-ASTR 204 Application of Astroimaging Techniques
Lab 5 - JPL Ephemeris, Binary Maker 3
In Lab 5 we’ll look at another ephemeris generating tool; Horizons Web-Interface from
JPL, and Binary Maker 3 program for generating radial velocity curves and 3-D modeling
of binaries.
Horizons Web-Interface
NASA JPL has a free online tool for generating ephemerides of various objects including
planets, known comets, and asteroids, called Horizons Web-Interface.
http://ssd.jpl.nasa.gov/horizons.cgi#top
Procedure
Go to Horizons Web-Interface website. The first section asks for user input parameters
(below). For Ephemeris Type choose Observer. Target Body allows you to type in a
specific name i.e. asteroid 4 Vesta, or comet C/2014 E2. This name must be exact.
Select Observer Location. Under California, choose Display Cities, then San Mateo
from the drop down menu, to apply the Longitude and Latitude of San Mateo. CSM
Observatory coordinates can also be input: Long. -122.33, Lat. +37.53. (decimal degrees)
As an example, we’ll use asteroid 4 Vesta
HORIZONS Web-Interface site
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Next, choose Time Span to request an ephemeris using specific Start Time, Stop Time,
Step Size, and period in days, hours, or minutes. All dates are UT.
HORIZONS Web-Interface site
In our asteroid 4 Vesta example above we have chosen:
Start time is 2014-05-29 UT, or 5:00 pm local time (12:00 midnight – 7 hours) May 28.
Stop time is 2014-05-30 UT, or 5:00 pm local time (12:00 midnight – 7 hours) May 29.
Step Size is 1 every Hour, to yield 24 positions for 4 Vesta during the 24 hour time span.
Select Use Specified Times, and from the main window, choose Create Ephemeris.
HORIZONS Web-Interface site
The ephemeris for asteroid 4 Vesta is now displayed for May 29, 2014 UT. The second
column shows times in one-hour increments. 04:00 would be 9:00 pm local time (4:00 UT
– 7 hours), May 28th. Each row also displays Right Ascension (R.A.) and Declination
(DEC) of 4 Vesta at that specific time, along with the magnitude.
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Binary Maker 3
Binary Maker is a powerful tool used by astronomers http://www.binarymaker.com for
calculating light and radial velocity curves of binary stars. BM3 shows 3-D rotating star
models along with graphing of the light curves. First, we will look at and analyze sample
stars in the BM3 library.
Procedure
Binary Maker 3 has a very
extensive library of files of numerous
binary systems and you will open
one of these files to see how the
program works. Click on the
programs icon, to get it started. Give
it a few seconds and you will see
four main windows pop up. They are
labeled User Input, Binary, Light
Curve Plot, and Radial Velocity.
To the right, is a screen shot of these
windows.
Binary Maker 3 screen shot.
The User Input window is the primary one that you will use to enter the star that you want
to investigate. The many tabs in this window allow you to configure the other 3 windows.
Once you have entered your star using the drop down File tab, you then click the Render
tab. Once you do that, the Binary window allows you to visualize the binary system. Its
light curve is displayed in the Light Curve window and the radial velocity curves are
shown in the Radial Velocity window.
Getting Started
Let’s begin by opening an already existing data file for the eclipsing binary
TXUMa_Maxted1995V.zip. Open the File tab in the User Input window, as shown below.
Binary Maker 3 screen shot.
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You will see the following window.
Binary Maker 3 screen shot.
Double click on the Zip folder and you will see the window below, which shows lots of
constellation files.
Binary Maker 3 screen shot.
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Since we are looking for a particular binary in the constellation of Ursa Major, double-click
on the folder entitled UMa, which will reveal the following display:
-ASTR 204 Application of Astroimaging Techniques
Binary Maker 3 screen shot.
Open the Zip file entitled TXUMa_Maxted1995V.zip by either double-clicking on the file
or clicking once and then clicking on the Open button. When you also press Render, the
screen will now look like the following:
Binary Maker 3 screen shot.
You can see the light curve of the binary, as well as the shape of the individual
components and their radial velocity.
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Exporting Your Photometry Data Files to Binary Maker 3
One of the things that you really want to do is to export your photometry data to Binary
Maker 3 (BM3). Doing so, will allow you to see what your binary system actually looks
like. For some of the more exotic systems, such as RS CVn stars, you can actually
model the distribution of star spots on the star’s surface. There are a series of steps
necessary to be able to import your data to BM3.
The first thing that must be done is to find the time of minimum light or ToM. There are a
number of ways to do this and the method is outlined below.
Once you have the ToM, you can then construct an ephemeris. After you have
determined an ephemeris for your data, you must then convert your Julian dates (x-axis)
to phases and your magnitudes (y-axis) to fluxes. You now have a two column file,
consisting of phase and flux. With this data, you can now construct two files: an nrm file
and a bm3 file. The nrm file contains the phase and flux data from your photometry run.
The bm3 file contains the input parameters of your eclipsing binary. These files are then
zipped and you can open them in BM3. These steps are detailed below in a number of
steps, using previously obtained data from student Peter Roomian’s data of the contact
binary W UMa.
Step 1 Constructing the ToM.
A good program for computing the ToM is Minima and is obtainable from Bob Nelson’s
website, http://members.shaw.ca/bob.nelson/software1.htm. Student Peter Roomian’s
W UMa data was input as a csv file to obtain the ToM.
Step 2: Constructing the Ephemeris
Using the method in step 1, it was found that the ToM or Tmin is 2456345.63646(33),
where the number in parentheses is the probable error. From Worden and Whelan
(MNRAS 163, 391 (1973)), the published period of W Uma is 0.333638 days. The
ephemeris then becomes,
where E is the epoch of the eclipse. Assuming a circular orbit, E = 0 for the first primary
eclipse, 0.50 for the secondary eclipse, 1 for the next primary eclipse, etc.
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Step 3: Calculating the Phase of the Data Here is the formula for calculating the phase: In our case, we have: The next step shows how to set this up as an Excel file. Step 4 Setting Up the Excel Function
In the screenshot below, column E represents the phase calculated in Step 3 and is
called Phase 1. The cell E3 is highlighted, showing the equation for calculating the
phase.
Excel screen shot.
If you pull this box down, you will calculate all of the initial phases in column E for your
data.
Step 5 Calculating the Actual Phase
In column F, called Phase 2, you subtract the integer part of E leaving only the fractional
part of the phase. Usually, your initial phase would have had some integral value other
than zero (this is actually the Epoch). However, this fractional part is the actual phase of
the light curve. Column F represents the final phases for your data.
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Step 6 Converting Magnitudes to Fluxes
To do this, we use the flux equation,
This is done in column G, and the screenshot below shows the flux conversion equation,
when cell G3 is highlighted.
Excell screen shot.
Step 7 Normalizing the Flux Values
The flux values should now be normalized, with the largest value normalized to 1.00. In
column H, this largest value is called Max Flux. The value H3, as shown below in the
screenshot, is actually the maximum value of all of your data in column G. We will be
dividing all of the values in column G by this value to normalize them to 1.00, as the
highest flux.
Excel screen shot.
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Column I represents the normalized flux, obtained by dividing all of the fluxes in column G
by the value of Max Flux. In the screenshot below, cell I3 is highlighted to show the
equation used.
Excel screen shot.
Step 8 Forming the .nrm File
The last two columns of the spreadsheet, columns J and K, are now exported to a new
file (phase, flux) with the name WUMa.nrm. The next paragraph outlines the steps
needed to make your bm3 file. Once this is done, and both files are combined in a zip
file, you will see what your data looks like.
Constructing the bm3 File
The bm3 file consists of the parameters for your binary system. You must find the paper
from the literature, that has the parameters for your binary. For example: If your binary
star is AE Phoenicis, the parameter file is obtained from C. Maceroni, et al, (1994)
Astronomy and Astrophysics, vol 288, pp. 529. Once you have the parameters, you must
input them into the User Input Dialog window. Once you have entered the necessary
parameters, you must now save them. Click on the File menu on the User Input window,
and select the menu choice Save BM3 File. See the figure below.
Binary Maker 3 screen shot.
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You will see a standard file save dialog box opened, and you should select an appropriate place to save the parameter file, as well as choosing an appropriately descriptive filename, such as AEPheVspot.BM3 as shown below: Binary Maker 3 screen shot.
You can now create a Zip file that would combine both the parameter file (bm3 file)
and the data file (nrm file) into a single compressed Zip file. The benefit of this is
that you can later read in both files simultaneously by just reading in the Zip file.
To create a Zip file, select the Save Zip File menu choice under the File menu of
the User Input dialog as shown below:
Binary Maker 3 screen shot.
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You can name the file whatever you want, but you must have zip after the dot.
Look at the screenshot below to get an idea of what to look for.
Binary Maker 3 screen shot.
Once you have the nrm and bm3 zip files, you can now load them into BM3 and see
what your star looks like!
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