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Spring break was a relaxing as it could of been. The sun was out mostly which is nice. Trying to distance. Things are a bit strange, but that’s alright. I’m excited to start focusing on some work. It’ll take my mind off of everything else for a bit. I’m trying to be on my Isaac Newton vibes and try to do some great work during quarantine. Really zen out and avatar state on some science. Anyways, I digress. Now to updates:
I didn’t do much over break but I did do a bit. I made a region file of the VLM targets in Praesepe outlined in the Boudreault et al. 2010 paper that Noah presented in the paper talk a couple weeks ago. The ADS link has the paper and the data products from the work: https://ui.adsabs.harvard.edu/abs/2010A%26A…510A..27B/abstract. From there I cross checked these targets with the the ones that we extracted even a further back in class in the Astrometry exercise. A screenshot of DS9 of the two files is shown below. The green is the Boudreault targets. None of them overlap with the other stars extracted from the Krauss catalog.
Besides that I watched the Fourier transform video. I thought it was SUPER informative. I feel like I’ve always known at a very general level what a FT does, but I was not very fluent at all in the math behind what it does. Rather, the intuition behind it all didn’t make sense. The ‘unmixing the paint’ analogy was nice, and his use of this 2-D plane where the circled up the signal using the ‘winding frequency’ in order to build up to the reason that we utilize imaginary numbers in FTs, and the elegance/usefulness of the complex plane. The integral for FTs make a lot more intuitive sense to me. That could also be a product of me being a lot more familiar with math concepts at this stage in my college carrer. Who knows. I was a little foggy about his comments about why we did not want that 1/(t1-t2) term in that expression that he presented. Also the big motivating idea of the ‘center of mass’ of the rings created by the wrapped signal puzzels me. I understand the purpose it serves in the transform, but I’m confused as to what it represents mathematically? Or say we were talking about sound waves, does that quantity represent anything physically? But I think another watch will clear it up. I’ve subscribed to the channel. This video is cool: https://www.youtube.com/watch?v=OkmNXy7er84.
The Templeton reading was also interesting. The formalism is nice and solidifies a lot of the ideas from the video. Puts the FT more in the context of statistics than interpreting it visually. Does the Nyquist frequency represent the ‘center of mass’ that I discussed above? The discussion of cautions with sampling was informative as I believe that we might run into similar problems. I think that our data could fall into the ‘gappy’ regime. I guess that would depend on the stack sizes, but I think our data will have to be stacked for each night as the objects we are observing are small and red. The discussion of autocorrelation functions for a more statistical approach to time series analysis was super interesting. Mostly because my last experiment for i-Lab last semester utilized one to try and measure light scattered off of a solution, and I did not really understand what is was at all. But now I do that that is cool. However learning about how it can be used in the context of variable stars was also informative. Figure 4 was a nice visual to represent that discussion. Overall a nicely written, digestible paper. I’m not 100% on everything, but maybe I can answer my own questions with some more reads.
Here are some recent papers that I think are relevant to my project:
- The TESS light curve of AI Phoenicis: https://arxiv.org/pdf/2003.09295.pdf
- The group aims to measure accurate and radii for stars in an eclipsing binary system AI Phe. They compare models with TESS photometry and spectroscopy. I thought it was relevant because they are analyzing some lightcurves in the same way we are. Examining plots like % amp difference vs. time similar to the Morris et al paper.
- Spectral library of age-benchmark low-mass stars and brown dwarfs: https://arxiv.org/pdf/1912.02806.pdf
- In this work the group uses data from the VLT X-Shooter spectrograph in order to more deeply understand ‘youth spectral characteristics.’ They take sample of brown dwarf members in different aged clusters: Chameleon I, Upper Scorpius Pleiades, and Praesepe. Even though they are using spectroscopic data and trying to measure different things, I think that the motivation and methods are similar to our project.
- The nature of the photometric variability of HgMN stars; A test of simulated light curves of $\phi$ Phe against the TESS data: https://arxiv.org/pdf/1912.07265.pdf
- Again this is not very similar to the data that w have, or necessarily what we are observing. But their measurements of light curves and they ways in which they analyze them using FTs and %amp vs wavelength graphs is somewhat similar to what we will be doing. They aim to compare their models of mecury-manganese star variability with observations from TESS.
In terms of recent data reduction stuff: I thought I was all set but after the OOC meeting on Monday, Kim let us know that we were in fact not stacking any of our images, simply aligning them and calling them a stack. That could also point to why the light curve I made a couple weeks ago looked funny. But anyways I have to go back. I think I will just align all of the images and then combine them how I see fit afterward. It might be a little expensive on the memory side. I’m running out of space on my SD card. Is it alright to delete all of the old images. Like the ones background subtracted but not flatfeilded? Anyways, it should be a quick fix, and will give me a chance to polish a couple things up.
My next steps are to:
- Properly shift images and then combine them
- Make new function to accomplish this
- Make stacks PER NIGHT –> 6 data points
- Make some lightcurves now that I have astroimageJ installed.
Owen H. ASTRO-341 Research Blog 