{"id":1542,"date":"2013-07-30T10:56:41","date_gmt":"2013-07-30T18:56:41","guid":{"rendered":"http:\/\/jazzistentialism.com\/blog\/?p=1542"},"modified":"2015-09-17T22:12:44","modified_gmt":"2015-09-18T06:12:44","slug":"determining-photometric-transform-coefficients","status":"publish","type":"post","link":"http:\/\/jazzistentialism.com\/blog\/?p=1542","title":{"rendered":"Determining photometric transform coefficients"},"content":{"rendered":"

\"Land2\"<\/a><\/p>\n

The following summarises attempts\u00a0to\u00a0determine magnitude and colour transform\u00a0coefficients for photometric projects (using the “UBVRI” colour system) undertaken at D21.<\/p>\n

The first attempts use Landolt equatorial fields near transit, which have since been found to contain some errors in published values, or more accurately – variations in on-line sources of the Landolt catalogues.<\/p>\n

<\/p>\n

Test 1<\/h3>\n

Date:\u00a07th July 2013<\/p>\n

Landolt field: centered on SA 104-440
\nExposures: B 75s x 2 (averaged), V 30s x 2 (averaged)<\/p>\n

The table below comprises measured and calculated values from 11 reference stars in the Landolt field\u00a0(v has been corrected to match the exposure for b by 2.5x)<\/em>.<\/p>\n

\"Land1Data\"<\/a><\/p>\n

Figure 1 shows the\u00a0plot for determining the colour transform coefficient (standard minus measured vs standard colour index). The plot uses raw instrumental magnitudes for b and v.<\/p>\n

\"Land2\"<\/a>

Figure 1: Determining the colour transform<\/p><\/div>\n

Figure 2 shows a plot for determining the magnitude transform (standard minus instrumental magnitude vs standard colour). Once again, the plot uses raw instrumental magnitudes for b and v.<\/p>\n

\"Land1\"<\/a>

Figure 2: Determining the magnitude transform<\/p><\/div>\n

<\/h3>\n

Both plots appear to provide good linear correlation for calculation of the colour and magnitude transforms.<\/p>\n

 <\/p>\n

Test 2<\/h3>\n

The second test\u00a0is centred on\u00a0Landolt SA 105-256 near transit. Exposures are identical to those used in Test 1. The table below\u00a0comprises measured and calculated values from 13 reference stars in the Landolt field\u00a0(v has been corrected to match the exposure for b by 2.5x)<\/em><\/p>\n

\"Land2Data\"<\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

The data exhibits significant scatter compared to Test 1. Figure 3 shows a the line of best fit and equation for deriving the colour transform. The results differ markedly from those in Test 1.<\/p>\n

\"Land3\"<\/a>

Figure 3<\/p><\/div>\n

Figure 4 shows a\u00a0line of best fit for deriving the magnitude transform\u00a0similar to the results in Test 1. However the plot is\u00a0less ‘convincing’ despite the slightly larger sample size.<\/p>\n

\"Land4\"<\/a>

Figure 4<\/p><\/div>\n

Fearing some discrepancy in the on-line published values for Landolt, additional tests were undertaken using both\u00a0Graham<\/em>\u00a0reference stars and \u00a0E Regions<\/em>\u00a0from the\u00a0Cape standards<\/em>.<\/p>\n

Test 3<\/h3>\n

The third test uses a combination of southern “E fields” from the\u00a0Cape Standards<\/em>\u00a0and a selection of \u00a0“Graham”\u00a0stars.<\/p>\n

The E Field test uses stars from three adjacent fields. These brighter stars from the Cape Standards required shorter exposures – 10 seconds for B and 2 seconds for V. An average of two exposures per star was used to provide the raw instrumental magnitude.<\/p>\n

\"EFieldData\"<\/a><\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

Figure 5\u00a0shows the\u00a0plot for determining the colour transform coefficient:<\/p>\n

\"Ecolour\"<\/a>

Figure 5<\/p><\/div>\n

Figure 6 shows the plot for determining the magnitude transform coefficient:<\/p>\n

\"Emag\"<\/a>

Figure 6<\/p><\/div>\n

Graham Stars<\/p>\n

An additional six fainter stars from those measured by Graham were added to the southern tests. The data appears to correlate well between the two.<\/p>\n

\"GrahamData\"<\/a><\/p>\n

 <\/p>\n

\"GrahamColour\"<\/a>

Figure 7<\/p><\/div>\n

 <\/p>\n

\"GrahamMag\"<\/a>

Figure 8<\/p><\/div>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

The following summarises attempts\u00a0to\u00a0determine magnitude and colour transform\u00a0coefficients for photometric projects (using the “UBVRI” colour system) undertaken at D21. The first attempts use Landolt equatorial fields near transit, which have since been found to contain some errors in published values, … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0},"categories":[20],"tags":[],"_links":{"self":[{"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1542"}],"collection":[{"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1542"}],"version-history":[{"count":3,"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1542\/revisions"}],"predecessor-version":[{"id":1621,"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1542\/revisions\/1621"}],"wp:attachment":[{"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1542"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1542"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/jazzistentialism.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1542"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}