Stellar mystery deepens as HERMES provides a closer look

The Messier 4 (M4) globular cluster (right) near the bright supergiant star Antares (left) and the NGC 6144 globular cluster (middle). Photograph from UK Schmidt plates by David Malin. Credit: AAO.

The first results from the Anglo-Australian Telescope's state-of-the-art new instrument, HERMES, uncovered an unexpected discovery that a large group of stars are dying prematurely. The work challenges our accepted view of stellar evolution.

 

The findings of this new study, published today in the Monthly Notices of the Royal Astronomical were made by Monash PhD student Ben MacLean supervised by Professor John Lattanzio (Monash), Dr Simon Campbell from the Max Planck Institute for Astrophysics and Dr Gayandhi De Silva from the Australian Astronomical Observatory (AAO) and the University of Sydney. Their results dispute the prevailing theory of stellar evolution, revealing that large numbers of helium burning stars are dying prematurely in the M4 globular cluster.

M4, the star cluster at the right of the image, is one of the closest and brightest globular clusters, and has already been very well studied - it was a surprise to make such a striking discovery in our stellar backyard.

“Globular clusters are some of the oldest objects in the Universe. Although we have some ideas for what is going on in them, every time we look carefully we find something unexpected. They are both fascinating and frustrating at the same time!” - Professor John Lattanzio, Monash University

 While the cause of this remains a mystery, the HERMES chemical analysis has revealed that premature death tends only to occur in the sodium-rich/oxygen-poor stars. This research would previously have been impossible to conduct in Australia, instead requiring the use of larger overseas’ telescopes. However, thanks to the recent construction and installation of the HERMES instrument, researchers can now use the AAT to analyse the chemical composition of up to 400 stars at a time.

“HERMES represents a significant step forward for Australia’s observational capacity. This incredible advance is unique in that it combines multi-object capability with high data quality. Otherwise we are limited to observing one star at a time to collect such high quality data. This capability makes HERMES and the AAT competitive against some of the worlds’ biggest telescopes and a new tool for making breakthrough discoveries.” – Dr Gayandhi De Silva, AAO / University of Sydney.

The scientific motivation behind building HERMES was to carry out a large-scale survey of one million stars in the Galaxy. This Australian-led survey called GALAH will obtain precise measurements of the motions and chemical content of over 15 different chemical elements that will provide an unprecedented view of how stars in our galaxy formed and evolved. HERMES is available for use by the broader astronomical community and is under very high demand.

 

Publication details:

B.T. MacLean (Monash), S.W. Campbell (MPA), G.M. De Silva (AAO/USyd), J. Lattanzio (Monash), V. D'Orazi (INAF-Padova), J. Simpson (AAO) and Y. Momany (INAF-Padova).
“An extreme paucity of second population AGB stars in the 'normal' globular cluster M4”. Published in Monthly Notices of the Royal Astronomical Society (MNRAS) through Oxford University Press. MNRAS Letters, 2016.

http://mnrasl.oxfordjournals.org/content/early/2016/04/20/mnrasl.slw073

 

Science Contacts:

Dr Gayandhi De Silva

Research Astronomer, Australian Astronomical Observatory and University of Sydney

M: +61 431 406 909    E: gayandhi.desilva@aao.gov.au

 

Prof. Andrew Hopkins

Head of Research and Outreach, Australian Astronomical Observatory,

M: +61 432 855 049    E: andrew.hopkins@aao.gov.au

 

Images:

The Messier 4 (M4) globular cluster (right) near the bright supergiant star Antares (left) and the NGC 6144 globular cluster (middle). Photograph from UK Schmidt plates by David Malin. Credit: AAO.

The Messier 4 (M4) globular cluster (right) near the bright supergiant star Antares (left) and the NGC 6144 globular cluster (middle). Photograph from UK Schmidt plates by David Malin. Credit: AAO.

 

A schematic of the HERMES spectrograph. The lines show the light path through the instrument that ultimately provides astronomers with high quality data for measuring stellar chemical content. Credit: AAO.

A schematic of the HERMES spectrograph. The lines show the light path through the instrument that ultimately provides astronomers with high quality data for measuring stellar chemical content. Credit: AAO.

 

Animation:

Screenshot of the HERMES path video. Credit: AAO

This animation shows what happens to the light collected from 400 stars from the AAT once it is fed inside the HERMES spectrograph. Inside HERMES the  star light is split up into four channels using state-of-the-art Volume Phase Holographic grating technology to ultimately provide astronomers with high quality data to measure the chemical content of the stars. Credit: AAO.