Main Sequence

I must wait until a supernova appears that is close/bright enough for me to accurately observe it in reasonable time. This range is around magnitude 11-14. In astronomy, the magnitude system simply tells you how bright an object looks. The higher the number, the dimmer it is. It is also exponential. Each magnitude is about 2.5 times dimmer or brighter than the last. For context, the sun’s magnitude is about -27, the full moon’s is -13, Venus’ is -5, Sirius, the brightest star is -2, and most stars that we can see well are in the 1-3 magnitude range. The naked eye can see down to magnitude 6. My telescope allows me to see down to magnitude 12-13, and with my camera I can image down to 18, which is millions of times dimmer than what I can see looking up. But, for accurate photometry—the measure of how bright something looks, I must observe things no dimmer than 14. But also no brighter than 10-11 because it would saturate my sensor. Once a supernova fits that range, I observe it once or twice a week over the course of a few months to cover the entire life cycle of the curve—the variability in its brightness over time. 

Each night I image, I go outside at sunset, and begin setting up. My telescope weighs well over 100 pounds so I bring it out in several parts. I ensure that it is facing directly north and that the initial orientation points it at an angle in the sky that’s the same as the latitude where I am (39-40º). This ensures that Polaris, the north star, is in view. At that point, I level it and then begin the aligning process. I align it by using the electronic controller that’s built into the telescope and allows me to move it around. On my computer, I used a software called Astroimager, a popular option for amateurs. I can view the live view that my camera sees in the telescope, and by centering the stars, my telescope creates a map of the sky so it knows where it is. I then polar align it using the physical adjustments on the mount, and then redo the normal alignment for accuracy. Once that is down, I slew it to the object, generally a galaxy, that I need to be imaging. Due to the alignment, it now rotates at the exact same rate that the earth does which keeps the object framed all night, at least for the most part as I do have to make minor adjustments here and there. Once the object is framed, I set an exposure time and spend hours taking hundreds of individual frames of the object. Once done, before I go inside, I wrap the aperture of my telescope with a white t-shirt and use a ring light to evenly illuminate it. Then I take 100 1-second long exposures that I can then use as calibration frames to account for the dust and vignetting that appears over the night. I take similar frames in the dark called dark flat, bias, and dark frames which reduce the inherent noise in my camera and the thermal noise from the sensor to minimize the image’s artifacts when I am analyzing it later. Once I go inside, that’s when I analyze my data. 

First, I must stack the data using a program called Siril, another common amateur stacking software. Any individual image alone isn’t a very strong image. There is lots of noise and not very much signal. So I stack the images together, effectively adding all of the information together to create a master image that I then use to analyze. I take that image, and I put it into another software that allows me to perform differential photometry. This process basically allows me to assign known magnitudes to stars in the frame so that it can deduce the brightness of the object I am interested in knowing about, in this case the supernova. This brightness value, I then plot, along with every other night throughout the whole time to make a time vs. magnitude graph. This graph is what I will use to statistically determine, with the help of Dr. Igel, when and how bright the peak magnitude was based on my data. This is the actual value—only one for each object compiled from many nights of imaging and analysis—that I use to determine the distance. I then take the brightness I found, factor in the galactic extinction (dust obstruction) and get the final “peak brightness I observed.” I plug it into the distance luminosity equation knowing that the literature says that the supernova peaks around -19.3 as an absolute magnitude (it would look -19.3 from 10 parsecs or 32 light years) and that pops out a distance. That distance is the distance to the supernova, and also the host galaxy of the supernova. Then, I will find a literature value of what the professionals have determined the distance to be to that supernova, and compare my number to theirs to determine if it is close or not. This will answer, very simply, if amateurs can or cannot determine the distances accurately. So far, based on the data that I’ve collected and the initial analysis that I have done, it looks very promising that I can in fact accurately use differential photometry to determine the distance to the host galaxies of SNe Ia. All of this information is provided in the user manual for my software and hardware. The choice of softwares has been chosen based off of online recommendations from other amateur astrophotographers and the AAVSO guides I discussed earlier.