sequence stars may explain the high
  Li abundance in weak G-band stars. No direct evidence is seen for the
  presence of hot subluminous companions. The peculiar abundances in
  these stars probably are not due to binary mass transfer.

---------------------------------------------------------
Title: The Puzzle of the UV Continua of the Hyades Giants
Authors: Bohm-Vitense, Erika
1984LNP...193..273B    Altcode: 1984csss....3..273B
  No abstract at ADS

---------------------------------------------------------
Title: Cepheid Companions and the Masses of Cepheids
Authors: Bohm-Vitense, E.; Borutzki, S.; Harris, H.
1984IAUS..105..449B    Altcode:
  The authors have observed in the ultraviolet the hot companions of the
  Cepheids SV Per, RW Cam, SY Nor and KN Cen. The study of the absolute
  and relative intensities reveals that all, except the companion for
  KN Cen are evolved stars which should fit on almost the same mass
  track as the Cepheid. The authors find however that with generally
  accepted reddening values the companions of at least SV Per and RW
  Cam are too faint. Either the Cepheid loops are more luminous than
  presently calculated or the reddening is larger than presently accepted.

---------------------------------------------------------
Title: Search for white dwarf companions of cool stars with peculiar
    element abundances
Authors: Boehm-Vitense, E.
1984STIN...8511923B    Altcode:
  A search for a white dwarf companions of cool stars with peculiar
  element abundances was undertaken. One additional star the xi Cet,
  was found with a white dwarf companion. It was found that HR 1016,
  56Uma, 16 Ser, have high excitation emission lines which indicate a
  high temperature object in the system. It is suggested that since these
  indications for high temperature companions were seen for all nearby
  Ba stars, it is highly probable that all Ba stars have white dwarf
  companions, and that the peculiar element abundances seen in the Ba
  stars are due to mass transfer. Observations, arguments and conclusions
  are presented. White dwarf companions were not found. Together with
  the Li and Be abundances and the chromospheric emission line spectra
  in these stars were studied. No white dwarf companions were seen for
  subgiant CH stars.

---------------------------------------------------------
Title: Book-Review - Be-Stars
Authors: Jaschek, M.; Groth, H. G.; Bohm-Vitense, E.
1984ApL....24..125J    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: EINSTEIN observations of three classical cepheids.
Authors: Bohm-Vitense, E.; Parsons, S. B.
1983ApJ...266..171B    Altcode:
  The authors have looked for X-ray emission from the classical Cepheids
  δ Cep, β Dor, and ζ Gem during phases when the later two stars
  show emission in low excitation chromospheric lines. No X-ray flux
  was detected except possibly from ζ Gem at phase 0.26. Derived upper
  limits are in line with emission flux or upper limits obtained for
  other F and G supergiants.

---------------------------------------------------------
Title: An attempt to determine stellar Lyman-Alpha emission-line
    fluxes for F stars with different metal abundances.
Authors: Bohm-Vitense, E.; Woods, J.
1983ApJ...265..331B    Altcode:
  We have studied stellar Lyα fluxes for F stars of different metal
  abundances which are presumably older the more metal deficient they
  are. We describe the correction procedure for the geocoronal emission
  and our estimate of the correction for interstellar absorption. We find
  stronger than average Lyα emission for the Hyades stars and for the two
  close binaries HR 1354 and α Tri. <P />For single non-Hyades stars we
  find increasing Lyα emission for decreasing metal abundances. Assuming
  that the total hydrogen emission, including H and H - continua and
  Lyman lines, is twice the amount of the Lyα emission, and that the
  metallic emission, including Mg II h and k and Ca II H and K lines,
  is 4 times the Mg II k emission, we find that the total chromospheric
  energy loss, and therefore also energy input, is nearly independent
  of metal abundance and therefore presumably independent of age, for
  ages larger than a few times 10<SUP>9</SUP> years.

---------------------------------------------------------
Title: White Dwarf Companions and Chromospheres of Stars with Peculiar
    Element Abundances
Authors: Bohm-Vitense, Erika
1983iue..prop.1408B    Altcode:
  During our studies of BaII and mild Ba stars we found 3 hot
  companions. An additional one was found by Schindler, et al. With
  these 4 cases we can start to do some preliminary statistics in order
  to guide us with further observations. We find that the Ba stars With
  companions have all been classified as luminosity class II or higher. We
  also find that 3 of the 4 have late G spectral types while most of
  the Ba stars have K types. Also, 3 of the 4 are mild Ba stars. They
  are, however, not the same 3 stars. We would like to check whether
  these correlations persist in further studies. Several mild Ba stars
  are fairly bright. For these we may have a good chance to see the
  companions. We would therefore like to observe preferentially mild
  Ba stars with G spectral classification and luminosity class 11 or
  higher. If the frequency of companions for these stars is indeed high,
  we may find enough to study the relation between companion temperatures
  and the properties of the peculiar abundance stars.

---------------------------------------------------------
Title: Chromospheric Emission of Close Binaries
Authors: Bohm-Vitense, Erika
1983iue..prop.1400B    Altcode:
  It is generally believed that rapid rotation of stars enhances
  chromospheric emission. Studies of G stars have led to this
  conclusion. Our studies of Mg II k emission in early F stars only
  shows that close binaries show increased emission while single rapidly
  rotating stars with v(r) sin i &gt; 40 km/sec do not. For G stars
  close binaries are usually the only ones that rotate at a measurable
  rate. Rapid rotation and binary nature are correlated. For early F
  stars this is not the case. We therefore propose to study early F star
  binaries of known periods and different rotational velocities in order
  to decide on the cause of enhanced emission: either tidal effects in
  close binaries or rapid rotation.

---------------------------------------------------------
Title: Lambda Bootis Stars
Authors: Bohm-Vitense, Erika
1983iue..prop.1586B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet radiation from the environment of the
    Cohen-Schwartz star.
Authors: Bohm, K. H.; Bohm-Vitense, E.
1982ApJ...263L..35B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The ultraviolet continuous and emission line spectra of the
    Herbig-Haro objects HH 2 and HH 1.
Authors: Boehm-Vitense, E.; Cardelli, J. A.; Nemec, J. M.; Boehm, K. H.
1982ApJ...262..224B    Altcode:
  Recent studies of the continuous spectrum of Herbig-Haro (HH) objects
  at optical and near-infrared wavelengths and the observation of
  continuous radiation in the ultraviolet have shown an unexpectedly
  steep increase of the flux toward shorter wavelengths. The present
  investigation provides the results of ultraviolet observations of HH
  2. The obtained data are compared with the HH 1 data. It is found that
  HH 2 has an ultraviolet continuous and emission-line spectrum which
  is similar to that of HH 1. The UV line spectrum of HH 2H indicates
  an even somewhat larger ionization than does the HH 1 spectrum. As
  in HH1, the UV emission-line spectrum shows a much higher degree of
  ionization than that derived from the optical spectrum. Consequently,
  the same difficulty arises as in the case of HH 1. The complete UV
  plus optical spectrum cannot be explained by a single plane-parallel
  shock-wave model.

---------------------------------------------------------
Title: The interstellar absorption-line spectrum of mu. Oph.
Authors: Cardelli, J.; Boehm-Vitense, E.
1982ApJ...262..213C    Altcode:
  UV interstellar lines have been measured on high-resolution, long-
  and short-wavelength IUE spectra of the B8 V star Mu Oph. Column
  densities for the observed atoms and ions have been determined as well
  as turbulent velocities. The interstellar spectrum of Mu Oph is similar
  to the ones for Rho Oph and Zeta Oph. The ionization equilibria of
  several elements give consistent limits for the electron density. The
  C I line arising from different fine-structure levels are studied
  to yield estimates on the physical conditions in the cloud. Relative
  depletion of elements in the cloud seen in the interstellar spectrum
  of Mu Oph follows the same pattern as seen in the interstellar spectra
  of Zeta Oph and six other stars in the Rho Oph cloud complex.

---------------------------------------------------------
Title: Suggested UV spectral classification criteria for A stars
Authors: Boehm-Vitense, E.
1982ESASP.182..121B    Altcode: 1982uvsc.conf..121B
  Criteria for determining effective temperature and electron
  density independently of abundances, for A, late B, and F stars are
  given. Comparison of IUE data with standard classification techniques,
  shows that for late B and A stars, temperature classification by UV
  spectra is more sensitive than classification using visual spectra. The
  long wavelength wing of the Lyman is recommended for these stars. For
  A and F stars, the ratio of the Mg (2580 A) and Mg+ (2800A) resonance
  lines gives a good temperature/electron density (ne) criterion which
  is nearly independent of metal abundance (Z). The SiI discontinuities
  give an excellent temperature classification for A and F stars, but it
  is dependent on Z and ne. If the absolute intensities of either of the
  Mg lines are added to the criteria, three classification criteria for
  a three dimensional classification, according to temperature, ne and Z,
  are obtained.

---------------------------------------------------------
Title: The MG II resonance lime emission at 2800 angstrom in stars
    with different rotational velocities and different metal abundances.
Authors: Boehm-Vitense, E.
1982ApJ...258..628B    Altcode:
  In many investigations, a study of the Mg II 2800 A emission was
  conducted in order to derive more information about the correlation of
  chromospheric emission with the properties of the convection zone. It
  has been suggested by Ayres and Linsky (1980) that there is a positive
  correlation between rotation and chromospheric emission at least
  for binary stars. The present investigation is concerned with such a
  correlation between rotation and chromospheric emission. Since large
  differences in rotational velocities are observed for F stars for which
  also strong chromospheric emission is observable, this particular study
  deals mainly with F stars. On the basis of observations of the Mg II
  emission in F and G stars, it is found that the emission is abnormally
  strong in close binary F stars. This may be explained by the generation
  of a large differential rotation due to tidal effects which may give
  very efficient dynamo generation of a surface magnetic field.

---------------------------------------------------------
Title: Effective temperatures of A and F stars.
Authors: Boehm-Vitense, E.
1982ApJ...255..191B    Altcode:
  Effective temperatures of late A and early F stars are determined from
  the observed fluxes in the visual at 1900 A and 1420 A. The observed
  ratios are compared with those calculated by Kurucz (1979). A correction
  of the theoretical fluxes at 1900 A brings the effective temperatures
  obtained from different ratios into reasonable agreement. The effective
  temperatures determined in this way for late A stars agree well with
  those obtained from the optical region. For F stars, however, the
  effective temperatures obtained from the UV are found to be higher
  than those obtained from the optical region if radiative equilibrium
  models are used for the comparison. It is thought that this discrepancy
  may derive from the effects of temperature, pressure, and absorption
  coefficient inhomogeneities caused by convection.

---------------------------------------------------------
Title: Mg II k emission lines in stars with different rotational
    velocities and metal abundances.
Authors: Böhm-Vitense, E.
1982SAOSR.392B..71B    Altcode: 1982csss....2...71B
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheric, transition layer and X-ray emission for stars
    with different rotational velocities.
Authors: Boehm-Vitense, E.
1982NASCP2238..247B    Altcode: 1982auva.nasa..247B; 1982NASCP2338..247B; 1982IUE82......247B
  In agreement with previous findings for the MgII k line emission in F
  stars an increase of Lya and transition layer emission with increasing
  V<SUB>r</SUB> sin i, if v<SUB>r</SUB> sin i greater than 30 km/sec. was
  not found. For V<SUB>r</SUB> sin i 30 km/sec., the measured line
  intensities are consistent with an increase in emission with increasing
  V<SUB>r</SUB> sin i. Such a relation between emission and rotation for
  single stars is also in agreement with X-ray observations. For the young
  F stars in the Hyades we find generally enhanced emission independently
  of rotational velocities. The enhancement is most pronounced for low
  excitation lines.

---------------------------------------------------------
Title: Binary F Stars
Authors: Bohm-Vitense, Erika
1982iue..prop.1252B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: X-Ray and Ultraviolet Observations of Classical Cepheids
Authors: Bohm-Vitense, E.; Parsons, S. B.; Schmidt, E. G.
1982pccv.conf..238B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet spectra of Herbig-Haro objects and of the
    environment of the Cohen-Schwartz star.
Authors: Boehm, K. H.; Boehm-Vitense, E.; Cardelli, J. A.
1982NASCP2238..223B    Altcode: 1982IUE82......223B; 1982auva.nasa..223B; 1982NASCP2338..223B
  Observations in both spectral regions were used in order to determine
  the continuous energy distribution and the emission line fluxes for
  H-H 2. The continuous spectrum is similar to that in H-H 1 and F lambda
  increases rapidly towards shorter wavelengths. This statement is found
  to be qualitatively correct for all obvious choices of the ultraviolet
  extinction curve if we use the E(B-V) value determined by the use of
  the S II method. The origin of the continuum remains enigmatic. The
  emission line spectrum of H-H 2 shows an even somewhat higher degree
  of ionization than the spectrum of H-H 1, indicating an even larger
  discrepancy between ionization information from optical data and
  that contained in the UV spectra. The immediate environment of the
  Cohen-Schwartz star emits a continuous spectrum similar to that of a
  H-H-object but increasing even more steeply towards shorter wavelengths.

---------------------------------------------------------
Title: Search for &amp; Study of Hot Companions of Cepheids
Authors: Bohm-Vitense, Erika
1982iue..prop.1058B    Altcode:
  Studies of the track of cepheid colors in the two color diagram during
  their pulsational cycle reveals that some cepheids show an additional
  blue light source, which is presumably due to a blue companion roughly
  two or three magnitudes fainter than the cepheid in the visual. During
  one exploratory shift we have taken low resolution short wavelength
  IUE spectra of 5 suspected binaries. Four of them did indeed show
  the spectrum of a hot companion. We suggest to take well exposed
  spectra of these companions in order to determine spectral type and
  luminosities. We also want to search for hot companions in other
  suspected cepheid binaries.

---------------------------------------------------------
Title: Hr 8752
Authors: Bohm-Vitense, Erika
1982iue..prop.1230B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheres &amp; White Dwarf Companions of Peculiar
    Abundance Stars
Authors: Bohm-Vitense, Erika
1982iue..prop.1062B    Altcode:
  It is proposed to continue to observe chromospheres and transition
  region emission of stars with peculiar element abundances. At the same
  time we want to continue the search for white dwarf companions of these
  stars. Since the studies of McClure et al. 1980 it is suspected that
  many if not all of the peculiar element abundance stars have white dwarf
  companions and that mass exchange has led to the exposure of the deeper
  layers of the stars in which peculiar abundances have been generated
  by nuclear reactions. This would especially explain the large nitrogen
  abundance and may explain the large Li abundance seen in weak G band
  stars, and the large C abundance seen in CH stars. While cool white
  dwarf companions may be too faint to be visible an active chromosphere
  may still indicate their presence. A study of the relative emission
  line intensities will confirm the peculiar element abundances and
  exclude peculiar surface temperature stratifications as a possible
  explanation for anomalous molecular line intensities.

---------------------------------------------------------
Title: Observation of Ultraviolet Light VAriations of POP II Cepheids
Authors: Bohm-Vitense, Erika
1982iue..prop.1055B    Altcode:
  We want to study the changes of the ultraviolet energy distributions
  in Pop II cepheids, and see whether emission lines during maximum
  light can be detected. The gradient of the energy distributions for
  longer wavelengths (lambda &gt;1900A) together with studies of the
  discontinuities at 2600A and at 1700A (for the brighter stars) will
  permit to determine the metal abundances and the effective temperatures
  as a function of phase. For k Pav we will in connection with radial
  velocity measurements be able to determine radii. Comparision with
  stellar evolution calculations will yield masses for these stars. A
  comparison of spectra for W Vir and ST Pup both with periods of 17^d
  but vastly different spectral types will be very interesting. The
  metal abundances are expected to be very different.

---------------------------------------------------------
Title: Chromospheric, transition layer and coronal emission of metal
    deficient stars.
Authors: Boehm-Vitense, E.
1982NASCP2238..231B    Altcode: 1982auva.nasa..231B; 1982NASCP2338..231B; 1982IUE82......231B
  It is shown that while MgII k line emission decreases for metal
  deficient stars, the Ly alpha emission increases. The sum of
  chromospheric hydrogen and metallic emission appears to be independent
  of metal abundances. The total chromospheric energy loss is estimated
  to be 0.0004 F<SUB>bol.</SUB> The chromospheric energy input does not
  seem to decrease for increasing age. The transition layer emission
  is reduced for metal deficient stars, but it is not known whether
  the reduction is larger than can be explained by curve of growth
  effects only. Coronal X-ray emission was measured for 4 metal deficient
  stars. Within a 12 limit it could still be consistent with the emission
  of solar abundance stars.

---------------------------------------------------------
Title: The ultraviolet spectrum of Herbig-Haro object 1.
Authors: Boehm, K. H.; Bohm-Vitense, E.; Brugel, E. W.
1981ApJ...245L.113B    Altcode:
  Continuum and emission line fluxes for HH 1 in the range of 1200-1300
  A have been determined using IUE spectra, and it is found that the
  luminosity of HH 1 in this wavelength interval is slightly larger than
  1 solar luminosity, or 20 times greater than for the wavelength range
  3200-11,000 A. If averaged over intervals of 100 A, it is shown that the
  UV continuum rises almost monotonically toward shorter wavelengths over
  the entire interval 1300-3000 A. The UV continuum energy distribution
  cannot be explained by a T Tauri stellar continuum that is scattered
  by dust. Emission line identifications and flux measurements strongly
  confirm the statement that the high-ionization emission lines are too
  strong to be explained by shock-wave models derived from the emission
  line spectrum in the interval 3700-11,000 A. A possible explanation
  for this fact is discussed.

---------------------------------------------------------
Title: Interstellar absorption in the MgII resonance line K2 and
    H2 emissions.
Authors: Boehm-Vitense, E.
1981ApJ...244..504B    Altcode:
  High-resolution (0.2 A) IUE spectra for the long wavelength range
  (1800-3000 A) have been studied. It is shown that narrow interstellar
  Mg II lines are seen in the center of the k2 and h2 emissions from
  nearby stars with large rotational velocities. For all observed stars,
  the radial velocity of the central k3 absorption component in the
  rest system of the star is strongly correlated with the mirror image
  of the radial velocity of the stars; this shows that a major fraction
  if not all of the k3 absorption is due to interstellar absorption in
  the solar neighborhood. The violet to red asymmetry of the k2 emission
  also correlates with the radial velocities of the star; this shows that
  the shift of k3 is due to the velocity shift of the local interstellar
  cloud with respect to the star.

---------------------------------------------------------
Title: The ultraviolet energy distributions of late A stars.
Authors: Boehm-Vitense, E.
1981ApJ...244..938B    Altcode:
  Observed late A star energy distributions for the wavelength range
  1400-2500 A are compared. No difference is found between energy
  distributions of Am stars and those of normal slowly rotating A
  stars. The fluxes of rapidly rotating stars, however, appear to be
  increased for wavelengths smaller than 1530 A; this cannot be understood
  as an effect of pole heating or reduced gravity. In addition, the
  comparison of the UV energy distributions with model atmosphere energy
  distributions of Kurucz indicates some problems with the theoretical
  Si I absorption edges at 1530 A.

---------------------------------------------------------
Title: Far-ultraviolet energy distributions of the metal-poor A
    stars HD 109995 and HD 161817.
Authors: Boehm-Vitense, E.
1981ApJ...243..213B    Altcode:
  Low-resolution IUE spectra at wavelengths between 1300 and 3400 A of
  the metal-poor stars HD 109995 (A1p) and HD 161817 (A4p) have been
  compared with model-atmosphere energy distributions computed by Kurucz
  (1979). Good overall agreement is found. Effective temperatures,
  metal abundances, and angular diameters could be determined. Assuming
  an absolute visual magnitude of 0.7, the previously determined gravity
  log = 3 yields masses of 0.5 solar masses for both stars. It is found
  that the theoretical UBV colors calculated earlier agree reaonably
  well with the ones observed for these stars.

---------------------------------------------------------
Title: The chromospheric and transition layer emission of stars with
    different metal abundances.
Authors: Boehm-Vitense, E.
1981NASCP2171..303B    Altcode: 1981uviu.nasa..303B; 1981NASCP3171..303B; 1980IUE80......303B
  Preliminary results on observations of chromospheric and transition
  layer emission of stars with different metal abundances are
  reported. Metal deficient stars generally show reduced emission in
  the Mg II resonance lines and also in the other chromospheric and
  transition layer emission lines. This is interpreted as showing that
  energy fluxes other than acoustic fluxes must at least be coresponsible
  for the coronal and transition layer heating.

---------------------------------------------------------
Title: University of Washington, Seattle, Washington 98195. Report.
Authors: Böhm-Vitense, E.
1981BAAS...13..470B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The effective temperature scale
Authors: Boehm-Vitense, E.
1981ARA&A..19..295B    Altcode:
  It is found that the agreement between the radiative equilibrium model
  atmosphere Teff (B-V) relation and observed direct determinations
  is generally rather good, which indicates that it may be possible to
  understand the structure of most atmospheres reasonably well. There are
  still some problems in the main-sequence O and F stars and in the M star
  regions. The red giants and supergiants also pose some problems. It is
  not known whether Rayleigh scattering alone can explain the red colors
  for giants around 3600 K; model atmosphere colors for such stars have
  not been published. The metal-poor giants seem to be well represented
  by the model calculations; for the metal-poor F stars there are still
  some uncertainties.

---------------------------------------------------------
Title: Outlook for ultraviolet astronomy.
Authors: Boehm-Vitense, E.
1981NASCP2171....3B    Altcode: 1981NASCP3171....3B; 1980IUE80........3B; 1981uviu.nasa....3B
  A brief overview of galactic and extragalactic research is given
  with emphasis on the problems of temperature determination, chemical
  abundance determination, and the question about the energy sources
  for the high temperature regions. Stellar astronomy, stellar winds,
  and the interstellar medium are among the topics covered.

---------------------------------------------------------
Title: The chromospheric Mg II k<SUB>2</SUB> emission in stars with
    different rotational velocities and different metal abundances.
Authors: Böhm-Vitense, E.
1981PASP...93Q.545B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Cepheid Variables
Authors: Bohm-Vitense, Erika
1981iue..prop..870B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The white dwarf companion of the Ba II star zeta Cap.
Authors: Boehm-Vitense, E.
1981NASCP2171..455B    Altcode: 1980IUE80......455B; 1981uviu.nasa..455B; 1981NASCP3171..455B
  The Ba II star zeta Cap has a white dwarf companion. Its T
  <SUB>eff</SUB> is determined to be 22000 K, its mass is approximately
  one solar mass. The importance of this finding for the explanation of
  abundance peculiarities is discussed.

---------------------------------------------------------
Title: Search for White Dwarf Companions of Stars with Peculiar
    Process &amp; CNO Abundances
Authors: Bohm-Vitense, Erika
1981iue..prop..722B    Altcode:
  We would like to continue our search for white dwarf companions of
  Ba, CH strong, CH weak and CN strong stars. The Ba II star zeta Cap
  was observed to have a white dwarf companion. The weak Ba II star
  zeta Cyg appears to have a somewhat cooler WD companion. HD 65699
  (BA II) and HR 2392 (Ba II) also show indications of companions but
  additional long exposures have to be taken to verify this. If mass
  exchange between binaries is responsible for the visibility of the
  excess s process elements we may speculate that mass exchange might
  also be responsible for the CH and CN peculiarities. We would also
  like to obtain and study a high resolution short wavelength spectrum
  of the Barium star zeta Cap which was observed to have a hot white
  dwarf companion, The emission line profiles will probably tell us the
  origin of these strong emission lines and give us information about
  circumstellar material which is probably present as judged from the
  strong central reversals in the Mg II emission lines. At the same time
  the chromospheric and transition layer emissions of these peculiar
  abundance stars will be studied. Peculiar CNO abundances might be
  verified by their chromospheric and transition layer line intensities
  as compared to normal stars

---------------------------------------------------------
Title: A comparison of the MG resonance lines in AM and non AM stars
    of similar temperatures.
Authors: Boehm-Vitense, E.
1980A&A....92..219B    Altcode:
  A comparison of the Mg II resonance lines in Am and none Am stars
  of similar effective temperatures does not show any measurable
  differences. The Mg I resonance lines may be weaker in the Am stars. The
  mechanism reducing the Ca II K line intensities in Am stars does not
  work for the Mg II k and h lines.

---------------------------------------------------------
Title: The white dwarf companion of the barium star ZET Cap.
Authors: Boehm-Vitense, E.
1980ApJ...239L..79B    Altcode:
  It is shown that the barium star Zeta Cap has a white dwarf companion
  with a mass of approximately 1.0 solar masses and an effective
  temperature of 23,000 K. Strong emission lines and very deep reversals
  in the Mg II emission line cores indicate circumstellar gas which
  may be due to mass transfer in the system. The Ba star HD 65699 also
  shows the very deep central reversals in very strong Mg II emission
  cores. The weak spectra of the barium stars Zeta Cyg, HD 65699, and HD
  116713 probably show excessive UV radiation also, but further studies
  are necessary.

---------------------------------------------------------
Title: The boundary line in the H-R diagram for stellar chromospheres
    and the theory of convection.
Authors: Boehm-Vitense, E.; Dettmann, T.
1980ApJ...236..560B    Altcode:
  Ultraviolet emission-line spectra of A, F, and early G stars have been
  observed with the International Ultraviolet Explorer. For supergiants,
  classical chromospheric and transition-layer emission is seen only on
  the red side of the Cepheid instability strip. For luminosity classes
  III-V, chromospheric emission can be detected for spectral types F2
  and later. For none of the A stars was normal chromospheric emission
  detected, regardless of their rotational velocities or peculiarities
  (i.e., Am or Ap).

---------------------------------------------------------
Title: Dependence of Stellar Chromospheres on Metal Abundance
    Rotation, and Age
Authors: Bohm-Vitense, Erika
1980iue..prop..412B    Altcode:
  It is proposed to study the stellar chromospheric emission and its
  dependence on metal abundances, rotation and age. If the emission is
  enhanced by rapid rotation of the stars it will indicate that acoustic
  heating will be unimportant for the formation of chromospheres and
  coronae since the acoustic flux generation should not depend on
  rotation. We want to study variability in the chromospheric emission
  of some supergiants. We also want to determine luminosity differences
  between normal stars and metallic line stars. These measurements
  will also provide bolometric corrections for these stars. For stars
  with known angular diameters effective temperatures can be determined
  directly. This study will show whether different surface metal abundance
  is the only major difference between metallic line A stars and normal
  A stars as suggested by the diffusion hypothesis.

---------------------------------------------------------
Title: Summary - Stellar Turbulence
Authors: Bohm-Vitense, E.
1980LNP...114..300B    Altcode: 1980IAUCo..51..300B; 1980sttu.coll..300B
  No abstract at ADS

---------------------------------------------------------
Title: Detection of a white dwarf in a visual binary system
Authors: Boehm-Vitense, Erika
1980STIN...9311075B    Altcode:
  The F6 giant HD 160365 was detected to have a white dwarf companion
  about 8 arcsec south of the star. The UV energy distribution observed
  with International Ultraviolet Explorer (IUE) shows that the white
  dwarf has an effective temperature of 23,000 +/- 2,000 K. If log g =
  8 the Ly(alpha) profile indicates an effective temperature around
  24,500 K. Using the theoretical models, one finds a visual magnitude
  of m<SUB>v</SUB> is approximately 16.5. For T<SUB>eff</SUB> = 24,500 K
  one expects for a white dwarf a luminosity of log L/solar luminosity is
  approximately -1.3 and M<SUB>V</SUB> is approximately 10.67. This gives
  a distance modulus for the system of m<SUB>v</SUB> - M<SUB>V</SUB> =
  5.83 and an absolute magnitude M<SUB>v</SUB> = 0.3 for the giant.

---------------------------------------------------------
Title: The influence of the helium abundance on the appearance of
    late-type spectra.
Authors: Boehm-Vitense, E.
1979ApJ...234..521B    Altcode:
  The paper studies the dependence of atomic, ionic, and molecular lines
  on the helium abundance in stars in which the continuous absorption
  is due to H(-) and the electrons are supplied by the metals, which
  are assumed to be mainly ionized. These conditions will approximately
  apply to subgiants and red giants. Possible applications to red giant
  studies in Omega Cen, M22, 47 Tuc, NGC 2420, and Draco are discussed.

---------------------------------------------------------
Title: On the energy distribution in Sirius B.
Authors: Boehm-Vitense, E.; Dettmann, T.; Kapranidis, S.
1979ApJ...232L.189B    Altcode:
  A spectrum of Sirius B in the wavelength region 1100-1900 A taken
  with the IUE satellite shows an absolute flux and spectral energy
  distribution in the continuum in agreement with theoretical white-dwarf
  models with T(eff) of 26,000 K plus or minus 1000 K for log g equals
  8.65 and R equals 5.08 x 10 to the 8th cm. The Lyman-alpha profile is
  also in agreement with these parameters. No obvious emission lines in
  the spectrum of Sirius B or A which could indicate the presence of a
  chromosphere or corona in either of the stars are observed.

---------------------------------------------------------
Title: Is "Sirius C" the X-ray Source?
Authors: Böhm-Vitense, E.
1979BAAS...11..465B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: University of Washington, Astronomy Department, Seattle,
    Washington 98195. Report.
Authors: Böhm-Vitense, E.
1979BAAS...11..372B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Classical Stellar Chromospheres and Dependence on Teff,
    and Chemical Abundances
Authors: Bohm-Vitense, Erika
1979iue..prop..171B    Altcode:
  I would like to continue to observe stars which appear in the HR diagram
  close to the dividing line between the convective and non-convective
  stars. Since convection is supposed to be a necessary condition for
  the formation of chromospheres we should be able to determine the
  boundary line for convection from the boundary line for the existence
  of classical chromospheres. I would like to continue to investigate
  whether the phenomenon of metallic line stars can in any way be related
  to the onset of convection and thereby to the presence or absence
  of chromospheres. We also want to observe a few manganese stars in
  order to check if any effects of the surface convection zone due to He
  ionization could be detected in the UV spectrum of Mn stars. I would
  like to extend the study of the onset of convection to the region
  of the He rich hot white dwarfs for which convection is expected
  for temperatures up to 30,000 K. Of special interest would be the
  observation of some dwarf novae. I would like to study chromospheres
  and transition layers of Pop II stars, red giants and subdwarfs and
  compare those to Pop I stars. Knowing the chromospheric spectra of
  field Pop II stars, I would like to analyse the integrated spectra of
  globular clusters and their center to limb variation. One might hope to
  be able to determine the population and perhaps the break off of the
  lower main sequence which appears to depend on the metal abundance of
  the cluster. The study of the globular clusters will also reveal the
  presence or absence of hot blue objects and their distribution in the
  cluster. If the lambda 2200 absorption could be detected this may give
  some information about the presence of interstellar dust and gas in
  the clusters, which is expected to be there but has not yet been found.

---------------------------------------------------------
Title: Observing with IUE.
Authors: Böhm-Vitense, E.
1979Mercu...8...29B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Energy Distribution of Sirius B
Authors: Boehm-Vitense, E.
1979wdvd.coll..114B    Altcode: 1979IAUCo..53..114B
  The origin of the X-ray emission observed from the DA white dwarf Sirius
  B is investigated on the basis of low-resolution short wavelength IUE
  spectrum. Following a correction for the influence of scattered light
  from Sirius A, the intensity distribution of Sirius B is obtained
  as a function of wavelength. Comparison of the continuous energy
  distribution with model atmosphere energy distributions indicates an
  effective temperature of 25,500 K, which is not high enough to explain
  the observed X rays as normal photospheric radiation. In addition,
  with the exception of an unusual feature in the neighborhood of the C I
  1657 line, no clear evidence is found of emission lines indicative of
  a corona, chromosphere or disk, and the origin of the X rays remains
  unknown.

---------------------------------------------------------
Title: Spectral Classification from a Theoretical Point of View
Authors: Bohm-Vitense, E.
1979RA......9..309B    Altcode: 1979IAUCo..47..309B
  Conditions are studied under which a two-dimensional spectral
  classification according to effective temperature and electron density
  is possible and when three- or four-dimensional spectral classification
  is necessary because the classification criteria are unavoidably
  influenced by the metal and helium abundances. For late-type stars,
  where molecular absorption becomes important for the continuum, a seven-
  or higher-dimensional classification may be necessary. At this point
  spectral classification may not be useful any more. It is found in
  general that a derivation of the gravitational acceleration from the
  spectroscopically determined electron density is possible only if the
  helium abundance is known.

---------------------------------------------------------
Title: Scanner observations of Am and Ap stars.
Authors: Böhm-Vitense, E.; Johnson, P.
1978ApJ...225..514B    Altcode:
  We have rescanned the three metallic4ine stars 15 Vul, T UMa, and 60
  Leo and find that we cannot reproduce the scanner results of Baschek
  and Oke for these stars. We conclude that these Am stars are variable
  on a time scale longer than weeks, possibly decades. The variations
  cannot be explained by a variable back-warming effect. Since all three
  Am stars which we rescanned are variable, we suspect that most Am stars
  may be variable on similar time scales. Subject headings: convection -
  spectrophotometry - stars: metallic-line - stars: peculiar A - stars:
  variables

---------------------------------------------------------
Title: Energy distribution in main-sequence A and F stars.
Authors: Boehm-Vitense, E.
1978ApJ...223..509B    Altcode:
  Scanner observations of A and F main-sequence stars are examined in
  order to check whether the observed continuum energy distributions
  match scaled Bilderberg models and whether some influence of rotation
  on convection can be detected. The continuum energy distributions of
  A and F field stars and of stars in different clusters with different
  rotational velocities are compared; the clusters include the Hyades,
  Praesepe, Coma, Alpha Persei, and the Pleiades. A comparison with
  radiative-equilibrium model-atmosphere computations reveals some UV
  flux reduction for many stars with B-V greater than 0.14 and a strong
  UV flux reduction for all stars with B-V greater than 0.22, regardless
  of rotational velocity. The energy distributions are found to match
  the scaled Bilderberg models, and this is attributed to a reduced
  temperature gradient in convectively unstable layers. It is shown that
  rotation does not impede convection, but even seems to enhance it,
  contrary to expectations.

---------------------------------------------------------
Title: Ultraviolet Observations of A and F Stars
Authors: Bohm Vitense, Erika
1978iue..prop....6B    Altcode:
  There are two main points of interest for which the IUE would be very
  helpful (1) line identification in A Stars. High resolution spectra
  of Vega / Sirius and --Cyg would permit the line identification. (2)
  Termination of Hydrogen Convection. The observation of the effects of
  stellar chromospheres may give us information about the termination
  point of the hydrogen convection.

---------------------------------------------------------
Title: Scanner observations of main-sequence A and F stars.
Authors: Böhm-Vitense, E.; Johnson, P.
1977ApJS...35..461B    Altcode:
  In order to understand the observed UB V colors of main-sequence
  A and F stars, and especially to understand the B - V gap observed
  for field stars and some clusters, we have made scanner observations
  of main-sequence stars with 0.20 &lt; B - V &lt; 0.45 in different
  clusters and with different Vr sin i. The results are given in Tables
  2-7. Subject heading: spectrophotometry

---------------------------------------------------------
Title: Observations bearing on the theory of stellar convection. II
Authors: Boehm-Vitense, E.
1977LNP....71...63B    Altcode: 1977stco.coll...63B; 1977IAUCo..38...63B; 1977psc..conf...63B
  Difficulties in determining the ratio of mixing length to pressure
  scale height from observations of stars and from stellar evolutionary
  tracks are discussed. An attempt is made to show that information
  about convection can sometimes be obtained from direct and indirect
  measurements of velocity fields as well as from observations of
  temperature inhomogeneities. The effect of convective energy transport
  on the continuous energy distribution of F stars is considered. Scanner
  observations of various field and cluster stars are examined which
  apparently indicate that convection generally becomes efficient for
  B-V of at least 0.22, while fast rotation causes an earlier onset of
  efficient convection.

---------------------------------------------------------
Title: Weshalb sind magnetische Sterne magnetisch?
Authors: Böhm-Vitense, E.
1977Umsch..77..355B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Neue Beobachtungsergebnisse für A<SUB>m</SUB>-Sterne
Authors: Böhm-Vitense, E.; Johnson, P.
1977MitAG..42..137B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: About the Proper Choice of the Characteristic Length in the
    Convection Theory
Authors: Bohm-Vitense, Erika; Nelson, George Driver
1976ApJ...210..741B    Altcode:
  It is known that convection sets in rather abruptly for stars with Teff
  &lt; Tb, where Tb depends on the luminosity. The boundary line Tb(L)
  goes through the H-R diagram from late A or early F main-sequence stars
  to late F or early G supergiants. In the mixing length approach to the
  theory of convection the exact theoretical position of this boundary
  temperature depends on the assumptions about the size of the mixing
  length 1. We make the assumption that the red boundary of the Cepheid
  instability strip agrees with the line Tb(L). If we also assume 1 = n
  pressure scale height H, with n being the same constant for all stars,
  we find 1 H to give the correct Tb(L). If we assume the region of large
  instability to determine 1, the relation 1 R2 also gives approximately
  the correct Tb(L). We do not think, however, that the latter relation
  has any physical significance. Subject headings: convection - stars:
  Cepheids - stars: chromosphere - stars: interiors

---------------------------------------------------------
Title: On the Interpretation of the AM Phenomenon
Authors: Böhm-Vitense, E.
1976paps.coll..633B    Altcode: 1976IAUCo..32..633B
  No abstract at ADS

---------------------------------------------------------
Title: Model stellar atmospheres and heavy element abundances.
Authors: Boehm-Vitense, E.
1975psae.book...21B    Altcode:
  Stars whose atmospheric structure depends in an observable way on the
  heavy element abundances are considered. Such stars have effective
  temperatures which do not exceed 8,000 K. The stellar temperature
  stratification is examined and a description of the gas and electron
  pressures is presented. Aspects concerning the energy distribution in
  the continuum are explored, taking into account the Balmer discontinuity
  and the ultraviolet continuum. The line absorption is discussed along
  with the UBV colors, the temperature calibrations, the bolometric
  correction, and questions related to convection and metal abundances.

---------------------------------------------------------
Title: The Gap in the Two-Color Diagram of Main-Sequence Stars
Authors: Bohm-Vitense, E.; Canterna, R.
1974ApJ...194..629B    Altcode:
  in the two-color diagrams of main-sequence stars a gap of A(B - V) 0.07
  is expected at B - V 0.25 due to the abrupt onset of convection. This
  gap is observed for field stars. it is also indicated for many clusters;
  however, it appears at different B - V and is less pronounced the more
  it is shifted to the red. Since in these clusters the stars on the blue
  side of the gap show large rotation, we interpret the shift as showing
  that large rotational velocities shift the onset of convection to lower
  Te . The abrupt decrease of the rotational velocities occurs at still
  lower Teff when convective energy transport becomes important in the
  helium ionization zones. Subject headings: convection - interiors,
  stellar - open clusters - rotation, stellar

---------------------------------------------------------
Title: Masses and luminosities of population II cepheids.
Authors: Böhm-Vitense, E.; Szkody, P.; Wallerstein, G.; Iben, I., Jr.
1974ApJ...194..125B    Altcode:
  Mean luminosities, effective temperatures, and radii of 11 Population
  II Cepheids are derived from three color photometry and, in some
  cases, radial velocities. From a comparison of the observed and the
  theoretical period-radius relation masses of 0.55 I 0.05 are derived
  for all Population II Cepheids except the variables No. 1 and 2 in
  M13, which appear to be less massive and possibly helium-rich. The
  period-luminosity relation is also discussed. Subject headings: Cepheids
  and W Virginis stars - globular clusters - luminosities - mass loss

---------------------------------------------------------
Title: UBVr Colors for Population II Giants
Authors: Bohm-Vitense, Erika; Szkody, Paula
1974ApJ...193..607B    Altcode:
  The UBVr colors for intermediate Population II giants with metal
  abundance Z = 1/10 of the solar metal abundance Z0 are computed from
  radiative equilibrium models. Line blanketing and Rayleigh scattering
  are taken into account. The colors are given for models with 4000 &lt;
  Tgtf &lt; 8000 K and 4.6 &lt; L/L0 &lt; 1800. The relation between B -
  V and Tgff is determined for different luminosities. Graphs for Tgff
  and U - B as functions of B - V for different luminosities and metal
  abundances are given and compared. It is shown that the U - B excess is
  not a simple function of the metal abundance alone but depends on B - V
  and L also. A simple method is described by which luminosity, effective
  temperature, and metal abundance can be determined simultaneously
  from B - V, U - B, and Mv. Subject headings: abundances, stellar -
  photometry - Population II stars

---------------------------------------------------------
Title: The luminosities of population II cepheids.
Authors: Böhm-Vitense, E.
1974ApJ...188..571B    Altcode:
  A method is described for the distance determination of pulsating
  stars from measured colors and radial velocities. it follows the line
  of thought given by Baade and Wesselink. This method does not require
  any calibration by conventional distance determinations once the depth
  variation of the expansion velocities in the pulsating stars is known
  from theory. A period-luminosity relation for Population ii stars with
  periods between 17.3 and 28.5 days is derived from the stars W Vir, TW
  Cap, and star No. 42 in MS. Subject headings: Cepheids and W Virginis
  stars - luminosities

---------------------------------------------------------
Title: On the Excitation of β Cephei Pulsation.
Authors: Bohm-Vitense, E.
1973BAAS....5..427B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The interpretation of the two-color and color-magnitude
    diagrams of M15 and M92.
Authors: Böhm-Vitense, E.; Szkody, P.
1973ApJ...184..211B    Altcode:
  From the theoretical relation between U - B, B - Vand Teff, g for
  Population II stars and the observed color-magnitude diagrams, we
  determine the Teff and L values for the red giants and horizontal-branch
  stars in M15 and M92. Several possibilities for the stellar masses, the
  metal abundances, and distance moduli are considered. The "empirical"
  (luminosity, )-diagrams are compared with theoretical evolutionary
  tracks. The comparison suggests that Z(M15) &lt; Z(M92), the age t(M15)
  &gt; t(M92), and the masses M(M15) &lt; M(M92), while possibly Y(M15)
  &gt; Y(M92). The average values found for both clusters are log Z = -4 +
  0.3, Y = 0.25 + 0.03, t10 = 1.36 t 0.05, MIM0 = 0.85 i 0.05. Subject
  headings: abundances, stellar - globular clusters - luminosities -
  RR Lyrae stars

---------------------------------------------------------
Title: The UBVr colors of extreme Pop II giants.
Authors: Böhm-Vitense, E.
1973A&A....24..447B    Altcode:
  Summary. The UB Colors of Pop II giants with metal abundances 1/100 and
  1/1000 times the solar metal abundances are computed. For these stars
  the Rayleigh scattering is extremely important for the U fluxes. The
  mean intensity j, the source function for the Rayleigh scattering,
  has been determined, considering not only the continuous absorption
  of hydrogen and the metals but also the line absorption. The UBYr
  colors are given in the range 42000 Teff 77000 and 4.6 &lt; L/L0 &lt;
  1800. From this the relation between B - V and Teff is determined for
  different luminosities and also the ultraviolet excess, which for a
  given B - V depends on the gravity, g, as well as on the metal abundance
  Z Key words: colors - Population II giants - Rayleigh scattering -
  source function

---------------------------------------------------------
Title: Line Effects on the Radiative Acceleration in Supergiant Stars
Authors: Bohm-Vitense, E.
1973ApJ...181..379B    Altcode:
  The radiative acceleration g is studied for supergiants with Teff 8000
  K. Nongray effects, including line absorption, raise g by a factor
  of at least 6-in comparison with the gray case-at the surface of the
  stars. The luminosity limit for stable stars set by g will probably
  be lowered by this factor in comparison with earlier estimates
  based on electron scattering only. No instability is found for red
  supergiants. Subject headings: atmospheres, stellar - late-type stars -
  luminous stars - mass loss - opacities

---------------------------------------------------------
Title: The theoretical relation between UBV colors and T<SUB>eff</SUB>
    and luminosity for extreme pop. II giants.
Authors: Boehm-Vitense, E.
1973BAAS....5..266B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The UBVr Colors of Supergiants
Authors: Bohm-Vitense, E.
1972A&A....17..335B    Altcode:
  The atmospheres of supergiants are studied in the range 40000&lt;
  T65&lt; 9 000 . The influence of radiation pressure and spherical
  effects are discussed. The observed colors of supergiants are obtained
  with radiative equilibrium and hydrostatic models. A calibration of
  B- V in terms of T1ff is given. The Tgff obtained here for G and
  K supergiants are about 10% lower than adopted so far. Key words:
  supergiants - radiation pressure - sphericity - microturbulence -
  effective temperatures

---------------------------------------------------------
Title: Surface Temperatures and the Curves of Growth for Population
    I and Population II Stars
Authors: Bohm-Vitense, E.
1972A&A....16...81B    Altcode:
  The dependence of the curve of growth on metal abundance is studied
  by comparing the solar curve of growth with that of a star with the
  same effective temperature and gravity but a metal content reduced
  by a factor 100 and also with that of a giant with reduced metal
  abundance. The T(r) turned out to be essentially the same for the models
  with the same T , therefore the curves of growth (computed for Fe 1
  and Fe H and Doppler broadening only) are also the same for the stars
  with the same and g but different metal abundances. A theoretical
  discussion of this result is given. Key words: curves of growth -
  metal abundance - surface temperature

---------------------------------------------------------
Title: Convection and Metal Abundance
Authors: Bohm-Vitense, E.
1971A&A....14..390B    Altcode:
  The influence of the metal abundance Z on the structure of the
  convection zone is studied. The velocities in the convective zones
  decrease and the depths of the convection zones increase with decreasing
  metal abundance. For lower metal content the transition from radiative
  to convective atmospheres therefore occurs at higher effective
  temperatures. Key words: convection - microturbulence - metal abundance

---------------------------------------------------------
Title: The UBVr colors of main sequence stars.
Authors: Böhm-Vitense, E.
1970A&A.....8..283B    Altcode:
  The UBVr colors of main sequence stars with spectral types between A
  0 and K 0 are computed into account theoretical line blanketing. The
  observed colors require turbulent velocities between 2 and 4 km/s
  provided the solar microturbulence is 2 km/s as assumed here. For
  late A and F stars good agreement with observations is obtained if
  scaled solar "Bilderberg" models are used, showing that convection
  in these stars is more effective than indicated by the local mixing
  length theory. The scarcity of stars with 0.2 &lt; B - V &lt;0.4 can
  be undsrsod if convection sets in abruptly for T 8Ooo . The relation
  between B - V and T is derived for B - V 0.90. Key words: colors -
  convection - F stars - microturbulence - Sun

---------------------------------------------------------
Title: Convection in A and F stars and metallicism.
Authors: Böhm-Vitense, E.
1970A&A.....8..299B    Altcode:
  Theoretical spectra of radiative and convective A and F stars with
  a given colour B - V are compared. The Hv lines are essentially the
  same. The Ca U K line is weakened in the convective star. Temperature
  inhomogeneities further weaken the K line. The possibility is discussed
  that the metallic line stars may be the convective version of late A
  stars. Key words: F stars - convection - temperature inhomogeneities -
  line profiles - metallic line stars

---------------------------------------------------------
Title: The UBV Colors of A, F, and G Main-Sequence Stars
Authors: Böhm-Vitense, Erika
1970BAAS....2R.297B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Stellar Analysis by Means of the Hydrogen Lines
Authors: Böhm-Vitense, E.
1970saac.book..107B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A simple approximation forJ <SUB> v </SUB> (σ <SUB>
    v </SUB>,κ <SUB> v </SUB>,τ <SUB> v </SUB>,B <SUB> v </SUB>),
    and its application for temperature-correction procedures
Authors: Böhm-Vitense, Erika
1969Ap&SS...4..233B    Altcode:
  For the case of isotropic coherent scattering plus absorption a simple
  expression is given (Equation 12) to compute the mean intensity of the
  radiationJ <SUB> v </SUB> (as a function of optical depth τ<SUB> v
  </SUB>) if the scattering coefficient σ<SUB> v </SUB>, the absorption
  coefficientK <SUB> v </SUB> and the Planck functionB <SUB>v</SUB>
  are given as a function of depth. In general the accuracy of this
  approximation is of the order of a few percent. A fairly simple
  temperature-correction procedure for the case when scattering is
  important is described.

---------------------------------------------------------
Title: The Pulsar NP 0532 and the Implications of the Oblique-Rotator
    Hypothesis
Authors: Böhm-Vitense, Erika
1969ApJ...156L.131B    Altcode:
  The light curve of the pulsar NP 0532 can be reproduced with the
  oblique-rotator hypothesis, pro- vided that the light emission is
  strongly concentrated at two opposite spots on the star and is confined
  to a narrow cone

---------------------------------------------------------
Title: Line statistics for solar type stars.
Authors: Böhm-Vitense, E.
1969JQSRT...9.1167B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: 36 et 12 Session mixte (Joint Meeting)
Authors: Böhm-Vitense, E.
1968IAUTB..13..198B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the Atmospheres of Helium Stars
Authors: Böhm-Vitense, Erika
1967ApJ...150..483B    Altcode:
  The appearance of the spectra of helium stars as a function of hydrogen
  abundance is investigated theoretically for dwarfs (log g = 4 5)
  and giants (log g = 2) with effective temperatures Teff = 7350 , 9900
  `and 129000 K For normal C, N, and 0 abundances, the He and the He I
  absorptions appear to be the most important absorption mechanisms for
  very low hydrogen abundances. H becomes weakened for hydrogen abundances
  less than 0 85 X 10-2 by numbers of atoms The metal line intensities
  increase. The colors of extreme helium stars are somewhat redder than
  for normal stars The helium convection zone becomes important for the
  stars with Teff &gt; 99000 K.

---------------------------------------------------------
Title: ON the Absolute Magnitude and Effective Temperature of the
    Hydrogen-Poor Star HD 30353
Authors: Danziger, I. J.; Wallerstein, George; Böhm-Vitense, Erika
1967ApJ...150..239D    Altcode:
  Interstellar polarization and reddening data for stars near HD 30353
  were used to obtain a reddening excess E(B - V) = 0.35 and an absolute
  visual magnitude of -3.2. An effective temperature of 100000 K for HD
  30353 was obtained by fitting photoelectric scans of the continuum to
  fluxes obtained from the model atmosphere of a hydrogen-poor star.

---------------------------------------------------------
Title: The variations of stellar magnetic fields and the oblique
    rotator hypothesis
Authors: Böhm-Vitense, E.
1967maco.conf..179B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Der "Crossover" Effekt bei α CVn und HD 98088
Authors: Böhm-Vitense, E.
1967ZA.....67....1B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The peculiar a stars and the oblique rotator hypothesis
Authors: Böhm-Vitense, E.
1967mamt.book...97B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Outer Convection Zones in Stars of Different Spectral Types
    and Luminosities
Authors: Böhm-Vitense, E.
1966IAUTB..12..547B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Zur Interpretation der Geschwindigkeits- und
    Intensitätsvariationen der Linien von α<SUP>2</SUP>C Vn
Authors: Böhm-Vitense, E.
1966ZA.....64..326B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Differential Equation for the Solution of the Non-LTE Line
    Transfer Problem
Authors: Böhm-Vitense, E.
1965SAOSR.174..165B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: An Integral Equation for the Temperature Correction in a
    Nongray Atmosphere
Authors: Böhm-Vitense, E.
1964SAOSR.167...99B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Introductory Remarks
Authors: Böhm-Vitense, E.
1964SAOSR.167....3B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Spectrum of γ Pegasi Between 3300 and 3030 Å.
Authors: Böhm-Vitense, Erika; Pyper, Diane M.; Wallerstein, George
1964ApJ...140..807B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Correlation Between Metal Deficiency of Stars and Their
    Distance from the Galactic Plane.
Authors: Böhm-Vitense, Erika; Holweger, H.; Kohl, K.
1963ApJ...138..604B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the Beat Phenomenon in β Cephei Stars
Authors: Böhm-Vitense, Erika
1963PASP...75..154B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Berechnung der Temperaturschichtung nichtgrauer Atmosphären
    im Strahlungsgleichgewicht. Mit 3 Textabbildungen
Authors: Böhm-Vitense, E.
1963ZA.....57..241B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Interpretation der Phasenbeziehungen zwischen Geschwindigkeits-
    und Leuchtkraftkurve bei δ Cephei-Sternen. Mit 2 Textabbildungen
Authors: Böhm-Vitense, E.
1962ZA.....56...53B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Theory of the hydrogen convection zone
Authors: Böhm-Vitense, E.
1960IAUS...12..338B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Convection and granulation: Preview on granulation -
    Observational studies - Observations
Authors: Böhm-Vitense, E.
1960IAUS...12..330B    Altcode: 1960IAUS...12Q.....
  No abstract at ADS

---------------------------------------------------------
Title: Zur Interpretation des Intensitätsabfalls am äuβeren
    Sonnenrand. Mit 1 Textabbildung
Authors: Böhm, K. -H.; Böhm-Vitense, E.
1960ZA.....50...69B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Über die Spektren einiger Metalliniensterne. Mit 10
    Textabbildungen
Authors: Böhm-Vitense, E.
1960ZA.....49..243B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Über die Wasserstoffkonvektionszone in Sternen verschiedener
    Effektivtemperaturen und Leuchtkräfte. Mit 5 Textabbildungen
Authors: Böhm-Vitense, E.
1958ZA.....46..108B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Extragalactic Nebulae Close to the Galactic Plane
Authors: Böhm-Vitense, Erika
1956PASP...68..430B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Widths of the Lines of Fe, Si, o, and N in the Spectrum
    of Gamma Pegasi.
Authors: Böhm-Vitense, Erika; Struve, Otto
1956ApJ...123..228B    Altcode: 1956ApJ...123..228S
  The unblended lines of 011 and N II in Pegasi are systematically
  broader than those of Si Ir, Si III, Si Iv, and especially Fe III. This
  phenomenon is explained in terms of thermal motions of the atoms. But
  there remains a number of abnormally broad lines whose half-widths
  cannot be accounted for by the present theory.

---------------------------------------------------------
Title: Variations in the Spectrum of 89 Herculis
Authors: Böhm-Vitense, Erika
1956PASP...68...57B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Hydrogen in the Solar Chromosphere and Photosphere
Authors: Böhm-Vitense, Erika
1955PASP...67...21B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Die Sonnenchromosphäre. Mit 11 Textabbildungen
Authors: Böhm-Vitense, E.
1955ZA.....36..145B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Spectrum of Beta Lyrae.
Authors: Böhm-Vitense, Erika
1954ApJ...120..271B    Altcode:
  The B5 absorption component of p Lyrae shows rapid changes in radial
  velocity between successive cycles and also during a single cycle
  when the exposures are separated by 1 or 2 hours. The absorption line
  Fe 114351 yields an average rotational velocity of the order of 4( 50
  km/sec. This line appears to be slightly broader during the elongations
  than near secondary eclipse. If this difference in rotational broadening
  is attributed to the ellipticity of the B8 component, the resulting
  ratio of the axes should be somewhat less than the photometric value of
  1.33. From the weakening of the equivalent width of the same line at
  elongation, as compared to the equivalent width measured at secondary
  minimum, a value of approximately 20 per cent is obtained for the
  fraction of the light at maximum which is caused by the secondary
  component and the gaseous stream.

---------------------------------------------------------
Title: Über die Temperatur- und Druckschichtung der
    Sonnenatmosphäre. Mit 6 Textabbildungen
Authors: Böhm-Vitense, E.
1954ZA.....34..209B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Spectrum of Beta Lyrae
Authors: Vitense, Erika
1953PASP...65..206V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Die Wasserstoffkonvektionszone der Sonne. Mit 11
    Textabbildungen
Authors: Vitense, E.
1953ZA.....32..135V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Der Aufbau von Sternatmosphären : I. kontinuierliche
    Absorption und Streuung als Funktion von Druck und Temperatur;
    II. über die mittleren Zustandsgrößen und spektralen Eigenschaften
    von Sternatmosphären in Abhängigkeit von Effektivtemperatur und
Schwerebeschleunigung 

---------------------------------------------------------
Title: Der Aufbau von Sternatmosphären
: I. kontinuierliche Absorption und Streuung als Funktion von
    Druck und Temperatur; II. über die mittleren Zustandsgrößen und
    spektralen Eigenschaften von Sternatmosphären in Abhängigkeit von
Effektivtemperatur und Schwerebeschleunigung 

---------------------------------------------------------
Title: The structure
of stellar atmospheres : I. continuous absorption and scattering
    as a function of pressure and temperature; II. On the mean state
    variables and spectral properties of stellar atmospheres as a function
    of effective temperature and gravity acceleration;
Authors: Böhm-Vitense, Erika Helga Ruth
1951PhDT........70B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Der Aufbau der Sternatmosphären. IV. Teil. Kontinuierliche
    Absorption und Streuung als Funktion von Druck und Temperatur. Mit
    16 Textabbildungen
Authors: Vitense, Erika
1951ZA.....28...81V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Über die mittleren Zustandsgröβen und spektralen
    Eigenschaften von Sternatmosphären in Abhängigkeit von
    Effektivemperatur und Schwerebeschleunigung. Mit 13 Textabbildungen
Authors: Vitense, E.
1951ZA.....29...73V    Altcode:
  No abstract at ADS