This web page describes how to prepare a data file for submission to the
AXA. Since I am now writing the program that will process data on Caltech's
IPAC computer (for the NStED archive), you can assume that the following
format requirements will be very similar to what Caltech will require. Whereas
I have been very willing to modify the format of data files submitted to
the AXA (almost all data files had to be modified), Caltech's computer will
automatically reject any files that fail to conform to the required format.
I therefore suggest that anyone currently submitting to the AXA consider
reviwing how their data files for submission are formatted.
Image Processing Considerations
Most observers will use several reference stars to produce a file that
lists JD and dMag, where dMag is a "differential magnitude" based on the
reference stars. To minimize scintillation at least 4 reference stars are
suggested (I typically use more than 20). For the task of producing an exoplanet
light curve (LC) it is not necessary to assign magnitudes to the reference
stars, so any star that's not saturated or close to the FOV edge can be used.
The AXA (and Caltech) will process only the first two columns to create a
LC, and they must be JD and dMag; other columns may be present but they will
There's one exception to the 2-column rule: a third column will be processed
as "extra losses" if there's a header line stating "Loss column
: Y". An "extra losses" column can be produced when an artificial
star is used for reference (with MaxIm DL, for example) or if an image processing
program is used that records fluxes instead of magnitudes (for all stars).
To calculate extra losses requires that a spreadsheet program be used to
analyze the sum of fluxes for all stars (not including the exoplanet star).
Very few observers include this third "extra losses" column, so if you're
not planning on calculating it you may ignore this paragraph.
The following is an example of the desired submission format. The program that reads an observer's text file is flexible, and can recognize a header line in any location within the header. Upper and lower case are not important.
Sample data submission showing required format.
The date format is YYYYMMDD, and please use UT for designating a start
date. This can be confusing for observers in the USA. The exoplanet name
can be in almost any format; for example, all of the following are acceptable:
GJ 436, GJ436, GJ436b, gj436, gj436b, etc.
The observer may use a last name only. If the name entry has a comma
the next name is assumed to be a first name. An observer code in parentheses
is optional. An observer's e-mail address is optional, but if your data
is used by a professional astronomer it is a good idea to include your e-mail
address to increase the probability that the professional will contact you
before publishing results that are partially based on your data. The "Location"
line should show the country where the observing site is located. Use your
judgement in deciding whether to specify "country" or "city, country" or
"state, country" etc. For USA observers I suggest including state and USA.
For someone near Madrid, Spain it's OK to use "Spain" or "Madrid" or "Madrid,
Spain". If anyone is uncertain about the location they can consult the site
Sometimes it may be difficult to decide whose name to use for "observer"
when more than one person is involved with observing, data analysis or data
file submission. An observation could be a "club project," or a "school project,"
in which an experienced observer tutors others in performing these tasks.
If all tasks are closely supervised then the experienced person's name should
be used in the "observer" header line. But if the tutor's principal role
is to provide advice and answer questions, or if the tutor's role is mostly
limited to submitting the data file to the AXA (when proficiency in English
is an issue), then one of the actual observers should be selected for the
"observer" line. It is OK to use two observer names, but I don't want more
than two. When two observer names are used please try to assign the first
one based on who had the greatest responsibility for producing or processing
the data (e.g., I frown on alphabetical listings). I recognize that sometimes
responsibilities can be shared in an enduring way, as when one person does
the observing while another does the image processing and data analysis.
Both tasks are important, and this could be a situation for using two names
in the "observer" line. The guiding principle in selecting the first (or
only) observer name is "Who assumes the greatest responsibility for the quality
of the final data product?" I realize that this can be a difficult question
to answer, especially with a student, but hopefully the "subjective phase"
for who's most responsible is likely to be brief. The e-mail doesn't have
to belong to any of the observers; it can be anyone who can act as a contact
for questions related to the observations that may arise later.
The word "Latitude:" must be included in its
entirety (case doesn't matter). Notice that I require the
use of "ELongitude" instead of "Longitude" because some observers may casually
use the wrong sign (e.g., all USA east longitudes are negative). Aperture
can be metric, but I prefer inches for amateur telescopes (which is easier
to understand: 14-inch or 0.35-meter). If only a number is given it will
be assumed to be inches. The hyphen is optional, as is the plural (inches
versus inch). The following filter entrires are permitted: B, V, R, I, C
(clear or unfiltered), BB (blue blocking), G (pretty picture green) and Bp
(pretty picture B-band). The BVRI filter designations are assumed to be "photometric
(e.g., B is Johnson B-band, R means Rc or Cousins R-band, I means Ic or Cousins
I-band). If you buy a color filter wheel with filters installed you have
to assume that the B filter is not photometric, but is what I call Bp, or
"pretty picture B band." Bp has a longer wavelength than B. Johnson and Cousins
V-band are essentially the same, so don't worry about which one you're using.
Exposure can be simply a number of seconds; it's optional to add "s" or
"sec" or "seconds". I hope you synchronize your computer clock with some
time standard to better than 10 seconds, because the JD time tag is based
on it being accurately set. Also, check to make sure the JD time tags correspond
to mid-exposure, not start of exposure. This is so important that a data
file will be rejected if this header line is not present. (To do this,
display the FITS header for an image and note the
exposure start time. Add 1/2 the exposure time and calculate
JD. Compare this JD with the JD in the "observations
data file" and if they differ enter the seconds equivalent
in the header.) Comments are optinal (as is the comment line). Comment
information is merely archived. In almost all cases the "Loss column" line
will have a "N" entry. It is present for those rare observers (like myself)
who calculate "extra losses" (due to clouds, dew, etc) and include a third
column in the data section.
May I suggest that you create a header text file that can be inserted
just above the data section of files that are recorded by your image analysis
program. After inserting this user-specific header file you can edit it to
show the correct observing date, object, etc using a program such as TotalCommander:
http://www.ghisler.com/ (I don't
know how anybody can use a PC without TotalCommander). A sample header text
file can be downloaded using this link: YMDDabc1.txt.
Here's an example of my preferred filename convention: 20080328-xo1-gbl.txt.
It conveys the information that
the observations began on the date
2008 March 28 (UT), the object was XO-1,
and the observer uses an observer code of GBL. If you don't
have a 3-letter observer code (assigned by AAVSO, for example) you should
use at least 4 letters of your last name. If your name is short, such as
James Roe, and you don't have a 3-letter observer code, use the last name
followed by letters from the first name (e.g., ROEJ). In other words,
start with date using yyyymmdd format,
insert a hyphen, "-", then add the exoplanet's
name (without hyphens, case not important),
and then add either your 3-letter observer code or a
4-letter name. Attach this file to an e-mail and send
a x a @ b r u c e g a r y . n e t [remove spaces between characters]
These format instructions for submitting data may seem excessive but remember that if you adhere to them it will save me time, and I'm processing your data and maintaining the AXA archive without pay. Also, when Caltech takes over the AXA they will require that you adhere to a format or your submission will be rejected. I think Caltech is inclined to accept the format described here.
Data Rejection Criteria
A data file will be rejected by the auto-fit pipeline for failing
to meet any of the following requirements.
1) The data file must include all 5 of the following header lines: Object, Observer, Latitude, ELongitude and StartDate.
2) The observing session length must exceed 2 hours.
3) The 2-minute equivalent RMS noise must average < 15 mmag.
4) The auto-fit solution search must succeed within 99 iterations.
5) The auto-fit systematic coefficients must be less than 10 mmag/hour and 15 mmag/air mass.
When an observing session does not include either an ephemeris ingress or egress program control is automatically transferred to AXA5 which treats the data as OOT.
Nothing on this
web page is copyrighted. This site opened: 2008 August
23. Last Update: 2008.12.16