The CALSPEC Stars P177D and P330E

Multicolor photometric data are presented for the CALSPEC stars P177D and P330E. Together with previously published photometry for nine other CALSPEC standards, the photometric observations and synthetic photometry from HST/STIS spectrophotometry agree in the B, V, R, and I bands to better than $\sim$1\% (10 mmag).Comment: 15 pages, 6 figure

Changes in Sensitivity of the Low Dispersion Modes

Significant changes in the STIS sensitivity are revealed by 2.3 years of observations of the same standard stars in the 52X2 arcsec slit. The largest changes are in G140L, where the sensitivity depends on both the time and temperature. The minor effect is a-0.25%/C temperature correlation, where the bulk of the observations are confined to the 34.5-38.5C temperature range. No significant change with temperature is detected for the near-UV MAMA or CCD modes. Following a correction for the correlation with temperature, the sensitivity of G140L decreases linearly with time. These losses vary with wavelength, ranging from a minimum of-0.8%/yr at 1325Å to a maximum of-2.8%/yr at 1575Å. For G230L, the mean sensitivity over all wavelengths increases by an average of 1.8 % in the first 1.3 years and then begins to drop. Two straight lines with different slopes fit the observed changes. The changes before 1998.7 also vary with wavelength, ranging from a minimum of +0.8%/yr at 2550 to a maximum at 2250Å of +2.1%/yr. The wavelength-dependent slopes of the currently decreasing sensitivity range from zero at the short wavelength end of the band to-1.9%/yr in the 2300-2400Å interval. Changes in the three low dispersion CCD modes are less severe. For G230LB and G750L, most wavelength bins are consistent within a three σ uncertainty of constant sensitivity over time. Only one wavelength bin for G230LB and two for G750L show sensitivity losses with more than three σ certainty. Those changes are small and lie in the 0.2-0.4%/yr range. However for G430L, the losses in every 200Å wavelength bin beyond 3300Å range from 0.5 to 0.7%/yr with a high statistical significance of 2-9 σ. After correcting the three low-dispersion modes for sensitivity changes, the 1 σ photometric broadband repeatability ranges from 0.2 % for G140L and G750L to 0.4 % for spectrophotometry in the other 3 modes

An analysis of the shapes of interstellar extinction curves. VII Milky Way spectrophotometric optical-through-ultraviolet extinction and its R-dependence

We produce a set of 72 NIR-through-UV extinction curves by combining new Hubble Space Telescope/STIS optical spectrophotometry with existing International Ultraviolet Explorer spectrophotometry (yielding gapless coverage from 1150 to 10000 ?) and NIR photometry. These curves are used to determine a new, internally consistent NIR-through-UV Milky Way mean curve and to characterize how the shapes of the extinction curves depend on R(V). We emphasize that while this dependence captures much of the curve variability, considerable variation remains that is independent of R(V). We use the optical spectrophotometry to verify the presence of structure at intermediate wavelength scales in the curves. The fact that the optical-through-UV portions of the curves are sampled at relatively high resolution makes them very useful for determining how extinction affects different broadband systems, and we provide several examples. Finally, we compare our results to previous investigations

New Grids of Pure-Hydrogen White-Dwarf NLTE Model Atmospheres \newline and the HST/STIS Flux Calibration

Non-local Thermodynamic Equilibrium (NLTE) calculations of hot white dwarf (WD) model atmospheres are the cornerstone of modern flux calibrations for the Hubble Space Telescope (HST) and for the CALSPEC database. These theoretical spectral energy distributions (SEDs) provide the relative flux vs. wavelength, and only the absolute flux level remains to be set by reconciling the measured absolute flux of Vega in the visible with the Midcourse Space Experiment (MSX) values for Sirius in the mid-IR. The most recent SEDs calculated by the \textsc{tlusty} and \textsc{tmap} NLTE model atmosphere codes for the primary WDs G191-B2B, GD153, and GD71 show improved agreement to 1\% from 1500~\AA\ to 30~\micron, in comparison to the previous 1\% consistency only from 2000~\AA\ to 5~\micron. These new NLTE models of hot WDs now provide consistent flux standards from the FUV to the mid-IR.Comment: 14 figure

IUE archived spectra

The International Ultraviolet Explorer (IUE) Satellite has been in continuous operation since January 26, 1978. To date, approximately 65,000 spectra have been stored in an archive at Goddard Space Flight Center in Greenbelt, MD. A number of procedures have been generated to facilitate access to the data in the IUE spectral archive. This document describes the procedures which include on-line quick look of the displays, search of an observation data base for selected observations, and several methods for ordering data from the archive