 The Magnitude
Measuring Tool is a new AIP4Win feature
that is still in active development. Its purpose is to
make doing CCD photometry fast, accurate, and efficient.
The MMT supports multicolor photometry and the AAVSO's
new Extended format.
To see how easy it
is to use the MMT, view the 10-minute Flash video by
clicking the link below. The video gives you a quick
run-through, then shows you how to set up the MMT the
first time you use it, and then recapitulates showing a
photometric run on a short ten-image sequence.
Further down this
page you'll find a brief description of the theory behind
the new MMT. Understanding the theory behind the tool
makes it much easier to set up and use the MMT.
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The
Concept Behind the Magnitude Measurement Tool
The Magnitude Measurement Tool is
the front end of a hierarchical photometry object. As you
use the tool with your images, you are really populating
a data structure with photometric measurements. When all
the data has been transferred to the data structure, the
data structure generates a report in the format of your
choice. Because the data remains in the data structure,
you can generate different reports; for example, you can
call for a report in the bare-bones AAVSO Extended Format
to send to the AAVSO offices, and then generate a much
more detailed report for your own data archive. You can
also generate a "quick-look" graph of
time-series data.
Data in the photometric structure
is hierarchical, meaning that different types of data are
"nested" inside one another like a set of
Russian dolls. Each level consists of
"properties" appropriate to that level. Data
extend from base objects to subordinate objects contained
within them. These concepts may seem a bit foreign at
first, but as you think about the hierarchy of
dependencies found in photometric data, you will find
that it all really make sense.
Observer
The base of the data pyramid is Observer.
The Observer is fundamental because all of the Observer's
properties are inherited by the images, stars, and
individual photometric measurements. In the MMT, the
Observer's properties are entered on the first (leftmost)
tab of the tool. Observer properties include:
- Name of Observer
- Longtitude of Observer
- Latitude of Observer
- Time Zone setting used
- Telescope aperture used
- Telescope focal length used
- CCD camera used
- Images()
created by the Observer, and array of Image.
Image
The next level in the
hierarchy is the array Images() that
belongs to the Observer. In the MMT,
you specify a set of images using the Images tab,
then pick a single Image for selecting Stars().
Luckily for us, CCD images contain this information
in the FITS header, so you only have to supply the
list of the images to the MMT, and the MMT obtains
the properties of each Image from
the image itself. Image properties
include:
- Time that Image
was made
- Exposure length (the
integration time)
- Filter (B, V, R, I) used
for Image
- Stars(),
an array of Star.
Star
Star
inherit the properties of Obsever
and Image that contains it. Star
properties come from two sources: 1) from star
data entered on the Stars tab of the MMT, and 2)
from the (x,y) coordinates that you enter by
clicking on star images that correpond to star
data entries. Star properties
include:
- Type (variable, comp
star, or field star)
- Name (chart
designation, AIUD, or catalog name)
- Right Ascension
- Declination
- B standard magnitude
- V standard magnitude
- Rc standard
magnitude
- Ic standard
magnitude
- (x,y) coordinates in
Image
- Measurement
of photometric properties.
Measurement
Measurement
properties are measured from a star
in an image taken by the observer,
in other words, Measurement inherits the
properties of Observer, Image,
and Star, and includes its
own properties. Measured properties include:
- Number of pixels
in the star aperture
- Total ADUs in
the star aperture
- Number of pixels
in the sky annulus
- Total ADUs in
the sky annulus
- Maximum ADU in
star image
Furthermore, there
are results derived from the measurement
properties described above combined with
properties inherited from Observer,
Image, and Star.
These include:
- Raw instrumental
magnitude
- Statistical
uncertainty in the magnitude
- JD of the
measurement
- Airmass of the
measurement
With data organized this way, the
magnitude (i.e., what you're looking for) can be linked
to all of the magnitudes obtained for all of the stars in
all of the images taken by the observer.
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Output
Generated by the Magnitude Measurement Tool
When you click the Run
Photometry button of the MMT, the MMT loads each
Image in Images(), photometers each Star in Stars(), and
for each Star, produces a Measurement. These properties
are passed into the photometry object. Now for the big
question: What data do you want to get out of the MMT?
The Magnitude Measurement Tool
produces a variety of different reports, and more can and
will be added. Furthermore, once the data has been passed
to the photometry object, you ask to get different
reports from the same data. The current selection of
output reports includes:
- AAVSO Format.
This format is required to report data to the
AAVSO. The format consists of a header with a
smattering of observer information plus one line
of data for each variable star measurement. The
data consists of a magnitude for a variable star
adjusted to match the standard magnitude of a
comparison star plus raw instrumental magnitudes
for one or two comp stars.
- CBA Report.
This is the bare-bones format described on the
CBA's website. It contains a truncated JD, V-C1,
and C2-C1. That's all! The advantage is that it
transmits hundreds of differential magnitude
measurements in a very compact text file. For
this report, you would normally select a variable
plus two comp stars.
- Differential
Photometry. This option gets you a
rather verbose set of measurements in an
Excel-friendly text format. You can select
apparent or differential magnitude, a sparse set
of data or everything but the kitchen sink, and
specify the number of decimal places. If you
select more than two comp stars, the report
includes V-Ens. You would normally select a
variable plus as many comp stars as you want.
- Raw Instrumental
Magnitudes. This option reports raw
instrumental magnitudes for as many images or
stars as you want. You might use this option to
collect data for computing the transformation
coeffcients (several dozen stars in a small
number of images shot with different filters) or
constructing the color-magnitude array of a
cluster (several hundred stars in a small number
of images), or collecting precision photometry on
exoplanet transits (a few dozen stars in several
hundred images) for detailed analysis in your own
spreadsheet.
- Signal and Noise.
This option was used in testing the software, and
may not be active.
- All Input Valuves.
This reports mirrors all the data collected to a
text file. Use this as a permanent record of an
observing session, or as a sanity check or
diagnostic if the data output by another report
format appears strange or confusing.
- In addition, on the Execute
tab, you can click the Light Curve for
Time Series button for a
"quick-look" graph of time-series data.
For a permanent record, however, it is best to
save your data in the appropriate text format.
and import it into Excel or other spreadsheet.
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