1,721,691 research outputs found
Intermediate Mass Stars
No full textIn this paper I discuss our current understanding of the formation mechanisms and evolution of the circumstellar material around intermediate mass stars. I review the evidence for and properties of circumstellar disks around Herbig Ae stars, as well as recent observational evidence for dust evolution within these disks. The status of the search for the more elusive disks around Herbig Be stars is also discussed. Finally I review the clustering properties of young stars around Herbig Ae/Be stars, and the possible link between clusters and the formation of the more massive stars
ALMA Science: the ESO-Garching Astronomers View
No full textAt the Garching Science Day 2007, proposals for observations with ALMA were presented. A comparison is presented with the ALMA Design Reference Science Plan. The comparison shows that ALMA can be exploited by the wider community for a variety of different science projects, many of which are beyond the expectations of the current community of millimetre astronomers
A low-resolution near-infrared spectral library of M-, L-, and T-dwarfs
No full textWe present complete near-infrared (0.85–2.45 μm), low-resolution
(R ~ 100) spectra of a sample of 54 disk M-, L-, and T-dwarfs with reliable
optical or near infrared spectral-type classification from the literature.
The observations were obtained with a prism-based optical element, the Amici device,
which provides a complete spectrum of the source on the detector.
Our observations indicate that low-resolution near-infrared spectroscopy can
be used to determine the spectral classification of late-type field dwarfs
in a fast but accurate way. We derive a set of near-infrared spectral indices
that are useful to the classification of field dwarfs not seriously affected by reddening.
Finally, we show that the comparison of Amici spectra with model atmospheres allows
us to obtain a reliable estimate of the dwarf effective temperatures
High angular resolution millimeter observations of circumstellar disks
No full textIn this lecture, we review the properties of protoplanetary disks as derived from high angular resolution observations at millimeter wavelengths. We discuss how the combination of several different high angular resolution techniques allow us to probe different regions of the disk around young stellar objects and to derive the properties of the dust when combined with sophisticated disk models. The picture that emerges is that the dust in circumstellar disks surrounding pre-main sequence stars is in many cases significantly evolved compared to the dust in molecular clouds and the interstellar medium. It is however still difficult to derive a consistent picture and timeline for dust evolution in disks as the observations are still limited to small samples of objects. We also review the evidence for and properties of disks around high-mass young stellar objects and the implications on their formation mechanisms. The study of massive YSOs is complicated by their short lifetimes and larger average distances. In most cases high angular resolution data at millimeter wavelengths are the only method to probe the structure of disks in these objects. We provide a summary of the characteristics of available high angular resolution millimeter and submillimeter observatories. We also describe the characteristics of the ALMA observatory being constructed in the Chilean Andes. ALMA is going to be the world leading observatory at millimeter wavelengths in the coming decades, the project is now in its main construction phase with early science activities envisaged for 2010 and full science operations for 2012
The imprint of accretion on the UV spectrum of young stellar objects: an X-Shooter view
No full textThe evolution of protoplanetary disks is regulated by its interaction with the central forming star. This interaction happens through accretion of matter from the disk onto the star, and its most significant signatures are the continuum excess in the UV part of the spectrum and the presence of various emission lines. With the VLT/X-Shooter spectrograph, the excess emission in the UV due to accretion can being studied simultaneously with the signatures in the visible and in the near-infrared, giving a simultaneous and complete view of this phenomenon. Here we present some results we obtained using observation and modeling of the UV-excess in young forming stars, which are: (1) the determination of stellar and accretion properties in candidate older accreting young stellar objects and (2) the study of the star-disk interaction in the early stages of planetary system evolution in transitional disk systems
ALMA Status and Science Verification Data
No full textALMA is rapidly progressing towards the end of the construction phase. At the beginning of August 2011, 17 antennas were interferometrically linked on the Chajnantor plateau at an altitude of 5000 metres. Twelve-metre antennas from all the vendors were used in this experiment, which is a major milestone towards the first Early Science guest observer observations, currently planned to begin soon. In the meantime, ALMA Science Verification datasets are becoming available on the ALMA webpages for users to download and gain familiarity with ALMA data reduction and analysis procedures
Report on the ESO Workshop The Origin and Fate of the Sun: Evolution of Solar-mass Stars Observed with High Angular Resolution
No full textThe goal of the workshop was to review recent results on solar-mass stars obtained with infrared and millimetre interferometers, and to discuss their importance for our understanding of stellar evolution from star formation to the late stages. The workshop was preceded by a one-day ALMA+VLTI interferometry primer. A brief summary of the workshop is presented
Report on the Workshop ''ALMA Community Days: Towards Early Science''
No full textALMA is rapidly approaching Early Science operations, and is scheduled to start the first observing projects for the astronomical community in the autumn of 2011. The Call for Proposals for ALMA Early Science Cycle 0 was published on 30 March, inviting the community to submit observing proposals by the deadline of 30 June 2011. Held just after the Call for Proposals was issued, the ALMA Community Days were designed to optimally prepare the European ALMA Community for Cycle 0 proposal submission. The workshop included a broad range of scientific and technical presentations as well as hands-on software tutorials for the ALMA simulators and the Observing Tool
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