Welcome to Sarawak
Skies. My interest in
astronomy ranges from astrophotography to,
increasingly, the science that can be done by a keen amateur
motivated mainly by the question, "Can I do
that?". I describe the successful implementation of a search
program that has discovered 3 supernovae so far. My current
project is to develop the tools and techniques for the detection and
discovery of transiting exoplanets.
My observations and imaging are
now done exclusively from my backyard in Perth, Western Australia,
where I have now built a roll-off observatory. I used to image
from my driveway when we lived in light-polluted Singapore and first started
doing astrophotography with a converted webcam when in Miri, Sarawak - hence the name of
This site shows what can be done with relatively
modest equipment, as well as knowledge picked
up from others via the internet.
I hope you find much of interest here, and enjoy your visit.
In order for these images to be displayed
properly, adjust your monitor so that all of the gradations of black
to white in the following chart are distinguishable, especially the
two darkest shades. Generally monitor contrast should be set as
high as is consistent with comfortable viewing, and then the
brightness adjusted. The darkest shade should appear black.
Exoplanet discoveries I have contributed to;
Star mass /
||Multi-planet system, beyond 'snow line'
||Multi-planet system, beyond 'snow line'
||Planet around a brown dwarf
Announcement (18th Oct 2012): Exoplanet discovery!
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
Since the observatory was built my telescope has been quite productive.
The ease of use has enabled me to collaborate with a number of scientists
and teams. Some of these;
- The MicroFUN
collaboration. The search for exoplanets through measurements of
gravitational microlensing events.
- HAT South.
Search for transiting exoplanets from the southern hemisphere.
KELT South collaboration. Search for transiting exoplanets.
- Pro-Am White Dwarf
Monitoring (PAWM). Search for exoplanets orbiting white dwarf
I am co-author of
the following papers;
Eclipses During the 2010 Eruption of the Recurrent Nova U Scorpii.
Schaefer et al. 2011
Characterizing Lenses and Lensed Stars of High-Magnification Gravitational
Microlensing Events With Lenses Passing Over Source Stars. Choi
et al. 2012
MOA-2011-BLG-293Lb: A testbed for
pure survey microlensing planet detections. Yee et al. 2012
4. Microlensing binaries
with brown dwarf companions. Shin et al. 2012
Low-Mass Binaries From Observation of Long Time-scale Caustic-crossing
Gravitational Microlensing Events. Shin et al. 2012
6. The second
multiple-planet system discovered by microlensing: OGLE-2012-BLG-0026Lb,
c, a pair of jovian planets beyond the snow line. Han et al.
Supernovae and Supernova Impostors. SN 2009ip, is this the end?
Pastorello et al. 2013
8. Physical properties,
transmission and emission spectra of the WASP-19 planetary system from
multi-colour photometry. Mancini et al. 2013
Discovery of a Tight, Low Mass-ratio Planetary-mass Object around an Old,
Field Brown Dwarf. Han et al. 2013
10. The Tell-Tale Heart:
Brightness Fluctuations in the Decline of SN 2009ip. Martin
et al. 2013
11. Searching for White
Dwarf Exoplanets: WD 2359-434 Case Study. Gary et al.
Proceedings, Society for Astronomical Sciences 2013
12. A Super-Jupiter
orbiting a late-type star: A refined analysis of microlensing event
OGLE-2012-BLG-0406. Tsapras et. al. 2013
13. The Mass-Radius
Relationship for Very Low Mass Stars: Four New Discoveries from the
HATSouth Survey. Zhou et. al. 2013
PEST has moved.
The observatory has now moved to a new location.
I now have a more unobstructed western horizon, but otherwise there has
been no major change. Here's a more detailed description of the observatory and photometry
October 2010: My backyard observatory is now running.
In 2010, I acquired a 12"
LX200GPS SCT, and built an observatory to house it. With the larger
telescope it is just not practical to set up, polar align for each night's
observation, and then stow away in the morning. In addition, for
high precision photometry, numerous flat frames must be taken, and to
avoid having to take flats for each night's observations, the camera needs
to be kept in place between nights.
I had thought that the solution
would be to build a trolley so that the scope and tripod could be wheeled
into and out of my shed. I did build a trolley (visible as the
wooded frame at the base of the tripod in the picture below), but my shed
would have needed modification and this turned out to be more difficult
than I expected. I then looked around for a kit shed which I could
modify so that the roof would roll off. This was another dead end as
all of the sheds I looked at were either not quite the right size, or
would be difficult to modify - most rely on a fixed roof for rigidity.
the end I designed and built a roll-off building out of wood sections and
plywood. It took two weeks to build and the result is very
satisfactory. The shelf inside serves as a desk, but is
also important structurally because it provides rigidity to the structure.
I recently added an Optec TCF-Si
focuser and together with observatory automation software
CCD Commander, plate solver
Pinpoint and focus
I have an almost completely automated set-up. The only exceptions
are that I have to open the observatory doors and roll the building off
A normal night's observation now
starts with the observatory being rolled back, power and computer switched
on and CCD Commander started. CCD Commander then runs a script that
starts CCDSoft, connects to the camera then starts camera cooling.
The script waits for the sun to be at a specified angle below the horizon
then starts an automatic sky flat sequence. Once this is finished
there is a further wait for darkness, then a slew to a specified arbitrary
location above the eastern horizon. An image is then taken, plate
solved, and the scope is synched to the coordinates thus obtained.
This step is probably not strictly necessary but since this takes place at
the start of the observation program for the night it gives me an
opportunity to confirm that scope pointing is accurate before leaving the
rest of the sequence to take place unattended. As the sky brightens
just before dawn (specified in terms of sun altitude), CCD Commander will
stop data acquisition, then wait for further light before starting to take
sky flats. When the sky is too bright for any further flats, CCD
Commander parks the scope. All I have to do when I wake up is copy
the night's data onto a USB stick, turn off the computer and close the
Variable star discoveries
A by-product of exoplanet transit observations that
require intensive time-series photometry is that other variable stars in
the field of view are picked up as well. The two I have reported to
VSX (the International Variable
Star Index) are listed.
||Phase Plot and Comments
||RA: 09 51 55.39
Dec: -45 27 39.8
|| This is an eclipsing binary with clear
primary (larger star passes in front of the smaller star) and
secondary eclipses. Period = 2.083 days. Because the
period is close to an integer number of days, it took nearly of a
month's worth of observations to build up the full light curve.
||RA: 15 51 15.36
Dec: -49 59 27.4
||An eclipsing binary but with no differentiation
between primary and secondary eclipses. Period = 0.659 days.
Exoplanet transit detections
A shallow transit of 6 mmag in a mag 11.7 star -
HAT-P-26b, on 1st March 2011, and the corresponding transit system
geometry compared to our Sun and Jupiter.
This is a good illustration of the effect of the
atmosphere on photometric precision. These observations were made at
airmass between 2.2 and 1.4. This is quite large - at my latitude
this star does not get very high. Despite the HAT-P-26 being
brighter than WASP-19 (mag 11.7 vs 12.3) precision is worse (2.9 mmag vs
An example of a transit observation made automatically
8th Feb 2011, of WASP-19b. Transit depth 25 mmags. Note that
with the 12" scope, a precision of 2 mmags was achieved for a star of mag
12.3, more than a magnitude dimmer than the C9.25 observation below.
For comparison, a transit
observation made with the C9.25 scope, on 3rd May 2010, of WASP-15b. Depth of transit is just
10 millimags. Precision of 2 mmags achieved.
These charts and transit model fitting
were done at the
Exoplanet Transit Database
(ETD) website. PEST stands for Perth Exoplanet Survey Telescope,
which is what I am calling my humble backyard setup!
My first exoplanet transit
detection. An important milestone towards what
I hope will be the discovery of new transiting exoplanets! The chart
below shows the 0.02 (2%) magnitude increase in brightness of the parent
star of the giant exoplanet WASP-17b as it exits from transit. The
end of transit was as predicted by the
Exoplanet Transit Database,
at HJD 2455265.27 (9th March 2010 UT). The camera was my new ST-8XME
and the scope the Celestron C9.25.
This was a relatively easy
detection. There were numerous problems with the observation run -
WASP-17 was just rising so that the start of the data set was obtained at
low elevation (high airmass), and guiding was lost just after end of
transit. Nevertheless the 0.02 mag transit is well within the
internal precision of the observations. Since then, I have been able
to achieve improved photometric precision such that a 3 millimag (0.3%)
transit of a magnitude 11 star should be detectable.
Supernova Search Program
In February 2007 I started a supernova search
program using my C9.25 telescope, Vixen GPD mount, ART 285 CCD camera and
several pieces of software which I wrote. These consist of;
1. GalaxyGen - a script to generate a list of
galaxy targets suitable for a night's observing run. This also
generates a list that can be used to download reference DSS images (see
below). The main issue the search algorithm has to account for is
that my polar alignment (non permanent mount) is not perfect, so that a
large excursion away from the initial alignment point in terms of azimuth
and altitude will lead to inaccurate pointing and failure to acquire the
target. This is overcome by picking targets within a narrow band of
declination, but with increasing RA through the observing run, such that
the telescope always points to approximately the same alt-az point.
2. TargetPoint - a script that controls the
mount and camera and successively points the telescope to each galaxy on
the list, acquiring a set number of images of each target.
3. Examiner - a script that enable quick
comparison of these images to reference images downloaded from the
Digitized Sky Survey (DSS).
Typically between 150 to 200 galaxies can be
observed in an automated overnight run. Using individual 20s
exposures, supernovae down to mag 17 should be detectable.
Proof of concept was achieved when a supernovae was
detected in PGC51820 (ESO385-32) on 14th March 2007. Subsequent
checking revealed that this SN had been discovered about a month
previously and is designated SN2007X. For more information on the
search program, see the Supernova Search page.
||Designation and discovery
|| SN2007rv, discovered on 7th Nov
2007 in NGC 689.
Location: RA: 01h 49m 52.86s
DEC: -27d 28' 4.1",
14" east and 4" south
of host galaxy nucleus
mV = 15.9 on 2007/11/11.51 UT
~200 mln light years away.
||SN2008ff, discovered on 29th Aug 2008 in
ESO284-32 (PGC 64319).
Location: RA: 20h 13m 59.96s
DEC: -44d 21' 7.8",
39" east and 1" south
of host galaxy nucleus
mV = 15.5 on 2008/09/1.52 UT
~260 mln light years away.
||SN2009gg, discovered on
16th June 2009 in ESO235-35 (PGC 65919).
RA: 21h 01m 29.91s
DEC: -52d 01' 00.2" ,
1.4" West and 3.4" South
of host galaxy nucleus
mV = 15.8 on 2009/06/15.591 UT
I recently acquired an SBIG ST-8XME
CCD camera with which I am doing mainly photometry.
The astrophotography on these pages
were taken with a
home-assembled CCD camera, the
This is a cooled 16-bit camera based on the 1.4 Megapixel Sony ICX285AL
chip, as well as with a Digital SLR (Canon
EOS300D), modified using a procedure
described by Terry
Gary Honis. The modification involves removing the internal IR-cut filter which severely reduces
the camera's sensitivity to the important
Some words of warning - making
this modification obviously invalidates your camera warranty. There
is also a fair bit of fine work involved and you run a real risk of
ruining your camera! I had to open up the camera and readjust some
connections 3 times, before the camera would work properly again. I
did not replace the original filter with a less aggressive IR cut filter,
nor another piece of glass, so the camera now does not auto-focus properly
and, because of it's response to IR, its colour rendition is severely
compromised for normal photographs. You have been warned...
A more complete set of images from the DSLR is at the
A summary of my equipment. I use an Orion 80ED
refractor, a Celestron C9.25 Schmidt-Cassegrain, usually
used with a x0.63 focal reducer, and a
Vixen GPD mount with
SkySensor 2000 PC. The Go To facility makes for very easy target
||The Trifid Nebula in
NGC 6726 with globular cluster NGC 6723
around NGC 6559 in Sagittarius.
||NGC 6334, the Cat's
Paw Nebula in Scorpius.
|NGC6164-5 in Norma
||NGC 6188 in Ara
||LRGB composite of the Eta Carinae
|IC 2944, LRGB - trying for a more
natural colour balance.
||NGC 3576 in Carina,
||NGC 3576 in Carina, with the
|The main part of the Eta Carinae
Nebula, H-alpha with the 80ED and ART285. Very good guiding
and conditions, so apologies as I've posted a large image here...
||The southern part of
the Eta Carinae Nebula.
|| Thor's Helmet
Nebula in H-alpha, with the Orion 80ED and ART285 camera.
|First light with an Orion 80ED.
A closer view of the optical performance of this scope.
||NGC 6888, The Crescent Nebula in
Looking through the Galactic bulge to the other side of our Galaxy.
|The Trifid Nebula
(M20) - RGB / H alpha composite.
||A colour/ H alpha composite of the
Omega Nebula, M17.
||A colour/ H alpha composite of the
Eagle Nebula, M16.
|The Dumbell Nebula, M27, a
planetary nebula in Vulpecula. Set in a very rich star field.
||First attempt at a composite H
alpha / RGB image of the Lagoon Nebula.
||Eagle Nebula, and open
cluster M16. Site of the "Pillars of Creation".
|The Omega (or Swan) Nebula, M17
in hydrogen alpha. Nearly 2 hours total exposure!
||The region around Eta
Carinae in hydrogen alpha. This is a mosaic of 4 frames that
extends about 2 deg of sky lengthwise.
||The Trifid Nebula (M20) in
hydrogen-alpha. Only the emission part of the nebula is visible,
the light of the reflection (blue) nebula being almost completely
blocked by the filter.
All DSLR images were acquired with the help of
DSLR Focus software, to help with
equatorial alignment, focusing, and automating the multiple exposures.
Shutter control was using a serial cable I made up following instructions
processing was in Iris, which has marvellous tools for handling DSLR RAW
files, and finished in Photoshop CS.
A selection of SAC7B images
This is a selection of older images made with a
commercially converted webcam - the SAC7B.
Other SAC7 images can be viewed in the
You are Visitor No.
since 20th Sept 2008 - the
original count since 7th June 2003 has been lost!
|This page is
maintained by TG Tan and was last updated on
11 November 2013
Email me (replace _at_ with @, and the _dot_): tgtan_at_bigpond_dot_net_dot_au