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发表于 2011-1-7 21:52:32
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最后一半。
To identify candidates for viewing, images are taken using the 48 inch Samuel Oschin telescope at the Palomar Observatory. Images are then calibrated to correct instrumental noise and compared automatically to reference images. Those in which an object appears with a change greater than five standard deviations from the general noise are flagged for inspection. While it may seem that this high threshold would eliminate other events, the Supernova Legacy Survey, starting with 200 candidates per night, would only end up identifying ~20 strong candidates. As such, nearly 90% of these computer generated identifications were spurious, likely generated by cosmic rays striking the detector, objects within our own solar system, or other such nuisances and demonstrating the need for human analysis.为了使候选天体被验证，帕洛玛（Palomar）天文台的48英寸的Samuel Oschin望远镜为它们进行了拍摄。随后图片将进行降噪处理并且自动与参考图片进行比较，那些与普通噪声信号相比信号强度偏离了超过5倍（标准值）的目标将被标记以便检测。这一高起点看起来会消除其他活动的影响。超新星遗迹观测每晚只能鉴别200个候选天体中的大约20个信号较强的天体（不是干扰信号）。计算机生成的大约90%的候选者是干扰信号，比如探测器被宇宙线击中（时生成的信号）。我们太阳系内的天体，或其他可解释的（麻烦的）东西。
Still, the PTF identifies between 300 and 500 candidates each night of operation. When exported to the Galaxy Zoo interface, users are presented with three images: The first is the old, reference image. The second is the recent image, and the third is the difference between the two, with brightness values subtracted pixel for pixel.Stars which didn’t change brightness would be subtracted to nothing, but those with a large change (such as a supernova), would register as a still noticeable star.目前，PTF运行一夜能鉴别300-500候选天体。当输出给星系动物园界面时，用户将被呈现3幅图片。第一幅是时间较早的参考图片。第二张是最近的图片，第三张是利用像素亮度值相减所得到的差异图像。那些没有亮度变化的恒星（的亮度值）将被减到零，不过那些有较大改变的恒星（例如超新星）将作为一个静止的显著目标（显示出来）。
Of course, this method is not flawless, which also contributes to the false positives from the computer system that the decision tree helps weed out. The first question (Is there a candidate centered in the crosshairs of the right-hand [subtracted] image?) eliminates misprocessing by the algorithm due to misalignment. The second question (Has the candidate itself subtracted correctly?) serves to drop stars that were so bright, they saturated the CCD, causing odd errors often resulting in a “bullseye” pattern. Third (Is the candidate star-like and approximately circular?), users eliminate cosmic ray strikes which generally only fill one or two pixels or leave long trails (depending on the angle at which they strike the CCD). Lastly, users are asked if “the candidate centered in a circular host galaxy?” This sets aside identifications of variable stars within our own galaxy that are not events in other galaxies as well as supernovae that appear in the outskirts of their hostgalaxies.当然，这个方法也不是完美的。也会出现虚假目标，这就需要树状问题（帮忙）剔除。第一个问题（右边图片中的十字丝中心上是否有候选天体？）排除了算法处理失误导致的不重合。第二个问题（候选者（信号）本身有没有被正确的相减）是为了舍弃太过明亮的恒星。它们使CCD饱和，从而导致经常出现在凸透镜里的奇特的错误。第三个问题（候选天体是不是恒星状的并且近似圆形？）用户剔除宇宙线（的影响）。宇宙线通常仅仅填充一两个像素或者遗留下一条轨迹（取决于击中CCD的角度）。最后，用户将被询问“候选天体是否在圆形的宿主星系中心？”。这将被用以排除银河系和其他星系中变星的影响（因为）超新星出现在宿主星系的边缘。
Each of these questions is assigned a number of positive or negative “points” to give an overall score for the identification. The higher the score, the more likely it is to be a true supernova. With the way the structure is set up, “candidates can only end up with a score of -1, 1 or 3 from each classification, with the most promising SN candidates scored 3.” If enough users rank an event with the appropriate score, the event is added to a daily subscription sent out to interested parties.每个问题将提交一系列的正向的或负向的“分数”用以得出每个被鉴别天体的总分。分数越高，是超新星的可能性就越大。基于这个方法（框架）结构被建立了起来，“候选天体（的得分）只可能是-1,1,3中的一个，因此最可能是超新星的候选者得分是3.”如果有足够的用户给出了相似的分数，该事件将被添加入每日提交给感兴趣方的每日记录中。
To confirm the reliability of identifications, the top 20 candidates were followed up spectroscopically with the 4.2m William Herschel Telescope. Of them, 15 were confirmed as SNe, with 1 cataclysmic variable, and 4 remain unknown. When compared to followup observations from the PTF team, the Galaxy Zoo correctly identified 93% of supernova that were confirmed spectroscopically from them. Thus, the identification is strong and this large volume of known events will certainly help astronomers learn more about these events in the future.为确认该认证的可靠性，（可靠性）前20的候选天体将利用口径4.2m的威廉 赫歇尔望远镜分光设备进行跟踪观测。在它们中间，15个被证实为超新星，1个为灾变变星，4个仍然未知。与PTF的后续观测进行对比，星系动物园正确的辨别了93%的经由分光设备确认的超新星。因此，认证是有力的。而且这些已知的案例将无疑帮助天文学家们在未来了解更多的案例。
If you’d like to join, head over to their website and register. Presently, all supernovae candidates have been processed, but the next observing run is coming up soon!如果你想加入，请登录他们的网站并注册，目前，所有的超新星候补天体已经被鉴定，不过下一轮的观测即将展开！ |
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发表于 2010-12-23 21:03:48