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Radial Velocities for 889 Late-Type Stars

A Strategy for Identifying the Grid Stars for the Space Interferometry Mission
We present a strategy to identify several thousand stars that areastrometrically stable at the microarcsecond level for use in the SpaceInterferometry Mission (SIM) astrometric grid. The requirements on thegrid stars make this a rather challenging task. Taking a variety ofconsiderations into account, we argue for K giants as the best type ofstars for the grid, mainly because they can be located at much largerdistances than any other type of star owing to their intrinsicbrightness. We show that it is possible to identify suitable candidategrid K giants from existing astrometric catalogs. However, double starshave to be eliminated from these candidate grid samples, since theygenerally produce much larger astrometric jitter than tolerable for thegrid. The most efficient way to achieve this is probably by means of aradial velocity survey. To demonstrate the feasibility of this approach,we repeatedly measured the radial velocities for a preselected sample of86 nearby Hipparcos K giants with precisions of 5-8 m s-1.The distribution of the intrinsic radial velocity variations for thebona fide single K giants shows a maximum around 20 m s-1,which is small enough not to severely affect the identification ofstellar companions around other K giants. We use the results of ourobservations as input parameters for Monte Carlo simulations on thepossible design of a radial velocity survey of all grid stars. Ourfavored scenario would result in a grid which consists to 68% of truesingle stars and to 32% of double or multiple stars with periods mostlylarger than 200 years, but only 3.6% of all grid stars would displayastrometric jitter larger than 1 μas. This contamination level isprobably tolerable.


CCD observations of the H-alpha line in late G and K supergiants and their interpretation
CCD echelle spectra of the H-alpha line at 6563 A have been obtained fora sample of 30 G and K supergiants with a spectral resolution of about0.24 A. The data clearly indicate that the observed H-alpha profile is adeep absorption, implying large optical depths in the chromosphere.Also, the line cores are blueshifted in all the stars which suggests thechromospheres are expanding outward. Detailed radiative transfercalculations of H-alpha have been carried out in a spherically symmetricatmosphere with outward-positive velocity and temperature gradients,including explicitly the effects of ionization. The H-alpha lineprofiles have been computed for a wide range of parameters in order toreproduce the observed features of the line. Within the framework of ourmodel, the calculations reinforce the idea that the nonthermalvelocities have to be as large as 25-30 km/s to explain the large widthsof the observed profiles. The rates of mass outflow have been calculatedto lie in the range 10 exp -8 to 10 exp -9 solar mass/yr.



Role of nonthermal velocity fields in determining the H-alpha widths in supergiant chromospheres
Radiative transfer calculations of the H-alpha line in sphericallysymmetric, expanding chromospheres explain the large widths of the lineobserved in late G and K supergiants. The role of various dynamicalprocesses as well as that of opacity in determining the H-alpha width isillustrated. The H-alpha line profile is basically characterized bylarge optical depths and large Doppler broadening velocity. Thecalculations show that the existence of large microturbulence has to beinvoked in the chromosphere to understand the observed widths.

Mass-losing M supergiants in the solar neighborhood
A list of the 21 mass-losing red supergiants (20 M type, one G type; Lgreater than 100,000 solar luminosities) within 2.5 kpc of the sun iscompiled. These supergiants are highly evolved descendants ofmain-sequence stars with initial masses larger than 20 solar masses. Thesurface density is between about 1 and 2/sq kpc. As found previously,these stars are much less concentrated toward the Galactic center thanW-R stars, which are also highly evolved massive stars. Although withconsiderable uncertainty, it is estimated that the mass return by the Msupergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpcyr. In the hemisphere facing the Galactic center there is much less massloss from M supergiants than from W-R stars, but, in the anticenterdirection, the M supergiants return more mass than do the W-R stars. Theduration of the M supergiant phase appears to be between 200,000 and400,000 yr. During this phase, a star of initially at least 20 solarmasses returns perhaps 3-10 solar masses into the interstellar medium.

Near-IR features in late type stars - Their relation with stellar atmosphere parameters
CCD spectroscopic observations for a sample of 106 late type stars plusthree galactic globular clusters in the near-IR are presented. The mostprominent features in that spectral region, the IR Ca-II triplet (8498,8542, 8662A) and the Mg-I line at 8807 A, are measured and theirdependence on the stellar atmosphere parameters (surface gravity,effective temperature and metal content) is analyzed. In agreement withwhat is found in previous studies, the Ca-II triplet strength showsbiparametrical behavior with surface gravity and metal abundance. The IRMg-I line strength is also biparametric, depending mainly on metalabundance and effective temperature. Principal component analysistechniques allow the prediction of the metal abundance and surfacegravity as a function of three observables: the IR Ca-II tripletstrength, the strength of the IR Mg-I line and the (R-I) color.

Supergiants and the Galactic metallicity gradient. II - Spectroscopic abundances for 64 distant F- to M-type supergiants
The metallicity gradient in the Galactic disk from in situ stars withvisual magnitude ranging from 6 to 10 is analyzed. Atmosphericparameters and detailed chemical abundances for 64 Population Isupergiants of spectral types F through M and luminosity classes Iathrough II have been determined. The derived Fe/H ratios ranging from-0.5 to + 0.7 show a mean value of +0.13 with an estimated uncertaintyof + or - 0.2. A subset of 25 supergiants fainter than 7th magnitudelying in the direction of the Galactic center shows a Fe/H mean of +0.18+ or - 0.04, while a similar sample of 15 faint supergiants lying in thedirection of the Galactic anticenter shows a lower Fe/H mean of +0.07 +or - 0.06. For a sample of bright supergiants analyzed by Luck andLambert (1985), the mean abundance pattern for all 64 stars showed thefollowing: deficient C and O along with enhancement of N, indicatingmixing of CNO-cycled material to the stellar surfaces; an apparent Srenhancement attributed to departures from LTE; and an essentially solarpattern of other chemical elements.

A search for lithium-rich giant stars

Consequences of a chromospheric temperature rise on the formation of the H-alpha line in late-type supergiants
Computations of the H-alpha line profiles were performed in a non-LTEmoving chromosphere with temperature rise to simulate the observedH-alpha characteristics in G and K supergiants. The comoving frameradiative transfer code was modified to incorporate explicitly theeffects of hydrogen ionization. The sensitivity of H-alpha profiles to avariety of temperature structures, velocity gradients, and chromosphericextents and densities is examined and illustrated. Comparison of theobserved profiles to computed ones gives total hydrogen densities in therange between 10 to the 9th and 10 to the 11th/cu cm at the base of theline forming region. Integrated chromospheric optical depths in therange of 50-5000 and expansion velocities in the range of 0.25-2 timesthe maximum random (microturbent and thermal) velocity are found. Themass loss rate is inferred to be in the range between 10 to the -7th and10 to the -9th solar masses/year.

Concentrations in the local association. III - Late-type bright giants, ages and abundances
Late-type, bright giants and supergiants in southern and northernconcentrations and in the general field, the ages of the stars fromstellar models, and the abundances, based on intermediate bandphotometric indices, are investigated. It is found that the brightgiants and supergiants of types F to K among association members in theconcentrations and in the general field are overabundant in metals, withP(Fe/H) approximately equal to 0.25. These bright giants, and theearly-type association members brighter than about M(V) = -1 mag (mode Bstars), are determined to be younger than 5-6 x 10 to the 7th yr. Thefainter (mode A) main-sequence members of the association are shown tobe near 2 x 10 to the 8th yr with P(Fe/H) approximately equal to 0.

New UBVRI photometry for 900 supergiants

The reddening, metal abundance, and luminosity of high-luminosity G-type stars
The abundance parameters of the sample of 100 G-type bright giants andsupergiants whose photometry is presently discussed indicate Fe/H valuesof between about + 0.6 dex and the solar value, using a preliminarycalibration of the photometric indices. The few long period Cepheidsthat are not heavily blanketed F-type stars give reddening values thatare in agreement with current results from other methods of analysis.Supergiants show no clear gradients in the galactic distribution ofabundances, and those nearest the sun range from an Fe/H of about + 0.3dex, for members of the Pleiades Group, to near solar abundance. A smallsample of Large Magellanic Cloud supergiants shows nearly the same rangein metal abundance as the galactic stars, and gives a modulus for thisCloud of 18.3 + or - 0.20 mag.

Nineteen new spectroscopic binaries and the rate of binary stars among F-M supergiants
Nineteen spectroscopic binaries (SBs) have been discovered in radialvelocity measurements made with the CORAVEL spectrophotometer on 181northern F-M supergiants. The rate of detected SBs among northern F-Msupergiants is 21 percent, without any dependence on spectral orluminosity class. The study of the binary F-M supergiants with knownorbital elements indicates that all the systems with a period smallerthan the critical value P(circ) have a nearly circular orbit. The valueof P(circ) depends on the luminosity class, being 400-600 d for class Iband 2000-7000 d for class Ia. This circularization of the orbits may bedue to the transfer of angular momentum during the phase of binary massexchange.

Supergiants and the galactic metallicity gradient. I - 27 late-type supergiants in the inner-arm regions
From an analysis of high-dispersion Kitt Peak echelle data, atmosphericparameters and chemical abundances have been derived for 27 supergiantsof spectral type F through M. Since the stars studied lie within about 1kpc of the sun, their abundances will form the local reference point forextensions of this study to larger distances. The derived Fe/H abundanceratios range from minus 0.6 to plus 0.1 dex, show a mean value of -0.15dex, and have an internal uncertainty of plus or minus 0.2 dex.

Standard Stars for Hα Photometry

On some extreme metal-deficient giants
Attention is given to the temperatures, metallicities, and colorexcesses of five giants with extreme metal deficiency. Observations withthe Vilnius photometric system, after correction for interstellarreddening, yield the following Fe/H abundance ratios: -3.0 for BD -18deg 5550 and HD 4306; -2.8 for CD -25 deg 13871 and HD 115444; and -2.6for HD 126587. Their effective temperatures are found to be within4800-4950 K.

Finding list and spectral classifications for southern luminous stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976AJ.....81..225M&db_key=AST


The space distribution and kinematics of supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..602H&db_key=AST

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Observation and Astrometry data

Right ascension:18h54m00.10s
Apparent magnitude:5.69
Distance:531.915 parsecs
Proper motion RA:3.1
Proper motion Dec:-19.4
B-T magnitude:7.254
V-T magnitude:5.815

Catalogs and designations:
Proper Names   (Edit)
Flamsteed33 Sgr
HD 1989HD 174947
TYCHO-2 2000TYC 6293-2525-1
USNO-A2.0USNO-A2 0675-30490574
BSC 1991HR 7114
HIPHIP 92747

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