PEST Main Logo

"In this way, we may resume (after a two century interruption!) the tradition of planet discoveries by amateur astronomers begun with William Herschel's 1787 discovery of the "solar" planet Uranus."

 "The Discovery of Extrasolar Planets by Backyard Astronomers", Castellano and Laughlin (2002). 

Welcome to the Perth Exoplanet Survey Telescope (PEST) website.

by Thiam-Guan 'TG' Tan

PEST is a private, backyard observatory that I set up to participate in the search for exoplanets (planets around stars other than our Sun).  PEST does high precision time series photometry so is well suited for observations of variable stars, novae and supernovae.

The observatory is situated just 8km from the city of Perth, Western Australia (pop. 1.9 mln), at close to sea level, so suffers from light pollution.  Nevertheless sky transparency is generally quite good, and the number of clear days in the year (144 days) is about the highest even in sunny Australia.  The observatory equipment is relatively modest, but nevertheless PEST has been very successful in its goal of helping to discover exoplanets.

PEST Observatory

A 12" Schmidt-Cassegrain Telescope mounted on a tripod is equipped with a CCD (Charge Coupled Device) camera and focuser.  A roll-off enclosure made from timber and plywood provides protection from the elements when the telescope is not in use.  This enclosure also houses the computer that runs the telescope and image acquisition programs.  Telescope pointing, focussing, imaging and calibration frames are all automated with CCD Commander.

The observatory is connected to my home network.  The night's data goes straight to my home office computer for image reduction and photometric analysis.

PEST has co-discovered 25 exoplanets.

Of which:

6 were through microlensing and

19 through transit detection.

As of 14th July 2016, 3302 exoplanets have been confirmed, of which 973 were discovered from the ground (the rest were from space, by Kepler).  So PEST has co-discovered 2.6% of all the planets that have ever been discovered from the ground!


14 July 2016:  KELT-17b: A hot-Jupiter transiting an A-star in a misaligned orbit detected with Doppler tomography

KELT-17 is amongst the most massive, hottest, and most rapidly rotating of known planet hosts.  The planet is in a 3.08 day period orbit misaligned at -115.9 +/- 4.1 deg to the rotation axis of the star.  We were able to measure this misalignment using Doppler tomographic detection of the shadow of the planet over two transits.  Planets around hot, rapidly rotating stars are hard to confirm via conventional RV because precise measurements are difficult.  This discovery demonstrates the use of Doppler tomography to confirm such a planet.

7 July 2016:  KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V=8 Subgiant HD 93396

An important discovery.  The brightest known transiting exoplanet host in the southern hemisphere and one of the most inflated planets known.  Likely to become a benchmark system for atmospheric characterization.  The shallowest transit depth (2.7 mmag) of any planet discovered by a ground-based survey.

4 July 2016:  HATS-31b Through HATS-35b: Five Transiting Hot Jupiters Discovered by the HATSouth Survey

The PEST co-discoveries are HATS-32b and HATS-34b, typical Hot Jupiters.

4 July 2016:  HATS-19b, HATS-20b, HATS-21b: Three Transiting Hot-Saturns Discovered by the HATSouth Survey

PEST co-discovery: HATS-20b, a dense Saturn-like mass planet orbiting  an older star with nearly-Solar metallicity.

3 June 2016:  HATS-25b through HATS-30b: A Half-dozen New Inflated Transiting Hot Jupiters from the HATSouth Survey

HATS-27b, a highly inflated Hot Jupiter was co-discovered by PEST. 

10 Mar 2016:  HATS-11b and HATS-12b: Two transiting Hot Jupiters orbiting sub-solar metallicity stars selected for the K2 Campaign 7

Two new Hot Jupiters. 

20 Nov 2015:  HATS-15b: A massive hot Jupiter transiting an old G dwarf star

A high-mass hot Jupiter in a 1.75 day orbit around an evolved (11 bln yrs old) G dwarf.  Most high-mass Jupiters are found at larger distances from their star.  The star is relatively dim at Vmag = 14.8 so that detection of the transit was quite challenging for my 12" telescope.  The discovery paper announces HATS-16b as well, but I did not contribute to that discovery so have not included it in my planet count.

21 Oct 2015:  HATS-17b: A Transiting Compact Warm Jupiter in a 16.3 Days Circular Orbit

The first transiting warm (as opposed to hot) Jupiter found by the HATSouth network.  HATS-17b is unusually compact for its mass, and is the longest period transiting planet discovered to date by a ground based photometric survey.

1 Oct 2015:  KELT-14b and KELT-15b:  An Independent Discovery of WASP-122b and a New Hot Jupiter

Two inflated Jupiter mass planets transiting a relatively bright stars (V ~ 11).  KELT-14b is an independent discovery of a planet that was recently announced by the WASP survey as WASP-122b.

8 Sep 2015:  KELT-10b: The First Transiting Exoplanet from the KELT-South Survey -- A Hot Sub-Jupiter Transiting a V = 10.7 Early G-Star

A highly inflated sub-Jupiter mass planet transiting a relatively bright star which exhibits the third largest transit depth of all transiting exoplanets with V < 11 in the southern hemisphere, making it a promising candidate for future atmospheric characterization studies.

29 Jun 2015:  OGLE-2012-BLG-0563Lb: a Saturn-mass Planet around an M Dwarf

Located about 4,300 light years away, this planet's mass was determined through detection of the light of it's host star using the 8.2m Subaru telescope and high resolution Adaptive Optics. 

3rd July 2014: Discovery of an Earth-like planet around a member of a ~15AU binary

OGLE-2013-BLG-0341LBb light curveAn important discovery, OGLE-2013-BLG-0341LBb.  A planet about twice the mass of Earth (so not a gas planet), orbiting one of the members of a binary star system.  The planet orbits its host at about the same distance as Earth.  Both stars are red dwarfs, much dimmer than our sun.   For the first time we have a demonstration that a rocky earth-like planet can form in a binary system.  Since binary stars make up about half the star systems in our galaxy, and red dwarfs are the most common star, the places where a habitable planet might be found has dramatically widened.  In this particular case the planet would be too cold for life (-200 deg C) because the host star is 400 times dimmer than the Sun. 

I was lucky to have been able to cover crucial parts of the light-curve (my data are those labelled 'PEST N' at right) of the microlensing event that led to this discovery.  Observations were made between cloudy periods, and in fact no observations were possible because of cloud after the 2nd peak.

An artist's impression of this system is shown below, courtesy of Cheongho Han of Chungbuk National University, Korea.

OB130341 artists impression

18th Oct 2012:  The first exoplanet discoveries!

I am pleased to announce that I have been credited with the co-discovery of a couple of Jupiter class planets around a sun like star 4.1 kiloparsecs away.  See the discovery paper;

The second multiple-planet system discovered by microlensing: OGLE-2012-BLG-0026Lb, c, a pair of jovian planets beyond the snow line

This was the very first microlensing event I observed for the MicroFUN collaboration in 2012.  It turned out to be a planetary system with 2 planets.

Amateur Astronomers and Exoplanet Discoveries

The quote at the top of this page is from a paper by Castellano and Laughlin calling for amateur participation in the search for exoplanets.  They demonstrated that exoplanet transits can be detected using off-the-shelf equipment.  That was in 2002.  As far as I can tell the first amateur astronomers credited with co-discovery of an exoplanet were my fellow MicroFUN team members Grant Christie and Jennie McCormick.  This was OGLE-2005-BLG-071, announced May 2005, just the 2nd planet discovered through microlensing.  The first amateur co-discoverers of a transiting exoplanet were Ron Bissinger, Bruce Gary and Tonny Vanmunster, of XO-1b, announced May 2006.



Exoplanet discovery requires work in multiple areas - wide field surveys to detect candidates, spectroscopic and photometric follow-up, and theorists to work out what's going on.  I collaborate with a number of scientists and teams.  Some of these;

Acknowledgement:  Thanks to the HAT South project for kindly funding the repair of my CCD camera in Nov 2015.

I am always interested in new challenges, so if you have an idea for a potential collaboration, please contact me at;


stats counter
Visitors since 28th March 2015.  Last updated 1st Nov 2016.

Copyright TG Tan.  All rights reserved.  Copyright exists in all original material available on this website.  This material is for your personal individual, nonprofit use only.  Redistribution and/or public reproduction of this material is strictly prohibited without prior express written permission from the author.