Information for Prospective Collaborators
MicroFUN would not be possible without the dedicated efforts of
astronomers around the world who contribute observations and expertise.
We are always seeking to expand our network of skilled observers,
professional and amateur alike, both to improve our 24-hour coverage and
to provide a hedge against poor weather by having redundant sites at
Because we get a lot of inquiries about how to join MicroFUN, this page
describes the basic information you need to see if you can contribute.
What does MicroFUN do?
MicroFUN is a network of small- and medium-aperture telescopes that does
intensive precision photometric follow-up of stellar microlensing events
occuring in the Galactic Bulge. We do not search for new microlenses ourselves,
but rely instead on events discovered by the OGLE-III
collaborations. We do not observe every microlensing event, only those
high-magnification events that have a strong potential for detecting
planetary "anomalies" that would signal the presence of a massive planet
around the lensing star. This selective strategy has so far paid off in
that most of the planetary systems discovered via microlensing have either
been primary discoveries of our group, or we have contributed substantially
to discoveries led by other groups.
When is our observing season?
The MicroFUN observing season runs from May through September each year
when the Galactic Bulge is in the night sky. Because the Bulge is at
, Dec=–30°, most of our sites are in the Southern
Hemisphere, or at relatively low northern latitudes (at or just below
30° North latitude).
How do we choose which events to follow up?
When a lensing event looks promising for followup, an alert is sent to
all MicroFUN members with instructions to observe the target during the
coming nights. By having members at many longitudes in the southern
hemisphere, weather permitting we can achieve almost continuous 24-hour
coverage during the critical peak magnification interval of the event.
Intensive imaging of the events is performed by each site, usually
taking an image every few minutes as long as the target is at a
favorable aspect from their location. The imaging data are then
uploaded the next morning to MicroFUN headquarters at OSU for
photometric processing. These data help us to decide how to proceed on
the following night (whether to hit the event harder or stop observing).
What do you do with the data?
We collect all of the imaging data at MicroFUN headquarters at Ohio State,
and perform basic photometric processing to measure the progress of the
lensing event using relative PSF-fitting photometry. PSF-fitting makes it
possible to do first-order deblending of the event from the very crowded
Bulge star fields. We measure the brightness of the lens relative to an
ensemble of 5 or more nearby non-variable "reference" stars, which allows us
to get good precision photometry even in non-photometric conditions.
By centralizing most of the basic photometry reduction at OSU (or using the
same software at other sites), we can ensure that the data are analyzed in a
uniform way. The imaging and photometric time-series data all become the
property of the consortium, and the raw, uncalibrated photometry is shared
online to all interested parties to help track on-going microlensing events.
If an event is particularly interesting, we will then perform a careful
photometric time-series analysis of the images using difference-imaging
photometry methods. This is another reason we require copies of the
images proper, and not just measurement of the stars as is often done in
other variable-star monitoring networks. Difference-imaging lets us achieve
the full potential of data taken in crowdes tar fields. The final reduced
microlensing time-series data are then collected, and a paper is
written describing the scientific results. All MicroFUN collaborators
who have contributed to an event become co-authors in the subsequent
published papers, which are submitted to refereed journals (usually the
ApJ and AJ). Order of authors is the persons who did most of the
analysis work, followed alphabetically by the members of the consortium
who contributed data and/or expertise. If the data are used as part of
a cross-collaboration effort (e.g., with PLANET, OGLE, or MOA), the
order of authors gets more complicated (by collaboration group), but
everyone gets their name on the paper.
MicroFUN Observatory Sites
The current list of MicroFUN members and
reveals a rough division of observing sites
into two groups by telescope aperture and accompanying equipment:
- Small-Aperture Telescopes (D<0.5-meters)
- These are primarily privately-owned telescopes operated by amateur
astronomers or private institutions. These are all 10- to 20-inch
diameter Cassegrain and Schmidt-Cassegrain telescopes on permanent
pier mounts equipped with research-grade CCD cameras and under
- Example Small Telescope Sites:
- Farm Cove Observatory,
Pakuranga, Auckland, New Zealand.
- Auckland Observatory, Auckland, New Zealand
Lane Observatory, Blenheim, New Zealand
- Southern Stars
Observatory, Faaa, Tahiti, French Polynesia
- Hunters Hill
Observatory, Canberra, Australia
- Bronberg Observatory, Pretoria, South Africa
- Medium-Aperture Telescopes (D>0.5-meters)
- These are primarily professional observatories owned and operated by
universities, government agencies, or consortia of universities and
equipped with 1- to 2.5-meter class research telescopes and modern
electronic instrumentation. Time is assigned competitively either
in block or queue-scheduled modes.
- Example Medium-Aperture Telescope Sites:
Each of these setups have different requirements and observing procedures,
as described below.
Small-Aperture Telescope Sites
The basic setup of a typical active small-telescope MicroFUN site
is as follows:
- A dedicated telescope with an aperture of 10-inches (0.30-m) to
16-inches (0.41-m). Our network has a mix of Schmidt-Cassegrain
and Classical Cassegrain telescopes.
- An automated equatorial mount on a permanent pier with precise
polar alignment. Both classical fork mounts as well as robotic
german equatorial mounts (e.g., Paramount GT) are used.
- A Science-Grade CCD Camera with a control computer. Most of the CCD
Cameras used by our network are made by SBIG or Apogee, and use
thermoelectrically cooled science-grade full-frame readout CCD detectors.
- A Personal computer to automate observing (operates telescope and camera)
and do basic data analysis
- A carefully-aligned and well-tuned, computer-controlled equatorial mount.
The degree of control at various sites ranges from proper periodic-error
correction for open-loop tracking to systems that employ closed-loop guide
corrections provided by an auxiliary CCD-based auto-guiding system.
- Access to a fast Internet connection to receive email alerts and upload
data to MicroFUN central.
Many of our first small-telescope sites are also southern-hemisphere
members of the Center for
(CBA) organized by Prof. Joe Patterson at
Columbia University. Most have had previous experience with doing
time-series photometry of variable stars, but not all.
The small privately-operated observatories have a distinct advantage
over some of the larger traditional professional facilities in their
ability to observe targets any time it is clear because the observer
owns (or has a large stake in) the telescope and equipment. The quality
and quantity of the data we receive is more a function of the dedication
and skill of the individual observer, aided by good equipment, than
aperture size or research credentials. Some of our most critical
observations have come from small telescopes operated by very skilled
Small telescopes have long provided high-quality relative photometry of
bright, isolated transient sources like Cataclysmic Variables. Because
microlensing planet searches occur in the very crowded star fields of
the Galactic Bulge, they presents special challenges for achieving
high-precision time-series photometry with small telescopes. In particular,
issues of pixel sampling that are not an a problem with larger telescopes
can become especially critical with small aperture telescopes.
An excellent overview of how to use small telescopes for microlensing
planet searches is this SAS2006 paper by Grant Christie, who operates
the Auckland Observatory:
- Detecting Exoplanets by
Gravitational Microlensing using a Small Telescope [1.2m PDF]
Prospective small-telescope observers should read this paper thoroughly
to decide if they can satisfy the requirements for microlensing
follow-up observations. To be useful for microlensing planet searches,
a photometric precision of a few percent is required.
One aspect of time-series photometry that is sometimes overlooked is
that computer time clocks are notoriously inaccurate. Your data-taking
computer will need to be synchronized with an external time reference
to ensure that you know the times your data were taken to within a few
seconds absolute accuracy. Please don't hesitate to ask us about possible
options for getting good timing for your computer.
Medium-Aperture Telescope Sites
The basic setup for a typical medium-aperture telescope in the MicroFUN
network is as follows:
- Research-class telescope with an aperture of 1- to 2.4-meters,
typically of Cassegrain design with a full complement of computer controls
and auxiliary autoguiding systems. Usually located at established mountain-top
observing sites in remote areas (e.g., Chilean Andes, Negev Desert, etc.).
- Research-grade low-noise, high-QE CCD camera, either cryogenically
or thermoelectrically cooled, and often using custom low-noise electronics.
Usually mounted behind a remotely-operated filter wheel, with or without
focal-reducing optics. Most are custom-built research instruments funded
by government or private research grants.
- An suite of dedicated computers to operate the telescope and
instrumention, and providing full Internet access.
- Either queue-scheduled, robotic remote operation, or on-site
observer operated, with time assigned to the member astronomers on a
The Galactic Bulge is a very crowded field, and presents special
challenges for high-precision time-series photometry of microlensing
events. Particular issues are:
- Pixel sampling should be 2.5 to 3 pixels FWHM on the best images.
This is even more critical for post-processing using differencing
imaging techniques, which can be supremely sensitive to undersampled
- I band (specifically the Kron-Cousins I band) is the best for
large-telescope observing. V, R, and bluer bands are mostly useless
given the high Galactic extinction towards the Bulge. Unfiltered
imaging should be avoided because of the problem of compressed dynamic
range due to high backgrounds (the sky is mostly blue but our objects
are mostly red).
- Good flat fielding and bias correction are important, but microlensing
presents no particularly stringent requirements compared to normal CCD
- A good, reliable source of accurate time is essential. Your data-taking
computer system should be synchronized to a GPS-based time service, either
an on-site GPS-based Stratum-0 network time server, or connected to a
reliable off-site Stratum-1 network time server using ntp. We can tolerate
timing inaccuracy of order 1-2 seconds, up to 5 seconds except in
high-cadence observing modes. Times should be stored in the image
FITS headers using standard keywords (DATE-OBS and TIME-OBS) referenced
to the start of the observation.
- The time-series cadence is fairly slow compared to observations of
rapidly variable sources. Sampling of every 2 to 5 minutes is desirable
during periods of high magnification where we are most sensitive to
planetary lensing anomalies.
- Excellent autoguiding control is essential for providing consistent
PSFs during an observing sequence, especially during high-cadence
observations, so that changes in PSF shape won't produce systematics in
the time series.
These are the basic requirements for making data from large telescopes
most useful for MicroFUN follow-up observations. Our goal is to achieve
few-percent relative photometry.
If you have more questions about MicroFUN observations, please contact
- Prof. Andrew Gould (OSU)