Last week I visited Jennifer Sobeck and my former Yale-colleague Nitya Kallivayalil at the University of Virginia. Jen is the deputy project manager of APOGEE-2, which is a large spectroscopic survey collecting 300,000 high-resolution spectra of Milky Way stars (and other bright targets). Hence, her head is full of stellar atmospheres and element abundances. Nitya is the go-to person for proper motions of Galactic satellites, which is why there’s tons of overlap between my work and both of theirs. Frequently distracted by great food and stunning weather, we scienced around for a few days. Our brainstorming for low hanging fruits in the APOGEE-2 dataset brought us a few great ideas, which we will hopefully pursue within the next weeks and months. Steve Majewski, PI of APOGEE and also based at UVa, outsourced the same task to all his undergrads. Let’s see who’s first to have some results!
During Adrian Price-Whelan’s dissertation talk today at the winter meeting (AAS227) of the American Astronomical Society in Kissimmee, Florida, I was reminded that I haven’t mentioned our publication here. Adrian went through a whole lot of effort and characterized regular and chaotic orbits in a typical galactic gravitational potential. Usually, orbits in such a potential can be broadly categorized into chaotic and non-chaotic orbits. Adrian looked at this distinction in terms of the streams that are formed by satellites on such orbits. Continue reading Chaos in the Galaxy→
The Milky Way consists of roughly 100 billion stars like our Sun, which form a huge stellar disk with a diameter of 100-200 thousand light years. The Sun is also part of this structure, hence, when we look into the sky, we look right into this gigantic disk of stars. The vast number of stars and the huge extent on the sky make it hard to measure fundamental quantities for the Milky Way – such as its weight. Continue reading How to weigh the Milky Way→
In my first year at Columbia I worked with grad student Sarah Pearson on an idea that Kathryn Johnston had while trying to find an orbit for Palomar 5 in a Law & Majewski potential. Wait what? Who’s Sarah, who’s Palomar 5, and what is a Law & Majewski potential?
Palomar 5 is a globular cluster in the halo of our Galaxy, the Milky Way. It is about 12 billion years old and consists of roughly 30,000 stars. The star cluster can be seen within the footprint of the Sloan Digital Sky Survey. But even more fascinating is that we can also see a stream, consisting of at least as many stars, stretching out from the cluster along its orbit. This stream – there are actually two, one in the leading direction and one in the trailing direction – spans about 23 degrees on the sky, while being on average half a degree wide. That’s about the size of 50 full moons! Continue reading Stream fanning→
For my presentation at the Gaia Challenge in Heidelberg, I made a quick ADS search for publications on tidal stream observations since their first discovery in 1995 by Carl Grillmair. Although tidal streams had been theoretically predicted before 1995, Grillmair showed for the first time that some star clusters have significant amounts of stars outside their tidal radii. At about the same time, the Sagittarius (Sgr) dwarf galaxy was discovered by Rodrigo Ibata, and people started finding patches of stars that belong to the stream emanating from this galactic satellite everywhere in the halo of the Milky Way. It took 6 more years until Michael Odenkirchen showed with commissioning data of the Sloan Digital Sky Survey that the globular cluster Palomar 5 has a coherent stream emanating from its Lagrange points out into the tidal field of the Milky Way. This publication also marked the onset of survey since in astronomy. Since 2000/2001 the rate of papers presenting new observational results on streams in the Galactic halo or around other galaxies grows exponentially. While this growth was initially driven by studies on the Sgr stream (red cumulative curve above), the focus is now shifting towards fainter streams like Palomar 5, NGC 5466 or GD-1 (blue curve). It’s a really exciting time to work in this field!