1,223 research outputs found
Preliminary optical design for the common fore optics of METIS
METIS is the Mid-infrared E-ELT Imager and Spectrograph, which will provide outstanding observing capabilities, focusing on high angular and spectral resolution. It consists of two diffraction-limited imagers operating in the LM and NQ bands respectively and an IFU fed diffraction-limited high-resolution (R=100,000) LM band spectrograph. These science subsystems are preceded by the common fore optics (CFO), which provides the following essential functionalities: calibration, chopping, image de-rotation, thermal background and stray light reduction. We show the evolution of the CFO optical design from the conceptual design to the preliminary optical design, detail the optimization steps and discuss the necessary trade-offs
Very Low-Mass Objects in the Coronet Cluster: The Realm of the Transition Disks
We present optical and IR spectra of a set of low-mass stars and brown dwarfs
in the Coronet cluster (aged ~1Myr), obtained with the multifiber spectrograph
FLAMES/VLT and IRS/Spitzer. The optical spectra reveal spectral types between
M1 and M7.5, confirm the youth of the objects (via Li 6708 A absorption), and
show the presence of accretion (via Halpha) and shocks (via forbidden line
emission). The IRS spectra, together with IR photometry from the IRAC/MIPS
instruments on Spitzer and 2MASS, confirm the presence of IR excesses
characteristic of disks around ~70% of the objects. Half of the disks do not
exhibit any silicate emission, or present flat features characteristic of large
grains. The rest of the disks show silicate emission typical of amorphous and
crystalline silicate grains a few microns in size. About 50% of the objects
with disks do not show near-IR excess emission, having "transitional" disks,
according to their classical definition. This is a very high fraction for such
a young cluster. The large number of "transitional" disks suggests lifetimes
comparable to the lifetimes of typical optically thick disks. Therefore, these
disks may not be in a short-lived phase, intermediate between Class II and
Class III objects. The median spectral energy distribution of the disks in the
Coronet cluster is also closer to a flat disk than observed for the disks
around solar-type stars in regions with similar age. The differences in the
disk morphology and evolution in the Coronet cluster could be related to fact
that these objects have very late spectral types compared to the solar-type
stars in other cluster studies. Finally, the optical spectroscopy reveals that
one of the X-ray sources is produced by a Herbig Haro object in the cloud.Comment: 51 pages, 13 figures, 10 table
Modules for Experiments in Stellar Astrophysics (MESA)
Stellar physics and evolution calculations enable a broad range of research
in astrophysics. Modules for Experiments in Stellar Astrophysics (MESA) is a
suite of open source libraries for a wide range of applications in
computational stellar astrophysics. A newly designed 1-D stellar evolution
module, MESA star, combines many of the numerical and physics modules for
simulations of a wide range of stellar evolution scenarios ranging from
very-low mass to massive stars, including advanced evolutionary phases. MESA
star solves the fully coupled structure and composition equations
simultaneously. It uses adaptive mesh refinement and sophisticated timestep
controls, and supports shared memory parallelism based on OpenMP. Independently
usable modules provide equation of state, opacity, nuclear reaction rates, and
atmosphere boundary conditions. Each module is constructed as a separate
Fortran 95 library with its own public interface. Examples include comparisons
to other codes and show evolutionary tracks of very low mass stars, brown
dwarfs, and gas giant planets; the complete evolution of a 1 Msun star from the
pre-main sequence to a cooling white dwarf; the Solar sound speed profile; the
evolution of intermediate mass stars through the thermal pulses on the He-shell
burning AGB phase; the interior structure of slowly pulsating B Stars and Beta
Cepheids; evolutionary tracks of massive stars from the pre-main sequence to
the onset of core collapse; stars undergoing Roche lobe overflow; and accretion
onto a neutron star. Instructions for downloading and installing MESA can be
found on the project web site (http://mesa.sourceforge.net/).Comment: 110 pages, 39 figures; submitted to ApJS; visit the MESA website at
http://mesa.sourceforge.ne
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