→ Widely unknown Exoplanet Astronomer

Credit: Swinburne Astronomy Productions

Like wildfire, the news about the diamond planet spreads across the web to the extent where the daily tabloid The Mirror decides to write about it. And why shouldn’t they? It is exciting, right? The only problem I see is that the oversimplified summary of the published result is treated as a certainty. Although this is a great theory, which causes a lot of interest around astronomy and exoplanets, it should be treated with a bit of caution before we start imagining a sparkling diamond planet about the weight of a Jupiter floating around in space. Now is the time for astronomers to debate and discuss the results. Then who knows, once the assumptions concerning the discovery have been constrained we might in a few years time know what part of this announcement was correct or not.  The way the news have presented the announcement makes it seem as if this announcement is the discovery of a diamond planet, which it is not.

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IRAF is short for Image Reduction and Analysis Facility and it is a program widely used by professional astronomers to reduce their data. The program if free and readily available on the web, so in theory there is nothing stopping amateurs from using the same software to reduce their images. IRAF has not changed much over the years, and many people starting off in IRAF will find it hard to deal with a command based program instead of a GUI (Graphical User Interface).

IRAF welcome screen

IRAF can be used on a number of platforms although it is mainly used on UNIX based systems such as Mac and Linux. The installation can be tricky, especially if you have not done it before. The full IRAF working environment requires two other pieces of software to be installed: DS9 and xterm/xgterm. IRAF will work without these environments being installed, but then you will not be able to display your astronomical images.

IRAF can be downloaded from: http://iraf.noao.edu/ and a support forum is available at: http://www.iraf.net/

Here I will go through the steps I use when deciding on which exoplanet to observe using an amateur telescope.

Step 1: Find objects which are bright enough.
Go to the exoplanets.org/table and from the drop down menu on the upper left choose transit planets. Then press the big pluss button (+) on the right and choose V mag under stellar params. You can move this table header next to the exoplanet name on the left side for convenience. Click the V mag tab to sort the magnitudes. To only display the transiting exoplanets where the host star has a know V magnitude write TRANSIT == 1 and V in the filter line. The table should now look something like this:

Step 2: Get the ephemeries

Now that you have an idea of which objects are bright enough you want to know when the transit will occur. To find this information go here. On the left you will se the names of the exoplanets. On the right you can click on ephemeris to get the transit times and dates. If you click on the ephemeris for one of the exoplanets you will be presented with a long list of numbers. The left most column is the date and times for when the transit begins. The middle column represents mid transit and the column on the right represents end of transit. At the top you have the transit duration. Remember that all times are given in UT. In this list of dates and times check to see when the next transit will be.

Step 3: Find out if the transit will be visible from your location

Copy the name of the star which the exoplanet is orbiting, like HD209458 and do a search on SIMBAD to find the coordinates. The name might change. The coordinates you are after are the ICRS coordinates. In this case it would be 22 03 10.78 +18 53 03.7 I would recommend you check the coordinates with those listed on the ephemeris page.

Now that you have the coordinates you want to see when the object is up in the sky (if at all). What a lot of professional astronomers use for this is staralt. Start of by choosing the date of  which the transit will occur. Next it is unlikely you are at a professional observatory so here you will have to enter the coordinates of your observing location. A nice and easy way to get these coordinates is using google maps. Navigate to your location on the map, right click and choose directions from here from the drop down menu. That should give you the coordinates in the text box found at the upper left of your screen. As an example of using staralt I will choose the Norman Lockyer Observatory, in the southern UK which I found (using google earth) has the coordinates 50.687901, -3.219783. The observatory is at a height of about 100 meters above sea level so in the observatory text box in staralt I write: 357.00 50.687901 100 The staralt page should look something like this:

Hit retrieve and a graph will appear. On the left y-axis we have elivation whilst on the x-axis we have time in UT. The dottet vertical lines represents astronomical twilight whilst the curved dottet line (if there is one), represents the moon. An ideal target will have a parabola shaped curve peaking at sometime during the night. Here is an example of an output showing two example targets:

Target1 22 00 00.0 +19 00 00.0
Target2 12 00 00.0 +19 00 00.0

Visibility plot showing two example targets

Target1 is seen on the left and it shows us that is is rising during the morning ours. This object would not be very suitable as I would not like to stay awake that long and also once it rises above 30 degrees twilight has begun. Pretty neat huh?

Target2 is on it’s way up in the beginning of the night peaking at a round 22 UT. The object is visible for quite a while not  setting before 4am. A target with such a visibility curve would be ideal.

So there you have it, repeat the 3 steps until you have a suitable target for the night you wish to observe. Keep in mind, if you are looking for transiting exoplanets with a host star brighter than about 10th magnitude you will definitely not have a transit happening every night.

If something was unclear in my description please comment below and I will answer the question. If you find that something is not clear I am sure other people think the same and will be glad you asked.

Clear skies!

This is a question of great interest to exoplanet astronomers who wish to measure the properties of exoplanets. Exoplanets have been found to orbit stars which are more than a 1000 times more active than our own sun. It is essential that astronomers know how the host star activity affects the exoplanet orbiting around it as a slight inaccurate measurement leads to wrong estimations of the exoplanet properties. Apart from our own sun, it is very hard to study the surface details on stars as they are so incredibly far away. We cannot simpy look directly at the surfaces of stars. Instead astronomers study the surface details on stars using indirect methods such as long time photometry and doppler imaging.

Shown are the sunpots(black) and faculae (bright yellow). Credit: NASA

Starspots (like sunspots on our own Sun) are darker areas on the surface of the star which are caused by magnetic fields. They are cooler than the surrounding area on the star and thus appear black when compared to the rest of the star. The brighter patches on the sun are known as the faculae. They usually occur at the same time as sun spots occur. Solar variability is very wavelength dependant. The irradiance (power incident on a surface) from the sun changes very little at visible wavelengths but it changes an order of magnitude more at shorter wavelengths (UV).

Understanding the host star’s change in flux as a function of activity is important when doing transit photometry. If for instance a big sunspot crosses the surface at the same time which the exoplanet is crossing, the exoplanet will seem as though it is bigger and that it is blocking out more light. This will lead to incorrect measurements of the size of the exoplanet. To be able to more accurately determine the size of exoplanets it is essential that one also knows something about the activity of the host star. Understanding the how the host star affects the measured properties of exoplanets is a active area of research at the moment.