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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 website.

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;

No.

Designation

Mass /

ME (Earth masses)

MJ (Jupiter masses)

Period /

days

Radius /

RE (Earth radii)

RJ (Jupiter radii)

Distance /

light-years

Star mass /

Solar masses

Remarks

1. OGLE-2012-BLG-0026Lb 0.11 MJ 3011 N/A 13307 0.82 Multi-planet system, beyond 'snow line'
2. OGLE-2012-BLG-0026Lc 0.68 MJ 4018 N/A 13307 0.82 Multi-planet system, beyond 'snow line'
3. OGLE-2012-BLG-0358Lb 1.85 MJ 1998 N/A 5740 0.022 Planet around a brown dwarf
4. HATS-4b 1.32 MJ 2.52 1.02 RJ 1370 1.0 A Dense Hot-Jupiter Transiting a Super Metal-Rich G Star
5. MOA-2013-BLG-220Lb 0.19 MJ 957 N/A <6600 0.05 Candidate for planet around a brown dwarf

 

 

Planet sizes in comparison with the planets in our Solar System:

Note that unless the radius has been determined through a transit observation, this is only an approximation (see Lissauer et al. 2011b).  Images taken from the Exoplanet Open Catalogue.

 

       

 

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 planets.

 

 

Collaborations.

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.

- The KELT South collaboration.  Search for transiting exoplanets.

- Pro-Am White Dwarf Monitoring (PAWM).  Search for exoplanets orbiting white dwarf stars.

 

Publications:

I am co-author of the following papers;

1.  Eclipses During the 2010 Eruption of the Recurrent Nova U ScorpiiSchaefer et al. 2011

2.  Characterizing Lenses and Lensed Stars of High-Magnification Gravitational Microlensing Events With Lenses Passing Over Source Stars.  Choi et al. 2012

3.  MOA-2011-BLG-293Lb: A testbed for pure survey microlensing planet detectionsYee et al. 2012

4.  Microlensing binaries with brown dwarf companionsShin et al. 2012

5.  Characterizing Low-Mass Binaries From Observation of Long Time-scale Caustic-crossing Gravitational Microlensing EventsShin 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 lineHan et al. 2012

7.  Interacting 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

9.  Microlensing 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

14.  HATS-4b: A Dense Hot-Jupiter Transiting a Super Metal-Rich G Star.  Jordan et. al. 2014

15.  MOA-2013-BLG-220Lb: Planetary Companion to a Possible Brown Dwarf Host.  Yee et. al. 2014

16.  Candidate Gravitational Microlensing Events for Future Direct Lens Imaging.  Henderson et. al. 2014

 

Aug 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 procedures.

 

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.

In 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 program FocusMax, 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 manually.

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 observatory. 

 

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 2.0 mmag).

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.

 

The Discoveries;

Image Designation and discovery information Other info.
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

 

Type 1a

~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

 

Type 1a

~260 mln light years away.

SN2009gg, discovered on 16th June 2009 in ESO235-35 (PGC 65919).

Location:  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

 

Type 1a

 

 

Astrophotography

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 Artemis 285.  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 Lovejoy and Gary Honis.  The modification involves removing the internal IR-cut filter which severely reduces the camera's sensitivity to the important hydrogen-alpha wavelength. 

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 DSLR Gallery.

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 location. 

   
    The Trifid Nebula in Sagittarius
Reflection nebula NGC 6726 with globular cluster NGC 6723 Nebulosity complex 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 Nebula.
IC 2944, LRGB - trying for a more natural colour balance. NGC 3576 in Carina, LRGB composite. NGC 3576 in Carina, with the ART285 camera.
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 H alpha Baade's Window.  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 here.  Image 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.  

M17, The Omega Nebula in Sagittarius M16, The Eagle Nebula. M27, The Dumbell Nebula

 

   
NGC 6888, The Crescent Nebula M8, The Lagoon Nebula NGC 6822, Barnard's Galaxy

Other SAC7 images can be viewed in the Webcam Gallery.

 

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This page is maintained by TG Tan and was last updated on 29 March 2014 Email me (replace _at_ with @, and the _dot_): tgtan_at_bigpond_dot_net_dot_au

 

Copyright 2003 to 2012, by 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.