GALEX FUV PDF
This site will provide support to GALEX guest investigator programs, FUV & NUV obtained simultaneously using dichroic beam splitter also acting as a field. NUV: Flux [erg sec-1 cm-2 Å-1] = x x CPS. To convert from GALEX counts per second (CPS) to magnitudes in the AB system (Oke ): FUV: mAB . GALEX uses microchannel plate detectors to obtain direct images in the near-UV (NUV) and far-UV (FUV) and a grism to disperse light for low resolution.
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GALEX performs its surveys with plans see Glossary for definitions of terms in bold that employ a simple operational scheme requiring only two observational modes and two instrument configurations.
Dashed Spectra for galaxies with varying burst history young to old.
Furthermore, MCP detectors do not require cooling, an important consideration in the contamination-sensitive UV band. The two instrument modes used for astronomical observations are imaging aka direct and grism. Figure 3 above shows time-series telemetry plots for a set of observations described in Table 2.
All are in normalized units with the exception of UIT. Relative and absolute astrometric correction of satellite motion is performed in short s time intervals using stars measured by the NUV detector. The layers of the anode form a pair of orthogonal delay lines. It turns out that the resulting deviation is low, a primary advantage to switch between imagery and slitless spectroscopy. These two components are mounted on a rotating wheel that also provides an opaque position, and is the only moveable part of the telescope.
Its reflecting entrance side corrects the FUV channel, whereas the exit side cancels the entrance side effects and brings in the required amount of correction for the NUV channel. These products will use an improved pipeline, with updated calibrations, to handle changes in the response of the NUV detector in and This switching is performed by exchanging the grism with a low power plano-convex CaF2 imaging window.
Currently sub-visits are only used for all-sky imaging survey AIS and in-flight calibration observations. During any visit or sub-visit observation the spacecraft attitude is controlled in a tight, spiraled dither.
Processing of observations made subsequent to February 1. Data Collection Modes GALEX performs its surveys with plans see Glossary for definitions of terms in bold that employ a simple operational scheme requiring only two observational modes and two instrument configurations. Area [deg 2 ]. For plans with sub-visit targets, a 20 second slew time is required to move between each leg of the observation.
These products can be accessed directly over the web in real time, or in the case of large volume requests, by ftp. The final set of tiles, observed with galsx remaining NUV camera and predominantly observed after February 1, comprise the GR7. With the final data release GR7the AIS coverage of the sky was greatly increased, in particular at fuf Galactic latitudes, thanks to a lifting of this safeguard towards the end of the mission.
The dichroic coating applied to the entrance face of the fused-silica aspheric ufv plate separates the FUV reflection fuf NUV transmission optical paths. For some survey plans e.
Some observations are shortened by SAA passages when the detector high voltage must be kept at a safe, low level. Because the satellite begins the eclipse inside the South Atlantic Anomaly the total exposure time is shorter than the maximum possible.
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But scan mode was performed at a time when the mission was operating on both minimal staff gslex budget, so while nominal data products were produced, the calibration pipeline was not optimized to handle these data, and no additional scientific support was available.
The adopted design meets the challenging requirements of providing moderate-resolution optics with a high throughput and large field of view in four different optical paths two UV simultaneous channels, with imagery and slitless spectroscopy modeswhile keeping the instrument compact and simple to build and adjust. The dither spiral has the following angular rate profile:.
Timing differences measured for the charge pulses at each corner of the anode are proportional to the position of the initiating photon event. A cross section of the instrument is shown in Figure 2 below.
This was in contrast to the traditional boresight dither, known as the “petal pattern”, and to AIS modes in which the spacecraft hovered over single sky pointings and was reduced to a low voltage non-observing state when orienting between pointings. Diamond symbols are spaced every seconds 1 revolution every two minutes. A summary of instrument optical specifications is presented in Table 1. Because GALEX records time-tagged photon positions with digitization ruv oversamples the instrumental PSF by a factor of 3—5the pipeline map accumulator can re-bin photon positions onto an idealized projection.
The field curvature is cancelled by the power in the detector windows, and the detectors are tilted to the best plane.
A remarkable feature is that a unique blaze angle on the grism facets is found to provide a well centered efficiency for each channel, owing to the CaF2 index variation with wavelength. A sample of the GR7 subdeliveries are:. These included a number of redelivered GR6 data additional visits and associated coadds from onwardsalong with new tiles within GR7, which span approximately from Jan.