Archivi tag: stellar populations

The Milky Way and its Stars

Studies of Galactic and stellar structure are entering an era replete with data from large space- and ground-based projects. The combination of large photometric surveys carried out in the last 15 years, extensive photometric-variability databases allowing the inner structure of thousands of stars to be studied, and vast high-resolution spectroscopic surveys probing the detailed chemical composition of hundreds of thousands of stars, hold the promise of a new synthesis of stellar and Galactic astrophysics. These data will in a few years be complemented by precise astrometric measurements from Gaia.
Continua a leggere The Milky Way and its Stars


RASPUTIN: Resolved And unresolved Stellar PopUlaTIoNs

The study of stellar populations is one of the most relevant diagnostics to constrain galaxy formation and evolution. Quantitative analyses of the stellar content of stellar systems pave the way to `convert’  starlight into physical quantities like stellar masses, chemical abundances and star formation rates, and to trace back in time the evolution and the chemical enrichment history of galaxies. Continua a leggere RASPUTIN: Resolved And unresolved Stellar PopUlaTIoNs

The Impact of Feedback on Star and Galaxy Formation

After several decades of theoretical developments and spectacular observations of star formation sites and star forming galaxies, our understanding of star formation in the universe has profoundly evolved. Designing a theory for star formation based on physical first principles is now within our grasp, but to reach this goal we must grapple with the central  role feedback processes from young stars play in regulating star formation in galaxies and in determining the properties of newly born stellar populations deep inside molecular clouds. Modeling feedback processes such as radiation from young stars, stellar winds and ultimately explosive events like supernovae is very challenging. The relative importance of different forms of feedback energy (thermal energy, ionizing and continuum radiation, cosmic rays,  kinetic energy in jets) is still under debate, and the energy injection often occurs at very small scales that are poorly resolved by computer simulations or telescope imaging. Moreover, this energy also couples to very large scales, driving turbulence within the ISM and powering the ejection of powerful galactic winds, both of which contribute to regulating the global star formation efficiency into disk galaxies.

The goal of this conference, the kick-off meeting for our program on the physics of star formation feedback, is to set the scene for the three following months in Santa Barbara.  Focus areas will include discussion of the detailed nature and efficacy of various stellar feedback mechanisms, new theoretical and observational developments on how feedback regulates star formation at a range of scales, and inter-comparisons of numerical methods for implementing feedback in molecular clouds and in galaxies. During the week, various sessions will be dedicated to discuss critical areas where new developments  and new collaborations are needed. For example, observations of large scale gas motions within the Galaxy will be used to set constraints on theoretical and numerical models of the galactic fountain,  while detailed post-processing of computer simulations could be used by observers to infer the physical  properties of stellar outflows. Interactions between theorists and observers, and between experts in small scale and  large scale phenomenon, will shed some light on the role of these feedback processes for regulating star formation.

Unveiling the Formation of Massive Galaxies

Recent observations have delivered new insight into the structure and evolution of massive galaxies. Once thought of as relatively simple systems, it is now clear that these galaxies are diverse and can contain multiple stellar populations. Their assembly was a drawn-out process influenced both by the dark matter halos which surround them and the supermassive black holes in their cores. Many of their stars were acquired by cannibalizing smaller galaxies from a surrounding group or cluster, yet their stellar initial mass function appears to depend on the mass of the final galaxy. In addition, the growth of massive galaxies has been shaped by interaction with a reservoir of circumgalactic gas whose structure and composition is now becoming observationally accessible.

This Aspen Winter Conference will explore the richness and diversity of the evolutionary paths of massive galaxies, attempting

(i) to synthesize a coherent picture from recent observational and simulation results,

(ii) to identify major areas of continuing uncertainty, and

(iii) to formulate observational and modeling strategies to eliminate the remaining gaps in our understanding.

Galaxies meet GRBs

We want to bring together two different communities that have more in common than they think. Birth, life and death of massive stars are a crucial part of every galaxies’ evolution at some point in its history. The chemical composition of the stellar populations in the galaxy is linked to the properties of the massive star and hence its final fate. Massive stars occur more often in star-bursting galaxies and heavily star-forming regions inside larger galaxies. But how was this star-formation triggered? In return, massive stars provide kinematical and chemical feedback to their surroundings often stretching beyond the galaxy via galactic winds. Shocks can lead to new star-formation or inhibit it, dust is created and destroyed. What is the imprint of massive stars on their environment and how can we detect them? Also, the known final states of massive stars have become more and more diverse in the last few years. Supernovae have diversified in many different classes, GRBs continue to be puzzling and some very odd ones are discovered every now and then. What are the different progenitors leading to different kinds of stellar explosions and why? Can stellar evolution modeling provide us with concrete conditions for different kinds of stellar explosions and observables of their environments? We will discuss about galaxies, star-formation and massive stars to better understand their mutual influence. Contributions from all wavelengths and redshifts are welcome from both observers and modelers.

Here is a list of topics that we plan to cover during the meeting:

  • GRBs, SNe, WR stars and their hosts
  • Diversity of GRBs and SNe
  • Life and death of massive stars
  • Influence of stellar explosions on their environment
  • Galaxy evolution and starburst galaxies
  • High-redshift star-forming galaxies
  • Star-formation triggers
  • Stellar populations and their evolution
  • Evolution of star-formation and chemical abundances over the history of the Universe
  • IFS and other resolved techniques
  • Multi-wavelength observations of star-forming galaxies
  • Stellar evolution modeling and end-states of massive stars

IAUS 298: Setting the Scene of Gaia and LAMOST

With the upcoming astrometric satellite Gaia and the complementary large scale ground based surveys, such as LAMOST, Galactic Astronomy is set to enter a new era. We will have access to high quality data for several hundred thousands of stars. Both to obtain as well as interpret such large amounts of data sets new challenges for the Galactic astronomers. The meeting in Lijiang was conceived out of a need to prepare the community for the challenges ahead and, in particular, to foster stronger relations between observers and modellers. Ultimately we wish to create a detailed map of our Galaxy and to understand why it looks like it does. That can only be achieved through constant intercourse between modellers and observers. The SOC hopes that the program at this meeting will help facilitate this process.

The formation and evolution of galaxies is a key topic in contemporary astrophysics. This topic can be studied in essentially two ways: through the study of large numbers of galaxies at different times of the evolution of the universe, or through the detailed study of the Milky Way and its close neighbours. The latter is often referred to as near-field cosmology, and can provide surprisingly strong constraints on models of galaxy formation and evolution. However, the study of the Milky Way as a galaxy is not an easy task. In particular the detailed knowledge of the distribution of the stellar content, both in space and in velocity space, is severely lacking. This means that it is difficult to fully constrain evolution and formation models of the different components of the Milky Way. In 1944 Walter Baade introduced the concept of Stellar Populations. The concept was has remained a highly useful tool to quickly identify and classify different generations of stars in galaxies. However, the last decades have seen a move away from this fairly static, even if complex, concept to a more dynamic and flexible way of characterizing the stellar components in the Galaxy by means of the individual star’s age, metallicity, orbit etc.  This shift in how we study major stellar populations in our own and nearby galaxies has  benefited from advances both in theory as well as in observations. In particular the advent of wide field CCDs and dedicated survey telescopes as well as advances in computer technology that now allows for truly detailed models of various aspects of the evolution of the Milky Way have moved the study of our Galaxy into the first part of a new era. The advent of Gaia will take us truly into the era of precision studies of the Milky Way. In the meantime several very large surveys have contributed and will continue to contribute to our deepening understanding of the Milky Way as a galaxy. Gaia is scheduled to launch 2013 and will provide parallaxes and proper motions for a billion objects and radial velocities for 150 million stars, enabling the exploration of the Milky Way to take an unprecedented quantum leap forward. We will be working in a completely new regime – that of precision Galactic astronomy. These changes put serious and new demands on our analysis of the data and modeling of the Galaxy. Around the world there are currently a number of on-going or planned major surveys that, although they have their own stand-alone science cases and goals, will complement Gaia in fundamental ways. One of the most ambitious of these projects is the innovative LAMOST telescope, equipped with some 4000 fibres and a 20 square degree field of view. LAMOST is the largest Chinese telescope and one of the National Major Scientific Projects undertaken by the Chinese Academy of Sciences. This and other projects, such as the Gaia-ESO Survey, SEGUE-2, HERMES/GALAH, and APOGEE, will provide vital complementary data to Gaia. Of great importance, they will supplement the high quality proper motions from Gaia with radial velocities of equal quality for stars fainter than Gaia’s limits, enabling a fully detailed 6D phase space map of the Milky Way to be constructed. Theorists and observers alike find these forthcoming projects exciting. This meeting offers a very timely opportunity to bring observers and theoreticians together to discuss in depth the possibilities to overhaul and update our traditional view of the Milky Way and its sub-components. Thus we have a very substantial section on the Milky Way galaxy as seen through observations, a dedicated session on the most recent advances in stellar abundance analysis, extensive coverage and update on on-going surveys, and the conference ends with a major session on modeling of galaxies with special emphasis on reviewing the state of the art of the various modeling approaches and their application to the Milky Way. The aim is to deepen the discussion and interplay between modelers and observers to take advantage of the challenges and possibilities that these new data sets offer. By bringing together theorists, observers, and survey scientists interested in our Galactic system, we will maximise the impact of the Symposium, which is sure to encourage and excite, leading to new insights and a community better prepared to take scientific advantage of Gaia, LAMOST and all the large (by then) on-going or upcoming surveys.

Caffau’s star, an astrophysical mystery

SDSS J102915 172927 as seen by ESO – VLT

To ordinary people, stars in the galaxy may seem like tiny specks of light. But to Penn State Brandywine Professor Timothy Lawlor and undergraduate researcher Nick Rufo, one of those bright balls of gas is actually more massive than scientists originally reported and holds implications for understanding the evolution of the Universe.

Research conducted by Rufo and Lawlor about the irregular characteristics of what is known as “Caffau’s Star” suggests that it could actually be considered part of the subgiant category rather than a main sequence star. This means that Caffau’s Star could actually be much more immense than initially described. This finding plays an important role in strengthening the understanding of star formation and helps researchers comprehend the evolution of the 13.8 billion-year-old Universe. “The puzzle of stellar evolution is really about the origin of every one of us”, explained Lawlor. “One of the most fascinating things about stellar evolution and the evolution of the Universe is how it becomes clear that a huge majority of all atoms that make up you, me and the entire planet can be traced back to the center of a very massive star that blew up long ago”. Rufo, who spent his first two years at the Brandywine campus and is now a meteorology major in the College of Earth and Mineral Sciences at University Park, worked closely with Lawlor to analyze data about Caffau’s Star. He was able to complete calculations using a computer code and produced all of the models that were compared to Caffau’s Star in the research process. “Nicholas was a dedicated researcher” Lawlor said. “He helped uncover that the mass did not fit that of a main sequence star, and that for the observed composition of lithium to match, the star would have to be significantly less massive, which was not likely based on the temperature. Working with Nicholas was one of the most productive collaborations I have had with an undergraduate researcher”. While at the campus, Rufo participated in Penn State Brandywine’s spring undergraduate research exhibition called EURECA, where he presented the beginning discoveries of the studies he conducted alongside Lawlor. “I feel honored to have worked with a great professor like Dr. Lawlor”, Rufo said. “I never imagined I would have an opportunity working with Dr. Lawlor on a paper and doing research on a fascinating subject like astronomy when I was a student at Brandywine. I really enjoyed the experience and feel it gave me confidence and motivation”.

Penn State University: Student and professor solve astronomical mystery
arXiv: The extremely low metallicity star SDSS J102915+172927: a subgiant scenario