Flares on Proxima Cen

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Today a majorly exciting astronomical discovery was announced: a planet has been found around our nearest neighbor, and it's named Proxima b. The planet is near Earth-mass, and orbiting right in the habitable zone for Proxima Cen – It's a huge deal!

While I wasn't involved with the discovery of Proxima b, I have been working with a team of other astronomers (led primarily by David Kipping) to study Proxima Cen. One byproduct of this work, which we are announcing today in conjunction with the Proxima b excitement, is a study of the flares from Proxima Cen. After coordinating with Guillem Anglada Escudé and the Pale Red Dot team, we're releasing this work today because it provides an important look at the stellar environment that Proxima b orbits in. This is naturally a critical piece of the habitability question!

Our Work

As many pundits and armchair astronomers will tell you, Proxima Cen is a flare star, meaning it produces many high energy flares on its surface. These events are driven by the star's magnetic field, and occur on the Sun too. Proxima Cen is a low mass star, called an M dwarf, which are known for sometimes exhibiting very high levels of flare activity.  M dwarf flares can produce much more X-ray and UV radiation than Solar flares. This radiation might be harmful for life, and a constant bombardment from it could even destroy a planet's atmosphere. Ouch.

Our data come from MOST, a nifty suitcase sized space telescope, which also happens to be Canada's first space telescope! While the Hubble this ain't, MOST is designed for pointing at bright stars and staring at them for long periods of time – perfect if you're in the business of finding these randomly occurring flare events.

As expected, Proxima flares a lot (not as much as some other flare stars, mind you). In 37 days of monitoring data on Proxima we found more than 60 flares. These events have energies comparable to the larger end of Solar flares... but keep in mind Proxima is only 12% the size of the Sun! These flares can be so bright they can raise the total brightness of Proxima (in the visible light) by 20-50%! Here's a couple as examples from our data:

If the Sun got 50% brighter for 5 or 10 minutes... that would be a very uncomfortable day.

See the characteristic shape of the flares? Very rapid rise, exponential decay. I found in a previous paper using Kepler that M dwarf flares typically have two phases of decay that are general among most all flare events. What's interesting, though I don't fully have my head around it yet: The example at Left of Proxima follows this 2-decay law, the example on the Right does not. Huh...


The rate of flares on Proxima Cen

Stellar (and Solar) flares occur with a range of energies and durations. Typically we describe the "flare rate" as a power law distribution, with infrequent large energy events, and tons of small ones. We see this on the Sun, and for basically every other star we've studied for flares. Proxima is no different, and shows a clear power law shape in the flare energy versus rate. Here is that result from our paper, with a few relevant energies highlighted:
The red line is the "power law" model. The key takeaways are both the high and low energy ends: small flares happen a lot on Proxima. While they don't appear to produce a worrisome amount of constant UV or X-ray radiation, these small flares will (and have!) definitely made searches for any transiting Earth-mass exoplanets difficult. Proxima produces on average about 66 flares per day with similar amplitudes in visible light as an Earth-mass planet would block. That's frustrating!

On the large-energy flare end, we still don't understand the full impact a "superflare" would have on an Earth-like atmosphere, though there has been some great work on the subject (and much more is being done!) What is important for this star is that the newly discovered Proxima b is being subjected to a lot of these big flares. We estimate Proxima produces roughly 8 of these superflares per year. If even only a few of these were to impact Proxima b, this might be very bad news for the atmosphere and anyone vacationing there... So more detailed models of how the atmosphere would truly respond (or even if it would survive) are needed, and thankfully smarter folks than me are working on it!


The Future

Of course, in the near future everybody and their uncle will be studying Proxima, trying to learn more about the planet (e.g. it's size, radius, maybe even the composition).  I believe this will soon produce a "paper flare", with a huge rise and then exponential decay in the number of papers on the Proxima Cen system.

A less talked about aspect of this important low mass star is it's rotation. Proxima rotates quite slowly,  83 days compared to ~25 days on the Sun. Typically we see an inverse connection between rotation and flare rates, with short rotation period (fast spinning) stars showing higher flare rates. Since rotation probably helps drive the star's magnetic field, this is thought to be an age effect: stars spin slower as they age (just like a child's top spinning on a table), which also leads to lower flare rates as they get older. Proxima flies in the face of this assumption, and flares A LOT compared to its rotation period. Interesting!

Since we only have 37 days of data for Proxima, we couldn't track the full rotation. But here's what we caught:
This matches nicely with the less dense tracking (but over a longer time period) shown here. With the flurry of activity I expect to follow the announcement of Proxima b, we'll hopefully get a TON of monitoring for Proxima. With this we could track the detailed spot sizes and positions over many rotation periods, and try to determine how long the spots live, and maybe something about their properties.

For our part, we're still processing the MOST data, looking for any sign of a transit. Results soon on that front!

Our paper is available now on the arXiv, and is submitted for review to the Astrophysical Journal Letters.


This work is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1501418 

A new email newsletter for SETI research

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A few months ago I became frustrated with the difficulty in conducting academic research on SETI (that is the Search for Extra Terrestrial Intelligence). Specifically it can be challenging to read the academic literature on SETI because articles are few, and are published in a variety of outlets.

SETI is a controversial topic, both for funding and for "legitimate" research, because it is often associated with conspiracy theories and blatant speculation. There's a lot of this kind of junk on the internet, so I'll let you find it if you're interested... but this material poses an extra layer of obfuscation towards scientists trying to read through the literature. When you search Google for SETI research you have to wade through a lot of junk.

Furthermore, professional astronomers have largely avoided publishing about SETI due to a lack of data. When new technology or new cutting edge datasets become available there's usually a handful of papers written about new imaginative ways we might detect alien life, or conversely that Earth might be detectable using similar techniques on other worlds. These papers get put in to any of a large number of academic journals that, despite heroic efforts by NASA and Harvard/SAO, still take a good deal of effort to read through.

Finally, given the low rate of academic papers on SETI research, it is easy for the occasional bit of brilliant work to slip by unnoticed by scientists. Like many astronomers, I read through the latest daily batches of papers on the "astro-ph" preprint server on arXiv.org every day. This can be dozens of new research articles to scan over each day. Typically I only read the titles for every paper, and the abstracts for only those that stand out. Sometimes I don't even see papers that I'm a co-author on appearing due to the volume of papers to look over!

For all these reasons, SETI is a difficult topic to learn about and stay abreast of!

After chatting with some folks who shared this concern, I decided one way to help was to start an email newsletter each month that highlights new research articles about SETI (and related topics). It's called SETI.news, it's free, and if you're interested in keep up to date on SETI research you should subscribe!

Each month, SETI.news simply sends a brief email listing articles I find on the arXiv that mention SETI. If there are other sources of research results (say, a GitHub project, a Zenodo group, or just a paper not on the arXiv) then I would also list those if people send them to me! SETI.news is not an academic journal or publisher, though I think an open journal of SETI research (run by academics, with editors, referees, etc) would be a great idea for collecting this material.

Check out the March edition of SETI.news here, and be sure to subscribe!

NFL Coaches Salary

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Recently in the local news I saw that our beloved Seattle Seahawks coach, Pete Carroll (or "Uncle Pete" as he's known at our house) is up for a contract negotiation soon. He's been the heart and soul behind turning the Seahawks from a national "meh" to one of the top teams in the NFL, including back to back Super Bowl appearances, and one of the best records in the league. Naturally, he'll be asking for more money.

So I was wondering: Does the Win/Loss record indicate Pete Carroll deserves more money?

For reference, I toyed with this idea a few years ago for NCAA coaches

I searched Google and quickly gathered some data on NFL Coaches Salaries, as well as their age. I then grabbed a few years of Win/Loss standings from ESPN (again, top hit on Google). Averaging together the results from the past 3 years of NFL play, let's see how they look! Of course I've highlighted the Seahawks with a bright green star.

The line of best fit was simply calculated using a least squares regression in Python. There's a lot of scatter (much more than in my NCAA analysis previously), but I'm only averaging 3 years of play instead of 10 this time. Here's how to read this graph: points above the line are winning more than average given their level of pay, and points below are winning less.

Right away you can see two interesting (or just obvious) things:

  1. Uncle Pete is already one of the top paid NFL coaches
  2. The Seahawks are one of the best performing teams in the NFL over this time period

So he might have a good case for being paid more! Let's see just how undervalued he might be. By subtracting the model from the data, we can compute the coaches "value":

This is a pretty noisy distribution, and not a great discriminant of "value", but thats ok... this is definitely not my most absurd football related article to date...

So, teams with the best value coaches by this metric are:
1 - Denver Broncos
2 - Carolina Panthers
3 - Cincinnati Bengals

and Seattle's Pete Carroll is a respectable 8th. Given that he's one of the oldest coaches in the NFL, I don't know how much room he'll have to negotiate. However, if the salary data I've grabbed is accurate, this year's NFL champions, the Denver Broncos, are getting a hell of a deal with Gary Kubiak.


Of course we have to talk about the other end of the distribution. The team with the "worst valued" coach in the NFL currently is:
32 - Tampa Bay Buccaneers

Look, don't put too much stock in what I'm saying based on random numbers from the internet. As I understand it the coach's salary doesn't count towards the team's salary cap, but still, it doesn't look great Tampa....


The data and Python code to make these figures is of course available for use on GitHub!

Spots and Flares animation

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Here's a fun astronomy data visualization I've been working on to put in talks, which I thought was worth sharing!

What you're seeing is a model of a spinning star that is covered in starspots (grey circles), and transient flares (red dots). The starspot sizes and impact on the resulting light curve (bottom panel) are generated using a real and super neat starspot modeling code one of my collaborators has built. The flares occur at random (based on some "rate" parameter I've set), but their sizes and shapes are based on results from a pair of papers my PhD thesis advisor and I wrote in 2014.

Remember, when studying stars with Kepler all we get is the light curve (bottom panel), and it is very difficult (sometimes impossible) to infer the true spatial distribution of spots and flares on the surface.   A model like this can help us visualize what really may be happening on the star, and how our intuition can betray us.



I've tried to make everything going in to the light curve as physically realistic as possible, making this a "phenomenological model" of sorts. As a result, we get a model that looks very similar to real data. For example, when I run the model forward 10 more rotations and stack all the data, you see there is no strong correlation between # of flares and rotation phase. This despite the presence of a large active polar starspot that dominates the spot light curve.


This looks very similar to a result from Hawley & Davenport et al. (2014). A modified version of the published figure is below that also shows no correlation with flare energy (labeled Ekp) and rotation, indicating big flares and small flares come from all over the star.

I originally made this toy model and animation to help explain results from Kepler in a talk. The cool thing is that we might actually be able to do some real science using this model, both in generating mock data to use for training, and in estimating flare rates and flare properties for real stars!


Of course, the code to make this is available on GitHub as well.
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