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Kinematics and metallicities of globular clusters in M104
We have obtained spectra for globular cluster candidates in M104 withthe Low Dispersion Survey Spectrograph (LDSS-2) on the William HerschelTelescope, confirming 34 objects as M104 globular clusters. We find acluster velocity dispersion of ~260kms^-1, and the projected massestimator gives a mass of 5.0 (3.5,6.7)x10^11Msolar for M104 within aprojected radius of ~330arcsec (14kpc for D=8.55Mpc). Our best estimatefor the mass-to-light ratio is M/L_V_T=16^+5.5_-5.0 within the sameradius. Considering all of the possible sources of uncertainty, we finda lower limit of M/L_V=5.3, which is larger than the M/L_V ratio foundfrom rotation curve analyses inside 180arcsec. We thus conclude that themass-to-light ratio increases with radius, or in other words that M104possesses a dark matter halo. There is a marginal detection of rotationin the M104 cluster system at the 92.5 per cent confidence level; largersamples will be needed to investigate this possibility. Interestingly,the M104 globular cluster and planetary nebulae (PNe) kinematics areroughly consistent inside ~100arcsec. Finally, we find a mean clustermetallicity of [Fe/H]=-0.70+/-0.3, which is more typical of clusters ingiant elliptical (gE)/cD galaxies than it is of clusters in otherspirals.
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
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Osservazione e dati astrometrici
| Costellazione: | Fenice |
| Ascensione retta: | 00h06m27.52s |
| Declinazione: | -52°55'59.3" |
| Magnitudine apparente: | 9.008 |
| Moto proprio RA: | 9.9 |
| Moto proprio Dec: | -1.4 |
| B-T magnitude: | 10.826 |
| V-T magnitude: | 9.159 |
Cataloghi e designazioni:
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