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تسجيل مستخدم جديدمسح علمي قيا للنجوم المعيارية الطيفية البصرية -- IV. نتائج الحملة الفوتومترية المطلقة
The Gaia spectrophotometric standard stars survey -- IV. Results of the absolute photometry campaign
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نقدم فوتومتريا Johnson-Kron-Cousins BVRI لـ 228 نجمة مرشحة لإستخدامها كمعيار طبقات الإشعاع للبيانات الخاصة بجايا. تم جمع البيانات في إطار حملة مراقبة تستمر على مدى عشر سنوات مع هدف بناء شبكة خارجية لمعايير الإشعاع لجايا، وحصلنا على فوتومتريا مطلقة وفوتومتريا نسبية لمراقبة الثبات، وطبقات الإشعاع. تم استخدام الإصدارات المبدئية من الجداول الإشعاعية لتعيين الإصدارين الأول والثاني من جايا. يركز هذا البحث على الإطارات التي تم التقاطها في ظروف سماء جيدة (حوالي 9100). سيتم استخدام الفوتومتريا للتحقق من جداول الإشعاع الأرضية لنجوم معيار طبقات الإشعاع لجايا ولتصحيح الطيف الذي تم الحصول عليه في ظروف غير فوتومترية بشكل صحيح لأخذ الصفات الصغيرة. يربط الفوتومتريا المطلقة المقدمة هنا بنظام نجوم معيار لاندولت بدقة تبلغ حوالي 1٪ أو أفضل، بحسب الحزمة الفوتومترية. وبعد مقارنة واسعة مع مصادر مختلفة من الأدب، تبين توافقاً عاماً تبلغ حوالي 1٪، وهذا يبدو أنه الحد الحالي في دقة تعيين الإشعاع عبر مختلف العينات والتقنيات في الأدب. ويبلغ دقة الفوتومتريا الخاصة بجايا حالياً ما بين 0.1٪ أو أفضل، لذلك تناقش هنا الأفكار المختلفة لتحسين دقة تعيين الفوتومتريا.
We present Johnson-Kron-Cousins BVRI photometry of 228 candidate spectrophotometric standard stars for the external (absolute) flux calibration of Gaia data. The data were gathered as part of a ten-year observing campaign with the goal of building the external grid of flux standards for Gaia and we obtained absolute photometry, relative photometry for constancy monitoring, and spectrophotometry. Preliminary releases of the flux tables were used to calibrate the first two Gaia releases. This paper focuses on the imaging frames observed in good sky conditions (about 9100). The photometry will be used to validate the ground-based flux tables of the Gaia spectrophotometric standard stars and to correct the spectra obtained in non-perfectly photometric observing conditions for small zeropoint variations. The absolute photometry presented here is tied to the Landolt standard stars system to $simeq$1 per cent or better, depending on the photometric band. Extensive comparisons with various literature sources show an overall $simeq$1 per cent agreement, which appears to be the current limit in the accuracy of flux calibrations across various samples and techniques in the literature. The Gaia photometric precision is presently of the order of 0.1 per cent or better, thus various ideas for the improvement of photometric calibration accuracy are discussed.
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