Keck Follow-up
Hello PlanetHunters! The Kepler field is finally visible and tonight, grad student John Brewer and I began observing a few of the candidates that you identified. We are operating the Keck telescope in Hawaii remotely from New Haven, CT. The weather in New Haven may not be great tonight, but it’s perfect in Hawaii – we have clear skies!
There were several steps involved in selecting the best candidates to observe tonight.
- You all did the hard first step, classifying data from Q1 to identify prospective transits.
- Stuart extracted 3500 prospective transits from the database.
- We examined all of your selections by eye – about 100 planet candidates survived (many transits per candidates).
- Yale grad student, Matt Giguere, wrote computer programs to model the light curves and to search for evidence of blended background binary stars. Visiting grad student, Thibault Sartori, has been using this code for the past several weeks to model all of the planet candidates – about half of the 100 planet candidates survived that analysis.
- John and I will analyze the spectra we collect tonight to derive stellar parameters (temperature, surface gravity and chemical composition) – this will help to better constrain the planet radius.
- Jason Rowe and Natalie Batalha from the Kepler team kindly agreed to analyze our top candidates with the Kepler data verification pipeline to help eliminate additional false positives.
It will be tough to go to the next level and confirm any of these as planets because the stars are faint. It is sure easy to understand why the Kepler team has more than 1200 planet candidates, but currently only 11 confirmed planet-hosting stars. It is a long road from planet candidate to a bonafide planet!
Telescope Proposal
Hey everyone,
Yesterday myself, Meg, Chris and the rest of the Planet Hunters team where working hard to get us to the next stage of discovery with Planet Hunters. As you all know we have been really successful at finding interesting objects that the Kepler team’s automated algorithm has missed. Our first trawl through the data has netted us lots of potential planet discoveries. While this is great we really want to remove the potential from the sentence! So yesterday the team submitted a proposal to to the Keck telescope to request time to follow up the results from the site.
The Keck telescope is a wonderful instrument located 4,145 metres up, near the summit of Mauna Kea in Hawai’i. Composed of two telescopes each with a mirror 10 metres across, it is one of the best astronomical instruments in existence.
Unfortunately this means Keck, like most modern telescopes, is large, complex and therefore expensive. It cant be run by any one team or even any one country. It might be many times larger than your telescope at home but at least you get to look through that telescope whenever you want, while astronomers have to share time on Keck. Infact share is even stretching it a little, what actually happens is astronomers compete each year for time on the telescope. Unfortunately this competition doesn’t involve some kind of X-Factor public voting system (otherwise we could get all you guys to rig it for us) but rather is decided by a board of scientists who run the Keck telescope. Each year they receive a lot of requests from scientists to use their magnificent instrument but there is only enough time for a limited number of observations. The science team for Keck will independently asses each request for scientific merit, practicality and interest to decide who gets those valuable hours gathering photons.
To make matters worse pretty much every telescope, on earth or in space, has this competition at the same time each year. This means that astronomers all over the world scramble to get their proposals in and astronomy departments are full of sleep-deprived, very stressed-out people. Meg, who did the lion’s share of the work for our proposal, also had another 2 due at the same time for different telescopes! She somehow managed to get them all in and I hope is even now sleeping to recover from her ordeal. Thanks, Meg!
We have asked them for two nights worth of observing time using the HIRES instrument on Keck. During this time we point the telescope at and take spectra of our top planet candidate hosts. This will let us do two things, learn more about the host stars themselves to lets us characterise the potential planets better, but more excitingly it will let us look for the telltale wobble of the host star. If we see this it would would give us independent confirmation what we are seeing is really an exo-planet! At that point we can bin that annoying “potential” prefix and say without fear of contradiction that you, the Zooites of Planet Hunters, have discovered a new world !
We are by no means guaranteed to get the time but we all have our fingers crossed and we will let you know as soon as we do.
New Kepler Data: Feb 1
By Zak Kaplan (Yale undergrad)
Planet Hunters has just completed its first analysis of the Kepler data! With your classifications, we were able to extract information about all of the 150,000 light curves. We would like to thank the more than 16,000 registered users who have helped make Planet Hunters such a success. Special thanks to the collectors and the top 14 users who each analyzed over 5000 light curves, accounting for over 10% of the 1.3 million classifications.
To give a better idea of what you’re measuring in a transit curve, a planet crossing a star causes about the same dimming of light as a small fruit fly passing in front of a car headlight. Now imagine that car is a few thousand light-years away, and you get a sense of just how amazing the Kepler data and your work have been.
The Kepler team will have a press conference on 2 February 2011, announcing their new candidates and releasing new data that will more than quadruple the amount of data that we can serve to you. You can join the live broadcast on NASA TV at 1pm EST and we will post the Kepler press release here next Wednesday.
For the past week, the Exoplanet Research Team at Yale has been analyzing over 3500 light curves that you marked with promising transits. We found that PH users marked transits that we would have missed. From this first set of data, we have culled approximately 300 strong planet candidates, as well as several new eclipsing binary star systems. We are formatting the new Candidates pages now so that they will appear before the Kepler press conference. Then, you can check to see which objects you detected independently, before the Kepler team announced them. It will be especially interesting to see if there are some good candidates that you all found that are not on their new list. If so, we will ask the Kepler team for feedback on your new candidates.
We hope you will help continue to prove the power of citizen science, as we look for more planets beyond our solar system. Until then, keep on hunting!
Uncertainty
Hello, I’m John, a graduate student at Yale University and a member of the Science Team. We have had some questions about the non-light curve information on the star pages, including: how accurate is the data, and why is it missing occasionally? This post will give you some background on where this data comes from and how to interpret it.
Before the Kepler spacecraft was launched, a lot of thought went into finding the optimal patch of sky to observe. Then, many years were spent collecting as much data as possible, from the ground, about the stars in that patch of sky. Photometry (a measure of star brightness, like you have been looking at on planethunters.org) was taken through multiple filters of most stars and spectra (with more detailed information) were taken of the brightest stars. These measurements all went into selecting the most promising stars for the Kepler mission to look at.
From these measurements, it is possible to calculate certain values which are useful in interpreting the data from Kepler. This includes spectral type, effective temperature, surface gravity, and radius. All of these values were compiled into the Kepler Input Catalog, which we use to show you the information on the star pages. However, because this data was taken en-masse and many of the stars are quite dim there is sometimes a large uncertainty in these parameters or there may be no derived values at all. When you look at the stellar radius on a star page, that number could be off by as much as 50%!
After interesting stars are found, much effort goes into closely examining the star with larger telescopes, more frequent observations with Kepler, or both. This results in much more accurate determinations of all parameters. One recent paper (Metcalfe et al. 2010) determined the radius and age of a Kepler star to within 1%.
Some of you have already been calculating the size of the transiting companion using the duration of the transit and the stellar radius. It has been great to see the phenomenal work people are doing in seeking to understand these stars. Keep in mind though that until more accurate follow up data can be taken, there will be a large amount of uncertainty in those numbers.
Quiet Stars (examples)
Thanks very much for your help with this project. At last count, roughly 50,000 light curves had been sorted at planethunters.org. Many of you have requested more examples about how to classify stellar variability, so we’ll start with the easiest case. All of the light curves below are examples of quiet stars. Random variations in brightness occur because of photon noise (similar to shot noise in electronics). The number of photons that are collected are small enough that there random fluctuations that have nothing to do with the actual brightness of the star. Photon noise (or Poisson noise) produces scatter, but the data remain in a nearly featureless band of points.
If you look closely at the light curve data for these quiet stars, you will see light gray error bars associated with each data point. In any physical measurement, the error bar simply captures our ignorance about the true value of the measurement. In the Kepler light curves, the brightness is represented as a discrete dot, however, any and all points along an error bar are equally correct values for that particular brightness measurement.
In the quiet light curves above, should any of those low points be flagged as possible transits? Probably not. A deviant point or two can still just be noise. A true transit event should have a series of low brightness points that last for the time it takes the planet to cross in front of its stars (i.e., a few to several hours, represented by a few to several data points). Low dips that repeat are also good indicators of a transit, however some of the most exciting transits (from planets in wider, more habitable orbits) will only occur once per month (for example, a true analog of our Earth would just transit once per year).
The quiet light curves above may seem like duds, but they are an extremely important aspect of research for this project. Stars that do not vary in brightness are particularly important objects for exoplanet searches with other techniques. The work that you’re doing will feed into our understanding for the next generation instruments and space missions that could be built to detect planets.
Happy Holidays to All! Debra Fischer
Gwiazdy podwójne zaćmieniowe
Nazywam się Debra Fischer i jestem profesorem astronomii na Uniwersytecie Yale. Wielu z Was odkryło już wspaniałe wykresy krzywych blasku gwiazd podwójnych zaćmieniowych, dlatego chcielibyśmy Wam dostarczyć nieco więcej informacji na ten temat. Przedstawione przykłady to odkrycia, które dzięki Wam znalazły się w naszych zbiorach. Więcej takich przykładów można znaleźć w pracy zespołu Keplera (Prsá i in., 2010 http://arxiv.org/abs/1006.2815).
Krzywe blasku uzyskane dzięki teleskoppowi Keplera pokazują zmiany jasności gwiazdy w czasie. Ilustracja 1 powyżej (APH10135736 = KID 6449358) przedstawia dwie gwiazdy orbitujące wokół siebie. Podobnie jak w przypadku planet w tranzycie, każda z tych gwiazd przesuwa się na tle drugiej. Wykres pokazuje poziom jasności gwiazd w czasie (liczonym w dniach). Przez większość czasu blask większej, bardziej gorącej gwiazdy oraz mniejszej, zimniejszej gwiazdy daje wspólną wartość na wykresie. Głęboki spadek jasności (minimum główne) oznacza, że mniejsza gwiazda przesłania większą, odpowiadajacą za większość wspólnego blasku. Z kolei mniejszy spadek (minimum wtórne) oznacza, że większa, bardziej gorąca gwiazda przesłania mniejszą, odpowiadającą za mniejszą część wspólnego blasku. Gwiazdy, których krzywe blasku mają postać płaskich linii poprzedzielanych dość ostrymi spadkami (jak na ilustracji 1) określa się mianem gwiazd podwójnych typu Algola.
Kluczowym elementem wskazującym na obecność gwiazd zaćmieniowych (lub planet w tranzycie) na wykresach krzywych blasku jest powtarzalność.
- możecie policzyć dni pomiędzy dużymi spadkami na ilustracji 1 i określić okres orbitalny (ok. 5 dni) tego układu podwójengo
- możecie określić czas mijania się gwiazd na podstawie czasu trwania tranzytu (liczonego na ilustracj 1 w godzinach)
- możecie być pewni, że gwiazdy mają różne wielkości, jeśli tranzyty na wykresie mają różne głębokości
Zwróćcie uwagę, że głębokość spadków jasności gwiazdy podwójnej podczas zaćmienia może być podobna do głębokości spadków jasności planet w tranzycie. Głębokość ta informuje nas o stosunku wielkości obiektu dokonującego tranzytu (lub zaćmienia) do wielkości gwiazdy, wokół której dany obiekt krąży. Najmniejsze gwiazdy mają średnicę zbliżoną do średnicy Jowisza (gwiazdy mają postac gazową i zwiększona siła grawitacyjna większej gwiazdy powoduje kondensację ich struktury).
Czasami gwiazdy podwójne znajdują się tak blisko siebie, że ich powierzchnie przybierają kształt elipsy, a krzywa blasku pomiędzy zaćmieniami jest zaokrąglona, tak jak na ilustracji 2 po lewej (APH10039007 = KID 9357275), gdzie okres orbitalny trwa niewiele dłużej niż jeden dzień. Na wykresie tym widać zarówno tranzyty główne, jak i wtórne. Z najdziwniejszymi krzywymi blasku gwiazd podwójnych zaćmieniowych mamy do czynienia, gdy gwiazdy te są jeszcze bardziej do siebie zbliżone – nazywamy to układem ponadkontaktowym. Przykład przedstawiony został na ilustracji 2 po prawej (APH10102932 = KID 4633285). Gwiazdy te znajdują się tak blisko siebie, że mają wspólną otoczkę. Głębokość zaćmienia na krzywej blasku jest zmienna, wykres jest nieregularny, a między gwiazdami może dochodzić do transferu masy.
Planet Hunters 