Situated in the central Mediterranean in the island of Malta, Flarestar Observatory is located on the rooftop of an apartment block. The observatory was constructed in a way to cover the least possible footprint without comprising operational capability. As the observatory was intended to be operated remotely, there was no need for a structure that includes enough space to roam inside. The observatory's design was inspired by the approach adopted by the SLOAN digital survey observatory at Apache Point where the observatory's structure rails off to expose the telescope to the sky. In contrast with the Sloan design that utilise rails, Flarestar employed rubber wheels to achieve the same aim. This design enables the telescope to gain an unobstructed view of the the heavens and greatly diminish set-up times and cooling down periods. This approach allows astronomical imaging at short notice, that is great when utilising the telescope during a short break in clouds.
The telescope's tripod that supports the mount has been substituted with a more solid design. The low profile modification helped to decrease vibrations considerably permitting imaging at wind speeds up to 22 knots. Additionally, as the observatory's site is located within a sub-urban environment, the low profile of the set-up helps to shield stray light from the not so distant artificial light sources.
Telescope, Cameras & Software
The main telescope at Flarestar is a Meade SSC-10 Schmidt-Cassegrain telescope with a native configuration of f/6.3 (1600mm F.L.). This configuration was chosen as it has a relatively fast f-ratio that is suitable for deep sky imaging.
The Optical Tube Assembly (OTA) has been previously mounted on a computerized Meade LXD650 mount but after a good number of years of service, this mount was retired to make way for a Skywatcher NEQ6 PRO mount that is a very popular choice around the European continent. This mount is well capable to drive the 10" Meade SSC-10 and as the previous LXD650, it has capability to be remotely controlled but with less periodic error, higher pointing accuracy and better stability than that of the previous set-up.
The tripod modification was kindly built by Winston Grech who is a mechanical engineer by day and an avid astrophotographer by night. The low-profile custom made tripod has the added advantage of having a smaller footprint than that of the tripod supplied with the NEQ6 mount. This permitted a more compact design for the observatory and has diminished the telescope's wind exposure factor considerably.
The NEQ6 PRO mount is connected to the observatory's PC via a HitecAstro EQDIR adapter that acts as an interface in between the EQMOD software and ASCOM system that allows all the functions necessary without the need to use the mount's standard handset. this system is well suited for remote telescope operation. ASCOM is a set of interface standards for the control of astronomical instruments and related devices. All the individual equipment drivers interact with the equipment via this platform.
Remote pointing and slewing of the telescope can be operated directly through the planetarium software GUIDE (Version 9). This program has a massive database that can virtually depict anything in the sky. Although this GUIDE is not so stimulating visually as other popular programs, this software is the champion for plotting star charts down to very faint magnitudes. Users can download a multitude of star catalogues that can depicts stars fainter than magnitude 20. When working with faint objects, this program is a must have for serious scientific imaging and is also very useful for planning of observational sessions.
The main scientific camera at Flarestar is a Moravian G2-1600 CCD camera that employs the KAF1603ME chip. This camera was purchased in 2015 after a number of other CCD's were considered. In the end, this camera was chosen over others as the workmanship is of high quality and the electronics inside produce very a low noise level that is desirable for achieving high quality data. Despite that the KAF1603ME has only 1536 × 1024 pixels, the 9 × 9 μm pixel size is just the right match to local atmospheric seeing. The dimension of the chip at 13.8 × 9.2 mm is big enough to cover a good range of comparison stars for aperture photometry. Furthermore, the CCD's sensitivity is very high at 80% QE while the Full Well Depth is ~100,000 e and this makes 1603ME as a very good sensor for photometric purposes. Camera cooling for the Moravian G2-1600 is capable to reach -50 degrees Celsius below ambient and this helps to diminish the noise to very low levels.
The Moravian G2-1600 CCD is also equipped with an internal 5-filter wheel that accommodates 1.25" filters without any detrimental effects from vignetting.
For photometric measurements, an Astrodon Johnson V-filter and Cousins Infrared (Ic) filter are fitted onto the CCD's filter wheel to convert CCD instrumental magnitudes into standard V and Ic magnitudes.
When it comes to image in colour, preference is directed towards the use of a Canon EOS1100D DSLR camera. This camera has been extensively used to take aesthetic pictures of celestial objects ranging from comets to distant galaxies and quasars. The quantum efficiency of this camera is around 37%, however its sensitivity is good enough considering the one shot colour capability and a generous wide field of view.
Camera Operation Software
Sequence Generator Pro (SGP) is the software of choice to operate all equipment remotely. SGP operates the main CCD camera, as well as the telescope's mount, the autoguider camera and the autofocuser motor. SGP interacts with the autoguiider via the PHD2 software avoiding the need to flip between program windows when in operation. SGP also operates the autofocuser routine as well as the programmable operation of the mount via a GUI interface. This program has also been used to operate the DSLR remotely when needed.
The pointing of the mount to centre targets is done through SGP's plate solving software that is achieved within seconds. Via plate solving, users can instruct the software to achieve pointing precision down to less than 1 arc minute easily. This ensures that no matter how small the field of view is, the target is always centred on the CCD chip.
The goal of SGP is to provide a best-in-class image capture suite for astrophotography. SGP's philosophy is based on the concept that a lot of equipment is rigged to the telescope and sometimes it is difficult to get it all working together. SGP was written in a way that is capable of executing complex sequences of capture events through a straightforward process without the need to go into any scripting processes. Thus, this great program allows spending more time acquiring images and less time dealing with rigging issues.
Sequence Generator Pro controls the all the operations at the observatory. Plate solving, interaction with the PHD2 guiding software, camera control and the setting of image sequencing permits the system to function with minimal user intervention. The only interaction required at Flarestar concerns the opening of the observatory and initial flat-field calibration. SGP then takes over all the necessary functions required for the night.
The Observatory's Structure
After some considerable deliberation, it was decided that marine plywood would be the best option for exterior of the observatory. This material is not only resistant against weather elements but also acts as a good thermal insulator against heat build up during the warm summer days. The framework that supports the exoskeleton of the structure is made up of 2 inch wide wooden beams. As an additional protection for the exterior shell, two layers of fibreboard resin and hardener were applied and finished by two coats of paint. To ensure maximum protection, three coats of paint including a base coat were also applied to the interior.
The build up of humidity inside an observatory is a major concern as equipment could be damaged in case of prolonged exposure. There are two ways to keep humidity from building up within an observatory. The first method is to seal the structure entirely that prevents humid air from accumulating inside. This can be either achieved through an active process such as the employment of a dehumidifier or through moisture absorbent material that have to be renewed continuously whenever the substance reaches saturation levels.
The alternative approach employs a passive approach that prevents the build up of a long term humid environment through the use of ventilation vents that allows passive air circulation during daytime hours. Flarestar Observatory employs the latter approach as Malta's climate is considered as a subtropical-Mediterranean climate where winter temperatures are rather mild and summers are warm and dry. As Malta is an island, humidity is well above average, however humidity inside the observatory is not persistent for long periods of time as during daytime, the temperature inside rises enough to dissipate away any excess humidity. This passive approach has never produced any problems to optics or electronic gear for a number of years.
Click the link above to watch a 3D rendering of the observatory's structure. Movie clip shows the dimensions of the structure and its uncomplicated shape. The simplistic design is not only easy to reproduce but also ensures a low maintenance routine that is set to deliver many productive hours of imaging under the stars.
Utility & Support Enclosure
An utility support storage was constructed next to the observatory to host the observatory's computer and power supplies that power up the cameras, autofocuser motor, telescope mount and dew-removal heaters. An internet LAN router, IR Camera and other accessories are also kept in here as they are enclosed and well protected against dew.
This structure referred to as USE (Utility Support Enclosure) and could be considered as the 'brain' of the observatory as the telescope receive all operational commands from here, even when operating directly next to the telescope.
Flat field Acquisition
At Flarestar, flat fields are taken by illuminating a translucent perspex that is illuminated by reflected light hitting the back wall of the observatory. The even reflection enhance the quality of the flat fields as the light from the strategically placed LED is evenly distributed. An colour-enhanced flat field is depicted above that shows the a maximum range of less than 3% across the image.
As the observational schedule often entails long hours of monitoring for time series photometry, remote operation was always considered as a necessity. Remote operation is conducted from a 'control room' at home situated 15 meters away. Nevertheless, the distance of the control room from the observatory is actually irrelevant as the system allows remote access from anywhere over the internet. The observatory's PC that controls all equipment is connected to the internet via an external LAN CAT-5 cable. A TP-Link IEEE 802.3 5-port 10/100 Mbps Ethernet Network switch also allows the simultaneous connection and operation of the PC and IP cameras that ensure the correct function of the telescope.
The operation of the observatory's PC is conducted through the TeamViewer software that allows access and operation of a remote PC through another computer over the internet.
Having control to the observatory's PC enables the operation of the telescope. cameras and autoguider. However this is not enough to ensure that the operation at the telescope is all well. Cables might get snagged and clouds might roll in. To overcome this problem, two IP cameras with IR capability have been employed. One camera oversee the status of the telescope's mount while the other acts as a cloud monitor. The cloud camera emplys a high definintion (HD) sensor that is sensitive enough to detect high thin clouds as well as stars down to 3rd magnitude. When the observatory is closed down, these cameras also act as security cameras.
This is an image capture of the telescope as seen during remote operation. The Infra Red camera can show well the telescope in pitch darkness without disrupting scientific data acquisition. As for the Skycam, this camera functions independently from the observatory's computer as it could be accessed through an IP connection.
Having a lot of equipment at stake at the mercy of unpredictable weather conditions is set to bring about sleepless nights. As an added precaution, a sensitive rain sensor has been installed that triggers an alarm at home in case the tiniest of rain droplets falls unexpectedly.
Autoguiding is achieved through the use of an Orion ST-80 Guidescope that is mounted on the telescope's OTA. This small 80 mm aperture (400 mm focal length) telescope is a very good instrument for guiding as its aperture is big enough to enable guiding on stars as faint as magnitude 9. The camera employed for autoguiding is a QHY 5 II that utilise a monochrome CMOS chip (1280 x 1024 pixels of 5.2 µm square). Through this set-up this system ensures that a guide star is always available to enable autoguiding.
The QHY5-II mono autoguider camera is USB connected to the PC that sends commands to the mount via the ASCOM protocol. The QHY5 camera can also be employed as a lunar/planetary imaging camera if needed. Its 5.2 micron pixels provide high resolution even for shorter focal length telescopes.
The software of choice for autoguiding is the popular PHD2 Guiding. PHD2 is the enhanced, second generation version of the popular PHD guiding software from Stark Labs. PHD2 is now an open-source project, supported by an active community of developers and astro-imagers.
In PHD Guiding, all calibration is taken care of automatically. There is no need to tell it anything about the orientation of the camera. The automatic calibration routine takes care of this. Once correctly configured through SGP, the software can also automatically choose a suitable guidestar and starts autoguiding without any further user intervention.