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The ACS Virgo Cluster Survey. VII. Resolving the Connection between Globular Clusters and Ultracompact Dwarf Galaxies
NO>1Based on observations with the NASA/ESA Hubble Space Telescopeobtained at the Space Telescope Science Institute, which is operated bythe association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Rotational Brightness Modulation and Starspots on the RS CVn-type Stars IN Com, IL Com, UX Ari, and V711 Tau
UBVRI photometric observations and models of spotting are presented forfour noneclipsing RS CVn systems: IN Com (G5III/IV), IL Com (F8V+F8V),UX Ari (K01V+G5V), and V711 Tau (K1IV+G5V). A low amplitude variabilitycaused by cold (T=1700K)spots which can occupy up to 19% of the star''ssurface is confirmed for the little-studied star IL Com. Long-term lightcurves are constructed and the stellar magnitudes and color indices ofthe unspotted photospheres are estimated for IN com, UX Ari, and V711Tau. It is shown that UX Ari becomes bluer with decreasing brightness,so its variability cannot be fully explained in terms of cold spots.Models of spotting on In Com and V711 Tau are constructed from the fullset of available photometric observations. The spots on both of thesevariables lie at middle latitudes and occupy up to 22% (In Com) and 33%(V711 Tau) of the stars'' surfaces. Both stars manifest a tendency forthe width of the spots to decrease as their area increases. This is acrude analog of the Maunder butterflies. These stars experience cyclicalspot activity and have a differential rotation of the type found on thesun.
| Ages and metallicities of globular clusters in NGC 4472
We have derived ages and metallicities from co-added spectra of 131globular clusters associated with the giant elliptical galaxy NGC 4472.Based upon a calibration with Galactic globular clusters, we find thatour sample of globular clusters in NGC 4472 span a metallicity range ofapproximately -1.6<=[Fe/H]<=0dex. There is evidence of a radialmetallicity gradient in the globular cluster system which is steeperthan that seen in the underlying starlight. Determination of theabsolute ages of the globular clusters is uncertain, but formally, themetal-poor population of globular clusters has an age of 14.5+/-4Gyr andthe metal-rich population is 13.8+/-6Gyr old. Monte Carlo simulationsindicate that the globular cluster populations present in these data areolder than 6Gyr at the 95per cent confidence level. We find that withinthe uncertainties, the globular clusters are old and coeval, implyingthat the bimodality seen in the broadband colours primarily reflectsmetallicity and not age differences.
| Three-colour Photometry of IN Comae
Not Available
| Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Lithium in the low-mass stars of the Coma Berenices open cluster
I report lithium abundances and radial velocities for 15 late F, G and Kstars in the Coma Berenices open cluster. All the stars are propermotion members, and the radial velocities enable us to confirmmembership for 11 single stars and identify three SB1 systems and oneshort-period SB2 system that are very probable cluster members. Thepattern of Li abundances is similar to that in the Hyades, with someevidence for higher Li abundances in Coma Ber for T_eff<5700 K. Iargue that these data do not support standard models for Li depletioninvolving only convective mixing, because the Coma Ber stars haveconsistently determined lower metallicities and shallower convectionzones than the Hyades and should have suffered a great deal less Lidepletion than observed. Instead, it seems that the Li abundances inthese and other young clusters are primarily ranked according to theirage rather than their metallicity. I propose a scenario where theextreme metallicity dependence of pre-main-sequence Li depletion istempered by a mechanism that severely inhibits convective mixing, wherecontinued main-sequence depletion occurs via non-standard mixingmechanisms, and where any dependence of Li depletion on metallicitytakes at least several hundred Myr to emerge.
| Membership and lithium abundances of late-type stars in NGC 6633
NGC 6633 is a young, open cluster with a similar age to the Hyades andPraesepe but lower metallicity. Using a new photometric survey andproper-motion information, a sample of candidate members of NGC 6633have been observed spectroscopically. Radial velocities are used toconfirm membership for 21 late-type stars including two spectroscopicbinaries. By combining the spectroscopy with existing UBV photometry, itis shown that NGC 6633 has a significantly lower metallicity than theHyades but not much lower than M/H = 0.0. The projected equatorialvelocities of the cluster members are compared with Hyades rotation dataand found to be consistent. The lithium abundances are indistinguishablefrom those in the Hyades for F stars but show a different pattern ofdepletion in the cooler stars that can be qualitatively attributed tothe lower metallicity. Comparison with younger Pleiades cool stars,which have a similar metallicity to NGC 6633, shows that Li depletionapparently occurs in G and K stars while they are on the main sequence.Standard models, incorporating only convective mixing, underpredict thedepletion in both the Hyades and NGC 6633, but match the lower envelopeof the Pleiades distribution. These data argue strongly against enhancedinterior opacities as a way of increasing Li depletion in the standardmodels, and instead point to extra mixing mechanisms on the mainsequence combined with a rotation-dependent Li depletion inhibitionprocess acting during pre-main-sequence evolution.
| A sample of galaxy clusters to study the fundamental plane: Redshift measurements
We present the results of spectroscopic observations of galaxies in asample of nearby clusters. We measured galaxy redshifts and estimatedcluster velocity dispersions. These observations were carried out at theObservatoire de Haute Provence as part of a program aiming at a moredetailed study of the Cluster Fundamental Plane. Based on observationsmade at Haute-Provence Observatory, CNRS, France.
| Doppler imaging of stellar surface structure. IV. The rapidly-rotating G5III-IV star HD 112313 = IN Comae.
We present the first Doppler image of the rapidly-rotating G5 giant inthe unusual IN Comae triple system. Our average image from threespectral regions and two continuum color indices shows mostly low tohigh latitude features but not a prominent polar cap-like spot. Aparameter study of the stellar and atomic input quantities aims tobetter quantify the reliability of our Doppler image. A time series of330 high-precision Stroemgren by and Johnson V measurements in 1996 showonly one real photometric period (5.913+/-0.005days) that we interpretto be the rotation period of the G5 giant. We found no evidence for the0.25-day period claimed earlier by Kuczawska & Mikolajewski(1993AcA....43..445K). Optical spectra of several activity indicatorsare presented and discussed. IN Comae exhibits an unusual broad Hαemission line and a central absorption feature. This profile shape isalso seen for the CaII infrared-triplet lines as well as for the sodiumdoublet and the HeI D_3_ line. No LiI 6707.8 line is present. New radialvelocity measurements from our red-wavelength spectra do not indicate ashort-period binary but would be consistent with the G5 star being theouter, third component of this triple system.
| Spectroscopic Orbits for Three Binaries with Low-Mass Companions and the Distribution of Secondary Masses near the Substellar Limit
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...466..415M&db_key=AST
| Nine Seasons of Velocity Measurements in the Draco and Ursa Minor Dwarf Spheroidal Galaxies with the MMT Echelle
We have used the Multiple Mirror Telescope echelle spectrograph tomeasure 112 velocities of 42 stars in the Draco and Ursa Minor dwarfspheroidal galaxies and three velocities of three foreground starsbetween 1982 April and 1990 September. We used 11 A resolution spectraobtained with the MX multifiber spectrograph at the Steward 90" to findadditional giant candidates; 5 UMi and 13 Draco stars were then observedat the MMT and added to the original sample of velocity members. Inaddition, the MX spectra were used to eliminate 74 stars in thedirection of UMI and 59 stars in Draco as likely foreground dwarfs. Wedetected 7 velocity variables, defined as those stars whose probabilityof exceeding the measured X^2^ by chance is less than 1.5%. Three ofthese stars are Carbon (C) stars (UMi K and VA 335 and Draco C1); twohave emission lines (Draco CI and UMi M). We show that the C star DracoC4, with a proper motion membership probability of 7%, has a velocityconsistent with membership. It is not surprising that these C (mostlikely CH) stars are binaries because McClure has shown that mostGalactic CH stars are in binary systems. Of the remaining 35 stars, only4 are velocity variables, with measured velocity extrema of 29.1 kms^-1^ (UMi M), 7.2 km s^-1^ (Draco XI-2), 9.0 km s^-1^ (Draco 24), and8.3 km s^-1^ (Draco 473). The velocity dispersions are 10.1 +/- 1.7 kms^-1^ for UMi, and 9.9 +/- 1.4 km s^-1^ for Draco. These dispersionschange to 10.5 +/- 2.0 for UMi, and 8.2 +?- 1.3 for Draco if weeliminate the velocity variables. Our dispersion for UMi differs fromthat of Hargreaves et al. [MNRAS, 271,693 (1994b)] by 1.3σ of thecombined errors. These velocities are combined with the one-componentKing models of Pryor & Kormendy [AJ, 100,127 (1990)] to give M/L =73 for UMi, and 77 for Draco.
| Abundances and velocities for open and globular cluster giants: The data.
We present a large dataset consisting of giants in the field, and inopen and globular clusters. A total of 122 giants were observed in thefields of 8 open clusters. A total of 342 giants were observed in thefields of 25 globular clusters. A total of 36 field stars with wellknown abundances and luminosities were also observed. Radial velocitiesare determined for most giants, some of which have no photometryavailable. We have analyzed several spectral features in order to definea grid that will allow the determination of metal abundances for haloand bulge giants. The errors involved in the determination of radialvelocities and [Fe/H] are carefully examined. We find that field andopen cluster stars on one side, and globular cluster giants on the otherside, do not follow the same calibration. This is possibly due toenhanced [α/Fe] abundances in globular clusters. Therefore, wehave defined a calibration based only on globular cluster giants, validfrom [Fe/H]=-2.0 to +0.5. This calibration is carried out with thepurpose of measuring metallicities for bulge and halo giants, with theunderlying assumption that the abundance ratios of the relevant elementsrelative to iron are similar to the calibrating stars. Adopting asstandards the globular clusters NGC 288, NGC 362, NGC 1851, NGC 6356,NGC 6624, 47 Tuc, M 4 , M 3, and M 22 we derive metallicities forglobular clusters with less well known compositions, like M 28, and NGC6637. In particular, we confirm a low metallicity for M 28([Fe/H]=-1.35+/-0.2), a cluster that has a disk orbit.
| Internal kinematics of the Leo II dwarf spherodial galaxy
We have obtained radial velocities of 31 red giants in the Leo II dwarfspheroidal (dSph) galaxy using the HIRES echelle spectrograph of theKeck 10 m telescope. These stars were selected using CCD photometryobtained with the Palomar 1.5 m telescope. The radial velocity of errorswere determined from repeat measurements of Leo II giants and faintradial velocity standards; the average error for the Leo II giants is2.4 km/s. The systemic velocity of Leo II is 76.0 +/- 1.3 km/s, and thevelocity dispersion is 6.7 +/- 1.1 km/s. Adopting the standardassumptions (mass follows light, isotropy, and equilibrium) we derive aglobal V-band mass-to-light ratio (Msub tot)/Ltot = 11.1 +/-3.8, and a central value rho0/I0 = 11.6 +/- 3.2(both in solar units). These values are larger than the M/L ratiosmeasured for local stellar populations (star clusters or the solarneighborhood). Monte Carlo simulations show that a large population ofbinaries probably has not inflated a small intrinsic velocity dispersionto the observed value. A model-independent lower limit of the centralmass density of Leo II yeilds rho0,min = solar masspc-3, larger than the central luminous mass density in Leo IIfor (M/L)lum = 2.2. This demands an extensive dark halo inthe outer regions of the galaxy to account for the observed dispersion.We conclude that Leo II contains a significant dark matter component.The total mass of the dark halo is 0.9X177 solar mass,consistent with the masses inferred in all well-studied dSph galaxies.Because it is remote from the Galaxy, tide cannot plausibly affect thevelocity dispersion of Leo II. However, we cannot use these results torule out the possibility that tides may influence the kinematics ofother dSph galaxies found closer to the Milky Way.
| The metallicities and kinematics of RR Lyrae variables, 1: New observations of local stars
In order to study the structure and formation history of the galaxy, wehave obtained low-to-moderate dispersion spectra of 302 nearby RR Lyraevariables of Bailey type 'ab'. We derived abundances, typically accurateto 0.15-0.20 dex and calibrated to the Zinn & West (1984) globularcluster metallicity scale, from the pseudoequivalent widths of the Ca IIK, H delta, H gamma, and H beta lines. Radial velocities accurate tobetween 2 and 30 km/s were obtained from the spectra and from theliterature. Distances accurate to between 5% and 20% were derived frompublished apparent magnitudes and Burstein & Heiles (1982)reddenings. The metallicity distribution of the RR Lyrae stars peaks at(Fe/H)K approximately equals -1.5, and is narrower than thatof the Ryan & Norris (1991) subdwarfs, as expected since the mostmetal-rich and metal-poor progenitors preferentially appear as stablered and blue horizontal branch stars, rather than as RR Lyrae. Themetal-rich tail of the RR Lyrae distribution extends to(Fe/H)K approximately equals 0, and a qualitative analysis ofthe distribution of distances from the galactic plane shows that thestars in this tail (i.e., (Fe/H)K greater than -1.0) are moreconcentrated to the plane than the more metal-poor stars. The abundancedistribution of the local RR Lyrae stars is in excellent agreement withthe changing abundance distributions of distant RR Lyrae stars as afunction of galactocentric distance, as derived by Suntzeff et al.(1991), who ascribed this change to systematic variation in horizontalbranch morphology (probably age variations) with galactocentricdistance. The abundance distribution of the local RR Lyrae stars alsoagrees well with those of the distant RR Lyrae stars as a function ofdistance from the galactic plane. There is no evidence for an abundancegradient in this direction, suggesting that gaseous dissipation did notplay a major role in the formation of the outer halo.
| A radial velocity survey of the open cluster IC 4665
A radial velocity survey of the open cluster IC 4665 is reported for agroup of candidate members previously identified on the basis of propermotion and photometry. Of those candidates observed, 20 out of 42 haveradial velocities consistent with membership; these cluster memberspopulate the F5-K0 dwarf region and represent the first relativelyconclusive membership determinations for such solar-type stars in IC4665. Three new spectroscopic binary members of the cluster have beenidentified. Rotational velocities have also been derived; the v sin idistribution among IC 4665 members reveals that most apparent G dwarfmembers of IC 4665 are seen to exhibit substantial rotation (v sin igreater than 10 km/s). When compared to evolutionary isochrones, thecurrent list of intermediate-mass members appears to support earliersuggestions that IC 4665 has an age comparable to the Pleiades.
| The central star of planetary nebula LT-5 - A triple system
IN Com, the central star of the planetary nebula LT-5, is concluded tobe a triple system as a result of photometric and spectroscopicexamination. Data from UBV photometric and high-dispersion spectroscopicstudies conducted between 1984 and 1989 are analyzed by means of a lightcurve and radial velocity studies. The radial velocity studies show thata single-lined binary with a period of 1.7545 days comprises the innersystem. Further analysis reveals that it is an evolved G-type star withan active chromosphere. The G star has a low-mass companion, and thethird body is a hot subdwarf that excites the surrounding planetarynebula. A change in the observed systemic velocities with a period ofapproximately 2000 days points toward the existence of the third body.Photospheric and chromospheric disturbances on the surface of the G staraccount for the changeable period of light variance on the central star.The masses of all the components are calculated, and the rotationalvelocity of the primary component and the orbital inclination of theinner system are determined. The statistical relation between distanceand apparent diameter for nebulae of this type suggests that thedistance d = 100-170 pc is accurate.
| Fe/H, age and distance for the F-stars of an unbiased radial velocity sample at the north Galactic pole
New limits for the normalization of stellar populations of the solarneighborhood have been suggested by Sandage and Fouts (1987). Log T(e),M(V), Fe/H abundance ratio, age A, distance and color excess arepresented for 183 stars of Sandage and Fouts' unbiased radial velocitysample located near the north Galactic pole.
| Velocities of stars in remote Galactic satellites and the mass of the Galaxy
Observations of the two most distant known dwarf spheroidal Galacticsatellites, Leo I and II, and of two remote globular clusters, Eridanusand Pal 14, are presented. It is demonstrated that etalon spectra can beused for accurate wavelength calibration across the entire observedspectral range. Measured velocities of three stars in Eridanus, twostars in Pal 14, six stars in Leo I, and five stars in Leo II are usedto derive that the heliocentric systemic velocities of these systems are- 21 + or - 4, 72 + or - 4, 285 + or - 3, and 70 + or - 4 km/s,respectively. The value of the velocity for Leo I is in significantdisagreement with previously published values. Timing arguments are usedto estimate that the mass of the Galaxy is at least 13 x 10 to the 11thsolar. This value is valid only if Leo I is gravitationally bound to theGalaxy, and arguments supporting this assumption are presented.
| Periodicity of the light variability of In COM - The peculiar central star of the planetary nebula LT5
Photoelectric UBV observations of IN Com in 1987-1988 have confirmed theperiodic light variations observed by Schnell and Purgathofer (1983). AFourier analysis of the 1983 and 1987-1988 observations led to the bestperiod of 5.9522d. It is suggested that the observed periodicity may becaused by the reflection effect in a binary system or by the axialrotation of a G star with a long-lived spot or group of spots.
| Blue stragglers and the binary hypothesis
An observational test of the binary hypothesis for the origin of bluestraggler stars is conducted by searching for radial velocity variablesamong 30 blue stragglers in several galactic clusters. Only one of theslowly rotating blue stragglers is detected as a radial velocityvariable, and it is shown that this finding does not correspond to theclose binary model at the 99 percent confidence level. It is concludedthat binarity is almost certainly not a causal requirement for any bluestraggler. The results are compared to the binary distribution expectedunder the model of Collier and Jenkins (1984).
| Spectroscopy of V471 Tau. I - Review of basic properties
Spectroscopic observations of the eclipsing binary V471 Tau are reportedand analyzed. Data obtained mainly in the red band at Mt. WilsonObservatory and KPNO during the period 1975-1983 are compiled inextensive tables and graphs, and the radial velocity of the K dwarfcomponent is determined using a Griffin-mask technique. Resultsdiscussed include: (1) distance 44 + or - 6 pc, (consistent withmembership in the Hyades), (2) apparent period variation consistent witha third component, (3) emissionlike features affecting theradial-velocity determination, (4) transient features consistent withthe presence of flares, and (5) phase-coherent variation in H-alpha(attributed to the action of the white-dwarf Lyman continuum emission onthe K dwarf).
| The visually brightest early-type supergiants in the spiral galaxies NGC 2403, M81, and M101
Moderate-resolution spectroscopy of the candidate brightest blue starsin the nearby spirals NGC 2403, M81, and M101 reveals that many are notsingle stars, but compact H II regions, clusters, and multiple systems.This is an additional and serious limitation on their use as distanceindicators. The derivation of the luminosities of the confirmed singleblue supergiants is discussed, and, combining these results withprevious work on the brightest red supergiants, a brief discussion andcomparison of the evolution of their most massive stars are given. Theproperties of the brightest blue and red stars in NGC 2403 and M81 arebasically in agreement with the pattern of massive-star evolutionobserved in Local Group galaxies. The distance to M101 is stillcontroversial, but at the larger distance modulus, the luminosities ofits brightest early and late-type supergiants place them beyond theEddington limit for their initial mass and temperature.
| U, V, W velocity components for the old disk using radial velocities of 1295 stars in the three cardinal Galactic directions
New radial velocities are presented for 1295 stars chosen at random nearthe three cardinal Galactic directions of l = 180 deg, b = 0; l = 90deg, b = 0 deg; and b = 90 deg, giving the distribution in U, V, and W,respectively, from the radial velocities alone. The measurements weremade with the coude spectrograph of the Mount Wilson 100 in. Hookerreflector. The purpose of the program is to set limits on the densitynormalization in the solar neighborhood of the old thin disk, the oldthick disk, and the halo. Many more high-velocity stars are present inthe unbiased sample than expected from previous estimates of thenormalization. The data suggest the density ratios in the solarneighborhood to be about 90 percent, 10 percent, and about 0.5 percentfor the thin disk, thick disk, and halo populations, respectively.
| Standard Velocity Stars
Not Available
| C1 - A white-dwarf-red-dwarf spectroscopic binary
Emission lines in the spectrum of the DA white dwarf star C1 indicatedthe existence of an unresolved companion, whose spectral type wasdetermined to be approximately dM2. A radial-velocity curve for eachstar was obtained by observing the H-alpha emission line of itscompanion, and by considering the average difference between measuredand standard velocities for each star. The proper motion of C1 issimilar in magnitude to that of the Ursa Major cluster but in the wrongdirection. A lower limit for the mass of the white dwarf component iscomputed by assuming that the M dwarf is a normal main sequence star.The system shows similarities to post-common-envelope binaries.
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Three - a Catalogue of Star Names and Positions
Not Available
| The establishment of 21 new ninth magnitude IAU standard radial velocity stars
Not Available
| Colors, luminosities, and motions of the nearer G-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1964AJ.....69..570E&db_key=AST
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Dades d'Observació i Astrometria
| Constel·lació: | Coma Berenices |
| Ascensió Recta: | 12h55m28.27s |
| Declinació: | +25°44'17.0" |
| Magnitud Aparent: | 8.402 |
| Distancia: | 64.103 parsecs |
| Moviment propi RA: | 35.3 |
| Moviment propi Dec: | -119.8 |
| B-T magnitude: | 9.075 |
| V-T magnitude: | 8.458 |
Catàlegs i designacions:
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INHABITED SKY
