Standard calibration observations are obtained and maintained in the HST archive at the STScI, and can be retrieved by external users using StarView. ... For WFPC2, the inherent stability and uniformity of the CCD sensors, the well-calibrated filters, the internal flat field calibration system, and an archive populated with flat field images obtained in SLTV prior to launch improve the scientific data analysis and productivity. Hence the need for on-orbit calibrations has been minimized. ...

... Stellar Evolution is driven entirely by the never ending battle between Pressure and Gravity . As imbalances are reached, the star is driven to find a new Energy source. ... Pressure and gravitational forces are equal, the star is stable and its core is sufficiently hot to fuse Hydrogen into Helium More about main sequence stars . ... The luminosity generated by the core fusion of Helium into Carbon is far greater than the shell luminosity associated with the fusion of Hydrogen into Helium. ...

... Classes . ... casa::Aberration . ... More... #include < Aberration.h > . ... Aberration (const Aberration &other) . ... operator() ( Double epoch) . ... Actual Aberration for a certain Epoch is calculated by the () operator as Aberration(epoch), with epoch Double MJD, values returned as an MVPosition . ... Double casa::Aberration::aval [3] [private] . ... Double casa::Aberration::checkEpoch [private] . ... Double casa::Aberration::dval [3] [private] . ... const Double casa::Aberration::INTV [static]...

... Updates to HST Standard-Star Fluxes . ... These data are in an STScI data base named CRCALSPEC and have been divided into two categories to help the user understand the origin and accuracy of these flux distributions. ... 1990, ApJS, 73, 413) and Oke (1990, AJ, 99, 1621) spectra are available. Oke (1990) used the DoubleSpectrograph on the 5-m Hale Telescope to obtain these spectra for HST calibration; and these data are identified in the HST data bases by the keyword OBSMODE=OKE DBSP. ...

... Canadian Astronomy Data Center, DAO/NRC . SkyCat is a tool that combines image visualization with access to astronomical catalogs and data archives. SkyCat uses a standardized URL syntax to access a large number of data sources on the net. ... More information on SkyCat can be found at the SkyCat Web site. The ESO SkyCat Tool includes the following features: . ... PostScript color printing of the display (image + graphics), . ... overlay catalog sources on an image, . ...