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px diameter] 69 fuv_ncat_flux_aper_4 1E cnts/sec FUV FLUX_APER #4 (-fd-ncat)(cnt/sec)[ 8. This position is the NUV source position, or the FUV source position for FUV-only sources. 16 delta_j2000 1D degrees Declination in degrees (-90 to 90) in a J2000 reference frame. Should Not be used for identification. (meta.record) (RECORD) objidG (char) GALEX source identifier (meta.id;meta.main) (ID_MAIN) Name (char) PMSU source identifier (Hawley+, 1997, III/198; <[RHG95] NNNN> in Simbad) (meta.id.cross) (ID_CROSSID) SpT Numeric Featured Image Site Search Chapter 5 - Data Analysis - Imaging Astrometric UncertaintiesPoint Spread Function This chapter describes in more detail some of the basic properties of GALEX data.

The diameters for the 7 fluxes are 2, 3, 5, 8, 12, 17, and 23 pixels. These include: Flat Field : New maps were created using millions of source measurements, effectively improving the non-Poisson flux error (on average) from 1.2% to 0.8% in the NUV and from For example, if the FUV source position is directly west of the NUV source position, the sourcepa value would be 180. px diameter] 86 fuv_ncat_mag_aper_7 1E raw_mag FUV MAG_APER #7 (-fd-ncat)(raw mag)[23.

If "nuv_flux" has a value of -999, then there was no NUV source detection. 37 nuv_fluxerr 1E flux (micro-Janskys) The error in nuv_flux in micro-Janskys. 38 nuv_mag 1E AB mag Calibrated Note (2): Some SDSS stars had multiple GALEX counterparts; to eliminate chance alignments and remove multiple detections, we used the proper motions in the DR7 M dwarf sample (Munn et al. This PSF was genreated by averaging together many point sources from the Medium Imaging Survey in sky coordinates. The curves for LDS 749B have the same overall shape as for the field stars although they are a bit broader, particularly in the FUV.

This depends on the separation between sources and an estimate of the positional error. We plan to correct for these long term trends in astrometry in future GALEX releases. The diameters for the 7 fluxes are 2, 3, 5, 8, 12, 17, and 23 pixels. Fluxes are counts/second unless stated to be in micro Janskys.

In Table 1 we list the aperture corrections in magnitudes for the standard GALEX aperture measurements. These values are also given as individual columns (shown below). This value is taken from the -nd-int.fits file image. 115 fuv_int 1E photons/second/pixel FUV intensity value in photons per second at the source position (center pixel). For faint sources, using a large aperture can greatly increase the error due to sky noise.

This is derived from the Galactic extinctions maps from Schlegel et al. (1998, ApJ, 500, 525). Using these positions, we were able to eliminate most of the multiple matches, keeping only the UV source that was closest to the position of the DR7 M dwarf at the Since the telescope is dithered and many eclipse observations are combined, this is only an estimate of the X position. The diameters for the 7 fluxes are 2, 3, 5, 8, 12, 17, and 23 pixels.

Hα activity (G2) 144-150 F7.3 0.1nm EWHa [-0.3/6]?=-99 Hα equivalent width (Å) 152-161 E10.3 --- LHa [-0.0001/0.0004]?=-999 Hα luminosity (G3)(1) 163-171 E9.3 --- e_LHa [0/0.0002] Uncertainty in LHa 173-181 E9.3 --- This page has been accessed 871 times. FAQ: Frequently Asked Questions to help in planning and analysis of GALEX observations. This section briefly describes the absolute astrometric uncertainties of GALEX data.

The value of "N_FUJ" is equal to 10 ^ ( (FUV_ZPMAG - 23.9) / -2.5 ) . Beijing (Ch) VizieR . GALEXFest 2012: A Conference in Pasadena on Sep 4-7, 2012 celebrating the GALEX Mission. A masked pixel is one whose response value (from the -rrhr.fits image) is NAN or is either less than 0.000001 or greater than 10 times the exposure time. 127 fuv_maskpix 1J

Please see the SExtractor web pages or Bertin and Arnouts (1996, A&A, 117, 393) for more information about the quantities measured by this progam. angle (CCW/world-x) 360 FUV_ERRTHETA_J2000 1E degrees J2000 error ellipse pos. The PSFs consist of a more or less Gaussian core with extended wings. GALEX Tools: Online tools to help you plan your GALEX observation.

The best fit values from the plate solution are stored in the file -cat_mch_rtastar_stats.txt. We have removed 26 columns which are either redundant or of questionable quality. The FUV counts/sec is converted to micro Janskys using the header card "F_CUJ" and the formula fuv_flux = = FUV_FLUX_AUTO * N_FUJ. This value is derived from the -fd-int.fits image, the -fd-skybg.fits image and the -fd-wt.fits images.

In each band, we subtracted a local background determined in a circular annulus around each star with an inner radius of 90” and a width of 30”. This difference in plate scale from that assumed when constrincting the images corresponds to an average relative position error across the enitre field (1.2 deg) of 0.7 arcsec on average. See section 3 for further explanations. The file with extension "-fd-ncat.fits" contains FUV flux values computed using positions given in the "-nd-cat.fits" file. 49 fuv_ncat_fluxerr 1E flux (micro-Janskys) Error for fuv_ncat_flux 50 fuv_ra_adj 1D degrees FUV adjusted

As the astrometric accuracy of the SDSS is about 0.1” even for relatively faint stars, we can consider it essentially an “absolute” reference for our purposes (Pier et al. (2003), AJ, Joining these two integers yields a 64 bit integer uniquely identifying this source including the tile number, band, product number, reduction try (path), etc. Artifact 5( 16):(brtedge) Bright star near field edge (NUV only) Artifact 6( 32):Detector rim(annulus) proximity(>0.6 deg fld ctr) Artifact 7( 64):(dimask) dichroic reflection artifact mask flag Artifact 8(128):(varmask) Masked pixel determined There is a small overall offset in Declination of +0.2 arcsec while the one-sigma spread in in each coordinate is about 0.4 arcsec.

Refers to the match (or lack of match) between the NUV source and the FUV source detection. File Summary: FileName Lrecl Records Explanations ReadMe 80 . Then these matches are fit with a six parameter plate solution including the RA and Dec of the field center, an x and y plate scale, and an x and y The NUV contours range from 5 x 10-5 to 0.5 in steps of a factor of 10.

We are planning to fix these trends in the astrometry in future GALEX releases. Also note that "nuv_flux" may be zero, in this case refer to the "NUV_FLUX_*" columns for flux values. If the value of "chkobj_type" for a source is 1, then that source (NUV position) has been matched to a known bright star. 32 chkobj_id 1J number For a source matched Featured Image Site Search GALEX Data Releases The GALEX data archive is hosted by the Multi-Mission archive at the Space Telescope Science Institute (MAST).

The average PSFs used in these plots can be found in the following two FITS files: PSFnuv_faint.fits (NUV) and PSFfuv.fits (FUV). All of the columns labeled fuv_ncat_mag_aper_X (where X ranges from 1 to 7) refer to measurements of the FUV magnitude in a fixed circular aperture with the specified diameter in pixels Point Spread Function We have characterized the GALEX point spread function (PSF) using various in-flight observations. This value is derived from the -nd-int.fits image, the -nd-skybg.fits image and the -nd-wt.fits images.

This prevents the resulting average PSF from blurring just due to sub-pixel shifts in the centroid of each star. for magnitudes NUV < 15. For mid-type M dwarfs, we show that NUV emission decreases with distance from the Galactic plane, a proxy for stellar age. The solid black line is the curve for the average field star PSF whereas the corresponding curve for the white dwarf calibration star LDS 749B is shown as the red dashed

This ratio will be between 0.0 and 1.0, inclusive. FUV to NUV Position Correction : The FUV photons are now corrected for temperature effects with adjustments of up to 2 arcseconds relative to GR4/5. Our complete matched source catalog is available online. Table 1: Aperture corrections for the average field star PSFs Aperture No.

Privacy policy About Galex Wiki Disclaimers Home About GALEX Overview Basics Team Newsroom Press Releases Feature Stories Status Updates Media Gallery Images Videos Education For Kids For Teachers Researcher The distribution is fairly consistent with a Gaussian distribution with a sigma of 0.4 arcsec.