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OSU College of Arts and Sciences Department of Astronomy

MicroFUN
MICROLENSING FOLLOW- UP NETWORK

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 similar longitudes.

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 and MOA 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 RA=18h, 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 observing sites 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 computer control.

Example Small Telescope Sites:

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

Basic Setup

The basic setup of a typical active small-telescope MicroFUN site is as follows: Many of our first small-telescope sites are also southern-hemisphere members of the Center for Backyard Astrophysics (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 observers.

Data Requirements

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:

Data Requirements

The Galactic Bulge is a very crowded field, and presents special challenges for high-precision time-series photometry of microlensing events. Particular issues are: 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.

More Questions?

If you have more questions about MicroFUN observations, please contact
Prof. Andrew Gould (OSU)
gould@astronomy.ohio-state.edu