Archivi tag: spectroscopy

Fifteen Years of Science with Chandra

The meeting will highlight key science results from the past fifteen years and a panel discussion focusing on key science topics for the next 10+ years of operation of the Chandra X-ray Observatory. Topics and themes will emphasize high resolution imaging and spectroscopy, observations and theory, including related data from other observatories. Continua a leggere Fifteen Years of Science with Chandra

GES 2014: Gaia-Eso Survey Second Science Meeting

The Gaia-ESO Survey (GES) is currently half way to achieve its goal to collect spectra for 100 000 stars over a period of five years. The survey is providing an homogeneous overview of the distributions of kinematics and elemental abundances for the major components of the Milky Way, namely the bulge, the thick and the thin discs and the halo. In addition to the field component, a very significant sample of open star clusters, covering all accessible cluster ages and stellar masses, as well as a handful of globular clusters are being observed. Continua a leggere GES 2014: Gaia-Eso Survey Second Science Meeting

Exoplanets with JWST – MIRI

The workshop is aimed on discussing the capabilities and techniques for characterising exoplanets with the James Webb Space Telescope, in particular with its MIRI instrument. The discussions will cover both transit spectroscopy and direct imaging, covering giant planets to rocky planets and their atmospheres.

Poster of the workshop

The decay of sterile neutrinos as signal of dark matter presence

Un gruppo di astrofisici dell’Università di Leiden, guidati da Alexey Boyarsky, potrebbero aver identificato alcune tracce della presenza di materia scura attraverso la rivelazione di una nuova particella, il neutrino sterile, un ipotetico tipo di neutrino che non interagisce con nessuna delle interazioni fondamentali. Intanto, qualche giorno fa, un altro gruppo di ricercatori di Harvard hanno riportato risultati simili.

The two groups this week reported that they have found an indirect signal from dark matter in the spectra of galaxies and clusters of galaxies. They made this discovery independent of one another, but came to the same conclusion: a tiny spike is hidden in the X-ray spectra of the Perseus galaxy cluster, at a frequency that cannot be explained by any known atomic transition. The Harvard group see the same spike in many other galaxy clusters, while Boyarsky also finds it in the nearby Andromeda galaxy. The researchers put it down to the decay of a new kind of neutrino, called ‘sterile’ because it has no interaction with other known neutrinos.

A sterile neutrino does have mass, and so could be responsible for the missing dark matter.

The first indications for the existence of dark matter in space were found more than eighty years ago, but there are still many questions surrounding this invisible matter. Sterile neutrinos are a highly attractive candidate for the dark matter particle, because they only call for a minor extension of the already known and extensively tested standard model for elementary particles. Boyarsky and his colleagues have already had this extension of the standard model ready for some time, but were waiting for the first observation of the mysterious particle. Measurements at higher resolution will shed light on the matter, and there is reason to hope that the spectral line just discovered will finally eliminate the problem of the missing mass.

University of Leiden: Glimmer of light in the search for dark matter

arXiv: An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster 

arXiv: Detection of An Unidentified Emission Line in the Stacked X-ray spectrum of Galaxy Clusters

SALT observes the power of quasars

Un gruppo di astrofisici di del Dartmouth College hanno studiato le modalità con cui i quasar, e i buchi neri che in essi risiedono, influenzano le galassie ospiti. I ricercatori hanno documentato l’immensa radiazione emessa dai quasar che si estende per migliaia di anni-luce nello spazio, fino ai bordi più esterni della galassia.

For the first time, we are able to see the actual extent to which these quasars and their black holes can affect their galaxies, and we see that it is limited only by the amount of gas in the galaxy” says Kevin Hainline. “The radiation excites gas all the way to the margins of the galaxy and stops only when it runs out of gas“. The illumination of gas can have a profound effect, since gas that is lit up and heated by the quasar is less able to collapse under its own gravity and form new stars. Thus, the tiny central black hole and its quasar can slow down star formation in the entire galaxy and influence how the galaxy grows and changes over time. “This is exciting because we know from a number of different independent arguments that these quasars have a profound effect on the galaxies in which they live“, Ryan Hickox says.

There is a lot of controversy about how they actually influence the galaxy, but now we have one aspect of the interaction that can extend on the scale of the entire galaxy. Nobody had seen this before“.

The radiation released by a quasar covers the entire electromagnetic spectrum, from radio waves and microwaves at the low-frequency end through infrared, ultraviolet, and X-rays, to high-frequency gamma rays. A central black hole, also called an active galactic nucleus, may grow by swallowing material from the surrounding interstellar gas, releasing energy in the process. This leads to the creation of a quasar, emitting radiation that illuminates the gas present throughout the galaxy. “If you take this powerful, bright radiation source in the center of the galaxy and blast the gas with its radiation, it will get excited in just the same way the neon gets excited in neon lamps, producing light“, says Hickox. “The gas will produce very specific frequencies of light that only a quasar can produce. This light functioned as a tracer that we were able to use to follow the gas excited by the black hole out to large distances“.

Quasars are small compared to a galaxy, like a grain of sand on a beach, but the power of their radiation can extend to the galactic boundaries and beyond.

Hickox, Hainline, and their co-authors based their conclusions on observations made with the Southern African Large Telescope (SALT), the largest optical telescope in the southern hemisphere. Dartmouth is a partner in SALT, giving faculty and students access to the instrument. The observations were performed using spectroscopy, where light is broken down into its component wavelengths. “For this particular kind of experiment, it is among the best telescopes in the world“, says Hickox. They also used data from NASA’s Wide-field Infrared Survey Explorer (WISE), a space telescope that imaged the whole sky in the infrared. The scientists used observations in infrared light because they give a particularly reliable measure of the total energy output by the quasar.

Dartmouth College: Shedding New Light on the Brightest Objects in the Universe

arXiv: SALT Long-slit Spectroscopy of Luminous Obscured Quasars: An Upper Limit on the Size of the Narrow-Line Region?

Brown Dwarfs come of Age

An international conference on Brown Dwarfs will be held next May in the sunny island of Fuerteventura, exactly 11 years after the first IAU Symposium devoted to these once elusive objects and 18 years after the definitive observational confirmation of their existence. Much work has been done in the last two decades, both from the theoretical and observational point of view. Time is ripe now to have a conference to provide a comprehensive overview of this very active field of research. Some of the most relevant work on Brown Dwarfs has been done in the Canarian Observatories, making Canary Islands an ideal location to host this conference. Fuerteventura is the easternmost island of the Canaries, rich of unique natural spaces and impressive landscapes. It is well connected by direct flights with many European cities and offers many possibilities of affordable and comfortable accommodation. This island is working to preserve its dark night sky and become a Starlight Reserve.

Wide-area surveys such as DENIS, SDSS and 2MASS have played a major role in the discoveries of some of the first brown dwarfs and the definition of the spectral classes L and T. Recently completed and ongoing surveys such as IPHAS, PANSTARS, UKIDSS and WISE are shedding new light on the field. An even cooler spectral class, the Y dwarfs, has been revealed. Detailed studies of brown dwarfs have uncovered surprising behaviours such as ultra-fast rotation rates, the presence of clouds, polarization and strong radio emission. Observations of dust in disks around very low-mass primaries with the Spitzer and Herschel satellites have provided information on the conditions of planet formation. Brown dwarfs have become prime interest targets for searches for habitable planets due to their small masses and radii, and the presence of a habitable regions very close to them for extended periods of time. Brown dwarfs populate the natural bridge between stars and planets. As such, they are connected with both types of objects. One of the main focus of this international conference will be to examine whether the fundamental properties of brown dwarfs represent a smooth continuity from stars to planets or not. Brown dwarfs and their extension into planetary masses represent the low-mass end of the stellar IMF. Deep observations of young open clusters and star-forming regions and microlensing surveys have found a population of very low-mass brown dwarfs or free-floating planets.

Our conference will provide a comprehensive update of the status of this active field of research. Here is a list of the scientific topics that will be treated:

  • Formation and early evolution of brown dwarfs
  • Angular momentum and disk evolution in very low mass systems
  • Large scale surveys
  • Deep surveys
  • Brown dwarfs in binary systems
  • The lower end of the IMF
  • Planets around brown dwarfs
  • Ultracool atmospheres
  • Spectroscopy of brown dwarfs
  • Time domain phenomena in brown dwarfs: activity and weather
  • Oncoming and future projects in the substellar world
  • The brown dwarfs-exoplanet connection

Spectral/timing properties of accreting objects: from X-ray binaries to AGN

“Spectral/timing properties of accreting objects: from X-ray binaries to AGN” is a 3-day workshop to be held at the European Space Astronomy Centre (ESAC) in April 2013. The aim of the workshop is to review the current understanding of the physics of accretion onto compact objects across the full range of masses, by bringing together young and active experts of the field. In order to encourage discussions and maximize collaborations, the attendance to the workshop will be limited to about 70 people, that will be selected on the basis of the proposed contribution after the registration deadline. There will be no registration fee.

The main scientific topics covered will be:

– Accretion modes at different scales;

– States and state transitions;

– Inflow/outflow connections;

– Accretion/ejection mechanisms;

– Unification schemes.