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Spectroscopy of candidate young globular clusters in NGC 1275
We present spectra of the brightest member of the population of compactblue objects discovered in the peculiar galaxy NGC 1275 by Holtzman etal. (1992) using Hubble Space Telescope images. These spectra showstrong Balmer absorption lines like those observed in A-type stars, asexpected if the object is a young globular cluster. The age estimatedfrom the strength of the Balmer lines is about 0.5 Gyr, although agesranging from 0.1 Gyr to 0.9 Gyr cannot be confidently excluded givencurrent models of stellar populations. If these estimated ages areadopted for the young cluster population of NGC 1275 as a whole, thefading predicted by stellar populations models gives a luminosityfunction which is consistent with that of the Galactic globular clustersystem convolved with the observational selection function for the NGC1275 system. We also use the equivalent widths of the Mg b and Fe 5270features to constrain the metallicity of the young cluster. Combiningthese absorption-line widths with the age estimates from the Balmerlines and stellar population models, we find a metallicity of roughlysolar, based on the Mg b index, and somewhat higher for the Fe 5270index. The radial velocity of the absorption lines of the clusterspectrum is offset from the emission lines of the galaxy spectrum at thesame position by - 130 km/s, providing further evidence for theidentification of the object as a global cluster and opening up thefuture possibility of studying the kinematics of young cluster systems.The discovery of objects with the characteristics of young globularclusters in NGC 1275, which shows evidence of a recent interaction ormerger, supports the hypothesis that galaxy interactions and mergers arefavorable sites for the formation of globular clusters.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Bika |
| Rektaszcenzió: | 04h12m47.86s |
| Deklináció: | +20°44'06.7" |
| Vizuális fényesség: | 9.118 |
| RA sajátmozgás: | 15.4 |
| Dec sajátmozgás: | -22.2 |
| B-T magnitude: | 9.707 |
| V-T magnitude: | 9.167 |
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