* Astronomy

Hubble Watches Stars' Clockwork Motion in Nearby Galaxy

Using the sharp-eyed NASA Hubble Space Telescope, astronomers have for the first time precisely measured the rotation rate of a galaxy based on the clock-like movement of its stars.
According to their analysis, the central part of the neighboring galaxy, called the Large Magellanic Cloud (LMC), completes a rotation every 250 million years. Coincidentally, it takes our Sun the same amount of time to complete a rotation around the center of our Milky Way galaxy.
Read more

Title: An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent
Authors: G. Pietrzyski, D. Graczyk, W. Gieren, I.B. Thompson, B. Pilecki, A. Udalski, I. Soszyski, S. Kozowski, P. Konorski, K. Suchomska, G. Bono, P. G. Prada Moroni, S. Villanova, N. Nardetto, F. Bresolin, R.P. Kudritzki, J. Storm, A. Gallenne, R. Smolec, D. Minniti, M. Kubiak, M. Szymaski, R. Poleski, . Wyrzykowski, K. Ulaczyk, P. Pietrukowicz, M. Górski, P. Karczmarek

In the era of precision cosmology it is essential to determine the Hubble Constant with an accuracy of 3% or better. Currently, its uncertainty is dominated by the uncertainty in the distance to the Large Magellanic Cloud (LMC) which as the second nearest galaxy serves as the best anchor point of the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to precisely and accurately measure stellar parameters and distances. The eclipsing binary method was previously applied to the LMC but the accuracy of the distance results was hampered by the need to model the bright, early-type systems used in these studies. Here, we present distance determinations to eight long-period, late- type eclipsing systems in the LMC composed of cool giant stars. For such systems we can accurately measure both the linear and angular sizes of their components and avoid the most important problems related to the hot early-type systems. Our LMC distance derived from these systems is demonstrably accurate to 2.2 % (49.97 ± 0.19 (statistical) ± 1.11 (systematic) kpc) providing a firm base for a 3 % determination of the Hubble Constant, with prospects for improvement to 2 % in the future.

Read more (1286kb, PDF)

Glistening cloud acts as cosmic centimetre

Object: Large Magellanic Cloud
Distance: 162,983.82 light years

Glittering like a cobweb covered in dew, the Large Magellanic Cloud floats lazily across the southern sky, blissfully unaware that it is at the centre of a raging controversy. The cloud - really a small galaxy orbiting the Milky Way - is part of a cosmic yardstick, helping us measure how far apart objects are in the universe.
But no one could quite agree on exactly how far away the Large Magellanic Cloud is from Earth. Now the most accurate measurement yet of its distance is helping astronomers use the aloof beauty as the first centimetre in their cosmic ruler. 
Read more

Title: A multi-wavelength investigation of newly discovered planetary nebulae in the Large Magellanic Cloud: Central stars
Authors: Warren A. Reid

Having completed my search for faint PNe in the LMC, including the outer 64 deg2 area not covered in the original UKST survey, I now have the most complete number of PNe within any galaxy with which to assess stellar parameters. I present preliminary estimates for planetary nebula central star temperatures for 688 LMC PNe using the excitation class parameter derived from emission lines in the nebula. These are then compared to a photoionisation model in order to evaluate the contribution of metallicity when determining stellar temperatures using only emission lines. I include measurements from my latest confirmatory spectroscopic observations which have yielded a further 110 new LMC PNe while confirming the 102 previously known PNe in the outer LMC. These observations, providing low and medium resolution spectra from 3650{\AA} to 6900{\AA}, have been added to my comparable data for PNe in the central 25deg2 of the LMC. The combined data were used to measure fluxes in preparation for a number of projects related to luminosity functions, chemical abundances, central star properties and LMC kinematics. Here I provide a preliminary look at the range of derived central star effective temperature estimates. I also show a correlation between the central star temperatures and the expansion velocity of the nebula.

Read more (105kb, PDF)