Work Experience Oct 2016 - Ethan Cardwell and Adam McQueen

Two projects 1. Solar and stellar flares 2. detection of meteors using the observatory's sky cameras.

Project 1: Solar and stellar flares

Solar flares are bursts of energy from the Sun that occur when the energy stored in the magnetic fields is transferred into kinetic and heat energy (see Fig . 1, panels 1-6 show how plasma is trapped in magnetic field lines). They give off energy across the entire spectrum and can release energy at a magnitude of around 1E25 Joules. They occur at areas of the sun where magnetic action is high e.g. sunspots (dark spots on the surface of the sun). The period of time for a flare is around 100 seconds for energy in the corona . Mega flares with 10,000 times as much energy than regular solar flares happen every 200 years. So to study dynamics such mega flaring events we uses example from Stellar flares.

Fig. 1: how flare is formed Credit:Adam Clinch
Fig. 2: Examples of solar flares. Image credit : left image : NASA/SDO right image : giphy.com

How stellar flares look ?

We studied a sample time series of a stellar flare. Here we see a long term trend in the data because of the flare and we wanted to investigate the short term periods. The First step before applying FT was to detrend the data then we applied the same method to find a power spectrum. In this case confidence or significance levels corresponding to various time periods.

Butterfly diagram
Fig. 3: Light curve showing intensity v/s time behaviour of flare representing impulsive and decay phases. We also see explosive events in the flares decaying phase. SDSSJ144738.47+035312.

Method ?

We wish to investigate various pulses or bursts that occur in the stellar flares. In order to investigate we need to filter the signal of such events from the flare signal. We do this by using boxcar average function (see Fig.4 top panel) . The output of this function is then applied to the original signal. This removes the long term trend in the data (see Fig.4 bottom panel).

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Fig. 4: Using Fig. 2 as an example. Top panel : De-trended data. Bottom panel : Trend subtracted data.

We use a method called wavelet analysis to investigate the time period of the pulses present in a flare. This method uses fourier transform (FT), a function derived from a given function and representing it by a series of sinusoidal functions. The output of this method gives a series of periods (frequency).

Fig. 5: 3-D power spectrum showing period, time and power.

We represent the outcome in 3-D graph. The contours of this plot represent probability and the highest period is represented by red colour in the Fig. 5. We can also represent the outcome in 2-D as shown in Fig. 6-7. For these figures the probability is represented by contours of solid black colour.

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Fig. 6: Noise spectrum with confidence levels (60%,70%,80%,90%,100%.). The various contours would signify probability of an occurrence of a time period. (red indcates most probable and black the least). This is a relation between Fourier periods (in logarithmic scale) and time (s). The cross-hatched region is called COI which denotes errors that arise due to FT.

If we have 2 dominant periods at the same probability, then we use different threshold of boxcar function to identify the dominant period. E.g. in bottom panel of Fig. 7 we see 2 peaks representing dominant periods of the pulses at 20 and 40 seconds. We then use a 50s filter and find that the period at 40s had maximum probability.

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Fig. 7: Noise spectrum with confidence levels (60%,70%,80%,90%,100%.). The various contours would signify probability of an occurrence of a time period. (red indcates most probable and black the least). This is a relation between Fourier periods (in logarithmic scale) and time (s). The cross-hatched region is called COI which denotes errors that arise due to FT. Top panel at 50s bin for filtering and bottom panel at 30s bin for filtering.

Physics of the analysis

Upon applying the similar wavelet analysis. We find that there are possible periodicity at 40s (90 to 100% confidence). We discussed causes of these periodicities. These could be due to the following : 1.) Planets - When planet goes in front of the parent star. But this would take at least days. 2.) Sunspots - Assuming the star is Sunlike, then we would expect sunpots to vary every 30 days. Thus this cannot be possible cause. 3.) Other eruptions like Coronal mass ejections (CMEs), prominences and so on. These would last for few days again. So we rule this out. 4.) Flares - These would last for days but we see variations in short periods of time. This variations could be due to fluctating plasma during the eruption. As this plasma is along a flux tube, such periodicities and be related to high-frequency waves.

Project 2 - Ethan Cardwell

There are various objects that can be observed from the observatory. These include stars, comets, asteroids, meteoroid, meteor and meteorite. The difference between the local solar system objects is: A comet is a relatively small solar system body that orbits the Sun. When close enough to the Sun they display a visible coma (a fuzzy outline or atmosphere due to solar radiation) and sometimes a tail. Asteroids are small solar system bodies that orbit the Sun. Made of rock and metal, they can also contain organic compounds. Asteroids are similar to comets but do not have a visible coma (fuzzy outline and tail) like comets do. A meteoroid is a small rock or particle of debris in our solar system. They range in size from dust to around 10 metres in diameter (larger objects are usually referred to as asteroids). A meteoroid that burns up as it passes through the Earth’s atmosphere is known as a meteor. If you’ve ever looked up at the sky at night and seen a streak of light or ‘shooting star’ what you are actually seeing is a meteor. A meteoroid that survives falling through the Earth’s atmosphere and colliding with the Earth’s surface is known as a meteorite.

Fig. 8: This is a figure of an asteroid we saw at the observatory. (Faulkes Telescope, 2004)

In the span of 6 nights (from the 7th-13th) I saw roughly 40 meteors using the 3 sky cameras at the observatory. You can tell the difference from a meteor and for example a bird or a plane or even a piece of space junk based on this: 1.) A meteor has a straight line of trajectory. 2.) A meteor doesn't flash (plane/helicopter lights). 3.) Meteors dont produce big bright flash.