Planethunters: How to ID a star on the Kepler Data Search site (updated to Q2)

Kepler Search Page (screencap)


A lot of people have asked how to identify a star that they see on the Planethunters website. Apparently the programming team will be adding something soon that says what the Kepler ID (KID) of the star is, but in the meantime I’ll show you how to track it down yourself!

The good news is that it is possible to go to the Kepler Data Search page at http://archive.stsci.edu/kepler/data_search/search.php (shown in the screencap on the left) and find all the stars listed on the PH site, but it’s not quite as straightforward as typing the ID of the star into the search forms there – the stars on the PH site have their own ID numbers with APH or SPH in front of them, and these are not the same as the official Kepler IDs used in the Kepler catalogues. However, all the information you need to find a star is on the PH site.

If you look at the source page for a star (e.g. http://www.planethunters.org/sources/SPH10052245 ) you’ll see on the right-hand side four “stats” for the star – “Type of star”, “Apparent visual magnitude”, “Teff“, and “Radius”. You don’t need the Type, but you’ll need the other three, so make a note of those numbers (or remember them).

If you look at the Kepler Data Search Page, you’ll see a lot of places where you can enter numbers to search for things! It might seem a little intimidating at first, but don’t panic! Here’s what you need to do:

    1) Type the value for Teff (the Effective Temperature of the star) from the PH source page into the text box under where it says “Teff” on the Kepler page. Don’t hit Enter yet, because we still have to enter the other values.

    Now, the numbers shown on the PH site (apart from the Teff, which is exact) are rounded up or down, we have to be a bit cunning when entering the values on the Kepler Search page. Instead of entering an exact value, we need to enter a range of values that include the value shown on the PH pages. Since we’re not sure whether PH has rounded up or down, the best way to do this is to include the whole range of numbers that can be rounded up or down to the PH value. So if your radius is 0.6x Solar, you’ll need to enter a range from 0.55 to 0.65. If the visual magnitude that you’re looking for is 14.8, then you’ll need to enter a range from 14.75 to 14.85. To enter a range of numbers into a box, type the lower number, then “..” (without the quotes) and then the higher number. So a radius of 0.55 to 0.65 would be entered as “0.55 .. 0.65”. Note that you’ll need to type a space on either side of the two dots for this to work!

    2) Type the appropriate range of values for “apparent visual magnitude” into the box below “KEP Mag” (Kepler Magnitude).

    3) You’ll notice that there isn’t a box for Radius. However, there are four dropdown lists (under the Teff box) that are labelled “User-specified Field X”. Click the downward-pointing arrow under where it says “User-specified Field 1” and you’ll see a list of all the other things that you can search for appear. Scroll down the list and 15 entries from the bottom you’ll see one called “Radius” – click on that to select it. Now you’ll see Radius appear in the box, and can enter your radius range into the text box next to it!

    4) (optional) Bring up another list in one of the other User-Specified fields (you can use 2 or 3 or 4, it doesn’t make any difference), but this time select “Quarter” (it’s the fifth entry from the top) and enter “0 .. 2” into the box next to it.

    The Kepler data is being released in packages known as “Quarters” – this will specify which Quarter you want to search through. There are at least 5 Quarters, but only Quarters 0 and 1 have been released to the public so far. Q2 was be released on Feb 1 2011 – that includes another 120 days of data on top of the 35 days that we’ve been looking at so far. After that, it’s a long wait til the public release of Q3 and Q4 – those won’t be available until June 2012, and Q5 won’t be released until June 2013! Most of the stars in the database have observations in several or all of the Quarters, particularly if they’ve been flagged as interesting already. However, there’s not much point in searching for the extra observations of stars that we won’t be able to see for years – so by entering “0 .. 1” we’re looking at the accessible Q0 and Q1 observations only (if you’re reading this after Q2 is released, you’ll need to enter “0 .. 2” instead to show everything up to and including Q2!)

    5) Now you can press Enter (or click the green-highlighted “Search” button) and you should get a result of either a single star or a handful of stars. The Kepler ID is the number in the first column on the left, after the “Mark” column. You may have multiple entries listed for this star – this is because the search results list the observations from different quarters separately. You’re probably going to be interested in the Q1 and Q2 data, because that’s what is shown on the PH site (the Q0 data is from about 9 days prior to the Q1 data).

So, here’s an example: To find APH10135234 (which has a Teff of 6792, a visual magnitude of 13.3, and radius of 1.6x Solar), you’ll need to enter:

Teff = 6792

KEP Mag = 13.25 .. 13.35

Radius = 1.55 .. 1.65

Quarter = 0 .. 2

Enter those values, and you’ll get three results (all from the same star, from Q0 to Q2) – the first column (next to the “Mark” button) tells you that the KID for the star is 11092273 (you can click on the image at the top of this post to see how I’ve entered the numbers if you have any issues).

Now, there are several useful things you can do with this KID number. For starters, if you wanted to know anything else about the star (e.g. its 2MASS catalogue number, metallicity, or its RA/Dec location in the sky) then that’s listed right there in the search results!

If you want to know if a planet (or candidate planet) has already been identified around that star, you can go to the Released Kepler Planetary Candidates page. When you get there, press Ctrl+F on your keyboard to open up a Search window, type (or copy/paste) the KID number into the box and press Enter to search for it on the page. If it’s listed there, it’ll appear and you can see the data associated with it – if it’s not listed then maybe you’ve found something new!

You can also use it to check on the Kepler Eclipsing Binary Catalogue page, which lists all 1832 of the known Eclipsing Binaries that have been observed by Kepler (you can also download the paper describing them, which also includes some useful examples of eclipsing binary lightcurves on page 18-22!). Again, press Ctrl+F to bring up the search box and see if your star is in there. If not, then you’ve either found a binary that wasn’t listed, or the star isn’t a binary! Note that if it is in that list and you suspected it was a planet, then it’s probably actually a binary system (but if it was a borderline case then that may not be so certain).

EDIT: Stars with “Unknown” parameters have started to appear on planethunters recently. It seems that some of the stars in the Kepler database just don’t have the stellar data listed for some reason (which is why they’re listed as “Unknown”, but I don’t think we were actually shown those on planethunters for the first few weeks. Since between us we’ve apparently seen all the stars at least once, the PH guys ‘reset’ the count so that people could go over the stars a few more times, and it looks like that has brought in the “Unknown” stars too. Unfortunately it’s very hard to track these “Unknown” stars using the methods I’ve described here since usually the only data we have for them is the visual magnitude, which brings up hundreds of different stars.

It is possible to find them, but it involves trawling through the database by hand (if you click “Teff” in the first row at the top of the results page, it’ll show all the stars with ‘blank’ Teff at the top of the list, and then you can go through those manually and plot the lightcurves for them and see which one resembles the PH graph you’re looking at – but it’s a long-winded, tedious process).

In the next post (probably tomorrow), I’ll tell you how to download the data and show you how to plot it in Microsoft Excel!

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