Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/jwst/science/sodrm/highlightClusters.pdf Дата изменения: Unknown Дата индексирования: Tue Feb 5 05:12:08 2013 Кодировка: Поисковые слова: universe

NASA's James Webb Space Telescope:

Age Dating of Clusters
Age dating of globular star clusters has revealed t h e m t o b e a m o n g t h e o l d e s t o bj e c t s k n o w n in the Milky Way. As such, precision ages for these object s represent an impor t ant cons t r a in t o n w h e n b a r y o ni c s t r u c t u r e f o r m a t i o n began in the Universe. JWST's Near Infrared Camera ( N IRCam) and Near Infrared Imager and Slitless Spectrograph (NIRISS) will enable unprecedented observations of this population at much higher sensitivity and resolution than currently available. For a dozen star clusters, JWST will map the complete white dwarf cooling sequences of each system using a combination of red-optical and near-infrared imaging (e.g., F090W and F150W filters on NIRCam). The luminosity function of these white dwar fs offers a precise age diagnostic for each cluster, one that is independent of the uncertainties in main-sequence turnoff methods.

A simulated JWST/NIRCam image of a star cluster observed at 0.9 microns

How Blue Can JWST Go? Although JWST is an infrared-optimized observatory, the NIRCam instrument offers broadband imaging at 0.7 and 0.9 microns. The superb sensitivity and resolution will enable a wide range of stellar astrophysics studies at red-optical and near-IR wavelengths.

JWST's Near Infrared Camera (NIRCam)
Dual channel imager covering 0.6 ­ 5 microns 2.2' x 4.4' field of view Nyquist sampled imaging at 2 micron (0.0317"/pixel) 26 filters (narrow, medium, and wide band) S/N = 10 at K = 27.5 AB mag in 10 min


Precision White Dwar f Cooling Ages for a Dozen Globular Clusters
An HST Legacy ­ Precision Ages of Star Clusters
Ultra-deep HST/optical imaging of the three nearest globular clusters has resolved their complete white dwarf cooling sequences (faint blue populations). Modeling the color-magnitude diagrams provides accurate and (main sequence) independent ages for these fundamental calibrators.

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NIRCam imaging of globular clusters and other dense astrophysical environments will take advantage of the instrument's multiplexing capabilities. NIRCam is a dual channel imager covering 0.6 - 5 microns, with a large 2.2' x 4.4' field of view. The two channels provide simultaneous imaging at short (<2.5 microns; 0.0317"/pixel) and long (>2.5 microns; 0.0648"/pixel) wavelengths. These capabilities will enable the first characterization of the complete stellar populations in a dozen clusters, extending from the coolest main-sequence dwarfs, through the turnoff and post main-sequence phases, down to the faintest remnant white dwarfs. The colormagnitude diagrams of these systems represent a fundamental calibration for many astrophysical relations. They are the best test of stellar evolutionary processes and form a critical input for population synthesis studies that are aimed at interpreting light from the Universe. JWST's high-precision imaging will enable the most sensitive characterization of the color-magnitude diagram and its dependencies on age and metallicity. Cluster NGC 6121 NGC 6397 NGC 104 N GC 6 6 5 6 NGC 6752 N GC 6 8 3 8 NGC 6254 NGC 6218 NGC 3201 NGC 5139 N GC 6 8 0 9 (m-M) 11.7 11.8 13.2 12.5 13.0 13.0 13.2 13.5 13.5 13.6 13.6
0

A

F814W

Target WD (F814W ) 27.4 27.4 28.5 28.2 28.3 28.6 28.8 29.0 29.0 29.0 28.9

F 0 9 0W (hours) 1.0 1.0 6.9 4.0 4.9 8.3 12.5 17.2 17.2 17.2 14.4

F150W (hours) 1.5 1.5 10.6 6.1 7.4 12.6 18.3 26.4 26.4 26.4 21.9

0.54 0.27 0.06 0.53 0.06 0.37 0.41 0.28 0.34 0.18 0.12

See more at ht tp: // w w w.s t sci.edu / jws t and jwst.nasa.gov and do your own E TC calculations at jwstetc.stsci.edu/etc

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