大溪天文台觀測日誌 TYGA TW 2021年03月27,28日 大溪 晴朗(低層雲霧) 西南風 滿月
這次變星觀測採用美國 Optec NextGEN Maxfield 0.33x 減焦修正鏡 安裝在14吋主鏡所做的實驗測光觀測.(修正測試中....)
溫度:22.6 - 26.3度C 濕度:70 - 72% 視狀 3/5 透明度 1/5 (1-5 最差到最佳程度) 無風狀態. 視狀非常穩定 seeing=1.95 arcsec 月齡:15
觀測變星: 17顆 CCD:17顆 目測:0顆 御夫座 GCVS Aur 雙子座 GCVS Gem
Celestron 14" SCT F/3.6 曝光 40-90秒 SBIG ST2000XM V FILTER 自由追蹤 (POLEMASTER 2017 0805 校對) Showa 20E kai +Vixen Skysensor 2000PC .+TheSky GOTO system
Observations submitted since last login:
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Name JD CalendarDate Mag Filter
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1 S GEM 2459301.09028 2021 Mar 27.5903 14.3 Johnson V ensemble ASTROART5.0 N
2 T GEM 2459301.09444 2021 Mar 27.5944 9.1 Johnson V ensemble ASTROART5.0 N
3 U GEM 2459301.09792 2021 Mar 27.5979 12.5 Johnson V ensemble ASTROART5.0 N
4 Z GEM 2459301.10139 2021 Mar 27.6014 11.7 Johnson V ensemble ASTROART5.0 N
5 W GEM 2459301.10556 2021 Mar 27.6056 7.1 Johnson V ensemble ASTROART5.0 N
6 R GEM 2459301.10764 2021 Mar 27.6076 7.2 Johnson V ensemble ASTROART5.0 N
7 Y GEM 2459301.11042 2021 Mar 27.6104 9.0 Johnson V ensemble ASTROART5.0 N
8 V GEM 2459301.11319 2021 Mar 27.6132 12.4 Johnson V ensemble ASTROART5.0 N
9 X GEM 2459301.11806 2021 Mar 27.6181 11.1 Johnson V ensemble ASTROART5.0 N
10
R AUR 2459301.95139 2021 Mar 28.4514 12.6 Johnson V ensemble ASTROART5.0 N
11 Z AUR 2459301.95764 2021 Mar 28.4576 10.0 Johnson V ensemble ASTROART5.0 N
12 X AUR 2459301.96458 2021 Mar 28.4646 9.2 Johnson V ensemble ASTROART5.0 N
13 V AUR 2459301.96667 2021 Mar 28.4667 10.1 Johnson V ensemble ASTROART5.0 N
14 Y AUR 2459301.97361 2021 Mar 28.4736 9.2 Johnson V ensemble ASTROART5.0 N
15 W AUR 2459302.00139 2021 Mar 28.5014 9.2 Johnson V ensemble ASTROART5.0 N
16 S AUR 2459302.01389 2021 Mar 28.5139 10.1 Johnson V ensemble ASTROART5.0 N
17 U AUR 2459302.02778 2021 Mar 28.5278 13.9 Johnson V ensemble ASTROART5.0 N
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14" SCT F/3.6 +ST2000XM 直焦點 溫度0度C 曝光 40-60秒 JOHNSON V FILTER
AAVSO Observatory Code : TYGA TW (大溪天文台 台灣)
當晚極限星等 03/28取樣 14.768mag (V band filter) image field:31'x22'*
大溪及世界各地業餘觀測者的觀測資料及曲線可參考 http://www.aavso.org/data/lcg
*.Vmag=photometry RADEC=astrometry by Astroart5.0
TYGA TW : AAVSO global obse code
曹大貓咪物語:Aperture Photometry:孔徑測光
Name Magnitiude(after fixing) ADU(by ST2000XM) Original Instrumental Magnituide
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GCVS R Aur 12.585mag 16197 13.476mag
參考星1 9.430mag(GSC1.1) 323212
參考星2 7.720mag(GSC1.1) 1027521
參考星3 12.730mag(GSC1.1) 13710
參考星4 8.640mag (GSC1.1) 436662
instrumental mag = 25.0 - 2.5*log10(counts - sky)
GSC視星等星圖目錄
http://gsss.stsci.edu/Catalogs/Catalogs.htm-------------------------------------------------------------------------------------------------------------------
k1=24.0 k2=-2.5 (instrumental mag index)
mag=k1 +k2 log(ADU) total stars=12 reference stars=4
k1=23.566 k2=-2.6193 (after fixing index)
mag=k1 +k2 log(ADU) total stars=12 reference stars=4
圖:對於孔徑測光,對於主星取樣是採用孔徑半徑設定為主星的1.5-2倍的FWHM(radius of an aperture is about 1.5 or 2.0 times the FWHM). Astroart 軟體最方便是能夠對孔徑測光模式,對應不同亮度的變星,自動修正適合取樣的星點範圍.測出正確的儀器ADU線性亮度值. 再經過參考星和背景亮度等修正為正常的視星等數據.最大的誤差取決於測定者取樣參考星的亮度和數量(軟體限定3顆參考星或以上).另外就是兩個外來因素.1是背景亮度(如透明度和月亮亮度),2視狀和風壓.露天式的天文台最大問題在於風壓的干擾! 好處是散熱快速,無熱對流的問題. 但如在冬天的東北季風影響,會造成取樣星點的晃動.增加測光的誤差.
大部分的天文觀測儀器設備再好再精良,若是在平地或都市內使用,都是事倍功半! 所以老貓無法將天文台安置於高山上.這是一生最大的遺憾.曹大貓咪 2021 0402