GeminiFocus 2017 Year in Review | Page 49

discovery that changes this old perception and opens a new window onto exoplanet formation .
Using GMOS spectra , Jay Farihi ( University College London ) and colleagues identified critical metal features in the system ’ s spectrum as well as the higher Balmer lines . In contrast to the carbon-rich icy material commonly found in double star systems , the planetary material identified in the SDSS 1557 system has a high metal content , including silicon and magnesium . These elements were identified as the debris flowed from its orbit onto the surface of the white dwarf , polluting it temporarily with at least 10 17 grams ( or 1.1 trillion US tons ) of matter , equating it to an asteroid at least 4 kilometers in size .
Farihi says : “ Building rocky planets around two suns is a challenge because the gravity of both stars can push and pull tremendously , preventing bits of rock and dust from sticking together and growing into full-fledged planets . With the discovery of asteroid debris in the SDSS 1557 system , we see clear signatures of rocky planet assembly via large asteroids that formed , helping us understand how rocky exoplanets are made in double star systems .”
The discovery came as a complete surprise , as the team assumed the dusty white dwarf
January 2018 / 2017 Year in Review was a single star , but co-investigator Steven Parsons ( University of Valparaíso and University of Sheffield ), an expert in binary systems , noticed the tell-tale signs of something unusual . “ We know of thousands of binaries similar to SDSS 1557 , but this is the first time we ’ ve seen asteroid debris and pollution ,” he says . “ The brown dwarf was effectively hidden by the dust until we looked with the right instrument . But when we observed SDSS 1557 in detail , we recognized the brown dwarf ’ s subtle gravitational pull on the white dwarf .”
From the Gemini data the team estimated that the white dwarf has a surface temperature of 21,800 Kelvin ( about 3.5 times hotter than the Sun ) and a mass of ~ 0.4 solar masses ; the brown dwarf companion has a mass of ~ 0.063 solar masses .
The research is published in the February 27th online issue of Nature Astronomy .
See the University College London press release here .
β Pictoris b : an Exoplanet with the Atmosphere of a Brown Dwarf
A team of astronomers led by Jeffrey Chilcote ( University of Toronto ) uses the Gemini Planet Imager ( GPI ) at the Gemini South telescope in Chile to refine our understanding of the β Pictoris system . The system contains the ~ 13 Jupiter mass companion β Pictoris b , which is at the mass boundary sometimes used to distinguish between an exoplanet and a brown dwarf . Brown dwarfs are objects that are not massive enough for sustained nuclear reactions ; and brown dwarfs less massive than 13 Jupiters cannot even start a nuclear reaction .
GeminiFocus
Figure 12 . [ O III ] emission-line profiles from the GMOS IFU spectra overlaid on the HST [ O III ] images for Mkn 1498 , one of the galaxies studied in this work . This galaxy displays a ringlike emission feature dominated by rotation with a velocity range of ± 175 km / sec , ( the 700 km / sec referenced in the legend refers to the entire velocity range shown in each miniature line profile plot ).
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