Saturday, July 14, 2018

Maltese discovery of a new variable star in the constellation of Aquila.

We report the discovery of a previously unknown variable star in the constellation of Aquila. This new variable star was discovered on 31st July 2017 by Stephen Brincat and myself through a set of images acquired which I acquired for the purposes of asteroid photometry.

At the time I used a 0.20-m aperture Schmidt-Cassegrain telescope and a scientific-grade CCD for data acquisition.

Stephen has analysed the images for any new variable star among the background field stars. Analysis of the unfiltered CCD frames yielded a possible candidate at coordinates (J2000) 19:18:20.60 -09:25:56.29 where the resultant lightcurve for the possible variable star depicted a decline in brightness.  The suspected variable star was monitored for an additional six nights from Flarestar Observatory through a 0.25-m f/6.3 Schmidt-Cassegrain telescope. We performed differential CCD aperture photometry on the suspected variable star using four field stars as comparison stars. The selected comparison stars were all of near-solar colour in order to mitigate atmospheric extinction effects that could diminish the quality of our results.



The analysis of the observations revealed that this star (identified as UCAC4 403-115663) varies its light in a regular fashion at a period of around half a day. Consequently, each night we viewed the same part of the phase. In such circumstances, it was very difficult to determine the nature of the star through its light curve from a single location as each night overlaps the others. As a result, we searched for data on this star from several professional catalogues.

As the star’s maximum magnitude in V-band is of magnitude 15.85, we found out that a number of surveys did not capture it adequately. However we discovered that the ASAS-SN survey (All-Sky Automated Survey for Super Novae) had a good number of data points for this star. The ASAS-SN survey picked out our target once or twice every few days.  Luckily we had appropriate algorithms in our arsenal for such instances. We employed the Lomb-Scargle and the Phase Dispersion Minimization (PDM) algorithms that are capable to extract a reliable period despite that the survey had acquired their data at irregular intervals.   Our data combined with those from the ASASSN-SN survey yielded a period of 0.498115 days.

The lightcurve revealed that the regular variation in brightness is due to two stars revolving around each other, typical of a binary star system of the W UMa class binary star system where two stars orbit each other and are close enough to distort their spherical shapes into ellipsoids. Our study revealed that the amplitude of this system range from magnitude 15.85 to 16.35, due to continuous eclipses where each component occults the other.  We reported our discovery to the American Association of Variable Star Observers (AAVSO) where it has been officially recognised and catalogued in the AAVSO International Variable Star Database (VSX). This newly discovered star system is now designated as AUID (AAVSO Unique Identifier) 000-BMP-328.



We wish to take the opportunity to thank AAVSO external consultant Sebastian Otero for his help and guidance. 

Thursday, May 24, 2018

Impressive globular cluster: Messier 3 (NGC 5272)

NGC 5272 (Messier 3)


My first deep sky target with my new Moravian cooled G2-1600 CCD camera. This wonderful globular cluster is NGC 5272 (Messier 3) has a bright core with a diameter of about 6 arcminutes and spans a total of 12 arcminutes. It is one of the finest globular clusters in the northern hemisphere and is also one of my favourite visual observation targets.

Saturday, June 11, 2016

UPDATED: South polar cap not prominent






























OBSERVATION PUBLISHED BY ALPO-JAPAN FOR COMPARATIVE ANALYSIS. 

This is my first imaging of Mars this season, taking the opportunity of a good clear night. Previous observations for this apparition season included the sketching the Martian surface using different colour filters. Hopefully, I plan to upload these sketches once I complete the full observation of the Martian surface.

During last night's session I decided to use my trusty old philips webcam. Camera settings included a 60fps to acquire 10,000 coloured images using my 2x televue barlow.

Surface features on Mars

The RGB image shows a very interesting albedo composition. Syrtis major is seen as dark blue compared to the neighbouring Iapygia region, which has a reddish-brown hue. Hellas region is brighter but lacks the usual bluish hue. Perhaps this is due to oversampling of red signal by the webcam.

The complex structure of Syrtis major together with the small protuberance of Moeris Lacus are very conspicuous. The indentation pattern of Sinus Sabaeus is very prominent especially at Sinus Meridiani, and shows the good atmospheric conditions present at the time of image acquisition.

The isolated Alcyonius Nodus next to S. major tip is very prominent. On the opposite site of S. major is Utopia which is lighter than S. major region. Ismenius lacus is subtle but visible.

The desolate expanse of Arabia region is prominent, and has a lighter colour when compared to its slightly darker borders in areas adjacent to S. Sabaeus and S. Major. Here I am referring to the regions of Aeria and Edom in particular.

The south polar cap is not visible. 

Wednesday, April 27, 2016

Bullialdus crater and its central peak.

Bullialdus lunar crater. 17 July 2013, 22:00-22:28 LT
The relatively isolated impact lunar crater Bullialdus is found in the western portion of Mare Nubium. This crater has a high outer rim that is circular with the usual subtle polygonal appearance. The inner terraced walls for which this crater is famous for are hidden in darkness. On the other hand the outer ramparts are conspicuous, and highlight a radial pattern of low ridges and valleys.

The illuminated part of the floor of the crater is generally rough with many low rises. In the center of the crater is a formation of several peaks and rises that climb to over a kilometer in height. The sketch shows this prominent peak that comes out of the surrounding shadow simply because of its height.

Klima et al., (2013) showed how the central peak of Bullialdus Crater is significantly enhanced in hydroxyl relative to its surroundings. This is indicative that the peak originated from deep down below the crater as result of the immense impact pressure and heat.

Two smaller but notable craters lie just to the south of the main crater. Bullialdus A lies just to the south-west of Bullialdus, within its ramparts. To the south of Bullialdus A is the slightly smaller Bullialdus B.To the Southwest is the conspicuous but smaller lunar crater Konig. Its shadow suggests a tapering side wall towards the northwest.


References:

R. Klima, J. Cahill, J. Hagerty, D. Lawrence (2013). Remote detection of magmatic water in Bullialdus Crater on the Moon. Nature Geoscience 6, 737–741 (2013) doi:10.1038/ngeo1909