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Getting apparent magnitude of a star for a specific date #102
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Hello! This can be done in a few steps. The prediction of the apparent magnitudes on future dates won't be as accurate as those from a dedicated eclipsing binary modeling code, but probably enough to plan observations. First, you need a light curve for Algol. I used STScI's MAST service to get one from the TESS archive [a full-frame-image (FFI) high level science product (HLSP)]: hlsp_qlp_tess_ffi_s0018-0000000346783960_tess_v01_llc.txt This is a CSV file that you can read in:
You can then use some astrobase functions to find the epoch of the primary eclipse phase (time at eclipse minimum), given the period of the eclipsing binary (2.867328 days from Wikipedia):
Then, you can use this to plot a phased flux time-series to estimate some parameters for an eclipsing binary model fit:
That gives you a plot like the one below: Next, you can fit a simple eclipsing binary model:
This makes a fit plot: Using this model, you can predict the magnitudes of the star into the future. First, convert the units of time in the light curve from TESS to BJD (Baryocentric Julian Date):
Generate an array of BJDs into the future:
Use the eclipse model to predict fluxes on these dates:
Convert model fluxes to TESS apparent magnitudes. The median TESS apparent magnitude of Algol is 3.3684 and the relation between the normalized flux in the TESS light curve and apparent magnitude is:
So we can do the following to get an array of apparent magnitudes:
To figure out the apparent brightness of Algol on specific dates, you can convert these to Julian dates and then use the model output to see the magnitudes on those dates. For example, let's get the apparent magnitude light curve for the next two weeks.
Now, you can plot the apparent magnitudes for the next two weeks:
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Thank you so much for your wonderfully elaborated response. Unfortunately, I'm pretty much a layman when it comes to astronomy and don't really understand it. Actually I need a function to calculate the apparent magnitude of Algol for a given time because I want to include it as a parameter in my AI project. (Later I will need the same for other variable stars, but if I understand correctly, the principle is exactly the same, just a different dataset will be needed.) I tried to make a function based on what you wrote, but I'm missing a step, so it doesn't work, could you please take a look?
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Ah okay, I think the problems I can see are:
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Someone advised me how to calculate the phase of Algol for a given date. This should give a number between 0.0 and 1.0 where 0.0 means Algol is at a minimum, 0.5 means Algol is half way between minima and 1.0 means Algol is at a minimum again.
Is there a way how to use this together with your code so that I can get the magnitude for the given phase? :) |
If you have series of times and associated magnitudes, you can get the phases and associated magnitudes at each phase using
Then, you can use numpy's array indexing or |
Hi. Can this library be used to find out what the apparent magnitude of a particular variable star was/will be at a particular time?
If so, would you please post an example source code for Algol? Thank you very much!
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